Photo-degradation of PADC by UV radiation at various wavelengths

The effects of ultraviolet (UV) photons at different wavelengths (namely UVA, UVA + B and UVC) on PADC (polyallyl diglycol carbonate) were investigated in this study. The chemical modifications were studied by Fourier Transform Infrared (FTIR) spectrometry and the corresponding nano-mechanical properties were also determined. The scission process could be revealed by the decreasing net absorbance at particular wavelengths in the infrared (IR) spectra. On the other hand, the cross-linking was indicated by the increased hardness and reduced modulus determined with a nanoindenter. UVA caused no chemical modifications as most of the UV photons in this range were not absorbed by PADC. Both UVA + B and UVC irradiation caused scission of the chemical bonds, which was also manifested by the faster chemical etching rates. The bulk etch rate increased from 1.37 to 5.73 μm/h for 60 h of UVA + B exposure for 3 h of chemical etching, and increased to 5.13 μm/h for 60 h of UVC exposure. For 3 h of etching, the bulk etch rate remained unchanged for UVC exposures longer than 20 h. The saturation of the bulk etch rate was due to formation of cross-linked structures on the surface of the PADC samples. It was also observed that a UVC exposure caused a comparatively higher bulk etch rate at the beginning of etching. However, the bulk etch rate decreased with the depth of the PADC sample due to the lower rate of oxygen diffusion into deeper regions.     

Effect of UV irradiation on epidermal cell cytokine production

Within the last decade it has been found that the keratinocyte is not only a mechanical barrier to the outside but is also a fully immunocompetent cell that can release immunomodulating cytokines such as interleukin (IL) 1, IL 3, IL 6 and colony-stimulating factors (CSF). The constitutive production of these mediators by keratinocytes both in vivo and in vitro is very low; however, it can be dramatically enhanced by various stimuli such as tumour promotors or endotoxin. In addition, UV light is one of the most potent inducers of cytokine release. Accordingly, UV exposure results in increased production of IL 1, IL 3, IL 6, tumour necrosis factor and granulocyte/macrophage-CSF by epidermal cells. The secretion of these cytokines causes local immunologic and inflammatory reactions following UV irradiation. These factors, however, may also enter the circulation and thus may be responsible for systemic effects. In addition, UV light causes keratinocytes to release immunosuppressive factors which block contact hypersensitivity reaction and IL 1 activity. The production of such immunoinhibitors may play an essential pathogenic role during systemic UV-induced immunosuppression. This review will focus on the biological effects of epidermal-cell-derived cytokines, whose release is induced by UV light, and their role in immunologic and inflammatory reactions following UV exposure will be discussed.     

Effect of UV irradiation on mechanical properties and structure of poly(1,3,4-oxadiazole) fibers

The accelerated ultraviolet aging behavior of poly(1,3,4-oxadiazole) fibers (POD fibers) exposed to artificial environment for different durations were studied. The influence of ultraviolet light on the intrinsic viscosity, structure, appearance and morphology, mechanical properties of POD fibers were investigated during aging by ATR-FTIR and UV-spectra, XPS, WXRD, SEM and tensile strength tester. The results revealed that the structure and properties of POD fibers were affected by UV light. Tensile strength and breaking elongation of POD fibers were severely decreased after 48 h UV light irradiation, and the change of intrinsic viscosity indicated that only degradation but not crosslink occurred. Disruption of oxadiazole rings and formation of carbonyl and amide were observed. UV aging process in nitrogen atmosphere suggested that the oxygen was indispensable and the essence of POD UV aging was photo-oxidation process. POD was amorphous and the recrystallization on surface was present after UV aging due to degradation. Morphology of POD fiber surface was damaged after UV aging.     

Effect of cyclobutane pyrimidine dimers on apoptosis induced by different wavelengths of UV.

