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Chiral chemistry of single molecules.
No full textIf a single chiral molecule stands alone in a chemical system
(sample) it provides necessarily 100 percent e.e. (enantiomeric
excess). This rule is an axiom of stereochemistry, which has
not been studied earlier. The present paper discusses conditions
when a single chiral molecule can appear in a chemical
sample and analyses consequences of such situations. One
of the most important consequences is, that the origin of
biological chirality can be traced back to such systems in
combination with asymmetric autocatalysis
Single-molecule chirality
No full textIf a chiral substance is prepared from achiral precursors, the first chiral molecule represents obligatorily 100 percent enantiomeric excess. Similar cases can be identified at the degradation of a racemate, for the last chiral molecule and the one-molecule excess obligatorily formed if a racemate contains an odd number of molecules. These cases have a particular significance in speculations regarding the origins of biological chirality and the molecular-level events in chiral autocatalysis. The paper gives a short summary of these problem
Astrobiology and Biological Chirality
No full textThe emerging discipline of astrobiology could gain valuable support from research dealing with the problems of biological chirality. The most profitable fields of common interest are: (a) living organisms under extraterrestrial conditions, (b) extraterrestrial signatures of life and (c) origin(s) of biological chirality. These areas of complementary and overlapping fields are analysed on the basis of selected references
First Molecules, Biological Chirality, Origin(s) of Life
No full textOrigin(s) of biological chirality appear(s) to be intimately connected to origin(s) of life. Prebiotic evolution toward these important turning points can be traced back to single chiral molecules. These can be small (monomeric) units as amino acids or monosaccharides or oligomers as oligo-RNA type molecules. Earlier speculations about these two kinds of entries to biological chirality are critically reviewe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Synthesis and X-ray powder diffraction characterization of (OC)(2)RhCl2Rh(cod) (cod = cycloocta-1,4-diene)
No full textIn order to elucidate the nature and the structure of the elusive (OC)(2)Rh(Ph3SiO)(2)Rh(cod) (cod)=cycloocta-1,5-diene) complex, an important model compound for surface catalysis, (OC)(2)RhCl2Rh(cod) has been synthesized, and structurally characterized by ab initio X-ray powder diffraction. Crystals of (OC)(2)RhCl2Rh(cod) are monoclinic, space group P2(1)/c, a = 6.659(1), b = 12.274(1) and c = 16.096(1) Angstrom, beta = 92.176(5)degrees, Z = 4, rho(calc),,,, = 2.209 g cm(-3). The structure has been solved, from powder diffraction data only, by Patterson and Fourier-difference methods and has been ultimately refined, by the Rietveld method, down to R-p, = 0.116 and R-wp, = 0.154 for 4050 data points collected in the 12-93 degrees (2 theta) range. The molecule contains two square-planar rhodium atoms, one bearing two terminal carbonyls and the other bound to the chelating cod fragment, and two chlorine atoms bridging the Rh ... Rh vector. The Rh2Cl2, core is markedly non-planar, the dihedral angle about the Cl ... Cl hinge being 135.4(6)degrees
A key process of aroma evolution: fatty acid ss-oxidation in Parmesan cheese ripening
No full textA study is described in which solid phase microextraction was used to investigate aroma evolution during the ripening of Parmesan cheese. The predominant organic acids produced during ageing were hexanoic and butanoic acids, whereas the major ketone was 2-heptanone. Metabolic processes leading to generation of these compounds are discussed. It is suggested that measurement of volatile compounds could be used as an indication of Parmesan cheese ripeness
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