铀(Ⅵ)与不对称希夫碱配合物的合成和热分解反应动力学

邻苯二胺与5－氯－2－羟基二苯酮、邻香草醛作用合成了一种不对称希夫碱配体C₂₇H₂₁N₂O₃Cl（H₂L）。在正丁醇和甲醇体系中硝酸铀酰与该配体反应合成了一种固体希夫碱配合物[UO₂(HL)(NO₃)(H₂O)]·H₂O。通过元素分析、IR、UV、¹H NMR、TG-DTG及摩尔电导率分析等手段对合成的配合物进行了表征,用非等温热重法研究了铀(Ⅵ)配合物的热分解反应动力学,推断出第三步热分解的动力学方程为：d α /d t = A · e^{- E/RT} ·3/2[(1- α )^-1/3-1]^-1,得到了动力学参数E和A。并计算出了活化熵△S^¹和活化吉布斯自由能△G^¹。     

Syntheses,spectroscopy, optical properties,and diastereoselectivity of copper(II)-complexes with chiral aminoalcohol based Schiff bases

Chiral aminoalcohol based Schiff bases (R or S)-2-{(E)-(2-hydroxy-1-phenylethylimino)methyl}phenol and (R/S)-2-{(E)-(2-hydroxy-2-phenylethylimino)methyl}phenol coordinate to copper(II)acetate to give enantiopure Λ/Δ- or Δ/Λ-bis[(R or S)-2-{(E)-(2-hydroxy-1-phenylethylimino)methyl}phenoxide-κ²N,O]copper(II), {Λ/Δ-Cu(R-L1)₂ (1) or Δ/Λ-Cu(S-L1)₂ (2)}, and racemic Δ/Λ- and Λ/Δ-bis[(R/S)-2-{(E)-(2-hydroxy-2-phenylethylimino)methyl}phenoxide-κ²N,O]copper(II), {Δ/Λ- and Λ/Δ-Cu(R/S-L2)₂ (3)}, respectively. The complexes are characterized by elemental analyzes, IR, UV–Vis, polarimetry, circular dichroism (CD), differential scanning calorimeter (DSC), and mass spectroscopy. Polarimetry shows the rotation to the left at ?113.6° (1) and to the right at +106.4^o (2). CD spectra show the expected mirror-image relationship with opposite sign of ellipticity maxima (Δε_max = +0.43 for 1 and ?0.42 M^?1 dm³ cm^?1 for 2 at 638 nm) due to the d-d transitions of the metal ion. CD spectral analyzes further reveal a diastereoselectivity or diastereomeric excess towards Λ-Cu(R-L1)₂ or Δ-Cu(S-L1)₂ configuration for 1 or 2 in solution. Similarly, the enantiomeric pair of Δ-Cu(R-L2)₂ and Λ-Cu(S-L2)₂ configurations (CD inactive) for 3 will be preferred in solution. Electronic spectra in different solvents reveal a negative solvatochromism by shifting absorption maxima of the MLCT band to higher energies in solvents of increasing polarity as well as acceptor number. DSC analyzes show an endothermic peak at 525.5 (1) or 528.7 K (2), corresponding to a thermally induced structural phase transformation from distorted square-planar to regular tetrahedral.     

Estimation of the Critical Temperature of Thermal Explosion for the Highly Nitrated Nitrocellulose Using Non-isothermal DSC

Two methods for estimating the critical temperature (T_b) of thermal explosion for the highly nitrated nitrocellulose (HNNC) are derived from the Semenov's thermal explosion theory and two non-isothermal kinetic equations, d/dt=Af()e^–E/RT and d/dt=Af()[1+E/(RT)(1–T_o/T)]e^–E/RT, using reasonable hypotheses. We can easily obtain the values of the thermal decomposition activation energy (E), the onset temperature (T_e) and the initial temperature (T_o) at which DSC curve deviates from the baseline of the non-isothermal DSC curve of HNNC, and then calculate the critical temperature (T_b) of thermal explosion by the two derived formulae. The results obtained with the two methods for HNNC are in agreement to each other.This revised version was published online in November 2005 with corrections to the Cover Date.     

