L-Phenyl­alanine-nitric acid (2/1)

In the title compound, 2 C₉H₁₁NO₂·H⁺·NO₃^-, both phenyl­alanine residues have a gauche I conformation. The aggregation of the hydro­philic zone is along z = 0 and the hydro­phobic zone is sandwiched between two such layers at z = 0 and z = 1.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.012 Å
• H-atom completeness 70%
• R factor = 0.069
• wR factor = 0.220
• Data-to-parameter ratio = 7.6

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSMU_01  Alert C The ratio of given/expected absorption coefficient lies
          outside the range 0.99 <> 1.01
          Calculated value of mu =     0.106
          Value of mu given      =     0.110

STRVAL_01
         From the CIF: _refine_ls_abs_structure_Flack    0.000
         From the CIF: _refine_ls_abs_structure_Flack_su    4.000
           Alert C Flack test results are meaningless.

General Notes



FORMU_01  There is a discrepancy between the atom counts in the
          _chemical_formula_sum and the formula from the _atom_site* data.
          Atom count from _chemical_formula_sum:C18 H23 N3 O7
          Atom count from the _atom_site data:  C18 H16 N3 O7

CELLZ_01
         From the CIF: _cell_formula_units_Z    2
         From the CIF: _chemical_formula_sum  C18 H23 N3 O7
         TEST: Compare cell contents of formula and atom_site data

         atom    Z*formula  cif sites diff
         C         36.00     36.00    0.00
         H         46.00     32.00   14.00
         N          6.00      6.00    0.00
         O         14.00     14.00    0.00
          Difference between formula and atom_site contents detected.
          WARNING: H atoms missing from atom site list. Is this intentional?

CHEMW_03
         From the CIF: _cell_formula_units_Z                    2
         From the CIF: _chemical_formula_weight           393.39
         TEST: Calculate formula weight from _atom_site_*
         atom     mass    num     sum
         C        12.01   18.00  216.20
         N        14.01    3.00   42.02
         O        16.00    7.00  111.99
         H         1.01   16.00   16.13
         Calculated formula weight              386.34
          The ratio of given/expected molecular weight as calculated
          from the _atom_site* data lies outside
          the range 0.99 <> 1.01

REFLT_03
         From the CIF: _diffrn_reflns_theta_max           25.00
         From the CIF: _reflns_number_total               1895
         Count of symmetry unique reflns         1899
         Completeness (_total/calc)             99.79%
         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.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 2 Alert Level C = Please check

---

S1. Comment

The crystal structures of L-phenylalanine hydrochloride (Gurskaya & Vainstein, 1963; Al-Karaghouli & Koetzle, 1975), L-phenylalanine L-phenylalaninium formate (Gorbitz & Etter, 1992), bis(L-phenylalanine) sulfate monohydrate (Nagashima et al., 1992) and L-phenylalanine L-phenylalaninium perchlorate (Srinivasan & Rajaram, 1997) have been reported. Even though the title compound, (I), has been studied (Srikrishnan et al., 1984), no structural data are available as the above publication does not contain the atomic coordinates and has a misprint in one of the cell dimensions. Therefore, in the present work, an independent X-ray diffraction study of the title compound was undertaken.

Both phenylalanine residues (1 and 2) have similar geometries (Fig. 1). In both residues, the bond distances C—O [1.313 (6) and 1.311 (7) Å] and C═O [1.202 (8) and 1.220 (7) Å] are nearly equal and the single-bonded O atoms of 1 and 2 (O12···O22) are at a distance of 2.426 (8) Å. This may refer to a short hydrogen bond between the singly bonded carboxyl O atoms (O12···O22), as found in L-phenylalanine L-phenylalaninium perchlorate (Srinivasan & Rajaram, 1997). However, this H atom could not be located objectively. Hence, taking into account the equality of the C—O distances (see above), it can be surmised that the two residues may be connected by either a symmetric hydrogen bond or an asymmetric hydrogen bond with the H atom disordered over two positions.

