Photolytic Effects Research Articles

Native and TMT Chestnut Extractives as Hydrophobic and Photostabylizing Additives for Wood Surfaces

Wood extractives have proven strong anti-oxidative properties which may be used to mitigate surface deterioration caused by photolytic effects and free radical formations. An interesting challenge regarding wood extractives is understanding how they behave in terms of treating natural wood surfaces to reduce anti-oxidative processes that arise from exposure to the main environmental factors. In this study, the possible efficacy of chestnut (Castanea sativa Mill.) extractives derived from native (CH) and thermally modified wood (TMT CH), as a means of protecting against UV exposure in poplar (Populus spp.) and spruce (Picea abies Karst.) wood, was evaluated. Chestnut wood was first thermally modified at 180 °C for 3 h, and the extractives were obtained by the accelerated solvent extraction technique (ASE) and subsequently used to treat wood surfaces. Samples were immersed in extractive solutions and exposed to artificial UV-weathering exposure, then contact angle and colour stability were monitored during the process. An FTIR analysis of the photo-degradation process of poplar and spruce surfaces was also executed. Extractives of TMT chestnut changed the total colour variation in both poplar and spruce wood. A much darker colour compared to the extractives of native wood was observed and an increase in ∆E* from 9.75 to 30.76 and 6.24 to 22.97 in poplar and spruce was calculated. The stability of the colour depended both on the surface wood and the type of extractive. The initial contact angle remained almost unchanged in the poplar wood surface and only slightly increased in spruce regardless of whether they were treated with extractives from native or TMT chestnut wood. A strong reduction in contact angle after the accelerated UV exposure test was observed, especially in spruce treated with CH extractives. FTIR analysis confirmed the lower levels of chemical degradation of surfaces observed by colorimetry, where TMT CH extractives formed more stable chemical bonds than native extractives. The comparative analysis in this study clarified the complex relationships between the effects of high-temperature modification of wood and the potential protective role of TMT extractives on some wood surfaces.

Modeling the Complete Nitrogen and Oxygen Isotopic Imprint of Nitrate Photolysis in Snow

AbstractSnow nitrate is vulnerable to photolytic loss that causes isotopic alteration, and thus its isotopes can potentially track the extent of snow nitrate photolysis and its impacts in environments where loss is significant. Large increases in δ15N‐NO3− below the snow surface have been attributed to photolysis and this behavior is generally consistent amongst theoretical as well as lab and field studies. Oxygen isotope ratios are thought to be influenced by photolysis as well as secondary condensed‐phase chemistry, but the competing effects have yet to be reconciled. Here we use a model that simulates nitrate burial, photolytic fractionation, and re‐oxidation in snow to quantitatively assess these processes with the aim of developing a consistent framework for interpreting the photolytic effects of the complete nitrate isotopic composition (δ15N, δ18O, and Δ17O). This study reveals that isotopic effects of nitrate photolysis and aqueous‐phase re‐oxidation chemistry are important sources of uncertainties in modeling δ18O‐NO3−.

Modeling Photolytic Decomposition of Energetically Functionalized Dodecanes.

The photolytic stability of explosives and energetic functional groups is of importance for those who regularly handle or are exposed to explosives in typical environmental conditions. This study models the photolytic degradation of dodecane substituted with various energetic functional groups: azide, nitro, nitrate ester, and nitramine. For the studied molecules, it was found that excitons localize on the energetic functional group, no matter where they were initially formed, and thus, the predominant degradation pathway involves the degradation of the energetic functional group. The relative trends for both 4 and 8 eV excitation energies followed with what is expected from the relative stability of the energetic functional groups to thermal and sub-shock degradation. The one notable exception was the azide functional group; more work should be done to further understand the photolytic effects on the azide functional group.

