Low-frequency vibrations of molecular solids: XV. Globular molecule 1,2-dichloroethane

The far infrared and Raman spectra of polycrystalline 1,2-dichloroethane and 1,2-dichloroethane-d₄ for the low temperature modification have been measured from 450 to 33 cm⁻¹ at various temperatures from −100 to −182°C. Raman spectra of the high temperature crystalline modification for both samples were also investigated. The Raman data are in conflict with those previously reported. Assignments are made for the lattice vibrations in terms of the crystallographic unit cell C_2h⁵ (P_21/c) with two molecules per unit cell. The spectra of the high temperature modification are consistent with those expected for orientationally disordered crystals.     

Large-scale synthesis of high purity “Phos reagent” useful for oligonucleotide therapeutics

A large-scale, cost-effective, and environmentally clean synthesis of high purity 2-cyanoethyl-N,N,N′,N′-tetraisopropylphosphorodiamidite (Phos reagent) has been accomplished on a commercial scale. Treatment of PCl₃ with diisopropylamine followed by 3-hydroxylpropionitrile furnished the Phos reagent in excellent yield. The ³¹P NMR of the Phos reagent prepared at large-scale show consistent purities >99% when several key factors are controlled. These controlling factors include sourcing high purity key raw materials, identification and elimination of critical impurities, stability and storage of Phos reagent.     

Dilactams. Synthesis of nonsymmetrical dibenzodiazocinediones

We report the first examples of nonsymmetrical dibenzodiazocinediones, mono-, di-, tri- and tetra-substituted in the aromatic rings including a benzo pyridino diazocine, by a new short method without the requirement of protection. The procedure involves conversion of an anthranilic acid to its sulfinamide lactone followed by direct heating with a different N-alkylanthranilic acid.     

Multicomponent analysis in luminescence spectroscopy

Multicomponent analysis of absorption spectra (infrared or electronic spectra) by factor analysis is a suitable method to use. The algorithm of factor analysis is now available for luminescence spectroscopy. The first possibility, as in absorption spectroscopy, is to determine pure components emission spectra for a unique set of spectra of mixtures in overdetermined conditions. On the other hand, it is also possible to extract pure components emission and excitation spectra of the only data corresponding to the 3D fluorescent spectrum of a single mixture. The results are evaluated in respect to noise level and concentrations ratio on both simulated and real spectra.     

Conformation of non-aromatic ring compounds: Part 77. The molecular structure of gaseous 1,1-dimethylcyclohexane; an electron diffraction study

The gas-phase molecular structure of 1,1-dimethylcyclohexane has been investigated by the electron diffraction technique. The results confirm the prediction of valence force calculations, viz., axial substitution causes a flattening (Φ_av = 51.7°) of the chair form of the cyclohexane ring.     

Shinsonefuran, a cytotoxic furanosesterterpene with a novel carbon skeleton, from the deep-sea sponge Stoeba extensa

Shinsonefuran, a cytotoxic sesterterpene with a novel carbon skeleton, was isolated from the deep-sea sponge Stoeba extensa. The gross structure and relative stereochemistry of shinsonefuran were determined by spectral and chemical methods. In addition, relative stereochemistry of halisulfate 7, previously reported from a marine sponge Coscinoderma sp., was revised. Shinsonefuran exhibited cytotoxicity against HeLa cells with an IC₅₀ value of 16 μg/mL.     

Utility of 4,6-dichloro-2-(methylthio)-5-nitropyrimidine. Part 2: Solution phase synthesis of tetrasubstituted purines

A simple synthesis of tetrasubstituted purines is disclosed based on the solution phase elaboration of 4,6-dichloro-2-methylthio-5-nitropyrimidine. One-pot sequential C4 and C6 chloride substitution by secondary and primary amines yields 4,6-diamino-2-methylthio-5-nitropyrimidines. mCPBA-mediated oxidation of the methylthio moiety to the corresponding sulfone allows facile substitution at the 2-position. CrCl₂ assisted reduction of the nitro group, followed by acid catalyzed orthoester cyclization, then provides novel tetrasubstituted purines not accessible by other methods.     

Electrochemistry of capillary systems with narrow pores. I. Overview

In capillary systems with narrow pores the Helmholtz electrochemical double layer located at the pore wall extends over the entire cross section of the pores. It loses its character as the “charge on the wall”. It will be shown that not only the electrokinetic phenomena but also the electrical conductivity and the dialysis potential of membranes with narrow pores can be understood from the same point of view, namely: the electrolyte solution in the pores of a membrane with narrow pores is considered to be an approximately homogeneous solution in contact with immobilised charges located at the pore wall. In this case the electrochemical equations contain the fixed ion concentration as a parameter instead of the ζ potential. This makes it possible to describe quantitatively to a good approximation data on the electroosmosis, the electrical conductivity, the streaming potential and the dialysis potential taken from the literature, as well as results of our own measurements, by using a single membrane constant.     

