Diprotic Acid Research Articles

Mechanisms of alkaline buffering by peat and quantitative estimation of its buffering capacity

The alkaline buffering capacity of humic substances in persistent organic materials such as peats has been utilized for remediation of alkaline soils. The purposes of the present study were to reveal the mechanism of alkaline buffering and to quantify the alkaline buffering capacity of humic substances contained in three peat samples obtained from Hokkaido, Canada, and Sri Lanka. Acidic functional groups in humic acid and fulvic acid extracted from the three natural peats were quantified by alkalimetric titration and pK distribution analyses of the titration curves. The results indicate that the inherent degree of humification of the organic matter can be identified from the pK distribution, which showed that the humic substances in peats contained diprotic acids. The present study also showed that the ratios of amounts of deprotonation to organic carbon content, as well as the organic carbon content, were needed for quantification of the pH buffering capacity. Moreover, the study showed that the composition of the peat from Sri Lanka was different from those of other peats and that it is a effective organic material for buffering under alkaline conditions.

Retention behavior ofo-phthalic, 3-nitrophthalic, and 4-nitrophthalic acids in ion-suppression reversed-phase high performance liquid chromatography using acids instead of buffers as ion-suppressors

In reversed-phase high performance liquid chromatography, the logarithm of the retention factor, log k, is usually correlated with the logarithm of the octanol-water partition coefficient, log Kow. The k and Kow of an ionizable analyte are greatly influenced by the mobile phase pH. In this paper, log kw of diprotic o-phthalic, 3-nitrophthalic, and 4-nitrophthalic acids, are obtained by extrapolation to pure aqueous fraction of mobile phase in ion-suppression reversed-phase high performance liquid chromatography with acetic acid and perchloric acid as the ion-suppressors. The Kow values of the three analytes are calibrated according to the apparent octanol-water partition coefficient, Kow, under different pH conditions, and the log K"ow values show a much better correlation with log kw than do log Kow. The influences of two ion-suppressors, acetic and perchloric acids, on the retention behavior of these diprotic acids at different pH are contrasted. An abnormal trend is found in the k vs. pHw plot of the acetic acid system when the methanol content is low. A possible reason is that acetic acid is an even stronger organic modifier than methanol, besides being an ion-suppressor. The results make the selection of mobile phase for the separation of acidic compounds by ion-suppression reversed-phase high performance liquid chromatography direct, accurate, and practical.

Reactions of 5,5\'-dithiobis(2-nitrobenzoate) with CysB5(23)β and CysF9(93)β Of Duck Minor Hemoglobin

The reactivities of the sulphydryl groups of duck minor hemoglobin have been studied for a comparison with those of duck major hemoglobin. Boyer titration with p-hydroxymercuri(II)benzoic acid (pMB) gave four reactive sulphydryl groups per (tetramer) molecule. Titration with 5,5'- dithiobis(2-nitrobenzoic acid) (DTNB) also gave four reactive sulphydryl groups per molecule. The kinetics of the reaction of DTNB with the oxy-, carbonmonoxy- and aquomet derivatives was studied at 20 0 C as a function of pH (7.0 9.0) under pseudo- first-order conditions. Biphasic time courses were obtained under all experimental conditions and the two kinetic phases were well separated along the time axis. The apparent second-order rate constants, k app , were calculated from the observed pseudo-first-order rate constant, k obs . The dependence of k app on pH for each of the two kinetic phases is simple, resembling the titration curve of a diprotic acid. For the fast kinetic phase, quantitative analyses of the simple pH dependence profiles gave pK a s of 5.5 ± 0.5 and 8.4 ± 0.3. The pK a of 5.5 is assigned to HisHC3(146) β; the pK a of 8.4 is assigned to CysF9(93)β. For the slow kinetic phase, quantitative analyses of the simple pH dependence profiles gave pK a s of 5.3 ± 0.3 and 8.7 ± 0.1. The pK a of 5.3 is assigned to HisG19(117) β; the pK a of 8.7 is assigned to CysB5(23) β. CysF9(93) β is responsible for the fast phase while CysB5(23) β is responsible for the slow phase. The result obtained showed that the reactivity of the CysF9(93) β sulphydryl of the minor hemoglobin differs from that of the major hemoglobin. It was observed that for the CysF9(93) β reaction, the oxy and aquomet derivatives of the major hemoglobin reacted about 3-fold faster than the corresponding derivatives of the minor hemoglobin. The carbonmonoxy derivative of the major hemoglobin reacted about 20-fold faster than the corresponding derivative of the minor hemoglobin. For the CysB5(23) β reaction, the oxy, carbonmonoxy and aquomet derivatives of the major hemoglobin reacted at about the same rate as the corresponding derivatives of the minor hemoglobin. KEY WORDS: Hemoglobin, sulphydryl groups, duck, p-hydroxymercuri (II) benzoate, 5,5'-dithiobis(2-nitrobenzoic acid). Global Journal of Pure and Applied Sciences Vol.11(2) 2005: 225-231

