Maria Kaliva

Microporous polystyrene particles for selective carbon dioxide capture.

This study presents the synthesis of microporous polystyrene particles and the potential use of these materials in CO(2) capture for biogas purification. Highly cross-linked polystyrene particles are synthesized by the emulsion copolymerization of styrene (St) and divinylbenzene (DVB) in water. The cross-link density of the polymer is varied by altering the St/DVB molar ratio. The size and the morphology of the particles are characterized by scanning and transmission electron microscopy. Following supercritical point drying with carbon dioxide or lyophilization from benzene, the polystyrene nanoparticles exhibit a significant surface area and permanent microporosity. The dried particles comprising 35 mol % St and 65 mol % DVB possess the largest surface area, ∼205 m(2)/g measured by Brunauer-Emmett-Teller and ∼185 m(2)/g measured by the Dubinin-Radushkevich method, and a total pore volume of 1.10 cm(3)/g. Low pressure measurements suggest that the microporous polystyrene particles exhibit a good separation performance of CO(2) over CH(4), with separation factors in the range of ∼7-13 (268 K, CO(2)/CH(4) = 5/95 gas mixture), which renders them attractive candidates for use in gas separation processes.

Systematic studies on pH-dependent transformations of dinuclear vanadium(V)-citrate complexes in aqueous solutions. A perspective relevance to aqueous vanadium(V)-citrate speciation.

Vanadium(V) involvement in interactions with physiological ligands in biological media prompted us to delve into the systematic pH-dependent synthesis, spectroscopic characterization, and perusal of chemical properties of arising aqueous vanadium(V)-citrate species in the requisite system. To this end, facile reactions led to dinuclear complexes (NH(4))(4)[V(2)O(4)(C(6)H(5)O(7))(2)].4H(2)O (1) and (NH(4))(6)[V(2)O(4)(C(6)H(4)O(7))(2)].6H(2)O (2). Complex 1 and 2 were characterized by elemental analysis, FT-IR and X-ray crystallography. Complex 1 crystallizes in the monoclinic space group C2/c with a=16.998(5) A, b=16.768(5) A, c=9.546(3) A, beta=105.22(1) degrees, V=2625(1) A(3), and Z=4. Complex 2 crystallizes in the triclinic space group P1;, with a=9.795(4) A, b=9.942(4) A, c=9.126(3) A, alpha=90.32(1) degrees, beta=111.69(1) degrees, gamma=108.67(1) degrees, V=774.5(5) A(3), and Z=1. The structures of 1 and 2 were consistent with the presence of a V(V)(2)O(2) core, to which citrate ligands of differing protonation state were bound in a coordination mode consistent with past observations. Ultimately, the aqueous pH dependent transformations of a series of three dinuclear complexes, 1, 2 and (NH(4))(2)[V(2)O(4)(C(6)H(6)O(7))(2)].2H(2)O (3), all isolated at pH values from 3 to 7.5, were explored and revealed an important interconnection among all species. Collectively, pH emerged as a determining factor of structural attributes in all three complexes, with the adjoining acid-base chemistry unfolding around the stable V(V)(2)O(2) core. The results point to the participation of all three species in aqueous vanadium(V)-citrate speciation, and may relate the site-specific protonations-deprotonations on the dinuclear complexes to potential biological processes involving vanadium(V) and physiological ligand targets.

Aqueous V(V)-peroxo-amino acid chemistry. Synthesis, structural and spectroscopic characterization of unusual ternary dinuclear tetraperoxo vanadium(V)-glycine complexes.

