High-resolution spectra of the 1(1,1) ← 0(0,0) rotational transition of water in argon and krypton matrices

The high-resolution spectra of H₂¹⁶O, H₂¹⁸O, HD¹⁶O, HD¹⁸O, D₂¹⁶O, and D₂¹⁸O isolated in argon and krypton matrices are reported in the 10–60 cm^?1 region. The high resolution is obtained by observing very dilute mixtures of water in the rare gases. No discrete absorbances attributable to pure argon or krypton are found in this region. In all cases the relative gas—matrix shifts of the isotopimers are consistent with the rotation—translation coupling model. The linewidths are found to correlate with rotation—translation coupling. The integrated intensity of the 1(1,1) — 0(0,0) transition of HDO exhibits a temperature dependence which does not deviate significantly from that expected from a Boltzmann distribution in rigid rotor energy levels.     

Biosynthesis of 2-deoxystreptamine-containing aminoglycoside antibiotics

The 2-deoxystreptamine-containing aminoglycosides are an important class of clinically valuable antibiotics. A deep understanding of the biosynthesis of these natural products is required to enable efforts to rationally manipulate and engineer the biological production of novel aminoglycosides. This review discusses the development of our biosynthetic knowledge over the past half-century, with emphasis on the relatively recent contributions of molecular biology to the elucidation of these biosynthetic pathways.     

Synthesis of MIL-102, a chromium carboxylate metal-organic framework, with gas sorption analysis

A new three-dimensional chromium(III) naphthalene tetracarboxylate, CrIII3O(H2O)2F{C10H4(CO2)4}1.5.6H2O (MIL-102), has been synthesized under hydrothermal conditions from an aqueous mixture of Cr(NO3)3.9H2O, naphthalene-1,4,5,8-tetracarboxylic acid, and HF. Its structure, solved ab initio from X-ray powder diffraction data, is built up from the connection of trimers of trivalent chromium octahedra and tetracarboxylate moieties. This creates a three-dimensional structure with an array of small one-dimensional channels filled with free water molecules, which interact through hydrogen bonds with terminal water molecules and oxygen atoms from the carboxylates. Thermogravimetric analysis and X-ray thermodiffractometry indicate that MIL-102 is stable up to approximately 300 degrees C and shows zeolitic behavior. Due to topological frustration effects, MIL-102 remains paramagnetic down to 5 K. Finally, MIL-102 exhibits a hydrogen storage capacity of approximately 1.0 wt % at 77 K when loaded at 3.5 MPa (35 bar). The hydrogen uptake is discussed in relation with the structural characteristics and the molecular simulation results. The adsorption behavior of MIL-102 at 304 K resembles that of small-pore zeolites, such as silicalite. Indeed, the isotherms of CO2, CH4, and N2 show a maximum uptake at 0.5 MPa, with no further significant adsorption up to 3 MPa. Crystal data for MIL-102: hexagonal space group P(-)6 (No. 169), a = 12.632(1) A, c = 9.622(1) A.     

Cobalt N-heterocyclic carbene alkyl and acyl compounds: synthesis, molecular structure and reactivity

The N-heterocyclic-carbene containing cobalt carbonyl compound [Co(IMes)(CO)3(Me)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene), 1, has been synthesised by tertiary phosphine displacement from [Co(PPh3)(CO)3(Me)]. Subsequent carbonylation afforded the acyl derivative [Co(IMes)(CO)3(COMe)], 2. Similarly, the compound [Co(IMes)(CO)3(COEt)], 3, has been synthesised. The compounds 2 and 3 have been shown to react with dihydrogen to form the cobalt hydride compound [Co(IMes)(CO)3(H)], 4. The molecular structures of compounds 1 and 2 have been determined.     

Thermal Methods in the Synthesis of New Ordered Mesoporous Adsorbents

The synthesis of new ordered mesoporous adsorbents, specifically of the MCM-41 type, involves a step of thermal elimination of the template (a surfactant) where CRTA is shown to provide a 'soft chemistry' route. Once the mesoporous (i.e. 2 to 50 nm pore width) material is obtained, the pore size is determined by thermoporometry, a convenient application for low temperature DSC. Finally, the hydrophobic - hydrophilic properties of the pore walls are explored by immersion microcalorimetry in water. This revised version was published online in July 2006 with corrections to the Cover Date.     

