Heat treatment improves the dispersion stability of rice bran milk through changing the settling behavior.

Poor dispersion stability of nutritious rice bran milk limits its production. In this study, the dispersion stability of rice bran milk after heating at 95 °C for 0-5 min was investigated. Visual observation revealed improved dispersion stability and changes in settling behavior with heat durations. After heating for 5 min, the serum turbidity increased from 1.86 to 2.95. The centrifugal sedimentation rate unexpectedly rose from 9.25% to 29.18%, indicating an increase in volumetric particle concentration. Fourier transform infrared spectroscopy revealed that heating induced starch gelatinization and protein denaturation in rice bran milk, leading to increased volumetric particle concentration. Rice bran protein aggregates after heating were developed and embedded in the gel-like network composed of swollen starch granules. These results suggested that rice bran milk, due to thermal-induced alteration in biomacromolecules, may behave progressively from free settling to hindered settling to compression settling, resulting in improved dispersion stability.

Influence of transition metals on halogen-bonded complexes of MCCBr∙∙∙NCH and HCCBr∙∙∙NCM' (M, M' = Cu, Ag, and Au).

We have performed quantum chemical calculations for the MCCBr∙∙∙NCH and HCCBr∙∙∙NCM' (M, M' = Cu, Ag, and Au) halogen-bonded complexes at the MP2 level. The results showed that the transition metals have different influences on the halogen bond donor and the electron donor. The transition metal atom in the former makes the halogen bond weaker, and that in the latter causes it to enhance. Molecular electrostatic potential and natural bond orbital analysis were carried out to reveal the nature of the substitution.

Theoretical elucidation on the regio-, diastereo-, and enantio-selectivities of chiral primary-tertiary diamine catalyst for asymmetric direct aldol reactions of aliphatic ketones.

The asymmetric direct aldol reactions of aliphatic ketones (acetone, butanone, and cyclohexanone) with 4-nitrobenzaldehyde catalyzed by a chiral primary-tertiary diamine catalyst (trans-N,N-dimethyl diaminocyclohexane) have been investigated by performing density functional theory calculations to rationalize the experimentally observed stereoselectivities. Focused on the crucial C-C bond-forming steps, we located several low-lying transition states and predicted their relative stabilities. The calculated results demonstrate that the catalytic direct aldol reactions of acetone favors the (S)-enantiomer and that butanone prefers the branched syn-selective product, while cyclohexanone yields predominantly the opposite anti-selective product. The theoretical results are in good agreement with the experimental findings and provide a reasonable explanation for the high enantioselectivity and diastereoselectivity, as well as regioselectivity, of the aldol reactions under consideration.

Docking Analysis and Multidimensional Hybrid QSAR Model of 1,4-Benzodiazepine-2,5-Diones as HDM2 Antagonists.

The inhibitors of p53-HDM2 interaction are attractive molecules for the treatment of wild-type p53 tumors. In order to search more potent HDM2 inhibitors, docking operation with CDOCKER protocol in Discovery Studio 2.1 (DS2.1) and multidimensional hybrid quantitative structure-activity relationship (QSAR) studies through the physiochemical properties obtained from DS2.1 and E-Dragon 1.0 as descriptors, have been performed on 59 1,4-benzodiazepine- 2,5-diones which have p53-HDM2 interaction inhibitory activities. The docking results indicate that π-π interaction between the imidazole group in HIS96 and the aryl ring at 4-N of 1,4-benzodiazepine-2,5-dione may be one of the key factors for the combination of ligands with HDM2. Two QSAR models were obtained using genetic function approximation (GFA) and genetic partial least squares (G/PLS) based on the descriptors obtained from DS2.1 and E-dragon 1.0, respectively. The best model can explain 85.5% of the variance (R (2) adj ) while it could predict 81.7% of the variance (R (2) cv ). With this model, the bioactivities of some new compounds were predicted.

The cooperativity between hydrogen and halogen bond in the XY···HNC···XY (X, Y = F, Cl, Br) complexes.

