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Urea coated with oxidized charcoal reduces ammonia volatilization

Paiva,Diogo Mendes de; Cantarutti,Reinaldo Bertola; Guimarães,Gelton Geraldo Fernandes; Silva,Ivo Ribeiro da
Fonte: Sociedade Brasileira de Ciência do Solo Publicador: Sociedade Brasileira de Ciência do Solo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2012 EN
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304.48656%
Urea is the most consumed nitrogen fertilizer in the world. However, its agronomic and economic efficiency is reduced by the volatilization of NH3, which can reach 78 % of the applied nitrogen. The coating of urea granules with acidic compounds obtained by charcoal oxidation has the potential to reduce the volatilization, due to the acidic character, the high buffering capacity and CEC. This work aimed to evaluate the effect of HNO3-oxidized carbon on the control of NH3 volatilization. These compounds were obtained by oxidation of Eucalyptus grandis charcoal, produced at charring temperatures of 350 and 450 ºC, with 4.5 mol L-1 HNO3. The charcoal was oxidized by solubilization in acidic or alkaline medium, similar to the procedure of soil organic matter fractionation (CHox350 and CHox450). CHox was characterized by C, H, O, N contents and their respective atomic relations, by the ratio E4 (absorbance 465 nm) by E6 (absorbance 665 nm), and by active acidity and total acidity (CEC). The inhibitory effect of CHox on the urease activity of Canavalia ensiformis was assessed in vitro. The NH3 volatilization from urea was evaluated with and without coating of oxidized charcoal (U-CHox350 or U-CHox450) in a closed system with continuous air flow. The pH of both CHox was near 2.0...

Propriedades ácido-base e de complexação de ácidos húmico e fúlvico isolados de vermicomposto

Colombo,Sandro de Miranda; Santos,Luciana Bagdeve de Oliveira dos; Masini,Jorge Cesar; Abate,Gilberto
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2007 PT
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284.4566%
Proton binding properties of humic and fulvic acids were studied by potentiometric titration. Carboxylic groups were the predominant ionizable sites in comparison to phenolic and amine groups. Total acidity of fulvic acid was 12 x 10-3 mol g-1, a number significantly higher than that obtained for humic acid (5.2 x 10-3 mol g-1). Copper ion binding was evaluated at pH 4, 5 and 6 by potentiometric titration with an ion selective electrode for Cu(II). Differential stability constants and complexation capacities were systematically higher for humic acid, despite its lower number of ionizable sites in comparison with fulvic acid.

Model compounds of humic acid and oxovanadium cations. Potentiometric titration and EPR spectroscopy studies

Mercê,Ana Lucia Ramalho; Spir,Ivana Helena Zamuner; Oruña Salmón,Maria José; Giannoni,Ricardo Alberto; Mangrich,Antonio Sálvio
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/1999 EN
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519.4542%
The stability constants and the isotropic EPR parameters Ao (hyperfine splitting constant) and g o (g value) were obtained by potentiometric titrations and EPR spectroscopy, respectively, of 85%v/v aqueous solutions of model compounds of humic acids - salicylic acid (SALA) - and both nitrohumic acids, a laboratory artifact - nitrosalicylic acids, 3-nitrosalicylic acid (3-NSA), 5-nitrosalicylic acid (5-NSA) and 3,5-dinitrosalicylic acid (3,5-DNSA) and oxovanadium cations. It was possible to record EPR spectra of those model compounds and the ion VO2+ (V(IV)), and the stability constants were obtained from a solution of VO3+ (V(V)), the values for the logarithms of the stability constants ranging from 12.77 ± 0.04 to 7.06 ± 0.05 for the species ML, and from 9.90 ±0.04 to 4.06 ± 0.05 for the species ML2 according to the decrease in the acidity of the carboxylic and the hydroxyl groups in the aromatic ring of the model compounds studied as the -NO2 substituents were added. Species distribution diagrams were also obtained for the equilibria studied. The EPR parameters showed that as the logarithm of the overall stability constants increase, g o values also increase, while Ao values show a tendency to decrease.

