Crystal structures of the isomeric dipeptides l-glycyl-l-me­thio­nine and l-me­thionyl-l-glycine

Babu, S.; Fronczek, F.R.; Uppu, R.M.; Claville, M.O.

doi:10.1107/S2056989024005504

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ISSN: 2056-9890

Volume 80| Part 7| July 2024| Pages 725-728

https://doi.org/10.1107/S2056989024005504

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Crystal structures of the isomeric dipeptides L-glycyl-L-methionine and L-methionyl-L-glycine

Sainath Babu,^a Frank R. Fronczek,^b Rao M. Uppu ^c and Michelle O. Claville ^d ^*

^aDepartment of Biological Sciences, School of Science, Hampton University, Hampton, VA, 23669, USA, ^bDepartment of Chemistry, Louisiana State University, Baton Rouge, LA, 70803, USA, ^cDepartment of Environmental Toxicology, Southern University and A&M College, Baton Rouge, LA 70813, USA, and ^dSchool of Science, Hampton University, Hampton, VA, 23669, USA
^*Correspondence e-mail: moclaville@gmail.com

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 4 June 2024; accepted 9 June 2024; online 14 June 2024)

The oxidation of methionyl peptides can contribute to increased biological (oxidative) stress and development of various inflammatory diseases. The conformation of peptides has an important role in the mechanism of oxidation and the intermediates formed in the reaction. Herein, the crystal structures of the isomeric dipeptides Gly-Met (Gly = glycine and Met = methionine) and Met-Gly, both C₇H₁₄N₂O₃S, are reported. Both molecules exist in the solid state as zwitterions with nominal proton transfer from the carboxylic acid to the primary amine group. The Gly-Met molecule has an extended backbone structure, while Met-Gly has two nearly planar regions kinked at the C atom bearing the NH₃ group. In the crystals, both structures form extensive three-dimensional hydrogen-bonding networks via N—H⋯O and bifurcated N—H⋯(O,O) hydrogen bonds having N⋯O distances in the range 2.6619 (13)–2.8513 (13) Å for Gly-Met and 2.6273 (8)–3.1465 (8) Å for Met-Gly.

Keywords: crystal structure; dipeptide; methionyl oxidation; absolute configuration.

CCDC references: 2361459; 2361458

1. Chemical context

Methionine and methionyl peptides play an important role in protein oxidation. The sulfur atom in methionine can easily be oxidized by free radicals or oxidants and lead to sulfur radical cations (Bobrowski & Holcman, 1989 ) or a corresponding sulfoxide (Schöneich, 2005 ). The formation of reactive radical cations is responsible for methionyl protein damage and misconformation, which has been implicated in numerous inflammatory (Vogt, 1995 ) and age-related diseases (Schöneich, 2005; Stadtman et al., 2005 ).

Gly-Met (Gly = glycine, Met = methionine) and its reverse sequence, Met-Gly, are two simple dipeptides. It has been shown that the position of methionine with respect to the N-terminus of the peptide determines the mechanism of oxidation of methionyl peptides. For instance, in photosensitized oxidation reactions, substantial amounts of radical cations stabilized with sulfur–nitrogen (S∴N) three-electron bonded species were observed with Met-Gly, while similar stabilization of the radical cations was not observed with Gly-Met (Pedzinski et al., 2009 ). In collision-induced radical dissociation, Gly-Met leads to the loss of a CH₃—S—CH=CH₂ fragment from the peptide, while such dissociation in Met-Gly leads to the loss of a CH₃S^· (Lau et al., 2013 ) radical. Thus, the difference in methionine position leads to quite different reaction intermediates, which may eventually affect the stability of the peptide and its biological function.

The oxidation of methionine peptides is determined by several factors, including peptide structure, the position of methionine within the sequence, neighboring groups to methionine, nature of the oxidants, and solvent properties. The conformation of the peptide is also an important factor that needs to be considered to understand the mechanism of oxidation. Peptides can exist in either cationic, zwitterionic, or anionic conformations, depending on the solvent and the pH. The present report describes the zwitterionic structures of Gly-Met and Met-Gly dipeptides. We believe that some of the differences observed in the literature related to methionyl peptide oxidations could be attributed to the conformation of the peptide in solution.