The cooperativity between hydrogen and halogen bonds in XY···HNC···XY (X, Y = F, Cl, Br) complexes was studied at the MP2/aug-cc-pVTZ level. Two hydrogen-bonded dimers, five hydrogen-bonded dimers, and ten trimers were obtained. The hydrogen- and halogen-bonded interaction energies in the trimers were larger than those in the dimers, indicating that both the hydrogen bonding interaction and the halogen bonding interaction are enhanced. The binary halogen bonding interaction plays the most important role in the ternary system. The hydrogen donor molecule influences the magnitude of the halogen bonding interaction much more than the hydrogen bonding interaction in the trimers with respect to the dimers. Our calculations are consistent with the conclusion that the stronger noncovalent interaction has a bigger effect on the weaker one. The variation in the vibrational frequency in the HNC molecule was considered. The NH antisymmetry vibration frequency has a blue shift, whereas the symmetry vibration frequency has a red shift. A dipole moment enhancement is observed upon formation of the trimers. The variation in topological properties at bond critical points was obtained using the atoms in molecules method, and was consistent with the results of the interaction energy analysis.

Theoretical investigations of the H···π and X (X = F, Cl, Br, I)···π complexes between hypohalous acids and benzene.

The H···π and X (X = F, Cl, Br, I)···π interactions between hypohalous acids and benzene are investigated at the MP2/6-311++G(2d,2p) level. Four hydrogen-bonded and three halogen-bonded complexes were obtained. Ab initio calculations indicate that the X···π interaction between HOX and C(6)H(6) is mainly electrostatically driven, and there is nearly an equal contribution from both electrostatic and dispersive energies in the case of XOH-C(6)H(6) complexes. Natural bond orbital (NBO) analysis reveals that there exists charge transfer from benzene to hypohalous acids. Atom in molecules (AIM) analysis locates bond critical points (BCP) linking the hydrogen or halogen atom and carbon atom in benzene.

Molecular docking and QSAR study on steroidal compounds as aromatase inhibitors.

In order to develop more potent, selective and less toxic steroidal aromatase (AR) inhibitors, molecular docking, 2D and 3D hybrid quantitative structure-activity relationship (QSAR) study have been conducted using topological, molecular shape, spatial, structural and thermodynamic descriptors on 32 steroidal compounds. The molecular docking study shows that one or more hydrogen bonds with MET374 are one of the essential requirements for the optimum binding of ligands. The QSAR model obtained indicates that the aromatase inhibitory activity can be enhanced by increasing SIC, SC_3_C, Jurs_WNSA_1, Jurs_WPSA_1 and decreasing CDOCKER interaction energy (ECD), IAC_Total and Shadow_XZfrac. The predicted results shows that this model has a comparatively good predictive power which can be used in prediction of activity of new steroidal aromatase inhibitors.

Catalytic and thermal 1,2-rearrangement of (alpha-mercaptobenzyl)trimethylsilane.

The mechanisms of catalytic and thermal 1,2-rearrangement of (alpha-mercaptobenzyl)trimethylsilane were studied by using density functional theory (DFT) at the MP2/6-31+G(d,p)//B3LYP/6-31G(d) levels. The results show that (alpha-mercaptobenzyl)trimethylsilane rearranges to (benzylthio)trimethylsilane through a trimethylsilyl group migration from C to S atom via a transition state of pentacoordinate Si atom with or without radical initiators. The low reaction activation energy (15.1 kcal/mol) is responsible for the fast rearrangement in the presence of radical initiators. Both radical and nonradical thermal rearrangement mechanisms were suggested, and the radical mechanism dominates through its self-catalyzing. These results are consistent with the experiment results. The activation energy (DeltaH(act) = 15.1 kcal/mol) for the rate-determining step within the self-catalytic cycle is low enough to make (trimethylsilylbenzyl)thiyl radical be a reasonable catalyst for the thermal rearrangement. The catalytic and thermal 1,2-rearrangement mechanisms of (alpha-mercaptobenzyl)trimethylsilane, especially the self-catalytic radical mechanism, were revealed for the first time. The comparison of the rearrangement mechanisms between (alpha-mercaptobenzyl)trimethylsilane and silylmethanethiol discloses the factors in determining the reaction mechanism of such kinds of mercaptoalkyl-functionalized organosilanes. The phenyl group is found to be favorable for the radical rearrangement, thus making (alpha-mercaptobenzyl)trimethylsilane instable.

