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PubMed2000

Spatial and temporal variability of ground-level ozone in Castilla-León (Spain).

Ozone is a secondary air pollutant that has received extensive attention in the literature, mainly because of the adverse effects that exposure to it can cause, particularly in vegetation during the growing season. Because meteorological conditions strongly influence the efficiency of photochemical processes leading to ozone formation and destruction, ground-level ozone air pollution is currently being considered as a regional-scale phenomenon rather than a local one. This role of O3 as a regional-scale pollutant often implies the handling of large data sets in order to obtain information about its spatial and temporal variability patterns over a given broad region. Rotated principal component analysis (RPCA) is known to be one of the most powerful mathematical tools that can be used to achieve this aim. RPCA was applied in this paper to the summer and winter hourly time series of ground-level O3, concentrations recorded during 2 consecutive years (1996-1997) at 26 urban and suburban sites in Castilla-León (Spain). This procedure permitted the identification of different subregions where O3 concentrations show different spatio-temporal variability patterns. These variability patterns are mainly associated with the interaction of regional-level meteorological and anthropogenic factors. Some differences between winter and summer patterns were also found.

Air Pollutants↗
PubMed2007

Interaction between atmospheric CO2 and glucosinolates in broccoli.

Total and individual glucosinolate contents of broccoli cv Marathon were assessed at ambient CO2 (430-480 ppm) and elevated atmospheric CO2 (685-820 ppm) to determine the ecological relationship between changing atmospheric CO2 concentrations and phytochemicals. Elevated atmospheric CO2 concentration had a differing effect on individual glucosinolates and glucosinolate groups. Total glucosinolate content increased at elevated atmospheric CO2 concentration as a result of a strong increase in both methylsulfinylalkyl glucosinolates glucoraphanin and glucoiberin. In contrast, indole glucosinolates simultaneously decreased, predominantly because of a reduction of glucobrassicin and 4-methoxy-glucobrassicin contents. We conclude that changes in N content and N/S ratios as well as alterations in photochemical processes at elevated atmospheric CO2 concentration can influence total and individual glucosinolates contents of Brassicaceae, as demonstrated in the greenhouse, for broccoli.

Atmosphere↗
PubMed1988

Presence of nontryptophan fluorophores specifically bound to gamma 2-crystallin.

alpha-, beta-, and gamma-crystallins have been purified from nonpathological lenses of calves. The pure proteins have been examined for nontryptophan fluorescence and fluorescent compounds have been found specifically bound to gamma 2-crystallin. The protein has been unfolded by 6 M guanidine hydrochloride (Gdn-HCl) and a separation of the fluorescent compounds has been obtained by gel chromatography in the presence of 6 M Gdn-HCl. The spectroscopic features (absorbance, fluorescence) of the protein returned to normal following removal of the chromophores. The low-molecular-weight separated fluorescent compounds have been fractionated and extracted from the Gdn-HCl solution by ethyl acetate. TLC chromatography has shown the presence of kynurenine, 3-OH-kynurenine, and free tryptophan. These data suggest that direct involvement of the intrinsic protein tryptophans in the photochemical processes leading to formation of fluorescent compounds has to be excluded. Free tryptophan and intrinsic metabolic factors are probably more relevant in determining the cataractous insult.

Animals↗
PubMed1995

Energy conversion at liquid/liquid interfaces: artificial photosynthetic systems.

This chapter focuses on multielectron reactions in organized assemblies of molecules at the liquid/liquid interface. We describe the thermodynamic and kinetic parameters of such reactions, including the structure of the reaction centers, charge movement along the electron transfer pathways, and the role of electric double layers in artificial photosynthesis. Some examples of artificial photosynthesis at the oil/water interface are considered, including water photooxidation to the molecular oxygen, oxygen photoreduction, photosynthesis of amphiphilic compounds and proton evolution by photochemical processes.

Chlorophyll↗
PubMed1985

Laboratory simulations of PH3 photolysis in the atmospheres of Jupiter and Saturn.

