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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A novel hexaaza macrocycle bearing two hydroxyethyl pendants (L), 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxyethyl)tricyclo[22,2,2,2(11,14)]triaconta-1,11,13,24,27,29-hexaene, was synthesized as a potential binucleating ligand. The corresponding Cu(II) complex [Cu(2)LCl(2)]Cl(2) small middle dot5.5H(2)O was isolated as a blue crystal, triclinic, space group P with a= 9.4920(19) A, b = 4.783(3) A, c = 16.553(3) A, alpha = 63.87(3) degrees, beta = 86.10(3) degrees, gamma = 83.8(3) degrees, V = 2072.8(7) A(-3), Z = 2, R1 = 0.0658, and wR2 = 0.1839. Both Cu ions adopt the geometry of a distorted trigonal bipyramid in a pentacoordinated environment. A complexation study on the novel title complex has revealed that the alcoholic OH groups of the complex Cu(2)L exhibit an obvious acidity with rather low pK(a) values at 25 degrees C. The Cu(II)-bound alkoxides, which act as reactive nucleophiles toward the hydrolysis of 4-nitrophenyl acetate in 10% (v/v) CH(3)CN at 25 degrees C, with I = 0.10 (NaNO(3)) and pH 9.3, have shown a second-order rate constant, 0.41 +/- 0.02 M(-1) s(-1), a value that is approximately 10 times greater than the corresponding value for the mononuclear Cu(II) complex formed by a relatively simple tripodal ligand (L1). The pH-rate profile gave a sigmoidal curve. The possible catalytic mechanism has been proposed, and the reason for the high catalytic activity of the title complex has been discussed.
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PMID:Carboxyester hydrolysis catalyzed by a novel dicopper(II) complex with an alcohol-pendant macrocycle. 1192 73

Copper complexation by the 1,4-benzodiazepines medazepam, diazepam, flurazepam, nitrazepam, and clonazepam was investigated using differential pulse polarography and cyclic voltammetry at a mercury electrode in 0.10 M KNO3 and pH 7.0 +/- 0.1. Because the 1,4-benzodiazepines are easily reduced at a mercury electrode through the two-electron reduction of the 4,5-azomethine functional group, copper reduction, as well as that of the ligands, was analyzed under varying experimental conditions. In most situations adsorption phenomena occurred and their influence on voltammetric signals had to be carefully analyzed. The voltammetric behavior was then interpreted in terms of complex formation. The results showed that all benzodiazepines can act as ligands toward copper(II) ions, forming 1:1 and 1:2 complexes with similar stabilities. The stoichiometric acidity constants of the benzodiazepines under study were also determined by potentiometric titration in water-ethanol medium and 0.10 M KNO3 and then extrapolated to 0% concentration of ethanol.
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PMID:Copper-psychoactive drug complexes: a voltammetric approach to complexation by 1,4-benzodiazepines. 1195 Feb 10

Luminol and 1,10-phenanthroline are widely used chemiluminescent (CL) reagents for the analysis of a wide range of metals and inorganic and organic complexes. While the fundamental mechanism for luminol and 1,10-phenantholine chemiluminescence is understood, the analytical application of these reagents is largely empirical and often poorly described mechanistically. For example, CL signals observed from metal-luminol systems are strongly dependent on the pH of the sample, even though the final pH of the reaction mixture is controlled to a narrow range by a buffer. Other investigators report significant changes in CL signal due to freshness and the acidity of reagents. Our work shows that many of these effects are due to dissolved CO2 present or formed in the analytical system. The hypothesis that carbon dioxide plays a pivotal role in enhancing luminol CL is supported by direct manipulation of CO2(aq) concentrations by the addition of CO2(g) or carbonic anhydrase. In contrast, Cu(II) analysis using the CL reagent 1,10-phenanthroline is completely quenched in the presence of CO2(aq). A plausible mechanism for these observations involves the reaction between superoxide, produced in these analytical systems, and CO2(aq) to form the peroxycarbonate radical, *C04-. The formation of *CO4- has very important analytical implications since this species appears to enhance or quench the CL signal from luminol and 1,10-phenanthroline, respectively.
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PMID:Carbon dioxide effects on luminol and 1,10-phenanthroline chemiluminescence. 1203 28

Sugar beet pulp, a common agricultural waste, was studied in the removal of metal ions from aqueous solutions. Potentiometric titrations were used to characterize the surface acidity of the polysaccharide. The acid properties of the material can be described by invoking three distinct types of surface functional groups with the intrinsic acidity constants (pKa(int)) values 3.43+/-0.1, 6.05+/-0.05, and 7.89+/-0.1, respectively. The contents of each functional group (i.e., the carboxyl and phenol moieties) were also determined. Then, a simple surface complexation model with the diffuse layer model successfully described the sorption of several metal ions (Cu2+, Zn2+, Cd2+, and Ni2+) onto the polysaccharide under various experimental conditions: pH ranging from 2 to 5.5, ionic strength from 0.01 to 0.1 M, metal concentration between 10(-4) and 10(-3) M, for a constant sorbent concentration equal to 2.5 g x L(-1). It was observed experimentally that the affinity of the polysaccharide was in the sequence of Cu2+ > Zn2+ > Cd2+ > Ni2+. Predictions of sorption in binary-metal systems based on single-metal data fits represented competitive sorption data reasonably well.
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PMID:Modeling of single and competitive metal adsorption onto a natural polysaccharide. 1203 36

