Synthesis and spectroscopic characterisation of fluorescent indicators for Na+ and K+

Abstract

The synthesis and the spectral and cation binding properties of new fluorescent indicators for Na ؉ , dicaesium 5-[5-(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin-15-yl)-2-thienyl]-isophthalate (Benzos), and for K ؉ , dicaesium 5-[5-(2,3,5,6,8,9,11,12,14,15-decahydro-1,4,7,10,13,16-benzohexaoxacyclooctadecin-18-yl)-2-thienyl]isophthalate (Benzop), are reported. Both indicators consist of a benzocrown ether with an appropriate cavity for the sodium and the potassium cation, respectively, linked to an aryl thiophene fluorophore. In aqueous solution, the indicators have an absorption maximum at 340 nm and an emission maximum at 430 nm. The chelating abilities of Benzos and Benzop with Na ؉ , K ؉ , Li ؉ , Cs ؉ , Mg 2؉ and Ca 2؉ were studied by means of their fluorescence properties. Upon cation binding, a change in the fluorescence intensity is observed, whereas the spectral distribution remains unaltered. While Benzos cannot discriminate between Na ؉ and other monovalent cations, Benzop shows a three-fold selectivity for K ؉ over Na ؉ .

Photophysics of the Fluorescent pH Indicator BCECF

“…The resulting decay surface with 44 traces was analyzed globally in terms of the rate constants k ij and the spectral parameters b 1 and c 1 . This global fit was slightly better than that with 52 traces (as judged from g 2 ) 1.09 and the plots of the weighted residuals and the autocorrelation functions) and yielded very similar k ij (except for k 21 21 no reliable value could be obtained.…”

“…In that case, the value of the amplitude R 1 associated with the limiting value of τ 1 ) (k 01 + k 21 …”

“…Determination of K a from Direct Fluorimetric Titration. If the photophysical system depicted in Scheme 1 is excited with light of constant intensity, and if the absorbance A of the sample is less than 0.1, and moreover, if the rate of proton binding in the excited state can be neglected, the total fluorescence signal F(λ ex ,λ em , [H + ]) at proton concentration [H + ], due to excitation at λ ex and observed at emission wavelength λ em can be expressed by 21,22 where F min stands for the fluorescence signal of the basic form of the pH indicator (2*), and F max denotes the fluorescence signal of the acidic form of the pH indicator (1* Fitting nonlinear eq 17 to the excitation ratiometric fluorescence data R as a function of [H + ] yields values for K a , n, R min , and R max . Because (λ em ,λ ex 2 )sthe ratio of the fluorescence signal of phenolate form (2) of BCECF over that of the phenol form (1) at the indicated excitation and emission wavelengthss is experimentally accessible, a value for K a can be recovered from ratiometric excitation fluorescence data.…”

“…In the excited state, the reaction of 1* with R to form 2* and RH is characterized by rate constant k 21 B . The reverse reaction of 2* and RH to give 1* and R is described by rate constant k 12 B .…”

“…The global (linkable) fitting parameters are k 01 , k 02 , k 21 , k 12 B , k 21 B , b 1 , and c 1 . The rate constants k ij can be linked over the whole fluorescence decay surface, the b 1 parameters can be linked for the samples at the same pH and λ ex , and the c 1 parameters can be linked for the samples at the same λ em .…”