Computational modeling study on formation of acyclic clavulanate intermediates in inhibition of class A beta-lactamase: water-assisted proton transfer.

Molecular dynamics (MD) simulation and quantum chemical (QC) calculations were used to investigate the reaction mechanism of the formation of acyclic clavulanate intermediates in the inhibition of class A beta-lactamase. The initial model for QC calculations was derived from an MD simulation. It was composed of a substrate clavulanate and four residues (Ser70, Gln237, Ser130, and Ser216), which form hydrogen bonds with the substrate. The QC calculation results indicate that the oxazolidine ring can undergo cleavage by proton transfer, which yields not only imine but also enamine products. A new mechanism involving hydrogen transfer from C6 to O1 has been suggested. Besides, MD simulation provided evidence that the water molecule can catalyze the proton transfer, and QC calculation shows water assistance can decrease the energy barrier greatly.

Theoretical study on the substitution reactions of silylenoid H2SiLiF with CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl.

DFT calculations at the B3LYP/6-31G(d,p) level have been performed to explore the substitution reactions of silylenoid H(2)SiLiF with XH(n) hydrides, where XH(n) = CH(4), NH(3), H(2)O, HF, SiH(4), PH(3), H(2)S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H(2)SiLiF + XH(n) --> H(3)SiF + LiXH(n-1), which involved the initial formation of an association complex via a five-membered cyclic transition state to form an intermediate followed by the substituted product H(3)SiF with LiXH(n-1) dissociating. These theoretical calculations suggest that (i) there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in the periodic table, and (ii) for the second-row hydrides, the substitution reactions are more exothermic than for the first-row hydrides and the reaction barriers are lower. The solvent effects were considered by means of the polarized continuum model (PCM) using THF as a solvent. The presence of THF solvent disfavors slightly the substitution reaction. Compared to the previously reported insertions and H(2)-elimination reactions of H(2)SiLiF and XH(n), the substitution reactions should be most favorable.

Theoretical study of the reaction from 6-methylidene penem to seven-membered ring intermediates.

A sort of beta-lactamase inhibitor, 6-methylidene penem can inhibit both class A and class C serine beta-lactamase. Its inhibition mechanism involves yielding a seven-membered ring intermediate after acylation of the serine. Density functional theory (DFT) method was used on the molecular model to determine the mechanism of producing the seven-membered ring intermediate. Solvent effects were considered via polarizable continuum model (PCM). Moreover, a water-assisted process was considered in the hydrogen transfer process. The results show that the seven-membered ring intermediate can be obtained via two possible mechanisms, namely, concerted mechanism and stepwise mechanism. In stepwise mechanism, a new thiirane intermediate which has never been reported was found. The product of stepwise mechanism, e, has five tautomerics, and they can be tautomerized by hydrogen transfer.

Theoretical study on the isomeric structures and the stability of silylenoid (Tsi)Cl2SiLi (Tsi = C(SiMe3)3).

