Photochemistry and Photobiology

During August 2011, anomalous southward movement of stratospheric ozone-poor air from tropical latitudes resulted in very low ozone levels (approximately 265 Dobson Units) over much of Southern Australia. Consequently, measured solar ultraviolet radiation (UVR) levels increased by up to 40% higher than normal. Given the populations involved in the major cities there (approximately 10 million people), it is likely that many people could have resultant higher solar UVR exposures and sunburns. Reporting procedures have been modified to warn the public of unusually low ozone and high UVR levels in the future.

Ultraviolet germicidal irradiation (UVGI) for air disinfection applications has relied on low-pressure mercury vapor lamps for decades. New design requirements have generated the need for alternatives in some uses. This study describes the current state of UVGI technology and describes future directions for technology development, including the use of lamps produced from nontoxic materials and light-emitting diode lamps. Important applications are discussed such as the use of ultraviolet germicidal lamps in developing countries, in heating, ventilating and air-conditioning systems to improve energy efficiency and indoor air quality, and for whole room disinfection.

This study assessed the UVR protection provided by shade structures over toddler pools at swimming pool centers in Melbourne, Australia using both UV sensitive film and handheld UV meters. The UV meter measurements showed the UV protection varied with position under the shade structure as well as with time of day. The UVR protection provided by the shade structures depended on factors such as location, size, and materials used and ranged from a protection factor (PF) of 2 to ca 16 for larger structures. Improvements to provide adequate protection and further reduce UV exposures are required and recommended.

An enlarged image taken of the sun using the LG Optimus smartphone camera at a wavelength of 380 nm. The image was achieved using attached narrowband and neutral density filters. The grayscale response can be used to determine the solar irradiance and aerosol optical depth with a high level of accuracy when compared with the readings obtained from a Microtops II sunphotometer.

We subjected six US-manufactured UV nail lamps to ANSI/IESNA RP-27 Photobiological Safety evaluation. Spectra were measured at three positions, 1 cm above the inner surface to approximate hand exposure and 20 cm normal and 45° to the opening. Interior UV levels classified these lamps into Risk Group 1-Low or 2-Moderate with permissible daily exposure limits ranging 29–276 min. At 20 cm, photobiological risks to skin and eyes of normal individuals were within Exempt classification. Total programmed exposure steps accumulate to only a small fraction of permissible daily exposure. Realistic risks are further mitigated because expected use is less frequent.

A portable “FOSD” device was developed and examined for the localized delivery of sensitizer molecules in ovarian cancer cells and production of singlet oxygen for their eradication in vitro. The device tip releases stored pheophorebide by attack of singlet oxygen from sensitized oxygen gas delivered through the hollow fiber using 669 nm laser light. Development of a sensitizer and singlet oxygen delivery device would be useful not only for cancer cell treatment, but also for bacteria, in cases where local delivery might be advantageous.

Microbial biofilms remain a major source of cross-contamination in both food and clinical environments. This study investigates the efficacy of 405 nm light (ca 140 m Wcm⁻²) for biofilm decontamination. Successful inactivation of Escherichia coli biofilms (10³–10⁷ CFU mL⁻¹) was demonstrated. Inactivation of Staphylococcus aureus, Pseudomonas aeruginosa and Listeria monocytogenes monolayer biofilms, and mixed-species biofilms (S. aureus and E. coli) was also shown. Results highlight that indirect exposure to 405 nm light can successfully inactivate biofilms: antimicrobial activity is retained when transmitted through transparent materials [glass(left)/acrylic(right)]. With further development, this technology may have potential use for practical biofilm decontamination applications.

The fluorescence wavelength is determined by emitter state, which depends on whether or not the protein motion provides the condition for the deprotonation of substrate in protein molecules. If the His22 is protonated, the emitter is phenolate anion as proton donor. If the hydrogen abstraction reaction occurs, the substrate as emitter is neutral state. The dynamics simulation and quantum chemical calculation are employed to investigate spectrum properties of deprotonation process of coelenteramide and two final states neutral state and phenolate anion.

The two-photon photophysical properties of a porphyrin–rhodamine B conjugate (TPP-Rh), previously demonstrated to target the mitochondria, were evaluated such as TPA cross sections (σ₂), RET kinetics, dynamics and singlet oxygen generation. Approximately doubled σ₂ of TPP-Rh (40 ± 4 GM) compared with its parent porphyrin (16 ± 4 GM) was measured. Furthermore, TPP-Rh produced singlet oxygen at a significantly faster rate than its parent porphyrin. This study indicates that conjugating photosensitizers to Rh B could provide greater TPA at near-infrared range.

