X-Ray Structural Analysis and Vibrational Spectra of Sodium
Cysteine-S-sulfonate, +H3N C H (C 00 )CH2S20 3Na -3/2H 20 [1]
Ralf Steudel*, Angela Albertsen, Monika Kustos, and Joachim Pickardt
Institut für Anorganische und Analytische Chemie, Technische Universität Berlin, Sekr. C2,
D-W-1000 Berlin 12
Dedicated to Prof. Dr. Dr. Techn. h. c. Ulrich Wannagat on the occasion o f his 70th birthday
Z. Naturforsch. 48b, 555 —560 (1993); received July 23, 1992
Cysteine, S-Sulfonate, Structure, Spectra, Hydrogen Bonds
The title compound crystallizes orthorhombically (space group C222,) with a = 797.0, b =
870.3 and c = 2739.0 pm. The anions are zwitterions which are heavily involved in intra- and
intermolecular NH -- O and OH -O hydrogen bonding. The two types of sodium cations are
coordinated by six oxygen atoms each of which belongs to either S 0 3 groups (Na2) or water
molecules and S 0 3 groups (N al). A second type of water molecules is not coordinated to the
cations. The SS bond length is 208.2 pm. Infrared and Raman spectra of the title compound
are reported and tentatively assigned. The SS stretching vibration is observed at 409 cm-1.
Introduction
Cystine is an important constituent of most pro
teins. Its disulfide bond links parts of the amino
acid chains and is therefore responsible for the
three-dimensional structure of the protein. Reduc
tive or nucleophilic cleavage of the disulfide
bridges change the chemical and physical proper
ties of the proteins considerably. The two most
important nucleophiles in this context are sulfide
(S2_ and H S ) and sulfite (S 032") which react with
organic disulfides according to eq. (1) and (2)
[2-9]:
RSSR + HS“ RSS~ + RS" + H + (1)
RSSR + S 032- ^ R SS03- + RS" (2)
In the case of cysteine (bis-alanyl-disulfane) the
“persulfide” (RSS-) (alanyldisulfide) has been
found to undergo autoxidation in air; eq. (3) [10]:
RSS" + 3/2 0 2 -»* RSSCV (3)
1
The cysteine-S-sulfonate 1 is also formed on
treatment of cysteine with thiosulfate at pH ~ 7
[11]:
RSH + S20 32~ ^ RSSCV + HS" (4)
Small amounts of 1 are formed on UV irradia
tion of aqueous cysteine in the presence of air
* Reprint requests to Prof. Dr. R. Steudel.
Verlag der Zeitschrift für N aturforschung,
D-W-7400 Tübingen
0932-0776/93/0500-0555/$ 01.00/0
[12]. However, the most convenient preparation of
1 starts from cysteine and sodium tetrathionate
and results in pure crystals of composition
C3H6OsNS2Na • 3/2 H 20[13]:
RSH + S40 62- ->
RSSOj- + H + + other products (5)
In this work we report the Raman and infrared
spectra as well as the crystal and molecular struc
ture of H3N +C H (C 0 0 )C H 2S203Na- 3/2H20.
X-Ray Structural Analysis
A single crystal of 1 of dimensions 0.5 x 0.3 x 0.3
mm3 was grown from aqueous ethanol (70/30 v/v
C2H50 H /H 20 ) by cooling to 4 °C. Using an auto
mated CAD 4 diffractometer (2 &-co scan) 1880 re
flections were measured at 22 °C (0 < 2.9 < 55°) of
which 838 were classified as observed [I > 2cr(I)].
A summary of crystallographic data is given in
Tab. I.
The structure was solved by direct methods
(program SHELXS-86 [14]) and refined using the
program SHELXS-76 [15]. Lorentz and polariza
tion corrections were applied. All non-hydrogen
atoms were refined anisotropically. All the hydro
gen atoms of the anion of 1 could be localized
refined isotropically. The refinement resulted in
R = S(|IF0I-IFCI|)/S|F0| = 0.04. The fractional
coordinates, bond lengths, bond angles, and tor
sional angles are given in Tables II-V and the
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556 R. Steudel et al. ■ X-Ray Structural Analysis and Vibrational Spectra of Sodium Cysteine-S-sulfonate
Compound
Formula
Formula weight
Space group
Systemat. absences
a [pm]
b [pm]
c [pm]
V [nm3]
Density [gem’3], calculated
Molecules in unit cell (Z)
F(000), electrons
Radiation
lin. absorpt. coeff. n (M oKa) [cm '1]
H3NCH(COO)CH,SX>3Na • 1.5 HUO
C3H6NS20 5Na ■ 1.5 H20
250.2
C222
h0/(h = 2«+ 1), 00/(/ = 2n+\),h+k = 2 n + \,k = 2n+\
797.0(1)
870.3(8)
2739.0(1)
1.899
1.624
Table I. Summary
of crystallographic
data (standard de
viations in brack
ets).
