Nadukkudy V. Eldho

Halogenated Squaraine Dyes as Potential Photochemotherapeutic Agents. Synthesis and Study of Photophysical Properties and Quantum Efficiencies of Singlet Oxygen Generation

Abstract— We describe the synthesis and photophysical studies, including measurements of quantum yields of triplet excited states and singlet oxygen generation of bis(3,5‐dibromo‐2,4,6‐trihydroxyphenyl)squaraine (2) and bis(3,5‐diiodo‐2,4,6‐trihydroxyphenyl)squaraine (3). These dyes exist in solution in the protonated, neutral, single and double depro‐tonated forms, depending on pH. The pKa values of these dyes were found to be relatively lower than those of the parent bis(2,4,6‐trihydroxyphenyl)squaraine (1). Only the single deprotonated forms (Sq) of 2 and 3 showed measurable fluorescence. In microheterogeneous media such as in the presence of β‐cyclodextrin, cetyltrunethylammonium bromide and polyvinylpyrrolidone), bathochromic shifts in the absorption and emission spectra of Sq were observed with a substantial enhancement in their fluorescence yields. Triplet excited states are the main transient intermediates obtained upon 532 nm laser excitation of the various forms of 2 and 3 in methanol. These triplets have lifetimes in the range from 0.061 to 132 μs. The triplet quantum yields of double deprotonated forms are low (φT = <0.01), whereas the neutral and Sq−forms of 2 (φr = 0.12 and 0.22) and 3 (φT= 0.24 and 0.5), respectively, exhibited significant triplet yields. Quantum yields of singlet oxygen generation by Sq−forms of 2 and 3 were determined in methanol and were found to be 0.13 and 0.47, respectively, which are in good agreement with the triplet yields obtained in these systems.

Collective and Noncollective Models of NMR Relaxation in Lipid Vesicles and Multilayers

NMR (13)C spin lattice relaxation (1/T(1)) rates of dipalmitoylphosphatidylcholine (DPPC) bilayers obtained from molecular dynamics simulations of 72 and 288 lipids are compared with each other, with experimental values from large liposomes obtained by magic angle spinning, and with previously published experimental data from small vesicles. The experimental results for multilayers and vesicles at the same frequencies differ only slightly. The simulation results indicate that T(1) relaxation in the 15.1 to 201.2 MHz carbon frequency range and up to 100 A length scale is dominated by fast isomerizations and slower lipid wobble (D perpendicular approximately 2.5 x 10(8) s(-1)). Rotational diffusion about the lipid long axis (described by D(parallel)) does not make a substantial contribution to the T(1). Modifications to the acyl chain torsional potential energy function used for the simulations substantially improve agreement with experiment.

One Pot Synthesis of Acridinylalkanoic Acids and Novel Bisacridines

Abstract The condensation reaction of diphenylamine with aliphatic dicarboxylic acids in presence of anhydrous zinc chloride gives rise to ω-(acridin-9-y1)alkan-α-oic acids and α,ω-bis(acridin-9-yl)alkanes, in moderate to high yields, under defined experimental conditions.

Phototransformations of bridgehead-substituted dibenzobarrerenes. Steady state and laser flash photolysis studies of 9-benzoyl- and 9-(α-hydroxybenzyl)-substituted dibenzobarrelenes

Abstract The photochemistry of 9-benzoyl- and 9-(α-hydroxybenzyl)-substituted dibenzobarrelenes (1 and 8) was investigated by steady state photolysis, product analysis and laser flash photolysis. The irradiation of 1 in benzene gave a 91% yield of the dibenzosemibullvalene 6, and its structure was confirmed by X-ray crystallographic analysis. The 9-(α-hydroxybenzyl)-substituted dibenzobarrelene (7) exists in the cyclic carbinol form 8, as revealed via X-ray structural determination. The irradiation of 8 in benzene gave a 52% yield of 4H-pyranodibenzopentalene 15. X-Ray single-crystal diffraction studies confirmed the structure of 15. The 308 nm laser pulse excitation of 1 and 8 in benzene gave rise to transient phenomena which could be attributed to the triplets, characterized by broad absorption spectra and relatively short lifetimes (0.46–0.83 μs). These transients were quenched by oxygen, 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy (HTEMPO) and ferrocene at rates in the range (0.23−4.05) × 109 M−1 s−1. The formation of the observed photoproducts from 1 and 8 was rationalized in terms of di-π-methane rearrangements leading to the dibenzosemibullvalenes 6 and 12 and the subsequent transformation of 12 to give 15.