Comparative alkane chemistry of Parthenium argentatum (guayule) and some F1 hybrids

The leaf alkanes of Parthenium argentatum (guayule), P. tomentosum var. stramonium, P. fruticosum var. trilobatum, and the first filial (F₁) generations obtained from crosses with guayule were investigated by GC and mass spectrometry and shown to be useful in chemotaxonomic studies. The identified n-alkanes ranged from C₁₉ to C₄₀ with either n-C₂₉ or n-C₃₁ as the main component. The alkane chemistry of guayule with n-C₃₁ being the main component predominated in most of the F₁ hybrids. The presence of iso-branched alkanes (C₂₇, C₂₉, C₃₁) in P. tomentosum and its hybrids could be detected by GC/MS. These preliminary investigations indicate that epicuticular wax alkanes can be useful in inheritance studies of guayule and its hybrids.     

Hydrocarbon profiles of diapausing and reproductive adult face flies (Musca autumnalis)

Hydrocarbons present on the cuticle surface of adult face flies, Musca autumnalis, were identified by GC-MS and quantified by GC. Hydrocarbons consisted of n-, monomethyl, and dimethyl alkanes ranging in chain length from 23–29 carbons. Also present were monounsaturated alkenes with chain lengths of 23, 25, 27, and 29 carbons. Wild-caught flies were extracted and hydrocarbon profiles determined for both diapausing and reproductive adult males and females. Few qualitative differences were found between males and females in the hydrocarbon profile. Differences in percent composition were found between diapausing and reproductive flies in monounsaturated alkenes, 4 and 45%, n-alkanes, 24 and 37%, monomethylalkanes, 57 and 15%, and dimethylalkanes, 15 and 2%, respectively, for females. A small difference was found in the total amount of hydrocarbon present, 7.3 ± 0.6 and 9.7 ± 1.1 μg/fly, between diapausing and reproductive female flies, respectively. Adult males also exhibited a similar change in hydrocarbon profile and amount between diapausing and reproductive flies. A laboratory strain of face flies originating in Minnesota was also analyzed, and again similar differences were observed in both male and female flies that were kept under a reproductive or diapause condition. Arch. Insect Biochem. Physiol. 37:206–214, 1998. © 1998 Wiley-Liss, Inc.     

The use of dosed and herbage n-alkanes as markers for the determination of digestive strategies of captive giraffes (Giraffa camelopardalis)

Selected aspects of digestion in captive giraffes were investigated in two trials with a type of marker that is new for digestive studies in non-domestic species. N-Alkanes were used as internal and external markers. In Trial 1, diet composition, intake, and digestibility were directly measured and estimated with the marker. Six giraffes were dosed once daily for 3 weeks with labeled pellets containing 3,800 ppm of each C₂₈, C₃₂, and C₃₆ alkanes at ˜100 mg/100 kg bodyweight. Intake of cabbage, browse, and a cattle pellet could accurately be estimated with the alkane method. For an oat/wheat mix and clover hay, however, there were large differences between directly measured intakes and those obtained using the alkane method, with the alkane method substantially underestimating. In Trial 2 mean retention times (MRTs) of fluid and particle phase were estimated. Three subadult giraffes were dosed once with cobalt-ethylenediamine tetraacetic acid (Co-EDTA) (260 mg) and alkanes C₂₉ (140 mg) and C₃₆ (370 mg). The average MRT for the fluid phase (Co-EDTA) was 31 hr and for the particle phase (alkanes) was 41 hr (C₃₆) and 43 h (C₂₉). This study showed that n-alkanes have potential as markers for investigating digestive strategies in non-domestic herbivores. Zoo Biol 17:295–309, 1998. © 1998 Wiley-Liss, Inc.     

