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A new paradigm about molecular symmetry is proposed. We advance the idea that, beside the symmetry operations possessed "in full" by a molecule and canonically characterizing its point group, other symmetry operations could exist "in part". As a matter of fact, the schematic representation of the molecule as built by the "Dreiding molecular modeling kit" is, obviously, too crude. In a more realistic description, the atoms should not be considered as point masses (since they take up up a certain volume) and their positions in the molecular structure should considered to be affected by a certain statistical uncertainty. Following this approach, here we suggest to construct suitable matrices to describe the "overlap" between the "virtual" images of the molecule before and after the "hypothetical" symmetry operations; then, by evaluating a properly defined parameter (function of the determinant of the overlap matrix), it will be possible to quantify how much a residual "symmetry operation" is present in the molecule, in a range from 0 to 100%, due to the less idealized description of the "object molecule". Demonstrative examples of this approach are extensively described in the present work, for cases where "traces" of residual symmetry operations are significant, amounting to values from about 20% to about 35%. In my opinion, the present work should be included in the general efforts to overcome and broaden the current canonical concepts and approaches to determine what are the symmetry operations the molecules are endowed with, so allowing for the possibility of exploring symmetry "grey scales" useful, for example, to possibly explain surprising experimental results (as, for example, the detection of unexpected signals, from some kind of spectroscopy, unexplainable otherwise). [ABSTRACT FROM AUTHOR]

The intrinsic asymmetric nature of biological compounds, fundamental for the origin of Life on Earth, and the explanation and description of emergence and evolution of homochirality of predominant species represent an important and intriguing challenge for many scientists (in 2005, the editors of Science magazine included the problem among the 125 most important scientific puzzles). Autocatalytic reactions, where a reaction product catalyzes the production of itself and suppresses its enantiomer, can represent a mechanism for the evolution of homochirality, and the model proposed by Frank (Biochim Biophys Acta 11:459–463, 1953) still represents a milestone in the field. Anyway, with due distinctions, the basic idea underlying the Frank model could be mathematically traced back to the Lotka–Volterra equations (also commonly known as the predator–prey equations), describing biological species competition: then, in principle, this inscribes the problem basically within that branch of Mathematics called population dynamics. In the present work, alternatively to the deterministic or stochastic numerical solutions of Frank's equations describing the evolution of a system towards the homochirality, I tried to describe the "proliferation" of the chiral species by the conceptual methods and tools often adopted in biomathematics (study of geometric progressions and so on). Interestingly, this approach led to solutions about the time-dependent populations of the two enantiomers of in a simple closed form (of course, our results have been quantitatively compared with results obtained from deterministic and stochastic models). Besides this, the length of the time required for the complete evolution of the system to homochirality (also called, sometimes in literature, relaxation time) as a function of the total amount of molecules and of the initial excess of one enantiomer has been explicitly obtained, and, mathematically, it resulted to be exactly twice the value of the time where is located the point of inflection of the curves describing the dynamics of the evolution of two enantiomers. Finally, an explicit realistic estimation of these times, compared with experimental and theoretical data available in literature, is given in the work. [ABSTRACT FROM AUTHOR]

The concept of Quantum Noise is intriguing, both from a fundamental and an applied point of view. The interest for this specific subject has recently increased more and more, thanks to the development of sophisticated technologies for the practical realization of real (not only gedanken) quantum experiments, and in view of possible applications in quantum cryptography. In the present paper, we suggest a heuristic approach, an alternative to the existing ones, to assess a priori the so-called Root Mean Square Quantum Noise, quantifying the incidence of measuring apparatuses in introducing noise in quantum measurements. [ABSTRACT FROM AUTHOR]

