Solubilization of n-alkylbenzenes into decanoyl-N-methylglucamide (Mega-10) solution

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, and n-hexylbenzene into micelles of decanoyl-N-methylglucamide (Mega-10) was studied, where equilibrium concentrations of the above solubilizates were determined spectrophotometrically at 303.2 K. The concentration of the above solubilizates remained constant below the critical micelle concentration (cmc) and increased linearly with an increase in Mega-10 concentration above the cmc. The Gibbs free energy change of the solubilizates from the aqueous bulk to the liquid solubilizate phase was evaluated from the dependence of their aqueous solubility on the alkyl chain length of the solubilizates, which leads to -3.46 kJ mol-1 for DeltaG(0)(CH), the energy change per CH2 group of the alkyl chain. The first stepwise solubilization constant (K(overline)1 ) was evaluated from the slope of the change of solubilizate concentration versus Mega-10 concentration. The Gibbs free energy change (DeltaG(0,s)) for the solubilization decreased linearly with the carbon number of the alkyl chain of the solubilizates, from which DeltaG(0,s)(CH2) as evaluated to be -2.71 kJ mol-1. The similar values above clearly indicate that the location of the alkyl chain is a hydrophobic micellar core, which is also supported by the absorption spectrum of the solubilized molecules.     

Photoinduced electron transfer reactions by SmI2 in THF: luminescence quenching studies and mechanistic investigations

Photoluminescence quenching studies of SmI2 in dry THF were carried out in the presence of five different classes of compounds: ketone, alkyl chloride, nitrile, alkene and imine. The free energy change (DeltaG0) of the photoinduced electron transfer (PET) reactions was calculated from the redox potentials of the donor (SmI2) and acceptors. The bimolecular quenching constants (k(q)) derived from the Stern-Volmer experiments parallel the free energy changes of the PET processes. The observed quenching constants were compared with the theoretically derived electron transfer rate constants (k(et)) from Marcus theory and found to be in good agreement when a value of lambda = 167 kJ mol(-1) (40 kcal mol(-1)) was used for the reorganization energy of the system. A careful comparison of the excited state dynamics of SmII in the solid state to the results obtained in solution (THF) provides new insight in to the excited states of SmII in THF. The activation parameters determined for the PET reactions in SmI2/1-chlorobutane system are consistent with a less ordered transition state and high degree of bond reorganization in the activated complex compared to similar ground state reactions. Irradiation studies clearly show that SmI2 acts as a better reductant in the excited state and provides an alternative pathway for rate enhancement in known and novel functional group reductions.     

Quantitative Structure—Activity Relationships in the Lithium and Sodium Affinities of n—Alkyl Fluorides

B3L YP/6-31 g(d,p)method was used to calculate the lithium and sodium affinities of n-alkyl fluoride. These affinities were found to obey the Holmes relationship, i.e.they correlate linearly with the quotient n/(n 1), where n is the number of carbon atoms in the alkyl chain. From the correlation the limiting values of lithium and sodium affinities for very long alkyl chain were predicted to be-153.3kJ/mol and -108.4kJ/mol,respectively.     

Structural and fluorescence quenching characterization of hematite nanoparticles

Nanoparticles of the dominant hematite form (α-Fe(2)O(3)) of iron oxide have been prepared by a simple route of dropping FeCl(3) solution into boiling water. The nanoparticles have been characterized by transmission electron microscopy (TEM), UV-visible electronic absorption spectroscopy, chemical stoichiometry, thermal analysis methods (TGA, DSC and DTA), XRD, FTIR and magnetic susceptibility measurements. Kinetic analysis of the DSC calorigram of thermal dehydration of the nanoparticles reveals one stage of the dehydration process of energy of activation of 29.0 kJ mol(-1). The role of iron oxide nanoparticles in fluorescence quenching of coumarin thiourea derivatives (I-IV) was investigated at room temperature (296 K) by means of steady-state fluorescence spectroscopy. The quenching process was characterized by Stern-Volmer (S-V) plots which display a positive deviation from linearity. This could be explained by static and dynamic quenching models. The positive deviation in the S-V plot is interpreted in terms of ground-state complex formation model and sphere of action static quenching model. Various rate parameters for the ?uorescence quenching process were determined by using the modi?ed Stern-Volmer equation. The sphere of action static quenching model agrees very well with experimental results. Quenching constants for iron oxide nanoparticles are about four orders of magnitudes higher than quenching by Fe(3+) ions.     

