N-alkyl Compounds Research Articles

Effect of salinity on the preservation of plant-derived n-alkyl compounds in the terrestrial-aquatic interface

In sediments, plant biomolecules (n-alkanes and fatty acids) serve as robust proxies in paleoenvironmental studies. Although the factors controlling preservation and isotopic composition of plant biomolecules are understood in soil systems, the effect of changes in depositional environments in land-sea interfaces, especially in hypersaline environments, is not so well constrained. In this study, we observed that in bed sediments, the plant biomolecules are preserved with carbon preference index (CPI) values > 1 in high molecular weight (HMW) n-alkanes in the hypersaline, metahaline, and euhaline regions of the Pulicat lagoon, India. However, in sub-surface sediments (up to 70 cm depth), the CPI values are consistently < 1 in the hypersaline region, but > 1 in the euhaline and metahaline regions. In the hypersaline region, the alteration of plant biomolecules possibly results from halophilic bacterial degradation and fatty acid to n-alkane reduction in anaerobic conditions (pristane/phytane values < 1), during the weaker northeast monsoon (44–60 cm sub-surface). Prolonged hypersaline conditions and associated anoxia resulted in a higher isotopic difference between fatty acids and n-alkanes (δ13CFA-ALK value) in the hypersaline region (3.1 ± 1.5‰) compared to metahaline (2.2 ± 1.0‰) and euhaline (1.5 ± 1.0‰) regions. Although in the hypersaline region the HMW fatty acids have CPI values > 1, the higher δ13CFA-ALK value also suggests the alteration of fatty acids. This study suggests that if plant-derived n-alkanes are altered, the δ13C values and distribution patterns of plant-derived fatty acids should be critically evaluated before using it as an alternative proxy in coastal environments.

Isotopic and molecular distribution of leaf-wax in plant-soil system of the Gangetic floodplain and its implication for paleorecords

The stable isotopic composition of bulk organic matter (OM), as well as the molecular and isotopic composition of n-alkanes and n-alkanoic acids, are compared in various plant growth-forms (trees, shrubs and grasses) and soils from the Gangetic floodplain. Abundance of higher molecular weight (HMW) n-alkanes is found to be highest in grasses and shrubs and lowest in trees, whereas n-alkanoic acids show an opposite trend. Total lipid production is highest in trees and lowest and comparable in shrubs and grasses, reflecting differences in metabolic conditions and water use efficiency during synthesis of these biomolecules in trees and overground species. In all plant growth-forms, higher (5‰) carbon isotopic composition (δ13C) are observed in bulk OM compared to 13C/12C ratio of n-alkyl compounds, while a small difference (0.2‰) is seen in between n-alkane and n-alkanoic acids. The trees and shrubs show lower average hydrogen isotopic composition (δD) in n-alkanes (δDalk) and higher values in n-alkanoic acids (δDacid) compared to the grass species. Interestingly, the grass and shrub species register higher variation (ca. 110‰) in δD values of n-alkyl compounds, reflecting the ability of groundcover species to proliferate under varying environmental conditions. The lower D/H (ca. 74‰) variation in the tree species possibly suggests consistent dependency on the perennial water sources. Although the study site is equally dominated by C3 and C4 vegetation, mean δ13C values of bulk OM and n-alkanoic acid in soil show proximity to the C4 end-member, while n-alkanes show proximity to C3 trees. Mean δDalk values in the soil reflect the cumulative hydrological condition of the overground vegetation, while average δDacid values mimic the ambient conditions specific to the C3 species. The variation in OM mixing from different plant types in soil was triggered by soil-forming processes, which possibly resulted in variation in responses between the n-alkyl compounds. Compared to the global record, the C3-C4 vegetation of the Gangetic floodplain is characterised by a lower (ca. 0.5–2‰) difference between bulk leaf tissues and n-alkyl compounds (Δ13CBulk–alk/acid). H-isotopic fractionation with respect to the ambient water (εapp) shows higher (ca. +30‰) values for n-alkanoic acids and lower (ca. −60‰) values for n-alkanes compared to the global datasets, implying a role of regional environmental conditions on the isotopic fractionation in n-alkyl compounds in plants. As molecular and isotopic compositions of plant-derived proxies are related to environmental conditions, emphasis must be given to establish the response of proxies to regional conditions before applying them in paleoenvironmental reconstructions.

