Synthesis of derivatives of ketocarboxylic acids by the decomposition of 1,4-cyclohexanedione monoethyleneketal hydroperoxide

The decomposition of 1,4-dihydroxy-1,4-dihydroperoxycyclohexane under the action of FeSO₄ and the decomposition of 1,4-cyclohexanedione monoethyleneketal hydroperoxide under the action of Fe^II salts in the presence of various ligands or under the action of Cu^II sulfate have been studied. A preparative method for the synthesis of derivatives of diketodicarboxylic or -functionally substituted ketocarboxylic acids from 1,4-cyclohexanedione monoethyleneketal has been developed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1231–1235, July, 1993.     

A configuration interaction study of phosphine using bonded functions

A computational study is made of the effect of basis set upon the energy, properties and inversion barrier of the phosphine molecule. The calculations are performed at both the SCF and CI level. The flexibility of the double zeta basis is discussed in the light of the results.     

Microenvironmental differences amongst micelles of various shapes and structures

Micelles of different amphiphiles adopt different shapes and internal packing arrangements in water, depending on their chemical structures and the conditions of the medium. Two microenvironmental features, namely the polarity and the microviscosity that the aggregate offers to a solubilized molecule, have been monitored using extrinsic fluorescence probes. While the differences between micelles of spherical and rod-like shapes are not always distinct, stacked micelles and peptide micelles offer distinctly lower polarity and higher microviscosity to solubilizates than the others.     

Preparative Separation and Analysis of Complex Mixtures of Leucomycins and Desmycarosyl Leucomycins Using HPLC and Mass Spectrometry

Composition and hydrolysis products of a biotechnical available complex of macrolides were analyzed by HPLC and ESI-CID-MSⁿ. Major components are leucomycin-type antibiotics (leucomycins A₁ (5), A₇ (3), A₉ (2), 9-desoxy-9-oxo-turimycin H₃ (4) and niddamycin B (6). Hydrolysis of the complex mixture yielded 9-, 13-isoforocidins (7, 8, 9, 11) and 9-oxo-forocidin (10). A preparative separation procedure was elaborated furnishing compounds 3 - 11 for semisynthetic experiments.Prof. Dr. Udo Gräfe deceased on 14.2.2003. For obituarity see: Schlegel B (2003) J Peptide Sci 9: 661–661.     

NMR determination of absolute site-specific natural isotope ratios of hydrogen in organic molecules. Analytical and mechanistic applications

It has been shown that the “internal” isotope distribution within a given molecular species at the natural abundance level is accessible by a new method, SNIF-NMR, which is based on deuterium NMR. Relative internal factors, R_i/j,have been defined which enable the isotope content of a given site, i, to be compared to that of another molecular site, j, taken as the reference. Several referencing methods intended to provide direct access to relative $\text{externals}$, T_i , and $\text{absolute}$, (D/H)_i , site-specific parameters, are now discussed from both the theoretical and the experimental points of view. In the $\text{intramolecular referencing method}$, which involves a time-consuming chemical transformation of the sample, the risk exists of more or leas systematic errors resulting from discriminating fractionation effects. However this technique offers, conversely, an interesting way of investigating kinetic isotope effects without the need for specific labelling. In spite of its lower spectral precision the $\text{external referencing method}$ has the advantage of being fast and less sensitive to systematic errois and may be used for direct rough routine determinations of the site-specific isotope contents. More precise results can be obtained, at the price of contaminating the sample, when an $\text{intermolecular reference}$ is added and signal heights are used, remembering however that the intensity parameters then have no strict physical meaning in terms of absolute isotope contents. The site-specific parameters, T_i and (D/H)_i thus accessible, provide new information on the mechanisms of the fractionation effects occurring in natural conditions and examples are considered.     

Description of the turbidity measurements near the phase transition temperature of poly(N-isopropyl acrylamide) copolymers: the effect of pH, concentration, hydrophilic and hydrophobic content on the turbidity

Absorbance values between 300 and 800 nm of aqueous solutions of poly(N-isopropyl acrylamide-co-itaconic acid-9.80), poly(N-isopropyl acrylamide-co-itaconic acid-52.05) and poly(N-isopropyl acrylamide)s containing Tegomer H-Si 2111 end groups and/or blocks were measured using a Shimadzu 160-A UV-visible spectrometer. Turbidities obtained from these absorbance values were used to interpret the macromolecular phase transition from a hydrophilic to a hydrophobic structure of the polymers. The effects of comonomer type and content, concentration of the solutions, pH and temperature on the coil-globule transition were discussed in terms of turbidity form factor, β related to size and shapes of particles and calculated by using the simplified form of Debye equation.The results presented in this work show that the presence of Tegomer H-Si 2111 (Si containing end groups and/or blocks) or high amount of itaconic acid (IA) in the chains prevent a collapse transition from hydrated extended coils to hydrophobic globules, which aggregate and form a separate phase (β<2). Furthermore, it was observed that in the case of concentrated solutions intermolecular hydrophobic interactions between isopropyl groups overcame the repulsive forces resulting from the ionized carboxylic acid groups of IA or surface active nature of Si containing hydrophobic groups (β>2). This stage of the transition corresponds to macroscopic phase separation after an intramolecular process.     

Modern Analysis

The important advances being made in modern analytical methods are indicative of the fundamental changes that are occuring in the theory and practice of “analytical chemistry”. “Information optimization” demands a new approach in teaching and research, and calls for the intergration of chemistry with other scientific and technical disciplines.     

Base-labile tert-butoxycarbonyl (Boc) group on phenols

Phenols are deprotected with weak bases from their tert-butoxycarbonyl (Boc) derivatives. Boc deprotection with bases can avoid side reactions during the deprotection with acids. We note the lability of the Boc to bases and are able to utilize it as a new cleavage condition for synthetic studies.     

Koordinative Verankerung von Nickelkomplexen an Hectorit-Schichtsilicaten mit Hilfe langkettiger Diphenylphosphinogruppen

Coordinative Anchoring of Nickel Complexes on Hectorite-Layer Silicates through long-chain Diphenylphosphine Groups The treatment of sodium and calcium hectorites with 2-diphenylphosphinoethyltriethoxysilane leads, by condensation of free hydroxyl groups, to functionalized layer silicates with long-chain diphenylphosphine groups onto which nickel chloride can be coordinated. In these modified hectorites the fourth coordination site of the tetrahedrally coordinated nickel is occupied by a labile solvent molecule. On the other hand, the complex bis(2-diphenylphosphinoethyltriethoxysilane)nickel(II) chloride prepared beforehand also reacts with sodium hectorite under condensation; but the square-planar coordination of the four stable ligands (two chloride and two phosphor atoms) is maintained. This finds its expression in a significant activity decrease in catalytic reactions as compared to the aforementioned products.     

Thermodynamic and spectroscopic properties of 2-pyrrolidinones. 2. Dielectric properties of 2-pyrrolidinone in binary mixtures

Dielectric permittivities of 2-pyrrolidinone - acetone, -dimethyl sulfoxide,-2-propanol, -dichloromethane and -water systems were measured as a function of mole fraction over the whole composition range at 30 and 50°C. The excess dielectric permittivities are predominantly negative for all the mixtures and the excess molar polarizations are negative except for 2-pyrrolidinone - water and 2-pyrrolidinone - dimethyl sulfoxide mixtures. The large negative excess quantities are indicative of the strong specific interactions between the like and unlike components of the solution mixtures.