Molecular structure of rubidium six-coordinated dihydrate complex with monensin A
Introduction
Ionophorous antibiotics belong to a group of highly bioactive molecules, because they are able to transport monovalent and bivalent metal cation across natural and artificial lipid membranes. Monensin A (see Scheme 1) isolated from Streptomyces cinnamonensis is a well-known representative of this class of compounds. It is able to form pseudomacrocyclic complexes with monovalent cations and to transport these cations across cell membranes. Monensin regulates many cellular functions, including apoptosis. It causes collapse of sodium and potassium gradients at the plasma membrane, blocks intracellular protein transport, and exhibits antibiotic, antimalarial, and other important biological activities [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Monensin A is used as a growth-promoting agent and as a coccidiostat in beef cattle, sheep, chickens and turkeys [4], [12], [13], [14], [15], [16].
The crystal structures of monensin complexes with several cations have been determined by X-ray diffraction [17], [18], [19], [20], [21], [22], [23], [24], [25]. In these structures the coordination of the cation by monensin A was always accompanied with the appearance of a pseudo-cyclic structure stabilized by the intramolecular hydrogen bonds.
Recently, we have studied the crystal structures of monensin A sodium salt as well as monensin A lithium salt [24], [25]. As a continuation of the studies a new crystal of monensin A rubidium dihydrate has been obtained and studied by X-ray diffraction and FT-IR spectroscopy. In this report, the structure of rubidium complex of monensin A determined by X-rays is compared with that calculated using the PM5 semiempirical method.
Section snippets
Experimental
Monensin A sodium salt (90–95%) was purchased from Sigma. CH3CN spectral-grade solvent was stored over 3 Å molecular sieves for several days. All manipulations with the substances were performed in a carefully dried and CO2-free glove box. Rubidium hydroxide hydrate RbOH·xH2O (99.995%) was purchased from Aldrich.
X-ray crystallography
As expected, the rubidium cation is complexed by the monensin A anion, as shown in Fig. 1. The cation is sixfold coordinated, by four tetrahydrofurane oxygen atoms and two hydroxyl oxygen atoms, the Rb···O distances range between 2.788 and 2.901 Å (Table 3). The anion, with the carboxyl group deprotonated is present in the pseudo-ring conformation. The selected torsion angles describing the monensin A anion conformation are listed in Table 4. The terminal carboxylate and two hydroxyl groups
Acknowledgement
Adam Huczyński wishes to thank the Foundation for Polish Science for fellowship.
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2020, Inorganica Chimica ActaCitation Excerpt :It belongs to the polyether ionophores (PI) family – membrane-active compounds, able to coordinate metal ions and to transfer them across cell membranes as neutral complex species. Although known as monovalent PI for its affinity to bind monovalent metal ions [8–25], Monensin A reacts also with divalent metal cations to form derivatives of various composition and structure. Divalent metal complexes of Monensin A were characterized by IR, FAB-MS, NMR, EPR spectroscopy and by X-ray diffraction on single crystals [26–31].
Spectroscopic and structural studies of allyl urethane derivative of Monensin A sodium salt
2013, Journal of Molecular StructureCitation Excerpt :Due to great flexibility of the skeleton, the allyl urethane of Monensin anion assumes the pseudo-cyclic conformation surrounding the Na+ cation. This conformation of the MON-UR2 anion is very similar to that of the neutral Monensin acid and its metal complexes [16,28–30]. The pseudo-cyclic conformation of allyl urethane of Monensin anion is stabilised by an electrostatic interaction between the negative polarised oxygen atoms and the positively charge Na+ cation.
Structure of 1:1 complex of 1-naphthylmethyl ester of monensin A with sodium perchlorate studied by X-ray, FT-IR and ab initio methods
2012, Journal of Molecular StructureMonensin a acid complexes as a model of electrogenic transport of sodium cation
2012, Biochimica et Biophysica Acta - BiomembranesStructural investigation of a new complex of N-allylamide of Monensin A with strontium perchlorate using X-ray, FT-IR, ESI MS and semiempirical methods
2011, Journal of Molecular StructureCitation Excerpt :The polyether skeletons of the pseudo-cyclic structure of ionophoric antibiotics are able to form complexes with metal cations [5]. The structures of monensin A salt complexes with several monovalent cations such as Li+, Na+, K+, Rb+ and Ag+ have been determined using X-ray crystallography [6–12] demonstrating that the coordination of the cations was always accompanied with the appearance of a pseudo-cyclic structure stabilized by the “head-to-tail” intramolecular hydrogen bonds between the carboxylate anion and two hydroxyl groups. Recently, Pantcheva et al. [13–18] have shown that monensin (MON) can form two types of salt complex species with divalent metal cations [13–18].
<sup>1</sup>H, <sup>13</sup>C NMR, FT-IR, ESI MS and PM5 studies of a new 3,6,9-trioxadecylamide of monensin A and its complexes with Li<sup>+</sup>, Na<sup>+</sup> and K<sup>+</sup> cations
2011, Journal of Molecular StructureCitation Excerpt :The regioselectivity of loss of the first water molecule, especially with formation of cation B, can be explained by strong engagement of the electrons of O(3) atom in complexation of the metal cation. This is in accordance with the previously published studies on the three-dimensional structure of monensin A, its derivatives in the solid and gas states and in solutions [7–9,25–25,33,35,38–39]. A similar regioselectivity of the dehydration steps was also previously observed for monensin sodium salt and was widely discussed in literature [35,40–42].