Andrei V. Churakov

Bio: Andrei V. Churakov is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Hydrogen bond & Crystal structure. The author has an hindex of 30, co-authored 428 publications receiving 4483 citations. Previous affiliations of Andrei V. Churakov include University of Marburg & Florida State University.

Intermolecular hydrogen bond energies in crystals evaluated using electron density properties: DFT computations with periodic boundary conditions

Abstract: The hydrogen bond (H-bond) energies are evaluated for 18 molecular crystals with 28 moderate and strong O-H···O bonds using the approaches based on the electron density properties, which are derived from the B3LYP/6-311G** calculations with periodic boundary conditions. The approaches considered explore linear relationships between the local electronic kinetic G(b) and potential V(b) densities at the H···O bond critical point and the H-bond energy E(HB). Comparison of the computed E(HB) values with the experimental data and enthalpies evaluated using the empirical correlation of spectral and thermodynamic parameters (Iogansen, Spectrochim. Acta Part A 1999, 55, 1585) enables to estimate the accuracy and applicability limits of the approaches used. The V(b)-E(HB) approach overestimates the energy of moderate H-bonds (E(HB) < 60 kJ/mol) by ~20% and gives unreliably high energies for crystals with strong H-bonds. On the other hand, the G(b)-E(HB) approach affords reliable results for the crystals under consideration. The linear relationship between G(b) and E(HB) is basis set superposition error (BSSE) free and allows to estimate the H-bond energy without computing it by means of the supramolecular approach. Therefore, for the evaluation of H-bond energies in molecular crystals, the G(b) value can be recommended to be obtained from both density functional theory (DFT) computations with periodic boundary conditions and precise X-ray diffraction experiments.

Pharmaceutical Cocrystals of Diflunisal and Diclofenac with Theophylline

Abstract: Pharmaceutical cocrystals of nonsteroidal anti-inflammatory drugs diflunisal (DIF) and diclofenac (DIC) with theophylline (THP) were obtained, and their crystal structures were determined. In both of the crystal structures, molecules form a hydrogen bonded supramolecular unit consisting of a centrosymmetric dimer of THP and two molecules of active pharmaceutical ingredient (API). Crystal lattice energy calculations showed that the packing energy gain of the [DIC + THP] cocrystal is derived mainly from the dispersion energy, which dominates the structures of the cocrystals. The enthalpies of cocrystal formation were estimated by solution calorimetry, and their thermal stability was studied by differential scanning calorimetry. The cocrystals showed an enhancement of apparent solubility compared to the corresponding pure APIs, while the intrinsic dissolution rates are comparable. Both cocrystals demonstrated physical stability upon storing at different relative humidity.

H-bond network in amino acid cocrystals with H2O or H2O2. The DFT study of serine-H2O and serine-H2O2.

Abstract: The structure, IR spectrum, and H-bond network in the serine–H2O and serine–H2O2 crystals were studied using DFT computations with periodic boundary conditions. Two different basis sets were used: ...

Structure and ion-complexing properties of an aza-15-crown-5 ether dye: synthesis, crystallography, NMR spectroscopy, spectrophotometry and potentiometry

Abstract: The perchlorate of 2-{2-[4-(13-aza-1,4,7,10-tetroxa-13-cyclopentadecyl)phenyl]ethenyl}-3-ethylbenzothiazolium (3) has been synthesised and its structure determined in the crystalline state by X-ray diffraction and in solution in acetonitrile by 1H NMR methods. Complexation with barium and silver cations in solution has been studied in comparison with other model azacrown molecules by spectrophotometric and potentiometric methods. With the exception of the puckered azacrown moiety, the structure of 3 is remarkably planar, consistent with extensive π-conjugation throughout the remainder of the molecule in both solid and solution states. Compound 3 forms a stable 1∶1 complex with Ba2+ ions in acetonitrile, with a stability constant of K1 = 80 ± 10 dm3 mol–1; the complexation results in major changes in the electronic absorption spectrum of 3, consistent with binding to the azacrown moiety. A model compound, phenylaza-15-crown-5 (2a), was found to bind Ba2+ to form both a 1∶1 ligand–metal complex (LM), with a stability constant of K1 = (2.0 ± 0.2) × 104 dm3 mol–1, and a 2∶1 (L2M) complex, with a stability constant of K2 = 220 ± 20 dm3 mol–1 for binding of the second ligand. The electronic absorption and NMR spectra both indicate binding of the ‘hard’ Ba2+ cation to the azacrown oxygen atoms. However, by contrast, the evidence from NMR data shows that the ‘soft’ Ag+ cation complexes with 2a mainly through a strong interaction with the azacrown nitrogen atom, giving a 1∶1 complex with a stability constant of K1 = 6 ± 1 dm3 mol–1, determined by potentiometry. No complexation of 3 with Ag+ is observed. Studies of the simple aza-15-crown-5 ether reveal strong complexation with both Ba2+ (K1 × K2 > 1012 dm6 mol–2) and Ag+ [K1 = (1.15 ± 0.10) × 104 dm3 mol–1 and K2 = 450 ± 20 dm3 mol–1].

Gold-Catalyzed Organic Reactions

Abstract: Although homogeneous gold catalysis was known previously, an exponential growth was only induced 12 years ago. The key findings which induce that rise of the field are discussed. This includes early reactions of allenes and furanynes and intermediates of these conversions as well as hydroarylation reactions. Other substrate types addressed are alkynyl epoxides and N-propargyl carboxamides. Important vinylgold intermediates, the transmetalation from gold to other transition metals, the development of new ligands for gold catalysis, and significant contributions from computational chemistry are other crucial points for the field highlighted here.

Secondary building units, nets and bonding in the chemistry of metal–organic frameworks

Abstract: This critical review presents a comprehensive study of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) towards construction and synthesis of metal–organic frameworks (MOFs). We describe the geometries of 131 SBUs, their connectivity and composition. This contribution presents a comprehensive list of the wide variety of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) in the construction and synthesis of metal–organic frameworks. The SBUs discussed here were obtained from a search of molecules and extended structures archived in the Cambridge Structure Database (CSD, version 5.28, January 2007) which included only crystals containing metal carboxylate linkages (241 references).

X-Ray Diffraction

Abstract: Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.