The conformation angles ψ¹ for residues 1 and 2 are -9.9 (7) and 2.5 (8)°, respectively (see Table 1). This tendency towards non-planarity is also found in various amino acids (Lakshminarayanan et al., 1967). The branched side conformation angle χ¹ shows a gauche I conformation for both residues [68.2 (7) and 71.0 (7)°], which agrees well with formate and perchlorate complexes. The χ²¹ [89.0 (8) and 97.0 (8)°] and χ²² [92.3 (8) and -84.3 (7)°] torsion angles indicate that the residues have folded conformation.

The aggregation of hydrophilic zone is along z = 0 plane. The hydrophobic zone at z = 1/2 consists of the phenyl groups of both molecules and is sandwiched between two hydrophilic layers at z = 0 and z = 1 planes (Fig. 2).

S2. Experimental

The title compound was crystallized from an aqueous solution of a 2:1 stoichiometric ratio of L-phenylalanine and nitric acid by slow evaporation.

S3. Refinement

H atoms bonded to C atoms were placed in geometrically calculated positions and allowed to ride on the attached atom. Attempts to introduce H atoms attached to the amino N atom yielded a slight increase in all discrepancy values. Therefore, these H atoms were not included in the final refinement.

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 structures of phenylalanine residues showing the atomic numbering scheme and 50% probability displacement ellipsoids (Johnson, 1976).
	Fig. 2. Packing diagram for the title compound viewed down the b axis

L-Phenylalanine–nitric acid (2/1)

Crystal data

2C9H11NO2·H^+·NO3^−	F(000) = 416
Mr = 393.39	Dx = 1.361 Mg m^−3 Dm = 1.350 Mg m^−3 Dm measured by flotation in a mixture of carbon tetrachloride and xylene
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 12.536 (16) Å	Cell parameters from 25 reflections
b = 5.378 (4) Å	θ = 14.5–23.4°
c = 14.962 (9) Å	µ = 0.11 mm^−1
β = 107.83 (8)°	T = 293 K
V = 960.2 (15) Å^3	Needle, colorless
Z = 2	0.45 × 0.3 × 0.15 mm

Data collection

Enraf-Nonius sealed tube diffractometer	1356 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 25.0°, θmin = 2.5°
ω–2θ scans	h = −14→14
Absorption correction: ψ scan (North et al., 1968)	k = 0→6
Tmin = 0.963, Tmax = 0.984	l = 0→17
1895 measured reflections	3 standard reflections every 60 min
1895 independent reflections	intensity decay: none

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)] = 0.069	H-atom parameters constrained
wR(F^2) = 0.220	w = 1/[σ^2(Fo^2) + (0.1548P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max < 0.001
1895 reflections	Δρmax = 0.30 e Å^−3
250 parameters	Δρmin = −0.34 e Å^−3
3 restraints	Absolute structure: Flack H D (1983)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0 (4)

