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The photochemical decomposition of ethyl(aqua)cobaloxime, [EtCo III (dmgH) 2 H 2 O], a vitamin B 12 derivative model complex, was investigated to understand the mechanism of the Co-C Et bond scission induced by light. Upon irradiation of [EtCo III (dmgH) 2 H 2 O], the Co-C Et bond undergoes homolytic scission, resulting in Et/Co(II) radical pair (RP) formation in a similar fashion observed in alkylcobalamins. The [EtCo III (dmgH) 2 H 2 O] complex acts as a potent quencher of a wide variety of excited states in the presence of organic molecules such as benzophenone. It has been proposed that the reaction mechanism involves Dexter energy transfer, resulting in the bond dissociation process. Two issues associated with the proposed mechanism have been investigated, namely, (i) how the energy transfer occurs from benzophenone to cobaloxime and (ii) how the Co-C Et bond is activated and cleaved. Both TD-DFT and CASSCF/NEVPT2 methods have been applied to show the feasibility of the energy transfer reaction via the triplet pathway from photocatalyst to substrate.

Sophisticated tools such as computer vision techniques in combination with 1D lineout type analyses have been used in automating the analysis of spectral data for high energy density (HED) plasmas. Standardized automation can solve the problems posed by the complexity of HED spectra and the quantity of data. We present a spectroscopic code written for automated and streamlined analysis of spatially resolved x-ray absorption data from the COAX platform on Omega-60. COAX uses radiographs and spectroscopic diagnostics to provide shock position and density information. We also obtain the more novel spectral-derived spatial profile of the supersonic radiation flow into a low-density foam. Considerable effort has been spent modernizing our previous spectroscopic analysis method, including the development of new tools characterized by a faster runtime and minimal user input to reduce bias and a testing suite for verifying the accuracy of the various functions within the code. The new code analyzes our spectroscopic images in 1-2 min, with added uncertainty and confidence., (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).)

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

In this study, the use of self-consistent field quasi-diabats is investigated for calculation of triplet energy transfer diabatic coupling elements. It is proposed that self-consistent field quasi-diabats are particularly useful for studying energy transfer (EnT) processes because orbital relaxation in response to changes in electron configuration is implicitly built into the model. The conceptual model that is developed allows for the simultaneous evaluation of direct and charge-transfer mechanisms to establish the importance of the different possible EnT mechanisms. The method's performance is evaluated using two model systems: the ethylene dimer and ethylene with the methaniminium cation. While states that mediate the charge-transfer mechanism were found to be higher in energy than the states involved in the direct mechanism, the coupling elements that control the kinetics were found to be significantly larger in the charge-transfer mechanism. Subsequently, we discuss the advantage of the approach in the context of practical difficulties with the use of established approaches.

CarH is a cobalamin-based photoreceptor which has attracted significant interest due to its complex mechanism involving its organometallic coenzyme-B 12 chromophore. While several experimental and computational studies have sought to understand CarH's mechanism of action, there are still many aspects of the mechanism which remain unclear. While light is needed to activate the Co-C 5' bond, it is not entirely clear whether reaction pathway involves singlet or triplet diradical states. A recent experimental study implicated triplet pathway and importance of intersystem crossing (ISC) as a viable mechanistic route for photoproduct formation in CarH. Herein, a combined quantum mechanics/molecular mechanics approach (QM/MM) was used to explore the involvement of triplet states in CarH. Two possibilities were explored. The first possibility involved photo-induced homolytic cleavage of the Co-C 5' where the radical pair (RP) would deactivate to a triplet state (T 0 ) on the ground state potential energy surface (PES). However, a pathway for the formation of the photoproduct, 4',5'-anhydroadenosine (anhAdo), on the triplet ground state PES was not energetically feasible. The second possibility involved exploring a manifold of low-lying triplet excited states computed using TD-DFT within the QM/MM framework. Viable crossings of triplet excited states with singlet excited states were identified using semiclassical Landau-Zener theory and the effectiveness of spin-orbit coupling by El-Sayed rules. Several candidates along both the Co-N Im potential energy curve (PEC) and Co-C 5' /Co-N Im PES were identified, which appear to corroborate experimental findings and implicate the possible role of triplet states in CarH., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

The goal of the Xflows experimental campaign is to study the radiation flow on the National Ignition Facility (NIF) reproducing the sensitivity of the temperature (±8 eV, ±23 μm) and density (±11 mg/cc) measurements of the COAX platform [Johns et al., High Energy Density Phys. 39, 100939 (2021); Fryer et al., High Energy Density Phys. 35, 100738 (2020); and Coffing et al., Phys. Plasmas 29, 083302 (2022)]. This new platform will enable future astrophysical experiments involving supernova shock breakout, such as Radishock (Johns et al., Laboratory for Laser Energetics Annual Report 338, 2020) on OMEGA-60 [Boehly et al., Rev. Sci. Instrum. 66, 508 (1995)], and stochastic media (such as XFOL on OMEGA). Greater energy and larger physical scale on NIF [Moses et al., Eur. Phys. J. D 44, 215 (2007)] will enable a greater travel distance of radiation flow, higher density, and more manufacturable foams and enable exploration of a greater range of radiation behavior than achievable in the prior OMEGA experiments. This publication will describe the baseline configuration for the Xflows experimental campaign and the roadmap to achieve its primary objectives.

In many inertial confinement fusion (ICF) experiments, the neutron yield and other parameters cannot be completely accounted for with one and two dimensional models. This discrepancy suggests that there are three dimensional effects that may be significant. Sources of these effects include defects in the shells and defects in shell interfaces, the fill tube of the capsule, and the joint feature in double shell targets. Due to their ability to penetrate materials, x rays are used to capture the internal structure of objects. Methods such as computational tomography use x-ray radiographs from hundreds of projections, in order to reconstruct a three dimensional model of the object. In experimental environments, such as the National Ignition Facility and Omega-60, the availability of these views is scarce, and in many cases only consists of a single line of sight. Mathematical reconstruction of a 3D object from sparse views is an ill-posed inverse problem. These types of problems are typically solved by utilizing prior information. Neural networks have been used for the task of 3D reconstruction as they are capable of encoding and leveraging this prior information. We utilize half a dozen, different convolutional neural networks to produce different 3D representations of ICF implosions from the experimental data. Deep supervision is utilized to train a neural network to produce high-resolution reconstructions. These representations are used to track 3D features of the capsules, such as the ablator, inner shell, and the joint between shell hemispheres. Machine learning, supplemented by different priors, is a promising method for 3D reconstructions in ICF and x-ray radiography, in general.

