COMMUNICATXONS TO THE EDITOR
Sept. 20, 1959
that the bulk of the reaction occurs with methyloxygen bond scission, and the carboxyl carbonoxygen bond breaks only in 2-3y0 of the events. When V++ is used as the reducing agent, the procedure for separating the fumaric acid is much simpler than with Cr++; the organic acid can be extracted directly from the reaction mixture. Complete hydrolysis of the ester again accompanies electron transfer. The tracer experiment shows that the CHy-0 bond breaks in 95% of the events. With the same reducing agent, but with the methyl maleate half-ester as ligand, bond rupture occurs a t the CH3-0 position in 97-9S% of the hydrolysis events. When the phenyl fumarate half-ester is the ligand and V++ is the reducing agent, complete hydrolysis of the ester also accompanies electron transfer. In this system, the isotopic compositions of both the phenol and the fumaric acid were determined. The results of a series of experiments are summarized.
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The absorption and fluorescence of tris-5-methyl1,lO-phenanthroline ruthenium chelate have been reported and utilized for a microdetermination of ruthenium5 although the electronic transition involved has not been discussed. The luminescence shown in Fig. 1 was obtained from a l(Ip4solution of tri~-2,2’-bipyridineruthenium(II) chloride a t 7 i ° K . The line-like character of the luminescence is re.miniscent of the f-f emission in the rare earth chelates. However, i t is a completely different phenomenon produced by an allowed transition whose mean lifetime is less than sec6 As shown by the absorption spectra in Fig. 1 there is no analogous allowed absorption band a t the wave length of the luminescence.
Acidity of the solution, If 1 0.50 0 . 2 5 0.05 Fraction of phenol enriched 0.071 ,094 ,105 .118 Fraction of fumaric acid enricheda 0 925 ,898 ,884 ,878 h s containing one oxygen derived from the solvent.
The isotope balance is good so that the fractions reported can be taken as indicating the fractions of bond rupture a t the two positions. I t is evident that the course of the reactions can be altered when an alcohol radical such as CEH6,which is reluctant to accept substitution is used. It is perhaps even more remarkable that a substantial fraction of the bond breaking occurs at the C8H5-O position. The results incidentally show that no exchange of the carboxyl oxygen with the solvent accompanies this type of hydrolysis reaction, in contrast to the behavior demonstrated for a number of other ester hydrolyses.4 (4) RI. L. Bender, THIS J O U R N A L , 7 9 , 1020 (1951); references t o other work cited by hl. L. Bender, R . D. Ginger a n d J. P. Unik, ibid., 80, 1044 (1958).
GEORGE HERBERT JONESLAB. UNIVERSITY OF CHICAGO R. T. M. FRASER H. TAUBE CHICAGO, ILLINOIS RECEIVED AVGWT5, 1959
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l.-Tri~-2,2’-bipyridineruthenium( 11) chloride: absorption spectra; --------- luminescence spectra (plotted on an arbitrary intensity scale).
We have explained our data in this manner. The broad absorption band between 17,000 and 27,000 cm.-’ may be due to a charge transfer absorption (E > lo4). That is, the d electron from CHARGE TRANSFER LUMINESCENCE OF A RUTHENIUM(I1) CHELATE the ruthenium atom may be excited to an antibondSir: ing orbital of the bipyridine molecule (d --c pi*). We would like to report the first example of lumi- Thus we may have a very broad absorption band nescence resulting from a charge transfer transition due t o excitation t o various vibrationally excited in the transition metal chelate tris-2,2’-bipyridine- levels of the pi* electronic state and yet have a sinruthenium(I1). The luminescence of chelates has, gle emission from the lowest vibrational level of the in general, been studied as a function of electronic excited state to the ground d orbital. This may transitions within the ligand itself except for a few be represented pictorially as shown in Fig. 2. As predicted there should also be an absorption isolated cases as for the rare earth chelates with energy transfer and luminescence from f-f transi- band from the d orbital to the second antibonding pi tions1#2and for luminescence characteristic of cop- orbital. This band was found experimentally to per(I1) in mixtures of copper(I1) and aminoanthra- have emax. a t 41250 em.-‘ as shown in Fig. 1. The q ~ i n o n e sas , ~pointed out by Kasha and M ~ G l y n n . ~remaining band with emax. a t 35000 cm.-’ is of course the pi + pi* transition of bipyridine. Ex.
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(1) S. I. Weissman, J . Chem. P h y s . , 10, 214 (1942). (2) G. A. Crosby and M. Kasha, Spectuochim. Acta, 10, 377 (1958). (3) A . V. Karyakin and Ya. 1. Kalenichenko, Doklady A k a d . N a u k S . S . S . R . , 66, 191 (1949). (4) h f . Kasha and S. P. McGlynn, A n n . R E V .Chem., 7 , 403 (1950).
