Calculated Mulliken Charges Research Articles

Insights into the binding mechanism of 2,5‐substituted 4‐pyrone derivatives as therapeutic agents for fused dimeric interactions: A computational study using QTAIM, dynamics and docking simulations of protein–ligand complexes

AbstractThe study is focused on examining 2,5‐Substituted 4‐Pyrone based compounds through quantum chemical and topological analysis techniques, evaluating the properties of these compounds, including their geometrical structure, intermolecular interactions and assess their possible applications. Additionally, the molecular stability, charge delocalization and UV‐Visible data was investigated and compared with the calculated energy and oscillator strength using the TD‐DFT approach. The researchers observed that charge transfer occurred within the molecule, indicated by the HOMO and LUMO energies. It was also found that the compound exhibited planarity and higher chemical reactivity. The calculated Mulliken charges and molecular electrostatic potential were used to interpret the Fukui index data that help predict reactive sites and understand the reactivity patterns of specific atoms in a compound. The study is aimed to understand the role of NCI in the molecule under investigation using electron localization functions and localized orbit locator methods. Molecular docking and ADMET studies were conducting involving a detailed MD simulation of a protein‐ligand complex using the OPLS3e force field and the SPC water model. These findings could prove to be beneficial in developing new therapeutic agents with various pharmacological effects and potential toxicities.

Photostability of Mannich‐type dyed silk fibroin with pyrazolone‐containing aromatic primary amine dyes

AbstractMannich‐type dyeing of silk fibroin with aromatic primary amine dyes (APADs) is a novel reactive dyeing method that requires mild conditions and exhibits high selectivity and good wet fastness. However, the primary amine group in the APADs significantly decreases the photostability of Mannich‐type dyed silk fabrics. To reveal the structure–activity relationship and photofading mechanism of the APADs by Mannich‐type dyeing, six pyrazolone‐containing APADs with similar structures were designed and synthesised. Variation in amino electron density among the dye analogues was related to differences in colour fixation of the Mannich‐dyed fabrics, as determined from the calculated Mulliken charge densities. Using mass spectrometry to monitor the photodecomposition of the dyed silk, it is demonstrated that the Mannich‐type dyed silk fabrics undergo photooxidative fading, in contrast to the conventional acidic‐type dyed fabrics that undergo photoreductive fading. Furthermore, it is shown that the Mannich‐type dyed silk fabric has a higher light fastness than conventional acidic‐type dyed fabrics using the same pyrazolone‐containing APADs. Evaluation of dye dipole moment and Mannich‐type dyeing shows that the APADs with increased dipole moments generally demonstrated increased light fastness.

The experimental and theoretical spectroscopic elucidation of molecular structure, electronic properties, thermal analysis, biological evaluation, and molecular docking studies of isococculidine

Experimental techniques, such as vibrational spectroscopy (FT-IR and FT-Raman), UV–visible, thermal analysis (DSC), along with quantum chemical calculations based on density functional theory (DFT) were conducted to explore the physicochemical properties of a plant-derived natural product, isococculidine. The potential energy distribution (PED) has been assigned to each of the vibrational bands observed in FT-IR and FT-Raman spectra. The reduced density gradient (RDG) analysis was used to demonstrate the non-covalent interactions (NCI). Natural bond orbital (NBO) study revealed that the benzene ring's hyper-conjugative interactions were primarily responsible for the molecular stability. The intramolecular charge transfer has been further verified by the HOMO-LUMO analysis. The molecular electrostatic potential (MEP) analysis signifies that the nucleophilic and electrophilic interaction sites are prone to oxygen of O1-CH3 and hydrogens of O2-CH3, respectively. The chemical activity and the toxicity of the molecule have been examined based on the calculated Mulliken charges, softness, hardness, and local reactivity parameters. The thermal properties like specific heat capacity, entropy and enthalpy which affect the drug's activities were studied. The large value of the first hyperpolarizability indicates its significant nonlinear optical (NLO) property. The molecular docking of isococculidine has been performed with nicotinic acetylcholine protein which deliberates the significant biological activity of the molecule.

