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The 1:2 complex of 1,4-dimethylpiperazine mono-betaine (MBPZ) with squaric acid (H2SQ) has been characterised by single-crystal X-ray analysis, FTIR and NMR spectroscopies, and by DFT calculations. The crystals are monoclinic, space groupP21/c. Two MBPZ cations and four hydrogen squarate anions (HSQ− ) are linked by strong O(1)–H…O(13) (2.525(4) Å), O(14)–H…O(21) (2.511(4) Å) and N(4)–H…O(23) (2.607(3) Å) hydrogen bonds into a cyclamer. In turn, the cyclamers are linked into a helixthrough two O(24)–H…O(11) hydrogen bonds of 2.516(4) Å. The piperazinium ring has a chair conformation with N(4)–CH3and N(1)–CH2COOH substituents in the equatorial positions, and N(1)–CH3in the axial position. The FTIR spectrum is consistent with the crystal data. Two models of the 1:2 complex of MBPZ with H2SQ have been optimised at the B3LYP/6-311++G(d,p) level of theory and have been used to calculate harmonic IR frequencies. One of the models (2) is dominated by electrostatic attraction between NH(4)+and HSQ− , whereas in the other (3) squaric acid interacts with a zwitterionic MBPZ through the O–H…O and O–H…N hydrogen bonds. [ABSTRACT FROM PUBLISHER]

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]