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The UV irradiation (lambda = 362 nm) of aflatoxin B1 (AfB1) dissolved in water resulted in the formation of an oxidized product. The process was not inhibited by ionol, a routine inhibitor of the radical processes. The oxidized product was not found in the system where AfB1 was metabolized by the 3-methylcholanthrene-activated rat liver microsomes. It is suggested that the product is identical with 2,3-dihydrodiol of AfB1.
Some insect virus produces proteinous occlusion bodies named polyhedra, on which it is possible to immobilize functional proteins, such as green fluorescent proteins, antibodies, and growth factors, with keeping their biological activity. In this work, several kinds of polyhedra were micro-patterned by applying a mechanical force induced by femtosecond laser irradiation of a water buffer. In the printing process, since the laser is not directly irradiated on polyhedra, damages of polyhedra due to dryness and photothermal and photochemical reactions will be suppressed. The ability of the pattering was demonstrated by micro-sized checkerboard pattern, on which polyhedra with and without occluding enhanced green fluorescent protein were sorted. Furthermore, it was indicated that polyhedra are available as a scaffold of animal cell. This patterning method will be a promising technique to realize a microdevice in which functions of cell are artistically activated.
It has long been known that readers of this page will move their eyes from one fixation to the next two to four times per second. It follows from this fact that each fixation triggers a unique optic nerve volley lasting up to 300 ms that contains all the information the retina processes between fixations. Here we give such volleys a name (Retinal Functional Unit, RFU) and use human subjects and interstimulus interval (ISI) experiments to define some of their properties. We report that RFUs can be dissected into an initial fraction that reaches the cortex and a later fraction that may not, depending on the ISI between successive stimuli. During the dissection process the perceptions of the stimuli change in an orderly way, such that successive thresholds of "twoness", color, and duration are reached as a function of increasing ISI. We conclude that volleys from the tens or hundreds of thousands of active axons contained in every RFU exit the retina in a precisely determined temporal order, and add this conclusion to three others for which we have already published the supporting data. 1) The mammalian retina normally takes about 300 ms to process a visual stimulus. 2) The ca. 300 ms end product, an RFU, contains in neuronal form all the photochemical information acquired during one fixation. 3) These information-rich volleys reach the cortex with little or no change thanks to monosynaptic transfer in the thalamus.
Through a systematic study of several diphenylcyclopropane derivatives, we have inferred that the cations present within a zeolite control the excited-state chemistry of these systems. In the parent 1,2-diphenylcylopropane, the cation binds to the two phenyl rings in a sandwich-type arrangement, and such a mode of binding prevents cis-to-trans isomerization. Once an ester or amide group is introduced into the system (derivatives of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid), the cation binds to the carbonyl group present in these chromophores and such a binding has no influence on the cis-trans isomerization process. Cation-reactant structures computed at density functional theory level have been very valuable in rationalizing the observed photochemical behavior of diphenylcyclopropane derivatives included in zeolites. While the parent system, 1,2-diphenylcylopropane, has been extensively investigated in the context of chiral induction in solution, owing to its failure to isomerize from cis to trans, the same could not be investigated in zeolites. However, esters of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid could be studied within zeolites in the context of chiral induction. Chiral induction as high 20% ee and 55% de has been obtained with selected systems. These numbers, although low, are much higher than what has been obtained in solution with the same system or with the parent system by other investigators (maximum approximately 10% ee).
[reaction: see text]. Photolysis of 3-(hydroxymethyl)benzophenone (1) in aqueous solution (pH < 3) results in clean formation of 3-formylbenzhydrol (2) at dilute (<10(-4) M) conditions. Evidence suggests that the highly efficient (Phi approximately 0.6) reaction involves a unimolecular mechanism and an overall formal intramolecular photoredox process, which requires electronic communication between the 1,3-positions of the benzene ring, an unprecedented example of the photochemical meta effect. The photoredox reaction was not observed in organic solvents, where only photoreduction of the benzophenone moiety was observed.
