Plant Surface Properties in Chemical Ecology

The surface of the primary aerial parts of terrestrial plants is covered by a cuticle, which has crucial autecological functions, but also serves as an important interface in trophic interactions. The chemical and physical properties of this layer contribute to these functions. The cuticle is composed of the cuticular layer and the cuticle proper, which is covered by epicuticular waxes. Whereas the cutin fraction is a polyester-type biopolymer composed of hydroxyl and hydroxyepoxy fatty acids, the cuticular waxes are a complex mixture of long-chain aliphatic and cyclic compounds. These highly lipophilic compounds determine the hydrophobic quality of the plant surface and, together with the microstructure of the waxes, vary in a species-specific manner. The physicochemical characteristics contribute to certain optical features, limit transpiration, and influence adhesion of particles and organisms. In chemical ecology, where interactions between organisms and the underlying (allelo-) chemical principles are studied, it is important to determine what is present at this interface between the plant and the environment. Several useful equations can allow estimation of the dissolution of a given organic molecule in the cuticle and its transport properties. The implementation of these equations is exemplified by examining glucosinolates, which play an important role in interactions of plants with other organisms. An accurate characterization of physicochemical properties of the plant surface is needed to understand its ecological significance. Here, we summarize current knowledge about the physical and chemical properties of plant cuticles and their role in interactions with microorganisms, phytophagous insects, and their antagonists.     

防止头发褪色和头皮损伤的新型紫外线过滤剂

介绍了禾大公司新开发出的一种防止头发褪色和头皮损伤的新型紫外线过滤剂Chromaveil,并介绍了该产品在香波、护发素以及头发免洗产品中的应用。Chromaveil具有广泛的紫外线吸收光谱,吸收范围为250nm-350nm,峰值为310nm,在波长为310nm时的消光系数为38．47L／（g·cm）。由于Chromaveil的正电荷作用,在冲洗产品中能很好地沉积在头发表面。经测试证明,Chromaveil具有很好的护色效果,可对头发表面的色氨酸、抗张力强度和表皮完整性提供很好的紫外线保护作用。     

Characterisation of the surface of wool and hair using microscopical and fluorescence probe techniques

Fluorescence probing methods, in combination with light microscopy, were used to image and characterise the hydrophobic surfaces of wool and human hair fibres. When applied from an aqueous dispersion, uncharged lipophilic fluorescent probes displayed a selective affinity for the boundaries of the cuticle cells on the fibre surface. Adsorption generally occurred on the surface of the lower scale emerging from each cell junction. An indication of the fibre surface polarity was given by the fluorescence fine structure of adsorbed pyrene molecules. Treatment of hair with the lipid stain Nile Red produced an unusual diamondshaped pattern (each segment approximately 40 μm in length and 10 μm in width) in areas where the cuticle had been damaged. Cuticle cells isolated from hair fibres showed distinct geometrical features on their surfaces when examined using differential interference contrast microscopy. The results are interpreted to indicate the presence of a residue of lipid-staining material adhering to the cuticle cells of hair, the residue possibly being derived from adhesive material produced at the areas of contact between presumptive cuticle cells during the early stages of cuticle shape differentiation.     

香烟烟雾为模型的污染环境对头发损伤的研究

基于香烟烟雾建立了模拟空气污染的环境,测试健康和受损发束在该污染环境中的损伤情况。通过对比多次处理前后暴露污染的样品发束和未暴露污染的对照发束的湿发和干发梳理性、表面接触角、色氨酸含量和表面毛鳞片特征的变化,表明该污染环境对头发有显著的化学损伤。尤其是健康头发暴露空气污染后表面毛鳞片受损和角蛋白损伤降解,表面更加亲水,梳理性变差。通过以上方法在健康发束上证明了聚合物聚酰亚胺-1具备抵御损伤的能力。     

