Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536802013442/cv6127sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536802013442/cv6127Isup2.hkl |
CCDC reference: 197461
Compound (I) was synthesized by a modified literature method (Kalopissis & Manousses, 1975). A solution of 5.35 g (0.0025 mol) of trans-1,4-dibromo-2-butene in 5 ml e thanol was added dropwise to a mixture of 0.88 g (0.005 mol) of L-cysteine hydrochloride monohydrate, 1 ml of 10 mol l−1 sodium hydroxide, 5 ml of water and 7.5 ml of ethanol. After that, the reaction mixture was stirred for 10 h at room temperature. The precipitate was filtered off and recrystallized from water. Needle-like colorless crystal were obtained (yield 68%; m.p. 513–515 K (decomposition)]; IR (KBr): 3479 (b), 3024 (b), 2924 (s), 1687 (w), 1613 (versus, b), 1483 (s), 1419 (s), 1393 (s), 1342 (s), 1303 (s), 1069 (w), 1045 (w), 966 (versus) cm−1; 1H NMR (D2O): δ 5.65 (2H, bs), 4.17 (2H, t), 3.23 (4H, bs), 3.14 (2H, d), 3.00 (2H, dd) p.p.m. 10 mg of (I) was dissolved in 10 ml hot distilled water and, after filtration, the solution was kept at room temperature for 10 d yielding colorless single crystals of (I) suitable for X-ray analysis.
The water atoms H1–H4 were located on a difference Fourier map and refined using constraints.
Data collection: SMART (Bruker, 1997); cell refinement: SMART); data reduction: SAINT (Bruker, 1997) and SHELXTL (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.
C10H22N2O6S2 | F(000) = 352 |
Mr = 330.42 | Dx = 1.453 Mg m−3 |
Monoclinic, P21 | Mo Kα radiation, λ = 0.71073 Å |
a = 11.672 (4) Å | Cell parameters from 1870 reflections |
b = 5.3982 (19) Å | θ = 2.7–23.1° |
c = 12.413 (4) Å | µ = 0.38 mm−1 |
β = 105.020 (5)° | T = 293 K |
V = 755.4 (4) Å3 | Prism, colourless |
Z = 2 | 0.30 × 0.15 × 0.10 mm |
Bruker CCD area-detector diffractometer | 2338 independent reflections |
Radiation source: fine-focus sealed tube | 1894 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.032 |
ϕ and ω scans | θmax = 25.0°, θmin = 2.1° |
Absorption correction: multi-scan (SADABS; Bruker, 1997) | h = −13→8 |
Tmin = 0.895, Tmax = 0.963 | k = −5→6 |
3157 measured reflections | l = −13→14 |
Refinement on F2 | H atoms treated by a mixture of independent and constrained refinement |
Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.04P)2] where P = (Fo2 + 2Fc2)/3 |
R[F2 > 2σ(F2)] = 0.041 | (Δ/σ)max = 0.026 |
wR(F2) = 0.089 | Δρmax = 0.22 e Å−3 |
S = 1.03 | Δρmin = −0.29 e Å−3 |
2338 reflections | Absolute structure: (Flack, 1983) |
197 parameters | Absolute structure parameter: 0.06 (10) |
5 restraints |
C10H22N2O6S2 | V = 755.4 (4) Å3 |
Mr = 330.42 | Z = 2 |
Monoclinic, P21 | Mo Kα radiation |
