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The structure of taurine (2-amino­ethane­sulfonic acid), C2H7NO3S, has been redetermined at 150 K, and is compared with the structures of glycine and [beta]-alanine which, like taurine, are enzymatically conjugated with bile acids.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270199016029/qb0156sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270199016029/qb0156Isup2.hkl
Contains datablock I

CCDC reference: 140864

Comment top

Bile acids are conjugated with glycine and taurine, (I), to become more water soluble, which facilitates secretion. This enzymatic activity seems to have a bimodal localization in rat liver with different Kms for glycine and taurine, but competition experiments indicate that the same enzymes are able to catalyse conjugation both with glycine and taurine (Kase & Björkhem, 1989). Furthermore, β-alanine (3-aminopropanoic acid, not to be misinterpreted as a second polymorph of L-alanine) is also a substrate. This makes a structural comparison of these three amino acids interesting. The strucure of taurine was first presented by Okaya (1966). We report here a more accurate low-temperature study.

Glycine has been crystallized in three polymorphic forms, α-glycine (Jönnson & Kvick, 1972), β-glycine (Iitaka, 1960) and γ-glycine (Kvick et al., 1980) with different hydrogen-bond patterns. The structure of α-glycine (Jönnson & Kvick, 1972) is very similar to the structure of β-alanine (Jose & Pant, 1965; Papavinasam et al., 1986) in that amino acid dimers (with centers of symmetry) connected by two hydrogen bonds occur in both structures. The corresponding first-level graph-sets (Etter, 1990; Bernstein et al., 1995) are R22(10) and R22(12), respectively. The conformation at the central C—C bond in β-alanine is gauche [N—C—C—C = 83.2 (2)°, Papavinasam et al., 1986]. A gauche orientation is found also for taurine with N1—C2—C1—S1 = 70.96 (5)°. In addition to a weak intramolecular contact between the amino- and sulfonic acid groups [graph-set S(6)], the hydrogen-bond pattern again incorporates the centrosymmetric R22(12) motif, involving not just one, but two different neighboring molecules resulting in formation of hydrogen-bonded ribbons along the a axis. In summary, the structures of glycine (in the α-modification, Jönnson & Kvick, 1972), β-alanine (Papavinasam et al., 1986) and taurine show several common features. In particular, the tendency of these molecules to form hydrogen-bonded ring systems may be important for substrate specificity when conjugation with bile acids occurs.

Experimental top

Taurine was purchased from Sigma. The crystals were obtained by diffusion of 2-propanol into 50 µl of an aqueous solution containing about 2.0 mg of the acid.

Refinement top

The data collection nominally covered over a hemisphere of reciprocal space by a combination of five sets of exposures; two with the detector set at 2θ = 30° and three with 2θ = 55°. Each set had a different ϕ angle for the crystal and each exposure covered 0.6° in ω. The crystal-to-detector distance was 4.97 cm. Coverage of the unique set is over 99% complete to at least 70° in 2θ. H atoms were refined isotropically.

Computing details top

Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1997); software used to prepare material for publication: SHELXTL (Sheldrick, 1997).

