Molecular Ordering and Structure of Quasi-spherical Solutes by Liquid Crystal NMR and Monte Carlo Simulations:  The Case of Norbornadiene

Aroulanda, Christie; Celebre, Giorgio; G, De Luca; Longeri, M.

doi:10.1021/jp061345s

Cited by 17 publications

(19 citation statements)

References 43 publications

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“…The example of such developments have been cited above. 116, 117, 121, 122, 129–131 The progress in this area, however, is limited by our relatively poor knowledge of the liquid crystal structure and dynamics.…”

Section: Resultsmentioning

confidence: 99%

Domain cooperativity in multidomain proteins: what can we learn from molecular alignment in anisotropic media?

2011

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Many proteins have modular design with multiple globular domains connected via flexible linkers. As a simple model of such system, we study a tandem construct consisting of two identical SH3 domains and a variable-length Gly/Ser linker. When the linker is short, this construct represents a dumbbell-shaped molecule with limited amount of domain-domain mobility. Due to its elongated shape, tandem SH3 efficiently aligns in steric alignment media. As the length of the linker increases, the two domains become effectively uncoupled and begin to behave as independent entities. Consequently, their degree of alignment drops, approaching that found in the (near-spherical) isolated SH3 domains. To model the dependence of alignment parameters on the length of the interdomain linker, we have generated in silico a series of conformational ensembles representing SH3 tandems with different linker length. These ensembles were subsequently used as input for alignment prediction software PALES. To test the accuracy of theoretical predictions, we prepared a number of tandem-SH3 samples in PEG/hexanol alignment media. These samples were used to measure backbone 1HN-15N residual dipolar couplings associated with the two globular domains within the tandem. The experimental alignment tensors determined in this fashion were compared with the results of the PALES-based simulations, broadly confirming the anticipated trends. The results of the comparison, however, fall short of quantitative agreement. In particular, it has been found that the isolated SH3 domain aligns much stronger than expected. This finding can be attributed to complex morphology of the PEG/hexanol media and/or to weak site-specific interactions between the protein and the media. In the latter case, there are strong indications that electrostatic interactions may play a role. The fact that PEG/hexanol does not behave as a simple steric media should serve as a caution for studies that use PALES as a quantitative prediction tool (especially for disordered proteins). Further progress in this area depends on our ability to accurately model the anisotropic media and its site-specific interactions with protein molecules. Once this ability is improved, it should be possible to use the alignment parameters as a measure of domain-domain cooperativity, thus identifying the situations where two domains transiently interact with each other or become coupled through a partially structured linker.

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Section: Resultsmentioning

confidence: 99%

Domain cooperativity in multidomain proteins: what can we learn from molecular alignment in anisotropic media?

2011

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“…Once our theoretical apparatus is fixed as we have described, we can proceed with the treatment. It is quite usual to assume that internal vibrations and overall reorientational (tumbling) motions of the molecule can be decoupled in Equation (2), because the dependence of s() on the vibrational state of the molecule is believed to be small enough to be neglected to a good approximation (for more details about this point, see [42,43,27] and the references therein). Of course, this approximation could affect the results: in principle, very accurate determinations of the structure of solutes dissolved in liquid crystals should take into account vibration-reorientation coupling effects, besides the usual harmonic and anharmonic vibrational corrections.…”

Section: Theorymentioning

confidence: 99%

Exploiting the information content of dipolar couplings: determination of the temperature dependence of the inter-ring twist angle of biphenyl dissolved in uniaxial mesophases

Celebre

Longeri

2010

Liquid Crystals

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In the present work, the quite intriguing question of the temperature dependence of the inter-ring angle of biphenyl in fluid condensed phases has been investigated by the proton liquid crystal nuclear magnetic resonance technique. The spectra of the molecule dissolved in three different thermotropic uniaxial solvents (one of which shows also a smectic A phase) at different values of temperature have been analysed by standard procedures, and the resulting temperature-dependent dipolar coupling sets have been rationalised by the additive potential for the treatment of the ordering interactions method, combined with the direct probability description of the torsional curve, in order to obtain the distribution of the twist angle j for each temperature. The results emphasise a very slight but unequivocal and systematic increase of j M (the most probable value of the dihedral angle) with temperature, so qualitatively confirming what was previously found by a cruder hybrid approach (based on experimental quadrupolar splittings of perdeuteriated biphenyl combined with computer-simulated order parameters) carried out by two of the present authors (Celebre, G.; De Luca, G.; Mazzone, G. J. Mol. Struct. (THEOCHEM) 2005, 728, 209-214).

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“…1,2 It also explains the change with liquid-crystal solvent of the order parameter asymmetries observed for the solutes 1,4-difluorobenzene, p-benzoquinone, and norbornadiene. 10,11 These observations are difficult to rationalize with other possible anisotropic interactions. The general trend found is that the change with liquid-crystal solvent of solute order parameter is consistent with the sign of Q mol .…”

Section: Introductionmentioning

confidence: 98%

“…Indeed, order parameters of solutes in the MMs have been fitted well with models for these short-range size and shape interactions; there is excellent evidence that longer-range anisotropic elec-trostatic interactions do not need to be invoked to any significant extent for the orientational ordering of solutes in these mixtures. 1,2,10,11 However, the size and shape models are not successful by themselves in explaining order parameters of solutes in nematic solvents other than MMs. The literature contains many papers that deal with the anisotropic intermolecular interactions that solutes experience in liquid-crystalline phases, 1,2,10,12-22 including theories that use a reaction-field approach.…”

Section: Introductionmentioning

confidence: 99%

Orientational order of near D3h solutes in nematic liquid crystals

Danilovič

Burnell

2009

The Journal of Chemical Physics

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Solutes that are similar in size, have a shape that is close to D(3h) symmetry but contain dissimilar substituent groups (methyl versus chloro, contributing different electrostatic interactions to the anisotropic intermolecular potential), are used to delineate the short- and long-range anisotropic intermolecular interactions that lead to solute orientational order in nematic liquid crystals. The short-range interactions should be similar for all solutes and for D(3h) symmetry should yield a single independent order parameter, whereas the long-range interactions are expected to differ with solute. Short-range size and shape mechanisms account for solute orientational order measured in magic mixtures (e.g., 55 wt % ZLI-1132/N-p-ethoxybenzylidene-p(')-n-butylaniline), whereas additional mechanisms are required in other nematic liquid-crystal solvents. The results obtained for long-range interactions cannot be rationalized in detail using simple mean-field models that incorporate solute dipoles, quadrupoles, or polarizabilities. The results suggest that details of the solute electrostatics may need to be incorporated into the description of the anisotropic intermolecular potential.

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Molecular Ordering and Structure of Quasi-spherical Solutes by Liquid Crystal NMR and Monte Carlo Simulations: The Case of Norbornadiene

Cited by 17 publications

References 43 publications

Domain cooperativity in multidomain proteins: what can we learn from molecular alignment in anisotropic media?

Domain cooperativity in multidomain proteins: what can we learn from molecular alignment in anisotropic media?

Exploiting the information content of dipolar couplings: determination of the temperature dependence of the inter-ring twist angle of biphenyl dissolved in uniaxial mesophases

Orientational order of near D3h solutes in nematic liquid crystals

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