Diglycolamide functionalized multi-walled carbon nanotubes for removal of uranium from aqueous solution by adsorption

Diglycolamide functionalized multi-walled carbon nanotubes (DGA-MWCNTs) were synthesized by sequential chemical reactions for removal of uranium from aqueous solution. Characterization studies were carried out using FT-IR spectroscopy, XRD and SEM analysis. Adsorption of uranium from aqueous solution on this material was studied as a function of nitric acid concentration, adsorbent dose and initial uranium concentration. The uranium adsorption data on DGA-MWCNTs followed the Langmuir and Freundlich adsorption isotherms. The adsorption capacity of DGA-MWCNTs as well as adsorption isotherms and the effect of temperature on uranium ion adsorption were investigated. The standard enthalpy, entropy, and free energy of adsorption of the uranium with DGA-MWCNTs were calculated to be 6.09 kJ mole⁻¹, 0.106 kJ mole⁻¹ K⁻¹ and −25.51 kJ mole⁻¹ respectively at 298K. The results suggest that DGA-MWCNTs can be used as efficient adsorbent for uranium ion removal.     

Synthesis of PHB nanoparticles from optimized medium utilizing dairy industrial waste using Brevibacterium casei SRKP2: A green chemistry approach

Polyhydroxyalkanoates (PHAs) are natural, biodegradable polymers accumulated by bacteria under nutritional exhausted condition where carbon source is in excess. A gram positive bacterium (designated strain SRKP2) that potentially accumulated polyhydroxybutyrate (PHB) was isolated from dairy industrial waste. From its morphological and physiological properties and nucleotide sequence of its 16S rRNA, it was suggested that strain SRKP2 was similar to Brevibacterium casei. PHAs were synthesized from a medium containing dairy waste, yeast extract and sea water. The synthesized PHAs were characterized by FT-IR as Polyhydroxybutyrate (PHB). Response surface methodology was applied to optimize the production of PHB. From the optimized medium the yield of PHB was found to be 2.940 g/L. Here we report the direct use of dairy waste and sea water as potential sources for the production of PHB. Produced PHB was used to synthesize nanoparticles using solvent displacement technique.     

Thermal degradation kinetics of thermoresponsive poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers prepared via RAFT polymerization

Reversible addition-fragmentation chain transfer polymerization at 70 °C in N,N-dimethylformamide was used to prepare poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers in various compositions to afford well-defined polymers with pre-determined molecular weight, narrow molecular weight distribution, and precise chain end structure. The copolymer compositions were determined by ¹H NMR spectroscopy. The reactivity ratios of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMA) were calculated as r _NIPAM = 0.838 and r _DMA = 1.105, respectively, by the extended Kelen–Tüdös method at high conversions. The lower critical solution temperature of PNIPAM can be altered by changing the DMA content in the copolymer chain. Differential scanning calorimetry and thermogravimetric analysis at different heating rates were carried out on these copolymers to understand the nature of thermal degradation and to determine its kinetics. Different kinetic models were applied to estimate various parameters like the activation energy, the order, and the frequency factor. These studies are important to understand the solid state polymer degradation of N-alkyl substituted polymers, which show great potential in the preparation of miscible polymer blends due to their ability to interact through hydrogen bonding.     

Human Mesenchymal Stem‐Cell Behaviour On Direct Laser Micropatterned Electrospun Scaffolds with Hierarchical Structures

Direct laser machining and electrospinning are utilized to obtain a bi‐layered hybrid scaffold with hierarchical topographical features to mimic extracellular matrix‐like microenvironment of cells. Adult bone marrow derived human mesenchymal stem cells (hMSCs) are cultured in vitro in these hybrid scaffolds, and cell orientation, proliferation, viability, and differentiation are evaluated. The results show that this novel hybrid scaffold not only supports cell growth like traditional scaffolds, but also elicits positive responses from the cells, like lineage commitment and alignment, which are essential features of future scaffolds.