The fluorometric behaviour of cellular objects is influenced during excitation by two nearly independent phenomena: (1) by the photochemical reaction of the DNA/AF dye complex, and (2) by the energy transfer among several DNA/AF dye complexes. Both processes show a distinct temperature-dependent behaviour and can therefore be characterized by the analysis of the fluorescence spectra at different temperatures. All microfluorometric measurements were performed with a self-constructed cooling device. The cryostat permits measurements of the cellular fluorescence within a range of temperatures between 4 K and 300 K. The cooling unit operates in accordance with the 'Continuous Flow Principle' and allows the application of objectives up to a numerical aperture of 0.6.
Study of the acid-base induced fluorescence transient, the so-called 'reverse electron flow', in chloroplasts revealed the following new properties: (1) Experiments in which the acid-base transition was performed in the absence of the measuring beam showed that the high fluorescence state induced by a pH-jump was attained and decayed even in complete darkness. These results indicated that a non-photochemical electron transfer was affected by the pH transition. A pH-induced reverse electron transfer from some secondary electron acceptor to Q probably occurred during that process. (2) This conclusion was supported by the effect of the Photosystem I electron acceptor methyl viologen. Methyl viologen accelerated the decay phase of the transient showing that this phase was controlled by the rate of electron flow to Photosystem I, but this acceptor did not diminish the size of the transient's initial rise, probably because this rise reflected a pH effect on a non-photochemical step located between Q and P-700. (3) The size of the fluorescence transient was dependent upon the reduction state of both parts of the secondary pool of electron acceptors, A2 and A1. (4) Redox potential measurements using ferricyanide-ferrocyanide mixtures showed that the size of the transient was directly dependent on a midpoint potential of +385 mV at pH 6.9 and with n = 1. This suggested the involvement of a high potential secondary electron acceptor in the acid-base induced reduction of Q.
The adsorption of Cr(III) in aqueous solution was investigated on a series of ozonised activated carbons, analysing the effect of oxygenated surface groups on the adsorption process. A study was carried out to determine the adsorption isotherms and the influence of the pH on the adsorption of this metal. The adsorption capacity and affinity of the adsorbent for Cr(III) increased with the increase in oxygenated acid groups on the surface of the activated carbon. These findings imply that electrostatic-type interactions predominate in the adsorption process, although the adsorption of Cr(III) on the original (basic) carbon indicates that other forces also participate in the adsorption process. Thus, the ionic exchange of protons in the -Cpi-H3O(+) interaction for Cr(III) accounts for the adsorption of cationic species in basic carbons with positive charge density. Study of the influence of pH on the adsorption of Cr(III) showed that, in each system, the maximum adsorption occurred when the charge of the carbon surface was opposite that of the species of Cr(III) present at the pH of the experiment. These results confirmed that electrostatic interactions predominate in the adsorption process.
Microspectrophotometry has been applied to single red blood cells to reinvestigate the linked processes of diffusion of gases inside the erythrocyte and their combination with hemoglobin. The experiments took advantage of the photosensitivity of the cabron monoxide derivative of hemoglobin, which allows ligand release from the CO-saturated red cells under strong illumination and recombination when the light is switched off. The photochemical method was also used to study the kinetics of sickling on ligand removal in single erythrocytes of Hb S carriers. The results give new information on the mechanism of the sickling process.
Sewage with high chemical requirements for oxygen /CRO/ and high content of halogenic hydrocarbons, e.r. effluents from dumping sites of ground waters with high content of polycyclic hydrocarbons can be purified with ozone alone or in combination with ultraviolet radiation or in combination with biological processing, UV and ozone. These methods enable the effluents to be processed properly from the ecological as well as economic standpoints, and the obtained values of CRO, CRO and WWA meet the requirements set down in regulations.
