Tetrel Bonds between Phenyltrifluorosilane and Dimethyl Sulfoxide: Influence of Basis Sets, Substitution and Competition.

Ab initio calculations have been performed for the complexes of DMSO and phenyltrifluorosilane (PTS) and its derivatives with a substituent of NH3, OCH3, CH3, OH, F, CHO, CN, NO2, and SO3H. It is necessary to use sufficiently flexible basis sets, such as aug'-cc-pVTZ, to get reliable results for the Si···O tetrel bonds. The tetrel bond in these complexes has been characterized in views of geometries, interaction energies, orbital interactions and topological parameters. The electron-donating group in PTS weakens this interaction and the electron-withdrawing group prominently strengthens it to the point where it exceeds that of the majority of hydrogen bonds. The largest interaction energy occurs in the p-HO3S-PhSiF3···DMSO complex, amounting to -122 kJ/mol. The strong Si···O tetrel bond depends to a large extent on the charge transfer from the O lone pair into the empty p orbital of Si, although it has a dominant electrostatic character. For the PTS derivatives of NH2, OH, CHO and NO2, the hydrogen bonded complex is favorable to the tetrel bonded complex for the NH2 and OH derivatives, while the σ-hole interaction prefers the π-hole interaction for the CHO and NO2 derivatives.

Influence of alkali substituents on the strength, properties, and nature of tetrel bond between TH3F and pyridine.

Ab initio calculations have been performed for the complexes of TH3F (T=C, Si, and Ge) with pyridine and its alkali derivatives to study the influence of an alkali substituent on the strength, properties, and nature of tetrel bond. The introduction of an alkali atom into the electron donor has a prominent enhancing effect on the strength of tetrel bond, which depends on the T atom as well as the alkali atom and its substitution position. The enhancing effect becomes larger in the C < Ge < Si, Li < Na < K, and para- < meta- < ortho- patterns. The interaction energy varies in a wide range from 2 to 40 kcal/mol. Both electrostatic and polarization including charge transfer are responsible for the enhancing effect of an alkali atom. The formation of a tetrel bond results in an elongation of F-T bond and a red shift of F-T stretch vibration, which is big enough to be detected with infrared spectroscopy. Electrostatic interaction is dominant in all complexes, while polarization is smaller or larger than dispersion in the complexes of CH3F or TH3F(T=Si and Ge).

Strengthening of halogen bond in XCl∙∙∙FH∙∙∙F- through cooperativity with a strong hydrogen bond and proton transfer.

A theoretical calculation has been performed for the ternary complexes XCl∙∙∙FH∙∙∙F- (X = CCH, CN, OH, NC, and F) and the corresponding binary complexes. The halogen bond in the dyad is very weak with the interaction energy less than 2.5 kcal/mol. Interestingly, the halogen bond gets a big enhancement when it combines with a very strong hydrogen bond in FH∙∙∙F-, and the largest interaction energy is up to ∼25.6 kcal/mol in FCl∙∙∙FH∙∙∙F-. The enhancement of halogen bond not only results in a larger elongation of X-Cl bond and a bigger redshift of the bond stretch vibration but also makes the blue-shifting halogen bond in NCCl∙∙∙FH be a red-shifting one in NCCl∙∙∙FH∙∙∙F-. The halogen bond belongs to a purely close-shell interaction in the dyad, while it becomes a partially covalent interaction in XCl∙∙∙FH∙∙∙F- (X = OH, NC, and F) with negative energy density. In FH∙∙∙F-, the proton is shared between the two F atoms, however, this proton transfers towards the F- end in XCl∙∙∙FH∙∙∙F-.

Se···N chalcogen bond and Se···X halogen bond involving F2C═Se: influence of hybridization, substitution, and cooperativity.

Quantum-chemical calculations have been performed for the chalcogen- and halogen-bonded complexes of F2CSe with a series of nitrogen bases (N2, NCH, NH3, NHCH2, NCLi, and NMe3) and dihalogen molecules (BrCl, ClF, and BrF), respectively. Both types of interactions are mainly driven by the electrostatic and orbital interactions. The chalcogen bond becomes stronger in the order of NCH (sp) < NH3 (sp(3)) < NHCH2 (sp(2)), showing some inconsistence with the electronegativity of the hybridized N atom. The Li and methyl groups have an enhancing effect on the strength of chalcogen bond; however, the former is jointly achieved through the electrostatic and orbital interactions, whereas the orbital interaction has dominant contribution to the latter enhancement. The halogen bond with F2CX (X = O, S, Se) as the electron donor is stronger for the heavier chalcogen atom, exhibiting a reverse dependence on the chalcogen atom with that in hydrogen bonds. The halogen bond is further strengthened by the presence of chalcogen bond in the ternary complexes. In addition, CSD research confirms the abundance of Se···N interaction in crystal materials.

