ISSN:
1572-9001
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Crystal structures ofN-acetyl-(DL)-methionine and its calcium adduct have been determined in order to examine possible calcium coordination through sulfur atom and conformation changes in the molecule upon calcium coordination. Crystals of the Ca adduct ofN-acetyl-(DL)-methionine are triclinic, space groupP¯1, a=11.356(2) Å,b=13.556(2) Å,c=15.035(3) Å,α=95.42(1)°,β=103.66(1)°, andγ=103.66(1)°, withZ=4 andd o= 1.40 g cm−3; 5834 reflections were collected at −125°C. TheN-acetyl-(DL)-methionine was also crystallized so that changes induced by the calcium coordination could be observed. TheN-acetyl-(DL)-methionine crystals are monoclinic, space groupP21/c,a=5.885(1) Å,b=9.290(1) Å,c=18.024(2) Å,β=92.51 (1)°, withZ=4 andd o=1.30 g cm−3. Both structures were solved using direct methods and refined using full matrix least squares. The final values ofR andR w were 0.051 and 0.053 for the Ca adduct and 0.048 and 0.039 for the free amino acid. All hydrogen atoms were located and included in the final calculations. Interatomic distances and angles of the four crystallographically independentN-acetylmethionine molecules in the Ca adduct are comparable to those of the free molecule, but the torsion angles change drastically. Calcium coordination through the sulfur atom is not found. The binding modes of all four independentN-acetylmethionine molecules in the Ca adduct are different. Of the two crystallographically independent calcium atoms one is 6 and the other is 7 coordinated. The calcium adduct shows several Ca-Ca bridges (with distances 4.722, 4.746, 5.503, and 6.265 Å) which can be described as a zigzag calcium chain or alternatively as slightly puckered sheets of calcium atoms parallel to theab plane atz ≈ O.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00674272
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