Ultraviolet radiation within three different wavelength ranges, UVA (340-400 nm), UVB (290-320 nm) or UVC (200-290 nm), was shown to induce apoptosis in OCP13 cells, derived from the medaka fish. Morphological changes such as cell shrinkage and a decrease in the number of nucleoli appeared 4 h after UVA, UVB or UVC irradiation, although with different relative efficiencies. Doses required to induce apoptosis with similar efficiencies were about 2500-fold higher for UVA and 10-fold higher for UVB than for UVC. The following phenomena occurred after UVA irradiation but not after UVB or UVC irradiation. (1) Ultraviolet-A-induced cell detachment occurred with or without cycloheximide pretreatment. (2) Cells attached to plastic showed morphological changes such as rounding up of nuclei without a change in the cell distribution. (3) Morphological changes after UVA irradiation could not be evaded by photorepair treatment. (4) Morphological changes did not occur in cells attached to glass coverslips but only those in plastic dishes. (5) Apoptosis occurred without detectable increase of caspase-3-like activity. (6) Morphological changes were inhibited by N-acetylcysteine, a scavenger of active oxygen species. These results suggest the existence of two different pathways leading to apoptosis, one for long- (UVA) and the other for short- (UVB or UVC) wavelength radiation.     

Effect of UV irradiation on the physico-chemical properties of iron crosslinked collagen

Collagen is the main component of connective tissue and finds immense applications as a biomaterial. In this study, effect of UV irradiation on collagen crosslinked with iron has been carried out. The physical and optical properties of crosslinked collagen affected by UV irradiation were analyzed using electrospectral and fluorescence studies. The electronic spectral studies showed that the photoproducts formed on UV radiation decrease in the presence of iron. Circular dichroic studies revealed that the conformational changes brought about in the protein due to UV irradiation have been reduced owing to the crosslinking with iron. However, prolonged irradiation does bring about conformational changes to the protein.     

Two-quantum photoprocesses in DNA under picosecond laser UV irradiation at 216 and 270 nm.

It is demonstrated that at high power picosecond laser irradiation of 216 and 270 nm, two-quantum photodestructions of the DNA secondary structure, such as interstrand covalent crosslinks, "weak" crosslinks, and B----C conformational transition, take place. Thermal effects do not contribute to the observed effects.     

Effects of solar UV irradiation on the tensile properties and structure of PPTA fiber

This paper comprehensively studied the effects of simulated solar ultraviolet irradiation on the mechanical and structural properties of the Twaron2000 para-aramid fiber by use of mechanical test, SEM, XRD, DSC, DMA and ATR-IR measurements. The results showed that after UV irradiation, the mechanical properties of the fiber were decreased obviously, and UV irradiation deteriorated the surface and defect areas of the fiber severely by photo-induced chain scission and end group oxidation in air with the crystalline structure remained almost unchanged although some local rearrangement of the crystalline area might occur. It was found that surface etching and shortening of the crystalline correlation length along the fiber axis were the main causes of the mechanical loss induced by UV irradiation.     

Preparation and characterization of DNA films induced by UV irradiation

Large amounts of DNA-enriched materials, such as salmon milts and shellfish gonads, are discarded as industrial waste. We have been able to convert the discarded DNA to a useful material by preparing novel DNA films by UV irradiation. When DNA films were irradiated with UV light, the molecular weight of DNA was greatly increased. The reaction was inhibited by addition of the radical scavenger galvinoxyl suggesting that the DNA polymerization with UV irradiation proceeded by a radical reaction. Although this UV-irradiated DNA film was water-insoluble and resistant to hydrolysis by nuclease, the structure of the DNA film in water was similar to non-irradiated DNA and maintained B-form structure. In addition, the UV-irradiated DNA film could effectively accumulate and condense harmful DNA-intercalating compounds, such as ethidium bromide and acridine orange, from diluted aqueous solutions. The binding constant and exclusion number of ethidium bromide for UV-irradiated DNA were determined to be 6.8 +/- 0.3 x 10(4) M(-1) and 1.6 +/- 0.2, respectively; these values are consisted with reported results for non-irradiated DNA. The UV-irradiated DNA films have potential uses as a biomaterial filter for the removal of harmful DNA intercalating compounds.     

