Systematic investigation of absorption, fluorescence and laser properties of some p- and m-oligophenylenes

Absorption, fluorescence and laser properties of ten selected aromatic compounds from the oligophenylene family are studied experimentally at room temperature (293 K). The first eight compounds are arranged in such way that odd numbered compounds reveal 1Lb --> 1A fluorescence, while even numbered compounds show 1La --> 1A fluorescence. All compounds are family related in pi-structure and are of the same degree of planarity and rigidity. The quantum yield of fluorescence, gamma, and the decay times, tau(f), of non-deaerated and deaerated cyclohexane solutions are measured. The oscillator strength, f(e), the fluorescence rate constant, Kf, natural lifetimes, tau(o)T, and intersystem crossing rate constant, K(ST), are calculated. The lowest 1Lb and 1La singlet and 3La, triplet (77 K) levels are determined. Investigations showed that transition from a polyphenyl molecule which shows 1La --> 1A fluorescence to a family related in the pi-structure molecule which reveals the 1Lb --> 1A fluorescence is accompanied by certain changes in all the fluorescence parameters. This indicates that gamma decreases, tau(f) increases, Kf and the FWRE of the fluorescence spectrum decrease. Moreover, K(ST) also decreases, sometimes very significantly. The decrease in the K(ST) value is explained by the fact that matrix elements of the spin-orbit coupling of the S alpha and Ti states are much lower in value than analogous elements of the spin-orbit coupling of Sp and Ti states. It is shown that all p-polyphenyles exhibit excellent laser action, while m-polyphenyles do not produce laser oscillation under any conditions. The values of K(ST) and other fluorescence parameters measured can be used for various practical purposes and theoretical considerations.     

Determination of oxalate in pharmaceutical matrices by indirect photometric chromatography

An indirect photometric ion chromatography method is developed for the quantitation of oxalate in typical pharmaceutical matrices. The column/mobile phase conditions used represent a trade off between resolving power and sensitivity and results in an assay with a total analysis time of less than 9 minutes. Method response is linear between concentrations of 10 to 80 ppm oxalate. The limit of quantitation is roughly 5 ppm. Precision in the range of 30 to 80 ppm is better than 1.0% RSD of replicate injections, and the accuracy in a variety of matrices is 100 +/- 2%. The method is quite rugged and meets rigorous suitability requirements even after 500 injections. Although the assay can be used to quantitate citrate as well, the retention time is relatively long (20 minutes) and sensitivity is limited due to the broadness of the peak.     

Efficient synthesis of an adenosine A2a agonist: glycosylation of 2-haloadenines and an N2-alkyl-6-chloroguanine

A convergent synthesis of adenosine A2a agonist 1 in the form of its maleate salt 2 was achieved. The key step in this approach was the highly selective 9beta-glycosylation reaction between 2-haloadenines or an N(2)-alkyl-6-chloroguanine and a D-ribose derivative containing a 2-ethyltetrazolyl moiety. Glycosylations of other purine derivatives were also examined, and the methods developed provide efficient access to a variety of adenosine analogues such as 2-alkylaminoadenosines, an attractive class of compounds with antiinflammatory activity.     

Corrigendum to “A tandem enol silane Formation-Mukaiyama aldol reaction mediated by TMSOTf” [Tetrahedron Lett. 48 (2007) 3559–3562]

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