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The effect of the presence of glucose and sucrose on the nonintrinsic contribution to partial molar volume (Θ)ni of bovine serum albumin (BSA) is determined by means of static and dynamic electronic polarizability measurements. For that aim, a combined strategy based on high-resolution refractometry, high exactitude densitometry, and synchronous fluorescence spectroscopy is applied. Both static and dynamic mean electronic molecular polarizability values are found to be sensitive to the presence of glucose. In the case of sucrose, the polarizability of BSA is not appreciably affected. In fact, our results revealed that the electronic changes observed occurred without a modification of the native conformation of BSA. On the contrary, a nonmonotonous behavior with the concentration is observed in presence of glucose. These results advocate the influence of the electronic polarization on the repulsive and attractive protein-carbohydrate interactions. An analysis using the scaled particle theory indicates that the accumulation of glucose on the protein surface promotes dehydration. Inversely, hydration and preferential exclusion occur in the vicinity of the protein surface for sucrose-enriched systems. [ABSTRACT FROM AUTHOR]

A chemical cosubstitution strategy was implemented to design potential ultraviolet (UV) and deep-UV nonlinear optical (NLO) materials. Taking the classic β- BaB2O4 as a maternal structure, by simultaneously replacing the Ba2+ and [B3O6]3- units with monovalant (K+), divalent (alkaline earth metal), trivalent (rare-earth metal, Bi3+) ions, and the [B5O10]5- clusters through two different practical routes, 12 new mixed-metal noncentrosymmetric borates K7MIIRE2(B5O10)3 (MII = Ca, Sr, Ba, K/RE0.5; RE = Y, Lu, Gd) as well as K7MIIBi2(B5O10)3 (MII = Pb, Sr) were successfully designed and synthesized as high-quality single crystals. The selected K7CaY2(B5O10)3, K7SrY2(B5O10)3, and K7BaY2(B5O10)3 compounds were subjected to experimental and theoretical characterizations. They all exhibit suitable second-harmonic generation (SHG) responses, as large as that of commercial KH2PO4 (KDP), and also exhibit short UV cutoff edges. These results confirm the feasibility of this chemical cosubstitution strategy to design NLO materials and that the three selected crystals may have potential application as UV NLO materials. [ABSTRACT FROM AUTHOR]

Three selenophene-incorporated quaterchalcogenophene-based donor-acceptor copolymers PFBT2Th2Se, PFBT2Se2Th, and PFBT4Se are designed and synthesized. To systematically fine-tune the molecular properties and investigate the chalcogen effect, PFBT2Th2Se and PFBT2Se2Th hybridize two thiophenes and two selenophenes as the donor with different isomeric main-chain placement while thiophene-free PFBT4Se uses quaterselenophene as the donor. On account of the selenophene's advantageous features such as higher quinoidal population and higher molecular polarizability, the three polymers show good light-harvesting ability, strong intermolecular interactions, high crystallinity, and high charge mobilities. Bulk-heterojunction solar cells incorporating these selenophene-containing polymers have exhibited promising photovoltaic performance with impressive current densities over 20 mA/cm². The device with the PFBT2Se2Th:PC71BM blend showed a PCE of 9.02% with a Jsc of 21.02 mA/cm². In addition, the device using quaterselenophene-based PFBT4Se:PC71BM blend exhibited a PCE of 8.92% with a superior Jsc of 22.63 mA/cm² which represents one of the highest current densities from polymer:fullerene-based solar cells reported in the literature. [ABSTRACT FROM AUTHOR]

Polyparameter Linear Free Energy Relationships (pp-LFERs), also called Linear Solvation Energy Relationships (LSERs), are used to predict many environmentally significant properties of chemicals. A method is presented for computing the necessary chemical parameters, the Abraham parameters (AP), used by many pp-LFERs. It employs quantum chemical calculations and uses only the chemical's molecular structure. The method computes the Abraham E parameter using density functional theory computed molecular polarizability and the Clausius-Mossotti equation relating the index refraction to the molecular polarizability, estimates the Abraham V as the COSMO calculated molecular volume, and computes the remaining AP S, A, and B jointly with a multiple linear regression using sixty-five solvent-water partition coefficients computed using the quantum mechanical COSMO-SAC solvation model. These solute parameters, referred to as Quantum Chemically estimated Abraham Parameters (QCAP), are further adjusted by fitting to experimentally based APs using QCAP parameters as the independent variables so that they are compatible with existing Abraham pp-LFERs. QCAP and adjusted QCAP for 1827 neutral chemicals are included. For 24 solvent-water systems including octanol-water, predicted log solvent-water partition coefficients using adjusted QCAP have the smallest root-mean-square errors (RMSEs, 0.314-0.602) compared to predictions made using APs estimated using the molecular fragment based method ABSOLV (0.45-0.716). For munition and munition-like compounds, adjusted QCAP has much lower RMSE (0.860) than does ABSOLV (4.45) which essentially fails for these compounds. [ABSTRACT FROM AUTHOR]

