Oscar Valdes-Aguilera

ROSE BENGAL AGGREGATION IN RATIONALLY SYNTHESIZED DIMERIC SYSTEMS

Abstract— Rose Bengal derivatives (I‐VI) have been synthesized as part of a program to study the spectroscopy of model systems for Hpd dimer. The absorption and emission spectra as a function of solvent are diagnostic for the formation of aggregated conformers. Based on our spectroscopic results we conclude that these compounds exist in open conformation in ethanol and other organic solvents, and that they form intramolecular dimers in aqueous solution.

A low temperature luminiscence study of the colored merocyanine form of substituted 6-nitrobenzo-spiropyrans☆

Abstract The emission spectra of colored merocyanine forms of substituted 6-nitrobenzospiropyrans (1-4)were studied at 77 K. The merocyanine form obtained by UV irradiation of a solution of spiropyrans at room temperature is a dynamic equilibrium mixture of stable trans forms. The merocyanine form obtained by UV irradiation of the same solution at 77 K is a short- lived intermediate. The assignment of this short-lived intermediate to the trans-cis-cis (TCC) form is based on MM2 calculations. This TCC intermediate was also observed during the visible light irradiation of the hydrochloric acid salt form of 1 (5) prepared at 197 K.

Aggregation of rose bengal ethyl ester induced by alkali metal cations in aqueous solution

Abstract The spectrum of Rose Bengal C-2′ ethyl ester, C-6 sodium salt dimer in 2% ethanol has been observed in the presence of alkali metal cations. It is proposed that aggregation occurs in two steps: (a) formation of a neutral complex between the anion of the dye and the alkali metal cation and (b) reaction between the neutral complex and a second dye anion to produce the dimeric species. Both equilibrium constants, as well as the geometry of the dimer, are sensitive to the identity of the cation. The equilibrium constant for the first step ranges from 3.37 M −1 for Li + to 257 M −1 for Rb + and that for the second step ranges from 2.81 × 10 5 M −1 for Li + to 1.05 × 10 6 M −1 for Cs + . The driving force of the first reaction is purely electrostatic whereas the dimerization step is controlled mainly by the hydrophobicity of the dye anion.

Pharmacological studies of arrhythmias induced by rose bengal photoactivation.

Singlet oxygen and superoxide production by rose bengal photoactivation leads to rapid electrophysiological changes and arrhythmias. To investigate which intermediate is causative and to probe possible mechanisms, hearts (n = at least 6/group) were perfused aerobically for 10 min without rose bengal followed by 5 min with rose bengal before illumination for 20 min. In controls, all or most hearts exhibited ventricular premature beats, ventricular tachycardia, and complete atrioventricular block. Most antioxidants tested had no protective effect; histidine, however, significantly delayed the onset of electrocardiographic (ECG) changes. In further studies, two antiarrhythmic agents (quinidine and verapamil) had no little protective effect, whereas R56865 significantly delayed the onset of ECG changes and reduced the incidence of arrhythmias. However, spectrophotometric and laser pulse radiolysis studies showed that this apparent protective effect might have resulted from an interaction between R56865 and the rose bengal molecule, leading to a reduction in singlet oxygen production. In conclusion, the electrophysiological changes induced by rose bengal photoactivation are likely to be due to singlet oxygen; antiarrhythmic drugs appear to be unable to protect against the injury unless there is some interaction with the photoactivation process.

Synthesis and spectral properties or Rose Bengal derivatives containing anthracene chromophores

Abstract Rose Bengal derivatives containing separated anthracene chromophores as C-2′ esters have been synthesized. The spectral properties of these compounds have been studied in aqueous solution, and both short-chain ( I ) and long-chain ( II ) compounds form intramolecular Rose Bengal—anthracene complexes. Equilibrium constants for complex formation have been determined by spectral methods and are 1.78 ± 0.23 for I and 10.06 ± 0.39 for II . Intramolecular singlet—singlet enrgy from anthracene to Rose Bengal has been observed in both long-chain and short-chain compounds in EtOH. Measurements of the triplet lifetimes of I , II , RBEt and RBEt + anthracene at 77 K indicate that there is neither triplet—triplet energy transfer nor chemical reaction between Rose Bengal and anthracene.

Photophysics and photochemistry of P-benzoylphenyldiphenylmethyl in solution

Abstract The photochemistry and photophysics of p-benzoylphenyldiphenylmethyl (I) is reported in benzene at room temperature. This report is the first of the photochemical properties of a stable radical conjugated with an n-π carbonyl group.

Electron relay in the photoinduced decomposition of a tunable perester

Abstract Evidence is provided from transient studies of Eosin (2′ t-butyl peroxy ester) (EoP) of a photochemically induced intramolecular electron transfer which anchimerically assists peroxide decomposition.

Quantitative studies of photopolymerization using fluorescent probes

The study of rates of photochemical polymerization processes in three-dimensions requires the development of new approaches to following chemical changes in the transient time domain. We report, herein, fundamental studies of acrylate polymerizations leading to the development of a simple fluorescence probe for such studies.