Solubilization of p-nitrophenol in aggregates formed by hydrophobically modified polyelectrolytes

The solubilization of p-nitrophenol into the hydrophobic microdomains provided by polyelectrolytes carrying alkyl side chains of different length has been investigated in aqueous solutions of pH 5.0 and 8.0. Under these pH conditions p-nitrophenol is predominantly present in its neutral and ionic forms, respectively. Potassium salts of poly(maleic acid-co-1-olefins), PA-nK2 with n = 12, 14, 16, 18, were synthesized, and the pseudo-phase model was used to determine the distribution coefficient KS, and the standard free energy of transfer Deltamut0 of p-nitrophenol between water and polymer aggregates. The results indicate that at both pH's the solubilization of p-nitrophenol increases with increasing size of the side alkyl chain; i.e., the values of KS follow the order PA-18K2 > PA-16K2 > PA-14K2 > PA-12K2. The free energies, Deltamut0, were plotted as a function of the number of carbon atoms in the side alkyl chain and a linear relation was found. From these plots contributions of -0.324 and -0.676 kJ mol(-1) per methylene group were determined at pH 5.0 and 8.0, respectively. The effect of aggregate size on the solubility of phenol is attributed to the hydrophobic contribution per CH2 group to the free energy of transfer. The hydrophobic nature of the CH2 group is suggested to derive largely from the enthalpic contribution.     

荧光光谱法研究橙皮甙与牛血清白蛋白的相互作用

在pH7.40的Tris-HCl 缓冲体系中,采用荧光光谱技术研究了橙皮甙与牛血清白蛋白(BSA)的相互作用.随着温度升高,橙皮甙与BSA 的猝灭常数逐渐增加.实验表明:橙皮甙对BSA的荧光猝灭为动态猝灭过程.由热力学参数焓变(△H=70.71 kJ/mol)大于零和熵变[△S=316.29J/(mol·K)]大于零,...     

Theoretical study on the spin-state energy splittings and local spin in cationic [Re]-Cn-[Re] complexes

Total spin-state energy splittings are calculated for mono- and dications of the formula {[Re]-Cn-[Re]}z+ where [Re] = eta5-(C5Me5)Re(NO)(PPh3). Cn is an even-numbered carbon chain with n ranging from 4 to 20, and z is 1 or 2. These complexes are experimentally known, and their potential role as molecular electronic devices initiated this work. We have considered the different total spin states monocation/doublet, monocation/quartet, dication/singlet, and dication/triplet. Data obtained for two density functionals BP86 and B3LYP were compared to verify the internal consistency of the results. In both ionization states, the low-spin state is the ground state, but the spin-state splittings decrease as the chain gets longer. For the dications, the splitting reaches a nearly constant value of about 10 kJ/mol with BP86 and about 4 kJ/mol with B3LYP when there are at least 14 carbon atoms in the chain, whereas for the monocations, no constant value appears to be reached asymptotically, not even if 20 carbon atoms are in the chain. For monocations, the splittings range from 138 kJ/mol (n = 4) to 68 kJ/mol (n = 20) with BP86 and from 134 kJ/mol (n = 4) to 73 kJ/mol (n = 20) with B3LYP and are thus considerably higher than those of the dications. The spin-state splittings are qualitatively mirrored by the energy splitting between the highest-occupied molecular orbital with beta spin (HOMObeta) and the lowest-unoccupied molecular orbital with alpha spin (LUMOalpha) as obtained in the low-spin state. Furthermore, the HOMOalpha-LUMOalpha gaps decrease as the carbon chain lengthens. In addition, the local distribution of the ?z expectation value is analyzed for the monocation/doublet, the monocation/quartet, and the dication/triplet state using a modified L?wdin partitioning scheme. In the monocation/doublet and the dication/triplet state, the electron spin is distributed mainly on the metal centers and slightly delocalized onto the carbon chain. In the monocation/quartet state for chain lengths of more than 8 carbon atoms, the electron spin is mainly localized on selected atoms of the chain and not on the metal centers. In all cases, the spin delocalization onto the chain increases as the chain gets longer.     

