Duan-lin Cao

A theoretical study on unusual intermolecular T-shaped X–H...π interactions between the singlet state HB=BH and HF, HCl, HCN or H2C2

AbstractThe unusual T-shaped X–H...π hydrogen bonds are found between the B=B double bond of the singlet state HB=BH and the acid hydrogen of HF, HCl, HCN and H2C2 using MP2 and B3LYP methods at 6-311++G(2df,2p) and aug-cc-pVTZ levels. The binding energies follow the order of HB=BH...HF>HB=BH...HCl>HB=BH...HCN>HB=BH...H2C2. The hydrogen-bonded interactions in HB=BH...HX are found to be stronger than those in H2C=CH2...HX and OCB≡BCO...HX. The analyses of natural bond orbital (NBO) and the electron density shifts reveal that the nature of the T-shaped X–H...π hydrogen-bonded interaction is that much of the lost density from the π-orbital of B=B bond is shifted toward the hydrogen atom of the proton donor, leading to the electron density accumulation and the formation of the hydrogen bond. The atoms in molecules (AIM) theory have also been applied to characterize bond critical points and confirm that the B=B double bond can be a potential proton acceptor. The unusual T-shaped X–H...π hydrogen bonds are found between the B=B double bond of the singlet state HB=BH and the acid hydrogen of HF, HCl, HCN and H2C2

A B3LYP and MP2(full) theoretical investigation into explosive sensitivity upon the formation of the molecule-cation interaction between the nitro group of 3,4-dinitropyrazole and H+, Li+, Na+, Be2+ or Mg2+.

AbstractThe explosive sensitivity upon the formation of molecule-cation interaction between the nitro group of 3,4-dinitropyrazole (DNP) and H+, Li+, Na+, Be2+ or Mg2+ has been investigated using the B3LYP and MP2(full) methods with the 6-311++G** and 6-311++G(2df,2p) basis sets. The bond dissociation energy (BDE) of the C3–N7 trigger bond has also been discussed for the DNP monomer and the corresponding complex. The interaction between the oxygen atom of nitro group and H+ in DNP…H+ is partly covalent in nature. The molecule-cation interaction and bond dissociation energy of the C3–N7 trigger bond follow the order of DNP…Be2+ > DNP…Mg2+ > DNP…Li+ > DNP…Na+. Except for DNP…H+, the increment of the trigger bond dissociation energy in comparison with the DNP monomer correlates well with the molecule-cation interaction energy, natural charge of the nitro group, electron density ρBCP(C3–N7), delocalization energy E(2) and NBO charge transfer. The analyses of atoms in molecules (AIM), natural bond orbital (NBO) and electron density shifts have shown that the electron density of the nitro group shifts toward the C3–N7 trigger bond upon the formation of the molecule-cation interaction. Thus, the trigger bond is strengthened and the sensitivity of DNP is reduced. FigureShifts of electron density as a result of formation of the complex. Purple regions denote gain, and yellow regions represent loss

A theoretical prediction of the possible trigger linkage of CH3NO2 and NH2NO2 in an external electric field

AbstractThe effects of an external electric field on the C/N–NO2 bond with C/N–H and N–O bonds in CH3NO2 or NH2NO2 were compared using the DFT-B3LYP and MP2 methods with the 6-311++G(2d,p) and aug-cc-pVTZ basis sets. The results show that such fields have a minor effect on the C–N or C–H bond but a major effect on the N–O bond in CH3NO2, while in NH2NO2 electric fields affect the N–N bond greatly but the N–O or N–H bond only slightly. Thus, in CH3NO2, oxygen transfer or unimolecular isomerization to methyl nitrite might precede breaking of the C–N bond in the initial stages of decomposition, and the N–O bond could be the trigger bond in electric fields. In NH2NO2, however, N–N bond rupture may be preferential in an electric field and, consequently, the N–N bond might always be the real trigger bond. Atoms in molecules and natural bond orbital delocalization analyses, together with examination of shifts in electron density and frequencies support the above viewpoints. Forty-eight good linear correlations were found along the different field orientations at different levels of theory, including those between field strength (E) and changes in N−O/N−N bond length (ΔRN−O/N−N), ρ(N−O/N−N) values [Δρ(N−O/N−N), or stretching frequencies of the N−O/N−N bond (ΔυN−O/N−N). Graphical AbstractExternal electric fields have a major effect on the N–O or N–N bond inCH3NO2 or NH2NO2 , leading to a possible N–O trigger bond inCH3NO2 or a real N–N trigger bond in NH2NO2 in an electric field

