Morphology and thermodynamics of selenium-containing nanosystems: The effect of polymer stabilizers

Nanosystems based on zero-valent selenium and biocompatible polymer stabilizers (polyvinylpyrrolidone with molecular weight (MW) М _w = (10–55) × 10³, poly-N,N,N,N-trimethylacryloyloxyethylammonium methylsulfate with М _w = (30–250) × 10³ and polyethylene glycol with М _w = (1–40) × 10³) are studied by means of static and dynamic light scattering, and the resulting data are compared. Dense spherical multimolecular nanosystems are found to be formed. Morphological and thermodynamic characteristics of selenium-containing nanosystems, depending on the nature and MW of the polymer stabilizer, are determined. It is shown that the properties of nanosystems can be adjusted by varying the molecular weight of the polymer stabilizer.     

Crystalline morphology and thermal properties for random copolyesters of (R)‐3‐hydroxybutyric acid with different hydroxyalkanoic groups

The solid‐state structures and thermal properties of melt‐crystallized films of random copolymers of (R)‐3‐hydroxybutyric acid (3HB) with different hydroxyalkanoic acids such as (R)‐3‐hydroxypentanoic acid (3HV), (R)‐3‐hydroxyhexanoic acid (3HH), medium‐chain‐length (R)‐3‐hydroxyalkanoic acids (mcl‐3HA; C8‐C12), 4‐hydroxybutyric acid (4HB), and 6‐hydroxyhexanoic acid (6HH) were characterized by means of small‐angle X‐ray scattering, differential scanning calorimetry, and optical microscopy. The randomly distributed second monomer units except for 3HV in copolyesters act as defects of P(3HB) crystal and are excluded from the P(3HB) crystalline lamellae. The lamellar thickness of copolymers decreased with an increase in either the main‐chain or the side‐chain carbon numbers of second monomer units. In addition, the growth rate of spherulites decreased with an increase in the carbon numbers of second monomer units for copolymers with an identical comonomer composition. These results indicate that the steric bulkiness of second monomer unit affects on the crystallization of 3HB segments in random copolyesters.     

New Quinoxaline-Containing Monomers for Narrow-Bandgap Polymers

Two new fused quinoxaline-containing monomers—2,3-bis(9-(2-decyltetradecyl)-9H-carbazol-3-yl)dithieno[3,2-f:2'3'-h]quinoxaline (М1) and 2,5-di(nonadecan-3-yl)bis[1,3]thiazolo[4,5-a:5',4'-c]bisthieno[3,2-h:2',3'-j]phenazine (М2)—have been synthesized in high yields of 88 and 83% as promising building blocks of D-A polymers for photovoltaic applications. The optical bandgaps, found from the absorption edge, are 2.79 and 2.88 eV, respectively. The HOMO/LUMO energies of М1 and М2 are–5.83/–2.96 and–5.83/–2.98 eV, respectively. Both monomers have low-lying HOMO levels, which is favorable for a high open-circuit voltage and a high stability in air in the development of PSCs. The E _g ^ec values of monomers М1 and М2 are 2.87 and 2.85 eV and are consistent well with the optical bandgap (2.79 and 2.88 eV, respectively).     

Crystal structure of tetramethylammonium hexafluoridoniobate(V) and hexafluoridotantalate(V)

Crystal structures of newly synthesized tetramethylammonium hexafluoridoniobate(V) and hexafluoridotantalate(V) (CH₃)₄N[МF₆] (M=Nb, Ta) have been determined; they crystallize in the tetragonal crystal system, sp. gr. P4/nmm. Crystal structures of isostructural compounds (CH₃)₄N[МF₆] (M=Nb, Ta) are formed by virtually regular tetrahedral tetramethylammonium cations (CH₃)₄N⁺ (NMe₄, TMA) and octahedral complex anions [МF₆]^– (M=Nb, Ta), fluorine atoms of the equatorial plane are statistically disordered over two positions. Ionic interactions and weak hydrogen bonds C–H???F join the cations and the complex anions in a 3D assembly.     