Fluorescence study on the interaction of human serum albumin with bromsulphalein

The binding of bromsulphalein (BSP) with human serum albumin was investigated at different temperatures, 298 and 308 K, by the fluorescence spectroscopy at pH 7.24. The binding constant was determined by Stern-Volmer equation based on the quenching of the fluorescence HSA in the presence of bromsulphalein. The effect of various metal ions on the binding constants of BSP with HSA was investigated. The thermodynamic parameters were calculated according to the dependence of enthalpy change on the temperature as follows: DeltaH and DeltaS possess small negative (9.3 kJ mol(-1)) and positive values (22.3 J K(-l)mol(-l)), respectively. The experimental results revealed that BSP has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The binding constants between BSP to HSA were remarkable and independent on temperature. The binding constants between HSA and BSP decreased in the presence of various ions, commonly decreased by 30-55%. The hydrophobic force played a major role in the interaction of BSP with HSA. All these experimental results and theoretical data clarified that BSP could bind to HSA and be effectively transported and eliminated in body, which could be a useful guideline for further drug design.     

The Chemical Ionization of Organic Compounds. 2nd Communication. Linear Alkyl Halides

The chemical ionization spectra of linear alkyl halides with up to nine carbon atoms have been studied using water as protonating agent. An alkyl ion with the same number of carbon atoms as the halide is produced. With more than six carbon atoms in the chain, fragmentation becomes important. The results show that excited hydronium ions participate as intermediates and the fragments of the resulting alkyl ions have branched structures.     

Kinetics of adsorption and desorption of sodium alkyl sulfates to and from nylon particles

The desorption rate of surfactant ions from nylon particles was investigated at the concentrations below the critical micelle concentration by applying the stopped-flow method. A mixing cell of stopped-flow spectrophotometer was modified with platinum electrodes for electric conductivity detection. The change in electric conductivity with time in the desorption process was monitored by a memory-recorder system. The surfactants used were sodium decyl, sodium dodecyl, sodium tetradecyl, and sodium hexadecyl sulfates. The desorption rate was independent of the surfactant concentration and the rate constants were obtained by applying the first-order reaction scheme. The adsorption rate constants were estimated from the experimental desorption rate constants and equilibrium constants assuming the second-order kinetics. The desorption rate constants were determined to be 1–6 sec^–1 and the adsorption rate constants to be 2–8×10⁴ mol^–1 dm³ sec^–1; the former decreased and the latter increased with increasing number of carbon atoms in alkyl chain of the surfactants.     

Binding of Benzyltrimethylammonium Bromide and its Alkyldimethylbenzylammonium Homologues by β-Cyclodextrin in Water

The binding constants, K′, for the reaction between some alkyldimethylbenzylammonium bromide homologues (alkyl = methyl, ethyl, propyl, butyl, hexyl, decyl, and dodecyl, respectively) and β-cyclodextrin in water at 25.0 ± 0.1 ^∘C have been determined, by applying the spectral displacement technique with phenolphthalein as the displacing anion. It has been shown that the ln K′ values increase linearly with the number of carbon atoms in the alkyl chain for the salts whose alkyl chain has at least four carbon atoms. The ln K′ values estimated for the parent compound benzyltrimetylammonium bromide and its two nearest homologues are distinctly lower than might be expected by extrapolation of the linear relation found for the higher homologues. Assuming that it is the organic cation that undergoes association with β-cyclodextrin, then one may suppose that a change occurs in the mode of inclusion of the cation upon passing to higher homologues. In the case of the lighter homologues, it is the phenylene group that undergoes inclusion. This model of inclusion is confirmed by analysis of rotating-frame overhauser effect spectroscopy (ROESY) spectra.     

