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A series of petroleum coke (petcoke)-derived solid acid catalysts were prepared via nitric acid treatment with or without ball milling pretreatment. The inherent sulfur in petcoke was converted to sulfonic groups, which were active sites for the esterification of octanoic acid and methanol at 60 °C, with ester yields of 14–43%. More specifically, samples without ball milling treated at 120 °C for 3 h had a total acidity of 4.67 mmol/g, which was 1.6 times that of the samples treated at 80 °C, despite their −SO3H acidities being similar (~0.08 mmol/g). The samples treated for 24 h had higher −SO3H (0.10 mmol/g) and total acidity (5.25 mmol/g) but not increased catalytic activity. Ball milling increased the defects and exposed aromatic hydrogen groups on petcoke, which facilitated further acid oxidation (0.12 mmol −SO3H/g for both materials and total acidity of 5.18 mmol/g and 5.01 mmol/g for BP-N-3/120 and BP-N-8/90, respectively) and an increased ester yield. DFT calculations were used to analyze the pathways of sulfonic acid group formation, and the reaction pathway with NO2• was the most thermodynamically and kinetically favourable. The activities of the prepared catalysts were related to the number of −SO3H acid sites, the total acidity, and the oxygen content, with the latter two factors having a negative impact. [ABSTRACT FROM AUTHOR]

The role of halogen bonding (XB) in chemical catalysis has largely involved using XB donors as Lewis acid activators to modulate the reactivity of partner Lewis bases. We explore a more uncommon scenario, where a Lewis base modulates reactivity via a spectator halogen bond interaction. Our computational studies reveal that spectator halogen bonds may play an important role in modulating the rate of SN2 reactions. Most notably, π acceptors such as PF3 significantly decrease the barrier to substitution by decreasing electron density in the very electron rich transition state. Such π-backbonding represents an example of a heretofore unexplored situation in halogen bonding: the combination of both σ-donation and π-backdonation in this "non-covalent" interaction. The broader implications of this observation are discussed. [ABSTRACT FROM AUTHOR]

Sulfur K-edge X-ray absorption spectroscopy (S K-edge XAS) was applied to investigate the electronic structure of primary and tertiary S-nitrosothiols. Our experimental data, supported by density functional calculations, indicate that changes at Ca affect the S-nitroso group through both inductive and direct orbital effects. Furthermore, our data are consistent with a weakening of the S-N bond in tertiary S-nitrosothiols as compared to their primary S-nitroso analogues. These results support existing computational models and suggest that the reactivity of S-nitrosothiols is not dominated by the electronics of the S-N bond. Key words: S-nitrosothiols, X-ray absorption spectroscopy (XAS), S-nitroso-N-acetylpenicillamine (SNAP), nitrosoglutathione. On a fait appel a la spectroscopie d'absorption des rayons-X pres du seuil K du soufre (SAX pres du seuil K du soufre) pour etudier la structure electronique de S-nitrothiols primaires et tertiaires. Les donnees experimentales et les calculs de la fonctionnelle de la densite indiquent que les changements au niveau du Ca affectent le groupe S-nitroso par des effets inductifs ainsi que par des effets directs d'orbitales. De plus, les donnees sont en accord avec un affaiblissement de la liaison S-N dans les S-nitrosothiols primaires par rapport a leurs analogues S-nitroso primaires. Ces resultats supportent les modeles existants derives de calculs theoriques et ils suggerent que la reactivite des S-nitrosothiols n'est pas dominee par les effets electroniques de la liaison S-N. Mots-cles: S-nitrosothiols, spectroscopie d'absorption des rayons X (SAX), S-nitroso-N-acetylpenicillamine (SNAP), nitrosoglutathion. [Traduit par la Redaction], Introduction S-Nitrosothiols are important nitric oxide (NO) derivatives with potential therapeutic applications. (1) Nitric oxide has been implicated in various physiological processes, including neurotransmission, (2) induction of smooth muscle relaxation, [...]

Spectroscopic and computational studies of the low-spin iron complexes [Fe(super III)(S(sub 2)(super Me2)N3(Pr,Pr))(N3)] and [Fe(super III)(S(sub 2)(super Me2)N3(Pr,Pr))](super 1+) are performed to investigate the electronic features of these species and their relation to the low-spin ferric active sites of nitrile hydratases. Density functional and semiempirical configuration interaction calculations are used to develop an electronic structure description of the two model complexes.

