Unclicking of thioureas: Base catalyzed elimination of anilines and isothiocyanates from thioureas

Bisaromatic thioureas are widely used in e.g. asymmetric organocatalysis and considered to be robust compounds. Herein we show, in strong contrast to common notion, that thioureas dissociate to amines and isothiocyanates in a base catalyzed reaction under mild conditions. This ‘unclicking’ process can occur in the presence of weak organic bases even at moderate temperatures. The influence of the substituents at the aromatic rings of the thiourea on the regioselectivity of this unclicking process is also shown.     

AIEgens in cell-based multiplex fluorescence imaging

Fluorescence imaging is an important branch of bioimaging. It is non-invasive and provides superior spatial and temporal resolution during the real-time monitoring of biological samples of interest. Although the spatial resolution limit of optical microscopes is about 200 nm, due to the diffraction limit, with the application of super-resolution fluorescence microscopy technologies this limit has been pushed below 30 nm. This makes it feasible to visualize biological structures in subcellular levels and to monitor subcellular biological processes in real time. However, due to the complexity of the biological structure and components within cells, simultaneous staining and monitoring multiple intracellular components with different coloured fluorophores is often needed during multiplex imaging, to better understand biological processes. Aggregation-induced emission luminogens(AIEgen) and AIEgen based nanoparticles(NPs) have presented many advantages in fluorescence imaging, with strong potential for biological science and nano-medicine. Herein this review, we focus on the advantages of AIEgen and AIEgen NP in cell-based fluorescence imaging, and the latest advances of AIEgens in cell-based multiplex imaging are summarized and discussed. The future perspectives are proposed.     

Molecular Design,Circularly Polarized Luminescence,and Helical Self‐Assembly of Chiral Aggregation‐Induced Emission Molecules

Aggregation‐induced emission luminogens (AIEgens) are a new class of luminophors, which are non‐emissive in solution, but emit intensively upon aggregation. By properly designing the chemical structures of the AIEgens, their aggregation process can be tuned towards a desired direction to give diverse novel luminescent architectures of micelles, rods, and helical fibers. AIEgens represent a kind of promising building block for the fabrication of luminescent micro/nanostructures with controllable morphologies. In this review, we describe our recent work in this research area, focusing on the molecular design, circularly polarized luminescence properties, and helical self‐assembly behavior of AIEgens.     

A Reversible Liquid Organic Hydrogen Carrier System Based on Methanol‐Ethylenediamine and Ethylene Urea

A novel liquid organic hydrogen carrier (LOHC) system, with a high theoretical hydrogen capacity, based on the unpresented hydrogenation of ethylene urea to ethylenediamine and methanol, and its reverse dehydrogenative coupling, was established. For the dehydrogenation only a small amount of solvent is required. This system is rechargeable, as the H₂‐rich compounds could be regenerated by hydrogenation of the resulting dehydrogenation mixture. Both directions for hydrogen loading and unloading were achieved using the same catalyst, under relatively mild conditions. Mechanistic studies reveal the likely pathway for H₂‐lean compounds formation.     

Snail Hepatopancreatic Lipase: A New Member of Invertebrates Lipases' Group

Higher animal's lipases are well characterized; however, much less is known about lipases from mollusks. A lipolytic activity was located in the land snail (Eobania vermiculata) digestive glands (hepatopancreas), from which a snail digestive lipase (SnDL) was purified. Pure SnDL has a molecular mass of 60 kDa; it does not present the interfacial activation phenomenon. It was found to be more active on short-chain triacylglycerols than on long-chain triacylglycerols. The NH₂-terminal sequence of the SnDL shows 66% of identity with the 17 NH₂-terminal amino acids of a putative lipase from sea urchin (Strongylocentrotus purpuratus). No sequence identity was found with known lipases. Interestingly, neither colipase nor bile salts were detected in the snail hepatopancreas. This suggests that colipase evolved in vertebrates simultaneously with the appearance of an exocrine pancreas and a true liver which produces bile salts. Altogether, these results suggest that SnDL is a member of a new group of digestive lipases belonging to invertebrates.     

