H.C. Cox

A cadinene biopolymer in fossil and extant dammar resins as a source for cadinanes and bicadinanes in crude oils from South East Asia

Abstract The chemical composition of a fossil resin from a Miocene outcrop in Brunei, South East Asia, is compared with its extant counterpart dammar, obtained from trees of the family Dipterocarpaceae, to establish the nature of the precursor of bicadinanes. The alcohol soluble fractions of the resins consist of functionalised triterpenoids and a small amount of sesquiterpenoids. None of the compounds present in this fraction bears any structural relation to bicadinanes. The alcohol insoluble fractions of the resins consist of a polymer based on cadinene. A structure for this polymer is proposed. Heating the polymer in dammar resin resulted in the formation of monomeric, dimeric, and trimeric cadinenes. It is thought that the naturally occurring bicadinanes result from dimeric cadinenes upon cyclisation.

Limited double bond isomerisation and selective hydrogenation of sterenes during early diagenesis

Abstract Relative differences in free energy of 32 cholestene isomers have been calculated by molecular mechanics using the MM2 empirical force field with adjusted increments for sp 2 hybridised carbon atoms. Based on the results and on a reinspection of the literature it has been concluded that some steps in the previously proposed early diagenetic pathways of steroid diagenesis have to be reconsidered; double bond isomerizations via secondary carbocations are not considered likely to occur in nature. To explain in an alternative way the sterene/sterane distribution patterns observed in Recent sediments a limited isomerization ( via tertiary carbocations only) occurring simultaneously with a selective reduction is proposed.

Qualitative and quantitative characterization of the total organic matter in a recent marine sediment (Part II)

Abstract The total organic matter of a recent marine diatomaceous ooze is studied by analysis of its water and acid extracts and residues. The extraction data relative to the total organic carbon reveal major contributions of carbohydrates (22%), “volatiles” (12%) and proteins (11%) and a smaller contribution of lipids (4%) and volatile fatty acids (1%). The residual organic carbon (50%) mainly shows aliphatic characteristics. Among the compounds identified in the extracts some with an algal and others with a bacterial origin are distinguishable.

Loliolides and dihydroactinidiolide in a recent marine sediment probably indicate a major transformation pathway of carotenoids

Abstract Loliolide, isololiolide and dihydroactinidiolide are encountered in a recent marine sediment; they are probably photo-oxidation products of algal carotenoids.

Carbohydrates in recent marine sediments—I. Origin and significance of deoxy- and O-methyl-monosaccharides

Abstract A qualitative and partly quantitative survey of the carbohydrates encountered in acid hydrolyzates of some recent marine sediments reveals the presence of a large variety of known and hitherto unknown monosaccharides. Apart from the well known major monosaccharides a great number of minor components (notably O -methyl and deoxy monosaccharides) are encountered. These minor components are considered to originate from bacteria. Since significantly larger amounts of major monosaccharides are encountered in carbohydrates associated with bacterial cell-walls the greater part of the carbohydrate carbon in these sediments is ascribed to these structures. Superimposed on the bacterial contribution the characteristics of the carbohydrates originating from the primary producers are recognizable. The results indicate that bacterial biopolymers formed by de novo synthesis in the sediment should be considered as a potential source for the insoluble organic matter in these sediments.

Carbohydrates in recent marine sediments—II. Occurrence and fate of carbohydrates in a recent stromatolitic deposit: Solar Lake, Sinai

Abstract In a study on the diagenesis of carbohydrates in a recent stromatolitic deposit (Solar Lake, Sinai) monosaccharides are quantitated after mild acid hydrolysis and gas chromatographic analysis as alditol acetates. From the depth profiles of the individual monosaccharides relative to the total organic carbon three categories of carbohydrates can be distinguished. The behaviour of the various categories upon burial is discussed in terms of their potential to become a part of the organic matter that survives geological periods. The distribution patterns of especially the mono- O -methyl monosaccharides at various depths are characteristics for the bacterial communities present in the corresponding parts of the sediment column.

Analysis of synthetic mixtures of partially methylated alditol acetates by capillary gas chromatography, gas chromatography-electron impact mass spectrometry and gas chromatography-chemical ionization mass spectrometry

Abstract The identification of naturally methylated neutral monosaccharides in acid hydrolysates as their alditol acetates requires appropriate standards. The availability of such standards also facilitates the analysis of complex mixtures of partially methylated alditol acetates (PMAAs) which appear upon methylation analysis of polysaccharides. For this purpose the alditols of eight common monosaccharides have been partially methylated using the Haworth methylation. The resulting mixtures of partially methylated alditols have been acetylated and analysed by capillary gas chromatography, gas chromatography—electron impact mass spectrometry and gas chromatography—chemical ionization mass spectrometry. Identification of the obtained PMAAs is further elaborated by reduction of the aldoses with sodium borodeuteride and the use of partially methylated aldoses or disaccharides.

The mode of occurrence of lipids in a Namibian shelf diatomaceous ooze with emphasis on the β-hydroxy fatty acids

Abstract Lipids present in a recent marine sediment were extracted, derivatized and analysed by GC and GCMS, without preseparation. This combination of methods offers the possibility to determine various classes of lipids simultaneously. Selective chemical treatment prior to the total lipid extraction, enables the determination of the mode of occurrence in the sediment and might yield more appropriate information about the origin of individual lipid moieties released. The significant relative abundancies of β-hydroxy fatty acids and the structural features of these acids among the lipids released after acid treatment point to the presence of bacterial cell wall material in the sediment sample. This suggestion was supported by a separate isolation of bacterial cell wall lipopolysaccharide.

Interaction of glucose and cellulose with hydrogen sulphide and polysulphides

Abstract This paper describes simulation experiments in which glucose and cellulose were reacted with polysulphide and hydrogen sulphide at ambient temperatures in an aqueous environment. Organic sulphur containing compounds were formed that yield several thiophenes upon pyrolysis/evaporation. The experiments show that interaction of carbohydrates with hydrogen sulphide or polysulphides is a possible way for carbohydrates to react in very recent sediments. From the results of this study it can be concluded that carbohydrate carbon can be preserved in sediments in a form that is resistant to microbial attack and that will have a greater potential for survival during diagenesis than the carbohydrate precursor.

Relative stabilities of sedimentary rearranged sterenes as calculated by molecular mechanics: a key to unravel further steroid diagenesis

Abstract Molecular mechanics calculations of rearranged cholestenes revealed that diacholest-13(17)-enes with 10α stereochemistry are more stable than their 10β counterparts and that a partly rearranged sterene with a Δ 8 double bond and 10β, 14β stereochemistry (compound 7) is relatively stable at thermodynamic equilibrium. The calculated data are in good agreement with sedimentary and experimental data and thus reinforce recent propositions for early-stage diagenesis of steroids.