Redetermined crystal structure of β-dl-me­thio­nine at 320 K

Görbitz, C.H.; Paulsen, J.C.; Borgersen, J.

doi:10.1107/S2056989015008749

organic compounds

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Volume 71| Part 6| June 2015| Pages o398-o399

doi:10.1107/S2056989015008749

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Redetermined crystal structure of β-DL-methionine at 320 K

Carl Henrik Görbitz,^a ^* Jan Christian Paulsen ^a and Jon Borgersen ^b

^aDepartment of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway, and ^bDepartment of Physics, University of Oslo, PO Box 1048 Blindern, N-0316 Oslo, Norway
^*Correspondence e-mail: c.h.gorbitz@kjemi.uio.no

Edited by H. Stoeckli-Evans, University of Neuchâtel, Switzerland (Received 30 April 2015; accepted 5 May 2015; online 13 May 2015)

The structure of β-DL-methionine, C₅H₁₁NO₂S, in the space group C2/c, is here confirmed to be fully ordered all the way up to the phase transition at approximately 326 K, where displacive sliding of molecular bilayers gives the disordered P2₁/c α form [data at 340 K; Görbitz (2014). Acta Cryst. E70, 341–343]. The geometry of hydrogen bonds in LD–LD hydrogen-bonding patterns [Görbitz et al. (2009). Acta Cryst. B65, 393–400] at the hydrophilic core of each molecular bilayer are virtually unperturbed by the phase shift, but the C—C—S—C torsion angle of the side chain changes from trans at 320 K to gauche+ for the major conformation at 340 K.

Keywords: crystal structure; amino acid; phase transition; disorder.

CCDC reference: 1063335

1. Related literature

For previous investigations of DL-methionine (DL-Met), see: Mathieson (1952 ); Taniguchi et al. (1980 ); Alagar et al. (2005 ); Görbitz (2014 ); Görbitz et al. (2014 ). For a discussion of displacive phase transitions of amino acids with linear side chains and structures of quasiracemic complexes, see: Görbitz & Karen (2015 ). For the phase behaviour of the corresponding enantiomeric substances, including L-Met and L-norvaline, see: Görbitz et al. (2015 ). For a discussion of hydrogen-bonding patterns in the crystal structures of hydrophobic amino acids, see: Görbitz et al. (2009 ).

2. Experimental

2.1. Crystal data

C₅H₁₁NO₂S
M_r = 149.21
Monoclinic, C 2/c
a = 31.774 (2) Å
b = 4.6969 (3) Å
c = 9.8939 (7) Å
β = 91.224 (2)°
V = 1476.20 (18) Å³
Z = 8
Mo Kα radiation
μ = 0.37 mm⁻¹
T = 320 K
0.72 × 0.15 × 0.10 mm

2.2. Data collection

Bruker D8 Advance single-crystal CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2014 ) T_min = 0.924, T_max = 1.000
10516 measured reflections
2060 independent reflections
1567 reflections with I > 2σ(I)
R_int = 0.031

2.3. Refinement

R[F² > 2σ(F²)] = 0.046
wR(F²) = 0.116
S = 1.03
2060 reflections
92 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.34 e Å⁻³
Δρ_min = −0.39 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O1ⁱ	0.90 (2)	1.88 (2)	2.7732 (17)	173.7 (19)
N1—H2⋯O2ⁱⁱ	0.92 (2)	1.92 (2)	2.8264 (18)	171.0 (18)
N1—H3⋯O2ⁱⁱⁱ	0.90 (2)	1.94 (2)	2.7973 (18)	159.2 (18)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[x, -y+1, z+{\script{1\over 2}}]$ ; (iii) $[x, -y+2, z+{\script{1\over 2}}]$ .

Table 2
Selected torsion angles (°)

Torsion angle	β-DL-Met, 320 K	α-DL-Met, 340 K^a	α-DL-Met, 340 K^b
N1—C2—C3—C4	−55.52 (18)	−59.3 (4)	73 (8)
C1—C2—C3—C4	−175.03 (14)	−178.0 (2)	−78 (5)
C2—C3—C4—S1	−179.16 (12)	176.7 (2)	178 (5)
C3—C4—S1—C5	−174.55 (16)	69.4 (3)	60 (3)
Notes: (a) major conformation, occupancy 0.9509 (18) (Görbitz et al., 2014); (a) minor conformation, occupancy 0.0491 (18).

Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT-Plus (Bruker, 2014); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS2014 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015 ); molecular graphics: Mercury (Macrae et al., 2008 ); software used to prepare material for publication: SHELXL2014.

