Interaction of poly(L-glutamic acid) with cationic surfactants carrying different head groups

Three cationic surfactants carrying a common hydrocarbon tail (dodecyl group) interact differently with fully ionized poly(L-glutamic acid)(PGA), depending on the type of their ionic head groups. Decrease of pH occurred in the order; dodecylammonium chloride (DAC) > dodecyldimethylammonium chloride (DDAC) > dodecyltrimethylammonium chloride (DTAC). The-helix of PGA was strongly induced by the addition of DAC and DDAC but weakly by DTAC. The induction was inhibited when NaCl concentration was greater than 0.05 M. In the solid state, proton transfer through hydrogen bonds from ionic heads of DDAC to carboxylate groups of the polypeptide was observed. Distortion of circular dichroism spectra occurred at high mixing ratios of surfactant to polymer, due to the aggregation of-helices, as confirmed by light scattering measurements and infrared absorption spectra.     

Characterization of water-soluble,cationic polyelectrolytes as exemplified by poly(acrylamide-co-trimethylammoniumethylethacryate chloride) and the establishment of structure-property relationships

The cationic copolymerization products of poly (acrylamide-co-trimethylammoniumethylmethacrylate chloride (PTMAC) having cationic monomer percentages of 8%, 25%, and 50% as well as the cationic homopolymer, were characterized with respect to their molecular dimensions. The light-scattering and viscometric measurements were carried out for molecular weights ranging from 200 000 to 12 800 000 g/mol in 1 M NaCl solution at 25°C. It was possible to establish a relationship between the molecular weight and the two parameters: intrinsic viscosity and radius of gyration, for all four polymers.Rheological investigations of the flow properties in 1 M NaCl solution were also carried out using the polymer with a cationic monomer of 50% (PTMAC 50). Structure-property relationships were formulated which made it possible to describe and predict the shear viscosity, both in the zero-shear region (Newtonian region) and in the shear-dependent region (non-Newtonian region) as a function of the polymer concentration, the molecular weight, and shear rate.Abbreviations a exponent of the []-M relationship - A ₂ 2^nd virial coefficient/mol·cm³·g^–2 - AAm acrylamide - b slope of the flow-curve in the shear-rate dependent region - c concentration/g·cm^–3 - dn/dc refractive index increment/cm³·g^–1 - f function - K constant of the []-M relationship/cm³·g^t-1 - m _c proportion of cationic monomers/mol % - M molecular weight/g·mol^–1 - M _w weight-average molecular weight/g·mol^–1 - M _n number-average molecular weight/g·mol^–1 - NaCL sodium chloride - PAAm polyacrylamide - PS polystyrene - PTMAC poly(acrylamide-co-trimethylammoniumethylme thacrylate chloride) - R_G ^20.5 radius of gyration/nm - TMAC trimethylammoniumethylmethacrylate chloride - shear rate/s^–1 - critical shear rate/s^–1 - viscosity/Pa·s - 0 zero-shear viscosity/Pa·s - _s solvent viscosity/Pa·s - _sp specific viscosity - [] intrinsic viscosity/cm³·g^–1 - relaxation time/s     

Counter ion condensation on mixed cationic/nonionic micellar systems: Bjerrum's electrostatic condition

The association of counter-ions with mixed ionic/nonionic micelles has been investigated in the case of dodecyl/tetradecyl/ and hexadecyl-trimethylammonium bromide with two nonionic surfactants: dodecylpolyoxyethylene 23 and Triton X-100. The degree of association has been measured by potentiometry using a Bromide ion-selective electrode. Previous results with sodium and copper dodecylsulfate suggesting that in the nonionic-rich composition domain, bare mixed micelles are formed without associated counter-ions have been confirmed. These results are in agreement with the prediction of Bjerrum's condition for ion association. The effect of copper dodecylsulfate on the cloud point of Triton X-100 has also been determined as a means of investigating mixed micelles with multivalent counter-ions. The dramatic cloud point increase observed, even larger than with sodium dodecylsulfate, has been discussed as evidence of the solvation of divalent ions by ether groups, a factor which complicates the analysis of multivalent counterion condensation on mixed micelles.     

