Ammonium N-acetyl-L-threoninate, NH4+·C6H10NO4-, and methylammonium N-acetyl-L-threoninate, CH6N+·C6H10NO4-, crystallize in the orthorhombic P212121 and monoclinic P21 space groups, respectively. The two crystals present the same packing features consisting of infinite ribbons of screw-related N-acetyl-L-threoninate anions linked together through pairs of hydrogen bonds. The cations interconnect neighbouring ribbons of anions involving all the nitrogen-H atoms in three-dimensional networks of hydrogen bonds. The hydrogen-bond patterns include asymmetric `three-centred' systems. In both structures, the Thr side chain is in the favoured (g-g+) conformation.
Supporting information
CCDC references: 144655; 144656
The compounds (I) and (II) were obtained as secondary products during
ammonolysis of the N-acetyl-L-threonine ethyl ester, using NH3
or CH3—NH2 in cold ethanol (Lilley, 1988; Sijpkes, 1990) with the
primary goal to prepare the N-acetyl-L-threoninamide or
-threoninmethylamide. After purification of the products, single crystals of
(I) and (II) were obtained by slow evaporation from
methylethylketone-ethylacetate solutions. The samples of (II) were sealed in
glass capillaries with a small amount of mother solution because they are
unstable in air at room temperature.
Systematic absences and intensity statistics led to the unique assignment of the
space group P212121 for (I) and P21 for (II).
Both structures were solved using SIR92 package (Altomare et al.,
1993). All H atoms were clearly observed in difference Fourier maps and
included, with expected geometry, in the final refinements as fixed atoms with
Biso set equal to Beq of the parent atom. All calculations were performed
using SDP software (Enraf–Nonius, 1985) on a MicroVAX 3100 computer.
The absolute configuration was chosen on the basis of the known configuration
of the ethyl ester used in the synthesis.
(I)
N-acetyl-
L-threoninate ammonium
top
Crystal data top
NH4+·C6H10NO4− | F(000) = 384.0 |
Mr = 178.19 | Dx = 1.246 Mg m−3 |
Orthorhombic, P212121 | Cu Kα radiation, λ = 1.54056 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 25 reflections |
a = 7.025 (1) Å | θ = 29–32° |
b = 8.0689 (4) Å | µ = 0.89 mm−1 |
c = 16.754 (2) Å | T = 293 K |
V = 949.7 (2) Å3 | Prism, colourless |
Z = 4 | 0.34 × 0.23 × 0.21 mm |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.036 |
Radiation source: monochromated | θmax = 75.5° |
Graphite monochromator | h = −2→8 |
ω–2θ scans as suggested by peak–shape analysis | k = −2→10 |
1478 measured reflections | l = −2→21 |
1165 independent reflections | 4 standard reflections every 120 min |
1154 reflections with I > 2σ(I) | intensity decay: 3% |
Refinement top
Refinement on F | 1/[σ2(Fo) + (0.02Fo)2 + 4] (Killean & Lawrence, 1969) |
Least-squares matrix: full | (Δ/σ)max = 0.003 |
R[F2 > 2σ(F2)] = 0.036 | Δρmax = 0.18 e Å−3 |
wR(F2) = 0.044 | Δρmin = −0.15 e Å−3 |
S = 0.96 | Extinction correction: Stout & Jensen (1968) |
1154 reflections | Extinction coefficient: 3.23 (4) x 10-5 |
111 parameters | Absolute structure: Rogers (1981) |
