PHOTOMORPHOGENIC RESPONSES TO UV RADIATION. II: A COMPARATIVE STUDY OF UV EFFECTS ON HYPOCOTYL ELONGATION IN A WILD-TYPE AND AN aurea MUTANT OF TOMATO (Lycopersicon esculentum Mill.)

Hypocotyl growth in etiolated seedlings of wild-type and an aurea mutant of tomato (Lycopersicon esculenturn Mill.), that appears to be deficient in labile phytochrome, is strongly inhibited by UV radiation in the region of 300–400 nm. The role of phytochrome in the UV-mediated inhibition of hypocotyl growth was studied using different experimental approaches: (1) by comparing the effectiveness of treatments of increasing duration of exposure to 692 nm and UV radiation; (2) by modifying the UV spectral range with specific cut-off filters. The experimental results suggest that the UV-induced inhibition of growth in wild-type tomato is mediated to a large extent by the longer wavelengths of the UV-A region and is mediated mainly by phytochrome. In contrast, at wavelengths < 305 nm a strong UV-B effect was found in the aurea mutant, suggesting a preeminent action of a specific UV-B absorbing photoreceptor that displays less action in the wild-type.     

Peroxidase based biosensors for the selective determination of D,L-lactic acid and L-malic acid in wines

A novel bioelectrochemical method for the direct determination of D(−) L(+) lactic acid and of L(−) malic acid in wines is presented. Multienzymatic biosensors were realized for the selective determination of the three analytes: D(−) and L(+) lactic acid were measured by a trienzymatic biosensor based on the catalytic activities of the enzymes L(+) lactate oxidase (LOD), D(−) lactate dehydrogenase (D-LDH) and horseradish peroxidase (HRP); L(−) malic acid was measured by a bienzymatic electrode, realized by coupling the enzymes L(−) malic dehydrogenase (L-MDH) and horseradish peroxidase (HRP). In both cases the enzymes were immobilized on an oxygen selective Clark electrode.The simultaneous determination of the two organic acids can be accomplished either in batch or in a flow injection analysis apparatus using the same biosensors as detectors. The analytical performance of the method, tested in standard aqueous solutions and on real samples of wines, showing high repeatability, short response times and reduced cost of analysis, suggest that the experimental approach here described could be followed to monitor the progress of malolactic fermentation.     

Synthesis,characterization and coordination chemistry of the new tetraazamacrocycle 4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-bis(methanephosphonic acid monoethyl ester) dipotassium salt

A new potentially hexadentate tetraazamacrocycle based on the cyclen skeleton has been synthesized and fully characterized. The macrocycle 4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-bis(methanephosphonic acid monoethyl ester) dipotassium salt (Me2DO2PME) contains mutually trans monoethyl ester phosphonate acid substituents on two nitrogen atoms, and trans methyl substituents on the other two nitrogen atoms. The protonation constants of this macrocycle and the stability constants of its complexes with Cu2+, Zn2+, Gd3+ and Ca2+ ions have been determined by pH potentiometric titrations. The protonation sequence of the macrocycle has been studied by 1H, 31P[1H] and 13C[1H] NMR spectroscopy: the first and second protonation steps take place at the methyl-substituted nitrogen atoms, while the third protonation involves one oxygen from a phosphonate group. Upon protonation, all the CH2 ring protons become magnetically inequivalent on the NMR time scale due to a slow conformational rearrangement, most likely occasioned by the formation of multiple hydrogen bonds within the macrocyclic ring. Me2DOPM forms neutral, mononuclear complexes with all the metals investigated. The presence of hydroxo complexes was observed for Ca2+ and Zn2+ at high pH values. Structural information on the neutral complex [Cu(Me2DO2PME)] has been obtained by a solution X-Band EPR study. It is proposed that Me2DO2PME binds Cu2+ in a distorted octahedral structure using all of its donor atoms, i.e. the four nitrogen atoms and the two phosphonate oxygen atoms. The redox chemistry of [Cu(Me2DO2PME)] in dimethyl sulfoxide and water has been studied by electrochemical measurements. Cyclic voltammetry in DMSO shows the complex to undergo a quasireversible one-electron reduction step leading to an unstable CuI species.     

