The effects of ultra-violet light and X-rays on aqueous solutions of poly-L-glutamic acid

Summary Poly-L-glutamic acid (PLGA) in aqueous solution in helical or random coil form was irradiated in air by X-rays or ultra-violet light. It was observed that both X-rays and ultra-violet light caused degradation of PLGA in either form. The changes in molecular weight of PLGA in alkaline solutions caused by X-ray irradiation were larger than those in acidic solutions. This fact indicates that the coil form suffers more degradation than the helix form. X-rays caused little change in the conformation of PLGA, while ultra-violet light effectively broke the helix form. The decrease in helix content brought about by ultra-violet exposure could not be explained just by degradation.     

Counter-ion dependence in salt-free,aqueous solutions of heparin

Chiroptical properties of heparin for various degrees of neutralization of the sulfate and carboxylic groups and for different counter-ions in salt-free aqueous solutions were investigated. Variations of optical rotation and ellipticity values at given wavelengths are compared to simultaneous pH and viscosity changes observed during the neutralization of heparin by sodium and calcium hydroxide. For Na⁺, variations of ellipticity at 210 nm are related to acid—base properties of uronic carboxylic groups. C.d. characteristics found for alkaline-earth counter-ions (Mg²⁺, Ca²⁺ and Ba²⁺), as compared to Na⁺, are assigned to effects of divalent ions on the ionization behavior of carboxylic groups. Among the divalent counter-ions considered, Ca²⁺ gave the strongest interaction with the heparin polyanion, but no specific complex formation was observed. O.r.d. and c.d. data are discussed on the basis of a randomly coiled structure for macromolecules composed of rigid, heterocyclic repeating-units that are independent of each other in so far as electronic transitions of chromophore groups contributing to optical activity are concerned.     

Adsorption characteristics of lignosulfonates in salt-free and salt-added aqueous solutions

Five sodium lignosulfonate (SL) fractions with narrow molecular weight distribution and known salt content were used as the polyanion to build up layer-by-layer self-assembly multilayers with poly(diallyldimethylammonium chloride) (PDAC) as polycation. It is interesting to find that the salt-free SL is hardly adsorbed on the PDAC surface, but the SL in salt-added solutions can be self-assembled well with PDAC to form SL/PDAC multilayers. When the five SL fractions dissolved in saline solutions are adsorbed on the PDAC surface by a self-assembly technique, SL with higher M(w) shows a higher adsorption amount than does SL with lower M(w). The driving forces of self-assembly of SL and PDAC are discussed based on the solution behaviors and adsorption characteristics of SL in salt-free and salt-added aqueous solutions. A possible self-assembled mechanism of SL and PDAC is electrostatic or cation-π interactions, but the SL cannot be adsorbed onto the PDAC surface without a hydrophobic interaction. With the addition of enough salt, the Coulomb interaction of SL becomes negligible, but the adsorption amount increases, indicating that the electrostatic interaction is not the main driving force of SL/PDAC self-assembly. For adsorption of SL in saline solution onto the PDAC surface, the cation-π interaction is the main driving force, and the hydrophobic interaction plays an important role in the adsorbed amount.     

Dielectric studies of aqueous solutions of poly(L-glutamic acid)

The dielectric features of poly(L -glutamic acid) are studied by the Fourier synthesized pseudorandom noise method in a time domain combined with a four-electrode cell. Polymer concentration dependence, the effect of the solvent viscosity, salt effects, and pH dependence are studied concomitantly with measurements of CD. A helix-to-coil transition occurs near pH 5.6 for a salt-free solution; at higher pH values, the polymer has an ionized random-coil conformation, and at lower pH, it has a deionized α-helical conformation. When it is in the ionized random-coil conformation, with the usual features of an electrolytic polymer, the solution shows a relaxation spectrum with a large dielectric increment at low frequencies. In the deionized α-helical state, no distinct relaxation curves are obtained, which does not deny the existence of a permanent peptide dipole. The pH dependence of the dielectric increment does not mainly correspond to the conformational change from helix to coil, but rather corresponds to the change of chain expansion on account of a charge–charge interaction under low ionic strength, which is conceived of by a viscosity measurement.     

Dielectric properties of aqueous solutions of sonicated DNA above 40 MHz

The dielectric properties of sonicated calf-thymus DNA sodium salt in aqueous solutions have been studied in the frequency range from 40 MHz to 2 GHz by time domain spectroscopy (TDS). A dielectric dispersion not previously reported was found, which has a characteristic frequency of about 150 MHz. All of the dielectric parameters are insensitive to the size of DNA fragments and to helix-to-coil transitions. The study of this dispersion as a function of DNA concentration and temperature allows us to conclude that it may be due to counterion fluctuation on short sections, probably in a direction transverse to the macromolecular axis.     

Dielectric relaxation of collagen in aqueous solutions

The complex dielectric constant of collagen in aqueous solutions (polymer concentration, C_p = 0.02–0.2%) was measured at 10°C in the frequency range from 3 Hz to 30 kHz. The loss peak for C_p = 0.02% is located at 90 Hz and the dielectric relaxation time τ_D is estimated to be 1.8 ± 0.3 msec. The τ_D agrees well with the rotational relaxation time estimated from the reduced viscosity, and the relaxation is ascribed to the end-over-end rotation of the molecule. The C_p dependence of τ_D and the dielectric increment Δε are interpreted in terms of the aggregation of molecules. The dipole moment of a molecule, obtained from Δε at C_p = 0.02% and pH 6.5, is (5.2 ± 0.2) × 10⁴D, which is explained by the asymmetrical distribution of the ionized side chains of the molecule.     

Dielectric spectroscopy on aqueous electrolytic solutions

In this work, detailed dielectric measurements are presented on aqueous electrolytic solutions of NaCl and KCl in a broad frequency range, typical for modern telecommunication techniques. The complex dielectric permittivity or equivalently the complex conductivity are systematically studied as function of frequency (100 MHz-40 GHz), temperature (10-60 degrees C) and molar concentration (0.001-1 mol/l). By a detailed analysis of the dielectric results using an asymmetrically broadened Cole-Davidson distribution of relaxation times, in addition to dc conductivity, the dielectric response as function of frequency, temperature, and molar concentration was fully parameterized by a total of 13 parameters. This model ansatz and the 13 parameters include an enormous predictive power, allowing a reasonable estimation of the dielectric constant, loss, and the conductivity for any set of external variables frequency, temperature and concentration. The proposed method is not only useful for rather simple electrolytic solutions, but also for cell suspensions and biological matter, if additional processes, especially at low frequencies, are adequately taken into account.     

Dielectric relaxation of DNA in aqueous solutions.

Using a four-electrode cell and a new electronic system for direct detection of the frequency differences specturm of solution impedance, the complex dielectric constant of calf thymus DNA (M_r = 4 × 10⁶) in aqueous NaCl at 10°C is measured at frequencies ranging from 0.2 Hz to 30 kHz. The DNA concentrations are C_p = 0.01% and 0.05%, and the NaCl concentrations are varied from C_s = 10^?4 M to 10^?3 M. A single relaxation regions is found in this frequency range, the relaxation frequency being 10 Hz at C_p = 0.01% and C_s = 10^?3 M. At C_p = 0.05% it is evidenced that the DNA chains have appreciable intermolecular interactions. The dielectric relaxaton time τ_d at C_p = 0.01% agrees well with the rotational relaxation time estimated from the reduced visocisty on the assumption that the DNA is not representable as a rigid rod but a coiled chain. It is concluded that the dielectric relaxiatioinis ascribed to the rotation of the molecule. Observed values of dielectric increment and other experimental findings are reasonably explained by assuming that the dipole moment of DNA results from the slow counterion fluctuation which has a longer relaxation time than τ_d.     

Dielectric dispersion in aqueous solutions of oxyhaemoglobin and carboxyhaemoglobin

The relative permittivity and conductivity of aqueous solutions of oxyhaemoglobin and carboxyhaemoglobin were measured over the frequency range 150kHz-100MHz. To minimize errors of measurement the investigations were carried out with three different samples of each type of haemoglobin, independent apparatus being used in two different laboratories. The dielectric increment and relaxation time were calculated at each of several temperatures from the results. These lead to a dipole moment of 400 Debyes and an activation enthalpy of 17.6+/-1.4kJ.mol(-1), both of which were found to be independent of temperature to within experimental error over the range 3-35 degrees C. The value of the dipole moment shows that the distribution of charge throughout the haemoglobin molecule is nearly symmetrical with respect to the centre of charge. The magnitude of the activation enthalpy is similar to that of the viscosity of water, in accord with the common observation that dielectric relaxation and viscosity are related phenomena. No significant differences are found between the dielectric parameters of oxyhaemoglobin and carboxyhaemoglobin. Combining the results with those obtained from X-ray diffraction of the solid a hydration value of 0.45g of water/g of protein is suggested, subject to the limitations of the model used. Finally, the results indicate the presence of a subsidiary dispersion, which could be attributed to the above quantity of bound water having a static permittivity of about 100 and a relaxation frequency in the region 100-200MHz.     

Dielectric properties of glucose in bulk aqueous solutions: Influence of electrode polarization and modeling

Impedance spectroscopy was applied to determine glucose concentration in the interstitial fluid for its potential use in diabetic monitoring. For this purpose, the changes in the measured dielectric properties due to the presence of glucose in water and saline solutions were examined between 40 Hz and 110 MHz. Electrode polarization (EP) was a dominant factor which shaped the spectrum at low frequencies. A theoretical model of EP using a constant phase-angle-element produced excellent matches to the measured data. By fitting the measured data to the model, the relative permittivity (?(h)) and conductivity (σ(l)) were obtained. For deionized water, the relative permittivity dropped from 80.1 to 73.2 and conductivity ranged between 0.142 and 0.212 mS/m when the glucose concentration was increased from 0 to 32 g/dl. For the same variation of glucose level in 0.15 M NaCl, ?(h) was reduced from 79.8 to 71.5 and σ(l) decreased from 1.384 to 0.522 S/m. Glucose level produced a definite change in dielectric properties. However, the changes within the physiological range of glucose (less than a few hundred mg/dl) were small and appeared to be within the measurement error.     

The equivalent conductivity of aqueous salt-free solutions of DNA: Influence of univalent counterions

The equivalent conductivity of salt-free solutions of deoxyribonucleates of alkali metals and ammonium obtained by filtering an isoionic DNA solution through a cation exchanger in the corresponding form has been investigated in the concentrations range of 1 × 10^?4 to 4 × 10^?3M. For all counterions investigated there is a linear dependence of the equivalent conductivity on \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {C_p} $\end{document}, where C_p is the nucleic phosphorus concentration. The limiting equivalent conductivity of deoxyribonucleates increases linearly with the limiting mobility of a counterion. By extrapolation to the zero mobility of the counterion, we have obtained the limiting mobility of a macroion, which is equal to 19 × 10^?4 Sm m² equiv.^?1, which is in good agreement with the literature data for denatured DNA obtained by the method of a moving boundary. It is shown that the degree of binding of counterions calculated from the conductometric data in diluted DTA solutions in independent of the nature of the univalent counterion. The degree of dissociation of H⁺-DNA in the isoionic solution calculated with allowance for the fraction of unprotonated bases practically coincides with this value for salts of DNA. The parameter of Manning's theory calculated from the experimental data corresponds to the distance between phosphates along the chain of the macroion, which is equal to 6.7 Å. We attribute the smaller value of this distance as compared with the theoretical one for denatured DNA to the aggregation of macroions.     

Cellulase immobilized on poly-L-glutamic acid

Cellulase (Cellulosin AC-8) was immobilized on poly-L-glutamic acid. This immobilized cellulase (IC) is water soluble in the neutral and alkaline solutions, where IC has the activity, while IC can be made insoluble by lowering the pH so that it can be recovered from the reaction mixture with its activity. The optimum pH and temperature were determined to be 5.5 and 55 degrees C, respectively. The stability of IC against change in the pH and temperature was improved by the immobilization. Solvolysis of 3N-NaOH-treated cellulose, with IC under the optimum conditions found here, led to the production of low-molecular-weight compounds.     

