organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890
Volume 71| Part 6| June 2015| Pages o398-o399

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

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.

1. Related literature

For previous investigations of DL-me­thio­nine (DL-Met), see: Mathieson (1952[Mathieson, A. McL. (1952). Acta Cryst. 5, 332-341.]); Taniguchi et al. (1980[Taniguchi, T., Takaki, Y. & Sakurai, K. (1980). Bull. Chem. Soc. Jpn, 53, 803-804.]); Alagar et al. (2005[Alagar, M., Krishnakumar, R. V., Mostad, A. & Natarajan, S. (2005). Acta Cryst. E61, o1165-o1167.]); Görbitz (2014[Görbitz, C. H. (2014). Acta Cryst. E70, 341-343.]); Görbitz et al. (2014[Görbitz, C. H., Qi, L., Mai, N. T. K. & Kristiansen, H. (2014). Acta Cryst. E70, 337-340.]). For a discussion of displacive phase transitions of amino acids with linear side chains and structures of quasiracemic complexes, see: Görbitz & Karen (2015[Görbitz, C. H. & Karen, P. (2015). J. Phys. Chem. B, 119, 4975-4984.]). For the phase behaviour of the corresponding enanti­omeric substances, including L-Met and L-norvaline, see: Görbitz et al. (2015[Görbitz, C. H., Karen, P., Dušek, M. & Petříček, V. (2015). IUCrJ. In preparation.]). For a discussion of hydrogen-bonding patterns in the crystal structures of hydrophobic amino acids, see: Görbitz et al. (2009[Görbitz, C. H., Vestli, K. & Orlando, R. (2009). Acta Cryst. B65, 393-400.]).

[Scheme 1]

2. Experimental

2.1. Crystal data

  • C5H11NO2S

  • Mr = 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[Bruker (2014). APEX2, SAINT-Plus and SADABS. Bruker AXS, Inc., Madison, Wisconsin, USA.]) Tmin = 0.924, Tmax = 1.000

  • 10516 measured reflections

  • 2060 independent reflections

  • 1567 reflections with I > 2σ(I)

  • Rint = 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

  • Δρmax = 0.34 e Å−3

  • Δρmin = −0.39 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA 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 Ka α-DL-Met, 340 Kb
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[Görbitz, C. H., Qi, L., Mai, N. T. K. & Kristiansen, H. (2014). Acta Cryst. E70, 337-340.]); (a) minor conformation, occupancy 0.0491 (18).

Data collection: APEX2 (Bruker, 2014[Bruker (2014). APEX2, SAINT-Plus and SADABS. Bruker AXS, Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT-Plus (Bruker, 2014[Bruker (2014). APEX2, SAINT-Plus and SADABS. Bruker AXS, Inc., Madison, Wisconsin, USA.]); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS2014 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. C71, 3-8.]); molecular graphics: Mercury (Macrae et al., 2008[Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466-470.]); software used to prepare material for publication: SHELXL2014.

Supporting information


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 T1. 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.

Refinement top

Coordinates were refined for amino H atoms with Uiso(H) = 1.5Ueq(N). The C-bound H atoms were positioned with idealized geometry and treated as riding atoms: C—H = 0.96 - 0.98 Å with Uiso(H) = 1.5Ueq(C) for methyl H atoms, allowing free rotation for the terminal side-chain methyl group, and with 1.2Ueq(C) for other H atoms.

