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In the title compound, C11H12N2O2·CH2O2, at 183 K. L-­tryptophan appears in the zwitterionic form, while the formic acid molecule is neutral. The formic acid molecule is the donor in a strong O-H...O hydrogen bond to the carboxyl­ate group of the tryptophan mol­ecule, with a short O...O contact of 2.487 (2) Å.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102012489/sk1566sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102012489/sk1566Isup2.hkl
Contains datablock I

CCDC reference: 195614

Comment top

In conjunction with our ongoing work of comparative charge-density studies on the 20 naturally occurring amino acids, we have directed our interest to tryptophan, Trp, one of the essential α-amino acids for humans. Compared with other amino acids, there are only a few tryptophan structures listed in the Cambridge Structural Database (Version?; Allen & Kennard, 1993), due to the difficulty of obtaining good quality crystals. The only solvent-free non-substituted tryptophan structure is that of DL-tryptophane (Bakke & Mostad, 1980), where the authors reported that `crystals were not as good as could be wished'. While our attempts to obtain good quality crystals suitable for charge-density experiments also failed for pure tryptophan (for both the DL– and L-forms), we could obtain nicely diffracting crystals of L-tryptophan formic acid solvate, (I), the X-ray structure of which was still unknown. Only the crystal structure of DL-tryptophan formate has been reported previously (Bye et al., 1973), where it was shown that the tryptophan molecule was protonated and the formate anion had a deprotonated carboxyl group. \sch

In contrast with these results, we found from our X-ray analysis at 183 K that, in the present case, the L-tryptophan is zwitterionic, as are most amino acids in the crystal, and that the formic acid is neutral (Fig. 1). There is a strong O17—H17···O13 hydrogen bond from the formic acid to the carboxylate group of L-tryptophan, with a remarkably short O···O contact of 2.487 (2) Å (Table 2). In DL-tryptophan formate, a hydrogen bond with almost the same donor-acceptor O···O distance was seen (2.492 Å). However, as already mentioned, the role of donor and acceptor was inverted.

The opposite donor-acceptor situation is reflected in the C—O bond lengths at these sites. Normally, a charged carboxylate group has two more or less equal C—O bonds of ~1.23–1.25 Å, while in a neutral COOH group, the two C—O bond lengths differ by ~0.1 Å. Due to the strong hydrogen bonds in both the L– and the DL-Trp formic acid derivatives, the C—O bond lengths in the COOH groups are less different [1.281 (3) and 1.213 (3) Å in the formic acid of the L-Trp derivative, and 1.295 and 1.214 Å in the carboxyl group of the DL-Trp structure]. On the other hand, the accepting C—O bonds in the carboxylate groups are enlarged [1.273 (2) versus 1.237 (2) Å for L-Trp, and 1.255 versus 1.232 Å in the COO- group in the formate anion of the DL-tryptophan derivative]. The other bond lengths in the zwitterionic and cationic forms of L– and DL-Trp are not affected and need no further discussion.

The overall molecular conformation, i.e. the relative orientation of the side chain with respect to the indole ring system, can best be described by the torsion angles along the bonds C3—C10 and C10—C11 (Table 3). While χ2.1 = C2—C3—C10—C11 = -104.4 (2)° has a similar value to that of L-tryptophan in the DL-tryptophan structure, the torsion angles χ1 and χ1.2 [for nomenclature, see IUPAC-IUB (1970)] along C10—C11, indicating + and - gauche arrangements, are different from both the free tryptophan molecular structure and the tryptophan cation in DL-tryptophan formate. Bakke & Mostad (1980) have summarized torsion angles for tryptophan derivatives and found that, in most cases, C12 is trans to C3. The molecular conformation of (I) is roughly similar to that of the hydrochloride of DL-tryptophan ethyl ester (Vijayalakshmi & Srinivasan, 1975). Due to the cis arrangement of the carboxylate group relative to the ring system and the strong hydrogen bonding to the formic acid molecule, a U-shaped arrangement of the entire donor-acceptor complex is formed.