In liquid crystals, while the second and fourth rank orientational order parameters characterizing a nematic phase can be experimentally determined via several techniques, there is no straightforward experiment rendering the positional order parameters characterizing a smectic A phase. This work illustrates a novel method to estimate the positional order parameters of a smectogenic liquid crystal solvent from knowledge of the orientational order parameters of a number of solutes dissolved therein. The latter order parameters can be experimentally determined via liquid crystal NMR spectroscopy. These data can be then analyzed with a statistical-thermodynamic density functional theory, whose basic ingredient is a model for solute-solvent intermolecular interactions. Its parametrization and the subsequent fitting procedure eventually permit one to obtain the positional order parameters of the solvent besides the positional-orientational distribution function of the solutes. The method is applied to the smectogen 4,4′-di-n-heptyl-azoxybenzene, in which the solutes 1,4-dichlorobenzene and naphthalene have been dissolved. With the help of this exploratory practical example, pros and cons of the method are pointed out and further developments prospected. [ABSTRACT FROM AUTHOR]

The proton NMR spectra of two 13C-labeled isotopomers of styrene dissolved in two liquid crystalline solvents have been obtained and analyzed to yield four sets each of 24 dipolar couplings. These couplings were then used to investigate the structure of the ring and the ene fragments of the molecule, and the position of the maximum, [lowercase_phi_synonym]0, in the ring–ene bond rotational probability distribution. To do this, the effect on the dipolar couplings of small-amplitude vibrational motion was taken into account using vibrational wave functions calculated by molecular orbital and density functional methods. It is concluded that the NMR data are consistent with the ring fragment, averaged over the ring–ene rotation, planar, while the ene fragment is not. The value of [lowercase_phi_synonym]0 is found to be 18.0°±0.2° for the two solutions, compared with a value of 27° calculated by the molecular method MP2/6-31G*. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recently, a new formulation has been proposed about a strictly short-range anisotropic potential acting on biaxial apolar particles dissolved in a uniaxial medium [Chem. Phys. Lett. 342, 375 (2001)], where the solute-solvent interactions are treated at a molecular level and the solute order parameters are calculated by making use of the Monte Carlo–Metropolis sampling scheme. In the present paper the cited model has been used for the study of 1,4-difluorobenzene, 1,4-dichlorobenzene, and 1,4-dibromobenzene molecules and the simulated order parameters have been compared with the [sup 1]H-NMR experimental data for the solutes in the nematic solvents ZLI1132 (a Merck commercial eutectic mixture of alkylcyclohexylcyanobenzenes and alkylcyclohexylcyanobiphenyl), EBBA [the N-(4-ethoxybenzylidene)-4[sup ′]-n-butylaniline], and in the zero average electric field gradient nematic mixture 55 wt% ZLI1132+EBBA (the so-called “magic” mixture). The orientations predicted by the model match almost perfectly the experimental Saupe matrices of the molecules dissolved in the “magic” mixture: implications of this result are discussed in terms of nature of the interactions in the different nematic phases and reliability and effectiveness of the suggested intermolecular potential. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The three-dimensional structure and conformational equilibrium of flexible bioactive molecules in solution are of considerable importance in clarifying their role in chemical and biological activity, since their action takes place in a liquid medium. The use of residual dipolar couplings (RDCs) recently emerged as a promising and effective method to address this kind of investigation. In this brief review, the conformational analysis of several flexible non-steroidal anti-inflammatory drugs, belonging to the class of salicylates and a-arylpropionic acids (profens), is described using the RDCs measured in weakly aligning poly-γ-benzyl-L-glutamate solutions. By combining these experimental parameters, extracted by using different mono- and bi-dimensional nuclear magnetic resonance experiments, with the theoretical additive potential-direct probability description approach, accurate descriptions of the probability distributions have been obtained for all the drug molecules selected. [ABSTRACT FROM AUTHOR]

