Photoactive barbiturate receptors: an ultimate lock-and-key system in which the key unlocks the lock

Conditional photofragmentation is achieved with binary systems incorporating the isophthaloyl bis-aminopyridine barbiturate recognition motif and dithiane- or trithiane-based photolabile modules, which cleave only in the presence of an external sensitizer. The components of the host-guest molecular recognition pair were each outfitted with either the sensitizer or the photocleavable module. In these pairs, photoinduced fragmentation is contingent on a molecular recognition event, which brings the sensitizer into the immediate proximity of the photolabile latch. [structure: see text]     

When ethyl is infinitely different from methyl: double addition of lithiated dithianes to aromatic carboxylates revisited

Addition of lithiated alkyl dithianes to benzoyl chloride or methyl benzoate does not produce the expected product of double addition, alpha,alpha-bis(alkyldithianyl) benzyl alcohol, for alkyls larger than methyl. Instead, the first step intermediate, i.e. 2-benzoylated dithiane, undergoes an electron-transfer reduction by the second molecule of the dithianyl anion. This reduction is followed by the ring-opening mesolytic fragmentation of the dithiane ring in the ketyl anion radical and subsequent radical recombination yielding acetophenone-tethered thioortho esters 4, alpha-[3-(2-alkyl-1,3-dithiane-2-ylthio)propylthio]-alpha-alkyl-acetophenones. It appears that the Corey-Seebach bisaddition of lithiated dithianes to methyl benzoate is an exception rather than the rule in the alkyl dithiane series.     

Photochemically amplified detection of molecular recognition events: an ultra-sensitive fluorescence turn-off binding assay

Amplified fluorescence quenching methodology based on massive autocatalytic photo-unmasking of a dual function sensitizer-quencher is developed and adopted for photoassisted ultra-sensitive detection of molecular recognition events. The resulting binding assay, based on a molecular recognition-triggered photo-amplified cascade with concomitant decrease of fluorescence is validated with the biotin-avidin pair, achieving attomolar detection.     

Dithiane,Trithiane, and Dithiazane-Based Photolabile Scaffolds for Molecular Recognition: Mechanism and Efficiency of the Photoinduced Fragmentation in Aqueous Reductive Environments

Abstract

Photoinduced fragmentation in dithiane and trithiane adducts of aromatic ketones and aldehydes was studied in aqueous reductive environments. Density functional computations were carried out for thioxanthone derivatives bearing donor and acceptor substituents in the aromatic ring to identify the substitution pattern that is most promising for the productive irreversible electron transfer.     

Anomalous C-C bond cleavage in sulfur-centered cation radicals containing a vicinal hydroxy group

1,3-dithianyl cation radicals having alpha-hydroxy-neopentyl or similar groups in position 2, which are generated via oxidative photoinduced electron transfer, undergo anomalous fragmentation necessitating refinement of the accepted mechanism. Experimental and computational data support a rationale in which proton abstraction from the hydroxy group in the initial cation radical does not cause a Grob-like fragmentation, but rather produces a neutral radical species, the alkoxy radical, that undergoes fragmentation in either direction, i.e., cleaving the C-C bond to dithiane or to the tertiary alkyl group.     

Speech on L. V. Kantorovich

An extended version of the talk at the memorial session dedicated to L. V. Kantorovich on January 11, 2004 at the Euler International Mathematical Institute (St. Petersburg). __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 312, 2004, pp. 24–29.     

Cofinite numbers,nonstandard analysis,and mechanics

We demonstrate the mathematical insignificance of the versions of nonstandard analysis proposed in the articles by A. F. Revuzhenko.     

The polyhedral Lagrange principle

The Lagrange principle is established for dominated polyhedral sublinear operators.     

Lyapunov’s Convexity Theorem,zonoids, and bang-bang

This is a short overview of the connections of the Lyapunov Convexity Theorem with the modern sections of analysis, geometry, and optimal control.