Noble gas-silicon cations: theoretical insights into the nature of the bond

3n

Deracemization of an axial chiral biphenylic structure in chiral micellar aggregates.

An example of deracemization(1) of an axially chiral biphenylic system in micellar type aggregates is reported. Two independent techniques (H-1 NMR and CD) give evidence of the phenomenon, which is due to a combination of chiral induction and organization

Selectivity in the oxidation of limonene by amphiphilized metalloporphyrins in micellar media

The weak interactions responsible for the aggregation and organization of micellar aggregates have been shown to control the regioselectivity of the epoxidation of limonene catalyzed by manganese porphyrins toward the endo double bond. The same reaction carried out in the presence of aggregates formed by sodium N-dodecanoyl-L-prolinate has shown the same regioselectivity, a selectivity toward the R enantiomer of limonene and a slight but significative stereoselectivity due to the organization of the molecular aggregates

Spectroscopic studies on the selective inclusion of amphiphilised porphyrin derivatives in micellar phases

The inclusion behavior of [5-(4-(3-trimethylammonium)propyloxyphenyl)-10,15,20-tryphenylporphyrin] chloride(1H2), 2-[2-(2-(4-(10,15,20-triphenyl-5-porphyrinyl)-phenoxy)-ethoxy)ethoxy]ethanol (2H2), and their Mn(III) derivatives, 1MnCl and 2MnCl, respectively, in micellar phases of CTAB and Brij 35 aqueous solutions has been studied by means of several spectroscopic techniques. The results obtained show that a suitable functionalisation of the periphery of the porphyrin macrocycle influences the specificity of their binding to different micellar aggregates. This, consequently, allows for a tuning of the location and the aggregation mode of inclusion. These findings give a sound basis for the interpretation of the, earlier reported, P450 biomimetic catalytic activity featured by 1MnCl and 2MnCl in the epoxidation of some probe olefins

Structural effects on the NaOCl epoxidation of styrene in micellar media catalysed by amphiphilised Mn(III)metalloporphyrins

A biomimetic system of cytochrome P450, constituted by [5-(4-(I-methylpyridinium))-10,15,20-triphenylporphyrinato] manganese(III) dichloride (Mn1) included in cetylpyridinium chloride (CPyCl) micellar phase, features good catalytic activity in the NaClO promoted epoxidation of styrene. A closely related system, i.e. [5-(4-(3-trimethylammonium) propyloxyphenyl)-10,15,20-tryphenyl-porphyrinato] manganese(ID) dichloride (Mn2) in cetyltrimethylammonium bromide (CTAB), presents a lower reactivity, similar to that achieved in ethanol-water solvent mixture. A crossover experiment, i.e. that carried out with Mn1/CTAB system, shows intermediate degree of conversion. These findings indicate that the catalytic properties of the investigated systems are deeply influenced by the specific non-covalent interactions established among the catalyst, substrate, and surfactant. (C) 2002 Elsevier Science B.V. All rights reserved

Neon behind the signs

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Spectroscopic studies on the selective inclusion of amphiphilised porphyrin derivatives in micellar phases

The inclusion behavior of [5-(4-(3-trimethylammonium)propyloxyphenyl)-10,15,20-tryphenylporphyrin] chloride (1H(2)), 2-[2-(2-(4-(10,15,20-triphenyl-5-porphyrinyl)-phenoxy)ethoxy)ethoxy]etha nol (2H(2)), and their Mn(III) derivatives, 1MnCl and 2MnCl, respectively, in micellar phases of CTAB and Brij 35 aqueous solutions has been studied by means of several spectroscopic techniques. The results obtained show that a suitable functionalisation of the periphery of the porphyrin macrocycle influences the specificity of their binding to different micellar aggregates. This, consequently, allows for a tuning of the location and the aggregation mode of inclusion. These findings give a sound basis for the interpretation of the, earlier reported, P450 biomimetic catalytic activity featured by 1MnCl and 2MnCl in the epoxidation of some probe olefins. Copyright (C) 2003 Society of Porphyrins & Phthalocyanines

Isomerism of Cycloserine and Its Protonated Form

A comprehensive ab initio investigation has been performed on the structure and stability of the isomers of cycloserine and its protonated forms in the unsolvated state. Many conformers of cycloserine in the ketonic (K), enolic (E4 and E2), and zwitterionic (Z7 and Z2) forms have been characterized. Enols E2 are only a few kilocalories per mole less stable than the K isomers. Enols E4, as well as Z7 and Z2 zwitterions, are several tens of kilocalories per mole less stable than K. All the above isomeric structures exhibit pronounced isoxazolidine ring puckering, which generates very rich conformeric landscapes. The relative stability of the conformers of K, E2, and E4 responds essentially to a complex balance between the attractive and repulsive electrostatic interactions among their functional groups. The preferred site of protonation of cycloserine in the gas phase has been also investigated computationally and experimentally by IR multiphoton dissociation (IRMPD) spectroscopy. The most basic center of cycloserine is the N(7) nitrogen atom (proton affinity (PA)=215.3 kcal mol−1). Another important basic site is the O(6) oxygen atom (PA=213.0 kcal mol−1). Their most populated conformers have been identified by IRMPD spectroscopy. Their predominance responds to the electrostatic interactions among the functional groups of the protonated molecule