Conformational Isomorphism. A General 21Helical Conformation for Poly(β-alkanoates)
Conformational Isomorphism. A General 21Helical Conformation for Poly(β-alkanoates)
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聚（β-链烷酸酯）的一般 21 螺旋构象。
DOI：
10.1021/ma60045a011
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发表时间：
1975
期刊：
影响因子：
5.5
通讯作者：
R. Marchessault
中科院分区：
文献类型：
--
作者：
J. Cornibert;R. Marchessault
聚（β-羟基链烷酸酯）被发现作为细菌中的内源性碳储备（例如，聚（β-羟基丁酸酯，PHB））和作为合成材料。在前者中，由于单个取代基，α碳是不对称的，而在后者（例如，聚（新戊内酯），PVL）中，存在α和α '取代基。X-射线衍射分析的结晶取向的纤维的聚羟基丁酸和聚乙烯吡咯烷酮揭示了几乎相同的纤维重复，和2 i链对称性。这两种聚酯的构象分析表明，对于每个大分子的可能的构象的最小能量的两个是准相同的骨架二面角，因此构象同构。基于取代的聚（d-丙内酯）主链的一般类别的聚酯被预测具有几乎相同的结晶构象;在这方面，它们类似于具有在结晶状态下呈现鲍林螺旋的趋势的多肽。在这些聚d-烷酸酯中没有分子内氢键，货车德瓦耳斯和静电相互作用是主要的稳定力。在结晶构象中，酯基偶极沿着链垂直于螺旋轴，相邻偶极反平行，它们之间的距离为3 π.从纤维图中可以看出，具有交替极性酯基的通式[COORi-OOCR 2] n（Carrothers型）的聚酯在结晶状态下存在于平面构象1 -6附近.对基于乙二醇和二元酸（己二酸和辛二酸，6个和8个碳原子，re-nitric）的均聚酯的仔细检查6证实，延伸的重复单元的平面性的偏离是在二醇部分。另一方面，最近的一项聚酯基
Poly (/3-hydroxyalkanoates) are found as endogenous carbon reserves in bacteria (eg, poly (/3-hydroxy butyrate, PHB) and as synthetic materials. In the former the ß carbon is asymmetric due to a single substituent while in the latter (eg, poly (pivalolactone), PVL) there are a and a'substituents. X-Ray diffraction analysis of crystalline oriented fibers of PHB and PVL has revealed near identical fiber repeats, and 2i chain symmetries. Conformational analysis of these two polyesters shows that of the possible conformations for each macromolecule the two of minimum energy are quasi-identical in terms of backbone dihedral angles, hence conformationally iso-morphous. The general class of polyesters based on the substituted poly (d-propriolactone) backbone are predicted to have nearly identical crystalline conformations; in this respect they resemble the polypeptides which have the tendency to assume the Pauling helix in the crystalline state. In these poly (d-alkanoates) there are no intramolecu-lar hydrogen bonds; van der Waals and electrostaticinteractions are the main stabilizing forces. In the crystalline conformations the ester dipoles along a chain are perpendicular to the helix axis and contiguous dipoles are antiparallel with 3 Á between them.From fiber diagrams it was shown that polyesters of the general formula [COORi-OOCR2] n (Carrothers’ type) with alternating polarity of the ester groups present near planar conformations1-6 in the crystalline state. Careful examination6 of the homopolyesters based on ethylene glycol and the diacids (adipic and suberic, six and eight carbons, re-spectively) confirmed that the departure from planarity of the extended repeating unit was in the glycol moiety. On the other hand a recent study7 of the polyester based