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ABSTRACTDimethyl sulfide (DMS) contributes significantly to beer aroma. Malt contains considerable amounts of its oxidized form dimethyl sulfoxide (DMSO), the precursor of DMS during fermentation. Yet, detailed information regarding mechanisms of DMSO formation in malt is limited. Recently, hydrogen peroxide was suggested as a potential DMS oxidant in malt. The aim of this study was to characterize the reaction of hydrogen peroxide and DMS in buffered model solutions. Initially, hydrogen peroxide was identified in green malt using leuco crystal violet and horseradish peroxidase. Based on these findings the reaction of DMS with H2O2was investigated in buffered model solutions at varying temperatures and pH using response surface modeling (RSM). Significant amounts of DMSO were formed by H2O2mediated oxidation of DMS (∼0–41%), which was determined by temperature and hydrogen peroxide concentration (P≤ 0.003). The effect of the pH was insignificant (P≥ 0.4). Kinetics of DMS oxidation by H2O2(DMS:H2O2= 1:3) at 95°C followed a pseudo first order mechanism (k = 0.0041 min−1). Molecular oxygen was not capable of oxidizing DMS, whereas hydroxyl radical mediated DMS oxidation was faster than DMS oxidation aroused by H2O2. Potential reaction mechanisms and their relevance in DMS oxidation are discussed as a first approach to minimize DMSO levels in malt.

We studied the course of a primary HIV infection in a 54-year-old woman. Probably the source of infection was sexual intercourse, since other risks, such as i. v. drug use, acupuncture and transfusion were excluded. On admission she presented with fever, a maculopapular rash, and moderate enlargement of nuchal lymph nodes. At that time the anti-HIV 1,2 enzyme immunoassay was negative. However, the HIV-p24 Ag test, which was performed in every HIV screening in our laboratory, was positive. The suspicion of an acute HIV infection was supported by a positive HIV-cDNA-PCR and confirmed by Western blot after seroconversion. As additional finding, the blood smear showed abnormal white cell differential count, indicating viral infection. Aminotransferases were slightly increased, and antibodies to hepatitis B surface and core antigens demonstrated former hepatitis B infection. It is concluded that in this case the HIV-p24 Ag test proved its suitability for early diagnosis of an acute HIV infection. In case of testing blood donors, none of the compulsory sero-logical screening methods would have detected the HIV infection.

The synthesis of the aluminum carbide clusters (AlH)6(AlNMe3)2(CCH2C5H4FeC5H5)6 (1), containing an assembly of ferrocenylmethylene substituents, and (AlH)6(AlNMe3)2(CCH2Ph)6 (2) was carried out by the hydroalumination of FcC&tbd1;CH (Fc = ferrocenyl) and (PhC&tbd1;C)3Al·NMe3, respectively, with AlH3·NMe3. Compound 1 is made up of an Al−C framework with eight aluminum atoms occupying the corners of a rhombic cube while the six carbon atoms cap the faces of the cube. The reaction of (AlH)6(AlNMe3)2(CCH2Ph)6 (2) with FcC&tbd1;CH and PhC&tbd1;CH leads to the formation of (AlH)2(FcC&tbd1;CAl)4(AlNMe3)2(CCH2Ph)6 (3) and (PhC&tbd1;C)3Al·NMe3 (4), respectively. Reaction of 4 with AlH3·NMe3 results in the formation of 2.

Solid-state NMR provides unique possibilities to study insoluble or noncrystalline molecules at the atomic level. High-resolution conditions can be established by employing magic-angle spinning at ultrahigh magnetic fields. We discuss NMR methods that make use of these experimental improvements and allow for the study of multiply or uniformly [¹³C,¹⁵N]-labeled polypeptides and proteins. Recent biophysical applications are reviewed.