952
M oK a (graphite-monochromated), k
5.7
71.07 pm
Table II. Fractional atomic coordinates for
H3N C H (C 00)C H 2S20 3Na ■ 1.5H20 . For numbering of
atoms see Fig. 2.
Atom x/a y/b z/c
SO) 0.1411(2) 0.2131(2) 0.3123(1)
S(2) 0.1888(3) 0.1766(2) 0.3861(1)
0(1)0.2466(7) 0.3375(6) 0.2963(2)
0(2) 0.1851(8) 0.0656(6) 0.2918(2)
0(3) -0.0344(7) 0.2549(8) 0.3078(2)
0(4) 0.2900(8) 0.6875(6) 0.4677(2)
0(5) 0.1211(8)0.7001(7) 0.4037(2)
N0.4196(8) 0.4159(8) 0.4426(2)
C(l) 0.1364(10) 0.3656(9) 0.4102(3)
C(2) 0.2854(10) 0.4772(8) 0.4107(3)
C(3) 0.2270(10) 0.6345(8) 0.4296(2)
N a(l) 0.5000(0) 0.3879(4) 0.2500(0)
Na(2) 0.0000(0) 0.4943(6) 0.7500(0)
H(l) 0.4700(8) 0.4800(8) 0.4490(2)
H(2) 0.4770(12) 0.3540(11) 0.4310(3)
H(3) 0.3360(13) 0.4900(11) 0.3670(3)
H(4) 0.6410(17) 0.3690(13) 0.0130(4)
H(5) 0.0880(8) 0.3400(7) 0.4440(2)
H(6) 0.0469(13) 0.4180(10) 0.3900(3)
0(6) 0.7064(0) 0.5000(0) 0.5000(0)
H(7) 0.7510(14) 0.4430(11) 0.4810(3)
H(8)0.7510(14) 0.5570(11) 0.5190(3)
0(7) 0.6112(6) 0.1877(6) 0.3017(2)
Table III. Interatomic distances [pm] in
H3N C H (C 00)C H 2S203N a -1.5 H20 (standard devia
tions in brackets).
Bonds Distances Bonds Distances
S(l)-S (2) 208.2(4) S (l)-0 (1 ) 143.9(6)
S (l)-0 (2 ) 144.5(6) S (l)—0(3) 145.1(6)
S(2)-C (l) 181.9(8) C (l)-C (2 ) 153.4(11)
C(2)-C(3) 153.6(10) N -C (2 ) 148.0(10)
0(4)-C (3) 124.7(8) 0 (5 )—C(3) 124.2(9)
C (l)-H (5) 103(6) C (l)-H (6)101(9)
C (2)-H (3) 127(9) N -H ( l) 71(7)
N -H (2) 78(9) N —H(4) 137(11)
N a (l)-0 (1 ) 242.5(6)
S (2 )-S (l)—0(1) 107.7(3) S (2 )-S (l)-0 (2 ) 101.4(3)
S (2 )-S (l)-0 (3 ) 107.3(3) 0(1) —S ( l) - 0(2)114.1(3)
0(1 )-S (1 ) —0(3) 110.4(4) 0(2) —S (l)—0(3) 115.1(4)
S(l) —0 (1 )—N a(l) 141.5(3) S (l)-S (2 )-C (l) 99.8(3)
S (2)-C (l)-C (2 ) 113.5(5) C (l)-C (2 )-C (3 ) 109.5(6)
C (2 )-C (3 )-0 (4 ) 119.3(7) C (2 )-C (3 )-0 (5 ) 115.0(6)
0 (4 )-C (3 )-0 (5 ) 125.6(7) C (l)-C (2 )-N 109.7(6)
N -C (2)-C (3) 109.9(6) C (2 )-N -H (l) 106.0(50)
C (2 )-N -H (2 ) 116.0(60) C (2 )-N -H (4 ) 111.0
H (l)-N -H (2 ) 108.0(90) H (l)-N -H (4 ) 102.0
H (2 )-N -H (4 ) 110.0 S (2 )-C (l)-H (5 ) 102.0(30)
S (2)-C (l)-H (6 ) 112.0(50) C (2 )-C (l)-H (5 ) 115.0(30)
C (2)-C (l)-H (6 ) 106.0(50) N -C (2 )-H (3 ) 111.0(50)
H (5)-C (l)-H (6 ) 109.0(60) C (3)-C (2)-H (3) 110.0(40)
C (l)-C (2 )-H (3 ) 107.0(40)
Table IV. Selected bond angles [deg] of
H3N C H (C 00)C H 2S20 3Na • 1.5H20 .
