Na+ and K+ transport by 4-chlorophenylurethane-monensin in Enterococcus hirae de-energized and energized cells studied by 23Na-NMR and K+ atomic absorption

In-cell NMR: Why and how?

NMR spectroscopy has been applied to cells and tissues analysis since its beginnings, as early as 1950. We have attempted to gather here in a didactic fashion the broad diversity of data and ideas that emerged from NMR investigations on living cells. Covering a large proportion of the periodic table, NMR spectroscopy permits scrutiny of a great variety of atomic nuclei in all living organisms non-invasively. It has thus provided quantitative information on cellular atoms and their chemical environment, dynamics, or interactions. We will show that NMR studies have generated valuable knowledge on a vast array of cellular molecules and events, from water, salts, metabolites, cell walls, proteins, nucleic acids, drugs and drug targets, to pH, redox equilibria and chemical reactions. The characterization of such a multitude of objects at the atomic scale has thus shaped our mental representation of cellular life at multiple levels, together with major techniques like mass-spectrometry or microscopies. NMR studies on cells has accompanied the developments of MRI and metabolomics, and various subfields have flourished, coined with appealing names: fluxomics, foodomics, MRI and MRS (i.e. imaging and localized spectroscopy of living tissues, respectively), whole-cell NMR, on-cell ligand-based NMR, systems NMR, cellular structural biology, in-cell NMR… All these have not grown separately, but rather by reinforcing each other like a braided trunk. Hence, we try here to provide an analytical account of a large ensemble of intricately linked approaches, whose integration has been and will be key to their success. We present extensive overviews, firstly on the various types of information provided by NMR in a cellular environment (the "why", oriented towards a broad readership), and secondly on the employed NMR techniques and setups (the "how", where we discuss the past, current and future methods). Each subsection is constructed as a historical anthology, showing how the intrinsic properties of NMR spectroscopy and its developments structured the accessible knowledge on cellular phenomena. Using this systematic approach, we sought i) to make this review accessible to the broadest audience and ii) to highlight some early techniques that may find renewed interest. Finally, we present a brief discussion on what may be potential and desirable developments in the context of integrative studies in biology.

FT-IR, 1H, 13C NMR, ESI-MS and semiempirical investigation of the structures of Monensin phenyl urethane complexes with the sodium cation

In this paper three forms of phenyl urethane of Monensin i.e. its acid form (H-MU) and its 1:1 complex with NaClO4 (H-MU-Na) and its sodium salt (Na-MU) were obtained and their structures were studied by FT-IR, (1)H and (13)C NMR, ESI MS and PM5 methods. The FT-IR data of Na-MU complexes demonstrate that the C=O urethane group is not engaged in the complexation of the sodium cation. However spectroscopic studies of H-MU-Na complex show that the structure in which this C=O urethane groups participate in the complexation is also present, but it is in the minority. The PM5 semiempirical calculations allow visualisation of all structures and determination of the hydrogen bond parameters.

Reinvestigation of the structure of monensin A phenylurethane sodium salt based on X-ray crystallographic and spectroscopic studies, and its activity against hospital strains of methicillin-resistant S. epidermidis and S. aureus

Monensin A phenylurethane sodium salt (MON-UR1-Na) crystals were studied by the X-ray, NMR, FT-IR and PM5 semi-empirical methods. The X-ray data show that the compound forms a pseudocyclic structure, stabilized by three intramolecular hydrogen bonds, and the sodium cation coordinated by five oxygen atoms in the hydrophilic sphere. The NMR and FT-IR data demonstrate that this pseudocyclic structure is also conserved in CH(2)Cl(2) solution. This structure of MON-UR1-Na is significantly different than the ones previously proposed by Westley et al. and Tanaka et al. The semi-empirical calculations of the MON-UR1-Na structures indicate that the one of the crystal is the most energetically favorable one. Other parameters, such as the size, chemical and biological nature of the urethane substituent, and especially the free carbonyl urethane group, may have a role in the biological activity of MON-UR1-Na. The in vitro microbiological tests provide evidence that MON-UR1-Na shows higher antibacterial activity against human pathogenic bacteria, including antibiotic-resistant Staphylococcus aureus and Staphylococcus epidermidis than the parent unmodified antibiotic-Monensin A.