A highly selective method is described for controlling the degradation of polyhydroxyalkanoates, PHA, via a reduction reaction that uses lithium borohydride. Using this method, ...oligo(hydroxyalkanoate)diols derived from a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) biopolyester poly(3HB-co-4HB) and from synthetic atactic poly(R,S)-3-hydroxybutyrate (a-PHB) were obtained. The structural characterization of the oligo(hydroxyalkanoate)diols was conducted using NMR and ESI-mass spectrometry analyses, which confirmed that oligomers that were terminated by two hydroxyl end groups were formed. The reduction of the ester groups occurred in a statistical way regardless of the chemical structure of the comonomer units or of the microstructure of the polyester chain. The presented method can be used to synthesize various PHA oligodiols that are potentially useful in the further synthesis of tailor-made biodegradable materials.
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► We report novel diblock copolymers of selected PHAs with atactic a-PHB. ► Structure of PHAs macroinitiators was established at the molecular level. ► The PHO-block-(a-PHB) ...copolymers are PHO/a-PHB blend compatibilizers. ► PHB-block-(a-PHB) copolymers reduce permeability of vascular prostheses.
Low-molecular weight macroinitiators derived from natural poly(3-hydroxyalkanoates) (PHAs), which contain olefinic and activated by 18-crown-6 ether carboxylic end groups, were used in anionic ring opening polymerization (ROP) of racemic β-butyrolactone and new diblock copolymers of selected PHAs (PHB, PHBV, PHO) with atactic poly(R,S)-3-hydroxybutyrate (a-PHB) were obtained. These novel copolymers were characterized using 1H NMR, GPC and DSC. Hydrolytic degradation studies of selected copolymers were also performed. Finally, the suitability of these polymeric materials for cardiovascular engineering and as blend compatibilizers was demonstrated.
Study on bacterial poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB4HB)) thermal degradation employing mild reaction conditions and carboxylate salt is described. The chemical structure of the ...obtained oligomers was determined with the aid of super(1)H NMR and ESI-mass spectrometry techniques. The comparison of a non-volatile degradation products obtained via carboxylate-induced thermal degradation of the P(3HB4HB) with products of the model polymer pyrolysis revealed significant differences in structure of the resulting oligomers. Exclusive formation of linear oligomers terminated with unsaturated, on one end, and carboxyl, on the other end, groups was noticed in case of base-catalyzed degradation contrary to oligomers produced via pyrolysis which contained also macrocyclic structures and gamma -butyrolactone. Moreover, the elaborated method demonstrates the ability to produce well-defined oligomers with controlled molar mass. The resulting oligomers have huge potential as macroinitiators or macromonomers and can be useful for further synthesis of more sophisticated polymeric materials.
Polysaccharide hydrogels have been increasingly utilized in various fields. In this review, we focus on polysaccharide-based hydrogels used as probiotic delivery systems. Probiotics are ...microorganisms with a positive influence on our health that live in the intestines. Unfortunately, probiotic bacteria are sensitive to certain conditions, such as the acidity of the gastric juice. Polysaccharide hydrogels can provide a physical barrier between encapsulated probiotic cells and the harmful environment enhancing the cells survival rate. Additionally, hydrogels improve survivability of probiotic bacteria not only under gastrointestinal track conditions but also during storage at various temperatures or heat treatment. The hydrogels described in this review are based on selected polysaccharides: alginate, κ-carrageenan, xanthan, pectin and chitosan. Some hydrogels are obtained from the mixture of two polysaccharides or polysaccharide and non-polysaccharide compounds. The article discusses the efficiency of probiotic delivery systems made of single polysaccharide, as well as of systems comprising more than one component.
A family of homo- and heteroleptic zinc complexes bearing aminonaphtholate ligands was synthesized and fully characterized. Using NMR spectroscopy and DFT calculation, bis-alkoxy-bridged complexes ...LZn(μ-OR)2 were confirmed to have dimeric structures in solution, analogous to those obtained via X-ray crystallography. Surprisingly, a detailed experimental and theoretical study of the catalytic activity of LZn(μ-OR)2 in the ring-opening polymerization (ROP) of lactides showed that although well-defined alkoxy dimers possess a single-site structural motif, the most active initiator is obtained during in situ alcoholysis of the alkylzinc precursor. These results indicate that rational ancillary and alkoxy ligand design that takes into account its mutual interaction on monomer coordination may be key to the synthesis of new high-performance ROP catalysts.
ANATOMIA POSTTOTALITARYZMU Michał Kwiecień, Michał Kwiecień
Porównania,
06/2019, Letnik:
24
Journal Article
Recenzirano
Odprti dostop
Celem niniejszego artykułu jest krytyczna analiza głównych tez książki Aviezera Tuckera The Legacies of Totalitarianism. A Theoretical Framework. Poglądy Tuckera na transformację ustrojową w Europie ...Środkowej i Wschodniej autor konfrontuje ze stanowiskami Janine J. Wedel, Andrzeja Zybertowicza i Krzysztofa Brzechczyna.
