α-Cyclodextrin (CD)-based rotaxanes showed induced circular dichroism (ICD) from the α-CD to the axle component via a through-space chirality transfer. The chirality induction was evaluated in detail to clarify the induction mechanism. The ICD sign and pattern were largely dependent on the coverage of the axle end groups by the rotaxane wheel. The observed ICD sensitively reflected the wheel position on the axle, suggesting the possibility of easy chirality transfer and applications toward various functional materials.
Controlling the reactive species during the synthesis of complex aliphatic chains containing a quaternary carbon is incredibly difficult. In this paper, we efficiently controlled both radical and cationic species in the presence of a copper catalyst. This radical-polar crossover reaction system enables the three-component coupling of styrenes, alcohols, and α-bromocarbonyl compounds as a tertiary alkyl source at room temperature. Mechanistic studies indicated that the reaction contains both radical and cationic species.
Photoluminescent metal-organic coordination polymers (PLMOCPs) have recently become an attractive material for sensing applications, however, fundamental study of PLMOCP for selective metal ion sensing is still lacking. Here, we report a highly water-stable silver-based photoluminescent metal-organic coordination polymer (PLMOCP) of Ag(BPY)(IPA-NH2) with 404 nm emission as a single probe for selectively detecting Pb2+ in aqueous solutions. The as-synthesized Ag(BPY)(IPA-NH2) was characterized with a high yield, well-defined crystalline structure, extraordinary water and thermal stabilities, and unique optical properties. A high quenching constant of 2*10^4 M−1 and low limit of detection (LOD) of 2.1 µM are determined. Systematic absorbance and PL spectroscopic studies suggest that the PL quenching caused by Pb2+ is the simultaneous dynamic quenching mechanism.
The structure prediction of Dictyostelium Histidine Kinase M (DhkM), a candidate for the receptor of differentiation inducing factor-1 (DIF-1), was carried out and the structural determination and refinement were performed with one hundred nanoseconds molecular dynamics (MD) simulations. Three simulations with different initial velocities generated by pseudo-random number seeds were performed to ensure the accuracy of our simulations and almost the same results were obtained. Docking simulations were executed employing the receptor-structures from the very early stage of the MD simulations. The obtained result exhibited that there is a very high possibility that DhkM could be the receptor of DIF-1. The residues in the core part which are adjacent to Leu111, Asp115, Arg150, Val151, Tyr351 and Val354 play a significant role in ligand binding mechanism. Furthermore, the binding energy was also estimated from free energy analysis for verification. The docking simulations for DIF-2 and DIF-3, which have molecular structures similar to DIF-1 have been explored as well. DIF-3 was especially found to have very low capacity of binding/no docking-simulation which was consistent with experimental data, and two chloro groups of DIF-1 could lead to a transition to a multicellular slug.
Macroporous cellulose beads having a three-dimensionally interconnected porous structure have been economically prepared from a cellulose acetate solution in a single step at room temperature. The water absorbency and stiffness of the obtained macroporous beads could be controlled by changing the CA concentration.
N-Acyl isoxazolidines were obtained in moderate to good yields by intramolecular hydroamination of N-alkoxyamides in the presence of a ruthenium photocatalyst. In this reaction, the N-alkoxyamide anion generated by deprotonation undergoes photocatalyzed single-electron-transfer (SET) oxidation to generate the corresponding radical, which cyclizes to afford the isoxazolidine ring. Notably, this method was applicable to a macrocyclic substrate, affording the corresponding 12-membered macrocycle-containing product.
Wedge-shaped phenylphosphonic acids with variation in the peripheral alkoxy chains have been synthesized. These derivatives show a hexagonal columnar liquid-crystalline behavior upon thermal treatment. These materials have potential to be used as efficient anisotropic proton conductors.
This work deals with the preparation of poly(sodium p-styrenesulfonate) (PSS) and poly[(3-acryloylaminopropyl)trimethylammonium chloride] (APTAC) modified ion exchange cellulose monoliths (C-g-PSS and C-g-APTAC, respectively). The obtained ion exchange monoliths were employed for the removal of cationic or anionic dyes from aqueous solutions with particular reference to the effects of initial dye concentration, flow rate and ionic strength on adsorption. Detailed adsorption characteristics of ion exchange monoliths including operational parameters, adsorption kinetics and adsorption isotherms were investigated. Results showed exceptional affinity for adsorption of dyes due to the charge-induced adsorption. The observations from dynamic adsorption experiments indicated that the modified monoliths allowed ultra-fast adsorption of dyes at relatively high flow rates and were more favourable under low ionic strength conditions. An ultrahigh equilibrium adsorption capacity of 606.3 mg g−1 and dye removal efficiency of 72.3% for methylene blue was observed for the C-g-PSS monolith, which exhibited better adsorption performance than that of APTAC functionalized monolith for acid red 70. However, C-g-APTAC monolith was found superior in dye recoveries and regeneration, the adsorption efficiency can be maintained at 97% after 7 adsorption-desorption cycles. Combining the ultrafast adsorption kinetics with high removal capacity and good recyclability, the ion exchange monoliths have great potential for effluent treatment applications.
The design and creation of chiral recognition elements are important for the synthesis, separation, and detection of chiral molecules. We prepare monoclonal antibodies (mAbs), which are chemically homogeneous antibodies, as tailored chiral recognition elements by immunizing mice with a racemic mixture of a binaphthyl derivative (BN (rac)) conjugated to keyhole limpet hemocyanin (KLH). Immunization with BN (rac) induces an immunoresponse that is as strong as that with enantiomerically pure antigens and yields mAbs for each enantiomer of BN, simultaneously. Notably, one of the mAbs prepared by immunization with BN (rac) recognizes the axial chirality of the BN enantiomer with a 14000-fold difference in affinity. These findings provide a strategy to obtain atroposelective antibodies for each enantiomer of BN with a single immunization. mAbs also recognize the axial chirality of 1,1′-bi-2-naphthol (BINOL) and 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (BNPA), which are an important chiral building block and a chiral organic catalyst, respectively. The cross reactivity of mAbs for the partial structure of BN is significantly low. Therefore, mAbs recognize the axial chirality of BN, BINOL, and BNPA by binding their binaphthyl moiety.
