B3LYP Level Of Theory Research Articles

Synthesis, spectroscopic characterization, computational studies, theoretical investigation of NLO properties and antibacterial activities of mixed ligand complexes of Co(II) and Cu(II)

The reaction of Schiff base 2-(4-(dimethylamino)benzylideneamino)phenol (DBAP) and diethylenetriamine/ethylenediamine with cobalt(II) and copper(II) metal ion in equimolar ratio afforded mixed ligand complexes [M(DBAP)(L)Cl(H2O)n] (1–4), where M = Co(II) 1, 2; Cu(II) 3, 4; L = diethylenetriamine (1, 3); n = 0 and ethylenediamine (2, 4); n = 1. All the newly synthesized complexes were characterized by elemental analysis, spectroscopic techniques viz., UV-vis, FT-IR, ESR, PXRD and mass spectrometry. The influence of chelation of cobalt(II) and copper(II) ion on nonlinear optical properties of Schiff base (DBAP) were examined with DFT study. The polarizability (α0) and first-order hyperpolarizability (β) of ligand and their metal complexes were calculated and compared with reference molecule p-nitroaniline. The hyperpolarizability of Schiff base and their metal complexes show a good nonlinear optical behavior. Theoretical investigation of the complexes was performed by DFT using B3LYP level of theory on the basis set 6-31 G (d, p)/LanL2DZ. On the basis of spectroscopic data and DFT computation, a six-coordinate geometry is tentatively proposed around the metal ion. In vitro antibacterial activities of these complexes were also screened against V. cholerae and E. coli, and found to have good antibacterial activity.

Experimental, computational analysis of new organic NLO crystal: Piperazinium nicotinic acid and its efficiency in optoelectronic applications

Abstract Slow evaporation solution growth method was adapted for the effective growth of single crystals of piperazinium nicotinic acid (PNA) in distilled water. Single crystal X-ray diffraction analysis was used to investigate the cell parameters of crystalline PNA and the grown crystal belongs to triclinic crystal family with the space group Pī. 3-D molecular hirshfeld surface analysis was supported to visualize the various inter contacts present within the crystal and their percentage contribution to the total hirshfeld surface area was quantified using the 2D finger print plot process. DFT approach was carried out to conduct the theoretical investigation and HOMO-LUMO energy band difference was calculated. B3LYP level of theory with 6-31++G (d,p) basis set was employed to compute the Molecular optimized geometry, FT-IR, FT-Raman and HOMO-LUMO energy distance. FT-IR and FT-Raman spectral studies have accompanied for looking into the modes of vibration of various functional groups in the PNA crystal. UV–visible NIR transmittance studies have revealed that the grown crystal has high transmittance in the entire visible region. Single beam Z-scan technique was explored to determine the third-order nonlinear optical nature and susceptibility of the grown PNA crystal. The results of computational and experimental values suggest suitability and potentiality of PNA crystal for NLO and optical limiting applications.

Rh(II)‐mediated one‐pot synthesis of dihydrobenzofuran and spiro[2.5]oct‐1‐ene: Experimental and DFT studies

AbstractThis study represents an experimental and computational approach to investigate the rhodium‐catalyzed one‐pot synthesis of dihydrobenzofuran‐4‐one (DBF) and spiro[2.5]oct‐1‐ene (SOE) derivatives. Density functional theory (DFT) calculations were performed at B3LYP and M06‐2X level theory. For mechanistic studies, the calculation employing B3LYP/GenECP/LanL2DZ/6‐311++G(d,p) level of theory demonstrated that a [3 + 2] cycloaddition reaction between diazo compound and phenylacetylene (PhA) proceeds through a two‐step mechanism via a barrierless and highly exergonic process with relative free energy 73.61 kcal/mol to yield the kinetically favored DBF derivatives (50%–62.5%). In contrast, the assemble of SOE derivatives follows [2 + 1] cycloaddition between in situ generated cyclohexane‐1,3‐dione carbene‐2 and PhA, with the potential energy barrier 4.41 kJ/mol. Thermochemistry calculation disclosed that the cycloaddition reactions are spontaneous, and DBF (6a) is thermodynamically more stable than its constitutional isomer SOE (7a) by 42.59 kcal/mol. However, natural bond orbital (NBO), HOMO–LUMO energy gaps (4.62–4.89 eV), dipole moments, polarizability, first‐order hyperpolarizability, and global reactivity descriptors were calculated to understand products' structural features. Additionally, Merck Molecular Force Field (MMFF94), followed by the B3LYP level of theory, was applied to predict the relative stability for the various conformations of 6b and 7b. The Boltzmann weighted average 1H chemical shift computed by GIAO‐B3LYP/6‐311+(2d,p) method and UV‐Vis absorption calculated using time‐dependent density functional theory (TD‐DFT) agree with experimental results. Finally, the synthesis of DBF and SOE derivatives is herein illustrated.

