Nonequilibrium liquid crystalline layered phase stabilized by light

The ability of light to alter/stabilize a particular thermodynamic phase is a power tool to investigate condensed matter from a new dimension. This field of photoinduced phase transitions is currently an important area of research. Being elastically soft and having subtle changes between its many phases a liquid crystal material is an attractive medium to investigate such light-driven phase transitions. The attraction is partly due to the large birefringence changes accompanying these transitions that are useful in developing photonic devices. In all of the cases reported to date, the photoinduced transition always leads to a phase that in any case exists in the thermal cycle. Recently we reported the first exception to such an established phenomenon (Adv. Mater. 2005, 17, 2086). The guest-host ternary mixture consisting of the photoactive azobenzene guest molecules does not exhibit smectic A phase in the absence of UV radiation. However, the smectic A phase is induced and stabilized only in the presence of UV light. In this paper, we map out hitherto unexplored temperature versus UV intensity phase diagrams for various mixtures, which illustrate that light mimics, in a limited sense, the role of a thermodynamic parameter such as, for example, pressure. The threshold UV intensity required to photodrive the appearance of the smectic A phase is seen to have a strong concentration dependence. Our studies also suggest the possibility of observing a double critical point by employing the UV intensity as a fine-tuning parameter.     

An expedient enantioselective strategy for the oxatetracyclic core of platensimycin

An enantioselective route for the synthesis of oxatetracyclic core of platensimycin is reported for the first time using a 5-exo-trig cyclization followed by intramolecular etherification as key reactions. The requisite dienynone for the radical cyclization is synthesized in eight steps from the Wieland-Miescher ketone employing a Claisen rearrangement.     

Photochromism of arylchromenes: remarkable modification of absorption properties and lifetimes of o-quinonoid intermediates

[reaction: see text] A significant pi-conjugation in 6- and 7-arylchromenes manifests dramatically in the absorption properties of their photogenerated o-quinonoid intermediates. This in conjunction with facile synthesis via Suzuki coupling may render a myriad of photochromic arylchromenes with wide-ranging spectrokinetic properties readily accessible.     

Monodispersive linear supermolecules stabilizing unusual fluid layered phases

The first examples of monodisperse liquid crystalline pentamers, synthesized by covalently linking five mesogenic segments through four flexible spacers, exhibiting mono-/partially bilayered phases with unusual textures, as established by optical, calorimetric, and X-ray diffraction studies, are reported. Importantly, the two types of multifunctional pentamers, namely, unsymmetric and C2 symmetric are soluble in organic solvents and exhibit analogous electrochemical features.     

Identification of a metagenome-derived esterase with high enantioselectivity in the kinetic resolution of arylaliphatic tertiary alcohols

35 metagenome-derived esterases bearing a GGG(A)X motif were screened for activity and enantioselectivity in the hydrolysis of a range of tertiary alcohol acetates. Most of the active esterases showed little or no enantioselectivity in the hydrolysis of the terpinyl acetate, linalyl acetate and 3-methylpent-1-yn-3-yl acetate. However, one esterase showed excellent enantioselectivity (E > 100) in the kinetic resolution of 1,1,1-trifluoro-2-phenylbut-3-yn-2-yl acetate as confirmed by a preparative scale reaction.     

Adsorptive Separation of Acetylene from Light Hydrocarbons by Mesoporous Iron Trimesate MIL‐100(Fe)

A reducible metal–organic framework (MOF), iron(III) trimesate, denoted as MIL‐100(Fe), was investigated for the separation and purification of methane/ethane/ethylene/acetylene and an acetylene/CO₂ mixtures by using sorption isotherms, breakthrough experiments, ideal adsorbed solution theory (IAST) calculations, and IR spectroscopic analysis. The MIL‐100(Fe) showed high adsorption selectivity not only for acetylene and ethylene over methane and ethane, but also for acetylene over CO₂. The separation and purification of acetylene over ethylene was also possible for MIL‐100(Fe) activated at 423 K. According to the data obtained from operando IR spectroscopy, the unsaturated Fe^III sites and surface OH groups are mainly responsible for the successful separation of the acetylene/ethylene mixture, whereas the unsaturated Fe^II sites have a detrimental effect on both separation and purification. The potential of MIL‐100(Fe) for the separation of a mixture of C₂H₂/CO₂ was also examined by using the IAST calculations and transient breakthrough simulations. Comparing the IAST selectivity calculations of C₂H₂/CO₂ for four MOFs selected from the literature, the selectivity with MIL‐100(Fe) was higher than those of CuBTC, ZJU‐60a, and PCP‐33, but lower than that of HOF‐3.     

An Elegant Synthesis of a New Class of 1‐(Substituted)‐1H‐1,2,3‐triazol‐4‐yl)methyl)diphenylphosphineoxides by Microwave Irradiation

A simple and efficient one‐pot microwave‐assisted click formation of 1‐(substituted)‐1H‐1,2,3‐triazol‐4‐yl)methyl)diphenylphosphineoxide derivatives via Huisgen regioselective [3+2]‐cycloaddition of an in situ generated organic azides and diphenyl(prop‐2‐yn‐1‐yl)phosphine oxide in highly polar DMSO‐H₂O medium. This synthetic protocol is mild, requires shorter reaction time, and afforded products in excellent yields with high regioselectivity.     

Synthesis,Characterization, and Antibacterial Activity of Some Novel Substituted Imidazole Derivatives via One‐pot Three‐Component

A simple and highly efficient one‐pot, three‐component synthesis of novel substituted imidazole derivatives has been reported by the reaction of 3‐(2‐bromoacetyl)‐2H‐chromen‐2‐one, ammonium thiocyanate, and phenacyl aniline in the presence of acetic acid as a solvent under reflux condition with good yields. The structures of newly synthesized compounds were characterized by their analytical and spectral data. One of these compounds 4a showed good antibacterial activity against Escherichia coli gram‐negative strains.