L-Aspartic acid monohydrate

In the title compound, C₄H₇NO₄·H₂O, the screw-related aspartic acid molecules are linked along the a axis by N—H...O hydrogen bonds to form helical structures. The adjacent helices are inter-linked through O—H...O hydrogen bonds and also by the water mol­ecules through N—H...O(W) and O(W)—H...O hydrogen bonds, to form a three-dimensional network.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.061
• wR factor = 0.173
• Data-to-parameter ratio = 12.2

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



RADNW_01  Alert C The radiation wavelength lies outside the expected range
          for the supplied radiation type. Expected range 0.71065-0.71075
          Wavelength given =    0.70165

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           24.63
         From the CIF: _reflns_number_total               1132
         Count of symmetry unique reflns          691
         Completeness (_total/calc)            163.82%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured       441
         Fraction of Friedel pairs measured     0.638
         Are heavy atom types Z>Si present           no
          ALERT: MoKa measured Friedel data cannot be used to
                 determine absolute structure in a light-atom
                 study EXCEPT under VERY special conditions.
                 It is preferred that Friedel data is merged in such cases.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

Aspartic acid is non-essential amino acid, widely distributed in proteins, which plays a major role in the energy cycle of the human body. The crystal structures of L-aspartic acid (Derissen et al., 1968), DL-aspartic acid (Rao, 1973; Sequeria et al., 1989), DL-aspartic acid nitrate monohydrate (Asath Bahadur & Rajaram, 1995), bis(DL-aspartic acid) sulfate (Srinivasan et al., 2001) and L-aspartic acid nitrate–L-aspartic acid (1/1) (Sridhar et al., 2002) have been reported. In the present paper, the crystal structure of L-aspartic acid monohydrate, (I), is reported.

The asymmetric unit of (I) contains one aspartic acid residue and one water molecule (Fig. 1). The equality of C—O bond distances [1.240 (4) and 1.259 (4) Å] and O—C—C bond angles [118.3 (3) and 115.3 (3)°] (Table 1) represent the deprotonated carboxylate group. The backbone conformation angle ψ¹ of −10.8 (4)° indicates the cis form. The side chain shows a gauche II conformation [χ¹ = −71.8 (3)°]. The branched chain conformation angles χ¹¹ and χ²¹ are in cis and trans form. The C^γ atom is in the gauche I [52.7 (3)°] conformation with respect to C' atom. The molecular structure is stabilized by a weak intramolecular N1—H1B···O3 hydrogen bond.

The screw-related aspartic acid molecules are linked along the a axis by N1—H1A···O1ⁱ hydrogen bonds to form a helical structure (Table 2 and Fig.1). This helical structure is further stabilized by N1—H1C···O3ⁱⁱ hydrogen bonds which link the molecules translated a unit along the a axis. The adjacent helices are interlinked through O4—H4···O2ⁱⁱⁱ hydrogen bonds and also by the water molecules through N1—H1B···O11^iv, O11—H11···O2^v and O11—H12···O2ⁱ hydrogen bonds, to form a three-dimensional network. Within the network, the O4—H4···O2ⁱⁱⁱ hydrogen bonds link the screw related molecules, to form zigzag chains along the c axis. Class II hydrogen-bonding pattern is observed in the present structure having two two-centered hydrogen bonding and one three-centered hydrogen bonding (Jeffrey & Saegner, 1991). In the present study, the water molecule shows planar 1B-1/one-dimensional orientation (Jeffrey & Saegner, 1991). All the symmetry codes are as in Table 2. A view of the molecular packing down the a axis is shown in Fig. 2.

S2. Experimental

The title compound was crystallized from the aqueous solution when attempts were made to grow the single crystals of L-aspartic acid with sulfuric acid.

