organic compounds
Redetermination of L-tryptophan hydrobromide
aSchool of Chemical and Physical Sciences, University of KwaZulu-Natal, Scottsville 3209, South Africa
*Correspondence e-mail: stewart@ukzn.ac.za
The redetermined 11H13N2O2+·Br−, is reported. Data collection at 100 K about three crystallographic axes resulted in a with significantly higher precision in comparison to the two-dimensional data collected at 176 K [Takigawa et al. [(1966) Bull. Chem. Soc. Jpn, 39, 2369–2378]. The carboxyl group and indole ring system are planar, with maximum deviations of 0.002 (2) and 0.007 (2) Å, respectively, and make an angle of 70.17 (1)° with each other. The molecules are arranged in double layers of carboxyl and amino groups parallel to the ab plane, stabilized by an extensive network of N—H⋯Br and O—H⋯Br hydrogen bonds. The polar layer is held together by a network of three N—H⋯Br hydrogen bonds and one O—H⋯Br hydrogen bond. In the non-polar layer, the indole rings are linked mainly by electrostatic N—H⋯C interactions between the polarized bond N—H (H is δ+) of the pyrrole unit and two of the ring C atoms (δ−) of the benzene rings of adjacent molecules. The distances of these electrostatic interactions are 2.57 and 2.68 Å, respectively. C—H⋯O and C—H⋯π interactions are also present.
of the title compound, CRelated literature
For a previous determination of the et al. (1966). Study of crystal structures of amino acids and their complexes has provided information about aggregation and the effect of other molecules on their interactions and molecular properties, see: Vijayan (1988); Prasad & Vijayan (1993). For the structure of histidine hydrochloride monohydrate, see: Takigawa et al. (1966). Donohue & Caron (1964). The structures of many amino acids with non-polar side chains feature a double-layered arrangement, see: Harding & Long (1968); Torii & Iitaka (1970, 1971, 1973).
of the title compound, see: TakigawaExperimental
Crystal data
|
Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell CrysAlis RED (Oxford Diffraction, 2008); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).
Supporting information
10.1107/S1600536809017322/at2781sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536809017322/at2781Isup2.hkl
L-tryptophan hydrobromide was obtained in the form of plate-like crystals by dissolving L-tryptophan in concentrated hydrobromic acid followed by slow evaporation at room temperature.
HRMS (ES-): Found [M—H] 283.0082 C11H12N2O2Br Expected 283.0080 (-0.7 ppm).
All H atoms were positioned in geometrically idealized positions and constrained to ride on their parent atoms with N—H = 0.91 Å, O—H = 0.84 Å and C—H distances in the range 0.95–1.00 Å. and Uiso(H)= 1.2–1.5 Ueq(parent atom).
Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell
CrysAlis RED (Oxford Diffraction, 2008); data reduction: CrysAlis RED (Oxford Diffraction, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).Fig. 1. Molecular structure of (L)-2-amino-3-(1H-indol-3-yl)-propionic acid hydrobromide, showing 50% probability displacement ellipsoids and atomic numbering. | |
Fig. 2. Packing diagram showing a view along the a axis. |
C11H13N2O2+·Br− | F(000) = 288 |
Mr = 285.13 | Dx = 1.626 Mg m−3 |
Monoclinic, P21 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2yb | Cell parameters from 4434 reflections |
a = 7.6272 (3) Å | θ = 3.8–31.9° |
b = 5.3840 (2) Å | µ = 3.52 mm−1 |
c = 14.4358 (5) Å | T = 100 K |
β = 100.688 (3)° | Needle, colourless |
V = 582.52 (4) Å3 | 0.40 × 0.15 × 0.15 mm |
Z = 2 |
Oxford Xcalibur2 CCD diffractometer | 2731 independent reflections |
Radiation source: Enhance (Mo) X-ray Source | 2507 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.024 |
Detector resolution: 8.4190 pixels mm-1 | θmax = 32.0°, θmin = 4.1° |
ω/2θ scans | h = −11→10 |
Absorption correction: multi-scan (SCALE3 ABSPACK in CrysAlis RED; Oxford Diffraction, 2008) | k = −6→7 |
Tmin = 0.334, Tmax = 0.621 | l = −21→21 |
5749 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.027 | H-atom parameters constrained |
wR(F2) = 0.063 | w = 1/[σ2(Fo2) + (0.0388P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.01 | (Δ/σ)max < 0.001 |
2731 reflections | Δρmax = 0.33 e Å−3 |
147 parameters | Δρmin = −1.14 e Å−3 |
1 restraint | Absolute structure: Flack (1983), 523 Freidel pairs |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: 0.009 (9) |
C11H13N2O2+·Br− | V = 582.52 (4) Å3 |
Mr = 285.13 | Z = 2 |
Monoclinic, P21 | Mo Kα radiation |
a = 7.6272 (3) Å | µ = 3.52 mm−1 |
b = 5.3840 (2) Å | T = 100 K |
c = 14.4358 (5) Å | 0.40 × 0.15 × 0.15 mm |
β = 100.688 (3)° |
Oxford Xcalibur2 CCD diffractometer | 2731 independent reflections |
Absorption correction: multi-scan (SCALE3 ABSPACK in CrysAlis RED; Oxford Diffraction, 2008) | 2507 reflections with I > 2σ(I) |
Tmin = 0.334, Tmax = 0.621 | Rint = 0.024 |
5749 measured reflections |
R[F2 > 2σ(F2)] = 0.027 | H-atom parameters constrained |
wR(F2) = 0.063 | Δρmax = 0.33 e Å−3 |
S = 1.01 | Δρmin = −1.14 e Å−3 |
2731 reflections | Absolute structure: Flack (1983), 523 Freidel pairs |
147 parameters | Absolute structure parameter: 0.009 (9) |
1 restraint |
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 > σ(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 | ||
C1 | 0.2755 (3) | 0.4954 (5) | 0.66336 (17) | 0.0112 (4) | |
H6 | 0.4001 | 0.5280 | 0.6774 | 0.013* | |
C2 | 0.1920 (3) | 0.3004 (4) | 0.69909 (15) | 0.0095 (5) | |
C3 | 0.0055 (3) | 0.3213 (4) | 0.65929 (15) | 0.0086 (4) | |
C4 | −0.1449 (3) | 0.1811 (5) | 0.66802 (15) | 0.0111 (4) | |
H1 | −0.1339 | 0.0367 | 0.7065 | 0.013* | |
C5 | −0.3108 (3) | 0.2569 (9) | 0.61935 (14) | 0.0141 (4) | |
H2 | −0.4140 | 0.1638 | 0.6253 | 0.017* | |
C6 | −0.3286 (3) | 0.4686 (5) | 0.56162 (17) | 0.0141 (5) | |
H3 | −0.4436 | 0.5159 | 0.5291 | 0.017* | |