2-amino-ethanesulfonic acid top
Crystal data top
C2H7NO3SF(000) = 264
Mr = 125.15Dx = 1.730 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 5.2729 (1) ÅCell parameters from 2830 reflections
b = 11.6565 (3) Åθ = 3.5–40.0°
c = 7.8383 (2) ŵ = 0.56 mm1
β = 94.011 (1)°T = 150 K
V = 480.59 (2) Å3Block, colourless
Z = 40.60 × 0.45 × 0.40 mm
Data collection top
Siemens SMART CCD
diffractometer
2891 independent reflections
Radiation source: fine-focus sealed tube2736 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.027
Detector resolution: 8.3 pixels mm-1θmax = 40.3°, θmin = 3.5°
Sets of exposures each taken over 0.6° ω rotation scansh = 98
Absorption correction: empirical (using intensity measurements)
(SADABS; Sheldrick, 1996)
k = 2120
Tmin = 0.755, Tmax = 0.844l = 1413
7640 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.026H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.075 w = 1/[σ2(Fo2) + (0.0408P)2 + 0.0602P]
where P = (Fo2 + 2Fc2)/3
S = 1.13(Δ/σ)max = 0.010
2891 reflectionsΔρmax = 0.53 e Å3
93 parametersΔρmin = 0.42 e Å3
0 restraintsExtinction correction: SHELXTL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.133 (10)
Crystal data top
C2H7NO3SV = 480.59 (2) Å3
Mr = 125.15Z = 4
Monoclinic, P21/cMo Kα radiation
a = 5.2729 (1) ŵ = 0.56 mm1
b = 11.6565 (3) ÅT = 150 K
c = 7.8383 (2) Å0.60 × 0.45 × 0.40 mm
β = 94.011 (1)°
Data collection top
Siemens SMART CCD
diffractometer
2891 independent reflections
Absorption correction: empirical (using intensity measurements)
(SADABS; Sheldrick, 1996)
2736 reflections with I > 2σ(I)
Tmin = 0.755, Tmax = 0.844Rint = 0.027
7640 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0260 restraints
wR(F2) = 0.075H atoms treated by a mixture of independent and constrained refinement
S = 1.13Δρmax = 0.53 e Å3
2891 reflectionsΔρmin = 0.42 e Å3
93 parameters
Special details top

Refinement. Refinement of F2 against ALL reflections.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
S10.20206 (2)0.349635 (11)0.350184 (17)0.01098 (5)
O10.34141 (10)0.24190 (4)0.35347 (7)0.01856 (9)
O20.06739 (9)0.33817 (4)0.29125 (7)0.01825 (9)
O30.23035 (9)0.41200 (4)0.51340 (5)0.01480 (8)
N10.26644 (10)0.63028 (4)0.33278 (6)0.01304 (8)
H10.199 (3)0.6079 (13)0.4132 (18)0.029 (3)*
H20.205 (3)0.6931 (13)0.3125 (19)0.026 (3)*
H30.418 (3)0.6326 (12)0.3580 (18)0.025 (3)*
C10.33923 (11)0.43962 (5)0.19717 (7)0.01318 (9)
H110.516 (3)0.4464 (12)0.2367 (18)0.027 (3)*
H120.318 (3)0.3986 (11)0.0901 (16)0.022 (3)*
C20.20939 (11)0.55634 (5)0.17965 (7)0.01411 (9)
H210.266 (3)0.5993 (12)0.0777 (17)0.026 (3)*
H220.037 (3)0.5455 (12)0.1644 (19)0.026 (3)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.00983 (7)0.00924 (7)0.01388 (7)0.00062 (3)0.00088 (4)0.00031 (3)
O10.0207 (2)0.01261 (17)0.0228 (2)0.00667 (14)0.00483 (15)0.00220 (14)
O20.01131 (18)0.01537 (17)0.0276 (2)0.00261 (13)0.00209 (15)0.00208 (15)
O30.01626 (17)0.01562 (17)0.01268 (15)0.00014 (13)0.00207 (12)0.00137 (12)
N10.01319 (19)0.01188 (16)0.01416 (17)0.00084 (14)0.00179 (13)0.00057 (13)
C10.0136 (2)0.01328 (19)0.01279 (18)0.00019 (15)0.00179 (14)0.00043 (14)
C20.0152 (2)0.01305 (19)0.01364 (18)0.00020 (15)0.00212 (15)0.00166 (14)
Geometric parameters (Å, º) top
S1—O11.4543 (5)N1—H30.810 (15)
S1—O21.4690 (5)C1—C21.5249 (8)
S1—O31.4699 (4)C1—H110.964 (15)
S1—C11.7842 (6)C1—H120.966 (13)
N1—C21.4911 (7)C2—H211.005 (14)
N1—H10.790 (15)C2—H220.919 (15)
N1—H20.812 (15)
O1—S1—O2113.79 (3)C2—C1—S1112.61 (4)
O1—S1—O3113.03 (3)C2—C1—H11111.9 (8)
O2—S1—O3110.84 (3)S1—C1—H11105.1 (9)
O1—S1—C1106.95 (3)C2—C1—H12109.8 (8)
O2—S1—C1105.71 (3)S1—C1—H12105.3 (8)
O3—S1—C1105.85 (3)H11—C1—H12111.9 (11)
C2—N1—H1112.0 (11)N1—C2—C1112.28 (4)
C2—N1—H2108.0 (10)N1—C2—H21107.4 (8)
H1—N1—H2105.0 (15)C1—C2—H21111.1 (8)
C2—N1—H3110.9 (10)N1—C2—H22109.1 (9)
H1—N1—H3107.9 (14)C1—C2—H22108.8 (9)
H2—N1—H3112.9 (14)H21—C2—H22108.0 (12)
O1—S1—C1—C2179.69 (4)O3—S1—C1—C259.53 (4)
O2—S1—C1—C258.11 (4)S1—C1—C2—N170.96 (5)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O30.790 (14)2.416 (15)2.924 (1)123.2 (13)
N1—H1···O3i0.790 (14)2.386 (15)3.000 (1)135.5 (13)
N1—H1···O2i0.790 (14)2.543 (14)3.218 (1)144.3 (14)
N1—H2···O2ii0.812 (15)1.991 (15)2.789 (1)167.1 (15)
N1—H3···O3iii0.811 (15)2.112 (14)2.879 (1)157.8 (14)
Symmetry codes: (i) x, y+1, z+1; (ii) x, y+1/2, z+1/2; (iii) x+1, y+1, z+1.