Mechanical properties of poly(ether-ether-ketone) for engineering applications

An outline of the characteristics of PEEK and the versatility of its compositional forms (micro and macro composites) are given to illustrate its wide potential for success in engineering applications. Although it is necessary to have particular tabulations of mechanical properties for engineering design, these are seldom available and consequently it is argued that an understanding of stiffness, toughness and strength properties are required to fully exploit available manufacturer's data and thus develop the full potential of PEEK and its composites. Stiffness characteristics are considered in terms of a modulus function which is dependent on time under load and temperature. In its composite forms, whether reinforced with short or continuous fibres, stiffness anistropy can be both considerable and complex, but some empirical ground-rules are apparent. For continuous fibre composites even in the form of complex lay-ups, it is also possible to attempt some stiffness prediction from certain pseudo-elastic constants. Toughness of PEEK and its composites is described in terms of both comparative and intrinsic properties. Instrumented falling weight impact data, particularly as a function of temperature enable some insight into ductile-brittle transitions for the unreinforced material, but crack initiation and crack propagation processes for the various fibre reinforced forms. Intrinsic toughness is described in terms of linear elastic fracture mechanics theory. Strength properties are described for static and dynamic loading configurations. In particular, PEEK and its composites are evaluated for increasing test severities for strength characteristics; stress concentration, loading form and test temperature are considered.     

Sex pheromones inCulicoides nubeculosus (diptera,ceratopogonidae): Possible sites of production and emission

This study was performed on virgin females ofCulicoides nubeculosus to determine sites of production and emission of sex pheromone. The ventral abdominal surface is the site of emission of the pheromone. Morphologically there is evidence of the presence of abdominal atrichial areas. The abdominal areas, eight per segment (four ventral and four dorsal), are covered by a cuticle devoid of micro- and macrotrichiae. The dorsal and ventral areas differ considerably in their structure. The dorsal atrichial areas have an unperforated cuticle covering a normal epidermis, whereas the ventral atrichial areas have a cuticle perforated by numerous tubular structures, with a loosely organized procuticle and no underlying epidermal cells. A pair of voluminous cells with the classical ultrastructural characteristics of enocytes is invariably located in the vicinity of the ventral atrichial areas. These cells undergo ultrastructural modifications tending towards involution according to the age of the insects, being correlated with the decrease in pheromone emission by older females. The hypothesis is put forward that enocytes are involved in pheromone production.     

Regulation of Nuclear Mechanics and the Impact on DNA Damage

In eukaryotic cells, the nucleus houses the genomic material of the cell. The physical properties of the nucleus and its ability to sense external mechanical cues are tightly linked to the regulation of cellular events, such as gene expression. Nuclear mechanics and morphology are altered in many diseases such as cancer and premature ageing syndromes. Therefore, it is important to understand how different components contribute to nuclear processes, organisation and mechanics, and how they are misregulated in disease. Although, over the years, studies have focused on the nuclear lamina—a mesh of intermediate filament proteins residing between the chromatin and the nuclear membrane—there is growing evidence that chromatin structure and factors that regulate chromatin organisation are essential contributors to the physical properties of the nucleus. Here, we review the main structural components that contribute to the mechanical properties of the nucleus, with particular emphasis on chromatin structure. We also provide an example of how nuclear stiffness can both impact and be affected by cellular processes such as DNA damage and repair.     

Altering Silk Film Surface Properties through Lotus‐Like Mechanisms

The nonwetting and self‐cleaning properties of the lotus depend on microscale and nanoscale roughness provided in part by a covering of epicuticular waxes that crystalize on the surface of its leaves. Wax deposition is driven by the evaporation of water, which carries waxes to the surface as it moves through the epidermis and cuticle. If the wax layer is damaged, repair occurs through the same mechanism. The experiments described herein have exploited this principle to establish a completely biologically derived system based on silk and lotus epicuticular wax, showing that it is possible to coat silk surfaces with waxes and thereby change their wetting characteristics and tensile properties. The robustness of the material is also documented by crystal regrowth after damage to the wax layer through abrasion (scratching and rubbing), resistance to water‐jetting, and UV exposure. To further characterize this system, the diffusion of natural and synthetic waxes through two types of silk films, Bombyx mori fibroin and engineered spider silk are studied, showing that the extent of wax diffusion through silk membranes depends upon wax type and protein structure, which remains unchanged through the process. Making use of the simple passive phenomenon of advection, these studies represent a method of low‐energy fabrication of completely biological, lotus‐inspired membranes with tunable surfaces.     

