Facile synthesis of imine/azine based organic ligands : sensing, bio-imaging and solid-state structural reactivity

Abstract

The work demonstrated in thesis entitled “FACILE SYNTHESIS OF IMINE/AZINE BASED ORGANIC LIGANDS: SENSING, BIO-IMAGING AND SOLID-STATE STRUCTURAL REACTIVITY” was initiated in January 2013 in the Discipline of Chemistry, Indian Institute of Technology Indore. The objectives of this thesis are to design and construct imine and azine ligands as fluorescent chemosensors for metal ion detection. Moreover, Varying structural motifs in the salen-based metal complexes of Cu(II), Co(II), Ni(II) and Zn(II) at varying conditions and their interactions with biomolecules such as CT-DNA and BSA protein and amino acid sensing by metal complex Cu(II) compound were studied. Furthermore, we explored the solid-state structural reactivity in molecular crystal in terms of unique non-bonding interaction, single-crystal-to-single-crystal (SCSC) transformation and elasticity. This thesis contains six chapters and it begins with a general introduction (Chapter 1), followed by different structural, photo- physical and electrochemical properties of the newly synthesized ligands/complexes as subsequent chapters. The introductory chapter (Chapter 1) of this thesis illustrates the brief background literature of fluorescent chemosensors (turn-on) for metal ions, specific for Zn(II) and Al(III) ions. Fluorescent chemosensors have been developed to be useful tools in in-vitro and in-vivo sensing of biologically important species such as metal cations and anions. A typical fluorescent chemosensor contains a receptor site linked to a fluorophore, which translates the recognition event into the fluorescence signal. Moreover, we have described the receptor molecule viz., Schiff base/Imine, azine, bipyridine, triazole, crown-ethers and quinoline etc. Furthermore, application of fluorescent chemosensor and their metal complexes in bio-imaging has been described. The interaction of metal complexes withbiomolecules like DNA and BSA protein has been discussed. Owing to their significant role in human biological process, the detection of amino acids has gained much attention. Thus, their sensing is very important and has been a persistent challenge. Moreover, introduction of bending crystal phenomenon has been discussed as well. In solid-state, crystalline materials have wide applications in mechanical actuators, phototransistors, light-emitting diodes (LEDs), solar cells, photonics and flexible electronics etc.Chapter 2, describes a novel imine based chemosensor (L1). A new multifunctional imine type ligand (L1) and its Al3+ complex (1) have been designed and synthesized. L1 acts as a chemosensor for Al3+ whereas 1 demonstrates specific staining of nucleus as well as nucleoli. The binding of 1 with nucleic acid is probed by DNase and RNase digestion in stained cells. 1 shows excellent photo stability. 1 is assumed to be a potential candidate as an alternative to expensive commercial dyes ‘SYTO RNA−Select’ for nucleus and nucleoli staining.In Chapter 3, four new salen based mononuclear complexes have been synthesized from the deprotonated imine based ligand L1. Single crystal X–ray diffraction analysis of 1−4 revealed that L possesses different conformations. Moreover, the compound 1 shows sensing nature towards L-tryptophan among various amino acids. The sensing nature of 1 towards L-trp was confirmed by UV-vis and cyclic voltammetry experiments. 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H2L detects Zn2+ selectively among the wide range of metal ions. The sentitration. Packing features of H2L reveals the presence of rare C−H∙∙∙C interactions, which leads to the formation of 1D-polymeric chains.Furthermore, in Chapter 5, we report the structural and biological activities of H2L towards Co(II), Ni(II) and Cu(II) complexes obtained under different conditions. Four new metal complexes have been synthesized: isostructural dimers [Co(L)]2 (1) / [Cu(L)]2 (3), monomer (Cl3NiH2L)·(Et3NH) (2) and tetramer [Cu(L)]4 (4). The biological activity of 1–3 have been investigated through molecular docking with DNA and various proteins, known to be involved in proliferation of viral diseases or progression of cancer.In Chapter 6, we report a rare combination of two unique properties of novel an azine based ligand H3L. In a solid-state crystalline material it shows highly flexible and elastic behavior which on triggering with light results in slight deviation with phase transformation at the SCSC level. Furthermore, in the solution state it acts as a highly selective, sensitive and reversible Al3+ sensor with a detection limit of 42 nM.sing behavior of H2L was identified by UV-vis, fluorescence and 1H NMR