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We present a theoretical investigation on the esterification process for boron ester synthesis, considering boric acid and 2(R),4(S)-pentanediol as model boron and diol derivatives, respectively. We report an unprecedented mechanistic pathway, able to rationalise, in contrast with the reported ones, the relatively low Gibbs energies of activation and the pH dependence experimentally observed in the formation of boron esters. We believe that these findings will improve the possibility to predict cross-link reaction rates of boron esters as a fundamental tool in the rational design of functional materials based on boron–oxygen linkages. [ABSTRACT FROM AUTHOR]

The stereoselective synthesis of several secondary propargylamines by the copper-promoted A3-coupling reaction of aliphatic and aromatic aldehydes with phenylacetylene and (R)-(+)-phenylethylamine is here reported. Two different synthetic methodologies have been investigated in this study, involving CuSO4 /NaI and -CeCl3 ·7H2 O/CuI promoting systems. The reported methodologies were compared in terms of efficiency, diastereoselectivity, and toxicity, both showing advantages with respect to the current methodologies. The relative configurations of each of the obtained propargylamines, previously unknown in the literature, were assigned by comparison of the1 H NMR experimental chemical shifts with those theoretically predicted via the DFT-GIAO method. [ABSTRACT FROM AUTHOR]

Correction for 'Elucidation of the mechanism of the esterification of boric acid with aliphatic diols: a computational study to help set the record straight' by Corrado Bacchiocchi et al., Chem. Commun., 2024, 60, 13239–13242, https://doi.org/10.1039/d4cc02999b. [ABSTRACT FROM AUTHOR]

In this work, we have synthesized and characterized bis-urea derivatives 1–3, featuring a biphenyl spacer, and studied their anion binding properties in DMSO solution and in the solid state. In solution, 1 : 1 complexes were observed with association constant K values in the 103–104 M−1 range with a general preference for acetate over dihydrogenphosphate for all three receptors. We were also able to obtain and characterize, by X-ray diffraction on single crystals, ten receptor–anion complexes including acetate and dihydrogenphosphate, as well as monohydrogenphosphate, halides and the nitrate ion. Linear (anion–receptor)n arrays, porous frameworks and non-centrosymmetric structures were observed and described in detail. [ABSTRACT FROM AUTHOR]

EPR spin probe spectra of the liquid crystal phases exhibited, in the bulk, by the 1",9"-bis(4- cyanobiphenyl-4'-yl)nonane (CB9CB) bent-shape dimer showed that, on cooling from the isotropic phase, this material forms a uniaxial nematic phase with a uniform director macroscopically aligned along the spectrometer field. Upon further cooling, a transition into the twist-bend nematic phase is observed after a biphasic region of approximately 4 K. In this lower temperature nematic phase, the director does not appear to be macroscopically aligned. The non-uniform director distribution is modelled as a collection of monodomains tilted with respect to the magnetic field and orientationally distributed around the tilt direction. [ABSTRACT FROM AUTHOR]

The director distribution in the nematic phases exhibited by the 1′′,11′′-bis(4-cyanobiphenyl-4′-yl)undecane (CB11CB) liquid crystal has been studied in the bulk using the EPR spin probe technique. EPR spectra confirmed the presence of a higher temperature uniaxial nematic phase and of a lower temperature nematic phase in which the director distribution is not uniform. Spectra recorded in the lower temperature nematic phase were not fully compatible with theoretical EPR spectra calculated according to the recently proposed model for the twist-bend phase in which the local domain director twists around an axis with a fixed tilt angle, ϑ0, but were well described by a “distributed-tilt” model in which the director has a relatively narrow distribution, centred at ϑ0. [ABSTRACT FROM AUTHOR]