Photohydrates are produced when uridine (Urd), 2′-deoxyuridine and 2′-deoxycytidine are irradiated with UVC in aqueous solution. We have found that such photohydrates undergo thermal reactions with several amines (e.g. spermine, spermidine, glycylglycine, ethylenediamine and glycine amide) at near neutral pH values to yield nucleoside-amine adducts, as displayed in the figure for the Urd hydrate (shown in one epimeric form). In general, these products display a strong absorption peak with λ_max in the range between 288 and 310 nm. The Urd-amine adducts are reasonably stable in frozen aqueous solution, but revert to Urd hydrates upon standing in liquid water.

The photoreaction of 8-MOP and thymine bases was studied by DFT. The monoadduct on the pyrone side is favored over the furan side when comparing reaction energies. The distinguishing feature is that the furan-side monoadduct displays a better photostability, which is a relatively high-barrier exothermic reaction, and thus the energy balance of the monoadduct on the furan side toward final diadduct formation is favored.

The photosensitizer-light parameters used to construct a photodynamic therapy (PDT) dose significantly impact tumor destruction and regrowth kinetics. A 3D ovarian cancer model (a) is used to evaluate a matrix of benzoporphyin derivative (BPD) and light combinations for three fixed PDT doses (b). PDT with 0.25 μM BPD (blue) provides maximum cytotoxic durability for all doses (c). Representative LIVE/DEAD (green/red) images (d) that were used to generate normalized viabilities in (c), depict increased killing in nodules treated with 0.25 μM BPD-PDT (2) compared to PDT with 1 μM (3) or 10 μM (4) BPD. These findings suggest that customization of PDT parameters could improve treatment outcomes.

This study describes a relatively simple method to calculate solar diffuse and total irradiances for using in environmental photobiology estimations instead of complex atmospheric radiative transfer computer programs. The model reproduced calculations for equinoxes and solstices at 35° latitude made by a computer-intensive and rather complex atmospheric radiative transfer program (MODTRAN) with a mean error <6%. The overall accuracy obtained by the regression model presented is usable in most radiative transfer scenarios found in the atmosphere. The approach and equations presented in this study should assist in estimating the maximum time during which microbial pathogens remain infectious after accidental or intentional aerosolization in open environments.

Topical treatment of SKH-1 hairless mice with α-santalol, a terpenoid isolated from santalum tree, caused reduction in tumor incidence, multiplicity and volume in UVB-induced skin carcinogenesis. In this study, the anticarcinogenic action of α-santalol against UVB-induced photocarcinogenesis was found to be associated with inhibition of inflammation and epidermal hyperplasia, cell cycle arrest and induction of apoptosis. Our results suggest that α-santalol is a safer and promising skin cancer chemopreventive agent with potential to target various pathways involved in photocarcinogenesis.

Upper-room Ultraviolet Germicidal Irradiation (UVGI) is commonly used as an environmental control measure to minimize the risk of transmission of airborne pathogens. Characterizing UVGI luminaires, in a laboratory and in situ, is essential in understanding the radiant intensity distributions delivered by the same designed luminaire, operating under different conditions. This understanding may be used in future design applications, such as computer-aided design (CAD), to calibrate the difference in behavior of luminaires between laboratory and in situ scenarios.

The photoreactions of 5-methylcytosine (5MeCyt), a minor base contained in eukaryotic DNA, with several cysteine analogs have been studied. The reaction of 5MeCyt with 3-mercaptopropionic acid (3MP) is shown schematically in the accompanying Figure. Irradiation with UVB light produces the opened-ring adduct Ia. Upon standing at ambient temperature in the presence of 3MP, the product IIa appears in solution. The latter reaction proceeds via a closed-ring intermediate that has been characterized using UV spectroscopy, proton NMR spectrometry and mass spectrometry. Either heating or irradiation of purified Ia with UVB light in aqueous solution converts it into 3-amino-2-methylacrylamidine.

A 96-well microplate is developed here as a platform for the detection of DNA damage in a number of DNA sequences simultaneously. This convenient mix-and-read assay uses smart probes, a hybridization assay composed of fluorescently labeled ssDNA hairpins complementary to the damaged target sequences, as general probes of DNA damage. The results show that the 96-well microplate platform is a simple, fast and inexpensive mix-and-read technique for multiplexed, sequence-specific DNA damage detection.

As part of their infection control strategy, hospitals use upper-room ultraviolet germicidal irradiation (UVGI) systems to inactivate airborne infectious agents. A computational fluid dynamics model was developed and applied to evaluate the design of the three hospital rooms, a patient and exam room with upper-room systems and a patient room with an exhaust duct system. One of the UVGI systems was not very effective, due to efficient ventilation design. The other two configurations were effective at inactivating airborne mycobacteria. The most effective application was the one for which the room air-exchange rate was very low.