Supporting information

CCDC reference: 1063335

Crystal structure: contains datablocks I, global. DOI: 10.1107/S2056989015008749/su5129sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S2056989015008749/su5129Isup2.hkl

Supporting information file. DOI: 10.1107/S2056989015008749/su5129Isup3.cml

checkCIF report

Comment top

The two known polymorphs of DL-methionine (DL-Met), called α and β, were originally described by Mathieson (1952). Taniguchi et al. (1980) established the (first and only) transition temperature T₁ to be about 326 K and carried out redeterminations at room temperature (β-form) and 333 K (α-form). β-DL-Met was subsequently redetermined at 105 K (Alagar et al., 2005; Görbitz, 2014) and α-DL-Met at 340 K (Görbitz et al., 2014). The transition between the two forms involves displacive sliding of molecular bilayers in the crystal. Recently, we have shown that such transitions are not limited to regular racemates of amino acids with linear side chains, but occur also for their quasiracemic complexes, including L-norvaline:D-norleucine (Görbitz & Karen, 2015), and for enantiomeric L-norvaline (Görbitz et al., 2015). A special property of just these two structures is that all side chains remain ordered up to T₁, but that one or more additional low-occupancy conformations appear at higher temperatures.

The side chain of β-DL-Met is ordered at 105 K (Alagar et al., 2005; Görbitz, 2014), while a minor component is found for α-DL-Met at 340 K (Görbitz et al., 2014), Fig. 1. As the quality of the available room-temperature crystal structure is rather low (R = 0.088; Taniguchi et al., 1980), it was not known, however, if disorder in this case develops gradually between 105 K and 326 K (T₁) or is introduced abruptly during the phase transition. The purpose of the present investigation was to settle this matter by collection of accurate experimental data with modern equipment at a temperature just below T_1. This initiative was triggered by new results for L-Met (Görbitz et al., 2015) that unexpectedly revealed disorder for both molecules in the asymmetric unit at room temperature.

The molecular structure of β-DL-Met at 320 K (I), depicted in Fig. 1, proves to be very well defined with no significant residual peaks in the electron density map. This means that the change from ordered to disordered side chain upon heating through a displacive phase transition, as observed for L-norvaline:D-norleucine and L-norvaline (see above), recurs for DL-Met. There is, however, one important tweak: while the dominating, major side-chain conformation of disordered molecules in the two other systems is always inherited from the ordered, lower-temperature polymorph, Fig. 1 shows that the gauche–, trans, trans conformation of β-DL-Met at 320 K (Table 1), is instead replaced by a gauche–, trans, gauche+ conformation in α-DL-Met at 340 K.

Hydrogen-bond parameters are listed in Table 2. N···O distances are marginally shorter at 320 K than at 340 K (Görbitz et al., 2014).

Related literature top

For previous investigations of DL-methionine (DL-Met), see: Mathieson (1952); Taniguchi et al. (1980); Alagar et al. (2005); Görbitz (2014); Görbitz et al. (2014). For a discussion of displacive phase transitions of amino acids with linear side chains, see: Görbitz & Karen (2015). For a discussion of structures of quasiracemic complexes, see: Görbitz & Karen (2015). For the phase behaviour of the corresponding enantiomeric substances, including L-Met and L-norvaline, see: Görbitz et al. (2015). For a discussion of hydrogen-bonding patterns in the crystal structures of hydrophobic amino acids, see: Görbitz et al. (2009).

Experimental top

From a saturated solution of DL-Met in water (approximately 30 mg mL^-1) 30 µL was pipetted into a 40 × 8 mm test tube, which was then sealed with parafilm. A needle was used to pierce a small hole in the parafilm and the tube placed inside a larger test tube filled with 2 ml of acetonitrile. The system was ultimately capped and left for one week at 20 °C. Suitable single crystals in the shape of needles and plates formed as the organic solvent diffused into the aqueous solution.

Computing details top

Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT-Plus (Bruker, 2014); data reduction: SAINT-Plus (Bruker, 2014); program(s) used to solve structure: SHELXS2014 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015).

Figures top

Fig. 1. The molecular structure of β-DL-methionine at 320 K, with atom labelling, flanked by the structures at 105 K (published with the alternative space group setting I2/a, Alagar et al., 2005; Görbitz, 2014) and 340 K (Görbitz et al., 2014). Thermal displacement ellipsoids are shown at the 50% probability level. Atoms of the minor side-chain conformation with occupancy 0.0491 (18) at 340 K (with H atoms omitted) are shown in a lighter tone. The side-chain conformation is gauche–, trans, trans (as defined by the N1—C2—C3—C4, C2—C3—C4—S1 and C3—C4—S1—C5 torsion angles of the L-enantiomer shown) at 105 and 320 K, while the major and minor conformations at 340 K are gauche–, trans, gauche+ and gauche+, trans, gauche+, respectively.

2-Amino-4-(methylsulfanyl)butanoic acid top

Crystal data top

C₅H₁₁NO₂S	F(000) = 640
M_r = 149.21	D_x = 1.343 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 31.774 (2) Å	Cell parameters from 4136 reflections
b = 4.6969 (3) Å	θ = 2.6–29.5°
c = 9.8939 (7) Å	µ = 0.37 mm⁻¹
β = 91.224 (2)°	T = 320 K
V = 1476.20 (18) Å³	Needle, colourless
Z = 8	0.72 × 0.15 × 0.10 mm

Data collection top

Bruker D8 Advance single-crystal CCD diffractometer	2060 independent reflections
Radiation source: fine-focus sealed tube	1567 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.031
Detector resolution: 8.3 pixels mm^-1	θ_max = 29.5°, θ_min = 2.6°
Sets of exposures each taken over 0.5° ω rotation scans	h = −44→39
Absorption correction: multi-scan (SADABS; Bruker, 2014)	k = −6→6
T_min = 0.924, T_max = 1.000	l = −13→13
10516 measured reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.046	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.116	w = 1/[σ²(F_o²) + (0.0458P)² + 1.6546P] where P = (F_o² + 2F_c²)/3
S = 1.03	(Δ/σ)_max = 0.001
2060 reflections	Δρ_max = 0.34 e Å⁻³
92 parameters	Δρ_min = −0.39 e Å⁻³

Crystal data top

C₅H₁₁NO₂S	V = 1476.20 (18) Å³
M_r = 149.21	Z = 8
Monoclinic, C2/c	Mo Kα radiation
a = 31.774 (2) Å	µ = 0.37 mm⁻¹
b = 4.6969 (3) Å	T = 320 K
c = 9.8939 (7) Å	0.72 × 0.15 × 0.10 mm
β = 91.224 (2)°

Data collection top

Bruker D8 Advance single-crystal CCD diffractometer	2060 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2014)	1567 reflections with I > 2σ(I)
T_min = 0.924, T_max = 1.000	R_int = 0.031
10516 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.046	0 restraints
wR(F²) = 0.116	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	Δρ_max = 0.34 e Å⁻³
2060 reflections	Δρ_min = −0.39 e Å⁻³
92 parameters

Special details top

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. Final R-factor is 0.0364 for a refinement based on 1300 reflections with 2 theta < 50 °.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
S1	0.44096 (2)	0.65785 (16)	0.45693 (7)	0.0684 (2)
O1	0.28350 (4)	0.4246 (2)	0.19616 (11)	0.0316 (3)
N1	0.29732 (4)	0.7975 (3)	0.39652 (12)	0.0252 (3)
H1	0.2705 (6)	0.826 (4)	0.3685 (19)	0.038*
H2	0.2998 (6)	0.627 (5)	0.441 (2)	0.038*
H3	0.3042 (6)	0.926 (4)	0.461 (2)	0.038*
C1	0.30472 (4)	0.6339 (3)	0.16326 (14)	0.0225 (3)
C2	0.32477 (5)	0.8093 (3)	0.27735 (13)	0.0229 (3)
H21	0.3278	1.0073	0.2479	0.028*
O2	0.31323 (4)	0.7062 (3)	0.04532 (10)	0.0383 (3)
C3	0.36823 (5)	0.6847 (4)	0.31133 (16)	0.0318 (3)
H31	0.3651	0.4828	0.3293	0.038*
H32	0.3858	0.7044	0.2329	0.038*
C4	0.39054 (5)	0.8220 (4)	0.43157 (19)	0.0406 (4)
H41	0.3739	0.7986	0.5118	0.049*
H42	0.3940	1.0242	0.4153	0.049*
C5	0.45831 (8)	0.8257 (7)	0.6094 (3)	0.0750 (8)
H51	0.4861	0.7596	0.6334	0.113*
H52	0.4393	0.7799	0.6804	0.113*
H53	0.4589	1.0282	0.5965	0.113*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.0405 (3)	0.0825 (5)	0.0809 (4)	0.0201 (3)	−0.0269 (3)	−0.0255 (4)
O1	0.0365 (6)	0.0287 (6)	0.0295 (6)	−0.0081 (5)	−0.0036 (4)	−0.0017 (4)
N1	0.0289 (6)	0.0278 (6)	0.0189 (6)	0.0044 (5)	−0.0031 (5)	−0.0035 (5)
C1	0.0270 (7)	0.0198 (6)	0.0204 (6)	0.0041 (5)	−0.0051 (5)	−0.0015 (5)
C2	0.0308 (7)	0.0192 (6)	0.0186 (6)	−0.0018 (5)	−0.0028 (5)	0.0008 (5)
O2	0.0657 (8)	0.0314 (6)	0.0176 (5)	−0.0024 (6)	−0.0001 (5)	0.0011 (4)
C3	0.0278 (7)	0.0356 (8)	0.0318 (8)	0.0003 (7)	−0.0033 (6)	−0.0050 (7)
C4	0.0336 (8)	0.0417 (10)	0.0458 (10)	0.0047 (7)	−0.0144 (7)	−0.0078 (8)
C5	0.0579 (14)	0.104 (2)	0.0620 (14)	0.0004 (14)	−0.0292 (12)	−0.0068 (15)

