Grafting of adipic anhydride to carbon nanotubes through a Diels-Alder cycloaddition/oxidation cascade reaction

Accepted Manuscript

Comparison of H/Al stoichiometry of mineral and organic soils in Brazil

Exchangeable Al has been used as a criterion for the calculation of lime requirement in several Brazilian States. However, the laboratory method with extraction by a 1 mol L-1 KCl solution followed by indirect alkaline titration is not accurate for some Brazilian soils, mainly in the case of soils with high organic matter content. The objective of this study was therefore to evaluate the stoichiometry of H+/Al3+ in KCl soil extracts. The results suggested that organically complexed Al is the main contributor to exchangeable acidity in soils enriched with organic matter. Liming recommendations for organic soils based exclusively on exchangeable Al determined by the NaOH titration method should therefore be revised.

Potencialidades do dióxido de chumbo eletrodepositado como sensor potenciométrico

This paper proposes an experiment to be performed in both instrumental analysis and experimental physical-chemistry curricular disciplines in order to open options to develop challenging basic research activities. Thus the experimental procedures and the results obtained in the preparation of electrodeposited lead dioxide onto graphite and its evaluation as potentiometric sensor for H3O+ and Pb2+ ions, are presented. The data obtained in acid-base titrations were compared with those of the traditional combination glass electrode at the same conditions. Although a linear sub-Nernstian response to free hydrogen ions was observed for the electrodeposited PbO2 electrode, a good agreement was obtained between them. Working as lead(II) sensing electrode, the PbO2 showed a linear sub-Nernstian behavior at total Pb2+ concentrations ranging from 3,5 x 10-4 to 3,0 x 10-2 mol/L in nitrate media. For the redox couple PbO2/Pb(II) the operational slope converges to the theoretical one, as the acidity of the working solution increases.

Avaliação da capacidade tamponante - um experimento participativo

The aim of this work is to show an experiment from which students can learn some of the main characteristics of buffer solutions. A mixture of some acid-base indicators, named as Yamada's indicator, can be used to estimate pH values in an acid-base titration of a buffer, with good approximation. In the experiment it is also possible to verify the relationship between the buffer capacity and the concentrations and the molar ratio of the components of a NH3 / NH4+ buffer solution. The shortage of experiments associated with the relative small importance given to many aspects of buffer solutions, is now explored with simplicity. In the proposed experiments, students prepare buffer solutions by themselves, calculate the pH, understand how acid-base indicators act and learn how buffer solutions work through graph constructed by sharing experimental data.

TitGer: uma planilha eletrônica para simulação de titulação de mistura de compostos polipróticos

The aim of this paper is to present a simple way of treating the general equation for acid-base titrations based on the concept of degree of dissociation, and to propose a new spreadsheet approach for simulating the titration of mixtures of polyprotic compounds. The general expression, without any approximation, is calculated a simple iteration method, making number manipulation easy and painless. The user-friendly spreadsheet was developed by using MS-Excel and Visual-Basic-for-Excel. Several graphs are drawn for helping visualizing the titration behavior. A Monte Carlo function for error simulation was also implemented. Two examples for titration of alkalinity and McIlvaine buffer are presented.

Development of a heavy metal sorption system through the P=S functionalization of coconut (Cocos nucifera) fibers

Lignocellulosic residues are interesting materials for the production of heavy metal adsorbents for aquatic systems. Whole fibers taken from coconut (Cocos nucifera) husks were functionalized with the thiophosphoryl (P=S) group by means of the direct reaction with CI(3)P=S, (CH(3)O)(2)CIP=S or (CH(3)CH(2)O)(2)CIP=S in order to obtain an adsorptive system for `soft` metal ions, particularly Cd(2+). These functionalized fibers (FFs) were characterized by means of elemental analysis, infrared spectroscopy, thermal analysis and acid-base titration. Adsorption isotherms for Cd(2+) fitted the Langmuir model, with binding capacities of 0.2-5 mmol g(-1) of FF at 25 degrees C. (C) 2009 Elsevier Ltd. All rights reserved.

Preparation of polymeric micelles for use as carriers of tuberculostatic drugs

Purpose: This paper focuses on the characterization of polymeric micelle-forming tuberculostatic prodrugs and the antimycobacterial activity of these prodrugs.Method: By the condensation of hydroxymethylpyrazinamide, isoniazid and rifampin with free carboxyl groups on the copolymer poly(ethyleneglycol)-poly(aspartic acid), micelle-forming carrier-drug conjugates were obtained. These micelles were characterized by dynamic light scattering, to measure the micelle diameter; by acid-base titration, to determine the percentage of carboxylic groups occupied by the tuberculostatic; by Sudan III solubility tests, to estimate the critical micelle concentration (CMC); and visual control and spectrophotometric measurement, to determine the stability of micelles. These micelles were tested in vitro against several Mycobacterium strains.Results: As expected, the size and distribution of the micelle-forming tuberculostatic prodrugs found to be small (78.2nm, 84.2nm and 98.9 nm) while the level of the drug conjugated was high (65.02-85.7%). Furthermore, the micelles were stable in vitro, exhibiting a low level of CMC and stronger antimycobacterial activity than the original drugs.Conclusion: the results demonstrate that polymeric micelles can be used as efficient carriers for drugs, which alone, exhibit undesired pharmacokinetics, poor solubility, and low stability. The synthesized micelle-forming tuberculostatic prodrugs opens a perspective of alternative prodrugs that prolong action and decrease the toxicity of the tuberculostatic drugs of choice.

