The adsorption configuration of organic molecules on mineral surfaces is of great interest because it can provide fundamental information for both engineered and natural systems. Here we have conducted surface-enhanced Raman spectroscopy (SERS) measurements to probe the attachment configurations of DOPA on nanorutile particles under different pH and surface coverage conditions. The Raman signal enhancement arises when a charge transfer (CT) complex forms between the nanopartides and adsorbed DOPA This Raman signal is exdusively from the surface-bound complexes with great sensitivity to the binding and orientation of the DOPA attached to the TiO2 surface. Our SERS spectra show peaks that progressively change with pH and surface coverage, indicating changing surface speciation. At low pH and surface coverage, DOPA adsorbs on the surface lying down, with probably three points of attachment, whereas at higher pH and surface coverage DOPA stands up on the surface as a species involving two attachment points via the two phenolic oxygens. Our results demonstrate experimentally the varying proportions of the two surface species as a function of environmental conditions consistent with published surface complexation modeling. This observation opens up the possibility to manipulate organic molecule attachment in engineered systems such as biodetection devices. Furthermore, it provides a perspective on the possible role of mineral surfaces in the chemical evolution of biomolecules on the early Earth. Adsorbed biomolecules on mineral surface in certain configurations may have had an advantage for subsequent condensation reactions, facilitating the formation of peptides.

The adsorption configuration of organic molecules on mineral surfaces is of great interest because it can provide fundamental information for both engineered and natural systems. Here we have conducted surface-enhanced Raman spectroscopy (SERS) measurements to probe the attachment configurations of DOPA on nanorutile particles under different pH and surface coverage conditions. The Raman signal enhancement arises when a charge transfer (CT) complex forms between the nanopartides and adsorbed DOPA This Raman signal is exdusively from the surface-bound complexes with great sensitivity to the binding and orientation of the DOPA attached to the TiO2 surface. Our SERS spectra show peaks that progressively change with pH and surface coverage, indicating changing surface speciation. At low pH and surface coverage, DOPA adsorbs on the surface lying down, with probably three points of attachment, whereas at higher pH and surface coverage DOPA stands up on the surface as a species involving two attachment points via the two phenolic oxygens. Our results demonstrate experimentally the varying proportions of the two surface species as a function of environmental conditions consistent with published surface complexation modeling. This observation opens up the possibility to manipulate organic molecule attachment in engineered systems such as biodetection devices. Furthermore, it provides a perspective on the possible role of mineral surfaces in the chemical evolution of biomolecules on the early Earth. Adsorbed biomolecules on mineral surface in certain configurations may have had an advantage for subsequent condensation reactions, facilitating the formation of peptides.

Recent studies reveal substantial variability in biosynthetic H-2/H-1 fractionation between lipids and water, which highlights the effect of central metabolic pathways on the H isotopic composition of the end products. Using multi-nuclear (H-1, H-2 and C-13) solid state nuclear magnetic resonance (NMR) spectroscopy and gas chromatography-mass spectrometry (GC-MS), we were able to track the incorporation of H-1 and H-2 metabolic fluxes into different cellular components of Escherichia coli during growth on two sets of media: (i) 10% deuterated water and non-deuterated glucose, and (ii) non-deuterated water and 10% deuterated glucose. In the 10% H-2 water experiment, the H-2 abundance of the bulk cell was 4.5%; the H-2 uptake by membrane lipids, aliphatic H in proteins, and all the non-aliphatic H positions (including nucleic acids and sugars) was 6.2%, 2.3% and 6.2%, respectively. In the 10% H-2 glucose experiment, the corresponding H-2 uptake was 2.0%, 1.4% and 2.5%, respectively, and 1.9% for the bulk cell. The net fractionation of fatty acids (FAs) relative to water and glucose was consistent with that in studies employing natural H-2 abundance, suggesting the 10% deuterated environment does not alter isotope fractionation during FA biosynthesis. Aliphatic H in proteins was significantly depleted in H-2 relative to FAs by 290-640 parts per thousand. This depletion is likely related to the dynamic regulation of central metabolic pathways that gradually builds up H-2 in tricarboxylic acid (TCA) cycle intermediates though continuous interaction with water, leading to the rapid synthesis of isotopically light amino acids early in the cell cycle and the production of isotopically enriched FAs late in the cell cycle. Besides, enzyme malfunctioning caused by H-2 substitution is likely to promote proteolysis, which could also contribute to the H-2 depletion in proteins. Non-aliphatic H positions as a whole exhibited similar net fractionation factors to the lipids. The study provides an overview of H isotope distribution in the major molecular constituents of intact bacterial cells, offering insight into the mechanisms underlying the metabolic control on the H isotopic composition of biomarker precursors. (c) 2013 Elsevier Ltd. All rights reserved.