Geometric parameters (Å, º) top

S1—C5	1.779 (2)	C2—H21	0.9800
S1—C4	1.7907 (17)	C3—C4	1.516 (2)
O1—C1	1.2398 (18)	C3—H31	0.9700
N1—C2	1.4825 (18)	C3—H32	0.9700
N1—H1	0.90 (2)	C4—H41	0.9700
N1—H2	0.92 (2)	C4—H42	0.9700
N1—H3	0.90 (2)	C5—H51	0.9600
C1—O2	1.2504 (18)	C5—H52	0.9600
C1—C2	1.5258 (19)	C5—H53	0.9600
C2—C3	1.530 (2)

C5—S1—C4	100.84 (11)	C4—C3—H31	108.6
C2—N1—H1	108.6 (12)	C2—C3—H31	108.6
C2—N1—H2	111.8 (12)	C4—C3—H32	108.6
H1—N1—H2	110.3 (17)	C2—C3—H32	108.6
C2—N1—H3	113.4 (12)	H31—C3—H32	107.6
H1—N1—H3	109.4 (17)	C3—C4—S1	109.19 (12)
H2—N1—H3	103.2 (16)	C3—C4—H41	109.8
O1—C1—O2	126.16 (13)	S1—C4—H41	109.8
O1—C1—C2	117.06 (12)	C3—C4—H42	109.8
O2—C1—C2	116.66 (13)	S1—C4—H42	109.8
N1—C2—C1	108.95 (12)	H41—C4—H42	108.3
N1—C2—C3	110.76 (11)	S1—C5—H51	109.5
C1—C2—C3	108.45 (12)	S1—C5—H52	109.5
N1—C2—H21	109.6	H51—C5—H52	109.5
C1—C2—H21	109.6	S1—C5—H53	109.5
C3—C2—H21	109.6	H51—C5—H53	109.5
C4—C3—C2	114.47 (13)	H52—C5—H53	109.5

O1—C1—C2—N1	−31.43 (17)	C2—C3—C4—S1	−179.16 (12)
O2—C1—C2—N1	152.41 (13)	C3—C4—S1—C5	−174.55 (16)
O1—C1—C2—C3	89.21 (16)	H1—N1—C2—C1	−44.4 (13)
O2—C1—C2—C3	−86.95 (16)	H2—N1—C2—C1	76.5 (13)
N1—C2—C3—C4	−55.52 (18)	H3—N1—C2—C1	−167.3 (14)
C1—C2—C3—C4	−175.03 (14)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1ⁱ	0.90 (2)	1.88 (2)	2.7732 (17)	173.7 (19)
N1—H2···O2ⁱⁱ	0.92 (2)	1.92 (2)	2.8264 (18)	171.0 (18)
N1—H3···O2ⁱⁱⁱ	0.90 (2)	1.94 (2)	2.7973 (18)	159.2 (18)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1ⁱ	0.90 (2)	1.88 (2)	2.7732 (17)	173.7 (19)
N1—H2···O2ⁱⁱ	0.92 (2)	1.92 (2)	2.8264 (18)	171.0 (18)
N1—H3···O2ⁱⁱⁱ	0.90 (2)	1.94 (2)	2.7973 (18)	159.2 (18)

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

Selected torsion angles (°) top

Torsion angle	β-DL-Met, 320 K	α-DL-Met, 340 K^a	α-DL-Met, 340 K^b
N1—C2—C3—C4	-55.52 (18)	-59.3 (4)	73 (8)
C1—C2—C3—C4	-175.03(14	-178.0 (2)	-78 (5)
C2—C3—C4—S1	-179.16 (12)	176.7 (2)	178 (5)
C3—C4—S1—C5	-174.55 (16)	69.4 (3)	60 (3)

Notes: (a) major conformation, occupancy 0.9509 (18) (Görbitz et al., 2014); (a) minor conformation, occupancy 0.0491 (18).

References

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