,March 20, 19.57
COMMUNICATIONS TO THE EDITOR
showed almost no activity as the amide donor. Under the conditions of the experiment shown in Table 11, glutamine supply limits DPN synthesis. Thus, in a separate experiment under similar conditions, with NA held constant a t 10 pmoles per vessel, DPN synthesis in the presence of 0, 4, 10 and 20 pmoles of glutamine was 0.052, 0.104, 0.172 and 0.274 pmole, respectively. Further investigations are in progress seeking t o elucidate the mechanism of pyridine nucleotide synthesis from nicotinic acid and its amide.
1515
/I
3
(7) Predoctoral Fellow of the National Institute9 of Health.
DEPARTMENT OF BIOCHEMISTRY DUKEUKIVERSITY SCHOOL OF MEDICINE J. PREISS’ DURHAM, NORTHCAROLINA PHILIPHANDLER 11, 1957 RECEIVED FEBRUARY pJ
THE ISOTROPIC LENGTH OF POLYMER NETWORKS
01.
Fig. 1.-Plot of ratio of isotropic length after cross-linking
Li t o initial length LOagainst the square root of the fraction Sir: A general theory of the elastic properties of of the units crosslinked p ’ l z . polymer networks was developed in a recent paper’ linking density decreases deviations from linearity and this theory was applied t o the cross-linking of occur and Li/Lo appears to approach unity. Achighly oriented chains. Whereas for a network cording to equation (38) of ref. 1, Li/Lo should formed in the usual way by cross-linking chain vary directly as p ’ l P for chains with perfect axial molecules in random arrangement the isotropic orientation, and for an infinitesimal amount of length Li of the network (;.e., its length under no cross-linking Li should shrink to zero. This bestress) must obviously be independent of the de- havior is indicated by the linear portion of the gree of cross-linking, it was shown t h a t for a net- curve and its extrapolation to the origin. Since work formed by the random cross-linking of highly the chains prior t o network formation are neither oriented chains Li should increase directly as the completely nor perfectly oriented, deviations from square root of the fraction p of the units cross- linearity would be expected a t low cross-linking linked. Although i t has been reported that the densities where L i should tend to remain constant cross linking of stretched rubber results in an in- as observed. The slope of the linear portion of the crease in its isotropic (zero stress) length,*v3 curve is fifteen while theoretically it is estimated to adequate data are not available to test the afore- be about ten. It appears that “racked rubber” mentioned deduction. We wish to report the re- can serve as a good model for the physical behavior sults of studies of the isotropic length of natural of the fibrous proteins. rubber networks formed from chains in a highly Further details of the experimental methods, a oriented state. These results give strong support more thorough discussion of these results as well to the theoretical conclusions. as a comparison of the isotropic melting temperaThe highly oriented state of the rubber, prior t o ture and swelling behavior of different type netcross-linking is obtained by modification of the works will appear in a forthcoming paper.6 “racking process” originally described by F e ~ c h t e r . ~ (6) D . E. Roberts and L. Mandelkern, in preparation. The wide angle X-ray pattern6 indicates that the DOKALD E. ROBERTS BUREAU OF STANDARDS specimen is in a highly oriented state and the ratio NATIONAL 25, D. C. LEOMANDELKERN of the extended length to retracted length is about WASHINGTON BAKERLABORATORY OF CHEMISTRY eleven. The samples were cross-linked by subject- CORNELL UNIVERSITY PAULJ. FLORY ing them to y-ray irradiation from a Co60 source. ITHACA, N. ‘17. The efficiency of cross-linking in the highly oriented RECEIVED JANUARY 28, 1957 racked’ rubber was found to be twice that for unoriented rubber. HORMONES AND RELATED COMPOUNDS. I n Fig. 1 the ratio of Ll to the initial length Lo ADRENAL V. FLUORINATED &METHYL STEROIDS is plotted against p a l z . A fiftyfold range in crosslinking is encompassed by these experiments and S i r : We recently have reported’ the preparation of a the isotropic length increases by a factor of two and a half. At the higher degrees of cross-linking the number of 6-methylated analogs of adrenal hordata are well represented by a straight line which mones which show unusual potentiation of glucoextrapolates to the origin. However, a s the cross- corticoid activity with no sodium-retaining properties. The group of Sa-fluoro- and 21-fluoro-6(1) P.J. Flory, THISJOURNAL, 78, 5222 (1956). methyl steroids reported herein represents a con(2) R. D. Andrews, E. E. Hanson and A. V. Tobolsky, J . A p p l . Phrs., 17, 352 (1946). tinuation of this work. Compound 111 described (3) J. P. Berry, J. Scanlan and W. F. Watson, Trans. Faraday SOC. below is by far the most potent glucocorticoid re62, 1137 (1956). ported to date. (4) H . Feuchter, Karrtschrrk, Dec.. p. 6 (1925); pp. 8, 28 (1928). ( 5 ) C. C. Davis and J. T. Blake, “The Chemistry and Technology of Rubber,” Reinhold Publishing Corporation, New York, N . Y.. 1937, p. 78.
(1) G. B. Spero, J. L. Thompson, R. J. Magerlein, A. R. Hanze, H. C. Murray, 0. K. Sebek and J. A. Hogg, TEIS JOURNAL,78, 6213 (195G).