Tricepyridinium-inspired QACs yield potent antimicrobials and provide insight into QAC resistance.

Quaternary ammonium compounds (QACs) comprise a large class of surfactants, consumer products, and disinfectants. The recently-isolated QAC natural product tricepyridinium bromide displays potent inhibitory activity against S. aureus but due to its unique structure, its mechanism of action remains unclear. A concise synthetic route to access tricepyridinium analogs was thus designed and four N-alkyl compounds were generated in addition to the natural product. Biological analysis of these compounds revealed that they display remarkable selectivity towards clinically-relevant Gram-positive bacteria exceeding that of commercially-available QACs such as cetylpyridinium chloride (CPC) and benzalkonium chloride (BAC) while having little to no hemolytic activity. Molecular modeling studies revealed that tricepyridinium and shorter-chain N-alkyl analogs may preferentially bind to the QacR transcription factor leading to potential activation of the QAC resistance pathway found in MRSA; however, our newly synthesized analogs are able to overcome this liability.

Mulching-induced preservation of soil organic matter quality in a burnt eucalypt plantation in central Portugal

Mulching has amply proven its effectiveness to mitigate post-fire soil erosion but its impacts on soil organic matter (SOM) quality and quantity continue poorly studied. The present study addressed this knowledge gap for a eucalypt plantation in central Portugal that had been burnt and, immediately after the wildfire, mulched with 13.6 Mg ha−1 of eucalypt logging residues some five years before. This was done by performing a range of analytical techniques (elemental and isotope analyses, analytical pyrolysis and 13C NMR spectroscopy) not only on the bulk soil samples but also on their humic acids (HAs) and free organic matter (FOM) fractions. While mulching reduced soil and SOM losses with 91 and 93%, respectively, it also improved SOM quality of the topsoil, in particular in terms of HAs and FOM. At 0–4 cm depth, both HAs and FOM contents were roughly twice as high in the mulched plots as in the control plots. The effects of mulching on the molecular composition of HAs and FOM fractions, however, varied markedly. Analytical pyrolysis (Py-GC/MS) revealed that mulching had led to a noticeable accumulation of labile, aliphatic SOM constituents such as carbohydrate-derived and alkyl compounds (fatty acids and n-alkanes) but that it hardly affected the composition of HAs. Even so, solid-state 13C NMR spectroscopy showed that mulching had resulted in a relative increase in aryl C in the FOM fraction, suggesting an enhanced preservation of the pyrogenic OM. Overall, the combined use of a range of analytical techniques allowed to conclude that, five years after their application, the forest logging residues had led to a greater preservation of the fire-derived pyrogenic OM (mainly aromatic compounds) in the topsoil as well as to higher contents of SOM's most labile molecular constituents (mainly carbohydrates and n-alkyl compounds). The former reflected the reduced erosion rates, while the latter was probably due to a combination of reduced erosion rates with the additional input of fresh organic matter.

Characteristics and compound-specific carbon isotope compositions of sedimentary lipids in high arsenic aquifers in the Hetao basin, Inner Mongolia

