Thermokinetic Research Method for Simple-order Reactions. Double-thermoanalytical curve method

A novel thermokinetic research method for determination of the rate constant of a reaction taking place in a batch conduction calorimeter under isothermal conditions is proposed: the double-thermoanalytical curve method. The method needs only the characteristic time parameter t _m, the peak height Δ_m at time t _m and the peak area a*_m after time t _m for two thermoanalytical curves measured with different initial concentrations of the reactants: it conveniently calculates the rate constants. The thermokinetics of four reaction systems were studied with this method, and its validity was verified by the experimental results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ion transport and states of water in charged poly(allylamine) membranes

Cationically charged poly(allylamine) (PAA) membranes having various water contents [0.49 < H < 0.63 (g H₂O/g wet membrane)] were prepared. Sorption and permeation of simple salts (sodium chloride and sodium tetraphenylborate) were investigated, taking into account the state of the water in these membranes. The weight ratios of freezable water and free water to total water (W_fz/W_t, and W_f/W_t) in the membranes were estimated by means of DSC and pulsed ¹H-NMR measurements, respectively. Partition coefficients K for total water were converted into those in freezable and free water, K_fz and K_f, using W_fz/W_t and W_f/W_t. The permeability of both salts in the membranes could be interpreted satisfactorily by an equation derived from the Teorell-Meyer-Sievers theory using values of K_f. The free water is mainly involved in the permeation of simple salts through PAA membranes while bound water hardly takes part.     

Calorimetric studies on the electrorefining process of copper

Calorimetric measurements were carried out on the electrorefining of copper using different current densities with a Calvet type microcalorimeter at room temperature. The ratio (R) of the measured heat (Q _m orW _m) to the input electric energy (Q _in orW _in) and the excess heat (Q _ex orW _ex), i.e. the difference betweenQ _m (orW _m) andQ _in (orW _in) during the electrorefining process were discussed in terms of general thermodynamics. It was found thatR andQ _ex were related to the current density employed in the experiment and varied as a logarithmic function. The results obtained here indicate that the heat generation under different conditions, such as different currents or voltages, may be caused partially by the irreversibility of the process or by some unknown processes.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThe authors would like to acknowledge the extreme encouragements and help of Professor Shuyi Liu (University of Science and Technology of China) and Professors Fu Tan and Guoquan Liu (Institute of Chemistry, Academia Sinica).This study was supported by the National Nature Science Foundation of China.     

Zymomonas mobilis as catalyst for the biotechnological production of sorbitol and gluconic acid

The conversion of glucose and fructose into gluconic acid (GA) and sorbitol (SOR) was conducted in a batch reactor with free (CTAB-treated or not) or immobilized cells of Zymomonas mobilis. High yields (more than 90%) of gluconic acid and sorbitol were attained at initial substrate concentration of 600 g/L (glucose plus fructose at 1:1 ratio), using cells with glucose-fructose-oxidoreductase activity of 75 U/L. The concentration of the products varied hyperbolically with time according to the equations (GA)=t(GA)_max/(W_GA +t), (SOR)=t (SOR)_max/(W_Sor+t), v_GA=[W_GA (GA)_max]/(W_GA+t)² and V_SOR=[W_SOR (SOR)_max]/(W_SOR+t)². Taking the test carried out with free CTAB-treated cells as an example, the constant parameters were (GA)_max= 541 g/L, (SOR)_max=552 g/L, W_GA=4.8h, W_SOR=4.9h, υ_GA=112.7 g/L· and υ_SOR=112.7 g/L·.     

t-Butyl isocyanide complexes of rhenium(I), chromium(O), tungsten(O,I) and platinum(II); X-ray crystal structures of bis(t-butylisocyanide)- tris(trimethylphosphine)chlororhenium(I) and tris(t-butylisocyanide)bis(trimethyl- phosphine)chlororhenium(I)