Mesoscale imperfections, such as pores and voids, can strongly modify the properties and the mechanical response of materials under extreme conditions. Tracking the material response and microstructure evolution during void collapse is crucial for understanding its performance. In particular, imperfections in the ablator materials, such as voids, can limit the efficiency of the fusion reaction and ultimately hinder ignition. To characterize how voids influence the response of materials during dynamic loading and seed hydrodynamic instabilities, we have developed a tailored fabrication procedure for designer targets with voids at specific locations. Our procedure uses SU-8 as a proxy for the ablator materials and hollow silica microspheres as a proxy for voids and pores. By using photolithography to design the targets' geometry, we demonstrate precise and highly reproducible placement of a single void within the sample, which is key for a detailed understanding of its behavior under shock compression. This fabrication technique will benefit high-repetition rate experiments at x-ray and laser facilities. Insight from shock compression experiments will provide benchmarks for the next generation of microphysics modeling.

Objective: To assess whether a multimodal opioid-limiting protocol and patient education intervention can reduce postoperative opioid use following transurethral resection of the prostate., Methods: This prospective, non-blinded, single-institution, randomized controlled trial (NCT04102566) assigned 50 patients undergoing a transurethral resection of the prostate to either a standard of care control (SOC) or multimodal experimental group (MMG). The intervention included adding ibuprofen to the postoperative pain regimen, promoting appropriate opioid use while hospitalized, an educational intervention, and discharging without opioid prescription. Data regarding demographics, operative data, opioid use, pain scores, and patient satisfaction were compared., Results: A total of 47 patients were included, n = 23 (MMG) and n = 24 (SOC). Demographic and operative findings were similar. Statistical analysis for noninferiority demonstrated non-inferior inpatient pain control (mean pain score 2.5 MMG vs 2.4 SOC, P = 0.0003). The multimodal group used significantly fewer morphine milligram equivalents after discharge (0 vs 4.1, P = 0.04). Inpatient use was reduced but did not reach statistical significance (6.0 vs 9.8, P = 0.2). Mean satisfaction scores with pain control were similar (9.6 MMG vs 9.2 SOC, P = 0.32). No opioid prescriptions were requested after discharge. Adverse events and medication side effects were infrequent and largely similar between groups., Conclusion: Implementation of an opioid-limiting postoperative pain protocol and patient education resulted in no outpatient opioid use while maintaining patient satisfaction with pain control. Eliminating opioids following a common urologic procedure will decrease risk of opioid-related adverse events and have a positive downstream impact., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The CarH photoreceptor exploits of the light-sensing ability of coenzyme B 12 ( adenosylcobalamin = AdoCbl) to perform its catalytic function, which includes large-scale structural changes to regulate transcription. In daylight, transcription is activated in CarH via the photo-cleavage of the Co-C 5' bond of coenzyme B 12 . Subsequently, the photoproduct, 4',5'-anhydroadenosine (anhAdo) is formed inducing dissociation of the CarH tetramer from DNA. Several experimental studies have proposed that hydridocoblamin (HCbl) may be formed in process with anhAdo. The photolytic cleavage of the Co-C 5' bond of AdoCbl was previously investigated using photochemical techniques and the involvement of both singlet and triplet excited states were explored. Herein, QM/MM calculations were employed to probe (1) the photolytic processes which may involve singlet excited states, (2) the mechanism of anhAdo formation, and (3) whether HCbl is a viable intermediate in CarH. Time-dependent density functional theory (TD-DFT) calculations indicate that the mechanism of photodissociation of the Ado ligand involves the ligand field (LF) portion of the lowest singlet excited state (S 1 ) potential energy surface (PES). This is followed by deactivation to a point on the S 0 PES where the Co-C 5' bond remains broken. This species corresponds to a singlet diradical intermediate. From this point, the PES for anhAdo formation was explored, using the Co-C 5' and Co-C 4' bond distances as active coordinates, and a local minimum representing anhAdo and HCbl formation was found. The transition state (TS) for the formation of the Co-H bond of HCbl was located and its identity was confirmed by a single imaginary frequency of i1592 cm -1 . Comparisons to experimental studies and the potential role of rotation around the N-glycosidic bond of the Ado ligand were discussed., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In this study, we report a pair of electrocatalysts for the hydrogen evolution reaction (HER) based on the noninnocent ligand diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-pyridinehydrazone) (H 2 DMTH, H 2 L 1 ). The neutral complexes NiL 1 and PdL 1 were synthesized and characterized by spectroscopic and electrochemical methods. The complexes contain a non-coordinating, basic hydrazino nitrogen that is protonated during the HER. The p K a of this nitrogen was determined by spectrophotometric titration in acetonitrile to be 12.71 for NiL 1 and 13.03 for PdL 1 . Cyclic voltammograms of both NiL 1 and PdL 1 in acetonitrile exhibit diffusion-controlled, reversible ligand-centered events at -1.83 and -1.79 V (vs ferrocenium/ferrocene) for NiL 1 and PdL 1 , respectively. A quasi-reversible, ligand-centered event is observed at -2.43 and -2.34 V for NiL 1 and PdL 1 , respectively. The HER activity in acetonitrile was evaluated using a series of neutral and cationic acids for each catalyst. Kinetic isotope effect (KIE) studies suggest that the precatalytic event observed is associated with a proton-coupled electron transfer step. The highest turnover frequency values observed were 6150 s -1 at an overpotential of 0.74 V for NiL 1 and 8280 s -1 at an overpotential of 0.44 V for PdL 1 . Density functional theory (DFT) computations suggest both complexes follow a ligand-centered HER mechanism where the metals remain in the +2 oxidation state.

A 71-year-old woman with history of asthma presented with 2 months history of shortness of breath; on imaging an incidental left renal mass was noted. Subsequent renal protocol CT was obtained that showed a 4.5 cm left upper pole exophytic mass with renal vein thrombus extending into the inferior vena cava to the level of the caudate lobe concerning for renal cell carcinoma. She underwent an open left radical nephrectomy and IVC thrombectomy with subsequent postoperative pathology demonstrating xanthogranulomatous pyelonephritis without renal cell carcinoma.

