Mechanochemistry of hexagonal boron nitride: 1. Destruction and amorphization during mechanical treatment

The regularities of the mechanical activation of hexagonal boron nitride are analyzed using the X-ray diffraction, IR spectroscopy, transmission electron microscopy, dynamic light scattering, and adsorption methods. At the initial state of mechanical activation, the main process is material destruction. At this stage, the specific surface area increases to 400 m²/g and crystallographically oriented nanosized needles are formed. At the same time, boron nitride crystal structure is disordered with an increase in interplanar distance d(002). The disordering is assumed to be due to a shift along planes (001). At a specific dose of supplied mechanical energy above 6–8 kJ/g, the disordering processes dominate and the material is amorphized. At this stage, the specific surface area of samples decreases.     

Grafting of Acrylamide On 1, 1, 2, 2-Tetra-Chloroethane Preswelled Polyethylene Terephthalate) Films Using Azobisisobutyronitrile Initiator

Abstract

Graft polymerization of acrylamide (AAm) on 1, 1, 2, 2 tetrachloro-ethane (TCE) preswelled poly(ethylene terephthalate) (PET) films were performed with chemical initiation method using asobisiso-butyronitrile (AIBN) initiator. Temperature was found to have a greater effect on the swelling then the swelling time. Variation of the graft yield with polymerization temperature, time, AIBN concentration, AAm concentration, AIBN and AAm inclusion times were investigated. The optimum temperature for grafting was found to be 70°CC. The graft yield was observed to increase with polymerization time, AAm concentration, initiator and monomer diffusion time up to a saturation graft yield and then leveled off. An increase in AIBN concentration first enhanced the percent grafting then showed a decrease. The addition of some salts (Ni²⁺, Cr³⁺, Co²⁺, Cu²⁺) on the rate of grafting was also investigated. From the temperature dependence of the initial rate of grafting, the overall activation energy was found to be 4. 1 kcal/mol and relevant rate equation have been derived. The effect of grafting on film propities, such as water absorption capacity, intrinsic viscosity were determined. Grafted films were characterized by FTIR spectros-copy and scanning electron microscopy (SEM).     

Electron Transfer in Frozen Media

Classical theories of electron transfer are modified to take into account the differences between electron transfer in a rigid medium and in a fluid. Intramolecular vibrations and part of the dielectric polarization are assumed to remain dynamic in rigid media while the remaining part of the polarization, arising from dipole reorientations, is frozen. In rigid media, electron transfer occurs with the solvent locked into the dipole orientations of the initial state. This causes an increase in the free energy change and a decrease in the solvent reorganizational energy. It also increases the activation free energy for electron transfer. For photoinduced electron transfer, the analysis is more complex because multiple states are involved. The activation free energy can either be greater or less than in a fluid depending on charge distributions before and after electron transfer. The same analysis can be applied to interconversion between excited states in rigid media.     

Nitrogen elimination in the mass spectra of diphenyl and triphenyl-v-triazoles

The mass spectra of seven v-triazoles (I to VII), having two or three phenyl substituents in 1, 4 and 5 positions, are described. Differences in the rate of nitrogen elimination from themolecular ions of I to III and IV to V are explained by the statement that this reaction requires a higher energy of activation for the transition state in IV to V than in I to III. At high electron voltages the relative intensities of fragment ions and metastable ions are very similar in the mass spectra of 1,4,5 triphenyl-v-triazole (I) and the ketenimine (VIII). Differences in the low electron voltage spectra of I and VIII, and energy measurements, however, show that probably an azirine ion IX is involved in the formation of the [M-N₂]⁺ ion from I. It is shown that production of the rearrangement ion m/e 165 (C₁₃H₉) isa high energy process.     

First-Principles Study of the Structures and Electronic Properties of Ni<Subscript><Emphasis Type="Italic">n</Emphasis>–1</Subscript>Al (<Emphasis Type="Italic">n</Emphasis> = 2-20) Clusters

The electronic properties, such as binding energy, magnetic property, charge transfer, ionization potential, and electron affinity, of Ni_n–1Al (n = 2-20) neutral and ionic clusters are studied using the density functional theory calculations with the PBE exchange-correlation energy functional. The calculated total magnetic moments and ionization potential can decrease and increase with the addition of the Al atom, respectively. The calculated electron affinity has occurred with no significant change, except the Ni₁₆Al cluster.     

