Photochemistry of dyes and fluorochromes used in biology and medicine: some physicochemical background and current applications.

An overview of the basic principles of photochemistry is presented to facilitate discussion of fluorescence, quenching and quantum yields. These topics in turn provide the foundation for an account of fluorescence spectroscopy and its application to microscopy. A brief overview of light microscopy and the application of fluorescence microscopy is given. The influences of molecular features, such as aromatic character and substitution patterns, on color and fluorescence are described. The concept of color fading is considered with particular reference to its effect on microscopic preparations. A survey of representative fluorescent probes is provided, and their sensitivity, application, and limitations are described. The phototoxicity of fluorescent molecules is discussed using biomembranes and DNA as examples of targets of toxicity. Photodynamic therapy, a relatively new clinical application of phototoxicity, is described. Both anticancer and antimicrobial applications are noted, and an assessment is given of the current ideas on the ideal physicochemical properties of the sensitizing agents for such applications.

Detection and determination of the hydrazo and azo photoproducts of 4-aminobenzoic acid by high-performance liquid chromatography.

The photochemistry of 4-aminobenzoic acid has been investigated using two validated reversed-phase HPLC methods. Up to nine photoproducts have been detected, with chromatographic evidence for the formation of 4,4'-azobenzenedicarboxylic acid and 4,4'-hydrazobenzenedicarboxylic acid. The synthesis and analytical characterization of 4,4'-hydrazobenzenedicarboxylic acid is reported.

A technique for assessing the effects of pH and photodegradation on the stability of the iron chelate of ethyl N-methyl-4-hydroxy-5-oxo-3-pyrroline-3-carboxylate.

Ethyl N-methyl-4-hydroxy-5-oxo-3-pyrroline-3-carboxylate forms a deep red chelate with iron salts. The color intensity is directly related to the iron concentration. The photostability of the red color was determined at pH 1.2 and 5 by spectrophotometric assay at 484 nm at intervals during irradiation by tungsten light at 1020 microW/cm2. After 528 hr of continuous irradiation in deionized water, 90.9% of the iron chelate had decomposed. The reaction followed zero order kinetics. Maximal stability was observed at pH 5 at both 10(-1) and 10(-2) molar concentrations of the iron chelate; no detectable decomposition occurred after 192 hr of continuous irradiation. The iron chelate in biological tissues is stable for 18 months. The staining technique is superior to other histological methods for estimating low concentrations of iron in tissue.

Membrane filtration method for bacteriological testing of water: enhanced colony visualization and stability on purification of phenol red indicator.

Commercially-available phenol red indicator, purified by adsorption chromatography was incorporated into lauryl sulphate broth (LSB) used in the membrane filtration method for the detection of Escherichia coli and other coliform bacteria. Relative to LSB containing the impure dye or its major contaminant, the purified phenol red provided clear visualization of discrete yellow colonies observed against a white background. The colonies remained stable for at least 24 h at 25 degrees C under standard laboratory lighting conditions. This simple procedure will enhance the detection of coliforms in samples.

Membrane filtration method for bacteriological testing of water: enhanced colony visualization and stability on purification of phenol red indicator.

Commercially-available phenol red indicator, purified by adsorption chromatography was incorporated into lauryl sulphate broth (LSB) used in the membrane filtration method for the detection of Escherichia coli and other coliform bacteria. Relative to LSB containing the impure dye or its major contaminant, the purified phenol red provided clear visualization of discrete yellow colonies observed against a white background. The colonies remained stable for at least 24 h at 25°C under standard laboratory lighting conditions. This simple procedure will enhance the detection of coliforms in samples.

Comparison of colourimetric methods for ammonia determination.

The precision of the Berthelot and Nessler methods of ammonia determination are compared at various ammonia concentrations. Recommendations are made regarding the most appropriate technique to use, dependent on the range of ammonia concentration expected. The effect of microdiffusion separation on the precision of ammonia determination is studied, together with an evaluation of a water soluble lid sealant and of the effect of a model amine contaminant.

A study of the leaching of aluminium ions from drink containers.

Lacquered aluminium drink cans were filled with deionised water and buffers (pH 1-13) and stored at 20 + 2 degrees C for 60 days. The aluminium content of the solutions contained therein was assayed by atomic absorption spectroscopy at time intervals and the leaching of aluminium from the cans examined. The possible toxicological hazard of the addition of aluminium to the diet from this source is discussed. It is concluded that drinks packaged in aluminium cans do not present a significant risk to people with healthy kidneys.

DNA binding studies on 1OH-pyrrolizino[1,2-b]quinolines.

1OH-Pyrrolizino [1,2-b]quinolines exhibited intercalation when tested by the following methods: effect of DNA on spectral properties, spectrophotometric titration, fluorescence enhancement of homidium bromide (ethidium bromide), thermal denaturation of DNA, effect on covalently closed circular double stranded PM-2 (Col E 1 plasmid) DNA. Some of the compounds showed antiproliferative activity in HeLa cells.

Photochemical processes of drugs and dyes.

The physicochemical properties of light and their interaction with organic material are reviewed. The photochemical reactions of a selected number of organic structures are appraised with the intention of facilitating prediction of likely degradation products from irradiation of drugs, dyes and mixtures thereof with solar and artificial light. There is a brief assessment of the problems associated with photochemical spoilage and some suggested means of remedy.

Photostability of cosmetic materials.

Synopsis The basic principles of photochemistry and photochemical reactions applicable to the topic are briefly reviewed. A more detailed survey of the photochemical reactions of raw materials used in the formulation of cosmetics is treated, according to the principal chemical classification of the material. In each group the photochemical reactions of the substance are reported with the more apparent implications for the cosmetic industry highlighted. The effects of photochemical catalysts are discussed, including the sources of impurities which can catalyse photochemical spoilage of cosmetic products. The methods of retarding photochemical degradation are appraised, including precautions which could be adopted in manufacturing processes and the use of additives collectively known as antioxidants.