906 research outputs found
"Understanding European Foreign Policy Cooperation"
[From the introduction] This paper examines questions about CFSP activity by studying it in the context of a random sample of world events. It asks to what kinds of events or issues does the Union respond, and compares the results with the Union’s Treaty-established interests. The results are somewhat surprising: the EU is not particularly sensitive to events in neighboring regions, nor is it particularly responsive to abuses of human rights. Human rights issues are actually much less likely to attract Union attention than almost any other type of issue, though this trend appears to decline with time. The impact of the 1995 expansion dissipates rapidly, and contrary to the conventional wisdom, the new members’ historic neutrality does not appear to have affected cooperation in any way. Two important conclusions emerge: first, cooperation does not appear to have expanded with time in either scope of issues addressed or volume of events addressed. At best, the development of the Union’s Common Foreign and Security Policy has kept pace with the growth of world interactions. Second, characteristics of the state holding the presidency are insignificant predictors of CFSP activity, suggesting at least moderate support for a norm of presidencies working for the general interest
Pitch perception of musicians and non-musicians: a comparison of psychological tuning curves and frequency limens
A group of classically trained musicians and a group of non-musicians were compared using psychophysical tasks of pitch perception to determine the effect of musical training on the auditory mechanism. Two measurements, frequency difference limens (DLFs) and psychophysical tuning curves (PTCs) were gathered for each subject at four frequencies in each ear separately. Results indicated a significant difference between musicians and non-musicians at three frequencies for DLF measures, and no significant findings regarding PTC measurements. These findings reveal a significant musical training effect on DLF outcomes, while the effect of musical training on PTCs, if any, remains to be determined. Implications of this study support changes in measureable auditory skills resulting from auditory training through music, and suggest that the frequency selectivity at the level of the cochlea is different between musicians and non-musicians. Additional studies are needed to demonstrate auditory differences between musicians and non-musicians using other psychophysical measurements beyond DLFs
Selective Prebiotic Synthesis of α‐Threofuranosyl Cytidine by Photochemical Anomerization
The structure of life's first genetic polymer is a question of intense ongoing debate. The “RNA world theory” suggests RNA was life's first nucleic acid. However, ribonucleotides are complex chemical structures, and simpler nucleic acids, such as threose nucleic acid (TNA), can carry genetic information. In principle, nucleic acids like TNA could have played a vital role in the origins of life. The advent of any genetic polymer in life requires synthesis of its monomers. Here we demonstrate a high‐yielding, stereo‐, regio‐ and furanosyl‐selective prebiotic synthesis of threo‐cytidine 3, an essential component of TNA. Our synthesis uses key intermediates and reactions previously exploited in the prebiotic synthesis of the canonical pyrimidine ribonucleoside cytidine 1. Furthermore, we demonstrate that erythro‐specific 2′,3′‐cyclic phosphate synthesis provides a mechanism to photochemically select TNA cytidine. These results suggest that TNA may have coexisted with RNA during the emergence of life
Selective Synthesis of Lysine Peptides and the Prebiotically Plausible Synthesis of Catalytically Active Diaminopropionic Acid Peptide Nitriles in Water
Why life encodes specific proteinogenic amino acids remains an unsolved problem, but a non-enzymatic synthesis that recapitulates biology's universal strategy of stepwise N-to-C terminal peptide growth may hold the key to this selection. Lysine is an important proteinogenic amino acid that, despite its essential structural, catalytic, and functional roles in biochemistry, has widely been assumed to be a late addition to the genetic code. Here, we demonstrate that lysine thioacids undergo coupling with aminonitriles in neutral water to afford peptides in near-quantitative yield, whereas non-proteinogenic lysine homologues, ornithine, and diaminobutyric acid cannot form peptides due to rapid