Mirela Enache - Academia.edu (original) (raw)

Papers by Mirela Enache

Phenalenyl is a triangular aromatic molecule made of three fused benzene rings, carrying an unpai... more Phenalenyl is a triangular aromatic molecule made of three fused benzene rings, carrying an unpaired electron, and many of its derivatives show crystal structures with stacked radicals. Here, we investigate the inter-molecular binding in phenalenyl dimers by state-of-the-art computational methods and phenomenological models. Aside from being important for the supramolecular assembly of such radical molecules, the theoretical insight is relevant in methodological aspects, due to the interplay of long-range exchange coupling effects and van der Waals forces. We used comparative wave function-based and density functional theories. Drawing the potential energy surfaces as a function of inter-planar separation and mutual rotation of the monomer units, we found an interesting pattern which is not discovered in previous computational reports on the title systems. The dependence can be nicely interpreted by a transparent phenomenological model based on an orbital overlap paradigm of exchange coupling. We also brought forth a simplified phenomenological valence bond (VB) model of inter-molecular coupling, which is realized on the background of the VB spin model inside of the aromatic monomers and calibrated with the corresponding ab initio data. As the systems can be considered good candidates with potential applications in spintronics and organic magnetism, the theoretical rationalization opens up prospective ways to realize such promises.

Revista de Chimie, 2018

The focus of the present work is to investigate the interaction of anticancer drug mitoxantrone w... more The focus of the present work is to investigate the interaction of anticancer drug mitoxantrone with sodium cholate (NaC) bile salt in phosphate buffer (pH 7.4) and carbonate buffer (pH 10) by UV-Visible absorption spectroscopy. The results indicate that mitoxantrone may bind to NaC monomers and micelles through electrostatic and hydrophobic interactions and the interaction with NaC induces the dissociation of dimers and higher aggregates of mitoxantrone. The stoichiometric ratio, binding constant, micelle/water partition coefficient and the corresponding thermodynamic parameters for binding and partitioning processes were estimated from the monomer absorbance changes occurred as a result of the interaction between mitoxantrone and NaC micelles. The binding process of mitoxantrone to NaC micelles is spontaneous and entropy controlled over the range of studied temperatures, at both pH values. The partition process of mitoxantrone between micellar and bulk aqueous phases is spontaneou...

Journal of Pharmacy and Pharmacology, 2012

Objectives The aim of this study was to investigate the interaction of the anticancer drug mitoxa... more Objectives The aim of this study was to investigate the interaction of the anticancer drug mitoxantrone with non-ionic micelles, as simple model systems of biological membranes. Methods UV-VIS absorption spectroscopy was used to quantify the drug–surfactant micelle interactions in terms of the binding constant and the micelle–water partition coefficient of the drug. Key findings Interaction of mitoxantrone with non-ionic micelles reduces the dimerization process of mitoxantrone, the drug molecules being encapsulated into micelles as monomer. The strength of the interaction between mitoxantrone and non-ionic micelles is higher at pH 10 than at pH 7.4, and depends on the surfactant in the order Tween 80 > Tween 20 > Triton X-100. The higher partition coefficient at pH 10 compared to pH 7.4 suggests that at basic pH the deprotonated mitoxantrone is incorporated more efficiently into the hydrophobic medium of non-ionic micelles compared to physiological pH, when the protonated dru...

Journal of Electroanalytical Chemistry, 2011

Gold electrode was functionalized with glutathione (GSH) by adsorption and analyzed by cyclic vol... more Gold electrode was functionalized with glutathione (GSH) by adsorption and analyzed by cyclic voltammetry and electrochemical impedance techniques. The structure and properties of the surface film are strongly dependent on the modification procedure, pH value and supporting electrolyte. The blocking properties and the electron transfer through the GSH film and the «ion gating» effect of Ca 2+ ions was analyzed in the frame of the model of a disk type electrode surface with active sites. The interaction of two antitumoral drugs, doxorubicin (+1) and mitoxantrone (+2) with the modified electrode was investigated using the same model. Both drugs exert an «ion gating» effect similar to Ca 2+ ions due to the electrostatic interaction of the positively charged drug with the ionized COO-groups of the GSH film. The results also show that doxorubicin interacts in a first step with the negatively charged surface of the film leading to a deprotonated species, which may penetrate the GSH film and undergo electron transfer at the electrode surface. Therefore it may be used as positively charged electroactive probe, in the potential range 0/À800 mV vs. SCE. The possible involvement of redox process of molecular oxygen in the reduction of doxorubicin at electrodes modified by SAM's terminated by hydrophilic groups is also suggested. The PM3 semiempirical MO-modeling accounts reasonably for the experimental features outlined by cyclic voltammetry and impedance results.

