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

Abstract

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 visibleirradiation 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. ( -4]. Recently, the functional crown compounds have been designed by introducing functional moieties that control metal-ion complexing abilities of their crown ether moieties, and their complexation behaviors have been studied [5][6][7][8][9][10][11][12]. Previously, we synthesized spirobenzopyran derivatives bearing a crown ether moiety, which we called crowned spirobenzopyran, and studied their metal-ion complexing abilities, photochromism, and applications for devices [13][14][15][16][17][18][19][20][21][22]. Spirobenzopyran derivatives, which are typical photochromic compounds, are isomerized from their spirobenzopyran forms to their corresponding colored merocyanine forms by UV irradiation and vice versa by visible irradiation or heating [23][24][25]. The detailed investigation of crowned spirobenzopyrans has proved that the photochromic crown compounds, when isomerized from the spiropyran form to the merocyanine form under dark and UV irradiation conditions, can bind metal ions strongly due to the ionic interaction between phenolate anion(s) of the merocyanine form and a metal ion complexed by the crown ether moiety. On the other hand, the isomerization back to the spiropyran form by visible irradiation weakens the metal-ion complexing ability due to the disappearance of the ionic interaction. It is, therefore, anticipated that the stability constants for metal-ion complexes of crowned spirobenzopyrans are changed by photoirradiation (Scheme 1).In general, stability constants for crown ether complexes with metal ions can be determined by using calorimetry, potentiometry, absorption spectrophotometry, 1 H-NMR spectroscopy, and so on [26,27]. The stability constants for metal-ion complexes of crowned spirobenzopyran derivatives are, however, difficult to determine even under dark conditions due to the thermal isomerization for their spirobenzopyran moiety. Recently, a sophisticated determination method for stability constants of crown ether/metal-ion complexes by using electrospray ionization mass spectrometry (ESI-MS) was reported by Kempen et al. [28]. Taking the use of the ESI-MS method, we have successfully det...

Electrospray ionisation mass spectrometric studies for the determination of palladium after pre‐concentration by disposable pipette extraction

“…However, the ESI response of the Pd‐BTU species showed, albeit not linear, a proportional relationship with the added amount of Pd. The suppression in the ESI response of the Pt‐BTU complex species on the addition of Pd might be due to the difference in the stability constant values of Pd(II) and Pt(II) with BTU . The addition of Pd(II) to a complexation system containing Pt(II) and the BTU ligand could cause a decrease in the ESI response of the Pt‐BTU complex due to the competitive complexation between the two metal ions.…”

“…The suppression in the ESI response of the Pt-BTU complex species on the addition of Pd might be due to the difference in the stability constant values of Pd(II) and Pt(II) with BTU. [20] The addition of Pd(II) to a complexation system containing Pt(II) and the BTU ligand could cause a decrease in the ESI response of the Pt-BTU complex due to the competitive complexation between the two metal ions. If the Pd-BTU complex has a lower stability constant than Pt-BTU, the peak intensity of Pt-BTU should remain unaffected by the addition of Pd(II).…”

Light Responsive Polymer Membranes: A Review

“…This accounts why Na + and K + hardly induce the isomerization. Upon visible light irradiation, the spiropyran form is retained, thus decreasing the Li + complexing ability, as confirmed by 7 Li-NMR spectroscopy [126] and electrospray ionization mass spectrometry [127,128]. …”

Photocontrollable Cation Extraction with Crowned Oligo(spirobenzopyran)s

“…We also found that the interaction between the phenolate anion of the merocyanine forms and a metal ion was stronger than that for the metal ion complexation of the corresponding crowned mono(spirobenzopyran)s. [16][17][18][19][20] We have also studied the metal ion extractabilities of crowed mono-and bis(spirobenzopyran)s. Even under dark conditions, these compounds extracted metal ions from an aqueous phase into an organic phase with counteranions. 21,22 The concentration of Li + extracted into the organic phase by (diaza-12-crown-4)-bis(spirobenzopyran) was increased by UV light irradiation, while it was remarkably decreased by visible-light irradiation.…”