The Effects of Structural Alterations in the Polyamine and Amino Acid Moieties of Philanthotoxins on Nicotinic Acetylcholine Receptor Inhibition in the Locust,Schistocerca gregaria

Alterations in the polyamine and amino acid (tyrosine) moieties of philanthotoxin-343 (PhTX-343) were investigated for their effects on the antagonism of nicotinic acetylcholine receptors (nAChRs) isolated from the locust (Schistocerca gregaria) mushroom body. Through whole-cell patch-clamp recordings, the philanthotoxin analogues in this study were shown to cause inhibition of the inward current when co-applied with acetylcholine (ACh). PhTX-343 (IC₅₀ = 0.80 μM at −75 mV) antagonised locust nAChRs in a use-dependent manner, suggesting that it acts as an open-channel blocker. The analogue in which both the secondary amine functionalities were replaced with methylene groups (i.e., PhTX-12) was ~6-fold more potent (IC₅₀ (half-maximal inhibitory concentration) = 0.13 μM at −75 mV) than PhTX-343. The analogue containing cyclohexylalanine as a substitute for the tyrosine moiety of PhTX-343 (i.e., Cha-PhTX-343) was also more potent (IC₅₀ = 0.44 μM at −75 mV). A combination of both alterations to PhTX-343 generated the most potent analogue, i.e., Cha-PhTX-12 (IC₅₀ = 1.71 nM at −75 mV). Modulation by PhTX-343 and Cha-PhTX-343 fell into two distinct groups, indicating the presence of two pharmacologically distinct nAChR groups in the locust mushroom body. In the first group, all concentrations of PhTX-343 and Cha-PhTX-343 inhibited responses to ACh. In the second group, application of PhTX-343 or Cha-PhTX-343 at concentrations ≤100 nM caused potentiation, while concentrations ≥ 1 μM inhibited responses to ACh. Cha-PhTX-12 may have potential to be developed into insecticidal compounds with a novel mode of action.     

Gelation Studies, 3

Summary: The sol‐gel transition of one thermoreversible gelling mixture made of xanthan gum and locust bean gum has been studied by using in situ time‐resolved dynamic light scattering (DLS) and measuring the spin‐lattice relaxation time T₁ of several protons. A critical dynamical behavior was observed near the sol‐gel transition, which is characterized by the presence of power‐law spectra over four decades of the delay time in the time‐intensity correlation function g₂(t)−1 ∼ t^−μ at 48 °C. The increase in T₁ with increasing temperature becomes steeper at 50 °C indicating a significant change in the local mobility of one anomeric proton of the xanthan side chain and the anomeric protons of the locust bean gum mannose backbone.

Temperature dependence of the spin‐lattice relaxation time T₁ for the equatorial anomeric proton of the mannopyranosic unit located next to the main chain of the xanthan.     

Locust Bean Gum Hydrogels Formed by Freezing and Thawing

Locust bean gum (LBG) hydrogels were prepared by freezing and thawing. It was found that the junction zone of LBG hydrogels is tightly formed by repeating freezing and thawing. During this process, LBG molecules not connected with the junction zone are excluded from the gel portion and the remaining molecules gradually form densely packed hydrogels. Molecular conformation in the sol state affects the rate of the junction formation. Obtained LBG hydrogels are thermally stable and no gel-sol transition was observed in temperatures from 40 to 100 °C by the observation of differential scanning calorimetry (DSC). Non-freezing water content calculated from the DSC melting peak of water in the gel indicates that the junction zone became dense with increasing freezing and thawing.     

激光辐照蝗虫不同身体部位致死效果研究

为研究激光对蝗虫不同身体部位的杀灭效果,选择近红外大功率连续型半导体激光器,针对亚洲车蝗成虫和幼虫的头部、翅根和腹部位置,距离激光发光面1cm处,进行不同时间的照射试验,分别观察照射后3天蝗虫的致死率.在1cm处对幼虫头部、翅根和腹部位置辐照5s,观察肌体组织宏观损伤情况.结果表明,随着辐照时间的增加,蝗虫的致死率增加;在相同的辐照条件下,幼虫比成虫致死率高,且辐照头部位置致死率最高、辐照翅根部位致死率次之、辐照腹部致死率最低.肌体宏观观测结果表明,头部和翅根被辐照部位有明显的碳化现象,腹部的宏观热损伤效果则不明显.试验结果说明近红外激光辐照蝗蝻的头部位置有较好的致死效果.     

