1,721,010 research outputs found
Thermodynamic study of Cd(II) complex formation with tripodal N-donor ligands in DMSO
No full textThe complex formation of Cd(II) with N-donor ligands in dimethylsulfoxide (DMSO) is investigated by means of potentiometry and titration calorimetry. The ligands considered in this work are tripodal polyamines and polypyridines: 2,2',2 ''-triaminotriethylamine (TREN), tris (2-( methylamino) ethyl) amine (Me(3)TREN), tris(2-(dimethylamino) ethyl) amine (Me(6)TREN), tris[(2-pyridyl) methyl] amine (TPA) and 6,6'-bis-[bis-(2-pyridylmethyl)aminomethyl]-2,2'-bipyridine (BTPA). These ligands are characterized by a systematic modification of the donor groups to relate their structure to the thermodynamics of the complexes formed. The TREN and Me(3)TREN ligands form highly stable species. The stability of the complex formed with the fully methylated Me(6)TREN is much lower than with other polyamines and the enthalpic and entropic terms suggest an incomplete coordination to the metal ion. In general, the TPA ligand forms complexes less stable than TREN and Me(3)TREN as a result of the combination of higher structural rigidity of TPA and lower basicity of pyridine moiety with respect to primary and secondary amines. Pyridine-containing ligands display, in general, a less unfavorable formation entropy than tripodal polyamines here considered. In particular, TPA forms a more stable 1: 1 species with respect to Me(6)TREN due to the entropic term, being the enthalpy less negative. The ligand BTPA is able to form only a monometallic complex, where the metal ion is likely to be encapsulated as indicated by the obtained thermodynamic parameters
Molecular interpretation of pharmaceuticals' adsorption on carbon nanomaterials: Theory meets experiments
Full text linkThe ability of carbon-based nanomaterials (CNM) to interact with a variety of pharmaceutical drugs can be exploited in many applications. In particular, they have been studied both as carriers for in vivo drug delivery and as sorbents for the treatment of water polluted by pharmaceuticals. In recent years, the large number of experimental studies was also assisted by computational work as a tool to provide understanding at molecular level of structural and thermodynamic aspects of adsorption processes. Quantum mechanical methods, especially based on density functional theory (DFT) and classical molecular dynamics (MD) simulations were mainly applied to study adsorption/release of various drugs. This review aims to compare results obtained by theory and experiments, focusing on the adsorption of three classes of compounds: (i) simple organic model molecules; (ii) antimicrobials; (iii) cytostatics. Generally, a good agreement between experimental data (e.g. energies of adsorption, spectroscopic properties, adsorption isotherms, type of interactions, emerged from this review) and theoretical results can be reached, provided that a selection of the correct level of theory is performed. Computational studies are shown to be a valuable tool for investigating such systems and ultimately provide useful insights to guide CNMs materials development and design
Intercalation Ability of Novel Monofunctional Platinum Anticancer Drugs: A Key Step in Their Biological Action
Full text linkPhenanthriplatin (PtPPH) is a monovalent platinum(II)-based complex with a large cytotoxicity against cancer cells. Although the aqua-activated drug has been assumed to be the precursor for DNA damage, it is still under debate whether the way in which that metallodrug attacks to DNA is dominated by a direct binding to a guanine base or rather by an intercalated intermediate product. Aiming to capture the mechanism of action of PtPPH, the present contribution used theoretical tools to systematically assess the sequence of all possible mechanisms on drug activation and reactivity, for example, hydrolysis, intercalation, and covalent damage to DNA. Ab initio quantum mechanical (QM) methods, hybrid QM/QM′ schemes, and independent gradient model approaches are implemented in an unbiased protocol. The performed simulations show that the cascade of reactions is articulated in three well-defined stages: (i) an early and fast intercalation of the complex between the DNA bases, (ii) a subsequent hydrolysis reaction that leads to the aqua-activated form, and (iii) a final formation of the covalent bond between PtPPH and DNA at a guanine site. The permanent damage to DNA is consequently driven by that latter bond to DNA but with a simultaneous π-πintercalation of the phenanthridine into nucleobases. The impact of the DNA sequence and the lateral backbone was also discussed to provide a more complete picture of the forces that anchor the drug into the double helix
Mechanism and thermodynamics of adsorption of diclofenac on graphene-based nanomaterials
No full text: Alpha-defensins block the early steps of HIV-1 infection: interference with the binding of gp120 to CD4
No full textThermodynamics of complex formation of silver(I) with substituted pyridines and cyclic amines in non-aqueous solvents
Full text linkThe understanding of the thermodynamic stability and speciation of metal complexes in solution requires access to their enthalpy and entropy of formation. In this work, we specifically focus our investigation on the complexation process of silver(I) ion in acetonitrile (AN) with substituted mono pyridines and cyclic monoamines. The aim of this study is to provide reliable thermodynamic data to obtain insights on metal complex formation, focusing on ligands donor properties and solvation effects. Carefully designed potentiometric and calorimetric experiments allowed to define the species present at different ligand/metal ratios and to obtain the complex formation constants and enthalpies. In general, the enthalpy terms associated with the complex formation are highly exothermic, while the entropy values are always unfavorable. The formation constants of AgLj species for the ligands investigated in AN are compared with those previously obtained in dimethyl sulfoxide (DMSO) and water. The trends in stability constants and enthalpy values are discussed in relation to the pKa data available in the different solvents. Higher pKa values correspond to greater ligand basicity and result in more stable and more enthalpy stabilized complexes
Thermodynamics of lanthanide(III) complexation in non-aqueous solvents
No full textLanthanide(III) coordination compounds are employed in several fundamental and applied research fields such as organic synthesis, bioinorganic chemistry, optical and magnetic imaging, catalysis, environment and geochemistry. All these applications have been favoured by the recent developments of a detailed knowledge of fundamental properties (electronic, spectroscopic, thermodynamic, magnetic, structural) of elements, ions and their compounds.