The structures and isomerization of silylenoid (Tsi)Cl(2)SiLi (Tsi = C(SiMe(3))(3)) were studied by density functional theory (DFT) at the B3LYP/6-31G(d) level. Four equilibrium structures and three isomeric transition states were located. The three-membered ring and p-complex structures, 1 and 2, are the two most stable forms. Two other local minima, the sigma-complex 3 and tetrahedron structure 4, should rearrange to 1 with very low barriers, and then to the most stable isomer 2. To exploit further the stability of silylenoid (Tsi)Cl(2)SiLi, the insertion reactions of 2 and silylene (Tsi)ClSi into the HF molecule have been investigated at the B3LYP/6-31G(d) level, respectively. The results show that the insertion of 2 into HF is very similar to that of (Tsi)ClSi into HF, but the latter is more favorable. To probe the influence of the substituent Tsi on the stability of silylenoid (Tsi)Cl(2)SiLi, the isomers and insertion reaction of silylenoid CH(3)Cl(2)SiLi were investigated in a similar way of those with (Tsi)Cl(2)SiLi. The results indicate that silylenoid containing very bulky group Tsi exhibits unusual stability because of the severe steric hindrance produced by Tsi at the center to which it is attached.

Insertion reactions of silylenoid Ph2SiLi(OBu-t) into X-H bonds (X = F, OH, and NH2).

The insertion reactions of silylenoid [(tert-butoxy)diphenylsilyl]lithium Ph(2)SiLi(OBu-t) into HF, H(2)O, and NH(3) molecules have been studied by using density functional theory at the B3LYP/6-31G(d) level. To better understand the reactivity of silylenoid Ph(2)SiLi(OBu-t), its two most stable isomers, the p-complex (1) and the three-membered ring (2), were selected for reactants. Natural bond orbital (NBO) analysis has been performed to study the effects of charge transfer and to understand the nature of different interactions between atoms or groups. The results indicate that (i) the insertion of Ph(2)SiLi(OBu-t) into X-H bond proceeds in a concerted manner via a three-membered-ring transition state to form substituted silane Ph(2)SiHX with dissociation of LiOBu-t; (ii) the activation barrier increases in the order of HF < H(2)O < NH(3), and the barrier heights of the 1 insertions are higher than those of the 2 insertions, respectively; (iii) both 1 and 2 display ambiphilic character in their insertion reactions.

An ab initio study on thermal rearrangement reactions of 1-silylprop-2-en-1-ol H3SiCH(OH)CH=CH2.

The thermal rearrangement reactions of 1-silylprop-2-en-1-ol H3SiCH(OH)CH=CH2 were studied by ab initio calculations at the G2(MP2) and G3 levels. The reaction mechanisms were revealed through ab initio molecular orbital theory. On the basis of the MP2(full)/6-31G(d) optimized geometries, harmonic vibrational frequencies of various stationary points were calculated. The reaction paths were investigated and confirmed by intrinsic reaction coordinate (IRC) calculations. The results show that the thermal rearrangements of H3SiCH(OH)CH=CH2 happen in two ways. One is via the Brook rearrangement reactions (reaction A), and the silyl group migrates from carbon atom to oxygen atom passing through a double three-membered ring transition state, forming allyloxysilane CH2=CHCH2OSiH3. In the other, the reactant undergoes a dyotropic rearrangement; the hydroxyl group migrates from carbon atom to silicon atom coupled with a simultaneous migration of a hydrogen atom from silicon atom to carbon atom, forming allylsilanol CH2=CHCH2SiH2OH (reaction B). The barriers for reactions A and B were computed to be 343.5 and 203.7 kJ/mol, respectively, at the G3 level. The changes of the thermodynamic functions, entropy (DeltaS), entropy (DeltaS(doubledagger)) for the transition state, enthalpy (DeltaH), and free energy (DeltaG) were calculated by using the MP2(full)/6-31G(d) optimized geometries, and harmonic vibrational frequencies of reactants, transition states, and products with statistical mechanical methods, and equilibrium constant K(T) and reaction rate constant k(T) in canonical variational transition-state theory (CVT) with centrifugal-dominant small-curvature tunneling approximation (SCT) were calculated over a temperature range 400-1300 K. The conventional transition-state theory (TST) rate constants were also calculated for the purposes of comparison. The influences of the vinyl group attached to the center carbon of the alpha-silyl alcohols on reactions were discussed.