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In order to explore how cucurbituril hosts accommodate an N-phenyl-pyridinium derivative guest, the complexation of the solvatochromic dye, 4-(4-(dimethylamino)styryl)-1-phenylpyridinium iodide (PhSt) with ,&prime, &delta, &prime, tetramethyl-cucurbit[6]uril (Me4CB6) and cucurbit[7]uril (CB7) was investigated by absorption spectroscopic, fluorescence and NMR experiments. In aqueous solutions, PhSt forms 1:1 complexes with both cucurbiturils, the complex with CB7 has a higher stability constant (Ka = 6.0 &times, 106 M&minus, 1) than the complex with Me4CB6 (Ka = 1.1 &times, 1). As revealed by NMR experiments and confirmed by theoretical calculations, CB7 encapsulates the whole phenylpyridinium entity of the PhSt cation guest, whereas the cavity of Me4CB6 includes only the phenyl ring, the pyridinium ring is bound to the carbonyl rim of the host. The binding of PhSt to cucurbiturils is accompanied by a strong enhancement of the fluorescence quantum yield due to the blocking of the deactivation through a twisted intramolecular charge transfer (TICT) state. The TICT mechanism in PhSt was characterized by fluorescence experiments in polyethylene glycol (PEG) solvents of different viscosities. The PhSt-CB7 system was tested as a fluorescence indicator displacement (FID) assay, and it recognized trimethyl-lysine selectively over other lysine derivatives.

Zinc finger protein 554 (ZNF554), a member of the Kr&uuml, ppel-associated box domain zinc finger protein subfamily, is predominantly expressed in the brain and placenta in humans. Recently, we unveiled that ZNF554 regulates trophoblast invasion during placentation and its decreased expression leads to the early pathogenesis of preeclampsia. Since ZNF proteins are immensely implicated in the development of several tumors including malignant tumors of the brain, here we explored the pathological role of ZNF554 in gliomas. We examined the expression of ZNF554 at mRNA and protein levels in normal brain and gliomas, and then we searched for genome-wide transcriptomic changes in U87 glioblastoma cells transiently overexpressing ZNF554. Immunohistochemistry of brain tissues in our cohort (n = 62) and analysis of large TCGA RNA-Seq data (n = 687) of control, oligodendroglioma, and astrocytoma tissues both revealed decreased expression of ZNF554 towards higher glioma grades. Furthermore, low ZNF554 expression was associated with shorter survival of grade III and IV astrocytoma patients. Overexpression of ZNF554 in U87 cells resulted in differential expression, mostly downregulation of 899 genes. The &ldquo, PI3K-Akt signaling pathway&rdquo, known to be activated during glioma development, was the most impacted among 116 dysregulated pathways. Most affected pathways were cancer-related and/or immune-related. Congruently, cell proliferation was decreased and cell cycle was arrested in ZNF554-transfected glioma cells. These data collectively suggest that ZNF554 is a potential tumor suppressor and its decreased expression may lead to the loss of oncogene suppression, activation of tumor pathways, and shorter survival of patients with malignant glioma.

Silica gel/alginate/poly(aspartic acid) composite beads were prepared for immobilization of lipase B enzyme from Candida antarctica (CaLB). CaLB was first adsorbed on functionalized mesoporous silica gel particles, which were then entrapped in the interpenetrating network of thiolated poly(aspartic acid) and alginate, cross-linked by zinc ions. Finally, the beads were chemically stabilized by poly(ethylene glycol) diglycidyl ether, a bisepoxide cross-linker. In this manner, spherical biocatalysts with a diameter of 3–4 mm were prepared and their biocatalytic performance was tested by kinetic resolution of racemic 1-phenylethanol. The activity of CaLB in the beads was comparable to that of CaLB physically adsorbed on silica gel particles. The composite beads were easy to recover after use and no loss of biocatalytic activity was observed even after five test reaction cycles. Furthermore, the CaLB in the composite beads showed sufficient thermal stability up to 90 °C, contrary to CaLB adsorbed only on silica gel particles.