C7 | −0.1815 (3) | 0.6103 (5) | 0.55101 (17) | 0.0125 (4) | |
H4 | −0.1932 | 0.7530 | 0.5116 | 0.015* | |
C8 | −0.0151 (3) | 0.5338 (5) | 0.60080 (16) | 0.0103 (4) | |
C9 | 0.2770 (3) | 0.0989 (5) | 0.76424 (16) | 0.0100 (4) | |
H7 | 0.3862 | 0.0421 | 0.7428 | 0.012* | |
H8 | 0.1939 | −0.0438 | 0.7591 | 0.012* | |
C10 | 0.3269 (3) | 0.1746 (5) | 0.86847 (15) | 0.0109 (4) | |
H9 | 0.3832 | 0.0280 | 0.9049 | 0.013* | |
C11 | 0.4583 (3) | 0.3889 (5) | 0.88531 (16) | 0.0124 (5) | |
N1 | 0.1513 (3) | 0.6363 (4) | 0.60405 (14) | 0.0120 (4) | |
H5 | 0.1746 | 0.7698 | 0.5733 | 0.014* | |
N2 | 0.1651 (2) | 0.2443 (6) | 0.90642 (12) | 0.0142 (3) | |
H13 | 0.1107 | 0.3761 | 0.8735 | 0.021* | |
H11 | 0.1972 | 0.2860 | 0.9683 | 0.021* | |
H12 | 0.0885 | 0.1133 | 0.9006 | 0.021* | |
O1 | 0.4357 (3) | 0.5748 (4) | 0.92793 (13) | 0.0166 (4) | |
O2 | 0.5974 (2) | 0.3408 (4) | 0.84628 (15) | 0.0229 (4) | |
H10 | 0.6731 | 0.4547 | 0.8596 | 0.034* | |
Br1 | 0.90610 (3) | 0.74408 (5) | 0.873511 (13) | 0.01394 (7) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0119 (10) | 0.0122 (12) | 0.0092 (10) | −0.0014 (9) | 0.0012 (8) | −0.0008 (8) |
C2 | 0.0108 (9) | 0.0105 (14) | 0.0072 (9) | 0.0005 (7) | 0.0017 (7) | −0.0011 (7) |
C3 | 0.0107 (10) | 0.0096 (10) | 0.0051 (9) | 0.0013 (7) | 0.0001 (7) | −0.0008 (7) |
C4 | 0.0132 (10) | 0.0116 (11) | 0.0080 (9) | 0.0002 (8) | 0.0005 (7) | 0.0008 (7) |
C5 | 0.0117 (9) | 0.0175 (11) | 0.0133 (9) | −0.0010 (17) | 0.0028 (7) | −0.0037 (17) |
C6 | 0.0122 (11) | 0.0190 (13) | 0.0104 (11) | 0.0051 (9) | 0.0002 (8) | 0.0005 (9) |
C7 | 0.0176 (11) | 0.0114 (11) | 0.0084 (10) | 0.0043 (9) | 0.0024 (8) | 0.0010 (8) |
C8 | 0.0150 (11) | 0.0099 (10) | 0.0063 (10) | −0.0006 (9) | 0.0027 (8) | −0.0012 (8) |
C9 | 0.0107 (10) | 0.0092 (10) | 0.0089 (10) | −0.0004 (8) | −0.0010 (8) | −0.0020 (8) |
C10 | 0.0142 (11) | 0.0095 (10) | 0.0081 (10) | −0.0010 (8) | −0.0002 (7) | −0.0002 (8) |
C11 | 0.0128 (10) | 0.0127 (12) | 0.0091 (10) | −0.0035 (9) | −0.0048 (8) | 0.0010 (9) |
N1 | 0.0172 (10) | 0.0092 (10) | 0.0095 (9) | −0.0020 (8) | 0.0023 (7) | 0.0019 (7) |
N2 | 0.0194 (8) | 0.0124 (8) | 0.0120 (7) | −0.0064 (15) | 0.0062 (6) | −0.0017 (14) |
O1 | 0.0216 (9) | 0.0114 (9) | 0.0158 (9) | −0.0046 (7) | 0.0009 (7) | −0.0030 (7) |
O2 | 0.0124 (9) | 0.0217 (10) | 0.0354 (11) | −0.0078 (8) | 0.0061 (8) | −0.0112 (9) |
Br1 | 0.01610 (10) | 0.01382 (11) | 0.01214 (9) | −0.00518 (15) | 0.00322 (6) | 0.00128 (14) |
C1—C2 | 1.377 (3) | C8—N1 | 1.377 (3) |
C1—N1 | 1.381 (3) | C9—C10 | 1.537 (3) |
C1—H6 | 0.9500 | C9—H7 | 0.9900 |
C2—C3 | 1.436 (3) | C9—H8 | 0.9900 |
C2—C9 | 1.502 (3) | C10—N2 | 1.488 (3) |
C3—C4 | 1.398 (3) | C10—C11 | 1.518 (3) |
C3—C8 | 1.413 (3) | C10—H9 | 1.0000 |
C4—C5 | 1.390 (3) | C11—O1 | 1.204 (3) |
C4—H1 | 0.9500 | C11—O2 | 1.316 (3) |
C5—C6 | 1.404 (5) | N1—H5 | 0.8800 |
C5—H2 | 0.9500 | N2—H13 | 0.9100 |
C6—C7 | 1.389 (4) | N2—H11 | 0.9100 |
