Electric field tunability of nuclear and electronic spin dynamics due to the hyperfine interaction in semiconductor nanostructures

We present formulas for the nuclear and electronic spin relaxation times due to the hyperfine interaction for nanostructed systems and show that the times depend on the square of the local density of electronic states at the nuclear position. A drastic sensitivity (orders of magnitude) of the electronic and nuclear spin coherence times to small electric fields is predicted for both uniformly distributed nuclear spins and delta-doped layers of specific nuclei. This sensitivity is robust to nuclear spin diffusion.     

Reactions of transition metal compounds with macrocyclic alkadiynes : II. Cyclopentadienylnickel and dicobalt hexacarbonyl complexes retaining the macrocyclic alkadiyne structure unit

The macrocyclic alkadiynes 1,7-cyclododecadiyne, 1,7-cyclotridecadiyne, 1,7-cyclotetradecadiyne, 1,8-cyclotetradecadiyne, and 1,8-cyclopentadecadiyne react with [C₅H₅NiCO]₂ in boiling benzene to give the dark green tetrametallic derivatives (alkadiyne) (NiC₅H₅)₄ and with Co₂(CO)₈ in pentane at room temperature to give the dark red tetrametallic derivatives (alkadiyne)[Co₂(CO)₆]₂. The reactions of 1,7-cyclododecadiyne with [C₅H₅NiCO]₂ and Co₂(CO)₈ can also be made to give the crystalline bimetallic derivatives 1,7-C₁₂H₁₆(NiC₅H₅)₂ and 1,7-C₁₂H₁₆Co₂(CO)₆. The macrocyclic alkadiyne ring system is retained in all of these new complexes.     

A Bairstow's type method for trigonometric polynomials

Summary. We construct in this paper an analogous method to Bairstow's one, for trigonometric polynomials with real coefficients. We also present some numerical examples which illustrate this method. Received November 11, 1992/Revised version received May 13, 1993     

Neue Molekülverbindungen des β-1,2,3,4,5,6-Hexachlorcyclohexans

Eight new molecular compounds between -1,2,3,4,5,6-hexachlorocyclohexane (-HCH) and some heterocyclic salts (hydrochlorides of - and -picoline, 2,4,6-collidine, ,-bipyridine, isoquinoline, acridine, 9-phenylacridine, and 2,4,6-triphenylpyrylium perchlorate), with the molecular ratio 12, were synthesised and described by means of spectroscopic (IR, UV, NMR) and X-ray-diffraction methods. Some of the molecular compounds may be used for quantitative separation of the heterocyclic salts from complex mixtures.

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Lehrstuhl für Mineralogie.     

Solvent and salting effects on sample preparation for the determination of fenofibric acid in human plasma by HPLC-DAD

The solvent and salting effects induced on the sample preparation procedure applied to plasma samples containing fenofibric acid and 4-chlorophenyl-4′-hydroxyphenyl methanone (internal standard) are evaluated. Sodium chloride addition during a deproteinization step using both methanol and phosphoric acid influences the recovery of the analytes as well as the selectivity of the process. The chromatographic method allows high sample volume injection (500 μl) with the focusing of both analytes in the stationary phase. The synthesized high porosity octadecylsilica material allows a fast elution gradient at 4 ml/min flow-rate and a complete analysis within 7 min. UV-detection is made at 295 nm and quantitation limit in the 20 ng/ml concentration level can be achieved. The method can be successfully applied for bioequivalence studies on fenofibrate, administrated as prodrug (fenofibric acid represents its main active metabolite) in pharmaceutical formulations. The main parameters used in studying the retention behavior of the internal standard and FEFA were also estimated.     