Environmental Degradation of Microbial Polyhydroxyalkanoates and Oil Palm-Based Composites

This paper investigates the degradation of polyhydroxyalkanoates and its biofiber composites in both soil and lake environment. Time-dependent changes in the weight loss of films were monitored. The rate of degradation of poly(3-hydroxybutyrate) [P(3HB)], poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-23?mol% 4HB)] and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate) [P(3HB-co-9?mol% 3HV-co-19?mol% 4HB)] were investigated. The rate of degradation in the lake is higher compared to that in the soil. The highest rate of degradation in lake environment (15.6?% w/w week^?1) was observed with P(3HB-co-3HV-co-4HB) terpolymer. Additionally, the rate of degradation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-38?mol% 3HV)] was compared to PHBV biofiber composites containing compatibilizers and empty fruit bunch (EFB). Here, composites with 30?% EFB displayed the highest rate of degradation both in the lake (25.6?% w/w week^?1) and soil (15.6?% w/w week^?1) environment.     

Crystal Chemistry of Lithium Intermetallic Compounds: A Survey

The structural chemistry of lithium intermetallic compounds that are formed in Li–М binary systems where М = Ca, Sr, Ba, Mg, Zn, Cd, and Hg is surveyed. It is for the first time that the crystal structures of intermetallic compounds are classified in terms of polyhedral precursor metal clusters (in the program package ToposPro). The precursor metal clusters of crystal structures are identified using the algorithms of partitioning structural graphs into cluster structures and via the design of the basal 3D network of the structure in the form of a graph whose nodes correspond to the positions of the centers of precursor clusters. Tetrahedral precursor metal clusters M₄ are identified for the crystal structures LiZn₃-oC4, LiMg₃-hP2, LiCd₃-hP2, LiHg₃-hP8, (LiMg₃)(Li₂Mg₂)-tI16, Li₂Zn₂-cF16, Li₂Cd₂-cF16, Li₂Hg₂-cP2, Li₃Cd-cF4, and Li₃Hg-cF16; tetrahedral metal clusters M₄ are found for the framework structures with spacer atoms Sr(Li₂Sr₂)-tP20, Ca₂(Li₄)-cF24, and Ca₂(Li₄)-cP12; tetrahedral metal clusters M₄ and rings M₆, for framework structures Ba₃Li₂(Li₁₀)-hP30 and Ba₃Li₂(Li₄In₆)-hP30; icosahedral metal clusters M13 for the framework structure Li(Zn₁₃)-cF112; bilayer tetrahedral metal clusters 0@М₄@M₂₂ for the framework structure Li₂₃Sr₆-cF116; and deltahedra М₁₇ and deltahedra М₃₀, for framework structures Sr₄Li₁₄ [Sr(Sr₄Li₁₂)] [(Sr₂ (Sr₈Li₁₈)]-tI252 and Ba₄Li₁₄ [Ba(Ba₄Li₁₂)][(Ba₂ (Ba₈Li₁₈)]-tI252. The scenario of crystal structure self-assembly from precursor metal clusters S₃⁰ in intermetallic compounds is reconstituted as: primary chain S₃¹→ microlayer S₃²→ microframework S₃³.     

Production of specific copolymers of polyhydroxyalkanoates from industrial waste

Polyhydroxyalkanoates, biodegradable plastics with the desired physical and chemical properties of conventional synthetic plastics, are extensively investigated. In this study, specific bacterial strains produced specific copolymers from food waste. Copolymers of HB and HV (poly[3-hydroxybutyrate-co-3-hydroxyvalerate]) were obtained using various ratios of butyric acid (C₄) and valeric acid (C₅) as carbon sources. The C₄ to C₅ ratio affected the melting points of the copolymers. Melting and glass transition temperatures and many other thermal properties are important parameters relative to in-service polymer applications. Higher ratios of butyrate to valerate gave higher melting points. When a mixed culture of activated sludge was employed to produce copolymers using food wastes as nutrients, the obtained copolymers showed various monomer compositions. Copolymers with a higher portion of HV were obtained using soy waste; copolymers with less HV were obtained using malt wastes. Pure strains, (i.e., Alcaligenes latus DSM 1122, and DSM 1124, Staphylococcus spp., Klebsiella spp.) produced specific copolymers from food waste. Only Klebsiella spp. produced different copolymers; the ratios of HB:HV were 93:7 and 79:21 from malt waste and soy waste, respectively. The other strains produced polymers of 100% HB. Selecting industrial food wastes as carbon sources can further reduce the cost of producing copolymers. Open Laboratory of Chirotechnology of the Institute of Molecular Technology for Drug Discovery and Synthesis The University Grants Committee Area of Excellence Scheme, Hong Kong     

