Infrared optical constants, dielectric constants, molar polarizabilities, transition moments, dipole moment derivatives and Raman spectrum of liquid cyclohexane

Previous studies have been done in this laboratory focusing on the optical properties of several liquid aromatic and aliphatic hydrocarbons in the infrared. The current study reports the infrared and absorption Raman spectra of liquid cyclohexane. Infrared spectra were recorded at 25 °C over a wavenumber range of 7400–490 cm⁻¹. Infrared measurements were taken using transmission cells with pathlengths ranging from 3 to 5000 μm. Raman spectra were recorded between 3700 and 100 cm⁻¹ at 25 °C using a 180° reflection geometry. Ab initio calculations of the vibrational wavenumbers at the B3LYP/6311G level of theory were performed and used to help assign the observed IR and Raman spectra. Extensive assignments of the fundamentals and binary combinations observed in the infrared imaginary molar polarizability spectrum are reported. The imaginary molar polarizability spectrum was curve fitted to separate the intensity from the various transitions and used to determine the transition moments and magnitudes of the derivatives of the dipole moment with respect to the normal coordinates for the fundamentals.     

In vitro release of citrate anions intercalated in magnesium aluminium layered double hydroxides

Layered double hydroxides (LDHs) present a potential application in medicine, as matrices, when intercalated with organic anions of pharmaceutical interest. Once encapsulated, the drug can be released at a rate, depending on the pH of the solution, which may be due to the destruction of the layer by acid attack.The main objective of this work was to evaluate Mg(II)–Al(III)-LDHs for the sustained release of citrate. The citrate intercalated LDHs were prepared by the constant pH coprecipitation technique followed by hydrothermal treatment. Materials were characterized by PXRD, FT-IR, SEM, specific surface area, mean pore diameter analysis, and in vitro release. The release studies were made in a dissolution system that simulates in vivo conditions, obeying the sink conditions. The amount of citrate released, which was determined by HPLC, was 63.8% within 12 h. The total amount released was less than that observed with physical mixture (100%). Thus, these systems seem to be promising for the sustained release of citrate. The data followed the Higuchi square root law (r>0.98) during the release.     

Acceleration of bromide mediated benzoylperoxide oxidations of secondary alcohols in aqueous organic solvents

The efficiency of the bromide mediated benzoylperoxide oxidation of 2° alcohols to ketones was greatly improved by the addition of water. The aqueous oxidation protocol allows also the direct use of off-the-shelf benzoylperoxide reagent without an otherwise necessary and potentially dangerous drying procedure. The oxidation of cyclopentanol, cyclohexanol, 1-phenyl-ethanol and three menthol isomers occurred in good to excellent yields. The oxidation reaction tolerated N,N-dimethylacetamide (DMA) as the solvent, which resulted in a slightly lower oxidation rate than acetonitrile. Chemoselective oxidation of vicinal diols to α-hydroxy ketones did not succeed under the aqueous organic conditions employed as over-oxidation and bromination side-reactions were observed. The impact of water content, solvent, oxidant source and type of alcohol substrates employed was investigated.     

Boundedness and blowup for nonlinear degenerate parabolic equations

The author deals with the quasilinear parabolic equation _ut=[u^α+g(u)]Δu+bu^α+1+f(u,∇u)$u_t=[u^{\alpha }+g\left(u\right)]\Delta u+b{u}^{\alpha +1}+f(u,\nabla u)$ with Dirichlet boundary conditions in a bounded domain Ω$\Omega$, where f$f$ and g$g$ are lower-order terms. He shows that, under suitable conditions on f$f$ and g$g$, whether the solution is bounded or blows up in a finite time depends only on the first eigenvalue of −Δ$-\Delta$ in Ω$\Omega$ with Dirichlet boundary condition. For some special cases, the result is sharp.     