Vanadium participation in cellular events entails in-depth comprehension of its soluble and bioavailable forms bearing physiological ligands in aqueous distributions of binary and ternary systems. Poised to understand the ternary V(V)-H(2)O(2)-amino acid interactions relevant to that metal ions biological role, we have launched synthetic efforts involving the physiological ligands glycine and H(2)O(2). In a pH-specific fashion, V(2)O(5), glycine, and H(2)O(2) reacted and afforded the unusual complexes (H(3)O)(2)[V(2)(O)(2)(mu(2):eta(2):eta(1)-O(2))(2)(eta(2)-O(2))(2)(C(2)H(5)NO(2))] x 5/4 H(2)O (1) and K(2)[V(2)(O)(2)(mu(2):eta(2):eta(1)-O(2))(2)(eta(2)-O(2))(2)(C(2)H(5)NO(2))] x H(2)O (2). 1 crystallizes in the triclinic space group P1, with a = 7.805(4) A, b = 8.134(5) A, c = 12.010(7) A, alpha = 72.298(9) degrees, beta = 72.991(9) degrees, gamma = 64.111(9) degrees, V = 641.9(6) A(3), and Z = 2. 2 crystallizes in the triclinic space group P1, with a = 7.6766(9) A, b = 7.9534(9) A, c = 11.7494(13) A, alpha = 71.768(2) degrees, beta = 73.233(2) degrees, gamma = 65.660(2) degrees, V = 610.15(12) A(3), and Z = 2. Both complexes 1 and 2 were characterized by UV/visible, LC-MS, FT-IR, Raman, NMR spectroscopy, cyclic voltammetry, and X-ray crystallography. The structures of 1 and 2 reveal the presence of unusual ternary dinuclear vanadium-tetraperoxo-glycine complexes containing [(V(V)=O)(O(2))(2)](-) units interacting through long V-O bonds and an effective glycinate bridge. The latter ligand is present in the dianionic assembly as a bidentate moiety spanning both V(V) centers in a zwitterionic form. The collective physicochemical properties of the two ternary species 1 and 2 project the chemical role of the low molecular mass biosubstrate glycine in binding V(V)-diperoxo units, thereby stabilizing a dinuclear V(V)-tetraperoxo dianion. Structural comparisons of the anions in 1 and 2 with other known dinuclear V(V)-tetraperoxo binary anionic species provide insight into the chemical reactivity of V(V)-diperoxo species in key cellular events such as insulin mimesis and antitumorigenicity, potentially modulated by the presence of glycinate and hydrogen peroxide.

Probing for missing links in the binary and ternary V(V)–citrate–(H2O2) systems: Synthetic efforts and in vitro insulin mimetic activity studies

In a pH-specific fashion, V(2)O(5) and citric acid in the absence and presence of H(2)O(2) reacted and afforded, in the presence of NaOH and (CH(6)N(3))(2)CO(3), two new dinuclear V(V) binary non-peroxo (CH(6)N(3))(6)[V(2)O(4)(C(6)H(4)O(7))(2)].2H(2)O (1) and ternary peroxo (CH(6)N(3))(4)[V(2)O(2)(Omicron(2))(2)(C(6)H(5)O(7))(2)].6Eta(2)Omicron (2) species, respectively. Complexes 1 and 2 were further characterized by elemental analysis, UV/Vis, FT-IR, NMR (solution and solid state Cross Polarization-Magic Angle Spinning (CP-MAS)) and Raman spectroscopies, cyclic voltammetry, and X-ray crystallography. Both 1 and 2 are members of the family of dinuclear V(V)-citrate species bearing citrate with a distinct coordination mode and degree of deprotonation, with 2 being the missing link in the family of pH-structural variants of the ternary V(V)-peroxo-citrate system. Given that 1 and 2 possess distinct structural features, relevant binary V(III), V(IV) and V(V), and ternary V(V) species bearing O- and N-containing ligands were tested in in vitro cell cultures to assess their cellular toxicity and insulin mimetic capacity. The results project a clear profile for all species tested, earmarking the importance of vanadium oxidation state and its ligand environment in influencing further binary and ternary interactions of vanadium arising with variable mass cellular targets, ultimately leading to a specific (non)toxic phenotype and glucose uptake ability.

Recombinant human bone morphogenetic protein 2 (rhBMP-2) immobilized on laser-fabricated 3D scaffolds enhance osteogenesis.

