Modification of the titrimetric method of analyzing pectin substances

A potentiometric variant of the titrimetric method of analyzing pectin substances has been developed which is distinguished by adequate accuracy and good reproducibility. The modified method has been tested on methyl (methyl 2,3-di-O-methyl-,-galactopyranosid)uronate and has been used for determining the free (K_f) and esterified (K_e) carboxy groups of the pectin substances of mint. The methods of isolating, purifying, and fractionating the pectin substances and determining their K_f and K_e values are given. Formulas are presented for calculating the percentage values of K_f and K_e.M. V. Frunze Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 428–431, July–August, 1984.     

Ultrasonic studies of polysaccharide (pectin) in aqueous media at 298.15 K

The ultrasonic velocity, density and viscosity of pectin in aqueous medium were measured at 298.15 K. The acoustical parameters such as adiabatic compressibility (β), free length (L _f), free volume (V _f), internal pressure (π_i), acoustical impedance (Z), and relative association (R _A), Rao’s constant (R) and Wada’s constant (W) are calculated. The results are interpreted in terms of molecular interaction between the components of the mixtures. Further, some more acoustical parameters such as relaxation time (τ), absorption coefficient (α/f ²) and relaxation strength (r) are calculated with various percentage of pectin has been studied which reveals interaction between the solvent and the polymer (pectin) at various concentration of the polymer. The observed values suggested the solute-solvent interaction is favored.     

Thermodynamic study of complex formation between Ce3+ and cryptand 222 in some binary mixed nonaqueous solvents

The stoichiometry, stability and the thermodynamic parameters of complex formation between cerium(III) cation and cryptand 222 (4,7,13,16,21,24-hexaoxa-1,10-diazabycyclo[8.8.8]-hexacosane) were studied by conductometric titration method in some binary solvent mixtures of dimethylformamide (DMF), 1,2-dichloroethane (DCE), ethyl acetate (EtOAc) and methyl acetate (MeOAc) with methanol (MeOH), at 288, 298, 308, and 318 K. A model based on 1: 1 stoichiometry has been used to analyze the conductivity data. The data have been fitted according to a non-linear least-squares analysis that provide the stability constant, K _f, for the cation-ligand inclusion complex. The results revealed that the stability order of [Ce(cryptand 222)]³⁺ complex changes with the nature and composition of the solvent system. A non-linear relationship was observed between the stability constant (logK _f) of [Ce(cryptand 222)]³⁺ complex versus the composition of the binary mixed solvent. Standard thermodynamic values were obtained from temperature dependence of the stability constant of the complex, show that the studied complexation process is mainly entropy governed and are influenced by the nature and composition of the binary mixed solvent solutions.     

A Branched Pore Model Analysis for the Adsorption of Acid Dyes on Activated Carbon

A new branched-pore adsorption model has been developed using an external mass transfer coefficient, K _f, an effective diffusivity, D _eff, a lumped micropore diffusion rate parameter, K _b, and the fraction of macropores, f, to describe sorption kinetic data from initial adsorbent-adsorbate contact to the long-term adsorption phase. This model has been applied to an environmental pollution problem—the removal of two dyes, Acid Blue 80 (AB80) and Acid Red 114 (AR114), by sorption on activated carbon. A computer program has been used to generate theoretical concentration-time curves and the four mass transfer kinetic parameters adjusted so that the model achieves a close fit to the experimental data. The best fit values of the parameters have been determined for different initial dye concentrations and carbon masses. Since the model is specifically applicable to fixed constant values of these four parameters, a further and key application of this project is to see if single constant values of these parameters can be used to describe all the experimental concentration-time decay curves for one dye-carbon system.The error analysis and best fit approach to modeling the decay curves for both dye systems show that the correlation between experimental and theoretical data is good for the fixed values of the four fitted parameters. A significantly better fit of the model predictions is obtained when K _f, K _b and f are maintained constant but D _eff is varied. This indicates that the surface diffusivity may vary as a function of surface coverage.     

