Photochemical Procedure Research Articles

Photochemical Induced Fluorescence for the Determination of Prednisolone and Triamcinolone

In the present work, a photochemical derivatization procedure to induce fluorescence from two synthetic glucocorticoids (triamcinolone acetonide and prednisolone) was developed. The procedure consisted of the exposure of analyte acidic solutions to ultraviolet (UV) radiation (254 and 300 nm) in a photochemical reactor at 65°C. Experimental parameters such as type and concentration of the acid, composition of the solvent system, and sample treatment time in the reactor were found to be critical, and, therefore, they were carefully optimized. The intensity of the fluorescence (240/350 nm) and the stability of the signal were, appropriated for analytical purposes. Limits of detection (LD) of 5 and 6 µg L−1, respectively, for triamcinolone acetonide and prednisolone were achieved. Linear dynamic range for both analytes extended up to 20 mg L−1. The spectrofluorimetric determination of prednisolone and triamcinolone acetonide was tested by the analysis of different anti‐inflammatory pharmaceutical formulations (tablets, ointment, and veterinary parenteral suspensions). The recoveries achieved were between 95% and 107%. A study to evaluate the effect of potential interferents (polimixine B and benzocaine) on the fluorescence signal of the analytes also has been done.

Crosslinking Photosensitized by a Ruthenium Chelate as a Tool for Labeling and Topographical Studies of G-Protein-Coupled Receptors

The purpose was to apply oxidative crosslinking reactions to the study of recognition and signaling mechanisms associated to G-protein-coupled receptors. Using a ruthenium chelate, Ru(bipy)(3)(2+), as photosensitizer and visible light irradiation, in the presence of ammonium persulfate, we performed fast and efficient covalent labeling of the B(2) bradykinin receptor by agonist or antagonist ligands possessing a radio-iodinated phenol moiety. The chemical and topographical specificities of these crosslinking experiments were investigated. The strategy could also be applied to the covalent labeling of the B(1) bradykinin receptor, the AT(1) angiotensin II receptor, the V(1a) vasopressin receptor and the oxytocin receptor. Interestingly, we demonstrated the possibility to covalently label the AT(1) and B(2) receptors with functionalized ligands. The potential applications of metal-chelate chemistry to receptor structural and signaling studies through intramolecular or intermolecular crosslinking are presented.

Palladium nanoparticles on silicon by photo-reduction using 172 nm excimer UV lamps

We report a photochemical procedure induced by ultraviolet (UV) radiation for the preparation of palladium (Pd) nanoparticles on silicon surface at room temperature. Palladium acetate (Pdac, Pd(OCOCH3)2) was used as the precursorwhich was sprayed-on to the Si and irradiated by UV light at a wavelength of 172nm. Scanning electron microscope (SEM), AFM, XRD, and UV-Vis spectroscopy have been used to characterize the as-prepared nanoparticles. The mechanism of growth of Pd particles and the photo-reduction induced by UV radiation are discussed. The effects of precursor concentration, UV-irradiation time, and annealing conditions on the size and distribution of the palladium nanoparticles on Si are also reported.

Photochemical Synthesis and Properties of Colloidal Copper, Silver and Gold Adsorbed on Quartz

Original methods for the photochemical production of stable copper, silver and gold colloids in the form of films on quartz, and dispersion in liquids were devised. It is shown that photochemical synthesis of colloidal metals is a difficult multiphase process, and includes the formation of low-valence forms of Cu(I), Au(I) and nonmetal clusters, colloidal particles and their agglomerates. Cluster stabilization and further growth to colloidal particles are achieved by adsorption onto the solid surface (quartz) or by increasing the viscosity of photolyte. In the absence of these methods of stabilization, the processes of intermediate reoxidation to Cu(II) and Au(III) and agglomeration of Ag and Au colloids proceed in a photolyte. Adsorption and the rate of cluster growth on a quartz surface are speeded up by the action of monochromatic UV light. Experimental models of the mechanism of colloidal formation are suggested. The dependence of the growth rate and the properties of the colloids on conditions of the photochemical procedure (energy and light intensity, concentration of initial complex) has been established.