Case Study in a Conceptual DFT Investigation of New Corrosion Inhibitor

Inhibition efficiency of thiosemicarbazide derivative, namely 4-ethyl-1-(4-oxo-4-phenylbutanoyl)thiosemicarbazide (EOPT) on corrosion of mild steel, was investigated utilizing the density functional theory (DFT) modeling techniques in the aqueous phase. Chemical parameters at the quantum level, such as energies of highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), dipole moment (µ), absolute electronegativity (χ), global hardness (η), softness (σ), and the fraction of electrons transferred (∆N) have been determined at the B3LYP level of theory with 6-31G (d, p) basis set.

Experimental and theoretical approach on third-order optical nonlinearity of a highly efficient anthracene-based chalcone derivative for optical power limiting

Herein the study reports a dual approach on theoretical and experimental studies of nonlinear optical properties of a novel chalcone derivative, (2E)-1-(Anthracen-9-yl)-3-(biphenyl-4-yl)prop-2-en-1-one [biphenyl-ANC]. The obtained experimental results have been supported by the theoretical calculations performed by density functional theory. The FT-IR, FT-Raman, and UV-visible absorption spectra were recorded and analyzed. The structural, electronic and charge transfer analyses were computed by B3LYP level of theory with 6–311++G(d,p) basis set. The second-order hyperpolarizability has been theoretically predicted using B3LYP and CAM-B3LYP hybrid functional. The third-order nonlinear optical properties, along with the optical limiting studies of biphenyl-ANC in polar and nonpolar solvents, were carried out by z-scan technique using Q-switched Nd:YAG laser with 5 ns pulses at 532 nm. The z-scan results reveal that the compound can act as a promising candidate for photonic and optoelectronic applications.

Application of borophene as catechol sensor: a computational study.

The efficacy of borophene (BP) as catechol (CC) sensor was explored using density functional theory (DFT) method. All calculations were performed at B3LYP level of theory and 6-31 + G(d) basis set employing the dispersion correction term of Grimme to consider dispersion interactions. The CC molecule is adsorbed on top of BP horizontally with the adsorption energy (Eads) of about - 13.5kcal·mol-1. The HOMO and LUMO levels of nanosheet destabilize by about 0.36 and 0.14eV, respectively, going from bare BP to BP-CC complex. Therefore, the Eg value decreases by about 10.5% upon adsorption process, which is a reasonable energy gap change for detection of CC. The negligible difference between the work function values (Φ, defined as the minimum amount of the energy needed to remove an electron from a solid to a point in the vacuum immediately outside the solid surface) of BP and its complex with CC indicates that the BP sheet is not an appropriate Φ-type sensor (in these sensors, adsorption of a chemical changes the gate voltage and produces an electrical signal that leads to the detection of chemical agent) for CC detection. The electrical conductivity of BP becomes 72 times higher after CC adsorption. The time needed for CC desorption from BP sheet is 7.6ns, based on conventional transition state theory, showing that BP benefits from a short recovery time. The effect of CC concentration was explored by adsorption of 2 and 3 CC molecules on top of BP nanosheet and the results showed that the sensor response does not change by increasing the CC concentration. Also, the effect of lateral dimensions of BP on the adsorption energy was explored and it was shown that Eads increases by enlargement of the nanosheet.