The (trans)esterification reaction of bacterial biopolymers with a selected bioactive compound with a hydroxyl group was applied as a convenient method for obtaining conjugates of such compound. ...Tyrosol, a naturally occurring phenolic compound, was selected as a model of a bioactive compound with a hydroxyl group. Selected biodegradable polyester and polyamide, poly(3-hydroxybutyrate-
-4-hydroxybutyrate) (P(3HB-
-4HB)) and poly-γ-glutamic acid (γ-PGA), respectively, were used. The (trans)esterification reactions were carried out in melt mediated by 4-toluenesulfonic acid monohydrate. The structures of (trans)esterification products were established at the molecular level with the aid of ESI-MS² (electrospray ionization tandem mass spectrometry) and/or ¹H NMR (nuclear magnetic resonance) techniques. Performed analyses confirmed that the developed method leads to the formation of conjugates in which bioactive compounds are covalently bonded to biopolymer chains. The amount of covalently bonded bioactive compounds in the resulting conjugates depends on the type of biopolymers applied in synthesis.
A Bacillus amyloliquefaciens strain was isolated from composted plastics and identified using microbial identification system BIOLOG and 16S rDNA sequences. The capability to attack virgin and ...ɣ-irradiation/high temperature-pretreated LLDPE films was investigated for comparison to evaluate the effect of pretreatment. A biodeteriorating effect characterized by low weight reductions of 1.1 ± 0.3 to 3.2 ± 1.3% was observed with the pretreated LLDPE within 40–60 days. The precision of the gravimetric method was sometimes negatively affected by the fragmentation of plastic films during the biological treatment or by traces of microbial biofilm firmly adhering to the plastic material. FTIR spectra before and after 60-day treatment indicated a decrease of carbonyl band and flattening of the 1300-1100 cm−1 zone due to bacterial action. GPC showed an increase of Mn and Mw of 2300–3700 and 32 200–35 500 g mol−1, respectively, and a decrease of polydispersity index suggesting presence of low molar weight LLDPE oligomers in pretreated LLDPE. The analysis of crystallinity and melting enthalpy detected the removal of oligomers during biodeterioration. ESI-MS analysis of the medium after 60-day biotreatment of pretreated LLDPE showed a presence of 3-hydroxybutyrate oligomers linked to the disappearance of low molar weight LLDPE oligomers that was not observed with virgin LLDPE. Coincidence of the removal of LLDPE oligomers and the appearance of 3-hydroxybutyrate oligomers suggested metabolization of low molecular LLDPE fractions present in the pretreated LLDPE by B. amyloliquefaciens. The experiments with virgin LLDPE demonstrated a positive effect of the pretreatment.
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•A Bacillus amyloliquefaciens strain was isolated from composted plastics material.•Bacterium was used for treatment of ɣ-irradiation/high temperature-pretreated LLDPE.•Physico-chemical analyses brought evidence of a biodeterioration action.•Low molar weight LLDPE oligomers disappeared after exposure to B. amyloliquefaciens.•Findings suggested metabolization of low molecular LLDPE fraction by the bacterium.
This article examines postwar repatriations of Polish citizens from the Lviv1 region, a territory in southeastern Poland (presently in western Ukraine) incorporated into the Soviet Union during World ...War II. The war that historians neatly consign to the familiar time brackets of 1939–1945 did not end with Germany's collapse. The unspeakable confrontation that decimated and uprooted millions of Europeans continued under the guise of postwar forced migrations, repatriations, and population transfers. Indeed, relocation and displacement provided fundamental building blocks in the Polish communist effort of reconstructing Poland. Building a Polish nation-state impelled the new regime to identify and claim Polish inhabitants of the so-called kresy, Poland's former eastern provinces ceded to the Soviet Union. Migrations of Poles to the territories that Poland acquired from the defeated Nazi state, comprised critical moments in the emergence of new Polish communities in former German lands. These repatriates considered relocation as an opportunity to escape a cherished homeland now under the domination of a foreign and detested power. This article, thus, explores the wider cultural context in which Polish women and children assigned meaning to their traumatic experiences. The meanings that these eastern Poles (kresowianie) attached to the conditions at embarkation points and on dirt and pathogen-infested transports are crucial to understanding how the experience of repatriation reshaped postwar Polish identities. Indeed, this study addresses pivotal questions for the understanding of post-1945 Eastern Europe: what was the role of mass population movements in the reconstruction of war-torn societies? How did displaced people start new lives in adverse and unpredictable circumstances? Most importantly, how did the new communist authorities and migrants from the kresy renegotiate the meaning of resettlement and the postwar national community in general?
The thermal stability of poly(3-hydroxybutyrate) (PHB) in an oxidation environment was investigated in bulk at temperatures ranging from 100 °C to 140 °C. The process carried out in pure oxygen ...resulted in PHB backbone degradation with resulting non-volatile products typical for regular PHB thermal degradation while thermal treatment of PHB in an oxygen/ozone mixture resulted in increased rate of polymer backbone scission. The non-volatile degradation product contained macromolecules with several types of terminal groups but also a part of the 3-hydroxybutyrate repeating units was transformed into 3-malic acid units. NMR and multi-stage MS characterization revealed the random distribution of 3-malic acid units in the oligomeric products as well as the content of the malic acid units being dependent on oxidation conditions.
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