Humic fraction (HF) functional group-type and content are expected to depend on molecular size, which in turn, is expected to influence formation of heavy-metal complexes. In this study, corn (Zea mays L.) stalks and leaves were decomposed for an 8-month period to produce water-soluble humic substances. These substances were separated into three water-soluble fractions, HF1, HF2 and HF3, from highest to lowest relative molecular size. Functional group determination showed that carboxylic, and phenolic OH acidity increased as relative molecular size of humic fractions decreased. We also observed decreasing C/O ratios from larger to smaller corn tissue-derived humic fractions, whereas N/C and H/C ratios remained relatively unaffected. Furthermore, using potentiometric titration and FTIR spectroscopy we studied formation of Ca2+-, Cd2+-, and Cu2+-humic fraction complexes and how they were affected by pH and molecular size. We determined that metal-humic complexes exhibited at least two types of functional group-sites with respect to Ca2+, Cd2+, and Cu2+ complexation. Strength of metal-ion humic complexes followed the order Cu2+ > Cd2+ > Ca2+ and was affected by pH, especially for low affinity sites. Carboxylic groups were most likely the dominant group-sites involved in complex formation. Magnitude of the metal-humic formation constants in the logarithmic form at the lowest equilibrium metal-ion concentration, under the various pH values tested, varied from 5.39 to 5.90 for Ca2+, 5.36 to 6.01 for Cd2+, and 6.93 to 7.71 for Cu2+. Furthermore, the formation constants appeared to be positively influenced by decreasing molecular size of water-soluble humic fraction, and increasing pH. However, our molecular spectra showed that the pKa of corn humic fractions increased with decreasing relative molecular size and that Cu2+ was more covalently bonded by humic fractions than were Ca2+ and Cd2+, and the nature of the covalent bond character was independent of pH.
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PMID:Potentiometric-spectroscopic evaluation of metal-ion complexes by humic fractions extracted from corn tissue. 1221 41

Copper is next to iron the most important element in the biological transport, storage and in redox reactions of dioxygen. A bioanalogous activation of dioxygen with copper complexes is used for catalytical epoxidation, allylic hydroxylation and oxidative coupling of aromatic substrates, for example. With stereochemical information in form of chiral ligands, enantioselective reactions may be possible. Another aspect of interest on copper catalyzed reactions with dioxygen is that the exact mechanism and biological function of some enzymes (especially catechol oxidase) is yet not fully clear. For studies mimicking the copper-containing catechol oxidase appropriate chiral steroid ligands with defined stereochemistry and conformation have been synthesized. The four diastereomeric 16,17-aminoalcohols of the 3-methoxy-estra-1,3,5(10)-triene series have been condensed with salicylic aldehyde and different beta-ketoenols to the chiral ligand types 1-5. These compounds with different steric and electronic properties and different arrangements of the neighboring hydroxy and nitrogen functions were reacted with copper(II) acetate to copper complexes. The structure of these complexes will be discussed. The bioanalogous oxidation of 3,5-di-tbutyl-catechol (dtbc) to the corresponding quinone was catalyzed by most of the complexes, indicating their ability to activate dioxygen. The trans configurations c and d showed an activity one magnitude higher than the cis configurations a and b. Comparing compounds with the same diastereomeric configuration, the main influence was that of the peripheral R(1-3) substituents at the beta-ketoenaminic group which are useful for the fine-tuning of the properties of the copper atoms like redox potential and Lewis acidity.
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PMID:Synthesis, structure and catechol-oxidase activity of copper(II) complexes of 17-hydroxy-16-(N-3-oxo-prop-1-enyl)amino steroids. 1223 Nov 19

Tin is considered to be a priority contaminant by the Codex Alimentarius Commission. Tin can enter foods either from natural sources, environmental pollution, packaging material or pesticides. Higher concentrations are found in processed food and canned foods. Dissolution of the tinplate depends on the of food matrix, acidity, presence of oxidising reagents (anthocyanin, nitrate, iron and copper) presence of air (oxygen) in the headspace, time and storage temperature. To reduce corrosion and dissolution of tin, nowadays cans are usually lacquered, which gives a marked reduction of tin migration into the food product. Due to the lack of modern validated published methods for food products, an ICP-AES (Inductively coupled plasma-atomic emission spectroscopy) method has been developed and evaluated. This technique is available in many laboratories in the food industry and is more sensitive than atomic absorption. Conditions of sample preparation and spectroscopic parameters for tin measurement by axial ICP-AES were investigated for their ruggedness. Two methods of preparation involving high-pressure ashing or microwave digestion in volumetric flasks were evaluated. They gave complete recovery of tin with similar accuracy and precision. Recoveries of tin from spiked products with two levels of tin were in the range 99+/-5%. Robust relative repeatabilities and intermediate reproducibilities were <5% for different food matrices containing >30 mg/kg of tin. Internal standard correction (indium or strontium) did not improve the method performance. Three emission lines for tin were tested (189.927, 283.998 and 235.485 nm) but only 189.927 nm was found to be robust enough with respect to interferences, especially at low tin concentrations. The LOQ (limit of quantification) was around 0.8 mg/kg at 189.927 nm. A survey of tin content in a range of canned foods is given.
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PMID:Determination of total tin in canned food using inductively coupled plasma atomic emission spectroscopy. 1232 43