Physicochemical properties of α, ω-type bolaform surfactant in aqueous solution. Eicosane-1,20-bis(triethylammonium bromide)

The physicochemical properties of the, - type (bolaform) surfactant, eicosane-1, 20-bis(triethylammonium bromide) (C₂₀Et₆), in aqueous solution have been investigated by means of surface tension, electrical conductivity, dye solubilization, and time-resolved fluorescence quenching (determination of average micelle aggregation number). Using electrical conductivity, the critical micelle concentration of C₂₀Et₆ was found to be 6.0×10^–3 mol dm^–3 and the ionization degree of C²⁰Et₆ micelle was found to be 0.42. From surface tension measurments, the molecular area of C₂₀Et₆ at the air-water interface was about twice that of normal type surfactants such as dodecyltrimethylammonium bromide (DTAB). The solubilizing power of micellar solution of C₂₀Et₆ toward Orange OT was 1.0×10^–2 mole of dye per mole of surfactant, i. e., slightly smaller than that of DTAB. The micelle aggregation number,N, was found to be 17±2 by time-resolved fluorescence quenching. C₂₀Et₆ showed a very small temperature dependence ofN, much less than for normal surfactants.     

The properties and behavior of supermolecular formations in aging aqueous poly (vinyl alcohol) solutions

The structure of supermolecular formations and the interparticle interaction in aqueous poly(vinyl alcohol) solutions aging at different concentrations were investigated. Integral light scattering was used to determine the single particle scattering functionP(K), the structure functionS(K), and hence the radial distribution functiong(r). Nonrandom arrangement of the supermolecular formations in solutions under study is much less intensive than that of particles in polymer latices.     

X-ray diffraction studies on homologous thallium soaps below the temperature range of the neat phase 2. Structure models of crystalline modifications in the temperature range below the neat phase

In Part 1 were discussed the results of X-ray diffraction measurements on homologous thallium soaps, the lattice parameters and the unit cells of the different phases: phase C₁, phase C₂, phase I, phase II, and the neat phase.The aim of Part 2 is the development of structural models, based on data on lattice parameters, packing densities of hydrocarbon chains and head groups. In order to supplement our experimental data we carried out infrared-spectroscopic measurements at different temperatures within the existence regions of these phases to get additional information on alterations in configurations of head groups and hydrocarbon chains of thallium soaps in these phase regions.By comparing the structural models we can generalize that the phase C₁, phase C₂, phase I, and phase II have some properties in common: they form crystalline structures, their unit cells are monoclinic, and the angles and are orthogonal. The amount of the lattice parametersc is equal to the distances of two molecular bilayers and/or twice the distance between the lamellae.Among the normal lamella, the molecules form a herring-bone-like packing. This indicates that the lamellar structure of the liquid-crystalline neat phase is already preformed in these crystalline modifications of phase C₁, phase C₂, phase I, and phase II. These crystalline phases differ in their lattice parameters and their packing coefficients. The transition from the crystalline phase I or phase II into the neat phase is accompanied by a temperature-dependent contraction of the distances between the lamellae, which originates in the fluidity of the hydrocarbon chains. Simultaneously, the lattice parametersa andb are drastically shortened and attain dimensions considerably lower than the values obtained in crystalline modifications. The X-ray scattering properties of the Tl⁺-ions suggest that the Tl⁺-ions exist in a fluid-like state within the head groups region of the neat phase.We came to the conclusion that the thallium-oxygen-bond is remarkably less polar than the bonds between alkali ions and oxygen resulting from the electro-negativity of the metal-oxygen-bonds of the alkali soaps, in comparison to the thallium soaps. Hence, the absence of polymorphic liquid-crystalline semiphases of thallium soaps is due to the low polarity of the thallium-oxygen-bond. Structure formation of Tl-soaps is mainly influenced by the hydrocarbon chain packing.     

Preparations and properties of polyurethane aqueous dispersion from uncatalyzed systems of H12MDI,PTAd/bisphenol A polyol,and DMPA

Aqueous dispersions of polyrethane (PU) containing ionic and nonionic hydrophilic segments were prepared in a prepolymer mixing process using substantial amount of solvent. The acid groups were neutralized with tertiary amine, and chain extension in aqueous media was carried out with triethylene tetramine. Average particle size and particle size distribution of the dispersion, and mechanical and viscoelastic properties of the emulsion cast films were determined.     