Reactions Of 5,5\'-Dithiobis(2 -Nitrobenzoate) with CysB5(23)β and CysF9(93)β 0f Duck Major Hemoglobin

Duck major hemoglobin contains ten sulphydryl groups per tetramer molecule as revealed by its amino acid sequence. Boyer titration of this hemoglobin with p-hydroxymercuri(II)benzoic acid (pMB) indicates that there are only six reactive sulphydryl groups per (tetramer) molecule, while titration with 5,5'dithiobis(2-nitrobenzoic acid) (DTNB) indicates only four. The kinetics of the reaction of DTNB with the oxy-, carbonmonoxy-, and aquomet derivatives of this hemoglobin were studied at 20oC as a function of pH (pH 7.0 9.0) under pseudo-first order conditions. Biphasic time courses were obtained under all experimental conditions and the two kinetic phases were well separated along the time axis. The apparent second-order rate constants, kapp, were determined from the observed pseudo- first-order rate constants, kobs. The dependence of kapp on pH for each of the two kinetic phases is simple, resembling the titration curve of a diprotic acid. For the fast kinetic phase, quantitative analyses of the simple pH dependence profiles gave pKas of 5.5 ± 0.5 and 8.6 ± 0.2. The pKa of 5.5 ± 0.5 is assigned to HisHC3(146)β, the pKa of 8.6 0.2 is assigned to CysF9(93)β. For the slow kinetic phase, quantitative analyses of the simple pH dependence profiles gave pKas of 6.2 ± 0.6 and 8.8 ± 0.1. The pKa of 6.2 ± 0.6 is assigned to HisG19(117) β; the pKa of 8.8 is assigned to CysB5(23) β. It is significant to note that the rates of both CysF9(93) β and CysB5(23) β of the carbonmonoxy derivative were found to be much greater than those of oxy and aquomet derivatives. KEY WORDS:- Hemoglobin, sulphydryl groups, duck, 5,5'-dithiobis(2-nitrobenzoic acid). Global Journal of Pure and Applied Sciences Vol.11(2) 2005: 209-215

External Stimuli‐Responsive Characteristics of Ionic Poly[(N,N‐diethylaminoethyl methacrylate)‐co‐(N‐vinyl‐2‐pyrrolidone)] Hydrogels

AbstractSummary: Polyelectrolyte hydrogels containing diprotic acid moieties sensitive to ionic strength changes of the swelling medium were synthesized from N,N‐diethylaminoethyl methacrylate (DEAEMA), N‐vinyl‐2‐pyrrolidone (VP) and itaconic acid (IA) by using ammonium persulfate (APS) as a free radical initiator in the presence of the cross‐linker, methylenebisacrylamide (MBAAm). The swelling behavior of the ionic poly[(N,N‐diethylaminoethyl methacrylate)‐co‐(N‐vinyl‐2‐pyrrolidone)] [P(DEAEMA/VP)] hydrogels were investigated in pure water; in NaCI solutions with pH 4 and 9; and in water‐acetone mixtures depending on the IA content in the hydrogel. The average molecular mass between cross‐links ($\overline M _{\rm c}$) and polymer‐solvent interaction parameter (χ) of the hydrogels were determined from equilibrium swelling values. The pulsatile swelling behavior was also observed in response to solvent changes between the solution in water and in acetone. The equilibrium swelling ratio of these hydrogels was basically unaffected with change in temperature. The swelling variations were explained according to the swelling theory based on the hydrogel chemical structure.Pulsatile swelling behavior of ionic P(DEAEMA/VP) hydrogels in response to solvent changes between water and acetone at 25 °C.magnified imagePulsatile swelling behavior of ionic P(DEAEMA/VP) hydrogels in response to solvent changes between water and acetone at 25 °C.