H-atom parameters not refined | Rogers parameter: 0.927 (4) |
Crystal data top
NH4+·C6H10NO4− | V = 949.7 (2) Å3 |
Mr = 178.19 | Z = 4 |
Orthorhombic, P212121 | Cu Kα radiation |
a = 7.025 (1) Å | µ = 0.89 mm−1 |
b = 8.0689 (4) Å | T = 293 K |
c = 16.754 (2) Å | 0.34 × 0.23 × 0.21 mm |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.036 |
1478 measured reflections | 4 standard reflections every 120 min |
1165 independent reflections | intensity decay: 3% |
1154 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.036 | H-atom parameters not refined |
wR(F2) = 0.044 | Δρmax = 0.18 e Å−3 |
S = 0.96 | Δρmin = −0.15 e Å−3 |
1154 reflections | Absolute structure: Rogers (1981) |
111 parameters | Rogers parameter: 0.927 (4) |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
O1 | 0.2585 (2) | 0.5753 (2) | 0.4578 (1) | 0.0584 (5) | |
O2 | −0.0464 (2) | 0.5101 (2) | 0.4570 (1) | 0.0539 (5) | |
O3 | 0.3314 (3) | 0.2943 (3) | 0.23530 (8) | 0.0745 (6) | |
O4 | 0.1444 (2) | 0.1655 (2) | 0.50359 (8) | 0.0434 (4) | |
N1 | 0.3656 (2) | 0.3157 (2) | 0.36790 (9) | 0.0372 (4) | |
C1 | 0.1630 (3) | 0.3341 (3) | 0.3841 (1) | 0.0353 (5) | |
C2 | 0.1243 (3) | 0.4854 (3) | 0.4368 (1) | 0.0387 (5) | |
C3 | 0.4334 (3) | 0.2950 (3) | 0.2947 (1) | 0.0445 (6) | |
C4 | 0.6468 (3) | 0.2696 (4) | 0.2889 (1) | 0.0630 (9) | |
C5 | 0.0798 (3) | 0.1783 (3) | 0.4232 (1) | 0.0381 (5) | |
C6 | 0.1176 (4) | 0.0211 (3) | 0.3764 (2) | 0.0585 (7) | |
N2 | 0.1234 (2) | 0.7942 (2) | 0.57657 (9) | 0.0386 (4) | |
H1 | 0.26152 | 0.10732 | 0.50770 | 0.0434* | |
H2 | 0.45235 | 0.31871 | 0.41137 | 0.0372* | |
H3 | 0.09740 | 0.35104 | 0.33038 | 0.0353* | |
H4 | 0.68855 | 0.28083 | 0.23085 | 0.0630* | |
H5 | 0.71466 | 0.35668 | 0.32266 | 0.0630* | |
H6 | 0.68083 | 0.15425 | 0.30931 | 0.0630* | |
H7 | −0.06461 | 0.19126 | 0.42318 | 0.0381* | |
H8 | 0.06778 | 0.03459 | 0.31959 | 0.0585* | |
H9 | 0.26048 | −0.00125 | 0.37488 | 0.0585* | |
H10 | 0.05005 | −0.07596 | 0.40322 | 0.0585* | |
H11 | 0.00658 | 0.85163 | 0.56961 | 0.0386* | |
H12 | 0.13095 | 0.70583 | 0.53922 | 0.0386* | |
H13 | 0.22654 | 0.86835 | 0.56822 | 0.0386* | |
H14 | 0.12968 | 0.75088 | 0.62924 | 0.0386* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
O1 | 0.0370 (7) | 0.0582 (8) | 0.0800 (10) | −0.0072 (7) | 0.0098 (8) | −0.0239 (8) |
O2 | 0.0307 (6) | 0.0505 (8) | 0.0805 (10) | 0.0050 (7) | 0.0163 (7) | −0.0043 (9) |
O3 | 0.0521 (9) | 0.1408 (17) | 0.0306 (6) | 0.0127 (13) | −0.0005 (7) | −0.0098 (10) |
O4 | 0.0346 (6) | 0.0572 (8) | 0.0383 (6) | 0.0055 (7) | 0.0031 (6) | 0.0041 (7) |
N1 | 0.0259 (6) | 0.0540 (9) | 0.0318 (6) | 0.0030 (8) | 0.0003 (6) | −0.0023 (7) |
C1 | 0.0237 (7) | 0.0500 (10) | 0.0324 (8) | 0.0030 (8) | −0.0007 (7) | −0.0015 (8) |
C2 | 0.0298 (8) | 0.0415 (9) | 0.0447 (9) | 0.0009 (9) | 0.0059 (9) | 0.0026 (8) |
C3 | 0.0379 (9) | 0.0607 (11) | 0.0348 (8) | 0.0027 (11) | 0.0056 (8) | −0.0042 (10) |
C4 | 0.0355 (10) | 0.0990 (19) | 0.0545 (11) | 0.0043 (14) | 0.0139 (10) | −0.0019 (14) |
C5 | 0.0280 (8) | 0.0454 (9) | 0.0410 (9) | 0.0000 (8) | −0.0014 (8) | −0.0044 (9) |
C6 | 0.0584 (13) | 0.0513 (12) | 0.0657 (13) | −0.0010 (13) | 0.0040 (13) | −0.0148 (11) |
