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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.

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 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.

The temperature dependence of the one-bond 13 C 1 H coupling constant of the methyl groups in pivalic acid, tert -butyl chloride and hexamethylethane has been studied in the liquid and plastic crystalline phases. A steady decrease in the coupling constant with falling temperature in the plastic crystalline phase has been observed for these organic solids. A maximum change in the 13 C 1 H coupling constant of 25 Hz has been found after deduction of the effect of overlap of the broadened lines in the methyl quartet. The CNDO/2 calculations indicate that the temperature dependence of the coupling constant is not caused by intramolecular transitions. The significant reduction of the 13 C 1 H coupling constant is largely attributed to intramolecular dipole-dipole interactions due to a slight anisotropic tumbling of the molecules in the plastic phase.

Use of the paramagnetic relaxation reagents, tris-(acetylacetonato)chromium(III) [Cr(acac) 3 ], in 13 C spin-lattice relaxation time measurements proves capable of differentiating the alkyl groups of short-chain alkylbenzenes and paraffinic hydrocarbons. A specific hydrogen-bond interaction between Cr(acac) 3 and a very weak hydrogen-bond donor, such as an α-benzylic group, is the most important factor controlling the observed electron-nuclear spin-lattice relaxation times ( T 1 e s) of carbon- 13 nuclei.