Studies on photoprotection and photo-oxidation in polystyrene with various wavelength regions

The photoprotection of styrene-2,2,6,6-tetramethyl-4-piperidinyl methacrylate copolymer (PDS) as an ultraviolet absorbent and the photo-oxidation in polystyrene (PS) film with various wavelength region irradiations have been studied. It was found that the photoprotection of PDS as the hindered amine for PS film was effective. In the full wavelength region irradiation, the Yellowness Index (YI) as the characterizing parameter was only 20%, corresponding to an exposure period as long as 80 hr. The results have proved that the photoprotection behavior of PDS was more effective a wavelength of 274 nm than of 318.5 nm, and the increment of the YI was proportional to the intensity absorbed by PS film. The infrared and ultraviolet spectra of PS film undergoing photooxidation have shown that (a) the dominant contribution to the increment of the ultraviolet characteristic absorption peak A (274 nm) of PS film belonged to the wavelength region (200–320 nm) rather than the singlet, and that (b) the infrared shifting of the wide-peak A (274 nm) could be considered as the relative changes of the constants of carbonyl compounds with the conjugating and non-conjugating structures from the end-products of the photo-oxidation process.     

Efficient flow injection and sequential injection methods for spectrophotometric determination of oxybenzone in sunscreens based on reaction with Ni(II)

Spectrophotometric determination of a widely used UV-filter, such as oxybenzone, is proposed. The method is based on the complexation reaction between oxybenzone and Ni(II) in ammoniacal medium. The stoichiometry of the reaction, established by the Job method, was 1:1. Reaction conditions were studied and the experimental parameters were optimized, for both flow injection (FI) and sequential injection (SI) determinations, with comparative purposes. Sunscreen formulations containing oxybenzone were analyzed by the proposed methods and results compared with those obtained by HPLC. Data show that both FI and SI procedures provide accurate and precise results. The ruggedness, sensitivity and LOD are adequate to the analysis requirements. The sample frequency obtained by FI is three-fold higher than that of SI analysis. SI is less reagent-consuming than FI.     

Influence of Cyclodextrin Complexation on the in vitro Human Skin Penetration and Retention of the Sunscreen Agent, Oxybenzone

The objective of this study was to investigate the influence of cyclodextrins on the cutaneous availability of the sunscreen oxybenzone. The interaction between oxybenzone and hydrophilic α-, β- and γ-cyclodextrin derivatives was studied in water by phase-solubility analysis. Among the available cyclodextrins, hydroxypropyl-β-cyclodextrin (HP-β-CD) and especially sulfobutylether-β-cyclodextrin (SBE-β-CD) had the greatest solubilizing activity. Ethanol–water solutions containing oxybenzone free or complexed with HP-β-CD or SBE-β-CD were applied to human skin in Franz diffusion cells and the amount of sunscreen permeated into the different cutaneous compartments was determined by HPLC. As much as 20.5% of the oxybenzone applied dose diffused within the skin tissue after 6 h application. Between 39.4% and 54.9% of the penetrated UV filter was localized in the stratum corneum, with no significant difference between uncomplexed oxybenzone or its complex with HP-β-CD. Conversely, the amount retained in the stratum corneum was markedly decreased (ca. 50%) by complexation with SBE-β-CD. Considerable quantities of oxybenzone accumulated into the viable epidermis (5.7% of the applied dose) and dermis (6.2% of the applied dose) from the preparation containing the free UV filter. The sunscreen penetration to the deeper living layers of the skin was remarkably lower (1.0% and 2.0% of applied dose for epidermis and dermis, respectively) upon application of the sunscreen complexed with SBE-β-CD, whereas HP-β-CD had no effect. In addition, photostability experiments demonstrated that SBE-β-CD complexation did not alter the sunscreen photochemical properties.     

