Sequential UV Research Articles

Preparation and Characterization of Poly(N‐isopropylacrylamide)‐modified Poly(2‐hydroxyethyl acrylate) Hydrogels by Interpenetrating Polymer Networks for Sustained Drug Release

In order to investigate the influence of hydrophobic moieties formed by poly(N-isopropylacrylamide) (PNIPAm) in a hydrogel matrix on the release behavior of the hydrogel, a series of poly(N-isopropylacrylamide) (PNIPAm)-modified poly(2-hydroxyethyl acrylate-co-2-hydroxyethyl 2-hydroxyethyl methacrylate) (P(HEA-co-HEMA)) via interpenetrating polymer networks (IPNs) were prepared by a sequential UV solution polymerization. Interestingly, it was found that P(HEA-co-HEMA)/PNIPAm IPN indicated a single glass transition temperature (T(g)) and the T(g)s of the IPNs increased with an increase in the PNIPAm component. This phenomenon may be attributed to hydrogen bonding between the two polymer networks, but the hydrogen bonding exerts less influence on the swelling behavior of the IPNs, due to the fact that IPNs can respond to changes in temperature like PNIPAm. Using 2-[(diphenylmethyl)sulphiny]acetamide (modafinil, MOD) and p-hydroxybenzoic acid (HBA) as model drug compounds, the release behavior of the IPNs was studied at body temperature, and it was found that the presence of PNIPAm could retard drug release regardless of the solubility of the drugs. Release profiles of HBA from the IPNs and their component samples as a function of time at 37 degrees C.

Optical pH Measurements with Water Dispersion of Polyaniline Nanoparticles and Their Redox Sensitivity

A new method for optical pH and redox measurements with a commercially available water dispersion of polyaniline (PANI) nanoparticles (mean particle size, 46 nm) is presented. The pH measurements are based on the acid-base equilibrium of PANI and were carried out either by combining both the automated sequential injection analysis (SIA) and UV-visible spectrophotometric techniques or with a fiber-optic light guide. In the former case, the detection was done in continuous mode at lambda = 800 nm by using the SIA technique for transporting the sample to a flow-through cell, which was placed in the light path of the photometer. With the fiber-optic light guide, the detection was done in batch mode at lambda = 400 and 580 nm. In both methods, fresh pH reagent (PANI) solution was used in each measurement, thus overcoming the problem with hysteresis (memory effect), which is usually observed with PANI films. The PANI nanoparticles were characterized with UV-visible spectroscopy in pH buffer solutions between pH 2-12 and a protonation constant of logK(0.5H,L)(H(0.5)L) = 4.4 was calculated from these data. Fast pH measurements can be done between pH 6 and 10.5 depending on the measuring technique. It is possible to determine pH with an accuracy of 0.1 pH unit between pH 8 and 10.5 (RSD, 0.5-2%). Redox transitions typical for PANI films were also observed for water solutions of PANI nanoparticles in the presence of the hexacyanoferrate(II/III) and the iron(II/III) oxalate redox couples. The absorbance at lambda = 875 nm is linearly dependent on the logarithm of the concentration ratio (0.1-10) of the iron oxalate redox couple.

Sequential UV–biological degradation of chlorophenols

The sequential UV–biological degradation of a mixture of 4-chlorophenol (CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP), and pentachlorophenol (PCP) was first tested with each pollutant supplied at an initial concentration of 50 mg l −1. Under these conditions, the chlorophenols were photodegraded in the following order of removal rate: PCP > TCP > DCP > CP with only CP and DCP remaining after 40 h of irradiation. The remaining CP (41 mg l −1) and DCP (13 mg l −1) were then completely removed by biological treatment with an activated sludge mixed culture. Biodegradation did not occur in similar tests conducted with a non-irradiated mixture due to the high microbial toxicity of the solution. UV treatment lead to a significant reduction of the phytotoxicity to Lipedium sativum but no further reduction of phytotoxicity was observed after biological treatment. Evidence was found that the pollutants were partially photodegraded into toxic and non-biodegradable products. When the pollutants were tested individually (initial concentration of 50 mg l −1), PCP, TCP, DCP, 4-CP were photodegraded according to first order kinetic model ( r 2 > 99) with half-lives of 2.2, 3.3, 5.7, and 54 h, respectively. The photoproducts were subsequently biodegraded. This study illustrates the potential of UV as pre-treatment for biological treatment in order to remove toxicity and enhance the biodegradability of organic contaminants. However, it also shows that UV treatment must be carefully optimized to avoid the formation of toxic and/or recalcitrant photoproducts and results from studies conducted on single contaminants cannot be extrapolated to mixtures.

Sequential UV–biological degradation of polycyclic aromatic hydrocarbons in two-phases partitioning bioreactors

A method based on UV-irradiation in organic solvent followed by transfer of the remaining pollutants into silicone oil for subsequent biodegradation in a biphasic system inoculated with a phenanthrene degrading Pseudomonas sp. was tested for the treatment of various mixtures of PAHs. Acetone was first selected as the most suitable solvent compared to methanol, acetonitrile and silicone oil for the removal of pyrene and phenanthrene. The sequential treatment was then applied to the treatment of a mixture of fluorene, phenanthrene, anthracene, fluoranthrene, pyrene, benzo( a)anthracene and benzo( a)pyrene in acetone. These compounds were photodegraded in the following order of initial removal rates (mg l −1 d −1): benzo( a)pyrene (7.8) > anthracene (5.0) > benzo( a)anthracene (2.5) > fluoranthrene (1.8) > pyrene (1.5) > phenanthrene (1.2) > fluorene (0.2). UV-treatment allowed complete removal of, anthracene, benzo( a)anthracene and benzo( a)pyrene and removals of 63% of pyrene and 37% of fluorene after 434 h or irradiation. The subsequent biological treatment removed the remaining phenanthrene and fluorene by 100% and 90%, respectively, after 790 h of cultivation. Although less efficient due to the presence of interfering compounds, the UV–biological treatment of a soil extract allowed a 63% removal of the seven PAHs named above. Microbial growth did not occur when the pollutants were directly supplied to the microorganism showing that biphasic systems reduced the toxicity effects cause by mixtures of PAHs at high concentrations. This study demonstrates the potential of selective UV treatment of high molecular weight PAHs followed by biological treatment of the low molecular weight species in biphasic systems.

IR induced cis↔trans isomerization of 2-naphthol: Catalytic role of hydrogen-bond in the photoinduced isomerization

An infrared laser induced cis↔trans isomerization has been investigated for 2-naphthol and its hydrogen(H)-bonded cluster with NH3 in the S1 electronic state by UV–IR double resonance excitation in a supersonic jet. A specific isomer was pumped to a X–H (X=O, C or N) stretching vibration in S1 by a sequential UV–IR two-photon excitation, and the resultant product species were analyzed by dispersing their fluorescence. It was found that the IR excitation induces the isomerization for the H-bonded cluster with the excitation less than 3000 cm−1, while no isomerization was found to occur for bare 2NpOH even with an input energy of 3610 cm−1. The substantial reduction of the isomerization barrier height represents evidence of the catalytic nature of H-bonding in the conformational isomerization. It was also found that the isomerization efficiency is very high at low IR frequency and exhibits a marked IR frequency dependence.

Dye-sensitized Solar Cell Fabricated by Electrostatic Layer-by-Layer Assembly of Amphoteric TiO2 Nanoparticles