In addition to the above-mentioned strong O17—H17···O13 hydrogen bond from the formic acid to the tryptophan zwitterion, three further hydrogen bonds exist, having the H atoms of the amino group as donors. Two of them link tryptophan molecules and the third one is a further weaker tryptophan-formic acid hydrogen bond with the donor on the tryptophan side. These hydrogen bonds establish a network mainly in the x and y directions close to z = 1/4, while double layers of the indole residues assemble close to z = 0, z = 1/2, ··· (Fig 2). Neighbouring indole layers have weak N1—H1···Ci linkages as short contacts, with H1···C7i 2.50 (3) Å [N1···C7i 3.314 (2) Å] and H1···C8i 2.56 (3) Å [N1···C8i 3.351 (2) Å] [symmetry code: (i) 1/2 + x, 1/2 - y, 2 - z]. An extensive overview of X—H···π interactions has been given by Desiraju & Steiner (1999), where N—H···π interactions are also discussed. No further close contacts of interest were found in (I).

Table 3. Selected torsion angles (°) for L-tryptophan formic acid solvate, (I), DL-tryptophan formate, (II), and DL-tryptophane, (III). All angles refer to the S configuration at C11, i.e. the L form.

Experimental top

Crystals of (I) were grown by cooling a hot solution of L-tryptophan (ex Sigma) in a mixture of propan-2-ol and formic acid (ex Merck AG) (ratio?).

Refinement top

All H atoms were found in difference Fourier maps and refined freely.

Computing details top

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SMART; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and SCHAKAL99 (Keller & Pierrard, 1999); software used to prepare material for publication: PLATON (Spek, 1990).

Figures top
[Figure 1] Fig. 1. The molecular structure and atom-numbering scheme of (I). Displacement ellipsoids are plotted at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
[Figure 2] Fig. 2. Packing diagram (SCHAKAL99; Keller & Pierrard, 1999) for (I).
L-2-Amino-3-(1H-indol-3-yl)-propionic acid formic acid solvate top
Crystal data top
C11H12N2O2·CH2O2F(000) = 528
Mr = 250.25Dx = 1.410 Mg m3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 5433 reflections
a = 5.3163 (3) Åθ = 2.1–32.4°
b = 8.1348 (4) ŵ = 0.11 mm1
c = 27.259 (2) ÅT = 183 K
V = 1178.87 (12) Å3Needle, colourless
Z = 40.2 × 0.1 × 0.1 mm
Data collection top
Bruker AXS SMART CCD area-detector
diffractometer
2492 independent reflections
Radiation source: fine-focus sealed tube2104 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.064
ω and ϕ scansθmax = 33.1°, θmin = 2.6°
Absorption correction: empirical (using intensity measurements)
(SADABS; Blessing, 1995; Siemens, 1996)
h = 88
Tmin = 0.761, Tmax = 1.000k = 1112
14392 measured reflectionsl = 4141
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.051Hydrogen site location: difference Fourier map
wR(F2) = 0.126All H-atom parameters refined
S = 1.06 w = 1/[σ2(Fo2) + (0.0702P)2 + 0.0077P]
where P = (Fo2 + 2Fc2)/3
2492 reflections(Δ/σ)max < 0.001
219 parametersΔρmax = 0.37 e Å3
0 restraintsΔρmin = 0.24 e Å3
Crystal data top
C11H12N2O2·CH2O2V = 1178.87 (12) Å3
Mr = 250.25Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 5.3163 (3) ŵ = 0.11 mm1
b = 8.1348 (4) ÅT = 183 K
c = 27.259 (2) Å0.2 × 0.1 × 0.1 mm
Data collection top
Bruker AXS SMART CCD area-detector
diffractometer
2492 independent reflections
Absorption correction: empirical (using intensity measurements)
(SADABS; Blessing, 1995; Siemens, 1996)
2104 reflections with I > 2σ(I)
Tmin = 0.761, Tmax = 1.000Rint = 0.064
14392 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0510 restraints
wR(F2) = 0.126All H-atom parameters refined
S = 1.06Δρmax = 0.37 e Å3
2492 reflectionsΔρmin = 0.24 e Å3
219 parameters
Special details top