Chromatographic behaviour of metal ions on tin(IV) and titanium(IV) antimonate papers

Summary The chromatographic behaviour of 49 metal ions has been studied on papers impregnated with Sn(IV) and Ti(IV) antimonates in aqueous HNO₃ and mixed solvent systems containing dimethyl sulphoxide. Numerous separations have been achieved and the Alberti equation, for Sn(IV) and Ti(IV) antimonate papers, in the modified form: –nloga K⁺=R_M + constant (a K⁺=activity of K⁺), has been verified. The effect of the concentration of impregnating reagents on these papers has been determined and compared with other papers. The effect of pH on R_f, R_i, log R_f and R_M values of metal ions has also been examined in aqueous systems.     

Accessibility of hydroxy groups of pectin substances for deuteration

An apparatus for the deuteration of solid samples and for recording their IR spectra in a current of D₂O vapor, and an IR-spectroscopic method of determining the degree of deuteration (q) of the hydroxy groups of pectin substances (PSs) are described. It has been established that there are no zones of structurally different nature in films of derivatives of PSs at the carboxy group. The rate of deuterium-exchange of the water of hydration of PSs is higher than for the hydroxy groups of the pyranose rings. The rate of deuterium exchange depends on the density of packing of the polymer chains of the pectin derivatives.Center for the Automation of Scientific Investigations and Metrology, Academy of Sciences of the Moldavian SSR, Kishinev. Translated from Khimiya Priorodnykh Soedinenii, No. 3, pp. 343–348, May–June, 1987.     

Synthesis of homologously pure bacteriochlorophyll-e and f analogues from BChls-c/d via transformation of the 7-methyl to formyl group and self-aggregation of synthetic zinc methyl bacteriopheophorbides-c/d/e/f in non-polar organic solvent

Homologously pure methyl bacteriopheophorbides-e and f (BPhes-e/f_M) were prepared from modification of naturally occurring bacteriochlorophylls-c and d (BChls-c/d), respectively, by transformation of the methyl to formyl group at the 7-position. The absolute configuration of the 1-hydroxyethyl group at the 3-position of (Zn-)BPhes-e/f_M was determined from comparison with structurally known BChl-c/d epimers. Visible spectra of synthetic (Zn-)BPhe-c/d/e/f_M showed that the 7¹-oxidation and the 8²/12¹/20-methylation affected Soret, Q_x and Q_y bands of both the monomeric (in a polar organic solvent) and oligomeric species (in a non-polar solvent).     

Organometallic polymers. XXIV. Radical-initiated copolymerization of ferrocenylmethyl acrylate and methacrylate with acrylonitrile,maleic anhydride,and N-vinyl-2-pyrrolidone

Ferrocenylmethyl acrylate (I) and ferrocenylmethyl methacrylate (II) have been readily copolymerized with maleic anhydride in benzene–ethyl acetate solutions. Similarly, II has been copolymerized with both acrylonitrile and N-vinyl-2-pyrrolidone in benzene solutions to give higher molecular weight copolymers in high yields. In all cases azobisisobutyronitrile has been the initiator. Based on e values obtained, the metal carbonyl substituent acts as an electron-withdrawing group. Over a wide range of comonomers (N-vinyl-2-pyrrolidone, styrene, vinyl acetate, methyl acrylate, acrylonitrile, and maleic anhydride) I and II exhibit r₁ values lower than (and r₂ values higher than) similar copolymerizations with methyl acrylate or methyl methacrylate. Further more, the Q values found for I (0.03–0.11) and II (0.08–0.18) are smaller than those for methyl acrylate (0.46) and methyl methacrylate (0.74). Thus, I and II are less reactive than expected, presumably due to steric effects.     

Determination of the formation constant for the inclusion complex between Lanthanide ions and Dansyl chloride derivative by fluorescence spectroscopy: Theoretical and experimental investigation

In this paper, a sensitive, easy, efficient, and suitable method for the calculation of K_f values of complexation between one derivative of Dansyl chloride [5-(dimethylamino) naphthalene-1-sulfonyl 4-phenylsemicarbazide] (DMNP) and Lanthanide(III) (Ln) ions is proposed, using both spectrofluorometric and spectrophotometric methods. Determination of K_f showed that DMNP was mostly selective towards the erbium (III) ion. The validity of the method was also confirmed calculating the Stern–Volmer fluorescence quenching constants (K_sv) that resulted in the same consequence, obtained by calculating the K_f of complexation values. In addition, the UV–vis spectroscopy was applied for the determination of K_f only for the Ln ions that had interactions with DMNP. Finally, the DFT studies were done on Er³⁺ and the DMNP complex for distinguishing the active sites and estimating the pair wise interaction energy. It can be concluded that this derivative of Dansyl chloride with inherent high fluorescence intensity is a suitable reagent for the selective determination of the Er³⁺ ion which can be used in constructing selective Er³⁺ sensors.     

A Correlation Between Solvatochromic Solvent Polarity Parameters and the Ionization Constants of Various Phenols in 1,4-Dioxane–Water Mixtures

Precise thermodynamic ionization constants K for 3-nitrophenol, 3,4-dichlorophenol, and 4-cyanophenol have been obtained in 1,4-dioxane-water mixtures (0–70% volume fraction in dioxane) at 25°C using a potentiometric method. The same information for another twelve cationic, neutral, and anionic phenols were taken from the literature. Three different methods were used to study the effects of the solvents on the ionization constants: one involves a single polarity parameter, E _T(30); the next involves the Kamlet–Taft multiparametric method; and the last involves the preferential solvation model. The pK values follow the preferential solvation model, but the parameters obtained are highly correlated. Using the data for the phenol molecule as reference, a linear correlation between ΔpK and E _T(30) has been used to develop a new method of obtaining pK values for any binary solvent composition, with only the pK in water known. The pK(s) values correlate with the molecular parameters for the dipolarity/polarizability of the solvent π* and its hydrogen-bond donor ability α. The preferential solvation parameter, f _12/1, correlates with the parameter for the hydrogen-bond donor ability of the solvent. All the phenols follow Hammett's equation and the reaction constants have been calculated for the different water–dioxane mixtures.     

Improved Accuracy of Low Affinity Protein–Ligand Equilibrium Dissociation Constants Directly Determined by Electrospray Ionization Mass Spectrometry

There is continued interest in the determination by ESI-MS of equilibrium dissociation constants (K_D) that accurately reflect the affinity of a protein–ligand complex in solution. Issues in the measurement of K_D are compounded in the case of low affinity complexes. Here we present a K_D measurement method and corresponding mathematical model dealing with both gas-phase dissociation (GPD) and aggregation. To this end, a rational mathematical correction of GPD (f_sat) is combined with the development of an experimental protocol to deal with gas-phase aggregation. A guide to apply the method to noncovalent protein–ligand systems according to their kinetic behavior is provided. The approach is validated by comparing the K_D values determined by this method with in-solution K_D literature values. The influence of the type of molecular interactions and instrumental setup on f_sat is examined as a first step towards a fine dissection of factors affecting GPD. The method can be reliably applied to a wide array of low affinity systems without the need for a reference ligand or protein.     