Redox and pH responsive hydrogels were synthesized, which can serve as matrices for smart drug delivery systems exploiting the redox and pH gradients in the human body. Water soluble thiolated poly(aspartic acid), a biocompatible synthetic polymer, enables us to cross-link in water with a non-cleavable cross-linker, poly(ethylene glycol) diglycidyl ether. The permanent cross-linker establishes stable polymer hydrogels regardless of the redox environment, thus the gels swell but do not dissolve upon redox stimuli. The reversible response upon redox stimulus was induced by thiol-disulphide transformation inside the hydrogel. The degree of swelling and the stiffness of the macroscopic hydrogels were controlled by their chemical composition including thiol content and cross-linking ratio as well as the redox state of the hydrogels. The degree of swelling of the hydrogels showed strong pH dependence due to the polyelectrolyte nature of the polymer network. Release of a macromolecular model drug was considerably faster in reducing than in oxidising environment, which indicates the potential use of the synthesized hydrogels as redox responsive drug delivery systems. Nanogels were prepared in water-in-oil emulsion and displayed redox-responsive properties. The hydrodynamic diameter of the nanogels strongly increased upon the cleavage of the disulphide linkages in reducing solution without the disruption of the gels.

A synthetic poly(amino acid), poly(aspartic acid) modified by thioethyl side groups was studied as an in situ gelling, mucoadhesive dosage form. The chemical structure and the controllable, large thiol content of the polymer were confirmed by 1H NMR spectroscopy and Ellman's assay. In situ gelation of the aqueous polymer solutions was induced by oxidation and monitored by oscillation rheometry. The strength of mucoadhesion towards excised mucosa was characterised by tensile tests in ex vivo experiments. Release kinetics of ophthalmic antibiotic ofloxacin was studied from an in situ cross-linked hydrogel and a liquid formulation to prove the sustained release of the former.

Polyaspartamides with dialkylaminoalkyl and short chain alkyl side groups were synthesized and characterized in order to prepare polymer films. Their structure was confirmed by nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy and their thermal decomposition temperature (Td) was determined by thermogravimetric analysis. The composition of the polymers was adjusted to obtain polyaspartamides with glass transition temperatures (Tg) at around room temperature and the relationship between the structure and the properties was examined. The dissolution profile of polymer films made of polyaspartamides was measured with the help of fluorescent marking to show that dissolution rate of the films depends on the pH and can be controlled by the composition of the polymers.

Responsive hydrogels have been extensively studied in the past decades because they are able to interact with their biological environment in a pre-programmed manner. Several biomedical applications have already been achieved (or at least approached) by in vivo experiments. As a class, injectable hydrogels gained considerable attention because of their minimally invasive implantation. However, the final shaping of hydrogel implants is not resolved, and their lifetime is limited because of their insufficient mechanical stability. The solution to these challenges can be given by two seemingly independent properties, shape memory and self-healing. Both properties are well-known for conventional polymers but research on the shape memory or self-healing of hydrogels is in its infancy. In this study, we introduce the molecular mechanisms behind these two properties with a focus on hydrogels, attempt to provide a general overview on the role of reversible physical and chemical interactions, and discuss the similarities between the background of shape memory and self-healing. There are a number of open questions regarding the uniform characterisation of such hydrogels, and their theoretical description is very incomplete, but the developed systems hold great promise for future applications. In the final part of the paper, we note that the synthesis of hydrogels providing both self-healing and shape memory is a difficult challenge, but some examples do exist. Future research in these fields should focus on a better understanding of structure-property correlations and should uncover additional fields of application for these advanced materials.

The human placenta maintains pregnancy and supports the developing fetus by providing nutrition, gas-waste exchange, hormonal regulation, and an immunological barrier from the maternal immune system. The villous syncytiotrophoblast carries most of these functions and provides the interface between the maternal and fetal circulatory systems. The syncytiotrophoblast is generated by the biochemical and morphological differentiation of underlying cytotrophoblast progenitor cells. The dysfunction of the villous trophoblast development is implicated in placenta-mediated pregnancy complications. Herein, we describe gene modules and clusters involved in the dynamic differentiation of villous cytotrophoblasts into the syncytiotrophoblast. During this process, the immune defense functions are first established, followed by structural and metabolic changes, and then by peptide hormone synthesis. We describe key transcription regulatory molecules that regulate gene modules involved in placental functions. Based on transcriptomic evidence, we infer how villous trophoblast differentiation and functions are dysregulated in preterm preeclampsia, a life-threatening placenta-mediated obstetrical syndrome for the mother and fetus. In the conclusion, we uncover the blueprint for villous trophoblast development and its impairment in preterm preeclampsia, which may aid in the future development of non-invasive biomarkers for placental functions and early identification of women at risk for preterm preeclampsia as well as other placenta-mediated pregnancy complications.