Electrochimica Acta, 2013

Self-assembled layers of 4,4-thio-bis-benzene-thiolate spontaneously adsorbed on p-doped GaAs(1 1... more Self-assembled layers of 4,4-thio-bis-benzene-thiolate spontaneously adsorbed on p-doped GaAs(1 1 1)A and GaAs(1 1 1)B electrodes were examined by EIS, XPS, and AFM investigations. XPS data provide evidence that (i) both As and Ga atoms are involved in the thiolate formation no matter which one is prevailing on the semiconducting surface and (ii) only one of the two thiol groups participates in the chemisorption bond. EIS and AFM results point to a more stable thiolate layer formed on the Asterminated surface than that formed on the Ga-terminated surface due to stronger self-assembling effects developed between the adsorbed species.

Electrochimica Acta, 2012

The effects of the self-assembled 4,4-thio-bis-benzenethiolate protected gold nanoclusters onto a... more The effects of the self-assembled 4,4-thio-bis-benzenethiolate protected gold nanoclusters onto a p-GaAs (1 0 0) electrode were examined by AFM, XPS, SHG and EIS investigations. The AFM and XPS results revealed a well-ordered overlayer exhibiting a bi-modal highly correlated fractal behavior which, however, cannot fully protect the semiconducting surface against the oxidation in air. The EIS data pointed out the influence exerted by the gold-monolayer protected clusters (Au-MPCs) over the charging/discharging processes observed at p-GaAs (1 0 0) electrode. Although the applied potential is varied linearly, the potential drop within the semiconductor space charge region as well as that across the Au-MPCs layer undergoes stepped changes supposed to result in the discrete charging of the Au-MPCs. These effects point to an electronic equilibrium between the Au-MPCs and the semiconducting substrate. Fermi level pinning and enhancement of the SHG response in the potential range where the surface/interface states in the semiconductor band gap become electrically active bring further proof in this respect.

Cell and Tissue Research, 2002

Bioelectrochemistry, 2008

The redox behaviour of the anti-cancer drug mitoxantrone was investigated in aprotic media (dimet... more The redox behaviour of the anti-cancer drug mitoxantrone was investigated in aprotic media (dimethylsulfoxide-DMSO) by coupled electrochemical and spectral EPR and UV/VIS absorption techniques. The cyclic voltammetry study with stationary and rotating disc electrode (RDE) of the reductive pathway of mitoxantrone points to two-electron transfers and evidences as intermediate species the anion radical, the dianion and the corresponding protonated species. EPR and optical spectra registered during the electrochemical reduction allow the identification of these species and suggest the possibility of back oxidation of the drug by electron transfer to molecular oxygen. The possibility of reductive activation of molecular oxygen by the intermediate species in the redox processes of mitoxantrone is discussed in connection with the cardiotoxicity of the drug. Gas phase and solvent-dependent AM1 and PM3 semiempirical MO calculations allow a rationalization of the experimental results regarding the reactivity in redox processes.

Acta Chimica Slovenica, 2020

Investigation of the interaction of quinizarin (Q), an analogue of the core unit of different ant... more Investigation of the interaction of quinizarin (Q), an analogue of the core unit of different anticancer drugs, with anionic SDS micelles has been performed by absorption and conductance measurements in 0.1 M phosphate buffer, pH 7.4 and over the temperature range of 298.15-323.15 K. The values of binding constant (Kb), partition coefficient (Kx) and the corresponding thermodynamic parameters (Gibbs free energy, enthalpy, entropy) for the binding and distribution of quinizarin between the bulk aqueous solution and surfactant micelles have been determined and discussed in terms of possible intermolecular interactions. Values of critical micelle concentration (CMC) and degree of ionization (?) for SDS in the absence and the presence of quinizarin have been evaluated from conductometric study. Comparing the absorption spectra of quinizarin in SDS micelles with the spectra in different solvents revealed that quinizarin molecules are located in the hydrophilic region of SDS micelles. The...

Revue Roumaine De Chimie, 2005

The interaction between the antitumor drug mitoxantrone and double stranded DNA in phosphate buff... more The interaction between the antitumor drug mitoxantrone and double stranded DNA in phosphate buffer solution was investigated by cyclic and linear voltammetry as well as by UV-VIS absorption spectroscopy. The results suggest that the diffusion coefficients of mitoxantrone determined by cyclic and linear voltammetry with stationary and rotating disc electrode decreased in the presence of DNA. The binding constants and binding site size of mitoxantrone to DNA were obtained by a titration curve and linear and nonlinear regression analysis of the data. The results indicate that mitoxantrone binds to calf thymus DNA with a high affinity and the electrochemical methods provide a useful complement to spectral methods in the characterization of the drug-DNA binding equilibria.

Acta chimica Slovenica, 2020

Binding of antitumor drug actinomycin D with double stranded DNA has been investigated by fluores... more Binding of antitumor drug actinomycin D with double stranded DNA has been investigated by fluorescence spectroscopy. The emission changes accompanying the interaction of the drug with DNA were rationalized in terms of the Scatchard and Schwarz models, in order to calculate binding parameters: binding constant, the number of binding sites and the cooperativity parameter. Scatchard plots indicate three distinct processes: two cooperative processes and a non-cooperative process. The results are discussed in comparison with those obtained by absorption spectroscopy.

