Reductive coupling of aldehydes by h(2) s in aqueous solutions, a C--C bond forming reaction of prebiotic interest.

We report here a novel reductive coupling reaction of conjugated, non- or poorly enolizable aldehydes induced by H(2) S and operative in aqueous solutions under prebiotically relevant conditions. This reaction leads from retinal to ß-carotene, and from benzylic aldehydes to the corresponding diarylethylenes. This novel reaction also opens a new potentially prebiotic pathway leading from glyoxylic acid to various compounds that are involved in the reductive tricarboxylic acid cycle. This C--C bond forming reaction of prebiotic interest might have been operative, notably, in the sulfide-rich environments of hydrothermal vents, which have been postulated as possible sites for the first steps of organic chemical evolution.

Cognitive reserve as one of the determinants of the progression of Alzheimer disease.

To assess the validity of Yaakov Stern's theory, which postulates that the first cognitive deficits of Alzheimer disease are delayed in patients with high cognitive reserve, compared to those with low cognitive reserve, but this is subsequently associated with faster cognitive decline when cerebral lesions have reached a certain degree of severity. A retrospective study of 318 patients with Alzheimer disease without associated cerebral disorders, was performed at the Memory Clinic of the University Hospital of Strasbourg. The patients were divided into five groups according to their degree of cognitive reserve, as assessed by their level of education (primary, middle school, intermediate, high school and higher education). Cognitive status was assessed by scores on the Mini Mental Status Examination (MMSE) at the first examination and during follow-up lasting four years or longer. Slopes of cognitive decline were computed and compared between groups using ß linear regression. Patients in the higher education group had higher MMSE scores than those in the other groups at the first consultation, but a statistically significant steeper slope during the follow-up. Our results are consistent with Stern's theoretical model, which assumes that high cognitive reserve is accompanied by compensation mechanisms which hinder the onset of clinical cognitive decline in patients with Alzheimer disease, but that is then associated with a faster decline at a later stage when the reserve is exhausted.

[Cognitive reserve, one of the determinants of the progression of Alzheimer's disease]. / La réserve cognitive, un des déterminants de l'évolution de la maladie d'Alzheimer.

To appraise the validity of the Yaakov Stern's theory, which postulates that the first cognitive deficits of Alzheimer's disease are delayed in patients with high cognitive reserve, compared to those with low cognitive reserve, but is subsequently associated with faster cognitive decline when cerebral lesions have reached some degree of severity. A retrospective study of 318 patients with Alzheimer's disease without associated cerebral disorders, was performed in the Memory Clinic of the University Hospital of Strasbourg. The patients were divided into 5 groups according to the degree of cognitive reserve assessed by the level of education (primary, middle school, intermediary, high school and higher education). Cognitive status was assessed by the scores on the Mini Mental Status at the first examination and during a 4-year or more follow-up. Slopes of cognitive decline were computed and compared between groups by ß linear regression. Patients in the higher education group had higher MMSE scores than those in the other groups at the first consultation, but a statistically significant steeper slope during the follow-up. Our results are congruent with the Stern's theoretical model, assuming that high cognitive reserve brings into play compensation mechanisms which hinder the onset of clinical cognitive decline in patients with Alzheimer's disease, but then is associated with a faster decline at a later stage when the reserve is exhausted.

Analysis of 13C labeling enrichment in microbial culture applying metabolic tracer experiments using gas chromatography-combustion-isotope ratio mass spectrometry.

The applicability of gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) for the quantification of 13C enrichment of proteinogenic amino acids in metabolic tracer experiments was evaluated. Measurement of the 13C enrichment of proteinogenic amino acids from cell hydrolyzates of Corynebacterium glutamicum growing on different mixtures containing between 0.5 and 10% [1-13C]glucose shows the significance of kinetic isotope effects in metabolic flux studies at low degree of labeling. We developed a method to calculate the 13C enrichment. The approach to correct for these effects in metabolic flux studies using delta13C measurement by GC-C-IRMS uses two parallel experiments applying substrate with natural abundance and 13C-enriched tracer substrate, respectively. The fractional enrichment obtained in natural substrate is subtracted from that of the enriched one. Tracer studies with C. glutamicum resulted in a statistically identical relative fractional enrichment of 13C in proteinogenic amino acids over the whole range of applied concentrations of [1-13C]glucose. The current findings indicate a great potential of GC-C-IRMS for labeling quantification in 13C metabolic flux analysis with low labeling degree of tracer substrate directly in larger scale bioreactors.

4,4'-Dimethyldinaphtho[a,d]cycloheptane, a naturally occurring polyaromatic derivative related to triterpenoids of the serratane series.