In this paper the pulsed field gradient-spin echo nuclear magnetic resonance (PFG-SE) experiment has been performed by computer simulation technique. The diffusive phenomenon is reproduced by letting particles, moving only by Brownian motion, travel among reflecting aggregates; in such a way it is possible to calculate the nuclear magnetic resonance (NMR) echo attenuation due to the solvent self-diffusion in lyotropic systems overcoming the problem of the analytical determination of the probability distribution of the spins. The results obtained on lamellar and inverted hexagonal lyomesophases are in good agreement with the previous functions reported in literature and new results are given for the hexagonal phase treated using this approach; in particular a new interpolation formula for the determination of the obstruction factor as a function of the structural parameters is proposed. [ABSTRACT FROM AUTHOR]

In this study we determine an analytical, effective expression of the rate coefficient j3 (governing the photolysis of the atmospheric Ozone) as a function of altitude h and wavelength λ of the incoming solar radiation, in the range 0 ≲ h ≲ 32 km. [ABSTRACT FROM AUTHOR]

Detailing the conformational equilibria between global and local minimum energy structures of anti-inflammatory α-arylpropionic acids directly in solution is of the utmost importance for a better understanding of the structure-activity relationships, hence providing valuable clues for rational structure-based drug design studies. Here the conformational preferences of the widely used pharmaceutical ibuprofen were investigated in solution by NMR spectroscopy in weakly ordering phases. A thorough theoretical treatment of the anisotropic interactions that are relevant for NMR spectra led to a conformational model characterized by six pairs of symmetry-related conformers, in particular four couples of gauche structures, with a total probability of 93%, and 2 couples of trans structures, counting for the remaining 7%. [ABSTRACT FROM AUTHOR]

The ionic liquid crystal 1-dodecyl-3-methylimidazolium tetrafluoroborate slightly doped with water is presented as a promising NMR alignment medium for the measurement of residual dipolar couplings for polar molecules dissolved therein. [ABSTRACT FROM AUTHOR]

Abstract: The mechanisms conferring to the trans-stilbene derivatives their well known important biological properties are not yet completely clear; then, it is reasonable to suppose that their conformational equilibrium could play some kind of role (as found for many other molecules of pharmacological interest). In this scenario, the 4,4′-dichloro-trans-stilbene (DCS) can be considered as the prototype of a series of stilbenes substituted in 4,4′ positions in order to enhance their properties. Following this starting idea, we decided to study the conformational distribution of DCS in solution by Liquid Crystal NMR Spectroscopy (LXNMR), one of the best techniques to obtain this kind of information in the liquid state of matter. Our results show that the molecule is basically not planar: the most populated conformations we found are (a) the couple of symmetry-related, propeller-like structures, belonging to the C 2 point group and characterized by the phenyl rings disrotated of about 18.7° with respect to the vinyl plane and (b) the couple of symmetry-related Ci structures (where the rings are parallel, like the pedals of a cycle) having this time the two rings conrotated of an angle of ∼18.7° with respect to the vinyl fragment. [Copyright &y& Elsevier]

Solute molecules were dissolved in the liquid crystal 4-cyano-4′- n-octyloxybiphenyl (8OCB), known to form a partial bilayer smectic-A phase. Through measurement of solutes' and solvent's orientational order parameters via nuclear magnetic resonance spectroscopy, and their analysis via a statistical thermodynamic density functional theory, values of the solvent's positional order parameters and solutes' positional-orientational distribution functions were obtained. Near to the transition to the nematic phase, the main positional order parameter of the smectic liquid crystal turned out to be comprised in the interval 0.4-0.6, though the quality of the fittings assuming the phase as nematic all across the temperature range investigated was only slightly worse. This may be ascribed to the looseness of the partial bilayer smectic structure. Solutes were found to preferentially lie in those regions where liquid crystal molecule terminal chains are located. [ABSTRACT FROM AUTHOR]

Biphenylene and pyrene were dissolved in the nematic and smectic-A phases of the liquid crystal 4,4'-di-n-heptyl-azoxybenzene and the orientational order parameters of both solutes and solvent measured via proton and deuteron nuclear-magnetic-resonance spectroscopy. This new data set was then merged with the one previously obtained, formed by 4,4'-di-chloro-benzene and naphthalene as solutes in the same solvent, and the resulting overall data set analyzed with a statistical thermodynamic density-functional theory to provide positional-orientational distribution functions of the various solutes along with the smectic solvent's positional order parameters. [ABSTRACT FROM AUTHOR]