The photo-reactivity of cobalamins (Cbls) is influenced by the nature of axial ligands and the cofactor's environment. While the biologically active forms of Cbls with alkyl axial ligands, such as methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl), are considered to be photolytically active, in contrast, the non-alkyl Cbls are photostable. In addition to these, the photolytic properties of Cbls can also be modulated in the presence of molecular oxygen, i.e. , under aerobic conditions. Herein, the photoreaction of the MeCbl in the presence of oxygen has been explored using density functional theory (DFT) and time-dependent DFT (TD-DFT). The first stage of the aerobic photoreaction is the activation of the Co-C bond and the formation of the ligand field (LF) electronic state through the displacement of axial bonds. Once the photoreaction reaches the LF excited state, three processes can occur: namely the formation of OO-CH 3 through the reaction of CH 3 with molecular oxygen, de-activation of the {Im⋯[Co II (corrin)]⋯CH 3 } + sub-system from the LF electronic state by changing the electronic configuration from (d yz ) 1 (d z 2 ) 2 to (d yz ) 2 (d z 2 ) 1 and the formation of the deactivation complex (DC) complex via the recombination of OO-CH 3 species with the de-excited [Co II (corrin)] system. In the proposed mechanism, the deactivation of the [Co II (corrin)] subsystem may coexist with the formation of OO-CH 3 , followed by immediate relaxation of the subsystems in the ground state. Moreover, the formation of the OO-CH 3 species followed by the formation of the {[Co III (corrin)]-OO-CH 3 } + complex stabilizes the system compared to the reactant complex.

The biologically active vitamin B 12 derivates, methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl), are ubiquitous organometallic cofactors. In addition to their key roles in enzymatic catalysis, B 12 cofactors have complex photolytic properties which have been the target of experimental and theoretical studies. With the recent discovery of B 12 -dependent photoreceptors, there is an increased need to elucidate the underlying photochemical mechanisms of these systems. This book chapter summarizes the photolytic properties of MeCbl- and AdoCbl-dependent enzymes with particular emphasis on the effect of the environment of the cofactor on the excited state processes. These systems include isolated MeCbl and AdoCbl as well as the enzymes, ethanolamine ammonia-lyase (EAL), glutamate mutase (GLM), methionine synthase (MetH), and photoreceptor CarH. Central to determining the photodissociation mechanism of each system is the analysis of the lowest singlet excited state (S 1 ) potential energy surface (PES). Time-dependent density functional theory (TD-DFT), employing BP86/TZVPP, is widely used to construct such PESs. Regardless of the environment, the topology of the S 1 PES of AdoCbl or MeCbl is marked by characteristic features, namely the metal-to-ligand charge transfer (MLCT) and ligand field (LF) regions. Conversely, the relative energetics of these electronic states are affected by the environment. Applications and outlooks for Cbl photochemistry are also discussed., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Nature employs two biologically active forms of vitamin B 12 , adenosylcobalamin (or coenzyme B 12 ) and methylcobalamin, as cofactors in molecular transformations both in bacteria and mammals. Computational chemistry, guided by experimental data, has been used to explore fundamental characteristics of these enzymatic reactions. In particular, the quantum mechanics/molecular mechanics (QM/MM) method has proven to be a powerful tool in elucidating important characteristics of B 12 -dependent enzymatic reactions. Herein, we will present a brief tutorial in conducting QM/MM calculations for B 12 enzymatic reactions. We will summarize recent contributions that target the use of QM/MM calculations in both photochemical and enzymatic reactions including AdoCbl-dependent ethanolamine ammonia lyase, glutamate mutase, and photoreceptor CarH., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Hydridocobalamin (HCbl), is a known member of the B 12 family of molecules (cobalamins, Cbls) yet unlike other well-studied Cbls, little is known of the electronic and photolytic properties of this species. Interest in HCbl has increased significantly in recent years when at least three experimentally proposed mechanisms implicate HCbl as an intermediary in the photoreaction of coenzyme B 12 -dependent photoreceptor CarH. Specifically, cleavage of the Co-C 5' bond of coenzyme B 12 could lead to a β-hydride or β‑hydrogen elimination reaction to form HCbl. HCbl is known to be a transient species where the oxidation state of the Co is variable; Co(I)-H + ↔ Co(II)-H ↔ Co(III)-H - . Further, HCbl is a very unstable with a pKa of ~1. This complicates experimental studies and to the best of our knowledge there are no available crystal structures of HCbl - either for the isolated molecule or bound to an enzyme. In this study, the electronic structure, photolytic properties, and reactivity of HCbl were explored to determine the preferred oxidation state as well as its potential role in the formation of the photoproduct in CarH. Natural bond orbital (NBO) analysis was performed to determine the oxidation state of Co in isolated HCbl. Based on the NBO analysis of HCbl, Co clearly had excess negative charge, which is in stark contrast to other alkylCbls where the Co ion is marked by significant positive charge. In sum, NBO results indicate that the CoH bond is strongly polarized and almost ionic. It can be described as protonated Co(I). In addition, DFT was used to explore the bond dissociation energy of HCbl based on homolytic cleavage of the CoH bond. TD-DFT calculations were used to compare computed electronic transitions to the experimentally determined absorption spectrum. The photoreaction of CarH was explored using an isolated model system and a pathway for hydrogen transfer was found. Finally, quantum mechanics/molecular mechanics (QM/MM) calculations were employed to investigate the formation of HCbl in CarH., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A reversible Van der Waals complex formation between the electron-deficient fluorinated aromatic ring and N,N-dimethylformamide (DMF) molecules followed by light irradiation resulted in charge transfer (CT) process. The complex was stabilized by ammonium formate and further decomposed to form the C-N bond. Control experiments revealed that the simultaneous S N Ar pathway also contributes to product formation. This methodology is mild, metal-free, and effective for the amination of a variety of substrates. The reproducibility of this methodology was also verified on gram-scale reactions. The CT states were supported by control UV/Vis spectroscopy and computational studies., (© 2021 Wiley-VCH GmbH.)