The interaction between ethionamide and pristine, Si-, Ga-, and Al-doped boron nitride nanoflakes: A computational study

In this study, the adsorption behavior of pristine, Si-, Ga- and Al-doped boron nitride nanoflakes (BNNFs) is investigated toward ethionamide (EA) using density functional theory (DFT) calculations. Total energies, geometry optimizations were obtained and density of state (DOS) analysis was performed at B3LYP level of theory with the 6-31G* basis set. The adsorption energy (E ad) between EA and the pristine, Si-, Ga- and Al-doped BN nanoflake is changed in the following order: Ga-Complex-N(ring) > Si-Complex-S > Al-Complex-S. The E ad of the EA/BNNF complex is −3.56 kcal/mol, which is low and shows that the adsorption is physical. The % ΔE g = −43.42% for EA/Al-BNNF indicates the high sensitivity of the Al-doped BN nanoflake to the adsorption of EA. The E ad of −28.10 kcal/mol is suitable and we can predict that the Al-doped BN nanoflake can be a good device for sensing EA.

An investigation of inter-ligand coordination and flexibility: IRMPD spectroscopic and theoretical evaluation of calcium and nickel histidine dimers

Metallated gas-phase structures consisting of an intact and deprotonated histidine (His) ligand, M(His-H)(His)+, where M = Ca and Ni, were examined using infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light from a free-electron laser (FEL). In parallel, ab initio quantum-chemical calculations identified several low-energy isomers for each complex. Experimental action spectra were compared to linear absorption spectra calculated at the B3LYP level of theory, using the 6-311+G(d,p) basis set. Single-point energies were calculated at B3LYP, B3LYP-GD3BJ, B3P86, and MP2(full) levels using the 6-311+G(2d,2p) basis set. For Ca(His-H)(His)+, the dominant structure has the metal center coordinating with the π nitrogen of the imidazole ring (Nπ) and both oxygen atoms of the carboxylate group of the deprotonated His ligand while coordinating with the backbone amine (Nα), Nπ, and the carbonyl oxygen of the carboxylic acid of the intact His ligand. The Ni(His-H)(His)+ species coordinates the metal ion through Nα, Nπ, and the carbonyl oxygen for both the deprotonated and intact His ligands, but also shows evidence for a minor secondary structure where the deprotonated His coordinates the metal at Nα, Nπ, and the deprotonated carbonyl oxygen and the intact His ligand is zwitterionic, coordinating the metal with both carboxylate oxygens. Different levels of theory predict different ground structures, highlighting the need for utilizing multiple levels of theory to help identify the gas-phase structure actually observed experimentally.

SWCNTs Interaction with Dopamine and Serotonin Anticancer Through QM/MM Methods: A Drug Delivery Approaches

Objetive: Dopamine and Serotonin are the two important biological transmitters that have hormonal activities and responsible for happiness and felling well. The aim of this article was to study theoretically the structure features of Dopamine and Serotonin in the complex of single-walled carbon nanotube as a neurotransmitter. Material and Methods: The structure of Dopamine and Serotonin binding with SWCNT with four different diameters (7.0,7.5,7.7,10.0 nm) was studied by using molecular mechanic (MM) and quantum mechanic (QM). The remarkable energies including potential energy, total energy and kinetic energy in time of simulation 10 ns steps in two temperatures (298, 310 kelvin degree) were investigated by Monte Carlo method with opls force filed. NMR shielding tensor data by B3LYP level of theory with 6-31 G(d) as a basis set and semi empirical method have been also fulfilled. Results: Theoretical computations were performed to study NMR chemical shift data including magnetic shielding tensor (σ, ppm), shielding asymmetry (η), magnetic shielding anisotropy (σaniso), magnetic shielding isotropy (σiso) , skew of a tensor (Κ) and chemical shift anisotropy (Δσ) and span (Ω) at various rotation angles around a specific rotation, physical and chemical properties of atomic nuclei. Semi empirical calculations such as total energy, binding energy, isolated atomic energy, electronic energy, core–core interaction and heat of formation in AM1 were revealed. Conclusion: It is figured out in Monte Carlo method our two specific drug and its nanotube with small diameter are the most stable one than the others. The larger diameter leads the combination stability into lower value.