and quantitative cyclization that irreversibly blocks peptide synthesis. We demonstrate for the first time that ornithine lactamization provides an absolute differentiation of lysine and ornithine during (non-enzymatic) N-to-C-terminal peptide ligation. We additionally demonstrate that the shortest lysine homologue, diaminopropionic acid, undergoes effective peptide ligation. This prompted us to discover a high-yielding prebiotically plausible synthesis of the diaminopropionic acid residue, by peptide nitrile modification, through the addition of ammonia to a dehydroalanine nitrile. With this synthesis in hand, we then discovered that the low basicity of diaminopropionyl residues promotes effective, biomimetic, imine catalysis in neutral water. Our results suggest diaminopropionic acid, synthesized by peptide nitrile modification, can replace or augment lysine residues during early evolution but that lysine's electronically isolated sidechain amine likely provides an evolutionary advantage for coupling and coding as a preformed monomer in monomer-by-monomer peptide translation
Selective Acylation of Nucleosides, Nucleotides, and Glycerol-3- phosphocholine in Water
A convenient selective synthesis of 2′,3′-di-O-acetyl-nucleo- tide-5′-phosphates, 2′,3′-di-O-acetyl-nucleotide-5′-triphosphates and 2′,3′,5′-tri-O-acetyl-nucleosides in water has been developed. Further- more, a long-chain selective glycerol-3-phosphocholine diacylation is elucidated. These reactions are environmentally benign, rapid, high yielding, and the products are readily purified. Importantly, this reac- tion may indicate a prebiotically plausible reaction pathway for the se- lective acylation of key metabolites to facilitate their incorporation into protometabolism
Analyses of Aliphatic Aldehydes and Ketones in Carbonaceous Chondrites
Aliphatic aldehydes and ketones are essential building blocks for the synthesis of more complex organic compounds. In spite of their potentially key role as precursors of astrobiologically-important molecules, such as amino acids and carboxylic acids, this family of compounds has scarcely been evaluated in carbonaceous chondrites. The paucity of such analyses likely derives from the low concentration of aldehydes and ketones in the meteorites, and from the currently used chromatographic methodologies that have not been optimized for meteorite analysis. In this work, we report the development of a novel analytical method to quantify the molecular distribution and compound-specific isotopic analysis of 29 aliphatic aldehydes and ketones. Using this method, we have investigated the molecular distribution and 13C-isotopic composition of aldehydes and ketones in ten carbonaceous chondrites from the CI, CM, CR and CV groups. The total concentration of carbonyl compounds ranged from 130 to 1000 nmolg-1 of meteorite, with formaldehyde, acetaldehyde, and acetone being the most abundant species in all investigated samples. The 13C-isotopic values ranged from 67 to +64 and we did not observe clear relationships between 13C-content and molecular weight. Accurately measuring the relative abundances, determining the molecular distribution, and isotopic composition of chondritic organic compounds is central in assessing both their formation chemistry and synthetic relationships
Prebiotic triose glycolysis promoted by co-catalytic proline and phosphate in neutral water
Proline and phosphate promote a near-quantitative aldol reaction between glycolaldehyde phosphate and formaldehyde at neutral pH in water. Our results demonstrate the important role of general acid-base catalysis in water and underscore the essential role that amino acid catalysis may have played in early evolution of life's core metabolic pathways
Selective aqueous acetylation controls the photoanomerization of α-cytidine-5′-phosphate
Nucleic acids are central to information transfer and replication in living systems, providing the molecular foundations of Darwinian evolution. Here we report that prebiotic acetylation of the non-natural, but prebiotically plausible, ribonucleotide α-cytidine-5′-phosphate, selectively protects the vicinal diol moiety. Vicinal diol acetylation blocks oxazolidinone formation and prevents C2′-epimerization upon irradiation with UV-light. Consequently, acetylation enhances (4-fold) the photoanomerization of α-cytidine-5′-phosphate to produce the natural β-pyrimidine ribonucleotide-5′-phosphates required for RNA synthesis
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