Influence of nano-alumina on curing kinetics and corrosion resistance of alumina based ceramic coatings

With thermal chemical reaction, the nano-alumina ceramic coatings were prepared on A3 steel. Influence of nano-alumina on curing kinetics was investigated by differential scanning calorimetry (DSC) analysis and thermogravimetric analysis (TGA). It was found that all samples show the outstanding heat resistance. However the temperature and the enthalpy of curing decreased with the increase in a nano-alumina content. A model was established to explain the decrease. The physical combination and the decrease in activation energy are the major reason for the decrease. Also electrochemical tests were conducted to investigate the corrosion behavior of the nano-alumina coatings. Corrosion current densities (i _corr) decreased with the increase in the nano-alumina content. This indicated that nano-alumina improved the corrosion resistance of the ceramic coatings. Because the uniformity of ceramic coatings is improved due to the fact that nano-alumina particles fill the pores and spaces of coatings, and nano-alumina particles provide the high physical combination between particles.

     

Thermokinetics on the reaction of formation of Dy[(C5H8NS2)3(C12H8N2)]

The enthalpy change of formation of the reaction of hydrous dysprosium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen•H₂O) in absolute ethanol at 298.15 K has been determined as (-16.12 ± 0.05) kJ•mol^-1 by a microcalormeter. Thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), rate constant and kinetics parameters (the apparent activation energy, the pre-exponential constant and the reaction order) of the reaction have also been calculated. The enthalpy change of the solid-phase reaction at 298.15 K has been obtained as (53.59 ± 0.29) kJ•mol^t-1 by a thermochemistry cycle. The values of the enthalpy change of formation both in liquid-phase and solid-phase reaction indicated that the complex could only be synthesized in liquid-phase reaction.

     

Theoretical Study of the Inner/sphere Reorganization Energy and Activation Energy of Self/exchange Electron Transfer Reaction for M(H2O)26+/3+ (M=V, Cr, Mn, Fe and Co) Systems

通过建立电子转移过程的活化模型和重组模型, 提出了用量子化学从头算方法研究电子转移过程内层重组能和活化能的新方法. 在UMP26/311G水平上获得了5对过渡金属水合离子体系M(H     

Electrical Conductivity and Physical Properties of Poly(Dipropargylsilane Derivatives) Doped with Electron Acceptors

Abstract

Films of poly(dipropargylsilane derivatives) were easily prepared by solvent casting. The resulting red-black films were relatively flexible and ductile. By doping with electron acceptors, the electrical conductivity increased up to the order of 10^?1-10⁰ S/cm. The activation energy for the conduction of doped film was 4 kcal/mol. The change in Raman, IR, and UV-visible spectra by doping suggests electron transfer from the poly(dipropargylsilane derivatives) to the dopant, leading to the formation of polaron. It also was observed that doping with I₂ drastically destroys the crystallinity of the polymer.     

The growth and interaction of conjugated polymer chains,the unpaired electron localization

An ESR method was used to study the structure of the macroradical of the propagating chain R_p in the low-temperature, solid-phase polymerization of p-diethynylbenzene (DEB). The ESR spectra for γ-irradiated DEB samples and those of DEB deuterated in the ethynyl group showed that in the range 77–230 K, the unpaired electron of the macroradical was localized on one of the monomer links. At 230–310 K, its delocalization in a polyconjugated system took place because of addition of a linear macroradical to a double bond of a polymer molecule. The encounter of the macroradical with double bond probably occurs as polymer chain propagation. © 1994 John Wiley & Sons, Inc.     

N-(邻氯苯基)苯甲酰胺在CuX(X=I,Br)催化下的分子内O-芳基化反应机理

采用密度泛函理论(DFT)中的B3LYP方法, 在6-31+G*基组水平上研究了N-(邻氯苯基)苯甲酰胺在CuX (X=I, Br)催化下发生分子内O-芳基化的反应机理. 优化了反应过程中的反应物、中间体、过渡态和产物, 通过能量和振动分析证实了中间体和过渡态的真实性. 并且在相同基组水平上应用自然键轨道(NBO)理论和分子中的原子(AIM)理论分析了这些化合物的成键特征和轨道间的相互作用. 比较了两种不同铜盐催化剂的催化活性, 计算结果表明两种催化剂的反应路径和反应的控制步骤完全相同, 在CuBr催化下标题化合物控制步骤的活化能比在CuI催化下的低, 证明了CuBr的催化活性要比CuI的高一些, 与实验结果一致.     

Physical-mechanical properties of Zr-(Re)-doped β-rhombohedral boron

Effect of doping with Zr(Re) on the structure and physical-mechanical properties of β-rhombohedral boron has been studied. In all specimens p-type conductivity was found. Internal friction and dynamic shear modulus of the specimens were investigated at frequencies of torsion oscillations (0.5-5 Hz) in the temperature range 80<T<1000 K. The increase of Zr(Re) concentration in the samples results in increase of their hole concentration, this increasing and shifting the observed IF maxima to lower temperatures; activation energy of the maxima and frequency factor of the relaxation processes decrease by 10-15%. Effects of change of the structure-sensitive properties observed in Zr-(Re)-doped boron are analyzed in view of changes of activation energy necessary for the motion of twinning boundaries and stacking faults.     

Energy of the quasi-free electron in supercritical krypton near the critical point

Field ionization measurements of high-n CH(3)I and C(2)H(5)I Rydberg states doped into krypton are presented as a function of krypton number density along the critical isotherm. These data exhibit a decrease in the krypton-induced shift of the dopant ionization energy near the critical point. This change in shift is modeled to within +/-0.2% of experiment using a theory that accounts for the polarization of krypton by the dopant ion, the polarization of krypton by the quasi-free electron that arises from field ionization of the dopant, and the zero point kinetic energy of the free electron. The overall decrease in the shift of the dopant ionization energy near the critical point of krypton, which is a factor of 2 larger than that observed in argon, is dominated by the increase in the zero point kinetic energy of the quasi-free electron.     

On The Electronic Structures of Metaphosphate PX3 (−) and Metaphosphite PX2 (−) Anions,X = CH2, SIH2, NH,PH, O,S

Abstract

Quantum chemical calculations at RHF/6-3 1+g(d,p) with electron correlation and vibrational energy corrections are reported on the metaphosphate and metaphosphite series, indicating a facile second-order Jahn Teller distortion of the planar geometries.     

Spectrophotometric Study on Kinetics of Solvatochromism of Methyl Violet in Aqueous Methanol

The kinetics of the reaction of methyl violet with iodide in aqueous methanol system was studied by spectrophotometric method. The rate of reaction of methyl violet in different alcoholic composition in presence of potassium iodide was observed at pH 4 and 6 at various temperatures (298–318 K). Solvatochromic effect was studied in different percentages of methanol (0–50%). Bathochromic shift was observed with the decrease in polarity of solvent. The color change was attributed to molecule's structure, the delocalization of unit electrical charge causes deepening of color and decrease of delocalization causes fading of color due to reduction of dye. Increase in the rate of reaction was observed with increase in alcoholic content and also affected by potassium iodide salt and increased with increase in concentration of potassium iodide. Energy of activation (E_a) and transition energy (E_T) were calculated with the help of kinetic data. Thermodynamic parameters such as enthalpy change of activation (ΔH*), Gibbs free energy change of activation (ΔG*) and entropy change of activation (ΔS*) were evaluated as a function of concentration of solvent and salt.     

AROMATIC AND HETEROCYCLIC NITRILES AND THEIR POLYMERS ⅩⅦ. THE POLYMERIZATION KINETICS OF CYANOPYRIDINES AND CHARACTERIZATION OF THE FORMED POLYMER*

The polymerization rates of three cyanopyridines catalyzed by cuprous chloride-zinc system are measured, and the structure of the formed polymer is also determined. Compared with aromatic nitrile, cyanopyridines polymerize faster and form polyconjugated polymer with skeleton—(C=N)—_n instead of triazine structure. This chain-polymer possesses semiconductive property, and can be converted into conductive material by thermal treatment. In addition, the polymerization kinetics of 3-cyanopyridine catalyzed by 3-cyanopyridinium perchlorate is investigated. It is found that the polymerization rate is directly proportional to the concentrations of monomer and catalyst, and the activation energy of the polymerization is 103.1 KJ/mol.     

Effect of Solvent on the Radical Copolymerizability of Styrene with 3(2-Methyl)-6-methylpyridazinone

Abstract

The radical copolymerization of styrene (St, M₁) with 3(2-methyl)-6-methylpyridazinone (I, M₂) has been carried out in several p-substltuted phenols at 60 and 70°C. Monomer reactivity ratios (r₁) and activation parameters of copolymerization were found to be affected by phenols. The values of the activation energy (δδE?) and entropy (δδS?) increased with the increase of the interaction of I with the solvents. Linear relationships were observed between the [sgrave]-values of p-substituents of phenols and the values of log 1/r₁ and also of δδE? and δδS?. The radical copolymerization of St (M₁) with 6-substituted 3(2-methyl)-pyridazinone was also carried out.     