An improved photochemical method for the rapid spectrophotometric detection of superoxide dismutase

A sensitive and convenient method is described for estimating superoxide dismutase activity using a photochemical augmentation procedure. This method is applicable to both liquid assays and polyacrylamide gel electropherograms. The flux of superoxide is generated by illuminating a reaction mixture containing dianisidine and riboflavin by either a laser source or light from a fluorescent lamp. The oxidation of dianisidine, as sensitized by riboflavin, is enhanced by superoxide dismutase. The increase is linearly dependent on superoxide dismutase concentration. The photochemical reaction is allowed to proceed uninterrupted for a standardized optimum time and intensity of illumination and then terminated by addition of a buffer, ‘finibuf’, which stabilizes the chromophoric complex formed. This permits the spectrophotometric absorbance measurements of a number of samples collectively and also eliminates the interruption of illumination with the concomitant requirement of a spectrophotometer for constant recording of the absorbance. This method is of utility to both biochemists and clinicians.

Thermal (Iodide) and Photoinduced Electron-Transfer Catalysis in Biaryl Synthesis via Aromatic Arylations with Diazonium Salts

The dediazoniative arylation of various aromatic hydrocarbons (Ar‘H) with diazonium salts (ArN2+) in acetonitrile can be readily effected to biaryls (Ar-Ar‘) in high yields, simply by the addition of small (catalytic) amounts of sodium iodide. [In the absence of Ar‘H, the competitive iodination to ArI is nearly quantitative.] Iodide catalysis of biaryl formation is efficiently mediated by aryl radicals (Ar•) that participate in an efficient homolytic chain process in which ArN2+ acts as a 1-electron oxidant. The complex kinetics of such an electron-transfer chain or ETC process (Scheme 1) is quantitatively verified by computer simulation of the Ar‘H-dependent (a) competition between arylation vs iodination and (b) catalytic efficiency of iodide, using the GEAR algorithms. ETC catalysis also pertains to the alternative photochemical procedure for arylation (in the absence of iodide), in which the deliberate irradiation of the charge-transfer band of the precursor complex [ArN2+, Ar‘H] initiates the same ho...

Preparation of selenoxides from the catalytic autoxidation of organoselenides with nitrogen oxides

Various alkyl, aryl and benzyl selenides (RSeR′) are readily converted in high yields to the corresponding selenoxide in the presence of dioxygen and catalytic amounts of either nitrogen dioxide, nitrosonium cation or nitric oxide in acetic acid. The selenoxides are initially isolated as the acetic acid adducts (from which the free selenoxides are readily liberated by treatment with base). Nitrogen dioxide is also capable of the stoichiometric oxidation of the selenoethers; and the electron donor-acceptor or EDA complex with nitrosonium, i.e.[R2Se·NO+]NO3– is formed as the first intermediate by the selenoether-induced disproportionation of NO2. The critical role of the nitrosonium EDA complex is further demonstrated by the production of selenoxide by an alternative (low-temperature) photochemical procedure involving the deliberate irradiation of the charge-transfer absorption band of [PhSeMe·NO+]NO3–. A scheme is shown that presents the sequence of redox changes of the nitrogen oxides involved in the catalytic conversion of selenoethers to their selenoxides.