Theoretical Values, Percentage Deviations and Calculated Values by Polynomial Equations of the Liquid Mixture with Equimolar Mixture of Ethanol and Formamide

Background: The binary mixtures of isopropanol/isobutanol/isoamyl alcohol with an equimolar mixture of ethanol and formamide consist of different ultrasonic properties, which have been studied at room temperature at a fixed frequency of 2 MHz. The ultrasonic-related physical parameters like velocity (U), density (ρ), adiabatic compressibility (βad), intermolecular free length (Lf), acoustic impedance (Z), etc., have been studied. The theoretical evaluation of ultrasonic velocity in liquid mixtures offers a transparent method for the study of the nature of molecular interactions in the mixtures besides verifying the applicability of different theories such as Nomoto’s, Van Dael and Vangeel’s, Impedance Dependence relation, Junjie’s relation, Rao’s specific sound velocity relation, and Jacobson’s relations, Percentage deviations of theoretical ultrasonic velocities from experimental values in the mixtures of all liquid mixture and also calculated values of ultrasonic velocity from polynomials for all the schemes with mole fraction (x) of isopropanol/isobutanol/ isoamyl alcohol. Objective: The main focus of the present work was to prepare the structural changes associated with the liquid mixtures having weakly interacting components and strongly interacting components. The study of molecular association in mixtures providing exact information of thermodynamic mixing properties, such as adiabatic compressibility, intermolecular free length, free volume, internal pressure, and molar volume, has significant importance in theoretical and applied areas of research. The ultrasonic study has been a subject of keen interest during the past many years. This branch of physical sciences has played a significant role in deciding the interactions between the molecules of compounds under study. It has a potential tool for evaluating energy exchange between various degrees of freedom and nonlinear properties in binary liquid mixtures. Methods: The binary liquid mixtures were prepared by mixing two components, by weight, using an electronic analytical balance (Reptech RA-2012), accurate up to ±0.0001 g. The average uncertainty in mole fraction of binary mixtures was estimated to be ±0.0001. To avoid loss of solvent due to evaporation, mixtures were stored in specially designed ground-glass airtight ampoules and placed in a dark place to prevent photolytic effects. Results: These empirical fittings of data are described qualitatively and quantitatively using experimental speed data even in the specific interaction predominant region where non-ideal behavior of the mixture is observed. The values of sound velocities and percentage deviation (after determining the co-efficient of the polynomial equations by applying the least squares method) are compiled in the tables, respectively. Conclusion: The ultrasonic velocities and densities for all three mixtures were measured, and the values were calculated. The observed trends of VEm, ΔkS and LEf indicate the presence of weak interactions, and the strength of these interactions follows the order EMM+IPA>EMM +IBA>EMM+IAA. Besides, the ultrasonic velocities measured from different velocity theories were found to be consistent with the experimentally measured ultrasonic velocities. Among these theories, Jacobson’s velocity equation showed a good result for the experimental and theoretical ultrasonic velocity values for all the binary mixtures used.

Marginative Delivery-Mediated Extracellular Leakiness and T Cell Infiltration in Lung Metastasis by a Biomimetic Nanoraspberry.

T lymphocytes infiltrate the most devastating metastatic tumors for immunotherapy, allowing the potential for tumor metastasis suppression. However, tumor heterogeneity often restricts the infiltration of immune cells and possesses immune privilege that leads to protection from the immune attack, especially for invading metastatic clusters. Here, an exosome-camouflaged nanoraspberry (RB@Exo) doubling as a metastases-targeting agent and T cell-infiltration inducer that delivers an anticancer drug and energy is reported. The RB@Exo integrated an exosome-derived margination effect, and density-mediated nanoparticle-induced extracellular leakiness (nanoEL) exhibited more than a 70% colocalization of the RB@Exo to metastatic tumors in the lung in vivo. The release of cancer cell-cell interactions at the metastasis via nanoEL also elicited the 10-fold infiltration of T lymphocytes. The synergy of the T cell infiltration and photolytic effects transported by the RB@Exo deep into the metastatic tumors effectively inhibited the tumor in 60 days when treated with a single alternating magnetic field (AMF).

Graphene Quantum Dots-Mediated Theranostic Penetrative Delivery of Drug and Photolytics in Deep Tumors by Targeted Biomimetic Nanosponges.

