Photodegradation of a polyamidehydroxyurethane type polymer in aqueous solution. The role of some dyes in the degradation

The influence of some dyes on the photodegradation of a polyamidehydroxyurethane type polymer in aqueous solution has been studied. It has been found that, among the dyes used, only riboflavin sensitizes and accelerates the degradation of the polymer. It is proposed that under ultraviolet irradiation riboflavin undergoes photoreduction to lumichrome, which sensitizes the photodegradation of the polymer. It is also possible that the mechanism of photodegradation involves the participation of singlet oxygen.     

A concise synthesis of 12(S),20-dihydroxyeicosa-5(Z),8(Z),10(E),14(Z)-tetraenoic acid, an endogenous vasoconstrictor

12(S),20-DiHETE, prepared by a combination of Evans-Crimmins asymmetric alkylation, Sonogashira alkynylation, and Suzuki-Miyaura cross-coupling, significantly sensitizes phenylephrine-induced vasoconstriction of rat renal interlobar arteries.     

TRIPLET ENERGY TRANSFER TO CHLOROPLASTS FROM PEROXIDASE-GENERATED EXCITED ALIPHATIC ALDEHYDES

Abstract Linear aldehydes trigger red emission from chloroplasts. If horseradish peroxidase is present, the aldehyde is oxidized to the next lower homologue in the triplet state, which in turn sensitizes chlorophyll fluorescence. Only certain chlorophylls are activated.     

Upconversion-powered photoelectrochemistry

Upconversion photochemistry occurring between palladium(II) octaethylporphyrin (PdOEP, 1) and 9,10-diphenylanthracene (DPA, 2) in toluene successfully sensitizes nanostructured WO(3) photoanodes (E(g) = 2.7 eV) to sub-bandgap non-coherent green photons at low power density.     

DARK MEMBRANE LYSIS AND PHOTOSENSITIZATION BY 3-CARBETHOXYPSORALEN*

Abstract— Aqueous solutions of 3-carbethoxypsoralen (3-CPs) induce lysis of egg lecithin liposomes and whole human erythrocytes in the dark. Near-UV irradiation of 3-CPs sensitizes the inactivation of lysozyme attributed to the production of reactive radical intermediates. The implications of these findings for the use of 3-CPs as a sensitizer in PUVA therapy of psoriasis are discussed.     

Gold‐Catalyzed Cyclization Leads to a Bridged Tetracyclic Indolenine that Represses β‐Lactam Resistance

A gold‐catalyzed desilylative cyclization was developed for facile synthesis of bridged tetracyclic indolenines, a common motif in many natural indole alkaloids. An antimicrobial screen of the cyclization products identified one compound which selectively potentiates β‐lactam antibiotics in methicillin‐resistant S. aureus (MRSA), and re‐sensitizes a variety of MRSA strains to β‐lactams.     

Zinc-adeninate metal-organic framework for aqueous encapsulation and sensitization of near-infrared and visible emitting lanthanide cations

Luminescent metal-organic frameworks (MOFs), Ln(3+)@bio-MOF-1, were synthesized via postsynthetic cation exchange of bio-MOF-1 with Tb(3+), Sm(3+), Eu(3+), or Yb(3+), and their photophysical properties were studied. We demonstrate that bio-MOF-1 encapsulates and sensitizes visible and near-infrared emitting lanthanide cations in aqueous solution.     

Phycocyanin-sensitized photoreduction of azo dyes

Abstract— Phycocyanin can sensitize the photobleaching of azo dyes in a reaction which is analogous to one sensitized by chlorophyll. The quantum yield of the phycocyanin-sensitized photobleaching of congo red is low compared to the analogous reaction as sensitized by chlorophyll in aqueous pyridine. A kinetic mechanism for the former reaction is proposed and it was found that the manner in which phycocyanin sensitizes photoreduction of azo dyes is in several respects similar to that proposed for chlorophyll.     