Janus PdSTe nanosheet as promising contender for detection of volatile organic compounds (VOCs) in human breath: A first principles investigation

Using the density functional theory and nonequilibrium Green’s function formalism, recent work report brings the interaction between the two-dimensional (2D) Janus PdSTe nanosheet and volatile organic compounds (VOCs) (i.e., acetone, ethanol, methanol, and propanol) to investigate the latent application of Janus PdSTe for excellent performance of VOCs sensors used for human breath analysis. The pristine Janus PdSTe monolayer is semiconducting with band gap of 0.32 eV, having the valence band maxima (VBM) at the Γ-point while, conduction band minima (CBM) at k-point in the Brillouin zone. The adsorption energies are revealed that all the targeted VOCs molecule are physiosorbed on the Janus PdSTe monolayer. We found that the acetone has greater sensitivity compare to other considered VOCs. To check the sensing mechanism of VOCs, the Mulliken charge transfer (CT), interaction distance and type of adsorption were analyzed. The calculated Mulliken charge is also reveals that the stronger electron exchange interation between ethanol and Janus PdSTe monolayer. Simultaneously, the I-V relation for before and after adsorption of VOCs molecules were also obtained using the Green’s function (NEGF) for experimental set up. Finally, our outcome indicates that Janus PdSTe monolayer is a potential and feasible candidate for aformentioned VOCs sensors for applications in room temperature breath analysis of VOCs.

Tuning the electronic and optical properties of silicon-germanium nanosheet through doping with boron and phosphorus: a first principle study

Under density functional theory (DFT), a first principle analysis is conducted to pure, boron (B)- and phosphorus (P)-doped silicon-germanium nanosheets. It has been revealed that through doping, we can tailor both electronic and optical properties of SiGe nanosheet. The alternation in the energy gap due to the process of impurity substitution could be attributed to the SiGe nanosheet’s sensitivity to a particular dopant and means that by applying a particular impurity, we can adjust the electronic properties. Shifting in Fermi energy due to doping of B and P attributed to p-type and n-type semiconductors. The calculated Mulliken charge analysis revealed the existence of charge transfer between the atoms in the doped and undoped nanosheet. From the calculation of time-dependent DFT (TD-DFT), we confirmed that the maximum absorption wavelength of pure SiGe nanosheet is redshifted when it is doped with boron and phosphorus atom; the maximum absorption wavelengths shift from visible to infrared region. The theoretical examination of the electronic and optical properties of doped SiGe nanosheet opens a new path for silicon-germanium nanosheet applications over nano-electronics and optical systems.

Microwave-Assisted Decarbonylation of Biomass-Derived Aldehydes using Pd-Doped Hydrotalcites.

Catalytic decarbonylation is an underexplored strategy for deoxygenation of biomass-derived aldehydes owing to a lack of low-cost and robust heterogeneous catalysts that can operate in benign solvents. A family of Pd-functionalized hydrotalcites (Pd-HTs) were synthesized, characterized, and applied to the decarbonylation of furfural, 5-hydroxymethylfurfural (HMF), and aromatic and aliphatic aldehydes under microwave conditions. This catalytic system delivered enhanced decarbonylation yields and turnover frequencies, even at a low Pd loading (0.5 mol %). Furfural decarbonylation was optimized in a benign solvent (ethanol) compatible with biomass processing; HMF selectively afforded an excellent yield (93 %) of furfuryl alcohol without humin formation; however, a longer reaction favored the formation of furan through tandem alcohol dehydrogenation and decarbonylation. Yields of the substituted benzaldehydes (37-99 %) were proportional to the calculated Mulliken charge of the carbonyl carbon. Activity and selectivity reflected loading-dependent Pd speciation. Continuous-flow testing of the best Pd-HT catalyst delivered good stability over 16 h on stream, with near-quantitative conversion of HMF.

