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A theoretical study has been carried out on the intermolecular interactions between tetrafluoro-benzochalcogenadiazoles (chalcogen = S, Se, Te) and a series of nitrogen bases (FCN, ClCN, NP, trans-N2H2, pyridine, pyrazole, imidazole) at the B97-D3/def2-TZVP level, to obtain a better insight into the nature and strength of Ch···N chalcogen bond and secondary interaction in the binary and 1:2 ternary complexes. The dispersion force plays a prominent role on the stability of the sulfur complexes, and the electrostatic effect enhanced for the heavier chalcogen complexes. Most of intermolecular bonds display the characters of closed-shell and noncovalent interaction. For the complexes involving pyridine and imidazole, chalcogen bond is stronger than hydrogen bond, while the strength of chalcogen bond is equivalent to the secondary interaction for other complexes. With the addition of nitrogen base in the 1:2 complexes, chalcogen bond is weakened, while the secondary interaction remains unchanged. In the 1:2 complexes formed by pyridine and imidazole, stronger chalcogen bond results in larger negative cooperativity than that of other complexes. [ABSTRACT FROM AUTHOR]

The bimolecular and termolecular complexes involving F2TO (T = Si, Ge, Sn) and XCN/BrY (X = H, Br, CH3, and PH2; Y = F, CN, OH, and H) were designed to form the π-hole tetrel bonds and different sorts of σ-hole interactions, to investigate the influence of π-hole tetrel bonds on the σ-hole interactions. The effect of π-hole tetrel bonds on the σ-hole interactions in three series HCN···F2TO···HCN, HCN···F2SiO···XCN, and HCN···F2SiO···BrY is reflected by the changes in geometry, interaction energy, and charge transfer. With the formation of π-hole tetrel bond, the VS, min value outside the oxygen atom of F2TO becomes more negative, resulting in a stronger σ-hole interaction. Comparing with the bimolecular complex, the σ-hole binding distance and binding angle in the corresponding termolecular complex changes a lot, with the formation of another tetrel bond. The σ-hole interaction energy is enhanced more than 100% in most of the complexes with the exception of HCN···F2SiO···BrCN. The enhancing effect is related to the strength of π-hole tetrel bond, but has no relationship with the strength of σ-hole interactions. In particular, the σ-hole tetrel bond between F2SiO and CH3CN varies from a weak tetrel bond in the bimolecular complex F2SiO···CH3CN to a moderate hydrogen bond in the termolecular complex HCN···F2SiO···CH3CN. [ABSTRACT FROM AUTHOR]

The π-hole of triphosphorus hydride (P3H3) and its derivatives Z3 X3 ( Z = P, As; X = H, F, Cl, Br) was discovered and analyzed. MP2/aug-cc-pVDZ calculations were performed on the π-hole interactions in the HCN... Z3 X3 complexes and the mutual influence between π-hole interactions and the hydrogen bond in the HCN...HCN... Z3 X3 and HCN... Z3 X3...HCN complexes studied. The π-hole interaction belongs to the typical closed-shell noncovalent interaction. The linear relationship was found between the most positive electrostatic potential of the π-hole ( VS,max) and the interaction energy. Moreover, the VS,max of the π-hole was also found to be linearly correlated to the electrostatic energy term, indicating the important contribution of the electrostatic energy term to the π-hole interaction. There is positive cooperativity between the π-hole interaction and the hydrogen bond in the termolecular complexes. The π-hole interaction has a greater influence on the hydrogen bond than vice versa. The mutual enhancing effect between the π-hole interaction and the hydrogen bond in the HCN...HCN... Z3 X3 complexes is greater than that in the HCN... Z3 X3...HCN complexes. [ABSTRACT FROM AUTHOR]

