A.M. Petrosyan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 486–491
487
Fourier map, partially placed on calculated positions and refined in
riding mode. The displacement parameters were refined at values
of 1.2 times of the equivalent isotropic displacement parameter
of the parent atom. The crystallographic data as well as details of
the measurement are listed in Table 1. Further crystallographic
data have been deposited with the Cambridge Crystallographic
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033), citing the title of this paper and the CCDC
No. 898710.
Experimental
Initial reagents and synthesis
As initial reagents we used
L
-tryptophan (Sigma) and picric acid
-tryptophan picrate were
obtained by slow evaporation of aqueous solution containing equi-
molar ratio of -tryptophan and picric acid at room temperature
‘‘pure’’ (made in Poland). The crystals of
L
L
according to Ref. [16]. The obtained crystals represent reddish nee-
dles, as was described in [16].
Registration of the infrared spectra
Attenuated total reflection Fourier-transform infrared spectra
(FTIR ATR) were registered by Nicolet 5700 spectrometer (ZnSe
prizm, Happ-Genzel apodization, ATR distortion is corrected, num-
ber of scans 32, resolution 4 cmꢁ1).
Results and discussion
Crystal and molecular structure
A comparison of the crystallographic data (unit cell parameters)
presented in Table 1 with those of Ref. [16] shows good agreement
and proves that we have obtained the same phase. The asymmetric
part of unit cell with atomic numbering is shown in Fig. 1, for clar-
Crystal structure determination
Single-crystal X-ray intensity data of L-tryptophan picrate were
collected at 296 K on an Bruker-Nonius APEX II diffractometer,
equipped with a CCD area detector and employing graphite-mono-
ity split into two parts, one of
(a), the other of picrate and picric acid (b). In accordance with
the results of Ref. [16] the asymmetric part comprises one -trypto-
phanium cation (the moiety A), one -tryptophan moiety in the
L-tryptophan and L-tryptophanium
chromated Mo Ka radiation (k = 0.71073 Å). For the measurement,
L
a suitable single crystal sample with the size of approximately
0.4 ꢂ 0.2 ꢂ 0.2 mm3 was mounted on a thin glass needle with lab-
oratory grease. Although the crystals were not very well crystal-
ized, the specimen proved acceptable for measurement purposes.
A full Ewald sphere was measured. The reflection data were col-
lected and processed using the Bruker-Nonius program suites Bru-
ker SAINT and related analysis software [17,18]. The structures
were solved by direct methods and subsequent Fourier and differ-
ence Fourier syntheses, followed by full-matrix least-square refine-
ments on F2, using the program SHELX [19]. All non-hydrogen
atoms have been refined with anisotropic displacement parame-
ters, the hydrogen atoms were partially located from the difference
L
form of zwitter-ion (moiety B), a picrate anion (moiety C) and a
neutral picric acid (moiety D). In Table 2 selected intramolecular
bond lengths are shown. Unfortunately the accuracy of these
parameters are not much better than those of Ref. [16] (e.s.d.’s
for bond lengths are in the range 0.005–0.014 Å compared to
0.006–0.024 Å [16]), as the crystal quality was not very high. They
are in agreement with respective data of Ref. [16] (CSD Refcode:
HAGBOG). Since the main difference between our results and the
results of Ref. [16] is in hydrogen bonding scheme, we will consider
hydrogen bonds in more detail. Hydrogen bonds’ parameters are
shown in Table 3. According to our expectation, the cationic
ptophanium (the moiety A) forms a strong O1A–H1Aꢀ ꢀ ꢀO1B hydro-
gen bond with the zwitter-ionic -tryptophan (the moiety B), with
L-try-
L
Table 1
an Oꢀ ꢀ ꢀO distance equal to 2.470(6) Å, thus forming Aꢀ ꢀ ꢀA+ type di-
meric cation (Fig 1a). This bond was also found in an electron den-
sity map (Fig. 2). This dimeric cation forms another hydrogen bond
with picrate anion via the N1B–H1B1ꢀ ꢀ ꢀO1C hydrogen bond, with
2.806 Å and 2.02 Å distances for N1Bꢀ ꢀ ꢀO1C and H1B1ꢀ ꢀ ꢀO1C,
respectively (Table 3). All other intermolecular hydrogen bonds
are weaker. For example, the N1AHþ3 group also forms a hydrogen
bond with picrate anion (N1A–H1A2ꢀ ꢀ ꢀO1C), which is, however,
weaker (Table 3). The N1AHþ3 group has also the N1A–H1A3ꢀ ꢀ ꢀO2B
contact, which, however, is on the level of van der Waals interac-
tion. The picrate anion, in addition, accepts two more weak hydro-
gen bonds: N2A–H21Aꢀ ꢀ ꢀO12C and N1B–H1B2ꢀ ꢀ ꢀO32C. The N1BH3þ
group forms also a weak hydrogen bond with the carbonyl oxygen
Crystal data and details of the refinement for L-tryptophan L-tryptophanium picrate
picric acid.
Formula
Mr
C34H30N10O18
866.68
Crystal system
Space group
a (Å)
Orthorhombic
P212121
7.7745(7)
15.462(2)
31.088(3)
3737.1(6)
4
b (Å)
c (Å)
V (Å3)
Z
Dcalcd (g cmꢁ3
)
1.540
0.127
l(Mo K
a
) (cmꢁ1
)
F(000)
1792
hkl range
T (K)
ꢁ9/12, ꢁ23/16, ꢁ45/36
296(2)
O2A atom of L-tryptophanium cation. It is worth to consider the
Reflections measured
Reflections unique
42,781
11,934
features of hydrogen bonds of picric acid moiety. The bond length
C1D–O1D (1.312(7) Å) indicates that the O1D oxygen atom should
be bonded with hydrogen atom. However, this hydrogen atom is
disordered and occupies two positions: H11D and H12D (both
half-occupied). The hydrogen atom in these positions forms intra-
molecular hydrogen bonds with the O11D and O32D oxygen atoms
of nitro groups (see Table 3). There is also a O1D–H12Dꢀ ꢀ ꢀO1B con-
tact, which, in spite of relatively short Oꢀ ꢀ ꢀO (2.666(7) Å) distance,
should be considered as a weak hydrogen bond, if one takes into
account the values of the H12Dꢀ ꢀ ꢀO1B distance and the OHO angle
(Table 3). At last it should be mentioned that similar to the N(2A)H
group the N(2B)H group also forms a weak hydrogen bond with
O21D atom of the picric acid’s nitro group.
Data with Fo > 4
r(Fo)
3087
Rint
0.131
Parameters refined
569
0.0895
0.1995
0.051/0.000
ꢁ0.15(19)
0.945
0.242/ꢁ0.257
R1(F)*(for Fo > 4
r(Fo))
wR2(F2)* (all reflections)
Weighting parameters a/b
Flack parameter [20]
GoF (F2)*
D
qfin (max/min) [e Åꢁ3
]
Note: Scattering factors for neutral atoms were employed in the refinement.
ꢂ
ꢃ
1=2
ꢀ
ꢁ
h
2
*
R1 =
R
2
||Fo| ꢁ |Fc||
R
|Fo|,
wR2 ¼
Rw
F2o ꢁ F2c
=R
wF4o
; w ¼ 1= r2ðF2o Þþ
ꢀ
ꢁ
ða ꢂ PÞ þ b ꢂ Pꢃ; P ¼ F2o þ 2Fc2 =3.