Protection of immobilized sulfhydryl groups against autooxidation by alterations in their microenvironment

Immobilized sulfhydryl groups were prepared by partial thiolation of NH₂-glass beads. The microenvironment of the immobilized SH groups was varied by different chemical modifications of neighboring NH₂ groups. Introduction of a strong charge in the surroundings of immobilized sulfhydryls results in their dramatic stabilization against autooxidation. This effect is due to the salting of O₂ from the surface microlayer of the thiolated beads.     

An electrothermal vaporization unit with axially focusing convection upstream. Part II: Modeling of the condensation process

A model is presented that describes quantitatively the condensation of analytes in pico- and nanogram masses sampled with electrothermal vaporization (ETV). It presumes that the analyte vapor condensation of such low amounts occurs mainly heterogeneously, predominantly on growing carbon particulates originating from the graphite furnace before the analyte vapor achieves saturation via cooling. The model regards the coagulation of carbon particles and the diffusion of analyte atoms. The criterion whether or not an analyte atom sticks to a colliding particle is chosen as a function depending on its temperature and on the common GFAAS pretreatment temperatures. Heterogeneous condensation of six analytes with different volatilities, Ag, Cu, Fe, Ni, Mn, and Pb, is calculated for the ETV unit with an axially focusing convection upstream described in Part I. Modifier effects are taken into account. The results are compared to measured data.     

New aspects of thermal analysis,Part I. Resolution of DSC and means for its optimization

The definitions of the temperature resolution, the so-called resolution of DSC instruments given in literature are discussed. A new definition of the resolution for DSC instruments is presented and outlined. The main characteristic introduced in this new definition is a minimum between two caloric events as a prerequisite of an existing resolution. Possible candidates of test substances have been evaluated. The oligomer n-hexatriacontane is revealing an interesting phenomenon, namely a lambda transition which is in the peak temperature only 2 K lower than the melting temperature of 76°C. The substance was selected as an ideal test substance for the quantification of the resolution of DSC instruments. The lambda transition is a second order process which may reach under certain conditions the saturation of the occurring molecular dislocation within 0.2 K, and after saturation the heat flow rate drops sharply down. Investigations concerning the main characteristics of n-hexatriacontane in respect to the temperatures of transition (lambda transition and melting), to the involved enthalpies, and to the resolution factors were performed as functions of the sample mass and the heating rate. The importance of relevant evaluation procedures increasing the resolution factors of DSC curves are discussed and these procedures are integrated into the testing of the resolution. The necessity for widening the experimental scope from instruments to evaluation procedures is forced by the existence of instruments with built-in signal treatments based on electronic devices and software procedures. A comparison with literature data is outlined for all of the mentioned characteristic values of n-hexatriacontane. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of protected peptides from the human IgG1 hinge region on PEG support using disulfide bond synthons and alkaline or enzymatic detachment

Peptides from the hinge region of human IgG1 are potential defined carriers of synthetic immunogens. Their synthesis was carried out on the soluble support—PEG-OMe 2000 using disulfide bond synthons. The loading capacity of the polymer was increased twofold by anchoring the lysine as a simple branching unit. The amino acid leucine was used as an enzymatically cleavable linker. Peptide detachment from the polymer was performed either by classical ester bond saponification or newly by peptide bond cleavage catalyzed by thermolysin in water.     

Magnetic behavior of copper diethyldithiocarbamate at low temperatures: A reinvestigation

The title compound, Cu(S₂CNEt₂)₂, behaves at low temperatures (1–20 K) as a normal spin-1/2 molecule, with 〈g〉 =2.06 and the Curie-Weiss θ = +0.25 K. This result contradicts an earlier investigation that led to the suggestion that the crystallographically-occurring dimers are coupled ferromagnetically.     

Vibrational and high pressure conformational studies of 1,1,2-trichloroethane

The infrared spectra of 1,1,2-trichloroethane were recorded from 4000 to 50 cm^?1 in the vapour and liquid states. Additional spectra above 200 cm^?1 of the low temperature crystal and of two crystalline solids, prepared by compressing the sample in a diamond anvil cell, were obtained. Also, infrared spectra of the liquid and of the compound dissolved in CS₂ were recorded at increased pressures. Raman spectral data of the liquid (including polarization measurements) and of the low temperature crystal were obtained.The fundamental frequencies for each of the two conformers, C₁ and C_s, were assigned and the results checked by normal coordinate analysis. The same diagonal and off-diagonal force constants were employed for the two conformers and the force fields were derived by means of a least squares refinement, including data for chloroethane, 1,1-dichloroethane and various deuterated species. A standard deviation of 3 % was obtained in the final fit.From the changes in relative intensities for infrared bands belonging to the C₁ and C_s conformers with increasing pressure, the volume differences (ΔV¯between the conformers were determined in CS₂ solution and in the pure liquid.     

An Electrostatic Bond Energy Model for Enthalpies of Formation of Chloroalkanes in Gaseous States

An electrostatic bond energy model is formulated to fit the enthalpies of formation and dipole moments of the alkanes and chloroalkanes. In this model, the charge distributions are calculated by an electrostatic approach similar to the "MSE" method, and the enthalpy of formation of a molecule is the sum of the bond energy terms plus the electrostatic energy of the interactions between the charges on all atoms. All parameters of this model are obtained by parameterization. The calculated dipole moments for 13 chloroalkanes and enthalpies of formation for 19 alkanes and non-geminal chloroalkanes agree with the determined values very well. To calculate the enthalpies of formation of geminal chloroalkanes, a correction mainly attributed to the van der Waals interactions in the geminal substituted group, about 24 kJ/mol per pair of geminal chlorine atoms, is introduced.     

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.