Organoplatinum(IV) tris-chelate complexes, each having a cyclic metallacarbonate ring: synthesis, characterization and kinetic studies of the formation

The complexes [Pt[(CH2)4](NN)], 1a (NN = 2,2'-bipyridine) and 1b (NN = 1,10-phenanthroline) react with 2,3-epoxypropylphenyl ether in the presence of CO2 to give tris-chelate platina(IV)cyclopentane complexes characterized by 1H and 13C NMR spectroscopy as [Pt[(CH2)4](CH2CHCH2OPhOCO2)(NN)], 2. The reactions proceed by the SN2 mechanism and the rates were independent of concentration of CO2. It is demonstrated that for 1a, the reaction proceeds 2.32 times faster than the similar reaction in which the dimethyl analog, [PtMe2(2,2'-bipyridine)], is used. The analog tris-chelate complex [Pt[(CH2)4](CH2CHPhOCO2)(phen)], 3a, was similarly synthesized.     

Multispectroscopic DNA interaction studies of a water-soluble nickel(II) complex containing different dinitrogen aromatic ligands

The water-soluble Ni(II) complex, [Ni(bipy)₂(phen-dione)](OAc)₂·2H₂O (bipy = 2,2′-bipyridine and phen-dione = 1,10-phenanthroline-5,6-dione) has been synthesized and characterized by physico-chemical and spectroscopic methods. The binding interactions of this complex with calf thymus DNA (CT-DNA) were investigated using fluorimetry, spectrophotometry, circular dichroism and viscosimetry. In fluorimetric studies, the enthalpy and entropy of the reaction between the complex and CT-DNA showed that the reaction is exothermic (ΔH = −123.9 kJ mol⁻¹; ΔS = −323.5 J mol⁻¹ K⁻¹). The competitive binding studies showed that the complex could not release methylene blue completely. The complex showed absorption hyperchromism in its UV–Vis spectrum with DNA. The calculated binding constant, K _b obtained from UV–Vis absorption studies was 2 × 10⁵ M⁻¹. Moreover, the complex induced detectable changes in the CD spectrum of CT-DNA, as well as changes in its viscosity. The results suggest that this nickel(II) complex interact with CT-DNA via a groove-binding mode.     

Study binding of Al-curcumin complex to ds-DNA, monitoring by multispectroscopic and voltammetric techniques

In this work a complex of Al3+ with curcumin ([Al(curcumin) (EtOH)2](NO3)2) was synthesized and characterized by UV-vis, FT-IR, elemental analysis and spectrophotometric titration techniques. The mole ratio plot revealed a 1:1 complex between Al3+ and curcumin in solution. For binding studies of this complex to calf thymus-DNA various methods such as: UV-vis, fluorescence, circular dichroism (CD), FT-IR spectroscopy and cyclic voltammetry were used. The intrinsic binding constant of ACC with DNA at 25°C was calculated by UV-vis and cyclic voltammetry as 2.1×10(4) and 2.6×10(4), respectively. The thermodynamic studies showed that the reaction is enthalpy and entropy favored. The CD results showed that only the Δ-ACC interacts with DNA and the Δ-ACC form has not any tendency to interact with DNA, also the pure curcumin has not any stereoselective interaction with CT-DNA. Fluorimetric studies showed that fluorescence enhancement was initiated by a static process in the ground state. The cyclic voltammetry showed that ACC interact with DNA with a binding site size of 2. From the FT-IR we concluded that the Δ-ACC interacts with DNA via partial electrostatic and minor groove binding. In comparison with previous works it was concluded that curcumin significantly reduced the affinity of Al3+ to the DNA.     

Synthesis of a new Pt(II) complex containing valganciclovir drug and calf-thymus DNA interaction study using multispectroscopic methods

A new complex, [Pt(valcyte)(DMSO)Cl]Cl, in which valcyte (trade name) served as valganciclovir hydrochloride drug ([2-[(2-amino-6-oxo-3H-purin-9-yl)methoxy]-3-hydroxypropyl](2S)-2-amino-3-methylbutanoate), was synthesized and characterized by different physicochemical methods. Binding interaction of this complex with calf-thymus DNA (ct-DNA) has been investigated by multispectroscopic techniques. The complex displays significant binding properties with ct-DNA. The results of fluorescence and UV–vis absorption spectroscopy indicated that this complex interacted with ct-DNA in a groove-binding mode, and the binding constant was 3.8 × 10⁴ M^?1. Furthermore, the complex induced detectable changes in the CD spectrum of ct-DNA and slightly changed its viscosity which verified the groove-binding mode. Finally, all results indicated that Pt(II) complex interact with DNA via groove-binding mode.     

