L-Alaninium maleate

In the title compound, C₃H₈NO₂⁺·C₄H₃O₄^-, the alanine mol­ecule exists in the cationic form and the maleic acid mol­ecule in the mono-ionized state. A head-to-tail hydrogen bond is observed between the amino acid mol­ecules. There are no direct hydrogen-bonded interactions between the semimaleate anions. The overall aggregation pattern is similar to that observed in the L-alanine-oxalic acid complex.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.035
• wR factor = 0.106
• Data-to-parameter ratio = 7.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           67.88
         From the CIF: _reflns_number_total               1024
         From the CIF: _diffrn_reflns_limit_ max hkl    6.    8.   25.
         From the CIF: _diffrn_reflns_limit_ min hkl    0.    0.    0.
         TEST1: Expected hkl limits for theta max
         Calculated maximum hkl    6.    8.   28.
         Calculated minimum hkl   -6.   -8.  -28.
          ALERT: Expected hkl max differ from CIF values

REFLT_03
         From the CIF: _diffrn_reflns_theta_max           67.88
         From the CIF: _reflns_number_total               1024
         Count of symmetry unique reflns         1066
         Completeness (_total/calc)             96.06%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured         0
         Fraction of Friedel pairs measured     0.000
         Are heavy atom types Z>Si present           no
          Please check that the estimate of the number of Friedel pairs is
          correct. If it is not, please give the correct count in the
          _publ_section_exptl_refinement section of the submitted CIF.

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S1. Comment

X-ray studies on crystalline complexes of amino acids with simple carboxylic acids, which are believed to have existed in the prebiotic earth (Miller & Orgel, 1974; Kvenvolden et al., 1971), are expected to throw light on the nature of intermolecular interactions and biomolecular aggregation patterns (Vijayan, 1988; Prasad & Vijayan, 1993). The crystal structures of complexes of oxalic acid with glycine (Subha Nandhini et al., 2001a), sarcosine (Krishnakumar et al., 1999), L-alanine (Subha Nandhini et al., 2001b) and DL-alanine (Subha Nandhini et al., 2001c) were elucidated recently. The present study reports the crystal structure of L-alaninium maleate, as part of a series of investigations being carried out, at atomic resolution, on amino acid–carboxylic acid complexes, in our laboratory.

Fig. 1 shows the molecular structure with the numbering scheme. The alanine molecule exists in the cationic form with a positively charged amino group and an uncharged carboxylic acid group. The maleic acid molecule exists in the mono-ionized state (i.e. as a semimaleate). A common feature observed among the crystal structures of L-alaninium oxalate, DL-alaninium oxalate and (I) is that their cell dimensions are almost similar. However, the crystals of the racemate are monoclinic and those of the isomers are orthorhombic. The semimaleate ion is essentially planar and the intramolecular hydrogen bond between atoms O3 and O5 is found to be asymmetric as in the crystal structure of maleic acid (James & Williams, 1974).

Fig. 2 shows the packing of molecules of (I) viewed down the a axis. The alaninium and semimaleate ions form alternate columns parallel to the b axis. There are no direct hydrogen-bond interactions between the semimaleate anions. They link the alaninium ions into a linear chain running parallel to the longer c axis. The overall aggregation pattern is similar to that observed in the L-alanine–oxalic acid complex. A comparison of the crystal structure of (I) with those of complexes of maleic acid with glycine (Rajagopal et al., 2001), DL– and L-arginine (Ravishankar et al., 1998) and L-histidine and L-lysine (Pratap et al., 2000) show that the intrinsic aggregation properties of individual molecules in a particular amino acid–carboxylic acid complex seem to largely depend on the nature of the amino acid.

S2. Experimental

Colorless single crystals of (I) were grown as transparent needles, from a saturated aqueous solution containing L-alanine and maleic acid in a 1:1 stoichiometric ratio. The density was determined by flotation method using a liquid mixture of xylene and bromoform.

S3. Refinement

The absolute configuration of L-alaninium maleate was not established by the analysis but is known from the configuration of the starting reagents. The H atoms were placed at calculated positions and were allowed to ride on their respective parent atoms with HFIX instructions using SHELXL97 (Sheldrick, 1997) defaults.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: CAD-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure of (I) with atom-numbering scheme and 50% probability displacement ellipsoids.
	Fig. 2. Packing diagram of the molecules of (I) viewed down tha a axis.

