In this paper, the interaction of rhodamine123 (R123) with calf thymus DNA has been studied using molecular modeling and other biophysical methods like UV-vis spectroscopy, fluoremetry, optical melting, isothermal titration calorimetry, and circular dichroic studies. Results showed that the binding energy is about -6 to -8 kcal/mol, and the binding process is favored by both negative enthalpy change and positive entropy change. A new method to determine different thermodynamic properties like calorimetric enthalpy and heat capacity change has been introduced in this paper. The obtained data has been crossed-checked by other methods. After dissecting the free-energy contribution, it was observed that the binding was favored by both negative hydrophobic free energy and negative molecular free energy which compensated for the positive free energies due to the conformational change loss of rotational and transitional freedom of the DNA helix.
Described
in this work is the synthesis of a novel dicyano-substituted
N
-2-aminoethyl-4-(3-pyridinyl)-2-pyridone organic compound
(
1
) that is characterized by several spectroscopic methods.
Compound (
1
) was utilized for the preparation of its
perchlorate (
2
), chloride (
3
), and bromide
(
4
) salts. Single-crystal X-ray structures of these three
salts were determined, and noncovalent weak interactions involving
the aromatic rings, anions, and water molecules in (
2
–
4
) were investigated in detail. Solid-state
UV–vis spectrum of the reported compounds (
1
–
4
) was utilized to calculate their optical band gaps, which
clearly indicated that they belong to the semiconductor family. Under
illumination condition, the magnitudes of electrical properties of
(
1
) and its salts (
2
–
4
) improve remarkably although the improvement differs from salt to
salt and the result was analyzed theoretically. Salt (
2
) was tested for its DNA binding ability.
Two polynuclear end‐to‐end dicyanamide (dca) bridged copper(II) Schiff base complexes [Cu(L1)(μ1,5‐dca)]n (1) and [Cu(L2)(μ1,5‐dca)]n (2) {[HL1=(1‐(2‐(diethylamino)ethylimino)ethyl) naphthalene‐2‐ol] and [HL2=(1‐(2‐(dimethylamino)ethylimino)methyl) naphthalene‐2‐ol]} were synthesized and X‐ray characterized. Complex 1 crystallizes in chiral space group C2 and complex 2 crystallizes in achiral space group P21/c. Interactions of both complexes with calf thymus DNA (CT DNA) were studied by UV‐vis and circular dichroism spectroscopy. Molecular docking studies were also carried out for both complexes to find their binding affinity using Alpha PMI as the placement methodology. Although docking studies indicated that the binding constants of both complexes with CT DNA were more or less same, UV‐Vis spectral data indicated that the binding constant of complex 1 with CT DNA is considerably large compared to that of complex 2. As complex 1 is chiral and complex 2 is achiral, it may be concluded that the chirality of complex 1 played very significant role to binding of chiral DNA molecule. The antimicrobial activity were estimated by the determination of the minimal inhibitory concentration (MIC) using the broth microdilution method. The complexes showed high in vitro cytotoxicity against MDA‐MB 468 cells.
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