Gene expression studies of molar pregnancy have been limited to a small number of candidate loci. We analyzed high-dimensional RNA and protein data to characterize molecular features of complete hydatidiform moles (CHMs) and corresponding pathologic pathways. CHMs and first trimester placentas were collected, histopathologically examined, then flash-frozen or paraffin-embedded. Frozen CHMs and control placentas were subjected to RNA-Seq, with resulting data and published placental RNA-Seq data subjected to bioinformatics analyses. Paraffin-embedded tissues from CHMs and control placentas were used for tissue microarray (TMA) construction, immunohistochemistry, and immunoscoring for galectin-14. Of the 14,022 protein-coding genes expressed in all samples, 3,729 were differentially expressed (DE) in CHMs, of which 72% were up-regulated. DE genes were enriched in placenta-specific genes (OR = 1.88, p = 0.0001), of which 79% were down-regulated, imprinted genes (OR = 2.38, p = 1.54 &times, 10&minus, 6), and immune genes (OR = 1.82, p = 7.34 &times, 18), of which 73% were up-regulated. DNA methylation-related enzymes and histone demethylases were dysregulated. &ldquo, Cytokine&ndash, cytokine receptor interaction&rdquo, was the most impacted of 38 dysregulated pathways, among which 17 were immune-related pathways. TMA-based immunoscoring validated the lower expression of galectin-14 in CHM. In conclusion, placental functions were down-regulated, imprinted gene expression was altered, and immune pathways were activated, indicating complex dysregulation of placental developmental and immune processes in CHMs.

An immobilization engineering approach using bioinformatics and experimental design tools was applied to improve the sol–gel enzyme entrapment methodology. This strategy was used for the immobilization of lipase B from Candida antarctica (CaLB), a versatile enzyme widely used even on the industrial scale. The optimized entrapment of CaLB in sol–gel matrices is reported by the response-surface methodology enabling efficient process development. The immobilized CaLBs characterized by functional efficiency and enhanced recovery provided economical and green options for flow chemistry. Various ternary mixtures of sol–gel precursors allowed the creation of tailored entrapment matrices best suited for the enzyme and its targeted substrate. The sol–gel-entrapped forms of CaLB were excellent biocatalysts in the kinetic resolutions of secondary alcohols and secondary amines with aromatic or aliphatic substituents both in batch and continuous-flow biotransformations.

A series of 14 cationic derivatives of poly(aspartic acid) i.e. cationic polyaspartamides with different (dialkylamino)alkyl and alkyl or hydroxyalkyl side groups was synthesized by nucleophilic addition on polysuccinimide. The resulting polyaspartamides have moderate amphiphilic properties. Relationships between the structure and ratio of side groups and in vitro properties of polyaspartamides, including their cytotoxic and membrane-damaging activity towards human cell lines, primary skin fibroblasts and erythrocytes, were established and discussed. Cationic polyaspartamides vary in their DNA-binding, condensing and nuclease-protecting characteristics depending on the concentration ratio of (dialkylamino)alkyl and alkyl or hydroxyalkyl side groups. Effective cell transfection was achieved upon polyaspartamide-mediated plasmid DNA delivery in serum-free medium in the presence of chloroquine. Effect of serum proteins adsorption onto polyaspartamide based polyplexes, and the role of concentration of polyplexes in culture medium in their colloidal stability and transfection process were demonstrated. Synthesized polyaspartamides are biocompatible and long-acting gene carriers, which are applied to cells after dilution and without washing, thus providing transfection level comparable to that of commercial transfection reagent.