2. Structural commentary

Both of the dipeptides are in their zwitterionic forms in the solid state (Fig. 1). The amide N1 atom of both Gly-Met and Met-Gly is in the protonated NH₃⁺ form, and the C6/O2/O3 carboxylic groups are in their deprotonated (COO)⁻ forms, as evidenced by the C—O distances of 1.2598 (13) and 1.2546 (13) Å in Gly-Met and 1.2534 (9) and 1.2635 (8) Å in Met-Gly. The C—NH₃ distance is 1.4809 (14) Å in Gly-Met and 1.4855 (8) in Met-Gly. The backbone of the Gly-Met molecule is extended, with its six torsion angle magnitudes in the range 163.44 (9)–177.94 (8)°. Thus, the ten atoms of the chain are close to coplanar with a mean deviation of 0.091 Å. The backbone of the Met-Gly molecule is substantially kinked at C3. The eight-atom segment containing the carboxylate group is planar to within a mean deviation of 0.056 Å, and the five-atom segment containing the S atom is planar to within a mean deviation of 0.086 Å. These two planes intersect at C3, forming a dihedral angle of 70.502 (13)°. The absolute configurations of both molecules were confirmed from their refined Flack parameters (Parsons et al., 2013 ), with values of 0.02 (2) for Gly-Met and 0.011 (11) for Met-Gly.

Figure 1
The molecular structures of Gly-Met and Met-Gly showing 50% displacement ellipsoids.

3. Supramolecular features

Intermolecular interactions in both structures are dominated by N—H⋯O hydrogen bonds, some of which are bifurcated. In Gly-Met (Table 1), the NH₃⁺ group donates hydrogen bonds to three separate molecules, and the N—H group donates to a fourth (Fig. 2), forming a complex three-dimensional array of hydrogen bonds. Graph sets (Etter et al., 1990 ) include C₁¹(5) and C₁¹(8) chains and R₄⁴(22) loops. In Met-Gly (Table 2), the NH₃⁺ group also donates hydrogen bonds to three different molecules (Fig. 3), but the N—H group does not participate in intermolecular interactions and makes a very non-linear [N—H⋯O = 110.6 (10)°] intramolecular contact to an O atom of the carboxylate group. Nevertheless, the hydrogen-bonding array is three-dimensional, and graph sets include C₁¹(8) chains, C₂²(6) chains and R₄⁴(22) loops.

Table 1
Hydrogen-bond geometry (Å, °) for Gly-Met

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H11N⋯O3ⁱ	0.83 (2)	2.15 (2)	2.8513 (13)	143.0 (18)
N1—H11N⋯O1	0.83 (2)	2.15 (2)	2.6619 (13)	120.1 (16)
N1—H12N⋯O2ⁱⁱ	0.886 (19)	1.850 (19)	2.7275 (12)	170.7 (18)
N1—H13N⋯O3ⁱⁱⁱ	0.849 (19)	1.86 (2)	2.7006 (13)	168 (2)
N2—H2N⋯O2^iv	0.832 (19)	2.000 (19)	2.8225 (12)	170.0 (18)
Symmetry codes: (i) ; (ii) ; (iii) $[-x+1, y+{\script{1\over 2}}, -z]$ ; (iv) .

Table 2
Hydrogen-bond geometry (Å, °) for Met-Gly

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H11N⋯O2ⁱ	0.885 (14)	1.854 (14)	2.7290 (8)	169.5 (13)
N1—H11N⋯O3ⁱ	0.885 (14)	2.593 (15)	3.1465 (8)	121.4 (11)
N1—H12N⋯O3ⁱⁱ	0.896 (13)	1.857 (13)	2.7531 (7)	179.6 (14)
N1—H13N⋯O3ⁱⁱⁱ	0.907 (14)	2.015 (14)	2.7529 (8)	137.5 (11)
N1—H13N⋯O1	0.907 (14)	2.211 (13)	2.6940 (8)	112.7 (10)
N2—H2N⋯O2	0.879 (15)	2.185 (13)	2.6273 (8)	110.6 (10)
Symmetry codes: (i) $[-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[-x+{\script{1\over 2}}, -y+1, z+{\script{1\over 2}}]$ ; (iii) $[-x+1, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Figure 2
Hydrogen bonding in Gly-Met. H atoms on C are not shown.