Contact electroresistance of metals in aqueous solutions during the anion adsorption involving charge transfer

Notions about charge transfer during adsorption of anions on metals in aqueous solutions are rendered. The role played by the electron tunneling on macrocontacts during the signal formation in the method of contact electroresistance (CER) is considered. It is shown that CER depends on the metal surface coverage by adsorbed species and their effective charge. Bell-like CER vs.E curves are obtained for copper, silver, and gold in solutions containing halide ions. Potentials of maximums in the curves,E _max, correspond to the charge transfer onset and depend on the nature of the metal and anion and on the anion concentration. AtE belowE _max, halides adsorb in the form of ions, involving no substantial charge transfer. At potentials exceedingE _max by 0.1 to 0.2 V, practically complete charge transfer occurs. With changing anion nature,E _max for a given metal rises in the series I^- < Br^- ≪ Cl^-. For a given anion (say, I^-),E _max increases with the metal nature in the series Cu ≤Ag ≪ Au. The link between the charge transfer during adsorption of anions and the surface reconstruction in single-crystal electrodes is discussed.     

Rigidity percolation model of polymer fracture

A theory of the fracture of polymers with network microstructure was developed that was based on the vector, or rigidity percolation (RP) model of Kantor and Webman, in which the modulus, E, is related to the lattice bond fraction p, via E ～ [p ? p_c]^τ. The Hamiltonian for the lattice was replaced by the strain energy density function of the bulk polymer, U = σ²/2E, where σ is the applied stress and p was expressed in terms of the lattice perfection via the bond density ν, with the entanglement molecular weight, ν = ρ/M_e and appropriate measures of crosslink density for rubber, thermosets, and carbon nanotubes. The stored mechanical energy, U, was released by the random fracture of νD_o[p ? p_c] over stressed hot bonds of energy D_o ≈ 330 kJ/mol. The polymer fractured critically when p approached the percolation threshold p_c, and the net solution was obtained as σ = (2EνD_o [p ? p_c])^1/2 with a fracture energy, G_1c ～ [p ? p_c]. The fracture strength of amorphous and semicrystalline polymers in the bulk was well described by, σ = [ED_oρ/16 M_e]^1/2, or σ ≈ 4.6 GPa/M_e^1/2. Fracture by disentanglement was found to occur in a finite molecular weight range, M_c < M < M*, where M*/M_c ≈ 8, such that the critical draw ratio, λ_c = (M/M_c)^1/2, gave the molecular weight dependence of the fracture as G_1c ～ [(M/M_c)^1/2 ? 1]². The critical entanglement molecular weight, M_c, is related to the percolation threshold, p_c, via M_c = M_e/(1 ? p_c). Fracture by bond rupture was in accord with Flory's suggestion, G/G* = [1 ? M_c/M], where G* is the maximum fracture energy. Fracture of an ideal rubber with p = 1 was determined not to occur without strain hardening at λ > 4, such that the maximum stress, σ = E (λ ? 1/λ) = 3.75E. The fracture properties of rubber were found to behave as σ ～ ν, σ ～ E, and G_1c ～ ν. For highly crosslinked thermosets, it was predicted that σ ～ (Eν)^1/2, σ ～ (X ? X_c)^1/2, and G_1c ～ ν^?1/2, where X is the degree of reaction of the crosslinking groups and X_c defines the gelation point. When applied to carbon nanotubes (SWNT and MWNT) of diameter d and hexagonal bond density ν = j/b², the nominal stress as a function of diameter is σ(d) = [16 ED_o(p ? p_c) j/b]^1/2/d ≈ 211/d (GPa.nm) and the critical force, F_c(d) ≈ 166 d (nN/nm), in which j = 1.15, b = 0.142 nm, E ≈ 1 Tpa, and D_o = 518 kJ/mol. For polymer interfaces with Σ chains per unit area of length L and width X ～ L^1/2, G_1c is then ～ [p ? p_c], where p ～ ΣL/X. The results predicted by the RP fracture model were in good agreement with a considerable body of fracture data for linear polymers, rubbers, thermosets, and carbon nanotubes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 168–183, 2005     