Dual-targeted delivery of drugs and energy by nanohybrids can potentially alleviate side effects and improve the unique features required for precision medicine. To realize this aim, however, the hybrids which are often rapidly removed from circulation and the piled up tumors periphery near the blood vessels must address the difficulties in low blood half-lives and tumor penetration. In this study, a sponge-inspired carbon composites-supported red blood cell (RBC) membrane that doubles as a stealth agent and photolytic carrier that transports tumor-penetrative agents (graphene quantum dots and docetaxel (GQD-D)) and heat with irradiation was developed. The RBC-membrane enveloped nanosponge (RBC@NS) integrated to a targeted protein that accumulates in tumor spheroids via high lateral bilayer fluidity exhibits an 8-fold increase in accumulation compared to the NS. Penetrative delivery of GQDs to tumor sites is actuated by near-infrared irradiation through a one-atom-thick structure, facilitating penetration and drug delivery deep into the tumor tissue. The synergy of chemotherapy and photolytic effects was delivered by the theranostic GQDs deep into tumors, which effectively damaged and inhibited the tumor in 21 days when treated with a single irradiation. This targeted RBC@GQD-D/NS with the capabilities of enhanced tumor targeting, NIR-induced drug penetration into tumors, and thermal ablation for photolytic therapy promotes tumor suppression and exhibits potential for other biomedical applications.

Picosecond excitation for reduction of photolytic effects in two-photon laser-induced fluorescence of CO

Two-photon laser-induced fluorescence for detection of carbon monoxide (CO) frequently shows interferences by emission from photolytically produced C2 radicals encountered under fuel-rich combustion conditions. Reduced C2 interference for excitation with laser pulses in the picosecond regime is here demonstrated by comparison with excitation using nanosecond pulses for measurements in laminar premixed ethene–air flames. Compared with nanosecond pulses of 8ns duration and 4mJ pulse energy, picosecond pulses of 80ps duration and around 0.5mJ pulse energy gave ∼10 times higher peak power, which allowed for efficient CO excitation and resulted in stronger signal with lower C2 interference. CO fluorescence with picosecond excitation showed a linear to quadratic power dependence, indicating photoionization, whereas a more quadratic dependence was found for the C2 interference. A sub-nanosecond effective lifetime of CO resulted in a rapid fluorescence decay compared with C2 and allowed for efficient reduction in C2 interference by minimizing the detection gate. In addition, interference compensation using time-resolved detection could be demonstrated. Altogether, picosecond pulses provide efficient two-photon excitation of CO in terms of signal strength as well as reduced C2 interference.

Gold‐polymer nanocomposites: studies of their optical properties and their potential as SERS substrates

AbstractPolymer‐nanometallic‐particle composites have demonstrated technological potential owing to their unique optical and electrical properties. In this article, we report on composites prepared via physical vapor deposition of gold metal onto pliable polydimethylsiloxane (PDMS) polymer. Rapid Au diffusion and nanometallic‐particle formation in a phase‐separated surface layer of the PDMS creates unique tunable sub‐surface‐based composites. The rate of deposition and average Au thickness can be manipulated to tune the optical properties, which are studied by visible wavelength optical extinction spectrometry and surface‐enhanced Raman scattering (SERS). DC conductivity measurements were made during Au deposition to study percolation conditions for the materials and depth profiling was performed by X‐ray photoelectron spectrometry (XPS). This work presents the use of Au‐PDMS nanocomposites in combination with a sample translation technique (STT) for the improved SERS qualitative and quantitative analysis. This translation approach considerably improves the reproducibility and the sensitivity of the technique by minimizing the thermal and photolytic effects inherent in SERS. The Au‐PDMS nanocomposites exhibit an affinity for amine and nitro‐based compounds that are biologically relevant and point toward the potential for being used as substrates for biologically based SERS experiments. Sample Raman spectra with the nanocomposite under STT‐SERS conditions are included. Copyright © 2005 John Wiley & Sons, Ltd.

