Nanometer-Scale Smectic Ordering of Genetically Engineered Rodlike Polymers: Synthesis and Characterization of Monodisperse Derivatives of Poly(
详细信息 查看全文
- 作者：Seungju M. Yu ; Carissa M. Soto ; and David A. Tirrell
- 刊名：Journal of the American Chemical Society
- 出版年：2000
- 出版时间：July 19, 2000
- 年：2000
- 卷：122
- 期：28
- 页码：6552 - 6559
- 全文大小：729K
- 年卷期：v.122,no.28(July 19, 2000)
- ISSN：1520-5126
文摘
Macromolecules with precisely defined architectures on the nanometer scale are ideal building blocksfor self-assembled materials and nanometer-scale devices. By utilizing recombinant DNA technology andbacterial protein expression, we have prepared a set of rodlike artificial proteins, Glu(OBzl)Asp(OBzl)[Glu(OBzl)17Asp(OBzl)]X-Glu(OBzl)Glu(OBzl) (PBLG-X, X = 3-6, 1), which serve as monodisperse analoguesof poly(
-benzyl 
,1">L-glutamate) (PBLG), with variation of rod length from 8.7 to 17 nm. Synthesis wasaccomplished by (i) bacterial production of a precursor polypeptide GluAsp(Glu17Asp)XGluGlu (PLGA-X,X = 3-6), as a fusion to mouse dihydrofolate reductase (DHFR), (ii) CNBr digestion of the expressed proteinto liberate PLGA-X, and (iii) side chain benzylation of PLGA-X via treatment with phenyldiazomethane. Thegrowth rates of cultures transformed with the recombinant genes, and the yields of protein expressed therein,depended on the number of Glu17Asp repeats appended to the fusion partner, decreasing as the number ofrepeats increased. PBLG-3, with the lowest aspect ratio (6.9), did not exhibit liquid crystalline (LC) behaviorwhile each of the other polymers formed lyotropic LC phases. The phase transition behavior of PBLG-X wasdistinctly different from that of conventional polydisperse PBLG; when the concentration of the polymer solutionwas gradually increased, the transition from the isotropic to the liquid crystalline state occurred uniformlythroughout the sample without formation of distinct birefringent droplets. Solution-cast films of PBLG-4 andPBLG-5 formed smectic supramolecular architectures with layer spacings (11.4 and 14.0 nm, respectively)precisely determined by the length of the monodisperse rods. Smectic ordering was observed only in filmscast from mixtures of chloroform (97%) and trifluoroacetic acid (3%). In films prepared from dioxane, bothpolydisperse and monodisperse PBLGs adopted columnar order without formation of smectic layers.
-benzyl ,1">L-glutamate) (PBLG), with variation of rod length from 8.7 to 17 nm. Synthesis wasaccomplished by (i) bacterial production of a precursor polypeptide GluAsp(Glu17Asp)XGluGlu (PLGA-X,X = 3-6), as a fusion to mouse dihydrofolate reductase (DHFR), (ii) CNBr digestion of the expressed proteinto liberate PLGA-X, and (iii) side chain benzylation of PLGA-X via treatment with phenyldiazomethane. Thegrowth rates of cultures transformed with the recombinant genes, and the yields of protein expressed therein,depended on the number of Glu17Asp repeats appended to the fusion partner, decreasing as the number ofrepeats increased. PBLG-3, with the lowest aspect ratio (6.9), did not exhibit liquid crystalline (LC) behaviorwhile each of the other polymers formed lyotropic LC phases. The phase transition behavior of PBLG-X wasdistinctly different from that of conventional polydisperse PBLG; when the concentration of the polymer solutionwas gradually increased, the transition from the isotropic to the liquid crystalline state occurred uniformlythroughout the sample without formation of distinct birefringent droplets. Solution-cast films of PBLG-4 andPBLG-5 formed smectic supramolecular architectures with layer spacings (11.4 and 14.0 nm, respectively)precisely determined by the length of the monodisperse rods. Smectic ordering was observed only in filmscast from mixtures of chloroform (97%) and trifluoroacetic acid (3%). In films prepared from dioxane, bothpolydisperse and monodisperse PBLGs adopted columnar order without formation of smectic layers.