S3. Refinement

The H atoms of the water molecule were located from a difference Fourier map and their isotropic displacement parameters were refined [U_iso(H) = 0.04 (1) and 0.07 (2) Ų]. All other H atoms were placed in geometrically calculated positions and included in the refinement in the riding-model approximation, with U_iso equal to 1.2U_eq of the carrier atom. Intensities for 442 Friedel pairs were measured, resulting in a Flack parameter of 0(3). Though the absolute structure could not be confirmed as a result of weak anamalous signal, the Friedel pairs were not merged due to resulting low r/p ratio.

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, 1997); 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 structure of the title compound, showing 50% probability displacement ellipsoids (Johnson, 1976) and the atom-numbering scheme.
	Fig. 2. A view of the helical structures formed along the a axis. For clarity, all H atoms except H1A have been omitted.
	Fig. 3. Hydrogen-bonding network viewed down the a axis.

'L-aspartic acid monohydrate'

Crystal data

C4H7NO4·H2O	F(000) = 320
Mr = 151.12	Dx = 1.548 Mg m^−3 Dm = 1.54 Mg m^−3 Dm measured by Flotation in a mixture of carbon tetrachloride and xylene
Orthorhombic, P212121	Mo Kα radiation, λ = 0.70165 Å
Hall symbol: P 2ac 2ab	Cell parameters from 25 reflections
a = 5.587 (4) Å	θ = 8.0–13.8°
b = 9.822 (5) Å	µ = 0.14 mm^−1
c = 11.813 (9) Å	T = 293 K
V = 648.2 (8) Å^3	Block, colorless
Z = 4	0.3 × 0.3 × 0.3 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	1091 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.085
Graphite monochromator	θmax = 24.6°, θmin = 2.7°
ω–2θ scans	h = 0→6
Absorption correction: ψ scan (North et al., 1968)	k = 0→11
Tmin = 0.958, Tmax = 0.958	l = −14→14
1318 measured reflections	3 standard reflections every 60 min
1132 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.061	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.173	H atoms treated by a mixture of independent and constrained refinement
S = 1.06	w = 1/[σ^2(Fo^2) + (0.136P)^2 + 0.3381P] where P = (Fo^2 + 2Fc^2)/3
1132 reflections	(Δ/σ)max < 0.001
93 parameters	Δρmax = 0.33 e Å^−3
0 restraints	Δρmin = −0.54 e Å^−3

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	0.8829 (4)	0.1742 (2)	−0.00394 (19)	0.0281 (6)
O2	0.9943 (4)	−0.0435 (2)	0.0011 (2)	0.0322 (6)
C1	0.8759 (5)	0.0573 (3)	0.0356 (2)	0.0211 (7)
C2	0.6928 (5)	0.0265 (3)	0.1294 (2)	0.0204 (7)
H2	0.5635	−0.0266	0.0948	0.025*
N1	0.5849 (5)	0.1570 (3)	0.1709 (2)	0.0225 (6)
H1A	0.5289	0.2043	0.1123	0.034*
H1B	0.6961	0.2057	0.2066	0.034*
H1C	0.4656	0.1386	0.2184	0.034*
C3	0.7905 (5)	−0.0570 (3)	0.2273 (3)	0.0236 (7)
H3A	0.8240	−0.1484	0.2008	0.028*
H3B	0.6686	−0.0634	0.2855	0.028*
C4	1.0170 (6)	0.0020 (3)	0.2793 (3)	0.0215 (7)
O3	1.1118 (4)	0.1059 (2)	0.2390 (2)	0.0301 (6)
O4	1.1037 (5)	−0.0630 (3)	0.3683 (2)	0.0451 (7)
H4	1.2247	−0.0242	0.3907	0.068*
O11	0.3015 (6)	0.7701 (3)	0.1132 (2)	0.0430 (7)
H11	0.2037	0.8162	0.0855	0.037 (11)*
H12	0.3390	0.7142	0.0674	0.072 (19)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0359 (11)	0.0217 (11)	0.0268 (11)	−0.0021 (9)	0.0069 (10)	0.0077 (10)
O2	0.0363 (12)	0.0256 (11)	0.0348 (12)	0.0058 (10)	0.0098 (11)	−0.0020 (10)
C1	0.0208 (14)	0.0244 (14)	0.0179 (13)	−0.0016 (11)	0.0004 (11)	0.0007 (12)
C2	0.0206 (14)	0.0162 (14)	0.0246 (15)	−0.0016 (12)	0.0014 (12)	−0.0001 (11)
N1	0.0232 (12)	0.0187 (12)	0.0256 (13)	0.0034 (10)	0.0022 (10)	0.0019 (10)
C3	0.0257 (15)	0.0171 (14)	0.0280 (15)	−0.0026 (12)	0.0053 (13)	0.0077 (12)
C4	0.0220 (13)	0.0180 (14)	0.0244 (14)	0.0025 (11)	0.0054 (12)	0.0027 (12)
O3	0.0275 (11)	0.0237 (12)	0.0391 (12)	−0.0059 (9)	−0.0041 (10)	0.0068 (10)
O4	0.0454 (16)	0.0453 (16)	0.0445 (14)	−0.0009 (14)	−0.0070 (14)	0.0067 (13)
O11	0.0516 (16)	0.0395 (14)	0.0380 (14)	0.0107 (13)	−0.0034 (13)	−0.0022 (12)