Metal ion-binding properties of (N3)-deprotonated uridine, thymidine, and related pyrimidine nucleosides in aqueous solution

Knobloch, Bernd; Linert, Wolfgang; Sigel, Helmut
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
395.02305%
The acidity constants for (N3)H of the uridine-type ligands (U) 5-fluorouridine, 5-chloro-2′-deoxyuridine, uridine, and thymidine (2′-deoxy-5-methyluridine) and the stability constants of the M(U–H)+ complexes for M2+ = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ were measured (potentiometric pH titrations; aqueous solution; 25°C; I = 0.1 M, NaNO3). Plots of documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} setlength{oddsidemargin}{-69pt} egin{document} egin{equation*}{mathrm{log}}K_{{mathrm{M}}({mathrm{U}}-{mathrm{H}})}^{{mathrm{M}}}end{equation*}end{document} vs. documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} setlength{oddsidemargin}{-69pt} egin{document} egin{equation*}{mathrm{p}}K_{{mathrm{U}}}^{{mathrm{H}}}end{equation*}end{document} result in straight lines that are compared with previous plots for simple pyridine-type and o-amino(methyl)pyridine-type ligands as well as with the stabilities of the corresponding M(cytidine)2+ complexes. The results indicate monodentate coordination to (N3)– in M(U–H)+ for Co2+ and Ni2+. For the M(U–H)+ species of Cd2+...

Synthesis and Thermodynamic Evaluation of Mixed Hexadentate Linear Iron Chelators Containing Hydroxypyridinone and Terephthalamide Units1

Abergel, Rebecca J.; Raymond, Kenneth N.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/05/2006 EN
Relevância na Pesquisa
284.9029%
A series of new linear iron chelators containing hydroxypyridinone and terephthalamide moieties has been prepared. All are hexadentate ligands composed of a systematically varied combination of me-3,2-hydroxypyridinone and 2,3-dihydroxyterephthalamide binding units; most are based on a spermidine scaffold but one incorporates the bifunctional 2,3-dihydroxyterephthalamide unit as an integral part of the backbone. Protonation and ferric iron complex formation constants have been determined from solution thermodynamic studies giving log ε110 values of 25.7, 30.7, 36.3, 43.8, and 45.0 respectively. The ferric complexes display reversible reduction potentials from −276 mV to −1032 mV (measured relative to the normal hydrogen electrode NHE) in alkaline solution. The incremental replacement of hydroxypyridinone units by terephthalamide binding groups progressively reduces the ligand acidity, markedly increases the iron-chelate stability, and improves the selectivity for ferric ion over ferrous ion. While the majority of iron chelators forming very stable ferric complexes are based on a tripodal backbone such as TREN, the ferric 5-LIO(TAMmeg)2(TAM) complex, despite its non-tripodal scaffold, is one of the most stable iron complexes yet reported. Moreover...

Lanthanide Complexes of Bifunctional Chelates as pH and Ca2+ Sensitive Contrast Agents for MR Imaging. Design, Synthesis and Characterization; Lanthanoidkomplexe von funktionalisierten Chelaten als pH- und Ca2+- abhängige Kontrastmittel für die Magnetresonanz-Bildgebung. Design, Synthese und Charakterisierung

Mammadov, Ilgar
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
402.72215%
A series of gadolinium based complexes have been designed, synthesized and characterized. Finally in vivo investigations of the compounds have been preformed by combined electrophysiological and fMRI methods. Acyclic bifunctional chelating agents were synthesized by two different ways starting from the dimethylester of nitro- or aminoisophtalic acid. Complexes with gadolinium and europium were obtained and relaxivities were measured at 300 MHz and 25oC. The very poor solubility of the complexes in water and most organic solvents indicate the formation of di- or polymer chains upon the complexation. This makes the complexes useless for further investigations as MRI contrast agents. Although the amino derivative can be modified and used as a building blocks in the syntheses of the specific chelators. The second set of compounds was designed to be sensitive to changes of pH. Protected and unprotected phosphonates were used to study the effect of the charge and acidity of the complexes on the relaxivity. Thermodynamic investigations of the ligands have been performed using glass-electrode potentiometric titrations and protonation constants of the phosphonates as well as stability constants of the ligand-calcium(II) complexes (as model for the stability of gadolinium(III) complexes) have been determined. pK values of the phosphonic functional groups increase with increase of the chain length of the pendant arm. The reverse behavior was observed for the second protonation constant of the nitrogen atom of the cyclen rim. Relaxometric measurements of the gadolinium(III) complexes have been performed at various magnetic fields (20...