Solar UV irradiation conditions on the surface of Mars

The UV radiation environment on planetary surfaces and within atmospheres is of importance in a wide range of scientific disciplines. Solar UV radiation is a driving force of chemical and organic evolution and serves also as a constraint in biological evolution. In this work we modeled the transmission of present and early solar UV radiation from 200 to 400 nm through the present-day and early (3.5 Gyr ago) Martian atmosphere for a variety of possible cases, including dust loading, observed and modeled O3 concentrations. The UV stress on microorganisms and/or molecules essential for life was estimated by using DNA damaging effects (specifically bacteriophage T7 killing and uracil dimerization) for various irradiation conditions on the present and ancient Martian surface. Our study suggests that the UV irradiance on the early Martian surface 3.5 Gyr ago may have been comparable with that of present-day Earth, and though the current Martian UV environment is still quite severe from a biological viewpoint, we show that substantial protection can still be afforded under dust and ice.     

Selective enzymatic labeling to detect packing-induced denaturation of double-stranded DNA at interfaces

The adsorption of DNA on surfaces is a widespread procedure and is a common way for fabrication of biosensors, DNA chips, and nanoelectronic devices. Although the biologically relevant and prevailing in vivo structure of DNA is its double-stranded (dsDNA) conformation, the characterization of DNA on surfaces has mainly focused on single-stranded DNA (ssDNA). Studying the structure of dsDNA on surfaces is of invaluable importance to microarray performance since their effectiveness relies on the ability of two DNA molecules to hybridize and remain stable. In addition, many of the enzymatic transactions performed on DNA require dsDNA, rather than ssDNA, as a substrate. However, it is not established that adsorbed dsDNA remains in its structure and does not denature. Here, two methodologies have been developed for distinguishing between surface-adsorbed single- and double-stranded DNA. We demonstrate that, upon formation of a dense monolayer, the nonthiolated strand comprising the dsDNA is released and the monolayer consists of mostly ssDNA. The fraction of dsDNA within the ssDNA monolayer depends on the length of the oligomers. A likely mechanism leading to this rearrangement is discussed.     

Effect of UV irradiation on stabilized collagen: role of chromium(III)

Research on the effect of UV radiation on stabilized collagen is an area of potential interest owing to the fact that collagen is an important biomaterial finding immense use in various fields. In this present study, effect of UV irradiation on collagen stabilized using chromium(III) has been studied. The physical and optical properties affected by UV irradiation have been detailed. Viscosity measurements have shown that chromium(III) treated collagen has better stability against UV radiation than native collagen. Circular dichroic studies indicate that increase in concentration of chromium(III) does not affect the conformation of collagen however, the duration of irradiation has profound impact on the conformation of collagen. The fluorescence intensity of native collagen has been found to decrease more than that of chromium(III) treated collagen. The difference absorption spectra also shows that chromium(III) treatment brings about more stability to collagen against UV irradiation.     

超氧化物歧化酶对TiO2光催化损伤DNA的影响

以小牛胸腺DNA为对象, 在超氧化物歧化酶(superoxide dismutase, SOD)存在下, 研究了纳米二氧化钛(TiO₂)光催化对DNA损伤特性及SOD对TiO₂光催化损伤DNA的影响. 采用凝胶电泳和高效液相色谱(HPLC)分析法, 探讨了DNA的损伤程度. 运用生物标准样8-羟基脱氧鸟苷(8-hydroxy-2 -deoxyguanosine, 8-OHdG)为内标物并通过高效液相色谱-电喷雾离子化串联质谱联用技术(HPLC-ESI-MS/MS)对DNA损伤产物进行了跟踪分析, 采用过氧化物酶催化分光光度法及顺磁共振技术(ESR)跟踪测定TiO₂光催化DNA损伤过程中H₂O₂和氧化物种的变化, 探讨了DNA氧化损伤机理. 结果表明, 在实验条件下紫外光照(UV, λ＝200～275 nm), Dark/TiO₂和UV/TiO₂体系中, DNA氧化损伤程度为UV/TiO₂＞UV＞Dark/TiO₂. 光催化260 min DNA损伤99%, 反应动力学常数K＝7.82×10^－3 min^－1. 抗氧化剂SOD具有清除光催化体系中超氧自由基( )的能力, 可以抑制DNA的损伤, 反应动力学常数K＝2.27×10^－3 min^－1. 8-OHdG为DNA损伤中鸟嘌呤氧化的特异产物, UV及光催化体系对DNA损伤主要涉及 及羟基自由基(•OH)历程, 光催化体系对DNA损伤伴随有深度氧化(矿化)过程, 实验条件下12 h DNA矿化75.06%.     