Prediction of Monomeric and Dimeric Structures of CYP102A1 Using AlphaFold2 and AlphaFold Multimer and Assessment of Point Mutation Effect on the Efficiency of Intra- and Interprotein Electron Transfer

The three-dimensional structure of monomers and homodimers of CYP102A1/WT (wild-type) proteins and their A83F and A83I mutant forms was predicted using the AlphaFold2 (AF2) and AlphaFold Multimer (AFMultimer) programs, which were compared with the rate constants of hydroxylation reactions of these enzyme forms to determine the efficiency of intra- and interprotein electron transport in the CYP102A1 hydroxylase system. The electron transfer rate constants (k_et), which determine the rate of indole hydroxylation by the CYP102A1 system, were calculated based on the distances (R) between donor-acceptor prosthetic groups (PG) FAD→FMN→HEME of these proteins using factor β, which describes an exponential decay from R the speed of electron transport (ET) according to the tunnelling mechanism. It was shown that the structure of monomers in the homodimer, calculated using the AlpfaFold Multimer program, is in good agreement with the experimental structures of globular domains (HEME-, FMN-, and FAD-domains) in CYP102A1/WT obtained by X-ray structural analysis, and the structure of isolated monomers predicted in AF2 does not coincide with the structure of monomers in the homodimer, although a high level of similarity in individual domains remains. The structures of monomers and homodimers of A83F and A83I mutants were also calculated, and their structures were compared with the wild-type protein. Significant differences in the structure of all isolated monomers with respect to the structures of monomers in homodimers were also found for them, and at the same time, insignificant differences were revealed for all homodimers. Comparative analysis for CYP102A1/WT between the calculated intra- and interprotein distances FAD→FMN→HEME and the rate constants of hydroxylation in these proteins showed that the distance between prosthetic groups both in the monomer and in the dimer allows the implementation of electron transfer between PGs, which is consistent with experimental literature data about k_cat. For the mutant form of monomer A83I, an increase in the distance between PGs was obtained, which can restrict electron transportation compared to WT; however, for the dimer of this protein, a decrease in the distance between PGs was observed compared to the WT form, which can lead to an increase in the electron transfer rate constant and, accordingly, k_cat. For the monomer and homodimer of the A83F mutant, the calculations showed an increase in the distance between the PGs compared to the WT form, which should have led to a decrease in the electron transfer rate, but at the same time, for the homodimer, the approach of the aromatic group F262 with heme can speed up transportation for this form and, accordingly, the rate of hydroxylation.     

Ab initio investigation of the diels-alder reaction between 2H-phosphole and phosphaethene: A model for phosphole dimerization

All four possible Diels-Alder reactions between 2H-phosphole and phosphaethene were examined at various theoretical levels, including HF, MP4SDQ, CCSD(T), and CASSCF. MP2/6-31G^* geometry optimizations could not be employed since the potential energy surface is qualitatively incorrect at this level of theory, due to the inherent underestimation of the activation energies (ameliorated at higher-order MP or coupled-cluster levels). Solvent effects were examined employing the Onsager, polarized continuum, and isodensity and surface polarized continuum models. At MP4SDQ/6-31G^*//HF/6-31G^* these reactions are exothermic by 34–38 kcal mol⁻¹ and have very low activation energies, 5–7 kcal mol⁻¹. The P P/C C regioisomer products are lower in energy than the C P isomers and, within each pair, the exo isomer is lower in energy. At low computational levels the smallest activation energy is for the reaction leading to the C P endo product. Larger basis sets, electron correlation, and solvent favor the transition state leading to the experimentally observed P P/C P endo isomer. The dimerization of phosphole is, therefore, kinetically controlled. Based on geometric and electron density analysis, the reactions are concerted and synchronous. © 1997 by John Wiley & Sons, Inc.     

Competition between halogen bond and hydrogen bond in complexes of superalkali Li3S and halogenated acetylene XCCH (X = F,Cl, Br,and I)

Complexes of superalkali Li₃S and XCCH (X = F, Cl, Br, and I) have been studied with theoretical calculations at the MP2/aug‐cc‐pVTZ level. Three types of structures are found: (A) the X atom combines with the S atom through a halogen bond; (B) the X atom interacts with the π electron of Li₃S by a π halogen bond; (C) the H atom combines with the S atom through a hydrogen bond. For A and B, a heavier halogen atom makes the interaction stronger, while for C, the change of interaction energy is not obvious, showing a small dependence on the nature of the X atom in HCCX. A is more stable than B and their difference in stability decreases as X varies from Cl to I. For the F and Cl complexes, A is weaker than C, however, the former is stronger than the latter in the Br and I complexes. The above three types of interactions have been analyzed by means of electron localization function, electron density difference, and energy decomposition, and the results show that they have similar nature and features with conventional interactions. © 2014 Wiley Periodicals, Inc.