Organic matter, as an electron donor, plays a vital role in As mobilization mediated by microorganisms during reductive dissolution of Fe/Mn oxides in shallow aquifers. However, the specific types and sources of organic matter involved in biogeochemical processes accelerating As mobilization are still controversial. Both sediment and groundwater samples were collected at different depths from aquifers of the Hetao Basin, a typical inland basin hosting high As groundwater. Sedimentary lipids and their compound-specific carbon isotope ratios were analyzed to evaluate characteristics and sources of organic matter. Results show that sedimentary As were well correlated with Fe and Mn oxides, suggesting that As exist as Fe/Mn oxide bound forms. Groundwater As far exceeded the drinking water guide value of 10 μg/L. Moreover, As concentrations in shallow groundwater were relatively higher. Lipids in clay were mainly originated from terrestrial higher plants, while that in fine sand samples were derived from terrestrial higher plants, microorganism and petroleum. Shallow fine sand samples were also characterized by evident in-situ biodegradation. Compound-specific carbon isotope compositions of sedimentary lipids showed that short-chain n-alkanes and n-alkanoic acids had more positive δ13C values compared to long-chain compounds, especially in shallow fine sand samples. δ13CTOC were also low in shallow fine sand samples. These results jointly indicate that these lipids in shallow fine sand samples acted as carbon source for indigenous microorganism and the short-chain components were particularly more vulnerable to biodegradation, which may contribute to high As concentrations in shallow groundwater. The new findings provide the first evidence that short chain length n-alkyl compounds afforded a source of potential electron donors for microbially mediated As mobilization process in the shallow aquifers.

Assessing the effects of UVA photocatalysis on soot-coated TiO2-containing mortars

The deposition of soot on building surfaces darkens their colour and leads to undesirable black crusts, which are one of the most serious problems on the conservation of built cultural heritage. As a preventive strategy, self-cleaning systems based on the use of titanium dioxide (TiO2) coatings have been employed on building materials for degrading organic compounds deposited on building surfaces, improving their durability and performance. In this study, the self-cleaning effect of TiO2-containing mortars coated with diesel soot has been appraised under laboratory conditions. The mortar samples were manufactured using lime putty and two different doses of TiO2 (2.5% and 5%). The lime mortars were then coated with diesel engine soot and irradiated with ultraviolet A (UVA) illumination for 30days. The photocatalytic efficiency was evaluated by visual inspection, field emission scanning electron microscopy (FESEM) and colour spectrophotometry. Changes in the chemical composition of the soot particles (including persistent organic pollutants) were assessed by analytical pyrolysis (Py-GC/MS) and solid state 13C NMR spectroscopy.The FESEM and colour spectrophotometry revealed that the soot-coated TiO2-containing mortars promoted a self-cleaning effect after UVA irradiation. The combination of analytical pyrolysis and 13C solid state NMR showed that the UVA irradiation caused the cracking of polycyclic aromatic structures and n-alkyl compounds of the diesel soot and its transformation into methyl polymers. Our findings also revealed that the inclusion of TiO2 in the lime mortar formulations catalysed these transformations promoting the self-cleaning of the soot-stained mortars. The combined action of TiO2 and UVA irradiation is a promising proxy to clean lime mortars affected by soot deposition.

ChemInform Abstract: Site‐Selective and Stereoselective Functionalization of Unactivated C—H Bonds.

Organic synthesis has traditionally relied heavily on the introduction and manipulation of functional groups, such as carbonoxygen or carbonhalogen bonds. Much current research is focused on a potentially powerful alternative strategy in which carbonhydrogen bonds, normally much less reactive and therefore resistant to functionalization, are somehow persuaded to be more easily modified. These authors report that it is possible to selectively functionalize an unactivated CH bond by the use of well-defined catalysts to control the site selectivity, without the need for a directing or anchoring group present in the molecule. They use dirhodium catalysts to achieve diastereoselective and enantioselective CH functionalization of n-alkanes and terminally substituted n-alkyl compounds. The reactions proceed in high yield and can be carried out on substrates containing other functional groups such as halides, silanes, and esters.