Recent studies reveal substantial variability in biosynthetic H-2/H-1 fractionation between lipids and water, which highlights the effect of central metabolic pathways on the H isotopic composition of the end products. Using multi-nuclear (H-1, H-2 and C-13) solid state nuclear magnetic resonance (NMR) spectroscopy and gas chromatography-mass spectrometry (GC-MS), we were able to track the incorporation of H-1 and H-2 metabolic fluxes into different cellular components of Escherichia coli during growth on two sets of media: (i) 10% deuterated water and non-deuterated glucose, and (ii) non-deuterated water and 10% deuterated glucose. In the 10% H-2 water experiment, the H-2 abundance of the bulk cell was 4.5%; the H-2 uptake by membrane lipids, aliphatic H in proteins, and all the non-aliphatic H positions (including nucleic acids and sugars) was 6.2%, 2.3% and 6.2%, respectively. In the 10% H-2 glucose experiment, the corresponding H-2 uptake was 2.0%, 1.4% and 2.5%, respectively, and 1.9% for the bulk cell. The net fractionation of fatty acids (FAs) relative to water and glucose was consistent with that in studies employing natural H-2 abundance, suggesting the 10% deuterated environment does not alter isotope fractionation during FA biosynthesis. Aliphatic H in proteins was significantly depleted in H-2 relative to FAs by 290-640 parts per thousand. This depletion is likely related to the dynamic regulation of central metabolic pathways that gradually builds up H-2 in tricarboxylic acid (TCA) cycle intermediates though continuous interaction with water, leading to the rapid synthesis of isotopically light amino acids early in the cell cycle and the production of isotopically enriched FAs late in the cell cycle. Besides, enzyme malfunctioning caused by H-2 substitution is likely to promote proteolysis, which could also contribute to the H-2 depletion in proteins. Non-aliphatic H positions as a whole exhibited similar net fractionation factors to the lipids. The study provides an overview of H isotope distribution in the major molecular constituents of intact bacterial cells, offering insight into the mechanisms underlying the metabolic control on the H isotopic composition of biomarker precursors. (c) 2013 Elsevier Ltd. All rights reserved.

Polymerization of interstellar formaldehyde, first through the formose reaction and then through subsequent condensation reactions, provides a plausible explanation for how abundant and highly chemically complex organic solids may have come to exist in primitive solar system objects. In order to gain better insight on the reaction, a systematic study of the relationship of synthesis temperature with resultant molecular structure was performed. In addition, the effect of the presence of ammonia on the reaction rate and molecular structure of the product was studied. The synthesized formaldehyde polymer is directly compared to chondritic insoluble organic matter (IOM) isolated from primitive meteorites using solid-state C-13 nuclear magnetic resonance, Fourier transform infrared, and X-ray absorption near edge structure spectroscopy. The molecular structure of the formaldehyde polymer is shown to exhibit considerable similarity at the functional group level with primitive chondritic IOM. The addition of ammonia to the solution enhances the rate of polymerization reaction at lower temperatures and results in substantial incorporation of nitrogen into the polymer. Morphologically, the formaldehyde polymer exists as submicron to micron-sized spheroidal particles and spheroidal particle aggregates that bare considerable similarity to the organic nanoglobules commonly observed in chondritic IOM. These spectroscopic and morphological data support the hypothesis that IOM in chondrites and refractory organic carbon in comets may have formed through the polymerization of interstellar formaldehyde after planetesimal accretion, in the presence of liquid water, early in the history of the solar system.