Experimental. A Bruker AXS low-temerature device was used. The crystal-detector distance was 4 cm and each frame covered 0.3° in ω. The reciprocal space was explored by a combination of three different runs with 2θ = 30°. No intensity decay was observed. SADABS (Siemens, 1996) was used to correct for absorption.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
N10.8375 (4)0.1803 (3)0.95189 (6)0.0285 (4)
C20.7169 (4)0.0686 (3)0.92251 (7)0.0260 (4)
C30.5132 (4)0.1397 (2)0.90033 (6)0.0206 (3)
C40.3415 (4)0.4396 (3)0.91063 (7)0.0241 (4)
C50.3909 (4)0.5876 (3)0.93428 (7)0.0283 (4)
C60.6012 (5)0.6056 (3)0.96504 (7)0.0319 (5)
C70.7655 (4)0.4768 (3)0.97318 (7)0.0288 (4)
C80.7143 (4)0.3275 (3)0.94962 (6)0.0242 (4)
C90.5058 (4)0.3075 (3)0.91776 (6)0.0209 (4)
C100.3366 (4)0.0536 (2)0.86617 (7)0.0223 (4)
C110.3690 (4)0.0946 (2)0.81137 (6)0.0198 (3)
C120.2877 (4)0.2696 (2)0.79913 (6)0.0204 (3)
O130.0556 (3)0.29944 (19)0.80642 (5)0.0255 (3)
O140.4480 (3)0.36826 (19)0.78453 (5)0.0278 (3)
N150.6339 (3)0.0692 (2)0.79503 (6)0.0221 (3)
H10.968 (6)0.164 (3)0.9700 (10)0.035 (7)*
H20.795 (6)0.040 (4)0.9198 (11)0.039 (8)*
H40.208 (5)0.429 (3)0.8900 (9)0.026 (6)*
H50.283 (6)0.682 (4)0.9283 (10)0.035 (7)*
H60.635 (5)0.711 (3)0.9802 (9)0.029 (7)*
H70.902 (5)0.486 (3)0.9933 (9)0.021 (6)*
H110.273 (6)0.019 (4)0.7942 (9)0.031 (7)*
H10A0.355 (5)0.070 (3)0.8708 (9)0.026 (6)*
H10B0.167 (5)0.081 (3)0.8746 (9)0.027 (6)*
H15A0.719 (5)0.162 (3)0.8003 (9)0.026 (7)*
H15B0.713 (7)0.018 (4)0.8124 (10)0.041 (8)*
H15C0.627 (5)0.040 (3)0.7663 (10)0.027 (7)*
O160.2042 (5)0.7887 (2)0.84447 (7)0.0525 (6)
O170.0386 (4)0.5973 (2)0.79702 (6)0.0362 (4)
C180.1563 (5)0.6461 (3)0.83536 (8)0.0329 (5)
H170.018 (7)0.478 (4)0.8008 (11)0.049 (10)*
H180.195 (6)0.557 (4)0.8602 (10)0.037 (8)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0245 (8)0.0381 (10)0.0228 (7)0.0063 (8)0.0043 (6)0.0012 (7)
C20.0281 (10)0.0301 (10)0.0199 (7)0.0063 (8)0.0016 (7)0.0018 (7)
C30.0218 (8)0.0245 (9)0.0156 (7)0.0017 (7)0.0026 (6)0.0011 (6)
C40.0251 (9)0.0253 (9)0.0218 (7)0.0024 (8)0.0000 (7)0.0019 (7)
C50.0340 (11)0.0233 (10)0.0277 (9)0.0014 (8)0.0041 (8)0.0025 (7)