Methyl transfer reactions, mediated by methyltransferases (MeTrs), such as methionine synthase (MetH) or monomethylamine: CoM (MtmBC), constitute one of the most important classes of vitamin B 12 -dependent reactions. The challenge in exploring the catalytic function of MeTrs is related to their modular structure. From the crystallographic point of view, the structure of each subunit has been determined, but there is a lack of understanding of how each subunit interacts with each other. So far, theoretical studies of methyl group transfer were carried out for the structural models of the active site of each subunit. However, those studies do not include the effect of the enzymatic environment, which is crucial for a comprehensive understanding of enzyme-mediated methyl transfer reactions. Herein, to explore how two subunits interact with each other and how the methyl transfer reaction is catalyzed by MeTrs, molecular docking of the functional units of MetH and MtmBC was carried out. Along with the interactions of the functional units, the reaction coordinates, including the Co-C bond distance for methylation of cob(I)alamin (Co I Cbl) and the C-S bond distance in demethylation reaction of cob(III)alamin (Co III Cbl), were considered. The functional groups should be arranged so that there is an appropriate distance to transfer a methyl group and present results indicate that steric interactions can limit the number of potential arrangements. This calls into question the possibility of S N 2-type mechanism previously proposed for MeTrs. Further, it leads to the conclusion that the methyl transfer reaction involves some spatial changes of modules suggesting an alternate radical-based pathway for MeTrs-mediated methyl transfer reactions. The calculations also showed that changes in torsion angles induce a change in reaction coordinates, namely Co-C and C-S bond distances, for the methylation and demethylation reactions catalyzed both by MetH and MtmBC., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Great strides have been made in improving the quality of x-ray radiographs in high energy density plasma experiments, enabled in part by innovations in engineering and manufacturing of integrated circuits and materials. As a consequence, the radiographs of today are filled with a great deal of detail, but few of these features are extracted in a systematic way. Analysis techniques familiar to plasma physicists tend toward brittle 1D lineout or Fourier transform type analyses. The techniques applied to process our data have not kept pace with improvements in the quality of our data. Fortunately, the field of computer vision has a wealth of tools to offer, which have been widely used in industrial imaging and, more recently, adopted in biological imaging. We demonstrate the application of computer vision techniques to the analysis of x-ray radiographs from high energy density plasma experiments, as well as give a brief tutorial on the computer vision techniques themselves. These tools robustly extract 2D contours of shocks, boundaries of inhomogeneities, and secondary flows, thereby allowing for increased automation of analysis, as well as direct and quantitative comparisons with simulations.

Vitamin B 12 derivatives (Cbls = cobalamins) exhibit photolytic properties upon excitation with light. These properties can be modulated by several factors including the nature of the axial ligands. Upon excitation, homolytic cleavage of the organometallic bond to the upper axial ligand takes place in photolabile Cbls. The photosensitive nature of Cbls has made them potential candidates for light-activated drug delivery. The addition of a fluorophore to the nucleotide loop of thiolato Cbls has been shown to shift the region of photohomolysis to within the optical window of tissue (600-900 nm). With this possibility, there is a need to analyze photolytic properties of unique Cbls which contain a Co-S bond. Herein, the photodissociation of one such Cbl, namely, N -acetylcysteinylcobalamin (NACCbl), is analyzed based on density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The S 0 and S 1 potential energy surfaces (PESs), as a function of axial bond lengths, were computed to determine the mechanism of photodissociation. Like other Cbls, the S 1 PES contains metal-to-ligand charge transfer (MLCT) and ligand field (LF) regions, but there are some unique differences. Interestingly, the S 1 PES of NACCbl contains three distinct minima regions opening several possibilities for the mechanism of radical pair (RP) formation. The mild photoresponsiveness, observed experimentally, can be attributed to the small gap in energy between the S 1 and S 0 PESs. Compared to other Cbls, the gap shown for NACCbl is neither exactly in line with the alkyl Cbls nor the nonalkyl Cbls.

The discovery of naturally occurring B 12 -depedent photoreceptors has allowed for applications of cobalamins (Cbls) in optogenetics and synthetic biology to emerge. However, theoretical investigations of the complex mechanisms of these systems have been lacking. Adenosylcobalamin (AdoCbl)-dependent photoreceptor, CarH, is one example and it relies on daylight to perform its catalytic function. Typically, in enzymes employing AdoCbl as their cofactor, the Co-C 5' bond activation and cleavage is triggered by substrate binding. The cleavage of the Co-C 5' bond is homolytic resulting in radical pair formation. However, in CarH, this bond is instead activated by light. To explore this peculiarity, the ground and first excited state potential energy surfaces (PESs) were constructed using the quantum mechanics/molecular mechanics (QM/MM) framework and compared with other AdoCbl-dependent enzymes. QM/MM results indicate that CarH is photolytically active as a result of the AdoCbl dual role, acting as a radical generator and as a substrate. Photo-cleavage of the Co-C 5' bond and subsequent H-atom abstraction is possible because of the specific orientation of the H-C 4' bond with respect to the Co(II) center. Comparison with other AdoCbl-dependent enzymes indicate that the protein environment in the CarH active center alters the photochemistry of AdoCbl by controlling the stereochemistry of the ribose moiety., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Cubic spline interpolation is able to recover temporally and spectrally resolved soft x-ray fluxes from an array of K-edge filtered x-ray diodes without the need for a priori assumptions about the spectrum or the geometry of the emitting volume. The mathematics of the cubic spline interpolation is discussed in detail. The analytic nature of the cubic spline solution allows for analytical error propagation, and the method of calculating the error for radiation temperature, spectral power, and confidence intervals of the unfolded spectrally resolved flux is explained. An unfold of a blackbody model demonstrates the accuracy of the cubic spline unfold. Tests of cubic spline performance using spectrally convolved detailed atomic model simulation results have been performed to measure the method's ability to conserve spectral power to within a factor of 2 or better in line-dominated regimes. The unfold is also demonstrated to work when information from the x-ray diode array is limited due to high signal-to-noise ratios or the lack of signal due to over-attenuation or over-filtration of the x-ray diode signal. The robustness of the unfold with respect to background subtraction and raw signal processing, signal alignment between diode traces, limited signal information, and initial conditions is discussed. Results from an example analysis of a halfraum drive are presented to demonstrate the capabilities of the unfold in comparison with previously established methods.

Photolysis of methylcobalamin (MeCbl) in the presence of molecular oxygen (O 2 ) has been investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). The key step involves the formation of the Cbl-O-O-CH 3 intermediate as a result of triplet O 2 insertion in the Co-C bond in the presence of light. Analysis of low-lying excited states shows that the presence of light is only needed to activate the Co-C bond via the formation of the ligand field (LF) state. The insertion of O 2 , as well as the change in the spin state, takes place in the ground state. The analysis of the structural and electronic properties of the Cbl-O-O-CH 3 intermediate is presented and possible decomposition also discussed.

Polarized X-ray absorption near-edge structure (XANES) at the Co K-edge and broadband UV-vis transient absorption are used to monitor the sequential evolution of the excited-state structure of coenzyme B 12 (adenosylcobalamin) over the first picosecond following excitation. The initial state is characterized by sub-100 fs sequential changes around the central cobalt. These are polarized first in the y -direction orthogonal to the transition dipole and 50 fs later in the x -direction along the transition dipole. Expansion of the axial bonds follows on a ca. 200 fs time scale as the molecule moves out of the Franck-Condon active region of the potential energy surface. On the same 200 fs time scale there are electronic changes that result in the loss of stimulated emission and the appearance of a strong absorption at 340 nm. These measurements provide a cobalt-centered movie of the excited molecule as it evolves to the local excited-state minimum.

