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The rotational and translational dynamics of cyclohexane and cyclopentane confined in a MCM-41 solid have been studied as a function of temperature by measuring the T1 and T2 relaxation times and diffusivities, and the results are compared with values obtained for the bulk substances. Filling degrees of 60%, 80% and 104% were used when investigating the confined samples. The T1 behaviour is remarkably similar for confined cyclohexane and cyclopentane although we compare compounds exhibiting different bulk phases at corresponding temperatures. T1 and T2 increase clearly with increasing pore filling, presumable as a result of a reduced contribution from surface relaxation. The self-diffusion rate of confined cyclopentane, however, decreases markedly with increasing pore filling in contrast to the situation for cyclohexane. In the former case, however, the diffusion experiment detects the diffusivity of all the liquid in the pores, while in the latter case only the diffusivity of the surface layer is monitored below the depressed melting point. The thickness of the surface layer inside the pores is approximately one molecular layer for both adsorbates, i.e., 0.65 and 0.52 nm for cyclohexane and cyclopentane, respectively.

When applying pulsed field gradient (PFG) NMR experiments to determine the molecular mobility characterized by the diffusion coefficient, it is crucial to have control over all experimental parameters that may affect the performance of the diffusion experiment. This could be diffusion measurement in the presence of magnetic field transients, internal magnetic field gradients, either constant or spatially varying, convection, mechanical vibrations, or in the presence of physical restrictions affecting the diffusion propagator. The effect of these parameters on the diffusion experiment is discussed and visualized. It is also outlined how to minimize their influence on the measured diffusivity that is extracted from the PFG-NMR experiment. For an expanded and more general treatment we refer to the excellent reviews by Dr William S. Price (Concepts Magn. Reson. 1997; 9: 299; 1998; 10: 197) and the references therein. Copyright © 2002 John Wiley & Sons, Ltd.

In this work the rotational and translational dynamics of cyclohexane confined in MCM-41 have been studied as a function of temperature by measuring intra-crystalline diffusivities and T1 and T2 relaxation times. The results are compared with values obtained for bulk cyclohexane and cyclohexane confined in 40 A silica. T1 was measured for three different samples, with three different filling grades of cyclohexane. The T1 curves are continuous over the studied temperature region, and the slope is practically unchanged. However, a marked increase in T1 with the degree of pore filling is seen owing to an increasing contribution from the bulk-like molecules at the interior of the pores. Only one surface component, attributed to the molecules at the pore walls, was observed when measuring the T2 relaxation. The relatively narrow spin-echo signal and the long T2 indicate that the liquid adsorbed on the pore surface does not freeze at all, even at temperatures far below the plastic-brittle solid transition point of the bulk material. The true intra-crystalline diffusivity was obtained by using the short diffusion time model and extrapolating to zero observation time. A high diffusion rate was observable over a wide temperature region, and the measured diffusivity is about three orders of magnitude larger than in the plastic phase of bulk cyclohexane.

It is evident that the study of diffusion of molecules confined in microporous material, such as zeolites, gives valuable information about the chemical and geometrical properties of the pores. However, due to the limited size of the microporous crystallites or grains, and a non-zero observation time, it is difficult to measure true intra-crystalline diffusivity directly. The measured value of the intra-crystalline diffusivity as derived from PFG-NMR measurements turns out to be dependent on the observation time even if this is very short. This difficulty is inherent to the PFG-NMR technique and due to the limited size of microporous crystallites. Here we present NMR diffusion measurements of ethane confined in H-ZSM-5 crystallites where the mean crystallite diameter was of the order of 20 μm prior to the sample preparation. We apply the short diffusion time model and extrapolate to zero observation time to obtain the unrestricted intra-crystalline diffusivity. The root-mean-square displacement in the diffusion measurements is then only a small fraction of the mean crystallite diameter. We will also describe pitfalls which are present when analysing the experimental data sets.

The rotational and translational dynamics of hexamethyldisilane confined within silica pores of diameter 4, 6 and 20 nm were studied as a function of temperature by measuring 1H and 13C NMR linewidths, self-diffusion coefficients, spin–spin relaxation times and spin–lattice relaxation times, and the results were compared with values obtained for the bulk material. The confinement in the pores gives rise to substantial changes in the molecular dynamics and phase behaviour. The lineshape, T2 and self-diffusion measurements revealed a two-phase system consisting of a liquid-like component at the surface and a crystalline solid in the centre of the pore. The highly mobile surface layer is observable far below the reduced transition temperature of the confined hexamethyldisilane. A high diffusion rate of the adsorbed hexamethyldisilane is observed over a wide temperature range, even well below the region of the depressed transition point. The diffusion coefficient of the molecules in the surface layer is three orders of magnitude larger than in the plastic phase of bulk hexamethyldisilane. © 1998 John Wiley & Sons, Ltd.