Nanocrystalline TiO2 amphoteric colloidal charged particles and polyelectrolytes have been used to fabricate a dye-sensitized solar cell. Two weak polyelectrolytes, poly(allylamine hydrochloride) and poly(acrylic acid), and two strong polyelectrolytes, poly(dimethyldiallylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate), have been utilized to assemble polyion/TiO2 nanocomposite multilayered films by the electrostatic layer-by-layer deposition technique. The layer-by-layer assembly of the TiO2 nanoparticles proceeds linearly as shown by sequential UV−vis absorption and thickness measurements. The morphology of these assemblies was characterized using atomic force microscopy. The nanoporous polyion/TiO2 films were sintered and used as working electrodes for cis-di(thiocyanato)-N,N-bis(2,2‘-bipyridyldicarboxylate)-ruthenium(II) (N3) sensitized solar cells. I−V characteristics of the solar cells made by the calcinated polyelectrolyte/TiO2 electrodes show several interesting results. (i) The short-circuit current does not linearly increase with the thickness of the TiO2 electrode, even though the adsorption behavior of the N3 dye shows a linear increase. (ii) The precursor polyelectrolytes used to assemble TiO2 play a major role in the photovoltaic performance of the solar cells. Thermogravimetric analysis studies show that the thermal stability of the polyelectrolytes may have a direct effect on the overall device efficiency. (iii) The photovoltaic performance of these solar cells is comparable to that of cells made by other methods such as spin casting, the layer-by-layer technique offers unsurpassed control in manipulating the final device thickness. An efficiency of 7.2% was obtained for the solar cell made from PDAC/TiO2 (200 bilayers) precursor film, under 1 sun at simulated Air Mass 1.5 direct irradiation.

Sequential injection analysis for benzophenone-4 and phenylbenzimidazole sulphonic acid in sunscreen sprays by solid-phase extraction coupled with ultraviolet spectrometry

A sequential injection UV method was developed to determine benzophenone-4 (BZ4) and phenylbenzimidazole sulphonic acid (PBS) simultaneously, these being the most commonly used UV-filters in aqueous formulations used as sunscreen sprays. The selective elution of both was performed by on-line solid-phase extraction, by retention on a SAX microcolumn and separation by varying the pH of elution. The sensitivity obtained was 0.042±0.001 ml μg −1 for PBS and 0.0159±0.0003 ml μg −1 for BZ4. The limit of detection was 1.6 μg ml −1 for PBS and 0.6 μg ml −1 for BZ4. The R.S.D. of the results was 1–6% for PBS and 1–12% for BZ4. The method was validated using commercial sunscreen formulations with concentrations determined by a liquid chromatographic procedure. The two procedures gave comparable results. Automation of the method means the amount of reagents used and residues generated are decreased. The system allows the required analysis sequence to be programmed using suitable software.

Slow Surface Charge Trapping Kinetics on Irradiated TiO2

Free and trapped charge carriers in polycrystalline TiO2 following band gap irradiation are characterized by diffuse reflectance IR spectroscopy (DRIFTS). A spectrum-wide absorption signal proportional to λ1.7 (λ = wavelength/μm) indicates the presence of free conduction band electrons coupled with acoustic phonons in the lattice. Free electrons appear to decay according to saturation kinetics. The fitted parameters indicate a limited number of trapping states. The concentration of these states appears to be diminished by sequential UV treatments. The free carrier decay lifetime is lengthened as the samples are dehydrated, which suggests an excited-state relaxation event during electron trapping. Photogenerated free electrons are comparable to conduction band electrons injected from surface-bound chromophores, and the lifetime of these electrons can be extended across several orders of magnitude. A broad IR absorption peak centered at 3380 cm-1 is attributed to an electronic transition from an occupied su...

Morphology of poly(methacrylic acid)/poly(N-isopropyl acrylamide) interpenetrating polymeric networks

The morphology of interpenetrating polymeric networks (IPNs) composed of the temperature-sensitive poly(N-isopropyl acrylamide) (PNIPAAm) and the pH-sensitive poly(methacrylic acid) (PMAA) were investigated by scanning electron microscopy (SEM). The IPN hydrogels were prepared by a sequential UV polymerization method. SEM studies were conducted on IPN hydrogel samples dried by different methods, and the influence on the IPN structure was discussed. The environmental conditions induced morphological changes for these dual sensitive IPN hydrogels which were studied by cryogenic SEM, when the gels were analyzed in their wet state. The results showed that the porous size in the IPN was strongly influenced by the environmental pH and temperature. Decrease in pH and increase in temperature resulted in significant pore size decrease for the swollen IPNs hydrogels.