Prediction and characterization of halogen bonds involving formamidine and its derivatives.

Ab initio calculations have been carried out for the complexes of formamidine (FA) and some representative halogenated molecules XY (X=Cl, Br, and I; Y=F, CCH, CF3, CN, and NC). The FA-(Z) complex combines with the halogenated molecule through a halogen bond, while the FA-(E) complex is stabilized jointly by both a halogen bond and a X⋯H interaction. The FA-(E) complex is more stable than the FA-(Z) counterpart, with the interaction energy of -3.4 to -23.4kcal/mol, indicating that FA is a good electron donor in halogen bonding. The methyl substituent particularly one at the imino nitrogen atom of FA has an enhancing effect on the strength of halogen bond. The similar effect is found for the phenyl and pyridyl substituents, depending on the FA conformation and substitution position of pyridyl. The stability of stronger halogen bonding is mainly attributed to electrostatic and polarization energies, which is different from the weak one with an electrostatic nature.

Influence of the nature of hydrogen halides and metal cations on the interaction types between borazine and hydrogen halides.

The interactions between the H atom of borazine and hydrogen halide (HX, X = F, Cl, Br, and I) have been studied systematically. Four structures (a, b, c, and d) have been observed. The cyclic structure a is combined through a NH···X hydrogen bond and a BH···HX dihydrogen bond, a NH···X hydrogen bond and a BH···X halogen-hydride interaction are responsible for the cyclic structure b, structures c and d are maintained by a dihydrogen bond and a halogen-hydride interaction, respectively. Structures a and b are stable in energy, while structures c and d are unstable in energy. Structures a and b can transform each other through structure c or d. The interaction mode and strength are related to the nature of HX. The cation-π interaction of borazine with Li(+) and Mg(2+) causes a change in the interaction mode in structures a and b, and has an enhancing effect on the interaction strength in a and b.

Competition between hydrogen bonds and halogen bonds in complexes of formamidine and hypohalous acids.

Quantum chemical calculations have been per-formed for the complexes of formamidine (FA) and hypohalous acid (HOX, X = F, Cl, Br, I) to study their structures, properties, and competition of hydrogen bonds with halogen bonds. Two types of complexes are formed mainly through a hydrogen bond and a halogen bond, respectively, and the cyclic structure is more stable. For the F, Cl, and Br complexes, the hydrogen-bonded one is more stable than the halogen-bonded one, while the halogen-bonded structure is favorable for the I complexes. The associated H-O and X-O bonds are elongated and exhibit a red shift, whereas the distant ones are contracted and display a blue shift. The strength of hydrogen and halogen bonds is affected by F and Li substitutents and it was found that the latter tends to smooth differences in the strength of both types of interactions. The structures, properties, and interaction nature in these complexes have been understood with natural bond orbital (NBO) and atoms in molecules (AIM) theories.

Substitution, cooperative, and solvent effects on π pnicogen bonds in the FH(2)P and FH(2)As complexes.

Ab initio calculations have been carried out to study the substitution effect on the π pnicogen bond in ZH(2)P-C(2)HM (Z = H, H(3)C, NC, F; M = H, CH(3), Li) dimer, cooperative effect of the π pnicogen bond and hydrogen bond in XH-FH(2)Y-C(2)H(4) (X = HO, NC, F; Y = P and As) trimer, and solvent effect on the π pnicogen bond in FH(2)P-C(2)H(2), FH(2)P-C(2)H(4), FH(2)As-C(2)H(2), and FH(2)As-C(2)H(4) dimers. The interaction energy of π pnicogen bond increases in magnitude from -1.51 kcal mol(-1) in H(3)P-C(2)H(2) dimer to -7.53 kcal mol(-1) in FH(2)P-C(2)HLi dimer at the MP2/aug-cc-pVTZ level. The π pnicogen bond is enhanced by 12-30 % due to the presence of hydrogen bond in the trimer. The π pnicogen bond is also enhanced in solvents. The natural bond orbital analysis and symmetry adapted perturbation theory (SAPT) were used to unveil the source of substitution, cooperative, and solvent effects.

Effect of food azo dye tartrazine on learning and memory functions in mice and rats, and the possible mechanisms involved.

