Using flow injection analysis to time-resolve rhythmic and pulsatile signals

Continuous monitoring can be used to detect rhythms, an important aspect of biology. But peaks of concentration are broadened by dispersion so that they overlap their neighbours and obscure high frequency chemoperiodicities. In this study, flow injection was found experimentally to be useful in resolving these. A rhythmically varying pattern of permanganate concentration was measured spectrophotometrically. The rhythm (frequency 0.08 Hz) was observable at a dispersion coefficient of 3.0 but not at 3.9 (when only a single peak was recorded). It was again observable using the same high dispersion manifold but positioned after an injection valve that subsampled the stream at intervals. A design based on this work is proposed for an automated instrument that outputs a time series of concentration measures.     

Oxygen capture by lithiated organozinc reagents containing aromatic 2-pyridylamide ligands

The sequential reaction of ZnMe2 with a 2-pyridylamine (HN(2-C5H4N)R, R = Ph: 1; 3,5-Xy (=3,5-xylyl): 2; 2,6-Xy: 3; Bz (=benzyl): 4; Me: 5), tBuLi and thereafter with oxygen affords various lithium zincate species, the solid-state structures of which reveal a diversity of oxo-capture modes. Amine 1 reacts to give both dimeric THF [Li(Me)OZn[N(2-C5H4N)Ph]2] (6), wherein oxygen has inserted into the Zn-C bond of a [MeZn[N(2-C5H4N)-Ph]2] ion, and the trigonal Li2Zn complex, bis(OtBu)-capped (THF x Li)2-[[(mu3-O)tBu]2Zn[N(2-C5H4N)Ph]2] (7). The structural analogue of 6 (8) results from the employment of 2, while the use of more sterically congested 3 yields a pseudo-cubane dimer [(THF x [Li(tBu)OZn(OtBu)Me]]2] (9) notable for the retention of labile Zn-C(Me). Amines 4 and 5 afford the oxo-encapsulation products [mu4-O)Zn4[(2-C5H4N)-NBz]6] (10b), and [tBu(mu3-O)-Li3(mu6-O)Zn3[(2-C5H4N)NMe]6] (11), respectively, with concomitant oxo-insertion into a Li-C interaction resulting in capping of the fac-isomeric (mu6-O)M3M'3 distorted octahedral core of the latter complex by a tert-butoxide group.     

EPR on Medically Relevant NO Adsorbed to Zn-LTA

For medical purposes, materials are required that store and target specifically deliver exogenous nitric oxide (NO). Partially zinc-exchanged Na-LTA (Linde type A) zeolite (Zn-LTA) has high potential in this respect due to its non-toxicity and adsorption capacity for NO. In contrast to NO adsorbed to LTA zeolites prepared for catalytic purposes, lower dehydration temperature prior to NO adsorption is used to achieve a balance between production cost and high activity. In order to study the interaction of NO with the metal sites in the samples prepared under these medical conditions, continuous-wave X-band electron paramagnetic resonance has been applied. In contrast to Na-LTA with only one weakly interacting NO monomer, three different monomers, having stronger interaction to the metal sites than in Na-LTA, were observed in Zn-LTA. To improve the storage capacity of Zn-LTA, higher dehydration temperatures would be necessary.     

Synthesis of azafluorenones and related compounds using deprotocupration–aroylation followed by intramolecular direct arylation

The efficiency of the deprotocupration–aroylation of 2-chloropyridine using lithiocuprates prepared from CuX (X=Cl, Br) and LiTMP (TMP=2,2,6,6-tetramethylpiperidido, 2 equiv) was investigated. CuCl was identified as a more suitable copper source than CuBr for this purpose. Different diaryl ketones bearing a halogen at the 2 position of one of the aryl groups were synthesized in this way from azines and thiophenes. These were then involved in palladium-catalyzed ring closure: substrates underwent expected CH-activation-type arylation to afford fluorenone-type compounds, and were also subjected to cyclization reactions leading to xanthones, notably in the presence of oxygen-containing substituents or reagents.     