纳米材料的进展及其在塑料中的应用

介绍了近年来的纳米技术发展的概况，其中包括纳米粒子表面特性和表面改性的方法以及有机相界面改性的工艺路线。通过普通粉末、亚微米、微米级粉末和纳米级粉末作为兼填充剂填充效果的对比，突出了纳米级粉末优良的填充特性以及赋予复合材料的性能上质的飞跃的能力。     

Hydrocarbon dynamics within and between nestmates inCataglyphis niger (Hymenoptera: Formicidae)

The objective of the present study was to evaluate the interrelationship between the cuticular and postpharyngeal glands' hydrocarbons, both in the individual ant and during its interaction with nestmates. In vivo radiochemical assays were employed to monitor the de novo hydrocarbon biosynthesis from acetate in the ant's body. The newly synthesized hydrocarbons appeared first internally and after 24 hr they accumulated in the postpharyngeal gland and on the cuticular surface. Blocking the possibility of external transfer of hydrocarbons between cuticle and postpharyngeal gland led to a significant decrease of labeled hydrocarbons in the postpharyngeal gland. In addition, during encounters between labeled and unlabeled ants, newly synthesized hydrocarbons were transferred, mainly via trophallaxis, but also by allo-grooming and physical contact. In view of these results, we propose as a model for their dynamics that hydrocarbons are synthesized in tissues associated with the integument. Through self-grooming, there is a constant exchange of hydrocarbons between the cuticular surface and the postpharyngeal gland. Furthermore, in encounters between nestmates, hydrocarbons are exchanged among them mostly by trophallaxis, with the mediation of the postpharyngeal gland. Thus, this gland acts as a pool for mixing colonial hydrocarbons and may serve to attain a unified colony odor.     

CONTINUUM MECHANICS APPLIED TO A VERY THIN LIQUID FILM: ESTIMATION OF SURFACE TENSION FOR THE n-ALKANES

This analysis demonstrates that, at least in some cases, continuum mechanics can be successfully applied in problems involving very thin films, so long as proper recognition is given to long-range intermolecular forces and to the finite size of molecules. In this particular case, the integral mechanical energy balance is used to analyze a simple thought experiment in which a thin liquid film is slowly stretched. The result is an expression for surface tension as a function of the Hamaker constant describing liquid-liquid, long-range intermolecular forces, the molecular weight, and the liquid density, which is in good agreement with previous experimental measurements for n-alkanes.     

Responses of two hymenopteran predators to surface Chemistry of their prey: Significance for an alkaloid-sequestering caterpillar

Larvae ofUresiphita reversalis (Guenée) (Lepidoptera: Pyralidae) sequester quinolizidine alkaloids from their leguminous hosts and store them primarily in the cuticle. Stored alkaloids are lost with the last larval molt. Extracts of late-instar larvae and of pupae were applied to larvae of the potato tuber moth,Phthorimaea operculella (Zeller) (Gelichiidae), which are normally palatable to two hymenopteran predators, the Argentine ant,Iridomyrmex humilis (Mayr) (Formicidae), and the paper wasp,Mischocyttarus flavitarsus (Sauss.) (Vespidae). Larvae ofP. operculella treated with alkaloid extracts ofU. reversalis larval exuviae, or with surface extracts of whole larvae, were deterrent to both predators, compared to untreated prey. Extracts of pupal exuviae added toP. operculella, however, were not deterrent.P. operculella larvae treated with the authentic alkaloids sparteine and cytisine were also deterrent to these hymenopteran predators. Storage of small but concentrated amounts of plant secondary compounds in the cuticle appears to be an efficacious means of defense against at least two common predators of lepidopteran larvae.     

Properties of cuticular oxidases used for sex pheromone biosynthesis byHeliothis zea

Biosynthesis of the aldehydic sex pheromone components released by females ofHeliothis zea was found to be catalyzed by primary alcohol oxidases residing in the cuticle that covers the glands. Activity, as indicated by conversion of primary alcohol to aldehyde, was as high in cell-free cuticle as it was in intact pheromone glands. Studies indicated that some activity was associated with the surface of the epicuticle and could be removed, into buffer, by sonication. However, the majority of activity lies within the inner epicuticle and exo- and endocuticular layers. The oxidase was not functional in pharate pupae that did not have mature adult cuticle but became functional just prior to adult emergence. The enzyme in individual glands was saturated at alcohol concentrations above 100 n. moles. Nonionic detergents did not affect the activity of the oxidase in the cuticle but treatment with either 7 M urea or 1% SDS resulted in total loss of activity. Studies on the effect of pH indicated an optimum at 6.4; however, activity was high throughout the range of 5–9. The oxidase was functional in both dichloromethane and hexane, suggesting that this enzyme system may have applications for organic synthesis of aldehydes.     