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R. Steudel et al. • X-Ray Structural Analysis and V ibrational Spectra of Sodium Cysteine-S-sulfonate 557
0 (1 )-S (1 )-S (2 )-C (1 ) 58.7(4)
0 (2 )-S (l)-S (2 ) -C (l) 178.8(4)
0 (2 ) -S ( l) -0 ( l)- N a ( l) - 7.6(6)
C (2 )-C (l)-S (2 )-S (l) - 89.2(6)
S (2 )-C (l)-C (2)-C (3 ) 177.9(5)
C(1 )-C (2 )-C (3 )-0 (5 ) - 63.4(8)
N -C (2 )-C (3 )-0 (5 ) 176.0(6)
0 (3 )-S (l)- S (2 )-C (l) - 60.2(4)
S (2 )-S (l)-0 (1 )-N a (l) 104.2(5)
0 (3 )—S (l)-0 (1 )-N a (l) -138.9(5)
S (2 )-C (l)-C (2 )-N - 61.4(7)
C (l)-C (2 )-C (3 )-0 (4 ) 118.5(8)
N —C (2)-C (3)—0(4) - 2.1(9)
Table V. Selected dihedral angles [deg]
of H3NCH (C 00)C H 2S20 3Na • 1.5 H20 .
crystal and molecular structure is shown in Fig. 1
and 2*.
The sodium cations are located on special posi
tions; there are two half cations per anion which
Fig. 1. Unit cell of H3N C H (C 00)C H 2S203Na- 1.5H20 .
Blank circles are oxygen atom of water molecules,
crossed circles are sodium cations.
03
Fig. 2. Molecular structure of the L-cysteine-S-sulfonate
anion and numbering of atoms.
* Further details of the crystal structure analysis may be
requested from Fachinformationszentrum Karlsruhe,
Gesellschaft für wissenschaftlich-technische Informa
tion mbH, D-W-7514 Eggenstein-Leopoldshafen 2,
citing the deposition number CSD 56521, the authors
and the journal source.
have different coordination spheres as will be dis
cussed below.
The anion of 1 is a zwitterion of C, symmetry
with the amino group protonated and the carboxyl
group deprotonated (see Fig. 2). The same situa
tion has been observed for L-cysteine [16, 17]. The
chain-like anion is of helical structure: the torsion
al angles S -S - C - C and S - C -C - N amount to
-89° and -61°, respectively. The carboxyl group
is practically coplanar with the neighboring CN
unit (dihedral angles N - C 2 - C 3 - 0 4 = 2.1° and
N -C 2 - C 3 - 0 5 = 176.0°). The positions of the
hydrogen atoms of 1 could only approximately be
determined and therefore the CH, NH and OH
bond distances are found in the large range of
70-137 pm. Nevertheless, quite a number of intra-
and intermolecular hydrogen bonds could be iden
tified which certainly will contribute to the overall
conformation of the anion. The strongest intramo
lecular hydrogen bond connects the NH3+ and
COO- groups. The distance HI •••04 is only
236 pm (van der Waals distance 270 pm) while the
distance H4 - 0 4 is 288 pm. The H1---04 inter
action may be responsible for the almost coplanar
arrangement of atoms N, C2, C3, 0 4 which min
imizes the N - 0 4 distance. There are also relative
ly close contacts between the oxygen atoms of the
sulfonate group and some of the hydrogen atoms
linked to C2 and Cl (e.g., H3 -Ol = 247 pm).
Most important are the hydrogen bonds be
tween neighboring anions and between the struc
tural water molecules (H 7 -0 6 -H 8 ) and the an
ions. Fig. 1 shows that neighboring anions are
linked both by cations and by C 3 - 0 4 - H 4 - N
bridges. The intermolecular H 4 - 0 4 distance is
only 144 pm and the N - H 4 -0 4 angle amounts
to 177°. The distance N •0 4 is 267 pm, a value
very similar to the values observed in amino acids
and small peptides. There are two such inter
actions between each pair of neighboring anions.
Although the positions of H atoms cannot be de
termined very accurately by X-ray diffraction, the
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558 R. Steudel et al. ■ X-Ray Structural Analysis and Vibrational Spectra of Sodium Cysteine-S-sulfonate
geometrical parameters just mentioned together
with the bond distance N -H 4 of 137 pm show
that strong N -H -O bridges are present.