Figure 3
Hydrogen bonding in Met-Gly. H atoms on C are not shown.

4. Database survey

A search of the Cambridge Structural Database (CSD, version 5.45, Update 1, March 2024; Groom et al., 2016 ) revealed that no crystal structures were reported for either Gly-Met or Met-Gly. Other dipeptides containing methionine have been reported, including L-Ala-L-Met hemihydrate (Gorbitz, 2003 ), DL-Ala-LD-Met (Jha et al., 2020 ), L-Pro-L-Met monohydrate (Padmanabhan & Yadava, 1983 ), L-Met-L-Met (Stenkamp & Jensen, 1975 ), L-Met-L-Ala (Gorbitz, 2000 ), and L-Met-L-Ser (Gorbitz et al., 2006 ).

5. Synthesis and crystallization

The dipeptides Gly-Met and Met-Gly were obtained commercially (Chem-impex International Inc., Wood Dale, IL, USA). A supersaturated solution of each dipeptide was prepared in a small test tube by mixing the compound with warm methanol. Approximately 100 mg of dipeptide was added to 10 ml of methanol and additional solvent was added slowly in small increments with agitation and keeping the test tube at 333 K in a water bath. The solutions were allowed to cool and left undisturbed at room temperature over two weeks for slow evaporation and crystallization to yield colorless plates of Gly-Met and large colorless needles of Met-Gly.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were located in difference maps and those on carbon were treated as riding in geometrically idealized positions with C—H distances = 1.00 Å for R₃CH, 0.99 Å for CH₂ and 0.98 Å for methyl. U_iso(H) values were assigned as 1.2U_eq for the attached C atom (1.5U_eq for methyl). The positions of the H atoms attached to N atoms were refined. Their U_iso values were assigned as 1.2U_eq for the NH groups and 1.5U_eq for NH₃.

Table 3
Experimental details

	Gly-Met	Met-Gly
Crystal data
Chemical formula	C₇H₁₄N₂O₃S	C₇H₁₄N₂O₃S
M_r	206.26	206.26
Crystal system, space group	Monoclinic, P2₁	Orthorhombic, P2₁2₁2₁
Temperature (K)	90	90
a, b, c (Å)	6.2517 (2), 5.4935 (2), 14.5686 (6)	5.2521 (3), 11.4126 (7), 16.5403 (10)
α, β, γ (°)	90, 91.147 (4), 90	90, 90, 90
V (Å³)	500.24 (3)	991.43 (10)
Z	2	4
Radiation type	Mo Kα	Mo Kα
μ (mm⁻¹)	0.30	0.31
Crystal size (mm)	0.38 × 0.29 × 0.03	0.25 × 0.24 × 0.17

Data collection
Diffractometer	Bruker Kappa APEXII DUO CCD	Bruker Kappa APEXII DUO CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )	Multi-scan (SADABS; Krause et al., 2015)
T_min, T_max	0.836, 0.991	0.872, 0.950
No. of measured, independent and observed [I > 2σ(I)] reflections	11393, 5922, 5356	33593, 6231, 5939
R_int	0.026	0.030
(sin θ/λ)_max (Å⁻¹)	0.909	0.909

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.033, 0.079, 1.04	0.023, 0.061, 1.06
No. of reflections	5922	6231
No. of parameters	131	131
No. of restraints	1	0
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.53, −0.30	0.44, −0.20
Absolute structure	Flack x determined using 2141 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] Parsons et al. (2013)	Flack x determined using 2494 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] Parsons et al. (2013)
Absolute structure parameter	0.02 (2)	0.011 (11)
Computer programs: APEX2 and SAINT (Bruker, 2016 ), SHELXS97 (Sheldrick, 2008 ), SHELXL2018/1 (Sheldrick, 2015 ), Mercury (Macrae et al., 2020 ), and publCIF (Westrip, 2010 ).