C60.0410 (12)0.0297 (11)0.0251 (8)0.0091 (10)0.0054 (8)0.0051 (8)
C70.0270 (10)0.0402 (12)0.0192 (7)0.0085 (9)0.0013 (7)0.0031 (7)
C80.0222 (8)0.0329 (10)0.0174 (7)0.0003 (8)0.0018 (7)0.0003 (7)
C90.0221 (8)0.0247 (9)0.0158 (7)0.0001 (7)0.0019 (6)0.0002 (6)
C100.0250 (9)0.0202 (9)0.0216 (7)0.0014 (7)0.0022 (7)0.0013 (6)
C110.0207 (8)0.0189 (8)0.0197 (7)0.0013 (7)0.0010 (6)0.0028 (6)
C120.0231 (8)0.0212 (9)0.0168 (7)0.0015 (7)0.0027 (6)0.0007 (6)
O130.0226 (6)0.0239 (7)0.0301 (7)0.0036 (6)0.0006 (5)0.0037 (5)
O140.0278 (7)0.0242 (7)0.0314 (7)0.0007 (6)0.0024 (6)0.0066 (6)
N150.0229 (7)0.0223 (8)0.0211 (7)0.0033 (6)0.0018 (6)0.0026 (6)
O160.0837 (16)0.0243 (9)0.0495 (10)0.0205 (11)0.0049 (11)0.0030 (7)
O170.0496 (10)0.0258 (8)0.0332 (7)0.0058 (7)0.0076 (7)0.0057 (6)
C180.0420 (12)0.0233 (10)0.0334 (10)0.0091 (9)0.0024 (9)0.0017 (8)
Geometric parameters (Å, º) top
N1—C81.366 (3)C8—C91.417 (3)
N1—C21.371 (3)C10—C111.540 (3)
N1—H10.86 (3)C10—H10A1.01 (3)
C2—C31.368 (3)C10—H10B0.96 (3)
C2—H20.98 (3)C11—N151.491 (3)
C3—C91.446 (3)C11—C121.524 (3)
C3—C101.496 (3)C11—H110.93 (3)
C4—C51.390 (3)C12—O141.237 (2)
C4—C91.399 (3)C12—O131.273 (2)
C4—H40.91 (3)N15—H15A0.89 (3)
C5—C61.405 (3)N15—H15B0.95 (3)
C5—H50.97 (3)N15—H15C0.82 (3)
C6—C71.382 (3)O16—C181.213 (3)
C6—H60.97 (3)O17—C181.281 (3)
C7—C81.400 (3)O17—H170.99 (4)
C7—H70.91 (3)C18—H181.01 (3)
O13···O172.487 (2)C2···H7ix2.88 (3)
O13···N15i2.938 (2)C2···H10Bii2.73 (3)
O13···C43.418 (2)C2···H15B3.08 (3)
O13···C183.137 (3)C3···H15B2.92 (3)
O14···C18ii3.384 (3)C3···H15A2.94 (2)
O14···N15iii2.750 (2)C4···H18ii2.98 (3)
O14···O173.206 (3)C5···H18ii3.00 (3)
O14···N152.641 (2)C6···H1ix2.91 (3)
O14···C11iii3.342 (2)C6···H18ii3.08 (3)
O16···C2iv3.144 (3)C7···H1ix2.49 (3)
O16···C10iv3.310 (3)C8···H1ix2.55 (3)
O16···N15iv2.786 (2)C9···H1ix3.07 (3)
O17···C12v3.254 (2)C9···H18ii3.02 (3)
O17···C123.181 (3)C12···H42.83 (2)
O17···O132.487 (2)C12···H15Ciii2.87 (3)
O17···O143.206 (3)C12···H172.35 (3)
O13···H171.51 (3)C18···H43.01 (3)
O13···H42.64 (2)C18···H15Biv2.89 (3)
O13···H182.88 (3)H1···C6vi2.91 (3)
O13···H15Ai2.12 (3)H1···C7vi2.49 (3)
O13···H10B2.64 (2)H1···C8vi2.55 (3)
O14···H15C2.88 (2)H1···C9vi3.07 (3)