Investigation of electronic structure and optical properties of thallium lead halides: First principle calculations

Using first principle calculations, we comprehend the electronic structure and optical constant of thallium lead halides TI3PbX5 (X = Cl, Br, I), which are viewed as potential materials for mid-infrared and near-infrared applications. The generalized gradient approximation function given by Perdew-Burke-Ernzerhof is used for geometry optimization and properties calculations. The calculated Mulliken charges are more positive for Pb than TI in the TI3PbCl5 system demonstrating a high electronic density contribution from the Pb-Cl bonds in contrast to the TI-Cl bonds. Similarly, the TI3PbCl5 configuration displays the smallest enthalpy value suggesting a more stable structure among different TI3PbX5 species studied in this work. The band gap value for TI3PbCl5 has been calculated as 3.52 eV, which decreases to 3.14 eV and 2.64 eV for the TI3PbBr5 and TI3PbI5, respectively. Additionally, the TI3PbI5 exhibits a high magnitude of real component of static dielectric function ε1(k) in contrast to TI3PbBr5 and TI3PbCl5. The optical absorption results display a redshift when TI3PbCl5 is doped with Br and I sequentially. These outcomes suggest that the concentration of halide elements can be adjusted to enhance the optical properties of TI3PbX5 for optoelectronic device applications.

Vibrational assignments, conformational analysis, and molecular structures of $$\left[ {\text{C}_{\text{n}} \text{mim}} \right]\left[ {\text{NTF}_{\text{2}} } \right]$$ C n mim NTF 2 (n = 2, 4, 6, and 8) imidazolium-based ionic liquids: a combined experimental and quantum chemical approach

This work is aimed at providing physical insights about the interactions of cations, anion, and ion pairs of four imidazolium-based ionic liquids of $$\left[ {{\text{C}}_{\text{n}} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]$$ with varying alkyl chain lengths (n = 2, 4, 6, and 8) using both DFT calculations and vibrational spectroscopic measurements (IR absorption and Raman scattering) in the mid- and far regions. The calculated Mulliken charge distributions of $$\left[ {{\text{C}}_{\text{n}} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]$$ ion pairs indicate that hydrogen-bonding interactions between oxygen and nitrogen atoms (more negative charge) on $$\left[ {{\text{NTF}}_{2} } \right]^{ - }$$ anion and the hydrogen atoms (more positive charge) on the imidazolium ring play a dominating role in the formation of ion pair. Thirteen stable conformers of $$\left[ {{\text{C}}_{2} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]$$ were optimized. According to our results, the strongest and weakest hydrogen bonds were existing in $$\left[ {{\text{C}}_{2} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]$$ and $$\left[ {{\text{C}}_{8} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]$$ , respectively. A redshift of 290, 262, 258, and 257 cm−1 has been observed for cations involving $$\left[ {{\text{C}}_{2} {\text{mim}}} \right]^{ + }$$ , $$\left[ {{\text{C}}_{4} {\text{mim}}} \right]^{ + }$$ , $$\left[ {{\text{C}}_{6} {\text{mim}}} \right]^{ + }$$ , and stretching vibrations of $${\text{C}}12{-}{\text{H}}3$$ , respectively. By increasing the chain length, the strength of hydrogen bonds decreases as a result of $${\text{C}}12{-}{\text{H}}3$$ bond elongation and less changes are observed in stretching vibrations of $${\text{C}}12{-}{\text{H}}3$$ compared to the free cations. To the best of our knowledge, this research is the first work which reports the far-IR of $$\left[ {{\text{C}}_{4} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]$$ , $$\left[ {{\text{C}}_{6} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]$$ , and $$\left[ {{\text{C}}_{8} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]$$ and the mid-IR of $$\left[ {{\text{C}}_{8} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]$$ .

Toward a new avenue in ruthenium-sulphur chemistry of binuclear μ-sulphido bridged (μ-S)2 complexes having Ru2S2 core: Targeted synthesis, crystal structure, biomolecules interaction and their in vitro anticancer activities