N2 | 0.0355 (7) | 0.0432 (8) | 0.0370 (7) | 0.0012 (8) | 0.0007 (7) | 0.0004 (7) |
Geometric parameters (Å, º) top
O1—C2 | 1.240 (3) | C4—H4 | 1.020 |
O2—C2 | 1.262 (2) | C4—H5 | 1.020 |
O3—C3 | 1.227 (2) | C4—H6 | 1.020 |
O4—C5 | 1.425 (2) | C5—C6 | 1.515 (3) |
O4—H1 | 0.950 | C5—H7 | 1.020 |
N1—C1 | 1.457 (2) | C6—H8 | 1.020 |
N1—C3 | 1.326 (2) | C6—H9 | 1.020 |
N1—H2 | 0.950 | C6—H10 | 1.020 |
C1—C2 | 1.531 (3) | N2—H11 | 0.950 |
C1—C5 | 1.533 (3) | N2—H12 | 0.950 |
C1—H3 | 1.020 | N2—H13 | 0.950 |
C3—C4 | 1.516 (3) | N2—H14 | 0.950 |
| | | |
O1···O4 | 3.488 (2) | O3···C5 | 3.730 (3) |
O1···C3 | 3.754 (3) | O3···C6 | 3.564 (3) |
O2···O4 | 3.183 (2) | C3···C6 | 3.418 (3) |
| | | |
C5—O4—H1 | 112.3 | H4—C4—H6 | 109.5 |
C1—N1—C3 | 122.4 (2) | H5—C4—H6 | 109.5 |
C1—N1—H2 | 118.8 | O4—C5—C1 | 110.0 (2) |
C3—N1—H2 | 118.8 | O4—C5—C6 | 111.9 (2) |
N1—C1—C2 | 111.2 (2) | O4—C5—H7 | 108.9 |
N1—C1—C5 | 111.6 (2) | C1—C5—C6 | 113.5 (2) |
N1—C1—H3 | 106.9 | C1—C5—H7 | 107.2 |
C2—C1—C5 | 109.8 (2) | C6—C5—H7 | 105.1 |
C2—C1—H3 | 108.8 | C5—C6—H8 | 109.5 |
C5—C1—H3 | 108.3 | C5—C6—H9 | 109.5 |
O1—C2—O2 | 123.6 (2) | C5—C6—H10 | 109.5 |
O1—C2—C1 | 119.7 (2) | H8—C6—H9 | 109.5 |
O2—C2—C1 | 116.7 (2) | H8—C6—H10 | 109.5 |
O3—C3—N1 | 122.8 (2) | H9—C6—H10 | 109.5 |
O3—C3—C4 | 121.7 (2) | H11—N2—H12 | 109.5 |
N1—C3—C4 | 115.6 (2) | H11—N2—H13 | 109.5 |
C3—C4—H4 | 109.5 | H11—N2—H14 | 109.5 |
C3—C4—H5 | 109.5 | H12—N2—H13 | 109.5 |
C3—C4—H6 | 109.5 | H12—N2—H14 | 109.5 |
H4—C4—H5 | 109.5 | H13—N2—H14 | 109.5 |
| | | |
H1—O4—C5—C1 | −88.4 (2) | C2—C1—C5—O4 | −51.7 (2) |
H1—O4—C5—C6 | 38.7 (2) | C2—C1—C5—C6 | −177.9 (2) |
H1—O4—C5—H7 | 154.4 (2) | C2—C1—C5—H7 | 66.5 (2) |
C3—N1—C1—C2 | −129.8 (2) | H3—C1—C5—O4 | −170.4 (2) |
C3—N1—C1—C5 | 107.1 (2) | H3—C1—C5—C6 | 63.3 (2) |
C3—N1—C1—H3 | −11.2 (3) | H3—C1—C5—H7 | −52.2 (2) |
H2—N1—C1—C2 | 50.2 (2) | O3—C3—C4—H4 | 13.4 (3) |
H2—N1—C1—C5 | −72.9 (2) | O3—C3—C4—H5 | 133.4 (2) |
H2—N1—C1—H3 | 168.8 (2) | O3—C3—C4—H6 | −106.6 (3) |
C1—N1—C3—O3 | 2.1 (3) | N1—C3—C4—H4 | −167.4 (2) |
C1—N1—C3—C4 | −177.2 (2) | N1—C3—C4—H5 | −47.4 (3) |
H2—N1—C3—O3 | −177.9 (2) | N1—C3—C4—H6 | 72.6 (3) |
H2—N1—C3—C4 | 2.8 (3) | O4—C5—C6—H8 | 179.2 (2) |
N1—C1—C2—O1 | 1.9 (3) | O4—C5—C6—H9 | −60.8 (3) |
N1—C1—C2—O2 | −177.6 (2) | O4—C5—C6—H10 | 59.2 (3) |
C5—C1—C2—O1 | 126.0 (2) | C1—C5—C6—H8 | −55.6 (3) |
C5—C1—C2—O2 | −53.5 (2) | C1—C5—C6—H9 | 64.4 (3) |
H3—C1—C2—O1 | −115.6 (2) | C1—C5—C6—H10 | −175.6 (2) |
H3—C1—C2—O2 | 64.9 (2) | H7—C5—C6—H8 | 61.1 (3) |
N1—C1—C5—O4 | 72.1 (2) | H7—C5—C6—H9 | −178.9 (2) |
N1—C1—C5—C6 | −54.1 (2) | H7—C5—C6—H10 | −58.9 (3) |
N1—C1—C5—H7 | −169.6 (2) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O4—H1···O2i | 0.95 | 1.75 | 2.676 (2) | 164 |
N1—H2···O4i | 0.95 | 1.97 | 2.915 (2) | 176 |
N2—H11···O1ii | 0.95 | 1.90 | 2.831 (2) | 167 |
N2—H12···O1 | 0.95 | 1.94 | 2.825 (2) | 154 |
N2—H12···O2 | 0.95 | 2.44 | 3.270 (2) | 146 |
N2—H13···O2iii | 0.95 | 1.92 | 2.862 (2) | 171 |
N2—H14···O3iv | 0.95 | 1.83 | 2.772 (2) | 168 |
C1—H3···O3 | 1.02 | 2.33 | 2.778 (2) | 105 |
