research communications
R,S)-2-hydroxy-4-(methylsulfanyl)butanoic acid
of (aDepartment of Biochemistry, University of Missouri, Columbia, MO 65211, USA, bExperiment Station Chemical Laboratories, University of Missouri, Columbia, MO 65211, USA, cDepartment of Molecular Microbiology and Immunology, University of Missouri, Columbia, MO 65211, USA, and dDepartment of Chemistry, University of Missouri, Columbia, MO 65211, USA
*Correspondence e-mail: mossinev@missouri.edu
The title compound, a major animal feed supplement, abbreviated as HMTBA and alternatively called DL-methionine hydroxy analogue, C5H10O3S, (I), was isolated in pure anhydrous monomeric form. The melting point is 302.5 K and the compound crystallizes in the monoclinic P21/c, with two conformationally non-equivalent molecules [(IA) and (IB)] in the The is formed by alternating polar and non-polar layers running along the bc plane and features an extensive hydrogen-bonding network within the polar layers. The Hirshfeld surface analysis revealed a significant contribution of non-polar H⋯H and H⋯S interactions to the packing forces for both molecules.
Keywords: crystal structure; methionine hydroxy analog; 2-hydroxy-4-(methylsulfanyl)butanoic acid; HMTBA; CAS 583–91-5; hydrogen bonding.
CCDC reference: 1979735
1. Chemical context
α-Hydroxy carboxylic acids are indispensable players in plant and animal metabolism, and many of these substances are commercially important chemicals, because of their wide use in chemical industries and as pharmaceuticals, skin-care agents, or nutritional supplements (Bhalla et al., 2013). 2-Hydroxy-4-(methylsulfanyl)butanoic acid (I) is a natural precursor in methionine biosynthesis, and, for decades, synthetic HMTBA has been used on an industrial scale as a supplement to animal feeds in order to boost methionine production, particularly in farmed poultry (Zhang et al., 2015). In spite of its large-scale manufacture and use, commercial HMTBA is supplied as a brown, syrupy, and it has not been reported to crystallize, even when isolated in chromatographically and enantiomerically pure preparations (Busto et al., 2014). One possible reason is that HMTBA readily forms dimeric and trimeric condensation products (Koban & Koberstein, 1984) which, along with the deliquescent behavior, may impede its crystallization. Crystal structures of free aliphatic α-hydroxy carboxylic acids are rare, as a result of their propensity to oligomerize. Metal salts provide a means for stabilization of the α-hydroxy carboxylate monomers, and structures of two HMTBA metal salts, Cu[(R,S)-HMTBA]2 (CCDC 1018852; Yang et al., 2015) and Zn[(R,S)-HMTBA]2 (CCDC 671417; Predieri et al., 2009), have been solved by X-ray diffraction. In our attempts to separate monomeric and oligomeric forms of HMTBA, we have successfully isolated a high-purity crystalline sample of (I), shown in Fig. 1, and report here its characterization by X-ray diffraction.
2. Structural commentary
(R,S)-HMTBA crystallizes in the monoclinic P21/c; the consists of two molecules in non-equivalent conformations, (IA) and (IB) (Table 1). The ORTEP views of the molecules and numbering of the atoms are shown in Figs. 2 and 3. Bond lengths and valence angles in (I) are within ranges expected for the given structure. The C1–C5 backbone in (R)-(IA) is in the trans, trans, gauche+ (t, t, g+) conformation, with the chain of atoms C1A through S1A located in one plane [maximum deviation 0.144 (1) Å for C3A]. In the crystal of (R,S)-HMTBA copper salt (Yang et al., 2015), a similar (t, t, g+) backbone rotamer exists in the (S)-HMTBA molecule. Likewise, the respective (t, t, g+) conformation of the L-methionine side chain was found in the α-isoform of DL-Met crystal (CCDC 1028063; Görbitz et al., 2014). The backbone conformation in (R)-(IB) is the gauche+, trans, gauche+ rotamer. An identical (g+, t, g+) conformation was adopted by (R)-HMTBA, molecule C, which is coordinated to the zinc ion in the crystal of (R,S)-HMTBA zinc salt trihydrate (Predieri et al., 2009). The conformation around the C1—C2 bond in (R)-(IB) is close to eclipsed, in respect to the O1B and O3B atoms, with a O3B—C2B—C1B—O1B torsion angle of −10.81 (19)°. A similar spatial arrangement of the O1 and O3 atoms was reported in the aforementioned copper and zinc salts of HMTBA (Table 1), where simultaneous coordination of the carboxylate and hydroxyl oxygen atoms to the metal ions provided for the formation of nearly flat five-membered chelate rings (Yang et al., 2015; Predieri et al., 2009). In crystal structures of the simplest α-hydroxy carboxylic acids, glycolic acid (CCDC 1169248; Pijper, 1971) and L(+)-lactic acid (CCDC 1303177; Schouten et al., 1994), the molecular fragments including non-hydrogen atoms of the hydroxyl and carboxyl groups are also nearly flat (Table 1).
