Shinpei Kado

Evaluation of photoinduced changes in stability constants for metal-ion complexes of crowned spirobenzopyran derivatives by electrospray ionization mass spectrometry

The photoinduced changes of metal-ion complexing ability of crowned spirobenzopyran derivatives were studied by using electrospray ionization mass spectrometry (ESI-MS). Stability constants for the complexation with various metal ions in methanol under visible-irradiation conditions were determined for the first time by ESI-MS. It was found that the stability constants of crowned bis(spirobenzopyran) derivatives with metal ions are decreased dramatically by visible irradiation due to the disappearance of powerful ionic interaction between phenolate anion(s) of the merocyanine form of their spirobenzopyran moiety and a metal ion bound to their crown ether moiety, and the decrease in the stability constants is more pronounced for the multivalent metal-ion complexes. A theoretical consideration was also made to attain reliable values of stability complexes for metal-ion complexes of crown compounds.

Studies on metal-ion complex formation of crown ether derivatives incorporating a photoionizable spirobenzopyran moiety by electrospray ionization mass spectrometry

Metal-ion complexation of crown ether derivatives incorporating one and two spirobenzopyran units was investigated by electrospray ionization mass spectrometry. The crowned spirobenzopyran derivatives exhibited very different metal ion-complexing behavior from their corresponding parent crown ether rings, preferring multivalent to monovalent metal ions owing to the additional ionic interaction with the nitrophenolate anion of the merocyanine moiety. The on-line photochemical reaction for mass spectrometry indicated that the metal ion-complexing ability and ion selectivities of the crowned spirobenzopyrans can be switched photochemically, taking advantage of the difference between the spiropyran and merocyanine isomers.

Potassium-ion-selective sensing based on selective reflection of cholesteric liquid crystal membranes

It is well-known that cholesteric liquid crystals have an optical property, selective reflection, due to changes in the pitch of their helical structure. This unique property of cholesteric liquid crystals can be used to attain a visual sensing system showing color changes as the detection signal. In this paper, we report a visual sensing membrane comprising cholesteric liquid crystals, in which a 15-crown-5 derivative was incorporated as ion recognizing sites, for K+ in aqueous solution. The resulting CLC membrane showed a shift of the reflection peak sensitive to K+ in water. We have also designed polymer-dispersed liquid crystal membranes that showed ion-selective reflection peak shifts with improved response time.

One-pot synthesis of silver nanoshells with near-infrared extinction by a thiocyanate-assisted approach

We report the one-pot synthesis of silver nanoshells with near-infrared extinction assisted by thiocyanate. Our protocol is based on sequential addition of NaSCN and NaBH4 to an aqueous solution of AgNO3 followed by addition of a water-soluble thiol, affording the silver nanoshell with an extinction band around 600–700 nm.

Single-molecule force spectroscopic study on chiral recognition of cysteine derivatives immobilized on a gold substrate by using AFM tips chemically modified with optically active crown ethers

The chiral recognition of cysteine derivatives immobilized on a gold substrate using atomic force microscopy (AFM) tips chemically modified with optically active crown ethers was quantitatively investigated with single-molecule force spectroscopy (SMFS). Interestingly, the chiral recognition ability of the optically active crown ether-modified tip was entirely opposite to that of its optical isomer-modified tip. The difference of rupture forces for the chiral recognition was determined to be about 40 pN under our experimental conditions.

Potential photoresponse of membranes containing a lipophilic crowned spirobenzopyran

Potential response and its photoresponse for plasticized-poly(vinyl chloride) membranes containing a lipophilic crowned spirobenzopyran were surveyed and compared with those for membrane systems of a spirobenzopyran deriative not carrying any crown ether moiety. On UV-light irradiation, an intriguing type of time-course change was found with the membrane potential for the crowned spirobenzopyran system in the presence of alkali metal ions, i.e., the potential first increases and then decreases. The photoresponse profile for the crowned spirobenzopyran system was affected considerably by the sort of metal ions and the pH conditions of aqueous phases. This phenomenon is explained by an ion-exchange mechanism specific to crowned spirobenzopyran, that is, fast proton exchange followed by slow metal-ion exhange of its merocyanine form. The system for the corresponding spirobenzopyran without crown ether moiety exhibited a steady potential photoresponse that depends on the pH conditions of aqueous phases.