Changqiao Zhang

The structures and properties of halogen bonds involving polyvalent halogen in complexes of FXOn (X = Cl, Br; n = 0–3)–CH3CN

To explore the nature of unconventional halogen bonds, the halogen bonds between a series of halides FXOn (X = Cl, Br; n = 0-3) and CH3CN have been studied at M05-2X/6-311++G(d,p), MP2/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ levels. Our calculations reveal that the electrostatic potentials of these hyper-valent halogen atoms are greatly different to those of monovalent halogen atoms and, accordingly, the strength and interaction modes of these halogen bonds show different characteristics. For complexes of monovalent and heptavalent halides, only one interaction mode was found, but for those of tervalent and pentavalent halides, three kinds of stable configurations with different interaction modes were recognized. Configuration I is a linear structure formed by a single halogen bond, while configurations II and III are cyclic structures formed by the cooperation of a halogen bond and a hydrogen bond. From an energy point of view, monovalent halides form the strongest halogen bonds, and heptavalent halides feature the weakest halogen bonds. For tervalent and pentavalent halides, the interaction energies of the three configurations are similar. In the two cyclic configurations of complexes formed by tervalent and pentavalent halides, due to the competition of the halogen bond with the hydrogen bond, the halogen bonds are weaker than that of configuration I. NBO analysis indicates that the three configurations of complexes display different donor-acceptor orbital interactions. AIM and LMO-EDA analysis reveal that the electrostatic interaction is the dominant driving force for the formation of the complexes, and all the halogen and hydrogen bonds in these complexes are closed-shell interactions.

A theoretical study on the halogen bonding interactions of C6F5I with a series of group 10 metal monohalides

AbstractThe halogen bonding interactions between C6F5I and a series of transition metal monohalides trans-[M(X)(2-C5NF4)-(PR3)2] (M = Ni, Pd, Pt; X = F, Cl, Br; R = Me, Cy) have been studied with quantum chemical calculations. Optimized geometries of the halogen bonding complexes indicate that angles C1-I···X are basically linear (178–180°) and angles I···X-M mainly range from 90 to 150°. The strength of these metal-influenced halogen bonds alters with different metal centers, metal-bound halogen atoms and the substitutes on phosphine ligands. Electrostatic potential and natural bond orbital analysis show that both of the electrostatic and orbital interactions make a contribution to the formation of halogen bonds, while the electrostatic term plays a dominant role. AIM analysis suggests that, for trans-[M(F)(2-C5NF4)-(PR3)2] (M = Ni, Pd, Pt) monomers, the formed halogen bonding complexes are stabilized by local concentration of the charge of intermediate character, while for the metal monomers containing chlorine and bromine, a typical closed-shell interaction exist. These results prove that the structures and geometries of these halogen bonding complexes can be tuned by changing the halogen atoms and metal centers, which may provide useful information for the design and synthesis of new functional materials. FigureThe properties and structural characteristics of a series of metal-influenced halogen-bonding complexes have been studied by using density functional theory (DFT) method. The calculation results indicate that metal centers and metal-bound halogen atoms have significant influence on the geometries and strength of halogen bonds

Synthesis of comb bipolymers and their pour point depressing properties

A bipolymer maleic anhydride-methyl acrylate (MAMA) was synthesized from maleic anhydride and methyl acrylate based on molecular design. MAMA further reacted with oleylamine or octadecyl alcohol to generate two comb polymers called Oleamide-MAMA (NMAMA) and Octadecanol-MAMA (OMAMA), respectively. The structure of both the polymers was confirmed by their infrared spectral analysis (IR), gel permeation chromatography analysis (GPC) and differential scanning calorimeter (DSC). Moreover, the pour point depressing (PPD) properties of these comb polymers were examined experimentally. Experimental results showed that besides the molecular weight and concentration of the polymers, the length of side chains and the number of functional groups also had great influence on the pour point depressing performance. The π bonds and hydrogen bonds between depressants were the key factors for improving the pour point depressing properties. These results suggest that both OMAMA and NMAMA are potential pour point depressants for industry.

Theoretical studies on the interaction of guanine riboswitch with guanine and its closest analogues

Experimental studies (M. Mandal, B. Boese, J.E. Barrick, W.C. Winkler and R.R. Breaker, Riboswitches control fundamental biochemical pathways in bacillus subtilis and other bacteria, Cell 113 (2003), pp. 577–586) demonstrated that, besides recognising guanine with high specificity, guanine riboswitch could also bind guanine analogues, but the alteration of every functionalised position on the guanine heterocycle could cause a substantial loss of binding affinity. To investigate the nature of guanine riboswitch recognising metabolites, molecular docking and molecular dynamics simulation were carried out on diverse guanine analogues. The calculation results reveal that (1) most guanine analogues could bind to guanine riboswitch at the same binding pocket, with identical orientations and dissimilar binding energies, which is related to the positions of the functional groups; (2) the two tautomers of xanthine adopt different binding modes, and the enol-tautomer shows similar binding mode and affinity of hypoxanthine, which agrees well with the experimental results and (3) the riboswitch could form stable complexes with guanine analogues by hydrogen bonding contacts with U51 and C74. Particularly, U51 plays an important role in stabilising the complexes.

