Abstract:
Dipicolylamine (dpa) moiety has received much attention due to its coordination versatility. Our
objective is to incorporate piperidinyl groups into the dpa system due to possibility of the piperidinyl
group to target sigma receptors as it shows high affinity to sigma receptors, which are expressed in
high densities in breast cancer cells. In this study, two novel ligands; N((CH2)2piperidine)dpa (L1)
and N((CH2)3piperidine)dpa (L2) (Figure 1) were synthesized by utilizing pendant piperidinyl groups
having different chain lengths. The platinum complexes of novel ligands; [PtClN((CH2)2piperidine)
dpa]Cl (C1) and [PtClN((CH2)3piperidine)dpa]Cl (C2) were also synthesized during the study.
Structural data obtained from single crystal X ray diffraction for C1 confirms that L1 serves
as a tridentate donor ligand. UV visible spectra of both ligands and complexes were recorded in
methanol. Absorption peaks in 200-300 nm range in UV visible spectra of ligands are due to intra
ligand π→π* transitions and peaks above 300 nm range are due to n→π* transitions in the ligands.
As expected, no absorption peaks corresponding to n→π* transitions were observed in UV visible
spectra of complexes due to lack of lone pairs in the coordination complexes. Methylene protons
observed as a singlet (3.87 ppm) in 1H NMR spectrum of L1. The N-H bond of secondary amine
group present in dpa gives an IR band in 3310-3350 cm-1 region. However, IR spectra of both ligands
and complexes gave no transmittance peaks in region 3310-3350 cm-1 confirming the absence of the
N-H group which also confirms the formation of ligands and complexes. Both ligands displayed
intense fluorescence in methanol. However, fluorescence spectra of platinum complexes showed
lower intensities than the respective ligands, possibly indicating static quenching of fluorescence
upon coordination to metal. These ligands and complexes can be explored towards treatment of
breast cancer due to incorporation of piperidinyl group.
