Liquid-liquid interfaces as potentiometric ion-sensors-I The n-butanol-water interface as indicating sensor for the potentiometric titration of some acids and bases

The property that liquid-liquid interfaces modify their electrical charge as a function of the composition of the two phases in contact has been used to detect the end-points in a series of acid-base titrations in the aqueous phase. Although the titration curves are not classical in shape, the equivalence points can be located if the solutions are not too dilute. Good results for concentrations down to 10(-3)N have been obtained. The electrode has a fast response. The influence of surface-active substances on the titration has also been investigated.     

Photocatalytic redox-neutral hydroxyalkylation of N-heteroaromatics with aldehydes

Hydroxyalkylation of N-heteroaromatics with aldehydes was achieved using a binary hybrid catalyst system comprising an acridinium photoredox catalyst and a thiophosphoric acid organocatalyst. The reaction proceeded through the following sequence: (1) photoredox-catalyzed single-electron oxidation of a thiophosphoric acid catalyst to generate a thiyl radical, (2) cleavage of the formyl C–H bond of the aldehyde substrates by a thiyl radical acting as a hydrogen atom transfer catalyst to generate acyl radicals, (3) Minisci-type addition of the resulting acyl radicals to N-heteroaromatics, and (4) a spin-center shift, photoredox-catalyzed single-electron reduction, and protonation to produce secondary alcohol products. This metal-free hybrid catalysis proceeded under mild conditions for a wide range of substrates, including isoquinolines, quinolines, and pyridines as N-heteroaromatics, as well as both aromatic and aliphatic aldehydes, and tolerated various functional groups. The reaction was applicable to late-stage derivatization of drugs and their leads.

Hydroxyalkylation of N-heteroaromatics with aldehydes was achieved using a binary hybrid catalyst system comprising an acridinium photoredox catalyst and a thiophosphoric acid organocatalyst.     

One-pot synthesis of symmetrical and unsymmetrical bisarylethynes by a modification of the sonogashira coupling reaction

A modification of the Sonogoshira coupling reaction employing an amidine base and a substoichiometric amount of water generates symmetrical and unsymmetrical bisarylethynylenes in one pot through in situ deprotection of trimethylsilylethynylene-added intermediates.     

Glucose recognition by a supramolecular complex of boronic acid fluorophore with boronic acid-modified cyclodextrin in water

A boronic acid fluorophore (C1-APB)/boronic acid-modified γ-cyclodextrin (3-PB-γ-CyD) complex as a supramolecular sensor has been designed for selective glucose recognition in water. The fluorescent response behavior of the C1-APB/3-PB-γ-CyD complex under various pH conditions revealed that a C1-APB/3-PB-γ-CyD complex solution containing glucose showed a large increase in the fluorescence intensity under alkaline pH conditions. In contrast, only small increases in the fluorescence intensity were noted for fructose and without sugar solutions. The observed response selectivity for the C1-APB/3-PB-γ-CyD complex was on the order of glucose > galactose, mannose > fructose. The evidence on a large value of the inclusion constant (K(L·CyD) = 6.5 × 10(3) M(-1)), a marked broadening of the (1)H NMR spectra, and an enhancement of induced circular dichloism (ICD) intensity for the C1-APB/3-PB-γ-CyD complex by glucose binding supported the multi-point interaction of the C1-APB/3-PB-γ-CyD complex with glucose. These results demonstrated that the C1-APB/3-PB-γ-CyD complex functioned as an efficient supramolecular sensor for selective glucose recognition in water.     

Macromolecular Recognition: Discrimination between Human and Bovine Serum Albumins by Cyclodextrins

The interactions of cyclodextrins (CDs) with human serum albumin (HSA) and bovine serum albumin (BSA) were investigated by two‐dimensional nuclear Overhauser effect spectroscopy (2D NOESY), steady state fluorescence, isothermal titration calorimetry, and circular dichroism spectroscopy. 2D NOESY indicates that α‐CD and β‐CD, but not γ‐CD, interact with the aromatic amino acid residues on HSA. On the other hand, the 2D NOESY signals between CDs and BSA are not significantly correlated. Hence, CDs can discriminate the subtle protein structural differences of HSA and BSA.

     

Heterogeneously Hybridized Porous Coordination Polymer Crystals: Fabrication of Heterometallic Core–Shell Single Crystals with an In‐Plane Rotational Epitaxial Relationship

MOF on MOF: Core–shell porous coordination polymer (PCP) crystals are fabricated at the single‐crystal level by epitaxial growth in solution. Synchrotron X‐ray diffraction measurements unveiled the structural relationship between the shell crystal and the core crystal, where in‐plane rotational epitaxial growth compensates the difference in lattice constant.

     

Asymmetric synthesis of 4,8-dihydroxyisochroman-1-one polyketide metabolites using chiral hypervalent iodine(III)

Stereoselective oxylactonization of ortho-alkenylbenzoate with chiral hypervalent iodine is applied to the asymmetric synthesis of 4-oxyisochroman-1-one polyketide metabolites including 4-hydroxymellein (1), a derivative of fusarentin 2, monocerin (3), and an epimer of monocerin epi-3.     

Molecular chirality and chiral capsule-type dimer formation of cyclic triamides via hydrogen-bonding interactions

Chiral properties of bowl-shaped cyclic triamides bearing functional groups with hydrogen-bonding ability were examined. Chiral induction of cyclic triamide 3a was observed by addition of chiral amine in solution, and chiral separation was achieved by simple crystallization to afford chiral capsule-type dimer structure of 4a.     

Photoreaction of Ketoprofen with Tryptophan and Tyrosine in Phosphate Buffer Solution

Reaction of excited ketoprofen (KP) with tryptophan (Trp) and tyrosine (Tyr) in a phosphate buffer solution was studied by the transient absorption spectroscopy. Both amino acids, which would interact with KP in bovine serum albumin [Monti, S. [2009] Phys. Chem. Chem. Phys., 11, 9104–9113], accelerated the proton transfer reaction to yield 3‐ethylbenzophenone ketyl biradical (EBPH) from KP carbanion, which was produced by photoexcitation of KP^? through decarboxylation. By means of the actinometry method with benzophenone, the reaction quantum yield was successfully estimated to be fairly large, and Trp, Tyr, DOPA and 4‐methylphenol were found to be a good proton donor for the carbanion. The formation rate constants of EBPH by the amino acids (k_r) were also determined to be (2.7 ± 0.1) × 10⁹ M^?1s^?1 for Trp and (7.8 ± 0.4) × 10⁸ M^?1s^?1 for Tyr, which were larger than those by basic amino acids and dipeptides reported. The reason for the highly efficient proton transfer reaction with Trp and Tyr would be explained by difference of the activation energy for the reaction. These results suggest that the proton transfer should be a key process for an initial photoreaction of KP with a protein, causing photosensitization in vivo.