In the present paper, the peculiar orientational behavior, studied by liquid crystal NMR (LXNMR) spectroscopy, of the D2dsymmetry quasi-spherical molecule of tetramethylallene (TMA) dissolved in the nematic solvent I52 is exploited to attempt a quantitative experimental assessment of the correlation between molecular vibrations and overall rotations in weakly oriented molecules. The analysis of the very small DHHand 1D13C–Hdipolar couplings, available from the natural abundance LXNMR spectra of TMA at different temperatures, allows for a derivation leading (by making a few approximations) to the quantification of the vibration–reorientation (also called nonrigid) contribution affecting the observed direct 1D13C–Hdipolar coupling. The obtained results show that, under the particular conditions of the studied system (very weak orientational ordering of a highly symmetric molecule), this contribution is particularly important, in order to reproduce the whole value of the “observed” dipolar coupling. This issue is discussed and commented on at length in the work, also, by making reference to the analogy with perfectly symmetric molecules (such as methane and analogues) dissolved in liquid crystalline phases. [ABSTRACT FROM AUTHOR]

Very accurate bond distances can be derived from dipolar couplings, Dij, obtained by analysis of the NMR spectra of samples dissolved in anisotropic solvents (LXNMR). To do this, however, the couplings must be corrected for the averaging produced by vibrational motion. The vibrational corrections require a knowledge of the force field, which may be obtained by fitting experimental vibrational frequencies or, much more easily, from quantum-mechanical computations. In the present study, the reliability of the methods used to calculate the force field and the effects on the accuracy of the vibrational corrections to the Dij is tested on benzene for which a very accurate structural study is available. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we suggest a new methodological approach to get in a very simple way a crude (but meaningful) conformational analysis of flexible molecules in fluid condensed phases (a very interesting matter where inter- and intra-molecular interactions are deeply involved). The test case we have chosen is the never-studied-before temperature dependence of inter-ring angle of biphenyl in a nematic solution. Undemanding 2H NMR experiments were carried out on perdeuterated biphenyl dissolved in the mesophase at different temperatures, to obtain deuterium quadrupolar splittings. Since the experimental data alone are not sufficient to allow the determination of the inter-ring angle for each temperature, they were supplemented with simulated orientational information: this ‘hybrid’ set of data was enough to obtain the searched conformational distribution versus T. The results, showing a very slight tendency of the inter-ring angle to increase with the temperature, lend themselves to immediate interesting speculations and encourages the accomplishment of more sophisticated and expensive experiments to investigate more in detail the phenomenology. In our opinion the suggested methodology, appealing for its easiness, could be useful, for example, for coarse grained conformational investigations of large flexible systems (as, e.g. biomolecules) in liquid media. [Copyright &y& Elsevier]

The induction of a cholesteric phase by doping an achiral nematic liquid crystal with an enantiopure solute is a phenomenon that, as in all general supramolecular phenomena of chiral amplification, depends in a subtle way on intermolecular interactions. The micrometric helical deformation of the phase director in the cholesteric phase is generated by the interplay of anisotropy and chirality of probe-medium interactions. In the case of a flexible chiral dopant, the solvent can influence the twisting power in two ways, difficult to disentangle: it is responsible for the solute orientational order, an essential ingredient for the emergence of phase chirality; but also it can affect the dopant conformational distribution and then the chirality of the structures present in the solution. In this work we have investigated methyl phenyl sulfoxide, a flexible, chiral molecule that, when dissolved in different nematics, can produce cholesteric phases of opposite handedness. This peculiar, intriguing sensitivity to the environment makes MPS a suitable probe for a thorough investigation of the effects of solute-solvent interactions on chiral induction in liquid crystals. NMR experiments in various nematic solvents have been performed in addition to twisting power measurements. From the analysis of partially averaged ¹H-¹H and 13C-¹H dipolar couplings, the effects of solvent on solute conformation and orientational order are disentangled, and this information is combined with the modeling of the chirality of intermolecular interactions, within a molecular field theory. The integration of different techniques allows an unprecedented insight into the role of solvent in mediating the chirality transfer from molecule to phase. [ABSTRACT FROM AUTHOR]