C6—H3 | 0.9500 | N2—H12 | 0.9100 |
C7—C8 | 1.399 (3) | O2—H10 | 0.8400 |
C7—H4 | 0.9500 | ||
C2—C1—N1 | 109.8 (2) | C2—C9—H7 | 108.5 |
C2—C1—H6 | 125.1 | C10—C9—H7 | 108.5 |
N1—C1—H6 | 125.1 | C2—C9—H8 | 108.5 |
C1—C2—C3 | 106.5 (2) | C10—C9—H8 | 108.5 |
C1—C2—C9 | 127.5 (2) | H7—C9—H8 | 107.5 |
C3—C2—C9 | 126.0 (2) | N2—C10—C11 | 108.5 (2) |
C4—C3—C8 | 119.2 (2) | N2—C10—C9 | 110.80 (18) |
C4—C3—C2 | 133.6 (2) | C11—C10—C9 | 113.26 (19) |
C8—C3—C2 | 107.1 (2) | N2—C10—H9 | 108.0 |
C5—C4—C3 | 118.8 (3) | C11—C10—H9 | 108.0 |
C5—C4—H1 | 120.6 | C9—C10—H9 | 108.0 |
C3—C4—H1 | 120.6 | O1—C11—O2 | 125.8 (2) |
C4—C5—C6 | 121.1 (3) | O1—C11—C10 | 124.1 (2) |
C4—C5—H2 | 119.4 | O2—C11—C10 | 110.0 (2) |
C6—C5—H2 | 119.4 | C8—N1—C1 | 108.9 (2) |
C7—C6—C5 | 121.4 (2) | C8—N1—H5 | 125.6 |
C7—C6—H3 | 119.3 | C1—N1—H5 | 125.6 |
C5—C6—H3 | 119.3 | C10—N2—H13 | 109.5 |
C6—C7—C8 | 117.1 (2) | C10—N2—H11 | 109.5 |
C6—C7—H4 | 121.4 | H13—N2—H11 | 109.5 |
C8—C7—H4 | 121.4 | C10—N2—H12 | 109.5 |
N1—C8—C7 | 129.9 (2) | H13—N2—H12 | 109.5 |
N1—C8—C3 | 107.7 (2) | H11—N2—H12 | 109.5 |
C7—C8—C3 | 122.4 (2) | C11—O2—H10 | 109.5 |
C2—C9—C10 | 114.9 (2) | ||
N1—C1—C2—C3 | 0.3 (3) | C2—C3—C8—N1 | 0.6 (2) |
N1—C1—C2—C9 | 178.4 (2) | C4—C3—C8—C7 | 0.1 (3) |
C1—C2—C3—C4 | 179.8 (2) | C2—C3—C8—C7 | −179.7 (2) |
C9—C2—C3—C4 | 1.6 (4) | C1—C2—C9—C10 | 78.8 (3) |
C1—C2—C3—C8 | −0.5 (2) | C3—C2—C9—C10 | −103.4 (3) |
C9—C2—C3—C8 | −178.7 (2) | C2—C9—C10—N2 | 62.4 (3) |
C8—C3—C4—C5 | −0.6 (3) | C2—C9—C10—C11 | −59.8 (3) |
C2—C3—C4—C5 | 179.1 (3) | N2—C10—C11—O1 | 4.3 (3) |
C3—C4—C5—C6 | 0.6 (4) | C9—C10—C11—O1 | 127.8 (3) |
C4—C5—C6—C7 | −0.1 (4) | N2—C10—C11—O2 | −175.31 (19) |
C5—C6—C7—C8 | −0.4 (4) | C9—C10—C11—O2 | −51.8 (3) |
C6—C7—C8—N1 | −179.9 (2) | C7—C8—N1—C1 | 179.9 (2) |
C6—C7—C8—C3 | 0.4 (3) | C3—C8—N1—C1 | −0.4 (3) |
C4—C3—C8—N1 | −179.7 (2) | C2—C1—N1—C8 | 0.1 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
C7—H4···Cg1i | 0.95 | 2.66 | 3.494 (3) | 146 |
N1—H5···Cg2i | 0.88 | 2.72 | 3.406 (2) | 136 |
N2—H11···Br1ii | 0.91 | 2.56 | 3.3208 (17) | 142 |
N2—H12···Br1iii | 0.91 | 2.42 | 3.322 (3) | 173 |
N2—H13···Br1iv | 0.91 | 2.52 | 3.320 (3) | 147 |
C4—H1···Br1iii | 0.95 | 2.85 | 3.750 (2) | 159 |
C10—H9···O1v | 1.00 | 2.49 | 3.404 (3) | 153 |
C10—H9···O1ii | 1.00 | 2.56 | 3.199 (3) | 121 |
O2—H10···Br1 | 0.84 | 2.34 | 3.173 (2) | 169 |
Symmetry codes: (i) −x, y−1/2, −z+1; (ii) −x+1, y−1/2, −z+2; (iii) x−1, y−1, z; (iv) x−1, y, z; (v) x, y−1, z. |
Experimental details
Crystal data | |
Chemical formula | C11H13N2O2+·Br− |
Mr | 285.13 |
Crystal system, space group | Monoclinic, P21 |
Temperature (K) | 100 |
a, b, c (Å) | 7.6272 (3), 5.3840 (2), 14.4358 (5) |
β (°) | 100.688 (3) |
V (Å3) | 582.52 (4) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 3.52 |
Crystal size (mm) | 0.40 × 0.15 × 0.15 |
Data collection | |
Diffractometer | Oxford Xcalibur2 CCD diffractometer |