Immobilization of lipases from Pseudomonas fluorescens (Lipase AK), Burkholderia (Pseudomonas) cepacia (Lipase PS) and lipase B from Pseudozyma (Candida) antarctica (CaLB) was investigated by entrapment in electrospun poly(vinyl alcohol) (PVA) nanofibers. The activity and selectivity of the lipases entrapped in PVA nanofibers were characterized in kinetic resolution of racemic secondary alcohols using acylation in organic media. Potential bioimprinting effect of eight substrate-mimicking additives [polyethylene glycols (PEGs), non-ionic detergents (NIDs) and various organosilanes] was tested with the fiber-entrapped lipases. The nanofibrous lipase biocatalyst entrapped in the presence of the additives were also characterized by rheology, differential scanning calorimetry and scanning electron microscopy. In addition to the known lipase-bioimprinting agents (PEGs, NIDs), phenyl- and octyltriethoxysilane also enhanced substantially the biocatalytic properties of lipases in their electrospun PVA fiber-entrapped forms. The reasons of bioimprinting effect of several additives were rationalized by docking studies in the open and closed form of CaLB.

Effect of poly(succinimide) (PSI) and poly(aspartic acid) (PASP) on free radical reactions and cell viability was assessed. Molecular weight (MW) of PASPs was determined by static light scattering technique and found as 3.9 and 8.3 kDa. Among PSIs and PASPs, only poly(aspartic acid) with higher MW was found to inhibit formation of hydroxyl-radical in Fenton’s reaction, although each polymers studied were not able to eliminate diphenylpicrylhydrazyl radical. PASPs were almost non-toxic for 3 T3 fibroblasts and PC-3 cells (IC50 ≫ 3 mg/mL), whereas PSIs diminished cell viability with different IC50 values depending on cell type and polymer MW. Our preliminary data indicate the MW dependence of bioactivity of l-aspartic acid-derived polymers designed as drug carriers and biocompatible materials.

Owing to their versatile chemistry, polyaspartamides have recently attracted increased interest in various biomedical uses such as drug delivery systems and scaffolding materials. Solubility of these polymers in organic solvents and in water at certain values of pH can be fine-tuned by their chemical composition, which was exploited here to fabricate fast-dissolving electrospun matrices in ethanol with no additives. Various side groups were tested to control the solubility of the polymers as well as the morphology and moisture uptake of the matrices produced. Tertiary amine groups were immobilized to ensure high solubility around neutral pH, while modification with alkyl side groups limited moisture uptake. Finally, 3-(diethylamino)propyl and n-butyl side groups were used in equal amounts. The effect of viscosity, surface tension and specific conductivity of polymer solutions on the fiber morphology was determined in order to optimize the conditions for preparing fibers with a narrow size distribution and large specific surface area. The polymer withstood the electrospinning process without any chemical degradation, as determined by IR, and was thermally stable. Furthermore, the matrices exhibited a glass transition temperature above room temperature. The complete release of vitamin B12 was observed within one minute due to the fast dissolution of the matrices in simulated salivary fluid at pH = 6.8, supporting the potential of the developed materials in oral drug delivery.

Ocular drug delivery formulations must meet anatomical, biopharmaceutical, patient-driven and regulatory requirements. Mucoadhesive polymers can serve as a better alternative to currently available ophthalmic formulations by providing improved bioavailability. If all requirements are addressed, a polymeric formulation resembling the tear film of the eye might be the best solution. The optimum formulation must not have high osmotic activity, should provide appropriate surface tension, pH and refractive index, must be non-toxic and should be transparent and mucoadhesive. We would like to highlight the importance of in vitro polymer testing from a pharmaceutical aspect. We, therefore, carried out physical-chemical investigations to verify the suitability of certain systems for ophthalmic formulations. In this work, in situ gelling, mucoadhesive thiolated poly(aspartic acid)s were tested from ophthalmic formulation aspects. The results of preformulation measurements indicate that these polymers can be used as potential carriers in ophthalmic drug delivery.