Polymerization of interstellar formaldehyde, first through the formose reaction and then through subsequent condensation reactions, provides a plausible explanation for how abundant and highly chemically complex organic solids may have come to exist in primitive solar system objects. In order to gain better insight on the reaction, a systematic study of the relationship of synthesis temperature with resultant molecular structure was performed. In addition, the effect of the presence of ammonia on the reaction rate and molecular structure of the product was studied. The synthesized formaldehyde polymer is directly compared to chondritic insoluble organic matter (IOM) isolated from primitive meteorites using solid-state C-13 nuclear magnetic resonance, Fourier transform infrared, and X-ray absorption near edge structure spectroscopy. The molecular structure of the formaldehyde polymer is shown to exhibit considerable similarity at the functional group level with primitive chondritic IOM. The addition of ammonia to the solution enhances the rate of polymerization reaction at lower temperatures and results in substantial incorporation of nitrogen into the polymer. Morphologically, the formaldehyde polymer exists as submicron to micron-sized spheroidal particles and spheroidal particle aggregates that bare considerable similarity to the organic nanoglobules commonly observed in chondritic IOM. These spectroscopic and morphological data support the hypothesis that IOM in chondrites and refractory organic carbon in comets may have formed through the polymerization of interstellar formaldehyde after planetesimal accretion, in the presence of liquid water, early in the history of the solar system.

Pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) analysis of Neolithic (4900-3800 BC) archeological rice grains (husked rice fruit) from the Tianluoshan site (Zhejiang Province, eastern China) revealed no polysaccharide products from starch present in the original rice fruit; however, benzene, toluene, dimethyl benzene, phenol, dimethyl phenol and n-alkanes > C-30 were detected, indicating their aromatic nature, plus some aliphatic components. On the contrary, polysaccharides were observed in husk material but in significantly lower concentration than in the modern equivalent. The molecular composition was supported by C-13 nuclear magnetic resonance spectroscopy (NMR) data. Variation in preservation quality was also detected in persimmon seeds, oak acorns and amanranthaceous seeds from the site. This variation in molecular preservation, which could also be observed at the micro-morphological level, was tracked with scanning electron microscopy (SEM). Variation in bulk tissue carbon isotopic values (delta C-13) was apparent among archeological samples, a net 1-2 parts per thousand positive shift in bulk tissue delta C-13 being found in most of the Tianloushan plant remains. Our data suggest the importance of post-excavation storage conditions and illustrate the power of the application of multiple analytical methods for the study of archeological plant remains. (c) 2013 Elsevier Ltd. All rights reserved.

Pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) analysis of Neolithic (4900-3800 BC) archeological rice grains (husked rice fruit) from the Tianluoshan site (Zhejiang Province, eastern China) revealed no polysaccharide products from starch present in the original rice fruit; however, benzene, toluene, dimethyl benzene, phenol, dimethyl phenol and n-alkanes > C-30 were detected, indicating their aromatic nature, plus some aliphatic components. On the contrary, polysaccharides were observed in husk material but in significantly lower concentration than in the modern equivalent. The molecular composition was supported by C-13 nuclear magnetic resonance spectroscopy (NMR) data. Variation in preservation quality was also detected in persimmon seeds, oak acorns and amanranthaceous seeds from the site. This variation in molecular preservation, which could also be observed at the micro-morphological level, was tracked with scanning electron microscopy (SEM). Variation in bulk tissue carbon isotopic values (delta C-13) was apparent among archeological samples, a net 1-2 parts per thousand positive shift in bulk tissue delta C-13 being found in most of the Tianloushan plant remains. Our data suggest the importance of post-excavation storage conditions and illustrate the power of the application of multiple analytical methods for the study of archeological plant remains. (c) 2013 Elsevier Ltd. All rights reserved.