Absorption correction | Multi-scan (SCALE3 ABSPACK in CrysAlis RED; Oxford Diffraction, 2008) |
Tmin, Tmax | 0.334, 0.621 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5749, 2731, 2507 |
Rint | 0.024 |
(sin θ/λ)max (Å−1) | 0.746 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.027, 0.063, 1.01 |
No. of reflections | 2731 |
No. of parameters | 147 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.33, −1.14 |
Absolute structure | Flack (1983), 523 Freidel pairs |
Absolute structure parameter | 0.009 (9) |
Computer programs: CrysAlis CCD (Oxford Diffraction, 2008), CrysAlis RED (Oxford Diffraction, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997), WinGX (Farrugia, 1999).
D—H···A | D—H | H···A | D···A | D—H···A |
C7—H4···Cg1i | 0.9500 | 2.66 | 3.494 (3) | 146 |
N1—H5···Cg2i | 0.8800 | 2.72 | 3.406 (2) | 136 |
N2—H11···Br1ii | 0.9100 | 2.56 | 3.3208 (17) | 142 |
N2—H12···Br1iii | 0.9100 | 2.42 | 3.322 (3) | 173 |
N2—H13···Br1iv | 0.9100 | 2.52 | 3.320 (3) | 147 |
C4—H1···Br1iii | 0.9500 | 2.85 | 3.750 (2) | 159 |
C10—H9···O1v | 1.00 | 2.49 | 3.404 (3) | 153 |
C10—H9···O1ii | 1.00 | 2.56 | 3.199 (3) | 121 |
O2—H10···Br1 | 0.8400 | 2.34 | 3.173 (2) | 169 |
Symmetry codes: (i) −x, y−1/2, −z+1; (ii) −x+1, y−1/2, −z+2; (iii) x−1, y−1, z; (iv) x−1, y, z; (v) x, y−1, z. |
Acknowledgements
The author gratefully acknowledges financial support from the University of Kwazulu-Natal. Thanks are also due to Ms C. Janse Van Rensburg for the
analysis.References
Donohue, J. & Caron, A. (1964). Acta Cryst. 17, 1178–1180. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Flack, H. D. (1983). Acta Cryst. A39, 876–881. CrossRef CAS Web of Science IUCr Journals Google Scholar
Harding, M. M. & Long, H. A. (1968). Acta Cryst. B24, 1096–1102. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Oxford Diffraction (2008). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England. Google Scholar
Prasad, G. S. & Vijayan, M. (1993). Acta Cryst. B49, 348–356. CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Takigawa, T., Ashida, T., Sasada, Y. & Kakudo, M. (1966). Bull. Chem. Soc. Jpn, 39, 2369–2378. CrossRef CAS PubMed Web of Science Google Scholar
Torii, K. & Iitaka, Y. (1970). Acta Cryst. B26, 1317–1326. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Torii, K. & Iitaka, Y. (1971). Acta Cryst. B27, 2237–2246. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Torii, K. & Iitaka, Y. (1973). Acta Cryst. B29, 2799–2807. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Vijayan, M. (1988). Prog. Biophys. Mol. Biol. 52, 71–99. CrossRef CAS PubMed Web of Science Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
The crystal structures of amino acids and their complexes have provided interesting information about aggregation, and the effect of other molecules on their interaction and molecular properties (Vijayan, 1988; Prasad & Vijayan 1993).
