Guadalupe Albarrán

Absorption Spectrum, Mass Spectrometric Properties, and Electronic Structure of 1,2-Benzoquinone

Absorption spectrophotometric and mass spectrometric properties of 1,2-benzoquinone, prepared in aqueous solution by the hexachloroiridate(IV) oxidation of catechol and isolated by HPLC, are reported. Its absorption spectrum has a broad moderately intense band in the near UV with an extinction coefficient of 1370 M(-1)cm(-1) at its 389 nm maximum. The oscillator strength of this band contrasts with those of the order-of-magnitude stronger approximately 250 nm bands of most 1,4-benzoquinones. Gaussian analysis of its absorption spectrum indicates that it also has modestly intense higher energy bands in the 250-320 nm region. In atmospheric pressure mass spectrometric studies 1,2-benzoquinone exhibits very strong positive and negative mass 109 signals that result from the addition of protons and hydride ions in APCI and ESI ion sources. It is suggested that the hydride adduct is formed as the result of the highly polar character of ortho-quinone. On energetic collision the hydride adduct loses an H atom to produce the 1,2-benzosemiquinone radical anion. The present studies also show that atmospheric pressure mass spectral patterns observed for catechol are dominated by signals of 1,2-benzoquinone resulting from oxidation of catechol in the ion sources. Computational studies of the electronic structures of 1,2-benzoquinone, its proton and hydride ion adducts, and 1,2-benzosemiquinone radical anion are reported. These computational studies show that the structures of the proton and hydride adducts are similar and indicate that the hydride adduct is the proton adduct of a doubly negatively charged 1,2-benzoquinone. The contrast between the properties of 1,2- and 1,4-benzoquinone provides the basis for considerations on the effects of conjugation in aromatic systems.

Concerted effects in the reaction of OH radicals with aromatics: radiolytic oxidation of salicylic acid

Abstract Liquid chromatographic and capillary electrophoretic studies have been used to resolve the products produced in the radiolytic oxidation of salicylic acid in aqueous solution. These studies have shown that, as in the case of phenol, OH radicals preferentially add to the positions ortho and para to the OH substituent. However, in contrast to its reaction with phenol, addition at the ortho position is favored over addition at the para position. Because OH radical is a strong electrophile this difference suggests that the electron population at the ortho position in the salicylate anion is enhanced as a result of the hydrogen bonding in salicylic acid.

A review of conditions affecting the radiolysis due to40K on nucleic acid bases and their derivatives adsorbed on clay minerals: Implications in prebiotic chemistry

This paper describes the possible effects of ionizing radiation arising from long-lived soluble radionuclides within clays, in particular40K, at the epoch of the emergence of life on Earth. The free dispersion of soluble radionuclides constitutes an effectivein situ irradiation mechanism that might have acted upon adsorbed nucleic bases and their derivatives on clays, inducing chemical changes on these organic molecules. Several types of well documented reactions for radiolysis of nucleic acid bases and their derivatives are known, even at low doses (i.e., 0.1 Gy). For example, estimates with a dose rate calculated from40K from deep sea clays at 3.8 Ga ago, indicates that over a period of 1000 years the amount of organic material transformated is 1.8 × 10−7 moles/kg-clay.Although ionizing radiation may also induce synthetic reactions with prebiological interest, all in all these considerations indicate that nucleic acid bases and their derivatives adsorbed on clays were exposed for long periods to degradation conditions. Such situation promotes decomposition of organic molecules rather than protection of them and enhancement of further polymerization, as it has been usually taken for granted.

Ion-moderated partition chromatographic determination of Ca14CO3 and Ba14CO3 self-radiolysis products

Abstract Ion-moderated partition chromatography, using strongly acidic cation-exchange resins, was used to separate five carboxylic acids (formic, oxalic, glyoxylic, glycolic and acetic) and seven one-and two-carbon non-ionic compounds (methanol, ethanol, ethylene glycol, formadehyde, glyoxal, acetaldehyde and methyl formate). The carboxylic acids could not be separated from their corresponding aldehydes. Quantification of the compounds was achieved by using a combined analysis: in the first run, the mixtures were separated using only the cation-exchange column; before the second run, a short anion-exchange column was inserted between the cation- exchange column and the detector to remove the acids, collecting only the non-ionic compounds. This method was used to identify and quantify the organic products formed in the self-radiolysis of solid Ca 14 CO 3 and Ba 14 CO 3 . All five acids, formaldehyde and methanol were found.