Supporting information

CCDC references: 2361459; 2361458

Crystal structure: contains datablocks Gly-Met, Met-Gly, global. DOI: https://doi.org/10.1107/S2056989024005504/hb8099sup1.cif

Structure factors: contains datablock Gly-Met. DOI: https://doi.org/10.1107/S2056989024005504/hb8099Gly-Metsup2.hkl

Structure factors: contains datablock Met-Gly. DOI: https://doi.org/10.1107/S2056989024005504/hb8099Met-Glysup3.hkl

checkCIF report

Computing details top

L-Glycyl-L-methionine (Gly-Met) top

Crystal data top

C₇H₁₄N₂O₃S	F(000) = 220
M_r = 206.26	D_x = 1.369 Mg m⁻³
Monoclinic, P2₁	Mo Kα radiation, λ = 0.71073 Å
a = 6.2517 (2) Å	Cell parameters from 5067 reflections
b = 5.4935 (2) Å	θ = 2.8–40.1°
c = 14.5686 (6) Å	µ = 0.30 mm⁻¹
β = 91.147 (4)°	T = 90 K
V = 500.24 (3) Å³	Plate, colourless
Z = 2	0.38 × 0.29 × 0.03 mm

Data collection top

Bruker Kappa APEXII DUO CCD diffractometer	5922 independent reflections
Radiation source: fine-focus sealed tube	5356 reflections with I > 2σ(I)
TRIUMPH curved graphite monochromator	R_int = 0.026
φ and ω scans	θ_max = 40.3°, θ_min = 2.8°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −9→11
T_min = 0.836, T_max = 0.991	k = −9→9
11393 measured reflections	l = −26→26

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.033	w = 1/[σ²(F_o²) + (0.0417P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.079	(Δ/σ)_max = 0.001
S = 1.04	Δρ_max = 0.53 e Å⁻³
5922 reflections	Δρ_min = −0.30 e Å⁻³
131 parameters	Absolute structure: Flack x determined using 2141 quotients [(I⁺)-(I^-)]/[(I⁺)+(I^-)] Parsons et al. (2013)
1 restraint	Absolute structure parameter: 0.02 (2)

Special details top

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.

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

	x	y	z	U_iso*/U_eq
S1	−0.20146 (4)	0.44474 (6)	0.42848 (2)	0.01468 (6)
O1	0.69310 (13)	0.51962 (16)	0.16278 (6)	0.01361 (15)
O2	0.19251 (13)	0.15688 (15)	0.17287 (6)	0.01189 (14)
O3	0.17853 (13)	0.50896 (16)	0.09597 (6)	0.01188 (13)
N1	0.87880 (15)	0.89936 (16)	0.08355 (7)	0.00999 (15)
H11N	0.913 (3)	0.757 (4)	0.0948 (13)	0.015*
H12N	0.981 (3)	0.994 (4)	0.1072 (12)	0.015*
H13N	0.865 (3)	0.912 (4)	0.0257 (13)	0.015*
N2	0.42247 (14)	0.73584 (17)	0.22578 (7)	0.00962 (14)
H2N	0.353 (3)	0.863 (4)	0.2171 (13)	0.012*
C1	0.67091 (16)	0.9440 (2)	0.12752 (8)	0.01317 (16)
H1D	0.563279	0.995080	0.080609	0.016*
H1E	0.686342	1.076254	0.173329	0.016*
C2	0.59716 (16)	0.71258 (19)	0.17425 (7)	0.00938 (15)
C3	0.30874 (16)	0.51654 (19)	0.25172 (7)	0.00890 (15)
H3	0.410296	0.406010	0.285399	0.011*
C4	0.22080 (16)	0.38311 (18)	0.16587 (7)	0.00835 (15)
C5	0.12523 (18)	0.5846 (2)	0.31603 (8)	0.01112 (17)
H5A	0.184307	0.675550	0.369448	0.013*
H5B	0.023082	0.692558	0.282903	0.013*
C6	0.00678 (19)	0.3600 (2)	0.34991 (8)	0.01315 (18)
H6A	0.109333	0.249024	0.381309	0.016*
H6B	−0.057507	0.272165	0.296822	0.016*
C7	−0.3286 (2)	0.1514 (2)	0.43812 (9)	0.0175 (2)
H7A	−0.381335	0.098919	0.377488	0.026*
H7B	−0.448752	0.163281	0.480064	0.026*
H7C	−0.224743	0.032488	0.462053	0.026*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.01416 (11)	0.01407 (11)	0.01605 (12)	−0.00108 (10)	0.00637 (8)	−0.00091 (10)
O1	0.0117 (3)	0.0077 (3)	0.0216 (4)	0.0011 (3)	0.0036 (3)	0.0016 (3)
O2	0.0114 (3)	0.0072 (3)	0.0170 (4)	−0.0006 (2)	−0.0009 (3)	−0.0006 (3)
O3	0.0144 (3)	0.0112 (3)	0.0100 (3)	0.0016 (3)	−0.0009 (2)	0.0005 (3)
N1	0.0094 (3)	0.0088 (4)	0.0118 (4)	−0.0009 (3)	0.0007 (3)	0.0011 (3)
N2	0.0087 (3)	0.0068 (3)	0.0133 (4)	−0.0008 (3)	0.0007 (3)	0.0006 (3)
C1	0.0119 (4)	0.0079 (3)	0.0199 (4)	0.0005 (4)	0.0050 (3)	0.0024 (4)
C2	0.0085 (4)	0.0074 (3)	0.0121 (4)	−0.0012 (3)	−0.0009 (3)	0.0003 (3)
C3	0.0086 (3)	0.0077 (3)	0.0104 (4)	−0.0009 (3)	0.0001 (3)	0.0014 (3)
C4	0.0068 (3)	0.0076 (3)	0.0107 (4)	0.0006 (3)	0.0011 (3)	−0.0006 (3)
C5	0.0121 (4)	0.0104 (4)	0.0110 (4)	−0.0013 (3)	0.0021 (3)	−0.0007 (3)
C6	0.0141 (4)	0.0113 (4)	0.0142 (4)	−0.0011 (3)	0.0054 (3)	−0.0003 (3)
C7	0.0147 (5)	0.0183 (5)	0.0194 (5)	−0.0046 (4)	0.0030 (4)	0.0025 (4)