A series of hybrid thiosemicarbazone derivatives (H2L1–3) were synthesized by the reactions of diacetyl-2-(4-methyl-3-thiosemicarbazone) with hydrazine derivatives such as 2-hydrazinoquinoline, 2-hydrazinobenzothiazole and 6-hydrazinonicotinic acid arm. The resulting hybrid diacetyl-2-(4-methyl-3-thiosemicarbazonato-hydrazine derivatives were successfully employed as tetradentate ligands to react with [RuHClCO(PPh3)3]. The reactions have led to the binuclear organo-ruthenium(II) complexes of the core type [Ru2(Ln)2(CO)2(μ-S)2], (n=1–3) in which the ruthenium(II) ion bridged by sulphur atoms (μ-S)2. In the new complexes, the ligand charge and stoichiometry proportions could be controlled by the addition of base. All the compounds have been characterized by IR, UV–vis, ESI-MS, (1H, 13C) NMR spectra and elemental analyses. The crystal structure of complexes 1, 2 has been determined by X-ray crystallography, which confirmed the coordination mode of the ligands and revealed a distorted octahedral geometry around the ruthenium ion. Natural bond orbital calculations of complexes 1 and 2 showed that the majority of the electron density of donors tends to the ruthenium ion, since the calculated Mulliken charge for the ruthenium ion is much lesser than the formal value. The binding mode of these complexes with biomolecules such as calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) protein have been investigated by diverse spectrophotometric methods and the results revealed an intercalative mode of interaction. Furthermore, the bio-catalytic efficiencies such as catecholase and phosphatase like activities of ruthenium complexes exhibited high rate (kcat) constant. Furthermore, the complexes (1–3) displayed more cytotoxicity against anticancer cell lines such as MCF-7 (breast), A549 (lung), and HepG2 (liver) than normal Vero cell line. The less cytotoxic activity towards normal cell lines showed that they affect only cancer cell lines. The antiproliferative efficacy of complexes (1–3) has also been analyzed using morphological staining properties (AO/EB, DAPI) by fluorescence microscopy visualization.

Peculiarities of Chemical Bonding in Crystals of the In-Se System

The investigation of the ab initio band structure and the resulting spatial electron density distribution of the In Se system in the framework of the density functional theory and the elementary energy bands concept is presented. It gives us reliable information about the valence band structure and peculiarities of the chemical bonding in these crystals. Some regularities in the evolution of the elementary energy bands topology is established, together with the choice of the actual Wycko position that is responsible for this topology and, at the same time, for the valence band formation in the InSe, In2Se3, In4Se3, and In6Se7 crystals. The calculated Mulliken charges and the degree of ionicity allow to estimate the character of chemical bonding in these crystals.

Cashew Nut Testa Tannin: Assessing its Effects on the Corrosion of Aluminium in HCl

Cashew nut testa tannin [CASTAN] has been found to inhibit the corrosion of aluminium in hydrochloric acid solutions using gravimetric, thermometric and UV/visible spectrophotometric techniques. CASTAN inhibition was by adsorption on aluminium following Temkin isotherm in 0.1 M HCl and Langmuir isotherm in 0.5 M and 2.0 M HCl at 303 Kelvin. Physical adsorption on aluminium has been proposed in studied HCl solutions; therefore, CASTAN is a cathodic inhibitor. Earlier reports [1] showed CASTAN to contain quercetin, azaleatin, catechin, epicatechin, cyanidin and delphinidin. However, UV/visible spectrophotometric analysis of CASTAN in ethanol reveals quercetin as its major component. This work therefore investigated the correlation between computed molecular parameters and inhibitive properties of CASTAN and adsorption sites on its components. Calculated quantum chemical parameters namely: E HOMO (highest occupied molecular orbital energy), E LUMO (lowest unoccupied molecular orbital energy), energy gap ( �E) and dipole moment ( μ ) suggest that CASTAN is a soft inhibitor and it’s components inhibited aluminium corrosion in protonated forms. Calculated Mulliken charges implicated some electron rich sites, namely: the aromatic and conjugated C=C, C=O and O-H as adsorption sites on the inhibitor molecules. Proposed kinetic model reveals complex reaction mechanism, parallel reactions, for aluminium corrosion inhibition by CASTAN.

Synthesis, spectral, DFT and X-ray study of a cis-MoO2 complex with a new isothiosemicarbazone ligand

2,4-Dihydroxybenzaldehyde S-allylisothiosemicarbazone hydrobromide, H2L, reacts with dioxo-molybdenum acetylacetonate in methanol to form a stable complex of dioxomolybdenum(VI). The ligand and complex are characterized with analytical and spectroscopic techniques. Single-crystal X-ray crystallography has been also carried out for the complex, showing it has distorted octahedral geometry. H2L is a tridentate dianionic ligand bonded as an ONN donor to molybdenum. Thermogravimetric analysis of the complex shows MoO3 as the final product above 780 °C. The results obtained from density functional theory calculations for the optimization and frequency analysis are in agreement with the experimental data. Natural bond orbital calculations show that the majority of the electron density of the donors tends to the molybdenum, since the calculated Mulliken charge for the central ion is much lesser than the formal value.