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
N	0.0352 (4)	0.1764 (13)	0.1120 (4)	0.0506 (15)
O1	0.0705 (6)	0.3884 (15)	0.1375 (8)	0.108 (3)
O2	0.0855 (7)	−0.0024 (15)	0.1021 (8)	0.123 (3)
O3	−0.0728 (4)	0.1534 (12)	0.0948 (4)	0.0692 (16)
O11	0.3355 (3)	0.1787 (8)	0.1035 (3)	0.0440 (11)
O12	0.5151 (3)	0.3053 (11)	0.1553 (4)	0.0585 (15)
C11	0.4061 (4)	0.3366 (13)	0.1292 (4)	0.0336 (14)
C12	0.3784 (4)	0.6101 (12)	0.1460 (4)	0.0357 (14)
H12	0.4126	0.7182	0.1096	0.043*
N11	0.2553 (4)	0.6363 (10)	0.1084 (4)	0.0403 (13)
C13	0.4206 (5)	0.6877 (13)	0.2472 (5)	0.0441 (16)
H13A	0.5017	0.6964	0.2655	0.053*
H13B	0.3933	0.8541	0.2524	0.053*
C14	0.3887 (5)	0.5242 (14)	0.3158 (5)	0.0443 (16)
C15	0.2900 (5)	0.5802 (18)	0.3395 (5)	0.0552 (19)
H15	0.2451	0.7153	0.3129	0.066*
C16	0.2629 (8)	0.427 (3)	0.4034 (7)	0.089 (4)
H16	0.1973	0.4636	0.4173	0.106*
C17	0.3202 (9)	0.235 (2)	0.4463 (7)	0.086 (3)
H17	0.2972	0.1401	0.4890	0.103*
C18	0.4198 (9)	0.1809 (19)	0.4236 (6)	0.083 (3)
H18	0.4641	0.0475	0.4529	0.099*
C19	0.4531 (6)	0.3232 (16)	0.3585 (5)	0.0526 (18)
H19	0.5181	0.2829	0.3440	0.063*
O21	0.7033 (3)	0.0586 (9)	0.0675 (3)	0.0398 (11)
O22	0.5975 (4)	−0.1005 (9)	0.1493 (4)	0.0555 (14)
C21	0.6790 (4)	−0.1115 (11)	0.1116 (4)	0.0341 (14)
C22	0.7352 (4)	−0.3568 (13)	0.1249 (4)	0.0353 (13)
H22	0.6804	−0.4810	0.0911	0.042*
N21	0.8277 (3)	−0.3404 (12)	0.0773 (4)	0.0440 (13)
C23	0.7814 (5)	−0.4392 (15)	0.2257 (5)	0.0482 (16)
H23A	0.7196	−0.4823	0.2490	0.058*
H23B	0.8262	−0.5876	0.2285	0.058*
C24	0.8516 (5)	−0.2462 (13)	0.2884 (5)	0.0433 (16)
C25	0.9652 (4)	−0.2161 (14)	0.2975 (4)	0.0495 (18)
H25	0.9992	−0.3195	0.2644	0.059*
C26	1.0260 (4)	−0.0366 (14)	0.3544 (4)	0.089 (3)
H26	1.1013	−0.0199	0.3589	0.107*
C27	0.9804 (7)	0.1255 (18)	0.4071 (5)	0.065 (2)
H27	1.0232	0.2470	0.4463	0.078*
C28	0.8721 (7)	0.0930 (18)	0.3970 (5)	0.063 (2)
H28	0.8376	0.1995	0.4288	0.076*
C29	0.8102 (6)	−0.0869 (16)	0.3430 (5)	0.0551 (19)