Structures and photoelectric properties of five benzotrithiophene isomers-based donor–acceptor copolymers

In this paper, we have investigated the structures, electronic and optical properties of five conjugated copolymers (BTT1-BTz, BTT2-BTz, BTT3-BTz, BTT4-BTz and BTT5-BTz) featuring benzotrithiophene (BTT) isomers as donor units and benzothiadiazole (BTz) as acceptor units, linked through thiophene spacers, employing many-body perturbation theory (MBPT). We have explored the isomer effects by configuration of the sulfur atoms in BTT units, aimed to get insight into how the structural modifications to the conjugated backbone can influence the molecular structures and electronic properties of conjugated polymers. Using the trimer as the computational model, the calculated low and high energy absorption bands (660 and 413 nm) for BTT1-BTz agree well with the experimental ones (645 and 430 nm) with a small offset of ~15 nm. On the basis of our calculations, it is found that the backbones of these polymers display different coplanarities, with the dihedral angles between the two neighboring rings varying from 12.3° to 79.0°. Importantly, both BTT1-BTz and BTT2-BTz exhibit intense adsorption around 660 and 623 nm, indicating their promising application in solar cells, whereas BTT3-BTz and BTT4-BTz display the intense adsorption at 569 and 551 nm, which are also usable in the tandem solar cells. BTT5-BTz has narrow and weak adsorption in the visible and infrared region, implying it is not conducive to the sunlight absorption. The blue shift of about 150 nm from BTT1-BTz to BTT5-BTz is suggested to be originated from the shorter effective conjugation lengths.

Polymerization Mechanism of α-Linear Olefin

The density functional theory on the level of B3LYP/6–31G was empolyed to study the chain growth mechanism in polymerization process of α-linear olefin in TiCl3/AlEt2Cl catalytic system to synthesize drag reduction agent. Full parameter optimization without symmetry restrictions for reactants, products, the possible transition states, and intermediates was calculated. Vibration frequency was analyzed for all of stagnation points on the potential energy surface at the same theoretical level. The internal reaction coordinate was calculated from the transition states to reactants and products respectively. The results showed as flloes: (i) Coordination compounds were formed on the optimum configuration of TiCl3/AlEt2Cl. (ii) The transition states were formed. The energy difference between transition states and the coordination compounds was 40.687 kJ/mol. (iii) Double bond opened and Ti–C(4) bond fractured, and the polymerization was completed. The calculation results also showed that the chain growth mechanism did not essentially change with the increase of carbon atom number of α-linear olefin. From the relationship between polymerization activation energy and carbon atom number of the α-linear olefin, it can be seen that the α-linear olefin monomers with 6–10 carbon atoms had low activation energy and wide range. It was optimum to synthesize drag reduction agent by polymerization.

Molecular Dynamic Simulation on the Absorbing Process of Isolating and Coating of α-olefin Drag Reducing Polymer

The absorbing process in isolating and coating process of α-olefin drag reducing polymer was studied by molecular dynamic simulation method, on basis of coating theory of α-olefin drag reducing polymer particles with polyurethane as coating material. The distributions of sodium laurate, sodium dodecyl sulfate, and sodium dodecyl benzene sulfonate on the surface of α-olefin drag reducing polymer particles were almost the same, but the bending degrees of them were obviously different. The bending degree of SLA molecules was greater than those of the other two surfactant molecules. Simulation results of absorbing and accumulating structure showed that, though hydrophobic properties of surfactant molecules were almost the same, water density around long chain sulfonate sodium was bigger than that around alkyl sulfate sodium. This property goes against useful absorbing and accumulating on the surface of α-olefin drag reducing polymer particles; simulation results of interactions of different surfactant and multiple hydroxyl compounds on surface of particles showed that, interactions of different surfactant and one kind of multiple hydroxyl compound were similar to those of one kind of surfactant and different multiple hydroxyl compounds. These two contrast types of interactions also exhibited the differences of absorbing distribution and closing degrees to surface of particles. The sequence of closing degrees was derived from simulation; control step of addition polymerization interaction in coating process was absorbing mass transfer process, so the more closed to surface of particle the multiple hydroxyl compounds were, the easier interactions with isocyanate were. Simulation results represented the compatibility relationship between surfactant and multiple hydroxyl compounds. The isolating and coating processes of α-olefin drag reducing polymer were further understood on molecule and atom level through above simulation research, and based on the simulation, a referenced theoretical basis was provided for practical optimal selection and experimental preparation of α-olefin drag reducing polymer particles suspension isolation agent.