[reaction: see text] The polyaromatic hydrocarbon 4,4'-dimethyldinaphtho[a,d]cycloheptane (1a) has been identified by NMR studies after isolation from an Oligocene sediment. The original symmetrical structure of 1a, which bears a central seven-membered ring, is closely related to higher plant triterpenoid precursor(s) of the serratane series and is believed to have been formed in the subsurface by a microbially mediated aromatization process.

Reductive desulfurization of allylic thiols by HS-/H2S in water gives clue to chemical reactions widespread in natural environments.

The reduction of allylic thiols to alkenes by hydrogen sulfide in aqueous solutions, a novel reaction that may explain reduction processes widely occurring in natural environments, has been discovered. Its mechanism has been studied and suggested to follow an S(RN)1-like pathway involving radical intermediates undergoing 1,4 hydrogen shifts. [reaction: see text]

Bridgehead alkylated 2-thiaadamantanes: novel markers for sulfurisation processes occurring under high thermal stress in deep petroleum reservoirs.

Two bridgehead-alkylated 2-thiaadamantanes (1,5-dimethyl and 1-methyl) have been identified in petroleum; these compounds give clues to sulfurisation processes affecting petroleum which has undergone high thermal stress.

Allosteric effects in norbadione A. A clue for the accumulation process of 137Cs in mushrooms?

A fruitful combination of potentiometry, absorption spectrophotometry, ESMS and 1H NMR enabled the characterisation of two caesium complexes with norbadione A and the determination of the respective stability constants of a mononuclear and a dinuclear caesium complex at pH approximately 6; a preliminary study allowed the assignment of five protonation sites of this pigment; a positively cooperative binding of the second Cs+ cation was observed.

Elucidation of an iterative process of carbon-carbon bond formation of prebiotic significance.

Laboratory experiments carried out under plausible prebiotic conditions (under conditions that might have occurred at primitive deep-sea hydrothermal vents) in water and involving constituents that occur in the vicinity of submarine hydrothermal vents (e.g., CO, H(2)S, NiS) have disclosed an iterative Ni-catalyzed pathway of C-C bond formation. This pathway leads from CO to various organic molecules that comprise, notably, thiols, alkylmono- and disulfides, carboxylic acids, and related thioesters containing up to four carbon atoms. Furthermore, similar experiments with organic compounds containing various functionalities, such as thiols, carboxylic acids, thioesters, and alcohols, gave clues to the mechanisms of this novel synthetic process in which reduced metal species, in particular Ni(0), appear to be the key catalysts. Moreover, the formation of aldehydes (and ketones) as labile intermediates via a hydroformylation-related process proved to be at the core of the chain elongation process. Since this process can potentially lead to organic compounds with any chain length, it could have played a significant role in the prebiotic formation of lipidic amphiphilic molecules such as fatty acids, potential precursors of membrane constituents.

Aromatized C-2 oxygenated triterpenoids as indicators for a new transformation pathway in the environment.

Four oleanane-related aromatic triterpenoids isolated from an archeological piece of oak wood have been identified by NMR studies. Their structures give clue to a novel diagenetic transformation pathway of 2,3-oxygenated higher plant triterpenoids in the environment.

Archaeological resinous samples from Asian wrecks: Taxonomic characterization by GC-MS.

Plant resins, and particularly dammars from the Dipterocarpaceae family, were widely used in the past, notably as part of caulking material. The organic composition of resins, already complicated, is not always preserved over time and can be considerably affected by ageing. Hence, their occurrence in archaeological items leads to the necessity to identify them taxonomically with precision. Resinous organic materials collected near and/or on wrecks discovered in South China Sea, supposed to contain dammar resins because of their geographical excavation context, were investigated by gas chromatography-mass spectrometry (GC-MS), together with freshly collected dammars, to establish taxonomic and alteration parameters allowing to identify dammar even in very altered samples or in mixtures together with other organic materials. This study specially focuses on three samples collected within or close to the M1J wreck, a Portuguese wreck lost in the Straight of Malacca during the 16th century. Our analyses establish that all three are made of dammar, two of them in association with pitch and bitumen. In addition, biodegradation biomarkers were detected in all these three samples, indicating that they were submitted to microbial degradation processes during their ageing.

Cyclic peroxides derived from the marine sponge Plakortis simplex.

Two new cyclic peroxides, 2 and 3, were isolated from a sample of the Norwegian sponge Plakortis simplex. Their structures including relative stereochemistry were elucidated by interpretation of MS and NMR data. Compound 3 exhibited moderate in vitro activity against six solid human tumor cell lines with IC50 values in the range 7-15 microg/mL.