The novel donor-acceptor-donor (D-A-D)-type fluorophore with an asymmetric structure is reported. The twisted-induced charge transfer (TICT) luminescence was observed. The degree of charge transfer and radiative rate constant in the luminescence increased simultaneously with increase in orientational polarizability of solvents. In contrast to the numerous CT fluorophore researches, this behavior has never been previously observed. This characteristic behavior reveals the existence of an effective exciton coupling between the CT states in the donor-acceptor-donor-type fluorophore for the first time. [ABSTRACT FROM AUTHOR]

The IPPP-CLOPPA method is applied to investigate the influence of a methyl group on the energy of the hydrogen bonds and the potential energy curve of the bridge protons in model compounds, which mimic the methylated and unmethylated cytosine-guanine base pairs. On the same grounds, this influence on the polarizability of the intermolecular hydrogen bonds of these compounds is also addressed, in order to determine whether this linear response property provides a significant proof of the electronic mechanisms that affect the stabilization of the hydrogen bonds. Results obtained show that the methyl electronic system delocalizes on the hydrogen bond region, and changes of these intermolecular hydrogen bonds are due to this effect of delocalization. [ABSTRACT FROM AUTHOR]

Conspectus Transition metal based high nuclearity molecular magnetic cages are a very important class of compounds owing to their potential applications in fabricating new generation molecular magnets such as single molecular magnets, magnetic refrigerants, etc. Most of the reported polynuclear cages contain carboxylates or alkoxides as ligands. However, the binding ability of phosphonates with transition metal ions is stronger than the carboxylates or alkoxides. The presence of three oxygen donor sites enables phosphonates to bridge up to nine metal centers simultaneously. But very few phosphonate based transition metal cages were reported in the literature until recently, mainly because of synthetic difficulties, propensity to result in layered compounds, and also their poor crystalline properties. Accordingly, various synthetic strategies have been followed by several groups in order to overcome such synthetic difficulties. These strategies mainly include use of small preformed metal precursors, proper choice of coligands along with the phosphonate ligands, and use of sterically hindered bulky phosphonate ligands. Currently, the phosphonate system offers a library of high nuclearity transition metal and mixed metal (3d-4f) cages with aesthetically pleasing structures and interesting magnetic properties. This Account is in the form of a research landscape on our efforts to synthesize and characterize new types of phosphonate based high nuclearity paramagnetic transition metal cages. We quite often experienced synthetic difficulties with such versatile systems in assembling high nuclearity metal cages. Few methods have been emphasized for the self-assembly of phosphonate systems with suitable transition metal ions in achieving high nuclearity. We highlighted our journey from 2005 until today for phosphonate based high nuclearity transition metal cages with VIV/V, MnII/III, FeIII, CoII, NiII, and CuII metal ions and their magnetic properties. We observed that slight changes in stoichiometry, reaction conditions, and presence or absence of coligand played crucial roles in determining the final structure of these complexes. Most of the complexes included are regular in geometry with a dense arrangement of the above-mentioned metal centers in a confined space, and a few of them also resemble regular polygonal solids (Archimedean and Platonic). Since there needs to be a historical approach for a comparative study, significant research output reported by other groups is also compared in brief to ensure the potential of phosphonate ligands in synthesizing high nuclearity magnetic cages. [ABSTRACT FROM AUTHOR]

Despitethe fact that polarizability of water is different in thebulk and in protein, simulations of protein–ligand complexesare mostly carried out in nonpolarizable water media. We present oxime(HI-6) unbinding from the active site gorge of AChE, known to be stronglyinfluenced by intermolecular cation-π, hydrogen bridge (HB)and water bridge (WB) interactions and by molecular simulations witheffective polarization in polarizable mean-field model of TIP3P water.Enabled by the recent availability of a method of obtaining microkineticsof rare events, we set out to investigate the rate constants of unbindingtransitions from one basin to the other through a combination of metadynamicsand hyperdynamics simulations. The results underpin the importanceof electronic polarization effects on the pathways, potential of meanforce, rate constants, and HB and WB dynamics of unbinding transitionsof a drug molecule ligated to protein interior. The method is alsoapplicable to unravel the binding mechanisms. [ABSTRACT FROM AUTHOR]

