Yumiko Kusano

Photocontrolled extraction ability of azobenzene-bridged azacrown ether

Abstract The extraction equilibrium of alkali metal salts between water and benzene with an azobenzene-bridged azacrown ether(I) is affected by photo(uv)-irradiation. This indicates that the binding ability of (I) can be controlled by photo-induced cis-trans isomerism of the azobenzene moiety.

Facile oxidation of aldehydes and α-keto acids as catalyzed by flavin and thiazolium ion

Abstract Oxidation of aldehydes and α-keto acids to carboxylic acids ocurrs readily in the presence of a flavin, thiazolium ion, and cationic micelles, the reaction involving trapping by the flavin of the intermediate formed from the substrate-thiazolium adducts through deprotonation or decarboxylation.

A new “switched-on” crown ether which exhibits a reversible all-or-none ion-binding ability

Abstract A new photoresponsive crown ether (2) in which the poly)oxyethylene) chain is linked to 4− and 4′-position of azobenzene was synthesized. Trans-(2) completely lacked the affinity to alkali metal cations, while photoisomerized cis-(2) was capable of binding K + , Rb + , and Cs + .

Photoresponsive crown ethers. Part 7. Proton and metal ion catalyses in the cis—trans isomerisation of azopyridines and an azopyridine-bridged cryptand

A 2,2′-azopyridine-bridged crown ether (5) has been synthesised for the purpose of controlling the ionbinding functions by an on-off light switch mechanism. Since the trans-azopyridine moiety of compound (5)[i.e. trans-(5)] is vertically over the crown ether ring and the photoisomerised cis-azopyridine moiety of (5)[i.e. cis-(5)] is almost parallel to the crown ether plane, it would be expected that only the pyridine nitrogens of trans-(5) are capable of co-ordinating to metal ions bound into the crown ether ring. The thermal Isomerisation of cis-2,2′-azopyridine [cis-(3)] to trans-2,2′-azopyridine [trans-(3)] was speeded up either by protonation of the pyridine nitrogen or by complexation with heavy-metal ions (e.g. Cu2+, Ni2+, and Co2+). Similarly, the thermal Isomerisation of cis-(5) to trans-(5) was speeded up by protonation of the azopyridine, but the metal ion catalysis was observed only for the metal ions which were bound into the crown ether ring (e.g. Cu2+ and Pb2+). The result of solvent extraction of alkali-metal ions with (5) was very similar to that with an azobenzene-bridged crown ether (1), indicating that the 2,2′-azopyridine-bridge of (5) has almost no effect on the extraction of alkali-metal ions. On the other hand, trans-(5) was capable of extracting considerable amounts of heavy-metal ions (Cu2+, Ni2+, Co2+, and Hg2+), whereas photoisomerised cis-(5) scarcely extracted these metal ions. Such a difference in the extractability was not observed between trans-(1) and photoisomerised cis-(1). Neither the trans- nor the cis-form of 6,6′-bis(morpholinocarbonyl)-2,2′-azopyridine[non-crown analogue of (5)] could extract these metal ions under comparable extraction conditions. These results suggest that pyridine nitrogens of trans-(5) are directed towards the crown ether plane so as to co-ordinate to metal ions in the crown ether ring, whereas those of cis-(5) have no such co-ordination ability due to the distorted configuration. Therefore, compound (5) would act as a ‘photoresponse cryptand’ for heavy metal ions.

Photoresponsive crown ethers. Part 3. Photocontrol of ion extraction and ion transport by several photofunctional bis(crown ethers)

Three photoresponsive bis(crown ethers) with an azo-linkage (2)–(4) were synthesised for the purpose of controlling ion extraction and ion transport by an on-off light swith. The compound trans-(2), in which azobenzene is linked with two monoaza-15-crown-5 compounds via an amide linkage, extracted K+ and Rb+ in 6.7% and 0.5%, respectively, whereas the extractive abilities (ex%) of photoisomerised cis-(2) were higher (16.7% and 8.0%, respectively). Similarly, the ex% of cis-(3)(methylene linkage between azobenzene and two monoaza-15-crown-5 compounds) was greater than that of trans-(3). The results suggest that in the photoisomerised cis-forms alkalimetal cations are extracted as intramolecular 1 : 2 cation–crown complexes. On the other hand, the ex% of compound (4), which has an unsymmetrical structure was scarcely affected by photoirradiation. The rate of ion transport across a liquid (o-dichlorobenzene) membrane with compounds (2) and (3) as ion carriers was accelerated by u.v. irradiation, but retarded by u.v. and visible irradiation. This implies that ion transport is accelerated by the photoconversion of the trans- to the cis-forms in the membrane phase. The difference in the ex% and the ion-transport ability is discussed in relation to the crown structure.

A photoresponsive cylindrical ionophore

A cylindrical ionophore in which two diaza-crown ethers are linked by two photoresponsive azobenzene pillars changes its binding ability for polymethylenediammonium ions in response to photoirradiation.

Coenzyme models. Part 23. Formation and reactivity of the stable ‘quinone form’ of flavin in cationic polymer matrices

The flavin covalently linked to quaternised poly(4-vinylpyridine)via 8α-position afforded, in alkaline solution, a blue species absorbing at 622 nm. On the basis of spectral examination, the species is assigned to the ‘quinone form’ of the flavin. The regioselective proton abstraction from the 8α-methylene is due to the enriched OH– concentration along the polymer chain, and probably also due to the stabilisation of the delocalised quinone form by the polyelectrolyte environment. The quinone flavin was insensitive to molecular oxygen and could oxidise neither NADH analogues nor thiols, indicating that the reactivity is markedly different from the normal flavin form.

Coenzyme models. Part 16. Studies of general-acid catalysis in the NADH model reduction

The reduction of trifluoroacetophenone was performed in an aqueous acetate (and analogues) buffer solution with an acid-stable NADH model compound, 1-benzyl-3-carbamoyl-1,4-dihydroquinoline. The resultant Bronsted plots had a slope of -0.20, indicating that the reduction process is general-acid catalysed. This is the first example of general-acid catalysis observed in an NADH model reduction performed in an aqueous system.

Biomimetic reduction of benzoylformic acid by an acid stable NADH analogue : a model reaction of lactate dehydrogenase

Abstract By the use of an acid-stable NADH analogue (3-carbamoyl-N-benzyl-1,4-dihydroquinoline) NADH model reduction of benzoylformic acid in aqueous solution was achieved, for the first time, at pH region where the carboxyl group is undissociated.

Steric acceleration of reductive desulfonation of 1,8-naphthalenedisulfonate by an NADH model compound

Abstract 1,8-Naphthalenedisulfonate was reductively desulfonated by N-benzyl-1,4-dihydronicotinamide, whereas no desulfonation was observed for the 1,6-isomer. The high reactivity of the 1,8-isomer is attributed to the steric-strain that enforces the shift of the initial state with the sp 2 -carbon close to the transition state with the sp 3 - carbon.