Optical constants, dielectric constants, molar absorption coefficients, molar polarizability, vibrational assignment and transition moments of liquid iodobenzene between 4000 and 400 cm(-1) at 25 degrees C

This paper reports the complex refractive index, molar absorption coefficient and imaginary molar polarizability spectra of liquid iodobenzene at 25 degrees C. The imaginary molar polarizability spectrum was fitted with 184 classical damped harmonic bands to determine the integrated intensity of the individual transitions. The standard deviation of the fitted spectrum from the experimental spectrum is 0.024 cm(3) mol(-1), and the R(2) value of the fit is 0.9968 indicating that the fitted spectrum is an accurate representation of the experimental spectrum. The dipole moment derivatives with respect to the normal coordinates and transition moments were determined for 26 of the 30 fundamentals. The total intensities of the in-plane and out-of-plane fundamentals were compared to benzene and other monosubstituted benzene derivatives using the F-sum rule. It was found that the total intensity of the out-of-plane fundamentals is essentially the same for the different compounds while the total intensities for the in-plane fundamentals varies according to the electronegativities of the substituents.     

Liquid-phase force field and dipole moment derivatives with respect to internal coordinates of benzene

This paper presents an analysis of the infrared vibrational intensities found for C(6)H(6), C(6)D(6) and C(6)H(5)D in the liquid phase, motivated in part by the quite marked intensity differences between the fundamentals of C(6)H(6) and C(6)D(6) in the liquid, and between corresponding vibrations in the liquid and gas phases. The analysis is carried out under the harmonic approximation and results from a determination of the force field for liquid C(6)H(6), C(6)D(6) and C(6)H(5)D. The force constants for the liquid-phase are presented and compared to those in the literature for the gas-phase. Previously reported experimental intensities are used along with the eigenvectors of the force field analysis to determine the dipole moment derivatives with respect to symmetry and internal coordinates. The dipole moment derivatives with respect to internal coordinates obtained are partial differentialmicro/ partial differentials=0.38+/-0.02DebyeA(-1), partial differentialmicro/ partial differentialt=0.24+/-0.01, partial differentialmicro/ partial differentialbeta=0.26+/-0.01, and partial differentialmicro/ partial differentialgamma=0.64+/-0.03DebyeA(-1). There is very little difference between the dipole moment derivatives with respect to internal coordinates obtained from non-linear least squares fitting of the two D(6h) isotopomers and those obtained from non-linear least squares fitting of the three isotopomers. The results show that there is significant intensity sharing in the CH stretch region of C(6)H(5)D between the fundamental and combination bands.     

Analysis of Local Anesthetics in Biological Samples via Kinetically Calibrated Liquid-Phase Solvent Bar Micro-Extraction Combined with HPLC

In this study, a liquid-phase solvent bar micro-extraction technique was used to investigate both the extraction and back-extraction processes of the target analyte. A novel concentration curve method and a classic time curve method, used under the same experimental conditions, verified the symmetry between the extraction process (target analyte moves from sample matrix to the organic solvent-based extraction phase) and the back-extraction process (target analyte moves from organic solvent to the sample matrix), providing the basis to use the target analyte in the back-extraction process to calibrate its extraction process. A quantitative calibration can be achieved using back extraction on the target analyte from the blank sample matrix in the organic solvent. Information from the process of back extraction of the target analyte, such as the time constant a, can be directly used to calculate the initial concentration of the target analyte in the sample matrix. This new kinetic calibration method employs a liquid-phase solvent bar micro-extraction technique combined with high-performance liquid chromatography with a diode array detector (HPLC-DAD) and was successfully used to analyze three local anesthetics in biological samples; it extends the application of the kinetic calibration to HPLC-DAD and establishes a novel, simple and accurate method to determine the concentration of the free drug in biological samples and its protein-binding ratio.

     

Subset-Sum Representations of Domination Polynomials

The domination polynomial D(G, x) is the ordinary generating function for the dominating sets of an undirected graph G = (V, E) with respect to their cardinality. We consider in this paper representations of D(G, x) as a sum over subsets of the edge and vertex set of G. One of our main results is a representation of D(G, x) as a sum ranging over spanning bipartite subgraphs of G. Let d(G) be the number of dominating sets of G. We call a graph G conformal if all of its components are of even order. Let Con(G) be the set of all vertex-induced conformal subgraphs of G and let k(G) be the number of components of G. We show that $$d(G) = \sum \limits_{H\in{\rm Con}(G)}2^{k(H)}$$ .