Photolysis of NH3-PH3 mixtures (11 Torr) at 175 degrees K resulted in the same initial rate of P2H4 formation as when the 11 Torr of pure PH3 was photolyzed. A higher yield of P2H4 is obtained at 175 degrees K than at 298 degrees K because some of the P2H4 condenses on the cell wall at 175 degrees K and is not subject to further reaction. Some reaction of P2H4 is taking place as observed by the decrease in its yield and on the formation of red phosphorus on extended photolysis of PH3 at 175 degrees K. No NH2PH2 or (PN)x were detected as photoproducts as indicated by the absence of change in the UV spectral properties of the P2H4 and red phosphorus fraction, respectively, when HN3 is present. Although the pathway for PH3 decomposition is changed, the outcome of the photochemical process is essentially the same in the absence or presence of NH3. The formation of P2H4 and red phosphorus was not inhibited by small amounts of C2H4 and C2H2, so the low levels of hydrocarbons on Jupiter and Saturn will not have a significant effect on the course of PH3 photolysis. The ratio of products of PH3 photolysis are only slightly affected by the wavelength of light used. Use of a xenon lamp, with a continuous emission in the ultraviolet where P2H4 absorbs, results in only a modest decrease in the yield of P2H4 and a modest increase in the rate of formation of red phosphorus as compared to the rates observed with a 206.2-nm light source. The quantum yield for P2H4 formation is pressure independent in the 0.5-11 Torr range. This quantum yield is not affected by lowering the temperature to 157 degrees K or by the addition of 100 Torr of H2. It is concluded that photolysis of PH3 to P2H4 and the subsequent conversion of P2H4 to red phosphorus are likely processes on Jupiter and Saturn and that particles of P2H4 condense in the atmospheres of these planets. The conversion of some of the P2H4 to red phosphorus may take place on Jupiter.

Ammonia↗
PubMed1989

Polynuclear aromatic hydrocarbon content of particulate matter suspended in the atmosphere of La Plata, Argentina.

Twelve polynuclear aromatic hydrocarbons (PAH) were evaluated by chromatographic procedures using a HPLC-UV detector and a GC-FID detector. The PAH were evaluated in airborne particulate matter collected in La Plata, Argentina, over a period of 2 years (with sampling periods of approximately 4 months). The samples were size fractionated, and the PAH in each fraction determined. The analytical procedure used was as follows: extraction in benzene, concentration at room temperature, clean-up in a silica gel column and, finally, evaluation by chromatographic procedures. The extraction recovery was 76.2 +/- 5.8% for naphthalene and 96.0 +/- 6.2% for chrysene. Clean-up recovery was 87.8 +/- 7.15% for phenanthrene and 98.1 +/- 8.3% for anthracene. The largest PAH load was present in the smallest fractions. The smallest particles were carbonaceous in nature. The concentration peak was associated both with the total mass of airborne particulate matter and the reduction in amounts of coarse particles. The PAH distribution could not be correlated with characteristic physicochemical properties such as water solubility or the octanol-water distribution coefficient. The PAH load was greater in fall and winter than in spring and summer. This could be attributed to the reduction of photochemical processes during the cold seasons.

Air Pollutants↗
PubMed1988

Local measurements of thrombus induced vasoconstriction in vivo.

No data is available describing the local effect of thrombus formation on the vessel's diameter in vivo. As platelet or thrombus induced vasoconstriction seems to be of clinical importance in various diseases, it is desirable to get insight into the interrelation of thrombus formation and local vasoactivity. With a contactless photochemical process, endothelial cells can be damaged and thrombogenesis may be initiated in vivo. After first platelets stick to endothelial cells, a strong vasoconstriction is observed in arterioles. In venules, no vascular reaction can be observed. Constriction is most pronounced at the site of thrombus formation and decreases at growing distance. The thrombus is squeezed by the vascular constriction and thus mechanically held in place and squeezed out. A slight relaxation follows 30-80 min later, but the vessel remains constricted during the following three hours. Thrombus induced vasoconstrictions can be reduced by papaverine, EP 092 (a thromboxane A2 antagonist) and phentolamine in dose-dependent manner in vivo. Papaverine was most effective followed by EP 092, Phentolamine was less effective, showing the minor importance of alpha-receptor stimulation in this model.

Animals↗
PubMed1993

Physiological effects of ozone on cultivars of watermelon (Citrullus lanatus) and muskmelon (Cucumis melo) widely grown in Spain.