The determination of n-alkanes in the cuticular wax of leaves of Ludwigia adscendens L

An n-hexane extract of fresh, mature leaves of Ludwigia adscendens, containing a thin layer of epicuticular waxes, has been analysed for the first time by TLC, IR and GC using standard hydrocarbons. The leaves contained 22 identified long chain (C15-C36) n-alkanes, accounting for 74.27% of the hydrocarbons present, and an unknown number of unidentified branched chain alkanes. The predominant n-alkane was C25 (11.02%), whilst C18 (7.62%), C20 (6.14%), C29 (5.36%) and C27 (5.29%) n-alkanes were moderately abundant: the C35 homologue was present only in minor amounts (0.22%).     

A mild and environmentally friendly scandium(III) trifluoromethanesulfonate-catalyzed synthesis of bis(3'-indolyl)alkanes and bis(3'-indolyl)-1-deoxyalditols

Bis(3'-indolyl)alkanes and bis(3'-indolyl) derivatives containing a 1-deoxyalditol moiety were synthesized in the presence of 5 mol% of scandium(III) trifluoromethanesulfonate [Sc(OTf)3] in CH3CN or EtOH-H2O mixture as a solvent from room temperature to 70 degrees C in good yields (78-97%).     

Biogeochemistry of organic matter in Lake Geneva: I — particulate hydrocarbons as biogenic and anthropogenic molecular markers

A study of the biogeochemistry of organic matter in Lake Geneva at a central station (SHL2), was carried out at key periods of the biological cycles from November 1985 to September 1986. The seasonal variability of particulate hydrocarbons was studied in the epilimnion and the hypolimnion, focusing on specific periods such as high phytoplankton productivity and rising herbivorous zooplankton activity (May 1986), clearness of waters (June 1986) and intense mixing of waters (February 1986).Analysis of non-aromatic hydrocarbons (NAH) indicated that their major source is the autochtonous phytoplankton. Year 1986 was characterized by a spring bloom of nanoplankton (chlorophyceae and cryptophyceae) which remained predominant during summer and fall. These biological events were correlated with an increase of biogenic NAH, particulary n-alkane and alkene concentrations; the latter increased by one order of magnitude in May. n-Alkane distributions maximized at n-C₁₇ or n-C₂₉, and the n-C₁₇/n-C₂₉ ratio varied in surface water from 2.8 in May to 0.06 in November of the preceding year, reflecting phytoplankton dominant species. Values of NAH/POC, n-alkanes/POC, alkenes/POC and pristane/phytane ratios underwent seasonal and vertical variations which could be related to grazing and/or settling of particles. NAH, n-alkane and alkene enrichment in hypolimnion particles was interpreted to be a result of zooplankton migrations.A series of 37 monoenes and polyenes having from 15 to 31 carbon atoms, originating from planktonic sources, were recognized in the particulate matter by gas chromatography/mass spectrometry (GC/MS). Their distribution was described in 3 sized particles (> 200 µm, 200-60 µm and < 60 µm, identified as adult zooplankton, young zooplankton and nanoplankton respectively) at two different periods of the biological cycle, May and June 1986. Low level inputs originating from terrestrial higher plants were evident in particles; the value of the Carbon Preference Index (CPI) in the carbon range 23–35 was less than 2.8.In all samples analyzed by GC, an unresolved complex mixture of hydrocarbons (UCM) was present and was interpreted, at least in May, as partly originating from the degradation of organic matter by microorganisms. Typical anthropogenic PAH, such as benzofluoranthene and dibenzo (a) anthracene, were found at a low level (9 and 3 ng l^–1 respectively). The absence of hopane-type hydrocarbons, except in November 1985 and in September 1986, and typical combustion PAH associated with particles indicated high temperature pyrolytic contaminants rather than petroleum-derived compounds.     

