Ligand exchange method is introduced as an alternative to Job’s and mole ratio methods for studying the stoichiometry of relatively weak metal complexes in solutions. The method involves adding ...varying amounts of a ligand (L) to an excess constant amount of a colored complex (MX) with appropriate stability and molar absorptivity. The absorbance of each solution is measured at the λ
max
of the initial complex, MX, and plotted against the concentration of the studied ligand, L. If the newly formed complex ML does not absorb at the λ
max
of the initial complex, then attenuation of the absorbance of the initial complex on adding varying quantities of the investigational ligand gives an inverse calibration line that intersects with the calibration curve of initial complex at a given point. If a line parallel to the ordinate is drawn from this point to the x-axis, the ratio of the two parts of the x-axis to the left and to the right (α/β) gives the metal to ligand molar ratio in the complex formed, ML. The new method has been applied to the study of the composition of iron (III) complexes with three bisphosphonate drugs: alendronate, etidronate, and ibandronate. The mole ratio was found to be 1:1 with the three investigated bisphosphonates and results were further confirmed by Job’s and mole ratio methods. The ligand exchange method is simpler, quicker, easier to perform and more accurate than Job’s and mole ratio methods for studying weak and relatively weak complexes.
The interaction of 3-amino-5,5′-dimethylhydantoin with nickel and zinc ions was investigated at different conditions by means of UV–Vis, FTIR spectroscopy and electrochemical methods as well as DFT ...quantum chemical calculations. Through calculated DFT frequencies and experimental FTIR spectra of the complexes the correlation analysis has been made. NBO analysis of the ligand and complexes provides the information about intramolecular resonance stabilization energy and charge transfer between ligand and metal ions. First derivative UV–Vis spectra were done in order to resolve the π→π* and n→π* carbonyl electron transitions of the ligand and complexes. We have shown that complexes with 1:2 stoichiometry were formed at pH closed to physiological. The stability constant was determined for 3-amino-5,5′-dimethylhydantoin (L) and Ni(II) ions using differential pulse polarography data. The existence of one complex (n¯ = 2) is proved in the presence of high ligand concentration (CL = 2 × 10−3 ÷ 6 × 10−3 mol L−1) and the values of the total constant is: lgβNI(II)-L=9.5±0.4 (I = 0.1). The UV–Vis spectroscopy and DFT calculations confirm the stoichiometry of the complexes. The results of the study are useful for incorporation with chemical equilibrium models for evaluation of the speciation and the reactions of metals with hydantoin derivatives in order to develop methods for determination of these metals in different milieu.
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•New complexes of metal (Ni2+; Zn2+): 3-amino-5,5-dimethylhydantoin = 1:2 were synthesized.•The stoichiometry of the compounds were confirmed by spectral methods and voltammetry.•Quantum chemical calculations were applied.•The proposed structures are essential in regard to biochemical properties of studied compounds.
We determined the binding constants for transition metal complexes of Cu2+, Co2+, Fe2+, Ni2+, and Zn2+ ions formed with the ligand picolinaldehyde-2-pyridylhydrazone (PapyH). Stoichiometry 2:1 ...(ligand: metal) was confirmed by single-crystal X-ray diffraction finding a propeller-like structure of the Fe(Papy)2 compound. PapyH and the metal complexes were characterized by 1H NMR and UV-Vis spectroscopy respectively. The Cu2+ complex exhibited the highest stability constant, which was confirmed by competitive reaction of different metal ions with the ligand PapyH.
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•Synthesis of novel PapyH based metal complexes of Cu2+, Co2+, Fe2+, Ni2+ and Zn2+.•The formation of all metal complexes occurs in a ratio ligand: metal ion of 2:1.•Cu2+ exhibits the highest binding constant among the metal ions tested with K = 4.91 × 1010 M−2.•X-ray crystal structure of the Fe(Papy)2 complex was determined.
Herein, we determined the binding constants for transition metal complexes of Cu2+, Co2+, Fe2+, Ni2+, and Zn2+ ions formed with the ligand picolinaldehyde-2-pyridylhydrazone (PapyH) using the Benesi-Hildebrand method. Stoichiometry 2:1 (ligand: metal) was previously determined by the Job’s method and confirmed by single-crystal X-ray diffraction finding a propeller-like structure of the Fe(Papy)2 compound. PapyH and the metal complexes were characterized by 1H NMR and UV-Vis spectroscopy, respectively. The Cu2+ complex exhibited the highest stability constant, which was confirmed by competitive reaction of different metal ions with the ligand PapyH.
A sensitive and environmentally benign spectrometric method was developed for quantifying Meprobamate (MEP). The analyzed MEP was derivatized into a colored complex and determined ...spectrometrically. The colorimetric analytical parameters were optimized and validated. Low limit of detection (LOD) was achieved down to 1.88×10-6 mol/l while the limit of quantification (LOQ) was extended over the range of 1.97×10-6 - 1.35×10-3 mol/l. The high precision has been denoted by the 1.54% value of the coefficient of variation. The recovery was 96.07%, while the RSD (n=3) was 1.05 - 1.19%. The apparent molar absorptivity (Æ) obtained within 1154.7 - 1691.9 L.mol-1.cm-1. The outcomes have signified the high sensitivity of the technique. Furthermore, the avoidance of any traditional sample preparation steps prior to the analysis make the method an excellent environmental approach. There were no analytical interferences with the common composites. The method has been successfully verified for the quantification of MEP content in bulk pharmaceutical matrix and can be applied to determine other environmentally toxic carbamates.