Different approaches (Mean Field theory, Monte Carlo simulations and a MF–MC hybrid model) to predict order parameters of model-solutes in nematic phases have been tested and compared among them and with experimental data (when available). Peculiarities of the methods are discussed in order to explore their potentialities in tackling the orientational problem. [Copyright &y& Elsevier]

The differences between experimental and calculated order parameters of polar solutes dissolved in zero electric field gradient nematic liquid crystal mixtures (magic mixtures) could be interpreted, in the context of a recently proposed model [1,2], as an evidence of small but detectable effects of solute polarity in the orientational mechanisms. [ABSTRACT FROM AUTHOR]

The non-polar rigid molecules 1,4-difluorobenzene and p-benzoquinone dissolved in ZLI1132 and EBBA nematic solvents show a bizarre ‘double face’ rod-like or disk-like orientational behaviour, depending on the used solvent. In the present Letter it is shown that the observed effect, unpredictable on the basis of solely short-range orientating mechanisms, can be qualitatively accounted when also electrostatic long-range interactions are taken into account (in particular, the coupling between the solute quadrupole moment and the solvent electric field gradient). The obtained result confirms the non-negligible role played by electrostatic interactions, even in the case of non-polar molecules. [Copyright &y& Elsevier]

The aim of this work has been to test the reliability of a simple relation connecting the order of probe molecules dissolved in binary nematic mixtures with that exhibited in each nematic component at the same reduced temperatures. In order to do this, a large amount of 1 H-LXNMR experiments at different temperatures has been performed, utilizing as solutes 1 ,4-difluorobenzene, 1,4-dichlorobenzene, 1,4-dibromobenzene and naphthalene in I52, EBBA and I52/EBBA mixtures at variable mixing percentages (50/50, 20/80 and 80/20 mol%). The results confirm that the orientations of the solutes in the mixtures can be predicted in a satisfactory way as a function of the mixing ratios, independently of the solutes and the temperatures. Finally, as a stimulation for future studies, a conjecture about the observed discrepancies is suggested. [ABSTRACT FROM AUTHOR]

For spin systems with N[sup I] and N[sup S] interacting nuclei of magnetogyric ratio γ[sub I] and γ[sub S] respectively, it is possible to obtain multiple quantum spectra characterized by changes in the magnetic numbers mX by N[sup I], (N[sup I]—1)…, 0 with X = I, S. The use of such heteronuclear MQ spectra as an aid in the automatic analysis of NMR spectra of both rigid and flexible molecules dissolved in liquid crystalline phases, is discussed. It has been found that when I = [sup 1]H and S = [sup 19]F, the decoupling efficiency of the standard multipulse sequences, developed and optimized for heteronuclear decoupling in isotropic liquids, depends on the spin system and also on the overall orientation of the molecule when orienting mesophases are involved. These facts impose limitations on the applicability of a procedure which, when the decoupled heteronuclear MQ spectrum is obtained, significantly reduces the computing requirements of the automated spectral analysis. [ABSTRACT FROM AUTHOR]

The orientational data of four rigid solutes dissolved in the nematic solvents ZLI1132, EBBA and in a 55 wt% ZLI1132+ EBBA mixture have been obtained from proton NMR spectra at different temperatures and used to find a relationship between the solute order in the two nematics and in their mixture. A crossed comparison of the data shows that a simple linear relation, where the normalized weights of the combination are coincident with the molar fractions of ZLI1132 and EBBA in the mixture, gives excellent agreement independently of the solutes and temperatures. Consideration is given to the possibility of a generalization of the results to any mixture of two nematics. [ABSTRACT FROM AUTHOR]

In this Letter, a general expression is derived for the conformational distribution function of a molecule dissolved in an anisotropic condensed fluid medium by combining an a priori model with the maximum entropy principle applied to treatment of liquid crystalline-NMR data. The recently proposed additive potential maximum entropy (APME) method is recovered as a special case, when the AP is chosen as the a priori model and the orientational order is low. [ABSTRACT FROM AUTHOR]

In this paper, a chirality-sensitive effective orientational potential is, for the first time, proposed. It describes, within the Molecular Field approximation, different solute-solvent ordering interactions, according to the P (clockwise) or M (counterclockwise) nature of helical particles dissolved in uniaxial anisotropic solvents composed, in their turn, of helical P or M particles. By making use of Monte Carlo-simulated order parameters, it is shown that the model is, in principle, able to lead to the absolute enantiorecognition of the unknown chirality of the helical solute particles. This makes it a possible interesting tool for exploiting NMR anisotropic observables in order to achieve the absolute enantiomer assignment of chiral helical solutes. Unlabelled Image • Helical solutes orientationally ordered in organized helical solvents are studied. • A mean torque potential sensitive to P (clockwise) and M (counterclockwise) chirality is formulated. • The effectiveness and reliability of the proposed model is tested on Monte Carlo simulated order parameters. • The model proved to be, in principle, a useful tool for absolute enantiorecognition of the solutes. [ABSTRACT FROM AUTHOR]

Using Monte Carlo numerical simulation, this work sketches the phase diagram of systems of certain hard C2h-symmetric particles, formed by gluing two aligned and displaced hard spherocylinders with a cylindrical-length-to-diameter ratio realistically, if viewed not only from the lyotropic colloidal liquid-crystal side but also from the thermotropic low-molecular-mass liquid-crystal side, equal to 5, as a function of the displacement. Several distinctive phases are observed, such as a nonperiodic smectic-B-like phase, a nonperiodic smectic-H-like phase, a smectic-C phase, and a short-layer-spacing uniaxial smectic-A phase but no biaxial nematic phase. [ABSTRACT FROM AUTHOR]

A correction related to the article "Publisher's Note: Rigid probe solutes in a smectic-A liquid crystal: An unconventional route to the latter's positional order parameters," that was published in the December 13, 2011 issue is presented.

Naproxen and flurbiprofen are among the most popular and widely used drugs for treating pain and inflammation and new different therapeutic uses are still being proposed. Their pharmacological activity comes from the specific binding to target proteins and is evidently driven by the spatial arrangement they adopt at the active sites. A detailed conformational elucidation analysis in solution able to probe equilibria between more possible conformers is then crucial for understanding and rationalizing their biological role and possibly for designing improved analogues. Here we combine NMR data obtained in weakly ordered media and suitable theoretical models to look for the energetically admissible conformers of these two anti-inflammatory drugs in a liquid medium. This approach leads to rather complex probability distributions characterized for both molecules by an equilibrium of different global and local minimum energy structures. [ABSTRACT FROM AUTHOR]

A weakly ordering organic-based lyotropic phase and a strongly ordering nematic liquid crystal have been used as NMR media for a parallel study of the conformation and orientational order of the same solute, trans-stilbene. A careful comparison allows to figure out some interesting conclusions on accessibility and precision of the experimental data and reliability and accuracy of the conformational descriptions into these two kinds of mesophases. [ABSTRACT FROM PUBLISHER]