Self-assembly ultrathin films based on dendrimers

A photosensitive ultrathin film with G1.5 PAMAM dendrimers (carboxylate salts) as polyanions and NDR (nitro-containing diazoresin) as polycations was fabricated via sequential deposition and subsequent UV irradiation which causes the linkage between the layers to change from ionic to covalent.

Synthesis and Characterization of pH- and Temperature-Sensitive Poly(methacrylic acid)/Poly(N-isopropylacrylamide) Interpenetrating Polymeric Networks

Hydrogels of an interpenetrating polymeric network (IPN) composed of the temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) and the pH-sensitive poly(methacrylic acid) (PMAA) were prepared by a sequential UV polymerization method. The IPN hydrogels were characterized for their temperature- and pH-responsive behavior by equilibrium swelling studies, oscillatory swelling studies, and differential scanning calorimetry. The permeability of these IPNs has been investigated under various pH and temperature conditions. The results showed that these hydrogels exhibited a combined pH- and temperature-sensitivity at a temperature range of 31−32 °C and a pH value of approximately 5.5. Permeation study results indicate a significant size exclusion behavior while model drugs with different sizes permeate through the IPN membranes. The permeability of the IPN membrane can be significantly affected by varying the pH and temperature conditions.

Photo-induced graft polymerization surface modifications for the preparation of hydrophilic and low-proten-adsorbing ultrafiltration membranes

Heterogeneous surface modifications of PAN UF membranes with either simultaneous or sequential UV irradiation-initiated graft polymerizations of monomers from water solutions were studied. Previous coating with a photo-initiator (benzophenone, BP) and saturation of the monomer solutions with BP mainly promoted simultaneous graft polymerization onto the membrane surface. Photo-induced formation and thermal decomposition of peroxides were assayed with the DPPH assay and then used for sequential grafting. For both approaches, and with acrylic acid, 2-hydroxyethyl methacrylate and various poly(ethylene glycol) methacrylates (PEG-MA's and MePEG-MA's) the impact of photo-initiation as well as monomer type and concentration was described. The polymerization conditions could be used as means to adjust the total degree of graft polymerization (DG) and the graft polymer chain length. Modified membranes were characterized with FTIR-ATR spectroscopy and contact angle measurements; the main conclusion was that even at high DG (1–2 mg/cm 2) the modified layer on the outer surface was thin (< 1 μm) and the modification extended into the active layer pores of the membranes. Membrane permeabilities diminished systematically with increasing graft polymer mass. For UF membranes with sufficient degree of modification (DG > 400 μg/cm 2) reduced contact angles, very little protein adsorption and almost no fouling due to BSA adsorption were observed. Results of UF experiments with γ-globulins. BSA and cytochrome C, applied as single and mixed protein solutions, suggested that with PAN-g-MePEG200MA, in contrast to the unmodified PAN UF membranes, protein/protein UF separations may become feasible because protein/polymer surface interactions are diminished.

Supramolecular hydrogen-bonded liquid-crystalline polymer complexes. Design of side-chain polymers and a host-guest system by noncovalent interaction

Supramolecular liquid–crystalline polymeric complexes based on a backbone that contains vinyl pyridine units and azobenzene or biphenyl derivatives that posses alkyl chains terminated by carboxylic acid have been obtained by the formation of intermolecular hydrogen bonds between the carboxylic acid and the pyridyl moieties. The polymeric complexes behave as side-chain liquid–crystalline polymers and exhibit smectic phases. A new type of H-bonded host-guest liquid–crystalline system is also reported. The liquid–crystalline host copolymers contain both mesogenic acrylate and 4-vinylpyridine units. The guest molecule is an azobenzene that has a carboxylic acid moiety at one of its extremities. The H-bonded polymeric host–guest complexes exhibit nematic phases. Sequential UV and visible light irradiation of the polymeric complex causes reversible photochemically induced phase transitions. The isothermal nematic–isotropic and isotropic–nematic transitions result from the trans-cis and cis-trans photoisomerization of the guest azobenzene in the host–guest system. © 1996 John Wiley & Sons, Inc.

