The rate coefficient of the CH3C(O)O2 + NO gas-phase reaction was measured over the temperature range of 218−370 K and total pressure of 2−5 Torr, using chemical ionization mass spectrometry ...detection of the CH3C(O)O2 radical. The temperature-dependent expression for the rate coefficient was determined to be k(T) = (6.0 ± 1.1) × 10-12 exp{(320 ± 40)/T} cm3 molecule-1 s-1, and a 298 K rate constant k 298 = (1.8 ± 0.3) × 10-11 cm3 molecule-1 s-1 was found. These results quell some of the ambiguity presented by previous studies of this reaction and validate the recommended value to be used in tropospheric chemistry models.
The presence of unreacted, free silicon lowers mechanical properties of reaction-bonded boron The fraction of free silicon can be reduced by the green density of the initial boron carbide The use of ...multimodal boron carbide mixtures 75% green density to be attained. After reaction with molten silicon, the composites consisted of phases, namely the original B4C particles, the phase, product of the dissolution-precipitation beta-SiC, and residual Si. The volume fraction of Si in the composites was in the 8-10% range. The composites, suitable for armour applications, elevated values of the mechanical properties with high Weibull modulus.
Psychopharmacological and neurochemical research suggests that alterations in monoamine transporters may be involved in the etiology of depression. We studied the expression of the brain-type ...vesicular monoamine transporter (VMAT2) in the Flinders sensitive line (FSL) rats, which represent a genetic animal model for clinical depression in humans. VMAT2 expression at the protein level was assessed by autoradiography using
3Hdihydrotetrabenazine (
3HTBZOH) binding, in the prefrontal cortex, the striatum and its subregions, nucleus accumbens (NAC), ventral tegmental area (VTA) and the substantia nigra pars compacta (SNC). The VMAT2 mRNA level was analyzed by in situ hybridization, in the VTA, SNC and the dorsal raphe (DR) nucleus. Reduced levels of
3HTBZOH binding were detected in the striatum and its subregions, NAC shell but not in the NAC core. A marked reduction of 21% was found in the VTA while only a slight reduction (13%) was observed in the SNC. The reduced levels of VMAT2 protein binding capacity were not accompanied by a parallel alteration in VMAT2 mRNA levels in the VTA, the SNC and the DR. Since the VMAT2 is responsible for the intracellular storage and regulated release of monoamines, the reduced
3HTBZOH binding levels in limbic brain regions of FSL rats may imply a reduced density of vesicular monoamine transporters, which can result in reduced monoamine transmission. Such reduction in the limbic neurotransmission, especially in NAC shell and VTA regions, may be involved in the depressive features of anhedonia and lack of motivation reported in the FSL rats.
Amber, a fossil tree resin, is known in the geological record from at least the Triassic period, 220-230 million years ago, to the sub-Recent. GC/MS analyses have shown that amber is composed mainly ...of macromolecular structures retaining the chemical fingerprints of the original resin. Diagenetic reactions seem to have relatively minor effects on the resin, suggesting that the amber can preserve most of the isotopic signature of the original resin. Recent pine (P. halepensis) and araucaria resins from Israel gave stable isotope ratio values of: delta 13C = -24 to -25.7 per thousand, delta D = -172 to -188 per thousand, and delta 18(O) of +14.5 to +16 per thousand. Philippine copal, 400 years old, gave values of delta 13C = -24 per thousand, delta D = -236 per thousand, and delta 18(O) of +14.5 per thousand. Fossil amber, mostly belonging to diterpenoids based polymers (Anderson's class I amber), gave delta 13C values ranging from -19 to -25 per thousand, delta D from -160 to -270 per thousand, and delta 18(O) of +16 to +19 per thousand. Because the isotopic composition of the original resin is influenced by the metabolic pathway of carbon fixation (for carbon) and the composition of environmental water (for oxygen and hydrogen) and presumably it is probably not strongly modified by diagenetic effects it is probable that paleobotanical, paleoclimatological and paleoenvironmental information can be potentially obtained from the stable isotope composition of the amber. In addition, the relatively small spread of the isotopic values of amber within a defined deposit, relative to the variance among isotopic values of amber from different sources, indicate the potential of amber as a stratigraphic marker as well as in identifying sources of amber in archaeological artifacts and gemology
Although the regulation of amino acid synthesis has been studied extensively at the biochemical level, it is still not known how genes encoding amino acid biosynthesis enzymes are regulated during ...plant development. In the present report, we have used the beta-glucuronidase (GUS) reporter gene to study the regulation of expression of an Arabidopsis thaliana aspartate kinase-homoserine dehydrogenase (AK/HSD) gene in transgenic tobacco plants. The polypeptide encoded by the AK/HSD gene comprises two linked key enzymes in the biosynthesis of aspartate-family amino acids. AK/HSD-GUS gene expression was highly stimulated in apical and lateral meristems, lateral buds, young leaves, trichomes, vascular and cortical tissues of growing stems, tapetum and other tissues of anthers, pollen grains, various parts of the developing gynoecium, developing seeds, and, in some transgenic plants, also in stem and leaf epidermal trichomes. AK/HSD-GUS gene expression gradually diminished upon maturation of leaves, stems, floral tissues, and embryos. GUS expression was relatively low in roots. During seed development, expression of the AK/HSD gene in the embryo was coordinated with the initiation and onset of storage protein synthesis, whereas in the endosperm it was coordinated with the onset of seed desiccation. Upon germination, AK/HSD-GUS gene expression in the hypocotyl and the cotyledons was significantly affected by light. The expression pattern of the A. thaliana AK/HSD-GUS reporter gene positively correlated with the levels of aspartate-family amino acids and was also very similar to the expression pattern of the endogenous tobacco AK/HSD mRNA as determined by in situ hybridization.
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