Triphenylphosphine-catalyzed isomerization of alkynyl ketones in aqueous solution

An efficient isomerization of alkynyl ketones to(E,E)-diene ketones was developed.The reaction catalyzed by 20 mol% triphenylphosphine in aqueous media gave the desired products in good yields.     

Combinational simulations of free energy of polymer solution

It is conceptually proposed that the total entropy of polymer solution is contributed from two distinct parts: the positional and the oomformational. The former can be represented analytically, while the latter can be simulated with the random self-avoiding walk model on the simple cubic lattice for multichain systems. The obtained results indicated that both the conformational entropy and the mixing heat are consistent with the scaling laws wry well.     

Protein conformation in solution by three-dimensional fluorescence spectrometry

The conformations of bovine serum albumin (USA) and egg albumin (EA) in solution and their conformation changes under different conditions were studied by using three-dimensional fluorescence spectrometry (TDFS) such as three-dimensional fluorescence (TDF) spectra and three-dimensional fluorescence polarization (TDFP) spectra with tryptophan residues in protein molecules as an intrinsic fluorescent probe. The results show that the microenvironment of tryptophan residues of protein molecules in various solutions can be directly indicated and TDFS is an effective tool for studying protein conformation in solution. Meantime, some valuable results were obtained.     

Rotamers or diastereomers? An overlooked NMR solution

The existence of rotamers in a solution of analyte complicates (1)H NMR analysis, especially when the presence of diastereomers is also possible. Organic chemists have often responded to this problem by conducting variable-temperature (VT) NMR experiments, changing NMR solvents, or adding complexing agents. Here, with specific examples, we illustrate the use of simple yet widely overlooked chemical-exchange NMR experiments which allow the nonintrusive rapid distinguishment of rapidly equilibrating small molecules such as rotamers from nonequilibrating diastereomers.     

Viscoelastic properties of κ-carrageenan in saline solution

Viscoelastic properties of κ-carrageenan in saline solution at various concentrations and pH were investigated by dynamic rheological techniques, viscosity, elasticity measurements, and IR spectrometry. The viscosity and elasticity at low concentrations of κ-carrageenan do not depend on pH, confirming that κ-carrageenan is in a disordered conformation. At 0.7% κ-carrageenan, the disordered confirmation transforms into an ordered helical confirmation with the possibility of weak-type gel formation. The transformation is also confirmed by dynamic measurements of loss and storage moduli. Furthermore, at this concentration, the viscosity and elasticity are highly dependent on pH. At higher concentrations of NaCl (0.5 M) at some pHs, we observed that storage moduli is greater than loss moduli for the entire frequency region. Hence, there is a possibility of structure transformation from weak-type gel to a somewhat intermediate gel. The lowest viscosity and elasticity were obtained at extreme pH, confirming that there are structural changes occurring at these pHs due to hydrolysis. This is confirmed by IR data.     

Coupling matrix element of electron self-exchange reactions in solution

On the basis of the common feature among the electron transfer process and the ion hydration process as well as the relevant experimental kinetic data of electron transfer reaction,a new accurate hydration potential function scheme for the determination of electron transfer coupling matrix element is presented.The coupling matrix element between two hydrated ions of the reacting system in solution is calculated.The results and the applicability of this scheme are discussed.     

A versatile and high-precision solution—reaction isoperibol calorimeter

A new solution-reaction isoperibol calorimeter was developed to measure enthalpies of solution and reaction. A new system of sample cell was developed to avoid the breaking of glass ampoules, hence making the sample cell reusable. The system is suitable for measuring molar enthalpies of solid-liquid and liquid-liquid interactions at different temperatures. The reproducibility and accuracy of the apparatus were tested by measuring the enthalpy of solution of KCl in water at 298.15 K and the enthalpy of protonation of THAM in HCl (0.1 M) at 298.15 K. The results showed the uncertainty taken as the reproducibility was ±0.3% and the difference with the literature values was within ±0.5%.     

What is the acidity of a plutonium solution?

The determination of the pH of a plutonium solution has traditionally depended on an electrode or a titration in the presence of a complexing agent. A new approach uses the equilibrium distribution of the Pu oxidation states to estimate the hydrogen ion concentration. The method is used to estimate the equilibrium constant of the first hydrolysis reaction of tetravalent plutonium.     