Supramolecular hydrogen‐bonded liquid–crystalline polymer complexes. Design of side‐chain polymers and a host–guest system by noncovalent interaction

Supramolecular liquid–crystalline polymeric complexes based on a backbone that contains vinyl pyridine units and azobenzene or biphenyl derivatives that posses alkyl chains terminated by carboxylic acid have been obtained by the formation of intermolecular hydrogen bonds between the carboxylic acid and the pyridyl moieties. The polymeric complexes behave as side-chain liquid–crystalline polymers and exhibit smectic phases. A new type of H-bonded host-guest liquid–crystalline system is also reported. The liquid–crystalline host copolymers contain both mesogenic acrylate and 4-vinylpyridine units. The guest molecule is an azobenzene that has a carboxylic acid moiety at one of its extremities. The H-bonded polymeric host–guest complexes exhibit nematic phases. Sequential UV and visible light irradiation of the polymeric complex causes reversible photochemically induced phase transitions. The isothermal nematic–isotropic and isotropic–nematic transitions result from the trans-cis and cis-trans photoisomerization of the guest azobenzene in the host–guest system. © 1996 John Wiley & Sons, Inc.

Ion chromatography of inorganic anions on a dynamically modified polystyrene—divinylbenzene packing material and its application to anion screening by sequential ultraviolet absorbance and electrochemical detection

Two isocratic eluent systems suitable for the high-performance liquid chromatography of inorganic anions on a polystyrene—divinyl benzene packing material are described. When used in conjunction with sequential UV and electrochemical detectors the systems permit a wide variety of inorganic anions to be characterised and quantitated. The separation systems have significant stability advantages over those based on silica packing materials. Some insight into the separation mechanism is provided by the comparison of the chromatographic behaviour of phenols, aromatic acids and inorganic anions.

Quantitative determination of vitamin E and oxidized and reduced coenzyme Q by high-performance liquid chromatography with in-line ultraviolet and electrochemical detection

We describe a sensitive quantitative high-performance liquid chromatographic (HPLC) assay for the simultaneous determination of vitamin E isomers (α, γ- and δ-tocopherol) oxidized coenzyme Q species (ubiquinone 9, ubiquinone 10) and reduced coenzyme Q homologues (ubiquinol 9, ubiquinol 10) in various tissues, including blood and plasma. The compounds of interest are quantitatively extracted with a fast one-step lipid extraction procedure and subjected to HPLC without further purification. The extract is separated on a reversed-phase column and the eluted compounds are monitored by sequential UV and electrochemical detection. Ubiquinones are detected at their 275 nm absorbance maximum, by the UV detector, whereas tocopherols and ubiquinols are monitored by the electrochemical detector with high sensitivity and selectivity. The method can detect as little as 1 pmol of the individual ubiquinones. Detection limits for tocopherols and ubiquinols are at least two orders of magnitude lower.

An Analytical Approach to Metabolic Profiling of Aromatic Compounds Using Liquid Chromatography

Abstract An analytical approach to metabolic profiling of aromatic compounds is described for both conjugated and “free” metabolites in biological systems. Initially, an ethyl acetate extraction removes the less polar metabolites. A salting-out procedure using Sephadex G-10 is combined with reverse-phase high-performance liquid chromatography (HPLC) to analyze the water-soluble conjugates directly using sequential uv and fluorescence detection. The “free” metabolites are also derived from individual conjugate peaks by enzymatic or hydrolytic procedures and then re-chromatographed by HPLC. Metabolites in the ethyl acetate fraction are similarly analyzed by reverse-phase HPLC. The utility of this method is demonstrated for 2-acetylaminofluorene (2-AAF and 4-ethylsulfonyl-naphthalene-1-sulfonamide (ENS), two compounds of interest in the study of murine bladder carcinogenesis.