Promising computational, structural, vibrational and optical properties of piperazinium bis(2-carboxypyridine)monohydrate (PBCPM) crystal for NLO device applications

The Slow Evaporation Solution Technique (SEST) was used to produce a single crystal of piperazinium bis(2-carboxypyridine)monohydrate (PBCPM). The lattice parameters and molecular structure of the grown crystal were determined using Single Crystal X-Ray Diffraction. The intramolecular and intermolecular interactions were visualised using Hirshfeld surface analysis. The B3LYP level of theory with a 6–31++G (d,p) basis set was used to compute the Molecular optimised geometry. The FT-IR and FT-R spectral studies that have been reported look at the modes of vibration of various functional groups in the PBCPM crystal. The grown crystal has a high transmittance in the entire visible field, according to UV–vis transmittance reports. Based on the finite-field approach, the polarizability and hyperpolarizability of PBCPM is determined using the DFT-B3LYP method and the 6–311G(d,p) basis set. The Z-scan technique is used to perform third order NLO studies on the PBCPM crystal. The result discussed confirms that PBCPM crystal is a potential candidate for future NLO device applications.

Ionic strength effect on the kinetics and mechanism of N-vinyl compound formation in the presence of heterocyclic biological base: empirical and theoretical approaches

In the current work, kinetics and mechanism of the reaction between dimethyl acetylenedicarboxylate (DMAD), thiazolidine-2,4-dione (heterocyclic biological base, TZD) and triphenylarsine (TPA) has been studied for the synthesis of N-vinyl compound in the presence of various salts and solvents by the UV–visible technique. Through an alternation in the reaction environment from lone methanol (kobs = 0.3121 M−1Min−1) or acetone alone (kobs = 0.008 M−1Min−1) to a mixture of methanol and salt (NaBr) (kobs = 21.35 M−1Min−1), the reaction rate extremely accelerates 70 or 2600 times more, respectively. These remarkable results indicated that the mentioned reaction has greatly proceeded and extremely faster in the mixture of a polar solvent and salt in comparison with the solvent alone. A mechanism involving four steps was proposed. Unfortunately, experimental data from the UV–visible technique were not adequate to determine the rate-determining step of the reaction mechanism. To clear this, Molecular Electron Density Theory computations have been consulted at the B3LYP level of theory using the standard 6-311 + G (d, p) and extra basis set of 6-311 + G (2df, 2pd) for the arsenic atom. The analysis of the relative schematic representation of the Gibbs free energy profiles revealed that 1,2-hydrogen shift proton is the rate-determining step of the reaction mechanism. The comparison of the rate constant of the reaction between DMAD, TZD and TPA in the presence of salt such as NaBr with this reaction in the absence of salt.

In silico identification of potential Hsp90 inhibitors via ensemble docking, DFT and molecular dynamics simulations

The molecular chaperone heat shock protein 90 (Hsp90) has emerged as one of the most exciting targets for anticancer drug development and Hsp90 inhibitors are potentially useful chemotherapeutic agents in cancer. Within the current study, Hsp90 inhibitors that entered different phases of clinical trials were subjected to Zinc15 structure query to find similar compounds (≥ 78%). Obtained small molecules (1-29) with defined similarity cut-off were docked into ensemble of Hsp90-α NTDs. Docked complexes were ranked on the basis of binding modes and Gibbs free energies as Hsp90 binders (cut-off point; ΔGb ≤ −12 kcal/mol). Top-ranked compounds were subjected to energy decomposition analysis per residue of binding pocket via density functional theory (DFT) calculations in B3LYP level of theory. Subsequent MD simulations of the top-ranked complexes were performed for 100 ns to explore the stable binding modes during a reasonable period in explicit water. Results of molecular docking and intermolecular binding analysis indicated that H-bond, hydrophobic and salt bridge interactions were determinant forces in complex formation. Compounds 19 and 20 were well accommodated in binding pocket of Hsp90 via relatively varied conformations. It was revealed that Asn51 and Phe138 were key residues that interacted stably to 19 and 20. Although primary mechanism of action for proposed molecules are unknown and yet to be explored, results of the present study revealed key structural features for future structure-guided optimization toward potent inhibitors of Hsp90-α NTD. Highlights Hsp90 inhibitors that entered different phases of clinical trials were subjected to Zinc15 based structure query to afford potential enzyme inhibitors 19 and 20. Quantum chemical calculations confirmed docking results and verified pivotal role of a conserved residues (Asn51, Leu103, Phe138 and Tyr139) in making effective hydrogen bonds. MD simulations of top-ranked docked derivatives revealed the achievement of stable binding modes with less conformational variation of 20 than 19 in the active site of Hsp90-α NTD. H-bond, hydrophobic contacts and salt bridge interactions were determinant forces in binding interactions of in silico hits. Resorcinol and isoxazole were important structural motifs of in silico hits in binding to the active site of Hsp90-α NTD. Communicated by Ramaswamy H. Sarma

