hlarch 20, 19ti1
1509
COMMUNICATIONS TRANSFORMATION OF POLYMERIC RUTHENIUM(1V) TO T H E MONOMERIC SPECIES ON ION EXCHANGE RESIN
Sir:
To
T H E EDITOR
monomeric Ru(IV), = 733, and polymeric Ru(IV), = 1003. T h e results, given in Table I, indicate that the absorbancy index in the resin phase is a constant, independent of the value for the original solutions and approximates the value for the monomeric Ru(1V).
-4lthough the existence of polymeric forms of ruthenium(1V) had been suspected, Gortsema and Cobble' were able to prepare both the monomeric TABLE I and polymeric species and study them extensively ABSORBANCY INDEX OF Ru(1V) ON RESIN in perchloric and nitric acid solutions. Ion exSample no. change provided a simple method for transforming A. Monomeric Ru(I1.) the polymeric form to the monomeric. This was Expt. 1 2 3 Average done by equilibrating a quantity of low cross1 800 863 785 linked Dowex 50&: resin (2 to 47,) with Ru(1V) 2 806 816 764 806 solution known to contain extensive amounts of B. Polymeric Ru(1Y) polymer and then eluting the resin with 0.1 :?P 1 686 895 882 ceriuni(II1) perchlorate or 1 M perchloric acid. 2 817 842 755 They make no statement as to whether the ion 3 808 782 80 1 exchange is a separation of RuO++ (the monomer) (4) From tlie Ph.D. thesis of D. K. A. entitled "A Study of R u ( I I I ) , from solutions of high polymer concentration, or and Ru(1V) Species in Aqueous Perchloric Acid Solutions," Purdue whether there is a transformation of the polymer Unirersity, August, 1980. to the monomer on the resin. From direct ob- DEPARTMEKT OF CHEMISTRY UNIVERSITY DONALD K. AT WOOD^ servation of the spectrum of Ru(1V) on the resin PURDCE INDIAXA THOS. DE VRIES it can be concluded that an actual transformation LAFAYETTE, RECEIVEDFEBRUARY 1, 1961 of polymer to monomer occurs as i t passes through the ion exchange resin. This is also significant in that i t shows that the polymeric Ru(1V) structure SPECIFIC CLEAVAGE OF METHIONYL PEPTIDES is not extremely stable and that i t can be broken Sir: down into monomer by use of rather mild condiSulfonium derivatives of methionine have been tions. known to undergo easy elimination of the sulfur The spectra were scanned with a Cary Model function with concomitant formation of homoserine 14 recording spectrophotometer. One cm. Beck- l a c t ~ n e . ' ,It ~ ~has ~ now been demonstrated that in man fused silica cells were fitted with cell spacers peptides of methionine this intramolecular displaceto reduce the optical path to 2 mm. By increasing ment occurs with participation and cleavage of the dynode voltage on the phototube it was pos- the C-peptide bond (I-IV) in high yields. The sible to record data down t o 250 m p or less. The data presented in Table I show that the extent of ruthenium(1V) perchlorate solutions were preTABLE I pared using a procedure described by Yaffe and Voight2 and by Niedrach and T e v e b a ~ g h . Gort~ JSFLUESCE OF *ILKYL GROUPO N T H E CLEAVAGE OF Svr.sema and Cobble' determined the absorbancy FOYIUM SALTS DERIVEDFROM ETHYL N-.~CETYLMETHIOSYI GLY CIpi AT E index, A (1 cm., moles/liter), to be about 700 for Molar Eauiva..-. the monomeric Ru(IV) and 800 to 1600 for the concn. 01 ients polymer a t 480 mp. The 0.0025 M ruthenium peptide in of alkyl- Per cent. of Alkylating reaction ating peptide perchlorate solutions with A480 ranging from 730 agent mixturea agents cleavageb to 1000 were stirred with Dowex 50WX2, 200 to Iodoacetic acid" 0,005 3 6 .0 400 mesh, ion exchange resin. After a short period Methyl iodide"Pd .01 4 3.6 of time the resin containing Ru(1V) was washed E t h y l brornoacetatcc,d .01 4 43 repeatedly with distilled water to remove any Iodoacetamidr" .O1 3 53 ruthenium ion not in the resin phase. A portion 2,4-Dinitrofl~orobenzcne~ .01 1 -2 of the loaded resin then was tapped and settled Diethyl bromomalonatee ,01 3 5 in one of the 2-mm. cells and the spectrum scanned a Reactions were allowed to proceed at room temperature versus a blank of the unloaded resin in the other 2 for 24 hr. * After removal of excess of alkylating agent by mm. cell. After equilibration with the resin, no ether extraction t h e reaction mixture was heated for one ruthenium could be found in the residual solution. hour at 100'. T h e liberated amino acid was determined b y ninhydrin assay.4 Reaction medium was 0.1 Af f H 3 This enabled calculation of the concentration of the citrate buffer. d Alkylation was conducted in a sealed tube. ruthenium in the resin phase. e Reaction medium was 1: 1 mixture of E t O H and 0.1 hl Data were were obtained for several determina- pH 3 citrate buffer. tions on three different preparations, both of (1) F. P. Gortsema, Doctoral thesis, Purdue University, January, 1980; Dissert. Abstracfs, 21, 48 (1960), L. C . Card No. Mic 60-2206. ( 2 ) R . P. Yaffe a n d A. F. Voight, J . A m . Chem. SOL., 74, 2500 (1952). (3) L. W. Niedrach and A. D . Tevebaugh, i b i d . , 73, 2836 (1951).
(1) G. Toennies and J. J . Kolb, THISJOURNAL, 67, 1141 (1945). ( 2 ) R . A. McRorie, G. L. Sutherland, M . I. Lewis, A. D. Barton, M. R . Glazener and W. Shive, rbid., 76, 115 (1954). (3) H. G. Gundlach, W, H. Stein and S. Moore, J . Bid. Chem., 234, 1754, 1761 (1959). (4) S . Noore and U'. H. Stein, J . B i d . Cheiir., 176, 367 (lQ48).