Geometric parameters (Å, º) top

S1—C7	1.8037 (13)	C1—H1D	0.9900
S1—C6	1.8114 (11)	C1—H1E	0.9900
O1—C2	1.2310 (13)	C3—C4	1.5415 (15)
O2—C4	1.2598 (13)	C3—C5	1.5417 (15)
O3—C4	1.2546 (13)	C3—H3	1.0000
N1—C1	1.4809 (14)	C5—C6	1.5262 (16)
N1—H11N	0.83 (2)	C5—H5A	0.9900
N1—H12N	0.886 (19)	C5—H5B	0.9900
N1—H13N	0.849 (19)	C6—H6A	0.9900
N2—C2	1.3437 (14)	C6—H6B	0.9900
N2—C3	1.4527 (14)	C7—H7A	0.9800
N2—H2N	0.832 (19)	C7—H7B	0.9800
C1—C2	1.5181 (16)	C7—H7C	0.9800

C7—S1—C6	98.22 (6)	C4—C3—H3	108.8
C1—N1—H11N	107.2 (13)	C5—C3—H3	108.8
C1—N1—H12N	111.5 (12)	O3—C4—O2	125.57 (10)
H11N—N1—H12N	107.1 (19)	O3—C4—C3	117.55 (9)
C1—N1—H13N	110.1 (12)	O2—C4—C3	116.86 (9)
H11N—N1—H13N	107.3 (19)	C6—C5—C3	111.85 (9)
H12N—N1—H13N	113.3 (18)	C6—C5—H5A	109.2
C2—N2—C3	118.29 (9)	C3—C5—H5A	109.2
C2—N2—H2N	115.1 (13)	C6—C5—H5B	109.2
C3—N2—H2N	118.5 (13)	C3—C5—H5B	109.2
N1—C1—C2	109.41 (9)	H5A—C5—H5B	107.9
N1—C1—H1D	109.8	C5—C6—S1	110.86 (8)
C2—C1—H1D	109.8	C5—C6—H6A	109.5
N1—C1—H1E	109.8	S1—C6—H6A	109.5
C2—C1—H1E	109.8	C5—C6—H6B	109.5
H1D—C1—H1E	108.2	S1—C6—H6B	109.5
O1—C2—N2	124.15 (10)	H6A—C6—H6B	108.1
O1—C2—C1	120.47 (9)	S1—C7—H7A	109.5
N2—C2—C1	115.37 (9)	S1—C7—H7B	109.5
N2—C3—C4	110.59 (8)	H7A—C7—H7B	109.5
N2—C3—C5	109.33 (9)	S1—C7—H7C	109.5
C4—C3—C5	110.53 (8)	H7A—C7—H7C	109.5
N2—C3—H3	108.8	H7B—C7—H7C	109.5