H29	0.7362	−0.1057	0.3422	0.066*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N	0.041 (2)	0.050 (4)	0.059 (4)	−0.010 (3)	0.012 (2)	0.006 (4)
O1	0.080 (4)	0.064 (5)	0.177 (9)	−0.014 (4)	0.036 (5)	−0.011 (6)
O2	0.093 (5)	0.070 (5)	0.223 (11)	0.037 (5)	0.072 (6)	0.003 (6)
O3	0.042 (2)	0.066 (4)	0.094 (4)	−0.004 (3)	0.013 (2)	0.004 (4)
O11	0.048 (2)	0.031 (2)	0.042 (3)	−0.009 (2)	−0.0024 (18)	−0.002 (2)
O12	0.0278 (16)	0.050 (3)	0.098 (4)	0.002 (2)	0.020 (2)	−0.019 (3)
C11	0.029 (2)	0.039 (4)	0.029 (3)	0.016 (3)	0.004 (2)	−0.005 (3)
C12	0.040 (3)	0.034 (4)	0.037 (3)	0.001 (3)	0.017 (2)	0.003 (3)
N11	0.040 (2)	0.033 (3)	0.054 (3)	0.002 (3)	0.025 (2)	−0.004 (3)
C13	0.055 (3)	0.028 (4)	0.052 (4)	0.003 (3)	0.020 (3)	−0.011 (3)
C14	0.053 (3)	0.042 (4)	0.043 (4)	−0.011 (3)	0.021 (3)	−0.002 (4)
C15	0.051 (3)	0.058 (5)	0.060 (4)	−0.002 (4)	0.022 (3)	−0.005 (4)
C16	0.090 (6)	0.130 (11)	0.060 (5)	−0.029 (7)	0.043 (5)	0.006 (7)
C17	0.123 (8)	0.087 (8)	0.052 (5)	−0.033 (7)	0.033 (5)	0.003 (6)
C18	0.117 (7)	0.052 (5)	0.057 (5)	−0.027 (6)	−0.008 (5)	0.024 (5)
C19	0.076 (4)	0.046 (4)	0.022 (3)	0.005 (4)	−0.005 (3)	0.000 (3)
O21	0.048 (2)	0.035 (2)	0.041 (2)	0.006 (2)	0.0207 (19)	0.000 (2)
O22	0.056 (2)	0.036 (3)	0.087 (4)	0.001 (2)	0.040 (3)	0.004 (3)
C21	0.032 (2)	0.027 (3)	0.047 (4)	−0.011 (3)	0.018 (2)	−0.009 (3)
C22	0.036 (2)	0.028 (3)	0.037 (3)	0.002 (3)	0.005 (2)	−0.010 (3)
N21	0.036 (2)	0.051 (3)	0.044 (3)	0.014 (3)	0.012 (2)	−0.003 (3)
C23	0.053 (3)	0.040 (4)	0.051 (4)	0.001 (3)	0.016 (3)	0.015 (4)
C24	0.040 (3)	0.036 (4)	0.041 (4)	0.003 (3)	−0.005 (3)	0.010 (3)
C25	0.046 (3)	0.066 (5)	0.037 (4)	−0.004 (4)	0.013 (3)	−0.006 (4)
C26	0.066 (5)	0.083 (8)	0.099 (8)	−0.004 (6)	−0.001 (5)	−0.018 (7)
C27	0.091 (5)	0.057 (5)	0.041 (4)	−0.022 (5)	0.013 (4)	−0.018 (4)
C28	0.083 (5)	0.061 (6)	0.040 (4)	0.012 (5)	0.010 (4)	−0.010 (4)
C29	0.071 (4)	0.055 (5)	0.045 (4)	0.013 (4)	0.025 (4)	−0.004 (4)