Inactivation of viruses by chemically and photochemically generated singlet molecular oxygen

Inactivation of viruses in blood plasma can be achieved by photodynamic procedures using methylene blue (MB) or other photoactive dyes. Singlet molecular oxygen ( 1O 2) probably contributes to the virucidal effects of photosensitization. We report the inactivation of herpes simplex virus type 1 (HSV-1) and suid herpes virus type 1 (SHV-1) by chemically generated singlet oxygen, produced by thermal decomposition of the endoperoxide of 3,3′-(1,4-naphthylidene)dipropionate (NDPO 2). We demonstrate that viruses can be inactivated by 1O 2 generated by chemiexcitation in a reaction in the dark, even in the presence of human plasma. Virus inactivation in phosphate-buffered saline (PBS) was enhanced when water was replaced by deuterium oxide (D 2O) and diminished when human plasma or quenchers (imidazole or histidine) were added. The singlet oxygen quenching activities of plasma, imidazole and histidine correlated with their inhibitory effects on virus inactivation. The production of 1O 2 was assessed by an indicator reaction: the bleaching of p-nitrosodimethylaniline (RNO) with imidazole as 1O 2 acceptor. Virus inactivation and singlet oxygen generation of NDPO 2 were compared with those of MB/light-mediated photosensitization. Based on similar amounts of 1O 2 generated by either procedure, virus inactivation by MB/light was more effective. Virus inactivation by MB/light was not affected by type I quenchers (e.g. mannitol), but was inhibited by human plasma or singlet oxygen quenchers. Furthermore, in D 2O-based PBS, virus inactivation was more effective than that in H 2O. These observations confirm that singlet oxygen is involved in virus inactivation by MB/light. Taken together, the results demonstrate that singlet oxygen produced by either procedure is virucidal. The enhanced effect of the photochemical procedure suggests that, in addition to type II, type I reactions and/or the binding affinity of the dye for the virus contribute to virus killing by MB/light.

Determination of trace amounts of organofluorines in water by photochemical decomposition and ion-selective electrode measurement

A simple and convenient photochemical decomposition procedure was developed for the determination of organoflourine in aqueous solutions. After irradiation, the released fluoride ion is measured with an ion-selective electrode. Any free fluorides present in the solution were determined before irradiation. The method described is suitable for determining ppb levels of fluoride ion in aqueous solutions of organofluorines. A total fluoride determination can be completed within 30–40 min. The relative standard deviation is 0.23%(for five measurements).

Post-PCR sterilization: a method to control carryover contamination for the polymerase chain reaction

We describe a photochemical procedure for the sterilization of polynucleotides that are created by the Polymerase Chain Reaction (PCR). The procedure is based upon the blockage of Taq DNA polymerase when it encounters a photochemically modified base in a polynucleotide strand. We have discovered reagents that can be added to a PCR reaction mixture prior to amplification and tolerate the thermal cycles of PCR, are photoactivated after amplification, and damage a PCR strand in a manner that, should the damaged strand be carried over into a new reaction vessel, prevent it from functioning as a template for the PCR. These reagents, which are isopsoralen derivatives that form cyclobutane adducts with pyrimidine bases, are shown to stop Taq polymerase under conditions appropriate for the PCR process. We show that effective sterilization of PCR products requires the use of these reagents at concentrations that are tailored to the length and sequence of the PCR product and the level of amplification of the PCR protocol.

Polymerizations of Alkenylsilanes Using Early Transition Metal Catalysts

ABSTRACTOxidative coupling of primary alkylsilanes catalyzed by Group IVB metallocene complexes leads predominantly to linear polysilanes, as first reported by Harrod. We have investigated the polymerization of ethylsilane and vinylsilane using dimethyltitanocene in order to determine the suitability of such polymers as precursors to Si-C based ceramics for application as coatings or composite matrices. A photochemical procedure for initiation of polymerization is described. Ethylsilane forms polysilanes (which contain a -Si-Si-Si-Si- backbone) by a step growth mechanism. Vinylsilane shows some Si-Si formation; however, polymerization by several different routes, including formation of polycarbosilanes (which contain a -Si-C-SI-C- backbone) by hydrosilation reactions and crosslinking via metathesis, predominate. The carbosilane polymer has high char yield (60-75%) and appears advantageous for conversion into silicon carbide, as determined by X-ray diffraction.