C3—N2—C2—O1	−15.40 (16)	C5—C3—C4—O3	93.47 (11)
C3—N2—C2—C1	163.44 (9)	N2—C3—C4—O2	153.99 (9)
N1—C1—C2—O1	−8.46 (15)	C5—C3—C4—O2	−84.80 (11)
N1—C1—C2—N2	172.66 (9)	N2—C3—C5—C6	−176.94 (9)
C2—N2—C3—C4	−62.19 (12)	C4—C3—C5—C6	61.10 (12)
C2—N2—C3—C5	175.89 (9)	C3—C5—C6—S1	177.94 (8)
N2—C3—C4—O3	−27.75 (13)	C7—S1—C6—C5	171.26 (9)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H11N···O3ⁱ	0.83 (2)	2.15 (2)	2.8513 (13)	143.0 (18)
N1—H11N···O1	0.83 (2)	2.15 (2)	2.6619 (13)	120.1 (16)
N1—H12N···O2ⁱⁱ	0.886 (19)	1.850 (19)	2.7275 (12)	170.7 (18)
N1—H13N···O3ⁱⁱⁱ	0.849 (19)	1.86 (2)	2.7006 (13)	168 (2)
N2—H2N···O2^iv	0.832 (19)	2.000 (19)	2.8225 (12)	170.0 (18)

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

L-Methionyl-L-glycine (Met-Gly) top

Crystal data top

C₇H₁₄N₂O₃S	D_x = 1.382 Mg m⁻³
M_r = 206.26	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P2₁2₁2₁	Cell parameters from 9827 reflections
a = 5.2521 (3) Å	θ = 3.0–40.2°
b = 11.4126 (7) Å	µ = 0.31 mm⁻¹
c = 16.5403 (10) Å	T = 90 K
V = 991.43 (10) Å³	Needle fragment, colourless
Z = 4	0.25 × 0.24 × 0.17 mm
F(000) = 440

Data collection top

Bruker Kappa APEXII DUO CCD diffractometer	6231 independent reflections
Radiation source: fine-focus sealed tube	5939 reflections with I > 2σ(I)
TRIUMPH curved graphite monochromator	R_int = 0.030
φ and ω scans	θ_max = 40.3°, θ_min = 2.2°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −8→9
T_min = 0.872, T_max = 0.950	k = −20→20
33593 measured reflections	l = −30→30

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.023	w = 1/[σ²(F_o²) + (0.0356P)² + 0.0451P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.061	(Δ/σ)_max = 0.001
S = 1.06	Δρ_max = 0.44 e Å⁻³
6231 reflections	Δρ_min = −0.20 e Å⁻³
131 parameters	Absolute structure: Flack x determined using 2494 quotients [(I⁺)-(I^-)]/[(I⁺)+(I^-)] Parsons et al. (2013)
0 restraints	Absolute structure parameter: 0.011 (11)