The effect of thermal processing on PVC—I. Chemical and physical changes in unstabilized PVC

Unstabilized PVC processed at 170 and 210°C was found to undergo immediate mechano-chemically induced thermal oxidation with the formation of unsaturation and peroxides. The peroxides were partially in the form of cross-links between polymer molecules at this stage and were manifested in the form of solvent insoluble gel. Conjugated double bonds and colour formation both increased linearly with time. The evidence suggests that the initial mechano-chemical process sensitizes the polymer to subsequent thermal degradation.     

Polarographic Determination of Bismuth Sensitization in the Presence of Nioxime

Abstract

Nioxime sensitizes the differential pulse polarographic determination of B1(III) in alkaline medium and in the presence of tart rate and citrate; detection limits of 8 and 12 ppb are obtained. Characterization of the electroactive process included an examination of the degree of reversibility and the effect on the peak current of pH, buffer composition, nioxime and bismuth concentrations and the presence of other metal ions.     

FURTHER STUDIES ON THE CRYSTAL-VIOLET-SENSITIZED PHOTOOXIDATION OF CYSTEINE TO CYSTEIC ACID

Abstract —Crystal violet sensitizes the selective photooxidation of cysteine to cysteic acid; hydrogen peroxide is also formed as an end product. The participation of singlet oxygen in the photoreaction has been ruled out, since exposure of cysteine to this reagent, generated by chemical or photochemical processes, gives only cystine as a product. The photoreaction is inhibited by radical scavengers such as hydroquinone and allylic alcohol. A mechanism is proposed involving hydrogen abstraction by the triplet dye from the thiol group of cysteine.     

Photoinduced electron transfer reactions: Oxidation of electron-rich dioxenes and 2,3,5,6-tetraphenyl-p-dioxin induced by 2,4,4,6-tetrabromocyclohexa-2,5,-dienone

2,4,4,6-Tetrabromocyclohexa-2,5-dienone (TBCHD) sensitizes the photo-oxygenation of dioxenes and 2,3,5,6-tetraphenyl-p-dioxin by electron transfer to yield ethane-1,2-diol dibenzoates and (Z)-stilbenediol dibenzoate respectively, together with small quantities of the corresponding α-diketones. A preliminary investigation of the physical properties of TBCHD supports a radical cation chain mechanism in which the active oxygen species involved is molecular oxygen. A comparison with the photo-oxygenation of the same substrates sensitized by 9,10-dicyanoanthracene is also reported.     

REVISED SPECTRA FOR THE INACTIVATION OF HAEMOPHILUS INFLUENZAE TRANSFORMING DNA BY MONOCHROMATIC ULTRAVIOLET LIGHT: EFFECT OF HISTIDINE

Abstract—It was reported previously that histidine sensitizes the genetic activity of Haemophilus influenzae transforming DNA to pure 334 nm ultraviolet light, Further measurements show that this apparent 334 nm sensitization was probably erroneous and that in fact, histidine protects DNA against inactivation by 334 nm light. This is now consistent with all previous observations that transforming DNA is protected by histidine against all near-UV wavelengths (above 320 nm) investigated.
A modified spectrum for the protection of H. influenza transforming DNA by histidine against ultraviolet light is described.     

PHOTOREACTIVATING ENZYME FROM STREPTOMYCES GRISEUS—IV. ON THE NATURE OF THE CHROMOPHORIC COFACTOR IN STREPTOMYCES GRISEUS PHOTOREACTIVATING ENZYME

Abstract— A structure for the chromophoric part of the intrinsic cofactor of Streptomyces griseus photo-reactivating enzyme is suggested on the basis of absorption and fluorescence spectra of cofactor and reference compounds at various pH. The essential chromogenic part of this cofactor is proposed to be a 7,8-didemethy]-8-hydroxy-5-deazaflavin derivative (Ia).
From whole S. griseus cells a compound SF420 (Ic) was isolated which contains the same chromophoric group. This compound sensitizes the splitting of thymine dimers when irradiated with blue light, supporting the structure proposed for the photoreactivating enzyme cofactor.     

