Field evaluation of some selected plant materials for the control of major insect pests of cowpea (Vigna unguiculata(L.) Walp.) in the Northern Guinea Savannah of Nigeria

Abstract

Field experiments were carried out at the Teaching and Research Farm of the Abubakar Tafawa Balewa University, Bauchi during the rainy season of 2005. The study was carried out with sole objective of evaluating the efficacy of six selected plant materials (sweetsop, red pepper, garlic, neem, mahogany and gmalina) against the major insect pests of cowpea variety, Dan Sokoto. The experiment was laid down in randomised complete block design with seven treatments. Each treatment was replicated three times. The results of the study showed that all the plant materials used were significantly (p < 0.05) better than control where no plant material was used in controlling the population of B. tabaci, E. dolichi, M. sjostedti and C. tomentosicollis at 1, 2 and 3 days after application of the treatments. Similarly the effects of these plant materials on the number of seeds/pod showed a significant (p < 0.05) difference between plots treated with plant materials and control. On the grain yield of the crop, all the plant materials showed significant effect except mahogany and the control which were statistically similar. Furthermore, the order of level of control indicated that sweet sop has (70.7%), garlic (69.3%), neem (61.0%), red pepper (54.0%), ash (30.9%), and mahogany (3.5%). The result of the present finding therefore recommends the use of sweet sop, garlic and neem as they were found to be the most promising in the control of major cowpea insect pests.     

Role of tyrosine hot‐spot residues at the interface of colicin E9 and immunity protein 9: A comparative free energy simulation study

The endonuclease activity of the bacterial colicin 9 enzyme is controlled by the specific and high‐affinity binding of immunity protein 9 (Im9). Molecular dynamics simulation studies in explicit solvent were used to investigate the free energy change associated with the mutation of two hot‐spot interface residues [tyrosine (Tyr): Tyr54 and Tyr55] of Im9 to Ala. In addition, the effect of several other mutations (Leu33Ala, Leu52Ala, Val34Ala, Val37Ala, Ser48Ala, and Ile53Ala) with smaller influence on binding affinity was also studied. Good qualitative agreement of calculated free energy changes and experimental data on binding affinity of the mutations was observed. The simulation studies can help to elucidate the molecular details on how the mutations influence protein–protein binding affinity. The role of solvent and conformational flexibility of the partner proteins was studied by comparing the results in the presence or absence of solvent and with or without positional restraints. Restriction of the conformational mobility of protein partners resulted in significant changes of the calculated free energies but of similar magnitude for isolated Im9 and for the complex and therefore in only modest changes of binding free energy differences. Although the overall binding free energy change was similar for the two Tyr–Ala mutations, the physical origin appeared to be different with solvation changes contributing significantly to the Tyr55Ala mutation and to a loss of direct protein–protein interactions dominating the free energy change due to the Tyr54Ala mutation. Proteins 2013. © 2012 Wiley Periodicals, Inc.     

Combinatorial materials research applied to the development of new surface coatings IV. A high-throughput bacterial biofilm retention and retraction assay for screening fouling-release performance of coatings

Abstract

A high-throughput bacterial biofilm retention screening method has been augmented to facilitate the rapid analysis and down-selection of fouling-release coatings for identification of promising candidates. Coatings were cast in modified 24-well tissue culture plates and inoculated with the marine bacterium Cytophaga lytica for attachment and biofilm growth. Biofilms retained after rinsing with deionised water were dried at ambient laboratory conditions. During the drying process, retained biofilms retracted through a surface de-wetting phenomenon on the hydrophobic silicone surfaces. The retracted biofilms were stained with crystal violet, imaged, and analysed for percentage coverage. Two sets of experimental fouling-release coatings were analysed with the high-throughput biofilm retention and retraction assay (HTBRRA). The first set consisted of a series of model polysiloxane coatings that were systematically varied with respect to ratios of low and high MW silanol-terminated PDMS, level of cross-linker, and amount of silicone oil. The second set consisted of cross-linked PDMS-polyurethane coatings varied with respect to the MW of the PDMS and end group functionality. For the model polysiloxane coatings, HTBRRA results were compared to data obtained from field immersion testing at the Indian River Lagoon at the Florida Institute of Technology. The percentage coverage calculations of retracted biofilms correlated well to barnacle adhesion strength in the field (R² = 0.82) and accurately identified the best and poorest performing coating compositions. For the cross-linked PDMS-polyurethane coatings, the HTBRRA results were compared to combinatorial pseudobarnacle pull-off adhesion data and good agreement in performance was observed. Details of the developed assay and its implications in the rapid discovery of new fouling-release coatings are discussed.     

Vapour-Liquid Phase Equilibria of n-alkanes by Direct Monte Carlo Simulations

Abstract

We report results of direct Monte Carlo simulations of n-pentane and n-decane at the liquidvapour interface for a number of temperatures. The intermolecular interactions are modeled using the last version of the anisotropic united atom model (AUA4). We have used the local long range correction energy and an algorithm allowing to select randomly with equal probability two different displacements. The liquid and vapour densities are in excellent agreement with experimental data and with those previously calculated using the GEMC method.     

Constitutive properties of contacting materials with a finite-sized microstructure

Materials consisting of macro-molecules that are set in a structure and interact via contact interactions are investigated. The analysis is analytical, based on the methodology developed for granular materials by Jenkins J.T. and Koenders M.A. “The incremental response of random aggregates of round particles” European Physics Journal E., 13, 2004 113–123. The stiffness tensor is obtained and the results are screened for auxetic properties. Two-dimensional materials are investigated. For regular packings isotropic and anisotropic structures are examined. It is demonstrated that isotropic materials in this category are never auxetic. Heterogeneous materials are also analysed. It is shown that auxetic behaviour is enhanced when structural variation is present. By contrast, auxetic behaviour is suppressed when constitutive heterogeneity is present. The results of the analysis may be employed to scrutinize numerical simulations.     