3. Supramolecular features
The I) consists of alternating polar and non-polar sheets running along the bc plane (Fig. 4) and containing short O—H⋯O contacts within the polar layers (Fig. 4 and Table 2). Such a double-layered arrangement is typical for crystal structures of aliphatic L-α-amino acids and many other polar molecules, and these are present in all reference structures of both HMTBA metal salts and methionine listed in Table 1. Within the polar sheets, the basic hydrogen-bonding pattern features infinite homodromic chains of hydrogen bonds spiraling along the b-axis direction (Fig. 5). The chains are linked through bifurcated hydrogen bonding that involves the hydroxyl O3B—H3B donor group and the carboxylate O1A acceptor. One can recognize three basic motifs in the hydrogen-bonding pattern (in accordance with the topological notation system by Bernstein et al., 1995): the C44(12) motif forms homodromic infinite chains, which link similarly oriented molecules; the small R22(4) ring and the large homodromic R88(24) ring, which are formed by the O3B—H3B⋯O1A links and the homodromic infinite chains that run along the b axis in opposite directions and are located on the opposite `half-sheets' of the polar layer. The resulting pattern of conjugated rings is shown in Fig. 5b: it represents one of two symmetrical, in respect to the twofold screw along the b axis, systems of hydrogen bonds that penetrate the polar layers.
of (
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In addition to the `classical' O—H⋯O hydrogen bonds, there is one intermolecular C2B—HA⋯O2A contact (Fig. 6 and Table 3) in the of (I) that is shorter than the sum of the van der Waals radii. The Hirshfeld surface analysis (CrystalExplorer17.5; Spackman & Jayatilaka, 2009), however, reveals that the C—H⋯O contacts do not contribute significantly to the crystal packing forces, but that a major proportion, over 63% for (IA) and over 68% for (IB), of the intermolecular contacts in the of (I) is provided by non- or low-polar H⋯H and H⋯S interactions (Fig. 7 and Table 4). Compared to other aforementioned structures (Table 4), the relative contributions of the polar and non-polar interactions in (I) are similar to those found in HMTBA metal salts. The relative contribution of the polar component in methionine structures is somewhat higher, possibly because of the higher number of heteroatom-bonded hydrogen atoms, three, as compared to only two such protons present in molecules of (I).
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4. Database survey
Search of SciFinder, Google Scholar, and the Cambridge Structural Database (version 5.40, 2019 data update 3; Groom et al., 2016), by both structure and chemical names, revealed no previous structural description of 2-hydroxy-4-(methylsulfanyl)butanoic acid in the solid state. Only two HMTBA structures, both of which are metal salts, Cu[(R,S)-HMTBA]2 (CCDC 1018852, Yang et al., 2015) and Zn[(R,S)-HMTBA]2 (CCDC 671417, Predieri et al., 2009), have been reported. The most closely related structure to (I) is methionine, for which a number of crystallographic studies have been published and these are referenced in Table 1. In addition to the structural features outlined in Tables 1 and 4, other similarities to (I) include L-methionine crystallizing in the monoclinic P21 (CCDC 1207980, LMETON02; CCDC 1207981, LMETON10; Torii & Iitaka, 1973; Dalhus & Görbitz, 1996). The in the of L-Met also contains two conformationally unequal molecules.