The reduction of ReCl₄(THF)₂ in the presence of excess t-butylisocyanide by sodium amalgam produces pentakis(t-butylisocyanide)chlororhenium(I), which has been converted to the corresponding methyl and ethyl derivatives. The reaction of pentakis(trimethylphosphine)chlororhenium(I) with Bu^tNC gives partially substituted complexes, ReCl(CNBu^t)₂(PMe₃)3 and ReCl(CNBu^t)₃(PMe₃)₂. The structures of both compounds have been determined by X-ray methods. Octahedral ReCl(CNBu^t)₂(PMe₃)₃ has trans isocyanide groups with one linear [C---N---C = 175(1)°] and one slightly bent [C---N---C = 159(1)°]. The Re---C bond lengths are equal within experimental error [2.004(7), 2.003(7)Å]. In the octahedral ReCl(CNBu^t)₃(PMe₃)₂, for which the structure is not well defined, due to disorder, the unique isocyanide trans to chlorine is considerably bent at the nitrogen atom [C--- ---C = 141(6)°] and appears to show the shortest Re---C bond length, 1.94(5) vs 2.02(5)Å for the other two isocyanides which are mutually trans. Protonation of these two isocyanide complexes with fluoroboric acid gives, respectively, the salts [ReCl(CNBu^t)CNHBu^t(PMe₃)₃]BF₄ and [ReCl(CNBu^t)₂CNHBu^t(PMe₃)₂]BF₄, whose configurations have been determined by NMR spectroscopy. The reduction by sodium amalgam of Cr₂(CO₂Me)₄ in tetrahydrofuran in presence of Bu^tNC gives a high yield of Cr(CNBu^t)₆ while similar reduction of the dimeric tungsten(II) complex of the anion (mhp) of 2-methyl-6- hydroxypyridine gives W(CNBu^t)₆. Interaction of W₂(mhp)₄ in methanol-ether with Bu^tNC gives a tungsten(I) complex W₂(η-mhp)₂(Bu^tNC)₄, which may be an intermediate in the reductive cleavage reaction. Interaction of cis-PtMe₂(PMe₃)₂ with Bu^tNC leads only to replacement of one PMe₃ group to give the complex cis-PtMe₂(PMe₃)(CNBu^t).     

Structure‐Directing Forces in Intercluster Compounds of Cationic [Ag14(CCtBu)12Cl]+ Building Blocks and Polyoxometalates: Long‐Range versus Short‐Range Bonding Interactions

Crystallization of [Ag₁₄(C?CtBu)₁₂Cl][BF₄] and different polyoxometalates in organic solvents yields a series of new intercluster compounds: [Ag₁₄(C?CtBu)₁₂Cl(CH₃CN)]₂[W₆O₁₉] ( 1 ), (nBu₄N)[Ag₁₄(C?CtBu)₁₂Cl(CH₃CN)]₂[PW₁₂O₄₀] ( 2 ), and [Ag₁₄(C?CtBu)₁₂Cl]₂[Ag₁₄(C?CtBu)₁₂Cl(CH₃CN)]₂[SiMo₁₂O₄₀] ( 3 ). Applying the same technique to a system starting from polymeric {[Ag₃(C?CtBu)₂][BF₄]?0.6 H₂O}_n and the polyoxometalate (nBu₄N)₂[W₆O₁₉] results in the formation of [Ag₁₄(C?CtBu)₁₂(CH₃CN)₂][W₆O₁₉] ( 4 ). Here, the Ag₁₄ cluster is generated from polymeric {[Ag₃(C?CtBu)₂][BF₄]?0.6 H₂O}_n during crystallization. In a similar way, [Ag₁₅(C?CtBu)₁₂(CH₃CN)₅][PW₁₂O₄₀] ( 5 ) has been obtained from {[Ag₃(C?CtBu)₂][BF₄]?0.6 H₂O}_n and (nBu₄N)₃[PW₁₂O₄₀]. The use of charged building blocks was intentional, because at these conditions the contribution of long‐range Coulomb interactions would benefit most from full periodicity of the intercluster compound, thus favoring formation of well‐crystalline materials. The latter has been achieved, indeed. However, as a most conspicuous feature, equally charged species aggregate, which demonstrates that the short‐range interactions between the “surfaces” of the clusters represent the more powerful structure direction forces than the long‐range Coulomb bonding. This observation is of significant importance for understanding the mechanisms underlying self‐organization of monodisperse and structurally well‐defined particles of nanometer size.     