Synthesis, Characterization, Computational, Antioxidant and Fluorescence Properties of Novel 1,3,5-Trimesic Hydrazones Derivatives

New photophysical and antioxidant materials of trimesic trihydrazide derivatives were synthesized by one-pot stage of trimesic trihydrazide and different aromatic aldehydes. All compounds were characterized by spectroscopic techniques (NMR, MS, and IR) and elemental analysis. The absorption and emission spectral characteristics of hydrazone derivatives were investigated. Their effectiveness as antioxidant was estimated by DPPH radical scavenging method in vitro which indicated that the derivatives could be used as potential antioxidants. Furthermore, molecular geometries of all prepared derivatives were fully optimized using density functional theory (DFT) calculations at the 6-31G(d)/B3LYP level of theory.

Investigation of different SWCNTs interaction with dopamine and serotonin anticancers: a theoretical study

Carbon nano tubes (CNTS) have two basic structure as single-walled and multi-walled based on hexagonal plexus of carbon atoms. CNTs can serve as platforms to conjugate other compounds specially in medications purposes by immobilization of biomolecules at their surface. Dopamine and serotonin are two biological molecules which have bifunctional activities as hormone and neurotransmitter. These two molecules have important roles as neurotransmitters in the central and peripheral nervous systems but serotonin functions as a mood regulator, while dopamine is connected to the “pleasure center”. In this article we optimized molecular and structural properties of connected dopamine and serotonin with SWNTS with four different diameters (7.0,7.5,7.7 and 10.0 nm) by using molecular quantum methods such as NMR shielding tensor data by B3LYP level of theory with 6-31 G(d) as a basis set, mk and frequency methods. Theoretical computations were performed to study NMR chemical shift data including magnetic shielding tensor (σ, ppm), shielding asymmetry (η), magnetic shielding anisotropy (σaniso), magnetic shielding isotropy (σiso) , skew of a tensor (Κ) and chemical shift anisotropy (Δσ) and span (Ω) at various rotation angles around a specific rotation , physical and chemical properties of atomic nuclei , frequency data by B3LYP/6-31g level of theory and POP method using gaussian 09 program.

The electrosorption of 3-bromo-2-nitrothiophene on gold as studied with surface-enhanced Raman spectroscopy

The electrosorption of 3-bromo-2-nitrothiophene on a polycrystalline gold electrode has been studied with surface-enhanced Raman spectroscopy SERS. Results imply a tilted orientation of the 3-bromo-2-nitrothiophene molecule with a sulfur atom of the thiophene ring and oxygen atoms of the nitro group interacting directly with the gold surface. The UV-Vis spectrum of the 3-bromo-2-nitrothiophene is recorded and its results indicated that the SERS spectra were measured under off-resonance conditions. Cyclic voltammetry measurements of the 3-bromo-2-nitrothiophene were made and the oxidation and reduction potentials of the 3-bromo-2-nitrothiophene at the gold electrode have been reported. The experimental infrared and Raman data are supported by density functional theory (DFT) calculations of 3-bromo-2-nitrothiophene using the B3LYP level of theory and 6-31G (d) basis set. The vibrational frequencies of the molecule were computed using the optimized geometry obtained from the DFT calculations. The calculated spectra are very close to the recorded infrared and Raman of the solid 3-bromo-2-nitrothiophene. No imaginary frequencies are observed in the calculated spectra. Also, DFT calculations are performed to predict and investigate the adsorption behavior of 3-bromo-2-nitrothiophene on the Au surface. In this DFT calculations, the adsorbed 3-bromo-2-nitrothiophene on the gold electrode surfaces was modeled as the metal−molecule complex. Synopsis: Electrosorption of 3-bromo-2-nitrothiophene on a polycrystalline gold electrode was discussed. The adsorption orientation and adsorption sites of the 3-bromo-2-nitrothiophene molecule at the gold surface were reported. Electrochemical investigations show a reversible redox behavior in the anodic and cathodic scan direction. The computed frequencies of the 3-bromo-2-nitrothiophene molecule support the results obtained from the recorded IR and Raman spectra.