Crystallization behaviors and morphology of biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Crystallization behaviors and spherulitic morphology of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] with different 4-hydroxybutyrate (4HB) molar fraction were investigated by differential scanning calorimetry and polarized optical microscopy. Crystallization behaviors of P(3HB-co-4HB) are significantly affected by 4HB molar fraction. The melting temperature (T _m), glass transition temperature (T _g), and crystallinity (X _c) decrease with the increase of 4HB molar fraction. Banded spherulites are observed in poly (3-hydroxybutyrate) (PHB) and P(3HB-co-4HB) copolymers. The band spacing decreases with the increase of 4HB molar fraction. The morphology and growth rate of the spherulites strongly depend on 4HB molar fraction and the crystallization temperatures. The introduction of 4HB unit can inhibit the emergence of cracks in PHB spherulites.     

Synthesis of Block Copolymers of Styrene with <Emphasis Type="Italic">D</Emphasis>,<Emphasis Type="Italic">L</Emphasis>-Lactide by the Sequential Controlled Cationic Polymerization and Ring-Opening Anionic Polymerization

The cationic polymerization of styrene initiated by the system 2-chloro-2-phenylpropane–TiCl₄–pyridine is studied in a mixture CH₂Cl₂–n-hexane at a temperature of –80°С. It is shown that under these conditions polymerization occurs via the living mechanism at [monomer]: [initiator] ≤ 100. The method of preparing polystyrenes with terminal primary hydroxyl groups (M_n = 4000–10000 g/mol) by the sequential controlled cationic polymerization of styrene and the in situ alkylation of 4-phenoxy-1-butanol by polystyrene macrocations is proposed. The resulting functionalized polystyrenes are used as macroinitiators of anionic-coordination ring-opening polymerization of D,L-lactide in the presence of tin bis(2-ethyl hexanoate) [Sn(Oct)₂] in toluene at 80°С. Copolymers polystyrene-block-poly(D,L-lactide) with the controlled length of the poly(D,L-lactide) block (M_n = 10000–17000 g/mol) and a relatively low molecular-weight distribution (M_w/M_n = 1.6–1.8) are synthesized. Formation of the block copolymers is confirmed by ¹Н NMR spectroscopy, gel-permeation chromatography, and atomic force microscopy.     

Influence of feeding strategies of mixed microbial cultures on the chemical composition and microstructure of copolyesters P(3HB‐co‐3HV) analyzed by NMR and statistical analysis

NMR spectroscopy was applied for quantitative and qualitative characterization of the chemical composition and microstructure of a series of poly(3‐hydroxybutyrate‐co‐3‐hydoxyvalerate) copolymers, P(3HB‐co‐3HV), synthesized by mixed microbial cultures at several different feeding strategies. The monomer sequence distribution of the bacterially synthesized P(3HB‐co‐3HV) was defined by analysis of their high‐resolution 1D ¹³C NMR and 2D ¹H/¹³C HSQC and ¹H/¹³C HMBC NMR spectra. The results were verified by employment of statistical methods and suggest a block copolymer microstructure of the P(3HB‐co‐3HV) copolymers studied. Definitive distinction between block copolymers or a mixture of random copolymers could not be achieved. NMR spectral analysis indicates that the chemical composition and microstructure of the copolymers can be tuned by choosing a correct feeding strategy. Copyright © 2009 John Wiley & Sons, Ltd.     