O14···H11iii2.88 (3)H2···O16vii2.48 (3)
O14···H172.67 (4)H4···O132.64 (2)
O14···H15A2.25 (3)H4···C122.83 (2)
O14···H15Ciii2.01 (3)H4···C183.01 (3)
O16···H2iv2.48 (3)H7···C2vi2.88 (3)
O16···H10Aiv2.71 (3)H10A···O16vii2.71 (3)
O16···H15Biv1.85 (3)H10B···O132.64 (2)
O17···H11v2.85 (3)H10B···N1i2.86 (3)
O17···H15Ciii2.83 (3)H10B···H2i2.53 (4)
N1···C7vi3.314 (3)H10B···C2i2.73 (3)
N1···C8vi3.350 (3)H11···O17x2.85 (3)
N15···O16vii2.786 (2)H11···O14viii2.88 (3)
N15···O13ii2.938 (2)H15A···O13ii2.12 (3)
N15···O14viii2.750 (2)H15A···O142.25 (3)
N15···O142.641 (2)H15A···C32.94 (2)
N1···H10Bii2.86 (3)H15B···O16vii1.85 (3)
C2···O16vii3.144 (3)H15B···C23.08 (3)
C4···C123.351 (3)H15B···C18vii2.89 (3)
C4···O133.418 (2)H15B···C32.92 (3)
C4···C7i3.518 (3)H15C···O142.88 (2)
C7···C4ii3.518 (3)H15C···O17viii2.83 (3)
C7···N1ix3.314 (3)H15C···C12viii2.87 (3)
C8···N1ix3.350 (3)H15C···O14viii2.01 (3)
C9···C123.449 (2)H17···O131.51 (3)
C10···O16vii3.310 (3)H17···O142.67 (4)
C11···O14viii3.342 (2)H17···C122.35 (3)
C12···O17x3.254 (2)H18···O132.88 (3)
C12···C43.351 (3)H18···C4i2.98 (3)
C12···C93.449 (2)H18···C5i3.00 (3)
C12···O173.181 (3)H18···C6i3.08 (3)
C18···O133.137 (3)H18···C9i3.02 (3)
C18···O14i3.384 (3)
C8—N1—C2109.31 (17)C8—C9—C3106.77 (17)
C8—N1—H1123.1 (19)C3—C10—C11115.58 (16)
C2—N1—H1127.6 (19)C3—C10—H10A108.9 (15)
C3—C2—N1110.36 (19)C11—C10—H10A108.9 (14)
C3—C2—H2133.1 (18)C3—C10—H10B109.4 (16)
N1—C2—H2116.4 (18)C11—C10—H10B106.7 (15)
C2—C3—C9105.98 (18)H10A—C10—H10B107 (2)
C2—C3—C10125.00 (19)N15—C11—C12109.39 (16)
C9—C3—C10129.00 (18)N15—C11—C10111.42 (15)
C5—C4—C9118.88 (19)C12—C11—C10112.53 (15)
C5—C4—H4120.9 (17)N15—C11—H11105.9 (19)
C9—C4—H4120.1 (17)C12—C11—H11110.9 (19)
C4—C5—C6121.1 (2)C10—C11—H11106.5 (17)
C4—C5—H5119.7 (18)O14—C12—O13126.46 (19)
C6—C5—H5119.1 (18)O14—C12—C11118.74 (17)
C7—C6—C5121.3 (2)O13—C12—C11114.78 (18)
C7—C6—H6119.2 (17)C11—N15—H15A108.3 (18)
C5—C6—H6119.5 (17)C11—N15—H15B112 (2)
C6—C7—C8117.4 (2)H15A—N15—H15B109 (2)
C6—C7—H7122.4 (16)C11—N15—H15C106 (2)
C8—C7—H7120.1 (16)H15A—N15—H15C115 (2)
N1—C8—C7130.23 (19)H15B—N15—H15C106 (3)
N1—C8—C9107.57 (18)C18—O17—H17106.0 (18)
C7—C8—C9122.2 (2)O16—C18—O17124.4 (2)