An action spectrum of the riboflavin-photosensitized inactivation of Lambda phage

The Action Spectrum of riboflavin (RB) sensitized inactivation of lambda phage was determined between 266 and 575 nm. Below 304 nm, RB depresses the phage reduction by screening phage from radiation that it would otherwise absorb directly. Between 308 and 525 nm, RB sensitizes the inactivation of phage. Enhanced phage reduction is observed at 320 and 500 nm because of binding of RB to the phage and the shifting of the absorption curve of the phage-bound flavin relative to free flavin in phosphate-buffered saline. Enhanced inactivation at 320 and 500 nm and depressed phage inactivation between 360 and 410 nm is also influenced by the inner filter effect.     

Crystal Structure and Luminescence of [Eu(TTA)3·DAF]·0.5C7H8 Complex Excited by Visible Light

The non‐ionic europium(III) complex [Eu(TTA)₃·DAF]·0.5C₇H₈ (TTA = 2‐thenoytrifluoroacetonate, DAF = 4, 5‐diazafluoren‐9‐one) was synthesized. The structural determination has been carried out. DAF coordination induces the both excitation spectra in the solid state and solution having a red shift and sensitizes Eu³⁺ luminescence under visible light excitation.     

A Small Molecule Inhibits Protein Disulfide Isomerase and Triggers the Chemosensitization of Cancer Cells

Resistance to chemotherapeutic agents represents a major challenge in cancer research. One approach to this problem is combination therapy, the application of a toxic chemotherapeutic drug together with a sensitizing compound that addresses the vulnerability of cancer cells to induce apoptosis. Here we report the discovery of a new compound class ( T8 ) that sensitizes various cancer cells towards etoposide treatment at subtoxic concentrations. Proteomic analysis revealed protein disulfide isomerase (PDI) as the target of the T8 class. In‐depth chemical and biological studies such as the synthesis of optimized compounds, molecular docking analyses, cellular imaging, and apoptosis assays confirmed the unique mode of action through reversible PDI inhibition.     

Visible Light-induced Oxygen Generation and Cyclic Water Cleavage Sensitized by Porphyrins

Zinctetramethylpyridylporphyrin (ZnTMPyP⁴⁺) in acidic aqueous solution sensitizes efficiently oxygen generation by visible light in the presence of acceptors such as Fe³⁺ - and Ag⁺-ions and colloidal RuO₂/TiO₂ redox catalyst. Hydrogen and oxygen are cogenerated under visible light illumination of ZnTMPyP⁴⁺ solutions when a bifunctional catalyst (Pt and RuO₂ codeposited onto TiO₂) is employed.     

Radioluminescence quenching of toluene scintillators by methyl methacrylate

It was established that singlet electronic excited state of toluene is quenched by MMA /but is not quenched by PMMA/. The value of quenching rate constant k_g=0.6×10⁹ l.mol^–1.s^–1 indicates that the quenching is a diffusion controlled process. It is assumed that the excitation energy of toluene sensitizes the polymerization process of MMA. The increase of radioluminescence intensity and quantum yield of excitation energy transfer is the result of diminishing the quantity of MMA in the solution during polymerization time.     

Study on the cocolouration effect in the β-complex formation reactions of rare earths with p-chloro-chlorophosphonazo (CPApC)

Terbium- and yttrium-group rare earths form β-complexes with CPApC in acidic medium.The sensitivities for determination of these rare earths by this reaction depend on their ionic radii.Cerium- or terbium-group rare earth in the presence of yttrium-group element produces the cocolourationeffect which remarkably sensitizes the reaction. Yb-CPApC-Eu complex has a molar composition of1:4:2 and gives a molar absorptivity of 2. 02 ×10~5 L·mol~(-1)·cm~(-1) at 746 nm for Eu. It is found thatthe closer the lengths of ionic radii of the rare earths are, the greater will be the cocolouration effect.