Experimental details

Crystal data
Chemical formulaC2H7NO3S
Mr125.15
Crystal system, space groupMonoclinic, P21/c
Temperature (K)150
a, b, c (Å)5.2729 (1), 11.6565 (3), 7.8383 (2)
β (°) 94.011 (1)
V3)480.59 (2)
Z4
Radiation typeMo Kα
µ (mm1)0.56
Crystal size (mm)0.60 × 0.45 × 0.40
Data collection
DiffractometerSiemens SMART CCD
diffractometer
Absorption correctionEmpirical (using intensity measurements)
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.755, 0.844
No. of measured, independent and
observed [I > 2σ(I)] reflections
7640, 2891, 2736
Rint0.027
(sin θ/λ)max1)0.909
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.026, 0.075, 1.13
No. of reflections2891
No. of parameters93
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.53, 0.42

Computer programs: SMART (Siemens, 1995), SAINT (Siemens, 1995), SHELXTL (Sheldrick, 1997).

Selected geometric parameters (Å, º) top
S1—O11.4543 (5)S1—C11.7842 (6)
S1—O21.4690 (5)N1—C21.4911 (7)
S1—O31.4699 (4)C1—C21.5249 (8)
O1—S1—C1106.95 (3)C2—C1—S1112.61 (4)
O2—S1—C1105.71 (3)N1—C2—C1112.28 (4)
O3—S1—C1105.85 (3)
O1—S1—C1—C2179.69 (4)S1—C1—C2—N170.96 (5)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O30.790 (14)2.416 (15)2.924 (1)123.2 (13)
N1—H1···O3i0.790 (14)2.386 (15)3.000 (1)135.5 (13)
N1—H1···O2i0.790 (14)2.543 (14)3.218 (1)144.3 (14)
N1—H2···O2ii0.812 (15)1.991 (15)2.789 (1)167.1 (15)
N1—H3···O3iii0.811 (15)2.112 (14)2.879 (1)157.8 (14)
Symmetry codes: (i) x, y+1, z+1; (ii) x, y+1/2, z+1/2; (iii) x+1, y+1, z+1.
 

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