New methods for spectrometric peak purity analysis in chromatography

Simple methods for peak purity analysis in chromatography are proposed for accurately assaying the chromatographic or electrophoretic process by spectroscopy. With these methods, the purity at each point of a chromatographic peak containing an unknown type and number of components can be detected and visualized. The ‘absorbance (A) diagram' is constructed by plotting the absorbance values of different wavelengths against each other. When only straight lines are obtained for different wavelength combinations, only one component was detected in the corresponding peak. Bent curves in the A diagrams mean that at least two components were registered. Straight lines in the absorbance difference quotient (ADQ) diagrams indicate that two components occur in the corresponding peak. Bent curves signify that at least three components were registered. The new methods are demonstrated using the HPLC technique for the separation of chlorogenic acid and epicatechin. Integral A and ADQ diagrams and the corresponding mean diagrams complete the new concept.     

Carbanion cyclisation of esters. Part 2: Enantiospecific construction of the tricyclic framework of the marine sesquiterpenes, spirodysins

Enantiospecific construction of the bicyclo[4.3.0]nonan-8-one 17 employing a lithium and liquid ammonia mediated carbanion cyclisation of the δ-methyl-δ,ε-unsaturated ester 13, and its elaboration to the tricyclic framework of the marine sesquiterpenes spirodysins are described.     

Influence de la taille du cycle sur le mecanisme de l'acetolyse de p-bromobenzenesulfonates de cycloalkylmethyle et de cycloalkenylmethyle

Cycloheptylmethyl brosylate (1b) and cyclooctylmethyl brosylate (1c) undergo acetolysis at 80°, about four times faster than isobutyl brosylate; this acceleration appears to be due to β-hydrogen participation. 4-Cycloheptenylmethyl brosylate (2b) and 4-cyclooctenylmethyl brosylate (2c) undergo acetolysis at 80°, with double bond participation, 250 and 350 times faster than isobutyl brosylate, respectively, the major products being endo 2-bicyclo[3.2.1]octyl acetate 8a and endo 2-bicyclo[3.3.1]-nonyl acetate 11a. Acetolysis of 3-cyclohexenylmethyl brosylate (2a) leads (without participation) to 3-cyclohexenylmethyl acetate (7).     

Photoelectron spectra of vinyl- and 1-alkynylgermanes and stannanes

Primary vinylic and acetylenic germanes and stannanes, synthesized by a chemoselective reduction of the corresponding trichloro derivatives, were investigated by ab initio quantum chemical methods and photoelectron spectroscopy. In particular, the PE spectra display very well-resolved bands which show the increasing destabilizing effect of 14 group heteroatom α-substitution of double or triple carbon–carbon bonds.     

Determination and fractionation of sulphur in a contaminated dredged sediment

Conversion of sulphur compounds in reduced, contaminated sediments that are brought in upland conditions may largely affect the potential mobility of heavy metal contaminants. We applied selected methods for the determination of total sulphur and sulphur fractions in a contaminated sediment in the reduced state and after gradual drying and oxidation during 1 month. Dry ashing, followed by ion chromatographic detection, was reliable for the determination of total sulphur. Good recoveries were obtained in both reference samples and spiked samples. Total sulphur was 14.5±0.6 g kg⁻¹ relative to dry sediment. Wet chemical methods that involve the determination of acid-volatile, Zn–HCl-reducible, chromium-reducible, acetone-soluble and HI-reducible sulphur were used to estimate specific sulphur forms. Results for acetone-soluble sulphur were to high and not consistent with results for other fractions. Major part of sulphur in the sediment (90%) was inorganic. Sulphides were converted partially to sulphate and to intermediary oxidised sulphur compounds upon oxidation of the sediment. The results suggested that the intermediary oxidised sulphur pool in the reduced sediment (2.5 g kg⁻¹) mainly consisted of pyrite, that was not converted during drying and oxidation. No significant changes in organic sulphur were detected.     

Gas phase characterization by photoelectron spectroscopy of unhindered α-heterosubstituted germylenes

Two unhindered α-heterosubstituted (O and S) cyclic germylenes have been generated and characterized by the combination of flash vacuum thermolysis of stable germacyclopentenes and ultraviolet photoelectron spectroscopy. This coupling associated with ab initio calculations with the hybrid functional B3LYP and the 6-311G(d) basis set allows to predict the electronic properties of the generated germylenes. The thermodynamic stabilization of these reactive molecules by electronic delocalization of the heteroatom π lone pairs within the 4π orbitals of the germanium atom is clearly shown.     