Dispersive interactions are known to play amajor role in molecularassociations in the gas phase and in the solid state. In solution,however, their significance has been disputed in recent years on thebasis of several arguments. A major problem until now has been theseparation of dispersive and hydrophobic effects, which are both maximizedin water due the low polarizability of this most important medium.Analyses of complexes between porphyrins and systematically variedsubstrates in water have allowed us to discriminate dispersive fromhydrophobic effects, as the latter turned out to be negligible forcomplexations with flat surfaces such as porphyrins. Also, for thefirst time, it has become possible to obtain binding free energy incrementsΔΔGfor a multitude of organic residuesincluding halogen, amide, amino, ether, carbonyl, ester, nitro, sulfur,unsatured, and cyclopropane groups, which turned out to be additive.Binding contributions for saturated residues are unmeasurably small,with ΔΔG> 1 kJ/mol, but they increaseto, e.g., ΔΔG= 5 kJ/mol for a nitrogroup, a value not far from, e.g., that of a stacking pyridine ring.Stacking interactions of heteroarenes with porphyrins depend essentiallyon the size of the arenes, in line with polarizabilities, and seemto be rather independent of the position of nitrogen within the rings. [ABSTRACT FROM AUTHOR]

In order to carry out a detailedanalysis of the molecular static polarizability, which is the responseof the molecule to a uniform external electric field, the molecularpolarizability was computed using the finite-difference method for21 small molecules, using density functional theory. Within nine chargepopulation schemes (Löwdin, Mulliken, Becke, Hirshfeld, CM5,Hirshfeld-I, NPA, CHELPG, MK-ESP) in common use, the charge fluctuationcontribution is found to dominate the molecular polarizability, withits ratio ranging from 59.9% with the Hirshfeld or CM5 scheme to 96.2%with the Mulliken scheme. The Hirshfeld-I scheme is also used to computethe other contribution to the molecular polarizability coming fromthe induced atomic dipoles, and the atomic polarizabilities in eightsmall molecules and water pentamer are found to be highly anisotropicfor most atoms. Overall, the results suggest that (a) more emphasisprobably should be placed on the charge fluctuation terms in futurepolarizable force field development and (b) an anisotropic polarizabilitymight be more suitable than an isotropic one in polarizable forcefields based entirely or partially on the induced atomic dipoles. [ABSTRACT FROM AUTHOR]

Effectivepolarizabilities of Na(NH3)n(n= 8–27) clusters were measuredby electric deflection as a function of the particle size. A significantfield-induced shift of the beam intensity profile without the occurrenceof broadening revealed that the clusters behave as liquidlike polarobjects in the conditions of the experiment (cluster temperatureswere estimated in the range of 110–145 K). Most of the clusterpolarity is attributed to the spontaneous promotion of the alkaliatom valence electron to a diffuse state stabilized by the clustersolvent field, with the consequent formation of (e–, Na+) pairs. The average modulus of the dipole of Na–NH3clusters, μ0, was determinedusing the Langevin-Debye theory, and the data was compared with previousmeasurements obtained for Na–H2O clusters. Sodium-dopedammonia clusters exhibit much larger μ0values and a step size dependence which is not present whenthe solvent is water. This evidence suggests that while the (e–, Na+) structure is rather compact in Na(H2O)nclusters and remains almostunchanged during the solvation process, in Na(NH3)nthe unpaired electron abandons the proximityof the Na+ion and gradually extends and occupies new solventshells. [ABSTRACT FROM AUTHOR]

Startingfrom a nonpolarizable rigid molecular model for DMSO,a polarizable rigid model for DMSO in the liquid phase is proposed.The molecular polarizability is represented by a charge-on-spring(COS) inducible dipole at the sulfur atom and its polarization isdamped for large values of the electric field strength. Some parametersof the model, the partial charge distribution, the polarizability,the value of the electric field at which damping sets in, were varied,and the overall depth and repulsion strength of the Lennard–Jonesinteractions were scaled with the aim of reproducing the experimentalvalues for the molecular dipole moment, the density, heat of vaporization,and static dielectric constant of liquid DMSO at ambient temperatureand pressure. The polarizable DMSO/D model well reproduces the experimentaldata, such as excess free energy, surface tension, translational,and rotational diffusion, for liquid DMSO. The model is further testedin mixtures with polarizable water models and in mixtures with nonpolarizableDMSO. The latter results suggest that it could serve as model forpolarizable cosolvent in aqueous solutions. [ABSTRACT FROM AUTHOR]

