Microencapsulation of cells by using biodegradable hydrogels offers numerous attractive features for a variety of biomedical applications including tissue engineering. This study highlights the fabrication of microcapsules from an alginate-gelatin crosslinked hydrogel (ADA-GEL) and presents the evaluation of the physico-chemical properties of the new microcapsules which are relevant for designing suitable microcapsules for tissue engineering. Alginate di-aldehyde (ADA) was synthesized by periodate oxidation of alginate which facilitates crosslinking with gelatin through Schiff's base formation between the free amino groups of gelatin and the available aldehyde groups of ADA. Formation of Schiff's base in ADA-GEL and aldehyde groups in ADA was confirmed by FTIR and NMR spectroscopy, respectively. Thermal degradation behavior of films and microcapsules fabricated from alginate, ADA and ADA-GEL was dependent on the hydrogel composition. The gelation time of ADA-GEL was found to decrease with increasing gelatin content. The swelling ratio of ADA-GEL microcapsules of all compositions was significantly decreased, whereas the degradability was found to increase with the increase of gelatin ratio. The surface morphology of the ADA-GEL microcapsules was totally different from that of alginate and ADA microcapsules, observed by SEM. Two different buffer solutions (with and without calcium salt) have an influence on the stability of microcapsules which had a significant effect on the gelatin release profile of ADA-GEL microcapsules in these two buffer solutions.

In the parent metal-organic framework Cu 3 (btc) 2 material the Cu(II) pairs in the paddle wheel building blocks of the framework give rise to an antiferromagnetic spin state with an electron spin resonance (ESR) silent S ) 0 ground state. The thermally excited S ) 1 state of the Cu(II) pairs can be observed for temperatures above 80 K by ESR spectroscopy but give rise to an exchanged narrowed resonance line preventing the exploration of any structural details in the environment of the paddle wheel units. However, magnetically diluted paramagnetic binuclear Cu-Zn clusters can be formed by substitution of Cu(II) ions by Zn(II) at low doping levels, as already known for zinc-doped copper acetate monohydrate. Indeed, ESR, hyperfine sublevel correlation spectroscopy (HYSCORE) and pulsed electron nuclear double resonance (ENDOR) verify the successful incorporation of zinc ions at cupric ion sites into the framework of the resulting Cu 3-x Zn x (btc) 2 coordination polymer. The formation of such paramagnetic binuclear Cu-Zn paddle wheel building blocks allows the investigation of the interaction between the Cu(II) ions and various adsorbates by advanced pulsed ESR methods with high accuracy. As a first example we present the adsorption of methanol over Cu 3-x Zn x (btc) 2 , which was found to coordinate directly to the Cu(II) ions via their open axial binding site.

The process of water adsorption on a dehydrated Cu(3)(BTC)(2) (copper (II) benzene 1,3,5-tricarboxylate) metal-organic framework (MOF) was studied with (1)H and (13)C solid-state NMR. Different relative amounts of water (0.5, 0.75, 1, 1.5, 2, and 5 mole equivalents with respect to copper) were adsorbed via the gas phase. (1)H and (13)C MAS NMR spectra of dehydrated and water-loaded Cu(3)(BTC)(2) samples gave evidence on the structural changes due to water adsorption within the MOF material as well as information on water dynamics. The analysis of (1)H spinning sideband intensities reveals differences in the (1)H-(63/65)Cu hyperfine coupling between dehydrated and water-loaded samples. The investigation was continued for 60 days to follow the stability of the Cu(3)(BTC)(2) network under humid conditions. NMR data reveal that Cu(3)(BTC)(2) decomposes quite fast with the decomposition being different for different water contents.

Incorporation of Zn2+ into the Cu3(btc)2 metal–organic framework (HKUST-1) was successfully done with Zn2+ replacing Cu2+ in the paddle wheel unit up to 21% zinc. Detailed spectroscopic characterization of the resulting binuclear Cu–Zn paddle wheel units was carried out by 1H and 13C solid-state nuclear magnetic resonance (SSNMR). By intensity analysis of the NMR signals a quantitative determination of the Zn2+ content incorporated into the Cu3(btc)2 framework is possible. X-ray and EPR data verify the analysis. Surface areas were determined for the different samples that indicate a decreasing porosity with increasing zinc content. Water molecules coordinated to the zinc atoms remain in the structure even after evacuation. Their assignment was also confirmed by calculation of the pseudocontact or dipolar shift contribution from all unpaired electrons of surrounding paddle wheels.