Resilin is a member of a family of elastic proteins that includes elastin, as well as gluten, gliadin, abductin and spider silks. Resilin is found in specialized regions of the cuticle of most insects, providing low stiffness, high strain and efficient energy storage; it is best known for its roles in insect flight and the remarkable jumping ability of fleas and spittle bugs. Previously, the Drosophila melanogaster CG15920 gene was tentatively identified as one encoding a resilin-like protein (pro-resilin). Here we report the cloning and expression of the first exon of the Drosophila CG15920 gene as a soluble protein in Escherichia coli. We show that this recombinant protein can be cast into a rubber-like biomaterial by rapid photochemical crosslinking. This observation validates the role of the putative elastic repeat motif in resilin function. The resilience (recovery after deformation) of crosslinked recombinant resilin was found to exceed that of unfilled synthetic polybutadiene, a high resilience rubber. We believe that our work will greatly facilitate structural investigations into the functional properties of resilin and shed light on more general aspects of the structure of elastomeric proteins. In addition, the ability to rapidly cast samples of this biomaterial may enable its use in situ for both industrial and biomedical applications.
The zirconocene complexes Cp2ZrMe2 and Cp*2ZrMe2 activated with B(C6F5)3 initiate the carbocationic polymerization of isobutene and isobutene-isoprene copolymerizations to IIR rubbers at temperatures as high as -30°C. Unlike conventional metal halide initiators, these metallocene-based initiator systems produce both homo-and copolymers of broadly similar molecular weights. Copolymers prepared in the presence of ca. 2 mol % isoprene show a diene incorporation rate of 1.4-1.7%, with the typical 1,4-trans structure. Comparison of the effectiveness of zirconocene dialkyls with that of the metallocene hydrolysis products Cp* 2Zr(OH)2 and (Cp2ZrMe)2(µ-O) in the presence of B(C6F5)3 suggests that initiation by traces of protons is less efficient than initiation by cationic metallocene alkyl species, while oxo-bridged complexes (Cp′2ZrMe)2(µ-O)/B(C6F5)3 (Cp′ ) C5H5 or C5H4SiMe3) are inactive.
The reaction of [CPh3][B(C6F4R)4] with [Cp‘2ZrH2]2 (Cp‘ = C5H4SiMe3) gives the new binuclear
hydrido complexes [Cp‘4Zr2H3][B(C6F4R)4] (R = F, SiPri
3),
which are highly active initiators for the polymerization
of isobutene and isobutene−isoprene copolymerizations
at near-zero concentrations of ionizing solvents. The
structure of the trinuclear hydride [Cp‘5(η1:η5-C5H3SiMe3)Zr3H4]+[B(C6F4SiPri
3)4]- is reported.
The cationic zirconocene trihydrides [Cp‘4Zr2H(µ-H)2]+X-, generated from [Cp‘2ZrH2]2 with various trityl salts of weakly coordinating anions, are powerful initiators for the polymerization of isobutene (IB) and its copolymerization with isoprene (IP) (Cp‘ = C5H4SiMe3). This study is concerned with the quantification of the effects of the counteranion and of trace moisture on IB/IP copolymers and the nature of the initiating species. Polymer molecular weights increase with decreasing anion nucleophilicity in the order X = [B(C6F5)4] ˜ [H2N{B(C6F5)3}2] > [CN{B(C6F5)3}2]. Using [Cp‘4Zr2H3]+ [CN{B(C6F5)3}2]-, high copolymer molecular weights are found (Mw ˜ 5 × 105 g/mol at -35 °C). There is little reduction in either rate or molecular weight on addition of isoprene. Polymer molecular weights are substantially higher than with the Et2AlCl/tBuCl initiator system under identical conditions. Water was shown to be an important chain-transfer agent; substoichiometric quantities of water reduced activity, and copolymer molecular weights decreased linearly with increasing [H2O]. Mechanistic studies suggest that [Cp‘4Zr2H(µ-H)2]+ does not itself act as a cationic initiator but is transformed into one or more other binuclear (polynuclear?) species, accompanied by alkene insertion into the Zr-H bond and a monomer hydrogenation step. Tentative structures for these reactive intermediates are suggested
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