Gerald J. Smith

THE EFFECTS OF AGGREGATION ON THE FLUORESCENCE and THE TRIPLET STATE YIELD OF HEMATOPORPHYRIN

Abstract— The fluorescence and triplet state yields of hematoporphyrin have been measured in wuter/methanol mixtures. There is a closely linked response of these yields to aggregation of the hematoporphyrin molecule. The monomer, which is the principal species present at high methanol content, has a triplet state yield of 0.91 and a fluorescence yield of 0.09. By contrast, hematoporphyrin solutions with a high water content containing aggregates have lower fluorescence and triplet state yields, e.g. 0.018 and 0.56, respectively, in water. Static, singlet state quenching in some of the aggregates is responsible for the reduced fluorescence yield. The results also show that in addition to these aggregates there are other types of aggregates where there is an increased singlet to ground state radiative transition probability, resulting from the interaction between transition dipoles in adjacent molecules.

New trends in photobiology (invited review) photodegradation of keratin and other structural proteins

Abstract Keratin and many other proteins are damaged when they are exposed to ultraviolet and visible radiation. In wool keratin, this is apparent as a colour change and a weakening or embrittlement of the fibre. Photodegradation of other structural proteins such as collagen, elastin and eye lens proteins (crystallins) have been linked with problems such as premature skin ageing and cataract formation; a possible involvement in skin cancer has even discussed. Despite several decades of research, the photochemistries of these processes are still imperfectly understood. This review deals with the photophysical and early photochemical events occurring in keratin upon exposure to ultraviolet and longer wavelength radiation. General aspects of the photochemistry of other proteins and model amino acid systems are also reviewed.

Solid state dye lasers based on 2-hydroxyethyl methacrylate and methyl methacrylate co-polymers

Abstract The laser performance of a range of solid state dye lasers based on rhodamine 590-doped co-polymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) has been investigated. The optimisation of preparation conditions, including polymerisation initiator and solvent for dye delivery is discussed in detail. Laser efficiency is compared for different polymeric hosts and dye concentrations with a range of output couplers, cavity lengths and repetition rates. Passive and dynamic loss have been determined for each host medium. Laser efficiencies of optimised polymers are among the highest reported for rhodamine 590-doped solid state dye lasers under these operating conditions. Highest slope efficiency of 35% and lowest threshold fluence of 0.06 J cm −2 were obtained with dimethyl sulphoxide (DMSO) additive in MPMMA at 10 Hz repetition rate.

THE ‘Q-BAND’ ABSORPTION spECTRA OF HEMATOPORPHYRIN MONOMER AND AGGREGATE IN AQUEOUS SOLUTION

Abstract The resolution of the absorption spectra in the Q band (480 nm‐620 nm) spectral region of monomeric and dimeric hematoporphyrin species present in aqueous solutions has been achieved using absorption, fluorescence and computer analysis methods. The absorption maxima of the dimer in this spectral region are red shifted about 12 nm with respect to those of the monomer. The significance of this finding in relationship to the well documented blue shift of hematoporphyrin aggregate observed in the Soret band region (λmalx∼400 nm) of the absorption spectrum is discussed.

THE PRESENCE OF PHOTOREACTIVE β‐CARBOLINE FLUOROPHORES IN WEATHERED WOOL KERATIN

Abstract Solvent‐cleaned Merino wool, which was enzymatically digested with protease K, displayed a fluorescence maximum at 500 nm when excited at 430 nm. The yield of this emission was approximately 15 times greater for a fiber tips digest than for a digest of the mid‐length region of the same fibers.

SEASONAL TRENDS IN ERYTHEMAL and CARCINOGENIC ULTRAVIOLET RADIATION AT MID-SOUTHERN LATITUDES1989–1991

A network of solar carcinogenic/erythemal ultraviolet radiometers has been established in New Zealand. Daily integrated irradiances of this biologically harmful ultraviolet radiation for 1989, 1990 and 1991 are reported from radiometers located at Wellington (41°S) and Christchurch (43.5°S) and for 1990 and 1991 from the Auckland (37°S) radiometer. Although the monitoring program has not been running sufficiently long to discern any long‐term changes in levels of solar ultraviolet radiation, shorter term trends are apparent, which are attributed to a seasonal cycle in levels of ozone at midlatitudes and changes in atmospheric aerosols.

The fluorescence and photostabilities of naturally occurring isoflavonesDedicated to the memory of Nobel Laureate, Lord George Porter FRSC FRS OM.

The 5,7-dihydroxyisoflavones do not emit detectable fluorescence and are significantly more photostable than the two 7-hydroxy-5-deoxyisoflavones, daidzein and formononetin. The latter isoflavones emit fluorescence that depends on the basicity of the solution and the polarity of the solvent. Comparison of the spectral distributions of the emission in methanol in the presence and absence of base indicates that it originates from the conjugate anion excited singlet states. The fluorescence of daidzein and formononetin exhibit large Stokes shifts to longer wavelengths in methanol, ethanol, hexanol and acetonitrile and the magnitudes of these shifts increase with solvent polarity. This indicates that the emission originates from excited singlet states with much larger dipole moments than those of the corresponding ground states. Values of 8.3 D and 6.5 D were determined for daidzein and formononetin respectively. The photostabilities of formononetin and daidzein both increase with increasing solvent polarity and in corresponding solvents, the photostability of daidzein is higher than that of formononetin, behaviour which is attributed to the greater antioxidant activity of daidzein.

The Effect of UV Absorbing Sunscreens on the Reflectance and the Consequent Protection of Skin

Abstract The in vivo reflectance spectra of Caucasian skin, coated with preparations containing sunscreen vehicle, vehicle with olive oil and vehicle with the UVB and UVA absorbers 2-ethylhexyl-4-methoxycinnamate and 4-t-butyl-4′-methoxydibenzoylmethane were determined. All preparations reduced the reflectance of skin throughout the UVA spectral range (320 to 400 nm), with the sunscreen preparations containing the UVB and UVB plus UVA absorbers reducing the reflectance more than the sunscreen vehicle alone. This phenomenon, which facilitates the penetration of UV radiation to the lower epidermis and dermal layers of skin and therefore lessens sunscreen efficacy, is attributed to optical coupling mediated by refractive index matching of the sunscreen to the upper epidermis. The greater reduction in skin diffuse reflectance caused by sunscreens containing methoxycinnamate is associated with this compounds high refractive index. Also, by determining the excitation spectra of the autofluorescence originating from the dermal layer of skin, the transmission spectra of the various components of sunscreen on skin were established, and these were in good general agreement with previously published spectra.

FLUORESCENCE OF TRYPTOPHAN IN KERATIN

The excitation and emission spectra have been determined for the fluorescence from trypto‐phan residues in dry keratin. The fluorescence decay was also measured and shown to be a single exponential with a rather long lifetime of 6.9 ns. It is suggested that the emission takes place from a state formed by interaction between the 1La state of the tryptophan residues and neighbouring polar or polarizable groups in the protein.

THE EFFECT OF CHANGES OR DIFFERENCES IN ROBERTSON-BERGER RADIOMETER RESPONSIVITY ON SOLAR ULTRAVIOLET-B MEASUREMENT

Two long‐term solar UV measurement campaigns, in the USA and in Austria, using Robertson‐Berger radiometers found opposite trends for measured levels of ultraviolet‐B radiation reaching the earths surface. This could be a consequence of the method used to calibrate the radiometers. Changes or differences in responsivity were compensated for by adjusting the sensitivity of the field radiometers to match the output of a reference radiometer.