Crystallization Behaviors and Regime Kinetics Analysis of Poly(<Emphasis Type="Italic">L</Emphasis>-lactide)-poly(butylene adipate)-poly(<Emphasis Type="Italic">L</Emphasis>-lactide) Based Multiblock Thermoplastic Polyurethanes

Poly(L-lactide)-based (PLLA) poly(ester-urethane)s are particularly relevant and gain significant attention due to their environment-friendly degradability and elastomeric shape memory capability. The tensile properties, resilience and degradation are strongly affected by their crystallization. This work was to investigate crystallization behaviors of the poly(L-lactide)-poly(butylene adipate)-poly(L-lactide) (PLLA-PBAPLLA) based thermoplastic polyurethane elastomers (PLAEUs) we synthesized previously. Dynamic scanning calorimetry (DSC) and polarized optical microscopy (POM) in combination with Avrami, Jezioney and Hoffman-Weeks models were used to analyze the impact of the PLLA block length on the crystallization temperature T_c, degree of crystallinity X_c, nucleation and spherulite growth mode and crystallization regime kinetics of the PLAEUs. The results indicate the low melting point poly(butylene adipate) (PBA) block resides in the amorphous domains while the PLLA block resides in both crystalline and amorphous phases. The X_c of the PLAEUs increase with the increased length of the PLLA block (i.e. higher content of PLLA block). The analyses with Avrami and Jezioney models show the PLAEU copolymers follow a disc-like spherulite growth. The covalently bonded PBA block decreases both nucleation velocity and spherulite growth rate in the isothermal crystallization. Such an impact is lessened as PLLA block length increases. The PLLA homopolymers demonstrate crystallization regime transition from II to III at a certain T_c of isothermal crystallization, while the crystallization regime kinetics of PLLA block in the PLAEUs are explained by a single regime III at low molecular weights of PLLA and the transition is restored as the PLLA block length increases (i.e. regime II to III).     

Binuclear copper(II) complexes with acyldihydrazones of <Emphasis Type="Italic">N</Emphasis>-benzenesulfonyl-<Emphasis Type="Italic">L</Emphasis>-aspartic acid

The structure and the EPR spectra of copper(II) coordination compounds with acyldihydrazones of N-benzenesulfonyl-L-aspartic acid and salicylaldehyde (2-hydroxyacetophenone) were described. The compounds were studied by chemical and thermal analyses, IR spectroscopy, and EPR. The molecular and crystal structures of copper(II) complexes with N-benzenesulfonyl-L-aspartic acid bis(salicylidene)hydrazone (H₄L¹) [Cu₂L¹ · 2Py] · 1.5 H₂O was determined by X-ray diffraction. The crystals are triclinic: a = 10.4714(4) Å, b = 12.9702(5) Å, c = 14.6187(9) Å, α = 104.763(2)°, β = 93.082(2)°, γ = 111.4240(10)°, space group P \(\bar 1\), Z = 2. The binuclear complexes containing copper cations whose coordination polyhedra are connected by an aliphatic spacer (Cu...Cu, 8.669 Å) are additionally linked by phenoxy bridges (Cu...Cu, 3.398 Å). The EPR spectra of these compounds in solutions exhibit an isotropic signal of seven HFS lines due to two equivalent copper ions with the spin Hamiltonian parameters g = 2.115?2.120, a _Cu = (35.5?38.0) × 10^?4 cm^?1, which is indicative of weak exchange interactions between the paramagnetic sites.     

Preparation of nanoparticle colloids of methoxy poly(ethylene glycol)-<Emphasis Type="Italic">b</Emphasis>-poly(<Emphasis Type="SmallCaps">D</Emphasis>,<Emphasis Type="SmallCaps">L</Emphasis>-lactide): effects of surfactant and organic solvent

Nanoparticle colloids of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) diblock copolymer were prepared by a modified spontaneous emulsification solvent diffusion method using acetone/ethanol as the mixture organic solvents. The MPEG-b-PDLL was synthesized by ring-opening polymerization of D,L-lactide using stannous octoate and MPEG with molecular weight of 5,000 g/mol as the initiating system. The MPEG-b-PDLL obtained was an amorphous polymer with molecular weight of 73,600 g/mol. Influences of acetone/ethanol (v/v) ratios and Tween 80 surfactant concentrations on characteristics of the colloidal nanoparticles were investigated and discussed. Light-scattering analysis showed that average diameters of the surfactant-free colloidal nanoparticles were in the range of 86–124 nm. The nanoparticle sizes decreased as the ethanol ratio increased. The Tween 80 did not show the significant effect on the nanoparticle sizes. Scanning electron micrographs of dried nanoparticles that demonstrated the aggregation of most particles suggested they were the soft nanoparticles. However, the dried nanoparticle morphology can be observed from scanning electron microscopy as having a spherical shape and smooth surfaces.     

