Plakilactones G and H from a marine sponge. Stereochemical determination of highly flexible systems by quantitative NMR-derived interproton distances combined with quantum mechanical calculations of ¹³C chemical shifts

• Simone Di Micco,
• Angela Zampella,
• Maria Valeria D’Auria,
• Carmen Festa,
• Simona De Marino,
• Raffaele Riccio,
• Craig P. Butts and
• Giuseppe Bifulco

Beilstein J. Org. Chem. 2013, 9, 2940–2949, doi:10.3762/bjoc.9.331

• configuration at C-7 and C-8. Through theoretical calculation and experimental data, Riguera demonstrated that bisphenylacetic acid ester derivatives of a diol with two asymmetric carbons have a specific and distinctive distribution of ΔδSR signs, determined by a combined anisotropy effect of the two auxiliares

Crystal design using multipolar electrostatic interactions: A concept study for organic electronics

• Peer Kirsch,
• Qiong Tong and
• Harald Untenecker

Beilstein J. Org. Chem. 2013, 9, 2367–2373, doi:10.3762/bjoc.9.272

• as pentacene [5], which act as p-type semiconductors. However, acenes in the crystalline state tend to form slightly tilted molecular stacks (“herring bone” pattern), which is resulting in a strong directional anisotropy for the charge carrier mobility along the stacking direction. Charge carrier

Chemoenzymatic synthesis and biological evaluation of enantiomerically enriched 1-(β-hydroxypropyl)imidazolium- and triazolium-based ionic liquids

• Paweł Borowiecki,
• Małgorzata Milner-Krawczyk and
• Jan Plenkiewicz

Beilstein J. Org. Chem. 2013, 9, 516–525, doi:10.3762/bjoc.9.56

• derivatives 9a and 10a. Comparison of the 1H NMR spectra of these two species for this particular alcohol (+)-5a shows that the phenyl ring of the chiral auxiliary reagent projects its magnetic anisotropy strongly toward the H(2’) proton in the (S)-derivative 9a, while the same proton in the (R)-MPA ester 10a

Thermotropic and lyotropic behaviour of new liquid-crystalline materials with different hydrophilic groups: synthesis and mesomorphic properties

• Alexej Bubnov,
• Miroslav Kašpar,
• Věra Hamplová,
• Ute Dawin and
• Frank Giesselmann

Beilstein J. Org. Chem. 2013, 9, 425–436, doi:10.3762/bjoc.9.45

• materials showing liquid-crystalline (LC) behaviour belong to two general classes: lyotropic materials, in which fluid anisotropy results from interactions between anisotropic aggregates of amphiphilic molecules; and thermotropic materials, in which the orientational order arises from interactions among

Spin state switching in iron coordination compounds

• Philipp Gütlich,
• Ana B. Gaspar and
• Yann Garcia

Beilstein J. Org. Chem. 2013, 9, 342–391, doi:10.3762/bjoc.9.39

• , for a polycrystalline sample. In a single-crystal study, anisotropy effects usually play an important role and can be observed through the g-value components gx, gy, gz. EPR spectroscopy is a highly valuable tool to decipher the structural information of a SCO system, which is otherwise barely or not

A new family of four-ring bent-core nematic liquid crystals with highly polar transverse and end groups

• Kalpana Upadhyaya,
• Venkatesh Gude,
• Golam Mohiuddin and
• Rao V. S. Nandiraju

Beilstein J. Org. Chem. 2013, 9, 26–35, doi:10.3762/bjoc.9.4

• principal polarizability components (αxx, αyy, αzz), isotropic polarizability αiso = (αxx + αyy + αzz)/3, polarizability anisotropy Δα = [αxx − (αyy + αzz)/2], and asymmetry parameter, η = [(αyy – αzz)/ (αxx − αiso)]. Parameters are relative to the molecular polarizability tensor in the Cartesian reference

Synthesis of fluorinated maltose derivatives for monitoring protein interaction by ¹⁹F NMR

• Michaela Braitsch,
• Hanspeter Kählig,
• Georg Kontaxis,
• Michael Fischer,
• Toshinari Kawada,
• Robert Konrat and
• Walther Schmid

Beilstein J. Org. Chem. 2012, 8, 448–455, doi:10.3762/bjoc.8.51

• a magnetogyric ratio comparable to 1H is highly sensitive and, due to its large chemical shift anisotropy (CSA), very responsive to changes of molecular weight that accompany the binding events. We thus anticipate 19F detection to be a general and versatile probe for indirect NMR studies of protein

• compound lacking the affinity to the ligand binding domain. Here we describe the possibility of monitoring protein interactions by 19F NMR, known as fluorine chemical-shift anisotropy and exchange for screening (FAXS) [5][6][7], with internal control by using 2-F labeled maltose as a reporter system. The

