Kinetics of acrylamide/glutathione binding by fast atom bombardment and thermospray mass spectrometry

The kinetics of the binding of the neurotoxin acrylamide to the cysteine residue of glutathione has been studied. At 37 °C and pH 7.3 the second order rate constant has been determined to be 0.72 ± 0.06 mol^?1 dm³ min^?1 by thermospray mass spectrometry. The critical energy at pH 11.5 measured over the temperature range 10–37°C by fast atom bombardment mass spectrometry was measured as 24.6 kJ mol^?1.     

INCREASED ENERGY TRANSFER FROM PHYCOBILISOMES TO PHOTOSYSTEM II IN HIGH LIGHT ADAPTED Anabaena cylindrica

Excitation energy transfer from phycobilisomes to photosystem II in high-light adapted cells of Anabaena cylindrica was studied by fluorescence spectroscopy and compared to that of low-light adapted cells. Measurements were made on membrane fragments containing phycobilisomes, photosystem I and II, isolated in 0.75 M K-phosphate. Relative efficiency of 430 to 590 nm light in the excitation of F₆₈₀ chlorophyll fluorescence was compared in low and high light adapted cells, respectively. The values indicate that light energy absorbed by phycobilisomes is transferred to photosystem II antenna chlorophylls with higher efficiency in high-light adapted cells than in low-light adapted cells. Partial dissociation and uncoupling of energy transfer caused by low ion concentration were different in the membrane fragments isolated from the two kinds of cells and indicated a higher aggregation state of pigment-protein complexes of phycobilisomes in high-light adapted A. cylindrica cells.     

Mercerization of primary wall cellulose and its implication for the conversion of cellulose I→cellulose II

The mercerization of homogenized primary wall cellulose extracted fromsugar beet pulp was investigated by transmission electron microscopy (TEM),X-ray diffraction together with ¹³C CP-MAS NMR, and FT-IR spectroscopy.For samples resulting from acid extraction, mercerization began at 9% NaOH, whereasfor samples purified by alkaline treatment, the mercerization started at 10%NaOH. The change in morphology when going from cellulose I to cellulose II wasspectacular, as all the microfibrillar cellulose morphology disappeared duringthe treatment. This change in morphology was very drastic as soon as the NaOHconcentrations were increased beyond 8 and 9% for the acid and alkalinepreparedsamples, respectively. On the other hand, the conversion was found to be moreprogressive in terms of increasing NaOH concentration when the transformationwas analyzed by X-ray diffraction or spectroscopy. Our observations of themercerization of isolated cellulose microfibrils are consistent with theconceptof cellulose microfibrils made of parallel chains in cellulose I and crystalsofcellulose II consisting of antiparallel chains.     

Theoretical study of the interaction of molecular oxygen with copper clusters

A new method based on frontier orbital theory has been used to investigate the binding site of molecular oxygen to neutral and anion copper clusters. It has been shown that one can make useful predictions of the binding sites based on the knowledge of the donor local reactivity of the cluster using the condensed Fukui function, f(-)(Ff). In this way, it was found that Cu(3), Cu(5), and Cu(5)(-) have the highest reactivity toward molecular oxygen.     

Production of232Pa from thorium

A procedure is described for the accelerator production of²³²Pa and its isolation in radiochemically pure form, suitable for isotope tracing of protactinium/thorium chemical separations.     

Polymerization studies on allylic compounds. III. α(substituted methyl)styrenes

The free-radical polymerization of a series of α-(substituted methyl)styrenes was investigated. These compounds were found to be inactive in homopolymerizations but copolymerized with methyl methacrylate and styrene with a retarding effect. Copolymerization characteristics were followed by rate and viscosity measurements.     