Improving the analytical figures of merit of SERS for the analysis of model environmental pollutants

AbstractThe presence of naphthalene, phenol and benzoic acid derivatives in natural waters constitutes a public health issue. The toxicity and chemical activity of these chemicals and their persistence in the environment depend on the types of functional groups attached to their basic aromatic structure. Surface‐enhanced Raman scattering (SERS) spectroscopy has shown promise for the analysis of aromatic compounds owing to a tremendous enhancement of the analytical response and also a large amount of available structural information. Despite these advantages, SERS has not been established as a routine analytical tool owing to limitations in the analytical figures of merit such as reproducibility and linear dynamic range. This paper reports the use of silver–polydimethylsiloxane nanocomposites in combination with a sample translation technique for the improved qualitative and quantitative analysis of model environmental pollutants in water. This novel approach considerably improves the reproducibility and the sensitivity of the technique by minimizing the thermal and photolytic effects inherent in SERS. The results show a linear dynamic range of at least two orders of magnitude with detection limits as low as 2.9 × 10−8 M and a precision of <10% relative standard deviation. The influences of different experimental variables such as irradiation time, translation rate and pH and the potential use of the technique for the analysis of environmental pollutants are presented. Copyright © 2004 John Wiley & Sons, Ltd.

Mechanical and tribological aspects on a-C films deposited by lamp assisted chemical vapour deposition

A novel approach to deposit amorphous carbon films (a-C) from the precursor CH 2I 2 at low cost and high efficiency is reported. The radiation of a halogen lamp was used to heat and to photo-dissociate the CH 2I 2 (g) precursor as well as the substrate surface. The combination of thermal and photolytic effects shows new interesting growth behaviour. Cemented carbide and Si were used as substrates. The films were investigated with respect to hardness and elastic modulus by nanoindention. A ball-on-disc tribometer was used to evaluate the friction and wear of the films in sliding contact against bearing steel. The adhesion between the film and substrate was investigated by Rockwell C indentation. The films were additionally analysed with scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The films showed extremely low surface roughness ( R a<0.7 nm) and were free from micro-voids. The hardness and elasticity was measured to 10 and 70 GPa, respectively. Low friction coefficients in the 0.15-region were measured. No influence of the substrate material on the film properties was found.

Investigations on the mechanisms responsible for Ar +-laser-induced growth enhancement of GaAs by chemical beam epitaxy

The mechanisms responsible for Ar +-laser-induced growth enhancement of GaAs by chemical beam epitaxy with triethylgallium and tris(dimethylamino) arsenic as precursors are investigated here using numerical models developed for simulating the epitaxial growth and Ar +-laser-induced temperature rise. Numerical simulations taking the laser pyrolytic effect into account alone cannot reproduce observed growth-rate enhancements. Procedures are established for examining catalytic and photolytic effects of laser irradiation on epitaxial growth. Calculation of photoinduced surface excess carrier concentrations corresponding to experimental conditions reported in the literature reveals that the catalytic effect should be negligible. Amount of precursors in the first and second adsorption layers is looked into quantitatively. It is concluded that photodecomposition of chemisorbed TEGa decomposition products, along with laser-induced temperature rise, is responsible for observed Ar +-laser-induced GaAs growth enhancements. Likely photodecomposition reactions are postulated. The triethylgallium absorption cross section required to reproduce observed growth enhancement is estimated. Group-V species are found to control the growth-enhancement temperature window because of their site-blocking effects.

Environmental Degradation of Polyacrylamides. 1. Effects of Artificial Environmental Conditions: Temperature, Light, and pH

A polyacrylamide thickening agent (PATA) was formulated at four concentrations in distilled–deionized water, without and with a glyphosate–surfactant herbicide (GH). Over a 6-week period, these mixtures were exposed to various controlled temperature and light conditions. Acrylamide concentration, ammonium concentration, and pH were measured at weekly intervals to assess the degradation of polyacrylamide and acrylamide. Satellite studies were conducted to examine the effect of altered pH on solutions of PATA (i.e., does pH promote polyacrylamide depolymerization?) and GH binding to amine groups (i.e., protection from degradation). The results of these studies suggest that polyacrylamide can degrade to acrylamide by thermal and photolytic effects, that changes in pH do not promote the depolymerization of polyacrylamide, and that GH does protect polyacrylamide and acrylamide from environmental degradation. Statistically there was no linear correlation between the various parameters measured.