Introduction: Previous studies examining patients with equivocal renal scans performed before robotic assisted pyeloplasty for ureteropelvic junction obstruction have shown conflicting results regarding outcomes. To address these conflicting reports we compared rates of symptom resolution and improvement in postoperative radiographic scans between patients at our institution presenting with equivocal vs obstructed preoperative diuretic renograms., Methods: We conducted a retrospective review of 143 patients who underwent robotic assisted pyeloplasty by a single surgeon at our institution from 2001 to 2017. Patients with preoperative and postoperative diuretic renograms available were included in study. Patients were analyzed in equivocal preoperative imaging or obstructed preoperative imaging groups., Results: A total of 102 patients were included in this study, 16 with equivocal diuretic renograms and 86 with obstructed diuretic renograms. Mean preoperative differential function was 34.9% in the obstructed group and 43.2% in the equivocal group (p=0.07). Postoperative symptom resolution was equivalent between equivocal and obstructed groups (87.5% vs 89.4%, p=0.69). However, improvement in diuretic renogram obstruction was significantly greater in obstructed compared with equivocal cases (84.7% vs 56.3%, p=0.01)., Conclusions: Surgical management of patients with equivocal obstruction can be challenging. Patients with preoperative equivocal diuretic renograms are less likely to have radiographic improvement after robotic assisted pyeloplasty but do experience equivalent symptom resolution compared to patients with obstructed preoperative diuretic renograms. Symptom improvement rather than improvement in radiographic obstruction should be the primary focus when offering robotic assisted pyeloplasty to patients presenting with equivocal diuretic renograms.

The zinc(II) complex of diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-hydrazonepyridine), ZnL 1 ( 1 ), was prepared and evaluated as a precatalyst for the hydrogen evolution reaction (HER) under homogeneous conditions in acetonitrile. Complex 1 is protonated on the noncoordinating nitrogen of the hydrazonepyridine moiety to yield the active catalyst Zn(HL 1 )OAc ( 2 ) upon addition of acetic acid. Addition of methyl iodide to 1 yields the corresponding methylated derivative ZnL 2 I ( 3 ). In solution, partial dissociation of the coordinated iodide yields the cationic derivative 3' . Complexes 1 - 3 were characterized by 1 H NMR, FT-IR, and UV-visible spectroscopies. The solid-state structures of 2 and 3 were determined by single crystal X-ray diffraction. HER studies conducted in acetonitrile with acetic acid as the proton source yield a turnover frequency (TOF) of 7700 s -1 for solutions of 1 at an overpotential of 1.27 V and a TOF of 6700 s -1 for solutions of 3 at an overpotential of 0.56 V. For both complexes, the required potential for catalysis, E cat/2 , is larger than the thermodynamic reduction potential, E 1/2 , indicative of a kinetic barrier attributed to intramolecular proton rearrangement. The effect is larger for solutions of 1 (+440 mV) than for solutions of 3 (+160 mV). Controlled potential coulometry studies were used to determine faradaic efficiencies of 71 and 89% for solutions of 1 and 3 , respectively. For both catalysts, extensive cycling of potential under catalytic conditions results in the deposition of a film on the glassy carbon electrode surface that is active as an HER catalyst. Analysis of the film of 3 by X-ray photoelectron spectroscopy indicates the complex remains intact upon deposition. A proposed ligand-centered HER mechanism with 1 as a precatalyst to 2 is supported computationally using density functional theory (DFT). All catalytic intermediates in the mechanism were structurally and energetically characterized with the DFT/B3LYP/6-311g(d,p) in solution phase using a polarizable continuum model (PCM). The thermodynamic feasibility of the mechanism is supported by calculation of equilibrium constants or reduction potentials for each proposed step.

Methionine synthase (MetH) is a methylcobalamin (MeCbl)-dependent mammalian enzyme which plays a critical role in carrying out the transfer of a methyl group from methyl tetrahydrofolate to homocysteine to generate methionine and tetrahydrofolate. This catalytic cycle proceeds via cleavage of a Co-C bond which is formally heterolytic. This cleavage results in a structural change in the MeCbl cofactor bound to an enzyme. Unlike the native catalysis, upon photoexcitation, the Co-C bond in MeCbl-bound MetH generates the Co(ii)/CH3 radical pairs (RPs). Protein residues of the cap domain, particularly phenylalanine708 (F708) and leucine 715 (L715), which surrounds the upper face of the MeCbl cofactor, inhibit the photolysis of MeCbl by caging the CH3 radical and inducing the geminate recombination of the Co(ii)/CH3 RP. A molecular-level understanding of these effects requires a detailed investigation of the low-lying electronic states. Toward this, we have mutated the F708 residue with alanine (A708) and constructed the potential energy surfaces (PESs) for the low-lying S1 electronic state using a combined quantum mechanics/molecular mechanics (QM/MM) approach. The S1 PESs for the wild-type (WT) and mutant enzymes are the result of crossing of two electronic states, namely metal-to-ligand charge transfer (MLCT) and ligand field (LF) states, indicated by a seam. It is shown that the topologies of the S1 PESs are significantly modulated by introducing a mutation at the F708 position. Specifically, for the WT enzyme, the energy barrier of photoreaction and the energy difference between MLCT and LF minima are markedly higher than those of its mutant counterpart. Moreover, mutation influences the photoactivation of the Co-C bond in enzyme-bound MeCbl by decreasing the rate of geminate recombination and altering the rate of radical pair formation. This theoretical insight was also compared with transient absorption spectroscopic (TAS) studies which are in good agreement with the present findings.

We use picosecond time-resolved polarized X-ray absorption near-edge structure (XANES) measurements to probe the structure of the long-lived photoexcited state of methylcobalamin (MeCbl) and the cob(II)alamin photoproduct formed following photoexcitation of adenosylcobalamin (AdoCbl, coenzyme B 12 ). For MeCbl, we used 520 nm excitation and a time delay of 100 ps to avoid the formation of cob(II)alamin. We find only small spectral changes in the equatorial and axial directions, which we interpret as arising from small (<∼0.05 Å) changes in both the equatorial and axial distances. This confirms expectations based on prior UV-visible transient absorption measurements and theoretical simulations. We do not find evidence for the significant elongation of the Co-C bond reported by Subramanian [ J. Phys. Chem. Lett. 2018 , 9 , 1542 - 1546 ] following 400 nm excitation. For AdoCbl, we resolve the difference XANES contributions along three unique molecular axes by exciting with both 540 and 365 nm light, demonstrating that the spectral changes are predominantly polarized along the axial direction, consistent with the loss of axial ligation. These data suggest that the microsecond "recombination product" identified by Subramanian et al. is actually the cob(II)alamin photoproduct that is produced following bond homolysis of MeCbl with 400 nm excitation. Our results highlight the pronounced advantage of using polarization-selective transient X-ray absorption for isolating structural dynamics in systems undergoing atomic displacements that are strongly correlated to the exciting optical polarization.