• LXNMR is used to study chirality-dependent conformations and order parameters of a chiral solute. • Two different R and S conformational distributions of a flexible case test molecule have been found. • Different R , S order parameter distributions of flexible chiral case test molecule have been found. The unique power of Liquid Crystal NMR (LXNMR) in obtaining information about the conformational equilibrium of small solutes dissolved in orienting media can be effectively used to study chirality-related phenomena. In this work we have been able, for the first time in our knowledge, to fully resolve the two different conformational distributions for the R and S enantiomers of a case test molecule (the chiral flexible 4FMBOH: 4-F-α-methyl benzyl alcohol), dissolved in a typical chiral non-racemic aligning solvent, made of PBLG (poly- γ -benzyl- L -glutamate, a helical chiral polypeptide) co-dissolved in CDCl 3. The two enantiomers show significant differences in their conformational behaviors, due to the different solute–solvent orientational molecular interactions experienced by the R and S species. In our opinion, fundamental studies of this kind could pave the way for a better understanding of chirality-dependent molecular interactions, often involved in a number of important chemical processes (concerning pharmaceuticals, biochemistry, advanced materials, etc.) [ABSTRACT FROM AUTHOR]

In this work, a sample of pure and certified bergamot essential oil (BEO) was extensively studied for the first time directly by NMR spectroscopy with the aim of investigating its metabolic composition, quantifying the main components of this complex natural matrix and simultaneously assessing whether the NMR technique is able to highlight possible frauds to which this high-cost product may be subjected. Eleven low molecular weight compounds have been identified by using 1D 1H and 13C-{1H} NMR experiments, 2D homo- and heteronuclear correlation NMR spectra, and 2D 1H DOSY experiments; the most abundant of them, i.e., about 90% of the sample analyzed, has been quantified by employing benzoic acid as an internal standard by 1H NMR spectrum. Moreover, since the commercial fraud of this precious oil is often due to the addition of less expensive oils, we have simulated a possible adulteration through the preparation of BEO samples to which different percentages of orange essential oil (OEO) were added. The results, obtained by combining the 1H NMR spectra collected on the adulterated samples and on pure BEO, with chemometric analysis, principal component analysis (PCA), indicate that it is possible to distinguish the sample of pure BEO from the adulterated ones and also, among them, to differentiate between the degrees of adulteration. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the potentialities of the Inverse Laplace Transform when applied to Pulsed Gradient Spin Echo NMR data from water in lyotropic liquid crystalline mesophases. This mathematical application should be able to produce structural information about the studied systems by the determination of the self-diffusion coefficient distribution, giving in this way a significant fingerprint of the molecular organisation in lamellar and reverse hexagonal phases. The critical point of finding the best algorithm to treat the data has been faced: several numerical methods have been tested comparing the performances of the different algorithms with results predictable by theory. [ABSTRACT FROM AUTHOR]

To inquire into whether two enantiomers can be absolutely distinguished on the sole basis of their different degrees of orientational ordering when dissolved in a chiral nematic liquid crystal, several enantiomeric pairs of hard helical particles are dissolved in a cholesteric (nematic) liquid crystal made of slender hard helical particles as well as in a screwlike nematic liquid crystal made of tortuous hard helical particles. While in the former ordinary chiral nematic solvent their nematic order parameters are (almost) coincident, in the latter new chiral nematic solvent the two enantiomeric solutes not only usually have more appreciably different nematic order parameters, but also always have significantly different screwlike order parameters. If also the latter orientational order parameter could be measurable in real experiments, it would constitute an additional decisive piece of information on the way to absolutely distinguishing two enantiomers on the sole basis of their different degrees of orientational order when dissolved in a chiral nematic liquid crystal that is in the apter screwlike nematic phase. Even in that event, however, the general absence of regularity and systematicity in the trend of the orientational order parameters, already manifest in these elementary hard helical-particle binary systems, would make this coveted achievement experimentally arduous without the assistance of very accurate and precise theoretical calculations. [ABSTRACT FROM AUTHOR]

The orientational order parameters of four aromatic solutes in nematic solvents, derived from proton dipolar couplings in NMR spectra, show a correlation with the dielectric anisotropy of the solvents. Explanation of the experimental behaviour is provided by a molecular theory based on the reaction field approximation. [ABSTRACT FROM AUTHOR]