Geometric parameters (Å, º)

N—O2	1.184 (9)	C19—H19	0.9300
N—O1	1.240 (10)	O21—C21	1.220 (7)
N—O3	1.304 (6)	O22—C21	1.311 (7)
O11—C11	1.202 (8)	C21—C22	1.480 (9)
O12—C11	1.313 (6)	C22—C23	1.508 (9)
C11—C12	1.549 (9)	C22—N21	1.539 (7)
C12—N11	1.478 (7)	C22—H22	0.9800
C12—C13	1.502 (9)	C23—C24	1.491 (10)
C12—H12	0.9800	C23—H23A	0.9700
C13—C14	1.496 (9)	C23—H23B	0.9700
C13—H13A	0.9700	C24—C29	1.390 (10)
C13—H13B	0.9700	C24—C25	1.398 (7)
C14—C19	1.383 (11)	C25—C26	1.3565
C14—C15	1.420 (8)	C25—H25	0.9300
C15—C16	1.382 (13)	C26—C27	1.408 (10)
C15—H15	0.9300	C26—H26	0.9300
C16—C17	1.307 (16)	C27—C28	1.332 (11)
C16—H16	0.9300	C27—H27	0.9300
C17—C18	1.421 (14)	C28—C29	1.344 (12)
C17—H17	0.9300	C28—H28	0.9300
C18—C19	1.400 (12)	C29—H29	0.9300
C18—H18	0.9300
O2—N—O1	129.1 (6)	C18—C19—H19	120.3
O2—N—O3	117.4 (7)	O21—C21—O22	123.7 (6)
O1—N—O3	113.5 (7)	O21—C21—C22	123.6 (5)
O11—C11—O12	127.0 (6)	O22—C21—C22	112.6 (5)
O11—C11—C12	122.9 (5)	C21—C22—C23	114.7 (5)
O12—C11—C12	109.8 (6)	C21—C22—N21	106.4 (5)
N11—C12—C13	111.2 (5)	C23—C22—N21	111.5 (4)
N11—C12—C11	106.8 (5)	C21—C22—H22	108.0
C13—C12—C11	113.5 (5)	C23—C22—H22	108.0
N11—C12—H12	108.4	N21—C22—H22	108.0
C13—C12—H12	108.4	C24—C23—C22	113.4 (6)
C11—C12—H12	108.4	C24—C23—H23A	108.9
C14—C13—C12	116.3 (6)	C22—C23—H23A	108.9
C14—C13—H13A	108.2	C24—C23—H23B	108.9
C12—C13—H13A	108.2	C22—C23—H23B	108.9
C14—C13—H13B	108.2	H23A—C23—H23B	107.7
C12—C13—H13B	108.2	C29—C24—C25	115.1 (7)
H13A—C13—H13B	107.4	C29—C24—C23	123.0 (6)
C19—C14—C15	118.8 (7)	C25—C24—C23	122.0 (6)
C19—C14—C13	122.4 (6)	C26—C25—C24	120.2 (4)
C15—C14—C13	118.9 (7)	C26—C25—H25	119.9
C16—C15—C14	117.6 (9)	C24—C25—H25	119.9
C16—C15—H15	121.2	C25—C26—C27	123.1 (4)
C14—C15—H15	121.2	C25—C26—H26	118.4
C17—C16—C15	126.7 (9)	C27—C26—H26	118.4
C17—C16—H16	116.7	C28—C27—C26	115.4 (7)
C15—C16—H16	116.7	C28—C27—H27	122.3
C16—C17—C18	115.8 (9)	C26—C27—H27	122.3
C16—C17—H17	122.1	C27—C28—C29	122.9 (8)
C18—C17—H17	122.1	C27—C28—H28	118.6
C19—C18—C17	121.7 (10)	C29—C28—H28	118.6
C19—C18—H18	119.1	C28—C29—C24	123.2 (7)
C17—C18—H18	119.1	C28—C29—H29	118.4
C14—C19—C18	119.5 (8)	C24—C29—H29	118.4
C14—C19—H19	120.3
O11—C11—C12—N11	−9.9 (7)	O21—C21—C22—C23	126.3 (7)
O12—C11—C12—N11	175.7 (5)	O22—C21—C22—C23	−56.3 (7)
O11—C11—C12—C13	112.9 (7)	O21—C21—C22—N21	2.5 (8)
O12—C11—C12—C13	−61.5 (6)	O22—C21—C22—N21	179.9 (5)
N11—C12—C13—C14	68.2 (7)	C21—C22—C23—C24	−49.9 (7)
C11—C12—C13—C14	−52.2 (7)	N21—C22—C23—C24	71.0 (7)
C12—C13—C14—C19	89.0 (8)	C22—C23—C24—C29	97.0 (8)
C12—C13—C14—C15	−92.3 (8)	C22—C23—C24—C25	−84.3 (7)
C19—C14—C15—C16	−0.9 (12)	C29—C24—C25—C26	−1.9 (8)
C13—C14—C15—C16	−179.7 (8)	C23—C24—C25—C26	179.3 (4)
C14—C15—C16—C17	1.2 (16)	C24—C25—C26—C27	0.4 (5)
C15—C16—C17—C18	−0.4 (17)	C25—C26—C27—C28	−0.5 (10)
C16—C17—C18—C19	−0.7 (15)	C26—C27—C28—C29	2.2 (13)
C15—C14—C19—C18	−0.1 (11)	C27—C28—C29—C24	−3.9 (14)
C13—C14—C19—C18	178.6 (7)	C25—C24—C29—C28	3.6 (11)
C17—C18—C19—C14	1.0 (13)	C23—C24—C29—C28	−177.6 (7)