Perhydroazulene-based liquid-crystalline materials with smectic phases

• Zakir Hussain,
• Henning Hopf and
• S. Holger Eichhorn

Beilstein J. Org. Chem. 2012, 8, 403–410, doi:10.3762/bjoc.8.44

• ; nematic phases; smectic phases; Introduction Liquid crystals for display applications have to fulfill a complex, interdependent set of properties [1]. First of all, they must display a broad nematic phase, typically ranging from −30 °C to +80 °C. The absolute value for the dielectric anisotropy Δε should

• LCs are cyclohexane, phenylcyclohexane, etc. We previously introduced [13] a completely new core unit: the perhydroazulene ring system. This system provides a segment that may align in such a way that the long molecular axes are parallel, with the capability to induce anisotropy, whereas if we

Liquid-crystalline nanoparticles: Hybrid design and mesophase structures

• Gareth L. Nealon,
• Romain Greget,
• Cristina Dominguez,
• Zsuzsanna T. Nagy,
• Daniel Guillon,
• Jean-Louis Gallani and
• Bertrand Donnio

Beilstein J. Org. Chem. 2012, 8, 349–370, doi:10.3762/bjoc.8.39

• characteristic of the liquid-crystalline state, due to the phase separation of the incompatible components [24][30][31][32][33]. Since the anisotropy of the molecular structure plays such an important role in the formation and properties of liquid-crystalline phases, the types of ligands involved are often

• LC phases. Therefore, it is clear that the ligands must impart sufficient anisotropy into the hybrid system to force the pseudospherical particles to form ordered self-assembled structures whilst maintaining a fluid state. Thus, parameters such as the orientational flexibility and mobility of the

• unable to distort to any significant extent, and furthermore, they would not have been of sufficient bulk to induce anisotropy to the hybrids, serving merely as potential "lubricants" to reduce interparticle interactions through their long terminal alkyl chains. At this point, it is worth noting that

Efficient oxidation of oleanolic acid derivatives using magnesium bis(monoperoxyphthalate) hexahydrate (MMPP): A convenient 2-step procedure towards 12-oxo-28-carboxylic acid derivatives

• Jorge A. R. Salvador,
• Vânia M. Moreira,
• Rui M. A. Pinto,
• Ana S. Leal and
• José A. Paixão

Beilstein J. Org. Chem. 2012, 8, 164–169, doi:10.3762/bjoc.8.17

• the chemical shift of 18-H (2.02 ppm) for compound 2. This value is much lower than the one of the parent substrate 1 (2.84 ppm), which may be explained by magnetic anisotropy induced by the 28,13β-lactone moiety. It is also interesting to note that a long-distance coupling between the 18-H and 12β-H

The preparation of 3-substituted-1,5-dibromopentanes as precursors to heteracyclohexanes

• Bryan Ringstrand,
• Martin Oltmanns,
• Jeffrey A. Batt,
• Aleksandra Jankowiak,
• Richard P. Denicola and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2011, 7, 386–393, doi:10.3762/bjoc.7.49

• the development of polar, zwitterionic nematic liquid crystals having large longitudinal dipole moments for formulation of nematic materials with positive dielectric anisotropy [24][25]. The zwitterions consist of six-membered sulfonium rings attached to a boron cluster, either [closo-1-CB9H10]− or

Tribenzotriquinacenes bearing three peripheral or bridgehead urea groups stretched into the 3-D space

• Jörg Tellenbröker and
• Dietmar Kuck

Beilstein J. Org. Chem. 2011, 7, 329–337, doi:10.3762/bjoc.7.43

• pronounced magnetic anisotropy effects. In the case of the peripheral TBTQ tris-ureas 5 and 6, 1H NMR measurements in DMSO and tetrachloroethane revealed a surprising effect which may also be attributed to aggregation of these molecules in low-polarity solvents. Both of these compounds were found to be only

EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

• Giorgio Bencivenni,
• Riccardo Cesari,
• Daniele Nanni,
• Hassane El Mkami and
• John C. Walton

Beilstein J. Org. Chem. 2010, 6, 713–725, doi:10.3762/bjoc.6.84

• spectrum is expected. The latter is more complex and requires a detailed understanding of the anisotropy of the system. The above equations are not suitable for such a situation and a more complete resonance condition that considers all the orientations is needed. In the case of a system with I = ½ the

• (19F) and nitrogen (14N) contributions. The anisotropy and the unresolved nuclear quadrupole of the nitrogen couplings make the spectra difficult to interpret. Each 1H contributes three sets of peaks to the spectrum times the number of 1H’s present. This represents an enormous number of lines in one

Symmetry breaking and structure of a mixture of nematic liquid crystals and anisotropic nanoparticles

• Marjan Krasna,
• Matej Cvetko and
• Milan Ambrožič

Beilstein J. Org. Chem. 2010, 6, No. 74, doi:10.3762/bjoc.6.74

• approximately given by where Δχ is the magnetic anisotropy of LC molecules [6] (which can be either positive or negative). Furthermore, introducing an elongated NP of length d into a LC, which via surface anchoring enforces elastic distortion in LC medium, typically gives rise to free energy penalties of the