Desenvolvimento de metodologia simplificada para análise de hexametilenotetramina (hmt) em medicamentos contendo corantes em sua formulação

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Comparison of three strip-type tests and two laboratory methods for salivary buffering analysis

This study evaluated the correlation between three strip-type, colorimetric tests and two laboratory methods with respect to the analysis of salivary buffering. The strip-type tests were saliva-check buffer, Dentobuff strip and CRT(®) Buffer test. The laboratory methods included Ericsson's laboratory method and a monotone acid/base titration to create a reference scale for the salivary titratable acidity. Additionally, defined buffer solutions were prepared and tested to simulate the carbonate, phosphate and protein buffer systems of saliva. The correlation between the methods was analysed by the Spearman's rank test. Disagreement was detected between buffering capacity values obtained with three strip-type tests that was more pronounced in case of saliva samples with medium and low buffering capacities. All strip-type tests were able to assign the hydrogencarbonate, di-hydrogenphosphate and 0.1% protein buffer solutions to the correct buffer categories. However, at 0.6% total protein concentrations, none of the test systems worked accurately. Improvements are necessary for strip-type tests because of certain disagreement with the Ericsson's laboratory method and dependence on the protein content of saliva.

(Supplement) Groundwater quality in Lahore Pakistan: emphasis on Arsenic and Fluoride levels

The dataset provides detailed information on the study that was conducted in Lahore's 7 major towns. The sample was taken from 472 tubewells and analyzed for major cations and anions using APHA 2012 techniques as explained herein. Besides, E.coli determination was done to check for microbial contamination. The data includes results from PHREEQC modeling of As(III)/ As(V) species and saturation indices as well as Aquachem's computed hydrochemical water facies. The WHO (2011) and EPA standards included in Aquachem identified the parameters that where in violation. Bicarbonates dominated the groundwater types with 50.21% of the samples exceeding the EPA maximum permissible limit of 250 mg/L in drinking water. Similarly, 30.51% of the samples had TDS values greater than 500 mg/L while 85.38 % of the samples exceed 10 µg/L threshold limit value of arsenic. Also, instances of high magnesium hazard values were observed which requires constant assessment if the groundwater is used for irrigation. Higher than 50% MH values are detrimental to crops which may reduce the expected yields. The membrane filtration technique using m-Endo Agar indicated that 3.59% samples had TNC (too numerous to count) values for E.coli while 5.06% showed values higher than 0 cfu/ 100 ml acceptable value in drinking water. Any traces of E-coli in a groundwater sample indicate recent fecal contamination. Such outcomes signify presence of enteric pathogens. If the groundwater is not properly dosed with disinfectants it may cause harm to human health. It is concluded that more studies are needed and proper groundwater management implement to safeguard the lives of communities that depend solely on groundwater in the city.

Bifunctional SO4/ZrO2 catalysts for 5-hydroxymethylfufural (5-HMF) production from glucose

The telescopic conversion of glucose to fructose and then 5-hydroxymethylfurfural (5-HMF), the latter a potential, bio-derived platform chemical feedstock, has been explored over a family of bifunctional sulfated zirconia catalysts possessing tuneable acid-base properties. Characterisation by acid-base titration, XPS, XRD and Raman reveal that submonolayer SO4 coverages offer the ideal balance of basic and Lewis-Brønsted acid sites required to respectively isomerise glucose to fructose, and subsequently dehydrate fructose to 5-HMF. A constant acid site normalised turnover frequency is observed for fructose dehydration to 5-HMF, confirming a common Brønsted acid site is responsible for this transformation. This journal is © The Royal Society of Chemistry.

Bifunctional SO4/ZrO2 catalysts for 5-hydroxymethylfufural (5-HMF) production from glucose

The telescopic conversion of glucose to fructose and then 5-hydroxymethylfurfural (5-HMF), the latter a potential, bio-derived platform chemical feedstock, has been explored over a family of bifunctional sulfated zirconia catalysts possessing tuneable acid-base properties. Characterisation by acid-base titration, XPS, XRD and Raman reveal that submonolayer SO4 coverages offer the ideal balance of basic and Lewis-Brønsted acid sites required to respectively isomerise glucose to fructose, and subsequently dehydrate fructose to 5-HMF. A constant acid site normalised turnover frequency is observed for fructose dehydration to 5-HMF, confirming a common Brønsted acid site is responsible for this transformation. This journal is © The Royal Society of Chemistry.