A theoretical prediction of the relationships between the impact sensitivity and electrostatic potential in strained cyclic explosive and application to H-bonded complex of nitrocyclohydrocarbon

AbstractSeven models that related the features of molecular surface electrostatic potentials (ESPs) above the bond midpoints and rings, statistical parameters of ESPs to the experimental impact sensitivities h50 of eight strained cyclic explosives with the C–NO2 bonds were theoretically predicted at the DFT-B3LYP/6-311++G** level. One of the models was used to investigate the changes of h50 for the nitrocyclohydrocarbon frameworks in the H-bonded complexes of HF with nitrocyclopropane, nitrocyclobutane, nitrocyclopentane, and nitrocyclohexane. The results show that the correlation coefficients of the obtained models are small. When adding the effect of ring strain, the value of correlation coefficient is increased. According to the calculated h50, the sensitivities in the frameworks are increased after hydrogen bonding. As a global feature of molecules, surface electrostatic potential is more available to judge the sensitivity change than the trigger bond dissociation energy or ring strain energy in H-bonded complex. Graphical AbstractA theoretical prediction of the relationships between the impact sensitivity and electrostatic potential in strained cyclic explosive and application to H-bonded complex of nitrocyclohydrocarbonᅟ

Synthesis and Properties of Alkyl Dibenzyl Ether Quaternary Ammonium Gemini Surfactant

Abstract Three gemini surfactants with dibenzyl ether spacer (10-B-10, 12-B-12, and 14-B-14) were synthesized and characterized. The surface activity and thermodynamic properties of micellization were determined by surface tension, steady-state fluorescence microscopy, and conductivity methods. The thermodynamic parameters of micellization (ΔmicG0, ΔmicH0, and ΔmicS0) derived from the electrical conductivity measurement implied that the micellization of these surfactants was driven by enthalpy. The enthalpy–entropy compensation of micellization showed that the stability of micelles increased with increasing alkyl chain length. Finally, we evaluated the effects of alkyl chain length on the interfacial tension, foam ability, and the emulsion stability.

Synthesis and Physicochemical Characterization of Chiral Pyrrolidinium-Based Surfactants

Chiral surfactants, (2S)-2-(hydroxymethyl)-1-methyl-1-alkyl pyrrolidinium bromides (L-CnPB, n = 12, 14, 16), were synthesized by the reaction of N-methyl-L-prolinol with long-chain alkyl bromides. The structures were characterized by IR spectra, 1H NMR, ESI-MS, and elemental analysis. Their surface activity, thermodynamic properties, and aggregation behavior were investigated by surface tension, electrical conductivity, and steady-state fluorescence. It was found that L-CnPB have lower critical micelle concentration (CMC) and surface tension at CMC (γcmc) in comparison with N,N,N-trimethyl-1-alkyl ammonium bromide (CnTAB) and N-alkyl-N-methyl pyrrolidinium bromide (CnMP). The CMC and the minimum average area per surfactant molecule (Amin) values of L-CnPB decreased with the increase in the alkyl chain length from 12 to 16. A series of thermodynamic parameters (, and ) of micellization obtained from electrical conductivity indicated that micellization is a spontaneous and entropy-driven process. Furthermore, the micelle aggregation number (Nagg) of L-CnPB obtained from steady-state fluorescence quenching was found to be 42, 48, and 53 for L-C12PB, L-C14PB, and L-C16PB, respectively. GRAPHICAL ABSTRACT

A B3LYP and MP2(full) theoretical investigation into the cooperativity effect between dihydrogen-bonding and H-M∙∙∙π (M = Li, Na, K) interactions among HF, MH with the π-electron donor C2H2, C2H4 or C6H6.

AbstractThe DFT-B3LYP/6-311++G(3df,2p) and MP2(full)/6-311++G(3df,2p) calculations were carried out on the binary complex formed by HM (M = Li, Na, K) and HF or the π-electron donor (C2H2, C2H4, C6H6), as well as the ternary system FH∙∙∙HM∙∙∙C2H2/C2H4/C6H6. The cooperativity effect between the dihydrogen-bonding and H–M∙∙∙π interactions was investigated. The result shows that the equilibrium distances RH∙∙∙H and RM∙∙∙π in the ternary complex decrease and both the H∙∙∙H and H–M∙∙∙π interactions are strengthened when compared to the corresponding binary complex. The cooperativity effect of the dihydrogen bond on the H–M∙∙∙π interaction is more pronounced than that of the M∙∙∙π bond on the H∙∙∙H interaction. Furthermore, the values of cooperativity effect follow the order of FH∙∙∙HNa∙∙∙π > FH∙∙∙HLi∙∙∙π > FH∙∙∙HK∙∙∙π and FH∙∙∙HM∙∙∙C6H6 > FH∙∙∙HM∙∙∙C2H4 > FH∙∙∙HM∙∙∙C2H2. The nature of the cooperativity effect was revealed by the analyses of the charge of the hydrogen atoms in H∙∙∙H moiety, atom in molecule (AIM) and electron density shifts methods. FigureShifts of electron density upon ternary-complex formation indicate the cooperativity effect between the dihydrogen-bonding and H–M∙∙∙π interactions

