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.     

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.     

Studying the Interaction of Xanthan Gum and Pectin with Some Functional Carbohydrates on the Rheological Attributes of a Low-Fat Spread

Effects of xanthan gum (XG) (0.1 wt%) and pectin (PE) (0.5 wt%) alone and in combination with different concentrations (0.2 and 0.4 wt%) of locust bean gum (LBG), modified starch (MS), and Na-alginate (ALG) on some of the rheological characteristics of low-fat spreads, including flow behavior curves, rheological modeling, apparent viscosity, rheological modules (storage modulus (G′) and loss modulus (G″)), and delta degree (G″/G′) were studied. Results showed the power-law model was better than the Herschel–Bulkley model to describe the flow curve of dispersions. The k-value in the power-law model increased with increase in biopolymers concentration in solution. All samples exhibited shear-thinning flow behavior with a low yield stress. Dynamic oscillatory shear test showed that the spreads had a viscoelastic solid behavior with a gel-like structure. The G′ value was increased by increasing frequency from 0.03 to 15 Hz, while the G″ and G″/G′ values decreased. Also, MS in combination with XG and PE led to increase the G′ values of spreads in comparison with ALG and LBG. Moreover, microstructural and stability observations revealed that the spreads prepared with 0.1% XG-0.2% LBG significantly had the highest oiling out.     

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.