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Francisco Franco Jr. 《Molecular simulation》2017,43(3):222-227
The effect of the alkyl side-chain length on the structural and optoelectronic properties of poly[N-9′-heptadecanyl-27-carbazole-alt-55-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) conjugated oligomers have been studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The study was carried out by varying the length of alkyl side-chain attached to the nitrogen atom of the carbazole unit of the PCDTBT oligomers. The structural properties of the optimised oligomers were then studied by determining the bond-length alternation and dihedral angles (Φ) for various side-chain lengths. Total energy calculations for the determination of HOMO energy (EHOMO), LUMO energy (ELUMO), and fundamental energy gap (EGap) were performed using DFT at the B3LYP/6-31G(d), while the first singlet excitation energies (EOpt) were calculated by TD-DFT also at the same level of theory. It was observed that there are no significant structural changes occurring as the alkyl chain lengths are varied. For the electronic properties, very small differences (i.e. ~0.01 eV) were observed for EGap and EOpt while the exciton binding energies (EB) were virtually the same. The results suggest that using shorter alkyl side-chains do not significantly affect the structural and optoelectronic properties of the carbazole-benzothiadiazole based polymer. The observations can aid future computational design studies of analogous systems by reducing large structures thus decreasing computational costs. 相似文献
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Robert L. Post Jr. 《Journal of molecular evolution》1990,31(4):257-264
Summary An equation is developed that describes the condition of homeostasis in a general molecular system containing catalysts. In a prebiotic environment, this condition first results from a critical level of catalytic feedback in feedback loops containing differing organic molecular species. This critical level results in temporary exponential growth in concentrations of those catalyst species participating in the feedback loops, leading to homeostasis as the steady-state endpoint. None of the molecules in any feedback loop need be self-replicating for this autocatalysis to occur. Homeostasis is regarded as a definition of life at the lowest possible hierarchical level. A general mathematical boundary condition is derived for the critical level of catalytic feedback mentioned above-in effect, an origin of life condition. The paper argues that any natural prebiotic system of organic molecules in an H2O medium will automatically form many catalytic feedback loops, even if of very low catalytic efficiency. The analysis in this paper indicates that high temperatures strongly increase the efficiency of such catalytic feedback. If the temperature and total concentration of carbon in the system (e.g., in CO2, CH4, etc.) are sufficiently high, the critical condition for initial exponential growth will be attained. High initial temperatures for the earth are predicted by the planetesimal accretion model. 相似文献
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Elen Arroyo Peres Márcio Bernardino DaSilva Manuel Antunes Jr Ricardo Pinto-Da-Rocha 《分类学与生物多样性》2018,16(2):171-187
The Brazilian Atlantic Rain Forest is amongst the most diverse biomes in the world, but the processes that shaped its biodiversity are still poorly understood. We used one mitochondrial and two nuclear markers to evaluate the phylogeographic patterns of the endemic harvestman Acutisoma longipes and its closely related species to investigate the biogeographic history of this biome. The results showed low intrapopulation diversity and strong population structure, suggesting poor dispersion amongst locations. Phylogenetic analyses pointed to three main mitochondrial lineages congruent with the geomorphology of the south-eastern region of Brazil (Serra do Mar, Serra da Mantiqueira, and interior plateau). These older divergences occurred in the middle-Neogene, suggesting that events in this period drove the diversification of the species, but Quaternary events also affected the populations locally. We detected some congruence between A. longipes demographic patterns and the areas of endemism delimited for harvestmen, suggesting that some regions of the distribution could have been more stable in the past (especially in Serra da Mantiqueira). Our findings corroborate that harvestmen are a suitable group for the study of ancient biogeographic events in the Atlantic Rain Forest, even at small-scale ranges. Acutisoma hamatum is here considered as a new junior synonym of A. longipes. 相似文献
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Qian Li Chuanyu Li Harry K. Mahtani Jian Du Aashka R. Patel Jack R. Lancaster Jr. 《The Journal of biological chemistry》2014,289(29):19917-19927
Dinitrosyliron complexes (DNIC) have been found in a variety of pathological settings associated with •NO. However, the iron source of cellular DNIC is unknown. Previous studies on this question using prolonged •NO exposure could be misleading due to the movement of intracellular iron among different sources. We here report that brief •NO exposure results in only barely detectable DNIC, but levels increase dramatically after 1–2 h of anoxia. This increase is similar quantitatively and temporally with increases in the chelatable iron, and brief •NO treatment prevents detection of this anoxia-induced increased chelatable iron by deferoxamine. DNIC formation is so rapid that it is limited by the availability of •NO and chelatable iron. We utilize this ability to selectively manipulate cellular chelatable iron levels and provide evidence for two cellular functions of endogenous DNIC formation, protection against anoxia-induced reactive oxygen chemistry from the Fenton reaction and formation by transnitrosation of protein nitrosothiols (RSNO). The levels of RSNO under these high chelatable iron levels are comparable with DNIC levels and suggest that under these conditions, both DNIC and RSNO are the most abundant cellular adducts of •NO. 相似文献
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Specific alloprecipitins were found in blood plasma of pigs, immunized by sera of Lpr1 positive donors. These precipitins detected a new allotype of the lipoprotein Lpr system which was designated Lpr3. Genetic studies confirmed its codominant inheritance and subgroup character. This linear subgroup of allotype Lprl is controlled by the allele Lpr1,3. Investigations in populations of 14 pig breeds showed significant interbreed differences in the frequencies of alleles Lpr1, Lpr2 and Lpr1,3. 相似文献
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The relation between hypertension and cognition in elders remains unclear, and studies on the effect of antihypertensive drugs on cognition have demonstrated conflicting results. This study was performed to evaluate if the association between hypertension and cognition in elders differed depending on serum concentrations of organochlorine (OC) pesticides, common neurotoxic chemicals. Participants were 644 elders aged 60–85 years who participated in the National Health and Nutrition Examination Survey 1999–2002 and were able to complete a cognitive test. We selected 6 OC pesticides that were commonly detected in the elderly. Cognition was assessed by the Digit Symbol Substitution Test (DSST), a relevant tool for evaluating hypertension-related cognitive function, and low cognition was defined by the DSST score < 25th percentile. When OC pesticides were not considered in the analyses, elders with hypertension had about 1.7 times higher risk of low cognition than those without hypertension. However, in analyses stratified by serum concentrations of OC pesticides, the associations between hypertension and low cognition were stronger the higher the serum concentrations of p,p’-DDT, p,p’-DDE, β-hexachlorocyclohexane, and trans-nonachlor increased. Among elders in the 3rd tertile of these pesticides, adjusted odds ratios were from 2.5 to 3.5. In contrast, hypertension was not clearly associated with the risk of low cognition in elders in the 1st tertile of these pesticides. Similar patterns were observed for the continuous DSST score dependent variable. The difference in the association between hypertension and DSST scores according to the levels of OC pesticides suggest a key role of OC pesticides in the development of hypertension-related cognitive impairment and may help to identify hypertensive elders who are at a high risk of cognitive impairment. 相似文献