1H and 13C NMR chemical shifts are reported for five anthraquinone glycosides from Rhamnus frangula (Alder Buckthorn). The investigation utilized data obtained by a variety of 1D and 2D NMR techniques such as homodecoupling, NOE, J-modulated spin-echo, COSY, HSC and COLOC. Assignments were made for frangulin A and B and glucofrangulin A and B. A further compound previously thought to be a glycoside of emodin is shown to be physcion-8-O-β-D-glucoside. © 1998 John Wiley & Sons, Ltd.

The analysis of anthocyanin pigments in the passion fruit Passiflora edulis and in the highly colored fruits of P. suberosa was performed using combinations of chromatographic and spectroscopic techniques. In addition to cyanidin 3-glucoside (97%), small amounts of cyanidin 3-(6″-malonylglucoside) (2%) and pelargonidin 3-glucoside (1%) were found in the rind of the passion fruit. The 3-(6″-malonylglucoside) and 3-glucoside of cyanidin, delphinidin, petunidin, and pelargonidin were identified in extracts of P. suberosa. Anthocyanins acylated with malonic acid constituted 27% of the total anthocyanin content in this latter species.

Complete assignment of the 1H and 13C NMR spectra of flavone and three flavone derivatives is reported. Proton–proton and carbon–proton coupling constants of the flavones, including the extreme seven-bond long-range coupling between H-7 and H-3 in 6-hydroxyflavone (0.52 Hz) and flavone (0.27 Hz), are presented. Hydrogen bonding between 5-OH and the keto group (C-4) in 5,7-dihydroxyflavone gives rise to a large coupling constant between H-3 and C-3 (169.1 Hz), in addition to the expected low-field shifts of the 5-OH hydroxyl proton (12.92 ppm) and C-4 (181.86 ppm). This investigation revises the previously reported carbon assignments of three of the examined flavones and provides new NMR data for 6-hydroxyflavone.

Using the nuclear magnetic resonance technique, two-dimensional inverse heteronuclear shift correlation through multiple quantum coherence (HMQC), the one-bond coupling constants between the carbon atoms and protons (1J(C, H)) have been measured for a number of anthocyanins represented by 6-hydroxydelphinidin and all the common aglycones (except peonidin) and monosaccharides found as building blocks of anthocyanins. The large anomeric 1J(C, H) values of rhamnopyranosyls (168-170 Hz) show that these protons are in equatorial positions while the smaller 1J(C, H) values of the other anomeric protons (162-165 Hz) correspond to axial positions, thus assigning the anomeric configurations of the examined anthocyanins to be β for the gluco-, galacto- and xylopyranosyls and α for the rhamno- and arabinopyranosyls. In the pentoses, xylo- and arabinopyranosyls, it was found that the 1J(C, H) couplings for the equatorial H-5 protons (149-150 Hz) are larger than for the corresponding axial H-5 protons (140-143 Hz).

5-Azido-2,5-dideoxy-beta-D-erythro-pentofuranosyl nucleosides 10 and their corresponding alpha-anomers 11 have been synthesized by condensation of methyl 3-O-acetyl-5-azido-2,5-dideoxy-beta-D-erythro-pentofuranoside (7) with silylated nucleobases followed by deprotection with methanolic ammonia. Reaction of silylated thymine (19) with methyl 2,3-di-O-benzoyl-5-deoxy-5-fluoro-D-arabino-pentofuranoside (15) and methyl 5-azido-2,3-di-O-benzoyl-5-deoxy-alpha-D-arabino-pentofuranoside (17 alpha) afforded a mixture of the alpha-nucleosides 20 and the acyclo nucleosides 5-fluoro- and 5-azido-2,3-O-dibenzoyl-5-deoxy-1-O-methyl-1-(thymin-1-yl)-D -arabinitol (22). Compounds 20 and 22 were deprotected with methanolic ammonia to give the acyclic nucleosides 21 and 23, respectively. The new nucleosides were inactive against HSV-1 and HIV-1.

A 1,2-dicarba-closo-dodecaborane(12) derivative, containing a hydrophilic diol group and an amino group 2-[2-(3-aminopropyl)-1,2-dicarba-closo-dodecaboran(12)-l-ylmethoxy]-1,3-propanediol (1a), has been synthesised from the dibenzyl ether of 2-[1,2-dicar