Zeolites with Continuously Tuneable Porosity

Zeolites are important materials whose utility in industry depends on the nature of their porous structure. Control over microporosity is therefore a vitally important target. Unfortunately, traditional methods for controlling porosity, in particular the use of organic structure‐directing agents, are relatively coarse and provide almost no opportunity to tune the porosity as required. Here we show how zeolites with a continuously tuneable surface area and micropore volume over a wide range can be prepared. This means that a particular surface area or micropore volume can be precisely tuned. The range of porosity we can target covers the whole range of useful zeolite porosity: from small pores consisting of 8‐rings all the way to extra‐large pores consisting of 14‐rings.     

Controlled Synthesis of Large Single Crystals of Metal-Organic Framework CPO-27-Ni Prepared by a Modulation Approach: In situ Single-Crystal X-ray Diffraction Studies

The size of single crystals of the metal-organic framework CPO-27-Ni was incrementally increased through a series of modulated syntheses. A novel linker modulated synthesis using 2,5-dihydroxyterephthalic acid and the isomeric ligand 4,6-dihydroxyisophthalic acid yielded large single crystals of CPO-27-Ni (∼70 μm). All materials were shown to have high crystallinity and phase purity through powder X-ray diffraction, electron microscopy methods, thermogravimetry, and compositional analysis. For the first time single-crystal structure analyses were carried out on CPO-27-Ni. High BET surface areas and nitric oxide (NO) release efficiencies were recorded for all materials. Large single crystals of CPO-27-Ni showed a prolonged NO release and proved suitable for in situ single-crystal diffraction experiments to follow the NO adsorption. An efficient activation protocol was developed, leading to a dehydrated structure after just 4 h, which subsequently was NO-loaded, leading to a first NO loaded single-crystal structural model of CPO-27-Ni.     

Controlling the size and alignment of ZnO microrods using ZnO thin film templates deposited by pulsed laser ablation

The production of dense arrays of well aligned ZnO nano- and microrods with a controllable distribution of diameters is demonstrated. The rods were grown using a hydrothermal method, on pre-deposited ZnO thin films exhibiting a range of different grain sizes. These template ZnO thin films were deposited by pulsed laser ablation, at 193 nm, in a low background pressure of O₂; average grain sizes ranged from 10 nm (room temperature deposition) to 50 nm when deposited at a substrate temperature (T_sub) of 500 °C. The morphology of the ZnO microrod arrays grown onto these ZnO thin films was found to depend on the T_sub used during film deposition. Increasing T_sub resulted in a lower density of larger nanorods, with a more pronounced [0001] alignment. The diameters of the rods produced are typically an order of magnitude greater than the grain size of the template ZnO film. Thus the rods cannot be a direct continuation of the grain structure of the template films. Rather, we suggest that the rod diameter is controlled by the density of sites at which the initial nucleation occurs, which is expected to be higher on the smaller grain size films deposited at lower temperatures. The factor controlling the final size of the rods is thus the available free space into which they can grow, which is smaller at the higher nucleation densities. The increased extent of [0001] texturing of the thin film templates deposited at higher T_sub is proposed as the reason for the improved [0001] alignment of rods grown on these templates. PACS 81.07.De; 81.10.Dn; 52.38.Mf     

An environmental pseudopotential approach to molecular interactions: Implementation in MOLPRO

We present the implementation into the MOLPRO package of a model for the interaction of a central system with its surrounding environment. The properties of a target system enclosed by a noncovalently bound environment or solvent are modeled as those of a system embedded into the effective pseudopotential arising from the exact electrostatic Coulomb potential and the approximated exchange-repulsion potential. For the latter we use the charge-density overlap model, which relates the exchange-repulsion interaction energy between two species with the overlap of their ground-state electron charge densities. The solutions of the modified Hartree-Fock equations for the target system are obtained self-consistently. This way the exchange-induction effects arising from the converged electron-charge density of the embedded system are implicitly included. Inclusion of the correlation effects is provided by the use of post-Hartree-Fock and density-functional techniques available in the MOLPRO package. The computational and conceptual advantages provided by this approach are shown in the calculation of the dipole polarizabilities of halide and chalcogenide anions in different environments.