大功率近红外半导体激光辐照蝗蝻致死作用研究

为研究大功率近红外半导体激光对蝗蝻的致死作用,选择采用功率2W、波长808nm的半导体激光器,针对三龄及以前龄期和三龄期后亚洲小车蝗蝻虫分组试验,激光束对准蝗蝻头部位置,进行小同功率密度、不同时间的照射试验,分别观察照射后即刻、照射后5小时和照射后次日蝗蝻的致死率.与对照组相比,照射试验组蝗蝻被照射部位受激光热损伤破坏,活性均有不同程度的降低,且随着激光剂量的增加和照射后时间的延长,活性降低程度和致死率呈现增长趋势.结果表明,近红外激光辐照蝗螭头部位置有较好的致死作用,且蝗蝻龄期越小致死效果越好.     

Phase transition of locust bean gum-, tara gum- and guar gum-water systems

Phase transition behaviour of neutral galactomannans, i.e., locust bean gum (LBG), tara gum (Tara-G) and guar gum (GG)-water systems is investigated. In this study, water content {W_c=(gram of water)/(gram of dry sample)} of these systems was varied from 0.2 to 3.6 g g^-1. In the DSC heating curves, glass transition (T_g), cold crystallization (T_cc) and melting (T_m) were observed in all three samples. In addition, liquid crystal transition (T*) was observed in GG-water systems at a temperature higher than Tm. Using T_g, T_cc, Tm and T*, phase diagrams of each system were established. From the melting enthalpy of ice in the systems, three types of water, non-freezing water (W_nf), freezing bound water (W_fb) and free water were calculated. The maximum amount of Wnf was observed at Wc=0.7 g g-1, where Tg showed the lowest temperature. The amount of Wnf in LBG and GG is higher than that of Tara-G, whereas the highest amount of Wfb is found in GG. T* was only observed in GG-water systems. It is concluded that frequency of the side chains in the repeating unit of the main chains of these three galactomannan affects the frozen structure of the glassy state in the presence of water. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamic model and performance analysis of landing buffer for bionic locust mechanism

The landing buffer is an important problem in the research on bionic locust jumping robots, and the differ-ent modes of landing and buffering can affect the dynamic performance of the buffering process significantly. Based on an experimental observation, the different modes of landing and buffering are determined, which include the different numbers of landing legs and different motion modes of legs in the buffering process. Then a bionic locust mechanism is established, and the springs are used to replace the leg muscles to achieve a buffering effect. To reveal the dynamic performance in the buffering process of the bionic locust mechanism, a dynamic model is established with different modes of landing and buffering. In particular, to analyze the buffering process conveniently, an equivalent vibration dynamic model of the bionic locust mechanism is proposed. Given the support forces of the ground to the leg links, which can be obtained from the dynamic model, the spring forces of the legs and the impact resistance of each leg are the important parameters affecting buffering performance, and evaluation principles for buffering performance are proposed according to the aforementioned parameters. Based on the dynamic model and these evaluation principles, the buffer-ing performances are analyzed and compared in different modes of landing and buffering on a horizontal plane and an inclined plane. The results show that the mechanism with the ends of the legs sliding can obtain a better dynamic per-formance. This study offers primary theories for buffering dynamics and an evaluation of landing buffer performance, and it establishes a theoretical basis for studies and engineer-ing applications.     

基于近红外光谱和系统聚类法的蝗虫识别模型研究

以蝗虫的近红外光谱图作为分析的对象,采用聚类分析方法对蝗虫进行快速的识别研究.结果表明:矢量归一化预处理后的光谱数据经最长距离法进行聚类分析,分类结果正确率为100%.此法可为蝗虫自动侦测系统中识别蝗虫提供一种可靠、简便的手段,盲样检测的准确率可达91.67%.     

Thermogravimetry/mass spectrometry analysis of energy crops

The aim of this work was to study the thermal decomposition of different plant species obtained from energy plantations. Thermogravimetry/ mass spectrometry (TG/MS) experiments have been performed with two herbaceous crops (Miscanthus sinensis, pelletized energy grass) and two wood samples (willow, water locust) in inert and oxidative atmospheres. Owing to the large number of data obtained in the experiments, a chemometric tool, principal component analysis (PCA) has been used to help the interpretation of the results. It has been found that the thermal decomposition of the studied wood species is similar, whereas that of the studied herbaceous samples exhibits significant differences. PCA has been found to be useful for finding correlations between the various experimental data.