The regeneration of bone via a tissue engineering approach involves components from the macroscopic to the nanoscopic level, including appropriate 3D scaffolds, cells and growth factors. In this study, hexagonal scaffolds of different diagonals were fabricated by Direct Laser Writing using a photopolymerizable hybrid material. The proliferation of bone marrow (BM) mesenchymal stem cells (MSCs) cultured on structures with various diagonals, 50, 100, 150 and 200μm increased significantly after 10days in culture, however without significant differences among them. Next, recombinant human bone morphogenetic protein 2 (rhBMP-2) was immobilized onto the hybrid material both via covalent binding and physical adsorption. Both immobilization types exhibited similar high releaseate bioactivity profiles and a sustained delivery of rhBMP-2. The collagen and calcium levels produced in the extracellular matrix (ECM) were significantly elevated for the samples functionalized with BMP-2 compared to those in the osteogenic medium. Furthermore, significant upregulation of gene expression in both types of BMP-2 immobilized scaffolds was observed for alkaline phosphatase (ALPL) and osteocalcin (BGLAP) at days 7, 14, and 21, for RUNX2 at day 21, and for osteonectin (SPARC) at days 7 and 14. The results suggest that the release of bioactive rhBMP-2 from the hybrid scaffolds enhance the control over the osteogenic differentiation during cell culture.

A Unique Dinuclear Mixed V(V) Oxo-peroxo Complex in the Structural Speciation of the Ternary V(V)-Peroxo-citrate System. Potential Mechanistic and Structural Insight into the Aqueous Synthetic Chemistry of Dinuclear V(V)-Citrate Species with H2O2

Diverse vanadium biological activities entail complex interactions with physiological target ligands in aqueous media and constitute the crux of the undertaken investigation at the synthetic level. Facile aqueous redox reactions, as well as nonredox reactions, of V(III) and V(V) with physiological citric acid and hydrogen peroxide, under pH-specific conditions, led to the synthesis and isolation of a well-formed crystalline material upon the addition of ethanol as the precipitating solvent. Elemental analysis pointed to the molecular formulation (NH4)4[(VO2){VO(O2)}(C6H5O7)2]·1.5H2O (1). Complex 1 was further characterized by Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), Raman spectroscopy, cyclic voltammetry, and X-ray crystallography. The crystallographic structure of 1 reveals the presence of the first dinuclear V(V)-citrate complex with non-peroxo- and peroxo-containing V(V) ions, concurrently present within the basic VV2O2 core. The nonperoxo unit VO2+ and the peroxo unit VO(O2)+ are each coordinated to a triply deprotonated citrate ligand in a distinct coordination mode and coordination geometry around the V(V) ions. These units are similar to those in homodinuclear complexes bearing oxo or peroxo groups. The unique assembly of both units in the anion of 1 renders the latter as a potential intermediate in the peroxidation process, from [V2O4(C6H5O7)2]4– to [V2O2(O2)2(C6H6O7)2]2–. The transformation reactions of 1 establish its connection with several V(V) and V(IV) dinuclear species present in the aqueous distribution of the V(IV,V)-citrate systems. The shown position of 1 as an intermediate in the mechanism of H2O2 addition to dinuclear V(V)-citrate species portends its role in the complex aqueous distribution of species in the ternary V(V)-peroxo-citrate system and its potential reactivity in (bio)chemically relevant media.

Nanoporous polystyrene–porphyrin nanoparticles for selective gas separation

Highly cross-linked polystyrene–porphyrin nanoparticles were synthesized by a facile approach using emulsion free-radical copolymerization of styrene (St) with a tetra-functional cross-linker, 5,10,15,20-tetrakis(4-phenylmethacrylate)-21H,23H-porphine (PO), and a bifunctional cross-linker, divinylbenzene (DVB), in aqueous solution. Two samples were prepared, PO-St-DVB(1) and PO-St-DVB(2), with 0.7 and 2.6 mol% PO, respectively. The cross-link density of the particles increased with the increase of the PO content at a constant St/cross-linkers mol feed ratio. The morphology and the size of the polymer particles were studied by scanning and transmission electron microscopies. Gas adsorption measurements showed that the polystyrene–porphyrin nanoparticles possessed an inherently large surface area when dried by supercritical CO2 from their dispersions in EtOH or DMF. In particular, the sample with the highest PO content (PO-St-DVB(2)) exhibited a Brunauer–Emmett–Teller (BET) surface area up to 334 m2 g−1 (282 m2 g−1 calculated from CO2 adsorption) with a total pore volume of 0.37 cm3 g−1 when dried from EtOH. Analysis of the CO2 and CH4 adsorption data using the ideal adsorption solution theory revealed that the PO-St-DVB(2) nanoparticles exhibited an adsorption selectivity for CO2 over CH4 of 25 at 263 K and 12 at 273 K, rendering them attractive candidates for use in CO2/CH4 separation and carbon dioxide sequestration processes.