Two cultivars of watermelon (Citrullus lanatus) and muskmelon (Cucumis melo), which are widely grown in Spain, were exposed to ozone (70 nl litre(-1), 6 h d(-1)) for 21 days. Ozone sensitivity was assessed by recording the extent of visible injury, changes in fast-fluorescence kinetics, the relative-growth rate (R) of root (RR) and shoot (RS), and effects on the number of flowers produced per plant. Leaf gas exchange was measured in order to provide some indication of the factors underlying differential response to ozone. After 9-10 days of fumigation, all the cultivars developed typical visible symptoms of zone injury on the older leaves. However, significant (P < 0.05) changes in fast-fluorescence kinetics were detected prior to the development of visible foliar injury, indicating that detectable effects of ozone on primary photochemical processes supersede the appearance of visible symptoms. In both muskmelon and watermelon, there was a marked reduction in the rate of CO(2) assimilation as a result of exposure to ozone, and this was accompanied by a parallel decrease in stomatal conductance. Mean plant-relative-growth rate (R) was markedly (P < 0.01) suppressed by ozone in the two cultivars of watermelon, but there were no significant effects on R in muskmelon. Ozone reduced root growth relative to the shoot in three out of four cultivars-an effect that may be of considerable ecological significance. Moreover, exposure to ozone reduced flower production in both muskmelon and watermelon, which indicated effects on yield. There was no correlation between a variety of methods used to assess ozone sensitivity and visible injury, and reasons for this are discussed. This observation draws clear attention to the dangers in ranking plants for ozone sensitivity purely on the basis of visible symptoms. It is concluded from this study that ozone-insensitive genotypes should be identified and considered for planting in the major areas of melon production concentrated on the Mediterranean coast of Spain.

Journal Article↗
PubMed1987

Supernovae, neutron stars and biomolecular chirality.

Recent theoretical and experimental investigations of the origin of biomolecular chirality are reviewed briefly. Biotic and abiotic theories are evaluated critically with the conclusion that asymmetric photochemical processes with circulary polarized light (CPL), particularly asymmetric photolyses, constitute the most viable mechanisms. Solar CPL sources appear too weak and random to be effective. We suggest an alternative CPL source, namely, the synchrotron radiation from the neutron star remnants of supernova explosions. This could asymmetrically process racemic compounds in the organic mantles of the dust grains in interstellar clouds, and the resulting chiral molecules could be transferred to Earth by cold accretion as the solar system periodically traverses these interstellar clouds.

Biological Evolution↗
PubMed1992

Protein engineering for molecular electronics.

Recombinant DNA technology allows the manipulation of the physical properties of proteins that perform electron transport and photochemical processes. Recent work is reviewed that has a potential impact on the development of molecular electronic devices, within a general framework outlining strategies for device fabrication. This review is also published in Current Opinion in Structural Biology 1992, 2:587-592.

Bacteriorhodopsins↗
PubMed2004

Monitoring of cAMP-imprinted polymer by fluorescence spectroscopy.

Conventional functional monomers together with fluorescent monomer, trans-4-[p-(N,N-dimethylamino)styryl]-N-vinylbenzylpyridinium chloride (vb-DMASP), were copolymerised in the presence of a target molecule, nucleotide-cAMP that acted as a molecular template. The polymer was copolymerised in thin-layer films. After removal of the template the functionalised cavities that exist in the fluorescent material are able to specifically bind the template. Subsequent adsorption of the template-cAMP causes quenching of fluorescence of the polymer. The specific photochemical processes accompanying the template adsorption are discussed further. The imprinted polymers monitored by both steady-state and time-resolved fluorescence techniques show specificity and selectivity of binding of the template on the imprinted functionalised cavities.

Aniline Compounds↗
PubMed2005

Isomeric analysis of BTEXs in the atmosphere using beta-cyclodextrin capillary chromatography coupled with thermal desorption and mass spectrometry.

An analytical method capable of determining trace levels of BTEX-aromatics (benzene, toluene, ethylbenzene, m-, p- and o-xylenes) in the atmosphere with as high resolution as possible has been developed. The method is based on the preconcentration of air samples using a multibed tube (Carbopack C, Carbograph 1) at ambient temperature, followed by thermal desorption, and analysis of aromatic species by a beta-cyclodextrin capillary chromatography coupled with mass spectrometry. The resolution achieved was sufficient for individual separation of BTEXs as well as m- and p-xylenes. The BTEX-ratios have been determined in an air tunnel and in on-road, suburban and rural forest atmosphere. The ethylbenzene/m-xylene ratios could provide a deep insight into anthropogenic related NMHC patterns at different locations and under different meteorological conditions and may reflect photochemical processes in the best way.