Glutamate mutase (GLM) is a coenzyme B 12 -dependent enzyme that catalyzes the conversion of S-glutamate to (2 S,3 S)-3-methyl aspartate. The initial step in the catalytic process is the homolytic cleavage of the coenzyme's Co-C bond upon binding of a substrate. Alternatively, the Co-C bond can be cleaved using light. To investigate the photolytic cleavage of the Co-C bond in GLM, we applied a combined density functional theory/molecular mechanics (DFT/MM) and time-dependent-DFT/MM method to scrutinize the ground and the low-lying excited states. Potential energy surfaces (PESs) were generated as a function of axial bond lengths to describe the photodissociation mechanism. The S 1 PES was characterized as the crossing of two electronic states, metal-to-ligand charge transfer (MLCT), and ligand field (LF). In GLM, radical pairs generate from the LF state. Two pathways, path A and path B, were identified as possible channels to connect the MLCT and LF electronic states. The S 1 PES in GLM was compared with the S 1 PES for coenzyme B 12 -dependent ethanolamine ammonia lyase as well as the isolated AdoCbl cofactor. Finally, the theoretical insights related to the photodissociation mechanism were compared with transient absorption spectroscopy, electron paramagnetic resonance, and resonance Raman spectroscopy.

Vitamin B 12 -dependent enzymes catalyze several difficult radical reactions. There are fundamental open questions that need to be addressed to fully understand the formation of highly reactive radical species, its dynamics, and interaction with the substrate and enzyme. In this work, ab initio molecular dynamics was performed within a QM/MM framework on a reduced AdoCbl cofactor, which was taken as a post proton-coupled electron transfer initial step for the activation of the AdoCbl-dependent methylmalonyl CoA mutase enzyme. The calculated free-energy profile reveals two possible pathways, stepwise (I) and concerted (II) for the reductive Co-C cleavage and subsequent H-abstraction. The computed activation barrier from metadynamics for both the pathways is comparable (78.5 and 76.2 kJ/mol, respectively); however, the concerted pathway may be preferred kinetically because it avoids the formation of a high-energy radical intermediate with possibly a larger recrossing rate. Our results are consistent with the previous conductor hypothesis, indicating the explicit role of cob(II)alamin in stabilizing the radical intermediate involved in the H-atom transfer.

Objective: To assess the impact of presenting symptom or incidental finding on symptomatic and radiographic outcomes after robotic-assisted pyeloplasty (RAP)., Methods: We retrospectively reviewed the records of 143 patients at our institution who received pyeloplasty from 2001-2017. Patients without both pre- and postoperative radiographic data were excluded. Patients were grouped by primary presenting symptom into either pain at presentation (pain) or nonpain primary presenting symptom, including incidental findings (nonpain). Primary outcomes were persistence of postoperative symptoms and improvement in diuretic renogram half-times., Results: The study inclusion criteria was met by 105 patients. Pain was the most common presenting symptom (70.0%), followed by incidental finding (10.5%), infection (7.6%), hematuria (4.8%), hypertension (2.8%), elevated creatinine (2.8%), and nausea (1.0%). Patients with nonpain presentations were significantly more likely to have postoperative symptoms (P = .04), and less likely to improve on diuretic renogram (P = .03). Incidental presentation was found to be associated with greater likelihood of persistent postoperative symptoms compared with other presentations (36.3% vs 8.5%, P = .02)., Conclusion: Ureteropelvic junction obstruction (UPJO) patients presenting with pain, experience better symptom and radiographic improvement following RAP compared with patients presenting without pain. Incidental UPJO was the most common nonpain presentation and is associated with less symptomatic and radiographic benefit after RAP. These findings will help reconstructive urologists counsel patients with UPJO regarding outcomes of RAP., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Coenzyme B 12 (Adenosylcobalamin = AdoCbl)-dependent enzymes catalyze complex molecular transformations where cleavage of the CoC bond initiates the catalytic cycle. Alternatively, the CoC bond can be cleaved with light. In both cases, rupture of the CoC bond results in the formation of Co(II)/Ado radical pair (RP). Within the field of B 12 chemistry, there has been a suspicion that photolytic cleavage can be used as a probe or a direct comparison of the native reaction. Herein, we seek to resolve what the connection between light induced RP formation and the native catalytic cycle is. We used a combined QM/MM approach to construct PESs for AdoCbl-dependent ethanolamine ammonia-lyase (EAL) as a function of axial bonds to describe the reaction mechanism. We have found that there is no direct comparison that can be made between photolysis and enzymatic cleavage as the mechanism associated with these involves different electronic states. With that being said, we have explored an alternate hypothesis for the connection which involves the one-electron reduced form of the AdoCbl cofactor. This hypothesis is in line with the concept based on proton-coupled electron transfer (PCET), which involves the formation of AdoCbl cofactor-tyrosine diradical complex. The topology of the PES for the one-electron reduced (D 1 ) cofactor is very similar to the PES associated with photo-induced cleavage (S 1 ). Both surfaces contain two energy minima that are, similarly, the result of two distinct electronic states. Thus, it appears that the reaction mechanism associated with the D 1 surface and the S 1 surface are very similar, providing a plausible connection between photolysis and native catalysis., (Copyright © 2018. Published by Elsevier B.V.)