A simple method for analysis of insect cuticular hydrocarbons

Cuticular hydrocarbons from tiny pieces of insect cuticle can be analyzed directly by gas chromatography without solvent. The cuticle, sealed in a glass capillary, is introduced into the heated injector area of a gas Chromatograph, and the glass capillary crushed after heating for 4 min. Linked gas chromatography-mass spectrometry can be performed on selected parts of individual insects, such as an antenna, leg, or abdominal sclerite, to give qualitative and quantitative analysis of the substances on a small area of the body.     

Surface Barrier Effects in Wool Dyeing Part I - The Location of the Surface Barrier

The properties of the surface layer on wool fibres which limits the rate of dye uptake have been examined. The removal of the barrier layer by mechanical means and its degradation by surface reduction using tri–butyl phosphine have been studied using the rate of dyeing as a parameter. The chemical properties of the barrier layer suggest that it is a cystine–rich component of the cuticle layer system, either the exocuticle or its ‘a’ layer sub-system.     

Theories of adhesion and uses of adhesives: a review

Theories of adhesion are based on adsorption and wetting, on diffusion, on donor/acceptor or electrostatic interactions and on simple mechanical interlocking of the adhesive into irregularities of its substrate. The principal contributions of recent work to these theories are outlined. Joint strength is also a matter of stress distribution and knowledge of this has been advanced both by formal mathematical methods and by the use of finite element analysis. The tack of adhesives is now better understood as involving the interaction of both bulk and surface properties with the rate of separation. Fracture mechanics has been applied to the investigation of the failure of structural adhesives in humid environments. The properties determining adhesive behaviour comprise T_g, solubility parameter, surface free energy, viscosity and the microstructure of the polymer. The latter, more recently explored, is examined in detail. The structure of the adhesives for use at high temperature and the changes in technology demanded by impending legislation conclude the review.     

发泡橡胶在冬季轮胎胎面中的应用机理及性能研究

研究了发泡橡胶在冬季轮胎胎面中的应用机理和发泡橡胶提高轮胎／冰面摩擦力的机理，以及发泡橡胶的微孔结构对拉伸性能、动态力学性能和摩擦性的影响。结果表明．改变微孔形貌完全可以调节发泡橡胶的力学性能及动态力学性能。     

由特殊形貌基材构建的耐磨双疏表面研究进展

双疏表面因在自清洁、防污、防腐蚀等方面的应用价值而受到广泛关注.然而,双疏表面在使用过程中因机械摩擦等作用,易造成微-纳结构及双疏官能团的破坏而影响双疏性能.因此,如何提高机械稳定性能已成为双疏表面在实际应用中的关键问题.首先,介绍了基材微结构对双疏表面的影响;接着,从化学刻蚀、电化学刻蚀、激光加工、电化学沉积、压印或模板等制备方法综述了微结构基材-机械稳定双疏表面的构建;指出特殊形貌基材通过尺度较大的规整凹凸结构为附着的尺度较小的纳米粗糙表面和疏液基团提供了保护,进而实现机械稳定性;最后,总结了该领域研究存在的问题,展望了未来的发展方向.     

The Complex and Critical Role of Glycine 12 (G12) in Beta-Connexins of Human Skin

Glycine is an amino acid with unique properties because its side chain is composed of a single hydrogen atom. It confers conformational flexibility to proteins and conserved glycines are often indicative of protein domains involving tight turns or bends. All six beta-type connexins expressed in human epidermis (Cx26, Cx30, Cx30.3, Cx31, Cx31.1 and Cx32) contain a glycine at position 12 (G12). G12 is located about halfway through the cytoplasmic amino terminus and substitutions alter connexin function in a variety of ways, in some cases altering protein interactions and leading to cell death. There is also evidence that alteration of G12 changes the structure of the amino terminus in connexin- and amino acid- specific ways. This review integrates structural, functional and physiological information about the role of G12 in connexins, focusing on beta-connexins expressed in human epidermis. The importance of G12 substitutions in these beta-connexins is revealed in two hereditary skin disorders, keratitis ichthyosis and erythrokeratodermia variabilis, both of which result from missense mutations affecting G12.