A direct potentiometric titration study of the dissociation of humic acid with selectively blocked functional groups

A direct potentiometric titration method was applied to commercial and soil humic acids in order to determine their carboxyl and phenol group concentrations and apparent and intrinsic pK. In that context, acid-base properties of humic acids are interpreted by selective blocking of carboxylic and phenolic groups by esterification and acetylation. Differences in underivatized and derivatized HA's acid-base properties are ascribed to carboxyl and phenol groups influence on total humic acidity. Potentiometric data were treated with the modified Henderson-Hasselbalch equation. Infra red results, the acidic group contents and the average values of apparent and intrinsic pK for underivatized and derivatized HAs confirmed the selectivity of esterification derivatization method. After blocking of the functional groups, the values of acidic group contents decreased, while the value of apparent pK increased after derivatization. Phenol groups cannot be specifically identified by the acetylation method, due to low selectivity of the acetylation method.

Development of a novel titration and off-gas analysis (TOGA) sensor for study of biological processes in wastewater treatment systems

The development of the new TOGA (titration and off-gas analysis) sensor for the detailed study of biological processes in wastewater treatment systems is outlined. The main innovation of the sensor is the amalgamation of titrimetric and off-gas measurement techniques. The resulting measured signals are: hydrogen ion production rate (HPR), oxygen transfer rate (OTR), nitrogen transfer rate (NTR), and carbon dioxide transfer rate (CTR). While OTR and NTR are applicable to aerobic and anoxic conditions, respectively, HPR and CTR are useful signals under all of the conditions found in biological wastewater treatment systems, namely, aerobic, anoxic and anaerobic. The sensor is therefore a powerful tool for studying the key biological processes under all these conditions. A major benefit from the integration of the titrimetric and off-gas analysis methods is that the acid/base buffering systems, in particular the bicarbonate system, are properly accounted for. Experimental data resulting from the TOGA sensor in aerobic, anoxic, and anaerobic conditions demonstrates the strength of the new sensor. In the aerobic environment, carbon oxidation (using acetate as an example carbon source) and nitrification are studied. Both the carbon and ammonia removal rates measured by the sensor compare very well with those obtained from off-line chemical analysis. Further, the aerobic acetate removal process is examined at a fundamental level using the metabolic pathway and stoichiometry established in the literature, whereby the rate of formation of storage products is identified. Under anoxic conditions, the denitrification process is monitored and, again, the measured rate of nitrogen gas transfer (NTR) matches well with the removal of the oxidised nitrogen compounds (measured chemically). In the anaerobic environment, the enhanced biological phosphorus process was investigated. In this case, the measured sensor signals (HPR and CTR) resulting from acetate uptake were used to determine the ratio of the rates of carbon dioxide production by competing groups of microorganisms, which consequently is a measure of the activity of these organisms. The sensor involves the use of expensive equipment such as a mass spectrometer and requires special gases to operate, thus incurring significant capital and operational costs. This makes the sensor more an advanced laboratory tool than an on-line sensor. (C) 2003 Wiley Periodicals, Inc.

Preliminary evaluation of acid mine drainage in Minas Gerais State, Brazil

Mining in the State of Minas Gerais-Brazil is one of the activities with the strongest impact on the environment, in spite of its economical importance. Amongst mining activities, acid drainage poses a serious environmental problem due to its widespread practice in gold-extracting areas. It originates from metal-sulfide oxidation, which causes water acidification, increasing the risk of toxic element mobilization and water resource pollution. This research aimed to evaluate the acid drainage problem in Minas Gerais State. The study began with a bibliographic survey at FEAM (Environment Foundation of Minas Gerais State) to identify mining sites where sulfides occur. Substrate samples were collected from these sites to determine AP (acidity potential) and NP (neutralization potential). The AP was evaluated by the procedure of the total sulfide content and by oxygen peroxide oxidation, followed by acidity titration. The NP was evaluated by the calcium carbonate equivalent. Petrographic thin sections were also mounted and described with a special view to sulfides and carbonates. Based on the chemical analysis, the acid-base accounting (ABA) was determined by the difference of AP and NP, and the acid drainage potential obtained by the ABA value and the total volume of material at each site. Results allowed the identification of substrates with potential to generate acid drainage in Minas Gerais state. Altogether these activities represent a potential to produce between 3.1 to 10.4 billions of m³ of water at pH 2 or 31.4 to 103.7 billions of m³ of water at pH 3. This, in turn, would imply in costs of US$ 7.8 to 25.9 millions to neutralize the acidity with commercial limestone. These figures are probably underestimated because some mines were not surveyed, whereas, in other cases, surface samples may not represent reality. A more reliable state-wide evaluation of the acid drainage potential would require further studies, including a larger number of samples. Such investigations should consider other mining operations beyond the scope of this study as well as the kinetics of the acid generation by simulated weathering procedures.