a = 11.672 (4) Å | µ = 0.38 mm−1 |
b = 5.3982 (19) Å | T = 293 K |
c = 12.413 (4) Å | 0.30 × 0.15 × 0.10 mm |
β = 105.020 (5)° |
Bruker CCD area-detector diffractometer | 2338 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 1997) | 1894 reflections with I > 2σ(I) |
Tmin = 0.895, Tmax = 0.963 | Rint = 0.032 |
3157 measured reflections |
R[F2 > 2σ(F2)] = 0.041 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.089 | Δρmax = 0.22 e Å−3 |
S = 1.03 | Δρmin = −0.29 e Å−3 |
2338 reflections | Absolute structure: (Flack, 1983) |
197 parameters | Absolute structure parameter: 0.06 (10) |
5 restraints |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
S1 | 0.98558 (8) | 0.4300 (2) | 1.10310 (7) | 0.0328 (3) | |
S2 | 0.45673 (9) | 0.1031 (2) | 0.85490 (8) | 0.0422 (3) | |
O1 | 0.6590 (3) | 0.2498 (7) | 0.6583 (2) | 0.0616 (10) | |
O2 | 0.5305 (3) | −0.0490 (7) | 0.5978 (3) | 0.0590 (9) | |
O3 | 0.8327 (3) | −0.1955 (6) | 1.2887 (2) | 0.0494 (8) | |
O4 | 1.0023 (2) | −0.1342 (5) | 1.4161 (2) | 0.0431 (8) | |
N1 | 0.3428 (3) | 0.2090 (7) | 0.5987 (2) | 0.0440 (9) | |
H1A | 0.2838 | 0.3031 | 0.6086 | 0.066* | |
H1B | 0.3398 | 0.0613 | 0.6298 | 0.066* | |
H1C | 0.3359 | 0.1902 | 0.5261 | 0.066* | |
N2 | 1.0210 (3) | 0.3356 (6) | 1.3602 (2) | 0.0344 (8) | |
H2B | 1.0007 | 0.3545 | 1.4240 | 0.052* | |
H2C | 1.0254 | 0.4834 | 1.3298 | 0.052* | |
H2D | 1.0913 | 0.2608 | 1.3735 | 0.052* | |
C1 | 0.5569 (4) | 0.1601 (10) | 0.6329 (3) | 0.0414 (12) | |
C2 | 0.4582 (3) | 0.3297 (8) | 0.6518 (3) | 0.0326 (9) | |
H2A | 0.4622 | 0.4892 | 0.6153 | 0.039* | |
C3 | 0.4690 (3) | 0.3735 (8) | 0.7745 (3) | 0.0369 (11) | |
H3A | 0.4079 | 0.4901 | 0.7811 | 0.044* | |
H3B | 0.5451 | 0.4508 | 0.8071 | 0.044* | |
C4 | 0.6099 (3) | 0.0045 (8) | 0.9034 (3) | 0.0387 (11) | |
H4A | 0.6131 | −0.1543 | 0.9406 | 0.046* | |
H4B | 0.6430 | −0.0166 | 0.8399 | 0.046* | |
C5 | 0.6824 (3) | 0.1883 (8) | 0.9819 (3) | 0.0348 (10) | |
H5A | 0.6677 | 0.2036 | 1.0517 | 0.042* | |
C6 | 0.7645 (3) | 0.3291 (8) | 0.9611 (3) | 0.0332 (10) | |
H6A | 0.7823 | 0.3120 | 0.8926 | 0.040* | |
C7 | 0.8319 (3) | 0.5170 (8) | 1.0413 (3) | 0.0357 (10) | |
H7A | 0.7925 | 0.5408 | 1.1004 | 0.043* | |
H7B | 0.8302 | 0.6738 | 1.0028 | 0.043* | |
C8 | 0.9649 (3) | 0.1480 (7) | 1.1733 (3) | 0.0282 (9) | |
H8A | 0.9037 | 0.0508 | 1.1233 | 0.034* | |
H8B | 1.0379 | 0.0531 | 1.1881 | 0.034* | |
C9 | 0.9306 (3) | 0.1825 (7) | 1.2825 (3) | 0.0266 (8) | |
H9A | 0.8539 | 0.2673 | 1.2674 | 0.032* | |
C10 | 0.9195 (3) | −0.0686 (9) | 1.3333 (3) | 0.0317 (9) | |
O5 | 0.2479 (3) | 0.2084 (8) | 0.3453 (3) | 0.0740 (11) | |
O6 | 0.7661 (3) | 0.2056 (7) | 0.4830 (3) | 0.0572 (9) | |
H4 | 0.8416 (16) | 0.266 (7) | 0.512 (3) | 0.038 (11)* | |
