Jean-Jacques Filippi

Non-racemic Amino Acid Production by Ultraviolet Irradiation of Achiral Interstellar Ice Analogs with Circularly Polarized Light

The delivery of organic matter to the primitive Earth via comets and meteorites has long been hypothesized to be an important source for prebiotic compounds such as amino acids or their chemical precursors that contributed to the development of prebiotic chemistry leading, on Earth, to the emergence of life. Photochemistry of inter/circumstellar ices around protostellar objects is a potential process leading to complex organic species, although difficult to establish from limited infrared observations only. Here we report the first abiotic cosmic ice simulation experiments that produce species with enantiomeric excesses (e.e.s). Circularly polarized ultraviolet light (UV-CPL) from a synchrotron source induces asymmetric photochemistry on initially achiral inter/circumstellar ice analogs. Enantioselective multidimensional gas chromatography measurements show significant e.e.s of up to 1.34% for (13C)-alanine, for which the signs and absolute values are related to the helicity and number of CPL photons per deposited molecule. This result, directly comparable with some L excesses measured in meteorites, supports a scenario in which exogenous delivery of organics displaying a slight L excess, produced in an extraterrestrial environment by an asymmetric astrophysical process, is at the origin of biomolecular asymmetry on Earth. As a consequence, a fraction of the meteoritic organic material consisting of non-racemic compounds may well have been formed outside the solar system. Finally, following this hypothesis, we support the idea that the protosolar nebula has indeed been formed in a region of massive star formation, regions where UV-CPL of the same helicity is actually observed over large spatial areas.

On the Origin of Primitive Cells: From Nutrient Intake to Elongation of Encapsulated Nucleotides

Recent major discoveries in membrane biophysics hold the key to a modern understanding of the origin of life on Earth. Membrane bilayer vesicles have been shown to provide a multifaceted microenvironment in which protometabolic reactions could have developed. Cell-membrane-like aggregates of amphiphilic molecules capable of retaining encapsulated oligonucleotides have been successfully created in the laboratory. Sophisticated laboratory studies on the origin of life now show that elongation of the DNA primer takes place inside fatty acid vesicles when activated nucleotide nutrients are added to the external medium. These studies demonstrate that cell-like vesicles can be sufficiently permeable to allow for the intake of charged molecules such as activated nucleotides, which can then take part in copying templates in the protocell interior. In this Review we summarize recent experiments in this area and describe a possible scenario for the origin of primitive cells, with an emphasis on the elongation of encapsulated nucleotides.

Circular Dichroism of Amino Acids in the Vacuum-Ultraviolet Region†

Biopolymers such as nucleic acids and proteins are composed of chiral monomers that show identical stereochemical configuration. Naturally occurring proteins are made up of l-amino acids. Hypotheses for the origin of symmetry breaking in biomolecules include the absolute asymmetric photochemistry model by which circularly polarized (CP) light induces an enantiomeric excess (ee) in chiral organic molecules. This model is supported by both the observation of CP light in the star-forming region of Orion and the occurrence of l-enantiomer-enriched amino acids in carbonaceous meteorites. However, the differential absorption of CP light by amino acid enantiomers, which determines the speed and intensity of enantioselective photolysis, is unknown over a large spectral range. Here we show that significant circular dichroic transitions in amino acids can be observed by extending circular dichroism (CD) spectroscopy to the vacuum-ultraviolet (UV) spectral range. a-H amino acids show the same CD magnitude and sign over a large wavelength range. In a given spectral window CP light is therefore capable of inducing enantiomeric excesses of the same handedness into the proteinogenic amino acids we have studied. Absolute asymmetric photochemistry might thus well have triggered the appearance of l-amino acid based life on Earth. Our results demonstrate that enantiomers of “meteoritic” a-methyl amino acids show dichroic absorption with equal magnitude, yet opposite sign to a-H amino acids. Therefore CP light cannot induce l enantiomeric excesses into a-methyl and a-H amino acids as found in meteorites. To explain the cause of symmetry breaking in biomolecules a well-known theory proposes that CP interstellar UV radiation—similar to that identified in the starforming region of Orion in the infrared—induced enantiomeric excesses into interstellar and circumstellar organic compounds by asymmetric photochemical reactions prior to their deposition on the early Earth. In support of this theory chiral amino acid structures were identified in interstellar ice analogues and a large number of l-enantiomer-enriched amino acids have been identified in the interior of the Murchison and Murray carbonaceous meteorites. To verify the absolute asymmetric photochemistry model the differential CP-light absorption of proteinogenic andmeteoritic amino acid enantiomers requires systematic examination. Until now, the popular and extensively used technique of CD spectroscopy has been used to record electronic CD for chiral molecules in aqueous solution above 190 nm. Water absorbs photons of l< 190 nm, making the vacuum-UV region inaccessible for CD spectroscopy in aqueous solution. By using a synchrotron radiation source for CP light and preparing isotropic amorphous solid-state samples immobilized on MgF2 windows, we have extended electronic CD measurements to the vacuum-UV spectral range. We observed intense CD-active transitions of amino acids between 140 and 190 nm (Figure 1), which are much more intense than the previously known CD bands between 190 and 330 nm. Figure 1a shows the CD spectra for dand l-alanine. As expected, the enantiomers of alanine show dichroic absorption of equal magnitude but opposite sign; the nice mirroring effect shows the high quality of the data. The CD spectra of l-alanine, l-valine, and l-leucine are characterized by maxima between 180 and 190 nm (Figure 1b), l-valine and l-leucine show minima between 160 and 170 nm, and l-serine and l-2-aminobutyric acid show maxima at 165– [*] Prof. Dr. U. J. Meierhenrich Laboratoire des Mol cules Bioactives et des Ar mes UMR 6001 CNRS-UNSA, Universit de Nice-Sophia Antipolis Facult des Sciences, Parc Valrose, 06108 Nice (France) Fax: (+33)4-9207-6151 E-mail: uwe.meierhenrich@unice.fr Homepage: http://www.unice.fr/lcmba/meierhenrich/