Methylcobalamin (MeCbl)-dependent enzyme methionine synthase (MetH), plays a critical role in the catalysis of methyl group transfer from methyltetrahydrofolate (CH 3 -H 4 folate) to homocysteine. It often performs a side reaction to generate cob(II)alamin through photolysis of the organometallic CoC σ bond. A hybrid QM/MM method has been applied to explore the photochemistry of MeCbl-bound MetH. The photolytic properties of MeCbl inside MetH are mediated by its manifold of low-lying excited states. The corresponding potential energy surfaces (PESs) of the electronically excited S 1 state has been constructed as a function of axial bond lengths to elucidate the mechanism of photo-induced activation of CoC bond inside the enzyme. The analysis of the S 1 PES has revealed that the two different electronic states of the S 1 PES, namely metal-to-ligand charge transfer (MLCT) and the ligand field (LF), are relevant to the photodissociation of the CoC bond. There are two possible pathways identified, Path A and Path B, that connect the MLCT to LF state that represent possible photodissociation mechanisms. In the case of MetH, one possible photodissociation pathway (Path B) was identified based on the energetics of the MLCT and LF states. The energetically accessible Path B involves the initial detachment of the Co-N Im bond followed by a subsequent displacement of the CoC bond prior to the formation of cob(II)alamin / CH 3 radical pair (RP). The photochemical data of base-on MeCbl in solution was compared with the computed result of MeCbl-bound MetH to understand the effect of the enzymatic environment on the photolytic properties of MeCbl., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In this study, we report the electrocatalytic behavior of the neutral, monomeric Ni(II) complex of diacetyl-bis( N-4-methyl-3-thiosemicarbazonato), NiL 1 , for ligand-assisted metal-centered hydrogen evolution in acetonitrile (ACN) and dimethylformamide (DMF). Using foot-of-the-wave analysis (FOWA), NiL 1 displays a maximum turnover frequency (TOF) of 4200 and 1200 s -1 for acetic acid (CH 3 COOH) in ACN and DMF, whereas for trifluoroacetic acid (CF 3 COOH) the TOFs are 1300 and 120 s -1 in ACN and DMF, respectively. In ACN, the overpotentials are 0.53 and 0.67 V for CH 3 COOH and CF 3 COOH, respectively. In DMF, the overpotential is 0.85 V for CH 3 COOH. First-order dependence with respect to the catalyst is established. NiL 1 displays a minimum Faradaic efficiency of 87% from controlled potential electrolysis. Gas analysis from controlled potential electrolysis in both ACN and DMF using CH 3 COOH and CF 3 COOH confirms NiL 1 as an electrocatalyst to produce H 2 . In ACN, TONs of 48 and 24 were obtained for CH 3 COOH and CF 3 COOH, respectively in 4 h. In DMF, TONs of 13 and 3 were obtained for CH 3 COOH and CF 3 COOH, respectively. The H 2 evolution reaction was evaluated using deuterated acid, demonstrating an inverse kinetic isotope, which is consistent with formation of a metal hydride intermediate. A proposed ligand-assisted metal-centered mechanism for HER is supported by computational investigations. All catalytic intermediates in the proposed mechanism were structurally and energetically characterized using density functional theory (DFT), with the B3LYP/6-311g(d,p) and BP86/TZV/P in solution modeled via polarizable continuum model. The final step of catalysis involves the reaction of [HNi(L 1 ·)] - with H + generating H 2 . The correctness of proposed mechanism was confirmed by location of corresponding transition state (TS) having single imaginary frequency ( i1786 cm -1 ).

Ultrafast time-resolved spectroscopy was used to study the photochemistry of hydroxocobalamin (HOCbl) and aquocobalamin (H 2 OCbl + ) in solution. Spectroscopic measurements and TD-DFT simulations provide a consistent picture of the spectroscopy and photochemistry. Excitation of H 2 OCbl + results in formation of an excited state followed by rapid internal conversion to the ground state (0.35 ± 0.15 ps) through an S 1 /S 0 seam at a slightly elongated Co-O bond length and a significantly elongated Co-N Im bond length. In contrast, the initial elongation of the axial bonds in HOCbl is followed by contraction to an excited state minimum with bonds slightly shorter than those in the ground state. Internal conversion to the ground state follows on a picosecond time scale (5.3 ± 0.4 ps). For both compounds, photodissociation forming cob(II)alamin and hydroxyl radicals (∼1.5% yield) requires excitation to highly excited states. Dissociation is mediated by competition between internal conversion to the S 1 surface and prompt bond cleavage.

Antivitamins B 12 represent an important class of vitamin B 12 analogues that have gained recent interest in several research areas. In particular, 4-ethylphenylcobalamin (EtPhCbl) and phenylethynylcobalamin (PhEtyCbl) exemplify two such antivitamins B 12 which have been characterized structurally and chemically. From a spectroscopic point of view, EtPhCbl is photolabile with a very low quantum yield of photoproducts, while PhEtyCbl is incredibly photostable. Herein, DFT and TD-DFT computations are provided to explore the photolytic properties of these compounds to shed light on the electronic properties that are indicative of these differences. Potential energy surfaces (PESs) were constructed to investigate the mechanisms of photodissociation leading to radical pair (RP) formation and the mechanisms of deactivation to the ground state. The S 1 PESs for each antimetabolite contain two energy minima, one being the metal-to-ligand charge transfer (MLCT) and another the ligand-field (LF) state. There are two possible pathways for photodissociation that can be identified for EtPhCbl but only one (path B) is energetically feasible and involves the lengthening of the Co-N Im bond through the MLCT region followed by the lengthening of the Co-C bond through the LF region. For PhEtyCbl, there is not an energetically favorable path for photolysis; rather, internal conversion (IC) is the significantly preferred photophysical event.

Polarized ultrafast time-resolved X-ray absorption near edge structure (XANES) allows characterization of excited state dynamics following excitation. Excitation of vitamin B 12 , cyanocobalamin (CNCbl), in the αβ-band at 550 nm and the γ-band at 365 nm was used to uniquely resolve axial and equatorial contributions to the excited state dynamics. The structural evolution of the excited molecule is best described by a coherent ballistic trajectory on the excited state potential energy surface. Prompt expansion of the Co cavity by ca. 0.03 Å is followed by significant elongation of the axial bonds (>0.25 Å) over the first 190 fs. Subsequent contraction of the Co cavity in both axial and equatorial directions results in the relaxed S 1 excited state structure within 500 fs of excitation.

In a comment on our article "Theory of Thomson scattering in inhomogeneous media", V. V. Belyi asserts that there is an inconsistency in our method of applying gradient effects via the dielectric superposition principle, in violation of the fluctuation-dissipation theorem; and that his Klimontovich-Langevin formulation would be more appropriate to our application. While we agree that a generalization, along the lines of Belyi's work, would be required for strongly coupled systems, for the weakly coupled systems which we considered, these corrections are not necessary and our approach is still appropriate.Replying to: V. Belyi, Sci. Rep. 8 (2018); https://doi.org/10.1038/s41598-018-25319-6 .

Biologically active forms of cobalamins are crucial cofactors in biochemical reactions and these metabolites can be inhibited by their structurally similar analogues known as antivitamins B 12 . Phenylethynylcobalamin (PhEtyCbl) or 4-ethylphenylcobalamin (EtPhCbl) exemplify recently synthesized and structurally characterized antivitamins B 12 . Herein, DFT and TD-DFT studies of EtPhCbl are provided to explore its photochemical behavior, which may lead to design of arylcobalamins that can be used as therapeutic agents in light activated drug applications. To understand the photolability of EtPhCbl, a potential energy surface (PES) for the photodissociation of the Co-C bond was constructed. The S 1 PES contains two energy minima, one being metal-to-ligand charge transfer (MLCT) and another the ligand-field (LF) state. There are two possible pathways for photodissociation: the first pathway (path A) involves initially lengthening the Co-C bond from the MLCT minimum and then elongation of Co-N Im while the second pathway (path B) involves the lengthening of the Co-N Im bond through the MLCT region followed by the lengthening of the Co-C bond through the LF region. It is shown that photodissociation involving path A is not energetically favorable whereas preferable photodissociation of the Co-C bond involves path B.

