Obtained by successive approximations in the refinement of the homopolymer and copolymer data. for homopolymers alone; this may tend to overweight the copolymer data so that one loses sight of the behavior of the homopolymers. However, we find that the PHBG parameters obtained in this manner differ little from those obtained using only the homopolymer data; hence, the PHBG homopolymer parameters in Table II appear to be good choices when PHBG is used as the host. The PHPG parameters obtained from the refinement are somewhat different from those obtained using only the homopolymer data. This is not unexpected since, as stated above, only the high-temperature ends of the melting curves are obtainable when the solvent is water.to be correct and a best fit was obtained to the experimental data for both PHBG and the copolymers. After several such cycles of refinement, the data converged to the results given in Table V for the homopolymers. It should be emphasized that the data of Table V are the result of curve fitting of data for copolymers and homopolymers rather than

cis- and trans-4-Chloro- and 4-bromo-L-prolines have been synthesized stereospecifically, the key step being SN2 displacement of a free or substituted 4-hydroxyl group in suitably protected 4-hydroxy-L- prolines. Similar displacements with azide ion followed by reduction provide convenient routes to cis- and trans- 4-amino-L-proline. A less satisfactory pathway to cis-4-aminoproline is reduction of a 4- oximinoproline derivative. In the course of the syntheses, which involve a variety of protecting groups, 45 new L-proline derivatives have been prepared. Unexpected side reactions were the formation of cis-4-hydroxyprolinamide by the action of ammonia on trans-4- bromoproline, and the reduction by sodium borohydride of N- benzyloxycarbonyl-4-oximinoproline methyl ester to N-benzyloxycar- bonyl-4-oximinoprolinol.

Water-soluble random copolymers containing L-serine and V5-(4-hydroxybutyl)-L-glutamine were prepared by copolymerization of the V-carboxy-a-amino acid anhydrides of O-trimethylsilyl-L-serine and -benzyl L-glutamate, followed by amidolysis with 4-amino-l-butanol. The copolymers were fractionated and characterized, and their thermally induced helixcoil transition curves determined from optical rotatory dispersion measurements. From an analysis of these curves, using an approximate theory for random copolymers and the host-guest technique, the Zimm-Bragg parameters and s (which characterize the (hypothetical) helix-coil transition of poly-L-serine in water) were obtained. The transition curves and the resulting values of and s demonstrate quantitatively that L-serine is a helix-breaking residue in water in the temperature range of 0-80 °. The conformational behavior of L-serine residues in proteins is discussed.

Nmr of Cis Isomers of Sarcosylsarcosine 535 set of four hydrogen atoms which are involved in bifurcated hydrogen bonds in which the oxygen atoms are in common.Conformations of type B (HGg, HGn, HG12, HG14, HGig, and HG23) also have a pair of intramolecular hydrogen bonds. It does not seem possible to decide from the present experimental data24 which one of these MEC's or a mixture of them is realized in solution.The calculations carried out in this paper should be regarded as the first step of a process to determine the most stable conformation of an isolated molecule in solu-(24) (a) K. D.

The proton magnetic resonance spectra of a series of 4-oxoprolines, and cis- and trans-4-substituted prolines, have been analysed. Correlations permitting assignment of configuration from the spectra are presented. The difficulty of deducing precise conformations from the spectral parameters is emphasized.