Effects of pH and phosphate on metal distribution with emphasis on As speciation and mobilization in soils from a lead smelting site

Arsenic in soils from the Asarco lead smelter in East Helena, Montana was characterized by X-ray absorption spectroscopy (XAS). Arsenic oxidation state and geochemical speciation were analyzed as a function of depth (two sampling sites) and surface distribution. These results were compared with intensive desorption/dissolution experiments performed in a pH stat reactor for samples from the site with the highest degree of As heterogeneity. The objectives of the study were to investigate the solid-phase geochemical As speciation, assess the speciation of As in solutions equilibrated with the solids under controlled pH (pH=4 or 6) and Eh (using hydrogen or air) environments, observe the effects of phosphate on the release of As into solution, and examine the effects of phosphate on metal mobility in the systems. Arsenic was predominantly found in the As(V) valence state, though there was evidence that As(III) and As(0) were present also. The dominant geochemical phase was scorodite (FeAsO 4·2H 2O). The pH was controlled in the pH stat experiments by the addition of equinormal solutions of monoprotic (HNO 3), diprotic (H 2SO 4), or triprotic (H 3PO 4) acids. For many of the divalent metal cations, solution concentrations greatly decreased in the presence of phosphate. Solutions were also analyzed for anions. Evidence exists for sulfate release into solution. More As was released into solution at lower pH. A slight increase in solution arsenate occurs with the addition of phosphate, but the risk posed from the increased desorption/dissolution of As must be weighed against the decrease in solution concentrations of many metals especially Pb. If tailings from this site underwent acidification (e.g., acid mine drainage), in situ sequestration of metals by phosphate could be combined with placement of subsurface permeable reactive barriers for capture of As to reduce the risk associated with arsenic and trace metal mobilization. Results from this study could be used in risk management plans for sites similar to the Pb smelter site examined here.

Swelling–Shrinking Behavior of Poly(Acrylamide‐co‐itaconic Acid) Hydrogels in Water and Aqueous NaCl Solutions

Polyelectrolyte hydrogels containing diprotic acid moieties sensitive to ionic strength changes of the swelling medium were prepared from acrylamide (AAm) and itaconic acid (IA) monomers with 0–21.4 mol% IA by using a radiation polymerization technique. The swelling and shrinking capacities of hydrogels were measured in water and in NaCl solutions. The equilibrium swelling ratio of hydrogels in water increased drastically when the mole percent of IA increased or NaCl concentration in the external solution decreased. The dynamics of the absorption process was investigated and found to be non‐Fickian controlled. On the other hand, it was shown that the hydrogels with high IA content shrank significantly faster than the hydrogels with low IA content in 1.0 M NaCl solution.

Independent control of lower critical solution temperature and swelling behavior with pH for poly(N-isopropylacrylamide-co-maleic acid)

Polymer solutions that gel in response to changes in temperature and pH are of interest for various forms of drug delivery, and it is desirable to increase swelling for diffusion-controlled release without bringing the lower critical solution temperature (LCST) above 37°C. N-isopropylacrylamide (NIP) was polymerized with maleic acid (MAc), a diprotic acid, and acrylic acid (AAc), a monoprotic acid, to compare swelling and temperature response with changes in pH. For samples with equal acid contents and almost identical LCST responses to pH, poly(N-isopropylacrylamide-co-maleic acid) (pNIP MAc) demonstrated greater swelling than poly(N-isopropylacrylamide-co-acrylic acid) (pNIP AAc). The LCST increase for MAc occurred at a pH corresponding to the deprotonation of almost all of the first acid groups. Further increases in pH led to the deprotonation of the second COOH and only served to increase the charge concentration at a given location. These results provide strong support for the theory that LCST results largely from uninterrupted chain lengths of NIP and that swelling results from the actual charge density of acid groups along the chain. Because the use of a diprotic acid copolymer allows swelling to be decoupled from LCST, pNIP MAc may be an appropriate candidate for pH-sensitive drug-delivery applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2110–2116, 2004

The pH at the First Equivalence Point in the Titration of a Diprotic Acid

The author argues that the validity of the simple result achieved by an earlier paper can be seen even more easily than its author indicates.