The crystal structure of L-tryptophan hydrobromide was determined some 40 years ago (Takigawa et al., 1966). The final refinement was carried out to only R = 0.101 with no data available for H atoms. The reported structure possesses almost identical crystal parameters to the structure reported here in terms of space group and unit-cell dimensions and angles. However, the collection of data at 100 K about three crystallographic axes in comparison to the data reported by Takigawa et al. resulted in more accurate data thus allowing some previously unidentified notable conclusions to be drawn about the crystal structure.
The C—N distance 1.488 (3) Å coincides well with those in e.g. histidine hydrochloride monohydrate (1.495 Å) (Donohue & Caron, 1964). The two C—O bond lengths are 1.316 (3) Å and 1.204 (3) Å for C11—O2 and C11—O1, respectively and the three angles around the C11 atom are O2—C11—O1 = 125.8 (2)°, O2—C11—C10 = 110.0 (2) ° and O1—C11—C10 = 124.1 (2) °.
The planarity of the carboxyl group with the α-carbon has been established in many investigations and the deviations of the amino nitrogen range from 0.00 to 0.82 Å for the amino acids so far investigated. For the present molecule, the amino nitrogen is 0.094 Å out of the plane, so the amide group is essentially planar in this case.
The mean plane through the atoms of the indole ring with the methylene carbon attached to it forms a dihedral angle of 70.17 (1) ° with the mean plane of the carboxyl group.
The structures of many amino acids with non-polar side chains have the arrangement of a double layered system (Torii & Iitaka 1970; Torii & Iitaka, 1971; Torii & Iitaka, 1973; Harding & Long, 1968) which is characteristic for a structure containing polar and non-polar groups together. The polar layer is held together by a network of hydrogen bonds between the halide ions and the amino nitrogen and the halide ions and the carboxyl group.
The amino nitrogen forms three N—H···Br hydrogen bonds, in the lengths of 2.56 (1) Å, 2.41 (1) Å and 2.52 (1) Å. The three acceptor halogen ions are approximately at the three vertices of a regular tetrahedron centred around the nitrogen atom, with the fourth vortex positioned in the direction of the α-carbon.
The fourth hydrogen bond completing the network is a O—H···Br- which is 2.34 (1) Å in length.
In the non-polar layer, the indole rings are packed in a manner similar to that found for typical aromatic molecules. A weak electrostatic interaction with a separation of 2.677 (1) Å exists between N1—H5 from the pyrrole moiety and the slightly positively charged C6 from the benzene moiety of a neighbouring symmetry related molecule [-x, -1/2 + y, 1 - z]. A similar interaction with a separation of 2.573 (1) Å exists between the same N1—H5 and C7 from the benzene moiety of molecule [-x, -1/2 + y, 1 - z]. The metrics of such interactions are reflected in the T-shaped edge-to-face geometry in the non-polar layer.