A facile method to prepare translucent anatase thin films in monolithic structures for gas stream purification.

In the present work, a facile method to prepare translucent anatase thin films on cellulose acetate monolithic (CAM) structures was developed. A simple sol-gel method was applied to synthesize photoactive TiO2 anatase nanoparticles using tetra-n-butyl titanium as precursor. The immobilization of the photocatalyst on CAM structures was performed by a simple dip-coating method. The translucent anatase thin films allow the UV light penetration through the CAM internal walls. The photocatalytic activity was tested on the degradation of n-decane (model volatile organic compound-VOC) in gas phase, using a tubular lab-scale (irradiated by simulated solar light) and pilot-scale (irradiated by natural solar light or UVA light) reactors packed with TiO2-CAM structures, both equipped with compound parabolic collectors (CPCs). The efficiency of the photocatalytic oxidation (PCO) process in the degradation of n-decane molecules was studied at different operating conditions at lab-scale, such as catalytic bed size (40-160 cm), TiO2 film thickness (0.435-0.869 µm), feed flow rate (75-300 cm3 min-1), n-decane feed concentration (44-194 ppm), humidity (3 and 40%), oxygen concentration (0 and 21%), and incident UV irradiance (18.9, 29.1, and 38.4 WUV m-2). The decontamination of a bioaerosol stream was also evaluated by the PCO process, using Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive) as model bacteria. A pilot-scale unit was operated day and night, using natural sunlight and artificial UV light, to show its performance in the mineralization of n-decane air streams under real outdoor conditions. Graphical abstract Normally graphics abstract are not presented with captions/legend. The diagram is a collection of images that resume the work.

Differentiating the roles of photooxidation and biodegradation in the weathering of Light Louisiana Sweet crude oil in surface water from the Deepwater Horizon site.

We determined the contributions of photooxidation and biodegradation to the weathering of Light Louisiana Sweet crude oil by incubating surface water from the Deepwater Horizon site under natural sunlight and temperature conditions. N-alkane biodegradation rate constants were ca. ten-fold higher than the photooxidation rate constants. For the 2-3 ring and 4-5 ring polycyclic aromatic hydrocarbons (PAHs), photooxidation rate constants were 0.08-0.98day(-1) and 0.01-0.07day(-1), respectively. The dispersant Corexit enhanced degradation of n-alkanes but not of PAHs. Compared to biodegradation, photooxidation increased transformation of 4-5 ring PAHs by 70% and 3-4 ring alkylated PAHs by 36%. For the first time we observed that sunlight inhibited biodegradation of pristane and phytane, possibly due to inhibition of the bacteria that can degrade branched-alkanes. This study provides quantitative measures of oil degradation under relevant field conditions crucial for understanding and modeling the fate of spilled oil in the northern Gulf of Mexico.

Highly efficient exciplex formation via radical ion pair recombination in X-irradiated alkane solutions for luminophores with short fluorescence lifetimes.

X-irradiation of alkane solutions of N,N-dimethylaniline with various organic luminophores produces characteristic emission bands ascribed to the corresponding exciplexes. In contrast to optical generation, which requires diffusion-controlled quenching of excited states, an additional channel of exciplex formation via irreversible recombination of radical ion pairs is operative here, which produces exciplexes in solution with high efficiency even for p-terphenyl and diphenylacetylene having fluorescence decay times of 0.95 ns and 8 ps, respectively. The exciplex emission band is sensitive to an external magnetic field and exerts a very large observed magnetic field effect of up to 20%, the maximum possible value under the conditions of the described experiment.

Structural, energetic, and UV-Vis spectral analysis of UVA filter 4-tert-butyl-4'-methoxydibenzoylmethane.

The growing awareness of the harmful effects of ultraviolet (UV) solar radiation has increased the production and consumption of sunscreen products, which contain organic and inorganic molecules named UV filters that absorb, reflect, or scatter UV radiation, thus minimizing negative human health effects. 4-tert-Butyl-4'-methoxydibenzoylmethane (BMDBM) is one of the few organic UVA filters and the most commonly used. BMDBM exists in sunscreens in the enol form which absorbs strongly in the UVA range. However, under sunlight irradiation tautomerization occurs to the keto form, resulting in the loss of UV protection. In this study we have performed quantum chemical calculations to study the excited-state molecular structure and excitation spectra of the enol and keto tautomers of BMDBM. This knowledge is of the utmost importance as the starting point for studies aiming at the understanding of its activity when applied on human skin and also its fate once released into the aquatic environment. The efficiency of excitation transitions was rationalized based on the concept of molecular orbital superposition. The loss of UV protection was attributed to the enol → keto phototautomerism and subsequent photodegradation. Although this process is not energetically favorable in the singlet bright state, photodegradation is possible because of intersystem crossing to the first two triplet states.

