95,680 research outputs found

    Dynamic water bridging and proton transfer at a surface carboxylate cluster of photosystem II

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    Proton-transfer proteins are often exposed to the bulk clusters of carboxylate groups that might bind protons transiently. This raises important questions as to how the carboxylate groups of a protonated cluster interact with each other and with water, and how charged protein groups and hydrogen-bonded waters could have an impact on proton transfers at the cluster. We address these questions by combining classical mechanical and quantum mechanical computations with the analysis of cyanobacterial photosystem II crystal structures from Thermosynechococcus elongatus. The model system we use consists of an interface between PsbO and PsbU, which are two extrinsic proteins of photosystem II. We find that a protonated carboxylate pair of PsbO is part of a dynamic network of protein–water hydrogen bonds which extends across the protein interface. Hydrogen-bonded waters and a conserved lysine sidechain largely shape the energetics of proton transfer at the carboxylate cluster

    On the ordeal of quinolone preparation via cyclisation of aryl-enamines; synthesis and structure of ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate

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    Recent studies directed to the design of compounds targeting the bc(1) protein complex of Plasmodium falciparum, the parasite responsible for most lethal cases of malaria, identified quinolones (4-oxo-quinolines) with low nanomolar inhibitory activity against both the enzyme and infected erythrocytes. The 4-oxo-quinoline 3-ester chemotype emerged as a possible source of potent bc(1) inhibitors, prompting us to expand the library of available analogs for SAR studies and subsequent lead optimization. We now report the synthesis and structural characterization of unexpected ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)quinoline-3-carboxylate, a 4-aryloxy-quinoline 3-ester formed during attempted preparation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate (4-oxo-quinoline 3-ester). We propose that the 4-aryloxy-quinoline 3-ester derives from 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate (4-hydroxy-quinoline 3-ester), the enol form of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate. Formation of the 4-aryloxy-quinoline 3-ester confirms the impact of quinolone/hydroxyquinoline tautomerism, both on the efficiency of synthetic routes to quinolones and on pharmacologic profiles. Tautomers exhibit different cLogP values and interact differently with the enzyme active site. A structural investigation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate and 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, using matrix isolation coupled to FTIR spectroscopy and theoretical calculations, revealed that the lowest energy conformers of 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, lower in energy than their most stable 4-oxo-quinoline tautomer by about 27 kJ mol(-1), are solely present in the matrix, while the most stable 4-oxo-quinoline tautomer is solely present in the crystalline phase.Fundacao para a Ciencia e Tecnologia (FCT - Portugal) [UID/Multi/04326/2013]; QREN-COMPETE-UE; CCMAR; FCT [SFRH/BD/81821/2011, RECI/BBB-BQB/0230/2012, UI0313/QUI/2013, UID/FIS/04564/2016]; FEDER/COMPETE-UE; [PTDC/QEQ-QFI/3284/2014 - POCI-01-0145-FEDER-016617]info:eu-repo/semantics/publishedVersio

    Methyl 2-[(ferrocenylcarbonyl)amino]thiophene-3-carboxylate

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    The title compound, [Fe(C₅H₅)(C₁₂H₁₀NO₃S)], was synthesized from ferrocenecarboxylic acid and methyl 2-aminothiophene-3-carboxylate in modest yield. The substituted ring system is essentially planar through the amidothienylcarboxylate moiety, η⁔-(C₅H₄)CONH(C₄H₂S)CO₂Me, with the amido unit at an angle of 3.60 (7)° to the five-atom thienyl group, which is oriented at an angle of 3.17 (7)° to the ester moiety. The primary hydrogen bond is an intramolecular N-H...O=Ccarboxylate interaction [N...O 2.727 (2) Å], and the main intermolecular hydrogen bond involves a thienyl carboxylate and the carboxylate of a symmetry-related molecule [C...O 3.443 (3) Å]

    Two modes of peri-interaction between an aldehyde group and a carboxylate anion in naphthalaldehydate salts