ABSORPTION MAXIMA OF CATIONS RELATED TO RETINAL AND THEIR IMPLICATION TO MECHANISMS FOR BATHOCHROMIC SHIFT IN VISUAL PIGMENT*

Abstract— The cations resulting from eleven retinal-related polyenes by placing the latter in n-butanol-sulfuric acid were examined spectroscopically in an effort to explain the batho-chromic effect observed in visual pigments. A comparison of the Λ_max values, intensities and 1/2-band widths of the model carbonium ions with those of the visual pigments does not seem to justify the representation of the chromophore in visual pigments as a pure carbonium ion.     

A DNMR study on the ring inversion of oxazolidines

Ring inversion of eight substituted 2-phenyl-4, 4-dimethyloxazolidines in o-dichlorobenzene-d₄ was studied by ¹H DNMR. Very high inversion barriers (ΔG_o^≠ = 86.7–93.4 kJ·mol^?1) were found for these oxazolidine rings. The magnitude of the inversion barrier is dependent on the polarity of the substituent on the phenyl group. A linear correlation is present between the ΔG_o^≠ of the inversion and the substituent constant, σ+, of the substituent.     

钐(Ⅲ)与不对称希夫碱配合物的合成、表征和热分解反应动力学

A new unsymmetrical Schiff base zwitterion （Ⅲ） was synthesized using L-lysine, salicylaldehyde and 2-hydroxy-l-naphthaldehyde. Samarium（Ⅲ） complex of this ligand [SmL（NO3）]NO3·2H2O has been prepared and characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation may be expressed as dα/dt=3/2Ae^E/RT（1-α）^2/3[1-（1 -α）^1/3）]^-1. The kinetic parameters （E, A）, activation entropy △S^x and activation free-energy △G^x were also gained.     

Spectrophotometric study of complexes of mercury(II) with mono- and dithiosemicarbazones

The formation of complexes at pH 4.7 of the Hg(II) with five monothiosemicarbazone and two dithiosemicarbazone has been studied. The mercury(II) reacts with monothiosemicarbazones of salicylaldehyde (λ_max = 363 nm, E = 1.69 × 10⁴liters · mol^?1cm^?1), pi-colinadehyde (λ_max = 363 nm, E = 2.38 × 10⁴liters · mol^?1cm^?1), 6-methyl-picolinaldehyde (λ_max = 363 nm, E = 2.28 × 10⁴liters · mol^?1cm^?1), di-2-pyridylketone (λ_max = 380 nm, E = 2.08 × 10⁴liters · mol^?1cm^?1), and o-naphthoquinone (λ_max = 540 nm, E = 1.03 × 10⁴liters · mol^?1cm^?1) and with dithiosemicarbazones of 1,4-dihydroxyphthalimide (λ_max = 430 nm, E = 2.56 × 10⁴liters · mol^?1cm^?1) and dipyridylglyoxal (λ_max = 363 nm, E = 2.37 × 10⁴liters · mol^?1cm^?1). A critical comparison of the stoichiometry and apparent stability constant of complexes with mono- and dithiosemicarbazones is given.     