The alkyl glycerol ether lipid composition of heterotrophic sulfate reducing bacteria strongly depends on growth substrate

Bacterial non-isoprenoid alkyl glycerol ether lipids (AGEs) are widespread in the environment but little is known about their biological precursors and mode of formation as a function of varying growth conditions. Here, we searched for the presence of AGEs in five pure strains of mesophilic (growth temperature between 20 and 40°C) and heterotrophic sulfate reducing bacteria from the family Desulfobacteraceae grown on a wide range of hydrocarbons and organic acids as sole carbon and energy source. Gas chromatography–mass spectrometry (GC–MS) analysis of hydrolyzed cells revealed the presence of monoalkyl glycerols (MAGEs) in one Desulfatiferula species and of MAGEs and dialkyl glycerols (DAGEs) in two Desulfatibacillum species. Species from the genus Desulfococcus did not produce AGEs. The ether lipid composition appeared strongly dependent on the nature and the chain length of the carbon substrate, with few to >50 homologues of AGEs formed from a single substrate. Growth on long chain n-alkyl compounds (C14 to C18 alk-1-enes and fatty acids) generated a much lower diversity of MAGEs and DAGEs than short chain substrates (nonanoate, octanoate and pyruvate) or isoprenoid alkenes (phytadienes). Such variation in alkyl glycerol production could be linked to the distinct pathways involved in the metabolism of the different substrates. Despite this substrate-dependent AGE composition, the average chain length and level of branching of each class of ether lipid remained remarkably stable whatever the growth substrate and the number of MAGE and DAGE homologues formed, indicating a compositional control of ether lipids by heterotrophic bacteria to maintain optimal membrane properties.

Site-selective and stereoselective functionalization of unactivated C–H bonds

The laboratory synthesis of complex organic molecules relies heavily on the introduction and manipulation of functional groups, such as carbon-oxygen or carbon-halogen bonds; carbon-hydrogen bonds are far less reactive and harder to functionalize selectively. The idea of C-H functionalization, in which C-H bonds are modified at will instead of the functional groups, represents a paradigm shift in the standard logic of organic synthesis. For this approach to be generally useful, effective strategies for site-selective C-H functionalization need to be developed. The most practical solutions to the site-selectivity problem rely on either intramolecular reactions or the use of directing groups within the substrate. A challenging, but potentially more flexible approach, would be to use catalyst control to determine which site in a particular substrate would be functionalized. Here we describe the use of dirhodium catalysts to achieve highly site-selective, diastereoselective and enantioselective C-H functionalization of n-alkanes and terminally substituted n-alkyl compounds. The reactions proceed in high yield, and functional groups such as halides, silanes and esters are compatible with this chemistry. These studies demonstrate that high site selectivity is possible in C-H functionalization reactions without the need for a directing or anchoring group present in the molecule.

Insight into Technetium Amidoxime Complex: Oxo Technetium(V) Complex of N-Substituted Benzamidoxime as New Basic Structure for Molecular Imaging

In search of benzamidoxime (BHam) derivatives that provide a single (99m)Tc-labeled compound of high in vivo stability, we synthesized three N-alkyl compounds of benzamidoxime (BHam) ligand. They provided a single (99m)Tc-labeled compound by ligand exchange reaction of (99m)Tc-glucoheptonate in high radiochemical yields (over 95% at MBHam concentration of 1 × 10(-5) M). (99m)Tc-N-methyl benzamidoxime ((99m)Tc-MBHam) showed higher stability than the parental (99m)Tc-BHam. The complex of this compound with (99g)TcO(3+) ion was prepared, isolated, and characterized by FT-IR and NMR spectra as well as X-ray diffraction. (99g)Tc-MBHam crystallized in an orthorhombic space group Pna2(1) with a = 13.4823(5), b = 15.5410(7), c = 7.7907(3) Å, V = 1632.39(11) Å(3), and Z = 4. The (99g)Tc complex possessed square base pyramid coordination geometry. The equatorial plane was formed by two-amine nitrogen and two-oxime oxygen atoms in trans position, while the oxo core of the technetium(V) occupied the apical position. The (99g)Tc-MBHam proved to be identical with the (99m)Tc-MBHam prepared at the no-carrier-added level by comparison of their HPLC profiles.