Deconstructing the excited-state dynamics of β-carotene in solution

The femtosecond to nanosecond dynamics of the all-trans β-carotene carotenoid dissolved in 3-methylpentane is characterized and dissected with excitation-wavelength and temperature-dependent ultrafast dispersed transient absorption signals. The kinetics measured after red-edge (490 nm) and blue-edge (400 nm) excitation were contrasted under fluid solvent (298 K) and rigid glass (77 K) conditions. In all four measured data sets, the S* population kinetics was resolved prompting the development of a modified multicompartment model. The temperature-dependent and excitation wavelength-dependent S* quantum yield is ascribed to a competition of population surmounting a weak (55 cm(-1)) energy barrier on the S(2) state to favor S(1) generation and rapid internal conversion that favors S* generation. When cooled from room temperature to 77 K, the S* decay time scale shifted significantly from 30 to 400 ps, which is ascribed to small-scale structural relaxation with a 115 cm(-1) energy barrier. For the first time under low-energy excitation conditions, the triplet state is observed and confirmed to not originate from S* or S(1), but from S(2). The interconnectivity of the S* and S(1) populations is discussed, and no observed population flow is resolved between S* and S(1). Comparison of samples obtained from different laboratories with different purity levels demonstrates that sample contamination is not the primary origin of the S* state.     

Voltammetric current–potential calculations using infinite series solution

Highly accurate analytical solution contributing to the theory of linear sweep voltammetry for single scan experiments is given by application of exponential infinite series. The cases of reversible or irreversible charge transfer with or without coupled chemical reaction are treated and calculated results are compared with the customary solution of Nicholson and Shain. Problems with partial divergence of the series were overcome by the series transformation and the use of arbitrary precision arithmetic.     

The solution conformation of cyclic β-casomorphin-5 analogues

The solution conformation of two cyclic-casomorphin-5 analogues H-Tyr-c(-d-Orn-Phe-Pro-Gly-)1 and H-Tyr-c(-Orn-Phe-Pro-Gly-)2 in DMSO-d ₆ was studied by NMR spectroscopy and accompanying force field calculations. By especially employing¹H,¹³C, and¹⁵N chemical shifts, respectively, the temperature coefficient of the amide proton chemical shifts,³ J _NH,CH andJ _CH.CH coupling constants, respectively, and nuclear Overhauser effects in the rotating frame (ROEs), in the case of1, only one preferred conformer could be identified. In the case of2, two or even more preferred conformers were found, readily interconverting on the NMR time scale. Empirical force field calculations using the SYBYL 6.0 software (TRIPOS) corroborate the experimental NMR results obtained. The conformational behavior of the compounds studied is discussed with respect to the receptor specificity of the-casomorphins studied.     

Résolution lagrangienne d'écoulements bidimensionnels turbulents

Turbulent two-dimensional incompressible flows are studied by means of a mixed Euler-Lagrange method. Transported properties are the vorticity ζ the turbulent kinetic energy k, and a turbulent characteristic frequency ω. This approach avoids the use of a permanent grid and the discretization of the convective terms. It is suitable for multibody configurations, particularly when wake/body interaction occurs.     

Aggregation of deuteroporphyrin IX diesters in aqueous-organic binary solution

The aggregation properties of a series of deuteroporphyrin IX diesters in the THF-Buffer (0.1 mol L-1 Tris-HCl) aquiorgano solvent have been studied by means of UV-Vis and fluorescence spectrometers.Experimental data show that the dimerization of porphyrins is mainly determined by π-πinteraction in pure organic solution while further aggregation of porphyrins with long hydrocarbon chains is more likely driven by hydrophobic-lipophilic interaction in aqueous-organic binary solution.The appearance of the aggregates induces a red shift in absorption spectra and fluorescence quenching in fluorescence spectra.The chain-length effect and chain-foldability effect have also been observed.     

Exact solution of Schrödinger equation for Pseudoharmonic potential

Exact solution of Schr?dinger equation for the pseudoharmonic potential is obtained for an arbitrary angular momentum. The energy eigenvalues and corresponding eigenfunctions are calculated by Nikiforov–Uvarov method. Wavefunctions are expressed in terms of Jacobi polynomials. The energy eigenvalues are calculated numerically for some values of ℓ and n with n ≤ 5 for some diatomic molecules.      