Qualitative and quantitative analysis of vetiver essential oils by comprehensive two-dimensional gas chromatography and comprehensive two-dimensional gas chromatography/mass spectrometry.

Vetiver essential oils (VEO) are important raw ingredients used in perfume industry, entering the formula of numerous modern fragrances. Vetiver oils are considered to be among the most complex essential oils, resulting most of the time in highly coeluted chromatograms whatever the analytical technique. In this context, conventional gas chromatography has failed to provide a routine tool for the accurate qualitative and quantitative analysis of their constituents. Applying comprehensive two-dimensional gas chromatography techniques (GC×GC-FID/MS) afforded the mean to separate efficiently vetiver oil constituents in order to identify them in a more reliable way. Moreover, this is the first time that a complete true quantitation of each constituent is carried out on such complex oils by means of internal calibration. Finally, we have studied the influence of the injection mode on the determined chemical composition, and showed that several alcohols underwent dehydration under defined chromatographic conditions (splitless mode) usually recommended for quantitation purposes.

Anisotropy spectra of amino acids.

Biopolymers such as enzymes and nucleic acids are composed of homochiral monomers; their molecular symmetry is broken. The origin of biomolecular symmetry breaking— a crucial step in the origin of life—remains unknown. Among various random and deterministic hypotheses that have been proposed, one well-known hypothesis is based on a photochemical model by which chiral photons, in the form of circularly polarized (CP) light, induce an enantioenrichment by interacting with racemic organic molecules, a process known as enantioselective photolysis. According to this model, asymmetric photoreactions took place in the extreme vacuum of interstellar space, prior to the delivery of enantioenriched chiral organic molecules to the early Earth. The hypothesis proposes that CP electromagnetic radiation, such as that detected in the Orion molecular cloud, interacts asymmetrically with chiral organic molecules in interstellar ices and with the early precursors of carbonaceous meteorites. Both enantiomers absorb CP photons triggering photolysis, but one enantiomer has a slightly smaller absorption coefficient. This enantiomer is photo-destroyed less rapidly than its optical antipode and it will therefore become enantioenriched. The induced enantiomeric excess (ee) is determined by the extent of reaction x and is function of the anisotropy factor g, defined by De/e, the ratio between the differential extinction coefficient De, and the extinction coefficient e. However, the sign and magnitude of g depend on the wavelength of the CP light. Here we report anisotropy spectra of amino acids yielding g(l) values, which were recorded for solid amorphous films in a wavelength range between 130 and 350 nm. The anisotropy spectra were measured with a new experimental setup at the synchrotron radiation facility ASTRID at Aarhus University (Denmark). The anisotropy spectra obtained for amino acids in the solid phase show well-resolved zero-crossings, extrema, and g values up to 0.024. These data allow: 1) the prediction of the sign of the induced ee, 2) the determination of the kinetics and the ee values of the enantioselective photolysis, and 3) the selection of the wavelength of the CP light best suited for inducing enantioenrichment. The enantioselective photolysis of a racemic mixture by CP light is an asymmetric transformation that can be represented by two competitive pseudo-first-order reactions with unequal rate constants, kR and kS, for the R and S enantiomer, respectively. The rate constants are proportional to the molar absorption coefficients (eR and eS, respectively), and the efficiency of the enantioselective photolysis depends on the difference between kR and kS or, in this case as Kuhn already outlined, on the anisotropy factor g [Eq. (1)]. 6] More recently it has been shown by Nakamura et al. that Equation (1) is valid even for non-firstorder kinetics.