The director configuration, the local order and the molecular-level reorientational dynamics (microviscosity) of the 5CB liquid crystal (LC) inside a polymer-stabilized LC (PSLC) cell prepared with the 4,4′-bis(6-(acryloyloxy)hexyloxy)biphenyl (BAB6) diacrylic monomer have been studied with the EPR spin probe technique across the nematic and the isotropic phase of the LC. The cells made from glass slides, either clean or coated with an aligning layer, were filled with pure 5CB or with 0.5, 1.0 or 2.0 wt% of BAB6, either in the monomeric state or polymerized. Local orientational order parameter () in the non treated cells was always slightly lower than in the coated ones and both were lower than in the bulk LC. Order appeared to be independent of polymerization state or BAB6 concentration up to 1.0 wt%. Reorientational dynamics was essentially bulk-like in all cases, indicating that in our PSLC cells a full molecular mobility is retained. At the concentration of 2.0 wt%, in the coated cell with polymerized BAB6, the monodomain did not reform after a 90° rotation of the cell in the magnetic field, suggesting that the polymer network is, as expected, stabilizing the preexisting director configuration. [ABSTRACT FROM PUBLISHER]

We have studied the effects of confinement on the order and dynamics of the 5CB liquid crystal (LC) inside nanosized droplets of a reflection-mode holographic-polymer dispersed LC (H-PDLC) device, consisting of alternating LC nanodroplets and polymer layers, forming a diffraction grating. Here we have investigated, taking advantage of the high sensitivity of the EPR spin probe technique, a series of temperatures spanning the nematic and isotropic phase of the LC. The occurrence of phase separation and the consequent formation of a diffraction grating was revealed by SEM images of the H-PDLC cross section and by the presence of a reflection peak around 565 nm. Differently from the case of BL038 LC based H-PDLCs, the results here indicate the absence of an ordered fraction of mesogens throughout the analysed temperature range. Taking into account a previous model of LC molecules arrangement in the same kind of device [Bacchiocchi, C., et al. (2009). J. Phys. Chem. B 113, 5391], we postulate the presence of very small droplets in which the surface anchoring constraints represent the dominant effect. This results in the hindrance of the LC uniform macroscopic alignment, providing a plausible explanation for the malfunctioning of these devices. [ABSTRACT FROM AUTHOR]

The effects of the cis and trans form of the 4-OMe-phenylazobenzene at 1% and 7% mole fraction on order, mesophase stability and dynamics of the 5CB liquid crystal were studied using the ESR spin probe technique. The presence of the trans azo-derivative induced a downshift of the nematic-isotropic transition temperature TNI which increased with the concentration but did not change the dependence of the order parameter on the reduced temperature. The cis isomer caused even larger TNI shifts, determining a marked decrease of the order parameter with a peculiar dependence on the reduced temperature, quite different from the standard Haller-type behavior. The spin probe dynamics appeared instead to be essentially unchanged by the presence of the azo-derivative. [ABSTRACT FROM AUTHOR]

Random disorder effects of an hydrophobic aerosil on the order and dynamics of the 3ß-DOXYL-5a-cholestane spin probe in the liquid crystal 4- n -pentyl-4'-cyanobiphenyl (5CB) were studied using the ESR technique. Increasing the aerosil concentration up to 10 wt% does not change the nematic–isotropic transition temperature but decreases the probe order parameter. The dynamics in the isotropic phase is of Arrhenius type and essentially independent of the concentration. Deviations from this behavior are clearly observed in the nematic phase even at 1 wt% of aerosil and are well represented by a Vogel-Fulcher-Tammann type law, suggesting that a glass-like behavior can be induced by a very small amount of random disorder. PACS numbers: 61.30. Gd, 76.30.-v, 82.70. Gg [ABSTRACT FROM AUTHOR]

We report on a comparison between the random disorder effects of an hydrophobic (R812) or an hydrophilic (A380) aerosil on the order and dynamics of the 3β-DOXYL-5α-cholestane spin probe in the liquid crystal 4-n-pentyl-4′-cyanobiphenyl (5CB) using the ESR technique. Increasing the aerosil concentration up to 3 wt% the probe order parameter is depressed with a larger effect for the hydrophilic aerosil. The dynamics in the isotropic phase is of Arrhenius type and essentially concentration and aerosil-type independent. Deviations from this behavior are observed in the nematic even at 0.3 wt% of hydrophilic aerosil and are well represented by a Vogel–Fulcher–Tammann type law, suggesting that a glass-like state can be induced by a very small amount of random disorder. [Copyright &y& Elsevier]