Electron transfer activation. Hydroperoxide intermediates in a novel and selective procedure for benzylic oxidations

A selective and mild photochemical procedure for benzylic oxidations with 9,10-dicyanoanthracene (DCA), an usual electron acceptor, in the presence of methyl viologen (MV 2+), an electron relay, has been developed. Methyl and methylene groups are oxidized in good to excellent yields to the corresponding hydroperoxides.

ChemInform Abstract: Reactions of Partially Acylated Aldohexopyranosides. Part 4. Photochemical Procedure for the Preparation of 3‐0‐ and 4‐O‐Protected Derivatives of Methyl 2,6‐Dideoxy‐a‐D‐arabino‐hexopyranoside and for the Synthesis of 2,6‐Dideoxy‐3‐O‐methyl‐ D‐arabino‐hexose (D‐Oleandrose).

AbstractDie Bestrahlung der aus dem Glucosid (Ia) gewonnenen Derivate (Ib) bzw. (Ic) (trennbares Gemisch) in ′HMPT/HZO (97 23) liefert die Didesoxyverbindungen (II) und Desoxyverbindungen (III) und (IV).

Reaktionen partiell acylierter Aldohexopyranoside, IV. Ein photochemisches Verfahren zur Darstellung von 3‐O‐ und 4‐O‐geschützten Derivaten des Methyl‐2,6‐didesoxy‐α‐D‐arabino‐hexopyranosids und zur Synthese von 2,6‐Didesoxy‐3‐O‐methyl‐D‐arabino‐hexose (D‐Oleandrose)

AbstractDie Bestrahlung des aus Methyl‐2,6‐di‐O‐pivaloyl‐α‐D‐glucopyranosid (6) gewonnenen Methyl‐3‐O‐[(tert‐butyl)(dimethyl)silyl]‐2,6‐di‐O‐pivaloyl‐α‐D‐glucopyranosids (7) in Hexamethylphosphorsäuretriamid/Wasser (97:3) ergibt Methyl‐3‐O‐[(tert‐butyl)(dimethyl)silyl]‐2,6‐didesoxy‐α‐D‐arabino‐hexopyranosid (10) neben Methyl‐3O‐[(tert‐butyl)(dimethyl)silyl]‐2‐desoxy‐6‐O‐pivaloyl‐α‐D‐arabino‐hexopyranosid (15) und Methyl‐3‐O‐[(tert‐butyl)(dimethyl)silyl]‐6‐desoxy‐2‐O‐pivaloyl‐α‐D‐glucopyranosid (20). Die Bestrahlung des regioisomeren 4‐O‐Silylethers 8 ergibt Methyl‐4‐O‐[(tert‐butyl)(dimethyl)silyl]‐2,6‐didesoxy‐α‐D‐arabino‐hexopyranosid (11), das in 2,6‐Didesoxy‐3‐O‐methyl‐D‐arabino‐hexose (D‐Oleandrose, 1a) umgewandelt wurde, und Methyl‐4‐O‐[(tert‐butyl)(dimethyl)silyl]‐2‐desoxy‐6‐O‐pivaloyl‐α‐D‐arabino‐hexopyranosid (14), das in 2‐Desoxy‐3‐O‐methyl‐D‐arabino‐hexose (1b) übergeführt wurde.

Diterpene Total Synthesis : An Improved Stereoselective Route to (±)-3,4,5,5a,7,8,8aα,8bα-Octahydro-2aα,5aβ-Dimethyl-2H-Naphto-|1,8-Bc|Furan-2,6-(2aH)-Dione

Abstract The synthesis of the title compound 13, via a photochemical (π2 + π2) annellation procedure and a highly stereo-selective hydrocyanation reaction, is described.

Inhibition of phytohemagglutinin-induced lymphocyte mitogenesis by lipoxygenase metabolites of arachidonic acid: structure-activity relationships.

