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Catalytic chain transfer copolymerisation of MMA and HEMA (70:30) has been carried out under semi-continuous emulsion polymerisation conditions, using CoBF as catalyst. It has been shown that macromonomers of low molar mass can be synthesised with an apparent chain transfer constant, C s E , of ca. 1300 down to a threshold value of ca. 20 ppm of CoBF. Below this value an initial 20% shot of monomer/catalyst mixture was necessary to prevent events involved in the catalytic chain transfer process becoming diffusion controlled and to prevent the reaction to proceed under monomer starved conditions. Analysis of the Co(II) species by SQUID has been carried out.?oBF shows a value for its effective magnetic susceptibility of 1.77μ B . It was found that a correction for the response of the sample container is essential for reliable data to be achieved. Diffusion ordered 2D-NMR spectroscopy (DOSY) has been used as a method to study the catalyst diffusion dependence for the rate coefficient of chain transfer. However, the apparent values of the found diffusion coefficients are an order of magnitude above the natural limit for center of mass diffusion.

Many of the perturbations that lead to t1 noise in 2D NMR spectroscopy cause fluctuations in the relative phases of pulses and coherences. Because the sensitivity of the phase of a coherence to changes in the phase of a pulse depends on the change of coherence order, P-type signals in homonuclear correlation experiments are insensitive to errors in the phase of the mixing pulse, and hence they show less t1 noise than N-type signals. This effect is illustrated for the gradient COSY experiment. © 1997 John Wiley & Sons, Ltd.

We have determined the structure in solution of a homodimeric protein that is a precursor to the locust neuropeptide adipokinetic hormone I using nuclear magnetic resonance spectroscopy. This precursor, called P1, is comprised of two 41 residue strands joined by a single inter-chain disulphide at Cys39. We have also determined the structure of an end product of P1 processing, called APRP1; this is a homodimer comprised of residues 14-41 of P1. Nuclear Overhauser Effect (nOe) data indicate that in both P1 and APRP1, residues 22-37 (numbered with respect to P1) form pairs of alpha-helices, with no evidence for any other secondary structure.

The proton, proton–{deuterium} and deuterium NMR spectra of partially deuteriated samples of 1,2,3-trimethoxybenzene dissolved in a nematic liquid crystalline solvent, I32, have been recorded and analysed to yield a set of dipolar couplings which have been used to test models for the conformational distribution. It is shown that the molecule must exist in more than one conformation. A conformational distribution has been obtained which is in agreement with the data, and which is based on the assumption that each methoxy group can occupy positions either orthogonal to, or coplanar with, the phenyl ring plane.

The 1H NMR spectrum of a sample of 1,2-dimethoxybenzene dissolved in a nematic solvent (I35) has been analysed to yield a set of partially-averaged dipolar couplings, Dij. These are used to test models for the conformations adopted for the two OCH3 groups relative to the ring. It is concluded that a single conformation, or a set of symmetry-related conformations is not consistent with the data. The dipolar couplings are used to derive the distribution among the 16 minimum energy structures which are possible if it is assumed that the C–O–C planes can only be either coplanar with, or perpendicular to, the phenyl ring plane.

The deuterium and proton NMR spectra of samples of 4-ethoxy-4'-cyanobiphenyl dissolved in the nematic liquid crystal 4-hexyloxy-4'-cyanobiphenyl have been analyis to yield quadrupolar splittings and dipolar couplings. The data are compared with values calculated for three models for the conformations adopted by the ethoxy group relative to the attached phenyl ring

The deuterium and proton NMR spectra of samples of 4-ethoxy-4'-cyanobiphenyl dissolved in the nematic liquid crystal 4-hexyloxy-4'-cyanobiphenyl have been analyzed to yield quadrupolar splittings and dipolar couplings. The data are compared with values calculated for three models for the conformations adopted by the ethoxy group relative to the attached phenyl ring. These models are (a) a set of four, symmetry-related structures, (b) discrete, minimum-energy structures generated by jumps about the C4-0, O-C7, and C7-C8 bonds, and (c) the same as (b) except that a continuous potential is adopted for the motion about the 0-C7 bond

Deuterium NMR spectra have been obtained from samples of biphenyl-d10, 4-bromobiphenyl-d9, 4-cyanobiphenyl-d9 and 4-methoxybiphenyl-d5 dissolved in the nematic solvent 4-methoxy-4′-cyanobiphenyl (1-OCB), and the data used to obtain the two principal, solute order parameters, Szz and Sxx —Syy . These order parameters are then used to determine the average solute-solvent interaction parameters, u 200 and u 202, in a simple potential of mean torque. This reveals that the changes in the biaxiality, λ= u 202/u 200, on going from biphenyl to 1-OCB by introducing CN and OCH3 groups are dominated by changes in u 200 whilst u 202 remains essentially unchanged.