Sequential injection spectrophotometric determination of oxybenzone in lipsticks

A sequential injection (SI) procedure for the spectrophotometric determination of oxybenzone in lipsticks is reported. The colorimetric reaction between nickel and oxybenzone was used. SI parameters such as sample solution volume, reagent solution volume, propulsion flow rate and reaction coil length were studied. The limit of detection was 3 microg ml(-1). The sensitivity was 0.0108+/-0.0002 ml microg(-1). The relative standard deviations of the results were between 6 and 12%. The real concentrations of samples and the values obtained by HPLC were comparable. Microwave sample pre-treatment allowed the extraction of oxybenzone with ethanol, thus avoiding the use of toxic organic solvents. Ethanol was also used as carrier in the SI system. Seventy-two injections per hour can be performed, which means a sample frequency of 24 h(-1) if three replicates are measured for each sample.     

Efficient flow injection and sequential injection methods for spectrophotometric determination of oxybenzone in sunscreens based on reaction with Ni(II)

Spectrophotometric determination of a widely used UV-filter, such as oxybenzone, is proposed. The method is based on the complexation reaction between oxybenzone and Ni(II) in ammoniacal medium. The stoichiometry of the reaction, established by the Job method, was 1:1. Reaction conditions were studied and the experimental parameters were optimized, for both flow injection (FI) and sequential injection (SI) determinations, with comparative purposes. Sunscreen formulations containing oxybenzone were analyzed by the proposed methods and results compared with those obtained by HPLC. Data show that both FI and SI procedures provide accurate and precise results. The ruggedness, sensitivity and LOD are adequate to the analysis requirements. The sample frequency obtained by FI is three-fold higher than that of SI analysis. SI is less reagent-consuming than FI.     

Inclusion Complexation of the Sunscreen 2-Hydroxy-4-Methoxy Benzophenone (Oxybenzone) with Hydroxypropyl-β-Cyclodextrin: Effect on Membrane Diffusion

It is desirable to minimize skin penetration of some drugs, such as sunscreens and insect repellents. Available in vivo and in vitro data suggest appreciable absorption of some sunscreen agents. The purpose of this study was to investigate the effect of hydroxypropyl--cyclodextrin (HPCD) on the release and permeation of the sunscreen agent 2-hydroxy-4-methoxy benzophenone (oxybenzone). The interaction between oxybenzone and HPCD was studied in water by phase solubility analysis. The inclusion complex was characterized by thermal analysis and nuclear magnetic resonance spectroscopy. UV transmittance and percent UVA transmittance, as a preliminary measure of sun protection factor (SPF), were determined. In vitro permeation experiments were conducted in Franz-type diffusion cells at 37 °C, using the model membrane poly(dimethyl siloxane) (PDMS) and 4% bovine serum albumin in phosphate buffer solution (pH 7.4) as the receptor phase. HPCD caused a marked increase in the aqueous solubility of oxybenzone. Data from the phase solubility experiment indicated the formation of 1:1 oxybenzone-cyclodextrin complex. UV transmittance studies indicated that the presence of HPCD did not suppress the UV absorbing properties of oxybenzone. The release and membrane permeation of oxybenzone was significantly reduced in the presence of equimolar, 2 times molar and 1, 2 and 4% of HPCD. It is concluded that HPCD can reduce the release/membrane diffusion of oxybenzone whilst retaining its efficacy as a sunscreen agent. This formulation strategy may be useful in controlling skin penetration of topically applied sunscreens and other chemicals.     

Reconstituted LH2 in multilayer membranes induced by poly-l-lysine: Structure of supramolecular and electronic states

To explore the effect of cell membrane stacking on the function of light-harvesting complex 2 (LH2) in purple nonsulfur photosynthetic bacteria, LH2 from Rhodobacter sphaeroides 2.4.1 (R. sph 2.4.1) was reconstituted into lipid bilayer vesicles (LH2@liposome) and further formed multi-layer structure by electrostatic interaction with poly-l-lysine (LH2@liposome/PLL), which was characterized by cryo-electron microscopy (cryo-EM) and TEM. When embedded in liposomes and additionally in multi-layer liposomes, the absorption band, zero-crossing point of CD signals and fluorescence emission of LH2 B850 excitons were observed to uniformly have 1–2 nm red-shifting. Combining with the corresponding fluorescence quench and the generation of shorter-living fluorescence species, a new excitonic species generated through B850 structural splitting was proposed. By FT-Raman and triplet carotenoid dynamics, the structural mechanism was deduced and discussed. Briefly, all environmental changes, including LH2 aggregating and multi-layer membrane stacking, eventually applied forces on B850 exciton molecules mainly through the hydrogen bonding between the C3-acetyl carbonyl groups of B850 BChls and Tyr44 and 45 residues at C-terminus of α-polypeptides. The effect of multi-layer structure on LH2 could be assigned as a kind of photoprotection.     

Thermochemistry and gas-phase ion energetics of 2-hydroxy-4-methoxy-benzophenone (oxybenzone)

We have investigated the thermochemistry and ion energetics of the oxybenzone (2-hydroxy-4-methoxy-benzophenone, C14H12O3, 1H) molecule. The following parameters have been determined for this species: gas-phase enthalpy for the of neutral molecule at 298.15K, (Delta(f)H0(m)(g) = -303.5 +/- 5.1 kJ x mol-1), the intrinsic (gas-phase) acidity (GA(1H) = 1402.1 +/- 8.4 kJ x mol-1), enthalpy of formation for the oxybenzone anion (Delta(f)H0(m)(1-,g) = -402.3 +/- 9.8 kJ x mol-1). We also have obtained the enthalpy of formation of, 4-hydroxy-4'-methoxybenzophenone (Delta(f)H0(m)(g) = -275.4 +/- 10 kJ x mol-1) and 3-methoxyphenol anion (Delta(f)H0(m)(C7H7O2-,g) = -317.7 +/- 8.7 kJ x mol-1). A reliable experimental estimation of enthalpy related to intramolecular hydrogen bonding in oxybenzone has also been obtained (30.1 +/- 6.3 kJ x mol-1) and compared with our theoretical calculations at the B3LYP/6-311++G** level of theory, by means of an isodesmic reaction scheme. In addition, heat capacities, temperature, and enthalpy of fusion have been determined for this molecule by differential scanning calorimetry.     

Detection of carbonyl groups in triterpenoids by hydroxylamine hydrochloride derivatization using electrospray ionization mass spectrometry

A rapid, simple electrospray ionization mass spectrometry (ESI-MS) sensitivity enhancement method for detecting carbonyl groups in triterpenoids has been developed by using hydroxylamine hydrochloride (NH(2)OH . HCl) as a derivatization reagent. We use the oxime formed during the derivatization reactions and its Beckmann rearrangement intermediates as a means of detecting the carbonyl groups originally present in these triterpenoids. In comparison with other derivatization methods reported in the literature, this method is simple, specific and can be used to detect carbonyl groups in triterpenoids which have low polarity and are poorly or non-ionizable. Moreover, it can also be used to detect hydroxyl groups by using the Dess-Martin periodinane (DMP) to convert primary and secondary hydroxyls into carbonyl groups.     

Simulated water adsorption in chemically heterogeneous carbon nanotubes

Grand canonical Monte Carlo simulations are used to study the adsorption of water in single-walled (10:10), (12:12), and (20:20) carbon nanotubes at 298 K. Water is represented by the extended simple point charge model and the carbon atoms as Lennard-Jones spheres. The nanotubes are decorated with different amounts of oxygenated sites, represented as carbonyl groups. In the absence of carbonyl groups the simulated isotherms are characterized by negligible amounts of water uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption-desorption hysteresis loops. In the presence of a few carbonyl groups the simulated adsorption isotherms are characterized by pore filling at lower pressures and by narrower adsorption-desorption hysteresis loops compared to the results obtained in the absence of carbonyl groups. Our results show that the distribution of the carbonyl groups has a strong effect on the adsorption isotherms. For carbonyl groups localized in a narrow section the adsorption of water may be gradual because a cluster of adsorbed water forms at low pressures and grows as the pressure increases. For carbonyl groups distributed along the nanotube the adsorption isotherm is of type V.     

Dialkylaluminum N,O-dimethylhydroxylamine complex as a reagent to mask reactive carbonyl groups in situ from nucleophiles

Aluminum complexes of N,O-dimethylhydroxylamine are effective reagents to mask carbonyl groups in situ from nucleophilic addition by organolithiums, Grignard reagents, and borohydrides. The utility of this process by selectively adding nucleophiles into carbonyl groups on a variety of structures as well as distinguishing between carbonyl groups on a sensitive natural product is demonstrated. (1)H NMR analysis supports the in situ masking of the more reactive carbonyl group.     

DELAY IN GROWTH AND DIVISION INDUCED BY NEAR ULTRAVIOLET RADIATION IN ESCHERICHIA COLI B AND ITS ROLE IN PHOTOPROTECTION AND LIQUID HOLDING RECOVERY

Abstract. Microscopic observations show that growth delay and division delay occur on nutrient agar after Escherichia coli B has been irradiated at 3341 Å. These effects also occur in nutrient broth.
A near u.v. action spectrum for growth delay in nutrient broth has been obtained. It shows a single peak at 3380 Å and is indistinguishable from the action spectrum for photo-protection from far u.v. (2537 Å) killing in the same organism. Furthermore, photoprotected cells show a much greater growth delay than cells that have not been photoprotected. These, as well as kinetic data, suggest that the essential action of a photoprotection treatment consists in the induction of a growth-division delay. This delay would presumably permit more time for intracellular recovery systems to operate on the far u. v. damage to nucleic acids.
Liquid holding recovery (effected by holding cells in phosphate buffer after far u. v. irradiation) shows complete overlap with photoprotection. It is concluded that photoprotection and liquid holding recovery operate on the same far u. v. damage. As with photoprotection, it is probable that the essential action of a liquid holding treatment is the induction of a growth-division delay.
No photoprotection is observed of intracellular T2 bacteriophage or of E. coli B_s-l (Hill).     

Hydrogen bonding structure and stability of alpha-chitin studied by 13C solid-state NMR

The structure and stability of hydrogen bonds in alpha-chitin were investigated by (13)C solid-state NMR measurements at different temperatures. Splitting of the carbonyl carbon signal for alpha-chitin was interpreted as two types of hydrogen bonding; the peaks at 173.5 and 175.8 ppm were assigned, respectively, to a carbonyl carbon hydrogen bonded exclusively to the NH group and a carbonyl carbon hydrogen-bonded to both NH and C(6)-OH groups. Approximately 60% of carbonyl groups exclusively contributed to the intermolecular hydrogen bonding and ca. 40% of them to the combination of intermolecular and intramolecular hydrogen bonding. Internal rotation around the C(5)-C(6) bond was detected at 55 degrees C.     

ULTRAVIOLET RADIATION INHIBITS BOTH ACCESSORY CELL AND RESPONDER T CELL FUNCTION IN THE PROLIFERATIVE RESPONSE TO HAPTENATED-SELF

Abstract— Photoprotection i. e. the increased resistance of the cells preilluminated with near ultraviolet light (300–380 nm) to the lethal action of 254 nm radiations is observed in wild-type Escherichia coli B cells (which exhibits the Fil phenotype) but requires either an integrated prophage or a rec A mutation to be detected in E. coli K12 strains. Here we have demonstrated that significant photoprotection occurs in an E. coli K12 rec A⁺ cell containing the Ion allele which is responsible for filamentous growth (Fil phenotype) after 254 nm irradiation. The Fil phenotype can be suppressed by the sfi A of sfi B suppressor genes. Since the E. coli K12 rec A⁺ Ion sfi B strain exhibits no more photoprotection, these data support the conclusion that in Ion strains photoprotection is due to the abolition of the 254 nm induced filamentation by the near ultraviolet treatment. In addition, we show here that near ultraviolet illumination of the cells leads to a severe restriction of the bulk protein synthesis, as well as of the inducibility of β-galactosidase and tryptophanase. These effects are observed only in nuv ⁺ cells that contains 4-thiouridine the chromophore responsible for photoprotection. We propose that in Ion (lysogenic) strains, photoprotection is due to prevention of the SOS response. During the growth lag, the low residual level of protein synthesis does not allow the induction of the SOS response and accordingly prevents filamentation (the lytic cycle). Concomitantly the SOS triggering signals are eliminated via DNA repair.     

Hydration changes of poly(2-(2-methoxyethoxy)ethyl methacrylate) during thermosensitive phase separation in water

Hydration changes of poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMoEoEMa) during thermosensitive phase separation in water have been investigated by infrared spectroscopy. The C=O stretching band can be separated into three components assigned to non-hydrated carbonyl groups and singly and doubly hydrogen-bonded carbonyl groups (1728, 1709, and 1685 cm-1, respectively). Relatively large parts of the carbonyl groups (50% in 30 wt % solution) do not form hydrogen bonds even below the transition temperature (Tp) probably because they possess crowded positions near the backbone. The fraction of hydrogen-bonding carbonyl groups decreased during phase separation by approximately 0.2. Among five nu(C-H) bands, the highest- and the lowest-frequency bands (nu(C-H)A and nu(C-H)E) exhibited relatively large red shifts of 8 and 11 cm(-1), respectively. DFT calculations indicate that the formation of a H-bond between the ether oxygen and water leads to blue shifts of nu(C-H) of adjacent alkyl groups and has a larger effect than a direct H-bond to the alkyl groups, namely, C-H...O H-bonds. The fraction of hydrogen-bonding methoxy oxygens estimated from the position of the nu(C-H)A is 1 at Tp. This result indicates that the methoxy oxygens and the carbonyl are more favorably hydrated than the other at Tp, respectively.     

The roles of the rel+ gene and of 4-thiouridine in killing and photoprotection of Escherichia coli by near-ultraviolet radiation

Abstract— Photoprotection is a reduction in response to far-UV (190–300. nm) radiation in cells that have been previously exposed to longer wavelengths. It has been proposed that photoprotection operates by means of a growth delay that permits more time for dark repair. Growth delay in Escherichia coli utilizes 4-thiouridine (⁴Srd) in transfer RNA as a chromophore and it requires the rel⁺ gene, which exerts a stringent control upon RNA synthesis. Mutants that were either rel or ⁴Srd^? were isolated from E. coli B, utilizing a near-UV-induced growth-delay selection technique. The rel mutants, which undergo little growth delay after near-UV irradiation, show only 50% as much photoprotection as wild types, while ⁴Srd^? mutants show no photoprotection at all. Thus, photoprotection appears to utilize ⁴Srd as its sole chromophore in E. coli B and B/r, and no more than 50% of photoprotection in these strains can be a result of near-UV-induced growth delay.     

Synthesis of novel thermosetting imide compounds having phenylethynyl carbonyl groups at both terminal ends and production of new network polymers based on the imide compounds

A novel thermosetting imide compound having a respective phenylethynyl carbonyl group at both terminal ends was newly synthesized from an acid anhydride having a phenylethynyl carbonyl group and various diamine compounds. The thermosetting behavior of the obtained novel thermosetting imide compound having phenylethynyl carbonyl groups was analyzed through differential scanning calorimetry measurements and infrared spectroscopic analysis. As a result, it became clear that a curing reaction of phenylethynyl carbonyl groups proceeds at approximately 200°C and that the curing reaction thereof proceeds at a temperature that is lower by 150°C or more compared with that of phenylethynyl groups. Examination of the polymerization reaction of the imide compounds having phenylethynyl carbonyl groups using model compounds revealed that a reaction that imparted an alkene C=C and polycyclic aromatic structure progressed. Moreover, a network polymer obtained from a thermosetting imide compound having respective phenylethynyl carbonyl groups at both terminal ends exhibited extremely superior heat resistance and thermal decomposition resistance. These superior thermal properties are thought to be due to the strong molecular interaction (molecular packing) that results from the polycyclic aromatic structures and alkenes produced through polymerization of the phenylethynyl carbonyl groups and to the suppression of the movement of the molecular chains.     

Phase behavior and structure in mesogen containing polyurethanes

The mesophase to crystal phase transition observed upon heating the monotropic liquid crystal polyurethane (2,6-LCPU-6), based on the mesogenic biphenol 4,4′-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and 2,6-toluenediisocyanate (2,6-TDI), has been investigated by differential scanning calorimetry (DSC), wide angle x-ray scattering (WAXS) and infrared (IR) spectroscopy. Hexafluoroisopropanol (HFIP) fast solvent-evaporation casting resulted in 2,6-LCPU-6 thin films with a glassy mesophase morphology. The mesophase to crystal exothermic transition has been observed by DSC between 130 and 140°C, depending on sample preparation. It is accompanied by a substantial increase of H-bonding between urethane C=O and N-H, as observed by IR. Curve fitting analysis of the conformationally sensitive amide I region revealed three bands; ordered H-bonded carbonyl groups, disordered H-bonded carbonyl groups, and “free” carbonyl groups. The prime feature of the 130°C transition is the substantial increase of ordered H-bonded carbonyl groups at the expense of disordered H-bonded carbonyl groups. Crystal melting occurs between 180 and 210°C and is accompanied by the complete disappearance of the ordered H-bonded peak along with substantial changes in the frequency and width at half-height of the disordered H-bonded peak     

Modulation of Photochemical Damage in Normal and Malignant Cells by Naturally Occurring Compounds†

Certain phytochemicals, such as the stilbene, resveratrol (RES, found in red grapes and berries), and the triterpenoid, ursolic acid (UA, found in waxy berries and herbs such as rosemary and oregano), have antioxidant, anti‐inflammatory and antiproliferative effects. Two human‐derived cell lines, hTERT‐RPE with a nonmalignant phenotype derived from retinal pigment epithelium, and ATCC CRL‐11147 derived from a malignant skin melanoma, were used as in vitro models of photooxidative stress produced by exposure to the broadband output of a 150 W Hg vapor arc lamp at an irradiance of 19–26 mW cm^?2. In untreated cells, UV–VIS broadband light exposure produced a loss of proliferative ability, an activation of NF‐κB and an increase in protein carbonyl adducts at 24 h postexposure. Pretreatment of the cells with RES or UA at 1–2 μm significantly reduced the amount of phosphorylated NF ‐κB at 24 h postexposure. RES pretreatment reduced the burden of light‐induced protein carbonyl adducts by up to 25% in exposed cells. UA treatment markedly increased the sensitivity of melanoma cells to UV radiation, while conferring some photoprotection to RPE cells. These observations indicate that phytochemicals modulate the cellular response to photochemical stress by interacting with specific cell‐signaling pathways.     

Steered molecular dynamics studies of the potential of mean force of a Na+ or K+ ion in a cyclic peptide nanotube

Potential of mean force (PMF) profiles of a single Na+ or K+ ion passing through a cyclic peptide nanotube, cyclo[-(D-Ala-Glu-D-Ala-Gln)2-], in water are calculated to provide insight into ion transport and to understand the conductance difference between these two ions. The PMF profiles are obtained by performing steered molecular dynamics (SMD) simulations that are based on the Jarzynski equality. The computed PMF profiles for both ions show barriers of around 2.4 kcal/mol at the channel entrances and exits and energy wells in the middle of the tube. The energy barriers, so-called dielectric energy barriers, arise due to the desolvation of water molecules when ions move across the nanotube, and the energy wells appear as a result of attractive interactions between the cations and negatively charged carbonyl oxygens on the backbone of the tube. We find more and deeper energy wells in the PMF profile for Na+ than for K+, which suggests that Na+ ions have a longer residence time inside the nanotube and that permeation of Na+ ions is reduced compared to K+ ions. Calculations of the radial distribution functions (RDF) between the ions and oxygens in the water molecules and in carbonyl groups on the tube and an investigation of the orientations of the carbonyl groups show that, in contrast with the dynamic carbonyl groups observed in the selectivity filter of the KcsA ion channel, the carbonyl groups in the cyclic peptide nanotube are relatively rigid, with only slight reorientation of the carbonyl groups as the cations pass through. The rigidity of the carbonyl groups in the cyclic peptide nanotube can be attributed to their role in hydrogen bonding, which is responsible for the tube structure. Comparison of the PMF profiles with the electrostatic energy profiles calculated from the Poisson-Boltzmann (PB) equation, a dielectric continuum model, reveals that the dielectric continuum model breaks down in the confined region within the tube that governs ion transport.