     

A novel approach for the control of drug release rate through hydrogel membrane: II. Thermodynamic modeling of the partition control scheme

In advanced drug delivery systems, drug permeation rate is the key parameter that governs performance. Among the factors that influence the permeation rate, partition effect is presently given less attention. In the first part of this study [L. Shang, S. Zhang, H. Du, S S. Venkatraman, A novel approach for the control of drug release rate through hydrogel membrane. I. Effect of drug immobilization on drug release rate by copolymerization method. Eur. J. Pharm. Biopharm. 68 (2008) 715–723], a scheme was proposed to alter the drug release rate through controlling the partition behavior by immobilizing drug molecules in the membrane. It was hypothesized that the immobilized drug contributes to the total chemical potential of all drug molecules, resulting in a reduction in the partition coefficient. In this paper, the working mechanism of the control scheme is studied through thermodynamic modeling on the assumption that substances in the system are dependent upon one another (rather than independent as they are usually treated). Experimental results provide satisfactory verification of the model. With this model, drug permeation rate can be quantitatively tailored.     

Biofunctionalization of polyelectrolyte microcapsules with biotinylated polyethylene glycol-grafted liposomes

Hollow polyelectrolyte microcapsules (PEMC) are prepared using layer-by-layer self-assembly of polyelectrolytes on melamine formaldehyde templates, followed by template dissolution, and subsequent coating with biotinylated polyethylene glycol-grafted liposomes. These potential site-specific carrier systems show a high specificity for NeutrAvidin binding and a strong resistance against unspecific protein binding. It is concluded that this design with NeutrAvidin as the outermost layer of such capsules provides an ideal platform for the biofunctionalization of PEMC as drug delivery systems or as artificial cell-like structures for biomimetic studies.     

Thermoluminescence mechanism in rare-earth-doped magnesium tetra borate phosphors

Magnesium tetra borate (MTB) doped with rare earths (REs) was prepared by the solid state sintering technique. Among the different RE dopants studied in this phosphor, gadolinium-doped phosphors resulted in a dosimetric peak at a relatively higher temperature. The thermoluminescence (TL) emission spectra of RE-doped MTB showed characteristic RE ³⁺ emissions. Electron paramagnetic resonance measurements were carried out in these phosphors to identify the defect centers formed during gamma irradiation and to establish a mechanism for the TL process. Signals corresponding to (BO ₃)^2?, O _v^? were seen upon irradiation which vanished on annealing at 250 °C, showing the role of these centers in the TL process. The thermal activation energies calculated based on the decay of these signals matched well with those calculated on the basis of the usual conventional method showing the validity of the mechanism of TL.     

Cocrystallization of melaminium levulinate monohydrate

Crystals of 2,4,6‐tri­amino‐1,3,5‐triazin‐1‐ium levulinate (4‐oxo­pentanoate) monohydrate, C₃H₇N₆⁺·C₅H₇O₃⁻·H₂O, are formed via self‐assembled hydrogen bonding by cocrystallization of mel­amine and levulinic acid. Two N—H⋯N hydrogen bonds and four N—H⋯O hydrogen bonds connect two melaminium entities such that each of two pairs of N—H⋯O bonds bridges two H atoms belonging to the amine groups of two different melaminium cations via the carbonyl O atom of one levulinate mol­ecule.     

Effect of the structure of the biodegradable triblock polymer polylactide-<Emphasis Type="Italic">block</Emphasis>-(polycaprolactone-<Emphasis Type="Italic">stat</Emphasis>-polylactide)-<Emphasis Type="Italic">block</Emphasis>-polylactide on its mechanical properties

The effect of the structure of the triblock biodegradable polymer synthesized from ɛ-caprolactone and L-lactide via coordination ring-opening polymerization on its mechanical properties is studied. Effects of the structure of the triblock polymer on its relative elongation at break, elastic modulus, and shape recovery after unloading are estimated by the modeling method. It is shown that the properties of the polymer in relation to its structure can be predicted. The structure-dependent characteristics of the polymers are in following ranges: relative elongation at break, 7–1500%; elastic modulus, 1–330 MPa; and shape recovery, 0–95%. The modeling data are confirmed by the back synthesis of the polymers with optimized desired characteristics.