Interconverting WW Triple Bonds and W4 Clusters: Structures of W4(OPrn)16 and [Li2W2(OPrn)8(DME)]2*

Alcoholysis of W₂(NMe₂)₆ with excess n-propanol in hexane yields the tetranuclear cluster, W₄(OPrⁿ, I. Reduction of I with two equivalents of Li₂COT in THF gives a small yield of Li₂W₂(OPrⁿ)₈. Single crystals were isolated by cooling the product mixture in DME and were shown to be [Li₂W₂(OPrⁿ)₈(DME)]₂, II, which consists of a unique “dimer of dimers” structure. In this reaction sequence, W₄¹⁶⁺ cluster formation is followed by four electron reduction to reform the (W≡W)⁶⁺ unit. Better yields of the lithium salt can be obtained by the addition of LiOPrⁿ/HOPrⁿ solutions to W₂(OBu^t)₆ in which case Li₂W₂(OPrⁿ)₈ has been obtained as a 1:1 adduct with LiOPr. This identity of this salt was confirmed by solution NMR spectroscopy. In the alternative reaction, the (W≡W)⁶⁺ center remains intact from reactant to product. No attempt has been made to separate the product from excess LiOPr. DFT (ADF 2004.01) molecular orbital calculations on the model cluster W₄(OH)₁₆ are used to help elucidate the disruption of the W₄ cluster upon four electron reduction. The molecular structures of compounds I and II are reported.*Dedicated to Professor F. A Cotton on the occasion of his 75th birthday.     

Unexpected products formed by the addition of halogens [X2 (= I2 or Br2)] to W2(O2CBut)4 (MM): The x=ray crystal structures of [W2(O2CBut)5·2ButCONMe2]+[W2I4(O2CBut)2]− and W2Br2(O2CBut)3·2THF

Addition of halogens, X₂ (X = I or Br), to hydrocarbon solutions of W₂(O₂CBu^t)₄·2L, where L = THF or Bu^tCONMe₂, does not lead to simple oxidative-addition products of formula W₂X₂(O₂CBu^t)₄ having axially aligned halogen-tungsten bonds [cf. W₂R₂(O₂CR′)₄ compounds, where R = CH₂CMe₃ or CH₂Ph, and R′ = Me, Et, Bu^t or Ph] but rather leads to facile carboxylate group exchange. The overall reactions are thus complex and two crystalline products isolated in ca 20% crystalline yield have been characterized by X-ray studies. Addition of I₂ has allowed isolation of the salt [W₂(O₂CBu^t)₅·2L]⁺[W₂I₄(O₂CBu^t)₂]⁻, where L = Bu^tCONMe₂, while addition of Br₂ gave W₂Br₂(O₂CBu^t)₃·2L, where L = THF.     

Effect of surfactant adsorption time on the observation of Newton black film in foam film

Observation of Newton black film (NBF) in foam film is possible only with a certain probability W which depends on the concentration C of surfactant in the solution and on the time t_a during which adsorption of surfactant at the solution/air interface has taken place. In the paper, the W(C,t_a) dependence is derived and used to analyze the effect of t_a on the critical surfactant concentration C_c below which NBF in foam film practically cannot be observed. An expression for the C_c(t_a) function is obtained which reveals that C_c decreases substantially with increasing t_a. This expression is found to describe well experimental C_c(t_a) data for foam films obtained from aqueous solution of the therapeutic surfactant INFASURF.     

A diphosphide adduct of ditungsten-hexaisopropoxide: X-ray crystal structure of W2(OPri)6(py)(μ-P2)

From the reaction between W₂(OPrⁱ)₆(py)₂ and CO₂(μ-P₂)(CO)₆ in hexane at room temperature a black crystalline product has been shown to be W₂(OPrⁱ)₆(py)(μ-P₂) by a single crystal X-ray determination. There is a central pseudo tetrahedral W₂P₂ moiety with WW = 2.695(1) Å, PP = 2.154(4) Å and WP = 2.45(2) Å (averaged) corresponding to essentially single bond distances. This new compound is an analogue of the ethyne adducts W₂(OR)₆(py)(μ-C₂H₂), where R = Bu^t and CH₂Bu^t, and these in turn are related to CO₂(CO)₆(μ-X) compounds (X = P₂, C₂R₂) by isolobal relationships.     

Thermokinetic analysis of the hydration process of calcium phosphate cement

A microcalorimeter (Setaram c-80) was used to study the thermokinetics of the hydration process of calcium phosphate cement (CPC), a biocompatible biomaterial used in bone repair. The hydration enthalpy was determined to be 35.8 J g^–1 at 37.0°C when up to 80 mg CPC was dissolved in 2 mL of citric buffer. In the present study, parameters related to time constants of the calorimeter were obtained by fitting the recorded thermal curves with the function θ=Ae^–?t(1– e^–?2t). The real thermogenetic curves were then retrieved with Tian function and the transformation rate of the hydration process of CPC was found to follow the equation α=1–[1–(0.0075t)³]³. The microstructures of the hydrated CPC were examined by scanning electron microscopy. The nano-scale flake microstructures are due to crystallization of calcium phosphate and they could contribute to the good biocompatibility and high bioactivity.     