The very low-pressure pyrolysis of phenyl methyl sulfide and benzyl methyl sulfide. The enthalpy of formation of the methylthio and phenylthio radicals

The kinetics and mechanisms of the unimolecular decompositions of phenyl methyl sulfide (PhSCH₃) and benzyl methyl sulfide (PhCH₂SCH₃) have been studied at very low pressures (VLPP). Both reactions essentially proceed by simple carbon-sulfur bond fission into the stabilized phenylthio (PhS·) and benzyl (PhCH₂·) radicals, respectively. The bond dissociation energies BDE(PhS-CH₃) = 67.5 ± 2.0 kcal/mol and BDE(PhCH₂-SCH₃) = 59.4 ± 2 kcal/mol, and the enthalpies of formation of the phenylthio and methylthio radicals ΔH° _,298K(PhS·, g) = 56.8 ± 2.0 kcal/mol and ΔH°_{f, 298K}(CH₃S·, g) = 34.2 ± 2.0 kcal/mol have been derived from the kinetic data, and the results are compared with earlier work on the same systems. The present values reveal that the stabilization energy of the phenylthio radical (9.6 kcal/mol) is considerably smaller than that observed for the related benzyl (13.2 kcal/mol) and phenoxy (17.5 kcal/mol) radicals.     

Gauge parameters for extrapolation of oscillator strengths ofE1 transitions along the boron isoelectronic sequence

The oscillator strengthsf forE1 transitions along an isoelectronic sequence can be written asf=aK ²+bK+c whereK is a gauge parameter representing the gauge condition of the electromagnetic field. The coefficientsa,b, andc are functions of length (f _l) and velocity (f _v) values of the oscillator strengths at the Hartree-Fock level. We have shown by making a perturbation expansion of oscillator strengthsf,f _l andf _v that the gauge parameterK is independent of the nuclear charge. This property has been exploited to extrapolatef values along the isoelectronic sequence of Boron for some representativeE1 transitions within then=2 complex. We obtain good agreement between the extrapolated results with the configuration interaction results.     

Spectrophotometric study on the charge transfer reaction between 2-amino-4-methylpyridine with chloranilic acid in polar solvents

Charge transfer (CT) complexes formed between 2-amino-4-methylpyridine as electron donor, chloranilic acid as electron acceptor was investigated spectrophotometrically in acetonitrile (AN), methanol (MeOH) and binary mixture of acetonitrile 50% + methanol 50% (MeOH-AN). Minimum–maximum absorbance method has been used for estimating the formation constants of the CT reactions (K_CT). Job’s method of continuous variation and photometric titration studies were used to detect the stoichiometric ratios of the formed complexes, and they showed that 1:1 complexes were produced. The molar extinction coefficient (e), oscillator strength (f), dipole moment (l), CT energy (E_CT), ionisation potential (I_P) and the dissociation energy (W) of the formed complexes were estimated; they reached acceptable values suggesting the stability of the formed CT complexes. The solid CT complexes were synthesised and characterised by elemental analyses, ¹H NMR and FTIR spectroscopies where the formed complexes included proton and electron transfer.     

Spectrophotometric, potentiometric and chromatographic pKa values of polyphenolic acids in water and acetonitrile-water media

The pK_a values of nine polyphenolic acid substances in water and acetonitrile-water mixtures using potentiometric, spectrophotometric, and liquid chromatographic (LC) measurements, have been determined. Also, a new method based on the absorbance spectra at the maximum of chromatographic peaks previously obtained has been applied. This method can be applied to data obtained from LC-UV (diode array detection (DAD)) instruments and retains all the advantages of LC and spectrophotometric methods, such as the possibility of working with impure samples. Finally, the advantages of the different methods to the determination of pK_a values of nine polyphenolic acids have been described in order to verify the applicability of the proposed methods in aqueous and acetonitrile-water media.     

Purification and Characterization of Pectin Lyase Produced by Aspergillus terricola and its Application in Retting of Natural Fibers

An indigenously isolated fungal strain identified as Aspergillus terricola with assigned fungal strain number MTCC 7588 has been used as source for pectin lyase production. The extracellular pectin lyase was purified to homogeneity from the culture filtrate of A. terricola by ion exchange and gel filtration chromatography. The determined molecular weight was 35 ± 01 kDa. The K _m and k _cat (turnover) values of the purified enzyme at 37 °C using citrus pectin as the substrate were found to be 1.0 mg/ml and 110.0 s⁻¹, respectively. The pH and temperature optima of the enzyme were 8.0 and 50 °C, respectively. The retting ability of the purified pectin lyase for natural fibers viz. Cannabis sativa and Linum usitatissimum has been demonstrated for the first time.     