ASCORBIC ACID GLYCATION OF LENS PROTEINS PRODUCES UVA SENSITIZERS SIMILAR TO THOSE IN HUMAN LENS

Soluble calf lens proteins were extensively glycated during a 4 week incubation with ascorbic acid in the presence of oxygen. Amino acid analysis of the dialyzed proteins removed at weekly intervals showed an increasing loss of lysine, arginine and histidine, consistent with the extensive protein cross-linking observed. Irradiation of the dialyzed samples with UVA light (1.0 kJ/cm2 total illumination through a 338 nm cutoff filter) caused an increasing loss of tryptophan, an additional loss of histidine and the production of micromolar concentrations of hydrogen peroxide. No alteration in amino acid content and no photolytic effects were seen in proteins incubated without ascorbic acid or in proteins incubated with glucose for 4 weeks. The rate of hydrogen peroxide formation was linear with each glycated sample with a maximum production of 25 nmol/mg protein illuminated. The possibility that the sensitizer activity was due to an ascorbate-induced oxidation of tryptophan was eliminated by the presence of a heavy metal ion chelator during the incubation and by showing equivalent effects with ascorbate-incubated ribonuclease A, which is devoid of tryptophan. The ascorbate-incubated samples displayed increasing absorbance at wavelengths above 300 nm and increasing fluorescence (340/430) as glycation proceeded. The spectra of the 4 week glycated proteins were identical to those obtained with a solubilized water-insoluble fraction from human lens, which is known to have UVA sensitizer activity. The incubation of lens proteins with dehydroascorbic acid or L-threose, but not fructose, produced equivalent glycation, protein crosslinking and sensitizer activity.(ABSTRACT TRUNCATED AT 250 WORDS)

UV laser-induced photochemistry of iron pentacarbonyl on single crystal surfaces in ultrahigh vacuum

The authors report the observation of dissociation resulting from irradiation of Fe(CO)/sub 5/ deposited onto single crystal Al/sub 2/O/sub 3/, Si(100), and Ag(110) surfaces in ultrahigh vacuum. Photolytic effects are observed without competition from laser-induced heating of the substrate. Decomposition is measured by mass spectrometric detection of the CO released from the surface. The postulated mechanism involves the direct absorption of 337-nm radiation by the physisorbed Fe(CO)/sub 5/ and subsequent fast dissociation. The Fe-containing photoproducts remain on the surface, although they are not identified. The dissociation yield is very similar for Fe(CO)/sub 5/ and Al/sub 2/O/sub 3/ and Ag(110) surfaces, which indicates that the rate of photofragmentation is competitive with energy transfer to the surface for each of the three substrates. Also, an annealing process, which results in a short initial burst of Fe(CO)/sub 5/ from the surface, is observed.

Photolytic effects in alumina chlorination

The temperature dependence of the rate of chlorination of α-alumina with CO/Cl2 gas mixtures exhibits an anomaly, a departure from the normal Arrhenius behavior, in the range 650 to 850°C; it is manifested as a local maximum in the Arrhenius plot at 670°C followed by a local minimum in the range 770 to 850°C. By carefully studying the effect of irradiation of the CO/Cl2 gas mixtures on the rate of chlorination of α-alumina, it is shown that such an anomaly, which has been observed in the chlorination of various metallic oxides, is most likely due to the photochemical formation of phosgene (COCl2) by ambient light incident on the reactant gas mixture during its transport to the main reactor. Phosgene is a better chlorinating agent than a CO/Cl2 mixture. The mechanism of chlorination of α-Al2O3 by CO/Cl2 mixtures subjected to the light emitted by a high-pressure Hg-vapor lamp is elucidated.