Microencapsulation of a cyclodextrin complex of the UV filter, butyl methoxydibenzoylmethane: in vivo skin penetration studies.

Lipid microparticles loaded with the complex between hydroxypropyl-ß-cyclodextrin (HP-ß-CD) and the sunscreen agent, butyl methoxydibenzoylmethane (BMDBM) were evaluated for their effect on the UV filter percutaneous penetration. The microparticles were prepared by the melt emulsification technique using tristearin as lipidic material and hydrogenate phosphatidylcholine as the surfactant. Human skin penetration was investigated in vivo by the tape stripping technique, a minimal invasive procedure based on the progressive removal of the upper cutaneous layers (stratum corneum) with adhesive tape strips. The amount of sunscreen fixed to each strip was determined by HPLC after solvent extraction. The recovery of the UV filter from spiked adhesive tapes was >94.4% and the precision of the method was better than 7.6% relative standard deviation. Non-encapsulated BMDBM, its complex with HP-ß-CD, the lipid microparticles loaded with the sunscreen alone or the BMDBM/HP-ß-CD complex were introduced into oil-in-water emulsions and applied to human volunteers. Compared to the cream with the non-encapsulated sunscreen agent (percentage of the applied dose penetrated, 9.7%±2.5), the amount of BMDBM diffusing into the stratum corneum was increased by the formulations containing the BMDBM/HP-ß-CD complex (17.1%±3.2 of the applied dose) or the microparticles loaded with BMDBM only (15.1%±2.7 of the applied dose). On the contrary, a significant decrease in the level of UV filter penetrated into the stratum corneum was achieved by the cream containing the microencapsulated BMDBM/HP-ß-CD complex (percentage of the applied dose penetrated, 6.0%±1.5). The reduced BMDBM percutaneous penetration attained by the latter system should enhance the UV filter efficacy and limit potential toxicological risks.

Synthesis and NMR elucidation of novel pentacycloundecane-based peptides.

The synthesis and NMR elucidation of two novel pentacycloundecane (PCU)-based peptides are reported. The PCU cage amino acids were synthesised as racemates and the incorporation of the cage amino acid with (S)-natural amino acids produced diastereomeric peptides. The diastereomeric 'cage' peptides were separated using preparative HPLC and the NMR elucidation of these PCU containing peptides are reported for the first time. The (1)H and (13)C NMR spectra showed series of overlapping signals of the cage skeleton and that of the peptide, making it extremely difficult to resolve the structure using one-dimensional NMR techniques only. The use of two-dimensional NMR techniques proved to be a highly effective tool in overcoming this problem.

Photoactivation of alkyl C-H and silanization: a simple and general route to prepare high-density primary amines on inert polymer surfaces for protein immobilization.

Surface modification through implanting functional groups has been demonstrated to be extremely important to biomedical applications. The usage of organic polymer phase is often required to achieve satisfactory results. However, organic surfaces usually have poor chemical reactivity toward other reactants and target biomolecules because these surfaces usually only consist of simple alkyl (C-H) and/or alkyl ether (ROR') structures. For the first time, we here report the potential to perform silanization techniques on alkyl polymer surface, which provide a simple, fast, inexpensive, and general method to decorate versatile functional groups at the molecular level. As an example, high-density primary amines could be obtained on a model polymer, polypropylene substrate, through the reaction between amine-capped silane, 3-aminopropyltriethoxysilane (APTES) and hydroxylated polypropylene surface. A model protein, immunoglobulin (IgG), could be effectively immobilized on the surface after transforming amines to aldehydes by the aldehyde-amine condensation reaction between glutaraldehyde (GA) and amines. The routes we report here could directly make use of the benefits from well-developed silane chemistry, and hereby are capable of grafting any functionalities on inert alkyl surfaces via changing the terminal groups in silanes, which should instantly stimulate the development of many realms such as microarrays, immunoassays, biosensors, filtrations, and microseparation.