Quinazoline derivatives are efficient chemosensitizers of antibiotic activity in Enterobacter aerogenes, Klebsiella pneumoniae and Pseudomonas aeruginosa resistant strains

Amongst the three series of quinazoline derivatives synthesised and studied in this work, some molecules increase the antibiotic susceptibility of Gram-negative bacteria presenting multidrug-resistant phenotypes. N-alkyl compounds induced an increase in the activity of chloramphenicol, nalidixic acid and sparfloxacin, which are substrates of the AcrAB-TolC and MexAB-OprM efflux pumps in clinical isolates. These molecules are able to increase the intracellular concentration of chloramphenicol in efflux pump-overproducing strains. Their activity depends on the antibiotic structure, suggesting that different sites may be involved for the recognition of substrates by a given efflux pump. Quinazoline molecules exhibiting a nitro functional group are more active, and structure–activity relationship studies may be undertaken to identify the pharmacophoric group involved in the AcrB and MexB affinity sites.

Sources markers in aerosols, oceanic particles and sediments

This review presents some diagnostic criteria used for identifying and quantifying terrestrial organic matter inputs to the ocean. Coupled to the isotopic composition of total organic carbon, the analysis of stable biomarkers permits to trace higher plant contributions in aerosols, dusts, sedimenting particles and dissolved phase in the water column and ultimately in recent and ancient sediments and soils. Some applications are presented, based on the analysis of n-alkyl compounds by a combination of gas chromatography and mass spectrometry (n-alkanes, n-alkanols, n-alkanoic acids and wax esters). Another approach has been developed using the analysis of macromolecular compounds present in higher plants. Abundances of the phenolic compounds from lignin, benzene carboxylic acids obtained during cupric oxide oxidation, Curie pyrolysis are used to characterise terrestrial organic matter sources and inputs. Finally due to the importance of biomass burning in continent-ocean transfers, biomarkers are presented in the polycyclic aromatic hydrocarbon class and for monosaccharide derivatives from the breakdown of cellulose.

δ13C and δD relationships among three n-alkyl compound classes ( n-alkanoic acid, n-alkane and n-alkanol) of terrestrial higher plants

Carbon ( δ 13C) and hydrogen ( δD) isotopic compositions of long-chain n-alkanoic acids, n-alkanes and n-alkanols from plant leaves including C3 angiosperm, C3 gymnosperm, C4 and CAM plants were determined in order to clarify detailed isotopic relationships among the three classes of n-alkyl compounds in terrestrial higher plants. For all plant species, the three classes of n-alkyl compounds have a similar range of δ 13C and δD values within a single species. However, most plants show a small but significant systematic difference in both δ 13C and δD values with respect to biosynthetically corresponding carbon-numbered compounds. In general, n-alkane and n-alkanol are enriched in 13C (averaging 1.4 ± 1.1‰ and 1.3 ± 1.3‰, respectively) but depleted in D (25 ± 16‰ and 15 ± 12‰, respectively) relative to the corresponding carbon-numbered n-alkanoic acid. Moreover, the magnitude of the isotope difference is quite similar in all plants including different types of photosynthesis (C3, C4 and CAM). These results suggest that 13C- and D-discriminations occur at biosynthetic branching points during synthesis of n-alkanoic acid, n-alkane and n-alkanol from a common precursor, and that their fractionation mechanisms are common to all plant species. This systematic isotopic relationship between plant n-alkyl compounds will be useful to compare isotope records between different n-alkyl compounds in various geological samples.