L-alaninium maleate

Crystal data

C3H8O2N^+·C4H3O4^−	Dx = 1.394 Mg m^−3 Dm = 1.40 (2) Mg m^−3 Dm measured by flotation in a liquid mixture of xylene and bromoform
Mr = 205.17	Cu Kα radiation, λ = 1.54180 Å
Orthorhombic, P212121	Cell parameters from 25 reflections
a = 5.5873 (11) Å	θ = 18–27°
b = 7.3864 (17) Å	µ = 1.08 mm^−1
c = 23.688 (3) Å	T = 293 K
V = 977.6 (3) Å^3	Needle, colorless
Z = 4	0.30 × 0.20 × 0.10 mm
F(000) = 432

Data collection

Enraf-Nonius CAD-4 diffractometer	977 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 67.9°, θmin = 3.7°
ω–2θ scans	h = 0→6
Absorption correction: ψ scan (North et al., 1968)	k = 0→8
Tmin = 0.76, Tmax = 0.90	l = 0→25
1024 measured reflections	2 standard reflections every 200 reflections
1024 independent reflections	intensity decay: 2%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.035	H-atom parameters constrained
wR(F^2) = 0.106	w = 1/[σ^2(Fo^2) + (0.0739P)^2 + 0.1453P] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max < 0.001
1024 reflections	Δρmax = 0.16 e Å^−3
130 parameters	Δρmin = −0.16 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.018 (2)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
O1	0.8011 (3)	0.4977 (3)	−0.05688 (7)	0.0578 (6)
H1	0.8917	0.5114	−0.0838	0.087*
O2	1.1022 (3)	0.6213 (2)	−0.00888 (6)	0.0434 (4)
O3	−0.1268 (3)	0.4926 (5)	0.79094 (8)	0.0725 (8)
H3	−0.1157	0.4609	0.7579	0.109*
O4	0.1121 (3)	0.5327 (3)	0.86261 (7)	0.0519 (5)
O5	−0.0899 (3)	0.4591 (4)	0.68949 (8)	0.0638 (7)
O6	0.1962 (3)	0.4362 (4)	0.62659 (8)	0.0640 (6)
N1	0.8367 (4)	0.6369 (3)	0.08669 (7)	0.0379 (5)
H1A	0.7545	0.6132	0.1180	0.057*
H1B	0.8063	0.7496	0.0755	0.057*
H1C	0.9925	0.6251	0.0936	0.057*
C1	0.9067 (4)	0.5515 (3)	−0.01082 (9)	0.0358 (5)
C2	0.7648 (4)	0.5082 (3)	0.04164 (9)	0.0377 (5)
H2A	0.5934	0.5213	0.0338	0.045*
C3	0.8171 (7)	0.3151 (4)	0.06115 (13)	0.0621 (9)
H3A	0.7258	0.2892	0.0945	0.093*
H3B	0.9846	0.3032	0.0694	0.093*
H3C	0.7739	0.2315	0.0318	0.093*
C4	0.0808 (4)	0.5129 (3)	0.81158 (10)	0.0422 (6)
C5	0.2939 (4)	0.5150 (6)	0.77490 (12)	0.0609 (9)
H5	0.4379	0.5342	0.7936	0.073*
C6	0.3133 (4)	0.4940 (6)	0.71949 (12)	0.0660 (10)
H6	0.4693	0.5012	0.7060	0.079*
C7	0.1314 (4)	0.4614 (4)	0.67550 (10)	0.0482 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0535 (11)	0.0857 (14)	0.0341 (10)	−0.0231 (12)	0.0043 (8)	−0.0119 (9)
O2	0.0419 (9)	0.0564 (9)	0.0319 (9)	−0.0125 (8)	0.0064 (7)	−0.0009 (7)
O3	0.0314 (9)	0.150 (2)	0.0362 (11)	−0.0095 (13)	0.0043 (7)	−0.0252 (13)
O4	0.0540 (10)	0.0730 (11)	0.0286 (9)	−0.0020 (10)	0.0005 (8)	−0.0059 (8)
O5	0.0292 (8)	0.1244 (18)	0.0378 (11)	0.0002 (11)	−0.0022 (7)	−0.0211 (11)
O6	0.0415 (10)	0.1157 (17)	0.0347 (11)	0.0010 (11)	0.0015 (8)	−0.0116 (11)
N1	0.0382 (10)	0.0485 (10)	0.0270 (10)	0.0039 (9)	0.0042 (8)	0.0021 (8)
C1	0.0384 (11)	0.0383 (9)	0.0308 (12)	−0.0026 (10)	0.0017 (9)	0.0002 (8)
C2	0.0346 (10)	0.0462 (12)	0.0323 (12)	−0.0037 (10)	0.0018 (9)	0.0032 (9)
C3	0.083 (2)	0.0442 (12)	0.0597 (17)	−0.0093 (15)	0.0104 (17)	0.0123 (12)
C4	0.0372 (11)	0.0568 (13)	0.0327 (14)	0.0015 (12)	−0.0015 (10)	−0.0065 (10)
C5	0.0266 (12)	0.118 (3)	0.0385 (15)	−0.0019 (16)	−0.0040 (10)	−0.0193 (16)
C6	0.0268 (12)	0.132 (3)	0.0388 (14)	−0.0023 (17)	0.0022 (10)	−0.0191 (18)
C7	0.0320 (11)	0.0828 (18)	0.0298 (12)	0.0021 (13)	0.0012 (10)	−0.0104 (12)