5. Synthesis and crystallization
Purely monomeric HMTBA in its free acid form is not commercially available because of the known propensity of α-hydroxy carboxylic acids to oligomerize when concentrated (Koban & Koberstein, 1984); thus, we have evaluated the composition of a commercially available (R,S)-2-hydroxy-4-(methylsulfanyl)butanoic acid (TCI America) as having 65-72% HMTBA monomer, 2.7–4.5% of its linear dimer, 0.14–0.35% of the linear trimer, and 28–35% water. A pure, anhydrous sample of racemic HMTBA monomer was prepared by employing a mild, short-path distillation technique that utilizes a apparatus (Fig. 1a), half submerged in an ethylene glycol bath that was maintained at 383 K. After 72 h, while under vacuum (10 torr) and the cold finger kept at 277 K, large colorless prisms of neat (I) were formed on the sublimator's condenser (Fig. 1b), which melted at 302.5 K.
6. Refinement
Crystal data, data collection and structure . O-bound H atoms were located from the difference map and those bonded to C were placed in calculated positions. The coordinates of all H atoms were refined freely while the thermal parameters were constrained to ride on the carrier atoms, Uiso(H) = 1.2–1.5Ueq(C,O).
details are summarized in Table 5
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Supporting information
CCDC reference: 1979735
https://doi.org/10.1107/S2056989020003138/lh5949sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989020003138/lh5949Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989020003138/lh5949Isup3.cml
Data collection: APEX3 and SAINT (Bruker, 2017); cell
APEX3 and SAINT (Bruker, 2017); data reduction: APEX3 and SAINT (Bruker, 2017); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2017 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2020); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009) and publCIF (Westrip, 2010).C5H10O3S | F(000) = 640 |
Mr = 150.19 | Dx = 1.374 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 16.0940 (14) Å | Cell parameters from 9911 reflections |
b = 8.8747 (8) Å | θ = 2.6–30.5° |
c = 10.558 (1) Å | µ = 0.38 mm−1 |
β = 105.654 (3)° | T = 100 K |
V = 1452.1 (2) Å3 | Plate, colourless |
Z = 8 | 0.34 × 0.25 × 0.07 mm |
Bruker VENTURE CMOS area detector diffractometer | 3474 reflections with I > 2σ(I) |
Radiation source: Incoatec IMuS microfocus Mo tube | Rint = 0.071 |
shutterless ω and phi scans | θmax = 30.6°, θmin = 2.6° |
Absorption correction: multi-scan (AXScale; Bruker, 2017) | h = −22→23 |
Tmin = 0.653, Tmax = 0.746 | k = −12→12 |
37191 measured reflections | l = −15→13 |
