Photochemistry and Photobiology

This special issue of the Journal contains a selection of research articles and reviews based on lectures presented at the 21st Conference of the Inter-American Photochemical Society (I-APS), which took place in Mendoza, Argentina, on May 2011. The topics relate to novel applications of photochemistry in the study and/or synthesis of novel materials, photochemistry and the environment, new tools for biophysical studies and photobiology studies.

Photochemistry is a powerful tool for controlled synthesis of metal nanoparticles, their modification and applications. Plasmon transitions offer a unique way of delivering energy with exquisite spatial and temporal control and can be used to advantage where visible wavelength control is required. This contribution summarizes details of the synthesis, modification and applications of silver nanostructures. The graphic emphasizes how visible light irradiation can be used to generate a rainbow of colors and shapes for silver nanoparticles.

The photoisomerization of 5E-α-calcidol sensitized by anthracene and triethylamine takes place by a one-way quantum chain mechanism, which renders the biologically active Z isomer in >95% fraction in the photostationary state, with a quantum yield exceeding 40

Compared with free-base photosensitizers, zinc-chelated porphyrins accumulate less in mitochondria but induce higher damage in this organelle, favoring apoptotic cell death in HeLa cells under illumination. Zinc chelation seems to protect the photophysical/photochemical properties of the photosensitizers in the intracellular environment and it should be considered in the development of more efficient PDT drugs.

Interactions between fluorescent dyes and the DNA nucleotides produce a decrease in their apparent diffusion coefficients, which is detected in fluorescence correlation spectroscopy experiments. Interactions are evident for TAMRA and Cy3B, but not for Alexa-546. The interactions between Cy3B with the four dNMPs, and between TAMRA and dAMP, dCMP and dTMP, do not result in substantial changes in the absorption or fluorescence properties of the dye. Therefore, FCS provides evidence of the association of these dyes with the DNA bases that is not apparent in the traditional spectroscopic and fluorescence quenching studies.

Both absorption and fluorescence properties of a series of dissolved humic substances from different sources are ruled by their molecular complexity (e.g. molecular size, aromaticity and oxidation degree), affecting the density of low energy charge-transfer absorbing and emitting states.

Energy transfer producing nonradiative deactivation of poly(vinyl carbazole) by poly[(9,9-dioctylfluorenyl-2,7-divinylene-fluorene)-co-alt-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}] in polymer blends is strongly dependent on the interchromophoric distances. Because of this critical distance requirement, lower Förster resonant energy transfer efficiency in polymer blends with phase separation is expected.

The reactions of Br₂˙^-/Br˙ radicals with Aldrich humic acid (AHA) were studied by laser flash-photolysis (λ^exc = 266 nm) of Na₂S₂O₈ solutions in the presence of NaBr. HO˙ and N₃˙ radicals were generated by pulse radiolysis of aqueous solutions containing AHA. From these time-resolved experiments information on the rate constants for the reactions of Br₂˙^-, Br˙, HO˙ and N₃˙ with AHA and on the intermediate species involved in the mechanism was obtained.

With industrialization and population growth, the environmental contamination caused by organic pollutants is becoming a preponderant problem all over the world, especially in developing countries. Photocatalysis technology may provide a promising green solution to address these urgent issues. Fe-doped sulfated titania photocatalysts, with high visible-light-driven photoactivity and remarkable thermal stability against the phase transformation from anatase to rutile, were prepared by one-step thermal hydrolysis method from industrial titanyl sulfate solution.

In this study, we report a histidine-based fluorescence probe for Cu2+ and Hg2+, in which the amino group and imino group were modified by two common protective groups, 9-fluorenylmeth-oxycarbonyl and trityl group, respectively. In a water/methanol mixed solution, the probe displayed a selective fluorescence “turn-off” response to Cu2+ when the ratio of CH3OH?H2O was higher than 1:1. Specifically, when the solvent is changed to 1:1 methanol/water, the 304 nm fluorescence peak is enhanced, while the 317 nm peak is weakened, upon addition of either Cu2+ or Hg2+ ions. The mechanism for such distinct responses of the probe to Cu2+ and Hg2+ was further clarified by using NMR and molecular simulation. The experiment results indicated that the polarity of solvent could influence the coordination mode of 1 with Cu2+ and Hg2+, and control the fluorescence response as a “turn-off” or ratiometric probe..