Geometric parameters (Å, º)

O1—C1	1.303 (3)	C1—C2	1.509 (3)
O1—H1	0.8200	C2—C3	1.527 (3)
O2—C1	1.209 (3)	C2—H2A	0.9800
O3—C4	1.267 (3)	C3—H3A	0.9600
O3—H3	0.8200	C3—H3B	0.9600
O4—C4	1.230 (3)	C3—H3C	0.9600
O5—C7	1.281 (3)	C4—C5	1.474 (3)
O6—C7	1.228 (3)	C5—C6	1.326 (4)
N1—C2	1.485 (3)	C5—H5	0.9300
N1—H1A	0.8900	C6—C7	1.475 (4)
N1—H1B	0.8900	C6—H6	0.9300
N1—H1C	0.8900
C1—O1—H1	109.5	C2—C3—H3B	109.5
C4—O3—H3	109.5	H3A—C3—H3B	109.5
C2—N1—H1A	109.5	C2—C3—H3C	109.5
C2—N1—H1B	109.5	H3A—C3—H3C	109.5
H1A—N1—H1B	109.5	H3B—C3—H3C	109.5
C2—N1—H1C	109.5	O4—C4—O3	121.6 (2)
H1A—N1—H1C	109.5	O4—C4—C5	117.6 (2)
H1B—N1—H1C	109.5	O3—C4—C5	120.8 (2)
O2—C1—O1	124.8 (2)	C6—C5—C4	130.4 (2)
O2—C1—C2	122.3 (2)	C6—C5—H5	114.8
O1—C1—C2	112.8 (2)	C4—C5—H5	114.8
N1—C2—C1	108.28 (18)	C5—C6—C7	131.4 (2)
N1—C2—C3	109.2 (2)	C5—C6—H6	114.3
C1—C2—C3	110.3 (2)	C7—C6—H6	114.3
N1—C2—H2A	109.7	O6—C7—O5	121.8 (2)
C1—C2—H2A	109.7	O6—C7—C6	119.2 (2)
C3—C2—H2A	109.7	O5—C7—C6	119.0 (2)
C2—C3—H3A	109.5
O2—C1—C2—N1	27.4 (3)	O3—C4—C5—C6	−1.8 (6)
O1—C1—C2—N1	−155.8 (2)	C4—C5—C6—C7	−0.1 (8)
O2—C1—C2—C3	−92.0 (3)	C5—C6—C7—O6	−175.9 (5)
O1—C1—C2—C3	84.8 (3)	C5—C6—C7—O5	3.7 (7)
O4—C4—C5—C6	178.7 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O4^i	0.82	1.78	2.593 (2)	174
O3—H3···O5	0.82	1.63	2.425 (3)	164
N1—H1A···O5^ii	0.89	2.00	2.887 (3)	175
N1—H1B···O2^iii	0.89	2.17	2.881 (2)	137
N1—H1B···O4^iv	0.89	2.43	2.996 (3)	122
N1—H1C···O6^v	0.89	1.96	2.828 (3)	165
C5—H5···O3^vi	0.93	2.45	3.264 (3)	146
C6—H6···O5^vi	0.93	2.51	3.419 (3)	165

Symmetry codes: (i) x+1, y, z−1; (ii) −x+1/2, −y+1, z−1/2; (iii) x−1/2, −y+3/2, −z; (iv) x+1/2, −y+3/2, −z+1; (v) −x+3/2, −y+1, z−1/2; (vi) x+1, y, z.