Paclitaxel as one of the most effective anticancer drugs has low aqueous solubility. This inevitably reveals its commercial formulation in Cremophor EL®/ethanol mixture. However, this formulation ...leads to several severe side effects such as hypersensitivity reactions, neurotoxicity and nephrotoxicity. Inclusion complexation has been introduced as a practical approach in increasing paclitaxel aqueous solubility. To this end, a hybrid nanocarrier system based on hyperbranched polyglycerol and β-cyclodextrin is designed with key components uniquely structured at nanoscale and evaluated according to medical requirements. Paclitaxel is included in the hydrophobic cavity of cyclodextrin as guest and was examined using isothermal titration calorimetry to determine the thermodynamic parameters of complexation. It is shown that the inclusion complex process between paclitaxel and β-CD-g-PG is entropy driven. The results revealed a significant enhancement in paclitaxel aqueous solubility, which is a key challenge in current cancer therapy.
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•Inclusion complexation of anticancer drug, paclitaxel, and modified β-cyclodextrin is investigated.•Thermodynamic parameters are determined using isothermal titration calorimetry.•The inclusion complex process is exothermic and the stoichiometry of complex is 1:3.•The system is introduced as a nanomedicine with a higher aqueous solubility than conventional systems.
In this study, a green and high yielding synthesis of novel pyrazoline‐containing Schiff bases via a one‐pot pseudo five‐component condensation reaction under catalyst‐free conditions in EtOH at room ...temperature is described. Initially, the reaction of 1,1‐bis(methylthio)‐2‐nitroethylene (BMTNE), with NH2NH2.H2O is used for situ preparation of 1,1‐dihydrazino‐2‐nitroethylene (DHNE). Then, wide varieties of aldehydes are added to the mixture to afford the desired products good to excellent yields. This synthetic route is presented with several unique merits such as simplicity in operation and workup, readily presented starting materials, and high functional group tolerance. Additionally, the stoichiometric complex formation of these Schiff bases as ligand (L) with various metal ions Mn(OAc)2, Cu(OAc)2 and Zn(OAc)2 in general molecular formula ML is examined via Job's method. Subsequently, theoretical analysis of the product is accomplished using density functional theory (DFT) calculations. According to the frontier molecular orbital (FMO) analysis, it is found that the aryl group linked to the imine bond contributes as an electron donor in the ligand–metal complex.
A green synthesis of novel Schiff bases via a one‐pot pseudo five‐component condensation reaction of BMTNE, NH2NH2 and aldehyde in EtOH at room temperature is described. Complex formation of this Schiff bases with metal ions Mn(OAc)2, Cu(OAc)2 and Zn(OAc)2 is examined via Job's method, FMO analysis and spectroscopic data.
The dissociation constants of Adefovir ({2-(6-amino-9H-purine-9-l)ethoximethyl}phosphoric acid) used in the treatment of hepatitis B and Cidofovir ({2-(6-amino-9H-purine-9-l)ethoximethyl}phosphoric ...acid), used in the treatment of cytomegalovirus retinitis in AIDS patients, together with the stability constants of its Cu2+, Ni2+, Zn2+, Co2+, Ca2+, and Mg2+ complexes were studied by potentiometric titration. Adefovir and Cidofovir were abbreviated to PMEA and HPMPC. All measurements were obtained under two sets of conditions: at 298K and ionic strength (I) of 0.1moldm−3 (NaCl) and at 310K and I of 0.16moldm−3 (NaCl), corresponding to the conditions of human blood. Equilibrium constants in aqueous solution were calculated using the program SUPERQUAD. Also, solvent effects on the equilibrium constants of the ligands were examined. Moreover, all coordination studies were carried out with the ligand/metal molar ratios of 1:1. This ligand/metal stoichiometric ratio was spectrometrically determined using Job's method.
Abstract
Metal ions, especially copper, zinc and iron, play an important role in the neurodegeneration process because they can affect protein misfolding, leading to the formation of the amyloid ...deposits and oxidative stress leading to reactive oxygen species (ROS). Here we report the synthesis and evaluation as antioxidant and metal chelating agents of 3,4-dihydroxybenzoic acid derivatives. Synthesized compounds were tested by the 2,2-diphenyl-2-picrylhydrazyl (DPPH) method showing a radical scavenging ability (EC50 = 0.093-0.118 μM) higher than Trolox used as reference. Furthermore, these compounds were able to bind both iron and copper, especially the iron (III), by the formation of hexa-coordinated complexes. Synthesized compounds were tested to evaluate their ability to inhibit acetyl- and butyryl-cholinesterase; the obtained results have demonstrated that they are selective inhibitors of AChE (Ki = 1.5-18.9 μM) and result weakly active versus butyrylcholinesterase (BChE).
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Chromium pyridine di-carboxylate complexes are synthesized from Chromium (III) with pyridine 2, 6- dicarboxylic acid, pyridine 2, 3 and 2, 5- dicarboxylic acids. Chromium forms colored complexes. ...Chromium (III) forms a violate complex with pyridine 2, 6- dicarboxylic acid and purple violate complex with pyridine 2, 3 and 2, 5- dicarboxylic acids. The job’s method indicates metal ligand ratio to be 1:2. The interpretation of UV-VIS spectra indicates octahedral geometry and IR spectra give clue about the presence of Metal – Nitrogen and Metal- Oxygen bond. We have also made an effort to compare the spectrum of all the three complexes.
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