A theoretical study of 17O, 14N and 2H nuclear quadrupole coupling tensors in the real crystalline structure of acetaminophen

A theoretical study on the characteristics of the intermolecular interactions in the active site of human androsterone sulphotransferase: DFT calculations of NQR and NMR parameters and QTAIM analysis

A theoretical study at the level of density functional theory (DFT) was performed to characterize noncovalent intermolecular interactions, especially hydrogen bond interactions, in the active site of enzyme human androsterone sulphotransferase (SULT2A1/ADT). Geometry optimization, interaction energy, (2)H, (14)N, and (17)O electric field gradient (EFG) tensors, (1)H, (13)C, (17)O, and (15)N chemical shielding (CS) tensors, Natural Bonding Orbital (NBO) analysis, and quantum theory of atoms in molecules (QTAIM) analysis of this active site were investigated. It was found that androsterone (ADT) is able to form hydrogen bonds with residues Ser80, Ile82, and His99 of the active site. The interaction energy calculations and NBO analysis revealed that the ADT molecule forms the strongest hydrogen bond with Ser80. Results revealed that ADT interacts with the other residues through electrostatic and Van der Waals interactions. Results showed that these hydrogen bonds influence on the calculated (2)H, (14)N, and (17)O quadrupole coupling constants (QCCs), as well as (1)H, (13)C, (17)O, and (15)N CS tensors. The magnitude of the QCC and CS changes at each nucleus depends directly on its amount of contribution to the hydrogen bond interaction.

Cooperative interaction between hydrogen bond and N···Y interactions (Y = H, Li, F, Cl, and Br): a comparative study

A comparative ab initio study is performed to investigate the cooperativity between the N···H hydrogen bond and the N···Y interactions in XCN···HCN···YCN complexes, where X = H, F, and Y = H, Li, F, Cl, and Br. To understand the properties of the systems better, the corresponding dimers are also studied. It is found that the lithium bond has a larger influence on the hydrogen bond than vice versa. The shortening of the N···H distances in the trimers is dependent on the strength of the H···Y interactions and they become larger in the order lithium bond > hydrogen bond > halogen bond. The estimated values of cooperative energy Ecoop are all negative with much larger Ecoop in absolute value for the systems including lithium.

CNXeCl and CNXeBr species as halogen bond donors: a quantum chemical study on the structure, properties, and nature of halogen···nitrogen interactions

In the present study, strength and characteristic of halogen bond interactions between CNXeY and NCZ molecules are investigated, where Y = Cl, Br and Z = H, CN, F, OH, CH₃, OCH₃, NH₂. MP2/aug-cc-pVTZ calculations indicate that the interaction energies for CNXeY⋯NCZ complexes lie in the range between -1.0 and -3.1 kcal mol⁻¹. Not surprisingly, the calculated interaction energies show a strong correlation with the negative electrostatic potentials on nitrogen atoms. One of the most important results of this study is that, according to energy decomposition analyses, Cl⋯N halogen bonds are largely dependent on dispersion effects, while electrostatic interactions are the major source of the attraction in Br⋯N bonds. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis are used in this study to deepen the nature of the interactions considered. This appears to be the first report on a halogen bond involving halogenated xenon isocyanides.

A DFT INVESTIGATION ON BASIS SET SIZE AND HYDROGEN-BONDING EFFECTS ON 17O AND 2H NQR PARAMETERS

A systematic theoretical study on various maleic acid (MA) clusters has been carried out employing density functional theory (DFT) methods. The performance of two different functionals namely B3LYP and M06 in the prediction of geometries, 17 O and 2 H nuclei quadrupole coupling constant (CQ) values of the MA clusters has been assessed comparing the results to those experimental data. For DFT calculations, several basis sets have been used, including the recently developed Jensen's polarization-consistent basis set families, pcJ-n and pcS-n (n = 0,1,2,3). Calculations at the basis set limit indicate that the value of CQ(2 H ) in monomer MA, changes by 0.01–0.04 kHz for each of the final two basis set increments, and seems reasonable to conclusion that the pcJ-3 result is within a few kHz of the basis set limit. Convergence with respect to basis set size was found to be very good, and the pcJ-1 and pcS-1 basis sets provided a good compromise between the basis set limit and computational expense. In most cases, the differences between B3LYP and M06 results for a given basis set are in a range of 1–2%. On the other hand, no systematic changes in the CQ(17 O ) or CQ(2 H ) were found for basis sets larger than double-ζ. Thus, the usual assumption that double-ζ basis set (pcJ-1 and pcS-1) results in the acceptable CQ values, seems to be valid in the case of 17 O and 2 H nuclei.

AB INITIO CALCULATIONS OF 14N NQR PARAMETERS AND 13C, 1H, AND 15N CHEMICAL SHIFTS INCLUDING A COMPARISON WITH EXPERIMENTAL NMR DATA FOR CYCLOTRISAZOBENZENE

Nuclear quadrupole coupling constant, χ, and asymmetry parameter, η, of 14 N nucleus and 13 C , 1 H , and 15 N chemical shifts for cyclotrisazobenzene at the level of B3LYP and MP2 methods have been studied using the Gaussian 98 suite of programs. Also, nuclear quadrupole resonance (NQR) frequencies (ν0, ν+, ν-) for 14 N have been calculated, thoroughly. The optimized structure of the compound was very similar to that given by the X-ray crystallographic data. The electric field gradient (EFG) calculation verified that the N = N bonds are highly localized in this molecule; therefore, electron-pairs of the nitrogen atoms remain nonbonding. The comparison of the calculated chemical shifts with the experimental values for cyclotrisazobenzene shows no significant structural changes in solution.

High-pressure diffraction studies of molecular organic solids. A personal view

This paper discusses the trends in the experimental studies of molecular organic solids at high pressures by diffraction techniques. Crystallization of liquids, crystallization from solutions and solid-state transformations are considered. Special attention is paid to the high-pressure studies of pharmaceuticals and of biomimetics.