Spectral Extinction of Colloidal Gold and Its Biospecific Conjugates

We have prepared gold sols with mean particle diametersd_min the range 4 to 50 nm and measured their extinction spectra and size dependences of the extinction peak position λ_maxand valueE_max. The measured increasing function λ_max(d_m) displays a pronounced bend near the particle diameterd_m∼ 10 nm, where the value of λ_maxsharply decreases with reduction in the particle size. To explain these findings, the extinction spectra of sols with the particle size and axial ratio polydispersity are calculated using Mie's theory, the T-matrix method, and various experimental sets of the bulk gold optical constants modified with regard to size-limiting effects. It is shown that the measured λ_max(d_m) andE_max(d_m) dependences are inconsistent with calculations based on Mie's theory and the bulk gold optical constants. The most generalized model including the size dependence of the imaginary part of the dielectric permeability and the size and shape polydispersity gives good agreement with experimental extinction spectra for 5-, 10-, 24-, and 40-nm sols, as well as with the measured functions λ_max(d_m) andE_max(d_m). Based on electron-microscopic and spectral data, calibration curves are obtained for efficient spectrophotometric control over the particle size and for estimation of the amount of restorer essential for the preparation of particles of a given size. A simplest two-layer spherical model is employed to elucidate the basic changes in sol spectra after conjugation with specific biomacromolecules and to draw some conclusions about the conjugate shell structure.     

CH3 + Cl = CH3Cl: RRKM/master equation modeling

Data for the title reaction have been fitted using an RRKM/master equation approach. Energy transfer was modeled using an exponential decay with downward step sizes, ΔE_d, as a fitting parameter. The low temperature (200 < T (K) < 300) combination of CH₃ with Cl atoms in He can be accommodated with ΔE_d (cm^?1) = 400. Higher temperature (1600 < T (K) < 2100) decomposition in Ar required ΔE_d(T) (cm^?1) = 694(T/300)^0.46. Previous analysis of the analogous system CH₄ = CH₃ + H required ΔE_d(T) (cm^?1) = 100(T/300) for He and ΔE_d(T) (cm^?1) = 150(T/300) for Ar. Understanding of the magnitudes and temperature dependence of ΔE_d remains the greatest detriment to quantitative calculation, extrapolation, and prediction of unimolecular rate constants. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 245–254, 2009     

Charge transfer interactions between nucleic acid bases and strong acceptors

The regularities of the donor-acceptor interaction of nucleic acid bases and some of their derivatives with the strong acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) in thin amorphous films at 77 K were studied using UV and visible spectroscopy. Purine and pyrimidine bases are shown to form charge transfer TCNQ complexes whose band energies hν_ct = I_p ? E_A ? (H* ? H⁰) are linearly dependent of the donor ionization potential I_p. Calculated differences between the interaction energies of uncharged molecules and ion radicals, ΔE ≈ 3.0 eV, are in good agreement with experimental variations of the complex dissociation energies in the ground and excited states, (H* ? H⁰) = 2.73 eV. Annealing of the films of complexes containing cytosine, 1-methylcytosine, uracil, and caffeine leads to ordering of their structure and the formation of ion radical salts.     

Catalytic Effect of Cetyltrimethylammonium Bromide on the Oxidation of Oxalic Acid by N-Bromophthalimide in Acidic Medium

The kinetics of micellar catalyzed oxidation of oxalic acid [OA] by N-bromophthalimide was studied in the presence of perchloric acid at 308 K. The orders of reaction with respect to [Oxalic acid], [oxidant], and [H⁺] were found to be fractional, first and negative fractional order respectively. Cationic micelles of cetyltrimethylammonium bromide increased the reaction rate. The effect of phthalimide, mercuric acetate and inorganic salts, that is, [Cl^?][Br^?] has also been done. The rate reaction decreases with increasing dielectric constant of the medium. The results are treated quantitatively in terms of Piszkiewicz and Berezin models. The rate constant (K_obs), cooperatively index (n), binding constant (k_s + k_o), and corresponding activation parameters (E_a, ΔH^#, ΔS^#, and ΔG^#) were determined. A suitable mechanism consistent with the experimental finding has been proposed.     