Hydrogen bonding with cellulose hydroxyl groups stabilizes the triplet state of Eosin Y and facilitates nonradiative deactivation of the excited state through dissipation of vibrational energy into the matrix. The magnitude of the interaction is larger in amorphous regions, leading to lower triplet energies and shorter lifetimes than in crystalline regions.

The electron-withdrawing trifluoroacetyl undergoes a nucleophilic addition with amines, and the complex (europium-(thenoyltrifluoroacetone)₃) was used to selectively detect BuNH₂ and Et₂NH by monitoring emissions.

An aniline-based receptor containing multiple thioether ligands binds Ag⁺ when utilized in a nitrobenzyl photocage. Upon photolysis, the photocage retains a high affinity for the metal ion suggesting that thioether ligands tend to inhibit the release of soft metal ions.

The detailed kinetics of excited-state proton transfer and associated relaxation dynamics of water around the probe 1-naphthol in the nanoclusters of water in dioxane has been investigated.

A new luminescent dinuclear Tb(III) complex was synthesized. The complex exists as discrete molecules that are linked by extensive O–H … O hydrogen bonds into a 3D network. It has a long-luminescence lifetime, typical and easily distinguished narrow line emissions in the green region in methanol solution. Interestingly, this material can be used to detect the purity of methanol sensitively. The volume ratio of the impurity (acetone, chloroform, DMF or THF) to methanol can determinate quantitatively by measuring the luminescence of the impure methanol solution.

This systematic comparison of dye-DNA interactions for conventional labels allows us to choose suitable fluorophores for efficient signaling in microarrays and immunoassays and future enhancement by rolling circle amplification (RCA) and can present a road map toward design and interpretation of experiments using these labels on DNA of known sequence.

Novel photochromic amphipathic molecules, KMR-AZn (Gd-DTPA-AZCn), composed of hydrophilic Gd-DTPA and hydrophobic alkylated azobenzene were prepared. In aqueous environment, KMR-AZn indicated self-assembly. The resulting aggregates were demonstrated to be able to include a hydrophobic drug substitute (hydrophobic fluorescent dye) into the internal core, and to release the included compound upon photoirradiation within 10 min through the influence of azobenzene photoisomerization. This micellar MRI contrast agent exhibited three- to four-fold higher r₁ relaxivity (r₁ = 14.5–16.5 mm⁻¹ s⁻¹, 0.47 T at 40°C) than the widely applied small molecule contrast agent Gd-DTPA (Magnevist^®r₁ = 4.1 mm⁻¹ s⁻¹, 0.47 T at 40°C). This dual functionality of encapsulated compound release and increased MR imaging contrast indicates that KMR-AZn is a potential candidate for application as a lipid-based MRI-traceable drug carrier.

Photoreaction of ketoprofen (KP), one of the nonsteroidal anti-inflammatory drugs (NSAIDs), was studied in the presence of basic amino acids. KP⁻ excited with UV light gave rise to carbanion, which abstracted a proton from the side chain of the protonated amino acids to yield 3-ethylbenzophenone ketyl biradical (EBPH). Histidine was found to make a huge contribution to the formation of EBPH, but Lys and Arg also play an important role as a proton donor for photochemistry of KP. The information on the photoreaction mechanism of NSAIDs with basic aminoacids was essential to understand primary reaction of excited NSAIDs in vivo.

Theoretical absorption and fluorescence spectra of luciferin, and its conjugate acids and bases, calculated by TDDFT, are helpful to assign the experimental spectra.

A novel pathway of photoinduced decomposition of sphingolipids resulting in bioactive 2-hexadecenal formation.

We have studied octocrylene’s reactivity toward different amino acid analogs to better understand the reason for its photoallergenic capacity. Benzylamine, a lysine analog, did react with octocrylene during the photolysis in an acylation reaction. The same type of acylation reaction took place when octocrylene alone was photolysed in ethanol, during which the ethyl ester was formed from octocrylene and ethanol. Our results suggest that octocrylene’s ability to cause photocontact allergy could be due to its photoinduced reactivity toward primary amines and alcohols.