Molecular and Silica‐Supported Mo and W d0 Imido‐Methoxybenzylidene Complexes: Structure and Metathesis Activity

5‐Coordinated methoxybenzylidene complexes M(=NAr)(=CH?C₆H₄?o‐OMe)(O^tBu_F3)₂ (Ar=2,6‐ⁱPr₂C₆H₃; ^tBu_F3=CMe₂(CF₃)) of Mo ( 1m_Mo ) and W ( 1m_W ) were synthesized by cross‐metathesis from the corresponding neophylidene/neopentylidene precursors and o‐methoxystyrene. 1m_Mo and 1m_W were grafted onto the surface of silica partially dehydroxylated at 700 °C to give well‐defined silica‐supported alkylidenes (≡SiO)M(=NAr)(=CH?C₆H₄?o‐OMe)(O^tBu_F3) (M=Mo ( 1_Mo ), W ( 1_W )). Supported methoxybenzylidene complexes were tested in metathesis of cis‐4‐nonene, 1‐nonene, and ethyl oleate, and compared to their molecular precursors and supported classical analogs (≡SiO)M(=NAr)(=CHCMe₂R)(O^tBu_F3) (M=Mo, R=Ph ( 2_Mo ), M=W, R=Me ( 2_W )). Both grafted complexes 1_Mo and 1_W show significantly better performance as compared to their molecular precursors 1m_Mo and 1m_W but are less efficient than the classical 4‐coordinated alkylidenes 2_Mo and 2_W . Noteworthy, both 1_Mo and 1_W can reach equilibrium conversion in metathesis of cis‐4‐nonene at catalyst loadings as low as 50 ppm.     

Diffusion with discontinuous swelling. V. Type II diffusion into sheets and spheres

Type II diffusion into uniform spheres (radius R) and sheets (thickness 2l) is calculated under the assumption that the glass-gel boundary proceeds at a constant velocity v from the surface towards the interior of the sample, that the diffusion coefficient D_g in the glass is constant and that the diffusion coefficient D_r of the rubbery gel is so much higher than vR or vl that practically no sorbate gradient is needed for the transport through the gel of the sorbate. The diffusion process is completed when this boundary reaches the center of the sample. The concentration profile of the sorbate in the glassy matrix in front of the boundary varies with time and velocity v. It does not, however, influence the boundary propagation velocity. Hence the often observed increase of the rate of the weight gain just at the end of the diffusion process is not considered at all. The relative weight gain of the sample W(t)/W_∞ as a function of time is the only quantity usually measured. From the ordinate intercept A and the initial slope B of the plot of W(t)/t^1/2W_∞ vs. t^1/2, one can calculate the characteristic transport properties, i.e., the diffusion coefficient D_g of the glass and the velocity v of the glass–gel boundary.     

The thermodynamic functions of fullerene derivative (<Emphasis Type="Italic">t</Emphasis>-Bu)<Subscript>12</Subscript>C<Subscript>60</Subscript> over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 420 K

The temperature dependence of heat capacity C _p ^o = f(T) of fullerene derivative (t-Bu)₁₂C₆₀ has been measured by a adiabatic vacuum calorimeter over the temperature range T = 6–350 K and by a differential scanning calorimeter over the temperature range T = 330–420 K for the first time. The low-temperature (T ≤ 50 K) dependence of the heat capacity was analyzed based on Debye’s the heat capacity theory of solids and its fractal variant. As a consequence, the conclusion about structure heterodynamicity is given. The experimental results have been used to calculate the standard thermodynamic functions C _p ^o (T), H ^o(T)−H ^o(0), S ^o(T) and G ^o(T) − H ^o(0) over the range from T → 0 to 420 K. The standard entropy of formation at 298.15 K of fullerene derivative under study was calculated. The temperature of decomposition onset of derivative was determined by differential scanning calorimetery and thermogravimetric analysis. The standard thermodynamic characteristics of (t-Bu)₁₂C₆₀ and C₆₀ fullerite were compared.     