The Clean Air Act Amendments (CAAA) of 1990 have established selected comprehensive, three-dimensional, Photochemical Air Quality Simulation Models (PAQSMs) as the required regulatory tools for analyzing the urban and regional problem of high ambient ozone levels across the United States. These models are currently applied to study and establish strategies for meeting the National Ambient Air Quality Standard (NAAQS) for ozone in nonattainment areas; State Implementation Plans (SIPs) resulting from these efforts must be submitted to the U.S. Environmental Protection Agency (U.S. EPA) in November 1994. The following presentation provides an overview and discussion of the regulatory ozone modeling process and its implications. First, the PAQSM-based ozone attainment demonstration process is summarized in the framework of the 1994 SIPs. Then, following a brief overview of the representation of physical and chemical processes in PAQSMs, the essential attributes of standard modeling systems currently in regulatory use are presented in a nonmathematical, self-contained format, intended to provide a basic understanding of both model capabilities and limitations. The types of air quality, emission, and meteorological data needed for applying and evaluating PAQSMs are discussed, as well as the sources, availability, and limitations of existing databases. The issue of evaluating a model's performance in order to accept it as a tool for policy making is discussed, and various methodologies for implementing this objective are summarized. Selected interim results from diagnostic analyses, which are performed as a component of the regulatory ozone modeling process for the Philadelphia-New Jersey region, are also presented to provide some specific examples related to the general issues discussed in this work. Finally, research needs related to a) the evaluation and refinement of regulatory ozone modeling, b) the characterization of uncertainty in photochemical modeling, and c) the improvement of the model-based ozone-attainment demonstration process are presented to identify future directions in this area.
Epidermal growth factor receptor (EGFR) targeted DNA polyplexes, containing polyethylenimine (PEI) conjugated with EGF protein as cell-binding ligand for endocytosis and polyethylene glycol (PEG) for masking the polyplex surface charge, mediated a 3- to 30-fold higher luciferase gene expression in HUH7, HepG2 and A431 cell transfections than analogous untargeted PEG-PEI polyplexes. Transfection levels can be further enhanced by treatment of cells with amphiphilic photosensitizers followed by illumination. In this process photosensitizers localized in membranes of endocytic vesicles are activated by light, resulting in the destruction of endocytic membrane structures and releasing co-endocytosed polyplexes into the cell cytosol. Photochemical enhanced gene expression was observed in all cell lines, with the magnitude of enhancement depending on the particular PEI polyplex formulation and cell line, ranging between 2- and 600-fold. Importantly, improved gene transfer retained EGF receptor specificity, as demonstrated by comparison with ligand-free polyplexes and by receptor antibody or ligand competition experiments. These results suggest that this combined procedure enables a dual mode of targeting polyplexes: biological targeting via EGFR interaction, combined with physical targeting with light to direct a photochemical delivery of therapeutic genes to a desired location.
Molecular oxygen in electronic singlet state is a very powerful oxidant. Its damaging action in a variety of biological processes has been well recognized. Here we report the singlet oxygen quenching action of proline. Singlet oxygen (1O2) was produced photochemically by irradiating a solution of sensitiser and detected by following the formation of stable nitroxide radical yielded in the reaction of 1O2 with the sterically hindered amine (2,2,6,6-tetramethylpiperidine, TEMP). Illumination of a sensitiser, toluidine blue led to a time dependent increase in singlet oxygen production as detected by the formation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) by EPR spectrometry. Interestingly, the production of TEMPO was completely abolished by the presence of proline at concentration as low as 20mM. These results show that proline is a very effective singlet oxygen quencher. Other singlet oxygen generating photosensitizer like hematopophyrin and fluorescein also produced identical results with proline. Since proline is one of the important solutes which accumulate in many organisms when they are exposed to environmental stresses, it is likely that proline accumulation is related to the protection of these organisms against singlet oxygen production during stress conditions. A possible mechanism of singlet oxygen quenching by proline is discussed.
Biologically/medically important compounds, when metabolized, can generate free radicals from which electrically excited products--often in the triplet state--are generated. Peroxidases are particularly apt to catalyze such processes, which usually entail oxidations by electron transfer. In the latter case, the chemiluminescence may derive from peroxyl and alkoxyl radicals or excited states derived from dioxetanes. Besides peroxidases, prostaglandin-H synthase and lipoxygenase may catalyze the formation of excited carbonyls. The pronounced similarity in the chemical behavior and reactivity of radicals and excited species derives in part from the biradical nature of the latter. Usually in analyzing the biological effects of xenobiotics, only radicals and/or reactive ground state products have been considered. However, in such processes the generation of excited species is possible, which should be tested for by direct and/or sensitized emission or by photochemical transformation.
