Metabolism and relative carcinogenic potency of chloroethylenes: A quantum chemical structure-activity study

Properties of six chloroethylenes which could serve as indicators of their relative metabolic behavior and carcinogenic activity have been calculated using Modified Neglect of Diatomic Overlap (MNDO), a semiempirical, all valence electron, molecular orbital method. Possible pathways of transformation of parent compounds to acylchlorides, chloroaldehydes and epoxides — their putative ultimate carcinogens — were considered, and heats of formation and relative stabilities of intermediates were calculated. Our results indicate that carbonyl compounds could be formed with and without the intermediacy of epoxides, suggesting the possibility of more than one pathway in activation of parent compounds. Electronic properties of carbonyl products and epoxide carbocations, putative ultimate carcinogens which could serve as indicators of their relative electrophilicities, were also calculated. The results obtained indicated that the relative extent of metabolism to carbonyl products, rather than their electrophilicity, is a determinant of the relative carcinogenic activity of the parent compound. Of the various thermodynamic criteria investigated, four were found to be indicators of both relative metabolic behavior and carcinogenic activity.     

Recent advances in nanobiotechnology and high-throughput molecular techniques for systems biomedicine

Nanotechnology-based tools are beginning to emerge as promising platforms for quantitative high-throughput analysis of live cells and tissues. Despite unprecedented progress made over the last decade, a challenge still lies in integrating emerging nanotechnology-based tools into macroscopic biomedical apparatuses for practical purposes in biomedical sciences. In this review, we discuss the recent advances and limitations in the analysis and control of mechanical, biochemical, fluidic, and optical interactions in the interface areas of nanotechnologybased materials and living cells in both in vitro and in vivo settings.     

Carbon quantum dots fluorescence quenching for potassium optode construction

Photophysical phenomena associated with carbon nanoparticles in combination with biocompatibility and readily functionalizable properties have attracted significant interest for sensing and imaging applications. A potassium ion optode based on the fluorescence quenching of carbon quantum dots (CQDs) was constructed. The CQDs were synthesized using a microwave method, citric acid and 2,2′‐(ethylene‐dioxy)bis(ethylamine). A quantum yield of 7.1% was calculated for the synthesized CQDs. A linear dynamic range of about one‐order of magnitude with a correlation coefficient of 0.99 was obtained. The optode was applied on real samples and a 0.60–1.60% error range was obtained relative to the ion‐selective electrode.     

Amyloid β aggregation induces human brain microvascular endothelial cell death with abnormal actin organization

Cerebral amyloid angiopathy (CAA) is a disease in which amyloid β (Aβ) is deposited on the walls of blood vessels in the brain, making those walls brittle and causing cerebral hemorrhage. However, the mechanism underlying its onset is not well understood. The aggregation and accumulation of Aβ cause the occlusion and fragility of blood vessels due to endothelial cell damage, breakdown of the blood-brain barrier, and replacement with elements constituting the blood vessel wall. In this study, we observed the effect of Aβ on human primary brain microvascular endothelial cells (hBMECs) in real-time using quantum dot nanoprobes to elucidate the mechanism of vascular weakening by Aβ. It was observed that Aβ began to aggregate around hBMECs after the start of incubation and that the cells were covered with aggregates. Aβ aggregates firmly anchored the cells on the plate surface, and eventually suppressed cell motility and caused cell death. Furthermore, Aβ aggregation induced the organization of abnormal actin, resulting in a significant increase in intracellular actin dots over 10 μm². These results suggest that the mechanism by which Aβ forms a fragile vessel wall is as follows: Aβ aggregation around vascular endothelial cells anchors them to the substrate, induces abnormal actin organization, and leads to cell death.     

Intrinsic reactivity of uric acid with dioxygen: Towards the elucidation of the catalytic mechanism of urate oxidase

Urate oxidase catalyzes the transformation of uric acid in 5-hydroxyisourate, an unstable compound which is latter decomposed into allantoïn. Crystallographic data have shown that urate oxidase binds a dianion urate species deprotonated in N3 and N7, while kinetics experiments have highlighted the existence of several intermediates during catalysis. We have employed a quantum mechanical approach to analyze why urate oxidase is selective for one particular dianion and to explore all possible reaction pathways for the oxidation of one uric acid species by molecular dioxygen in presence of water. Our results indicate the urate dianion deprotonated in N3 and N7 is among all urate species that can coexist in solution it is the compound which will lose the most easiestly one electron in presence of molecular dioxygen. In addition, the transformation of this dianion in 5-hydroxyisourate is thermodynamically the most favorable reaction. Finally, several reaction pathways can be drawn, each starting with the spontaneous transfer of one electron from the urate dianion to molecular dioxygen. During that period, the existence of a 5-hydroperoxyisourate intermediate, which has been proposed elsewhere, does not seem mandatory.     

Analysis of the cuticular wax composition and ecophysiological studies in an arid plant - Ziziphus nummularia (Burm.f.) Wight & Arn.

Plants in arid regions are exposed to various abiotic stresses and the presence of the waxy cuticular layer acts as a defensive barrier, which consists mainly of long chain fatty acids, hydrocarbons and other derived compounds. Studies on the chemical composition and properties of cuticles of arid plants are scanty. The present study deals with the analysis of cuticular wax composition and effect of temperature on some ecophysiological parameters of an important arid plant Ziziphus nummularia. A total of 59 different wax compounds were detected from the leaf cuticle by capillary GC–MS. 4-Hydroxycyclohexanone, Heptacosane and 2,7-Dimethyloctane-3,5-dione were the dominant wax compounds in Z. nummularia. The variation of photosynthetic rate varied from 0.70 to 7.70 µmol CO2 m-2s-1 against the studied temperature range of 15–55 °C. The transpiration rate varies from 1.80 to 8.40 mmol H2O m-2s-1 within the temperature range of 15–55 °C. The quantum yield of photosystem II (Fv/Fm) also exhibited much variation due to the variation of temperature. The results clearly shows that Z. nummularia is highly adapted to restrict water loss and can tolerate high temperatures and can be considered as an appropriate species for vegetating the arid areas.     

Quantum efficiency requirements for an anaerobic photobioreactor

Summary The effect of light intensity, surface area of illuminated bioreactor, H₂S flow rate and various wavelength regions of light on oxidative sulfur metabolism byChlorobium was examined. The regulation of oxidative sulfur metabolism by light intensity led to the determination of the photobioreaction quantum efficiency (PQE) for this system. This efficiency is defined as the molecules of sulfur (S^o) produced per photon utilized and can be used in designing a light efficient photobioreactor. Included in our analysis of requirements for a light efficient photobioreactor is a summary of some fed-batch equations which can be used to model a productive path for the formation of sulfur duringChlorobium's photosynthesis. It is suggested that the incorporation of PQE and fed-batch formulae into expressions for wavelength dependent rates of photosynthetic product formation will lead to a more accurate mathematical model for anoxygenic as well as oxygenic photosynthesis.