Synthesis of functional poly(amino acids) on cyclophosphazene templates

With the use of hexakis(p-aminophenoxy)cyclotriphosphazene and tetraphenyltetraaminocyclotetraphosphazene whose primary groups initiated the polymerization of L-α-alanine and γ-esters of L-α-glutamic acid n-carboxyanhydrides, poly(amino acids) containing an inorganic central ring have been prepared. Polypeptide chains of various lengths have been obtained by variation of the monomer-to-initiator molar ratio. The molecular masses of the synthesized samples are in good agreement with the calculated parameters, and the polymers show a narrow molecular-mass distribution (M _w /M _n < 1.3). The circular dichroism (CD) spectra and IR studies indicate a predominantly helical conformation of poly(amino acid) chains with the central triphosphazene ring and the disordered structure of poly(amino acid) chains bonded to cyclotetraphosphazene.     

Interaction of polyanions with electroneutral liposomes in a slightly acidic medium

In this study, the interaction between poly(styrene sulfonic acid), polyacrylic acid, poly(meth-acrylic acid), poly(L-glutamic acid), poly(vinyl sulfate), and ternary copolymer of styrene with maleic anhydride and methacrylic acid (3: 2: 1), as well as DNA with lipid vesicles composed of zwitterion (electroneutral) lipid phosphatidylcholine, has been investigated. The methods of centrifuge ultrafiltration and dynamic light scattering reveal that, at pH 4.2, all polyacids under study are effectively adsorbed on the phospholipid membrane. The polymer-membrane complex is stabilized by hydrogen bonds and hydrophobic interactions in addition to electrostatic bonds. Even though, to a greater or lesser extent, all polyacids are capable of undergoing adsorption on the membrane in a slightly acidic medium, their effect on the membrane permeability is substantially different and is correlated with the ability of a polymer to form multiple interactions with phospholipid molecules. Poly(acrylic acid), poly(methacrylic acid), poly(styrene sulfonic acid), and the ternary copolymer of styrene with maleic anhydride and methacrylic acid can produce the membrane pores that are permeable to low-molecular-mass compounds. At the same time, poly(L-glutamic acid), poly(vinyl sulfate), and DNA exert no effect on the membrane permeability, although they are sorbed on the membrane surface.     

Conformational studies of copoly (N 5-ω-hydroxyalkyl-L-glutamine-L-glutamic acid)s

Copoly (α-amino acid)s consisting ofL-glutamic acid residue andN ⁵-ω hydroxyalkyl-L-glutamine residue, i.e., 2-hydroxyethyl, 3-hydroxypropyl, and di-2-hydroxyethyl derivatives were prepared by the reactions of copoly (L-glutamic acid) containing succinimide ester with corresponding amino alcohols. The conformation of these copolymers was examined by the CD and infrared measurements. These three copolymers containing about 20–30% hydroxyalkyl groups undergo a methanol-induced and a pH-induced conformational transitions. The copolymer containing about 50% 3-hydroxypropyl group assumes the α-helical conformation in the pH region from 2.5 to 11.6, and in a methanol-water mixture (9∶1). On the other hand, the copolymer containing about 60% di-2-hydroxyethyl groups does not allow any helical conformation even at lower pH and also even in a trifluoroethanol-water mixture (9∶1), suggesting that the branched hydroxyalkyl group is unfavorable for the formation of α-helix. Furthermore, the poly(N ⁵-di-2-hydroxyethyl-L-glutamine) is shown to have a rather disordered structure in the solid state.     

Synthesis of metal-organic frameworks from the system metal/L-glutamic acid/TEA/H2O

Three metal-organic frameworks (MOFs) with similar zeolite-like 3-D structures, Zn(L-Glu)(H₂O) · H₂O, Cu(L-Glu)(H₂O) · H₂O, and Co(L-Glu)(H₂O) · H₂O, have been obtained from metal/L-glutamic acid/TEA/H₂O systems, whereby the weak base triethylamine (TEA), rather than the more typically used NaOH or Na₂CO₃, has been used to adjust the pH of the solution. A systematic and detailed exploration of the synthesis conditions has revealed that not all transition metals may be coordinated to L-glutamic acid and that the range of conditions under which the three MOFs remained stable was different. The metal/L-glutamic acid/TEA/H₂O system offers an effective means of obtaining MOFs.     