Symmetry codes: (i) x+1/2, −y+1/2, −z+1; (ii) x−1/2, −y+3/2, −z+1; (iii) x+1/2, −y+3/2, −z+1; (iv) −x+1/2, −y+1, z+1/2. |
(II)
N-acetyl-
L-threoninate methylammonium
top
Crystal data top
CH6N+·C6H10NO4− | F(000) = 208.0 |
Mr = 192.21 | Dx = 1.312 Mg m−3 |
Monoclinic, P21 | Cu Kα radiation, λ = 1.54056 Å |
Hall symbol: P 2y1 | Cell parameters from 25 reflections |
a = 8.1400 (9) Å | θ = 29–30° |
b = 7.178 (2) Å | µ = 0.91 mm−1 |
c = 9.081 (1) Å | T = 293 K |
β = 113.52 (1)° | Prism, colourless |
V = 486.5 (2) Å3 | 0.63 × 0.34 × 0.22 mm |
Z = 2 | |
Data collection top
Enraf-Nonius CAD-4 diffractometer | 1079 reflections with I > 2σ(I) |
Radiation source: monochromated | Rint = 0.021 |
Graphite monochromator | θmax = 75° |
ω–2θ scans as suggested by peak–shape analysis | h = 0→10 |
Absorption correction: ψ scan North et al. (1968) | k = 0→9 |
Tmin = 0.727, Tmax = 0.819 | l = −11→11 |
1149 measured reflections | 5 standard reflections every 180 min |
1086 independent reflections | intensity decay: 2% |
Refinement top
Refinement on F | 1/[σ2(Fo) + (0.02Fo)2 + 12] (Killean & Lawrence, 1969) |
Least-squares matrix: full | (Δ/σ)max = 0.00012 |
R[F2 > 2σ(F2)] = 0.041 | Δρmax = 0.17 e Å−3 |
wR(F2) = 0.049 | Δρmin = −0.25 e Å−3 |
S = 0.99 | Extinction correction: Stout & Jensen (1968) |
1079 reflections | Extinction coefficient: 5.42 (13) x 10-5 |
119 parameters | Absolute structure: Rogers (1981) |
H-atom parameters not refined | Rogers parameter: 1.023 (8) |
Crystal data top
CH6N+·C6H10NO4− | V = 486.5 (2) Å3 |
Mr = 192.21 | Z = 2 |
Monoclinic, P21 | Cu Kα radiation |
a = 8.1400 (9) Å | µ = 0.91 mm−1 |
b = 7.178 (2) Å | T = 293 K |
c = 9.081 (1) Å | 0.63 × 0.34 × 0.22 mm |
β = 113.52 (1)° | |
Data collection top
Enraf-Nonius CAD-4 diffractometer | 1079 reflections with I > 2σ(I) |
Absorption correction: ψ scan North et al. (1968) | Rint = 0.021 |
Tmin = 0.727, Tmax = 0.819 | 5 standard reflections every 180 min |
1149 measured reflections | intensity decay: 2% |
1086 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.041 | H-atom parameters not refined |
wR(F2) = 0.049 | Δρmax = 0.17 e Å−3 |
S = 0.99 | Δρmin = −0.25 e Å−3 |
1079 reflections | Absolute structure: Rogers (1981) |
119 parameters | Rogers parameter: 1.023 (8) |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
O1 | 0.7947 (3) | 0.5000 | 0.4299 (3) | 0.0581 (7) | |
O2 | 0.7339 (2) | 0.8018 (3) | 0.4319 (2) | 0.0470 (6) | |
O3 | 0.3201 (3) | 0.4346 (4) | −0.0266 (2) | 0.0631 (8) | |
O4 | 0.4044 (2) | 0.6192 (3) | 0.5026 (2) | 0.0423 (5) | |
N1 | 0.4533 (3) | 0.4053 (3) | 0.2428 (2) | 0.0355 (6) | |
C1 | 0.4923 (3) | 0.6029 (4) | 0.2767 (3) | 0.0338 (7) | |
C2 | 0.6886 (3) | 0.6349 (4) | 0.3886 (3) | 0.0390 (7) | |
C3 | 0.3693 (3) | 0.3384 (4) | 0.0955 (3) | 0.0381 (8) | |
C4 | 0.3353 (4) | 0.1299 (5) | 0.0849 (4) | 0.0517 (10) | |
C5 | 0.3683 (3) | 0.6921 (4) | 0.3462 (3) | 0.0358 (8) | |
C6 | 0.1720 (4) | 0.6777 (4) | 0.2362 (4) | 0.0492 (9) | |
N2 | 0.8823 (3) | 0.1338 (4) | 0.3464 (3) | 0.0435 (7) | |
C7 | 0.9330 (5) | 0.2195 (7) | 0.2266 (4) | 0.0784 (14) | |