Bimolecular electron transfers that follow a Sandros-Boltzmann dependence on free energy

Rate constants (k) for exergonic and endergonic electron-transfer reactions of equilibrating radical cations (A(?+) + B ? A + B(?+)) in acetonitrile could be fit well by a simple Sandros-Boltzmann (SB) function of the reaction free energy (ΔG) having a plateau with a limiting rate constant k(lim) in the exergonic region, followed, near the thermoneutral point, by a steep drop in log k vs ΔG with a slope of 1/RT. Similar behavior was observed for another charge shift reaction, the electron-transfer quenching of excited pyrylium cations (P(+)*) by neutral donors (P(+)* + D → P(?) + D(?+)). In this case, SB dependence was observed when the logarithm of the quenching constant (log k(q)) was plotted vs ΔG + s, where the shift term, s, equals +0.08 eV and ΔG is the free energy change for the net reaction (E(redox) - E(excit)). The shift term is attributed to partial desolvation of the radical cation in the product encounter pair (P(?)/D(?+)), which raises its free energy relative to the free species. Remarkably, electron-transfer quenching of neutral reactants (A* + D → A(?-) + D(?+)) using excited cyanoaromatic acceptors and aromatic hydrocarbon donors was also found to follow an SB dependence of log k(q) on ΔG, with a positive s, +0.06 eV. This positive shift contrasts with the long-accepted prediction of a negative value, -0.06 eV, for the free energy of an A(?-)/D(?+) encounter pair relative to the free radical ions. That prediction incorporated only a Coulombic stabilization of the A(?-)/D(?+) encounter pair relative to the free radical ions. In contrast, the results presented here show that the positive value of s indicates a decrease in solvent stabilization of the A(?-)/D(?+) encounter pair, which outweighs Coulombic stabilization in acetonitrile. These quenching reactions are proposed to proceed via rapidly interconverting encounter pairs with an exciplex as intermediate, A*/D ? exciplex ? A(?-)/D(?+). Weak exciplex fluorescence was observed in each case. For several reactions in the endergonic region, rate constants for the reversible formation and decay of the exciplexes were determined using time-correlated single-photon counting. The quenching constants derived from the transient kinetics agreed well with those from the conventional Stern-Volmer plots. For excited-state electron-transfer processes, caution is required in correlating quenching constants vs reaction free energies when ΔG exceeds ～+0.1 eV. Beyond this point, additional exciplex deactivation pathways-fluorescence, intersystem crossing, and nonradiative decay-are likely to dominate, resulting in a change in mechanism.     

Transition state for alkyl group hydrogenation on Pt(111)

Substituent effects have been used to probe the characteristics of the transition state to hydrogenation of alkyl groups on the Pt(111) surface. Eight different alkyl and fluoroalkyl groups have been formed on the Pt(111) surface by dissociative adsorption of their respective alkyl and fluoroalkyl iodides. Coadsorption of hydrogen and alkyl groups, followed by heating of the surface, results in hydrogenation of the alkyl groups to form alkanes, which then desorb into the gas phase. Temperature-programmed reaction spectroscopy was used to measure the barriers to hydrogenation, DeltaE(H)(double dagger), which are dependent on the size of the alkyl group (polarizability) and the degree of fluorination (field effect). This example is one of only two surface reactions for which the influence of the substituents on DeltaE(H)(double dagger) has been correlated with both the field and the polarizability substituent constants of the alkyl groups in the form of a linear free energy relationship. Increasing both the field and the polarizability constants of the alkyl groups increases the value of DeltaE(H)(double dagger). The substituent effects are quantified by a field reaction constant of rho(F) = 27 +/- 4 kJ/mol and a polarizability reaction constant of rho(alpha) = 19 +/- 3 kJ/mol. These suggest that the transition state for hydrogenation is slightly cationic with respect to the alkyl group on the Pt(111) surface, RC + H <--> {RC(delta+)...H}(double dagger).     