Adsorption↗
PubMed2006

Photodegradation of bisphenol Z by UV irradiation in the presence of beta-cyclodextrin.

In this work, the formation of the inclusion complex of bisphenol Z (1,1-bis(4-hydroxyphenyl)cyclohexane, abbreviated as BPCH) with beta-cyclodextrin (beta-CD) has been studied, 1:1 inclusion complex can be obtained, the formation constant of the beta-CD/BPCH complex is 5.94x10(3)M(-1). The photodegradation behavior of BPCH was investigated under monochromatic UV irradiation (lambda=254 nm). The photodegradation rate constant of BPCH in aqueous solutions with beta-CD showed a 9.0-fold increase, and simultaneously the mineralization of BPCH can be enhanced by beta-CD. The influence factors on photodegradation of BPCH were also studied and described in details, such as concentration of beta-CD, initial concentration of BPCH, organic solvent and pH. The photodegradation of BPCH in the presence of beta-CD includes the direct photolysis and the photooxidation of BPCH during the photochemical process. Some predominant photodegradation products are 4-(2,4,5-trihydroxy-phenyl)-4-(4-hydroxyphenyl) butanoic acid, 5,5-bis(4-hydroxyphenyl)pentanoic acid, meta-hydroxylated BPCH, ortho-hydroxylated BPCH and 4-(1-(4-hydroxyphenyl)pentyl)phenol respectively. The enhancement of photodegradation of BPCH mainly results from moderate inclusion depth of BPCH molecule in the beta-CD cavity. This kind of inclusion structure allows BPCH molecule sufficient proximity to secondary hydroxyl groups of the beta-CD cavity, and these hydroxyl groups could be activated and converted to hydroxyl radicals under UV irradiation, which can enhance the photooxidation of BPCH.

Acetonitriles↗
PubMed2004

Selective reversed-phase liquid chromatography method for the kinetic investigation of 3-hydroxyflavone photostability.

This paper reports a fast and accurate RP-HPLC chromatographic method for the simultaneous determination of 3-hydroxyflavone (3-OH F) and its photodegradation products. Solutions (5 x 10(-5) M) in acetonitrile (ACN) of the molecule were subjected to forced degradation by exposure to artificial UV-A light source (black-light, lambda(max) 354 nm) and the changes appearing in chromatograms were monitored at selected irradiation times. A multistep gradient was optimised to achieve complete elution of all photoproducts in the shortest analysis time. UV spectra recorded by the diode array detector system (285 and 340 nm) clearly showed the structural changes in the new species formed, with respect to the parent compound. The analytical method was subjected to a validation procedure in which linearity and range, as well as specificity, precision and accuracy were determined according to ICH guidelines. Quantitative evaluation of the photochemical process was performed on the basis of the calculated kinetic parameters: photodegradation rate constant k, half-life time t(0.5), time degradation of 10% of the drug t(0.1).

Algorithms↗
PubMed2005

Molar extinction coefficients and the photon absorption efficiency of dental photoinitiators and light curing units.

OBJECTIVES: The light absorption of dental photoinitiators should correlate with the spectral emission profiles of dental light curing units compared on an equivalent basis. Spectral data of dental photoinitiators and light curing units can be used to define the photon absorption efficiency (PAE) obtained by integrating the product of the absorption and emission spectra in terms of photons. This parameter can be used to identify the best performance for photochemical process with specific photoinitiators. METHODS: The efficiency of two LED and one QTH lamps were tested comparing their performances with the photoinitiators camphorquinone (CQ); phenylpropanedione (PPD); monoacylphosphine oxide (Lucirin TPO); and bisacylphosphine oxide (Irgacure 819). Absorption and emission spectra of the photoinitiators and the LED (Ultrablue I and Ultrablue IS) and QTH (Optilux 401) LCUs were determined in the 360-550nm range. RESULTS: CQ exhibited an absorption centered in the blue region and, although the maxima of PPD, MAPO, and BAPO were in the UV-A region, their absorption extended to the visible region. Power output maxima of the LCUs were at 467 (Ultrablue I), 454 (Ultrablue IS) and 493nm (Optilux 401), and the total power densities were 170+/-1, 470+/-4 and 444+/-4mW/cm(2), respectively. SIGNIFICANCE: The use of the PAE allows a prediction of the most efficient photoinitiator/LCU systems. For similar photoinitiator concentrations, Lucirin and CQ are most efficiently photoinitiated by the QTH unit, whereas the high-power LED device is more efficient for Irgacure. PPD is photoactivated similarly by both LCUs.

