Mössbauer effect of 129I in a sulfenyl iodide (RS129I)

Volume 45A, number 6

5 November 1973

PHYSICS LETTERS

M6SSBAUER

EFFECT

OF 12gI IN A SULFENYL

IODIDE

(RS’2gI)*

M.J. POTASEK Physics Department, University oflllinois at Urbana-Champaign, Urbana, Illinois 61801, USA Received 6 September 1973 We have used the Mdssbauer effect of 1291to study the sulfenyl iodide bond in N-p-Chlorophenyl-2-(benzyloxycarbonamido)_3-‘29iodothio-3-Methyl-butanamide. This compound has been proposed as a model for protein sulfenyl iodides. We believe that this is the first Mossbauer measurement of a sulfenyl iodide.

Recently, Field and White [l] prepared a stable sulfenyl iodide compound, N-pChlorophenyl-2(benzyloxycarbonamide)3-iodothio-3-Methylbutanamide (RSI) as a model for protein sulfenyl iodides. Sulfenyl iodides ari of considerable importance in biochemistry. Generally, iodine reacts with proteins by oxidizing the sulfhydryl groups or by substitution on the aromatic rings of tyrosine and histidine. Oxidation was believed to proceed to the disulfide level, and a sulfenyl iodide was postulated as an intermediate. Tobacco mosaic virus [2] and other proteins [3] were later found to form relatively stable sulfenyl iodides. There is also accumulating evidence that protein sulfenyl iodides play an important role in thyroid metabolism by serving as an intermediate in the iodination of tyrosine groups [4]. In the past, few attempts have been made to isolate the sulfenyl iodide moiety, and those that were isolated were only relatively stable in solution [S-9]. The solid compound of Field and White [l] (RSI) is stable

at ambient temperatures for ten weeks. Furthermore, it contains linkages that simulate the two peptide linkages in the vicinity of the sulfenyl iodide complex in proteins. Few physical studies have been made on sulfenyl iodides. Because of its sensitivity to small changes in the 12g1 electron density, the Mijssbauer effect of 12gI provides a powerful tool for investigating the sulfuriodine bond. Furthermore, comparison of the MBssbauer spectra of RS12gI and of a protein sulfenyl 12giodide will be a good indication of the former compound’s suitability as a model for protein sulfenyl iodides. RSl*gI was synthesized according to the method of Field and White [ 11. HSCMe2CH(NHCbz)CONHPh-p-Cl, (RSH), was a generous gift from Dr. Lamar Field. 100 mg of 1*912 in a solution of 5 ml CH2C12 was added * Work supported in part by the National Science Foundation under grant NSF GH 36966.

%

f

LO-

:.

k 8 \.

2.0I -15

I

-10

I

-5

.

I

I

I

I

0

5

IO

15

VELOCITY

hn/sec)

Fig. 1. The Mossbauer spectrum of N-p-Chlorophenyl-2-(benzyloxycarbonamidol-3-

129iodothio-3-MethyIbutanamide.

489

Volume

45A, number

PHYSICS

6

to a solution of 80 mg of recrystallized RSH (Anal. calcd. for RSH: C, 58.08;H, 5.39;found, C, 58.01; H, 5.79) in a mixture of 3 ml of CH,CI, and 1 ml of H,O. This mixture was stirred for 30 minutes at room temperature. The resulting solution was titrated with 0.1 N aqueous Na,S,O, until the aqueous layer just became colorless. The solution of RS1291 in CH,Cl, was washed several times with H20 and dried over anhydrous MgSO,. The CH Cl, was evaporated. The infrared spectrum of RS 13 vI agreed with that reported by Field and White [ 11. The standard Mossbauer transmission geometry was used for the measurements. During the experiment, both the source (Zn12vmTe) and the absorber were kept at a temperature of 4.2”K. The RS12vI absorber contained 5 mg/cm2 of 12vI. The well-resolved splitting in RS12vI, resulting from the nuclear quadrupole interaction, is shown in fig. 1. The smooth curve in fig. 1 was obtained by a computer least-squares fit of a theoretical nuclear quadrupole interaction to the data. The background, intensity, thickness broadening, quadru-. pole coupling constant (e24Q), asymmetry parameter (n), isomer shift relative to the source (6) the full width at half maximum (I’), and the ratio of the excited and the ground state nuclear quadrupole constant (Qe/Q,) were the parameters varied to obtain a minimum chi-square. The fitted parameters are: e*qQ = - (15 10 f 15) MHz, 6 = (0.4 1 + 0.02) mm/set, 17= 0.07.k 0.03, P = (0.82 f 0.04) mm/set, and Qe/Q, = 1.236 f 0.004. Using expressions from Greenwood and Gibb [lo], the isomer shift relative to a Zn12vTem source can be written as 6 = -8.2 h, t 4.5 h, - 3 UP - 0.54 (mm/set)

(1)

Here h, and h, are the number of 5s and 5p, electron holes in the 5~25~6 configuration, respectively, and UP = -e2qm,,Q/e2q,tQ

= 11 SO/ 1607 = 0.94.

(2)

Considering an admixture of 5p u and 71bonding, the number of holes in the 5p, and 5p,, orbitals can be ex-

5 November

LETTERS

pressed as h,=h,-Up(l+7)/3),andhy=h,-(/p(l-n/3).(3) The minimum value of h, (h, = 0.07) is obtained from eq. (1) with the additional conditions on hi, 0
References [l] L. Field and J.E. White, Proc. Nat. Acad. Sci. 70 (1973) 328. [2] H. Fraenker-Conrat, J. Biol. Chem. 217 (1955) 373. [3] L.W. Cunningham, Biochemistry 3 (1964) 1629. [4] L. Jirousek and E.T. Pritchard, Biochim. Biophys. Acta 243 (1971) 230. [5] H. Rheinboldt and E. Motzkus, Chem. Ber. 72B (1939) 657. 161 E. Field, J.L. VanHorne and L.W. Cunningham. J. Org. Chem. 35 (1970) 3267. 171 J.P. Danehy, C.P. Egan and J. Switalski, J. Org. Chem. 36 (1971) 2530. [8] E. Ciuffarin and G. Guaraldi, J. Org. Chem. 35 (1970) 2006. IV] A. Burawoy, F. Liversedge and C.E. Vellins, J. Chem.

sot. (1954) 4481.

[lo] N.N. Greenwood and T.C. Gibb, Mijssbauer spectroscopy (Chapman and Hall, London, 1971) pp. 465-468.

490

1973