The nature of the Ru-S bond in the parent thiolato complexes and mono- (sulfenato) and bis- (sulfinato) oxygenated species including the affect of substituents on the sulfur and arene are compared. Sulfur K-edge XAS results have shown that [S.sub.3p] donation into the [Ru.sub.4d] manifold has depended on the oxidation state of the sulfur atom, whereas Ru K-edge data has shown little change at the metal center, and the DFT results have allowed a more detailed analysis of the electronic contributions to the Ru-S bond.

The photochemistry of methionine, methionine sulfoxide and methionine sulfone are examined by using sulfur K-edge X-ray absorption spectroscopy to analyze the redox photochemical processes under different conditions. Photooxidation has occurred only under aerobic conditions, whereas methionine sulfone is photochemically inert, thus providing new insights into potential photochemical processes leading to cataract formation.

N-heterocyclic carbenes (NHC)-Rh complexes are synthesized, which has bound dioxygen giving square planar complexes with no net change in the oxidation state of the metal. The effect of bonding arrangement on the reactivity is being examined.

The experimentally verifiable rationale is provided for the differences in initiation rates between the two precatalysts, based on the electronic differences between P[R.sub.3] and N-heterocyclic carbenes (NHC) ligation in these and related complexes. The studies have shown that the rate of phosphine dissociation is slower due to the enhanced electron-deficiency of the metal center.

The synthesis and characterization of 1,4- and 1,3-benzene-bridged N,N'-diisopropyl-6-oxoverdazyls is described. The reaction provides insight into the intramolecular electronic and magnetic coupling between verdazyl chromophores.

It is proved that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz) are measured as a calibration standard.

Research has been conducted on rubredoxin electron transfer kinetics. The study of the kinetics has been carried out via the use of density functional methods in order to determine electronic structure characteristics affecting electron exchange in electron-transport proteins.

Research has been conducted on reduction potential difference between [FeCl (sub)4] (super)2-,1- and [Fe(SR) (sub)4] (super)2-,1-. The authors describe the use of photoelectron spectroscopy and theoretical methods in determining the rolw of electronic structure in these differences.

Research has been conducted on [FeX (sub)4] (super)2-, 1- complexes, where X= Cl, SR. The autors have investigated the electronic relaxation, the molecular electronic structure change as an oxidation response, and they report the results.

The details of ligand-induced backbonding in nickel diphosphine π complexes are explored using nickel L-edge (3d←2p) X-ray absorption spectroscopy as a means of quantifying the degree of backbonding derived from direct Ni 3d donation into the π ligand. It is observed that backbonding into weakly π acidic ligands such as alkenes and arenes is dominated by contributions from the diphosphine ligand via σ-donation, leading to activated metallacycles with a Ni(0) d10 metal centre. With more strongly π acidic ligands, however, metal contributions to backbonding increase substantially leading to a more electron-deficient metal centre that is best described as having a Ni(I) spectroscopic oxidation state. [ABSTRACT FROM AUTHOR]

The electronic nature of Ni π‐complexes is underexplored even though these complexes have been widely postulated as intermediates in organometallic chemistry. Herein, the geometric and electronic structure of a series of nickel π‐complexes, Ni(dtbpe)(X) (dtbpe=1,2‐bis(di‐tert‐butyl)phosphinoethane; X=alkene or carbonyl containing π‐ligands), is probed using a combination of 31P NMR, Ni K‐edge XAS, Ni Kβ XES, and DFT calculations. These complexes are best described as square planar d10 complexes with π‐backbonding acting as the dominant contributor to M−L bonding to the π‐ligand. The degree of backbonding correlates with 2JPP from NMR and the energy of the Ni 1s→4pz pre‐edge in the Ni K‐edge XAS data, and is determined by the energy of the π*ip ligand acceptor orbital. Thus, unactivated olefinic ligands tend to be poor π‐acids whereas ketones, aldehydes, and esters allow for greater backbonding. However, backbonding is still significant even in cases in which metal contributions are minor. In such cases, backbonding is dominated by charge donation from the diphosphine, which allows for strong backdonation, although the metal centre retains a formal d10 electronic configuration. This ligand‐induced backbonding can be formally described as a 3‐centre‐4‐electron (3c‐4e) interaction, in which the nickel centre mediates charge transfer from the phosphine σ‐donors to the π*ip ligand acceptor orbital. The implications of this bonding motif are described with respect to both structure and reactivity. Backbonding like never before: A series of Ni π‐complexes were explored using a combination of spectroscopic and computational methods to reveal an intriguing contribution to backbonding: metal‐mediated ligand‐to‐ligand backdonation. Such ligand‐induced backdonation is the dominant contribution for weakly π‐acidic ligands such as alkenes and allows for strong bonding while retaining a formal d10 electronic configuration. [ABSTRACT FROM AUTHOR]