Miscibility and crystallinity of poly(3-hydroxybutyrate)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends

With the objective of developing new biodegradable materials, the miscibility and the crystallinity of blends of poly(3-hydroxybutyrate), P(3HB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), P(3HB-co-3HV), have been studied. P(3HB) (300 kg mol⁻¹)/P(3HB-co-3HV)–10% 3HV (340 kg mol⁻¹) blends were prepared by casting in a wide range of proportions, and characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The experimental values for the glass transition temperatures (T_g) are in good agreement with the values provided by the Fox equation, showing that the blends are miscible. It was observed that the T_g and the melting temperature (T_m) decreases with the increase in the P(3HB-co-3HV)–10% 3HV content, while the crystallization temperature (T_c) increases. FT-IR analyses confirmed the decrease on the crystallinity of P(3HB)/P(3HB-co-3HV)–10% 3HV blends with higher copolymer contents. Bands related to the crystallinity were changed, due to the copolymer content that produced miscible and less crystalline blends.     

Enhancement of Stress Tolerance in the Polyhydroxyalkanoate Producers without Mobilization of the Accumulated Granules

Poly(3-hydroxybutyrate) [P(3HB)], a polymer belonging to the polyhydroxyalkanoate (PHA) family, is accumulated by numerous bacteria as carbon and energy storage material. The mobilization of accumulated P(3HB) is associated with increased stress and starvation tolerance. However, the potential function of accumulated copolymer such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] remained unknown. In this study, Delftia acidovorans DS 17 was used to evaluate the contributions of P(3HB) and P(3HB-co-3HV) granules during simulated exogenous carbon deprivation on cell survival by transferring cells with PHAs to carbon-free mineral salt medium supplemented with 1 % (w/v) nitrogen source. By mobilizing the intracellular P(3HB) and P(3HB-co-3HV) at 11 and 40 mol% 3HV compositions, the cells survived starvation. Surprisingly, D. acidovorans containing P(3HB-co-94 mol% 3HV) also survived although the mobilization was not as effective. Similarly, recombinant Escherichia coli pGEM-T::phbCAB _Cn (harboring the PHA biosynthesis genes of Cupriavidus necator) containing P(3HB) granules had a higher viable cell counts compared to those without P(3HB) granules but without any P(3HB) mobilization when exposed to oxidative stress by photoactivated titanium dioxide. This study provided strong evidence that enhancement of stress tolerance in PHA producers can be achieved without mobilization of the previously accumulated granules. Instead, PHA biosynthesis may improve bacterial survival via multiple mechanisms.     

Biosynthesis and Characterization of Poly (3-hydroxybutyrate-<Emphasis Type="Italic">co</Emphasis>-3-hydroxyvalerate-<Emphasis Type="Italic">co</Emphasis>-4-hydroxybutyrate) Terpolymer with Various Monomer Compositions by <Emphasis Type="Italic">Cupriavidus</Emphasis> sp. USMAA2-4

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate) [P(3HB-co-3HV-co-4HB)] terpolymer was produced using Cupriavidus sp. USMAA2-4 via one-step cultivation process through combination of various carbon sources such as 1,4-butanediol or γ-butyrolactone with either 1-pentanol, valeric acid, or 1-propanol. Oleic acid was added to increase the biomass production. The composition of 3HV and 4HB monomers were greatly affected by the concentration of 1,4-butanediol and 1-pentanol. Terpolymers with 3HV and 4HB molar fractions ranging from 2 to 41 mol.% and 5 to 31 mol.%, respectively, were produced by varying the concentration of carbon precursors. The thermal and mechanical properties of the terpolymers containing different proportions of the constituent monomers were characterized using gel permeation chromatography (GPC), DSC, and tensile machine. GPC analysis showed that the molecular weights (M _w) of the terpolymer produced were within the range of 346 to 1,710 kDa. The monomer compositions of 3HV and 4HB were also found to have great influences on the thermal and mechanical properties of the terpolymer P(3HB-co-3HV-co-4HB) produced.     