Molecular dynamics simulation of the Al2O3 film structure during atomic layer deposition

Based on an understanding of atomic layer deposition (ALD) from prior experimental and computational results, all-atom molecular dynamics (MD) simulations are used to model the Al₂O₃ film structure and composition during ALD processing. By separating the large time-scale surface reactions from the small time-scale structural relaxation, we have focused on the growth dynamics of amorphous Al₂O₃ films at the atomic scale. The simulations are able to reproduce some important properties and growth mechanisms of Al₂O₃ ALD films, and hence provide a bridge between atomic-level information and experimental measurements. Information about the evolution of the microscopic structures of the Al₂O₃ films is generated, and the influence of operation parameters on the Al₂O₃ ALD process. The simulations predict a strong influence of the initial surface composition and process temperature on the surface roughness, growth rate and growth mode of the deposited films.     

Understanding the specificity of serpin–protease complexes through interface analysis

Serpins such as antithrombin, heparin cofactor II, plasminogen activator inhibitor, antitrypsin, antichymotrypsin, and neuroserpin are involved in important biological processes by inhibiting specific serine proteases. Initially, the protease recognizes the mobile reactive loop of the serpin eliciting conformational changes, where the cleaved loop together with the protease inserts into β-sheet A, translocating the protease to the opposite side of inhibitor leading to its inactivation. Serpin interaction with proteases is governed mainly by the reactive center loop residues (RCL). However, in some inhibitory serpins, exosite residues apart from RCL have been shown to confer protease specificity. Further, this forms the basis of multi-specificity of some serpins, but the residues and their dimension at interface in serpin-protease complexes remain elusive. Here, we present a comprehensive structural analysis of the serpin-protease interfaces using bio COmplexes COntact MAPS (COCOMAPS), PRotein Interface Conservation and Energetics (PRICE), and ProFace programs. We have carried out interface, burial, and evolutionary analysis of different serpin-protease complexes. Among the studied complexes, non-inhibitory serpins exhibit larger interface region with greater number of residue involvement as compared to the inhibitory serpins. On comparing the multi-specific serpins (antithrombin and antitrypsin), a difference in the interface area and residue number was observed, suggestive of a differential mechanism of action of these serpins in regulating their different target proteases. Further, detailed study of these multi-specific serpins listed few essential residues (common in all the complexes) and certain specificity (unique to each complex) determining residues at their interfaces. Structural mapping of interface residues suggested that individual patches with evolutionary conserved residues in specific serpins determine their specificity towards a particular protease.     

Transmembrane helix 6 observed at the interface of β2AR homodimers in blind docking studies

Peptide– and protein–protein dockings were carried out on β₂-adrenergic receptor (β₂AR) to confirm the presence of transmembrane helix 6 (TM6) at the interface region between two β₂AR monomers, thereby its possible role in dimerization as suggested in numerous experimental and computational studies. Initially, a portion of TM6 was modeled as a peptide consisting of 23 residues and blindly docked to β₂AR monomer using a rigid body approach. Interestingly, all highest score conformations preferred to be near TM5 and TM6 regions of the receptor. Furthermore, longer peptides generated from a whole TM region were blindly docked to β₂AR using the same rigid body approach. This yielded a total of seven docked peptides, each derived from one TM helix. Most interestingly, for each peptide, TM6 was among the most preferred binding site region in the receptor. Besides the peptide dockings, two β₂AR monomers were blindly docked to each other using a full rigid-body search of docking orientations, which yielded a total of 16,000 dimer conformations. Each dimer was then filtered according to a fitness value based on the membrane topology. Among 149 complexes that met the topology requirements, 102 conformers were composed of two monomers oriented in opposite directions, whereas in the remaining 47, the monomers were arranged in parallel. Lastly, all 149 conformers were clustered based on a root mean-squared distance value of 6 Å. In agreement with the peptide results, the clustering yielded the largest population of conformers with the highest Z-score value having TM6 at the interface region.     

Electrotactile stimulation on the tongue: Intensity perception,discrimination, and cross-modality estimation

Due to its high sensitivity and conductivity, electrotactile stimulation (ETS) on the tongue has proven to be a useful and technically convenient tool to substitute and/or augment sensory capabilities. However, most of its applications have only provided spatial attributes and little is known about (a) the ability of the tongue's sensory system to process electrical stimuli of varying magnitudes and (b) how modulation of ETS intensity affects subjects’ ability to decode stimulus intensity. We addressed these questions by quantifying: (1) the magnitude of the dynamic range (DR; maximal comfortable intensity/perception threshold) and its sensitivity to prolonged exposure; (2) subjects’ ability to perceive intensity changes; and (3) subjects’ ability to associate intensity with angular excursions of a protractor's handle. We found that the average DR (17 dB) was generally large in comparison with other tactile loci and of a relatively constant magnitude among subjects, even after prolonged exposure, despite a slight but significant upward drift (p < 0.001). Additionally, our results showed that as stimulus intensity increased, subjects’ ability to discriminate ETS stimuli of different intensities improved (p < 0.05) while estimation accuracy, in general, slightly decreased (increasing underestimation). These results suggest that higher ETS intensity may increase recruitment of rapidly adapting mechanoreceptor fibers, as these are specialized for coding stimulus differences rather than absolute intensities. Furthermore, our study revealed that the tongue's sensory system can effectively convey electrical stimuli despite minimal practice and when information transfer is limited by memory and DR drift.