Considerable attention has been focused on developing a synthetic route to a carbon−nitrogen material with mechanical and thermal properties comparable or superior to those of diamond. To date, no substance with the desired C3N4 stoichiometry in a silicon-nitride crystal lattice has been reported. One of the principal difficulties in the pursuit of ultrahard carbon−nitrogen (CN) solids is the characterization of amorphous CN samples. We describe a solid-state NMR study of a paracyanogen-like solid utilizing ¹³C-¹⁵N adiabatic-passage Hartmann−Hahn cross-polarization (APHH-CP) to perform dipolar filtering and show that this method is well-suited for recoupling ¹³C-¹⁵N in network solids. In addition, high-frequency electron paramagnetic resonance (EPR) indicates a density of electron spins of approximately 1 × 10¹⁷ e^-/cm³. We conclude by discussing how NMR and EPR data may be useful for optimizing CN-polymer samples as potential precursors for ultrahard carbon nitrogen solids.

Abstract:  Chédiak-Higashi-Steinbrinck syndrome (CHS) is a rare autosomal recessive disorder which is usually lethal in early childhood. Diagnostic hallmark is the occurrence of giant inclusion bodies in peripheral leukocytes and their bone marrow precursors. We report on a 27-year-old female patient who was admitted for treatment of a skin abscess. She recovered after intravenous antibiotic treatment and surgical incision. Hematological investigation was initiated because of a persisting neutropenia of 15%, with a leukocyte count initially in the normal range but subsequent leukopenia. Case history revealed recurrent skin infections from childhood on, regularly requiring surgical intervention. One year prior to admission a neuropathy had been diagnosed, while a partial albinism had been known for years. Microscopic examinations of peripheral blood and bone marrow aspirate smears were diagnostic for CHS. Additionally, a secondary antibody deficiency was found. Normalization of the white blood cell count, including the differential count, was observed following initiation of G-CSF treatment. Functional assessment of phagocytosis and oxidative burst activity of granulocytes revealed normal results before and after stimulation with G-CSF, however, natural killer cell activity was only weak, with slight improvement after G-CSF treatment in vivo. Cytogenetic analysis showed a normal female karyotype. Although the haploidentical brother of the patient may serve as an allogeneic stem cell donor, transplantation has been postponed because of further deterioration of her already existing CHS-specific neurological impairment. Nevertheless, while receiving G-CSF maintenance treatment our patient experienced no further infectious episodes within 6 months after diagnosis of CHS.

A pulse sequence is described that leads to a broadband recoupling of the dipolar interaction in magic-angle-spinning solid-state NMR experiments of13C spins. The sequence is based on a combination of rotating frame and laboratory frame transfer periods. The recovered dipolar interaction is only weakly dependent on spectral parameters but is a faithful measure for the internuclear distances. Furthermore, a pure zero-quantum term is recovered (of the type found in static “spin-diffusion” experiments). This makes the pulse sequence particularly suited for incorporation into two-dimensional total through-space correlation experiments that deliver simultaneous information about all dipolar couplings in a single 2D experiment. It is found that the necessary decoupling from abundant protons is best performed in two steps: first, the strong homonuclear couplings between the high-γ spins are averaged by Lee–Goldburg irradiation and, second, the heteronuclear dipolar interaction is averaged by the combined application of an RF field to the low-γ spins and magic-angle sample spinning. Phase-inversion and amplitude attenuation in the rotating frame and refocusing pulses in the laboratory frame part of the pulse sequence are introduced to achieve an optimum chemical-shift offset-independence and for the suppression of unwanted double-quantum transitions. The design principles are explained in detail. Finally, the pulse scheme is applied to total-correlation spectroscopy of a uniformly labeled amino acid. The experimental cross-peak intensities are in qualitative agreement with the known crystal structure of the model compound.

An object-oriented programming environment for numerical simulation of magnetic resonance spectra is introduced and applied to NQR and NMR of quadrupolar nuclei. Using a Floquet approach it is possible to perform simulations of spin systems that are described by explicitly time-dependent Hamiltonians in full analogy to simulations of time-independent systems. Applications to magic angle spinning and double rotation are discussed.

Reaction of a new β-diketiminato derivative of scandium, LScBr2 (L = Et2NCH2CH2NC(Me)CHC(Me)NCH2CH2NEt2), with (C3H5)MgBr gave the unexpected scandium complex (LMgBr)2ScBr (1), whose structure was established by X-ray analysis, liquid and solid-state NMR, EPR, UV−vis, and magnetic measurements. Correlation of all results leads to the conclusion that the formal oxidation state of scandium in this complex is one (Sc(I)) having no unpaired electrons.