Controlled biosynthesis and characterization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) from mixtures of palm kernel oil and 3HV-precursors

This study investigates the biosynthesis and characterization of P(3HB-co-3HV-co-3HHx) terpolymer from mixtures of palm kernel oil and 3HV-precursors by using recombinant Cupriavidus necator PHB⁻4/pBBREE32d13. Sodium valerate and propionate have been evaluated for the generation of 3HV monomers. The feeding time of these precursors was a crucial factor that significantly affected the 3HV molar fractions, which ranged from 2 to 60 mol%. Sodium valerate was generally the better precursor in initiating the accumulation of 3HV monomers while maintaining high cell dry weight (7.9 g/L) and good PHA accumulation (79 wt%). However, the 3HHx molar fractions in the terpolymers at 72 h were consistent at about 2-7 mol%. P(3HB-co-3HV) copolymers have been known to exhibit approximately the same degree of crystallinity throughout a wide range of 3HV composition. Interestingly, in this study, terpolymers containing 58 mol% 3HB, 39 mol% 3HV and 3 mol% 3HHx showed elastomeric behavior. This study demonstrates the suitability of palm kernel oil as the main carbon source and both sodium propionate and sodium valerate as 3HV-precursors for the synthesis of novel compositions of P(3HB-co-3HV-co-3HHx) terpolymers with interesting properties.     

Electrolyte systems for primary lithium-fluorocarbon power sources and their working efficiency in a wide temperature range

New compositions of liquid organic electrolytes with working temperatures of up to–50°С were developed for low-temperature primary Li/CF _x power sources. Five different compositions of organic electrolytes with a 15-crown-5 (2 vol %) addition and without it were studied on laboratory Li/CF _x power sources. 1МLiBF₄ (LiPF₆) in an ethylene carbonate/dimethyl carbonate/methyl propionate/ethylmethyl carbonate (EC/DMC/MP/EMC) (1: 1: 1: 2) mixture and 1 М LiPF6 in an EC/DMC/EMC (1: 1: 3) mixture each with a 15-crown-5 (2 vol %) addition were found to be the best compositions of organic electrolytes with working temperatures of up to–50°С. The electrochemical tests at 20 and–50°С in the Li/CF _x system showed that the 15-crown-5 addition increased the length of the discharge plateau at–50°С three- or fourfold. The mechanisms responsible for the increase in the discharge capacity of the CF _x cathode in the presence of a crown ether addition were suggested.     

Biosynthesis of High Quality Polyhydroxyalkanoate Co- and Terpolyesters for Potential Medical Application by the Archaeon Haloferax mediterranei

Summary : Haloferax mediterranei was investigated for the production of two different high-performance polyhydroxyalkanoates (PHAs). A copolyester containing 6 mol-% 3-hydroxyvalerate (3HV) was produced from whey sugars as sole carbon source. The maximum specific growth rate (µ_max.) and the maximum specific PHA production rate (q_{p max.}) were determined with 0.10 1/h and 0.15 1/h, respectively. The cells contained 72.8 wt.-% of P-(3HB-co-6%-3HV) which featured low melting points between 150 and 160 °C and narrow molecular mass distribution (polydispersity PDI = 1.5). Further, a PHA terpolyester with an increased 3HV fraction as well as 4-hydroxybutyrate (4HB) building blocks was accumulated by feeding of whey sugars plus 3HV - and 4HB precursors. Kinetic analysis of the process reveals a µ_max. of 0.14 1/h and a q_{p max.} of 0.23 1/h, respectively. The final percentage of P-(3HB-co-21.8%-3HV-co-5.1%-4HB) in biomass amounted to 87.5 wt.-%. Also this material showed a narrow molecular mass distribution (PDI = 1.5) and a high difference between the two melting endotherms of the material (between 140 and 150 °C) and the onset of decomposition at 236 °C. The accomplished work provides viable strategies to obtain different high-quality PHAs which might be potential candidates for application in the medical and pharmaceutical field.     