The ophthalmic formulations on the market suffer from poor bioavailability, and it would therefore be useful to design a new formulation which is able to prolong the residence time and reduce the administration frequency. Polymer matrices which exhibit strong mucoadhesion are promising platforms in ocular drug delivery from the aspect of improved bioavailability. In the present study, an in situ gelling, mucoadhesive drug delivery system was fabricated from thiolated poly(aspartic acid) (ThioPASP). The thiol groups of ThioPASP are able to form disulphide linkages with the mucin glycoproteins and prolong the residence time on the eye. The effects of the thiol groups on the structure, swelling behaviour and mucoadhesive character of the gel and on the drug release profile were determined. The gel structure was characterized by means of rheology. The ThioPASP gel was demonstrated by rheology, tensile test and 'wash away' measurements to display strong mucoadhesion. The drug release from the ThioPASP gel was studied on a vertical Franz diffusion cell: a burst release of sodium diclofenac occurred in the first hour, followed by sustained release of the encapsulated drug for up to 24h. The results proved the importance of the presence of the thiol groups and suggested that a ThioPASP formulation can be useful as an in situ gelling, ocular dosage form.

A 2,4,6-trinitrobenzenesulphonic acid (TNBS)-based assay is developed to determine the degree of chemical cross-linking in aspartic acid-based polymer gels. The conventional colourimetric method for the quantitative determina- tion of amine groups is difficult to use in polymer networks; thus, an improved method is developed to analyse polymer gels swollen in dimethyl sulfoxide (DMSO). Reaction products of the derivatizing reaction are examined by NMR. The chemical stability of the reagent is increased in DMSO, and the method shows satisfactory linearity and accuracy. The degree of chemical cross-linking in the investigated gels is close to its theoretical maximum, but the conversion of the pen- dant amine groups to cross-linking points is strongly dependent on the feed composition of the gels.

As an example of acyclic P-chiral phosphine oxides, the resolution of ethyl-(2-methylphenyl)-phenylphosphine oxide was elaborated with TADDOL derivatives, or with calcium salts of the tartaric acid derivatives. Besides the study on the resolving agents, several purification methods were developed in order to prepare enantiopure ethyl-(2-methylphenyl)-phenylphosphine oxide. It was found that the title phosphine oxide is a racemic crystal-forming compound, and the recrystallization of the enantiomeric mixtures could be used for the preparation of pure enantiomers. According to our best method, the (R)-ethyl-(2-methylphenyl)-phenylphosphine oxide could be obtained with an enantiomeric excess of 99% and in a yield of 47%. Complete racemization of the enantiomerically enriched phosphine oxide could be accomplished via the formation of a chlorophosphonium salt. Characterization of the crystal structures of the enantiopure phosphine oxide was complemented with that of the diastereomeric intermediate. X-ray analysis revealed the main nonbonding interactions responsible for enantiomeric recognition.

In situ gelling poly(aspartic acid) thiomers are investigated to demonstrate their potential application in the development of injectable formulations. The chemical stability of the thiomer solutions is measured against air to determine the maximum storage time of the solution before injection. Hydrogels exhibit considerably large storage moduli after the chemical oxidation of the low-viscosity thiomer solution. The gelation time can be controlled within 2–6 min, which is advantageous for injection because the thiomer solution and the oxidising agent can be mixed safely in a two-chamber system before injection into the desired site of the body.

Multiresponsive conetwork hydrogels, PASP-l-PNIPAAm, composed of pH-responsive, biodegradable poly(aspartic acid) (PASP) and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) were synthesized by the reaction of allylamine-grafted polysuccinimide and N-isopropylacrylamide in organic medium and a subsequent hydrolysis. The composition of allylamine-modified polymer was determined by nuclear magnetic resonance (NMR) and Fourier transformation infrared spectroscopy (FTIR). pH and temperature sensitivities were studied by measurement of swelling degrees. Scanning electron microscopic (SEM) analysis revealed that the pore size and the morphology of the PASP-l-PNIPAAm hydrogel could be controlled by the ambient pH and temperature. The volume phase transition temperature of the gels was determined by differential scanning calorimetry (DSC). A widely used non-steroidal anti-inflammatory drug, DiclofenacNa (DFS) was chosen as a model drug for drug release experiments. The hydrogel was non-toxic for human epithelial cells. According to the results these hydrogels are suitable for colon-specific controlled drug delivery.