Theeffect of solvent polarizability and multipole effects on theamide I vibrational spectra of a peptide unit is investigated. Fourmolecular dynamics force fields of increasing complexity for the solventare used to model both the linear absorption and two-dimensional infraredspectra. It is observed that, at least in chloroform solution, thepredicted solvent shift is considerably improved when accounting forthe polarizabiltiy and multipole effects. The latter are typicallyconnected with halogen bonding. Significant deviations are still observedfor more sensitive line shape parameters such as the spectral widthand line skewness. However, the findings demonstrate that previouslyobserved deviations have an origin in the force field treatment ratherthan in the electrostatic mapping procedure frequently employed tosimulate linear absorption and two-dimensional infrared spectroscopy. [ABSTRACT FROM AUTHOR]

Theintermolecular potential energy of the C6H6–SH2and C6H6–NH3dimersis formulated as combination of independent electrostaticand nonelectrostatic contributions. The relevant parameters of thenonelectrostatic terms, derived from molecular polarizability components,have been proved to be useful to describe in a consistent way bothsize repulsion and dispersion attraction forces. The representationadopted for the electrostatic contribution asymptotically reproducesthe dipole quadrupole interaction. To test the validity of the proposedpotential formulation, the features of the most stable configurationsof the systems predicted have been compared with the available abinitio and experimental data. Moreover, the strength of the C6H6–HX interaction has been analyzed comparingthe obtained results with the corresponding ones for the C6H6–H2O and C6H6–CH4systems, investigated previously with thesame methodology. Information on the relative orientation dependenceof the partners, arising from the anisotropy of the intermolecularinteraction, evaluated at different intermolecular distances, hasbeen also obtained. Such information is crucial to evaluate sterodynamicseffects in bimolecular collisions. [ABSTRACT FROM AUTHOR]

We have developed an automated parameteroptimization softwareframework (ParOpt) that implements the Nelder–Mead simplexalgorithm and applied it to a coarse-grained polarizable water model.The model employs a tabulated, modified Morse potential with decoupledshort- and long-range interactions incorporating four water moleculesper interaction site. Polarizability is introduced by the additionof a harmonic angle term defined among three charged points withineach bead. The target function for parameter optimization was basedon the experimental density, surface tension, electric field permittivity,and diffusion coefficient. The model was validated by comparison ofstatistical quantities with experimental observation. We found verygood performance of the optimization procedure and good agreementof the model with experiment. [ABSTRACT FROM AUTHOR]

Tröster et al. (J. Phys. Chem B2013, 117, 9486−9500) recently suggested a mixed computational and empirical approach to the optimization of polarizable molecular mechanics (PMM) water models. In the empirical part the parameters of Buckingham potentials are optimized by PMM molecular dynamics (MD) simulations. The computational part applies hybrid calculations, which combine the quantum mechanical description of a H2O molecule by density functional theory (DFT) with a PMM model of its liquid phase environment generated by MD. While the static dipole moments and polarizabilities of the PMM water models are fixed at the experimental gas phase values, the DFT/PMM calculations are employed to optimize the remaining electrostatic properties. These properties cover the width of a Gaussian inducible dipole positioned at the oxygen and the locations of massless negative charge points within the molecule (the positive charges are attached to the hydrogens).The authors considered the cases of one and two negative charges rendering the PMM four- and five-point models TL4P and TL5P. Here we extend their approach to three negative charges, thus suggesting the PMM six-point model TL6P. As compared to the predecessors and to other PMM models, which also exhibit partial charges at fixed positions,TL6P turned out to predict all studied properties of liquid water at p0= 1 bar and T0= 300 K with a remarkable accuracy. These properties cover,for instance, the diffusion constant, viscosity, isobaric heat capacity, isothermal compressibility, dielectric constant, density, and the isobaric thermal expansion coefficient. This success concurrently provides a microscopic physical explanation of corresponding shortcomings of previous models. It uniquely assigns the failures of previous models to substantial inaccuracies in the description of the higher electrostatic multipole moments of liquid phase water molecules. Resulting favorable properties concerning the transferability to other temperatures and conditions like the melting of ice are also discussed. [ABSTRACT FROM AUTHOR]