The homogeneous, nonaqueous catalytic activity of the rhenium-thiolate complex ReL 3 (L = diphenylphosphinobenzenethiolate) for the hydrogen evolution reaction (HER) has been transferred from nonaqueous homogeneous to aqueous heterogeneous conditions by immobilization on a glassy carbon electrode surface. A series of modified electrodes based on ReL 3 and its oxidized precursor [ReL 3 ][PF 6 ] were fabricated by drop-cast methods, yielding catalytically active species with HER overpotentials for a current density of 10 mA/cm 2 , ranging from 357 to 919 mV. The overpotential correlates with film resistance as measured by electrochemical impedance spectroscopy and film morphology as determined by scanning and transmission electron microscopy. The lowest overpotential was for films based on the ionic [ReL 3 ][PF 6 ] precursor with the inclusion of carbon black. Stability measurements indicate a 2 to 3 h conditioning period in which the overpotential increases, after which no change in activity is observed within 24 h or upon reimmersion in fresh aqueous, acidic solution. Electronic spectroscopy results are consistent with ReL 3 as the active species on the electrode surface; however, the presence of an undetected quantity of catalytically active degradation species cannot be excluded. The HER mechanism was evaluated by Tafel slope analysis, which is consistent with a novel Volmer-Heyrovsky-Tafel-like mechanism that parallels the proposed homogeneous HER pathway. Proposed mechanisms involving traditional metal-hydride processes vs ligand-centered reactivity were examined by density functional theory, including identification and characterization of relevant transition states. The ligand-centered path is energetically favored with protonation of cis-sulfur sites culminating in homolytic S-H bond cleavage with H 2 evolution via H atom coupling.

Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B 12 , cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV-visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributions and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co-CN bond and Co-N Im bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. These observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.

Foams are a common material for high-energy-density physics experiments because of low, tunable densities, and being machinable. Simulating these experiments can be difficult because the equation of state is largely unknown for shocked foams. The focus of this experiment was to develop an x-ray scattering platform for measuring the equation of state of shocked foams on OMEGA EP. The foam used in this experiment is resorcinol formaldehyde with an initial density of 0.34 g/cm 3 . One long-pulse (10 ns) beam drives a shock into the foam, while the remaining three UV beams with a 2 ns square pulse irradiate a nickel foil to create the x-ray backlighter. The primary diagnostic for this platform, the imaging x-ray Thomson spectrometer, spectrally resolves the scattered x-ray beam while imaging in one spatial dimension. Ray tracing analysis of the density profile gives a compression of 3 ± 1 with a shock speed of 39 ± 6 km/s. Analysis of the scattered x-ray spectra gives an upper bound temperature of 20 eV.

The methylation of Hg(II) (SCH3 )2 by corrinoid-based methyl donors proceeds in a concerted manner through a single transition state by transfer of a methyl radical, in contrast to previously proposed reaction mechanisms. This reaction mechanism is a consequence of relativistic effects that lower the energies of the mercury 6p1/2 and 6p3/2 orbitals, making them energetically accessible for chemical bonding. In the absence of spin-orbit coupling, the predicted reaction mechanism is qualitatively different. This is the first example of relativity being decisive for the nature of an observed enzymatic reaction mechanism., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A mechanism of Co-C bond photodissociation in the base-on form of adenosylcobalamin (AdoCbl) was investigated by time-dependent density functional theory (TD-DFT). The key mechanistic step involves singlet radical pair (RP) generation from the first electronically excited state (S1). To connect TD-DFT calculations with ultra-fast excited state dynamics, the potential energy surface (PES) of the S1 state was constructed using Co-C and Co-NIm axial coordinates. The S1 PES can be characterized by two minima separated by a seam resulting from the crossing of two surfaces, of metal-to-ligand charge transfer (MLCT) character near the minimum, and a shallow ligand field (LF) surface at elongated axial bond distances. Only one possible pathway for photolysis (path A) was identified based on energetic grounds. This pathway is characterized by the first elongation of the Co-C bond, followed by photolysis from an LF state where the axial base is partially detached. A new perspective on the photolysis of AdoCbl is then gained by connecting TD-DFT results with available experimental observations.

A new pathway for homogeneous electrocatalytic H2 evolution and H2 oxidation has been developed using a redox active thiosemicarbazone and its zinc complex as seminal metal-free and transition-metal-free examples. Diacetyl-bis(N-4-methyl-3-thiosemicarbazone) and zinc diacetyl-bis(N-4-methyl-3-thiosemicarbazide) display the highest reported TOFs of any homogeneous ligand-centered H2 evolution catalyst, 1320 and 1170 s(-1), respectively, while the zinc complex also displays one of the highest reported TOF values for H2 oxidation, 72 s(-1), of any homogeneous catalyst. Catalysis proceeds via ligand-centered proton-transfer and electron-transfer events while avoiding traditional metal-hydride intermediates. The unique mechanism is consistent with electrochemical results and is further supported by density functional theory. The results identify a new direction for the design of electrocatalysts for H2 evolution and H2 oxidation that are not reliant on metal-hydride intermediates.

Thomson scattering of laser light is one of the most fundamental diagnostics of plasma density, temperature and magnetic fields. It relies on the assumption that the properties in the probed volume are homogeneous and constant during the probing time. On the other hand, laboratory plasmas are seldom uniform and homogeneous on the temporal and spatial dimensions over which data is collected. This is particularly true for laser-produced high-energy-density matter, which often exhibits steep gradients in temperature, density and pressure, on a scale determined by the laser focus. Here, we discuss the modification of the cross section for Thomson scattering in fully-ionized media exhibiting steep spatial inhomogeneities and/or fast temporal fluctuations. We show that the predicted Thomson scattering spectra are greatly altered compared to the uniform case, and may lead to violations of detailed balance. Therefore, careful interpretation of the spectra is necessary for spatially or temporally inhomogeneous systems.

The photolysis of the methylcobalamin cofactor (MeCbl) in its base-off form was investigated by considering the extent of spin-orbit coupling (SOC). Triplet Co-C photodissociation pathways previously invoked at the density functional theory level using Landau-Zener theory were further validated with ab initio calculations that combine SOC based on multi-state second order perturbation theory. It was determined that SOC is feasible between singlet and triplet states at elongated Co-C distances, leading to photodissociation from the state having dominant σ(dz(2)) character, by either direct coupling with the lowest singlet states or by crossing with SOC mixed triplets.