At some point in life's development, membranes formed, providing barriers between the environment and the interior of the 'cell.' This paper evaluates the research to date on the prebiotic origin of cell membranes and highlights possible areas of continuing study. A careful review of the literature uncovered unexpected factors that influence membrane evolution. The major stages in primitive membrane formation and the transition to contemporary cell membranes appear to require an exacting relationship between environmental conditions and amphiphile composition and phase behavior. Also, environmental and compositional requirements for individual stages are in some instances incompatible with one another, potentially stultifying the pathway to contemporary membranes. Previous studies in membrane evolution have noted the effects composition and environment have on membrane formation but the crucial dependence and interdependence on these two factors has not been emphasized. This review makes clear the need to focus future investigations away from proof-of-principle studies towards developing a better understanding of the roles that environmental factors and lipid composition and polymorphic phase behavior played in the origin and evolution of cell membranes.

There is a contradiction between theory and empirics with respect to portfolio allocation in parliamentary democracies. While the canonical model of legislative bargaining predicts the existence of a 'formateur bonus', empirical studies show that portfolios are allocated in a manner that favours smaller parties. This article argues that the difference between the empirical pattern and the theoretical predictions can be explained by the vote of no confidence, which provides an incentive for large formateur parties to overcompensate smaller coalition partners in exchange for their sustained support over time. This argument is tested by exploiting variations in the presence of no confidence votes across national and regional levels in France. As predicted, we find that larger formateur parties receive a greater share of portfolios if the vote of no confidence is absent than if it is present.

A common approach to the synthesis of oxazolines is ring closure of hydroxyamides using a dehydrating agent such as SOCl 2 , P 2 O 5 , EtO 2 CN=NCO 2 Et/PPh 3 and, more recently, Burgess reagent. [1][2][3][4][5] The mechanism for this ring closure is believed to involve an internal S N 2 displacement of an alcohol derived leaving group, for example, a phosphate group, with accompanying inversion at the carbon carrying the hydroxyl group. 3 An alternative mechanistic pathway for oxazoline synthesis would be an initial hydroxyl group attack on the amide carbonyl followed by elimination of water leading to the oxazoline, but this has never been established. Such a process would involve retention of configuration at the carbon carrying the hydroxyl group, opposite to what is observed when a chemical dehydrating agent is used. Such a mechanism might take place under thermal conditions, in the absence of a dehydrating agent, to give other stereospecific oxazolines. To establish this mechanism we selected norephedrine (erythro) and norpseudoephedrine (threo) as our precursors to the β-hydroxyamides (1,2). In our work, reaction of the β-hydroxyamide (1) derived from norephedrine (erythro) with P 2 O 5 in refluxing toluene gave only the trans-oxazoline (3) with inversion at C-1, while the norpseudoephedrine (threo) derived hydroxyamide (2) gave the cis-oxazoline (4) as the major product; trans-oxazoline (3) was always less than 15%.However, thermal cyclization (heating to 290°C, 2 min) of threo-(2) gave only trans-oxazoline (3), i.e., retention of configuration at C-1; similar treatment of erythro-(1) gave cisoxazoline (4) as the major product, again retention of configuration at C-1, along with trans-(3) (33-40%). The trans and cis-oxazolines were clearly distinguished from each other by proton-NMR (trans-(3a), 5.08 ppm, J 4,5 =8.3 Hz; cis-(4a), 5.78 ppm, J 4,5 =10 Hz). 6 That the same β-hydroxyamide gives two different oxazolines with opposite configurations, depending on the conditions used (chemical or thermal), clearly supports our assumption that, under thermal conditions, the hydroxyl group initially attacks the carbonyl carbon, followed by elimination of water to give the oxazoline. The formation of mixtures of oxazolines (cis and trans) in the reaction threo (2) with P 2 O 5 and erythro (1) under thermal conditions may arise from a dual mechanistic pathway (S N 2 and S N 1). This aspect is under study.Thermal conversion is described of amides derived from erythro and threo ephedrines yields stereospecific oxazolines.

Thermal Cyclization of β-Hydroxyamides to Oxazolines.-Thermolysis of amides (I) and (III), derived from threo-and erythro-ephedrine, resp., yields stereospecifically oxazolines (II) and (IV) with inversion of configuration at C-1. Reaction of these amides with P 2 O 5 in refluxing toluene takes an opposite stereochemical course. -(SOMANATHAN, RATNASAMY; AGUILAR, HUGO R.; RIVERO, IGNACIO A.; AGUIRRE, G.; HELLBERG, LARS H.; YU, ZHENG; THOMAS, JACQUELYN A.; J.