The Relationship Between Lipid Composition of Red Blood Cells and Their Susceptibility to Lipid Peroxidation

Red blood cells from 31 healthy donors were examined for the cholesterol content, the fatty acid composition. and the susceptibility to lipid peroxidation induced by either hydrogen peroxide or phenylhy-drazine. Lipid peroxidation was monitored by the release of pentane and ethane. In addition, plasma fatty acids were measured in order to find out, whether plasma and red cell fatty acids were correlated. In experiments with hydrogen peroxide, a significant positive correlation was found between the proportion of arachidonic acid (C 20:4n – 6; r = 0.57, p < 0.01) and docosahexaenoic acid (C 22:6; - 3; r = +0.71, p < 0.01), and the release of pentane and ethane, respectively. A significant negative correlation was found between the membrane cholesterol content and the pentane release (r -0.44, p< 0.05). In experiments performed with phenylhydrazine, red cell membrane lipid composition did not influence the susceptibility of red cells to lipid peroxidation. A close correlation was found between plasma and red cell fatty acids (palmitic acid, r = +0.46, p < 0.01; linoleic acid, r = +0.41, p < 0.05; arachidonic acid, r = +0.59, p < 0.01; docosahexaenoic acid, r = +0.67, p < 0.01). The results demonstrated that the degree of peroxide-induced oxidation of erythrocyte lipids depends on the content of polyunsaturated fatty acids in the membrane, which on the other hand, is determined by plasma fatty acids. It is suggested that dietary variations may influence the susceptibility of red cells to lipid peroxidation.     

甲基-辅酶M还原酶结构、功能及催化机制研究进展

产甲烷古菌是目前发现唯一能产生甲烷气体的微生物,也是自然界中生物甲烷的主要贡献者。甲基-辅酶M还原酶 (Methyl-coenzyme M reductase,Mcr) 负责产甲烷代谢中最后一步甲烷的生成与甲烷氧化代谢中第一步甲烷的激活反应。该酶的基因高度保守,被广泛应用于古菌的鉴定与系统发育研究。其特殊的辅因子F430及催化碳氢 (C-H) 键裂解的酶学机制也一直备受关注。近年来,在高分辨率蛋白结构和反应过渡态结构方面的重要突破有效地推动了Mcr结构与功能的研究。特别是最新发现的激活非甲烷烷烃厌氧降解的类甲基-辅酶M还原酶 (Mcr-like),引起了众多研究者对该类酶激活惰性烷烃分子机制的浓厚兴趣。因此,文中概述了Mcr结构、功能及催化机制的最新研究进展,包括新发现的Mcr-like的研究情况,并展望了Mcr/Mcr-like酶在烷烃厌氧氧化及温室气体控制方面的未来研究方向。     

Bacterial patterning at the three-phase line of contact with microtextured alkanes

Aliphatic crystallites, characteristic of the eicosane and docosane components of naturally occurring lipids, were found to form microtextures that were structured by specific interactions with ordered graphite (HOPG) used as the underlying substratum, as confirmed by scanning electron microscopy (SEM) and fast Fourier transform (FFT) analysis. Confocal scanning laser microscopy (CLSM) showed highly directed bacterial alignment for two bacterial species (spherical and rod-shaped), reflecting the preferential orientation of the crystallite–air–water interfaces to give linear and triangular bacterial patterning. The mechanisms of bacterial attachment are demonstrated in terms of the balance between effective radial adhesional forces and the capillary forces resulting from the water contact angle of the bacteria at the three-phase line (TPL) of the lipid surface. It is suggested that these microtextured surfaces, which exhibit the ability to limit bacterial adhesion to a precise patterning at the lipid TPL, could be used as a means of controlling bacterial colonization.     

A comparative study of critical temperature estimation of atomic fluid and chain molecules using fourth-order Binder cumulant and simplified scaling laws

Grand-canonical transition-matrix Monte Carlo simulation with histogram reweighting and finite-size scaling technique are used to calculate fourth-order Binder cumulant of order parameter along the vapour–liquid coexistence line to calculate the critical temperature of bulk and confined square-well fluid in slit pore of two pore sizes. Further, this approach is utilised to estimate the critical temperatures of relatively more complex fluids such as n-alkanes confined in graphite and mica slit pores of different slit widths. The estimated critical temperatures are compared with the critical temperature obtained for the same systems using simplified form of the scaling law. This investigation reveals that critical temperatures of simple and complex fluids in bulk state and under confinement, estimated using the scaling law, are within reasonable accuracy with that obtained using more accurate and rigorous approach of fourth-order Binder's cumulant.