C4—C9—C8119.01 (19)O16—C18—H18120.4 (17)
C4—C9—C3134.19 (18)O17—C18—H18114.9 (17)
C8—N1—C2—C30.1 (2)H4—C4—C5—C6178.1 (19)
N1—C2—C3—C90.7 (2)H4—C4—C9—C8179.2 (19)
C2—C3—C9—C81.0 (2)H5—C5—C6—H61 (3)
C2—C3—C10—C11104.4 (2)H6—C6—C7—H72 (3)
C5—C4—C9—C3179.1 (2)C3—C10—C11—H11169 (2)
C5—C6—C7—C80.0 (3)H10A—C10—C11—H1146 (3)
N1—C8—C9—C30.9 (2)H10B—C10—C11—H1169 (3)
C7—C8—C9—C41.8 (3)H1—N1—C2—C3179 (2)
N15—C11—C12—O13172.45 (15)H1—N1—C8—C9178 (2)
C10—C11—C12—O14115.27 (19)H15A—N15—C11—H11156 (3)
C2—N1—C8—C7179.7 (2)H15B—N15—C11—H1183 (3)
N1—C2—C3—C10179.33 (18)H15C—N15—C11—H1132 (3)
C10—C3—C9—C41.6 (4)C2—C3—C10—H10A18.5 (15)
C9—C3—C10—C1177.3 (3)C9—C3—C10—H10B43.2 (16)
C5—C4—C9—C81.3 (3)H4—C4—C5—H51 (3)
C6—C7—C8—N1177.9 (2)C4—C5—C6—H6177.8 (17)
N1—C8—C9—C4177.44 (18)C5—C6—C7—H7179.3 (18)
C3—C10—C11—N1553.5 (2)H7—C7—C8—N11.4 (18)
N15—C11—C12—O149.1 (2)H10A—C10—C11—N1569.5 (16)
C2—N1—C8—C90.5 (2)H10B—C10—C11—N15175.4 (15)
C2—C3—C9—C4177.0 (2)H11—C11—C12—O1355.9 (19)
C10—C3—C9—C8179.54 (18)H1—N1—C2—H25 (3)
C9—C4—C5—C60.2 (3)H15A—N15—C11—C1088.0 (17)
C4—C5—C6—C70.4 (3)H15B—N15—C11—C1032 (2)
C6—C7—C8—C91.2 (3)H15C—N15—C11—C10147.9 (18)
C7—C8—C9—C3179.83 (18)H2—C2—C3—C9176 (3)
C3—C10—C11—C1269.8 (2)C2—C3—C10—H10B135.1 (15)
C10—C11—C12—O1363.2 (2)C9—C4—C5—H5177 (2)
C8—N1—C2—H2177 (2)H4—C4—C9—C33.0 (19)
H1—N1—C8—C71 (2)H5—C5—C6—C7178 (2)
H15A—N15—C11—C1237.0 (17)H6—C6—C7—C8178.3 (17)
H15B—N15—C11—C12157 (2)H7—C7—C8—C9179.5 (18)
H15C—N15—C11—C1287.1 (18)H10A—C10—C11—C12167.3 (16)
H2—C2—C3—C105 (3)H10B—C10—C11—C1252.2 (15)
C9—C3—C10—H10A159.8 (15)H11—C11—C12—O14125.7 (19)
Symmetry codes: (i) x1, y, z; (ii) x+1, y, z; (iii) x+1, y+1/2, z+3/2; (iv) x1, y+1, z; (v) x, y+1/2, z+3/2; (vi) x+1/2, y+1/2, z+2; (vii) x+1, y1, z; (viii) x+1, y1/2, z+3/2; (ix) x1/2, y+1/2, z+2; (x) x, y1/2, z+3/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N15—H15A···O13ii0.89 (3)2.12 (3)2.938 (2)153 (2)
N15—H15A···O140.89 (3)2.25 (3)2.641 (2)106 (2)
N15—H15B···O16vii0.95 (3)1.85 (3)2.786 (2)167 (3)
N15—H15C···O14viii0.82 (3)2.01 (3)2.750 (2)151 (2)
O17—H17···O130.98 (3)1.51 (3)2.487 (2)171 (4)
Symmetry codes: (ii) x+1, y, z; (vii) x+1, y1, z; (viii) x+1, y1/2, z+3/2.