Constant transformation rate thermal analysis of HGdP<Subscript>2</Subscript>O<Subscript>7</Subscript>·3H<Subscript>2</Subscript>O

Summary The aim of this work is the optimization of the preparation of anhydrous gadolinium hydrogen phosphate with good fluorescence properties. The products obtained by dehydration of gadolinium hydrogen phosphate trihydrate depend on the conditions chosen for the thermal treatment. For this reason, the dehydration was followed by Constant Rate Thermal Analysis whilst strictly controlling the water vapour pressure above the sample. Intermediate samples, obtained during dehydration were characterised by IR spectroscopy and X-ray diffraction. It has thus been shown that the thermal pathway taken for the dehydration depends on the water vapour pressure above the sample in the region from 10^-2to 5 mbar. Under the lowest water vapour pressure (5·10^-3mbar), the elimination of the crystallization water is carried out in a continuous way and produces a quasi-amorphous intermediate. Under higher water vapour pressure (5 mbar), well crystallized intermediate products are obtained. The results obtained suggest that the trihydrate contains zeolitic water which confirms a prior structural study.     

Manipulating solute nucleophilicity with room temperature ionic liquids

In this work we report the effect of ionic liquids on a class of charge-neutral nucleophiles. We have studied the reactions of (n)butylamine, di-(n)butylamine, and tri-(n)butylamine with methyl p-nitrobenzenesulfonate in [bmpy][N(Tf)(2)], [bmpy][OTf], and [bmim][OTf] (bmpy = 1-butyl-1-methylpyrrolidinium; bmim = 1-butyl-3-methylimidazolium) and compared their reactivities, k(2), to those for the same reactions in the molecular solvents dichloromethane and acetonitrile. It was shown that all of the amines are more nucleophilic in the ionic liquids than in the molecular solvents studied in this work. Comparison is also made with the effect of ionic liquids on the reactivity of chloride ions, which are deactivated in ionic liquids. The Eyring activation parameters revealed that changes in the activation entropies are largely responsible for the effects seen. This can be explained in part by the differing hydrogen-bonding properties, as shown by the Kamlet-Taft solvent parameters, of each of these solvents and the formation of hydrogen bonds between the solvents and the nucleophiles.     

Engineering micromechanics of soft porous crystals for negative gas adsorption

Framework materials at the molecular level, such as metal–organic frameworks (MOF), were recently found to exhibit exotic and counterintuitive micromechanical properties. Stimulated by host–guest interactions, these so-called soft porous crystals can display counterintuitive adsorption phenomena such as negative gas adsorption (NGA). NGA materials are bistable frameworks where the occurrence of a metastable overloaded state leads to pressure amplification upon a sudden framework contraction. How can we control activation barriers and energetics via functionalization of the molecular building blocks that dictate the frameworks'' mechanical response? In this work we tune the elastic and inelastic properties of building blocks at the molecular level and analyze the mechanical response of the resulting frameworks. From a set of 11 frameworks, we demonstrate that widening of the backbone increases stiffness, while elongation of the building blocks results in a decrease in critical yield stress of buckling. We further functionalize the backbone by incorporation of sp³ hybridized carbon atoms to soften the molecular building blocks, or stiffen them with sp² and sp carbons. Computational modeling shows how these modifications of the building blocks tune the activation barriers within the energy landscape of the guest-free bistable frameworks. Only frameworks with free energy barriers in the range of 800 to 1100 kJ mol⁻¹ per unit cell, and moderate yield stress of 0.6 to 1.2 nN for single ligand buckling, exhibit adsorption-induced contraction and negative gas adsorption. Advanced experimental in situ methodologies give detailed insights into the structural transitions and the adsorption behavior. The new framework DUT-160 shows the highest magnitude of NGA ever observed for nitrogen adsorption at 77 K. Our computational and experimental analysis of the energetics and mechanical response functions of porous frameworks is an important step towards tuning activation barriers in dynamic framework materials and provides critical design principles for molecular building blocks leading to pressure amplifying materials.

We characterise the elastic properties of molecular building blocks and how they impact the mechanical properties of soft porous crystals.