醇和N,N-二甲基乙酰胺分子间相互作用的FTIR光谱研究

The association between alcohols and N,N-dimethylacetamide in carbon tetrachloride was investigated using FTIR spectroscopy at 298 K.The formation constants for 1∶1 and 1∶2 complexes were calculated using the method of Whetsel and Kagarise.The observed 1∶1 complex values were also verified using the method of Nash.The rate of change in C=O bond moment on complexing with alcohols increased with increasing acidity of alcohols.The formation constant and values of free energy change increased with the increase in carbon chain length of alcohols,which suggested that the degree of complex formation varied with the length of the carbon chain of alcohols.     

UV photolysis products of propiolic acid in noble-gas solids

Photolysis (193 nm) of propiolic acid (HCCCOOH) was studied with Fourier transform infrared spectroscopy in noble-gas (Ar, Kr, and Xe) solid matrixes. The photolysis products were assigned using ab initio quantum chemistry calculations. The novel higher-energy conformer of propiolic acid was efficiently formed upon UV irradiation, and it decayed back to the ground-state conformer on a time scale of approximately 10 min by tunneling of the hydrogen atom through the torsional energy barrier. In addition, the photolysis produced a number of matrix-isolated 1:1 molecular complexes such as HCCH...CO2, HCCOH...CO, and H2O...C3O. The HCCH...CO2 complex dominated among the photolysis products, and the computations suggested a parallel geometry of this complex characterized by an interaction energy of -9.6 kJ/mol. The HCCOH...CO complex also formed efficiently, but its concentration was strongly limited by its light-induced decomposition. In this complex, the most probable geometry was found to feature the interaction of carbon monoxide with the OH group via the carbon atom, and the computational interaction energy was determined to be -18.3 kJ/mol. The formation of the strong H2O...C3O complex (interaction energy -21 kJ/mol) was less efficient, which might be due to the inefficiency of the involved radical reaction.     

自由能微扰法研究系列烷基芳基磺酸盐的胶束化焓-熵补偿现象

为了研究不同结构的表面活性剂分子在水溶液中的胶束化焓-熵补偿现象, 采用自由能微扰(FEP)法计算了系列烷基芳基磺酸盐的溶剂化自由能, 并根据胶团化过程的质量作用模型讨论了相关热力学性质. 结果表明: 自由能微扰法得到的溶剂化自由能大小与用传统热力学表面张力法测定的吉布斯自由能相近, 能够用于比较不同结构的烷基芳基磺酸盐间胶束化能力; 烷基芳基磺酸盐在水溶液中的胶束化过程是自发进行的, 且存在焓-熵补偿现象, 补偿温度范围均在(302±2) K; 随着分子结构中芳环向长烷基链中间位置移动, 胶束化能力和胶束的稳定性均下降; 而随着芳环上短烷基链或长烷基链碳数的增加, 形成胶束的能力与稳定性均提高.     

Electroanalysis of Caffeic Acid in Red Wine and Investigation of Thermodynamic Parameters Using an Ag Nanoparticles Modified Poly(Thiophene) Film Glassy Carbon Electrode

A silver nanoparticle decorated poly(thiophene) modified glassy carbon electrode (GCE) was prepared for determination of caffeic acid. The Ag/PTh/GCE surface was characterized by scanning electron microscopy (SEM) and energy‐dispersive X‐ray (EDX) spectroscopy. The modified electrode has shown higher electrocatalytic activity towards the oxidation of caffeic acid. The peak current of was found linear in the concentration range from 1.00×10^?8 to 4.83×10^?6 M with a detection limit of 5.3×10^?9 M (S/N=3). The modified electrode was used for determination of CA concentration in red wine samples. The thermodynamic constants, entropy change (ΔS), enthalpy change (ΔH) and Gibbs free energy change (ΔG) were calculated as ?166.34 J/(mol K), ?154.24 kJ/mol and ?104.75 kJ/mol at 25 °C, respectively.     