Laser and Thermal Induced Reactions of Mo(CO)6, CH3CH2OH, and NO on Si(111)7 × 7

AbstractLaser induced reactions of Mo(CO)6, CH3CH2OH, and NO adsorbed on Si(111)7 × 7 at 257 and 514 nm were studied and compared with thermally induced reactions under ultrahigh vacuum conditions utilizing laser induced desorption spectroscopy, thermal desorption spectroscopy, high resolution electron energy loss spectroscopy, and Auger electron spectroscopy. By using continuous wave laser irradiation, photolytic effects are clearly distinguished from pyrolytic effects. Mo(CO)6 and CH3CH2OH adsorbed on Si behave similarly as in the gas phase, whereas a substrate-mediated reaction channel is observed for NO adsorbed on Si.

Photoinduced electron-transfer reactions of aryl glycosides

The photolytic effects of ultraviolet, as well as other electromagnetic, radiation on carbohydrates are of interest in connection with photodegradation of cellulose and potential application in the photolytic cleavage of lignocellulosic bonds. Aryl glycosides, model compounds for lignocellulosic systems, were irradiated under conditions selected to achieve photoinduced electron-transfer. Various anomeric phenyl d-gluco- and d-galacto-pyranoside solutions in acetonitrile saturated with oxygen, air, or nitrogen and containing 1,4-dicyanonaphthalene (DCN) were irradiated at 350 nm for extended periods, and cleavage of the radical cation formed upon electron transfer to give the simple monosaccharide and phenol was observed. In the presence of methanol, it is possible to intercept the cationic intermediate, with formation of the correspondingmethyl glycosides. Control experiments conducted in the presence of oxygen, air, or nitrogen in the absence of DCN showed little or no conversion. Comparison of the modes of fragmentation in solution with those observed in the gas phase upon electron impact in the mass spectrometer was made, and mechanisms for the reactions induced by electron transfer under these conditions are proposed.

Photolytic effects of solar radiation at stratospheric levels during sunrise and sunset

The different terms of the photochemical mechanisms involved in the ozone steady state at upper stratospheric levels have been computed and followed as a function of time during twilight. The photodissociation coefficients have been calculated as functions of [Formula: see text] and [Formula: see text] which represent the column densities of oxygen and ozone above a given level. Chlorine chemistry has not been considered. It is shown that, at 45 km, the ozone behavior during twilight is governed mainly by photochemical processes. Under "usual conditions" defined by a night-time NO2 density of 6 × 108 cm−3, the ozone decreases by approximately 1%. Under "high NO2 conditions" defined by a night-time NO2 density of 3 × 1010 cm−3, the ozone decreases by several percent. Due to its action upon the kinetic rate constants, an increase of the atmospheric temperature emphasizes this decrease.The calculated ozone variations are compared with measurements by different experimenters using various methods. The increase during morning twilight measured by one of them cannot be reproduced with the model developed hereafter. The decrease measured by the others shortly before sunrise is more important than is calculated in the present work.

Mössbauer spectroscopy of radiolytic and photolytic effects on ferric citrate

The effect of radiolysis and photolysis on ferric citrate has been studied using Mössbauer spectroscopy. Non-irradiated ferric citrate, FeC 6H 5O 7 · 5H 2O, has a well-resolved Fe(III) doublet. After radiolysis or photolysis there is in addition a Fe(II) doublet. Some mechanisms of the transition as well as some applications are discussed.

Photolytic Effects Relevant to Theories of Solarization

AbstractBy means of a heavy high-intensity latent-image exposure and partial development. tabular silver bromide grains were coated with a layer of very small particles of developed silver. On further exposure in the absence of a halogen acceptor this silver was bleached off the sur(ace of the majority of grains and replaced by internal silver. This constitutes a direct demonstration of the feasibility of the rehalogenation theory of solarization.On the remaining grains rehalogenation of surface silver also occurs, since the initial uniform distribution of small surface specks is converted into a few large surface particles. usually near the centre of the grain. This process continues up to very heavy exposures, but ultimately conversion to an internal silver distribution occurs. Apparently in such grains the electrons released at the same time as the holes responsible for the bleaching are preferentially trapped at certain of the surface sites, and. together with silver ions. form silver there. As a resu...