Mechanical Properties of Uniaxially Cold-Drawn Films of Poly[(R)-3-hydroxybutyrate] and Its Copolymers

Uniaxially oriented films of poly[(R)-3-hydroxybutyrate] (P(3HB)) and two kind of copolymers, poly[(R)-3-hydroxybutyrate-co-8%-[R]-3-hydroxyvalerate] (P(3HB-co-8%-3HV)), and poly[(R)-3-hydroxybutyrate-co-[R]-5%-3-hydroxyhexanoate] (P(3HB-co-5%-3HH)), were prepared by cold-drawing from amorphous preforms at temperatures near to the respective glass transition temperatures. Melt-quenched films in a rubber state could be stretched reproducibly to a draw ratio of 500%∼1800%, and subsequent annealing under tension led to improvement of the tensile strength and Young's modulus. Two-step drawing resulted in further improvement of the mechanical properties. The mechanical properties remained unchanged after storing for 6 months at room temperature, suggesting that high orientation and crystallinity suppress the secondary crystallization.     

Supramolecular 2D structure of [Co(2-Me-Pyz)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

The complex [Co(2-Me-Pyz)₂(H₂O)₄](NO₃)₂ is synthesized and its structure is determined. The crystals are monoclinic: space group P2₁/n, a = 10.685(2) Å, b = 6.837(1), c = 12.515(3) Å, β = 91.84(3)°, V = 913.8(3) ų, ρ_calcd = 1.042 g/cm ³, Z = 2. The Co²⁺ ion (in the inversion center) is coordinated at the vertices of the distorted octahedron by two nitrogen atoms of methylpyrazine and four oxygen atoms of the water molecules (Co(1)–N(1) 2.180(3), average Co(1)–O(w) 2.079(3) Å, angles at the Co atom 87.9(1)–92.1(1)°). Supramolecular pseudometallocycles are formed in the structure through the O(w)–H…N(1) hydrogen bonds between the coordinated H₂O molecules and the terminal nitrogen atoms of the 2-methylpyrazine molecules. Their interaction results in the formation of supramolecular layers joined by the NO₃ groups into a three-dimensional framework.     

Synthesis of water soluble metalloporphyrin-cored amphiphilic star block copolymer photocatalysts for an environmental application

Two series of water-soluble metalloporphyrin-cored amphiphilic star block copolymers were synthesized by controlled radical polymerizations such as atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT), which gave eight amphiphilic block copolymer arm chains consisting of poly(n-butyl acrylate-b-poly(ethylene glycol) methyl ether methacylate) (PnBA-b-PEGMEMA, M_n,GPC = 78,000, M_w/M_n = 1.2, 70 wt% of PPEGMEMA) and poly(styrene-b-2-dimethylamino ethyl acrylate) (PS-b-PDMAEA, M_n,GPC = 83,000, M_w/M_n = 1.2, 67 wt% of PDMAEA), yielding porphyrin(Pd)-(PnBA-b-PPEGMEMA)₈ and porphyrin(Pd)-(PS-b-PDMAEA)₈, respectively. Obtained metalloporphyrin polymer photocatalysts were homogeneously solubilized in water to apply to the removal of chlorophenols in water, and was distinguished from conventional water-insoluble small molecular metalloporphyrin photocatalysts. Notably, we found that the water-soluble star block copolymers with hydrophobic–hydrophilic core–shell structures more effectively decomposed the chlorophenol, 2,4,6-trichlorophenol (2,4,6-TCP), in water under visible light irradiation (k = 1.39 h^?1, t_1/2 = 0.5 h) in comparison to the corresponding water-soluble star homopolymer, because the hydrophobic core near the metalloporphyrin effectively captured and decomposed the hydrophobic chlorophenols in water.     

Relationships of lignosulfonate adsorption onto the zinc sulfide surface

Low-molecular-mass lignosulfonates (M _w = 9250 amu) are adsorbed more strongly onto ZnS from neutral solutions (pH 4.5–4.8), and high-molecular-mass lignosulfonates (M _w = 46300 rpm), from acid solutions (pH 1.4–1.5). The sorption of the low-molecular-mass sample at pH 1.5 is affected by competing sorption of the solvent (Н₂SO₄). The lignosulfonate samples studied are adsorbed onto zinc sulfide by the chemisorption mechanism.