Intramolecular charge-transfer interactions in a julolidine–Bodipy molecular assembly as revealed via 13C NMR chemical shifts

13C NMR spectra were recorded in a series of six deuterated solvents of disparate polarity for three difluoroborondipyrromethene (Bodipy) derivatives bearing an aryl group at the meso position; these aryl residues were julolidine ( JULBD), 4-nitrobenzene ( NITBD) and phenylene ( PHBD). Complete 13C chemical shift assignments were made for all three compounds using a combination of COSY, HMBC and HMQC NMR spectroscopic techniques. The extreme assembly, JULBD, displays pronounced charge-transfer character in polar solvents owing to effective electron donation from the nitrogen atom of the julolidine unit to the electron-affinic Bodipy residue. The 13C chemical shift differences (Δ δ) between the meso and N-α dipyrrin carbon atoms recorded for JULBD exhibit a linear correlation with certain solvent polarity functions, including Reichardt’s E T N parameter and Catalán’s solvent dipolarity/polarizability (SPP) function. Similar correlations are not found for NITBD, where the charge-transfer vector lies in the opposite direction and the computed dipole moment is close to zero. Quantum chemical calculations performed on JULBD, PHBD and four other Bodipy derivatives at the DFT (B3LYP/6-311++G ∗∗) level afforded the Mulliken charges resident on the dipyrrin carbon centers. A reasonable correlation is found between these calculated Mulliken charges and the corresponding 13C chemical shifts for the various Bodipy derivatives.

Reaction Pathways of 2-Iodoacetic Acid on Cu(100): Coverage-Dependent Competition between C−I Bond Scission and COOH Deprotonation and Identification of Surface Intermediates

The chemistry of 2-iodoacetic acid on Cu(100) has been studied by a combination of reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reaction/desorption (TPR/D), and theoretical calculations based on density functional theory for the optimized intermediate structures. In the thermal decomposition of ICH(2)COOH on Cu(100) with a coverage less than a half monolayer, three surface intermediates, CH(2)COO, CH(3)COO, and CCOH, are generated and characterized spectroscopically. Based on their different thermal stabilities, the reaction pathways of ICH(2)COOH on Cu(100) at temperatures higher than 230 K are established to be ICH(2)COOH --> CH(2)COO + H + I, CH(2)COO + H --> CH(3)COO, and CH(3)COO --> CCOH. Theoretical calculations suggest that the surface CH(2)COO has the skeletal plane, with delocalized pi electrons, approximately parallel to the surface. The calculated Mulliken charges agree with the detected binding energies for the two carbon atoms in CH(2)COO on Cu(100). The CCOH derived from CH(3)COO decomposition has a CC stretching frequency at 2025 cm(-1), reflecting its triple-bond character which is consistent with the calculated CCOH structure on Cu(100). Theoretically, CCOH at the bridge and hollow sites has a similar stability and is adsorbed with the molecular axis approximately perpendicular to the surface. The TPR/D study has shown the evolution of the products of H(2), CH(4), H(2)O, CO, CO(2), CH(2)CO, and CH(3)COOH from CH(3)COO decomposition between 500 and 600 K and the formation of H(2) and CO from CCOH between 600 and 700 K. However, at a coverage near one monolayer, the major species formed at 230 and 320 K are proposed to be ICH(2)COO and CH(3)COO. CH(3)COO becomes the only species present on the surface at 400 K. That is, there are two reaction pathways of ICH(2)COOH --> ICH(2)COO + H and ICH(2)COO + H --> CH(3)COO + I (possibly via CH(2)COO), which are different from those observed at lower coverages. Because the C-I bond dissociation of iodoethane on copper single crystal surfaces occurs at approximately 120 K and that the deprotonation of CH(3)COOH on Cu(100) occurs at approximately 220 K, the preferential COOH dehydrogenation of monolayer ICH(2)COOH is an interesting result, possibly due to electronic and/or steric effects.