The Use of Solar Radiation by the Photosynthetic Bacterium,Rhodopseudomonas palustris: Model Simulation of Conditions Found in a Shallow Pond or a Flatbed Reactor

Photosynthetic bacteria are attractive for biotechnology because they produce no oxygen and so H₂‐production is not inhibited by oxygen as occurs in oxygenic photoorganisms. Rhodopseudomonas palustris and Afifella marina containing BChl a can use irradiances from violet near‐UV (VNUV) to orange (350–650 nm) light and near‐infrared (NIR) light (762–870 nm). Blue diode‐based pulse amplitude modulation technology was used to measure their photosynthetic electron transport rate (ETR). ETR vs Irradiance curves fitted the waiting‐in‐line model—ETR = (ETR_max × E/E_opt) × exp (1 ? E/E_opt). The equation was integrated over pond depth to calculate ETR of Afifella and Rhodopseudomonas in a pond up to 30 cm deep (A₃₇₆, 1 cm = 0.1). Afifella saturates at low irradiances and so photoinhibition results in very low photosynthesis in a pond. Rhodopseudomonas saturates at ≈15% sunlight and shows photoinhibition in the surface layers of the pond. Total ETR is ≈335 μmol (e^?) m^?2 s^?1 in NUV + photosynthetically active radiation light (350–700 nm). Daily ETR curves saturate at low irradiances and have a square‐wave shape: ≈11–13 mol (e^?) m^?2 day^?1 (350–700 nm). Up to 20–24% of daily 350–700 nm irradiance can be converted into ETR. NIR is absorbed by water and so competes with the bacterial RC‐2 photosystem for photons.     

Influence of basic residues on dissociation kinetics and dynamics of singly protonated peptides: time‐resolved photodissociation study

Product ion yields in postsource decay and time‐resolved photodissociation at 193 and 266 nm were measured for some peptide ions with lysine ([KF₆ + H]⁺, [F₆K + H]⁺, and [F₃KF₃ + H]⁺) formed by matrix‐assisted laser desorption ionization. The critical energy (E₀) and entropy (ΔS^?) were determined by RRKM fitting of the data. The results were similar to those found previously for peptide ions with histidine. To summarize, the presence of a basic residue, histidine or lysine, inside a peptide ion retarded its dissociation by lowering ΔS^?. On the basis of highly negative ΔS^?, presence of intramolecular interaction involving a basic group in the transition structure was proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of molecular entanglements on craze microstructure in glassy polymers

Thin films of ten glassy polymers are bonded to copper grids and strained in tension to produce crazes, which are then examined in the transmission electron microscope. The average craze fibril extension ratio λ for each polymer is determined from microdensitometer measurements of the mass thickness contrast of the crazes. The extension ratio λ is found to increase approximately linearly with the chain contour length l_e between entanglements, as determined from melt elasticity measurements of the entanglement molecular weight of these polymers. These results are analyzed by comparing them with λ_max, the maximum extension ratio of an entanglement network in which polymer chains neither break nor reptate (i.e., permanent entanglement crosslinks are assumed). The values of λ_max are given by l_e/d where d, the entanglement mesh spacing in the unoriented glass, is computed from d = k(M_e)^1/2 with k determined either from small-angle neutron scattering results on isolated chains in the glass or from coil size measurements in dilute solutions of a θ solvent. The craze extension ratios fall somewhat below λ_max at low λ but increase to well above λ_max for polymers with high l_e. This comparison suggests a significant contribution due to chain breakage (or reptation) in the higher-λ crazes of large-l_e polymers, which may arise from the higher true stresses in the craze fibrils (which for a given applied stress increase proportionally to λ). The results also imply that a useful way to increase the “brittle” fracture stress and decrease the ductile-to-brittle transition temperature of a glassy polymer is to decrease its entanglement contour length l_e.     

Kinetics of the mercury(II)‐catalyzed substitution of coordinated cyanide ion in hexacyanoruthenate(II) by nitroso‐R‐salt