H3 | 0.728 (4) | 0.178 (12) | 0.539 (3) | 0.099* | |
H2 | 0.297 (3) | 0.345 (5) | 0.351 (4) | 0.063* | |
H1 | 0.277 (4) | 0.051 (4) | 0.340 (4) | 0.066* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.0318 (6) | 0.0388 (6) | 0.0288 (5) | −0.0032 (5) | 0.0096 (4) | 0.0045 (5) |
S2 | 0.0360 (6) | 0.0594 (8) | 0.0322 (6) | −0.0110 (6) | 0.0109 (4) | 0.0029 (6) |
O1 | 0.0337 (18) | 0.099 (3) | 0.058 (2) | 0.0064 (17) | 0.0206 (14) | 0.0044 (19) |
O2 | 0.067 (2) | 0.052 (2) | 0.063 (2) | 0.0183 (19) | 0.0257 (16) | −0.009 (2) |
O3 | 0.060 (2) | 0.045 (2) | 0.0472 (18) | −0.0201 (16) | 0.0211 (15) | −0.0082 (16) |
O4 | 0.0511 (18) | 0.040 (2) | 0.0407 (16) | 0.0058 (14) | 0.0159 (14) | 0.0122 (14) |
N1 | 0.040 (2) | 0.059 (3) | 0.0305 (17) | 0.0137 (18) | 0.0058 (15) | −0.0003 (18) |
N2 | 0.052 (2) | 0.026 (2) | 0.0259 (17) | −0.0014 (16) | 0.0129 (15) | −0.0032 (15) |
C1 | 0.042 (3) | 0.061 (4) | 0.026 (2) | 0.020 (3) | 0.0178 (19) | 0.013 (2) |
C2 | 0.029 (2) | 0.037 (3) | 0.033 (2) | 0.0042 (18) | 0.0106 (17) | 0.0027 (19) |
C3 | 0.035 (2) | 0.040 (3) | 0.035 (2) | 0.0093 (19) | 0.0090 (17) | −0.008 (2) |
C4 | 0.048 (3) | 0.040 (3) | 0.028 (2) | −0.003 (2) | 0.0088 (18) | 0.001 (2) |
C5 | 0.038 (2) | 0.043 (3) | 0.0222 (19) | 0.001 (2) | 0.0049 (16) | −0.001 (2) |
C6 | 0.038 (2) | 0.038 (3) | 0.024 (2) | 0.006 (2) | 0.0082 (17) | 0.0041 (19) |
C7 | 0.037 (2) | 0.034 (3) | 0.035 (2) | −0.0011 (18) | 0.0061 (17) | 0.0037 (19) |
C8 | 0.034 (2) | 0.031 (3) | 0.0194 (18) | 0.0010 (18) | 0.0053 (15) | 0.0005 (18) |
C9 | 0.027 (2) | 0.025 (2) | 0.0286 (19) | 0.0030 (16) | 0.0087 (15) | 0.0012 (17) |
C10 | 0.040 (2) | 0.030 (2) | 0.033 (2) | 0.004 (2) | 0.0224 (18) | −0.002 (2) |
O5 | 0.056 (2) | 0.064 (3) | 0.110 (3) | −0.0246 (19) | 0.037 (2) | −0.011 (3) |
O6 | 0.043 (2) | 0.076 (3) | 0.0567 (19) | −0.0064 (18) | 0.0217 (15) | −0.0144 (19) |
S1—C8 | 1.801 (4) | C3—H3B | 0.9700 |
S1—C7 | 1.821 (4) | C4—C5 | 1.491 (5) |
S2—C3 | 1.794 (4) | C4—H4A | 0.9700 |
S2—C4 | 1.812 (4) | C4—H4B | 0.9700 |
O1—C1 | 1.249 (5) | C5—C6 | 1.301 (5) |
O2—C1 | 1.220 (6) | C5—H5A | 0.9300 |
O3—C10 | 1.229 (5) | C6—C7 | 1.494 (5) |
O4—C10 | 1.265 (4) | C6—H6A | 0.9300 |
N1—C2 | 1.487 (5) | C7—H7A | 0.9700 |
N1—H1A | 0.8900 | C7—H7B | 0.9700 |
N1—H1B | 0.8900 | C8—C9 | 1.522 (4) |
N1—H1C | 0.8900 | C8—H8A | 0.9700 |
N2—C9 | 1.483 (5) | C8—H8B | 0.9700 |
N2—H2B | 0.8900 | C9—C10 | 1.514 (6) |
N2—H2C | 0.8900 | C9—H9A | 0.9800 |
N2—H2D | 0.8900 | O5—H2 | 0.93 (3) |
C1—C2 | 1.536 (6) | O5—H1 | 0.92 (3) |
C2—C3 | 1.514 (5) | O6—H4 | 0.92 (3) |
C2—H2A | 0.9800 | O6—H3 | 0.93 (4) |
C3—H3A | 0.9700 | ||
C8—S1—C7 | 100.41 (18) | C5—C4—H4B | 109.3 |
C3—S2—C4 | 102.09 (18) | S2—C4—H4B | 109.3 |
C2—N1—H1A | 109.5 | H4A—C4—H4B | 108.0 |