Wharton's Jelly Mesenchymal Stem Cell Response on Chitosan-graft-poly (ε-caprolactone) Copolymer for Myocardium Tissue Engineering

Cell therapy and tissue engineering attract increasing attention as a potential approach for cardiac repair. Although a plethora of interesting concepts in the emerging field of cardiac stem cell-based tissue engineering are reported, there are still challenges that this field needs to overcome to achieve therapeutic translation into the clinical praxis. Engineering biomaterial scaffolds that facilitate stem cell engraftment, survival and homing are crucial for successful cellular cardiomyoplasty after myocardial infarction (MI). In this study we investigate for the first time the cellular response of Whartons jelly (WJ) Mesenchymal Stem Cells (MSCs) on a copolymeric material comprising chitosan (CS) and poly(ε-caprolactone) (PCL). First we synthesize a copolymer consisting of poly(ε-caprolactone) grafted on a chemically modified chitosan-backbone (CS-g-PCL). Furthermore, we investigate the morphology, viability and proliferation of WJMSCs on material coatings and examine the cellular response from different donors. Our results show strong cell adhesion on the CS-g- PCL material surface from the first hours in culture, and a proliferation increase after 3 and 7 days. These findings support the potential use of our proposed cell-material combination in myocardium tissue engineering.

Osteogenic Potential of Pre-Osteoblastic Cells on a Chitosan-graft-Polycaprolactone Copolymer

A chitosan-graft-polycaprolactone (CS-g-PCL) copolymer synthesized via a multi-step process was evaluated as a potential biomaterial for the adhesion and growth of MC3T3-E1 pre-osteoblastic cells. A strong adhesion of the MC3T3-E1 cells with a characteristic spindle-shaped morphology was observed from the first days of cell culture onto the copolymer surfaces. The viability and proliferation of the cells on the CS-g-PCL surfaces, after 3 and 7 days in culture, were significantly higher compared to the cells cultured on the tissue culture treated polystyrene (TCPS) control. The osteogenic potential of the pre-osteoblastic cells cultured on CS-g-PCL surfaces was evaluated by determining various osteogenic differentiation markers and was compared to the TCPS control surface. Specifically, alkaline phosphatase activity levels show significantly higher values at both time points compared to TCPS, while secreted collagen into the extracellular matrix was found to be higher on day 7. Calcium biomineralization deposited into the matrix is significantly higher for the CS-g-PCL copolymer after 14 days in culture, while the levels of intracellular osteopontin were significantly higher on the CS-g-PCL surfaces compared to TCPS. The enhanced osteogenic response of the MC3T3-E1 pre-osteoblasts cultured on CS-g-PCL reveals that the copolymer underpins the cell functions towards bone tissue formation and is thus an attractive candidate for use in bone tissue engineering.

Biodegradation of weathered polystyrene films in seawater microcosms

A microcosm experiment was conducted at two phases in order to investigate the ability of indigenous consortia alone or bioaugmented to degrade weathered polystyrene (PS) films under simulated marine conditions. Viable populations were developed on PS surfaces in a time dependent way towards convergent biofilm communities, enriched with hydrocarbon and xenobiotics degradation genes. Members of Alphaproteobacteria and Gammaproteobacteria were highly enriched in the acclimated plastic associated assemblages while the abundance of plastic associated genera was significantly increased in the acclimated indigenous communities. Both tailored consortia efficiently reduced the weight of PS films. Concerning the molecular weight distribution, a decrease in the number-average molecular weight of films subjected to microbial treatment was observed. Moreover, alteration in the intensity of functional groups was noticed with Fourier transform infrared spectrophotometry (FTIR) along with signs of bio-erosion on the PS surface. The results suggest that acclimated marine populations are capable of degrading weathered PS pieces.