TY - JOUR
T1 - Macromolecular Stereochemistry of Poly(P-biphenylmethyl l-glutamate)
T2 - Linkage Between Biphenyl Twist Sense and Polypeptide Conformation and Observation of Microaggregation-Driven, Sudden, Temperature-Dependent Chiral Optical Changes
AU - Reidy, Michael P.
AU - Green, Mark M.
PY - 1990
Y1 - 1990
N2 - In the expectation that the normally equally populated left- (M) and right-handed (P) twist senses of a biphenyl moiety would, in the side chain of a polypeptide, be perturbed by the helical conformation of the main chain and therefore potentially reveal characteristics of the side-chain conformation, we have carried out the syntheses of the ortho- and para-substituted biphenylmethyl esters of poly(L-glutamic acid) and poly(L-aspartic acid). In the aspartate series the appropriate N-carboxyanhydrides yielded polymer for both the ortho- and para-substituted biphenylmethyl esters. The para isomer was not soluble in solvents appropriate to ultraviolet circular dichroism measurements while the ortho isomer indicated the absence of the a-helical conformation. In the glutamate series although we could not obtain a crystalline iV-carboxyanhydride from the ortho isomer, in the para isomer we were able to obtain a high polymer, which, in a variety of solvents, both adopts the a-helical conformation and displays a strong positive circular dichroism band associated with the biphenyl chromophore. This chiral optical characteristic is almost entirely lost on dichloroacetic acid denaturation of the polypeptide. As a complete surprise, dilute solutions of poly(pbiphenylmethyl L-glutamate) in several helicogenic solvents, with the notable exception of chloroform, exhibit a sudden, large, almost concentration-independent, reversible change in their optical activity properties just below 0 °C. Intrinsic viscosity and light-scattering measurements point to aggregation associated with this change while ultraviolet, infrared, and excimer fluorescence measurements offer no evidence for significant conformational changes of the polypeptide chain or of the relationships among the biphenyl groups.
AB - In the expectation that the normally equally populated left- (M) and right-handed (P) twist senses of a biphenyl moiety would, in the side chain of a polypeptide, be perturbed by the helical conformation of the main chain and therefore potentially reveal characteristics of the side-chain conformation, we have carried out the syntheses of the ortho- and para-substituted biphenylmethyl esters of poly(L-glutamic acid) and poly(L-aspartic acid). In the aspartate series the appropriate N-carboxyanhydrides yielded polymer for both the ortho- and para-substituted biphenylmethyl esters. The para isomer was not soluble in solvents appropriate to ultraviolet circular dichroism measurements while the ortho isomer indicated the absence of the a-helical conformation. In the glutamate series although we could not obtain a crystalline iV-carboxyanhydride from the ortho isomer, in the para isomer we were able to obtain a high polymer, which, in a variety of solvents, both adopts the a-helical conformation and displays a strong positive circular dichroism band associated with the biphenyl chromophore. This chiral optical characteristic is almost entirely lost on dichloroacetic acid denaturation of the polypeptide. As a complete surprise, dilute solutions of poly(pbiphenylmethyl L-glutamate) in several helicogenic solvents, with the notable exception of chloroform, exhibit a sudden, large, almost concentration-independent, reversible change in their optical activity properties just below 0 °C. Intrinsic viscosity and light-scattering measurements point to aggregation associated with this change while ultraviolet, infrared, and excimer fluorescence measurements offer no evidence for significant conformational changes of the polypeptide chain or of the relationships among the biphenyl groups.
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U2 - 10.1021/ma00221a008
DO - 10.1021/ma00221a008
M3 - Article
AN - SCOPUS:0025488460
SN - 0024-9297
VL - 23
SP - 4225
EP - 4234
JO - Macromolecules
JF - Macromolecules
IS - 19
ER -