A new biodegradable polydepsipeptide microsphere for application in drug delivery systems

A sequential polydepsipeptide containing a tripeptide sequence L-alanyl-Lalanyl-ethyl L-glutamyl and an-hydroxy acid L-lactic acid, poly(Ala-Ala-Glu(OEt)-Lac), was synthesized to prepare the microspherical particles by the solvent evaporation process. In this case, the solvents play the most important role for the preparation of polydepsipeptide microspheres and, as an example, when 200 mg of the polydepsipeptide dissolved in 10 ml of 98/2% chloroform/dichloroacetic acid mixture was stirred at 400 rpm and 30 C, the microspherical particles with mean diameter of 58m were formed after pouring into 200 ml of 1% (w/v) poly(vinyl alcohol) solution. 17-Estradiol was incorporated into the particles, and the resulting particles were found to contain 5 mg of drug per 25 mg of the particle. The in vivo release of drug from the microspherical formulation was evaluated by measuring the pharmacological influence on rat prostate. It was found that the sufficient amount of drug, keeping the effective pharmacological influence, is supplied during the first 12-week period, followed by an incomplete supplying of drug intil the implant is perfectly degraded in vivo in the 25th week from the start of implantation.     

Phase diagrams and phase structure of theN-octanoyl-L-glutamic acid oligomer benzyl esters-CHCl3 systems

N-Octanoyl-L-glutamic acid oligomer benzyl esters (residue number,N=1–4, 6, 8, and 12) have been synthesized. For the solid samples ofN=3–12, x-ray powder diffraction pattern and vibrational spectroscopic measurements have led to the assumption of a -sheet structure. For the CHCl₃-solutions of theN-octanoyl tetramers, hexamers, and octamers, the phase diagram consists of three regions (I, II, and III). Region I is an isotropic phase, in which the aggregate structure strongly depends upon concentration, and region II is a lyotropic liquid crystal area. Region III is a two-phase area in which regions I and II coexist. In the case of the trimer solutions, it consists of two regions (I and II). For the oligomers withN=3–12 in region I, it was assumed that micellization induces preferential stabilization of the -sheet structure depending on the concentration. Further stabilization of the -sheet structure, was found to occur in region II. For the hexamer, octamer, and dodecamer in CHCl₃, results from light-scattering measurements have led to an estimate of the apparent weight-average molecular weights and aggregation numbers of the micelle in region I.     

Lamellar phases in mixtures of low molecular weight alkanols and cetyltrimethylammonium bromide (CTAB)

Partial phase diagrams showing the domains of existence of a transparent, viscous, lamellar-structured (D)-phase that transforms reversibly into fluid single phase solutions at high temperature are presented for the system: cetyltrimethylammonium bromide (CTAB), two low molecular weight alcohols, and water with and without additives. At constant temperature and with a fixed amount of surfactant, the size and location of this phase in the phase diagram depends upon three composition variables: i) the ratio of concentrations of medium chain alcohol to long chain alcohol (R), ii) the ratio of concentrations of medium chain alcohol to surfactant (R), and iii) the concentrations of small amounts (up to 10 % by weight) of additives such as ethylene glycol, propylene glycol, and dimethylformamide, as well as NaBr. Small-angle x-ray scattering measurements of these mixtures reveal a lamellar structure. The observed lamellar repeat distances range from 60 A to 290 Å and depend upon the ratiosR andR and the concentration of the additives. The mechanical and structural properties of theseD-phases can be tuned by adjustingR andR. TheD-phase-to-isotropic transition temperature can be varied from near room temperature to above 80 °C by adjustingR andR.     

Poly(styrene-b-2-vinylpyridine-1-oxide) and poly(dimethyl-siloxane-b-2-vinylpyridine-1-oxide) diblock copolymers 2. Micellar solutions in water/propan-2-ol mixtures

Dynamic light scattering and viscometry measurements have been carried out on three AB diblock copolymers in water/propan-2-ol mixtures. The A moieties in each case were poly(2-vinylpyridine-1-oxide) for which both water and propan-2-ol are good solvents. The B Moieties were either polystyrene or polydimethylsiloxane, for which both water and propan-2-ol are poor solvents, but water is the worse solvent. In all cases, the hydrodynamic size of the micelles (assumed spherical) was found to increase with increasing water content in the solvent mixture; the aggregation number was also found to increase. The former finding is in agreement with the theoretical predictions of Munch and Gast, but not the latter.     

Colloidal copper in aqueous solutions: radiation-chemical reduction,mechanism of formation,and properties

Colloidal copper has been obtained by -irradiation of aqueous solutions of copper (II) perchlorate in the presence of alcohol and polyethyleneimine (PEI). The sols are spherical particles about 4 nm in diameter, which are quickly oxidized by oxygen or other oxidants. When Cu^II is not entirely incorporated into the complex with PEI, disproportionation of Cu^I aqua complexes formed affords the metal, along with Cu₂O. Reduction of the PEI complex of Cu^I by hydrated electrons gives only colloidal copper. The copper ions can be reduced on the surface of silver sols. Optical parameters of the resulting bimetallic particles have been studied. The presence of copper ions leads to broadening of the absorption band associated with the silver sols and shifts it to the UV region, which is due to the transfer of electrons from copper to silver. Three copper monolayers are enough to cause plasmon absorption of colloidal copper.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 25–30, January, 1994.     