Theory of titration curves. VIII. A new interpretation of acid-base titration curves for polymeric acids. The significance of the Kern-equation parameters pKa and n

The Kern equation, pH = pK_a + n logf/(1 ? f), has been widely used in interpreting the potentiometric titration curves obtained on titrating polymeric acids with bases, and various interpretations of its empirical parameters pK_a and n have been advanced. Values of n similar to those generally obtained for polymeric acids are also obtained for dibasic and other monomeric polybasic acids for which the ratios of successive dissociation constants, K_i/K_(i+1), exceed the corresponding statistical values by a constant factor. The dependences of n on this factor and on the basicity of the acid are described. It is argued that the traditional picture of a dissociation constant varying continuously with the fraction titrated cannot be correct, and that the data can be more properly interpreted in terms of a constant non-statistical free-energy contribution to the successive values of K_i/K_(i+1).     

The linear correlation of the (ΔR′m)i function determined for the ortho derivatives of phenol,aniline, benzaldehyde,and nitrobenzene

The additivity of selected chromatographic data with a group of ortho derivatives of phenol, aniline, benzaldehyde, and nitrobenzene has been proved with the help of the theoretical approach developed by Snyder (1–5), and this concept is assumed to be useful in the attempt to predict the R_f, values of substances with known structures or in elucidating such structures with compounds having known R_f, values.     

Solvent effects on complexation of crown ethers with LiClO4, NaClO4 and KClO4 in methanol and acetonitrile

The thermodynamic formation constants K_f for complexation of Li⁺, Na⁺ and K⁺ with the crown ethers 12C4 and 15C5 have been determined in methanol and acetonitrile at 25°C using precision conductivity data. The method permits evaluation of very small K_f values (e.g., K_f=6.98 mol^–1-dm³ for LiClO₄+12C4 in methanol) as well as fairly large values (e.g., K_f=2.73×10⁴ mol^–1-dm³ for NaClO₄+15C5 in acetonitrile). The determination of K_f values from conductivity data takes into consideration the often neglected ion pair formation of both the uncomplexed and the complexed cations. Our results for K_f are generally consistent with previously reported values based on potentiometry, calorimetry and polarography, but there are significant differences in several cases which we attribute to neglect of ion association both for the uncomplexed or free cation K_a and the macrocyclic complexed cation K_a2. Our results are also consistent with the well known concepts relating the magnitude of K_f to both the cavity diameter and ion-solvent interactions. Limiting molar conductivities ₂ ⁰ for the complex salt (M-crown ether) (ClO₄) in both solvents were generally found to be smaller or very close to the corresponding quantity ₁ ⁰ for the binary MClO₄-solvent system. However, in methanol, single ion limiting molar conductivities for the cationic complexes ₂ ⁰ exhibit anomalous behavior which is attributed to solvation differences between free cations and complexed cations.     

Thermoelastic properties of networks in swelling equilibrium: Poly(vinyl alcohol)

The energy component of the stress has been determined for poly(vinyl alcohol) networks in swelling equilibrium with a series of water–ethylene glycol compositions. The data are analyzed by using the equations describing the thermoelasticity of networks in swelling equilibrium. The ratio f_e/f of the energy component to the total force, as calculated from these equations, varies systematically with diluent composition but is independent of elongation in a given diluent. For a network crosslinked by terephthalaldehyde, f_e/f varied from ?0.33 to ?0.42 as the diluent composition was changed from pure water to 20% ethylene glycol. Similar effects were found in a network crosslinked by formaldehyde. It is not yet certain whether this effect represents a real solvent dependence of f_e/f or a failure of the equation of state to account for the effect of composition changes on the force.