<Emphasis Type="Italic">Z</Emphasis>-and <Emphasis Type="Italic">E</Emphasis>-conformers of <Emphasis Type="Italic">N</Emphasis>-chloroacetylcytisine

N-Chloroacetylcytisine was synthesized by acylation of (–)-cytisine. Stable Z- and E-conformers with respect to rotational isomerism around the N-12–CO bond were found in PMR spectra at room temperature. The point at which PMR resonances of the Z- and E-conformers coalesced upon heating was measured. The transition barrier between the conformers was estimated.     

Copolymer of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diallyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylammonium chloride with maleic acid as drug carrier

A copolymer of N,N-diallyl-N,N-dimethylammonium chloride with maleic acid of constant composition was prepared under the conditions of radical initiation. The possibility of the functionalization of the copolymer with drugs containing amino groups by polymer-analogous transformations was examined. Conditions were found for preparing conjugates of the copolymer with isoniazid. The structures and the quantitative compositions of the conjugates were determined by ¹³С NMR spectroscopy, and the possibility of preparing conjugates with controlled drug content was demonstrated.     

Molecular properties of the copolymers of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diallyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylammonium chloride and maleic acid

The hydrodynamic and conformational properties of molecules of poly(N,N-diallyl-N,N-dimethylammonium chloride) and N,N-diallyl-N,N-dimethylammonium chloride-maleic acid copolymers of different compositions in solutions with various ionic-strength and pH values, as well as of the polyelectrolyte complex based on the copolymer with dodecyl sulfate anions in chloroform, are studied. For poly(N,N-diallyl-N,N-dimethylammonium chloride) molecules in a 1 M NaCl solution, the Kuhn segment length and the hydrodynamic diameter of the chain are estimated as A = 3.9 nm and d = 0.48 nm, respectively. In acidic solutions with pH 3.5, the copolymers demonstrate behavior typical for polyelectrolytes. In an alkaline solution with pH 13, when 1 M NaCl is added to the solution of the copolymer containing 29 mol % maleic acid units, there is an antipolyelectrolyte effect that manifests itself as an increase in the intrinsic viscosity of the copolymer and in the hydrodynamic radius of its molecules. It is found that an increase in the fraction of maleic acid units in the copolymer from 12 to 42 mol % brings about a reduction in the equilibrium rigidity of its macromolecules from 4.1 to 2.2 nm. The equilibrium rigidity of polyelectrolyte-complex molecules is higher than that of initial copolymer molecules owing to steric interactions arising between the aliphatic chains of dodecyl sulfate anions. In an electric field, the molecules of the complex are oriented owing to the induced dipole moment resulting from the displacement of dodecyl sulfate anions along the chain contour.     

Synthesis of (<Emphasis Type="Italic">E</Emphasis>)-<Emphasis Type="Italic">N</Emphasis>-(3-alkoxy-4-acyloxyphenylmethylene)-<Emphasis Type="Italic">N</Emphasis>-(<Emphasis Type="Italic">e</Emphasis>-cyclohexyl)amines

Previously unknown E isomers of azomethines (Schiff bases) were synthesized from vanillal and vanillin esters by their reaction with cyclohexylamine.     

Poly(<Emphasis Type="SmallCaps">d,l</Emphasis>-lactic acid) nanoparticle preparation and colloidal characterization

Nano size-ranged poly(d,l-lactic acid) (PLA) particles were obtained from 2 and 10 w% PLA solution in water-saturated ethyl acetate by the emulsification-diffusion method. An increase in the PLA solution concentration resulted in an increase of the particle mean size from ca 260 nm to 530 nm with a broadening of the distribution. After fractionation by centrifugation, the particle mean size was 980 nm. The Pluronic F68 used in the formulations at concentration ranging from 0.5 to 5% w/v, was shown to adsorb at the interface at 0.5 mg/m ² for both particle sizes. The molecular occupied area of 24 nm ²/molecule suggested an expanded conformation of the surfactant at the interface, though an incomplete coverage could not be excluded. Coagulation kinetics measurements revealed a critical coagulation concentration (CCC) of 1.5 M sodium chloride, indicating a steric stabilization of the colloids by the adsorbed triblock copolymer. Nonetheless, variations in zeta potential with increasing salt concentration were observed, suggesting that the surface carboxylate groups were still accessible for further modifications.     