Ultrasonic synthesis, XRD/HSA-interactions, DFT, time-dependence spectrophotometric stability and thermal analysis of the water-bridge {[Cu(phen)2Br]Br·H2O} complex

The monocationic Cu-phen mononuclear complex was assembled under ultrasonic vibration in a high yield, the presence of one water-bridge connecting both inner with outer-sphere bromides in {[Cu(phen)2Br..]..H2O..Br} was confirmed by XRD-crystal measurement. Moreover, the complex was analyzed by CHN-EA, FT-IR, MS, EDX, UV–Vis., and TGA. The XRD-diffraction analyses indicated the formation of distorted square pyramid [CuBr(phen)2]Br·H2O complex geometry, where the uncoordinated H2O behaved as a bridge-molecule connecting outer-sphere Br- anion with inter-sphere one via two short hydrogen bonds. The thermal decomposition behavior via TG/DTG was also recorded. Moreover, to evaluate the complex stability over time in an aqueous medium the time-repentance spectrophotometric method was performed. The [CuBr(phen)2]Br DFT/B3LYP optimized parameters and Hirschfield surface analysis (HSA) computations were matched to the experimental XRD-structural parameters and XRD-packing results respectively in order to evaluate the accuracies of the B3LYP and HSA theory levels on such complexes.

Synthesis and DFT Study of the Complexation of Schiff Base Derived Curcumin and L-Tyrosine with Al(III), Ag(I), and Pb(II) Metal Ions

The multi-dentate Schiff base ligand (H2L), where H2L=2,2'-(((1,3,5,6)-1-(3-((l1-oxidaneyl)-l5-methyl)-4-hydroxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-diylidene)bis(azaneylylidene))bis(3-(4-hydroxyphenyl)propanoic acid), has been prepared from curcumin and L- Tyrosine amino acid. The synthesized Schiff base ligand (H2L) and the second ligand 1,10-phenanthroline (phen) are used to prepare the new complexes [Al(L)(phen)]Cl, K[Ag(L)(phen)] and [Pb(L)(phen)]. The synthesized compounds are characterized by magnetic susceptibility measurements, micro elemental analysis (C.H.N), mass spectrometry, molar conductance, FT-infrared, UV-visible, atomic absorption (AA), 13C-NMR, and 1H-NMR spectral studies. The characterization of the synthesized complexes shows that the environment surrounding the central metal ion in the complexes adopted a distorted octahedral configuration. Moreover, the conductivity measurements show a non-electrolytic character for the [Pb(L)(phen)] complex and an electrolytic character for the [Al(L)(phen)]Cl and K[Ag(L)(phen)] complexes. The experimental infrared data are supported by density functional theory (DFT) calculations using the B3LYP level of theory and LANL2DZ basis set. The vibrational frequencies of the molecules are computed using the optimized geometry obtained from the DFT calculations. The calculated vibrational frequencies have been compared with obtained experimental values. 1H and 13C-NMR chemical shifts were computed for the H2L ligand using the DFT/GIAO method. Additionally, the molecular electronic structures of the complexes have been investigated by DFT calculations.

Experimental and Computational Studies on Structure and Energetic Properties of Halogen Derivatives of 2-Deoxy-D-Glucose.

The results of structural studies on a series of halogen-substituted derivatives of 2-deoxy-D-glucose (2-DG) are reported. 2-DG is an inhibitor of glycolysis, a metabolic pathway crucial for cancer cell proliferation and viral replication in host cells, and interferes with D-glucose and D-mannose metabolism. Thus, 2-DG and its derivatives are considered as potential anticancer and antiviral drugs. X-ray crystallography shows that a halogen atom present at the C2 position in the pyranose ring does not significantly affect its conformation. However, it has a noticeable effect on the crystal structure. Fluorine derivatives exist as a dense 3D framework isostructural with the parent compound, while Cl- and I-derivatives form layered structures. Analysis of the Hirshfeld surface shows formation of hydrogen bonds involving the halogen, yet no indication for the existence of halogen bonds. Density functional theory (DFT) periodic calculations of cohesive and interaction energies (at the B3LYP level of theory) have supported these findings. NMR studies in the solution show that most of the compounds do not display significant differences in their anomeric equilibria, and that pyranose ring puckering is similar to the crystalline state. For 2-deoxy-2-fluoro-D-glucose (2-FG), electrostatic interaction energies between the ligand and protein for several existing structures of pyranose 2-oxidase were also computed. These interactions mostly involve acidic residues of the protein; single amino-acid substitutions have only a minor impact on binding. These studies provide a better understanding of the structural chemistry of halogen-substituted carbohydrates as well as their intermolecular interactions with proteins determining their distinct biological activity.