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
[Figure 1] 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
C5H11NO2SF(000) = 640
Mr = 149.21Dx = 1.343 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 31.774 (2) ÅCell parameters from 4136 reflections
b = 4.6969 (3) Åθ = 2.6–29.5°
c = 9.8939 (7) ŵ = 0.37 mm1
β = 91.224 (2)°T = 320 K
V = 1476.20 (18) Å3Needle, colourless
Z = 80.72 × 0.15 × 0.10 mm
Data collection top
Bruker D8 Advance single-crystal CCD
diffractometer
2060 independent reflections
Radiation source: fine-focus sealed tube1567 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.031
Detector resolution: 8.3 pixels mm-1θmax = 29.5°, θmin = 2.6°
Sets of exposures each taken over 0.5° ω rotation scansh = 4439
Absorption correction: multi-scan
(SADABS; Bruker, 2014)
k = 66
Tmin = 0.924, Tmax = 1.000l = 1313
10516 measured reflections
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.046H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.116 w = 1/[σ2(Fo2) + (0.0458P)2 + 1.6546P]
where P = (Fo2 + 2Fc2)/3
S = 1.03(Δ/σ)max = 0.001
2060 reflectionsΔρmax = 0.34 e Å3
92 parametersΔρmin = 0.39 e Å3
Crystal data top
C5H11NO2SV = 1476.20 (18) Å3
Mr = 149.21Z = 8
Monoclinic, C2/cMo Kα radiation
a = 31.774 (2) ŵ = 0.37 mm1
b = 4.6969 (3) ÅT = 320 K
c = 9.8939 (7) Å0.72 × 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)
Tmin = 0.924, Tmax = 1.000Rint = 0.031
10516 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0460 restraints
wR(F2) = 0.116H atoms treated by a mixture of independent and constrained refinement
S = 1.03Δρmax = 0.34 e Å3
2060 reflectionsΔρmin = 0.39 e Å3
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
xyzUiso*/Ueq
S10.44096 (2)0.65785 (16)0.45693 (7)0.0684 (2)
O10.28350 (4)0.4246 (2)0.19616 (11)0.0316 (3)
N10.29732 (4)0.7975 (3)0.39652 (12)0.0252 (3)
H10.2705 (6)0.826 (4)0.3685 (19)0.038*
H20.2998 (6)0.627 (5)0.441 (2)0.038*
H30.3042 (6)0.926 (4)0.461 (2)0.038*
C10.30472 (4)0.6339 (3)0.16326 (14)0.0225 (3)
C20.32477 (5)0.8093 (3)0.27735 (13)0.0229 (3)
H210.32781.00730.24790.028*
O20.31323 (4)0.7062 (3)0.04532 (10)0.0383 (3)
C30.36823 (5)0.6847 (4)0.31133 (16)0.0318 (3)
H310.36510.48280.32930.038*
H320.38580.70440.23290.038*
C40.39054 (5)0.8220 (4)0.43157 (19)0.0406 (4)
H410.37390.79860.51180.049*
H420.39401.02420.41530.049*
C50.45831 (8)0.8257 (7)0.6094 (3)0.0750 (8)
H510.48610.75960.63340.113*
H520.43930.77990.68040.113*
H530.45891.02820.59650.113*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.0405 (3)0.0825 (5)0.0809 (4)0.0201 (3)0.0269 (3)0.0255 (4)
O10.0365 (6)0.0287 (6)0.0295 (6)0.0081 (5)0.0036 (4)0.0017 (4)
N10.0289 (6)0.0278 (6)0.0189 (6)0.0044 (5)0.0031 (5)0.0035 (5)
C10.0270 (7)0.0198 (6)0.0204 (6)0.0041 (5)0.0051 (5)0.0015 (5)
C20.0308 (7)0.0192 (6)0.0186 (6)0.0018 (5)0.0028 (5)0.0008 (5)
O20.0657 (8)0.0314 (6)0.0176 (5)0.0024 (6)0.0001 (5)0.0011 (4)
C30.0278 (7)0.0356 (8)0.0318 (8)0.0003 (7)0.0033 (6)0.0050 (7)
C40.0336 (8)0.0417 (10)0.0458 (10)0.0047 (7)0.0144 (7)0.0078 (8)
C50.0579 (14)0.104 (2)0.0620 (14)0.0004 (14)0.0292 (12)0.0068 (15)
Geometric parameters (Å, º) top
S1—C51.779 (2)C2—H210.9800
S1—C41.7907 (17)C3—C41.516 (2)
O1—C11.2398 (18)C3—H310.9700
N1—C21.4825 (18)C3—H320.9700
N1—H10.90 (2)C4—H410.9700
N1—H20.92 (2)C4—H420.9700
N1—H30.90 (2)C5—H510.9600
C1—O21.2504 (18)C5—H520.9600
C1—C21.5258 (19)C5—H530.9600
C2—C31.530 (2)
C5—S1—C4100.84 (11)C4—C3—H31108.6
C2—N1—H1108.6 (12)C2—C3—H31108.6
C2—N1—H2111.8 (12)C4—C3—H32108.6
H1—N1—H2110.3 (17)C2—C3—H32108.6
C2—N1—H3113.4 (12)H31—C3—H32107.6
H1—N1—H3109.4 (17)C3—C4—S1109.19 (12)
H2—N1—H3103.2 (16)C3—C4—H41109.8
O1—C1—O2126.16 (13)S1—C4—H41109.8
O1—C1—C2117.06 (12)C3—C4—H42109.8
O2—C1—C2116.66 (13)S1—C4—H42109.8
N1—C2—C1108.95 (12)H41—C4—H42108.3
N1—C2—C3110.76 (11)S1—C5—H51109.5
C1—C2—C3108.45 (12)S1—C5—H52109.5
N1—C2—H21109.6H51—C5—H52109.5
C1—C2—H21109.6S1—C5—H53109.5
C3—C2—H21109.6H51—C5—H53109.5
C4—C3—C2114.47 (13)H52—C5—H53109.5
O1—C1—C2—N131.43 (17)C2—C3—C4—S1179.16 (12)
O2—C1—C2—N1152.41 (13)C3—C4—S1—C5174.55 (16)
O1—C1—C2—C389.21 (16)H1—N1—C2—C144.4 (13)
O2—C1—C2—C386.95 (16)H2—N1—C2—C176.5 (13)
N1—C2—C3—C455.52 (18)H3—N1—C2—C1167.3 (14)
C1—C2—C3—C4175.03 (14)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O1i0.90 (2)1.88 (2)2.7732 (17)173.7 (19)
N1—H2···O2ii0.92 (2)1.92 (2)2.8264 (18)171.0 (18)
N1—H3···O2iii0.90 (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···AD—HH···AD···AD—H···A
N1—H1···O1i0.90 (2)1.88 (2)2.7732 (17)173.7 (19)
N1—H2···O2ii0.92 (2)1.92 (2)2.8264 (18)171.0 (18)
N1—H3···O2iii0.90 (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 angleβ-DL-Met, 320 Kα-DL-Met, 340 Kaα-DL-Met, 340 Kb
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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ISSN: 2056-9890
Volume 71| Part 6| June 2015| Pages o398-o399
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