Chain transfer by addition–substitution–fragmentation mechanism. I. End–functional polymers by a single-step free radical transfer reaction: Use of a new allylic linear peroxyketal

A new chain transfer agent, ethyl 2-[1-(1-n-butoxyethylperoxy) ethyl] propenoate (EBEPEP) was used in the free radical polymerization of methyl methacrylate (MMA), styrene (St), and butyl acrylate (BA) to produce end-functional polymers by a radical addition–substitution–fragmentation mechanism. The chain transfer constants (C_tr) for EBEPEP in the three monomers polymerization at 60°C were determined from measurements of the degrees of polymerization. The C_tr were determined to be 0.086, 0.91, and 0.63 in MMA, St, and BA, respectively. EBEPEP behaves nearly as an “azeotropic” transfer agent for styrene at 60°C. The activation energy, E_atr, for the chain transfer reaction of EBEPEP with PMMA radicals was determined to be 29.5 kJ/mol. Thermal stability of peroxyketal EBEPEP in the polymerization medium was estimated from the DSC measurements of the activation energy, E_ath = 133.5 kJ/mol, and the rate constants, k_th, of the thermolysis to various temperature. © 1994 John Wiley & Sons, Inc.     

Mechanism and rate constants for the decomposition of 1-pentenyl radicals

This paper is concerned with the mechanisms and rate constants for the decomposition of 1-penten-3-yl, 1-penten-4-yl, and 1-penten-5-yl radicals. They are formed from radical attack on 1-pentene, which is an important decomposition product of normal alkyl radicals with more than 6 carbon atoms in combustion systems. This work is based on related data in the literature. These involve rate constants for the reverse radical addition process under high-pressure conditions, chemical activation experiments, and more recent direct studies. The high-pressure rate constants are based on detailed balance. The energy transfer effects and the pressure dependences of the rate constants are determined through the solution of the master equation and are projected to cover combustion conditions. The low barriers to these reactions make it necessary to treat these thermal reactions as open systems, as in chemical activation studies. The multiple reaction channels make the nature of the pressure effects different from those usually described in standard texts. The order of stability is 1-penten-3-yl approximately 1-penten-4-yl > 1-penten-5-yl and straddles those for the n-alkyl radicals. A key feature in these reactions is the effects traceable to allylic resonance. However, the 50 kJ/mol allylic resonance energy is not fully manifested. The important unsaturated products are 1,3-butadiene, the pentadienes, allyl radicals, and vinyl radicals. The results are compared with the recommendations in the literature, and significant differences are noted. Extensions to larger radicals with similar structures are discussed.     

Interfacial properties of poly(maleic acid-alt-1-alkene) disodium salts at water/hydrocarbon interfaces

The interfacial properties of poly(maleic acid-alt-1-alkene) disodium salts at hydrocarbon/water interfaces are determined. In all the studied systems, the interfacial tension decreases markedly with the polyelectrolyte concentration as the side-chain length increases. The results of the standard free energy of adsorption, DeltaG(ads)(0), are a linear function of the number of carbon atoms in the polyelectrolyte side chain. The contribution to DeltaG(ads)(0) per mol of methylene group varies from -0.64 to -0.52 kJ/mol for the n-octane/water to n-dodecane/water interfaces. DeltaG(ads)(0) data also reveal that the adsorption process is mainly determined by adsorption efficiency. Comparatively, the adsorption effectiveness seems to play a less important role. The theoretical interaction energies calculated for the insertion of one hydrocarbon molecule into the space formed by two neighboring polyelectrolyte side chains are in good agreement with the experimental results. The latter results are consistent with van der Waals-type interactions between the hydrocarbon molecules and the polyelectrolyte side chains.