Electrical properties of poly(bis(β-phenoxyethoxy)phosphazene) and its complexes

Electrical and dielectrical properties of poly(bis(-phenoxyethoxy)phosphazene) (I) and its complexes with various content ratios of AgSO₃CF₃ to monomeric unit (0.25/1 (II) and 0.5/1 (III) in molar ratio) were investigated.Dc conductivity of respective samples at 18 °C were 6.1×10^–12, 4.4×10^–9, and 7.1×10^–8 S/m.Dc conduction was considered to be due to ion hopping. Charge mobility ranged from 3×10^–12 to 6× 10^–11 m²/Vs depending on the applied field in sample II. In sample I, a tan peak was found which can be ascribed to molecular relaxation of main chains. The peak vanished upon introducing AgSO₃ CF₃. Temperature dependence of total conductivity ( _T ) measured byac method in the temperature range between –150 °C and 50 °C showed several peaks at the temperatures corresponding to the peak temperatures of tan. Total conductivities of respective samples at 100 kHz were 4.9×10^–7 (69 °C), 1.7×10^–4 (45 °C), and 1.5×10^–4(40°C)S/m.     

Schiff base derivatives of lanthanons-synthesis of La(III), Pr(III) and Nd(III) derivatives of β-ketoimines derived from 2,4-pentanedione

Reactions of the isopropoxides of some of the lighter lanthanons with bidentate -ketoimines, such asAAH-n-C₄H₉ andAAH-C₆H₅ (donor system: N,OH) and tridentate -ketoimines such asAA(CH₂CH₂)H₂ andAA(CH₂CHCH₃)H₂ (donor system: HO,N.OH) have led to products of the typesLn(O-i-C₃H₇)_3n (AA-R) _n ,Ln(Oi-C₃H₇) (AAR') andLn ₂(AAR')₃ [Ln=La(III), Pr(III) or Nd(III);n=1 or 2;R=-n-C₄H₉ or-C₆H₅ andR'=-CH₂CH₂-or-CH₂CHCH₃-]. Some undergo exchange reactions with an excess oftert-butanol, leading to the corresponding complexesLn(O-tert-C₄H₉)_3n (AA-n-C₄H₉) _n andLn(O-tert-C₄H₉) (AA-CH₂CH₂). All these have been characterised by elemental analysis, molecular weight determinations and their ir spectra. A thermogravimetric analysis of the diisopropoxy derivatives has also been carried out.

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Schiff-Basen Derivate von Lanthaniden-Synthese von La(III), Pr(III) und Nd(III) chelaten mit -Ketoiminen

Zusammenfassung Reaktionen von Lanthanid-Isopropoxiden mit zweizähnigen -Ketoiminen [AAH-n-C₄H₉ undAAH-C₆H₅; Donorsystem: N,OH] und dreizähnigen -Ketoiminen [AA(CH₂CH₂)H₂ undAA(CH₂CHCH₃)H₂; Donorsystem: OH, N,OH] führten zu Produkten vom, TypLn(O-i-C₃H₇)_3-n (AA-R) _n ,Ln(O-i-C₃H₇) (AAR') undLn ₂(AAR')₃ [Ln=La(III), Pr(III) oder Nd(III);n=1 oder 2;R=n-C₄H₉ oder C₆H₅ undR'=CH₂CH₂ oder CH₂CHCH₃]. Einige Komplexe unterliegen bei Behandlung mit einem Überschuß vontert-Butanol einer Austauschreaktion, die zu den entsprechenden Butoxid-Komplexen führt [Ln(O-tert-C₄H₉)_3-n , (AA-n-C₄H₉) _n undLn(O-tert-C₄H₉) (AACH₂CH₂)]. Alle Derivate wurden mittels Elementaranalyse, Molgewichtsbestimmung und IR-Spektroskopie charakterisiert. Eine thermogravimetrische Analyse der Diisopropoxi-Derivate wurde ebenfalls ausgeführt.