Electronic absorption spectra of M2L6 compounds containing metal-metal triple bonds of σ2π4 configuration

The electronic absorption spectra of compounds containing metal-metal triple bonds of σ²π⁴ valence electronic configuration are presented and discussed. The lowest-energy transition of M₂L₆ compounds (M = Mo or W, L = CH₂Bu^t or OBu^t) is expected to be the dipole-allowed π → π* (e_u → e_g) transition. This appears to be the case for M₂(CH₂Bu^t)₆ and M₂(OBu^t)₆ compounds, in which the lowest energy absorption bands occur between 26,000 and 28,000 cm⁻¹ (ε = 1.1 x 10³-1.8 x 10³ M⁻¹ cm⁻¹). For M₂(NMe₂)₆ compounds, the lowest energy absorption is not the π → π* transition but is assigned instead to a LMCT transition originating from nitrogen lone-pair orbitals, N_1p → π*, observed at 30,800 cm⁻¹ (ε = 1.4 x 10⁴-1.9 x 10⁴ M⁻¹ cm⁻¹). The π → π* transition is not observed in these compounds, but is presumably masked by the more intense LMCT. These assignments are derived from Xα-SW calculations performed and described by other authors (Bursten et al., J. Am. Chem. Soc. 1980, 102, 4579).     

Thermal decomposition of microbial poly(γ-glutamic acid) and poly(γ-glutamate)s

The thermal decomposition of poly(γ-glutamic acid), poly(α-methyl γ-glutamate) and ionic complexes of the polyacid with alkyltrimethyl ammonium salts was studied by TGA, GPC, and FTIR and NMR spectroscopies. It was found that both poly(γ-glutamic acid) and poly(α-methyl γ-glutamate) depolymerised above 200 °C by unzipping mechanism with generation of pyroglutamic acid and methyl pyroglutamate, respectively. On the other hand, the ionic complexes degraded through a two-stage process, the first stage being cyclodepolymerisation of the poly(γ-glutamate) main chain along with decomposition of the ionic complex promoted by the adsorbed water. Decomposition of the previously generated alkyltrimethyl ammonium compound followed by unspecific cracking of the resulting nitrogenated compounds accounted for the second degradation step, at higher temperatures. Mechanisms explaining the decomposition of the three studied systems were proposed according to collected data.     

Radiation induced transformation of CO in cyclohexane

The radiation induced incorporation of CO in cyclohexane leads to formation of: bicyclohexylketone (G_i = 2.40), α, α-bicyclohexyldiketone (G_i = 0.90), cyclohexanone (G_i = 0.24), cyclohexanol (G_i = 0.20), cyclohexanecarboxylic acid (G_i = 0.10), in addition to bicyclohexyl (G_i = 1.30) and polymers. The G_i-values are strongly dependent on the CO-concentration in the solution. Probable reaction mechanisms are presented.     

Bi-ionic membrane potential across a liquid anion-exchange membrane containing triphenyltin chloride

Potentiometric selectivities of a liquid anion-exchange membrane containing triphenyltin chloride (TPTCl) to several inorganic anions were evaluated via measurements of the membrane potential of a bi-ionic system, also called bi-ionic membrane potential. Addition of TPTCl to the liquid anion-exchange membrane, based on the quaternary ammonium salt, gave rise to a quite different selectivity pattern from the so-called Hofmeister anion series observed for the liquid anion-exchange membrane. An additivity rule of the bi-ionic membrane potential was observed to hold for the liquid anion-exchange membrane containing TPTCl. Thus, the following multiple chain rule was derived for selectivity coefficients; k_1,n^pot = k_1,2^pot · k_2,3^pot … k_i,(i+1)^pot … k_n−1,n^pot where k_i,i+1^pot is the selectivity coefficient of the membrane for the (i + 1)th ion over the ith ion.     