In this work, the treatment of landfill leachates by a photoelectrochemical procedure is reported. When applied to untreated leachates the photochemical system was significantly hindered on account of the characteristic dark coloration of the samples. At this condition the degradation process was essentially electrochemical permitting typical color and COD removal of about 50% and 20%, respectively. When a previous chemical precipitation process was applied aiming the elimination of colored species (mainly humic substances) the decolorization and COD removal was extended to 90% and 60%, respectively. Considering the extremely complex character of the leachates and its usual resistance to conventional degradation processes the result reported here attest the high potentiality of photoelectrochemical processes to remediation of recalcitrant residues.
PURPOSE: To evaluate the benefit of photochemical keratodesmos (PKD) in acute wound closure of penetrating keratoplasty (PKP) corneal incisions in vivo. SETTING: Massachusetts General Hospital and Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. METHODS: Penetrating keratoplasty incisions were performed in both eyes of 6 New Zealand white rabbits, followed by application of 1.5 mM rose bengal dye at the wound edges. The incision in 1 eye of each rabbit was irradiated with neodymium:YAG laser light at 532 nm and fluence of 40 J/cm2; the contralateral control eye was untreated. Intraocular pressure at which fluid leaked at the edges (IOPL) was determined immediately after surgery. RESULTS: The mean IOPL was 410 mm Hg +/- 70 (SD) in the PKD-treated eyes and 250 +/- 150 mm Hg in the unirradiated eyes. The difference was statistically significant by paired t test (P<.05). CONCLUSIONS: Photochemical keratodesmos may be a useful adjunct to sutures for approximating PKP corneal incisions in the immediate postoperative period. This process does not induce high temperature, and thus denaturation can be avoided and structural integrity restored.
The VPP mouse is a transgenic strain carrying three mutations (P23H, V20G, P27L) near the N-terminus of opsin, the apoprotein of rhodopsin, the rod photopigment. These animals exhibit a slowly progressive degeneration of the rod photoreceptors, and concomitant changes in retinal function that mimic those seen in humans with autosomal dominant retinitis pigmentosa resulting from a point mutation (P23H) in opsin. In the present study we attempted to determine whether the disease process prevents the translocation of mutant opsin to the rod outer segments of transgenic mice, and whether it affects the photochemical properties of the rhodopsin present within their rod outer segments. Immunocytochemistry with a monoclonal antibody against a region of the C-terminus that recognizes epitopes common to both normal and mutant opsin (monoclonal antibody-1D4), and a polyclonal antibody that reacts preferentially with the mutant opsin (anti-VPP), were used to identify the opsin present in the rods of three-week-old VPP mice and normal littermates. Absorbance spectra, photosensitivity, and regeneration kinetics of rhodopsin in rod outer segment disc membranes were analysed by spectrophotometry. Western blot analysis with anti-VPP antibody indicated the specific binding of this antibody to the mutant opsin. Immunolocalization with monoclonal antibody-1D4 and anti-VPP antibodies suggested a normal translocation of the mutant protein to the outer segments. Aside from a small disparity in the absorbance spectra of rhodopsin obtained from normal and VPP retinas, there were no significant differences in either the ability of opsin to bind 11-cis retinal chromophore, or in the photic sensitivity of rhodopsin. The results indicate that mutant opsin is translated and incorporated into the rod outer segment disc membranes of VPP mice, and that the photochemical properties of rhodopsin in the rods of VPP retinas are similar to those of rhodopsin in normal retinas.
The rearrangement of nitrones to lactams can be carried out by photochemical activation or by treatment with Tf(2)O followed by KOH-promoted rearrangement (a modification of conditions originally introduced by Barton). Substrates in which the nitrone is part of a fused bicyclic ring system have traditionally proven problematic for this kind of reaction. In this study, a series of mono-, bi-, and tricyclic ring-fused nitrones were prepared to investigate the dependence of products on nitrone ring size and tether length. Results indicated that photochemical rearrangement of nitrones in benzene afforded reasonably good yields (30-68%) of lactams, while the two-step nonphotochemical process provided slightly better average yields (30-95%) of the same targets.