Co-loading of a photostabilizer with the sunscreen agent, butyl methoxydibenzoylmethane in solid lipid microparticles.

The sunscreen agent, butyl methoxydibenzoylmethane (BMDBM), one of the most widely used UV-A filter, undergoes decomposition under sunlight exposure, which is a limiting factor on its overall performance. To reduce the sunscreen photodegradation, this study investigates the incorporation into solid lipid microparticles (SLMs) of BMDBM together with the photostabilizer, 4-methylbenzylidene camphor (MBC). The microparticles were produced by the melt dispersion technique using various lipid materials (tristearin, glyceryl behenate, and stearic acid) and hydrogenated phosphatidylcholine as the surfactant. The highest retention capacity for BMDBM and MBC was achieved with tristearin microparticles. These SLMs were characterized by scanning electron microscopy and powder X-ray diffraction analyses. The BMDBM and MBC loading was 10.4 and 10.1%, respectively. The efficacy of the SLMs was evaluated after their introduction in a conventional cream (oil-in-water emulsion). The light-induced decomposition of BMDBM was decreased by encapsulation into the SLMs (the extent of degradation was 33.8 +/- 5.5% for unencapsulated BMDBM/MBC and 25.3 +/- 4.2% for BMDBM-loaded microparticles in conjunction with free MBC). Moreover, the co-loading of the MBC stabilizer in the SLMs produced a further reduction of the photodegradation of the UV-A filter (the BMDBM loss was 16.9 +/- 5.9%) compared with the microparticles containing BMDBM without MBC. Therefore, incorporation in lipid microparticles of BMDBM together with the MBC photostabilizer is more effective in enhancing the UV-A filter photostability than the SLMs loaded with BMDBM alone.

Hydrocarbon oxidation catalyzed by vanadium polyoxometalate supported on mesoporous MCM-41 under ultrasonic irradiation.

Vanadium polyoxometalate (PVMo) supported on mesoporous MCM-41, MCM-41-NH(2), as efficient and heterogeneous catalysts, with large surface area, for hydrocarbon oxidation with hydrogen peroxide is reported. Oxidation of the alkenes and alkanes gave product selectivities, which are similar to those observed for corresponding homogeneous catalyst. PVMo-MCM was prepared by introduction of PVMo into the mesoporous molecule sieves of MCM-41 by impregnation and adsorption techniques. The samples were characterized by X-ray diffraction (XRD), thermal gravimetric-differential thermal analysis (TG-DTA), FT-IR, scanning electron microscopy (SEM), UV-Vis and cyclic voltametry (CV). Ultrasonic irradiation has a particular effect on MCM-41 structural uniformity and reduced the reaction times and improved the product yields. In addition, the solid catalysts could be recovered and reused several times without loss of its activity.

Forming microstructured alkanethiol self-assembled monolayers on gold by laser ablation.

A process to form microstructured alkanethiol self-assembled monolayers (SAMs) on gold is described. It is well known that alkanethiols spontaneously form homogenous SAMs on gold surfaces. By means of laser ablation, the exposed areas of alkanethiol monolayers can be removed from the gold surface. Free gold is obtained which can react further with second and third thiols. By this technique, structured alkanethiol SAMs are obtained reliably and easily. In a rather narrow window of pulse intensities, in our example 120 MW/cm2 +/- 10% from a frequency-doubled Nd: YVO4 laser with 6-ns pulsewidth operating at a repetition rate of 20 kHz, ablation of alkanethiol monolayers is obtained without causing any damage to the gold substrate. Examples are presented where lines down to 10 microm in width were laser ablated into an SAM formed either from a hydrophilic or a hydrophobic alkanethiol and filled with a monolayer of a second alkanethiol of opposite hydrophilicity. The patterned structures were examined by optical and fluorescence microscopy as well as by lateral force microscopy. The presented method enables the preparation of microstructured SAMs on gold and probably on a wide variety of other substrates.

Encapsulation in lipospheres of the complex between butyl methoxydibenzoylmethane and hydroxypropyl-beta-cyclodextrin.