Acrylic Resins↗
PubMed2006

Are saturating pulses indeed saturating? Evidence for considerable PSII yield underestimation in leaves adapted to high levels of natural light.

The "saturating pulse" method of in vivo Chl fluorescence measurement has been widely used by physiologists and especially ecophysiologists, as it allows a simple, rapid and non-invasive assessment of PSII function and the allocation of absorbed energy into photochemical and non-photochemical processes. It is based on the accurate determination of the so-called Fm('), i.e. the fluorescence signal emitted when a "saturating" light pulse closes all PSII centers. In this methodological investigation, we examined whether the saturating pulse intensities required to obtain maximal fluorescence yields differ between leaves of various species receiving varying actinic light irradiances. It was shown that, in leaves adapted to comparatively high (yet realistic) levels of natural irradiances, the saturating pulses usually applied are not able to close all PSII reaction centers. As a result, there is a high risk of considerable Fm(') underestimation. Accordingly, the derived values of effective PSII yields and linear electron transport rates (ETR) are also underestimated, even at the highest saturation pulse levels afforded by commercial instruments. Since the extent of underestimation increases with actinic irradiance, the ETR versus light curves are considerably distorted. The possible reasons for the apparent inability of "saturating" pulses to close all PSII centers at high actinic light and the practical implications, especially in field work, are discussed.

Adaptation, Physiological↗
PubMed2005

Biogenic volatile organic compounds (BVOCs) emissions from Abies alba in a French forest.

Air quality studies need to be based on accurate and reliable data, particularly in the field of the emissions. Biogenic emissions from forests, crops, and grasslands are now considered as major compounds in photochemical processes. Unfortunately, depending on the type of vegetation, these emissions are not so often reliably defined. As an example, although the silver fir (Abies alba) is a very widespread conifer tree in the French and European areas, its standard emission rate is not available in the literature. This study investigates the isoprene and monoterpenes emission from A. alba in France measured during the fieldwork organised in the Fossé Rhénan, from May to June 2003. A dynamic cuvette method was used. Limonene was the predominant monoterpene emitted, followed by camphene, alpha-pinene and eucalyptol. No isoprene emission was detected. The four monoterpenes measured showed different behaviours according to micrometeorological conditions. In fact, emissions of limonene, alpha-pinene and camphene were temperature-dependant while eucalyptol emissions were temperature and light dependant. Biogenic volatile organic compounds emissions were modeled using information gathered during the field study. Emissions of the three monoterpenes previously quoted were achieved using the monoterpenes algorithm developed by Tingey et al. (1980) [Tingey D, Manning M, Grothaus L, Burns W. Influence of light and temperature on monoterpene emission rates from slash pine. Plant Physiol 1980;65: 797-801.] and the isoprene algorithm [Guenther, A., Monson, R., Fall, R., 1991. Isoprene and monoterpene emission rate variability: observations with eucalyptus and emission rate algorithm development. J Geophys Res 26A: 10799-10808.]; [Guenther, A., Zimmerman, P., Harley, P., Monson, R., Fall, R., 1993. Isoprene and monoterpene emission rate variability: model evaluation and sensitivity analysis. J Geophys Res 98D: 12609-12617.]) was used for the eucalyptol emission. With these methods, simulation results and observations agreed fairly well. The standard emission rate (303 K) and beta-coefficient averaged for limonene, camphene and alpha-pinene were respectively of 0.63 microg gdw-1 h-1 and 0.06 K-1. For eucalyptol, the standard emission rate (T=303 K and PAR=1000 micromol m-2 s-1) was 0.26 microg gdw-1 h-1. This classified A. alba as a weak monoterpenes emitter.

Abies↗