Thermochemistry of the Ir+ + SO2 reaction using guided ion beam tandem mass spectrometry and theory.

Kinetic energy dependences of the reactions of Ir+ (5F5) with SO2 were studied using a guided ion beam tandem mass spectrometer and theory. The observed cationic products are IrO+, IrS+, and IrSO+, formed in endothermic reactions. Bond dissociation energies (BDEs) of the products are determined by modeling the kinetic energy dependent product cross sections: D0(Ir+-O) = 4.27 ± 0.11 eV, D0(Ir+-S) = 4.03 ± 0.06 eV, and D0(Ir+-SO) ≥ 2.95 ± 0.06 eV. The oxide BDE agrees well with literature values, whereas the two latter results are novel measurements. Quantum mechanical calculations are performed at the B3LYP level of theory using the def2-TZVPPD basis set for all product BDEs with additional calculations for IrS+, IrO2 +, and IrSO+ at the coupled cluster with single, double, and perturbative triple excitation levels with def2-QZVPPD and aug-cc-pVXZ (X = T and Q and for IrS+, also X = 5) basis sets and complete basis set extrapolations. These theoretical BDEs agree reasonably well with the experimental values. 1A1 (IrO2 +), 5Δ4 (IrS+), and 3A″/1A' (IrSO+) are found to be the ground states after including empirical spin-orbit corrections. The potential energy surfaces including intermediates and transition states for each reaction are also calculated at the B3LYP/def2-TZVPPD level. The formation of MO+ (M = Re, Os, and Ir) from M+ + SO2 reactions is compared with those from the M+ + O2 and M+ + CO reactions, where interesting trends in cross sections are observed. Overall, these studies suggest that the M+ + O2 reactions had restrictions associated with reactions along A' and A″ surfaces.

Experimental 1H and 13C Solid-State NMR Signal Assignment of Paramagnetic Copper (II) 2-Pyrazine-Carboxylate Complex using Density Functional Theory Calculations

We have acquired 1H and 13C solid-state NMR (ssNMR) spectra of the paramagnetic Cu(II)-2-pyrazine-carboxylate (Cu-Py) complex and assigned paramagnetic 1H/13C signals using density functional theory (DFT) calculations. The unpaired electron in Cu(II) ionexacerbates the 1H and 13C chemical shifts in the Cu-Py complex through hyperfine interactions, making the conventional NMR signal assignment non-feasible. Further, the nuclear fast relaxation in paramagnetic metal-organic system hampers application of routine ssNMR techniques for signal acquisition. In our work we have employed simple DEPTH experiment at 50 kHz magic angle spinning (MAS) for acquiring 1H and 13C 1D ssNMR spectra of the paramagnetic Cu(II)-2-pyrazine-carboxylate (Cu-Py) complex. The paramagnetic augmented (diamagnetic chemical shift + paramagnetic shift) 1D 1H and 13C ssNMR signals (shifts) from Cu-Py complex have major contribution from Fermi contact interaction due to proximity of the organic arm to Cu2+ ion (Cu2+-C/H atoms 0-5 Å). The unpaired electron spin density distributed over the pyrazine-carboxylate organic arm is crucial in understanding Fermi contact shifts and hence accounts for 1H and 13C ssNMR signal assignment. The theoretical Fermi contact shifts together with diamagnetic shifts, calculated using density functional theory (DFT) at B3LYP level with basis sets viz. 6-311G, 6-311G+(D) and 6-311G++(D), were compared with the experimental shifts to facilitate the process of signal assignment. Vibrational analysis of Cu-Py complex was performed at B3LYP level of theory with various basis sets in comparison with experimental IR data. This further assisted in double validation of DFT optimized Cu-Py structure used here for extracting Fermi contact shifts. Furthermore molecular orbital analysis on the DFT optimized Cu-Py structure articulates the spin density distribution mechanism, thereby stipulating the location of the unpaired electron in the Cu(II) dx 2 -y 2 orbital in Paramagnetic Cu-Py complex.