H1 | 0.31744 | 0.52715 | 0.49479 | 0.0423* | |
H2 | 0.48989 | 0.32066 | 0.33040 | 0.0355* | |
H3 | 0.46948 | 0.66601 | 0.16965 | 0.0338* | |
H4 | 0.22167 | 0.10119 | −0.01384 | 0.0517* | |
H5 | 0.32011 | 0.08584 | 0.18554 | 0.0517* | |
H6 | 0.44131 | 0.06263 | 0.07597 | 0.0517* | |
H7 | 0.39567 | 0.83130 | 0.35657 | 0.0358* | |
H8 | 0.09640 | 0.73383 | 0.29158 | 0.0493* | |
H9 | 0.14882 | 0.74861 | 0.13242 | 0.0493* | |
H10 | 0.13831 | 0.54115 | 0.21036 | 0.0493* | |
H11 | 0.98523 | 0.08139 | 0.42871 | 0.0435* | |
H12 | 0.83154 | 0.22515 | 0.39137 | 0.0435* | |
H13 | 0.79675 | 0.03846 | 0.29777 | 0.0435* | |
H14 | 0.82815 | 0.29546 | 0.14929 | 0.0784* | |
H15 | 1.04030 | 0.30500 | 0.28160 | 0.0784* | |
H16 | 0.96641 | 0.11858 | 0.16440 | 0.0784* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
O1 | 0.0416 (8) | 0.0258 (9) | 0.0922 (14) | 0.0028 (9) | 0.0111 (9) | −0.0094 (10) |
O2 | 0.0432 (8) | 0.0237 (8) | 0.0702 (10) | −0.0070 (8) | 0.0186 (7) | −0.0092 (9) |
O3 | 0.0901 (14) | 0.0441 (12) | 0.0414 (9) | −0.0095 (12) | 0.0117 (9) | 0.0021 (10) |
O4 | 0.0580 (8) | 0.0271 (9) | 0.0423 (7) | −0.0031 (8) | 0.0207 (6) | −0.0001 (8) |
N1 | 0.0431 (9) | 0.0174 (9) | 0.0419 (9) | −0.0026 (8) | 0.0126 (7) | −0.0008 (8) |
C1 | 0.0404 (10) | 0.0171 (10) | 0.0411 (10) | −0.0024 (10) | 0.0133 (8) | 0.0002 (9) |
C2 | 0.0402 (10) | 0.0252 (11) | 0.0519 (11) | −0.0046 (10) | 0.0186 (8) | −0.0036 (11) |
C3 | 0.0410 (10) | 0.0290 (13) | 0.0434 (10) | −0.0035 (10) | 0.0159 (8) | −0.0043 (10) |
C4 | 0.0620 (14) | 0.0278 (12) | 0.0631 (13) | −0.0106 (13) | 0.0227 (10) | −0.0134 (13) |
C5 | 0.0419 (10) | 0.0212 (11) | 0.0426 (10) | −0.0011 (9) | 0.0149 (8) | 0.0014 (10) |
C6 | 0.0409 (11) | 0.0382 (16) | 0.0631 (14) | 0.0010 (12) | 0.0149 (10) | 0.0022 (13) |
N2 | 0.0417 (9) | 0.0291 (10) | 0.0597 (10) | −0.0013 (10) | 0.0201 (7) | 0.0033 (11) |
C7 | 0.100 (2) | 0.075 (2) | 0.0594 (15) | −0.032 (2) | 0.0308 (13) | −0.0019 (18) |
Geometric parameters (Å, º) top
O1—C2 | 1.251 (3) | C4—H6 | 1.020 |
O2—C2 | 1.270 (4) | C5—C6 | 1.513 (3) |
O3—C3 | 1.230 (3) | C5—H7 | 1.020 |
O4—C5 | 1.430 (3) | C6—H8 | 1.020 |
O4—H1 | 0.950 | C6—H9 | 1.020 |
N1—C1 | 1.459 (3) | C6—H10 | 1.020 |
N1—C3 | 1.326 (3) | N2—C7 | 1.446 (5) |
N1—H2 | 0.950 | N2—H11 | 0.950 |
C1—C2 | 1.530 (3) | N2—H12 | 0.950 |
C1—C5 | 1.529 (4) | N2—H13 | 0.950 |
C1—H3 | 1.020 | C7—H14 | 1.020 |
C3—C4 | 1.518 (4) | C7—H15 | 1.020 |
C4—H4 | 1.020 | C7—H16 | 1.020 |
C4—H5 | 1.020 | | |
| | | |
O1···O4 | 3.597 (3) | O3···C5 | 3.738 (4) |
O1···C3 | 3.764 (3) | O3···C6 | 3.535 (5) |
O2···O4 | 3.271 (3) | C3···C6 | 3.433 (5) |
| | | |
C5—O4—H1 | 109.2 | O4—C5—C6 | 112.1 (2) |
C1—N1—C3 | 123.2 (2) | O4—C5—H7 | 108.4 |
C1—N1—H2 | 118.4 | C1—C5—C6 | 113.4 (2) |
C3—N1—H2 | 118.4 | C1—C5—H7 | 107.0 |
N1—C1—C2 | 111.6 (2) | C6—C5—H7 | 105.2 |
N1—C1—C5 | 111.7 (2) | C5—C6—H8 | 109.5 |
N1—C1—H3 | 106.8 | C5—C6—H9 | 109.5 |
C2—C1—C5 | 110.5 (2) | C5—C6—H10 | 109.5 |
C2—C1—H3 | 108.1 | H8—C6—H9 | 109.5 |
C5—C1—H3 | 108.0 | H8—C6—H10 | 109.5 |
O1—C2—O2 | 123.9 (3) | H9—C6—H10 | 109.5 |
O1—C2—C1 | 119.7 (2) | C7—N2—H11 | 109.5 |