The second carboxylic oxygen atom (O 5) is also
envolved in intermolecular hydrogen bonding
since the distance N - H 2 - 0 5 amounts to
192 pm. With other words, each N H 3 group is tri
ply hydrogen bridged: vw Hl to the intramolecular
0 4 , via H 2 to an intermolecular 0 5 and via H4 to
0 4 of a neighboring molecule. The strength of
these bridge bonds increases in that order. Since
H4 is 137 pm apart from its nitrogen neighbor but
144 pm from its oxygen bridge head, a small shift
of H 4 towards the oxygen atom would transform
the zwitterion into a normal monoanion with
-N H 2 and -C O O H groups. A similar three-di
mensional intermolecular network of hydrogen
bonds has been observed for L-cysteine [17].
The structural water molecules H 7 -0 6 - H 8
are located on special positions (mirror planes)
and are hydrogen bonded to four different anions
as shown in Fig. 3. The distances N - H 1 - 0 6 of
235 pm and O 6 - H 7 • • • O 4 of 228 pm indicate rela
tively weak hydrogen bonds; the coordination of
0 6 is a distorted tetrahedron. There is one such
H20 molecule per two anions.
Despite the low degree of symmetry in the anion
the carboxyl group shows two equal C -O dis
tances of 124.5 pm; the O -C -O angle amounts to
125.6°. The bond angles at the nitrogen atom are
in the range of 106-116°. The thiosulfate group
exhibits the expected distorted tetrahedral struc
ture with an average S -O bond length of 144.5 pm
and an S -S distance of 208.2 pm. For compari
son, the S~S bond length of 2-aminoethane-
thiosulfuric acid, +H 3N -C 2H4- S 20 3~ [18], has
Fig. 3. Pseudo-tetrahedral coordination of the structur
al water molecules which are located on mirror planes.
been determined as 205.4 pm. This zwitterionic
compound is also heavily envolved in intra- and
intermolecular hydrogen bonding. In the case of
L-cysteine the S -S bond length is 203.2 pm (hex
agonal form) [19] and 204.3 pm (tetragonal form)
[20], respectively. The CC, CS, CN and CO bond
length are all very close to the values reported for
L-cysteine [17].
The sulfonate groups of neighboring anions of 1
are bridged by sodium cations (see Fig. 1). There
are two types of cations: type 1 (N a2) is coordinat
ed by six oxygen atoms belonging to four different
anions, and type 2 (Nal) is coordinated by two
water molecules and four oxygen atoms (Ol or
0 2 ) of four different anions. The hydrogen atoms
of these two water molecules could not be located.
The distances N a 2 -0 are in the range 270-
280 pm and the angles 0 - N a 2 - 0 are ranging
from 51-159°. This coordination, although of Cs
symmetry, is far from being octahedral. The same
holds for the coordination sphere of N al. The dis
tances N a l-O are in the narrow range of 141 —
142 pm. A second type of water molecules is locat
ed on a special position (H 7 - 0 6 - H 8) and not
coordinated to any cation. Since only one such
H20 molecule is present per 2 formula units, the
overall water content is 1.5 H20 per formula.
Vibrational Spectra
In Table VI the results of the infrared and Ra
man spectroscopic investigation of solid 1 are list
ed. The IR and Raman spectra are both highly
characteristic and may be used to identify the com
pound. The vibrational assignment given in Ta
ble VI is tentative and based on the accurate as
signments of the spectra of L-cysteine [21] and
various ionic thiosulfates [22, 23], polythionates
[24] as well as the hydrogenthiosulfate ion HS20 3~
[23]. The most intense Raman line at 409 cm-1 is
assigned to the SS stretching vibration which has
been observed at 403 cm 1 in HS20 3~ [23] and near
390 cm“ 1 in polythionates [24], Of very high Ra
man and infrared intensity is the symmetrical
stretching mode of the S 03 group near 1045 cm-1,
whereas the asymmetrical S 03 stretch at 1218 cm-1
gives rise to a strong IR but weak Raman band.
With 48 vibrational degrees of freedom of the
anion and 8 molecules in the unit cell the spectrum
of 1 is too complex for any detailed analysis unless
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R. Steudel et al. • X-Ray Structural Analysis and Vibrational Spectra of Sodium Cysteine-S-sulfonate 559
Table VI. Raman and infrared spectra of solid
H3N C H (C 00)C H 2S20 3Na 1.5H20 at 20 °C (wave-
numbers in cm-1; Raman intensities in brackets; abbrev.:
vs = very strong, s = strong, m = medium, w = weak,
vw = very weak, sh = shoulder, v = stretching, S = bend
ing, q = rocking, y = wagging, x = torsion).