PHOTOSENSITIZED FORMATION OF ASCORBATE RADICALS BY RIBOFLAVIN: AN ESR STUDY

Abstract— The riboflavin-sensitized photooxidation of ascorbate ion (HA^-) to ascorbate radical (A^-) was followed by electron spin resonance (ESR) spectroscopy in conjunction with oxygen depletion measurements. In air-saturated aqueous media, steady-state amounts of A^- are rapidly established upon irradiation. The ESR signal disappears within a few seconds after the light is extinguished–more slowly under constant irradiation as oxygen is depleted. No photooxidation was observed in deaerated media. Similar results were obtained with other flavins and when ascorbyl palmitate was substituted for HA^-. The effect of added superoxide dismutase, catalase, desferrioxamine, and singlet oxygen scavengers (NaN₃ and tryptophan) was studied, as was replacement of water by D₂O and saturation with O₂. The results are indicative of ascorbate free radical production via direct reaction between ascorbate ion and triplet riboflavin in the presence of O₂. While the presence of superoxide ion tends to reduce the steady-state concentration of A^-, competition from the reaction of HA^- with singlet oxygen is less apparent in this system (at HA^-≥ 1 m M ) than in the previously studied aluminum phthalocyanine tetrasulfonate-photosensitized reaction.     

Observation of Intact and Proteolytically Cleaved Amyloid-Beta (1–40)-Oleuropein Noncovalent Complex at Neutral pH by Mass Spectrometry

Mass spectrometry analyses carried out on mass spectrometers equipped with soft ionization sources demonstrated their utility in the assessment of the formation of noncovalent complexes and the localization of the binding sites. Direct analyses by mass spectrometry of the noncovalent complex formed in acidic and mildly acidic environments by amyloid beta (1–40) peptide and oleuropein have been previously described, and, in several studies, the absorption, metabolism, excretion, and the implications in the prevention and therapy of Alzheimer’s disease of oleuropein have been investigated. Our paper presents modifications of the method previously employed for noncovalent complex observation, namely, the amyloid beta (1–40) pretreatment, followed by an increase in the pH and replacement of the chemical environment from ammonium acetate to ammonium bicarbonate. The formation of noncovalent complexes with one or two molecules of oleuropein was detected in all chemical solutions used, and the amyloid beta (17–28) binding site was identified via proteolytic experiments using trypsin prior to and after noncovalent complex formation. Our results highlight the importance of further studies on the effect of oleuropein against amyloid beta aggregation.     

[3 + n] Cycloaddition Reactions: A Milestone Approach for Elaborating Pyridazine of Potential Interest in Medicinal Chemistry and Optoelectronics

During the last few decades, pyridazine derivatives have emerged as privileged structures in heterocyclic chemistry, both because of their excellent chemistry and because of their potential applications in medicinal chemistry and optoelectronics. This review is focused on the recent advances in [3 + n] cycloaddition reactions in the pyridazine series as well as their medicinal chemistry and optoelectronic applications over the last ten years. The stereochemistry and regiochemistry of the cycloaddition reactions are discussed. Applications in optoelectronics (in particular, as fluorescent materials and sensors) and medicinal chemistry (in particular, antimicrobials and anticancer) are also reviewed.     

Thin adsorbed films of a strong cationic polyelectrolyte on silica substrates

The adsorption of poly(diallyldimethyl ammonium chloride) (DADMAC) on planar silica substrates was examined as a function of ionic strength and pH. The study was carried out with reflectometry in an impinging-jet cell and complemented by atomic force microscopy (AFM) and ellipsometry investigations. The adsorption process is initially transport limited, whereby the adsorption rate increases somewhat with increasing ionic strength. This effect is caused by a simultaneous decrease of the hydrodynamic radius of the polymer. After a transient period, the adsorption process saturates and leads to an adsorption plateau. The plateau value increases strongly with increasing ionic strength. This increase can be explained by progressive screening of the electrostatic repulsion between the adsorbing polyelectrolyte chains, as can be rationalized by a random sequential adsorption (RSA) model. The adsorbed amount further increases with increasing pH, and this effect is probably caused by the corresponding increase of the surface charge of the silica substrate.     

Pyridazine and phthalazine derivatives with potential antimicrobial activity

Fifteen new pyridazine and phthalazine derivatives were prepared (in good to excellent yields) and tested in vitro as antimicrobial compounds. All the compounds have proved to have a remarkable activity against Gram positive germs, the results on Sarciria Luteea being spectacular. Correlation structure ‐ biological activity have been done. Stereo‐ and region‐ chemistry involved in these reactions are discussed.