Decomposition of gibberellic acid in aqueous solutions

Исследовалось влияние рН и температуры на гидролитическое разложение гибберелевой кислоты в бу?ерных водных растворах. Отдельные продукты гидролиха определяли с помощью хроматогра?ии на бумаге при одновременной спектро?отометриче ской оцерке концентрации образующейся гиббереленовой кислоты. Было установлено, что разложение гибберелевой кислоты в кислой, нейтральной и щелочной среде начинается с образования 1-карбокси-2,3,7-тригидрок си-1-метил-8-метиленгиб б-4-ен 1–3лактон 10 карбоно войкислоты. Это вещес твоприсутствует так же в?ерментационных средах и на различных этапах выделения гибберелевой кислоты. Дальнейшее разложение в растворах с рН 2–8 проходит потом через гиббереленовую кислоту до аллогибберовой кислоты. Следующее превращение аллогибберовой кислоты в гибберовую наблюдалось только в растворе с рН 2 иосле 24-часового прогревания при при 100° С. В растворе с рН 9 процесс разложения приводие к образованию 2,3,7-тригидрокси-1-метил-8-м етиленгибб-4-ен 1,10 дикарбоновой кислоты, которая возникает как главный окончательный продукт гидролиза, наряду с небольшим количеством гиббереленовой кислоты, при данном рН также уже не подвергающейся дальнейшим изменениям. Наибольшей устойчивостью гиььерелевая кислота отличается в растворах с рН 3–4. В нейтральной, а в особенности в слабо щелочной среде ее устойчивость резко понижается. Разложение гибберелевой кислоты в водных растворах значительно ускозяется также при повышении температуры.     

Rheological properties of salt-free solutions of H+- and Na+-DNA

Rheological properties of the water solutions of H+- and Na+-DNA were studied at shear rates in the range of 0.12-126 sec-1. It was found that the concentration dependences of reduced viscosity of these systems have the maxima which displaced to the left along abscissa after ultrasonic degradation or long keeping and to the right after the salt or urea addition. Na+-DNA solutions have the rheological curve of flow typical of pseudoplastical systems (RCF-1): the viscosity decreases with increasing shear rate. H+-DNA solutions undergo RCF-1 RCF-2 transition leading to reverse dependence of viscosity on shear rate after long keeping or sonicating (i. e. the systems become dilatant). At centrifugation and in shear fields RCF-2 RCF-1 transition occurs. Urea prevents both transitions. These discovered phenomena as well as weakening of the dilatant properties in concentrated H+-DNA solutions allow us to assume that in these systems exist circular structures consisting of single strands of DNA associated by means of ionic bonds between phosphates and protonated bases. Rheological behaviour of DNA obtained by the method of Georgiev and Struchkov was explained by the presence of circular double stranded DNA molecules in their preparations. The analysis of the non-equilibrium behavior of water solutions of DNA allows to determine the rate constants of H+- and Na+-DNA unwinding.     

Electrophoretic behavior of poly-L-glutamic acid and poly-L-lysine

Two electrophoretic components have been detected on the ascending boundary in unbuffered solutions of polyglutamic acid and polylysine under certain experimental conditions. If the conditions are favorable to aggregation, another maximum, the third in order, is formed on this boundary. We attribute this maximum to the formation of aggregates. The behavior of both boundaries and all components at various pH, concentrations, and temperature of solutions and at different molecular weights of polymers was described.     

Dielectric studies of electrolytic poly(α-amino acid)s in aqueous solutions

The dependence of the dielectric constant and dielectric loss of aqueous solutions of poly-ε, N-succinyl-L -lysine on its degree of polymerization, degree of neutralization, concentration of the polymer, and counterion type was studied in a frequency range from 300 Hz to 5 MHz. Regardless of the conformation, a low-frequency dispersion in a frequency range lower than 10 kHz and a high-frequency dispersion in a range higher than 100 kHz were found. The large value of the dielectric increment, its nonlinear dependence on concentration, its remarkable dependence on counterion type, and its dependence on the degree of polymerization suggest that the low-frequency dispersion is mainly due to the polarization of loosely bound counterions. These data were found for both the helical and coiled forms. The rotational motion of the electric dipole on the molecule could not have been primarily responsible for these results. On the other hand, the high-frequency dispersions may be attributable to the Maxwell–Wagner-type effect. The results were compared with the dispersions of poly(L -glutamic acid), poly(L -lysine), and their salts reported previously.     

Surface properties of aqueous solutions of L-leucine

The surface tension, sigma, of solutions of L-leucine (CH3)2CHCH2CH(NH2)COOH in water, as well as in aqueous solutions of NaOH and HCl were measured in the temperature range between 278 and 308 K using the Wilhelmy plate method. L-Leucine was found to be a very weak surfactant, which can be understood if assuming strong interactions of this solute with the water structure. Striking differences were observed in the surface entropy of L-leucine solutions in water, 0.5 M HCl and 0.5 M NaOH. Moreover, surface activity of the solute is much lower than that supposed taking into account the hydrophobicity of this amino acid. It was concluded that the observed phenomena are caused by the water structure changes close to the side chain of leucine, caused by enforced hydrophobic hydration, i.e. formation of clathrate-like hydrates.