O2—C2—C1 | 116.4 (2) | C7—N2—H12 | 109.5 |
O3—C3—N1 | 123.9 (2) | C7—N2—H13 | 109.5 |
O3—C3—C4 | 120.7 (3) | H11—N2—H12 | 109.5 |
N1—C3—C4 | 115.4 (2) | H11—N2—H13 | 109.5 |
C3—C4—H4 | 109.5 | H12—N2—H13 | 109.5 |
C3—C4—H5 | 109.5 | N2—C7—H14 | 109.5 |
C3—C4—H6 | 109.5 | N2—C7—H15 | 109.5 |
H4—C4—H5 | 109.5 | N2—C7—H16 | 109.5 |
H4—C4—H6 | 109.5 | H14—C7—H15 | 109.5 |
H5—C4—H6 | 109.5 | H14—C7—H16 | 109.5 |
O4—C5—C1 | 110.4 (2) | H15—C7—H16 | 109.5 |
| | | |
H1—O4—C5—C1 | −100.3 (2) | H3—C1—C5—C6 | 57.9 (3) |
H1—O4—C5—C6 | 27.1 (3) | H3—C1—C5—H7 | −57.6 (3) |
H1—O4—C5—H7 | 142.8 (2) | O3—C3—C4—H4 | −29.6 (4) |
C3—N1—C1—C2 | −130.4 (3) | O3—C3—C4—H5 | −149.7 (3) |
C3—N1—C1—C5 | 105.4 (3) | O3—C3—C4—H6 | 90.3 (4) |
C3—N1—C1—H3 | −12.5 (3) | N1—C3—C4—H4 | 150.2 (3) |
H2—N1—C1—C2 | 49.6 (3) | N1—C3—C4—H5 | 30.2 (4) |
H2—N1—C1—C5 | −74.6 (3) | N1—C3—C4—H6 | −89.8 (3) |
H2—N1—C1—H3 | 167.5 (2) | O4—C5—C6—H8 | 51.4 (3) |
C1—N1—C3—O3 | 1.9 (4) | O4—C5—C6—H9 | 171.4 (2) |
C1—N1—C3—C4 | −178.0 (2) | O4—C5—C6—H10 | −68.6 (3) |
H2—N1—C3—O3 | −178.1 (3) | C1—C5—C6—H8 | 177.2 (2) |
H2—N1—C3—C4 | 2.0 (4) | C1—C5—C6—H9 | −62.8 (3) |
N1—C1—C2—O1 | 4.5 (3) | C1—C5—C6—H10 | 57.2 (3) |
N1—C1—C2—O2 | −176.6 (2) | H7—C5—C6—H8 | −66.2 (3) |
C5—C1—C2—O1 | 129.5 (3) | H7—C5—C6—H9 | 53.8 (3) |
C5—C1—C2—O2 | −51.6 (3) | H7—C5—C6—H10 | 173.8 (2) |
H3—C1—C2—O1 | −112.6 (3) | H11—N2—C7—H14 | −169.9 (3) |
H3—C1—C2—O2 | 66.3 (3) | H11—N2—C7—H15 | −49.9 (4) |
N1—C1—C5—O4 | 67.4 (3) | H11—N2—C7—H16 | 70.1 (4) |
N1—C1—C5—C6 | −59.3 (3) | H12—N2—C7—H14 | −49.9 (4) |
N1—C1—C5—H7 | −174.7 (2) | H12—N2—C7—H15 | 70.1 (4) |
C2—C1—C5—O4 | −57.4 (3) | H12—N2—C7—H16 | −169.9 (3) |
C2—C1—C5—C6 | 175.9 (2) | H13—N2—C7—H14 | 70.1 (4) |
C2—C1—C5—H7 | 60.4 (3) | H13—N2—C7—H15 | −169.9 (3) |
H3—C1—C5—O4 | −175.4 (2) | H13—N2—C7—H16 | −49.9 (4) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O4—H1···O2i | 0.95 | 1.86 | 2.710 (3) | 148 |
N1—H2···O4i | 0.95 | 2.02 | 2.961 (3) | 169 |
N2—H11···O1ii | 0.95 | 1.83 | 2.775 (3) | 170 |
N2—H12···O1 | 0.95 | 2.05 | 2.903 (3) | 149 |
N2—H12···O4i | 0.95 | 2.58 | 3.144 (3) | 118 |
N2—H13···O2iii | 0.95 | 2.27 | 2.914 (3) | 125 |
N2—H13···O3iv | 0.95 | 2.38 | 3.061 (3) | 129 |
C1—H3···O3 | 1.02 | 2.38 | 2.816 (3) | 104 |
Symmetry codes: (i) −x+1, y−1/2, −z+1; (ii) −x+2, y−1/2, −z+1; (iii) x, y−1, z; (iv) −x+1, y−1/2, −z. |
Experimental details
| (I) | (II) |
Crystal data |
Chemical formula | NH4+·C6H10NO4− | CH6N+·C6H10NO4− |
Mr | 178.19 | 192.21 |
Crystal system, space group | Orthorhombic, P212121 | Monoclinic, P21 |
Temperature (K) | 293 | 293 |
a, b, c (Å) | 7.025 (1), 8.0689 (4), 16.754 (2) | 8.1400 (9), 7.178 (2), 9.081 (1) |
α, β, γ (°) | 90, 90, 90 | 90, 113.52 (1), 90 |
V (Å3) | 949.7 (2) | 486.5 (2) |
Z | 4 | 2 |
Radiation type | Cu Kα | Cu Kα |
µ (mm−1) | 0.89 | 0.91 |
Crystal size (mm) | 0.34 × 0.23 × 0.21 | 0.63 × 0.34 × 0.22 |
|
Data collection |
Diffractometer | Enraf-Nonius CAD-4 diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | – | ψ scan North et al. (1968) |
Tmin, Tmax | – | 0.727, 0.819 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1478, 1165, 1154 | 1149, 1086, 1079 |
