2-Nitro-1,4-diaminobenzene-Functionalized Poly(vinyl amine)s as Water-Soluble UV-Vis-Sensitive pH Sensors
- ملخص البحث
Nucleophilic aromatic substitution of 2,6-O-dimethyl-β-cyclodextrin (β-DMCD)-complexed 4-fluoro-3-nitroaniline derivatives with poly(vinyl amine) (PVAm) in water results in 2-nitro-1,4-benzenediamine-functionalized water-soluble PVAms in one step. The 2-nitro-1,4-benzenediamine moiety linked to the polymer is solvatochromic and undergoes protonation and deprotonation as function of pH as shown by UV-Vis spectroscopy. The occurrence of an isosbestic point in the UV-Vis spectrum is suitable to directly determine the pKa value using the Henderson-Hasselbalch equation. The influence of the methyl group substitution of the polymer and the 2-nitro-1,4-benzenediamine moiety on the pKa is discussed.
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- الكلمات المفتاحية
cyclodextrins,polyamines,poly(vinyl amine),UV-Vis spectroscopy
A comparative spectroelectrochemical study of the redox electrochemistry of nitroanilines
- ملخص البحث
The oxidative and reductive electrochemistry of the three isomeric nitroanilines has been studied in neutral (0.1 mol L−1 KClO4) and acidic (0.1 mol L−1 HClO4) aqueous electrolyte solutions by cyclic voltammetry and surface enhanced Raman spectroscopy (SERS). The cyclic voltammograms recorded for o- and p-nitroanilines with a gold electrode in acidic solution, scanning toward negative potentials, revealed formation of phenylenediamine not observed in neutral solution. Similar behavior of nitroanilines and phenylenediamines was observed on gold and platinum electrodes. An oxygen–gold adsorbate stretching mode was detected between 400 and 430 cm−1 in the SER-spectra of the three isomeric nitroanilines in both electrolyte solutions at positive electrode potentials, implying perpendicular adsorption via the nitro group.
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- الكلمات المفتاحية
Spectroelectrochemistry,Nitroanilines,Phenylenediamines,Electroreduction
A spectroelectrochemical study of the electrosorption of 4-isopropylsulfanylmethyl-1,2,3-triazole on gold
- ملخص البحث
The electrosorption of 4-isopropylsulfanylmethyl-1,2,3-triazole (ISMT) on a polycrystalline gold electrode has been studied with cyclic voltammetry and surface enhanced Raman spectroscopy (SERS). Vibrational wavenumbers were calculated for the conceivable tautomers with density function theory (DFT) at the B3LYP level using the 6-31G* basis set. The data obtained from vibrational frequency calculations are used to assign vibrational bands obtained in infrared and Raman spectroscopy as well as in surface enhanced Raman spectroscopy of the molecule adsorbed on a roughened gold electrode surface. Results imply a gold–sulfur interaction with ISMT adsorbed intact (i.e. without C–S bond cleavage) onto the gold surface from neutral solution. Beyond a gold–sulfur stretching mode, this suggestion is supported by significantly enhanced internal modes of the methyl groups in the isopropyl substituent and an almost complete lack of shift of band positions of the triazole ring itself being expected in case of a gold–nitrogen interaction. With an acidic electrolyte solution, a gold–sulfur vibrational mode typical of a thiolate-like adsorbate is found, this indicates dissociative adsorption.
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- الكلمات المفتاحية
Spectroelectrochemistry; Substituted triazole; Electrosorption; Surface enhanced Raman spectroscopy; Surfactant
Cordination Compound of Dimethyltin(IV) with N,N,N’N’-Tetraethylethylenediamine: Speciation and Theoretical approach
- ملخص البحث
The formation equilibria of the dimethyltin(IV) complexes with of N,N,N’,N’-tetraethylethylenediamine (Et4en) in solution were investigated. The stoichiometry and stability constants of the complexes formed in solution phase were determined at different temperatures (15 oC – 35 oC) and in solutions of dioxane-water mixtures of different compositions (15% - 62.5%). The accepted model is composed of the 110, 111, 11-1 and 11-2 species. The thermodynamic parameters H and S associated with the protonation of N,N,N`,N`-tetraethylethylendiamine (Et4en) and its complex formation with the dimethyltin(IV) species were determined. The complex formation reaction is exothermic. The equilibrium constant for the displacement of N,N,N’,N’-tetraethylethylenediamine coordinated to dimethyltin(IV) by some selected DNA constituents was calculated. The Keq values clearly indicate the ability of DNA to displace the coordinated Et4en from its dimethyltin(IV) complex. The nucleotides IMP and GMP have the highest values. The DFT/B3LYP method was used for geometric optimization of the ligand and the complex using the Gaussian 09 program. Also the vibrational frequencies of the ligands and complexes were computed for the optimized geometries. The results shows that there is no imaginary frequencies as found in the calculated vibrational frequencies. The binding energies of the dimethyltin(IV) complexes were calculated. All calculated binding energy values are negative.