Tetrahydrophthalazine derivatives have found important applications in pharmaceutical research, but existing synthetic methods are unable to access them regio‐ and stereoselectively. Here, a new approach is presented that addresses these challenges by utilizing a 6‐endo‐trig radical cyclization in the key step. The desired tetrahydrophthalazines can be accessed in high yields (55–98 %) and high diastereoselectivities for the trans‐product (>95:5) starting either from readily accessible hydrazones, or from the corresponding aldehydes and substituted Boc‐hydrazides in a one‐pot process. The synthetic versatility of the tetrahydrophthalazine core was demonstrated by its straightforward conversion to dihydro‐phthalazines, phthalazines, or pyrazolo dione derivatives. Furthermore, the N−N bond was reduced to afford a new route to 1,4‐diamines. Selective at last: Tetrahydrophthalazine derivatives have found important applications in pharmaceutical research, but existing synthetic methods are unable to access them regio‐ and stereoselectively. Here, a new approach is presented that addresses these challenges by utilizing a 6‐endo‐trig radical cyclization in the key step. The desired tetrahydrophthalazines can be accessed in high yields and high diastereoselectivities for the trans‐product starting either from readily accessible hydrazones or the corresponding aldehydes and substituted Boc‐hydrazides in a one‐pot process. [ABSTRACT FROM AUTHOR]

An experimental analysis is conducted to determine the usefulness of X-ray absorption spectroscopy (XAS) at the sulfur K-edge to complement the spectroscopic characterization of sulfur-centered radicals. The approach provides the benefits of element-specificity as well as the ability to detect and characterize electron paramagnetic resonance (EPR)-silent intermediates.

Electron paramagnetic resonance (EPR) spectroscopy was used in combination with X-ray fluorescence (XRF) spectroscopy to quantify the reacted copper and the total copper concentrations in monoethanolamine amended micronized copper (MCEA) treated red pine and lodgepole pine. A simulation procedure using Microsoft Excel Solver was used to resolve the EPR spectral areas and calculate the levels of Cu-N-wood and Cu-O-wood species. The MCEA treated wood was found to contain mainly a Cu-N-wood species at the surface, the concentration of which diminished quickly as the sampling depth increased. The retentions of Cu-O-wood species were almost zero and only increased slightly with sample depth, but never exceeded 0.03 %. The total copper content determined by XRF was reduced as the sample locations moved from the wood surface to the interior of the sample. Comparison of the combined reacted copper levels and the total copper retention showed most of the micronized copper in the treated wood remained unreacted. [ABSTRACT FROM AUTHOR]

The interactions between a surface-adsorbed dye and a soluble redox-active electrolyte species in the dye-sensitized solar cell has a significant impact on the rate of regeneration of photo-oxidized dye molecules and open-circuit voltage of the device. Dyes must therefore be designed to encourage these interfacial interactions, but experimentally resolving how such weak interactions affect electron transfer is challenging. Herein, we use X-ray absorption spectroscopy to confirm halogen bonding can exist at the dye-electrolyte interface. Using a known series of triphenylamine-based dyes bearing halogen substituents geometrically positioned for reaction with halides in solution, halogen bonding was detected only in cases where brominated and iodinated dyes were photo-oxidized. This result implies that weak intermolecular interactions between photo-oxidized dyes and the electrolyte can impact device photovoltages. This result was unexpected considering the low concentration of oxidized dyes (less than 1 in 100,000) under full solar illumination. [ABSTRACT FROM AUTHOR]

The properties of halogen bonds (XBs) in solid-state I2X− and I4X− materials (where X = Cl, Br) are explored using donor K-edge X-ray absorption spectroscopy (XAS) to experimentally determine the degree of charge transfer in such XB interactions. The degree of covalency in these bonds is substantial, even in cases where significantly weaker secondary interactions are observed. These data, in concert with previous work in this area, suggests that certain halogen bonds have covalent contributions to bonding that are similar to, and even exceed, those observed in transition metal coordinate bonds. For this reason, we suggest that XB interactions of this type be denoted in a similar way to coordination bonds (X → Y) as opposed to using a representation that is the same as for significantly less covalent hydrogen bonds (X…Y). [ABSTRACT FROM AUTHOR]