We investigated Cu complexation by three dissolved organic matters (DOMs) collected by reverse osmosis (RO). Alkalimetric titration, pH-stat Cu and Ca titrations, pH edges of Cu-DOM complexation, and Ca/Mg-Cu exchange experiments were investigated at 1 = 109-2)M for DOM samples of 10mg C/L. The proton and Cu binding characteristics indicated similarity for all three DOMs. All Cu titrations employed ion selective electrode measurement and indicated the presence of relatively small amounts of strong Cu-binding sites. Four distinct classes of Cu binding sites are required for FITEQL 4.0 to provide good fits to the entire curves. The estimated total Cu binding site density is 4.55 mmol/g C, much less than the total acidity but very close to the phenolic site content. Cu-DOM complexation increases approximately 10-fold per pH unit, even at relatively high pH (> 8). We suggest that sites characterized as phenolic based on alkalimetric titration, not carboxyl sites, account for the majority of Cu complexation under natural water conditions, and Cu-DOM complexation is principally through the replacement of H + by Cu2+ at the phenolic binding sites. The Cu-H exchange ratio is 1:1 for the first three sites and about 1:2 for the 4th site. This 4-site model describes well the pH dependency of Cu-DOM complexation and provides good estimates of free Cu concentrations throughout wide total copper (Cu(T)) and pH ranges. Comparison between Ca-DOM and Cu-DOM complexation demonstrated that (i) Ca-DOM complexation increases much less than an order of magnitude per pH unit and decreases at higher Ca concentration, different from that of Cu-DOM complexation; and (ii) Cu-DOM complexation is highly non-linear, in contrast to the much reduced extent of non-linearity of Ca-DOM complexation. Ca/Mg-Cu exchange experiments showed small competition effect, less than expected by a simple competition model, and the competition tended to reduce with increasing Ca or Mg concentrations. The extent of the competition by Mg and Ca are essentially comparable. Put all together, it suggests that Ca and Mg are preferably bound by carboxyl sites, especially at relatively high concentrations, resulting in a weakened apparent competition effect.
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PMID:Characterization of copper complexation with natural dissolved organic matter (DOM)--link to acidic moieties of DOM and competition by Ca and Mg. 1244 57

In this paper, extraction chromatography by which Co2+ can be separated from Cu2+, Cd2+, Mn2+, Zn2+, Fe3+ is developed. The chromatographic column was 17 mm i.d. x 520 mm, containing polymers synthesized by styrene, divinylbenzene and P204 (volume fraction was 40%), with particle size of 100-200 mesh. The effects of transformation of P204 from the H(+)-form to the Na(+)-form by NaAc solution, the eluent acidity, and eluent composition were investigated. The results indicated that this extraction chromatographic method is good to separate Co2+ from Cu2+, Cd2+, Mn2+, Zn2+ and Fe3+, and the condition of separation is simple and convenient. When the P204 is transformed from the H(+)-form to the Na(+)-form by pH 4.0 NaAc (0.5 mol/L), and the column is eluted with pH 2.5 ClCHCOOH-ClCHCOONa (0.1 mol/L), the separation can be completed effectively.
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PMID:[Study on the separation of Co2+ from Cu2+, Cd2+, Mn2+, Zn2+ and Fe3+ by extraction chromatography]. 1254 30

The Tinto river in Spain, with its high acidity and heavy metal concentrations (As, Cu, Cr, Zn), is an example of an environment hostile to life. Yet despite these extreme conditions, the site possesses a great diversity of eukaryotic life forms. We report the isolation of a filamentous fungus able to grow at 200 mM arsenic ( approximately 15 000 p.p.m.), i.e. a concentration 20-fold above that withstood by the reference microorganisms Escherichia coli, Saccharomyces cerevisiae and Aspergillus nidulans, and 200 times greater than that tolerated by Aspergillus niger. Based on morphological, physiological and genotypic criteria, the strain belongs to the genus Aspergillus. High concentrations of the metalloid induced vacuolation, suggesting that this organelle is someway connected to arsenic tolerance. Concentrations that are lethal to other organisms do not stress Aspergillus sp. P37. The fungus was capable of removing arsenic from culture media. In addition to arsenic hyper-resistance, it also displayed a polyresistant phenotype to copper and chromium.
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PMID:Testing the limits of biological tolerance to arsenic in a fungus isolated from the River Tinto. 1255 96


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