4437 independent reflections |
Refinement on F2 | Primary atom site location: dual |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.044 | Hydrogen site location: mixed |
wR(F2) = 0.106 | Only H-atom coordinates refined |
S = 1.05 | w = 1/[σ2(Fo2) + (0.0433P)2 + 0.6797P] where P = (Fo2 + 2Fc2)/3 |
4437 reflections | (Δ/σ)max = 0.001 |
223 parameters | Δρmax = 0.53 e Å−3 |
0 restraints | Δρmin = −0.47 e Å−3 |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
S1A | 0.84095 (3) | 0.20993 (6) | 0.52925 (4) | 0.03405 (12) | |
S1B | 0.92449 (3) | 0.76333 (6) | 0.21950 (6) | 0.04228 (14) | |
O3A | 0.55286 (6) | 0.36868 (11) | 0.33141 (9) | 0.0159 (2) | |
H3A | 0.5659 (12) | 0.439 (2) | 0.3057 (18) | 0.024* | |
O1A | 0.53671 (6) | 0.35894 (11) | 0.06723 (9) | 0.0184 (2) | |
O3B | 0.64397 (7) | 0.61637 (11) | 0.07733 (10) | 0.0179 (2) | |
H3B | 0.5982 (13) | 0.587 (2) | 0.0729 (19) | 0.027* | |
O2A | 0.56541 (7) | 0.11169 (10) | 0.08154 (10) | 0.0175 (2) | |
H2A | 0.5570 (11) | 0.123 (2) | −0.005 (2) | 0.026* | |
O2B | 0.66367 (7) | 0.88568 (11) | 0.33618 (10) | 0.0205 (2) | |
H2B | 0.6535 (12) | 0.880 (2) | 0.412 (2) | 0.031* | |
O1B | 0.60884 (7) | 0.65325 (11) | 0.31386 (10) | 0.0217 (2) | |
C2A | 0.59189 (8) | 0.24683 (14) | 0.28125 (13) | 0.0131 (2) | |
H2AA | 0.5714 (10) | 0.1576 (19) | 0.3142 (16) | 0.016* | |
C1A | 0.56017 (8) | 0.24609 (14) | 0.13230 (13) | 0.0134 (2) | |
C3B | 0.74743 (9) | 0.81369 (16) | 0.13945 (14) | 0.0183 (3) | |
H3BA | 0.7508 (11) | 0.820 (2) | 0.0534 (18) | 0.022* | |
H3BB | 0.7552 (11) | 0.914 (2) | 0.1762 (17) | 0.022* | |
C2B | 0.65613 (9) | 0.76258 (14) | 0.13541 (13) | 0.0150 (2) | |
H2BA | 0.6158 (11) | 0.8295 (19) | 0.0850 (16) | 0.018* | |
C3A | 0.69066 (9) | 0.25339 (16) | 0.32158 (13) | 0.0173 (3) | |
H3AA | 0.7133 (11) | 0.167 (2) | 0.2847 (17) | 0.021* | |
H3AB | 0.7095 (11) | 0.340 (2) | 0.2816 (17) | 0.021* | |
C4A | 0.72730 (10) | 0.25292 (19) | 0.47077 (15) | 0.0231 (3) | |
H4AA | 0.7001 (12) | 0.174 (2) | 0.5080 (18) | 0.028* | |
H4AB | 0.7168 (12) | 0.347 (2) | 0.5062 (18) | 0.028* | |
C4B | 0.81668 (10) | 0.70791 (19) | 0.21803 (19) | 0.0280 (3) | |
H4BA | 0.8093 (12) | 0.610 (2) | 0.1778 (19) | 0.034* | |
H4BB | 0.8140 (12) | 0.696 (2) | 0.307 (2) | 0.034* | |
C5A | 0.88873 (13) | 0.3629 (3) | 0.4614 (2) | 0.0441 (5) | |
H5AA | 0.8738 (17) | 0.356 (3) | 0.359 (3) | 0.066* | |
H5AB | 0.9499 (17) | 0.348 (3) | 0.497 (3) | 0.066* | |
H5AC | 0.8699 (16) | 0.455 (3) | 0.489 (3) | 0.066* | |
C5B | 0.93633 (15) | 0.9292 (3) | 0.3193 (3) | 0.0578 (7) | |
H5BA | 0.898 (2) | 1.008 (4) | 0.280 (3) | 0.087* | |