A substantial effort has been made in the last few decades to develop responsive materials that produce a selective answer to well-defined environmental stimuli. In our present review, we focus on the chemistry of thiol–disulphide equilibrium and its incorporation into polymer-based soft materials. Because several papers and extensive reviews have focused on reduction-sensitive drug delivery and gene transfer, we would like to especially emphasise the importance of disulphide formation and the exploitation of reversible thiol–disulphide interconversion in synthesis and its applications. We report the most important synthetic strategies that utilise disulphide formation. However, a major portion of our overview will concentrate on taking advantage of the thiol–disulphide exchange and the reversibility of this reaction in a wide range of applications, such as advanced drug delivery vehicles, bioartificial implants and self-healing and shape-imprinting polymers. In certain cases, the reversibility is only proven and used in one cycle, but in some cases, the process is practically reversible, at least in the time range of the dedicated application. The reversibility of the reaction is an important requirement for the long-term use of these polymers as implant materials; therefore, aside from better understanding the redox processes in living cells, the future direction of this research can lead to the improvement of reversible responses.

Poly(N-isopropylacrylamide-co-N,N'-methylene-bisacrylamide) (P(NIPAAm-co-MBA)) hydrogels were prepared in water using redox initiator. The copolymer composition at high conversion (> 95%) was determined indirectly by HPLC (high performance liquid chromatography) analysis of the leaching water and directly by solid state 13C CP MAS NMR (cross polarization magic angle spinning nuclear magnetic resonance) spectroscopy of the dried gels, and was found to be close to that of the feed. The effect of cross-linker (MBA) content in the copolymer was investigated in the concentration range of 1.1–9.1 mol% (R:90–10; R = mol NIPAAm/mol MBA) on the rheological behaviour and mechanical strength of the hydrogels. Both storage and loss modulus decreased with decreasing cross-linker content as revealed by dynamic rheometry. Gels R70 and R90 with very low cross-linker content (1.2–1.5 mol% MBA) have a very loose network structure, which is significantly different from those with higher cross-linker content manifesting in higher difference in storage modulus. The temperature dependence of the damping factor served the most accurate determination of the volume phase transition temperature, which was not affected by the cross-link density in the investigated range of MBA concentration. Gel R10 with highest cross-linker content (9.1 mol% MBA) behaves anomalously due to heterogeneity and the hindered conformation of the side chains of PNIPAAm.

Thiolated polymers are a promising new group of excipients, but their stability against atmospheric oxidation has not been investigated in detail, and only a few efforts have been made to improve their stability. The oxidation of the thiol groups in solutions of thiolated polymers may result in a decrease of mucoadhesion and unpredictable in situ gelation. The aims of our work were to study the stability of aqueous solutions of thiolated polymers and the effects of stabilizing agents. We investigated thiolated poly(aspartic acid) polymers stabilized with dithiothreitol, glutathione or acetylcysteine. The effects of these antioxidants on the gel structure, mucoadhesion and drug release were determined by means of scanning electron microscopy, swelling, rheology, adhesion and drug release tests. It was concluded that the stability of polymer solutions containing antioxidants is sufficient for one day. Polymers stabilized with dithiotreitol demonstrated fast swelling and drug release, but weaker mucoadhesion as compared with the other samples. Polymers stabilized with glutathione displayed the weakest cohesive properties, resulting in fast and uncontrolled drug release and moderate mucoadhesion. Acetylcysteine-stabilized polymers exhibited an optimum cross-linked structure, with free thiol groups ensuring polymer-mucin interactions, resulting in the best mucoadhesive properties.

Phenylalanine ammonia-lyase (PAL), found in many organisms, catalyzes the deamination of l-phenylalanine (Phe) to (E)-cinnamate by the aid of its MIO prosthetic group. By using PAL immobilized on magnetic nanoparticles and fixed in a microfluidic reactor with an in-line UV detector, we demonstrated that PAL can catalyze ammonia elimination from the acyclic propargylglycine (PG) to yield (E)-pent-2-ene-4-ynoate. This highlights new opportunities to extend MIO enzymes towards acyclic substrates. As PG is acyclic, its deamination cannot involve a Friedel-Crafts-type attack at an aromatic ring. The reversibility of the PAL reaction, demonstrated by the ammonia addition to (E)-pent-2-ene-4-ynoate yielding enantiopure l-PG, contradicts the proposed highly exothermic single-step mechanism. Computations with the QM/MM models of the N-MIO intermediates from L-PG and L-Phe in PAL show similar arrangements within the active site, thus supporting a mechanism via the N-MIO intermediate.