Synthesis, acid–base and coordination properties towards Cu(II), Zn(II), and Cd(II) ions of two new polyamino-phenolic ligands, including the crystal structure of a fully protonated ligand

The synthesis of the two new ligands 2,6-bis{[bis-(2-aminoethyl)ethylamino]methyl}phenol ( L1) and bis{[2(2-aminoethylamino)ethylamino]methyl}phenol ( L2) is reported. Both ligands have two diethylenetriamine subunits separated by two phenolic spacers; the simple phenol is present in the framework of L1, while the longer 4,4′-bis(1-phenol) is in L2. The acid–base behavior of both ligands in aqueous solution was studied by potentiometry (25 °C, I=0.15 mol dm −3, NaCl). As a neutral molecule, L1 behaves as hexaprotic base and as monoprotic acid, L2 behaves as hexaprotic base and as diprotic acid. The stability constants for their Cu(II), Zn(II), and Cd(II) complexes were determined by potentiometry and UV–Vis experiments under the same experimental conditions and compared. Both ligands form stable mono- and dinuclear complexes. The analysis of the data revealed a similar coordination arrangement in the mononuclear complexes, while a different arrangement is suggested for the dinuclear one. The role of the phenol and of the 4,4′-bis(1-phenol) as spacers of two amine functions in metal ion coordination is discussed. The crystal structure of the fully protonated species of L1 ( L1·6HBr) is reported and discussed.

Determination of the dissociation constants of the cephalosporins cefepime and cefpirome using UV spectrometry and pH potentiometry

UV spectrometry and pH potentiometry were used for the determination and direct characterization of the dissociation constants of cefepime (Cef) and cefpirome. The absorbance/pH profiles at two analytical wavelengths and different conditions were assessed and found to conform to those of diprotic acids. The titration curves indicated a triprotic acid profile with two overlapping dissociation constants. The comparison of the results of both techniques permitted the direct attribution of the three dissociation constants to the carboxylic group at position 4 of the Δ-3 cephem nucleus, the aminothiazole group and the amide group at position 7 of the Δ-3 cephem nucleus. Stability studies of Cef in alkaline solutions were also performed in order to evaluate the accuracy of the measurements carried out for the determination of the third p K a value. The experimental p K a values were compared to the corresponding predicted values derived by pallas/ pkalc and Advanced Chemical Development (ACD) software packages.

Capillary electrophoresis of methyl-substituted phenols in acetonitrile

The separation of mono- and dimethylphenols by capillary electrophoresis in pure acetonitrile was investigated. In acetonitrile, uncharged phenols interact with background electrolyte anions forming negatively charged complexes, which can be separated from each other by capillary electrophoresis. The background electrolyte anions tested were acetate, bromide and chloride. The calculated formation constants for phenol–anion complexes were highest with acetate and smallest with bromide. Complex formation was found to be sensitive to traces of water in the background electrolyte. The separation of methylphenols was also carried out in acetonitrile at high pH using background electrolytes prepared from diprotic acids and tetrabutylammonium hydroxide. At high pH the phenols were partly dissociated, providing an additional mechanism for the separation. All methylphenols were separated with the use of malonate background electrolyte. However, this approach was prone to interference from methanol resulting from the tetrabutylammonium hydroxide solution.

Development of Iterative Methods for the Exact Determination of Acid Dissociation Constants and Specific Reaction Rates in Various Ionic or Electrochemical Systems. A Review

Theory and iterative methods for analysis of potentiometric titration data are presented in this paper. The methods concern titrations of (i) weak monoprotic acids, (ii) mixtures of weak acids with their conjugate bases (buffer solutions), (iii) mixtures of two monoprotic acids, (iv) solutions of polyprotic (di- and triprotic) acids with overlapping ionisation steps, and (v) mixtures of two diprotic acids. Using equations derived without approximations and data exclusively resulting from the buffer region of a titration curve, it is possible to extract the accurate values of the concentration(s) and thermodynamic dissociation constant(s) of the titrated acid(s), even when the titration is stopped well before the end-point of the titration. The main principles of the iterative methods can also be applied to the evaluation of chronoamperometric curves for various electrochemical mechanisms (ECECE, ECE, irreversible, quasi-reversible, and CE). Thus, it is possible to extract the kinetic parameters k1 and k2 of an ECECE mechanism using exclusively chronoamperometric data. The analysis of the chronoamperometric curves for the other mechanisms (ECE, irreversible, quasi-reversible, and CE) permits the extraction of the corresponding kinetic parameters even when the values of the diffusion coefficient D and the effective area A of the electrode are not known. A review with 52 references.

