An Isoreticular Family of Microporous Metal-Organic Frameworks Based on Zinc and 2-Substituted Imidazolate-4-amide-5-imidate: Syntheses, Structures and Properties

We report on a new series of isoreticular frameworks based on zinc and 2-substituted imidazolate-4-amide-5-imidate (IFP-1-4, IFP=imidazolate framework Potsdam) that form one-dimensional, microporous hexagonal channels. Varying R in the 2-substitued linker (R=Me (IFP-1), Cl (IFP-2), Br (IFP-3), Et (IFP-4)) allowed the channel diameter (4.0-1.7??), the polarisability and functionality of the channel walls to be tuned. Frameworks IFP-2, IFP-3 and IFP-4 are isostructural to previously reported IFP-1. The structures of IFP-2 and IFP-3 were solved by X-ray crystallographic analyses. The structure of IFP-4 was determined by a combination of PXRD and structure modelling and was confirmed by IR spectroscopy and (1) H?MAS and (13) C?CP-MAS?NMR spectroscopy. All IFPs showed high thermal stability (345-400?°C); IFP-1 and IFP-4 were stable in boiling water for 7?d. A detailed porosity analysis was performed on the basis of adsorption measurements by using various gases. The potential of the materials to undergo specific interactions with CO(2) was investigated by measuring the isosteric heats of adsorption. The capacity to adsorb CH(4) (at 298?K), CO(2) (at 298?K) and H(2) (at 77?K) at high pressure were also investigated. In situ IR spectroscopy showed that CO(2) is physisorbed on IFP-1-4 under dry conditions and that both CO(2) and H(2) O are physisorbed on IFP-1 under moist conditions.     

Single-fiber diffuse optical time-of-flight spectroscopy

We demonstrate interstitial diffuse optical time-of-fight spectroscopy based on a single fiber for both light delivery and detection. Detector saturation due to the massive short-time reflection is avoided by ultrafast gating of a single photon avalanche diode. We show that the effects of scattering and absorption are separable and that absorption can be assessed independently of scattering. Measurements on calibrated liquid phantoms and subsequent Monte Carlo-based evaluation illustrate that absorption coefficients can be accurately assessed over a wide range of medically relevant optical properties. Our findings pave the way to simplified and less invasive interstitial in vivo spectroscopy.     

Copolymerization of ethylene and 1-butene using a Cr—silica catalyst in a slurry reactor

A novel slurry reactor was used to investigate the copolymerization behavior of ethylene and 1-butene in the presence of 1 wt % Cr on Davison silica (Phillips-type) catalyst over the temperature range of 0–50°C, space velocity of about 0.0051 [m³ (STP)]/(g of catalyst) h, and a fixed ethylene to 1-butene feed mole ratio of 95 : 5. The effect of varying the ethylene to 1-butene feed ratios, 100 : 0, 96.5 : 3.5, 95 : 5, 93 : 7, 90 : 10, 80 : 20, and 0 : 100 mol/mol at 50°C was also studied. The addition of 1-butene to ethylene typically increased both copolymerization rates and yields relative to ethylene homopolymerization with the same catalyst, reaching a maximum yield for an ethylene: 1-butene feed ratio of 95 : 5 at 50°C. The incorporation of 1-butene within the copolymer in all cases was less than 5 mol %. The average activation energy for the apparent reaction rate constant, k_a, based on total comonomer mole fraction in the slurry liquid for the ethylene to 1-butene feed mole ratio of 95 : 5 in the temperature range of 50–30°C measured 54.2 kJ/mol. The behavior for temperatures between 30 to 0°C differed with an activation energy of 98.2 kJ/mol; thus, some diffusion limitation likely influences the copolymerization rates at temperatures above 30°C. A kinetics analysis of the experimental data at 50°C for different ethylene to 1-butene feed ratios gave the values of the reactivity ratios, r₁ = 27.3 ± 3.6 and r₂ ≅ 0, for ethylene and 1-butene, respectively. © 1996 John Wiley & Sons, Inc.     

Construction of recurrent bivariate fractal interpolation surfaces and computation of their box-counting dimension

Recurrent bivariate fractal interpolation surfaces (RBFISs) generalise the notion of affine fractal interpolation surfaces (FISs) in that the iterated system of transformations used to construct such a surface is non-affine. The resulting limit surface is therefore no longer self-affine nor self-similar. Exact values for the box-counting dimension of the RBFISs are obtained. Finally, a methodology to approximate any natural surface using RBFISs is outlined.     

Loss of alignment gain in the πh 9/2[541 1/2−] ⊗ (νi 13/2)2 band in 167Tm and neighbouring odd-Z N = 98 nuclei

Theπh_9/2[541 1/2^?] band in ¹⁶⁷Tm has been studied through the ¹²⁴Sn(⁴⁸Ca, p4n)¹⁶⁷Tm reaction at E _beam = 210 MeV. The favoured signature of the πh_9/2[541 1/2^?] band is observed to spin 61/2h?. A remarkable small gain in aligned angular momentum at the AB-band crossing has been found. The crossing frequency and the gain in aligned angular momentum for ¹⁶⁷Tm are compared with data for the N = 98 isotones of Lu, Ta and Re, and contrasted with Cranked Shell Model predictions, based on frequency diabatic configurations. Large deviations are found for the gain in aligned angular momentum.     

Inherently chiral uranyl-salophen macrocycles: computer-aided design and resolution

[structure: see text] A flipping motion rapidly inverts the bent structure of uranyl-salophen compounds and, consequently, causes fast enantiomerization of nonsymmetrically substituted derivatives. This process has been previously slowed by introducing bulky substituents in the imine bond region. Since the resulting complexes dissociate upon chromatographic treatment, an alternative approach to the design and synthesis of robust, nonflipping uranyl-salophen compounds is here described. Such an approach is based on the idea that the flipping motion would be blocked by connecting the para positions with respect to the phenoxide oxygens by means of polymethylene bridges of suitable length. Analysis of a number of uranyl-salophen compounds by molecular mechanics, while showing that bulky substituents in the imine bond region cause severe distortions of the ligand backbone, suggested that the best chain lengths are those that fit the gap between the phenoxide rings without altering the natural geometry of the parent uranyl-salophen compound. Calculations showed that such chains are those composed of 12 and 13 methylene units. Accordingly, chiral uranyl-salophen macrocycles bridged with 12- and 13-methylene chains were synthesized in fairly good yields and resolved by chiral HPLC.     

Determination of 3-methylhistidine in hydrolysed proteins by fluorescamine derivatization and high-performance liquid chromatography

A method is described for the determination of the 3-methylhistidine content in myofibrilar proteins (myosin and actin) using reversed-phase high-performance liquid chromatography with ultraviolet detection. Proteins were hydrolysed and free amino acids were derivatized with fluorescamine. Elution was performed isocratically with acetonitrile-water (24:76). This method allows the detection of picomole amounts of 3-methylhistidine in myosin and actin.