Photolysis of rac-Leucine with Circularly Polarized Synchrotron Radiation

Amino acids that pass the RNA machinery in living organisms occur in L‐configuration. The question on the evolutionary origin of this biomolecular asymmetry remains unanswered to this day. Amino acids were detected in artificially produced interstellar ices, and L‐enantiomer‐enriched amino acids were identified in CM‐type meteorites. This hints at a possible interstellar/circumstellar origin of the amino acids themselves as well as their stereochemical asymmetry. Based upon the current knowledge about the occurrence of circularly‐polarized electromagnetic radiation in interstellar environments, we subjected rac‐leucine to far‐UV circularly‐polarized synchrotron radiation. Asymmetric photolysis was followed by an analysis in an enantioselective GC/MS system. Here, we report on an advanced photolysis rate of more than 99% for leucine. The results indicate that high photolysis rates can occur under the chosen conditions, favoring enantioselective photolysis. In 2014, the obtained results will be reexamined by cometary mission Rosetta.

Solvent-free thionation of γ-lactones under microwave irradiation

A series of γ-thionolactones was synthesized, with good yields, using a new combination of Lawessons reagent (LR) and hexamethyldisiloxane (HMDO) in solvent-free conditions under microwave irradiation.

Photochirogenesis: Photochemical Models on the Origin of Biomolecular Homochirality

Current research focuses on a better understanding of the origin of biomolecular asymmetry by the identification and detection of the possibly first chiral molecules that were involved in the appearance and evolution of life on Earth. We have reasons to assume that these molecules were specific chiral amino acids. Chiral amino acids have been identified in both chondritic meteorites and simulated interstellar ices. Present research reasons that circularly polarized electromagnetic radiation was identified in interstellar environments and an asymmetric interstellar photon-molecule interaction might have triggered biomolecular symmetry breaking. We review on the possible prebiotic interaction of ‘chiral photons’ in the form of circularly polarized light, with early chiral organic molecules. We will highlight recent studies on enantioselective photolysis of racemic amino acids by circularly polarized light and experiments on the asymmetric photochemical synthesis of amino acids from only one C and one N containing molecules by simulating interstellar environments. Both approaches are based on circular dichroic transitions of amino acids that will be presented as well.

Composition and Biological Properties of the Volatile Oil of Artemisia gorgonumWebb

The chemical composition of Artemisia gorgonum Webb essential oil from Cape Verde was analyzed by GC and GC/MS. A total of 111 volatile compounds, accounting for 94.9% of the essential oil, were identified by GC and GC/MS. The major compounds were camphor (28.7%), chrysanthenone (10.8%), lavandulyl 2‐methylbutanoate (9.5%), α‐phellandrene (5.5%), lavandulyl propanoate (4.2%), camphene (4.0%), and p‐cymene (3.4%). The volatile oil of this endemic plant, which is used in Cape Verdean folk medicine against several ailments, was tested for its antioxidant and antimalarial properties, and was found to exhibit free‐radical scavenging on 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH), prevention of lipid peroxidation–in vitro by TBARS (thiobarbituric acid reactive species) assay, and antiplasmodial activity.

Use, analysis, and regulation of pesticides in natural extracts, essential oils, concretes, and absolutes

AbstractNatural extracts used by the fragrance and cosmetics industries, namely essential oils, concretes, resinoids, and absolutes, are produced from natural raw materials. These are often cultivated by use of monoculture techniques that involve the use of different classes of xenobiotica, including pesticides. Because of these pesticides’ potential effect on public health and the environment, laws regarding permitted residual levels of pesticides used in cultivation of raw materials for fragrance and cosmetic products are expected to become stricter. The purpose of this review is to present and classify pesticides commonly used in the cultivation of these natural raw materials. We will summarize the most recent regulations, and discuss publications on detection of pesticides via chemical analysis of raw natural extracts. Advances in analytical chemistry for identification and quantification of pesticides will be presented, including both sample preparation and modern separation and detection techniques, and examples of the identification and quantification of individual pesticides present in natural extracts, for example essential oils, will be provided. FigureThe multidimensional gas chromatogramm depicts coelution of molecular ingredients of a rose essential oil spiked with an ethion pesticide