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    Crystal structures of the salts of 1,8-naphthalaldehydic acid (8-formyl-1-naphthoic acid) show one of two types of interaction between the functional groups. In the more commonly observed case, a carboxylate oxygen lies close to the aldehyde carbonyl carbon atom (O⋯C: 2.445–2.630 Å) and makes an n–pi* interaction. However, in two other cases the carboxylate group has rotated so that the aldehyde now directs its hydrogen atom at the face of the carboxylate group and forms a surprisingly short contact with the carbon atom (H⋯C: 2.29 and 2.42 Å). This interaction is likely to be electrostatic in nature

    Temporal changes in carboxylate content of ryegrass with stepwise change in nutrition

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    A detailed scheme of carboxylate formation and retention by plant tissues as a result of ion uptake and utilization is given. By means of discontinuities in the supply with nutrient ions, carboxylate retention by the tissues of perennial ryegrass was followed as a function of growth. It was found that translocation of potassium nitrate to the shoot and subsequent nitrate metabolism was the only process capable of supplying the shoot with sufficient carboxylates and of removing the excess from the foliage to the root system with maintenance of the normal carboxylate content. Absorbed bicarbonate was a good source of carboxylates in the roots, but the rate of translocation to the plant tops was too slow relative to growth. Therefore, the carboxylate concentration in the foliage fell progressively to one half the normal value. Constancy of carboxylate concentration in the dry matter was related to the early establishment of the proportion of carboxylates to dry material in the new growth, making it independent of subsequent changes in water content of the tissues. Changes in carboxylate concentrations due to changes in the supply were continuous with time. Nitrate caused a depression in the roots during nitrate accumulation, but the nitrate metabolism in the follage made sufficient carboxylates available for replenishment and maintenance of their normal level in the whole plant

    Synthetic polymers with anticoagulant activity

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    Polymers with C=C bonds have been modified by reaction with chlorosulfonyl isocyanate (CSI). Addition products were obtained in yields varying from 60% to 75%. Reaction of these products with NaOH yielded polyelectrolytes with sulfamate and carboxylate groups, whereas from the reaction with NH4OH polyelectrolytes with sulfamate and carbonamide groups, were obtained. The polyelectrolytes showed anticoagulant activity depending on the structure and on the presence of both sulfamate and carboxylate groups. These groups are essential for the anticoagulant activity, because N-S bond cleavage in the sulfamate groups as well as substitution of carboxylate by carbonamide groups resulted in loss of activity. From the recalcification times of bovine plasma, it could be concluded that the most active polyelectrolyte had an activity of 6-7% compared with heparin. However, determination of the activated clotting time of blood from rabbits showed that this compound had an in vivo activity of 50% in comparison with heparin

    HYDROGEN-BONDED SUPRAMOLECULAR ARRAY IN THE CRYSTAL STRUCTURE OF ETHYL 7-HYDROXY-2-OXO-2H-CHROMENE-3-CARBOXYLATE MONOHYDRATE

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    IndexaciĂłn: Web of Science; ScieloThe crystal structure of ethyl 7-hydroxy-2-oxo-2H-chromene-3-carboxylate monohydrate (1), C12H10O5.H2O, was established by X-ray crystallographic analysis. The molecule of the title compound is essentially planar except for the carboxylate substituent group. The crystal packing supramolecular array arises from hydrogen bonds and intermolecular C-H - O=C contacts of the organic molecules and solvent water molecules, with graph-set descriptor R24 (8), R21 (6), R44 ( 20) and C (5) motifs. The water molecules are involved as donors and acceptors. The hydrogen bond and intermolecular interaction network is reinforced by stacking of the sheet through p-p interactions.http://ref.scielo.org/qhfkn

    Electrochemical deposition of a copper carboxylate layer on copper as potential corrosion inhibitor

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    Carboxylic acids and sodium carboxylates are used to protect metals against aqueous and atmospheric corrosion. In this paper we describe the application of a layer of copper carboxylate on the surface of a copper electrode by means of cyclic voltammetry technique, and tests which measure the corresponding resistance to aqueous corrosion. Unlike the soaking process, which also forms a film on the surface, the use of cyclic voltammetry allows one to follow the deposition process of the copper carboxylates onto the electrode. The modified electrodes have been characterized with infrared spectroscopy. In addition the corrosion resistance of the film has been investigated using polarization resistance and Tafel plot measurements
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