We employ a recently developed methodologyto study structural and energetic properties of the first solvationshells of the potassium ion in nonpolar environments due to aromaticrings, which is important to understand the selectivity of severalbiochemical phenomena. Our evolutionary algorithm is used in the globaloptimization study of clusters formed of K+solvated withhexafluorobenzene (HFBz) molecules. The global intermolecular interactionfor these clusters has been decomposed in HFBz–HFBz and inK+–HFBz contributions, using a potential model basedon different decompositions of the molecular polarizability of hexafluorobenzene.Putative global minimum structures of microsolvation clusters up to21 hexafluorobenzene molecules were obtained and compared with theanalogous K+–benzene clusters reported in our previouswork (J. Phys. Chem. A2012, 116, 4947–4956). We have found that both K+–(Bz)nand K+–(HFBz)nclusters show a strong magic number aroundthe closure of the first solvation shell. Nonetheless, all K+–benzene clusters have essentially the same first solvationshell geometry with four solvent molecules around the ion, whereasthe corresponding one for K+–(HFBz)nis completed with nine HFBz species, and its structuralmotif varies as nincreases. This is attributed tothe ion–solvent interaction that has a larger magnitude forK+–Bz than in the case of K+–HFBz.In addition, the ability of having more HFBz than Bz molecules aroundK+in the first solvation shell is intimately related tothe inversion in the sign of the quadrupole moment of the two solventspecies, which leads to a distinct ion–solvent geometry ofapproach. [ABSTRACT FROM AUTHOR]

Thehyperpolarizabilities of three p-quinodimethanederivatives with low diradical character have been evaluated. As electroncorrelation effects rule the electric field response properties, wavefunction and density functional theory-based methods have been comparedto benchmark values calculated with the coupled cluster method includingsingle and double excitations as well as perturbative estimate ofthe triples [CCSD(T)]. The basis set effects have been further assessed.This study shows that the determination of the second hyperpolarizabilitywith the CCSD method provides results in closest agreement with theCCSD(T) reference values. The use of MP2 level of theory performswell for the closed-shell compound but not for open-shell ones. Spin-projectionUMP3 and UMP4 methods reproduce well UCCSD(T) values for the p-quinodimethane but not for the charged compound. Withoutspin projection correction, density functional theory with a largerange of exchange-correlation functionals does not perform well forthese systems. Similar effects have been observed for the polarizabilityand first hyperpolarizability, although these effects are smaller. [ABSTRACT FROM AUTHOR]

Electrophotoluminescence(E-PL) spectra, i.e., plots of the electric-field-induced change inphotoluminescence intensity as a function of wavenumber, have beenmeasured for pyrene solution. At high concentrations of pyrene whereexcimer fluorescence is observed along with the monomer fluorescenceemitted from the locally excited state, both excimer fluorescenceand monomer fluorescence are enhanced by application of electric fields.The results show that the nonradiative decay process at the excimeremitting state is decelerated by application of electric fields. Itis also found that molecular polarizability of pyrene excimer is largerthan that of pyrene monomer in the ground state by ∼270 ±90 Å3, based on the analysis of the Stark shift ofthe excimer fluorescence. [ABSTRACT FROM AUTHOR]

In the companion paper, we presented a set of induced dipole interaction models using four types of screening functions, which include the Applequist (no screening), the Thole linear, the Thole exponential model, and the Thole Tinker-like (another form of exponential screening function) functions. In this work, we evaluate the performance of polarizability models using a large set of amino acid analog pairs in conformations that are frequently observed in protein structures as a benchmark. For each amino acid pair, we calculated quantum mechanical interaction energies at the MP2/aug-cc-pVTZ//MP2/6-311(d,p) level with the basis set superposition error (BSSE) correction and compared them with molecular mechanics results. Encouragingly, all polarizable models significantly outperform the additive F94 and F03 models (mimicking AMBER ff94/ff99 and ff03 force fields, respectively) in reproducing the BSSE-corrected quantum mechanical interaction energies. In particular, the root-mean-square errors (RMSEs) for three Thole models in Set A (where the 1−2 and 1−3 interactions are turned off and all 1−4 interactions are included) are 1.456, 1.417, and 1.406 kcal/mol for model AL (Thole Linear), model AE (Thole exponential), and model AT (Thole Tinker-like), respectively. In contrast, the RMSEs are 3.729 and 3.433 kcal/mol for F94 and F03 models, respectively. A similar trend was observed for the average unsigned errors (AUEs), which are 1.057, 1.025, 1.011, 2.219, and 2.070 kcal/mol for AL, AE, AT, F94/ff99, and F03, respectively. Analyses based on the trend line slopes indicate that the two fixed charge models substantially underestimate the relative strengths of noncharge−charge interactions by 24 (F03) and 35% (F94), respectively, whereas the four polarizable models overestimate the relative strengths by 5 (AT), 3 (AL, AE), and 13% (AA), respectively. Agreement was further improved by adjusting the van der Waals parameters. Judging from the notably improved accuracy in comparison with the fixed charge models, the polarizable models are expected to form the foundation for the development of high quality polarizable force fields for protein and nucleic acid simulations. [ABSTRACT FROM AUTHOR]