Unusual hydrogen bonding inL-cysteine hydrogen fluoride

Abstract

L-Cysteine hydrogen fluoride, or bis(L-cysteinium) difluoride-L-cysteine-hydrogen fluoride (1/1/1), 2C3H8NO2S(+)·2F(-)·C3H7NO2S·HF or L-Cys(+)(L-Cys···L-Cys(+))F(-)(F(-)...H-F), provides the first example of a structure with cations of the 'triglycine sulfate' type, i.e. A(+)(A···A(+)) (where A and A(+) are the zwitterionic and cationic states of an amino acid, respectively), without a doubly charged counter-ion. The salt crystallizes in the monoclinic system with the space group P2(1). The dimeric (L-Cys···L-Cys(+)) cation and the dimeric (F(-)···H-F) anion are formed via strong O-H···O or F-H···F hydrogen bonds, respectively, with very short O···O [2.4438 (19) Å] and F···F distances [2.2676 (17) Å]. The F···F distance is significantly shorter than in solid hydrogen fluoride. Additionally, there is another very short hydrogen bond, of O-H···F type, formed by a L-cysteinium cation and a fluoride ion. The corresponding O···F distance of 2.3412 (19) Å seems to be the shortest among O-H···F and F-H···O hydrogen bonds known to date. The single-crystal X-ray diffraction study was complemented by IR spectroscopy. Of special interest was the spectral region of vibrations related to the above-mentioned hydrogen bonds.

Studies on the growth and characterization of L-cysteine hydrogen fluoride single crystal

“…The obtained lattice parameters were a = 11.78 Å, b = 5.32 Å and c = 15.43 Å, α = γ = 90°, β = 106.7°, unit cell volume = 913 Å 3 . It was confirmed by XRD analysis that the grown crystal had a monoclinic crystal structure with the space group P 21 , which was in good agreement with reported data [10]. It was also confirmed that LCHF was not incorporated in the organic host lattice sites.…”

Common patterns of hydrolysis initiation in P-loop fold nucleoside triphosphatases

“…On the one hand, this value is somewhat lower than the threshold of 3.5 Å, as suggested for H-bonds in protein structures by Martz [81]. On the other hand, this distance corresponds to the longest F-H-N bond reported for crystalized L-cysteine-hydrogen fluoride [82]. Still, this threshold is rather arbitrary; according to Jeffrey, weak H-bonds in proteins can have donor-acceptor distances up to 4.0 Å long [83].…”

“…6) and the acceptors were oxygen/fluorine atoms of the substrate. The presence of an H-bond was inferred from the atomic distance: an H-bond was stated at distances less or equal 3.2Å, a weak H-bond stated at distances between 3.2 and 4Å, and no possibility of a H-bond was stated for distances over 4 Å [82, 120, 121]).…”

-Cysteine halogenides: A new family of salts with an -cysteine⋯ -cysteinium dimeric cation

“…Lcysteine salts with dimeric cations (L-Cys···L-Cys + ) have not been documented to date. Lcysteine hydrogen fluoride was assumed to be known for almost five decades, but its crystal structure has been solved only very recently and was shown to be considerably more complex than those with either simple, or dimeric cations [15]. In fact, L-cysteine hydrogen fluoride has both dimeric and simple cations in the crystal structure, similar to triglycine sulfate Gly + (Gly···Gly + )·SO 4 2-.…”