The substitution structure of nitroethylene

The ^15N- and ¹⁸O-species of nitroethylene have been assigned in natural abundance using microwave-microwave double resonance techniques. Additional transition frequencies have been measured for previously assigned isotopic species in order to have the same set of transitions for all species. The ground state rotational constants of nitroethylene, all eight mono-, three di- and two trisubstituted species have been used to determine the complete substitution structure. The results of the conventional Kraitchman-Constain method are compared to those of a least-squares method.     

Influence of nanoparticle surface functionalization on the thermal stability of colloidal polystyrene films

The installation of large scale colloidal nanoparticle thin films is of great interest in sensor technology or data storage. Often, such devices are operated at elevated temperatures. In the present study, we investigate the effect of heat treatment on the structure of colloidal thin films of polystyrene (PS) nanoparticles in situ by using the combination of grazing incidence small-angle X-ray scattering (GISAXS) and optical ellipsometry. In addition, the samples are investigated with optical microscopy, atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). To install large scale coatings on silicon wafers, spin-coating of colloidal pure PS nanoparticles and carboxylated PS nanoparticles is used. Our results indicate that thermal annealing in the vicinity of the glass transition temperature T(g) of pure PS leads to a rapid loss in the ordering of the nanoparticles in spin-coated films. For carboxylated particles, this loss of order is shifted to a higher temperature, which can be useful for applications at elevated temperatures. Our model assumes a softening of the boundaries between the individual colloidal spheres, leading to strong changes in the nanostructure morphology. While the nanostructure changes drastically, the macroscopic morphology remains unaffected by annealing near T(g).     

Quantum chemistry predicted correlations between geometric isomerism (conformation) of -OH and =NH substituents and typical group frequencies of nucleic acid bases: cytosine

Results of a search for correlations between typical group mode frequencies and conformation of -OH and =NH substituents is reported. The study is based on quantum chemical data (HF/6-31G (d, p) and MP2 (full)/6-31G (d, p) approximations) of 13 isomers of cytosine. It is closely related to investigations of stability and energetics of all isomers of the more common nucleic acid bases, which revealed correlations between conformation (geometric isomerism) of OH and =NH substituents on the one hand and conversion energies, relaxation of internal structural parameters, electric field gradients, etc. on the other hand. In the majority of cases alteration of conformation of these substituents is accompanied by systematic frequency shifts of stretching, in-plane and out-of-plane bending (torsional) modes conventionally assigned to such groups and by alteration of quantum chemically predicted estimates of harmonic valence force constants and structural parameters dominating the mode frequencies. For identification of group modes 'fractional' mass (other than 'natural' mass) isotope shifts of frequency and normal vectors proved useful. Likewise, estimation of effects of force constant and structural parameter alterations on frequency shifts by first order perturbation theory of the FG problem of partial structures contributed valuable insight into the origin of the shifts.     

Single crystal ERP and powder endor spectra of a five coordinated low-spin Co(II) schiff base complex: N,N'-ethylene-bis (salicylideniminato)-cobalt(II

The magnetic parameters g and A^Co of Cosalenpy doped in a Znsalenpy single crystal have been measured and the orientations of their principal axes with respect to the molecular structure have been determined. Furthermore, the hfs and quadrupole tensor of the axial nitrogen were obtained from powder ENDOR. Data are discussed using well-established theories.     

Chemoenzymatic Synthesis of a Glycolipid Library and Elucidation of the Antigenic Epitope for Construction of a Vaccine Against Lyme Disease

Lyme disease (LD) is the most common tick‐borne disease in Europe, North America, and Asia. The etiologic agents of LD are spirochetes of the group Borrelia burgdorferi sensu lato, which possess a lipid content of 25–30 % of the dry weight. The major glycolipid cholesteryl 6‐O‐acyl‐β‐D ‐galactopyranoside (ACGal), present in B. burgdorferi sensu stricto, B. afzelii, and B. garinii, is a specific and highly prevalent antigen frequently recognized by antibodies in late‐stage LD. Here we report a convenient route for the chemical synthesis of ACGal by employing a combination of chemical synthesis steps with enzymatic transformations. This synthesized molecule was compared with bacterial extracts by immunoblots with patient sera, confirming the preserved antigenicity. Next, a glycolipid library derived from the native molecules with variations in the fatty acyl moiety and derivatives in which the cholesterol has been replaced was designed and synthesized. The chemical structures were confirmed by 1D and 2D NMR spectroscopy and mass spectrometry. The native and synthetic glycolipids were utilized in immunoblots to determine the epitope recognized by antibodies in patient sera. By this method we could demonstrate that galactose, cholesterol, and a fatty acid with a minimal chain length of four carbon atoms comprises the essential structure for recognition by antibodies. Finally, this finding allowed the synthesis of a functionalized ACGal with an ω‐mercapto group at the fatty acid and a facile protection and deprotection strategy. This antigenic hapten can be conjugated to a carrier protein to effect immunization against Lyme disease.     

HPTLC-Bestimmung von Paracetamol im Serum

Ohne Zusammenfassung

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Determination of paracetamol in serum by HPTLC

     

Magnetic behavior of the oxide spinels: Li0.5Fe2.5−2x Al x Cr x O4

In order to study the effect of substitution of Fe³⁺ by Al³⁺ and Cr³⁺ in Li_0.5Fe_2.5O₄ on its structural and magnetic properties, the spinel system Li_0.5Al _x Cr _x Fe_2.5?2x O₄ (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and ⁵⁷Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al³⁺ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mössbauer spectra (x>0.5).     

联苯胺分光光度法测定食盐中碘含量

基于在盐酸介质中,碘酸钾氧化联苯胺使其显色,提出了光度法测定食盐中微量碘的方法。在40℃的水浴中,当2 mol.L-1盐酸溶液用量为1.00 mL0、.42 g.L-1联苯胺溶液用量为0.80 mL时,方法的线性范围为100~1 400μg.L-1,最大吸收波长在425 nm处,表观摩尔吸光率为1.4×105L.mol-1.cm-1。用于测定加碘食盐中碘含量的测定,回收率在97.5%~101.2%之间,相对标准偏差(n=7)在0.9%~1.9%之间。     

Solution of the rotation-internal rotation problem of glyoxal type molecules by infinite matrix technique

A numerical solution, using a truncated matrix diagonalization is presented of the rotation-internal rotation problem of a semirigid molecular model consisting of two equivalent tops with C_s local symmetry. Starting from the classical hamiltonian various aspects of the isometrie group of this system are discussed. The coefficient of the energy matrix are calculated analytically and their asymptotic behavior is derived. Furthermore the selection rules and analytical expressions are given for electric dipole transition matrix elements and polarizability tensor matrix elements.     

Harmonic force constants of formic acid: ab initio results and the uniqueness problem of force fields derived from vibrational data

A complete set of harmonic force constants of formic acid (HCOOH) is calculated using a 6-31G basis set. It is used to determine a modified valence force field consistent with both ab initio results and vibrational data.