Cadmium adsorption by an organic soil: a comparison of some humic – metal complexation models

The retention of Cd by an organic soil was investigated as a function of pH and ionic strength. The adsorption of Cd at pH values from 2 to 11 at two ionic strengths (0.053 M and 0.017 M LiNO3) were found to be a function of both pH and ionic strength. Four Cd-humic complexation models were evaluated in order to test the applicability of these models to fit data from batch adsorption experiments. The models varied greatly in their complexity and implicit assumptions. Three were discrete functional group models – a simple diprotic acid model, a two diprotic acid model and the Windermere Humic Aqueous Acid (WHAM) model, and a continuous functional group model - the non-ideal competitive adsorption (NICA) model. The concentration of proton binding sites in the soil was found to be 4.51 mol kg-1. The NICA and WHAM models were more successful than either a simple diprotic acid model or a two diprotic acid model at modeling Cd complexation by the organic soil, although both underestimated adsorption at very high pH values.

A Colorful Investigation of a Diprotic Acid: A General Chemistry Laboratory Exercise

A general chemistry laboratory experiment that can be completed in a single laboratory period is described that familiarizes students with the acid—base chemistry of a diprotic acid and with the use of visible spectroscopy to determine species concentrations. This experiment is a modified version of a previously described laboratory exercise developed for an upper-division quantitative analysis course. Students work in teams and as a class to generate different ionization states of various highly absorbing dyes. Both spectroscopic and potentiometric (pH) data is collected using LabWorks II stations, but other inexpensive pH meters and visible spectrometers (e.g., Spec 20s) are suitable. A spreadsheet template is used to determine the percent composition of various ionization states of a diprotic acid and to determine the pKa values. Besides introducing students to fundamental tools and key chemical concepts, this laboratory is also inexpensive to operate and utilizes nontoxic, colorful solutions.

New Density Functional and Atoms in Molecules Method of Computing Relative pKaValues in Solution

A theoretical structure−property relation between pKa and Bader's atoms in molecules (AIM) energy of the dissociating proton was obtained by an approximation of the standard gas-phase expression for the equilibrium constant expressed in terms of molecular partition functions. This relation was then tested by solvated density functional computations on a series of aliphatic carboxylic acids, substituted benzoic acids, phenols, anilinium ions, and pyridinium ions using the COSMO solvation model. Comparison with accurate experimental values indicates that average unsigned errors of generally less than 0.2 pKa units can be achieved in the calculation of relative pKa values. The inclusion of specifically hydrogen-bonded water molecules in the vicinity of the dissociating proton was found to improve the agreement between theory and experiment greatly. Computed pKa values for some diprotic acids were also investigated.

Acidity function p(a(H) gamma(Cl)) as a step to pH assessment.

The conventional assignment of pH reference buffer standards, pH(S), is achieved by means of a series of procedures that follow from measurement of Harned cell potentials for an electrolyte solution which is the buffer solution of interest. An intermediate step is assessment of the acidity function p( a(H) gamma(Cl))(0), the extrapolated value of a linear representation of the dependence of p( a(H) gamma(Cl)) on m(Cl) for at least three different molalities, m(Cl), of added alkali chloride (0.005; 0.010; 0.015 mol kg(-1) KCl). This experimental value can be compared with a theoretically expected value calculated from the dissociation constants of the buffer species. Whereas these calculations always give negative slopes for diprotic and triprotic acids and zero slope for monoprotic acids, experimental values with negative or positive slopes can be obtained for well fitting straight lines obtained for buffer solutions with ionic strengths from 0.0025 to 0.144 mol kg(-1). Such disagreement between theoretically and experimentally obtained values introduce an extra source of uncertainty in the establishment of pH(S) and on its traceability chain. In this work examples are presented and discussed for which the discrepancy between expected and experimental values leads to different intercept p( a(H) gamma(Cl))(0).