The aim of this study was to investigate the incorporation into lipospheres of the complex between hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and the sunscreen agent, butyl methoxydibenzoylmethane (BMDBM) and to examine the influence of this system on the sunscreen photostability. The formation of the inclusion complex was confirmed by thermal analysis and powder X-ray diffraction. Lipid microparticles loaded with free BMDBM or its complex with HP-beta-CD were prepared using tristearin as the lipid material and hydrogenated phosphatidylcholine as the emulsifier. The obtained lipospheres were characterized by scanning electron microscopy and differential scanning calorimetry. The microparticle size (15-40 microm) was not affected by the presence of the complex. Release of BMDBM from the lipospheres was lower when it was incorporated as inclusion complex rather than as free molecule. Unencapsulated BMDBM, its complex with HP-beta-CD, the sunscreen-loaded lipospheres or the lipoparticles containing the BMDBM/HP-beta-CD complex, were introduced into a model cream (oil-in-water emulsion) and irradiated with a solar simulator. The photodegradation studies showed that all the examined systems achieved a significant reduction of the light-induced decomposition of the free sunscreen agent (the BMDBM loss decreased from 28.9 to 17.3-15.2%). However, photolysis experiments performed during 3 months storage of the formulations, demonstrated that the photoprotective properties of the HP-beta-CD complex and of BMDBM alone-loaded lipospheres decreased over time, whereas the microencapsulated HP-beta-CD/BMDBM complex retained its photostabilization efficacy. Therefore, incorporation in lipid microparticles of BMDBM in the cyclodextrin complex form is more effective in enhancing the sunscreen photostability than the complex alone or the liposphere-entrapped free BMDBM.

Photopolymerization of developmental monomers for dental cationically initiated matrix resins.

OBJECTIVES: The objectives were to investigate the structure and selected physical properties of products resulting from the photopolymerization of a binary mixture containing an aliphatic dioxirane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ECHM-ECHC) and a potential expanding monomer, 3,9-bis(oxiranylcyclohexylmethyl)-1,5,7,11-tetraoxaspiro[5.5]undecane (BOCHM-TOSU). METHODS: Reaction mixtures were irradiated with a dental curing lamp at room temperature. Some reactions were quenched prior to gel point. Oligomeric products were separated from unreacted monomers by column chromatography, and analyzed by NMR. Physical properties of polymeric solids were measured using accepted standard methods. Protonation energies for monomers were calculated using semi-empirical quantum mechanical methods. RESULTS: Types of oligomers found included poly(ether)s and poly(carbonate)s. Quantum mechanical calculations indicated preferential attack at the more nucleophilic oxaspirocyclic ring sites. For cured solid polymer samples, the elastic modulus was 2.39 +/- 0.24 GPa and the fracture toughness was 0.73 +/- 0.10 MPa m(1/2). These values were similar to those measured for a cured conventional BISGMA/TEGDMA matrix resin. SIGNIFICANCE: The room-temperature photopolymerization of an aliphatic dioxirane and a potential expanding monomer demonstrates the possibility of making cross-linked copolymer resins with improved polymerization shrinkage characteristics for use in dental composites.

Control of photoreaction of amphiphilic spiropyran/n-alkane Langmuir and Langmuir-Blodgett films using the phase transition of n-alkane.

The structures and photoreactions of Langmuir and Langmuir-Blodgett (LB) films of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-1'-octadecyl-8-(docosanoyloxymethyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP), mixed with n-alkane are investigated. The mixing ratio was fixed at 1/2 for SP/n-alkane. The surface pressure-area isotherms of SP/octadecane are categorized into two regimes: a low-temperature regime where octadecane is packed with the alkyl chains of SP, and a high-temperature regime where the addition of octadecane does not influence the isotherms significantly. The temperature dividing the two regimes is related with the melting point of the n-alkane mixed with SP in the bulk. UV irradiation of the Langmuir film in the high-temperature regime gives rise to light-induced J-aggregation, whereas that in the low-temperature regime causes only the isomerization of SP to the corresponding merocyanine, indicating that J-aggregation is hindered by the presence of n-alkane in the low-temperature regime. IR external reflection spectroscopy of the Langmuir films shows that n-alkane is released from the film during J-aggregation. The structural changes of the mixed Langmuir and LB films during J-aggregation are almost the same with those of the films of pure SP.