Experimental details

Crystal data
Chemical formulaC11H12N2O2·CH2O2
Mr250.25
Crystal system, space groupOrthorhombic, P212121
Temperature (K)183
a, b, c (Å)5.3163 (3), 8.1348 (4), 27.259 (2)
V3)1178.87 (12)
Z4
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.2 × 0.1 × 0.1
Data collection
DiffractometerBruker AXS SMART CCD area-detector
diffractometer
Absorption correctionEmpirical (using intensity measurements)
(SADABS; Blessing, 1995; Siemens, 1996)
Tmin, Tmax0.761, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
14392, 2492, 2104
Rint0.064
(sin θ/λ)max1)0.769
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.051, 0.126, 1.06
No. of reflections2492
No. of parameters219
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.37, 0.24

Computer programs: SMART (Siemens, 1996), SMART, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEPIII (Burnett & Johnson, 1996) and SCHAKAL99 (Keller & Pierrard, 1999), PLATON (Spek, 1990).

Selected geometric parameters (Å, º) top
N1—C81.366 (3)C10—C111.540 (3)
N1—C21.371 (3)C11—N151.491 (3)
C2—C31.368 (3)C11—C121.524 (3)
C3—C91.446 (3)C12—O141.237 (2)
C3—C101.496 (3)C12—O131.273 (2)
C5—C61.405 (3)O16—C181.213 (3)
C6—C71.382 (3)O17—C181.281 (3)
C8—N1—C2109.31 (17)C7—C8—C9122.2 (2)
C3—C2—N1110.36 (19)N15—C11—C12109.39 (16)
N1—C8—C7130.23 (19)O14—C12—O13126.46 (19)
N1—C8—C9107.57 (18)O16—C18—O17124.4 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N15—H15A···O13i0.89 (3)2.12 (3)2.938 (2)153 (2)
N15—H15A···O140.89 (3)2.25 (3)2.641 (2)106 (2)
N15—H15B···O16ii0.95 (3)1.85 (3)2.786 (2)167 (3)
N15—H15C···O14iii0.82 (3)2.01 (3)2.750 (2)151 (2)
O17—H17···O130.98 (3)1.51 (3)2.487 (2)171 (4)
Symmetry codes: (i) x+1, y, z; (ii) x+1, y1, z; (iii) x+1, y1/2, z+3/2.
Selected torsion angles (°) for L-tryptophan formic acid solvate, (I), DL-tryptophan formate, (II), and DL-tryptophane, (III). All angles refer to the S configuration at C11, i.e. the L form. top
TorsionNomenclature*(I)(II)(III)
C2-C3-C10-C11χ2.1-104.4 (2)105.1-106.6
C3-C10-C11-C12χ1.2-69.8 (2)-174.668.6
C3-C10-C11-N15χ153.5 (2)-53.7-168.6
N15-C11-C12-O13ψ2172.45 (15)-175.3-19.5
N15-C11-C12-O14ψ1-9.1 (2)-0.5156.0
C10-C11-C12-O13-63.2 (2)-52.6101.9
*For nomenclature see IUPAC-IUB (1970).
 

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