Rint | 0.036 | 0.021 |
(sin θ/λ)max (Å−1) | 0.628 | 0.627 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.036, 0.044, 0.96 | 0.041, 0.049, 0.99 |
No. of reflections | 1154 | 1079 |
No. of parameters | 111 | 119 |
No. of restraints | ? | ? |
H-atom treatment | H-atom parameters not refined | H-atom parameters not refined |
Δρmax, Δρmin (e Å−3) | 0.18, −0.15 | 0.17, −0.25 |
Absolute structure | Rogers (1981) | Rogers (1981) |
Rogers parameter | 0.927 (4) | 1.023 (8) |
Selected geometric parameters (Å, º) for (I) topO1—C2 | 1.240 (3) | O4—C5 | 1.425 (2) |
O2—C2 | 1.262 (2) | N1—C1 | 1.457 (2) |
O3—C3 | 1.227 (2) | N1—C3 | 1.326 (2) |
| | | |
C1—N1—C3 | 122.4 (2) | O3—C3—N1 | 122.8 (2) |
N1—C1—C2 | 111.2 (2) | O3—C3—C4 | 121.7 (2) |
N1—C1—C5 | 111.6 (2) | N1—C3—C4 | 115.6 (2) |
O1—C2—O2 | 123.6 (2) | O4—C5—C1 | 110.0 (2) |
O1—C2—C1 | 119.7 (2) | O4—C5—C6 | 111.9 (2) |
O2—C2—C1 | 116.7 (2) | C1—C5—C6 | 113.5 (2) |
| | | |
C3—N1—C1—C2 | −129.8 (2) | N1—C1—C2—O1 | 1.9 (3) |
C1—N1—C3—O3 | 2.1 (3) | N1—C1—C5—O4 | 72.1 (2) |
C1—N1—C3—C4 | −177.2 (2) | N1—C1—C5—C6 | −54.1 (2) |
Hydrogen-bond geometry (Å, º) for (I) top
D—H···A | D—H | H···A | D···A | D—H···A |
O4—H1···O2i | 0.95 | 1.75 | 2.676 (2) | 164 |
N1—H2···O4i | 0.95 | 1.97 | 2.915 (2) | 176 |
N2—H11···O1ii | 0.95 | 1.90 | 2.831 (2) | 167 |
N2—H12···O1 | 0.95 | 1.94 | 2.825 (2) | 154 |
N2—H12···O2 | 0.95 | 2.44 | 3.270 (2) | 146 |
N2—H13···O2iii | 0.95 | 1.92 | 2.862 (2) | 171 |
N2—H14···O3iv | 0.95 | 1.83 | 2.772 (2) | 168 |
C1—H3···O3 | 1.02 | 2.33 | 2.778 (2) | 105 |
Symmetry codes: (i) x+1/2, −y+1/2, −z+1; (ii) x−1/2, −y+3/2, −z+1; (iii) x+1/2, −y+3/2, −z+1; (iv) −x+1/2, −y+1, z+1/2. |
Selected geometric parameters (Å, º) for (II) topO1—C2 | 1.251 (3) | N1—C1 | 1.459 (3) |
O2—C2 | 1.270 (4) | N1—C3 | 1.326 (3) |
O3—C3 | 1.230 (3) | N2—C7 | 1.446 (5) |
O4—C5 | 1.430 (3) | | |
| | | |
C1—N1—C3 | 123.2 (2) | O3—C3—N1 | 123.9 (2) |
N1—C1—C2 | 111.6 (2) | O3—C3—C4 | 120.7 (3) |
N1—C1—C5 | 111.7 (2) | N1—C3—C4 | 115.4 (2) |
O1—C2—O2 | 123.9 (3) | O4—C5—C1 | 110.4 (2) |
O1—C2—C1 | 119.7 (2) | O4—C5—C6 | 112.1 (2) |
O2—C2—C1 | 116.4 (2) | C1—C5—C6 | 113.4 (2) |
| | | |
C3—N1—C1—C2 | −130.4 (3) | N1—C1—C2—O1 | 4.5 (3) |
C1—N1—C3—O3 | 1.9 (4) | N1—C1—C5—O4 | 67.4 (3) |
C1—N1—C3—C4 | −178.0 (2) | N1—C1—C5—C6 | −59.3 (3) |
Hydrogen-bond geometry (Å, º) for (II) top
D—H···A | D—H | H···A | D···A | D—H···A |
O4—H1···O2i | 0.95 | 1.86 | 2.710 (3) | 148 |
N1—H2···O4i | 0.95 | 2.02 | 2.961 (3) | 169 |
N2—H11···O1ii | 0.95 | 1.83 | 2.775 (3) | 170 |
N2—H12···O1 | 0.95 | 2.05 | 2.903 (3) | 149 |
N2—H12···O4i | 0.95 | 2.58 | 3.144 (3) | 118 |
N2—H13···O2iii | 0.95 | 2.27 | 2.914 (3) | 125 |
N2—H13···O3iv | 0.95 | 2.38 | 3.061 (3) | 129 |
C1—H3···O3 | 1.02 | 2.38 | 2.816 (3) | 104 |
Symmetry codes: (i) −x+1, y−1/2, −z+1; (ii) −x+2, y−1/2, −z+1; (iii) x, y−1, z; (iv) −x+1, y−1/2, −z. |
Detailed investigations of the crystal structures of amino acid and oligopeptide derivatives are a useful step to arrive at the conformational preferences of polypeptide chains in proteins.