UNLABELLED: Tartrazine is an artificial azo dye commonly used in human food and pharmaceutical products. The present study was conducted to evaluate the toxic effect of tartrazine on the learning and memory functions in mice and rats. Animals were administered different doses of tartrazine for a period of 30 d and were evaluated by open-field test, step-through test, and Morris water maze test, respectively. Furthermore, the biomarkers of the oxidative stress and pathohistology were also measured to explore the possible mechanisms involved. The results indicated that tartrazine extract significantly enhanced active behavioral response to the open field, increased the escape latency in Morris water maze test and decreased the retention latency in step-through tests. The decline in the activities of catalase, glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) as well as a rise in the level of malonaldehyde (MDA) were observed in the brain of tartrazine-treated rats, and these changes were associated with the brain from oxidative damage. The dose levels of tartrazine in the present study produced a few adverse effects in learning and memory functions in animals. The mechanisms might be attributed to promoting lipid peroxidation products and reactive oxygen species, inhibiting endogenous antioxidant defense enzymes and the brain tissue damage. PRACTICAL APPLICATION: Tartrazine is an artificial azo dye commonly used in human food and pharmaceutical products. Since the last assessment carried out by the Joint FAO/WHO Expert Committee on Food Additives in 1964, many new studies have been conducted. However, there is a little information about the effects on learning and memory performance. The present study was conducted to evaluate the toxic effect of tartrazine on the learning and memory functions in animals and its possible mechanism involved. Based on our results, we believe that more extensive assessment of food additives in current use is warranted.

Novel halogen-bonded complexes H3NBH3...XY (XY = ClF, ClCl, BrF, BrCl, and BrBr): partially covalent character.

Quantum chemical calculations have been performed to study the interaction of H(3)NBH(3) with dihalogen molecules XY (XY = ClF, ClCl, BrF, BrCl, and BrBr) at the MP2/aug-cc-pVTZ level. It is shown that a halogen-hydride halogen bond is formed between the two molecules, in which the sigma electron of the B-H bond in H(3)NBH(3) acts as the electron donor. The strength of the halogen bond ranges from 14.82 kJ/mol in H(3)NBH(3)-ClCl complex to 40.13 kJ/mol in H(3)NBH(3)-BrF complex at the CCSD(T)/aug-cc-pVTZ level, which is comparable to medium strong hydrogen bonds. The B-H and X-Y bonds are elongated with a concomitance of a red shift. The analyses of natural bond orbital and atoms in molecules have been carried out to understand the nature of properties of this novel interaction. The results show that this interaction has partially covalent character.

Theoretical study of the interplay between lithium bond and hydrogen bond in complexes involved with HLi and HCN.

The lithium- and hydrogen-bonded complex of HLi-NCH-NCH is studied with ab initio calculations. The optimized structure, vibrational frequencies, and binding energy are calculated at the MP2 level with 6-311++G(2d,2p) basis set. The interplay between lithium bonding and hydrogen bonding in the complex is investigated with these properties. The effect of lithium bonding on the properties of hydrogen bonding is larger than that of hydrogen bonding on the properties of lithium bonding. In the trimer, the binding energies are increased by about 19% and 61% for the lithium and hydrogen bonds, respectively. A big cooperative energy (-5.50 kcal mol(-1)) is observed in the complex. Both the charge transfer and induction effect due to the electrostatic interaction are responsible for the cooperativity in the trimer. The effect of HCN chain length on the lithium bonding has been considered. The natural bond orbital and atoms in molecules analyses indicate that the electrostatic force plays a main role in the lithium bonding. A many-body interaction analysis has also been performed for HLi-(NCH)(N) (N=2-5) systems.

Cooperativity between the dihydrogen bond and the NHC hydrogen bond in LiH-(HCN)n Complexes.

The cooperativity between the dihydrogen bond and the NHC hydrogen bond in LiH-(HCN)(n) (n=2 and 3) complexes is investigated at the MP2 level of theory. The bond lengths, dipole moments, and energies are analyzed. It is demonstrated that synergetic effects are present in the complexes. The cooperativity contribution of the dihydrogen bond is smaller than that of the NHC hydrogen bond. The three-body energy in systems involving different types of hydrogen bonds is larger than that in the same hydrogen-bonded systems. NBO analyses indicate that orbital interaction, charge transfer, and bond polarization are mainly responsible for the cooperativity between the two types of hydrogen bonds.

Influence of substitution, hybridization, and solvent on the properties of C-HO single-electron hydrogen bond in CH3-H2O complex.