Electrochemistry of capillary systems with narrow pores. II. Electroosmosis

Manegold and Solf have reported systematic deviations of the electroosmotic properties of collodion membranes with narrow pores from predictions based on the Helmholtz–Smoluchowski model. To interpret the electroosmotic data quantitatively it is necessary to replace the assumption of the Helmholtz–Smoluchowski model that the thickness of the electric double layer is small compared with the pore radius by a new assumption. We have assumed that the counter ions are distributed homogeneously in the pore fluid. In Part I of this series of contributions, equations have been given describing the electroosmotic properties of a membrane with narrow pores based on the new assumption. These equations are derived here in detail and are applied to an analysis of the experimental data given by Manegold and Solf.     

Hydrogen bond studies 70. ab initio calculations of some properties of water molecules in the free state and in solid hydrates

Equilibrium geometry, infrared frequencies and intensities, and electrostatic field gradients have been calculated for the free water molecule and water molecules in solid hydrates. The calculations have been performed within the MO-LCAO framework, using Gaussian expansions for the molecular orbitals. The values so obtained are compared to experimental values and found to be in good qualitative agreement.     

Heteroatom derivatives of indene: V. Vibrational spectra of benzimidazole

Infrared and Raman measurements for benzimidazole are presented and discussed, including its argon-matrix infrared spectrum. To assist in the assignment, benzimidazole's harmonic force fields for the 321G* and 631G* levels were scaled by scaled factors derived by fitting the respective computed force fields of other indene derivatives to previously reported experimental vibrational frequencies. Comparison to the best set of experimental wavenumbers, usually taken from the matrix, shows mean 321G* and 631G* deviations of 7.0 and 5.8 cm⁻¹ for the planar modes, and 14.0 and 6.8 cm⁻¹ for the nonplanar modes, respectively, with much of the error residing in imino-hydrogen group modes. Standard entropies are derived with the matrix wavenumbers and the methods of statistical mechanics. An attempt to determine standard entropies by calorimetric methods was unsuccessful. The triple-point temperature T_tp and enthalpy of fusion Δ¹_crH_m only are reported.     

Electrochemistry of capillary systems with narrow pores III. Electrical conductivity

The extension of the Teorell–Meyer–Sievers theory of the dialysis potential to a general theory of capillary systems with narrow pores outlined in Part I of this series of publications has been applied to electroosmotic phenomena in Part II. In this Part, the electrical conductivity, including the electrical convection conductivity, will be treated in terms of the new theory. The corresponding equations already referred to in Part I are derived. In addition, results of measurements of the electrical conductivity of collodion membranes with graded porosity and graded electrochemical activity in aqueous KCl solutions of different concentrations are reported. They are used to test the new theory. It will be shown that it is possible to determine the fixed ion concentration A of the membranes by using electrical conductivity data. The theory predicts that the value of A should be identical with the `selectivity constant' of the Meyer–Sievers theory of the dialysis potential. This prediction will be checked in Part IV of this series of contributions.     

Seventeen new 14- and 15-crown-formazans: their synthesis and evaluation in spectrophotometric determination of lithium

A number of new crown-formazans with 14 and 15 membered rings have been synthesized, characterized and investigated as selective spectrophotometric chelating agents for lithium. The effect of sodium ion concentration on the background lithium signal was studied. A comparative study for the sensitivity of these new crown-formazans in spectrophotometric determinations was studied and compared with those reported previously. The three new 14- and 15-crown-formazans 4a–c containing the pyridyl N-oxide at the formazyl carbon showed the highest selectivity to lithium determination in the presence of sodium ion.     

Multielemental speciation of As, Se, Sb and Te by HPLC-ICP-MS

An anion exchange HPLC-ICP-MS procedure allowing the simultaneous multielemental speciation analysis of arsenic, selenium, antimony and tellurium has been developed. Four arsenic species (As^III, As^V, monomethylarsonic acid and dimethylarsinic acid), two selenium species (Se^IV and Se^VI) may be determined in a single run as well as one antimony (Sb^V) and one tellurium species (Te^VI). Alternatively Sb and/or Te may be used as internal standards for As and Se speciation studies. Optimisation of ICP-MS conditions led to satisfactory relative (0.01 (Sb^V) to 1.8 (Se^VI) ng ml⁻¹) and absolute detection limits (1–180 pg). Reproducibility ranged from 3.1 to 5.6% and the linearity was verified in the 0–200 ng ml⁻¹ range.