• reorient LC molecules perpendicular to them. This tendency is similar to that of an external electric or magnetic field acting on LCs with negative field anisotropy which tends to orient LC molecules perpendicularly to the field direction [6][28]. In such LC materials an external field imposes a finite

The C–F bond as a conformational tool in organic and biological chemistry

• Luke Hunter

Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38

• are aligned gauche to one another [42]. Hence, both fluorine atoms are presented on the same face of the molecule, resulting in a substantial molecular dipole moment as measured in the large negative dielectric anisotropy value (Δε). This system can be extended to incorporate a third vicinal fluorine

• crystal molecules. Arrows indicate the orientation of the molecular dipole moments, which are quantified in the negative dielectric anisotropy values, Δε. Di-, tri- and tetra-fluoro liquid crystal molecules 60–62. Collagen mimics of general formula (Pro-Yaa-Gly)10 where Yaa is either 4(R)-hydroxyproline

Competition between local disordering and global ordering fields in nematic liquid crystals

• Matej Cvetko,
• Milan Ambrožič and
• Samo Kralj

Beilstein J. Org. Chem. 2010, 6, No. 2, doi:10.3762/bjoc.6.2

• anisotropy field type of disorder. The Lebwohl–Lasher lattice type of semi-microscopic approach is used at zero temperature. Therefore, results are valid well below the transition into the isotropic phase. We calculate the correlation function of systems as a function of B, concentration p of impurities

• imposing random anisotropy field disorder, the disorder strength W and system dimensionality (2D and 3D systems). In order to probe memory effects we calculate correlation length ξ for random and homogeneous initial configurations. We determine the crossover fields Bc(p) separating roughly the ordered and

• the double sum counts all the particles, and the indices β run over the 1st nearest neighbours of the α-th particle. At randomly chosen sites of concentration p we additionally place rigid impurities which are coupled with surrounding directors by the random anisotropy type interaction [24][25] of

Low temperature enantiotropic nematic phases from V-shaped, shape-persistent molecules

• Matthias Lehmann and
• Jens Seltmann

Beilstein J. Org. Chem. 2009, 5, No. 73, doi:10.3762/bjoc.5.73

• , in which phase anisotropy of crystals is combined with fluid properties of liquids. In the nematic phases of calamitic mesogens only the molecular long axes are oriented along a so called director [2] and the molecular centres of gravity are distributed like in a liquid. In models, the molecules are

• revealed positive optical anisotropy, thus the molecules’ long axes are aligned perpendicular to the glass substrate. The black texture between the crossed polarisers at all rotation angles of the sample indicates the uniaxial nature right after the phase transition, further confirmed by the conoscopic

Coaxial electrospinning of liquid crystal-containing poly(vinylpyrrolidone) microfibres

• Eva Enz,
• Ute Baumeister and
• Jan Lagerwall

Beilstein J. Org. Chem. 2009, 5, No. 58, doi:10.3762/bjoc.5.58

• unexpected when considering the viscosity anisotropy of the liquid crystal kept in its smectic phase during electrospinning. Keywords: coaxial electrospinning; composite material; core-sheath fibres; liquid crystal; smectic phase; Introduction Electrospinning is a versatile process for producing nano- and

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

• Alberta Ferrarini,
• Silvia Pieraccini,
• Stefano Masiero and
• Gian Piero Spada

Beilstein J. Org. Chem. 2009, 5, No. 50, doi:10.3762/bjoc.5.50

• induction can be explained in general terms as the result of the competition between (i) a chiral force, which originates from the chirality of intermolecular interactions and promotes a twist of the nematic director and (ii) an elastic restoring force, which can be traced back to the anisotropy of

• organisation, the Surface Chirality (SC) model has been shown to be particularly useful [31][32]. This is a phenomenological mean field theory wherein the anisotropy and chirality of the interactions of the dopant with the surrounding molecules are parameterized on the basis of the geometric features of the

• very small and we can see that they are obtained just for the two derivatives with the lowest measured HTPs. Indeed, the twisting ability of a given dopant results from a delicate balance of chirality and anisotropy of dopant–host interactions and predictions of small effects would require a very

Shape- persistent macrocycle with intraannular alkyl groups: some structural limits of discotic liquid crystals with an inverted structure

• Sigurd Höger,
• Jill Weber,
• Andreas Leppert and
• Volker Enkelmann

Beilstein J. Org. Chem. 2008, 4, No. 1, doi:10.1186/1860-5397-4-1

• to cross the rings and to fill their interior completely. The investigation of the thermal behavior has shown that the smaller cycles do not exhibit thermotropic mesophases. Single crystal x-ray analysis indicates that the anisotropy in these compounds is too small to describe them as plates rather

• compounds the lateral extension of the macrocycles 9 is rather small. The distance between the two diacetylene bridges in 9 is around 1.2 nm compared to 2.3 nm in 1. Since the intraannular alkyl chains are located above and below the macrocyclic framework, the anisotropy of the compound is remarkably lower