Complexation of β-cyclodextrin with carborane derivatives in aqueous solution

β-Cyclodextrin formed the most robust complexes with o-carboranols 1b and 1c in aqueous solution, and the association constants estimated from NMR titration studies indicated K_a >1 × 10⁶ M⁻¹ and K_a = 6 × 10⁵ M⁻¹, respectively.     

Hydration numbers of α-alanine in an aqueous urea solution

Literature data on the apparent molar volumes ϕ of alanine in water and aqueous urea solutions at 298 K are analyzed. It is shown that the slope of the ϕ dependence on the alanine concentration is not dependent on the urea concentration. The standard partial volume of alanine increases linearly with the increase in the urea concentration (wt.%). The structural characteristics of hydrated complexes of alanine (hydration number, molar volume of water inside and outside the hydration sphere, and proper volume of alanine in solution) are given. The hydration number of alanine decreases by a factor of two in passing from water to a saturated (20m) urea solution. The effects of urea additions on the hydration numbers of alanine and glycine are compared.     

Production and properties of polyacenaphthylene—V dilute solution properties

Polyacenaphthylene was synthesized by thermal bulk polymerization, fractionated into 11 fractions by fractional precipitation and characterized by gel permeation chromatography, light scattering and osmometry. Long chain branching was observed in polyacenaphthylenes with $\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{> 1 × 10}{}^6\text{g/mol}$. θ-temperatures of branched and linear polyacenaphthylenes were determined in 1,2-dichloroethane and are different in magnitude. Polyacenaphthylene undergoes chemical degradation in manufacturers' grade 1,2-dichloroethane. Intrinsic viscosities in benzene, toluene, tetrahydrofuran at 25°C, and in 1,2-dichloroethane at 41.1°C have been measured and the Mark-Houwink constants of the viscosity molar mass relationship evaluated.     

Electron emission from photo-excited testosterone in water–ethanol solution

Testosterone (TES; 4-androstene-17β-ol-3-on) is found for the first time to eject electrons from its singlet excited state in water–ethanol solvent mixture. This ability was very recently also observed for 17β-estradiol (17βE2) and progesterone (PRG)/1/. With increasing TES-concentration, the yield of solvated electrons (${\text{e}}_{\text{s}}^{-}$) is decreasing, because of “associate” formation. At higher absorbed UV-doses (λ = 254 nm) the ${\text{e}}_{\text{s}}^{-}$ yield is passing a sharp maximum by formation of TES–ethanol adducts, which are able likewise to emit electrons when excited. At prolonged irradiation the resulting photolytic products of TES–ethanol adducts are also able to emit electrons.The capability of the hormones: 17βE2, PRG and TES to eject electrons and the resulting metabolites, some of which can induce cancer, is discussed.     

Calorimetric characterization of 2′,3′-dideoxyinosine water solution

A study of 2′,3′-dideoxyinosine (ddI) stability and its interaction with human serum albumin (HSA) was carried out by differential scanning microcalorimetry DSC. Scan rate dependent and irreversible endothermic thermal degradation of ddI was analyzed with use of kinetic approach. Observed process could be interpreted in terms of simple first-order one step kinetic model. Moreover it was shown that ddI bound weakly to the human serum albumin and stabilized this protein.     

Separation characteristics of some phenoxy herbicides from aqueous solution

The adsorption and desorption characteristics of some phenoxy herbicides (CPA 2,4-D, and MCPA) from an aqueous solution on the active carbon materials (GAC, F-400) were studied. Adsorption equilibrium capacities of the phenoxy herbicides increased with a decrease in pH of the solution. Adsorption equilibrium isotherms were represented by the Sips equation. Kinetic parameters were measured in a batch adsorber to analyze the adsorption rates of the phenoxy herbicides. The internal diffusion coefficients were determined by comparing the experimental concentration curves with those predicted from the surface diffusion model and the pore diffusion model. The adsorption model based on the linear driving force approximation (LDFA) was used to simulate the adsorption behavior of the phenoxy herbicides in a fixed bed adsorber. Over 95 percent desorption of the phenoxy herbicides was obtained using distilled water.