C2—N1—H1B | 109.5 | C6—C5—C4 | 125.6 (3) |
H1A—N1—H1B | 109.5 | C6—C5—H5A | 117.2 |
C2—N1—H1C | 109.5 | C4—C5—H5A | 117.2 |
H1A—N1—H1C | 109.5 | C5—C6—C7 | 123.5 (3) |
H1B—N1—H1C | 109.5 | C5—C6—H6A | 118.3 |
C9—N2—H2B | 109.5 | C7—C6—H6A | 118.3 |
C9—N2—H2C | 109.5 | C6—C7—S1 | 113.4 (3) |
H2B—N2—H2C | 109.5 | C6—C7—H7A | 108.9 |
C9—N2—H2D | 109.5 | S1—C7—H7A | 108.9 |
H2B—N2—H2D | 109.5 | C6—C7—H7B | 108.9 |
H2C—N2—H2D | 109.5 | S1—C7—H7B | 108.9 |
O2—C1—O1 | 125.8 (4) | H7A—C7—H7B | 107.7 |
O2—C1—C2 | 118.4 (4) | C9—C8—S1 | 115.3 (3) |
O1—C1—C2 | 115.7 (5) | C9—C8—H8A | 108.5 |
N1—C2—C3 | 110.1 (3) | S1—C8—H8A | 108.5 |
N1—C2—C1 | 107.4 (4) | C9—C8—H8B | 108.5 |
C3—C2—C1 | 112.1 (3) | S1—C8—H8B | 108.5 |
N1—C2—H2A | 109.0 | H8A—C8—H8B | 107.5 |
C3—C2—H2A | 109.0 | N2—C9—C10 | 110.6 (3) |
C1—C2—H2A | 109.0 | N2—C9—C8 | 109.9 (3) |
C2—C3—S2 | 115.8 (3) | C10—C9—C8 | 109.4 (3) |
C2—C3—H3A | 108.3 | N2—C9—H9A | 109.0 |
S2—C3—H3A | 108.3 | C10—C9—H9A | 109.0 |
C2—C3—H3B | 108.3 | C8—C9—H9A | 109.0 |
S2—C3—H3B | 108.3 | O3—C10—O4 | 125.2 (4) |
H3A—C3—H3B | 107.4 | O3—C10—C9 | 117.4 (3) |
C5—C4—S2 | 111.4 (3) | O4—C10—C9 | 117.3 (4) |
C5—C4—H4A | 109.3 | H2—O5—H1 | 121 (4) |
S2—C4—H4A | 109.3 | H4—O6—H3 | 111 (4) |
O2—C1—C2—N1 | −11.6 (5) | C5—C6—C7—S1 | 108.5 (4) |
O1—C1—C2—N1 | 170.3 (3) | C8—S1—C7—C6 | −61.1 (3) |
O2—C1—C2—C3 | 109.5 (4) | C7—S1—C8—C9 | −77.6 (3) |
O1—C1—C2—C3 | −68.6 (5) | S1—C8—C9—N2 | −56.9 (3) |
N1—C2—C3—S2 | 57.6 (4) | S1—C8—C9—C10 | −178.5 (3) |
C1—C2—C3—S2 | −61.9 (4) | N2—C9—C10—O3 | 165.9 (3) |
C4—S2—C3—C2 | 91.0 (3) | C8—C9—C10—O3 | −72.9 (4) |
C3—S2—C4—C5 | 66.2 (3) | N2—C9—C10—O4 | −16.4 (4) |
S2—C4—C5—C6 | −110.4 (4) | C8—C9—C10—O4 | 104.9 (4) |
C4—C5—C6—C7 | 177.8 (4) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1C···O5 | 0.89 | 2.22 | 3.053 (5) | 157 |
O6—H3···O1 | 0.93 (4) | 1.90 (3) | 2.787 (4) | 159 (6) |
N2—H2D···O5i | 0.89 | 1.97 | 2.788 (5) | 152 |
N2—H2B···O4ii | 0.89 | 1.99 | 2.864 (4) | 165 |
O6—H4···O4iii | 0.92 (3) | 1.89 (3) | 2.805 (4) | 174 (4) |
O5—H2···O2iv | 0.93 (3) | 2.03 (3) | 2.821 (5) | 142 (4) |
O5—H2···O1iv | 0.93 (3) | 2.26 (2) | 3.122 (5) | 156 (4) |
O5—H1···O1v | 0.92 (3) | 1.80 (2) | 2.709 (5) | 175 (5) |
Symmetry codes: (i) x+1, y, z+1; (ii) −x+2, y+1/2, −z+3; (iii) −x+2, y+1/2, −z+2; (iv) −x+1, y+1/2, −z+1; (v) −x+1, y−1/2, −z+1. |
Experimental details
Crystal data | |
Chemical formula | C10H22N2O6S2 |
Mr | 330.42 |
Crystal system, space group | Monoclinic, P21 |
Temperature (K) | 293 |
a, b, c (Å) | 11.672 (4), 5.3982 (19), 12.413 (4) |
β (°) | 105.020 (5) |
V (Å3) | 755.4 (4) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.38 |
Crystal size (mm) | 0.30 × 0.15 × 0.10 |
Data collection | |