Radiolysis of cyanocobalamin (vitamin B12)

Abstract Research on the radiolysis of vitamins is of considerable interest since these compounds are important nutritional constituents in foods and in dietetic supplements. In spite of these considerations there are few data and very often difficult to compare for the radiolytic behavior of vitamins. In this work we focused our attention on to the study of the radiolysis of cyanocobalamin (vitamin B 12 ) in solid state and in aqueous solutions. The procedure was followed by HPLC and UV-spectroscopy. The results obtained in aqueous solutions showed a dependence of the decomposition as a linear function of the dose. The G of decomposition for a 1×10 −5 M solution was 3.3. In the solid state the vitamin was very stable towards the irradiation in the conditions used in this study with a G =2.1×10 −3 . A study made with Serratia marcescens as a microbiological contaminant showed that at the sterilization dose there is a destruction of the vitamin in aqueous solution. In the solid state the degree of decomposition was 7%.

Formation of organic products in self-radiolyzed calcium carbonate

SummaryCalcium carbonate labeled with carbon-14 was self-irradiated by means of the β-decay of its carbon-14. A number of products containing one or two carbon atoms were identified by high performance liquid chromatography. Formic and oxalic acids were produced in relatively high yields, while glyoxylic, glycolic, and acetic acids, as well as formaldehyde and methanol, were formed in lower yields. These results support the suggestion that carbonates subjected to ionizing radiation could have been a source of carbon for organic synthesis on the primitive earth.

Enhance decarboxylation reaction of carboxylic acids in clay minerals

Abstract Clay minerals are important constituents of the Earths crust. These minerals catalyze reactions in several ways: by energy transfer processes, redox reactions, stabilization of intermediates and by Bronsted or Lewis acidity behavior. Important set of organic reactions can be improved in the precedence of clay minerals. Besides the properties of clays to catalyze chemical reactions, it is possible to enhance some of its reactions by using ionizing radiation. The phenomenon of radiation-induced catalysis may be connected with ionizing process in the solid and with the trapped non-equilibrium charge cariers. In this paper we are reporting the decarboxylation reaction of carboxylic acids catalyzed by clay and by irradiation of the system acid-clay. We studied the behaviour of several carboxylic acids and analyzed them by gas chromatography, X ray and infrared spectroscopy. The results showed that decarboxylation of the target compound is the dominating pathway. The reaction is enhance by gamma radiation in several orders of magnitude.

Micellar electrophoretic capillary chromatographic analysis of the products produced in the radiolytic oxidation of toluene and phenol

Abstract In this paper, we consider the effect of CH 3 and OH substitution on a benzene ring in directing the site of OH radical attack in oxidative processes initiated by the gamma radiolysis of aqueous solutions of phenol and toluene. The analytical method used was micellar electrophoretic capillary chromatography. This approach permits the resolution of the radiolytic products resulting from the oxidation of the hydroxycyclohexadienyl radicals initially produced by addition of OH to the aromatic compounds and allows one to obtain a complete mechanistic picture of the radiation chemical processes.

Clays as Natural Catalyst in Prebiotic Processes

The role of clay minerals in prebiotic chemistry is discussed in some of the more relevant questions about its importance. So far, data published about laboratory experiments show that clays can act as adsorbers, concentrator and catalyst for polymerization. However, there are still inconclusiveness due to: the amount of adsorbed material, type of clay used, he pH of the bulk solution, etc. All these factors affect the extent in which these capacities occurred at conditions that can be relevant to geological scenarios. Finally, some light in the role of clays can be brought by further experiments dealing with energy transfer process.

Synthesis of 1, 2, 3, 4-butanetetracarboxylic acid from the irradiation of aqueous succinic acid

Abstract This paper deals with the action of ionizing radiation on diluted aqueous solutions of succinic acid in order to synthesize 1, 2, 3, 4- butanetetracarboxylic acid. This compound has a variety of industrial and agricultural applications. The chemical synthesis of this compound involves several steps. In contrast the radiation-induced synthesis can be achieved in one step and with a good yield. The results obtained show that one of the most important reactions was the demerization of the target compound yielding the tetracarboxylic acid.