Geometric parameters (Å, º)

O1—C1	1.240 (4)	C3—C4	1.522 (5)
O2—C1	1.259 (4)	C3—H3A	0.97
C1—C2	1.538 (4)	C3—H3B	0.97
C2—N1	1.499 (3)	C4—O3	1.244 (4)
C2—C3	1.519 (4)	C4—O4	1.322 (4)
C2—H2	0.98	O4—H4	0.82
N1—H1A	0.89	O11—H11	0.78
N1—H1B	0.89	O11—H12	0.80
N1—H1C	0.89
O1—C1—O2	126.2 (3)	H1A—N1—H1C	109.5
O1—C1—C2	118.3 (3)	H1B—N1—H1C	109.5
O2—C1—C2	115.3 (3)	C2—C3—C4	113.6 (2)
N1—C2—C3	110.9 (2)	C2—C3—H3A	108.8
N1—C2—C1	109.5 (2)	C4—C3—H3A	108.8
C3—C2—C1	114.6 (2)	C2—C3—H3B	108.8
N1—C2—H2	107.2	C4—C3—H3B	108.8
C3—C2—H2	107.2	H3A—C3—H3B	107.7
C1—C2—H2	107.2	O3—C4—O4	123.0 (3)
C2—N1—H1A	109.5	O3—C4—C3	120.8 (3)
C2—N1—H1B	109.5	O4—C4—C3	116.2 (3)
H1A—N1—H1B	109.5	C4—O4—H4	109.5
C2—N1—H1C	109.5	H11—O11—H12	107.5
O1—C1—C2—N1	−10.8 (4)	N1—C2—C3—C4	−71.9 (3)
O2—C1—C2—N1	173.9 (3)	C1—C2—C3—C4	52.8 (3)
O1—C1—C2—C3	−136.2 (3)	C2—C3—C4—O3	−2.9 (4)
O2—C1—C2—C3	48.5 (3)	C2—C3—C4—O4	177.0 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1^i	0.89	1.93	2.813 (4)	171
N1—H1C···O3^ii	0.89	2.02	2.809 (4)	147
O4—H4···O2^iii	0.82	2.15	2.933 (4)	161
N1—H1B···O11^iv	0.89	2.22	2.854 (4)	128
O11—H11···O2^v	0.78	2.06	2.837 (4)	170
O11—H12···O2^i	0.80	2.05	2.817 (4)	160
N1—H1B···O3	0.89	2.55	3.093 (4)	120

Symmetry codes: (i) x−1/2, −y+1/2, −z; (ii) x−1, y, z; (iii) −x+5/2, −y, z+1/2; (iv) −x+1, y−1/2, −z+1/2; (v) x−1, y+1, z.