Diffractometer | Bruker CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 1997) |
Tmin, Tmax | 0.895, 0.963 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3157, 2338, 1894 |
Rint | 0.032 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.041, 0.089, 1.03 |
No. of reflections | 2338 |
No. of parameters | 197 |
No. of restraints | 5 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.22, −0.29 |
Absolute structure | (Flack, 1983) |
Absolute structure parameter | 0.06 (10) |
Computer programs: SMART (Bruker, 1997), SMART), SAINT (Bruker, 1997) and SHELXTL (Bruker, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL.
N1—C2 | 1.487 (5) | C4—C5 | 1.491 (5) |
N2—C9 | 1.483 (5) | C6—C7 | 1.494 (5) |
C1—C2 | 1.536 (6) | C8—C9 | 1.522 (4) |
C2—C3 | 1.514 (5) | C9—C10 | 1.514 (6) |
O2—C1—O1 | 125.8 (4) | C5—C6—C7 | 123.5 (3) |
O2—C1—C2 | 118.4 (4) | C9—C8—S1 | 115.3 (3) |
O1—C1—C2 | 115.7 (5) | N2—C9—C10 | 110.6 (3) |
N1—C2—C3 | 110.1 (3) | N2—C9—C8 | 109.9 (3) |
N1—C2—C1 | 107.4 (4) | C10—C9—C8 | 109.4 (3) |
C3—C2—C1 | 112.1 (3) | O3—C10—O4 | 125.2 (4) |
C2—C3—S2 | 115.8 (3) | O3—C10—C9 | 117.4 (3) |
C6—C5—C4 | 125.6 (3) | O4—C10—C9 | 117.3 (4) |
O2—C1—C2—N1 | −11.6 (5) | C8—S1—C7—C6 | −61.1 (3) |
O1—C1—C2—N1 | 170.3 (3) | C7—S1—C8—C9 | −77.6 (3) |
O2—C1—C2—C3 | 109.5 (4) | S1—C8—C9—N2 | −56.9 (3) |
O1—C1—C2—C3 | −68.6 (5) | N2—C9—C10—O3 | 165.9 (3) |
C4—S2—C3—C2 | 91.0 (3) | C8—C9—C10—O3 | −72.9 (4) |
C3—S2—C4—C5 | 66.2 (3) | N2—C9—C10—O4 | −16.4 (4) |
S2—C4—C5—C6 | −110.4 (4) | C8—C9—C10—O4 | 104.9 (4) |
C5—C6—C7—S1 | 108.5 (4) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1C···O5 | 0.89 | 2.22 | 3.053 (5) | 157 |
O6—H3···O1 | 0.93 (4) | 1.90 (3) | 2.787 (4) | 159 (6) |
N2—H2D···O5i | 0.89 | 1.97 | 2.788 (5) | 152 |
N2—H2B···O4ii | 0.89 | 1.99 | 2.864 (4) | 165 |
O6—H4···O4iii | 0.92 (3) | 1.89 (3) | 2.805 (4) | 174 (4) |
O5—H2···O2iv | 0.93 (3) | 2.03 (3) | 2.821 (5) | 142 (4) |
O5—H2···O1iv | 0.93 (3) | 2.26 (2) | 3.122 (5) | 156 (4) |
O5—H1···O1v | 0.92 (3) | 1.80 (2) | 2.709 (5) | 175 (5) |
Symmetry codes: (i) x+1, y, z+1; (ii) −x+2, y+1/2, −z+3; (iii) −x+2, y+1/2, −z+2; (iv) −x+1, y+1/2, −z+1; (v) −x+1, y−1/2, −z+1. |
L-Cysteine is one of the essential amino acids in nature. Some of its derivatives present remarkable bioactivities, and they can be used as antioxidants, antibacterial agents (Rabinkov et al., 1998) and chemical precursors of antitumor medicines (Hakimelahi et al., 2002). Although the crystal structure of both L-cysteine (Kerr & Ashmore, 1973, 1975; Görbitz & Dalhus, 1996; Harding et al., 1968) and DL-cysteine (Luger & Weber, 1999) have been reported, structures of bis(L-cysteine) derivatives are rare in the literature (Bigoli et al., 1982).