Special details top

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

	x	y	z	U_iso*/U_eq
S1	0.29353 (4)	0.65791 (2)	0.59184 (2)	0.01687 (4)
O1	0.56607 (10)	0.47315 (6)	0.32954 (3)	0.01617 (10)
O2	−0.07675 (10)	0.65590 (6)	0.16589 (4)	0.01625 (10)
O3	0.24892 (10)	0.71309 (4)	0.08834 (3)	0.01128 (8)
N1	0.29316 (11)	0.32887 (5)	0.42498 (3)	0.00925 (8)
H11N	0.230 (3)	0.2667 (12)	0.4002 (8)	0.014*
H12N	0.280 (3)	0.3155 (11)	0.4782 (8)	0.014*
H13N	0.461 (3)	0.3287 (11)	0.4122 (7)	0.014*
N2	0.21065 (12)	0.55612 (5)	0.27617 (3)	0.01213 (9)
H2N	0.044 (3)	0.5631 (11)	0.2749 (8)	0.015*
C1	0.37117 (14)	0.56727 (6)	0.50511 (4)	0.01293 (10)
H1D	0.471236	0.613218	0.465519	0.016*
H1E	0.475036	0.499402	0.522492	0.016*
C2	0.12412 (13)	0.52445 (6)	0.46605 (4)	0.01108 (9)
H2A	0.028903	0.593014	0.445308	0.013*
H2B	0.017812	0.486494	0.507971	0.013*
C3	0.16563 (12)	0.43738 (5)	0.39633 (3)	0.00966 (9)
H3	−0.003367	0.416245	0.372606	0.012*
C4	0.33345 (12)	0.48982 (6)	0.32997 (4)	0.01035 (9)
C5	0.34421 (13)	0.61524 (6)	0.21120 (4)	0.01259 (10)
H5A	0.459462	0.559260	0.183793	0.015*
H5B	0.448980	0.679543	0.233724	0.015*
C6	0.15608 (12)	0.66476 (6)	0.15042 (3)	0.00962 (9)
C7	0.59992 (18)	0.66260 (8)	0.64043 (6)	0.02365 (16)
H7A	0.662481	0.582565	0.648561	0.035*
H7B	0.584132	0.701884	0.692882	0.035*
H7C	0.719997	0.705915	0.606324	0.035*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.01555 (8)	0.01596 (7)	0.01911 (8)	0.00057 (6)	0.00040 (6)	−0.00632 (6)
O1	0.00866 (19)	0.0242 (2)	0.0157 (2)	0.00274 (18)	0.00070 (17)	0.00795 (19)
O2	0.00915 (19)	0.0230 (2)	0.0166 (2)	−0.00048 (18)	0.00041 (16)	0.01047 (19)
O3	0.0129 (2)	0.01408 (18)	0.00689 (15)	−0.00366 (14)	0.00063 (14)	0.00177 (14)
N1	0.00953 (18)	0.01015 (17)	0.00807 (17)	0.00097 (16)	−0.00063 (15)	0.00075 (14)
N2	0.0095 (2)	0.0172 (2)	0.00969 (19)	0.00194 (19)	0.00069 (17)	0.00605 (17)
C1	0.0123 (2)	0.0118 (2)	0.0147 (2)	−0.0001 (2)	0.0012 (2)	−0.00119 (19)
C2	0.0104 (2)	0.0112 (2)	0.0117 (2)	0.00167 (18)	0.00146 (18)	0.00075 (18)
C3	0.0085 (2)	0.0115 (2)	0.0090 (2)	0.00079 (17)	−0.00053 (16)	0.00217 (16)
C4	0.0096 (2)	0.0131 (2)	0.00842 (19)	0.00101 (18)	−0.00038 (17)	0.00254 (17)
C5	0.0094 (2)	0.0181 (3)	0.0103 (2)	0.0009 (2)	0.00068 (18)	0.00519 (19)
C6	0.0102 (2)	0.0109 (2)	0.00774 (19)	−0.00110 (18)	−0.00008 (16)	0.00155 (17)
C7	0.0228 (4)	0.0199 (3)	0.0283 (4)	−0.0025 (3)	−0.0075 (3)	−0.0061 (3)

Geometric parameters (Å, º) top

S1—C7	1.7995 (9)	C1—H1D	0.9900
S1—C1	1.8150 (7)	C1—H1E	0.9900
O1—C4	1.2365 (8)	C2—C3	1.5379 (9)
O2—C6	1.2534 (9)	C2—H2A	0.9900
O3—C6	1.2635 (8)	C2—H2B	0.9900
N1—C3	1.4855 (8)	C3—C4	1.5297 (9)
N1—H11N	0.885 (14)	C3—H3	1.0000
N1—H12N	0.896 (13)	C5—C6	1.5186 (9)
N1—H13N	0.907 (14)	C5—H5A	0.9900
N2—C4	1.3342 (8)	C5—H5B	0.9900
N2—C5	1.4499 (9)	C7—H7A	0.9800
N2—H2N	0.879 (15)	C7—H7B	0.9800
C1—C2	1.5296 (10)	C7—H7C	0.9800

