Synthesis of the aminocyclopentitol moieties of the hopanoids of Zymomonas mobilis and 'Anacystis montana'

The first synthesis of the cyclopentitol units in bacterial hopanoids has been accomplished from D-glucosamine and the possible biological activity of the free cyclitols as glycosidase inhibitors has been studied.     

Identification of phenolic compounds in artichoke waste by high-performance liquid chromatography-tandem mass spectrometry

A new fast and efficient method combining liquid chromatography coupled to ionspray mass spectrometry in tandem mode with negative ion detection is described for the qualitative analysis of artichoke waste. Forty-five phenolic compounds were identified on the basis of their mass spectra in full scan mode, mass spectra in different MS-MS modes, and retention times compared with those of available reference substances. The major compounds were found to be both caffeoylquinic and dicaffeoylquinic acids, luteolin glucuronide, luteolin galactoside, quercetin, and some quercetin glycosides.     

Metal Complexes with a New Tetrapyridyl Pendant Armed Macrocyclic Ligand. X‐ray Crystal Structures of CuII and NiII Complexes

A new pendant‐armed macrocyclic ligand, L¹, bearing four pyridyl pendant groups has been synthesized by N‐alkylation of the tetraazamacrocyclic precursor L with 2‐picolyl chloride hydrochloride. Metal complexes of L¹ have been synthesized and characterized by microanalysis, MS‐FAB, conductivity measurements, IR, UV‐Vis, ¹H and ¹³C NMR spectroscopy and magnetic studies. Crystal structures of the ligand L¹ as well as of the complexes [Ni₂L¹](ClO₄)₄·5CH₃CN and [Cu₂L¹](ClO₄)₄·4.5CH₃CN have been determined by single crystal X‐ray crystallography. The X ray studies show the presence of two metal atoms within the macrocyclic ligand in both metal complexes showing five coordination arrangement for the metal ions.     

Simulation of the photodissociation of Ar 3 +

A simulation of the photodissociation of Ar ₃ ⁺ is performed in the range 200–650nm. The approach relies on Diatomic in Molecules electronic modelling, Molecular Dynamics and the Hemiquantal method. The results are used to interpret the experimental abundance of slow ions in terms of the various absorption bands. Kinetic energy distributions of all fragments are analysed at 530 and 280nm for two internal energies. The time evolution of the cluster is discussed and a concerted one-step mechanism emerges involving charge fluctuations. The simulation only yields fast-fast and fastslow photoneutral-photoneutral coincidences.     

A simple structural-based approach to prevent aminoglycoside inactivation by bacterial defense proteins. Conformational restriction provides effective protection against neomycin-B nucleotidylation by ANT4

Herein, we describe how the conformational differences exhibited by aminoglycosides in the binding pockets of the ribosome and those enzymes involved in bacterial resistance can be exploited in the design of new antibiotic derivatives with improved activity in resistant strains. The simple modification shown in the figure, leading to the conformationally restricted 5, provides an effective protection against aminoglycoside inactivation by Staphylococcus aureus ANT4, both in vivo and in vitro.     

Molecular dynamics with quantum transitions study of the vibrational relaxation of the HOD bend fundamental in liquid D2O

The molecular dynamics with quantum transitions method is used to study the vibrational relaxation of the HOD bend fundamental in liquid D(2)O. All of the vibrational bending degrees of freedom of the HOD and D(2)O molecules are described by quantum mechanics, while the remaining translational and rotational degrees of freedom are described classically. The effect of the coupling between the rotational and vibrational degrees of freedom of the deuterated water molecules is analyzed. A kinetic mechanism based on three steps is proposed in order to interpret the dynamics of the system. It is shown that intermolecular vibrational energy transfer plays an important role in the relaxation process and also that the transfer of energy into the rotational degrees of freedom is favored over the transfer of energy into the translational motions. The thermalization of the system after the relaxation is reached in a shorter time scale than that of the recovery of the hydrogen bond network. The relaxation and equilibration times obtained compare well with experimental and previous theoretical results.     

Ni(II) complexes of stereo-isomeric hexazamacrocyclic ligands derived from 2,6-diacetylpyridine

The nitrate and perchlorate Ni(II) complexes of the stereo-isomeric hexazamacrocyclic ligands L¹ (3,6,14,17,23,24-hexaazatricyclo[17.3.1.18,12]tetracosa-1(23),8,10,12(24),19,21-hexaene,2,7,13,18-tetramethyl) and L² (3,7,15,19,25,26-hexaazatricyclo[19.3.1.19,13]hexacosa-1(25),9,11,13(26),21,23-hexaene,2,8,14,20-tetramethyl) derived from 2,6-diacetylpyridine have been synthesized and characterized by microanalysis, LSI-MS, conductivity measurements, IR, UV–Vis spectroscopy and magnetic studies. Crystal structures of L¹·2H₂O as well as of the complexes [NiL¹](ClO₄₎₂$[{\text{NiL}}^1]({\text{ClO}}_4{)}_2$ and [NiL²](NO₃₎₂$[{\text{NiL}}^2]({\text{NO}}_3{)}_2$ have been determined. The X-ray studies show the presence of mononuclear endomacrocyclic complexes with the metal ion coordinated to all the nitrogen donor atoms from the macrocyclic framework in a N6 core. The geometry around the metal ions can be described as distorted octahedral. The nitrate and perchlorate anions do not coordinate to the metal ions, but they are involved in intermolecular interactions through hydrogen bonds to the amine groups of the macrocyclic ligands.     

Exceptionally Inert Lanthanide(III) PARACEST MRI Contrast Agents Based on an 18‐Membered Macrocyclic Platform

We report a macrocyclic ligand based on a 3,6,10,13‐tetraaza‐1,8(2,6)‐dipyridinacyclotetradecaphane platform containing four hydroxyethyl pendant arms (L¹) that forms extraordinary inert complexes with Ln³⁺ ions. The [EuL¹]³⁺ complex does not undergo dissociation in 1 M HCl over a period of months at room temperature. Furthermore, high concentrations of phosphate and Zn²⁺ ions at room temperature do not provoke metal‐complex dissociation. The X‐ray crystal structures of six Ln³⁺ complexes reveal ten coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and the four oxygen atoms of the hydroxyethyl pendant arms. The analysis of the Yb³⁺‐ and Pr³⁺‐induced paramagnetic ¹H NMR shifts show that the solid‐state structures are retained in aqueous solution. The intensity of the ¹H NMR signal of bulk water can be modulated by saturation of the signals of the hydroxy protons of Pr³⁺, Eu³⁺, and Yb³⁺ complexes following chemical‐exchange saturation transfer (CEST). The ability of these complexes to provide large CEST effects at 25 and 37 °C and pH 7.4 was confirmed by using CEST magnetic resonance imaging experiments.     

Modulating Weak Interactions for Molecular Recognition: A Dynamic Combinatorial Analysis for Assessing the Contribution of Electrostatics to the Stability of CH–π Bonds in Water

Electrostatic and charge‐transfer contributions to CH–π complexes can be modulated by attaching electron‐withdrawing substituents to the carbon atom. While clearly stabilizing in the gas phase, the outcome of this chemical modification in water is more difficult to predict. Herein we provide a definitive and quantitative answer to this question employing a simple strategy based on dynamic combinatorial chemistry.