Synthesis of N-unsubstituted bis[1,2]dithiolo[1,4]thiazines and bis[1,2]dithiolopyrroles

The parent bis[1,2]dithiolo[1,4]thiazine-3,5-dione 8, -3,5-dithione 11, the unsymmetrical 3-oxo-5-thione 10 and the bis[1,2]dithiolopyrrole-3,5-dione 9 are synthesised by acid catalysed cleavage of their various N-benzyl, ethyl, ethoxycarbonylethyl and propanoic acid derivatives. These N-alkyl compounds are prepared in the usual way from the appropriate N-alkyldiisopropylamine and S2Cl2. N-Benzyl derivatives 2 and 5 of the thiazine and pyrrole diones give 8 (100%) and 9 (58%) respectively with conc. H2SO4 in dilute DCM solution, and the N-ethyl thiazine derivatives of the dione 12 and the keto-thione 13 give 8 (89%) and 10 (75%) respectively in conc. H2SO4 at 120 °C. Ethyl 3-(diisopropylamino)propanoate 16 with S2Cl2 gives the three thiazines 17 (30%), 18 (15%) and 19 (13%), and 17 and 19 are converted into the pyrroles 20 (95%) and 21 (90%) respectively by thermal extrusion of sulfur in refluxing xylene. All five ethyl esters, 17–21, are hydrolysed with aqueous acid to 22–26 respectively in 92–100% yield, and the N-propanoic acids 22–25 with hot conc. hydrochloric or hot 80–90% sulfuric acid are dealkylated to the corresponding parent products 8–11. It is also shown that the hydrolysis and dealkylation steps 17→22→8 can be combined in one operation (75%).

Chemistry of indoles: new reactivities of indole nucleus and its synthetic application

This review summarizes our studies on the development of new reactivities of the indole nucleus and on its application for the synthesis. These studies involve the following five main subjects: 1) The Vilsmeier-Haack reaction was applied to 1,2,3,4-tetrahydrocarbazole and its N-alkyl compounds. The conditions and the mechanisms of the formation of three kinds of products obtained from the latter compound were clarified, and among the three products, 1,9-dimethylcarbazole-3-aldehyde was found to be useful for the syntheses of olivacine and ellipticine. 2) The Fischer indole synthesis of various 2-substituted phenylhydrazones was examined in detail and it was found that the Fischer indole synthesis of 2-sulfonyloxyphenylhydrazones served a new and convenient method for the synthesis of 7-oxygenated indoles. This reaction was applied to the synthesis of eudistomidin-A. 3) The reactivities of ethyl indole-2-carboxylate for acylation and bromination were also studied, and the use of this compound as a starting material for the synthesis of 4-methoxy-beta-carbolines was successfully investigated. 4) Acylation of ethyl pyrrole-2-carboxylate was concisely studied and this reaction was applied to the syntheses of benzene ring-substituted indoles and benz[f]indoles involving eupolauramine. 5) Two kinds of method for the debenzylation of N-benzylindoles were developed using either AlCl3-benzene or methyl lithium, and they are complementary with each other.

Manipulation of substituents at nitrogen in tropanes, homotropanes, and dehydro- derivatives

Trop-6-ene (8-methyl-8-azabicyclo[3.2.1]oct-6-ene) and substituted N-benzylnortrop-6-enes are synthesised. N-Debenzylation of tropanes fails using a wide variety of non-hydrogenolytic conditions despite effective application in model piperidine derivatives; debenzylation of homotropanes is more successful, giving norhomotropane and norhomotrop-7-ene. Bridged N-benzyl compounds react more slowly than N-methyl analogues with chloroformates; the resulting quaternary intermediates are more prone than the N-methyl analogues to suffer competitive reversion to the starting amine, especially in the tropanes, consistent with slower S N2 attack at the benzylic carbon during decomposition; the use of an N- p-methoxybenzyl group does allow partial debenzylation to nortrop-6-ene, suggesting greater S N1 character in the decomposition step in this case. “Equatorial” attack is preferred in methylation of N-benzyl-nortrop-6-ene and -homotrop-7-ene with CH 3I; subsequent reductive debenzylation of the quaternary salt achieves overall replacement of N-benzyl by N-methyl in both cases. VT NMR studies show the presence of a single “equatorial” invertomer (Cl syn- to the 2C-bridge) in N-chloro-norhomotropanes and -7-enes and, by analogy, in the N-alkyl compounds.