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- الكلمات المفتاحية
Dimethyltin(IV), N,N,N’,N’-tetraethylethylenediamine, stability constants, DFT calculation
Synthesis and DFT Calculations of Dinuclear complex of Co2+, Ni2+ and Cu2+ with macrocyclic Schiff base Ligands
- ملخص البحث
The 20-, 34- and 36-membered macrocyclic of bis (dithiodimine) Schiff base ligands, BisN,N’(dithiocarbonyl) terephthliden (L1), Bis-N,N’[1,3(o-aminophenylthio)-propane] terephthylidene (L2) and Bis-N,N-[1,4(o-amino phenylthio)-butane] terephthylidene (L3), have been prepared by a (2+2) condensation of terephthaldehyde with dithiooxamide or 1,3-bis-(o-aminophnylthio) propane,or1,4-bis-(o-aminophenylethio)-butane. Air stable dinuclear complexes of Co2+, Ni2+ and Cu2+ were obtained from reaction of metal salts with L1, L2 and L3 in tetrahydrofuran. Ligands consist of two S2N2 donor sites coordinated with the metal ions. Also, adducts of the cobalt complex with 1,4-phenelyene diamine was also presented. CHN elemental analysis, metal content, molar conductivity,magnetic measurements, proton nuclear magnetic resonance, UV-visible and infrared spectral studies have characterized the complexes and adducts. In addition to this, the DFT i.e. Density Functional Theoretical calculations has been used for supporting experimental data. This process used B3LYP functional method. It is the method which has been introduced due to Yang, Parr and Lee. This method is comprised of 3-parameter functional because of the presence of Axel Becke. It further incorporates the basis set of Los Alamos National Laboratory 2 double-zeta (LANL2DZ). Furthermore, the calculation associated with the molecule’s vibrational frequencies was calculated with the help of optimized geometry. Tetrahedral and square planar geometry around Co2+,Ni2+ and Cu2+have been deduced on the basis of magnetic and spectra studies.
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- الكلمات المفتاحية
Dinuclear complexes, Schiff base; macrocyclicbis (dithiodimine); density functional theory (DFT)
Reactions of Pd2+ and Pt2+ with pyrrolidinedithio carbamate and cystine ligands: synthesis and DFT calculations
- ملخص البحث
Mono- and dinuclear complexes of the type M(cys), M(PTD)2 and M2(PTD)4, where M=Pd (II) or Pt(II), cys=(SCH 2CH (NH 2)COOH)2 and PTD=pyrrolidine thiocarbanoyl disulfide, have been prepared through oxidative addition reaction. They are characterized by microanalyses of metal content, molar conductance, magnetic measurements, infrared and UV–visible spectral studies. The experimental infrared data are supported by density functional theory (DFT) calculations using the B3LYP level of theory and LANL2DZ basis set. The vibrational frequencies of the molecules were computed using the optimized geometry obtained from the DFT calculations. The diamagnetic nature, the electronic spectral studies and calculated geometries suggest a distorted square planner environment around Pd(II) and Pt(II) complexes.
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- الكلمات المفتاحية
DFT (density functional theory),cystine,pyrrolidine dithiocarbamate,mono- and dinuclear complexes
The electrosorption of 3-bromo-2-nitrothiophene on gold as studied with surface-enhanced Raman spectroscopy
- ملخص البحث
The electrosorption of 3-bromo-2-nitrothiophene on a polycrystalline gold electrode has been studied with surface-enhanced Raman spectroscopy SERS. Results imply a tilted orientation of the 3-bromo-2-nitrothiophene molecule with a sulfur atom of the thiophene ring and oxygen atoms of the nitro group interacting directly with the gold surface. The UV-Vis spectrum of the 3-bromo-2-nitrothiophene is recorded and its results indicated that the SERS spectra were measured under off-resonance conditions. Cyclic voltammetry measurements of the 3-bromo-2-nitrothiophene were made and the oxidation and reduction potentials of the 3-bromo-2-nitrothiophene at the gold electrode have been reported. The experimental infrared and Raman data are supported by density functional theory (DFT) calculations of 3-bromo-2-nitrothiophene using the B3LYP level of theory and 6-31G (d) basis set. The vibrational frequencies of the molecule were computed using the optimized geometry obtained from the DFT calculations. The calculated spectra are very close to the recorded infrared and Raman of the solid 3-bromo-2-nitrothiophene. No imaginary frequencies are observed in the calculated spectra. Also, DFT calculations are performed to predict and investigate the adsorption behavior of 3-bromo-2-nitrothiophene on the Au surface. In this DFT calculations, the adsorbed 3-bromo-2-nitrothiophene on the gold electrode surfaces was modeled as the metal−molecule complex.