In this paper, the structure of the title compound, trans-s,s'-(but-2-ene-1,4-diyl)bis(L-cysteine) dihydrate, (I), is reported. The molecular structure of (I) is illustrated in Fig. 1.
The molecule of (I) has a trans configuration. The distance between atoms C5 and C6 is 1.299 (5) Å, which is shorter than the distance of 1.34 (1) Å for a normal C═C bond (Lide, 1992–1993) and the distance of 1.326 Å in trans-2,5-dimethyl-3-hexene-2,5-diol. The angles C4—C5—C6 and C5—C6—C7 are 125.6 (3) and 123.5 (3)°, respectively, which are slightly smaller than those of 127.4 and 124.9° in trans-2,5-dimethy-3-hexene-2,5-diol (Ruysink & Vos, 1974). The torsion angle C4—C5—C6—C7 is 177.7 (4)°, indicating that the butenediyl group is almost planar. The C—S bond lengths [C3—S2 = 1.794 (4), C4—S2 = 1.812 (4), C7—S1 = 1.820 (4) and C8—S1 = 1.80 (4) Å] are in the same magnitude compared with the value of 1.811 (3) Å in L-cysteine (Kerr & Ashmore, 1973). The bond angles C3—S2—C4 and C8—S1—C7 are 102.1 (2) and 100.4 (2)°, respectively, slightly larger than the value of 99.05° in dimethyl sulfide (Lide, 1992–1993).
The difference in the C—O bond lengths of the two carboxyl groups is obviously influenced by hydrogen-bond environment (Table 2). Atoms O1 and O4 are involved in more than one hydrogen bond (O6—H3···O1, O5—H2···O1 and O5—H1···O1; N2—H2b···O4 and O6—H4···O4), while atoms O2 and O3 only take part one hydrogen-bond interaction, which may explain why the C1—O1 [1.252 (5) Å] and C10—O4 [1.263 (4) Å] bond lengths are longer than those of C1—O2 [1.218 (6) Å] and C10—O3 [1.231 (5) Å].
The two cysteine moieties (zwitterions), separated by the rigid butene-1,4-diyl skeleton, adopt different conformations. Atom S1 is anti to the C10/O3/O4 carboxyl group, with a S1—C8—C9—C10 torsion angle of 178.4°. However, atom S2 is gauche with respect to both the C1/O1/O2 carboxyl and protonated amino groups; the corresponding torsion angles, S2—C3—C2—C1 and S2—C3—C2—N1, are 61.8 (4) and 57.8 (4)°, respectively. The difference is clearly illustrated by the Newman projection shown in Fig. 4.
The molecules are arranged in the crystal lattice parallel to the ac plane, in which two N—H groups of the protonated amino group and two C—O groups of the carboxyl group, as well as two water molecules, form a 14-membered ring via hydrogen bonds. Interestingly, these molecules are linked together through hydrogen bonds along the b axis to form a three-dimensional network with an infinite tunnel.
Besides overwhelming intermolecular hydrogen bonding, there exists one intramolecular hydrogen-bond interaction (N2—H2b···O4) in the S1/C8/C9/C10/N2 moiety. No such interaction is found in the other moiety, which may explain the conformational differences of the two zwitterion moieties.