Studies on the Fast Atom Bombardment Mass Spectrometry Fragmentation of Amino Sugars Using Synthetic Derivatives of the Trisaccharide Unit β-D-Glucopyranosyl-(1-3)-O-2-deoxy-2-amino-β-d-glucopyranosyl-(1-4)-O-d-glucopyranose

N-Phthaloyl, N-acetyl, N-benzyl, N-acetyl-N-methyl, N,N-dimethyl, N-benzoyl, and N,N-dibenzoyl derivatives of the trisaccharide β-D-glucopyranosyl-(1-3)-O-(2-deoxy-2-amino-β-D-glucopyranosyl)-(1-4)-O-β-D-glucopyranose were synthesized and analyzed by FAB MS. The intensity ratios of the peaks resulting from cleavage of the anomeric bond of the glucosamine residue and the respective molecular ion peaks turned out to be high for the N-acyl derivatives and up to two orders of magnitude lower for the N-alkyl compounds. These results show that fragmentation at the anomeric carbon of the amino sugar may be assisted by the carbonyl group and the resulting cation is stabilized by delocalization of the positive charge.

13C NMR relaxation in neutral and charged tetra- n-alkyl compounds

NMR T 1 relaxation times have been measured for 13C nuclei in the alkyl chains of symmetric tetra- n-alkylstannanes dissolved in CDCl 3. The results are interpreted in terms of conformational transitions occurring in the aliphatic chains superimposed to rotational diffusion of the whole molecule. A comparison with analogous tetra- n-alkylammonium salts is performed. Differences are ascribed to changes in the overall rotational diffusion deriving from effects of charge upon formation of ion-pairs and larger aggregates.

Mononuclear alkyl and acyl derivatives of rheniumpentacarbonyl: synthesis, characterization and properties

The extensive homologous series of acyl and n-alkyl compounds, [Re(COR)(CO) 5] and [Re(RXCO) 5] (R = CH 3 to n-C 18H 37), has been synthesized. The majority of the compounds are new and have been fully characterized by elemental analysis, IR, 1H and 13C NMR and mass spectrometry. The data for the series are discussed. Some properties of the compounds are described, including reactions of the alkyl compounds with PPh 3, which yield cis-[Re(R)(CO) 4(PPh 3)] and not cis-[Re(CORXCO) 4(PPh 3)] as might have been expected.

Compound-specific δ 13C analyses of leaf lipids from plants with differing carbon dioxide metabolisms

The stable carbon isotope (δ 13C) values of (1) total leaf tissue (2), total surface lipid extracts and (3) individual n-alkanes isolated from leaves were determined for plants utilizing the C 3, C 4, and Crassulacean Acid (CAM) pathways of carbon fixation. The C 4 and CAM species had leaf tissue δ 13C values of −10 to −16‰; the total surface lipid extract δ 13C values were on average 8‰ more depleted. The C 3 plants had leaf tissue values of −25 to −30‰; total surface lipid extracts were on average 4‰ more depleted in 13C. The average n-alkane values for all plants were around 4‰ more depleted in 13C than the total surface lipid extracts and were between 1.6 and 13.8‰ depleted in 13C relative to total tissue. This depletion relative to the total tissue was on average greater for CAM (11.0‰) and C 4 plants (9.9‰) than for C 3 plants (5.9‰). Variations ranging from 0.1 to 6‰ were observed between n-alkalene homologues for the plants studied, emphasizing the need for caution when interpreting small variations in the isotopic compositions of individual compounds isolated from sedimentary environments. n-Aldehydes from C 3 plants had carbon-isotopic compositions similar to the n-alkanes from the same plants, suggesting that other biosynthetically related n-alkyl compounds (e.g. n-acids and n-alcohols) will have δ 13C values similar to the n-alkanes. Phytol isolated from C 3 plants was, on average, 1.5‰ enriched in 13C relative to the average n-alkane δ 13C values.