Precipitable silver compound catalysts for the selective catalytic reduction of NOx by ethanol

The Ag/Al 2O 3, Ag 3PO 4/Al 2O 3, Ag 2SO 4/Al 2O 3 and AgCl/Al 2O 3 catalysts showed high activities for the selective catalytic reduction (SCR) of NOx by ethanol. AgCl was highly crystalloid on Al 2O 3, however, AgCl/Al 2O 3 gave the highest catalytic turnover frequency (TOF) for NOx reduction among the four catalysts. Calculated Mulliken charges of Ag compounds support the TOF results. The activity test and characterization results confirm that Ag + is the active silver species for NOx reduction. The in situ FT-IR results of Ag 3PO 4/Al 2O 3, Ag 2SO 4/Al 2O 3 and AgCl/Al 2O 3 for NOx reduction further reveal a positive correlation between the high dispersion of Ag + and the formation of active intermediates (the enolic and –NCO species), indicating a similar reaction pathway to that of the ethanol-SCR over Ag/Al 2O 3. Using the precipitable silver compounds greatly facilitates the preparation of monolith Ag/Al 2O 3 catalyst for practical usage. In fact, the high performance of the AgCl/Al 2O 3 honeycomb catalyst was confirmed by heavy duty diesel engine bench tests.

Pressure-induced structural and electronic changes inα−AlH3

Pressure-induced structural, electronic, and thermodynamic changes in $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Al}{\mathrm{H}}_{3}$ were investigated using synchrotron x-ray powder diffraction and density-functional theory. No first-order structural transitions were observed up to $7\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. However, increasing Bragg peak asymmetry with pressure suggests a possible monoclinic distortion at moderate pressures $(1--7\phantom{\rule{0.3em}{0ex}}\mathrm{GPa})$. The pressure-volume relationship was fit to the Birch-Murnaghan equation of state to give a bulk modulus of approximately $40\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The reduced cell volume at high pressure is accommodated by octahedral tilting and a decrease of the Al-H bond distance. Ab initio calculations of the free energy indicate that hydrogenation becomes favorable at ${\mathrm{H}}_{2}$ pressures above $0.7\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Electronic density of states calculations reveal a slight decrease in the band gap with pressure but no evidence of an insulator-to-metal transition predicted by previous high-pressure studies. Calculated Mulliken charges and bond populations suggest a mixed ionic and covalent Al-H bond at $1\phantom{\rule{0.3em}{0ex}}\mathrm{atm}$ with an increase in covalent character with pressure.

Strong intramolecular hydrogen bonding involving nitro- and acetyl groups. Deuterium isotope effects on chemical shifts

A number of o-hydroxyacetylnitrobenzenes have been synthesized and their structures (X-ray and/or ab initio DFT calculations) have been determined. The intramolecular hydrogen bonds show correlations between the distances: O⋯O, O–H, C O and O⋯H for both hydrogen bonds to acetyl and nitro groups. Rather short O⋯O distances and strong hydrogen bonds are obtained in a number of compounds, e.g. 1,3-diacetyl-5-nitro-2,4,6-trihydroxybenzene. Deuterium isotope effects on 1H and 13C chemical shifts have been determined. 2ΔC(OD) isotope effects correlate well with O⋯O distances, whereas 4ΔC O(OD) isotope effects do not. The latter become unusually large in 3,5-dinitro substituted derivatives. Deuterium isotope effects on 13C chemical shifts especially 2ΔC(OD), 5ΔCH 3(OD) and 4ΔC O(OD) are used to evaluate steric and electronic contributions to resonance assisted hydrogen bonds. The effects are analysed using principal component analysis (PCA) techniques. Direct transmission of isotope effects via hydrogen bonds is demonstrated. DFT calculated NMR chemical shifts are shown to be useful in choosing between possible rotameric structures. X-ray analysis is used to determine structures in the solid. ‘Bond localization’ is shown to be important in understanding the effects of substituents. Intra molecular hydrogen bonds with acetyl or nitro groups as acceptors and OH groups as donors are compared. They are structurally similar but hydrogen bonds involving nitro groups are weaker for similar compounds. An unusual hydrogen bond pattern is observed in 1-acetyl-3,5-dinitro-2,4,6-trihydroxybenzene (two OH groups forms hydrogen bonds to the same nitro group). OH chemical shifts correlate with calculated Mulliken charges of OH for both hydrogen bonds to acetyl and nitro groups.