This research evaluated the photostability of four nanoencapsulated E-resveratrol (E-RSV) formulations and the skin penetration profile of the two most stable formulations. Different supramolecular structures were developed: liposomes, nanostructured lipid carriers, polymeric lipid-core nanocapsules and nanospheres. The skin penetration profiles of the stable formulations were obtained using vertical diffusion cells (protected from light and under UVA radiation). Photoisomerization was significantly delayed by nanoencapsulation. E-RSV-loaded liposomes showed low-physical stability under UVA radiation and nanospheres low-chemical stability. In the dark, the skin penetration profiles were very similar, but under UVA radiation the nanoencapsulated E-RSV showed increasing amounts in the total epidermis.

A point mutant of P77D of bacteriorhodopsin (BR) was made. The site selection is based upon the difference of the 77th residues of BR and another retinal protein archaerhodopsin 4 (AR4), which has a reserved time order of light-driven proton release and uptake at neutral pH. The BR-P77D exhibited a time order between those of wild-type BR and AR4, which confirms our prediction that this site is very important. The pK_a value of the proton release complex of the new mutant in the M intermediate state was also determined and found to be raised up compared to that of the wild-type BR, yet less than that of AR4.

Purple young leaves of the cv. Purpurascens of Coffea arabica have lower reflectance for the light interval between 500 and 600 nm (green light) compared with green young leaves of cv. Catuai, but higher reflectance at the red light band (600 and 700 nm). Thus, it seems the anthocyanins in leaves of Purpurascens alter the quality and the amount of light reaching the cells beneath the adaxial epidermis layer, where anthocyanins are primarily located. In general, photons reaching mesophyll cells have more associated energy (lower wavelengths) in Catuai leaves than in Purpurascens.

The simulation of the radiation field in suspensions of microalgae is crucial for the analysis, optimization and rational scaling-up of photobioreactors. In this article, a combined experimental and computational procedure is presented, specifically devised for the assessment of the coefficients of absorption and scattering. The Monte Carlo simulation algorithm developed in this study, when used as a supporting subroutine of a main optimization program based on a genetic algorithm, permits the assessment of the physical parameters of the radiation field model. This model was tested on suspensions of two algal species of dissimilar cell shapes: Chlorella sp. and Scenedesmus quadricauda.

A Monte Carlo simulation program is developed and used as a predictive autonomous program applied to the modeling of experiments that reproduce the common illumination conditions found in processes of large scale production of microalgae. It can be applied to assess to what extent the scattering phenomena are important for the prediction of the radiant energy density and to compute this property inside photobioreactors with the goal to optimize its design and their operating conditions. The module is validated by comparing the results of experimental measurements made on algal suspensions with those predicted by the Monte Carlo program.

UVA plays a role in the pathogenesis of premature skin aging through keratinocyte cytotoxicity and degradation of collagen. Oxidative stress caused by UVA irradiation might involve induction of matrix metalloprotease-1 (MMP-1). This study aimed to assess inhibitory effects of caffeic acid (CA) and ferulic acid (FA), powerful plant-based phenolic antioxidants, on UVA-induced cytotoxicity and MMP-1 up-regulation in association with modulation of antioxidant defenses in keratinocyte (HaCaT) cells. CA and FA exerted protective effects on UVA-mediated MMP-1 induction possibly through restoration of antioxidant defenses including GSH, catalase and glutathione peroxidase at the cellular and molecular level.

Photodynamic therapy (PDT) provides an effective option for treatment of tumors and other diseases. By coupling the molecular kinetics to cell killing, we present a model of Type-II PDT to understand the complex processes of molecular interactions and subsequent cell killing in time domain in the presence of oxygen transport within a spherical cell configuration. The model allows quantitative investigation of PDT cytotoxicity caused by singlet oxygen and calculation of the cell survival ratio as a function of light fluence or initial photosensitizer concentration with different photon density or irradiance of incident light and other parameters of oxygen transport.

The port wine stains (PWS) lesions were scanned by the laser speckle perfusion imaging; it showed significantly higher perfusion than the contralateral healthy controls and had heterogeneous perfusion from site to site even in the same patient before vascular targeted photodynamic therapy (V-PDT). During V-PDT, the perfusion of the PWS lesions increased rapidly after the initiation of V-PDT, reached a maximum within 10 min, lasted for several minutes, and slowly returned to a relatively lower level at the end of V-PDT.