A novel polymer gel exhibiting simultaneous temperature and magnetic field sensitivity has been prepared and studied. Poly(N-isopropylacrylamide) (PNIPA) and magnetic nanoparticles (magnetite, Fe 3 O 4 ) loaded PNIPA gel beads with mm size and monolith gels with cm size were prepared. The dependence of swelling degree on the temperature has been studied. The effects of cross-linking density and the presence of magnetic nanoparticles on the equilibrium swelling degree as well as on the collapse transition have been investigated. Swelling kinetic measurements were also made. By comparing the equilibrium swelling properties of PNIPA and magnetite loaded PNIPA gels it was found that the built in magnetic nanoparticles do not modify the temperature sensitivity of these gels. Within the experimental accuracy the temperature of the collapse transition was not sensitive to the presence of magnetic particles. We have compared the swelling behaviour of mm size gel beads to the cm size monolith gels in order to study the influence of surface skin layer on the swelling equilibrium. It was established that the extent of surface skin formation was decreased by the presence of magnetic particles.

Interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly( N -isopropylacrylamide- co -X) (PNIPAAm- co -X) were prepared by using a two-step method. Hydrophilicity of PNIPAAm chains was increased by adding acrylamide (AAm; hydrophilic neutral monomer) or 2-acrylamido-2-methylpropylsulfonic acid (AMPS; anionic charged monomer). The effect of the incorporation of chemically crosslinked PVA into the temperature induced phase transition as well as swelling behavior of the responsive hydrogels were studied. The volume phase transition (VPT) of IPNs was investigated by cloud point measurement and differential scanning calorimetry. Significant differences in volume phase transition enthalpies of PNIPAAm (Δ H VPT ) and volume phase transition temperatures ( T VPT ) were found. The Δ H VPT decreases with increasing co-monomer concentration. In several cases the phase transition was not followed by macroscopic shrinking of IPNs. Thus this property is advantageous for several technical applications.

The combination of polymers with nanomaterials displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The electric- and magnetic- field-sensitive elastomers represent a new type of composites consisting of small particles, usually from nanometer range to micron range, dispersed in high elastic polymeric matrix. Coupling of electric and/or magnetic fields with elastic properties leads to a number of striking phenomena that are exhibited in response to impressed external fields. The ability of such materials to change their size and mechanical properties in a reversible manner has inherent interest, if for no other reason than the uniqueness having giant elastic response to polarization. The giant deformational effect, high elasticity, anisotropic properties, and quick response to either electric or magnetic fields open new opportunities for using such materials for various applications. Since electric and magnetic fields are convenient stimuli from the point of signal control, it is of great importance to develop and study such flexible, smart polymeric systems.

Several attempts have been made recently in order to develop smart windows, which can moderate light and heat intensities. Thermotropic gels have met with growing interest because of their advanced properties. Based upon phase transitions of polymer gels, a novel thermally adjustable window, which includes a gel layer, has been developed in our laboratory. The so-called gel-glass becomes opaque when the temperature exceeds a certain value and goes back to its original transparent state when it is cooled below the critical value again. Intelligent gel-glasses made of these materials can moderate the amount of sunlight and radiated heat. The optical properties of the gel layer are also modified by the Joule heat of audio frequency AC current. Two types of gel-glasses have been developed and investigated. Phase transition temperature of a poly(N-isopropylacrylamide) based gel was adjusted by copolymerization and by changing of the solvent composition. The cloud point of a poly(methyl vinyl ether) - water system in a PVA gel was varied by modifying the composition of the swelling agent. In the case of electrically adjustable thermotropic windows, optical properties, energy consumption and temperature changes during the switching process were studied.

Magnetic iron oxide (magnetite, Fe3O4) nanoparticles were encapsulated with polystyrene to give a stable water-based magnetic polymer latex, using the miniemulsion polymerization technique. The resulting magnetic latexes were characterized with transmission electron microscopy (TEM), dynamic light scattering (DLS), vibrating sample magnetometer measurements (VSM), and 57Fe Mossbauer spectroscopy measurements. TEM revealed that all magnetite nanoparticles were embedded in the polymer spheres, leaving no empty polystyrene particles. The distribution of magnetite particles within the polystyrene spheres was inhomogeneous, showing an uneven polar appearance. The DLS measurements indicated a bimodal size distribution for the particles in the latexes. According to our magnetometry and Mossbauer spectroscopy data, the encapsulated magnetite particles conserve their superparamagnetic feature when they are separated in the polymer matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4802–4808, 2004

c ¨¨ ´ ´ ´ ´ ´ ´ Abstract Some structural features underlying the increased thermostability of enzymes from thermophilic organisms relative to their homologues from mesophiles are known from earlier studies.We used cellulase C from Clostridium thermocellum to test whether thermostability can be increased by mutations designed using rules learned from thermophilic proteins.Cellulase C has a TIM barrel fold with an additional helical subdomain.We designed and produced a number of mutants with the aim to increase its thermostability.Five mutants were designed to create new electrostatic interactions.They all retained catalytic activity but exhibited decreased thermostability relative to the wild-type enzyme.Here, the stabilizing contributions are obviously smaller than the destabilization caused by the introduction of the new side chains.In another mutant, the small helical subdomain was deleted.This mutant lost activity but its melting point was only 3 8C lower than that of the wild-type enzyme, which suggests that the subdomain is an independent folding unit and is important for catalytic function.A double mutant was designed to introduce a new disulfide bridge into the enzyme.This mutant is active and has an increased stability (DT s3 8C, m D(DG )s1.73 kcalymol) relative to the wild-type enzyme.Reduction of the disulfide bridge results in destabilization u and an altered thermal denaturation behavior.We conclude that rules learned from thermophilic proteins cannot be used in a straightforward way to increase the thermostability of a protein.Creating a crosslink such as a disulfide bond is a relatively sure-fire method but the stabilization may be smaller than calculated due to coupled destabilizing effects. 2002 Elsevier Science B.V. All rights reserved.

Glycerol diglycidyl ether (GDE) is a convenient and inexpensive bis-epoxide cross-linker as demonstrated by the preparation of cross-linked enzyme aggregates (CLEAs) from two different enzyme classes. GDE cross-linked CLEAs of lipases from Pseudomonas fluorescens (AK), Burkholderia cepacia (PS) and lipase B from Candida antarctica (CaL B) and further of phenylalanine ammonia-lyase (PAL) from Petroselinum crispum showed improved properties as compared to their glutaraldehyde (GA) cross-linked counterparts. Ultrasonication studies indicated GDE cross-linked CLEAs of lipase PS and PAL as mechanically more stable than the GA-based forms. In the kinetic resolution of racemic 1-phenylethanol 1 catalytic activity of GDE-based lipase CLEAs (U= 69.6, 134.8 and 127.4 U g-1; for AK, CaL B and PS prepared at 22 °C, respectively) surpassed those of the corresponding GA-based lipase CLEAs (U= 24.4, 131.0 and 119.2 U g-1; for AK, CaL B and PS prepared at 22 °C, respectively). GDE-based PAL-bovine serum albumin co-CLEAs could be recycled at least three times when used for the stereoselective ammonia addition in 6M ammonia onto (E)-3-(thiophen-2-yl)acrylic acid 4 whereas recycling of conventional GA-based PAL CLEAs from this medium failed.

Hydrogenases are redox metalloenzymes in bacteria that catalyze the uptake or production of molecular hydrogen. Two homologous nickel-iron hydrogenases, HupSL and HydSL from the photosynthetic purple sulfur bacterium Thiocapsa roseopersicina, differ substantially in their thermal stabilities despite the high sequence similarity between them. The optimum temperature of HydSL activity is estimated to be at least 50 degrees C higher than that of HupSL. In this work, homology models of both proteins were constructed and analyzed for a number of structural properties. The comparison of the models reveals that the higher stability of HydSL can be attributed to increased inter-subunit electrostatic interactions: the homology models reliably predict that HydSL contains at least five more inter-subunit ion pairs than HupSL. The subunit interface of HydSL is more polar than that of HupSL, and it contains a few extra inter-subunit hydrogen bonds. A more optimized cavity system and amino acid replacements resulting in increased conformational rigidity may also contribute to the higher stability of HydSL. The results are in accord with the general observation that with increasing temperature, the role of electrostatic interactions in protein stability increases. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00894-001-0071-8.