The kinetics and mechanism of Hg²⁺‐catalyzed substitution of cyanide ion in an octahedral hexacyanoruthenate(II) complex by nitroso‐R‐salt have been studied spectrophotometrically at 525 nm (λ_max of the purple‐red–colored complex). The reaction conditions were: temperature = 45.0 ± 0.1°C, pH = 7.00 ± 0.02, and ionic strength (I) = 0.1 M (KCl). The reaction exhibited a first‐order dependence on [nitroso‐R‐salt] and a variable order dependence on [Ru(CN)₆^4?]. The initial rates were obtained from slopes of absorbance versus time plots. The rate of reaction was found to initially increase linearly with [nitroso‐R‐salt], and finally decrease at [nitroso‐R‐salt] = 3.50 × 10^?4 M. The effects of variation of pH, ionic strength, concentration of catalyst, and temperature on the reaction rate were also studied and explained in detail. The values of k₂ and activation parameters for catalyzed reaction were found to be 7.68 × 10^?4 s^?1 and E_a = 49.56 ± 0.091 kJ mol^?1, ΔH^≠ = 46.91 ± 0.036 kJ mol^?1, ΔS^≠ = ?234.13 ± 1.12 J K^?1 mol^?1, respectively. These activation parameters along with other experimental observations supported the solvent assisted interchange dissociative (I_d) mechanism for the reaction. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 215–226, 2009     

Combined relaxation study of poly(vinyl chloride) blends with chlorinated poly(ethylene), hydroxyl-terminated poly(butadiene), and ethylene-propylene-diene terpolymer

A number of blends based on suspension poly(vinyl chloride) and stabilizers with poly(ethylene) chlorinated in a fluidized-bed reactor containing 21.8% chlorine, hydroxyl-terminated poly(butadiene), and ethylene-propylene-diene terpolymer have been studied using such methods as thermally stimulated current depolarization and dynamic mechanical analysis. Some dielectric and thermodynamic parameters (τ_max, τ_o, E_a, ΔH^*, ΔS_E^*, ΔG^*, μ_eff) have been determined. Blends containing randomly chlorinated poly(ethylene) exhibited dipole–dipole interactions between the macromolecules of poly(vinyl chloride) which decreased at the expense of the long sequences of nonchlorinated methylene groups. Simultaneously, an increased physical interaction between poly(vinyl chloride) and the additives was observed in blends containing chlorinated poly(ethylene) and/or hydroxyl-terminated poly(butadiene), and ethylene-propylene-diene terpolymer. On the basis of the data of dynamic mechanical analysis obtained a heterogeneous structure of the blends is suggested. The development of a boundary interfacial layer with a proper region of relaxation proves the formation of compatible structures between the components. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1595–1608, 1998     

Pulse radiolysis study of 2-Mercapto-benzothiazole-a corrosion inhibitor

Pulse radiolysis of 2-Mercaptobenzothiazole (2-MBT) has been undertaken in aqueous solution. The semi-oxidized species formed at pH 4.5 due to the reaction of OH^•, Br₂ ^•− and N₃ ^• and at pH 10.5 with OH^• yielded a spectrum with λ_max = 348 and 595 nm. These semi-oxidized species were able to oxidize phenothiazine drugs (E^o⋟0.8 V). Reducing species such as e_aq ⁻, CO₂ ^•− and H^• atoms react with 2-MBT resulting in the formation of a transient having λ_max = 350 nm and reducing in nature. Kinetic and spectroscopic data of interest are reported.     

The thermodynamic effect of fluorine as a substituent: Vinylic CF2 and CFH and allylic CF2C

I₂-catalyzed isomerizations of 3-fluoropropene and 3,3 - difluoropropene, and a Cope rearrangement of 1,1 - difluoro - 1,5 - hexadiene provide thermodynamic data which allow the determination of a number of important group values for contributions to ΔH^o_f which when combined with those determined in the preceding paper allow the calculations of ΔH^o_f's of most simple F-substituted hydrocarbons: [C_d(F)(H)] = ? 38.4, [C_d(F)₂] = ? 88.0, [C(F)₂(C)(C_d)] = ? 103.9, [C(F)₂(C)₂] = ? 104.9 kcal/mole. A kinetic study of the conversion of 1,1 - difluoro- to 3,3 - difluoro - 1,5 - hexadiene provided activation parameters for the process: Log A = 10.8, E_a = 33.0 kcal/mole and ΔS^≠ = ? 12.2 e.u. Incremental geminal stabilizations of F and other substituents are discussed and contrasted.