Stress development during drying of calcium carbonate suspensions containing carboxymethylcellulose and latex particles

Stress development during drying of coatings produced from aqueous dispersions of calcium carbonate particles in the presence and absence of organic binders was studied using a controlled-environment stress apparatus that simultaneously monitored drying stress, weight loss, and relative humidity. Specifically, the influence of two organic binders on drying stress evolution was investigated: (1) carboxymethylcellulose, a water-soluble viscosifying aid, and (2) a styrene-butadiene latex emulsion of varying glass transition temperature. The stress histories exhibited three distinct regions. First, a period of stress rise was observed, which reflected the capillary tension exerted by the liquid on the particle network. Second, a maximum stress was observed. Third, it was followed by a period of either stress decay or rise depending on the organic species present. Significant differences in stress histories were observed between coatings containing soluble and nonsoluble binders. Maximum drying stresses (sigmamax) of 0.2-0.5 MPa were observed for coatings produced from pure calcium carbonate or calcium carbonate-latex suspensions, whereas coatings with carboxymethylcellulose exhibited substantially higher sigmamax values of 1-2 MPa. Upon drying, these coatings were quite hygroscopic, such that cyclic variations in relative humidity induced large cyclic changes in residual stress.     

Synthesis of 2-(p-R-benzoylmethylene)-3-(p-R-phenyl)-1H-quinoxalines

The reaction of 1,2-diaminobenzenes with substituted 1,2-dibenzoyl-1,2-dibromoethanes constitutes a convenient synthetic route to the hitherto 2-(p-R-benzoylmethylene)-3-(p-R-phenyl)-1H-quinoxalines. Structures of all products were elucidated by ir, ¹H and ¹³C-nmr, mass spectra data. X-Ray crystallography data confirm assigned structures.     

Synthesis and conformational analysis of novel N(OCH3)-linked disaccharide analogues

N(OMe)-linked disaccharide analogues, isosteric to the corresponding natural disaccharides, have been synthesized by chemoselective assembly of unprotected natural monosaccharides with methyl 6-deoxy-6-methoxyamino-alpha-D-glucopyranoside in an aqueous environment. The coupling reactions were found to be chemo- and stereoselective affording beta-(1-->6) disaccharide mimics when using Glc and GlcNAc; in the case of Gal, the beta-anomer was prevalent (beta:alpha=7:1). An iterative method for the synthesis of linear N(OMe) oligosaccharide analogues was demonstrated, based on the use of an unprotected monosaccharide building block in which an oxime functionality at C-6 is converted during the synthesis into the corresponding methoxyamino group. The conformational analysis of these compounds was carried out by using NMR spectroscopy, ab initio, molecular mechanics, and molecular dynamics methods. Optimized geometries and energies of fourteen conformers for each compound have been calculated at the B3LYP/6-31G* level. Predicted conformational equilibria were compared with the results based on NMR experiments and good agreement was found. It appears that N(OMe)-linked disaccharide analogues exhibit a slightly different conformational behavior to their parent natural disaccharides.     

The reactivity of the A-CH=N-NR-CX-B system. 1,3,4-Oxadiazoles and 2,3,4,5-tetrahydro-1,2,4-triazin-3-ones through the 1–5 and 1–6 cyclization reactions of α-thienylglyoxal monosemicarbazones

The factors influencing the reactivity of α-thienylglyoxal monosemicarbazones when treated with cyclizing reagents (bromine/sodium acetate and hydrobromic acid in acetic acid) were investigated. Depending on the experimental conditions, on the position of the substituent on the semicarbazide residue, and on the cyclizing agent, the substrates 1a-e give the semicarbazone bromides 2a-b, 5 , the 1,3,4-oxadiazoles 3a-c , the 1,2,4-triazine 11 and the 2,3,4,5-tetrahydro-1,2,4-triazine-3-ones 6, 8 and 9 . Compound 6 by thermolysis undergoes ring contraction in the Δ²-1,3,4-oxadiazoline 12 , while treatment with base involves the conversion of 6 into 1,2,4-triazol-5-one 13 . Ir, nmr and mass spectra support the reported structures.     

Determination of phosphorus in samples of vegetable origin Mineralization with molten alkali and spectrophotometric determination

For determination of phosphorus in samples of vegetable origin (leaves and wheat flour) decomposition by means of molten alkali is proposed. Two procedures have been studied, one with dry reagents including an auxiliary oxidant, and the other with initially moist alkali with no extra oxidant. The fusion product is easily soluble and produces a solution suitable for elemental analysis. The phosphorus is determined by the molybdenum blue method. The suggested mineralization is rapid, accurate and precise.