H5BB | 0.994 (2) | 0.959 (3) | 0.336 (3) | 0.087* | |
H5BC | 0.9255 (19) | 0.895 (3) | 0.407 (3) | 0.087* | |
C1B | 0.64041 (8) | 0.75921 (14) | 0.27099 (13) | 0.0151 (2) |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1A | 0.02048 (19) | 0.0455 (3) | 0.0314 (2) | 0.00432 (17) | −0.00131 (16) | 0.00794 (19) |
S1B | 0.0198 (2) | 0.0453 (3) | 0.0635 (3) | −0.00015 (17) | 0.0142 (2) | −0.0085 (2) |
O3A | 0.0236 (5) | 0.0107 (4) | 0.0148 (5) | 0.0014 (4) | 0.0076 (4) | 0.0001 (4) |
O1A | 0.0248 (5) | 0.0136 (4) | 0.0156 (5) | 0.0012 (4) | 0.0035 (4) | 0.0024 (4) |
O3B | 0.0208 (5) | 0.0159 (5) | 0.0179 (5) | −0.0047 (4) | 0.0067 (4) | −0.0036 (4) |
O2A | 0.0291 (5) | 0.0118 (4) | 0.0122 (5) | 0.0001 (4) | 0.0063 (4) | −0.0007 (4) |
O2B | 0.0331 (6) | 0.0147 (5) | 0.0154 (5) | −0.0045 (4) | 0.0097 (4) | −0.0017 (4) |
O1B | 0.0305 (5) | 0.0159 (5) | 0.0219 (5) | −0.0040 (4) | 0.0126 (4) | 0.0002 (4) |
C2A | 0.0176 (6) | 0.0100 (5) | 0.0119 (6) | 0.0006 (4) | 0.0044 (5) | −0.0002 (4) |
C1A | 0.0142 (6) | 0.0119 (6) | 0.0148 (6) | −0.0017 (4) | 0.0050 (5) | −0.0002 (5) |
C3B | 0.0209 (6) | 0.0180 (6) | 0.0170 (7) | −0.0025 (5) | 0.0070 (5) | 0.0005 (5) |
C2B | 0.0192 (6) | 0.0130 (6) | 0.0127 (6) | −0.0002 (5) | 0.0045 (5) | 0.0011 (5) |
C3A | 0.0184 (6) | 0.0185 (6) | 0.0148 (6) | −0.0003 (5) | 0.0043 (5) | −0.0005 (5) |
C4A | 0.0193 (7) | 0.0309 (8) | 0.0175 (7) | 0.0011 (6) | 0.0021 (5) | −0.0003 (6) |
C4B | 0.0212 (7) | 0.0227 (7) | 0.0392 (10) | −0.0007 (6) | 0.0067 (7) | 0.0013 (7) |
C5A | 0.0252 (9) | 0.0575 (13) | 0.0474 (12) | −0.0085 (9) | 0.0058 (8) | 0.0033 (10) |
C5B | 0.0321 (10) | 0.0452 (12) | 0.0835 (19) | −0.0106 (9) | −0.0059 (11) | −0.0134 (12) |
C1B | 0.0170 (6) | 0.0137 (6) | 0.0143 (6) | 0.0006 (5) | 0.0040 (5) | 0.0005 (5) |
S1A—C5A | 1.801 (2) | C3B—C2B | 1.5273 (19) |
S1A—C4A | 1.8063 (15) | C3B—H3BA | 0.926 (18) |
S1B—C5B | 1.791 (3) | C3B—H3BB | 0.967 (17) |
S1B—C4B | 1.7995 (16) | C2B—C1B | 1.5197 (19) |
O3A—C2A | 1.4227 (15) | C2B—H2BA | 0.934 (17) |
O3A—H3A | 0.736 (19) | C3A—C4A | 1.526 (2) |
O1A—C1A | 1.2155 (16) | C3A—H3AA | 0.974 (18) |
O3B—C2B | 1.4259 (16) | C3A—H3AB | 0.968 (18) |
O3B—H3B | 0.77 (2) | C4A—H4AA | 0.967 (19) |
O2A—C1A | 1.3197 (15) | C4A—H4AB | 0.95 (2) |
O2A—H2A | 0.89 (2) | C4B—H4BA | 0.96 (2) |
O2B—C1B | 1.3171 (16) | C4B—H4BB | 0.95 (2) |
O2B—H2B | 0.86 (2) | C5A—H5AA | 1.04 (3) |
O1B—C1B | 1.2131 (16) | C5A—H5AB | 0.96 (3) |
C2A—C1A | 1.5167 (18) | C5A—H5AC | 0.95 (3) |
C2A—C3A | 1.5318 (19) | C5B—H5BA | 0.95 (3) |
C2A—H2AA | 0.959 (17) | C5B—H5BB | 0.94 (3) |
C3B—C4B | 1.521 (2) | C5B—H5BC | 1.03 (3) |