Detailed electrostatic potential (ESP) analyses were performed to compare the directionality of halogen bonds with those of hydrogen bonds and lithium bonds. To do this, the interactions of HOOOH with the molecules XF (X = Cl, Br, H, Li) were investigated. For each molecule, the percentage of the van der Waals (vdW) molecular surface that intersected with the ESP surface was used to roughly quantify the directionality of the halogen/hydrogen/lithium bond associated with the molecule. The size of the region of intersection was found to increase in the following order: ClF < BrF < HF < LiF. The maximum ESP in the region of intersection, V, was observed to become more positive according to the sequence ClF < BrF < HF < LiF. For ClF and BrF, the positive electrostatic potential was concentrated in a very small region of the vdW molecular surface. On the other hand, for HF and LiF, the positive electrostatic potential was more diffusely scattered across the vdW surface than for ClF and BrF. Also, the optimized geometries of the dipolymers HOOOH··· XF (X = Cl, Br, H, Li) indicated that halogen bonds are more directional than hydrogen bonds and lithium bonds, consistent with the results of ESP analyses. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The nature of the interactions of cyanide with lithium and hydrogen halides was investigated using ab initio calculations and topological analysis of electron density. The computed properties of the lithium-bonded complexes RCN···LiX (R = H, F, Cl, Br, CCH, CHCH2, CH3, C2H5; X = Cl, Br) were compared with those of corresponding hydrogen-bonded complexes RCN···HX. The results show that both types of intermolecular interactions are 'closed-shell' noncovalent interactions. The effect of substitution on the interaction energy and electron density at the bond critical points of the lithium and hydrogen bonding interactions is similar. In comparison, the interaction energies of lithium-bonded complexes are more negative than those of hydrogen-bonded counterparts. The electrostatic interaction plays a more important role in the lithium bond than in the hydrogen bond. On complex formation, the net charge and energy of the Li atom decrease and the atomic volume increases, while the net charge and energy of the H atom increase and the atomic volume decreases. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The character of the cooperativity between the HOX···OH/SH halogen bond (XB) and the Y-H···(H)OX hydrogen bond (HB) in OH/SH···HOX···HY (X = Cl, Br; Y = F, Cl, Br) complexes has been investigated by means of second-order Møller−Plesset perturbation theory (MP2) calculations and 'quantum theory of atoms in molecules' (QTAIM) studies. The geometries of the complexes have been determined from the most negative electrostatic potentials ( V) and the most positive electrostatic potentials ( V) on the electron density contours of the individual species. The greater the V values of HY, the larger the interaction energies of halogen-bonded HOX···OH/SH in the termolecular complexes, indicating that the ability of cooperative effect of hydrogen bond on halogen bond are determined by V of HY. The interaction energies, binding distances, infrared vibrational frequencies, and electron densities ρ at the BCPs of the hydrogen bonds and halogen bonds prove that there is positive cooperativity between these bonds. The potentiation of hydrogen bonds on halogen bonds is greater than that of halogen bonds on hydrogen bonds. QTAIM studies have shown that the halogen bonds and hydrogen bonds are closed-shell noncovalent interactions, and both have greater electrostatic character in the termolecular species compared with the bimolecular species. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Series of typical π-type and pseudo-π-type halogen-bonded complexes B ···ClY and B ···BrY and hydrogen-bonded complex B ···HY (B = C2H4, C2H2, and C3H6; Y = F, Cl, and Br) have been investigated using the MP2/aug-cc-pVDZ method. A striking parallelism was found in the geometries, vibrational frequencies, binding energies, and topological properties between B ···XY and B ···HY (X = Cl and Br). It has been found that the lengths of the weak bond d(X ···π)/ d(H ···π), the frequencies of the weak bond ν(X ···π)/ν(H ···π), the frequency shifts Δν(XY)/Δν(HY), the electron densities at the bond critical point of the weak bonds ρc(X ···π)/ρc(H ···π), and the electron density changes Δρc(XY)/Δρc(HY) could be used as measures of the strengths of typical π-type and pseudo-π-type halogen/hydrogen bonds. The typical π-type and pseudo-π-type halogen bond and hydrogen bond are noncovalent interactions. For the same Y, the halogen bond strengths are in the order B ···ClY < B ···BrY. For the same X, the halogen bond strength decreases according to the sequence F > Cl > Br that is in agreement with the hydrogen bond strengths B ···HF > B ···HCl > B ···HBr. All of these typical π-type and pseudo-π-type hydrogen-bonded and halogen-bonded complexes have the 'conflict-type' structure. Contour maps of the Laplacian of π electron density indicate that the formation of B ···XY halogen-bonded complex and B ···HY hydrogen-bonded complex is very similar. Charge transfer is observed from B to XY/HY and both the dipolar polarization and the volume of the halogen atom or hydrogen atom decrease on B ···XY/B ···HY complex formation. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The nature of the interactions of furan and thiophene with hydrogen halides and lithium halides has been investigated using ab initio calculations and QTAIM analysis. The concept of molecule formation density difference (MFDD) is introduced to study weak hydrogen bond (HB) and lithium bond (LB) interactions. The results have shown the molecular electrostatic potentials of furan and thiophene, as well as of the hydrogen halides and lithium halides, determine the geometries of the complexes. Both the studied HB and LB interactions can be classified as 'closed-shell' weak interactions. The topological properties and energy properties at the bond critical points of HB and LB have been shown to be exponentially dependent on intermolecular distances d(H-bond) and d(Li-bond), which enables interpretation of the strength of the HB and LB interactions in terms of these ρ(r) properties. Electron transfer plays a more important role in the formation of HB than in that of LB, while electrostatic interaction in LB is more dominant than that in HB. Table of Contents (TOC) Image [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We present theoretical evidence that the two types of interactions exist in the complexes formed between methylenecyclopropane (MECP) and XY (X, Y = H, F, Cl, and Br). Two seats of XY interacted with MECP are located: (a) is via the pseudo‐π bonding electron pair associated with a CC bond of the cyclopropane ring and (b) is via the typical‐π bonding of electron pair of the CC bond of MECP. These two types of weak interactions are compared based on the calculated geometries, interaction energies, frequency changes, and topological properties of electron density. The integration of electron density over the interatomic surface is found to be a good measure for the strength of weak interaction. Furthermore, the total electron density and separated σ and π electron densities are also computed and discussed in this article. The separated electron density shows σ electron density determined the strength and π electron density influenced the direction of the hydrogen/halogen bond. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Abstract: Ab initio and “Atoms in Molecules” studies have been carried on the intermolecular interactions between oxygen-containing σ-electron donors B (B=H2O, H2CO, (CH2)2O) and hydrogen halide HY and dihalogen molecules XY (X, Y=F, Cl, Br). The geometries, energies and topological characteristics of hydrogen-bonded systems have been compared with those of halogen-bonded systems. In general, many properties of the halogen bond are analogous to those of the hydrogen bond. For the same electron acceptor H or X atom, the properties such as bond distance, binding energy, electron density and charge transfer decrease in the sequence of B···HF>B···HCl>B···HBr, B···ClF>B···Cl2, B···BrF>B···BrCl>B···Br2. The bond distance, frequency shift and electron density may be applied as the measure of strength of hydrogen and halogen bond. The decrease in the atomic dipolar polarization and the atomic volume are dependent of the strength of halogen-bonded interaction, while they are independent of the strength of hydrogen-bonded interaction. [Copyright &y& Elsevier]