Modules which share the same consensus sequence are assumed to have common structural features, at the secondary and tertiary level. In order to test the extent of such similarities, it is necessary to examine the structures of several examples from each module family. Recently, the first three-dimensional structure of a complement control protein (CCP) module (the 16th repeat of human factor H, H16) was determined using a combination of two-dimensional NMR and simulated annealing (Norman, D. G., Barlow, P. N., Baron, M., Day, A. J., Sim, R. B., & Campbell, I. D. (1991) J. Mol. Biol. 219, 717-7251. Using the same techniques, the three-dimensional structure of a second CCP module (the 5th repeat of human factor H, H5) has now been determined. The primary sequence of H5 contains 17 residues which are identical and in equivalent position to those in H16. Thirteen of these 17 are part of the consensus sequence. The similarities between the secondary structure of H5 and that of H16 are extensive. This implies that the consensus sequence dictates a particular secondary structure. The tertiary structure of H5, a compact hydrophobic core wrapped in P-strand and sheet, bears much overall resemblance to that of H16. However, there is a deletion in the first strand of H5, and an insertion in a loop, resulting in slightly shorter overall length. This is associated with a rearrangement of residues within the hydrophobic core. The side chain of the highly conserved Tyr29, which occupies a central position within the core of H16, lies on the periphery of the core of H5.

The two principal orientational order parameters of anthracene and anthraquinone as solutes in several liquid crystal solvents have been obtained via deuterium NMR spectra. The ordering of anthraquinone is much more solvent dependent than that of anthracene, and possible explanations of this behaviour are examined. In particular, the possibility that electrostatic as well as dispersive and repulsion forces could contribute to a mean field potential is explored. It is concluded that the most probable cause of the large differences in orientational ordering of these two molecules in some solvents, but not in others, is a dependence on both solute and solvent of order parameters C + 4,0 and C + 2,0 for the distribution of solute-solvent intermolecular vectors.

The proton N.M.R. spectra of two partially deuteriated samples of the mesogen 4-methoxy-4′-cyanobiphenyl (1-OCB) have been obtained. The spectra were simplified by decoupling the interactions between protons and deuterons and analysed to yield sets of dipolar couplings, [Dtilde]ij . The [Dtilde]ij are used to investigate the angle φ between the two ring normals and the conformation of the methoxy group relative to the attached phenyl ring. If the potential governing rotation, V(φ), is assumed to have a deep minimum such that only structures with the minimum value of φ are appreciably populated, then φmin is determined to be 30·4° ± 0·4°. However, adopting a continuous form for V(φ) changes φmin to 36°. For the methoxy group the data are consistent with the potential governing rotation about the ring-oxygen bond being zero when the carbon atom is in the ring plane and infinite otherwise; in addition, we have investigated the consequences for the structure and ordering of adopting more realistic forms for this potential. The 24 structures of equal, minimum energy, which are generated by rotation about the inter ring bond, the phenyl-O bond and the O—CH3 bond, all have the same shape, and hence each of these conformations has the same ordering matrix, with principal elements Szz and Sxx — Syy . The magnitudes of Sxx and Sxx — Syy have been obtained, together with the orientation of x, y and z with respect to a frame fixed in the methoxylated ring, with the assumption that only these minimum energy structures are populated. The magnitudes of these principal order parameters are used to test the form of a potential of mean torque.

The structure of 4-cyanobiphenyl when dissolved in nematic liquid-crystalline solvents has been investigated. This has been achieved by recording and analysing the proton and deuterium NMR spectra of samples dissolved in the nematic solvents. The dipolar couplings obtained are compared with values calculated by averaging over the bond rotational motion, and the conclusion is reached that the minimum-energy structure has an angle between the two ring normals of 37.0 ± 0.1° in each of three solvents, compared with a value for biphenyl, obtained previously by the same method, of 37.4 ± 0.2°.

The proton and fluorine n.m.r. spectra of samples of 4-fluoro- and 4-iodo-α,α,α-trifIuoromethoxybenzene dissolved in the nematic liquid crystal solvent 135 have been obtained. Analysis of these spectra yields a set of dipolar coupling constants whose values are used to investigate the form of V(φ), the potential governing rotation about the phenyl O-bond. V(φ) is found to be very different from the form found for the corresponding potential in methoxybenzene in that the minimum occurs when the O–CF3 bond is in the plane orthogonal to the phenyl ring (φ= 90°). The data cannot, however, distinguish between a potential of the form V0+V2 cos 2φ, and one containing a substantial V4 term, that is V(φ)=V0+V2 cos 2φ+V4 cos 4φ.

The proton, proton–{deuterium} and deuterium NMR spectra of partially deuteriated samples of 1,2,3-trimethoxybenzene dissolved in a nematic liquid crystalline solvent, I32, have been recorded and analysed to yield a set of dipolar couplings which have been used to test models for the conformational distribution. It is shown that the molecule must exist in more than one conformation. A conformational distribution has been obtained which is in agreement with the data, and which is based on the assumption that each methoxy group can occupy positions either orthogonal to, or coplanar with, the phenyl ring plane.