Structural Origins of Chiral Second-Order Optical Nonlinearity in Collagen: Amide I Band

The molecular basis of nonlinear optical (NLO) chiral effects in the amide I region of type I collagen was investigated using sum-frequency generation vibrational spectroscopy; chiral and achiral tensor elements were separated using different input/output beam polarization conditions. Spectra were obtained from native rat tail tendon (RTT) collagen and from cholesteric liquid crystal-like (LC) type I collagen films. Although RTT and LC collagen both possess long-range order, LC collagen lacks the complex hierarchical organization of RTT collagen. Their spectra were compared to assess the role of such organization in NLO chirality. No significant differences were observed between RTT and LC with respect to chiral or achiral spectra. These findings suggest that amide I NLO chiral effects in type I collagen assemblies arise predominantly from the chiral organization of amide chromophores within individual collagen molecules, rather than from supramolecular structures. The study suggests that sum-frequency generation vibrational spectroscopy may be uniquely valuable in exploring fundamental aspects of chiral nonlinearity in complex macromolecular structures.     

A literature synthesis resolves litter intrinsic constraints on fungal dynamics and decomposition across standing dead macrophytes

The standing dead phase is an important stage in the decomposition of emergent vegetation in marsh wetlands, yet few studies have examined how intrinsic litter traits constrain rates of standing litter decomposition or fungal colonization across plant tissue types or species. To address broad constraints on the decomposition of standing dead litter, we conducted a systematic survey of emergent standing dead decomposition studies that measured decay rates and/or fungal biomass, and litter % lignin, carbon:nitrogen (C:N) and/or carbon:phosphorus (C:P). Across 52 datasets, litter of low C:N and C:P ratios exhibited increased decomposition rates (r = −0.737 and −0.645, respectively), whereas % lignin was not significantly correlated with decomposition rates (r = 0.149). Mixed-effects models for litter decomposition rates indicated significant effects of litter molar C:N and C:N + lignin as an additive model, with the former providing marginally better support. Litter % lignin, however, was strongly negatively correlated with fungal biomass (r = −0.669), indicating greater fungal colonization of low-lignin litter, and not correlated with C:N (r = −0.337) and C:P (r = −0.456) ratios. The best-supported model predicting fungal biomass was litter molar C:N, with the C:N + lignin additive model also showing significant effects. Fungal carbon-use efficiency (CUE) also had a strong negative correlation with % lignin (r = −0.604), molar C:N (r = −0.323) and C:P (r = −0.632) across datasets. Our study demonstrates the constraining effects that litter stoichiometry and % lignin elicit on decomposition of standing dead litter and fungal colonization, respectively. These findings improve our understanding of biogeochemical cycling and prediction of the fates of C and nutrients in wetlands.     

Theoretical study on the thermal decomposition of model compounds for Poly (dialkyl fumarate)

The thermal decomposition of model compounds for poly (dialkyl fumarate) was studied by using ab initio and density functional theory (DFT) calculations. To determine the most favorable reaction pathway of thermal decomposition, geometries, structures, and energies were evaluated for reactants, products, and transition states of the proposed pathways at the HF/6-31G(d) and B3LYP/6-31G(d) levels. Three possible paths (I, II and III) and subsequent reaction paths (IV and V) for the model compounds of poly (dialkyl fumarate) decomposition had been postulated. It has been found that the path (I) has the lowest activation energy 193.8 kJ mol⁻¹ at B3LYP/6-31G(d) level and the path (I) is considered as the main path for the thermal decomposition of model compounds for poly (dialkyl fumarate).      

Life history of the mealybug, Maconellicoccus hirsutus (Hemiptera: Pseudococcidae), at constant temperatures

Important life history parameters of the mealybug, Maconellicoccus hirsutus (Green), were characterized on hibiscus (Hibiscus rosa-sinensis L.) cuttings at six constant temperatures between 15 and 35 degrees C. The development of M. hirsutus was the fastest at 27 degrees C, where the mealybugs completed development in approximately 29 d. The lower (T(min)) and upper (T(max)) developmental thresholds and the optimal developmental temperature (T(opt)) for the development of female mealybugs were estimated as 14.5, 35, and 29 degrees C, respectively. The thermal constant (K), which is the number of temperature-day or degree-day units required for development, of the females was 347 DD. The original distribution range prediction (based on T(min) = 17.5 degrees C and K = 300 DD) indicated that M. hirsutus could complete at least one generation in all of the continental United States. However, results of this study suggested that the distribution range of M. hirsutus may expand northward because of the lower T(min), and the predicted number of generations in a year may be lower because of the higher K required to complete each generation. The average cumulative survival rate of M. hirsutus at 25 and 27 degrees C was 72%, which was significantly higher than 51 and 62% at 20 and 30 degrees C, respectively. M. hirsutus reproduced sexually, with each mated female producing 260-300 eggs between 20 and 27 degrees C but only approximately 100 eggs at 30 degrees C. Female longevity was reduced from 28 d at 20 degrees C to 19-21 d at 25-30 degrees C. At 27 degrees C, the net reproductive rate (R(o)) was estimated at 165 female symbol/female symbol, the intrinsic rate of population increase (r(m)) was 0.119 (female symbol/female symbol/d), the generation time (T(G)) was 43 d, and the doubling time (DT) was 5.8 d. The life table statistics suggested that the currently released biological control agents, which have higher r(m) than M. hirsutus, will be able to complete more generations than the mealybug within the tested temperature range; thus, they are effective against M. hirsutus.     

K+ and Na+-induced self-assembly of telomeric oligonucleotide d(TTAGGG)n

The telomeric DNA oligomers, d(TTAGGG)(n), where n=1, 2, 4, could self-associate into the multi-stranded structures in appropriate condition, exhibited different CD spectra. The presense of Na(+) was more advantage to facilitate the formation of anti-parallel conformation, but the presense of K(+) enhanced their thermal stability. Spectroscopic analysis of 3, 3'-diethyloxadicarbocyanine (DODC) showed the formation of hairpin quadruplex structures for d(TTAGGG)(2) and d(TTAGGG)(4), but d(TTAGGG) could not. The four-stranded tetraplexes and branched nanowire formed in the presense of K(+) or Na(+) alone were observed by atomic force microscopy (AFM). The ability of d(TTAGGG)(n) to self-assemble into four-stranded tetraplexes and nanowires depends strongly on the number of repeating units and ionic environment. A model to explain how these structures formed is proposed.     

芳香羧酸衍生物驱避剂的非线性定量构效关系

【目的】驱避剂可使害虫不敢接近受用者从而保护受用者免遭其害。建立高精度、可解释性强的非线性定量构效关系(quantitative structure activity relationship, QSAR)模型对设计合成新的高效昆虫驱避剂有重要意义。【方法】基于37个芳香羧酸类化合物对家蝇Musca domestica的驱避活性,以量子化学计算软件PCLIENT获取每一化合物初始描述符,以二元矩阵重排过滤器、多轮末尾淘汰实施特征非线性筛选,以支持向量回归(support vector regression, SVR)建立非线性QSAR模型,以SVR非线性解释体系分析各保留描述符对驱避活性的影响。【结果】1 542个初始描述符的SVR模型F=1.2,特征筛选后6个保留描述符的SVR模型F=184.6,特征筛选对QSAR模型精度有重要影响。6个保留分子描述符的重要性依次为p4BCD>GATS7v>T(O..O)> JGI8>SssO>nArCONR2。【结论】保留描述符与芳香羧酸类化合物对家蝇驱避活性的非线性关系明显,获得了高精度、普适性强的非线性SVR-QSAR模型。