The binding mechanism and binding forces of API-CCF cocrystal with BSA and cell inhibitory rates vary with the kinds of weak forces between API and CCF. • Novel curcumine(CUR)-isonicotinamide (1) and CUR-gallic acid (2) cocrystals were prepared. • C O and O H groups in CUR involved in the hydrogen bonds in cocrystal 1 and 2, respectively. • Hydrogen bonds and/or van der Waals forces occurred between cocrystal 1 and BSA binding reaction. • Hydrophobic forces occurred in the binding reaction with BSA for cocrystal 2. • Cell inhibitory rates of cocrystal 1 differed from that of cocrystal 2. Screening of cocrystal has been proved to be a powerful approach to improve the solubility, dissolution rate and even the bioavailability of poorly water-soluble active pharmaceutical ingredient (API). Typically, the formation of cocrystal induces no change on the pharmacological profile of the APIs. However, so far, it is not clear whether a cocrystal would induce changes in biological profiles of API and, if so, which factors induce those changes. To clarify these aspects, two CUR-isonicotinamide (cocrystal 1) and CUR-gallic acid (cocrystal 2) cocrystals with enhanced physical properties and pharmacokinetic profile for potential pharmaceutical application were screened. We focused on the effects of the type of hydrogen bonds occurred in cocrystal on the binding between cocrystal and BSA as well as cell inhibiting activity. The appearance of new peaks in the X-ray powder diffraction (PXRD) and a single different melting point in the differential scanning calorimetry (DSC) measurements revealed that homogeneous, single phase formulations were obtained by forming cocrystals between CUR and coformers in a 1:2 M ratio. The results of Fourier-transform infrared and solid-state 13C nuclear magnetic resonance spectra as well as density function theory simulation indicated that different hydrogen bonds were formed in two cocrystal, which were the C O⋯H N hydrogen bond between the C O group in CUR and the N H groups in isonicotinamide in cocrystal 1, and C O⋯H O hydrogen bond between phenol O H group in CUR and the C O group in gallic acid in cocrystal 2, respectively. Interestingly, the different type of weak interactions in cocrystal induced various binding pattern between cocrystal and BSA and cancer cell cytotoxicity supported by fluorescence spectroscopy and MTT assay in vitro. It was reasonable that the affinity of cocrystal for proteins varied with specific and concerted weak interactions in cocrystal, which would induce changes in the biological profiles of the parent drug. Furthermore, in vivo pharmacokinetics of CUR and CUR-based cocrystals in SD rats were evaluated through UPLC-MS/MS method. Compared with intact CUR, the pharmacokinetics parameters C max , T max , AUC 0-t and AUC 0-∞ of CUR-based cocrystals were improved (P < 0.05); C max increased 30-fold, T max shortened 6-fold, and AUC 0-t increased 6-fold. Overall, the present results inferred different effects induced by cocrystals on a biologic system, not only bioavailability but biological profiles. [ABSTRACT FROM AUTHOR]

Abstract: The crystal and electronic structures, the formation energy of H vacancies, and the diffusion path of the H atom (i.e., diffusion path of H vacancy) in unsubstituted and substituted LiNH2 crystal were investigated by periodic first-principles calculations. The bonding characters between atoms were studied by topological analysis of electron density. Our calculations reveal that substitution of the Li atom with Ti or Nb favors the formation of hydrogen vacancies adjacent to substitution, and the existence of an H vacancy and Ti or Nb substitution can cause weakening of nearby N–H bonds, which facilitates N–H bond dissociation. The minimum energy paths of H diffusion show that the substitution can reduce the energy barrier and thus favor H diffusion in the bulk phase of LiNH2. [Copyright &y& Elsevier]