Abstract:
Hydroxamic acids are a group of naturally occurring or synthetic organic acids having the general
formula RCONR'OH and they are weaker proton donors than the structurally related carboxylic
acidsRCOOH.The hydroxamicacids have one or more -CONHOH group which is related with
theirabilityto form metal ions complexes. The aim of this research was to synthesise and study
tluoroionophores consisting hydroxamic acid as the ion-receipting group linked to the
tluorophore which is naphthalene. The compounds, 1-
naphthalenemethyliminodiacetohydroxamic acid (1) and 1-naphthaleneiminodiacetohydroxamic
acid (2) were synthesized. These two hydroxamic acids were examined as complexing agents for
the transition metal ions Fe(Ill), Cu(II), and Zn(lI) in pure methanol and aqueous O.O2M ~-
cyclodextrin while changing the concentration of metal ions and pH.
Theabsorptionspectra of Fe(lII) with compound 1 and compound2 at differentpH indicatedone
isosbesticpoint suggesting the formation of two types of complexes. There is no absorption in
the visibleregion for the compound 1 with Fe(III) and ~-cyclodextrinas well as the complexesof
Cu(II) and Zn(II) with compound 1 and compound 2. Emission of Fe(lII), Cu(II), and Zn(II)
complexes show two (1:1and 1:2) and one (1 :1) types of quenching mechanisms according to the
Stem-Volmer plots and it is seen that fluorescence is higher in compound 1 than that of the
compound 2. Furthermore, it is observed that the fluorescence intensities of these compounds in
~-cyclodextrin are higher than that in methanol. The quantum yields depend on the metal
concentration and pH in the medium. The formation constants of compound 1 and 2 with Fe(lII),
Cu(II) and Zn(II) were calculated as a function of metal ion concentration. Further, it can be seen
that these formation constants are higher in ~-cyclodextrin than that in pure methanol medium.
Therefore, it can be concluded that the medium of ~-cyclodextrin has an influence to increase
formation constants in complexes. The fluorescent sensors consisting fluorophore and ionophore
is one of the attractive subject in the studies of chemosensors in the analysis of trace metal ions
because of its high sensitivity due to the easy measurement of low analyte concentration and its
selectivity due to the excitation and emission wavelength of fluorescent species.