In this work, the [2+2] photocycloaddition of carbonyl compounds with olefins, the Paternò-Büchi-type photoreaction, was performed in a flow microreactor under slug flow (two-phase flow) conditions which are constructed by alternatively introducing nitrogen gas as an unreactive substance into the organic reaction phase. The use of N2 gas-liquid slug flow conditions permitted the organic photoreactions to proceed more efficiently compared to one-phase flow conditions. A detailed investigation of the influence of the flow mode, the viscosity of the solvents, and the segment length (length of each phase) on the efficiency of the photoreaction was conducted. Based on the results, we concluded that these three factors contribute to the improvement in photoreaction efficiency under slug flow conditions using N2 gas as an unreactive substance. Furthermore, the use of N2 gas as an unreactive substance was found to be applicable to other Paternò-Büchi-type photoreactions.
We describe here the syntheses of velutinol A (1) and the structurally similar compounds 2–4 sharing a highly oxygenated seco-pregnane cage-like structure. The synthesis of velutinol A (1, 15,16-seco-pregnane) features the highly regioselective construction of Δ14 silyl enol ether from 15-keto-21,22-diol, followed by stereoselective introduction of a sterically hindered β-hydroxy group at the C14 position by Rubottom oxidation. Prolonged reaction time and the use of an excess amount of mCPBA at this step allowed double Rubottom oxidation, enabling us to introduce the requisite hydroxy groups at the C14 and C16 positions in one pot. Subsequent oxidative cleavage of the C15–16 bond, deprotection, and intramolecular acetalization allowed the concise total synthesis of velutinol A (1). Utilization of α,α-dihydroxyketone, the double Rubottom oxidation product, for formation of the ether F-ring by 5-exo-cyclization, and subsequent C14–21 oxidative cleavage, effectively achieved the synthesis of pentalinonside-aglycon (2). Construction of the 14,15-seco-structures of two other analogs, argeloside aglycon (3) and illustrol (4), was achieved by Baeyer–Villiger oxidation of 15(21)-keto derivatives. Introduction of the 20-oxo group potentially embedded in argeloside aglycon was accomplished by Wacker oxidation of Δ20, which was constructed by Grieco–Nishizawa syn-β-elimination of the C21-primary alcohol obtained by reduction of the Baeyer–Villiger product. Intramolecular double acetalization of the 15,16-dihydroxy-14,20-oxo derivative to form the cage-like structure of the DEF-rings required a moderately weak acid. This step was the key to accessing argeloside aglycon (3), as otherwise the easily aromatized β,γ-dihydroxyketone moiety was transformed to furan. Sharpless asymmetric dihydroxylation of Δ20 to set the C20 stereocenter, followed by intramolecular double acetalization, achieved the stereoselective synthesis of illustrol With all synthesized compounds, structural requirements of steroidal bradykinine B1 receptor antagonist would be revealed.
We report on a new multifocus optical system developed for fluorescence correlation spectroscopy (FCS). This system utilizes a beamsplitter array to spatially separate excitation beams. Fluorescence from each spot is individually detected with a single-photon avalanche photodiode (SPAD) through a fiber bundle. The combined use of beamsplitters and multiple SPADs is beneficial to give a higher detection uniformity among focal spots than the existing multifocus FCS systems. Applications of this setup show that the variation of the optical parameters among seven focal spots are as small as ∼5% and prove its high performance in FCS measurements. High efficiency of this system is also demonstrated in application to an advanced FCS method, two-dimensional fluorescence lifetime correlation spectroscopy. Along with the results of these applications, we describe a method for proper correction of the crosstalk effect in the multifocus setup.
Thiamine deficiency is an important issue for many diseases and thus a facile method of detection is clinically important to improve the health of humans. For that purpose, we have developed a new thiamine sensor using starch stabilized copper nanoparticles (CSNP) at neutral pH and also improved the sensitivity of the sensor using cucurbituril (CB) through host-guest chemistry. Often thiamine is not detected directly, but through the oxidation of thiamine to thiochrome (TC); TC is a fluorescent emitting molecule, through which thiamine has been measured indirectly. Here, we have demonstrated a new approach for a thiamine sensor, based on the formation of TC by the addition of hydrogen peroxide and CSNP. Unlike the other reported thiamine sensors, our method works advantageously at physiological pH conditions (pH 7, 27 °C). Furthermore, addition of CB to TC, increased the sensitivity of the sensor approximately one order magnitude, through encapsulation; which can be reversed upon addition of a stronger competitive guest such as adamantylamine to confirm the encapsulation of TC. Thus, this new thiamine sensor not only performed well under physiological pH conditions, but also improved the fluorescence of TC, when encapsulated by CB.
The helical structures and optoelectronic functions of conjugated polymers were dynamically controlled using an external force-responsive liquid crystal field, leading to cultivation and development of a novel research field named “Interdisciplinary Chemistry Based on Integration of Liquid Crystals and Conjugated Polymers”. First the external stimuli-responsive liquid crystal field was prepared to construct super-hierarchical helical structures of the conjugated polymers. Subsequently, the chiroptical properties including circularly polarized luminescence were enhanced and controlled. Furthermore, the helical carbons and graphites films were prepared via morphology-retaining carbonization using chemically or electrochemically doped conjugated polymers as precursors.