Synthesis and property characterization of cassava starch grafted poly[acrylamide-co-(maleic acid)] superabsorbent via γ-irradiation

Graft copolymerizations of acrylamide and maleic acid onto cassava starch by a simultaneous irradiation technique using γ-rays as an initiator were carried out. Various important parameters of total dose, dose rate, monomer-to-cassava starch ratio and maleic acid content were studied. Addition of 2%ww−1 diprotic acid of maleic acid into the reaction mixture yields a saponified starch graft copolymer with a water absorption in distilled water as high as 2256gg−1 of its dried weight. The water absorption of these saponified graft copolymers in saline and buffer solutions was also measured. The water absorption depends largely on the cationic type and concentration of these solutions in terms of ionic strength. This research explains a charge transfer mechanism for graft copolymerization of maleic acid and acrylamide onto cassava starch, and describes the influential parameters that affect grafting efficiency and water absorption.

Quantitation of Mixtures of Diprotic Organic Acids by FT-IR Flow Titrations and Multivariate Curve Resolution

The combination of FT-IR flow titrations and second-order calibration methods is assessed for the first time as a potential method for quantifying mixtures of organic acids. FT-IR spectral information is richer and more specific than that provided by other spectrometric techniques. Also, the flow titration of the sample allows the use of second-order data analysis methods, such as multivariate curve resolution, which can quantify multianalyte systems using pure analyte standards in the presence of unknown interferents. Problems linked to FT-IR flow titrations, such as the impossibility of using buffer substances and the presence of major baseline contributions in the measurements due to changes in the water structureless absorption, have been overcome through the design of an adapted experimental setup and the use of second derivative spectra. Malic and/or tartaric acid are the model substances chosen to be quantified in the presence or absence of interferents. Both substances are diprotic acids with similar p Ka values and, therefore, similar pH-dependent evolution. Samples with one or both acids with their related standards in the presence or absence of an inert interferent (sugar) are successfully resolved and quantified for a wide range of [analyte]: [interferent] ratios with no need for pH control in the process. These results suggest this methodology as an optimal and robust alternative for routine analysis.

Haemoglobins with multiple reactive sulfhydryl groups: reactions of 5,5'-dithiobis(2-nitrobenzoate) with CysF9[93] and CysH3[125] of guinea pig haemoglobin

Guinea pig haemoglobin has six sulfhydryl groups, one at each of the positions F9[93], G11[104] and H3[125], which appear in pairs. Titration with p-hydroxymercuri(II)- benzoic acid and with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) indicate that four of the six sulfhydryls are reactive. The time course of the DTNB reaction is triphasic at pH > 7. The fast phase is about 2 orders of magnitude faster than the intermediate phase and can be clearly separated from it. The intermediate phase, where it exists, is about 3-4 times faster than the slow phase. However, the amplitude of the intermediate phase, which has a maximum of about 15% of the total signal amplitude, becomes negligible as it approaches pH 7, so that the kinetics eventually becomes biphasic. The pH dependence profile of kapp, the apparent second-order rate constant, for the fast phase resembles the titration curve of a diprotic acid. Quantitative analysis indicates that the reactivity of the sulfhydryl group to which this phase may be attributed is linked to two ionizable groups with pKas of 6.4 0.1 and 7.8 0.2. These values are assigned to HisHC3[146] and CysF9[93], respectively. The pH dependence profile of kapp for the slow phase resembles the titration curve of a monoprotic acid. Quantitative analysis indicates that the sulfhydryl group to which this phase may be attributed is linked to a single ionizable group with a pKa of 6.1 0.2. Examination of the structure of guinea pig haemoglobin near the H3[125] position shows that there is a lysine residue, LysA5[8], which is only 4 (0.4 nm) away from CysH3[125]. The presence of this lysine lowers the pKa of CysH3[125] from the normal value for sulfhydryl groups (between 8 and 8.5) to 6.1. (Received July 31, 2001; revised May 1, 2002) (Bulletin of The Chemical Society of Ethiopia: 2002 16 (2): 175-186)