Electronic and geometric properties of alkali-C60 molecules

First-principle electronic structure calculations are carried out for MxC 60 q , where M = Li, Na, K and ( x , q ) = (1, 0),(1,±1),(2, 0),(3, - 1),(6, 0),(6, - 1),(12, 0) using the local density functional. The electric dipole moment for MC60 agrees with the experimental results. The calculated Mulliken charge indicates that the bonding of the alkali atom with C60 is mostly ionic except for lithium. The alkali atom prefers to make many bonds with the carbon atoms rather than a single bond with the neighbor carbon atom. The calculated adsorption energy suggest that the metal-metal bonding of sodiums and potassiums on C60 arises for more than the six valence electrons in the alkali atoms. The lithium-lithium bond is, on the other hand, not appeared for x ? 12. The difference in the most stable geometry between lithiums and the other alkali atoms on C60 comes from the covalent character of the lithium-carbon bond.

Control of oxo-molybdenum reduction and ionization potentials by dithiolate donors.

The compounds (L-N3)MoO(qdt) and (L-N3)MoO(tdt) [(L-N3) = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; tdt = toluene-3,4-dithiolate; qdt = quinoxaline-2,3-dithiolate] have been studied by cyclic voltammetry and photoelectron, magnetic circular dichroism, and electronic absorption spectroscopies, and the experimental data have been interpreted in the context of ab initio molecular orbital calculations on a variety of dithiolate dianion ligands. The PES data reveal very substantial differences between (L-N3)MoO(qdt) and (L-N3)MoO(tdt) in that the first ionization (originating from the Mo dxy orbital) for (L-N3)MoO(qdt) is about 0.8 eV to deeper binding energy than that of (L-N3)MoO(tdt). This stabilizing effect is also reflected in the solution reduction potentials, where (L-N3)MoO(qdt) is approximately 220 mV easier to reduce than (L-N3)MoO(tdt). A direct correlation between the relative donating ability of a given dithiolate ligand and the reduction potential of the (L-N3)MoO(dithiolate) complex has been observed, and a linear relationship exists between the calculated Mulliken charge on the S atoms of the dithiolate dianion and the Mo reduction potential. The study confirms previously communicated work (Helton, M. E.; Kirk, M. L. Inorg. Chem. 1999, 38, 4384-4385) that suggests that anisotropic covalency contributions involving only the out-of-plane S orbitals of the coordinated dithiolate control the Mo reduction potential by modulating the effective nuclear charge of the metal, and this has direct relevance to understanding the mechanism of ferricyanide inhibition in sulfite oxidase. Furthermore, these results indicate that partially oxidized pyranopterins may play a role in facilitating electron and/or atom transfer in certain pyranopterin tungsten enzymes which catalyze formal oxygen atom transfer reactions at considerably lower potentials.

Deboronation of 9-substituted- ortho- and - meta-carboranes

A systematic study has been carried out of deboronation reactions of a series of icosahedral carborane derivatives bearing a variety of substituents on selected (generally antipodal) boron atoms. Reactions of the 9-substituted meta-carboranes, 9-R-1,7-C 2B 10H 11 (R=OH, 4-MeC 6H 4, F, Cl, Br, I), with tetrabutylammonium fluoride hydrate (TBAFH) in refluxing THF gave nido-carborane salts containing a mixture of 1- and 6-R-7,9-C 2B 9H 11 − nido-anions. Regioselective deboronation occurred with the 9-halo- meta-carboranes, 9-X-1,7-C 2B 10H 11 (X=F, Cl, Br, I), producing a 2:1 ratio mixture of nido 6-X-7,9-C 2B 9H 11 − and 1-X-7,9-C 2B 9H 11 −. Calculated Mulliken charges at B2 and B3 of some 9-substituted- meta carboranes show that these vary in line with observed deboronation rates and product ratios in their reactions with TBAFH. The ortho-carborane derivative 9-I-1,2-C 2B 10H 11 and TBAFH gave the tetrabutylammonium salt of the nido anion 5(6)-I-7,8-C 2B 9H 11 −. The mercurated and thallated meta carboranes, 9-M-1,7-C 2B 9H 11 (M=HgOCOCF 3 and Tl(OCOCF 3) 2), with TBAFH underwent boron–metal bond cleavage to yield mainly the nido anion 7,9-C 2B 9H 12 −. Multinuclear ( 11B, 13C, 1H, 19F) NMR spectra of the carboranes have been recorded and assigned.