(5) H. Veening, Ph.D. Thesis, Purdue University, 1958. Submitted t o Analyfical Chemistry. (6) T h e lifetime estimate was kindly provided by Dr. M. Kasha a t the Florida S t a t e University.
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COMMUNICATIONS TO THE EDITOR
VOl. 81
Fig. 2.-Energy scheme for the absorption and luminescence processes for tris-2,Z’-bipyridinerutheniuni(I1) chloride.
citation of fluorescence by any of the three absorption bands results in the same characteristic luminescence. Thus we have shown internal conversion from the higher excited level in the ultraviolet to the lowest excited level yielding fluorescence. We wish to thank the National Science Foundation for its support of this work.
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Fig. 1.-Optical rotatory dispersion curves (methanol DEPARTMENT OF CHEMISTRY solution) of S-dithiocarbomethoxy-L-( )-valine, -; PURDUE UNIVERSITY J. P. PARIS and LAFAYETTE, IND. WARRENW. BRANDT N,N’-bis-dithiocarbethoxy-L-( - )-cystine, --------- ; L-( - )-malic acid ethyl dithiocarbonate, -+-+--$. RECEIVED MARCH18, 1959
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~ - s e r i e s ,which have so f a r been examined, show a positive Cotton effect, the reverse being true of members of the D-series. This has been tested with the dithiocarbamates of alanine, valine, phenylglycine, isoleucine, alloisoleucine, proline, aspartic acid, glutamic acid and cystine. The nearly identical Sir: positive Cotton effect curves of L-isoleucine and Anomalous Cotton effect curves recently have L-alloisoleucine demonstrate the unimportance found extensive application^^^ in many areas of of the @-asymmetriccenter in this type of analysis. organic chemistry. Unfortunately, most a-amino Similarly, N-dithiocarbomethoxy L-alanyl-L-alaacids3b and their higher polymers3c exhibit only nine and N-dithiocarbomethoxy L-alanyl-D-alanine plain ‘dispersion curves4 over the presently ac- exhibit positive Cotton effect curves of virtually cessible spectral range. We have now discovered identical amplitude. This suggests that the techthat N-dithiocarbalkoxy a-amino acids (I) (di- nique may be employed to determine the conthiocarbamate derivatives) are almost uniquely figuration of the a-asymmetric center of a terminal suited for this purpose and that their use may repre- amino acid in a peptide chain, which may be of sent an important advance in a-amino acid or importance in antibiotic chemistry. peptide methodology. The preparation5 of such The “optical activity’’ of the dithiocarbamate is derivatives is simple and often lends itself to work so strong as to overcome the structural factors on a micro-scale.6 which often confuse stereochemical correlations of The long wave length absorption band near 330 the parent acid based on [a]D (e.g., L-(+)-alanine mp of such dithiocarbamates (I) is strongly ns. L-( -)-cystine possessing dispersion curves of optically active and leads to Cotton effect curves4 opposite sign3bwhile their dithiocarbamates exhibit (Fig. 1). T h e sign of the Cotton effect of the dithio- positive Cotton effect curves). carbamate will indicate the absolute configuration of Xanthatederivatives of certain alcohols have been the a-asymmetric center and all a-amino acids of the shown’ to give anomalous dispersion curves and (1) Paper XXX, C. Djerassi, K . Finch and R. hIauli, THISJ O U R we have now examined such derivatives (11) of aN A L , 81, 4997 (1959). hydroxy acids. (2) Supported by grant No. CY-2919 from t h e National Cancer OPTICAL ROTATORY DISPERSION STUDIES. XXXI. ANOMALOUS DISPERSION CURVES O F DITHIOCARBAMATES OF a-AMINO ACIDS AND PEPTIDES. STEREOCHEMICAL CORRELATIONS BETWEEN Q-HYDROXY AND a-AMINO ACIDS2
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S Institute, National Institutes of Health, U. S. Public Health Service. ( 2 ) (a) C. Djerassi, “Optical Rotatory Dispersion: Applications OCSR‘ t o Organic Chemistry,” McGraw-Hill Book Co., New York, S . Y., HSCSR’ Chapters 5-14; (b) Sec. 15-4 by J. A. Schellman in ref. 3 a ; (c) Chapter R-CH-COLH R-CH-CO*H 17 by E. R. Blout in ref. 3a. (1) For nomenclature see C. Djerassi and W. Klyne. Puoc. Ckein. I I1 SOL.,5 5 (1957). ( 5 ) See A. Fredga, Szensh K e m . T i d . , 63,221 (1911); 54, 26 (1942). (7) L. Tschugaeff and A . Ogorodnikoff, 2. p h y s i k . Chern., 86, 481 (1913). and earlier papers; T. M. Lowry and H. Hudson, Phil. T r a n s . , (6) E.g., 5.8 mg. of L-(-)-proline afforded 2.2 mg. of recrystallized dithiocarbamate. 11182, 117 (1933).
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