Changes in cell cycle distribution of V79 Chinese hamster fibroblasts after irradiation at different wavelengths

Changes in cell cycle distribution of V79 Chinese hamster fibroblasts were investigated at different wavelengths between 254 and 313 nm. The fluences applied led to surviving fractions of 0.61. In all cases, the S fraction was temporarily increased within 8-12 h after irradiation, whereas the G1 fraction was decreased. The maximum deviations from the initial values did not significantly depend on the wavelength.     

Geometric properties of covalently bonded DNA on single-crystalline diamond

Diamond is a promising candidate for bioapplications. Properties of hybridized DNA arrays on single-crystalline diamond are studied on a microscopic level by atomic force microscopy (AFM) in buffer solutions. Compact DNA layers in a thickness of 76 A are resolved by optimizing phase and height contrast in AFM. The height shows some long-range (30 nm) undulations of +/-5 A due to tip and DNA interactions. The axis of double helix DNA is oriented at about 36 degrees with respect to the diamond surface. DNA molecules can be removed by contact-mode AFM with forces >45 nN, indicating stronger DNA bonding than on gold substrates.     

Dramatic change in the tertiary structure of giant DNA without distortion of the secondary structure caused by pteridine-polyamine conjugates

Pteridine-polyamine conjugates, such as 2-polyamine (1,3-diaminopropane and spermine) substituted 6,7-dimethyl-3H-pteridine-4-one, induce a folding transition of a giant DNA molecule more effectively than the corresponding polyamines. However, since neither a DNA high-temperature shift of denaturation (Tm) curve nor distortion of the UV/fluorescence spectra is observed in a mixture of these compounds with DNA, they do not interact with the DNA duplex strongly.     

Uncoupled analysis of secondary and tertiary protein structure by circular dichroism and electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) applied to protein conformational studies is a powerful new method that seems to provide specific information about protein tertiary structure. In this study, we analyzed the effect of trifluoroethanol (TFE) on a myoglobin peptide and cytochrome c (cyt c) at low pH by circular dichroism (CD) and ESI-MS. These experiments show that coil-to-helix transition per se does not affect ESI mass spectra, confirming that this technique is insensitive to the local conformation of the polypeptidic chain and, rather, reports on the tertiary contacts characterizing different protein conformations. This property makes ESI-MS an excellent method, complementary to CD, for the characterization of protein conformational changes. Fluorinated alcohols have been suggested to induce molten globule formation in acid-unfolded cyt c. The experiments described here show that TFE does not induce major changes in the ESI mass spectrum of cyt c at pH 2.2, indicating that no stabilization of compact, globular structures is detectable under the conditions employed. On the other hand, even low concentrations of TFE (2-5%) are shown to destabilize the folded state of the protein around the mid-point of its acid-induced unfolding transition.     

Characterization of single- and double-stranded DNA on gold surfaces

Single- and double-stranded deoxy ribonucleic acid (DNA) molecules attached to self-assembled monolayers (SAMs) on gold surfaces were characterized by a number of optical and electronic spectroscopic techniques. The DNA-modified gold surfaces were prepared through the self-assembly of 6-mercapto-1-hexanol and 5'-C(6)H(12)SH -modified single-stranded DNA (ssDNA). Upon hybridization of the surface-bound probe ssDNA with its complimentary target, formation of double-stranded DNA (dsDNA) on the gold surface is observed and in a competing process, probe ssDNA is desorbed from the gold surface. The competition between hybridization of ssDNA with its complimentary target and ssDNA probe desorption from the gold surface has been investigated in this paper using X-ray photoelectron spectroscopy, chronocoulometry, fluorescence, and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). The formation of dsDNA on the surface was identified by PM-IRRAS by a dsDNA IR signature at approximately 1678 cm(-)(1) that was confirmed by density functional theory calculations of the nucleotides and the nucleotides' base pairs. The presence of dsDNA through the specific DNA hybridization was additionally confirmed by atomic force microscopy through colloidal gold nanoparticle labeling of the target ssDNA. Using these methods, strand loss was observed even for DNA hybridization performed at 25 degrees C for the DNA monolayers studied here consisting of attachment to the gold surfaces by single Au-S bonds. This finding has significant consequence for the application of SAM technology in the detection of oligonucleotide hybridization on gold surfaces.