Human serum albumin interaction studies of a new copper(II) complex containing ceftobiprole drug using molecular modeling and multispectroscopic methods

A copper(II) complex containing the ceftobiprole drug and 1,10-phenanthroline (phen) has been synthesized and characterized by UV–vis, FT-IR and mass spectra, and elemental analysis. The binding interaction between [Cu(cef)(phen)Cl₂] complex and human serum albumin (HSA) was investigated using absorption, fluorescence emission and circular dichroism spectroscopies, and molecular docking. Thermodynamic parameters (ΔH < 0 and ΔS < 0) indicated that the hydrogen bond and van der Waals interactions played main roles in the binding of complex [Cu(cef)(phen)Cl₂] to HSA. The results of CD and UV–vis spectroscopy showed that the binding of [Cu(cef)(phen)Cl₂] to HSA induces some conformational changes in HSA. Displacement experiments predicted that the binding of [Cu(cef)(phen)Cl₂] complex to HSA is located within domain III, Sudlow’s site 2, and these observations were substantiated by molecular docking studies.     

Multispectroscopic Studies on the Interaction of a Platinum(II) Complex Containing l-Histidine and 1,10-Phenanthroline Ligands with Bovine Serum Albumin

The mechanism of the interaction between bovine serum albumin (BSA) and [Pt(phen) (histidine)]⁺ complex was studied employing ultraviolet (UV) absorption, circular dichroism (CD), FT-IR, differential pulse voltammetry (DPV), and fluorescence spectral methods. Fluorescence data showed that the intrinsic fluorescence of BSA was strongly quenched by Pt(II) complex in terms of an untypical static quenching process. The corresponding number of binding sites (n) and binding constant (K _b) of BSA and complex at 283, 298, and 310 K were calculated to be 0.61?×?10⁶, 19?×?10⁶, and 42?×?10⁶ M^?1, respectively. The results showed that the increasing temperature improves the stability of the complex–BSA system, which results in a higher binding constant and the number of binding sites of the complex–BSA system. The positive ΔH and positive ΔS indicated that hydrophobic forces might play a major role in the binding between complex and BSA. Based on Forster’s theory of non-radiation energy transfer, the binding distance (r) between the donor (BSA) and acceptor (Pt(II) complex) was evaluated. The results of CD, UV–vis, DPV, and FT-IR spectroscopy showed that the binding of Pt(II) complex to BSA induced conformational changes in BSA     

Sub-terahertz on-off switch based on a two-dimensional photonic crystal infiltrated by liquid crystals

A sub-terahertz switch is realized by infiltration of a two-dimensional photonic crystal (PC) with the liquid crystal 5CB. On-off switching is based on a shift of the bandgap of the PC by applying an external electric field which rotates the 5CB molecules. We confirm theoretically and experimentally that rotating the optical axis of the 5CB molecules considerably affects the transmission of the electromagnetic waves of TM polarization in the stop band. The effect can be used for on-off switching of the electromagnetic waves in the sub-terahertz range. Experimentally we demonstrate an extinction ratio of 13.3 dB at 91 GHz.     

Spectrophotometric simultaneous determination of cobalt, copper and nickel using nitroso-R-salt in alloys by partial least squares

Partial least squares modeling as a powerful multivariate statistical tool applied to spectrophotometric simultaneous determination of cobalt, copper, and nickel in aqueous solutions. The concentration range for cobalt, copper and nickel were 0.4-2.6, 0.6-3.4, 0.5-5.5 ppm, respectively. The experimental calibration set was composed with 36 sample solutions using a mixture design for three component mixtures. The absorption spectra were recorded from 470 to 600 nm. The effect of pH on the sensitivity and selectivity was studied according to net analyte signal (NAS). The values of root mean square difference (RMSD) for cobalt, copper and nickel using partial least squares (PLS) were 0.0192, 0.0263 and 0.0446 ppm, respectively. The effects of various cations and anions were investigated. The method was used to determination of cobalt, copper and nickel in two sample alloys based on copper, nickel and cobalt (known as cunico) and based on cobalt, nickel and iron (known as conife).     

EIT based tunable metal composite spherical nanoparticles

Optical polarizability of a composite metal–dielectric and dielectric–metal spherical nanoparticle is investigated in view of achieving all-optical tunability. In this work, the Electromagnetically Induced Transparency (EIT) implemented in the shell or core of the nanoparticle is used. For the proposed nanoparticle, we show that EIT phenomenon can be utilized to tune the resonance frequency in the frequency response of polarizability. We present a quasi-static analysis for determining polarizability of the nanoparticle. According to our simulation results, all-optical tunability of polarizability can be achieved for reasonable values of optical pump power. Also, we demonstrate how the extinction quality factor and electric field distribution can be controlled for the introduced nanoparticle.     

Full-wave analysis of photonic-crystal structures with multi quantum well active region

In this paper, a semi-classical formulation for modeling photonic-crystal (PC) structures with a four-layer multi quantum well (MQW) active region is presented. The formulation treats the electromagnetic fields as a classical entity, while employing the quantum-mechanically derived rate equations to analyze the active medium. Using the Poynting theorem, we interrelate the two sets of equations, namely the MQW rate equations and Maxwell's equations. The formulation involves the stimulately emitted photon density in the former and a virtual volume current density representing the generated photons in the latter. With the help of this formulation, we then model a PC optical amplifier as well as a PC hexagonal-defect cavity laser and solve the obtained equations after replacing the involved spatial and temporal derivatives by pseudo-spectral and Runge-Kutta's formulations, respectively. The formulation also takes the effect related to gain saturation and frequency broadening into account.