Raman Infrared Assignment
53(46)
64(39)
88(29)
111(37) see s
140 (sh)
153 (25)
188 (sh)
205(34) rCOCT
219(34) ssso
235(14) sssc
309 (29)
328(1) 322 w ss so3
363(31) 362 m
409(100) 408 vw vSS
428 (sh) 426 w
473(16) 460 w, b tNH 3
535(8) 532 vw ■S,sS 0 3
550(8) 554 sh
565(8) 566 m <5CCO
651 (sh) 636 s sc ocr
660(19) vCS
687(10) 686 vw
807(7) 808 w
832(13) 832 w yCOCT
924(10) 922 w 0NH3
943(7) 942 m
1049 (40) 1038 vs vsS 03
1075(6) 1075 vw
1102(6)1102 w
1134(6) 1132 w
1136 sh
■ öNH3
1214(6)
1245 (9)
1218 vs
1236 s • vasS 0 3+yCH2
1308(6) 1306 w
1352 w
1350(12) 1360 m -s SC H
1400(9) 1400 s <sch2
1416(8) 1415 w
1528 s <5sNH3
1570 w <5asNH3
1610 sh S H20
1632 vs VasCOO-
2030 w, b vN -H 4
2420 vw, b
2500 vw, b combination
2620 vw, b ■ and
2760 vw, b overtones
2812(8, b)
2920 (29)
2964(10)
2925 vw
2960 w, b • vCH and CH2
2979(10) 2980 w, b vN -H 2
3222 (6, b) 3220 m vN -H 1
3440 (6, b) 3440 w vsH20
3537(5, b) 3540 m vasH20
isotopic substitution is carried out. Therefore, a
simple deuteration experiment was carried out by
recrystallization of 1 from D20 which exchanges
the labile H atoms linked to either oxygen or nitro
gen for D. The infrared spectrum of the deuterated
product showed that the following absorptions of
1 had shifted to lower wavenumbers: 3540, 3440,
3220, 2980, 2030, 1610, 1570, 1528, 1132, 1102,
942, 922, and 460 cm“1. Therefore, these bands
have been assigned as shown in Table VI. Some of
the bending and rocking modes of the -N H 3
group occur as two neighboring bands of unequal
intensity.
Discussion
This work confirms the chemical composition of
1 which originally was given with 1.5 H20 per for
mula unit [5] while later authors used a formula
with 2 H20 per sodium atom [13]. Surprisingly,
there are two types of H20 molecules and two
types of sodium cations but only one type of an
ions in the structure of 1, which is three-dimen-
sionally linked by a network of NH -O and
0H - -0 hydrogen bonds. These bridging bonds
not only show up in the close contacts of the corre
sponding atoms but also in the vibrational spectra:
the NH stretching vibrations of the -N H 3+ group
are partly observed at lower wavenumbers (3220-
2812 cm-1) than the corresponding vibrations of
L-cysteine (3166-3064 cm-1 [14]). In addition to
the intermolecular hydrogen bonds there are also
strong intraanionic NH -O interactions. This
complex network of hydrogen bonds is probably
responsible for the torsional angles at the various
comparable CC axes which are very different in 1,
in orthorhombic L-cysteine [17] and in the two in
dependent molecules of monoclinic L-cysteine
[16], For example, the torsional angle S - C - C —C
amounts to 178° in 1, -17° in orthorhombic
L-cysteine, and -51° and 68° in monoclinic
L-cysteine. Similarly, the angles S -C - C - N vary
between -170° and 73°.
Experimental
1 was prepared as colorless crystals according to
ref. [13].
Analytical data:
Calcd C 14.4 H 3.6 N 5.6 S 25.6%,
Found C 14.2 H 3.7 N 5.4 S 25.5%.
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560
_________
R. Steudel et al. ■ X-Ray Structural Analysis and Vibrational Spectra of Sodium Cysteine-S-sulfonate
The spectroscopic equipment used has been de
scribed earlier [24, 25], IR spectra were recorded of
KBr discs.
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Financial support by the Deutsche Forschungs
gemeinschaft and the Verband der Chemischen In
dustrie is gratefully acknowledged.
[14] G. M. Sheldrick, SHELXS-86, Universität Göttin
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[15] G. M. Sheldrick, SHELXS-76, Universität Cam
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