Threonine (threo-α-amino-β-hydroxy-n-butyric acid) is an important amino acid necessary for the human diet and a significant constituent of many common proteins (egg albumin and lactalbumin, bovine and human serum albumin, casein, insulin, hemoglobin). Thr is among the ammino acids with polar side chains that can favour, by means of intrachain hydrogen bonds, the arrangement of β-turn and β-sheet structures enhancing the folding of globular proteins.
As part of our ongoing researches concerning crystallographic, conformational and thermodynamic studies of solid N-acetyl derivatives of several aminoacids and peptides (Puliti et al., 1996, 1997, 1998, and references therein), we present here the crystal structures of the title salts, (I) and (II). \sch
In the two structures, the geometry and conformation of the N-acetyl-L-threoninate moieties do not present any significant discrepancy (Tables 1 and 3): the corresponding bond lengths and angles differ within three times the s.u.'s. All the values are in the expected ranges (Sequeira et al., 1981; Ashida et al., 1987; Engh & Huber, 1991). The geometry of carboxyl groups is typical of an ionized form (Parthasarathy et al., 1974): the asymmetry between the two C—O distances and O—C—C angles can be ascribed to the different hydrogen-bonding patterns involving the two carboxylic O atoms (see Tables 2 and 4). In fact, O2 is more strongly involved in hydrogen-bond interactions in comparison with O1 that shows the shorter distance and the larger angle. In both structures, the acetyl group is oriented to make an almost planar five-membered cyclic system, C1—H3···O3—C3—N1. In this way, an intramolecular C—H···O interaction is formed between the activated C1—H3 group and O3 oxygen (Taylor & Kennard, 1982). Figs. 1 and 2 show perspective views of the asymmetric units of crystals of (I) and (II), respectively, together with the used labelling schemes for non hydrogen atoms.
The side-chain conformation of Thr residue can be described by the torsion angles χ1,1 (N1—C1—C5—C6) and χ1,2 (N1—C1—C5—O4) and is (g-g+) type in both structures (Tables 1 and 3). This conformation with the hydroxyl group in gauche+ conformation dominates over the (tg-) one in peptide structures (Benedetti et al., 1983; Doi et al. 1993; Banumathi et al., 1999) and is the most favoured according to conformational energy calculations (Vasquez et al., 1983).
The two packings present strict analogies and are ruled by three-dimensional networks of hydrogen bonds which involve all the donor groups. A view of the packing of (I) is shown in Fig. 3. The N-acetyl-L-threoninate ions, related by screw symmetry along the a axis, are linked through two hydrogen bonds (O4—H···O2 and N1—H···O4) forming infinite ribbons parallel to the a direction. The NH4+ cations at the distance 4.408 (2) Å alternate with chains of anions. All the ammonium H atoms are involved in a three-dimensional network of hydrogen bonds that interconnects screw related Thr- ions of neighbouring ribbons. In particular, the N2—H12 is involved in an asymmetric 'three-centered' hydrogen-bond system with O1 and O2 as acceptors: the last one corresponding to the weaker component (Taylor et al., 1984; Jeffrey & Saenger, 1991). Details of the hydrogen-bond geometry are reported in Table 2. The shortest methyl-methyl distance is C4···C6(1 - x,1/2 + y,1/2 - z) = 3.811 (4) Å.
Fig. 4 presents the packing of structure (II) projected along the b direction. Also in this crystal, pairs of hydrogen bonds (O4—H···O2 and N1—H···O4) link together the Thr- moieties, related by screw symmetry, forming infinite ribbons of anions that wind parallel to the b direction. These ribbons alternate with methylammonium cations whose nitrogen H atoms are all involved in hydrogen-bond interactions (Table 4). In this structure there are two asymmetric 'three-centered' hydrogen bonds, both involving N2 as donor, one is formed by H12 with the acceptors O1 and O4 (weaker component), the other by H13 that is shared between the O2 carboxylic and the O3 acetylic (weaker) of different Thr- moieties (Table 4). The shortest distance between methylammonium N atoms is 4.480 (3) Å and the ones concerning methyl carbons are C4···C6(x,y - 1,z) = 3.956 (5) and C6···C7(x - 1,y,z) = 3.805 (6) Å.