Equilibrium studies of 2,2'-(5-bromo-6-methylpyrimidine-2,4-diyl)bis(azanediyl)dipropanoic acid with some transition-metal ions in aqueous solution

Sajadi,Seyed A. A.; Bagherzadeh,Ghodsieh; Khaleghian,Marzieh; Mirbagheri,Maryam; Safaie,Hosein
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 EN
Relevância na Pesquisa
714.7632%
The stability constants of the 1:1 complexes formed between M2+ (M2+: Mn2+, Ni2+, Cu2+, or Cd2+) and BMADA2- (BMADA: 2,2'-(5-bromo-6-methylpyrimidine-2,4 diyl)bis(azanediyl)dipropanoic acid) were determined by potentiometric pH titration in aqueous solution (I = 0.1 mol L-1, NaNO3, 25 °C). The stability of the binary M - BMADA complexes is determined by the basicity of the carboxyl or amino groups. All the stability constants reported in this work exhibit the usual trend, and the order obtained was Mn2+< Ni2+ < Cu2+ > Cd2+. The observed stability order for BMADA approximately follows the Irving - Williams sequence. In the M - BMADA complexes, the M ion is able to form a macrochelate via the pyrimidine group of BMADA.

Substituent Effects on the Thermodynamic Stability of Imines Formed from Glycine and Aromatic Aldehydes: Implications for the Catalytic Activity of Pyridoxal-5'-Phosphate (PLP)

Crugeiras, Juan; Rios, Ana; Riveiros, Enrique; Richard, John P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 04/11/2009 EN
Relevância na Pesquisa
292.0237%
Equilibrium constants for addition of glycine to substituted benzaldehydes to form the corresponding imines and pKas for ionization of the iminium ions were determined by 1H NMR analysis in D2O. The introduction of a phenoxide anion substituent into the aromatic ring of benzaldehyde leads to a substantial increase in the pKa of the iminium ion from 6.3 to 10.2 for p-hydroxybenzaldehyde and to 12.1 for salicyaldehyde. An analysis of the differential effect of ortho- versus para-substitution shows that the iminium ion to salicylaldehyde is stabilized by an intramolecular hydrogen bond in aqueous solution, with an estimated energy ca. 3 kcal/mol larger than can be accounted for by a simple electrostatic interaction. A comparison of the o-O− substituent effect on the acidity of the iminium ions of glycine to benzaldehyde and 4-pyridine-carboxaldehyde provides evidence for the existence of an internal hydrogen bond of similar strength in pyridoxal 5'-phosphate (PLP) iminium ions in water. The effects of other ring substituents on the stability of PLP iminium ions are discussed.

Nickel(II), Copper(II) and Zinc(II) Complexes of 9-[2- (Phosphonomethoxy)ethyl]-8-azaadenine (9,8aPMEA), the 8-Aza Derivative of the Antiviral Nucleotide Analogue 9-[2-(Phosphonomethoxy)ethyl] adenine (PMEA). Quantification of Four Isomeric Species in Aqueous Solution

Gómez-Coca, Raquel B.; Holý, Antonín; Vilaplana, Rosario A.; González-Vílchez, Francisco; Sigel, Helmut
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em //2004 EN
Relevância na Pesquisa
402.5043%
The acidity constants of the twofold protonated acyclic nucleotide analogue 9-[2-(phosphonomethoxy)- ethyl]-8-azaadenine, H2(9,8aPMEA)±, as well as the stability constants of the M(H;9,8aPMEA)+ and M(9,8aPMEA) complexes with the metal ions M2+ =Ni2+, Cu2+ or Zn2+, have been determined by potentiometric pH titrations in aqueous solution at I=0.1 M (NaNO3) and 25℃. The result for the release of the first proton from H2(9,8aPMEA)+ (pKa= 2.73), which originates from the (N1)H+ site, was confirmed by UV-spectrophotometric measurements. Application of previously determined straight-line plots of log KMM(R-PO3) versus PKH3(R-HPO3)' for simple phosph(on)ate ligands, R- PO-, where R represents a residue without an affinity for metal ions, proves that the primary binding site of 9,8aPMEA2- is the phosphonate group for all three metal ions studied. By stability constant comparisons with related ligands it is shown, in agreement with conclusions reached earlier for the Cu(PMEA) system [PMEA2-=dianion of 9-[2- (phosphonomethoxy)ethyl]adenine], that in total four different isomers are in equilibrium with each other, i.e. (i) an open isomer with a sole phosphonate coordination, M(PA)op, where PA2-=PMEA2-or 9,8aPMEA2-, (ii) an isomer with a 5-membered chelate involving the ether oxygen...