Molecular structure of <Emphasis Type="Italic">N</Emphasis>-(<Emphasis Type="Italic">o</Emphasis>-and <Emphasis Type="Italic">p</Emphasis>-hydroxybenzyl)cytisine

The molecular structures of N-(o-and p-hydroxybenzyl)cytisine were investigated by NMR spectroscopy, x-ray structure analysis, and molecular modeling. It was found that NMR resonances of the OH and aromatic protons in N-(o-hydroxybenzyl)cytisine were doubled because of the presence of two conformers in solution. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 165–168, March–April, 2008.     

Spectrophotometric determination of <Emphasis Type="Italic">L</Emphasis>-ascorbic acid in pharmaceuticals

A simple and sensitive spectrophotometric method for the determination of L-ascorbic acid with leuco crystal violet is proposed. The determination is based on the oxidation of analyte by potassium iodate. The colourless oxidation products were formed in the quantity equivalent to iodide ions. The iodide ions react with the excess of iodate ions in acidic medium, to form free iodine which oxidized leuco crystal violet (LCV) to the liberated crystal violet (CV ⁺) dye, showing maximum absorption at 588 nm. The absorbance was measured at pH of 4.1–4.2 in 1 cm cuvettes. Beer’s law was obeyed in the concentration range 0.5–4.0 μg/mL. The molar absorptivity of the coloured compound is 4.14 × 10⁴ L/mol cm for L-ascorbic acid. The analytical parameters were optimized and the method was successfully applied to the determination of L-ascorbic acid in pharmaceuticals. The results were compared with those obtained by methods proposed in Polish Standard.     

Conformations and properties of <Emphasis Type="Italic">O</Emphasis>-Alkyl-<Emphasis Type="Italic">S</Emphasis>-(2-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dialkylamino)-ethylmethylthiophosphonates

Conformers of the biologically active compounds CH₃P(O)(OR)(SCH₂CH₂NR ₂ ^′ ), where (I) R = i-C₄H₉, R′ = C₂H₅ and (II) R = C₂H₅, R′ = i-C₃H₇, are calculated within the AM1 level of theory. The elongated and twisted forms with maximum and minimum distances between a nitrogen atom and those of a phosphorus tetrahedron, respectively, and bearing a syn and anti oriented alkoxy group relative to a phosphoryl oxygen, are studied. It is found that the differences between the energy, electronic, and geometric parameters of these forms are apparent in differences between their properties, e.g., the ability to participate in complexation and protonation, reactions that to some extent simulate the interaction between a substance and a biological object.     

Synthesis of amino acid conjugates of glycyrrhizic acid using <Emphasis Type="Italic">N</Emphasis>-hydroxyphthalimide and <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>'-dicyclohexylcarbodiimide

Synthesis of amino acid conjugates of glycyrrhizic acid with the use of N-hydroxyphthalimide, N,N'-dicyclohexylcarbodiimide, and tert-butyl esters of L-amino acids (valine, isoleucine, phenylalanine, and methionine) was performed followed by deprotection with trifluoroacetic acid. The target amino acid conjugates were isolated by column chromatography on silica gel in 40–45% yield. The structure of the prepared compounds was confirmed by IR and ¹³C NMR spectroscopy.     

Synthesis of <Emphasis Type="Italic">ortho</Emphasis>-carboranyl derivatives of (<Emphasis Type="Italic">S</Emphasis>)-asparagine and (<Emphasis Type="Italic">S</Emphasis>)-glutamine

(S)-Asparagine and (S)-glutamine ortho-carboranyl derivatives with free amino and carboxy groups in the α-position were synthesized. By an example of N ^γ-(1,2-dicarba-closo-dodecarboran-3-yl)-(S)-glutamine it was demonstrated that the developed synthetic approach carboranyl derivatives of amino acids allowed the preparation of optically pure isomers.     

Mixtures poly((<Emphasis Type="Italic">R</Emphasis>)-3-hydroxybutyrate) and poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) subjected to DSC

Blends of bacterial poly((R)-3-hydroxybutyrate) (PHB) and poly(l-lactic acid) (PLLA) synthesized by polycondensation of l-lactic acid or by ring-opening polymerization of l-lactide were studied. Miscibility was investigated through both conventional differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC). PHB and low-molar mass PLLA were miscible in a whole concentration range, and a single glass transition temperature was observed. On the other hand, PHB/high-molar mass PLLA mixtures phase separate, giving rise to two glass transition temperatures corresponding to PHB and PLLA. A treatment of blends at 190 °C leads to formation of block/multiblock/random copolymers, and blends become miscible.     

