A family of Fe³⁺based double-stranded helicates showing a magnetocaloric effect, and Rhodamine B dye and DNA binding activities

Abstract

Herein, the synthesis, structural characterization, magnetic properties and guest binding activities of four Fe(3+) based double-stranded helicates namely; [Fe2(L)2](ClO4)(Cl)·4(CH3OH)·2(H2O) (), [Fe2(L)2](BF4)2·2(H2O) (), [Fe2(L)2](NO3)2·3(CH3OH)·2(H2O) (), and [Fe2(L)2](Cl)2·2(CH3OH)·4(H2O) () are reported. Complexes have been synthesized using the hydrazide-based ligand H2L (H2L = N'1,N'4-bis(2-hydroxybenzylidene)succinohydrazide) and the corresponding Fe(2+) salts. Each of the independent cationic complexes [Fe2(L)2](2+) shows double-stranded helicates from the self-assembly of the ligand and metal ions in a 2 : 2 ratio, where the individual Fe(3+) centre is lying on a C2-axis and the ligand strands wrap around it. In , ligand L adopts "pseudo-C" conformations and forms a double-stranded dinuclear helicate with a small cage in between them. Moreover, in , each of the independent cationic complexes [Fe2L2](2+) is inherently chiral and possesses P for right-hand and M for left-hand helicity and as a consequence is a racemic solid. Detailed magnetic studies of all the complexes reveal that the Fe(3+) centres are magnetically isolated and isotropic in nature. Estimation of the Magnetocaloric Effect (MCE) from magnetization data unveils a moderate MCE at a temperature of 3 K with magnetic entropy changes (-ΔSm) of 22.9, 27.7, 24.1, 26.5 J kg(-1) K(-1) at a magnetic field of 7 T for complexes , respectively. Also, the variation of the -ΔSm values was justified by considering the parameter of magnetization per unit mass. Stability of all the complexes in solution phase was confirmed by ESI-mass spectrometric analysis and liquid phase FT-IR spectroscopy. Further, the interaction of the complexes with Rhodamine B dye was examined by UV-vis and fluorescence spectroscopic study. The observed blue-shift in the fluorescence study and hyperchromicity and hypochromicity with the appearance of two isosbestic points in the UV-vis study ascertain the interactions of the dye with the complexes. A DNA binding study by absorption spectral titration suggests the weak external intercalation of complex within the nucleotide of calf thymus DNA. Computational study supports the isotropic nature of the metal centres and the consequent high spin multiplicity, which assists the complexes to show significant magnetic entropy changes.

Coordination‐Cluster‐Based Molecular Magnetic Refrigerants

“…Previous reports of 3d‐metal‐based molecular magnetic refrigerants are mainly discrete clusters,30–35 but rare examples of 3d‐metal‐based multidimensional CPs have been documented;26b–d,36–38 moreover, to our best knowledge, there are only three cases of 3d‐metal‐cluster‐based extended structures (Table ) 36–38…”

“…Furthermore, the target molecular refrigerants cover various structural types, including discrete clusters and cluster‐based 1D, 2D, and 3D extended structures. Herein, we mainly summarize recent progress in the structures and magnetocaloric properties of cluster‐based molecular magnetic refrigerants, in which isolated mononuclear CPs and extended structures constructed from isolated monomers and linkers are not included in the following descriptions 25–28…”

Intercalation of Rhodamine B into Calf Thymus DNA in presence and absence of olive leaf extract: A fluorescence study

“…It is observed that in high salt concentrations the binding of RB to the DNA phosphate backbone decreases and the binding constant decreases moderately. 34 In addition, the binding of RB to the minor groove of DNA was further indicated by circular dichroism, fluorescence quenching, and molecular docking studies. 25,34 On addition of 100µl of AOLE (stock: 5g/15ml), a further reduction in RB fluorescence intensity was seen due to the interaction between free unbound RB and AOLE as mentioned above.…”

“…34 In addition, the binding of RB to the minor groove of DNA was further indicated by circular dichroism, fluorescence quenching, and molecular docking studies. 25,34 On addition of 100µl of AOLE (stock: 5g/15ml), a further reduction in RB fluorescence intensity was seen due to the interaction between free unbound RB and AOLE as mentioned above. The inset of Figure 2 shows differences in the fluorescence intensities of system A and system B. Fluorescence intensity of the system B is higher than that of the system A because the AOLE did not allow the RB to interact with the ct-DNA and more free (unbound) RB is exposed to the excitation light and then produces more emission fluorescence light.…”

Complexes of Metals With Dihydrazones of Succinic Acid Dihydrazide

“…Complexes of metals with salicylidene dihydrazones succin acid dihydrazide exhibit catalytic activity in the oxidation reaction of alkenes [1], are able to bind to DNA [2], and possess antimicrobial activity [3]. Salicyliden dihydrazone dihydrazide succinic acid, like dihydrazone derivatives of other dibasic acids, is potentially hexadentate and 4 anionic, due to deprotonation of two phenolic hydroxyls and two enolic groups, as in structure E. [9], helicate clusters of lanthanides and the influence of anions on their configuration [10] and dimeric and polymer complexes of Sn [11] were also obtained.…”