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Abstract: The ionophoric antibiotic lasalocid acid has been converted to a novel 6-bromohexyl ester (LASBR) and its structure has been determined in the crystal by X-ray diffraction and in solution by NMR and FT-IR methods. In the crystal two symmetry-independent LASBR molecules are present. The structure of LASBR in solution is slightly different because the strongest intramolecular C(1)Hogen bond in the pseudo-aromatic ring becomes partially broken and a new hydrogen bond between O(4)H and carbonyl group C(13)ed. LASBR forms complexes with Li+, Na+ and K+ cations of exclusively 1:1 stoichiometry. The structures of complexes have been studied and visualized using semi-empirical calculation based on results of spectrometric and spectroscopic investigation. It is demonstrated that in contrast to lasalocid acid the novel ester forms preferential complexes with Li+ cation. [Copyright &y& Elsevier]

Abstract: Crystal structure of monensin A rubidium salt dihydrate, [Rb(C36H61O11)·2H2O], has been studied by X-ray diffraction, FT-IR spectroscopy and PM5 semiempirical methods. The crystal space group is P212121 with a =12.6153(7), b =16.4841(10), c =19.4840(12) and Z =4. The Rb–O bond lengths are between 2.788(7) and 2.901(6)Å. The carboxyl group of monensin A is deprotonated and engaged in two intramolecular O(11)–H···O(1) of 2.52(1)Å and O(10)–H···O(2) of 2.60(1)Å hydrogen bonds with hydroxyl groups, accompanied with formation of a pseudo-cyclic structure. This structure is stabilised by the coordination of the Rb+ cation by oxygen atoms. Two water molecules are involved in the weak intermolecular hydrogen bond between the different species forming a supramolecule. The IR spectrum of the crystal is consistent with the results obtained by the X-ray study and provides spectroscopic evidence for the complex formation. The calculated structure and the structural parameters of the monensin A rubidium salt are comparable with those determined by the X-ray study. [Copyright &y& Elsevier]

The molecular structure of 1:1 complex formed between the naturally occurring polyether ionophore, called lasalocid acid (LAS) and propargylamine (PROP) is studied by X-ray, FT-IR, 1 H NMR, 13 C NMR and ESI-MS methods. The complex formed between deprotonated LAS acid and protonated PROP molecule is stabilized by intra- and inter-molecular hydrogen bonds. The protons of the protonated amine group are hydrogen bonded to etheric and hydroxyl oxygen atoms of the LAS anion. The similarity of the FT-IR spectra of the LAS–PROP complex in solid state and in solution demonstrated that the molecular structures of the complex in both states are comparable. It is shown that LAS in solution can form concurrent complexes with metal cations (M = Li + , Na + , K + ) and amine existing in equilibrium. Analysis of the structures of lasalocid complexes is important for a better understanding of the antibacterial and anticancer properties of lasalocid acid. [ABSTRACT FROM AUTHOR]

Abstract: For the first time the structure of the complex formed between N-allylamide of monensin A (M-AM2) and divalent cation (Sr2+) has been studied by X-ray crystallography and FT-IR spectroscopy. The crystal structure of this complex contains one Sr2+ cation coordinated by six O atoms of M-AM2 molecule, one oxygen atom of the perchlorate anion and the nitrogen atom of the acetonitrile molecule. The M-AM2 molecule is additionally tied by an intramolecular hydrogen-bonded chain [O(3)H⋯O(9)H⋯O(10)H⋯O(1)e crystal data, FT-IR spectra and semiempirical calculations show that the oxygen atom of the amide group is not involved in the coordination of the Sr2+ cation. In the gas phase the formation of two types of (M-AM2+Sr)2+ and (M-AM2+Sr+ClO4)+ complexes is detected using ESI mass spectrometry and their structures are visualized by PM5 semiempirical calculations. [Copyright &y& Elsevier]

Abstract: A complex between a new N-phenylamide of monensin A (M-AM1) and sodium chloride has been synthesised and studied by X-ray diffraction and FT-IR spectroscopy. The crystal structure of the complex between M-AM1 and sodium chloride with acetonitrile was examined using X-ray diffraction and discussed in detail. Its structure is stabilised by coordination of the Na+ cation with oxygen atoms. The Na–O bond lengths are between 2.382(2) and 2.562(2)Å. The chloride anion is involved in a weak intermolecular hydrogen bond between different species forming a supramolecule. The ESI-MS spectra indicate that the amide forms stable complexes of exclusively 1:1 stoichiometry with Na+ cations. The FT-IR spectrum of the crystal is consistent with the results obtained by the X-ray study and provides spectroscopic evidence for the complex formation. Due to its specific structural properties N-phenylamide of monensin A efficiently binds sodium chloride. The result of the PM5 semiempirical calculation is in agreement with the spectroscopic data and allows visualisation of the structure of the M-AM1–Na+ complex. The new amide of monensin A has been additionally tested in view of its antimicrobial properties. It shows great activity towards some strains of Gram-positive bacteria (MIC=6.25–12.5μg/ml). [Copyright &y& Elsevier]

Abstract: A new lasalocid 2-naphthylmethyl ester (NAFB) has been synthesised and studied by X-ray, 1H NMR, 13C NMR, FT-IR, UV–vis, fluorescence-spectroscopy as well as by the PM5 semiempirical method. The crystals of NAFB are monoclinic, space group P21 with a =10.120(2)Å, b =18.245(3)Å, c =12.354(3)Å, β =109.65(3)˚ and Z =2. The molecular conformation of NAFB in the solid state is stabilized by three intramolecular hydrogen bonds, and no intermolecular H-bonds are formed. The FT-IR spectrum of NAFB in chloroform indicates equilibrium between two NAFB conformers. In the first conformer the keto group forms an intramolecular hydrogen bond, while in the second one this group is not involved in any hydrogen bonds. The two structures of NAFB are calculated by the PM5 method and discussed in detail. [Copyright &y& Elsevier]