Phytohemagglutinin (PHA)-induced mitogenesis of mixed mouse spleen lymphocyte populations, measured by [3H]thymidine incorporation, was completely inhibited by micromolar concentrations of certain hydroxyeicosatetraenoic acids (HETE's). These are lipoxygenase metabolites of arachidonic acid which are synthesized in considerable concentrations by macrophages, lymphocytes, and other components of the immune system when appropriately stimulated. In the studies described here, the structural requirements for the maximum antimitogenic activities were examined. A series of monohydroxylated HETE's were prepared using a singlet oxygen photochemical procedure or by enzymatic synthesis from arachidonic acid substrate, and isolated by HPLC. Isomers containing different numbers of double bonds were synthesized using the appropriate unsaturated fatty acid as substrate, and the functional importance of the OH and carboxylic functions was tested using various acetoxy- and carbomethoxy derivatives. A serum-free mitogenesis assay system was used for testing, which minimized binding of the fatty acids by serum proteins and increased the inhibitory potency of the various HETE's several-fold. It was found that inhibition of cell proliferation was related to: hydroxyl proximity to the center of the eicosatetraenoic acid, decreasing in the order: 9 greater than 11 greater than 12 greater than 15 greater than 8 much greater than 5; the number of double bonds in the fatty acid chain, decreasing in the order: 15-OH, 20:4 greater than 15-OH 20:3 much greater than 15-OH, 20:2 much greater than 15-OH, 20:0; and the 15-position functional group as well as the 1-carboxylic group, decreasing in the order: 15-hydroxy, 1-carboxylic greater than 15-acetoxy, 1-carboxylic much greater than 15-hydroxy, 1-carbomethoxy greater than 15-acetoxy, 1-carbomethoxy.(ABSTRACT TRUNCATED AT 250 WORDS)

Photochemical procedure used in South Africa for automated photometric determination of dissolved carbon in seawater

Photochemical procedure used in South Africa for automated photometric determination of dissolved carbon in seawater

ChemInform Abstract: NUCLEOPHILIC ALKENES. IX. ADDITION OF 1,1‐DIMETHOXYETHENE TO AZANAPHTHOQUINONES: SYNTHESIS OF BOSTRYCOIDIN AND 8‐O‐METHYLBOSTRYCOIDIN

AbstractUmsetzen der Azanaphthochinone (II), (VI) und (VIII) mit Dimethoxyethen (III) liefert die isomeren Dimethoxyanthrachinone (IV), (VII) bzw. (IX) und (X).

Nucleophilic alkenes. IX. Addition of 1,1-dimethoxyethene to azanaphthoquinones: synthesis of bostrycoidin and 8-O-methylbostrycoidin

Reaction of 1,1-dimethoxyethene with azanaphthoquinones leads to pairs of isomeric dimethoxy-azaanthraquinones by means of 1:2-addition. A photochemical procedure has been developed for substituting these dimethoxy products by a further methoxy, amino or a hydroxy group peri to carbonyl. In this way the antibiotic bostrycoidin (1) and its 8-O-methyl derivative (2), the only natural 2-azaanthraquinones, have been synthesized for the first time.

Photochemistry of alkyl halides—VII : Cyclopropanation of alkenes

The previously observed cyclopropaoation of alkenes by irradiation of diiodomethane ( I) in their presence has been studied in more detail and found to be a synthetically useful procedure which is significantly less subject to steric effects than the traditional Simmons-Smith method. The results from photocyclopropanation of a variety of alkenes are summarized in Tables 1 and 3–4. In a number of cases the photochemical procedure afforded improved results over the Simmons-Smith method, particularly with sterically congested alkenes. Cycloalkenes showed relative rates of photocyclopropanation as a function of ring size similar to those of the Simmons-Smith method (Table 5). However, the photocyclopropanation reaction exhibited steadily increasing relative rates with increasing substitution about the double bond—in contrast with the Simmons-Smith method (Table 6), in which steric effects offset increasing nucleophilicity of the alkene with increasing substitution. The α-iodocation 2 is suggested as the methylene transfer species. In the presence of lithium bromide cation 2 was trapped to afford bromoiodomethane.