Characterization of n-butyl acrylate centered triads in poly(n-butyl acrylate-co-carbon monoxide-co-ethylene) by isotopic labeling and two dimensional NMR

Poly(n-butylacrylate-co-carbon monoxide-co-ethylene) (polyEBC) samples prepared from 13C-labeled monomer, n-butyl acrylate, were characterized using two dimensional (2D) pulsed field gradient (PFG) 750 MHz NMR spectroscopy. To elucidate the complex structure of the terpolymer, 2D-1H/13C-heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) experiments were conducted by selectively exciting the enhanced resonances in the spectra of two polymer samples, one polymer resulting from synthesis with 1-13C-n-butylacrylate monomer and a second polymer obtained from a synthesis with 2-13C-n-butylacrylate monomer. High-resolution 2D-NMR combined with 13C-labeling of the polymer greatly simplifies the 2D-NMR spectra, selectively enhances the weak peaks from low occurrence B-centered triad structures, and aids in their resonance assignments. In all experiments, the sample temperature was 120 degrees C, to ensure a homogeneous solution and sufficient molecular mobility. Electronic Supplementary Material: Supplementary material (1D 13C NMR spectra of the 13C-labeled and unlabeled polymers) is available in the online version of this article at http://dx.doi.org/100.1007/s00216-003-2402-3.     

Novel bifunctional acridine-acridinium conjugates: synthesis and study of their chromophore-selective electron-transfer and DNA-binding properties

Novel bifunctional conjugates 1-3, with varying polymethylene spacer groups, were synthesized, and their DNA interactions have been investigated by various biophysical techniques. The absorption spectra of these systems showed bands in the regions of 300-375 and 375-475 nm, corresponding to acridine and acridinium chromophores, respectively. When compared to 1 (Phi(f) = 0.25), bifunctional derivatives 2 and 3 exhibited quantitative fluorescence yields (Phi(f) = 0.91 and 0.98) and long lifetimes (tau = 38.9 and 33.2 ns). The significant quenching of fluorescence and lifetimes observed in the case of 1 is attributed to intramolecular electron transfer from the excited state of the acridine chromophore to the acridinium moiety. DNA-binding studies through spectroscopic investigations, viscosity, and thermal denaturation temperature measurements indicate that these systems interact with DNA preferentially through intercalation of the acridinium chromophore and exhibit significant DNA association constants (K(DNA) = 10(5)-10(7) M(-1)). Compound 1 exhibits chromophore-selective electron-transfer reactions and DNA binding, wherein only the acridinium moiety of 1 interacts with DNA, whereas optical properties of the acridine chromophore remain unperturbed. Among bifunctional derivatives 2 and 3, the former undergoes DNA mono-intercalation, whereas the latter exhibits bis-intercalation; however both of them interact through mono-intercalation at higher ionic strength. Results of these investigations demonstrate that these novel water-soluble systems, which exhibit quantitative fluorescence yields, chromophore-selective electron transfer, and DNA intercalation, can have potential use as probes in biological applications.     

Ullmann diaryl ether synthesis: rate acceleration by 2,2,6,6-tetramethylheptane-3,5-dione

[reaction: see text]. In the copper salt catalyzed ether formation from aryl bromides or iodides and phenols, 2,2,6,6-tetramethylheptane-3,5-dione (TMHD) was found to greatly accelerate the ordinarily difficult reaction, making it occur under more moderate temperatures and reaction times. A series of aryl halides and phenols were shown to form ethers in NMP as the solvent, cesium carbonate as the base, and CuCl and TMHD as the catalysts. The reaction was shown to tolerate electron-rich aryl bromides and electron-neutral phenols.     

Recent highlights in stationary phase design for open-tubular capillary electrochromatography

This review examines the most recent innovations made to achieve high performance in open-tubular capillary electrochromatography (OT-CEC) separations, focusing on the ingenious chemical and physical solutions made to increase the surface area and equip the stationary phase with exploitable selectivity. Among the approaches taken are chemically bonded ligands, etching with chemical bonding, sol-gels, molecularly imprinted polymers, porous layers, physically attached or adsorbed phases, and nanoparticle coatings. Particularly noteworthy are modern developments with macrocyclic receptor ligands, nanoparticles and open channel electrochromatography on-chip.