Redox-responsive degradable PEG cryogels as potential cell scaffolds in tissue engineering.

A Michael addition strategy involving the reaction between a maleimide double bond and amine groups is investigated for the synthesis of cryogels at subzero temperature. Low-molecular-weight PEG-based building blocks with amine end groups and disulfide-containing building blocks with maleimide end groups are combined to synthesize redox-responsive PEG cryogels. The cryogels exhibit an interconnected macroporous morphology, a high compressive modulus and gelation yields of around 95%.

Solvent-resistant nanofiltration for product purification and catalyst recovery in click chemistry reactions.

The quickly developing field of "click" chemistry would undoubtedly benefit from the availability of an easy and efficient technology for product purification to reduce the potential health risks associated with the presence of copper in the final product. Therefore, solvent-resistant nanofiltration (SRNF) membranes have been developed to selectively separate "clicked" polymers from the copper catalyst and solvent. By using these solvent-stable cross-linked polyimide membranes in diafiltration, up to 98 % of the initially present copper could be removed through the membrane together with the DMF solvent, the polymer product being almost completely retained.

'Click' functionalization of cryogels conveniently verified and quantified using high-resolution MAS NMR spectroscopy.

Chemical modification reactions of alkyne containing polyHEMA-based macroporous network structures (cryogels) by Cu(I) catalyzed azide-alkyne 'click' cycloaddition reactions and their monitoring and quantification with high-resolution magic angle spinning (hr-MAS) NMR spectroscopy are reported. Complete conversion is obtained when benzylazide is reacted with the grafted alkyne function, but only partial conversion is observed when using azide-modified poly(ethylene glycol) (PEG-N(3) ). Subsequent addition of benzylazide consumes all remaining alkyne groups.

Facile Access to an Efficient Solid-Supported Click Catalyst System Based on Poly(ethyleneimine).

A novel heterogeneous copper(I) catalyst system, which is based on readily available poly(ethyleneimine), has been used as a recyclable catalyst for Cu(I) catalyzed "click" 1,3 dipolar cycloaddition reactions of azides and alkynes in organic media. Branched poly(ethyleneimine) was first methylated and then cross-linked with 1,9-dibromononane. Subsequently, after the immobilization of Cu(I)Br, this system was applied for heterogeneous copper catalyzed click chemistry of a few model reagents and polymeric compounds.

Biodegradable microcapsules designed via 'click' chemistry.

Dextrans modified with alkyne and azide groups through hydrolysable carbonate esters form degradable microcapsules after Cu(I) catalysed 'click' reaction between azides and alkynes yielding triazole cross-links.

Morphological transition during the thermal deprotection of poly(isobornyl acrylate)-b-poly(1-ethoxyethyl acrylate).

A set of poly(isobornyl acrylate)--poly(1-ethoxyethyl acrylate) polymers has been prepared by atom transfer radical polymerization. The 1-ethoxyethyl protecting group can be removed by a mild thermal treatment yielding the poly(acrylic acid) segment. The thin film morphological behavior of selected block copolymers was studied for as well as deprotected block copolymers using atomic force microscopy (AFM).

Yield enhancement genes: seeds for growth.

Yield is a multifactorial trait, integrating various developmental and physiological processes. Despite this complexity, evidence is mounting that yield can be increased by the genetic modification of single genes. Positive results have been obtained by targeting different yield constituents, indicating that there is ample room for further yield improvement by genetic means.

Different responses of tobacco antioxidant enzymes to light and chilling stress.

The effect of elevated light treatment (25 degrees C, PPFD 360 mumol m-2 sec-1) or chilling temperatures combined with elevated light (5 degrees C, PPFD 360 mumol m-2 sec-1) on the activity of six antioxidant enzymes, guaiacol peroxidases, and glutathione peroxidase (GPx, EC 1.11.1.

Comprehensive analysis of gene expression in Nicotiana tabacum leaves acclimated to oxidative stress.

The molecular mechanisms by which plants acclimate to oxidative stress are poorly understood. To identify the processes involved in acclimation, we performed a comprehensive analysis of gene expression in Nicotiana tabacum leaves acclimated to oxidative stress. Combining mRNA differential display and cDNA array analysis, we estimated that at least 95 genes alter their expression in tobacco leaves acclimated to oxidative stress, of which 83% are induced and 17% repressed.