Semi-maleate salts ofL- andDL-serinium: the first example of chiral and racemic serinium salts with the same composition and stoichiometry

Abstract

L-serinium semi-maleate, (I), and DL-serinium semi-maleate, (II), both C3H8NO3(+)·C4H3O4(-), provide the first example of chiral and racemic anhydrous serine salts with the same organic anion. A comparison of their crystal structures with each other, with the structures of the pure components (L-serine polymorphs, DL-serine and maleic acid) and with other amino acid maleates is important for understanding the formation of the crystal structures, their response to variations in temperature and pressure, and structure-property relationships. As in other known crystal structures of amino acid maleates, there are no direct links between the semi-maleate anions in the two new structures. The serinium cations have different conformations in (I) and (II). In (I), they are linked into infinite chains via hydrogen bonds between carboxylic acid and hydroxy groups. In (II), there are no such chains formed by the serinium cations. In both (I) and (II), there are C2(2)(12) chains consisting of alternating semi-maleate anions and serinium cations. Two types of such chains are present in (I) and (II), termed C2(2)(12) and C2(2)(12)'. In (I), these chains, lying in the same plane, are further linked to each other via hydrogen bonds, whereas in (II) they are not.

Energetics of Glycine Cocrystal or Salt Formation with Two Regioisomers: Fumaric Acid and Maleic Acid

“…As observed for FA:Gly 2 , the main structural features of MA:Gly are also present in known binary crystals of MA with other amino acids namely, alanine (MA:Ala), ,, valine (MA:Val , and MA:Val 2 ), leucine (MA:Leu), methionine (MA:Met), phenylalanine, (MA:Phe), ,,, serine (MA:Ser), threonine (MA:Thr), lysine (MA:Lys), and histidine (MA:His, and MA 2 :His) . Regardless of the stoichiometry: (i) they are all salts.…”

“…The preference of FA to form cocrystals and of MA to form salts with amino acids seems to be of general scope since it has been observed in all published cases mentioned above. [23][24][25][26]28,[30][31][32][33][34][35][36][37][38][39]43,59,61,62 This tendency cannot be unequivocally predicted from commonly used ΔpK a rules, 40−42 albeit a larger proton transfer ability of MA compared to FA might be anticipated given that pK a1 (MA) < pK a1 (FA). Thus, in the case of the FA + Gly and MA + Gly systems studied here, based on pK a1 (Gly) = 2.35, pK a1 (FA) = 3.02, and pK a1 (MA) = 1.92, at 298 K, 63 it can be concluded that ΔpK a (FA) = −0.67 and ΔpK a (MA) = 0.43.…”

“…A number of binary crystals of MA and FA with amino acids have been prepared, mainly driven by questions such as how biomolecular homochirality evolved from a prebiotic environment, the preparation of new materials for second-order nonlinear optical (NLO) applications, − the importance of noncovalent interactions in the aggregation and interaction patterns of biological molecules, − or the ionization states and main connectivities of the supramolecular synthons that, from a crystal engineering perspective, sustain crystal structures. − The available data, which by large refers to materials obtained through crystallization from water, indicates that amino acids show a strong tendency to give salts with MA and cocrystals with FA, where they adopt a zwitterionic form. This tendency seems to be difficult to predict from commonly used Δp K a rules, − a feature that was confirmed here.…”

Structural Variety of Alkali Hydrogen Maleates at High Pressure

“…This resonance-assisted hydrogen bond (RAHB) locks the ring in a rigid, planar cis conformation, with an estimated stabilization of 21.5(2) kcal/mol . The properties of this particular hydrogen bond have been the subject of extensive research, including X-ray − and neutron − diffraction and NMR, vibrational, , and photoelectron spectroscopies, as well as theoretical investigations. ,− This relatively simple system is used as a prototype for the hydrogen transfer processes in enzymatic reactions − and DNA intercalations by ortho -hydroxyaryl Schiff bases. , However, the features of this RAHB depend on the environment, including the effect of solvation by polar solvents. − …”

l-serine picrates

“…(L-SerH).H 2 PO 4 [11], di-L-serinium hexafluorosilicate (L-SerH) 2 SiF 6 [12], L-serinium hydrogen oxalate (L-SerH)HC 2 O 4 , two forms of di-L-serinium oxalate dihydrate (LSerH) 2 C 2 O 4 .2H 2 O [13,14], L-serinium hydrogen maleate [15].…”