Study on the Synthesis and Surface Activities of Novel Alkyl Sulfonate Gemini Surfactants

Abstract Three novel dialkyl disulfonate gemini surfactants (Cn-6-Cn, n = 6, 8, 12; n is carbon number of hydrophobic chain) were synthesized from cyanuric chloride, aliphatic amine and taurine. The chemical structures of the prepared compounds were confirmed by 1H NMR, 13C NMR, IR spectra and ESI-MS. Their critical micelle concentrations (CMC) in the aqueous solutions at 25°C were determined by surface-tension method. With the increasing length of the hydrophobic carbon chain, the values of their CMC decreased. The surface tension measurements of Cn-6-Cn give low CMC, great efficiency in lowering the surface tension, and strong adsorption at air–water interface. In addition, adsorption and micellization behavior of Cn-6-Cn were estimated by the parameter of pC20, the minimum average area per surfactant molecule (Amin).

A B3LYP AND MP2(FULL) THEORETICAL INVESTIGATION INTO THE C–NO2 BOND STRENGTH UPON THE FORMATION OF HF OR Na+ COMPLEX INVOLVING THE NITRO GROUP OF NITRO-1,2,4-TRIAZOLE

The change of bond dissociation energy (ΔBDE) in the C–NO2 bond upon the formation of the intermolecular hydrogen-bonding or molecule-cation interaction between the nitro group of seven kinds of nitro-1,2,4-triazoles and HF or Na+ was investigated using the B3LYP and MP2(full) methods with the 6-311++G**, 6-311++G(2df, 2p) and aug-cc-pVTZ basis sets. The C–NO2 bond strength was enhanced and the charge of nitro group turned more negative in complex in comparison with those in isolated nitro-1,2,4-triazole molecule. The increment of the C–NO2 BDEs correlated well with the H-bonding interaction energy or molecule-cation interaction energy. The analysis of AIM, NBO and electron density shifts showed that the electron density shifted toward the C–NO2 bond upon complex formation, leading to the strengthened C–NO2 bond and the possibly reduced explosive sensitivity. The ΔBDE of the C–NO2 bond in the Na+ complex is far larger greater than that in the corresponding HF system. Thus, introducing cation into the structure of the nitrotriazole might be more efficacious to reduce explosive sensitivity than the formation of the intermolecular hydrogen-bonded complex.

Theoretical investigation into the cooperativity effect between the intermolecular π∙π and H-bonding interactions in the curcumin∙cytosine∙H2O system

AbstractIn order to reveal the mechanism of drug action and design of DNA/RNA-targeted drugs containing aromatic rings, the cooperativity effects between the intermolecular π∙∙∙π and H-bonding interactions in curcumin(drug)∙∙∙cytosine(DNA/RNA base)∙∙∙H2O were investigated by the B3LYP-D3 and MP2(full) methods with the 6–311++G(2d,p) basis set. The π∙∙∙π interaction plays an important role in stabilizing the linear ternary complexes with the cooperativity effects, and the cyclic structures suffer the anticooperativity effects. The cooperativity or anticooperativity effects are notable, which could lead to a possible significant change in drug activity. The hydration is essentially the cooperativity or anticooperativity effect. These results were confirmed by the atoms in molecules (AIM), reduced density gradient (RDG), and surface electrostatic potentials analyses. The cyclic complexes are more stable, from which it can be deduced that the drug always links with the DNA/RNA base and H2O by the π∙∙∙π or H-bonding interactions, and only in this way can the drug activity be shown. Therefore, the designed DNA/RNA-targeted drugs should possess a certain number of hydrophilic groups in contact with the DNA/RNA base and H2O to reconcile drug activity by the cooperativity effect between the π∙∙∙π and H-bonding interactions, as is in agreement with many of the drugs in use. Graphical abstractRDG isosurface of ternary complex