C7—S1—C1	99.74 (4)	N1—C3—C2	111.31 (5)
C3—N1—H11N	110.5 (9)	C4—C3—C2	111.53 (5)
C3—N1—H12N	114.9 (8)	N1—C3—H3	108.9
H11N—N1—H12N	106.8 (12)	C4—C3—H3	108.9
C3—N1—H13N	111.5 (8)	C2—C3—H3	108.9
H11N—N1—H13N	105.0 (12)	O1—C4—N2	124.13 (6)
H12N—N1—H13N	107.6 (12)	O1—C4—C3	120.88 (6)
C4—N2—C5	121.62 (6)	N2—C4—C3	114.95 (6)
C4—N2—H2N	123.3 (8)	N2—C5—C6	110.43 (6)
C5—N2—H2N	115.0 (8)	N2—C5—H5A	109.6
C2—C1—S1	108.98 (5)	C6—C5—H5A	109.6
C2—C1—H1D	109.9	N2—C5—H5B	109.6
S1—C1—H1D	109.9	C6—C5—H5B	109.6
C2—C1—H1E	109.9	H5A—C5—H5B	108.1
S1—C1—H1E	109.9	O2—C6—O3	125.28 (6)
H1D—C1—H1E	108.3	O2—C6—C5	118.01 (5)
C1—C2—C3	113.76 (6)	O3—C6—C5	116.70 (6)
C1—C2—H2A	108.8	S1—C7—H7A	109.5
C3—C2—H2A	108.8	S1—C7—H7B	109.5
C1—C2—H2B	108.8	H7A—C7—H7B	109.5
C3—C2—H2B	108.8	S1—C7—H7C	109.5
H2A—C2—H2B	107.7	H7A—C7—H7C	109.5
N1—C3—C4	107.17 (5)	H7B—C7—H7C	109.5

C7—S1—C1—C2	165.35 (5)	C2—C3—C4—O1	93.98 (8)
S1—C1—C2—C3	−174.71 (4)	N1—C3—C4—N2	154.05 (6)
C1—C2—C3—N1	62.23 (7)	C2—C3—C4—N2	−83.89 (7)
C1—C2—C3—C4	−57.41 (7)	C4—N2—C5—C6	169.26 (6)
C5—N2—C4—O1	0.09 (11)	N2—C5—C6—O2	4.52 (9)
C5—N2—C4—C3	177.89 (6)	N2—C5—C6—O3	−176.26 (6)
N1—C3—C4—O1	−28.08 (9)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H11N···O2ⁱ	0.885 (14)	1.854 (14)	2.7290 (8)	169.5 (13)
N1—H11N···O3ⁱ	0.885 (14)	2.593 (15)	3.1465 (8)	121.4 (11)
N1—H12N···O3ⁱⁱ	0.896 (13)	1.857 (13)	2.7531 (7)	179.6 (14)
N1—H13N···O3ⁱⁱⁱ	0.907 (14)	2.015 (14)	2.7529 (8)	137.5 (11)
N1—H13N···O1	0.907 (14)	2.211 (13)	2.6940 (8)	112.7 (10)
N2—H2N···O2	0.879 (15)	2.185 (13)	2.6273 (8)	110.6 (10)

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

Acknowledgements

SB is currently affiliated with the MED Institute and MOC is currently affiliated with Council for Higher Education Accreditation.

Funding information

Funding for this research was provided by: National Science Foundation, Directorate for Biological Sciences (award No. HRD-1238828 to M.O. Claville; award No. CHE-1230357 to M.O. Claville); Louisiana Board of Regents (award No. LEQSF (1999–2000)-ENH-TR-13 to F. R. Fronczek).

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research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Crystal structures of the isomeric dipeptides L-glycyl-L-me­thio­nine and L-me­thionyl-L-glycine

1. Chemical context

2. Structural commentary

3. Supra­molecular features

4. Database survey

5. Synthesis and crystallization

6. Refinement

Supporting information

Acknowledgements

Funding information

References

research communications

Crystal structures of the isomeric dipeptides L-glycyl-L-methionine and L-methionyl-L-glycine

3. Supramolecular features