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- الكلمات المفتاحية
,spectroelectrochemistry, 3-bromo-2-nitrothiophene, electrosorption, Raman, DFT
A Comparative Spectroelectrochemical Study of the Redox Electrochemistry of N-(Polyvinylamine)-Substituted-o-Nitroaniline
- ملخص البحث
The electrochemistry and spectroelectrochemistry of polyvinylamine (PVAm) and N-(polyvinylamine)-substituted-o-nitroaniline at a polycrystalline gold electrode in contact with different electrolyte solutions (0.1 M HClO4 and 0.1 M KClO4) have been investigated with cyclic voltammetry and surface enhanced Raman spectroscopy (SERS). Cyclic voltammograms recorded with in acidic electrolyte solution showed formation of N-(polyvinylamine)-o-phenylenediamine in the negative going potential scan; in neutral solution reduction proceeds only to N-(polyvinylamine)-o-phenylhydroxylamine. Vibrational modes are discussed and assigned to monomer-surface interactions of adsorbates at the gold surface in both electrolyte solutions. A variety of adsorption behaviors of these polymers at a gold surface is concluded; they apparently depend on the applied electrode potential, pH of electrolyte (acidic or neutral), type and mole percentage of the o-nitroaniline moiety. The adsorption at the gold surface is strongly enhanced with 12.7 mole% of o-nitroaniline moiety, respectively, at its PVAm-backbone. The direct coordination of these polymers with the gold surface occurred via the nitro-group of the o-nitroaniline moiety and primary amino-groups located at the polymer backbone.
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Synthesis and DFT Study of the Complexation of Schiff Base Derived Curcumin and L-Tyrosine with Al(III), Ag(I), and Pb(II) Metal Ions
- ملخص البحث
The multi-dentate Schiff base ligand (H2L), where H2L=2,2'-(((1,3,5,6)-1-(3-((l1-oxidaneyl)-l5-methyl)-4-hydroxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-diylidene)bis(azaneylylidene))bis(3-(4-hydroxyphenyl)propanoic acid), has been prepared from curcumin and L- Tyrosine amino acid. The synthesized Schiff base ligand (H2L) and the second ligand 1,10-phenanthroline (phen) are used to prepare the new complexes [Al(L)(phen)]Cl, K[Ag(L)(phen)] and [Pb(L)(phen)]. The synthesized compounds are characterized by magnetic susceptibility measurements, micro elemental analysis (C.H.N), mass spectrometry, molar conductance, FT-infrared, UV-visible, atomic absorption (AA), 13C-NMR, and 1H-NMR spectral studies. The characterization of the synthesized complexes shows that the environment surrounding the central metal ion in the complexes adopted a distorted octahedral configuration. Moreover, the conductivity measurements show a non-electrolytic character for the [Pb(L)(phen)] complex and an electrolytic character for the [Al(L)(phen)]Cl and K[Ag(L)(phen)] complexes. The experimental infrared data are supported by density functional theory (DFT) calculations using the B3LYP level of theory and LANL2DZ basis set. The vibrational frequencies of the molecules are computed using the optimized geometry obtained from the DFT calculations. The calculated vibrational frequencies have been compared with obtained experimental values. 1H and 13C-NMR chemical shifts were computed for the H2L ligand using the DFT/GIAO method. Additionally, the molecular electronic structures of the complexes have been investigated by DFT calculations.
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- الكلمات المفتاحية
curcumin; L-tyrosine; silver; aluminium; lead; Schiff base
Base hydrolysis of α-amino acid esters catalysed by [Pd(N-ethylethylenediamine)(H2O)2]2+. Kinetic study and DFT calculations
- ملخص البحث
Amino acid esters (L) react with [Pd(Eten)(H2O)2]2+ (Eten = N-ethyl ethylenediamine) giving mixed ligand complexes of the type [Pd(Eten)L]2+. Base hydrolysis of [Pd(Eten)L]2+ was studied by pH-stat technique from which rate constants for the base hydrolysis of the esters were obtained. The glycine methyl ester hydrolysed significantly, whereas the methionine methyl and histidine methyl esters hydrolysed much slower. The mode of coordination of the ester plays a role in the catalysis, and possible mechanisms for these reactions are considered. Activation parameters were determined for the hydrolysis of the glycine methyl ester. The effect of the dielectric constant of the medium on the hydrolysis process was also investigated. The B3LYP/LANL2DZ method was used for geometric optimization of the free ligand and the complex using the Gaussian 09 program. The calculations are compared with the kinetic data. In addition, the vibrational frequencies of the molecules were computed for the optimized geometries.
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- الكلمات المفتاحية
N-EthylethylenediamineAmino acid ester hydrolysisPd(II)pH-stat techniqueDFT calculation
The electrosorption of 1,2,3-triazole on gold as studied with surface-enhanced Raman spectroscopy
- ملخص البحث
The electrosorption of 1,2,3-triazole on a polycrystalline gold electrode has been studied with surface-enhanced Raman spectroscopy (SERS) and cyclic voltammetry. Vibrational wavenumbers were calculated for the 1H- and 2H-1,2,3-triazole at the B3LYP and MP2 levels using 6–31G* basis set. The data obtained from vibrational wavenumber calculations are used to analyze the SERS spectra. Results imply a tilted orientation of the triazole molecule both from acidic and neutral perchlorate solution with a nitrogen atom interacting directly with the gold surface. Strong adsorption in both cases is also evident from cyclic voltammograms of polycrystalline gold electrodes, indicating strong inhibition of gold hydroxide formation.
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- الكلمات المفتاحية
spectroelectrochemistry ,triazole,electrosorption