Synthesis of L-Lysine and L-Glutamic Acid Derivatives with Long Alkyl Chains and Polycondensation of Langmuir-Blodgett Films

Two esters of L-lysine and L-glutamic acid containing long alkyl groups were synthesized and their polycondensation in monolayers and multilayers was investigated. The pressure-area isotherms of the ester of L-lysine depend markedly on the time of residence at the air-water interface. The change of FT-IR spectra of the deposited film, which can be lifted as a Z-type film, indicates that polycondensation can occur in the monolayer at 10°C without any treatment. The spectrum of the film cast from chloroform hardly changed with time. These results lead to the conclusion that a regular arrangement of monomer molecules in the monolayer, where the amino and ester carbonyl groups are concentrated, is more suitable for the polycondensation. The ester of L-glutamic acid can also form stable monolayers which can be easily deposited on a hydrophobic plate as a Y-type film by the Blodgett technique. The polycondensation of multilayers under an atmosphere of triethylamine was investigated by IR spectroscopy. It indicates that the condensation in multilayers proceeds via intermolecular and intramolecular reactions, by which poly(L-glutamate) derivatives and 2-pyrrolidone derivatives are formed, respectively. The condensation in the bulk crystalline powder gives exclusively the 2-pyrrolidone derivative by intramolecular reaction. These results suggest that the monomer molecules in the multilayers are favorably aligned for the intermolecular reaction, in contrast to the situation in the bulk crystalline powder.     

Radiation-induced degradation of aqueous 2,3-dihydroxynaphthalene

The degradation of aqueous 2,3-dihydroxynaphthaline (2,3-DHN) under the influence of γ-ray was investigated under various experimental conditions. Using 2.5×10⁻⁵ mol L⁻¹ 2,3-DHN in aerated media (pH=6–6.8) an initial degradation yield, G_i-(2,3-DHN)=0.32 was obtained, whereas in solutions saturated with N₂O the yield come to G_i-(2,3-DHN)=0.50.In airfree media the substrate decomposition was negligible. Possible reaction mechanisms are presented.Further, the rate constant, k(OH+2,3-DHN)=2.14×10¹⁰ L mol⁻¹ s⁻¹ was determined by competition reactions with PNDA.     

Quadruple thermo-photo-redox-responsive random copolypeptide nanogel and hydrogel

Quadruple stimuli-responsive random copolypeptide of poly(methoxydiethyleneglycol-L-glutamate)-co-poly(S-(o-nitrobenzyl)-L-cysteine) was synthesized by ring-opening copolymerization, simultaneously presenting thermo-photo-redox-responsive self-assembly behavior and forming nanogel and hydrogel in water.     

Calcium ion selective membrane electrode

The calcium salts of the mono- and diesters of [4-(1,1,3,3-tetramethylbutyl)phenyl phosphoric acid] have been prepared, and the individual esters as well as mixtures of the esters have been used with several varieties of polyvinyl chloride to construct macro membrane electrodes selective to calcium ions. These electrodes have been calibrated by using solutions of CaCl₂ and Ca ion buffers. The mixed ester electrodes showed Nernstian response in the concentration range 10^-1 to 10^-7M; the diester electrodes showed Nernstian response down to 7.9 x 10^-8M. The detection limit of the mixed ester electrode was 10^-8M, whereas that of the diester electrode was 7.9 x 10^-9M. Contrary to these results, the monoester electrodes showed unsatisfactory behavior. The responses of both the mixed ester and diester electrodes to calcium ions were not affected by the presence of sodium, potassium, or other divalent ions. Only ferric and lanthanum ions showed interferences with the electrode response to calcium ions. p]The electrode response was independent of pH in the approximate range 5–8 at a CaCl₂ concentration of 10^-4M. As the Ca ion concentration was increased, the range of pH independence widened to approximately 4–8. The dynamic response time constant of the mixed ester electrode was in the range 0.7–1.5 sec, whereas that of the diester electrode was in the range 0.5–0.75 sec.     

Selective salt transport through a crosslinked poly(L-glutamic acid) membrane for KCl/LiCl mixed systems

Selective salt transport of KCl over LiCl has been studied for a crosslinked poly(L -glutamic acid) membrane immersed in 80 vol.-% ethanol. The permeabilities (P_s) and solubilities were measured for various mixing ratios of the salts. The highest permselectivity (P_s (KCl)/P_s (LiCl) = 4,3) has been obtained at a LiCl mole fraction of 0,2. It is similar to that obtained in single salt systems.     

Solubilities of polypeptides with hydrophobic and negatively charged side-chains into cationic artificial membrane vesicles

The influence of relatively low molecular weight polypeptides on the structure of membrane vesicles composed of distearyldimethylammoniumchloride (DSACl) was investigated by means of calorimetric, fluorescence spectroscopic and fluorescence polarization measurements, and correlated with the degree of hydrophobicity and/or dissociation of the polypeptide side chains. The polypeptides used were poly(-methyl L-glutamate) (PMLG,M _v =4400), copoly(methyl L-glutamate L-glutamic acid) containing 20 mol % of L-glutamic acid (80/20 MG/GA,M _v =4200) and poly(L-glutamic acid) (PLGA,M _v =9200). The hydrophobic polypeptide, PMLG, was readily incorporated into the DSACl membrane vesicles to form membrane-spanning helices, resulting in a decrease in the microviscosity of the hydrophobic region of the membrane phase. The partially charged hydrophobic polypeptide, 80/20 MG/GA, was almost insoluble into the membrane below the phase transition temperature of the DSACl vesicle,T _c 40.4 °C, however, the solubility of the copolymer into the membrane was drastically increased aboveT _c . The negatively charged polypeptide, PLGA, can hardly penetrate through the membrane vesicle and formed crosslinking between the positively charged DSACl vesicles. It was also confirmed that aggregation or clustering of the hydrophobic PMLG-helices progressed in the membrane phase belowT _c .     

Measurement of L x-ray production cross sections by 60 keV photons and average L shell fluorescence yields of lanthanides

L x-ray production cross sections have been measured for lanthanides with 60 keV. The measured L x-ray production cross section values for the lanthanides are in good agreement with the theoretical ones evaluated using L _i subshell fluorescence yields ω_i, Coster-Kronig transition probabilities ? _ij based on the Relativistic-Hartree-Slater theory, K to L _i subshell vacancy transfer probabilities n _KLi, fractions of the ratiative width of the subshell F _ny and L _i subshell photoionisation cross section σ_Pi. The average L shell fluorescence yields ω_L have also been derived using the presently measured total L x-ray production cross section values and the theoretical K to L shell vacancy transfer probabilities. These results are compared with theoretically predicted values.     

Nanofiltration membrane behavior in a supercritical medium

The permeability values of “TN” organomineral nanofiltration membranes to water, L, and to supercritical CO₂, G, were compared. The resulting values for G were an order of magnitude higher than for L. The difference may be directly related to the viscosity difference between the two fluids. Temperature- and pressure-related variations in G were also analyzed; for this purpose, Poiseuille's model satisfactorily accounts for experimental behavior, while Knudsen's model is unsuitable. A hysteresis effect was observed on the isotherms corresponding to variations in G versus pressure, suggesting partially irreversible CO₂ adsorption on the micropore walls, that would diminish the radius. This phenomenon could be enhanced by an increased fluid density and viscosity.     

Dielectric polarization of a partially neutralized poly(methacrylic acid) in dilute aqueous solutions: Conformational transition