     

Linear silver clusters in aqueous solution (clusterites): radiation-induced chemical synthesis and properties

The formation and properties of the products of the radiation-induced chemical reduction of silver ions in aqueous solutions containing sodium polyacrylate were investigated. The absorption spectra of these species exhibit a band at 290 mn and a band in the visible region. The latter shifts from 470 nm to -800 nm with time or after the addition of silver ions. The species obtained (clusterites) arc linear silver clusters bound to the carboxyl groups of the ion exchanger. The red shift of the visible band is due to the increase in their size. The mechanism of the formation and the structure of the clusterites are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1429–1435, June, 1996.     

Spectroscopic detection of theendo-enol form of 2-acetylcyclopentane-1,3-dione

According to vibrational spectroscopic data, in the gas phase at 280 °C and in crystals prepared by sublimation, 2-acetylcyclopentane-1,3-dione was established to exist not as trione 1 but as the enol-form 2 with an exo-cyclic C=C bond (v(C=C) = 1593 cm^–1) and an intramolecular hydrogen bond. The enol 3 prepared by crystallization from CCl₄ is also stabilized by an intramolecular H-bond but has anendo-cyclic C=C bond (v(C=C) = 1545 cm^–1). In a trichloroethylene solution, both theexo- andendo-enol forms co-exist, and the percentage of the latter is 11 %. The frequencies in the vibrational spectra have been assigned using the normal coordinate calculation of2, 3, and their OD-analogs. The mechanism of tautomer transfer is discussed in terms of PMO theory.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 57–62, January, 1994.The authors are grateful to professor J. G. Ramos (Madrid Institute of Optics) for making it possible to record the far IR and Raman spectra in his laboratory, to Dr. V. Z. Kurbako for the registration of spectra and its discussion, and to Dr. N. A. Kubasova for recording the Raman spectra with a Coderg Ar-300 instrument.     

A Novel Cyclodextrin-containing Glass Thermoplastic System (GTS) for Formulating Poorly Water Soluble Drug Candidates: Preclinical and Clinical Results

We present a novel solid solution/dispersion technology with glass thermoplastic properties that provide good dissolution rates and oral bioavailabilities for poorly water-soluble weak bases. In this process, a thermoplastic gum was prepared by mixing a polyhydroxy acid such as citric acid or tartaric acid with a weakly basic drug, hydroxypropyl--cyclodextrin (HP--CD) and a cellulose polymer such as hydroxypropylmethylcellulose (HPMC) in a protic solvent. Removal of the solvent gave a material which could be loaded into hard gelatin capsules. Several model compounds were processed in this manner including methylene blue and itraconazole. The resulting data indicated that dissolution properties of GTS's based on methylene blue was pH independent and rapid with 80% dissolved within 30 min. Three GTS formulations of itraconazole containing 100 mg of the drug and 500 mg of citric acid as well as various concentrations of HP--CD and HMPC were found to dissolve rapidly (100% in 45 min). One of these formulations was selected for human pharmacokinetic evaluation and demonstrated significant oral bioavailability relative to unmanipulated drug.The studies suggest that the components of the GTS provide for solubilization through complexation and reduced pH and that the cellulose polymer acts to inhibit recrystallization of the supersaturated solution formed. The rationaldevelopment of the GTS dosage form can be useful for generating acceptable formulations for poorly water-soluble drug candidates.     

The complexation of 2,3-anthracenedicarboxylate by β- and γ-cyclodextrins in mixed solvent systems as studied by induced circular dichroism. The role of cosolvent hydrophobicity

The complexation of 2,3-anthracenedicarboxylate (ADC) by- and-cyclodextrins in water containing an organic solvent has been studied by induced circular dichroism. It has been shown that an increase of organic solvent ratio causes the degradation of the 1:1 ADC:-CD complex and the liberation of one guest molecule from the 2:1 ADC:-CD complex in water. The higher the hydrophobicity of the cosolvent, the weaker the complexation of ADC by-CD.     

Solvatochromic parameters for binary mixtures and a correlation with equilibrium constants. Part I. Dioxane-water mixtures

The values of the solvatochromic parameters and were determined at 25°C for dioxane-water mixtures from 0 to 100% of dioxane. These values as well as those of the Reichardt polarity parameter E _T (30) and the polarity-polarizability ^* are correlated with acid dissociation constants and other equilibrium constants in solvent mixtures of the same composition. As a general rule, two linear zones with different slopes are obtained, one zone covering water-rich solutions, and the other dioxane-rich solutions. The change in behavior takes place at about 55% (v/v) dioxane for all equilibria studied. A fit of pK to an equation of the multiparametric form proposed by Kamlet and Taft shows in most cases a linear dependence on ^* alone, in other cases a dependence on ^* and .