W values of protons in alkane-based TE gases and dimethylether in the energy range 1-100 keV: measurements and additivity models.

W values of tissue-equivalent gases based on propane and butane were measured for protons in the energy range 1-100 keV and compared with those of dimethylether and water vapour. The experimental values of the tissue-equivalent gas mixtures were compared with data calculated from the W values of the mixture components using five existing additivity models and two new models derived within the scope of the present work. Apart from one model--the simplest one--all models show a good agreement with the experimental data.

Selectivity and efficiency of pyrene attachment to alkanes induced by broadband X-rays.

Bombardment of pyrene-doped n-heneicosane (C21H44) in its orthorhombic solid phase with <1.3> MeV broadband X-rays results in the formation of both mono- and di-heneicosylpyrenes, whereas the same dose in liquid cyclohexane yields only monosubstituted pyrene. In both cases, the reaction efficiency decreases as pyrene concentration is increased from 10-5 to 10-2 M. Qualitatively, the overall attachment efficiency is higher in orthorhombic n-heneicosane than in liquid cyclohexane, but the selectivity of attachment is greater in cyclohexane. Differences between these results and those from irradiations of the same samples with eV range photons are discussed.

Influence of hydroxypropyl-beta-cyclodextrin on photo-induced free radical production by the sunscreen agent, butyl-methoxydibenzoylmethane.

The aim of the study was to investigate the effect of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on the photo-induced production of free radicals by the sunscreen agent, butyl-methoxydibenzoylmethane (BMDBM). Spin-trapping/electron paramagnetic resonance spectroscopy was used to evaluate the formation of radicals and the extent of BMDBM photodegradation was measured by high-performance liquid chromatography. The stable 2,2,6,6-tetramethylpiperidine-1-oxyl, nitroxide radical (TEMPO) was used as spin-trap. Any free radicals generated during irradiation of the sunscreen agent will couple with the TEMPO radicals giving diamagnetic species and thus a decrease of the signal intensity in the electron paramagnetic resonance spectrum. Following 2-h illumination with simulated sunlight, the solution containing free BMDBM exhibited a 93.9% decrease of the intensity of the TEMPO signal. Under the same irradiation conditions, only a 12.2% reduction of the TEMPO concentration was measured in the sample containing BMDBM complexed with HP-beta-CD. Moreover, the decrease of the spin-trap level observed for the HP-beta-CD/BMDBM complex was not significantly different from that produced when solutions containing TEMPO only or TEMPO in the presence of HP-beta-CD alone were subjected to irradiation. In addition, the photodegradation of the sunscreen agent was reduced by complexation with HP-beta-CD (the extent of degradation was 27.6% for the complex compared with 63.1% for free BMDBM). The results obtained indicate that the free radicals generated by BMDBM when exposed to simulated sunlight are effectively scavenged by inclusion complexation of the sunscreen agent with HP-beta-CD.

The linear energy transfer dependence of excited singlet-state lifetimes of hydrocarbon liquids exposed to X rays.

The absorption of X rays in liquids provides low-energy electrons in the energy range 2 to 20 keV when synchrotron radiation is used as the X ray source. Such low-energy electrons have short ranges and produce a dense track of ionization where dE/dx = 10(7) to 10(8) eV/cm. Fluorescent molecules provide a sensitive probe of the early-time structure of such tracks. From the extent of quenching of excited states and the consequent decrease in fluorescence lifetimes, the concentration of free radicals in the track can be inferred. Experiments done with the hydrocarbons cis-decalin and dodecane demonstrate this effect. In both hydrocarbons, the lifetimes (tau) are significantly smaller with excitation by X rays than with UV radiation, and tau-1 increases linearly with dE/dx.

Determination of the stopping cross-sections of N2, H2, CH4, C4H10 and C3H6 using alpha particles in the range 1 . 3--4 . 2 MeV.

The stopping cross-sections of N2, H2, CH4, C4H10 and C3H6 have been measured using natural alpha particles from a 238Pu source, with facilities to vary the energy in the range 1.3--4.2 MeV. The work is the extension of measurements made earlier, using C2H4 as the absorber, which showed discrepancies in comparison with results of other authors. The comparison is continued with the results presented here and brief comments made on the degree of agreement obtained.