Methylene blue, used as photosensitizer in photodynamic inactivation (PDI) experiment, demonstrated a strong killing effect against Listeria monocytogenes. The colony forming unit of L. monocytogenes approximately showed a 10⁷-fold decrease after irradiation with MB. Atomic force microscopy was used to observe the morphological alteration; meanwhile, the leakage of intracellular contents was estimated by spectrophotometer at OD₂₆₀ and OD₂₈₀, which correlated with morphological alterations. Furthermore, genomic DNA cleavage and protein degradation were also detected through agarose gel electrophoresis, real-time PCR and SDS-PAGE after PDI treatment.

This is an in vitro study on the phototoxic effect of the 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin (TMPyP) in Paracoccidioides brasiliensis, a human pathogenic fungus, which causes systemic mycoses called paracoccidoidomycosis. The results suggest that TMPyP is an effective sensitizer for photoinactivation treatment and that the oxidative stress generated under our experimental conditions greatly induces antioxidant activity in P. brasiliensis cells. These results are important to the development of therapeutic tools that could be applied in vivo.

Ultraviolet radiation is known to cause both benefits and harmful effects on humans. The adverse effects mainly involve two target organs, skin and eye, and can be further divided into short- and long-term effects. The present case report describes an accidental exposure of two healthcare workers to ultraviolet radiation produced by a germicidal lamp in a hospital pharmacy. The germicidal lamp presented a spectrum with an intense UV-C component as well as a modest UV-B contribution. In this study, the authors describe acute and potentially irreversible effects caused by high UV exposure.

The light source spectrum used in calculation has an important influence on in vitro sun protection factor (SPF) values. So, to establish a reliable in vitro SPF method for predicting in vivo SPF, which is obtained under relative cumulative erythema effectiveness (RCEE) light, it is important to employ RCEE light. But, to estimate the real protective efficacy of sunscreens in our daily life, it would be better to use a natural sunlight spectrum. In the future, it may be desirable to label sun-care products with an estimate of sun protection under actual use instead of SPF under RCEE light.

A measurement system is described that allows an objective review and evaluation of the amount of use by different population groups of provided shade structures. The technique provides a linear relationship with an R² of 0.99 between the exposure ratio and the time spent in the shade for the solar zenith angle range of 19–53^o and for both low and high cloud levels. It provides an objective determination of the amount of shade use by population groups that have set periods of time outdoors.

The subcellular localization of the chemotherapeutic agent tamoxifen (TAM) was assessed by confocal fluorescence microscopy in DU145 and MCF7 cells. In both cell lines TAM largely accumulates in the mitochondria and endoplasmic reticulum, but not lysosomes. Moreover, in MCF7, but not in DU145 cells, mitochondrial electron transport chain complex I and III inhibitors exacerbate TAM toxicity with an order of potency of myxothiazol ≥ stigmatellin > rotenone > antimycin A, suggesting a cell-specific cytotoxic interplay between mitochondrial complex I and III function and TAM action.

This prospective study suggests that methyl-aminolevulinic acid (MAL)-photodynamic therapy (PDT) is a safe and efficient treatment of renal transplant patients. This study shows that MAL-PDT is better than keratolytic treatment in reducing area of recalcitrant hand warts in renal transplant patients, but not in reducing the number. Most patients claimed that PDT had clearly improved their skin condition and general comfort. This was due to the decrease of warts’ areas and hyperkeratosis.

Nucleotide excision repair of cyclobutane dimers and (6-4) photoproducts was greatly reduced in engineered 3-D constructs of human oral tissues (EpiGingival^TM and EpiOral^TM) compared with human skin constructs (EpiDerm^TM). The data suggest that ultraviolet radiation (UVR) exposure of oral tissues can result in accumulation of DNA damage and increase the risk for carcinoma and melanoma of the mouth. Because NER is a broad-spectrum defense against DNA damage caused by a variety of agents in addition to UVR, the data also suggest that the relatively low NER efficiency observed in oral tissues may have wide-ranging consequences in this highly exposed environment.