This study suggest that related bacteria have a characteristic sensitivity to sunlight with their survival depending mainly on the fluence (photons) received in a dose-dependent manner that is otherwise relatively independent from latitude, atmospheric ozone and other local conditions. Conditions that inactivated P. aeruginosa did not result in measurable impairment of specific PCR or ELISA tests suggesting that this germ could still be amenable to detection after inactivation by sunlight. The results presented in this study should assist in predicting the survival of P. aeruginosa outdoors and in monitoring the risk posed by this widespread organism in a variety of environmental settings.

Although the cornea absorbs most of the ultraviolet (UV) radiation, still considerable radiation may reach the lens. By measuring the UV absorption of human lens sections we found that the UV-C and UV-B absorption of the human lens increased toward the posterior parts of the lens. Two-dimensional gel electrophoresis and mass spectroscopy analysis identified significantly different protein spots in the anterior and posterior section pools. Beta-crystallin B2 and A3 along with glyceraldehyde 3-phosphate dehydrogenase were enriched in the anterior part of the lens while elevated levels of Alpha-crystallin A chain and Beta-crystallin B1 proteins were found in the posterior portion.

Activated MMP-1, which is a member of the collagenase subfamily of MMPs, initiates collagen breakdown by cleaving type I and type III collagen, which are further degraded by MMP-2 and -9. Fucosterol reduced UV-irradiated MMP-1 production by 7% at 0.5 µm, 23% at 1 µm, and 38% at 5 µm compared with the UV-induced control. The results suggest that fucosterol could be a potential anti-photoaging agent via downregulation of MMP expression.

Low-Level Laser Therapy (LLLT) reduces loss of renal function in rat model of progressive chronic kidney injury induced by spontaneous metabolic syndrome. The laser treatment improved the glomerular filtration rate (GFR) and decreased the interstitial fibrosis.

Scrapie is the most widespread transmissible spongiform encephalopathy (TSE) affecting sheep and goats worldwide. The current work aims at developing mice retina as a convenient model system to diagnose scrapie and other fatal TSE diseases in animals such as sheep and cows. Steady-state fluorescence and hyperspectral imaging has been used as tools to investigate the fluorescence from the retinas of scrapie-infected mice and compared with those of healthy (uninfected) control mice. The fluorescence from the retinas of scrapie-infected mice was significantly more intense and showed more heterogeneity than that from the retinas of uninfected mice.

Bi₂WO₆ and Bi₂WO₆–TiO₂ were synthesized by hydrothermal method and evaluated in the photodegradation of Rhodamine B/Phenol mixtures with two illumination conditions. Previous studies revealed that these materials were very effective in Rhodamine B degradation by the influence of a mixed photocatalytic and photosensitized mechanism. In this work, it is demonstrated that when a molecule with no influence of photosensitization as Phenol is used as substrate, the photoactivity considerably decreases and that the photoinduced mechanism via Rhodamine B photosensitization is a key factor in the increased activity of this kind of materials.

Ceiling fans are considered an essential adjunct in the application of upper-room ultraviolet germicidal irradiation (UR-UVGI), especially in the resource-limited countries and areas. Numerical evaluation of UR-UVGI disinfection efficacy using TB infection probability by Wells–Riley equation indicated that air exchange rate was the decisive factor for determining UR-UVGI performance in disinfecting indoor air, and using a ceiling fan could improve the performance in general. The results also indicated the possibility of increasing the TB infection risk by using ceiling fan without effective air disinfection by ventilation or UR-UVGI.

The resurgence of tuberculosis (TB) in the United States in the mid-1980s led to a revival of interest in upper-room UVGI air cleansing technology, a focus that had almost disappeared because alternate means of controlling TB had inaccurately been deemed successful. For all those working in the field of UVGI, safety issues must be a concern because when UVGI fixtures are placed improperly, or precautions ignored, room occupants are placed at risk of photokeratoconjunctivitis and photodermatitis. If safety is so prominent a concern, why do incidents of UV side effects continue to occur? See Murphy's Law.

Our work explores the potential of computer airflow simulation in predicting the performance of upper-room ultraviolet germicidal irradiation (UVGI) effectiveness. Experimentally measured irradiance fields are combined with Computational Fluid Dynamics (CFD) methodology to predict the dose distribution (J m⁻²) within a small mechanically ventilated room for a range of test conditions. A series of detailed sensitivity studies illustrate the importance of the numerical grid size, the turbulence model employed and the fidelity of the irradiance field. We demonstrate that a two-dimensional UV field is sufficient for modeling purposes and the resulting dose distribution offers valuable insight into predicted disinfection performance.