PHOTOCHEMICAL REACTIONS OF THYMINE WITH CARBOXYLIC ACIDS. A MODEL FOR NUCLEIC ACID-PROTEIN PHOTOCROSSLINKING

When nucleic acid bases are UV-irradiated in the presence of carboxylic acids or carboxylate anions new photoproducts are formed as compared to the bases irradiated in the absence of carboxylic acids. The behavior of thymine and thymidine has been examined in detail. At least four photoproducts are formed in the presence of propionic acid and three in the presence of butyric acid. None of them appears to be a cyclobutyl dimer. From the concentration dependence of the rate of photoproduct formation it is concluded that the reactive excited species is the first excited singlet state of thymine. When ¹⁴C-labelled thymine is irradiated in the presence of polyglutamic acid an important part of the radioactive material is covalently linked to the polymer. Photochemical reaction of thymine with glutamic (or aspartic) acid could thus induce crosslinks between proteins and nucleic acids. It is also shown that these photoproducts are stable under usual conditions of acidic hydrolysis of UV-irradiated DNA.     

Action du N-bromosuccinimide sur les dioxolannes. Intermediaires réactionnels

1,3-Dioxolan-2-ylium ion intermediates formed by reaction of bromine or NBS on 4-syn-aryl-3,5-dioxa-tricyclo [5.2.1.0^2.6] décanes have been isolated. 2-Succinimido-1,3-dioxolanes have been prepared for the first time.     

Different approaches for fabrication of low-cost electrochemical sensors

Electrochemistry combined with economical and sustainable platforms (such as paper) provides portable, affordable, robust, and user-friendly devices. In general, techniques, such as photolithography and sputtering, are excellent alternatives for producing these platforms. However, owing to the requirement of expensive and sophisticated instrumentation, as well as cleanroom facilities, these techniques have limited access. Thus, the search for easy to use and produce approaches have been reported, using consumables, including adhesives, carbon ink, graphite, pencil, office paper, paperboard, among others. In this sense, in this mini-review, we discuss various strategies explored to fabricate low-cost electrochemical sensors, including its main applications. Different manufacturing methods, such as screen and stencil printing, laser-scribing, and pencil drawing, will be discussed here, emphasizing the performance of the obtained devices, in addition to their advantages and disadvantages.     

PHOTODYNAMIC INHIBITION OF ESCHERICHIA COLI DNA POLYMERASE I BY 8-METHOXYPSORALEN PLUS NEAR ULTRAVIOLET IRRADIATION

Abstract— Morphological abnormality due to the UV irradiation of sperm and its modification by photoreactivation (PR) were studied in the sea urchin, Hemicentrotus pukherrimus. When sperm was UV-irradiated and allowed to fertilize unirradiated eggs, the effect of the UV was manifested as an abnormal morphology of embryos in the gastrula or later stages. The UV-induced morphological abnormality was prevented by photoreactivation when the fertilized eggs were illuminated with visible light. In the experiments on a stage-dependent change of PR effectiveness, it was found that an illumination sufficed to effect a nearly complete PR when applied up to the onset of the first DNA synthetic phase, while the PR effectiveness declined thereafter. Illumination after the completion of DNA synthesis had little effect for PR.     

Valenzisomere aromatischer systeme. Die Synthese des Pyrrolo-3-azabenzvalens

Valence Isomers of Aromatic Systems. The Synthesis of Pyrrolo-3-azabenzvalene 4-Azapentalenyl anion ( 4 ) is shown to react with dichloromethane/butyl lithium in two fundamentally different ways depending on whether diethyl ether or tetrahydrofuran is chosen as solvent. In the first case a tetracyclic valence isomer of indolizine, i.e. pyrrolo-3-azabenzvalene ( 6 ) is formed together with indolizine ( 8 ) itself. In THF however, a pyrrylbutenyne ( 9 ), isomeric with the products mentioned above is obtained in a stereospecific reaction. Once again the appearance of indolizine ( 8 ) accompanies the reaction. Mechanistic implications, based on the finding that the heterovalene 6 is not a precursor of the pyrrylbutenyne 9 , are discussed.     

Electrochemical quantification of 2,6-diisopropylphenol (propofol)

2,6-Diisopropylphenol (propofol) is a potent anesthetic drug with fast onset of the anesthetic effect and short recovery time for the patients. Outside of the United States, propofol is widely used in performing target controlled infusion anesthesia. With the long term vision of an electrochemical sensor for in vivo monitoring and feedback controlled dosing of propofol in blood, different alternatives for the electrochemical quantification of propofol using diverse working electrodes and experimental conditions are presented in this contribution. When the electrochemical oxidation of propofol takes place on a glassy carbon working electrode, an electrochemically active film grows on the electrode surface. The reduction current of the film is proportional to the propofol concentration and the accumulation time. Based on these findings a stripping analytical method was developed for the detection of propofol in acidic solutions between 0 and 30 μM, with a detection limit of 5.5±0.4 μM. By restricting the scanned potential window between 0.5 V and 1.0 V in cyclic voltammetric experiments, the formation of the electrochemically active polymer can be prevented. This allowed the development of a direct voltammetric method for assessing propofol in acidic solutions between 0 and 30 μM, with a 3.2±0.1 μM (n=3) detection limit. The stripping method has a better sensitivity but somewhat worse reproducibility because the electrode surface has to be renewed between each experiment. The direct method does not require the renewal of the electrode surface between measurements but has no adequate selectivity towards the common interfering compounds.     

Synthesis of novel selenium and tellurium-containing tetrazoles: a class of chalcogen compounds with antifungal activity

We describe herein the synthesis and antifungal activity of new 5-arylchalcogenoalkyl-1H-tetrazoles 4. Arylchalcogenoalkyl-1H-tetrazoles 4 have been synthesized in high yields by reaction of arylchalcogenolate anions with chloronitriles 2, and subsequent [2+3] cycloaddition of resulting arylchalcogenoalkylnitriles 3 with sodium azide by zinc catalysis in aqueous solution. The obtained compound 4a was screened for antifungal activity and presented inhibitory property against seven fungal strains. This protocol is an efficient method to produce new selenium–nitrogen compounds with antifungal activity.     

Synthesis and characterization of mononuclear iron silanethiolato complexes containing an unsupported Fe-S-Si bond system: X-ray crystal structure of CpFe(CO)2SSiPh3 and its reaction with SO2

Mononuclear iron silanethiolato complexes of the type CpFe(CO)(2)SSiR(3), where R = Ph (1a) and (i)()Pr (1b), were prepared via treatment of [CpFe(CO)(2)(THF)]BF(4) with LiSSiPh(3).Et(2)O and NaSSi(i)()Pr(3), respectively. The molecular structure of 1a was determined by X-ray crystallography. Complex 1a was reacted with 1 equiv of SO(2) to give the corresponding O-silyl thiosulfite, CpFe(CO)(2)SS(O)OSiPh(3) (2), via 1,2-insertion of SO(2) into the S-Si bond. This reaction models the activation of SO(2) in the homogeneously catalyzed Claus process.