Wood preservatives using micronized particulate copper as the main active ingredient recently introduced in the USA have generated controversies due to their limited intrinsic solubility compared to the conventional soluble copper treatments. Because the availability of soluble copper ions is essential for these preservatives to provide an effective treatment, concerns centered on whether they are able to produce soluble copper when introduced into wood, and the copper fixation mechanism of the treatment is little understood. A combination of Electron Paramagnetic Resonance (EPR) spectroscopy and X-ray Fluorescence (XRF) spectroscopy has been successfully utilized to characterize and quantify solubilized and fixed copper species in micronized copper treated wood, which also contains unreacted particulate copper. On the basis of the experimental results, the fixation mechanism is thought to be triggered by the reaction between the carboxylic acid protons in hemicellulose of wood with the particulate copper, and the quantities of the solubilized and fixed copper species are determined by the availability of these acidic protons. [ABSTRACT FROM AUTHOR]

The reaction of MesP=CPh2 with the least sterically demanding N-heterocyclic carbene (NHC = IMe) results in formation of the ‘abnormal’ (C4-substituted) 4-phosphino-NHC (1). In contrast, reaction with Me2IMe gives the unprecedented ‘normal’ C2 adduct, Me2IMe → P(Mes)=CPh2 (2). Particularly striking is the asymmetric and weak bonding of the NHC to the P=C moiety in 2. DFT calculations indicate that the P=C natural bond order in 2 (1.54) still reflects significant π-character to the bond (cf. MesP=CPh2: NBO = 1.98). Further computational analysis suggests that π-delocalization into the remote C-phenyl substituents is key to stabilizing the NHC adduct. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance was used in conjunction with X-ray fluorescence spectroscopy to quantify total copper and reacted copper retentions in MCQ and MCA treated Canadian red pine sapwood and western hemlock heartwood. Total copper retentions were distinctly different between earlywood and latewood of both softwood species examined. Earlywood of red pine sapwood had higher total copper content than the latewood, while western hemlock heartwood had higher total copper contents in latewood than earlywood. The reacted copper concentrations were similar in earlywood and latewood, reflecting a similar capacity of each to solubilize and complex the reacted copper. [ABSTRACT FROM AUTHOR]

Rh-containing metallacycles, [(TPA)RhIII(κ2-( C, N)-CH2CH2(NR)2-]Cl; TPA= N, N, N,N-tris(2-pyridylmethyl)amine have been accessed through treatment of the RhI ethylene complex, [(TPA)Rh(η2 -CH2CH2)]Cl ([ 1]Cl) with substituted diazenes. We show this methodology to be tolerant of electron-deficient azo compounds including azo diesters (RCO2NNCO2R; R=Et [ 3]Cl, R= iPr [ 4]Cl, R= tBu [ 5]Cl, and R=Bn [ 6]Cl) and a cyclic azo diamide: 4-phenyl-1,2,4-triazole-3,5-dione (PTAD), [ 7]Cl. The latter complex features two ortho-fused ring systems and constitutes the first 3-rhoda-1,2-diazabicyclo[3.3.0]octane. Preliminary evidence suggests that these complexes result from N-N coordination followed by insertion of ethylene into a [Rh]N bond. In terms of reactivity, [ 3]Cl and [ 4]Cl successfully undergo ring-opening using p-toluenesulfonic acid, affording the Rh chlorides, [(TPA)RhIII(Cl)(κ1-( C)-CH2CH2(NCO2R)(NHCO2R)]OTs; [ 13]OTs and [ 14]OTs. Deprotection of [ 5]Cl using trifluoroacetic acid was also found to give an ethyl substituted, end-on coordinated diazene [(TPA)RhIII(κ2-( C,N)-CH2CH2(NH)2-]+ [ 16]Cl, a hitherto unreported motif. Treatment of [ 16]Cl with acetyl chloride resulted in the bisacetylated adduct [(TPA)RhIII(κ2-( C,N)-CH2CH2(NAc)2-]+, [ 17]Cl. Treatment of [ 1]Cl with AcNNAc did not give the RhN insertion product, but instead the N,O-chelated complex [(TPA)RhI (κ2-( O,N)-CH3(CO)(NH)(NC(CH3)(OCHCH2))]Cl [ 23]Cl, presumably through insertion of ethylene into a [Rh]O bond. [ABSTRACT FROM AUTHOR]