The effect of substitution, hybridization, and solvent on the properties of the C...HO single-electron hydrogen bond has been investigated with quantum chemical calculations. Methyl radical, ethyl radical, and vinyl radical are used as the proton acceptors and are paired with water, methanol, HOCl, and vinyl alcohol. Halogenation (Cl) of the proton donor strengthens this type of hydrogen bond. The methyl group in the proton donor and proton acceptor plays a different role in the formation of the C...HO single-electron hydrogen bond. The former is electron-withdrawing, and the latter is electron-donating, both making a constructive contribution to the enhancement of the interaction. The contribution of the methyl group in the proton acceptor is larger than that in the proton donor. The increase of acidity of the proton is helpful to form a single-electron hydrogen bond. As the proton acceptor varies from the methyl radical to the vinyl radical, the interaction strength also increases. The solvent has an enhancing influence on the strength of the C...HO single-electron hydrogen bond. These factors affect the C...HO single-electron hydrogen bond in a similar way that they do other types of hydrogen bonds.

Cooperativity between two types of hydrogen bond in H(3)C-HCN-HCN and H(3)C-HNC-HNC complexes.

Hydrogen-bonded clusters, H(3)C-HCN, HCN-HCN, H(3)C-HCN-HCN, H(3)C-HNC, HNC-HNC, and H(3)C-HNC-HNC, have been studied by using ab initio calculations. The optimized structures, harmonic vibrational frequencies, and interaction energies are calculated at the MP2 level with aug-cc-pVTZ basis set. The cooperative effects in the properties of these complexes are investigated quantitatively. A cooperativity contribution of around 10% relative to the total interaction energy was found in the H(3)C-HCN-HCN complex. In the case of H(3)C-HNC-HNC complex, the cooperativity contribution is about 15%. The cooperativity contribution in the single-electron hydrogen bond is larger than that in the hydrogen bond of HCN-HCN and HNC-HNC complexes. NMR chemical shifts, charge transfers, and topological parameters also support such conclusions.

Regulating function of methyl group in strength of CH...O hydrogen bond: a high-level ab initio study.

An ab initio computational study of the regulating function of the methyl group in the strength of the CH...O hydrogen bond (HB) with XCC-H (X = H, CH3, F) as a HB donor and HOY (Y = H, CH3, Cl) as a HB acceptor has been carried out at the MP2/aug-cc-pVDZ and MP2/aug-cc-pVTZ levels. The bond lengths, interaction energies, and stretching frequencies are compared in the gas phase. The results indicate that the methyl substitution of the proton acceptor strengthens the CH...O HB, whereas that of the proton donor weakens the CH...O HB. NBO analysis demonstrates that the methyl group of the proton acceptor is electron-withdrawing and that of the proton donor is electron-donating in the formation of the CH...O HB. The electron-donation of the methyl group in the proton acceptor plays a positive contribution to the formation of the CH...O HB, whereas the electron-withdrawing action of the methyl group in the proton donor plays a negative contribution to the formation of the CH...O HB. The positive contribution of methyl group in the proton acceptor is larger than the negative contribution of methyl group in the proton donor.

Spectroscopic and theoretical evidence for the cooperativity between red-shift hydrogen bond and blue-shift hydrogen bond in DMSO aqueous solutions.

The cooperativity between red-shifted hydrogen bond and blue-shifting hydrogen bond in dimethyl sulfoxide aqueous solutions was studied by methods of quantum chemical calculations and infrared spectroscopy. The water molecule plays a different role in two types of hydrogen bonds: proton-donor in red-shifted hydrogen bond and proton-acceptor in blue-shifting hydrogen bond. The cooperativity is not prominent if the ring structure is formed through the OHcdots, three dots, centeredOS H-bond and CHcdots, three dots, centeredO(w) H-bond. However, if the methyl groups in the above ring structure participate in second CHcdots, three dots, centeredO(w) H-bond, the cooperativity is increased. The second CHcdots, three dots, centeredO(w) H-bond enhances OHcdots, three dots, centeredOS H-bond and weakens the first CHcdots, three dots, centeredO(w) H-bond.

Cooperativity between OH...O and CH...O hydrogen bonds involving dimethyl sulfoxide-H2O-H2O complex.

The cooperativity between the O-H...O and C-H...O hydrogen bonds has been studied by quantum chemical calculations at the MP2/6-311++G(d,p) level in gaseous phase and at the B3LYP/6-311++G(d,p) level in solution. The interaction energies of the O-H...O and C-H...O H-bonds are increased by 53 and 58%, respectively, demonstrating that there is a large cooperativity. Analysis of hydrogen-bonding lengths, OH bond lengths, and OH stretching frequencies also supports such a conclusion. By NBO analysis, it is found that orbital interaction plays a great role in enhancing their cooperativity. The strength increase of the C-H...O H-bond is larger than that of the O-H...O H-bond due to the cooperativity. The solvent has a weakening effect on the cooperativity.