C5A—S1A—C4A | 101.91 (9) | C4A—C3A—H3AB | 111.9 (10) |
C5B—S1B—C4B | 100.32 (10) | C2A—C3A—H3AB | 109.5 (10) |
C2A—O3A—H3A | 108.2 (15) | H3AA—C3A—H3AB | 105.0 (15) |
C2B—O3B—H3B | 110.7 (14) | C3A—C4A—S1A | 115.28 (11) |
C1A—O2A—H2A | 108.0 (12) | C3A—C4A—H4AA | 109.3 (11) |
C1B—O2B—H2B | 109.6 (13) | S1A—C4A—H4AA | 103.5 (11) |
O3A—C2A—C1A | 109.29 (10) | C3A—C4A—H4AB | 110.1 (11) |
O3A—C2A—C3A | 113.39 (11) | S1A—C4A—H4AB | 108.8 (11) |
C1A—C2A—C3A | 108.79 (10) | H4AA—C4A—H4AB | 109.5 (16) |
O3A—C2A—H2AA | 105.3 (10) | C3B—C4B—S1B | 113.51 (11) |
C1A—C2A—H2AA | 108.7 (10) | C3B—C4B—H4BA | 109.5 (12) |
C3A—C2A—H2AA | 111.3 (10) | S1B—C4B—H4BA | 104.8 (11) |
O1A—C1A—O2A | 124.01 (12) | C3B—C4B—H4BB | 112.4 (12) |
O1A—C1A—C2A | 123.28 (11) | S1B—C4B—H4BB | 108.6 (12) |
O2A—C1A—C2A | 112.61 (11) | H4BA—C4B—H4BB | 107.6 (17) |
C4B—C3B—C2B | 112.94 (12) | S1A—C5A—H5AA | 111.3 (15) |
C4B—C3B—H3BA | 110.1 (11) | S1A—C5A—H5AB | 104.0 (16) |
C2B—C3B—H3BA | 107.5 (11) | H5AA—C5A—H5AB | 109 (2) |
C4B—C3B—H3BB | 110.7 (10) | S1A—C5A—H5AC | 108.7 (16) |
C2B—C3B—H3BB | 107.7 (10) | H5AA—C5A—H5AC | 112 (2) |
H3BA—C3B—H3BB | 107.7 (15) | H5AB—C5A—H5AC | 112 (2) |
O3B—C2B—C1B | 110.41 (10) | S1B—C5B—H5BA | 113.0 (18) |
O3B—C2B—C3B | 107.56 (11) | S1B—C5B—H5BB | 106.3 (19) |
C1B—C2B—C3B | 112.52 (11) | H5BA—C5B—H5BB | 112 (3) |
O3B—C2B—H2BA | 109.9 (10) | S1B—C5B—H5BC | 105.4 (17) |
C1B—C2B—H2BA | 106.4 (10) | H5BA—C5B—H5BC | 111 (3) |
C3B—C2B—H2BA | 110.0 (10) | H5BB—C5B—H5BC | 108 (2) |
C4A—C3A—C2A | 111.71 (11) | O1B—C1B—O2B | 123.66 (12) |
C4A—C3A—H3AA | 109.2 (10) | O1B—C1B—C2B | 124.04 (12) |
C2A—C3A—H3AA | 109.3 (10) | O2B—C1B—C2B | 112.30 (11) |
O3A—C2A—C1A—O1A | 27.77 (17) | C2A—C3A—C4A—S1A | 164.16 (10) |
C3A—C2A—C1A—O1A | −96.52 (15) | C5A—S1A—C4A—C3A | 62.16 (15) |
O3A—C2A—C1A—O2A | −155.72 (10) | C2B—C3B—C4B—S1B | 178.17 (10) |
C3A—C2A—C1A—O2A | 79.99 (13) | C5B—S1B—C4B—C3B | 69.76 (16) |
C4B—C3B—C2B—O3B | −59.22 (16) | O3B—C2B—C1B—O1B | −10.81 (19) |
C4B—C3B—C2B—C1B | 62.59 (16) | C3B—C2B—C1B—O1B | −130.99 (14) |
O3A—C2A—C3A—C4A | 58.73 (15) | O3B—C2B—C1B—O2B | 170.24 (11) |
C1A—C2A—C3A—C4A | −179.44 (11) | C3B—C2B—C1B—O2B | 50.06 (15) |
D—H···A | D—H | H···A | D···A | D—H···A |
O3A—H3A···O1B | 0.736 (19) | 2.013 (19) | 2.7044 (14) | 156.4 (19) |
O3B—H3B···O1A | 0.77 (2) | 2.246 (19) | 2.8480 (14) | 135.6 (18) |
O3B—H3B···O1Ai | 0.77 (2) | 2.325 (19) | 2.9048 (14) | 132.9 (18) |
O2A—H2A···O3Aii | 0.89 (2) | 1.71 (2) | 2.5995 (14) | 172.7 (18) |
O2B—H2B···O3Biii | 0.86 (2) | 1.79 (2) | 2.6493 (14) | 172.6 (19) |