Ln(3+) are hard acids and present strong affinity for charged ligands or neutral O- and N-donors, as indicated by a wide number of papers concerning formation of their complexes in solution. These studies allowed one to gain information on the complex stabilities, the metal-ion selectivity of a given ligand, the influence of the solvent on the nature and stability of the species in solution. Most of the above studies deal with aqueous solutions, while studies in non-aqueous media are less common. Despite more limited, investigations in aprotic solvents are particularly interesting as they allow one to extend the knowledge on the coordination chemistry of lanthanide(III), disclosing metal-ligand interactions not easily accessible in water due to ligand protonation equilibria, Ln(III) hydrolysis and strong hydration of the cations, which hampers interactions with neutral donors.
This review analyzes a wide number of thermodynamic studies concerning formation of lanthanide(III) complexes with selected, simple neutral N-donors (amines, pyridines), O-donors (crown ethers, aza-crown ethers and cryptands) and charged inorganic ligands (halides, thiocyanate, nitrate, perchlorate, triflate) in non-aqueous solvents. The main aim of the review is to face the basic question of what are the factors governing the complex stability and selectivity within the lanthanide series and how are they influenced by different coordinating media. Fundamental properties of Ln ions, such as ionic radii, common oxidation states and structural aspects of their solvates are as well analyzed.
Several points emerged from a critical analysis of the papers reviewed:
i) Ln(3+) salts used in thermodynamic studies in poor coordinating solvents are often not completely dissociated and, in this case, the data obtained reflect multiple simultaneous equilibria in solution. Comparisons between thermodynamic results in poor and high solvating media must be therefore regarded with caution as they may refer to different reacting metal-species, hence, to different metal-ligand equilibria.
ii) High solvating aprotic media can be considered as ideal for thermodynamic studies since lanthanide(III) is only present as Ln(solv)(n)(3+) species. However, in this case, the strong salvation of Ln(3+) ions hinders complex formations with weak or relatively weak donors.
iii) Salvation of lanthanide(III) cations in non-aqueous solutions is generally a major factor in determining the complex stabilities which, for the different kinds of ligands examined, follow the general trend: PC > AN > MeOH > DMF> DMSO
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Lanthanides(III) and Silver(I) complex formation with triamines in DMSO: The effect of ligand cyclization
No full textThe thermodynamic functions of complexation between lanthanides(III) and 1,4,7-triazacyclononane (TACN) together with those of some of the above metal ions with the TACN-linear-analogue,N′-methyl-N′′-(2-(methylamino)ethyl)ethane-1,2-diamine (DMDIEN), are determined in dimethylsulphoxide (DMSO). The study aims to investigate the effect of ligand cyclization and methylation on the stability and nature of the complexes in non-aqueous solution. The stability constants of Ln3+/TACN complexes were obtained by means of potentiometric titrations at 298 K and I = 0.1 mol dm−3, using Ag+ as competitive ion. Ln3+-ligand complexation enthalpies were obtained by calorimetric titrations, extended also to the silver(I)-TACN system, whose thermodynamic data in DMSO are not published. Calorimetry was applied also to obtain simultaneously enthalpy values and stability constants of the Ln3+/DMDIEN systems, for which the difference in stabilities between Ag+ and Ln3+-DMDIEN complexes did not allow the competitive potentiometric method to work. The Ag+ ion forms mono- and poly-nuclear AgiLji+ complexes with TACN (i:j = 1:1, 1:2 and 2:3), whereas all lanthanide ions form with TACN both 1:1 complexes and 1:2, from Tb3+ to Lu3+. Only 1:1 species were detected for the Ln3+-DMDIEN systems. The 1:1 TACN complexes show an extra stability both with respect to those of DIEN and those of the linear analogue DMDIEN. Negative enthalpies favor the formation of all complexes, while entropies partially counteract the complexation. The results for TACN systems are compared with those here obtained for DMDIEN and for DIEN, reported previously. Density Functional Theory (DFT) calculations, carried out in presence of DMSO introduced as implicit solvent, were performed on some of the Ln3+ complexes with TACN and DIEN to provide insights into the structures and related solvation energies of the species formed in solution. Calculations support a tri-dentate coordination of both ligands. The effects of ligand methylation and cyclization on the stability constants, enthalpies and entropies of complex formation are discussed. The thermodynamic and DFT integrated data indicate that the trends of the thermodynamic functions concerning the complexation reactions of lanthanide ions in DMSO depend on the different solvation of the complexes
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