Revista de Chimie

The location of mitoxantrone molecule in micelles formed by bile salts (sodium taurocholate (NaTC... more The location of mitoxantrone molecule in micelles formed by bile salts (sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC)) and sodium dodecyl sulfate (SDS) have been investigated by electron spin resonance (ESR) spectroscopy, using three doxylstearic acid probes (5-, 12- and 16-doxylstearic acid abbreviated as 5-DSA, 12-DSA and 16-DSA). The analysis of ESR parameters of these spin probes evidenced slower dynamics induced by mitoxantrone that vary in the following order: 12-DSA > 5-DSA > 16-DSA for both bile salts micelles and 5-DSA > 12-DSA > 16-DSA for SDS micelles. The ESR parameters are slightly sensitive to variation of pH. These results indicate that the spin probes target different regions in these aggregates. Keywords: mitoxantrone, bile salts micelles, SDS micelles, ESR spectroscopy

ECS Meeting Abstracts

Electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and atomic f... more Electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) have been used to investigate the effects of the sodium dodecyl sulfate (SDS) at the electrified p-GaAs(100) / H2SO4 interface. The analysis of the EIS data revealed that the surfactant adsorption brings about a pronounced decrease of the capacitive contributions of the semiconductor surface state (Fig. 1 B) accompanied by a shift to more positive potentials of the Mott-Schottky plot (Fig. 1 A). According to the XPS (Fig 1 C) and AFM data, SDS forms a well-ordered protective overlayer on p-GaAs(100) which prevents the surface oxidation in air. However, the field-dipole interactions acting under the applied potential control become preponderant at the electrified GaAs / solution interface yielding distinct effects at the end of the direct and forward potential scans as seen in Fig 1 C. These results suggest that SDS interaction with GaAs substrate might be an efficie...

Journal of The Electrochemical Society

Journal of Surfactants and Detergents

Molecules (Basel, Switzerland), Jan 5, 2018

A wide range of hybrid biomaterials has been designed in order to sustain bioremediation processe... more A wide range of hybrid biomaterials has been designed in order to sustain bioremediation processes by associating sol-gel SiO₂ matrices with various biologically active compounds (enzymes, antibodies). SiO₂ is a widespread, chemically stable and non-toxic material; thus, the immobilization of enzymes on silica may lead to improving the efficiency of biocatalysts in terms of endurance and economic costs. Our present work explores the potential of different hybrid morphologies, based on hollow tubes and solid spheres of amorphous SiO₂, for enzyme immobilization and the development of competitive biocatalysts. The synthesis protocol and structural characterization of spherical and tubular SiO₂ obtained by the sol gel method were fully investigated in connection with the subsequent immobilization of lipase from . The immobilization is conducted at pH 6, lower than the isoelectric point of lipase and higher than the isoelectric point of silica, which is meant to sustain the physical inte...

Waste and Biomass Valorization

AimOne of the main by-products resulted from the biodiesel industry is represented by waste glyce... more AimOne of the main by-products resulted from the biodiesel industry is represented by waste glycerol which is known as a mixture between glycerol and various salts, soaps, fatty acids and other chemical compounds. This composition makes it very difficult to be used in other domains and the large amounts in which it is obtained raise storage and environmental problems. Within this framework, its bioconversion to other products by several microorganisms could be regarded as a most valuable and convenient alternative. In this work, the transformation of waste glycerol to carotenoid compounds, namely phytoene and β-carotene by several wild strains of halophilic microorganisms isolated from a saline lake is presented.MethodsThe structures of the investigated carotenes were analysed by FT-IR and UV–Vis spectrometry while differential scanning microcalorimetry (μDSC) evaluated the thermal behaviour of the methanol solution of the pigments obtained from microbial cultures. The growth of microorganisms was estimated by measuring optical density at 660 nm using a BMG LABTECH FLUOstar Omega microplate reader and carotenes were extracted with methanol.Results and ConclusionsThe data recorded until now revealed that the presence of waste glycerol from several sources in the composition of culture medium resulted in growing of phytoene content. These compounds are known as precursors for obtaining other carotenoid compounds either in natural synthesis or in chemical industry. In case of β-carotene, the preliminary results revealed a slow decrease of its content in the presence of waste glycerol as a major growth substrate. The presence of waste glycerol in culture medium leads to thermograms for pigments’ methanol solutions with larger thermal effects than those obtained in the absence of waste glycerol. The absorption spectra of the pigments isolated form strains LD2 and LN1-10 display a typical shape for carotenoids in the 400–500 nm wavelength range and for phytoene in the 250–300 nm wavelength range. The absorption spectra of the strains LN4-1, LC37 and LN2-5 indicate the presence of phytoene and the absence of carotenoids.