Dielectric permittivity ε′ (at a frequency of 1 MHz) of aqueous solutions of a partially neutralized poly(methacrylic acid) Na-PMAA was studied with varying the degree of ionization α_i from 0 to 0.78 and concentrations w ₂ (g/g) from 1.25 × 10^?4 to 6 × 10^?3 at 25°C. It was shown that the concentration dependence of ε′ for Na-PMAA aqueous solutions at all α_i values contains two regions corresponding to different changes in ε′, and the above regions are separated by the crossover point w*₂. In the first region, ε′ increases with the increasing concentration Δε′/Δw ₂ > 0; in the second region, ε′ decreases with the increasing concentration Δε′/Δw ₂ < 0. The sign inversion of Δε′/Δw ₂ is explained by different structures of water and mechanisms of hydration in regions I and II. In the region corresponding to the ascending branch of the ε′-w ₂ curve, the dipole moments of macromolecules per repeating unit, μ = (〈M ²〉/N)^1/2, were calculated according to the Buckingham theory. The μ value is high; as a macromolecule is saturated with ionized units, this value nonmonotonically changes from ～10 D at α_i = 0 to ～18 D at α_i ～ 0.24. This dependence peaks at ～30 D at α_i ～ 0.1. As is assumed, (〈M ²〉/N)^1/2 depends on the vector sum of partial dipole moments of hydrated nonionized monomer units (μ ～10 D) and fluctuation-induced dipole moments of ionized monomer units. The profile of μ as a function of the degree of ionization of Na-PMAA indicates the occurrence of the conformational transition in an individual macromolecule. This transition takes place at the degree of ionization α_i ～ 0.1. An analysis of molecular interactions in the (ionized coil)-solvent system explans the conformational transition in Na-PMAA.     

Preparation and properties of novel environment-sensitive membranes prepared by graft polymerization onto a porous membrane

The present work is concerned with the preparation and some properties of novel environment-sensitive membranes. A porous poly (vinylidene fluoride) membrane (pore size 0.22 μm) was pretreated by air plasma; subsequently, hydrophilic monomers were graft polymerized on the treated surface. Since the filtration characteristics of the obtained membranes reflect the configuration of the grafted chains, these can be changed reversibly from ultrafilter to microfilter and vice versa in response to the membrane environment such as pH, solvent composition and ionic species. Grafted chains act as a sensor and a valve to regulate filtration characteristics. The poly(acrylic acid) grafted membrane for example is very sensitive to environmental pH. In the pH region of 1 to 5, the filtration rate sharply decreased with increasing solution pH, the filtration rate at pH 1.4 being about ten times higher than at pH 5.2. Together with this decrease in filtration rate, the membrane gained the ability of ultrafiltration of macromolecular solutes such as dextran (M_w = 2,000,000) and albumin (M_w = 67,000). In the pH region of 5.2 to 7.5, filtration rate and solute rejection did not depend on pH. The pH sensitivity is reversible and reproducible. Because of characteristics such as the drastic alteration in filtration rate and solute separation properties and the quick response to solution conditions, the environment-sensitive membranes developed here may find applications in various areas of membrane technology.     

Relaxation phenomena involved in the L3M4,5M4,5;1G4 auger process in zinc metal

A detailed analysis is presented of the L₃M_4,5M_4,5;¹G₄ Auger transition in metallic zinc. An extra-atomic relaxation term, neglected until now, is taken into account. This results in excellent agreement between calculated and experimental values of the Auger-transition energy.     

Ionic solvation in water + co-solvent mixtures. Part 8. Total free energies of transfer and free energies of transfer with the “neutral” component removed of single ions from water into water + acetone

The acid dissociation constants of a wide range of acids in water+acetone mixtures have been combined with values for the free energy of transfer of the proton. ΔG⁰_t(H⁺ to calculate values for the free energy of transfer of ions which derive only from the charge on the ion. ΔG⁰_t(i)_c. As the values of ΔG⁰_t(H⁺) have been revised, revised values for the total free energies of transfer of cations and anions, ΔG⁰_t(M⁺) and ΔG^o_t(X^-), are given. New data for ΔG^o_t(MX_n) is also split into values for ΔG⁰_t(Mⁿ⁺) (where n=1 and 2) and ΔG⁰_t(X^?). These free energies of transfer, both total and those deriving from the charge alone, are compared with similar free energies in other mixtures water+co-solvent. Values for ΔG^o_t(i)_c do not conform to a Born-type relationship and show the importance of structural effects in the solvent even when only the transfer of the charge is involved.