Low-temperature thermodynamic properties of <Emphasis Type="Italic">L</Emphasis>-cysteine

Heat capacity C _p(T) of the orthorhombic polymorph of L-cysteine was measured in the temperature range 6–300 K by adiabatic calorimetry; thermodynamic functions were calculated based on these measurements. At 298.15 K the values of heat capacity, C _p; entropy, S _m⁰(T)-S _m⁰(0); difference in the enthalpy, H _m⁰(T)-H _m⁰(0), are equal, respectively, to 144.6±0.3 J K⁻¹ mol⁻¹, 169.0±0.4 J K⁻¹ mol⁻¹ and 24960±50 J mol⁻¹. An anomaly of heat capacity near 70 K was registered as a small, 3–5% height, diffuse ‘jump’ accompanied by the substantial increase in the thermal relaxation time. The shape of the anomaly is sensitive to thermal pre-history of the sample.     

Magnolol entrapped ultra-fine fibrous mats electrospun from poly(ethylene glycol)-<Emphasis Type="Italic">b</Emphasis>-poly(L-lactide) and <Emphasis Type="Italic">in vitro</Emphasis> release

Ultra-fine fibrous mats with magnolol entrapped have been prepared by electrospinning biodegradable copolymer poly(ethylene glycol) blocked poly(L-lactide). Drug entrapment was perfect which was confirmed by scanning electron microscopy and differential scanning calorimetry. According to in vitro drug release investigation by high performance liquid chromatography, it was found that fibers with 10%, 20% and 30% drug entrapped respect to polymer (mass ratio) presented dramatically different drug release behavior and degradation behavior under the effect of proteinase K. The reason may be that fibers with 10% drug entrapped was more easily affected by enzyme while, to some degree, magnolol in fibers with 20% and 30% entrapped prevented polymer from being degraded by enzyme.     

Synthesis of ethyl (2<Emphasis Type="Italic">E</Emphasis>,4<Emphasis Type="Italic">E</Emphasis>)- and (2<Emphasis Type="Italic">E</Emphasis>,4<Emphasis Type="Italic">Z</Emphasis>)-5-chloropenta-2,4-dienoates

An efficient synthetic approach to 2E,4E and 2E,4Z isomers of ethyl 5-chloropenta-2,4-dienoate has been developed on the basis of one-pot oxidation–olefination of readily accessible (E)- and (Z)-3-chloroprop-2-en-1-ols by the action of barium manganate and ethyl (triphenyl-λ⁵-phosphanylidene)acetate.     

Relationship between electrical resistivity and particle dispersion state for carbon black filled poly (ethylene-<Emphasis Type="Italic">co</Emphasis>-vinyl acetate)/poly (<Emphasis Type="SmallCaps">L</Emphasis>-lactic acid) blend

It is known that the electrical volume resistivity of insulating polymers filled with conductive fillers suddenly decreases at a certain content of filler. This phenomenon is called percolation. Therefore, it is known that controlling resistivity in the semi-conductive region for carbon black (CB) filled composites is very difficult. When poly (ethylene-co-vinyl acetate) (EVA) is used as a matrix, the percolation curve becomes gradual because CB particles disperse well in EVA. In this study, the relationship between the dispersion state of CB particles and electrical resistivity for EVA/poly (L-lactic acid) (PLLA) filled with CB composite was investigated. The apparent phase separation was seen in the SEM photograph. It was predicted that the CB particles located into the EVA phase in the light of thermodynamical consideration, which was estimated from the wetting coefficient between polymer matrix and CB particles. The total surface area per unit mass of dispersed CB particles in the polymer blend matrix was estimated from small-angle X-ray scattering and the volume resistivity decreased with increasing CB content. The values of the surface area of CB particles in CB filled EVA/PLLA (25/75 wt%) and EVA/PLLA (50/50 wt%) polymer blends showed a value similar to that of the CB filled EVA single polymer matrix. In electrical volume resistivity measurement, moreover, the slopes of percolation curves of EVA/PLLA (25/75 wt%) and EVA/PLLA (50/50 wt%) filled with CB composite are similar to that of EVA single polymer filled with CB composite. As a result, it was found that CB particles selectively locate in the EVA phase, and then the particle forms conductive networks similar to the networks in the case of EVA single polymer used as a matrix.