Symmetry codes: (i) −x+1, −y+1, −z; (ii) x, −y+1/2, z−1/2; (iii) x, −y+3/2, z+1/2. |
C1—C2—C3—C4 | C2—C3—C4—S1 | C3—C4—S1—C5 | O1—C1—C2—O3/N1b | Ref | |
(IA)a | 179.4 (1) | -164.2 (1) | -62.2 (2) | -27.8 (2) | This work |
(IB)a | -62.6 (2) | -178.2 (1) | -69.8 (2) | 10.8 (2) | This work |
Cu(HMTBA)2 a | 175.0 (4) | 164.9 (3) | 63.2 (5) | -14.2 (5) | (Yang et al., 2015) |
Zn(HMTBA)2 : molecule A (S) | -60.6 (7) | -157.5 (4) | -58.8 (6) | 3.9 (6) | (Predieri et al., 2009) |
molecule B (R) | 64.6 (7) | -76.7 (7) | -68.2 (7) | 9.5 (6) | |
molecule C (R) | 60.0 (7) | 173.4 (5) | 66.2 (7) | 9.7 (6) | |
molecule D (S) | -57.7 (9) | -174.7 (6) | -122.9 (8) | -1.3 (7) | |
L-Met: molecule A | 71.8 (3) | 171.6 (3) | -178.5 (3) | -16.3 (2) | (Dalhus & Görbitz, 1996) |
molecule B | 74.1 (3) | 71.5 (3) | 72.4 (3) | -32.4 (2) | |
α-DL-Met a | -178.0 (2) | 176.7 (2) | 69.4 (3) | -29.4 (3) | (Görbitz et al., 2014) |
β-DL-Met a | -173.6 (2) | -179.2 (1) | -175.0 (2) | -32.6 (2) | (Alagar et al., 2005) |
L-(+)-lactic acid | 7.6 (1) | (Schouten et al., 1994) | |||
glycolic acid: molecule A | -6.16 (2) | (Pijper, 1971) | |||
molecule B | -2.93 (2) |
Notes: (a) Signs of the angle values are given for the (S)-enantiomer; (b) N1 in methionine. |
D—H···A | D—H | H···A | D···A | D—H···A |
C2B—H2BA···O2Ai | 0.933 (17) | 2.630 (17) | 3.4068 (16) | 141.1 (13) |
Symmetry code: (i) x, 1 + y, z. |
Backbone rotamer a | H···H | S···H | O···H | Other | ||||
HMTBA | O···O; | C···O; | C···H; | S···S | ||||
(IA) | ttg- | 48.9 | 14.3 | 32.3 | 1.7; | 1.7; | 0.9; | 0.1 |
(IB) | g-tg- | 50.4 | 18.2 | 28.5 | 1.0; | 1.7; | 0.2; | 0.1 |
O···O; | C···O; | C···H; | Cu···O | |||||
Cu(HMTBA)2 | ttg+ | 44.0 | 18.0 | 25.2 | 2.9; | 1.7; | 1.3; | 6.9 |
Zn(HMTBA)2 | O···O; | C···H; | S···S; | Zn···O | ||||
molecule A (S) | g-tg- | 48.4 | 18.4 | 22.0 | 2.4; | 1.1; | 0.3; | 7.5 |
molecule B (R) | g+g-g- | 49.2 | 13.9 | 28.0 | 0.9; | 1.0; | 1.0; | 4.9 |
molecule C (R) | g+tg+ | 48.2 | 15.7 | 28.7 | 0.8; | 0.8; | 0.3; | 5.0 |
L-Met | O···O; | C···O; | C···H; | C···C | ||||
molecule A | g+tt | 48.3 | 14.9 | 34.7 | 0.1; | 0.6; | 0.6; | 0.5 |
molecule B | g+g+g+ | 46.7 | 15.1 | 35.6 | 0.5; | 0.6; | 0.6; | 0.5 |
β-DL-Met | ttt | 48.7 | 14.6 | 35.6 | 0.3; | 0.4; | 1.3 |
Note: (a) Refer to Table 1 for chirality of the molecules and the actual torsion-angle values. |
Funding information
Funding for this research was provided by: University of Missouri Agriculture Experiment Station Chemical Laboratories ; National Institute of Food and Agriculture (grant No. MO-HABC0002).
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