Calorimetric study of adduct formation at 300 K between H2Os3(CO)10 and Lewis bases

The enthalpies of the reactions H₂Os₃(CO)₁₀(I)+L=H₂Os₃(CO)₁₀L(II),L=PR₃, P(OR)₃, in chloroform were determined by means of microcalorimetry. Satisfactory agreement was found between the basicity parameters and the measured reaction enthalpies. As concerns the kinetics, qualitative correlation of a thermokinetics parameter with the steric factor of the ligand was observed.     

Distribution of polymer chain lengths inside a spherical volume: Solution in terms of a diffusion problem

The probability W(t) that a given number t of segments of an infinite chain lie within a given sphere can be expressed in terms of the single-pass length probability and the probability of reentrance into the sphere. The problem of calculating these two probabilities is equivalent to that of a diffusing particle exiting or entering the sphere after a given time, when the surface of the sphere is an absorbing wall. It is shown that the boundary condition, c = 0, usually applied to an absorbing surface cannot be used for the present purpose. The boundary condition used instead is the so-called radiation condition ?c/?z = kc; it is shown that when k approaches infinity the final answer for W(t), which is given in the form of an infinite series, approaches the correct limit. In this same limit the ratio 〈t〉²/〈t〉² has the value 2.4     

Low-temperature adiabatic calorimeter with a built-in cryo-refrigerator

An adiabatic calorimeter was constructed for heat-capacity measurement between 13.8 and 350 K. The cryogenic temperature was produced by a cryo-refrigerator built into the cryostat. This made it possible to make a prolonged experiment at low temperatures without an external supply of liquid helium or liquid hydrogen. With precautions against possible adverse effects of the mechanical vibration of the refrigerator, the accuracy and precision of the calorimeter as proved by measurements on standard reference benzoic acid were comparable with those of the best low-temperature adiabatic calorimeters. Satisfactory performance of the present apparatus has been demonstrated by detection of a glass transition of CsNO₂(c) around 40 K.     

六棱柱型金属团簇化合物W2Ag4S8(dppy)4的纳秒光限幅特性

新合成了一种金属团簇化合物W2Ag4S8(dppy)4,(分子式为C68H56Ag4N4P4S8W2)并用X-射线单晶衍射结构分析方法测定了其晶体结构.单晶X-射线衍射数据表明这种金属团簇化合物具有六棱柱型.在纳秒激光脉冲作用下研究了W2Ag4S8(dppy)4的二甲基甲酰胺(DMF)溶液的光限幅特性.实验结果表明W2Ag4S8(dppy)4的DMF溶液在放置一段时间后光限幅特性明显优于新配制的DMF溶液,其光限幅特性明显强于C60甲苯溶液,表现出其具有较强的光限幅特性.为了研究W2Ag4S8(dppy)4的光限幅机制及光限幅特性在放置一段时间后发生变化的原因,又做了非线性散射和泵浦探测实验,并对其光限幅机制和光限幅特性在放置一段时间后发生变化的原因进行了分析.     

Preparation and Mössbauer study of iron-mercury halide complexes containing isocyanide and carbonyl ligands

Summary Complexes [Fe(t-BuNC)_n(CO)_5-n](n = 1 or 2) react with equimolar amounts of mercury(II) halides in acetone to form neutral iron-mercury adducts [Fe(t-BuNC) (CO)_4–(HgX₂)] and [Fe(t-BuNC)₂(CO)₃(HgX₂)] (X = Cl or I), while [Fe(t-BuNC)₅] reacts with solid mercury halides in petroleum ether to give the salts [Fe(t-BuNC)₅(HgX)]-HgX₃ (X = Br or I). Product assessment was based upon analytical and spectroscopic data, the Mössbauer effect and on molar conductivity studies.     

Thermokinetic Research Method for Bacterial Growth in Conduction Calorimeter

This paper presents the basic equations of thermokinetics and the thermoanalytical curve equation for bacterial growth in conduction calorimeter on the basis of the basic theory of thermokinetics. The bacterial growths in the log phase for Vibro metschnikovii and Bacillus subtilis at different temperatures were calorimetrically investigated. The rate constant of bacterial growth, the cooling constant of the thermokinetic system, the generation time and the pre-exponential factor at different temperature were obtained, which allowed to evaluate the activation energy of bacterial growth (E _a). According to the transition-state theory of chemical kinetics, the activation enthalpy (ΔS ^≠), the activation Gibbs free energy (ΔG ^≠) and equilibrium constant (K ^≠) of the activated state at different temperatures were also obtained. The above results showed that the research method suggested in this paper was reasonable. This revised version was published online in August 2006 with corrections to the Cover Date.