New Analytical Method using Coupled Enzymes for Determination of Polyunsaturated Fatty Acid Content in Olive Oil

A new, simple, and original method is described for specific measurement of polyunsaturated fatty acid content in olive oil. This analytical system uses coupled enzymes, lipase and lipoxygenase. The system consists of lipase-catalyzed hydrolysis of triacylglycerol and subsequent lipoxygenation of liberated polyunsaturated fatty acids. The hydroperoxy-fatty acids formed were easily monitored by spectrophotometry at 234 nm. After being optimized, the method was validated in terms of linearity, precision sensitivity, and recovery. Linear calibration graph was obtained in the range 50–500 µg mL^?1, with a correlation coefficient higher than 0.921 and a detection limit (S/N?=?3) of 15 µg mL^?1. The precision of the method (relative standard deviation) for within and between days is better than 7% and 12%, respectively. The proposed method was successfully applied to the estimation of polyunsaturated fatty acids level in olive oil samples and results obtained were in excellent agreement with those obtained by the classical official method. The proposed method is accurate, simple, cheap, and can be satisfactorily used for routine analysis of edible oils.     

Monolayers as models for supported catalysts: zirconium phosphonate films containing manganese(III) porphyrins

Organized monolayer films of a manganese tetraphenylporphyrin have been prepared and used as supported oxidation catalysts. Manganese 5,10,15,20-tetrakis(tetrafluorophenyl-4'-octadecyloxyphosphonic acid) porphyrin (1) has been immobilized as a monolayer film by a combination of Langmuir-Blodgett (LB) and self-assembled monolayer techniques that use zirconium phosphonate linkages to bind the molecule to the surface. Analysis by FTIR, XPS, UV-vis and polarized optical spectroscopy show that the films consist of noninteracting molecules effectively anchored and oriented nearly parallel to the surface. The monolayer films are stable to the solvent and temperature conditions needed to explore organic oxidations. The activity of films of 1 toward the epoxidation of cyclooctene using iodosylbenzene as the oxidant was compared to that of Manganese 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin (2) and 1 under equivalent homogeneous conditions. The immobilized porphyrin 1 shows an enhanced activity relative to either homogeneous reaction. The main difference between 1 and 2 is the four alkyl phosphonate arms in 1 designed to incorporate the porphyrin within the films. The increased activity of immobilized 1 is a combination of the porphyrin structure, which prohibits the formation of mu-oxo dimers even in solution, and a change in conformation when anchored to the surface. The study demonstrates that careful monolayer studies can provide useful models for the design and study of supported molecular catalyst systems.     

A chiroptical molecular switch with distinct chiral and photochromic entities and its application in optical switching of a cholesteric liquid crystal

Two new structurally related photoswitches are described, in which azobenzene photochromism is combined with the chirality of a 2,2'-dihydroxy-1,1'-binaphthyl unit. In system 1 the chiral binaphthyl moiety is bridged by a methylene tether, locking the biaryl chirality while in system 2 the biaryl core is unbridged and has considerable conformational flexibility. Both compound are capable of inducing cholesteric liquid crystalline phases and proved to be good photoswitches both in solution and in a liquid crystalline matrix. Compound 2 is capable of completely reversing the liquid crystalline chirality which is unique for a chiroptical molecular switch where the switching unit and the chiral moiety are separate entities.     

Synthesis, nuclear, and magnetic structures and magnetic properties of [Mn3(OH)2(SO4)2(H2O)2

[Mn(3)(OH)(2)(SO(4))(2)(H(2)O)(2)] and its deuterated analogue were synthesized by a hydrothermal technique and characterized by differential thermal analysis, thermogravimetric analysis, and IR spectroscopy. Its nuclear structure, determined by single-crystal X-ray analysis and Rietveld analysis of neutron powder-diffraction data, consists of a 3D network of chains of edge-sharing Mn(1)O(6), running along the c axis, connected by the apices of Mn(2)O(6) and SO(4) units. It is isostructural to the nickel analogue. Determination of the magnetic structure and measurements of magnetization and heat capacity indicate the coexistence of both magnetic long-range ordering (LRO) and short-range ordering (SRO) below a Néel temperature of 26 K, while the SRO is retained at higher temperatures. The moments of the two independent Mn atoms lie in the bc plane, and that of Mn(1) rotates continuously by 54 degrees towards the c axis on decreasing the temperature from 25 to 1.4 K. While the SRO may be associated with frustration of the moments within a Mn(3) trimer, the LRO is achieved by antiparallel alignment of the four symmetry-related trimers within the magnetic unit cell. A spin-flop field, measured by dc and ac magnetization on a SQUID, is observed at 15 kOe.     

Large‐scale extrusion processing and characterization of hybrid nylon‐6/SiO2 nanocomposites

Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide‐6 (PA‐6) is achieved using a twin‐screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h^?1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA‐6 showed higher amounts of γ‐phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E‐modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E′ and E″) increased and tan δ decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd.