Protonation behavior of 6-deoxy-6-(2-aminoethyl)amino cellulose: a potentiometric titration study

The protonation behavior of 6-deoxy-6-(2-aminoethyl)amino cellulose as a novel soluble aminated derivate of cellulose was studied by means of the potentiometric titration technique. The resulting proton binding isotherms exhibit two equivalent steps, which can be described by the standard macroscopic two-pK model, in which the degree of protonation is averaged over all the amine groups. In addition, a microscopic proton binding model was applied, in which the protonation sites are distinguished and the protonation free energy is expanded into an intrinsic term and an electrostatic repulsion between the primary and secondary amine groups. The protonation behavior of 6-deoxy-6-(2-aminoethyl)amino cellulose was compared with a model compound (N-methylethylenediamine).     

Direct synthesis of Cbz-protected (2-amino)-6-(2-aminoethyl)pyridines

A novel series of (2-amino)-6-(2-aminoethyl)pyridines were prepared by a convenient Suzuki-Miyaura coupling approach from 2-amino-6-bromopyridines. Benzyl vinylcarbamate was first treated with 9-BBN followed by aqueous NaOH and then the appropriate bromopyridine precursors were added into the mixture. The mixture was finally heated in presence of a palladium catalyst to provide the corresponding products in overall high yields. The procedure is extended to the preparation of related pyrazine and pyrimidine compounds as well as (2-amido)- and (2-alkoxy)-6-(2-aminoethyl)pyridines.     

Synthesis,characterization, electrochemical and crystal structure investigation of bis(2-((2-aminoethylimino)methyl)-6-methoxyphenolato) cobalt(III)

The mononuclear cobalt(III) complex [Co(L)₂]Cl ·?H₂O (1) (where L is H₂N(CH₂)₂N=CC₆H₃(OMe)(O^?)) has been prepared and characterized by IR, UV-Vis spectroscopy, conductivity measurements, elemental analysis, TGA, cyclic voltammetry and an X-ray structure determination. The cobalt(III) coordination sphere in [Co(L)2] is cis-CoN₄O₂ with the NNO ligands. Electrochemical studies of 1 using cyclic voltammetry indicate an irreversible cathodic peak (E _pc, ca ?0.60 V) corresponding to reduction of cobalt(III) to cobalt(II).     

Thermodynamics of Ni(II) Complexation with L-Asparagine in Aqueous Solution

Complexation of the Ni²⁺ ion with L-asparagine (HAsn^±) is studied by potentiometric titration at 298.15 K and at the 0.3, 0.5 and 1.0 ionic strength of the solution (KNO₃). The formation of the NiAsn⁺ and NiAsn₂ complexes was established and their stability constants were determined. The thermodynamic stability constants of the mono- and bis(L-asparagine)nickel(II) complexes were obtained by extrapolation to zero ionic strength. The direct calorimetry method was used to measure the heat effect of the L-asparagine reaction with the Ni(II) nitrate solution in different pH intervals at 298.15 K and at the 0.5, 1.0, and 1.5 ionic strength (KNO₃). The standard enthalpies of the NiAsn⁺ and NiAsn₂ formation were found using extrapolation and the equation with one individual parameter. The enthalpies of the formation of the Ni(II) complexes with L-asparagine in aqueous solution were calculated in the standard hypothetically undissociated state.     

Studies on Antimicrobial Evaluation of Some 1-((1-(1H-Benzo[d]imidazol-2-yl)ethylidene)amino)-6-((arylidene)amino)-2-oxo-4-phenyl-1, 2-dihydropyridine-3,5-dicarbonitriles

A new series of 1-((1-(1H-benzo[d]imidazol-2-yl)ethylidene)amino)-6-((arylidene)amino)-2-oxo-4-phenyl-1,2-dihydropyridine-3,5-dicarbonitriles (4a–o) have been synthesized for the development of antimicrobial agents. Newly synthesized compounds were evaluated for their in vitro antibacterial activity against Gram-positive bacteria (Pseudomonas aeruginosa, Streptococcus pyogenes), Gram-negative bacteria (Escherichia coli, Staphylococcus aureus), and antifungal activity (Candida albicans, Aspergillus niger, Aspergillus clavatus). These compounds were characterized by infrared, ¹H NMR, ¹³C NMR, and mass spectra. The synthesized compounds 4b, 4e, 4 h, and 4k showed potent antimicrobial activity against tested microorganisms.     

Kinetic study of CO2 absorption in aqueous solutions of 2-((2-aminoethyl)amino)-ethanol using a stirred cell reaction calorimeter

In the literature, aqueous 2-((2-aminoethyl)amino) ethanol (AEEA) is identified as a promising solvent for postcombustion CO₂ capture. In this work, the kinetics of CO₂ absorption in the aqueous AEEA, containing a primary and a secondary amino group, is studied over a wide temperature range of 303.15-343.15 K and the amine concentration in the range of 0.47-2.89 M using the fall-in-pressure technique in a stirred cell reaction calorimeter setup with a horizontal gas-liquid interface. The overall rate constants for (AEEA + H₂O + CO₂) reaction system are estimated in the pseudo–first-order reaction regime. The kinetic models based on zwitterion and the termolecular reaction mechanisms are used to predict kinetic rate constants. The experimental kinetic data are better correlated using the zwitterion mechanism (AAD 9.18%) than that of the termolecular mechanism (AAD 10.4%). The density, viscosity, and physical solubility of pure components and aqueous binary mixtures of AEEA are also measured at the similar temperature and concentration ranges of rate kinetics. Empirical models are proposed to predict pure component density and viscosity data with AAD of 0.02% and 7.17%, respectively. The Redlich-Kister model, the Grunberg-Nissan model, and the O'Connell's model are used to correlate experimental density, viscosity, and physical solubility data of the binary mixtures with AAD of 0.034%, 4.92%, and 6.5%, respectively. The reaction activation energy (E_a ∼ 32 kJ/mol) of the (AEEA + H₂O + CO₂) system is calculated from the Arrhenius power-law model using the zwitterion mechanism, which indicates lower energy barrier than that of the reported value for monoethanolamine (∼44 kJ/mol) in the literature.     

Proton-lithium binding behavior of tris(2-((pyrid-2-ylmethyl)uredio)ethyl)amine

Tris(2-((pyrid-2-ylmethyl)uredio)ethyl)amine (2) and its perchlorate salt, 2.HClO(4), bind with Li+ in nitromethane in a 1:1 fashion. The stability constants of K(Li+) and K(H)(Li+) were found to be 112 +/- 25 and 130 +/- 30 M(-)(1) in CD(3)NO(2), respectively. Formation of the 1:1 complexes were further evidenced by electrospray ionization mass spectrometry (ESI-MS). The slight increase, or at least the same order of magnitude, of K(H)(Li+) compared to K(Li+) points to a remarkable preorganization of the protonated podand in 2.HClO(4), that essentially overcomes the increased Columbic repulsion occurring on complexation to Li+.     

Synthesis,structure, spectroscopic,and DNA binding properties of Co(III) and Ni(II) complexes with ((E)-2-(amino((pyridin-2-ylmethylene)amino)methylene)maleonitrile)

Two new complexes, [Co(L)₂]Cl·(MeOH)₂ (1) and [Ni(L)₂]₄·EtOH (2) (L?=?(E)-2-(amino((pyridin-2-ylmethylene)amino)methylene)maleonitrile), were synthesized and characterized by X-ray crystallography, IR, UV, and fluorescence spectroscopy. According to X-ray crystallographic studies, each metal was six-coordinate with six nitrogens from two ligands. Both complexes form two-dimensional supramolecular networks via hydrogen bonding and π–π interactions. Ultraviolet and visible spectra showed that absorptions arise from π–π ^?, MLCT, and d–d electron transitions. Fluorescence spectroscopy revealed moderate intercalative binding of these two complexes with EB–DNA, with apparent binding constant (K _app) values of 9.14?×?10⁵ and 3.20?×?10^5?M^?1 for Co(III) and Ni(II) complexes, respectively. UV–visible absorption spectra showed that the absorption of DNA at 260?nm was quenched for 2 but quenched then improved for 1 with addition of complexes, tentatively attributed to the effect of the combined intercalative binding and electrostatic interaction for 1.     

Synthesis and Crystal Structure of 1,4,7,10-Tetrakis （2-（（4-hydroxy）phenoxy）ethyl）-1,4,7,10- tetraazacyclododecane

A novel molecule tetra-N-alkylation of cyclen （1,4,7,10-tetraazacyclododecane）, 1,4,7,10-tetrakis（2-（（4-hydroxy）phenoxy）ethyl）-1,4,7,10-tetraazacyclododecane 2, was synthesized and structurally characterized by single-crystal X-ray diffraction. The molecule turned into chiral helical compound crystals grown from EtOH by slow diffusion at room temperature and three of the four hydroquinone groups of the benzene ring formed a g-electron-rich cavity by C-H…π stacking interaction. The crystal belongs to the monoclinic system, space group P21/C with a = 13.9192（9）, b = 13.2871（6）, c = 22.1894（15）A^°, β = 91.4600（10）°, V = 4102.5（4）A^°3, Z = 4, Dc = 1.219 g/cm^3, C40H52N4O8, Mr = 752.89, F（000） = 1616,μ = 0.088 mm^-1, MoKa radiation （λ = 0.71073）, R = 0.0578 and wR = 0.1389 for 5588 observed reflections with I 〉 2σ（I）. Moreover, compound 2 was characterized with ^1H NMR, ^13C NMR, IR spectra and MS.     

Measuring solubility of carbon dioxide in aqueous blends of N-methyldiethanolamine and 2-((2-aminoethyl)amino)ethanol at low CO2 loadings and modelling by electrolyte SAFT-HR EoS

In this work, new solubility values for CO₂ absorption in aqueous solutions of N-methyldiethanolamine (MDEA) in the presence of different mole ratios of 2-((2-aminoethyl)amino)ethanol (AEEA) at low pressures are obtained. The total molar amine concentration of all the solutions has been fixed equal to 3.360 mol · L⁻¹ (5.370 mol amine · kg⁻¹ water). The mole ratio of AEEA/MDEA was set to 0.12500, 0.10000 and 0.05000. The experimental total pressure varied from (7.3 to 386.6) kPa and the experimental temperature was set to (313.15, 328.15, 343.15 and 358.15) K. The electrolyte SAFT-HR (eSAFT-HR) equation of state (EoS) (Najafloo et al., 2014) has been successfully applied to model the solubility of CO₂ in aqueous mixtures of AEEA and MDEA. The overall average absolute relative per cent deviation (AAD%) in calculating the total pressure as a function of CO₂ loading is 7.74 for (AEEA + MDEA + CO₂ + H₂O) quaternary system at the four values of temperature. To verify the predictive ability of the model, the eSAFT-HR EoS was extrapolated to the Zoghi and Feyzi (2013) solubility results of the same quaternary system that were obtained at higher pressures or higher CO₂ loadings at the same temperatures. The AAD of the present model is 11.39% lower.     

Formation, characterization, and reactivity of bis(mu-oxo)dinickel(III) complexes supported by a series of bis[2-(2-pyridyl)ethyl]amine ligands.

Bis(mu-oxo)dinickel(III) complexes supported by a series of bis[2-(2-pyridyl)ethyl]amine ligands have been successfully generated by treating the corresponding bis(mu-hydroxo)dinickel(II) complexes or bis(mu-methoxo)dinickel(II) complex with an equimolar amount of H(2)O(2) in acetone at low temperature. The bis(mu-oxo)dinickel(III) complexes exhibit a characteristic UV-vis absorption band at approximately 410 nm and a resonance Raman band at 600-610 cm(-1) that shifted to 570-580 cm(-1) upon (18)O-substitution. Kinetic studies and isotope labeling experiments using (18)O(2) imply the existence of intermediate(s) such as peroxo dinickel(II) in the course of formation of the bis(mu-oxo)dinickel(III) complex. The bis(mu-oxo)dinickel(III) complexes supported by the mononucleating ligands (L1(X) = para-substituted N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine; X = OMe, Me, H, Cl) gradually decompose, leading to benzylic hydroxylation of the ligand side arm (phenethyl group). The kinetics of the ligand hydroxylation process including kinetic deuterium isotope effects (KIE), p-substituent effects (Hammett plot), and activation parameters (Delta H(H)(*) and Delta S(H)(*)) indicate that the bis(muxo)dinickel(III) complex exhibits an ability of hydrogen atom abstraction from the substrate moiety as in the case of the bis(mu-oxo)dicopper(III) complex. Such a reactivity of bis(mu-oxo)dinickel(III) complexes has also been suggested by the observed reactivity toward external substrates such as phenol derivatives and 1,4-cyclohexadiene. The thermal stability of the bis(mu-oxo)dinickel(III) complex is significantly enhanced when the dinucleating ligand with a longer alkyl strap is adopted instead of the mononucleating ligand. In the m-xylyl ligand system, no aromatic ligand hydroxylation occurred, showing a sharp contrast with the reactivity of the (mu-eta(2):eta(2)-peroxo)dicopper(II) complex with the same ligand which induces aromatic ligand hydroxylation via an electrophilic aromatic substitution mechanism. Differences in the structure and reactivity of the active oxygen complexes between the nickel and the copper systems are discussed on the basis of the detailed comparison of these two systems with the same ligand.     

A ring-like coordination structure constructed by Cu(II) and bis(2-(pyridin-2-ylthio)ethyl)ether ligand

The reaction of bis(2-(pyridin-2-ylthio)ethyl)ether (L) with CuCl₂ in CH₃OH/CHCl₃ solution gives a novel 24-membered ring-like coordination structure which has been characterized by elemental analysis, IR, and X-ray single-crystal diffraction. The X-ray diffraction analysis reveals that [Cu₂L₂Cl₄] crystallizes in the triclinic, space group $P\bar 1$ . The ring-like structure is consisted of two ligands with two copper ions coordinated to the pyridyl nitrogen atoms from two ligands respectively. The largest diameters of the planarshaped dinuclear ring are about 12.7 Å. The adjacent ring-like units are linked via C-H…O hydrogen bonds to generate an infinite linear chain, which are further linked by C-H…Cl hydrogen bonds and weak intermolecular interactions to form a three-dimensional network.     

Mono-(BOC)-Protected Diamines. Synthesis of tert-Butyl-N-alkyl-N-(2-aminoethyl)carbamates and tert-Butyl-N-[2-(alkylamino)ethyl] Carbamates

We wish to report preparative pathways to the mono-(BOC)-protected diamines 1a-d and 2a-c.     

Synthesis and tautomerism of ethyl 2-(2-benzothiazolyl)-2-(6-purinyl)acetate and related compounds

Reaction of 6-chloro-9H-(2-tetrahydropyranyl)purine ( 2d ) with the sodium salt of ethyl benzothiazole-2-ace-tate ( 1 ) in dimethylformamide effects condensation of the two compounds (with loss of sodium chloride) to give the corresponding ethyl diarylacetate 4 (35%), present largely as an enol chelate tautomer. Isolated as a by-product is 6-(2-aminophenyl-1-thio)-9H-(2-tetrahydropyranyl)-purine (4%), formed via opening of the thiazole ring. Removal of the tetrahydropyranyl protective group from 4 occurs by treatment with p-toluenesulfonic acid in aqueous ethanol to produce ethyl benzothiazole-2-(6-purinyl)acetate (80%), existent largely as two enol chelate isomers. Spectral data for the various products are presented. An attempt to use 6-chloro-9-acetyl-9H-purine in place of 2d in the first reaction gives acetylation of 1 instead of condensation.     

Complexation of Cu(II) with Glycine in Aqueous Solution of an Anionic Surfactant

The complexation of Cu²⁺ with glycine in aqueous solution of an anionic surfactant, sodium dodecyl sulfate, was studied spectrophotometrically. Sodium dodecyl sulfate in concentrations above the critical micellization concentration participates in the complexation. The composition of the complexes and the equilibrium constants of the complexation were determined.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 3, 2005, pp. 383–385.Original Russian Text Copyright © 2005 by Vladimirova, Morgunova, Ramenskaya.     

ATRP法制备聚(甲基丙烯酸氨乙酯-co-甲基丙烯酸N,N-二乙基氨乙基酯)基因载体

为得到低毒、高效的聚阳离子基因载体,以甲基丙烯酸氨乙酯(AMA)和甲基丙烯酸N,N-二乙基氨乙基酯(DEAEMA)为单体,以2-溴代异丁酸乙酯(EBIB)为引发剂,通过原子转移自由基聚合(ATRP)制备了两种聚(甲基丙烯酸氨乙酯-co-甲基丙烯酸N,N-二乙基氨乙基酯)阳离子无规共聚物(P(AMA-co-DEAEMA),简称P).琼脂糖凝胶电泳实验结果表明聚合物P作为阳离子载体可以有效地络合DNA,通过粒径仪测定的复合物粒子的尺寸在400 ～ 600 nm之间.扫描电镜观察的P/DNA复合物形貌是分散均匀的球形颗粒.以25kDa PEI为阳性参照,利用MTT比色法考察了聚合物P对HEK293T细胞的毒性.结果表明,聚合物P的细胞毒性低于25 kDa PEI的细胞毒性.以25 kDa PEI和裸质粒DNA作为参照,我们进一步考察了聚合物P与DNA形成的复合物在HEK293T细胞中的转染效率.结果表明P/DNA复合物在HEK293T细胞中的转染效率远远高于裸质粒DNA的转染效率,并且接近于25 kDa PEI/DNA复合物的转染效率.     

Electrocatalytic reduction of O2 at pyrolytic graphite electrode modified by a novel copper(II) complex with 2-[bis(2-aminoethyl)amino]ethanol and imidazole ligands

A new complex formed by Cu(II) with 2-[bis(2-aminoethyl)amino]ethanol and imidazole is prepared, and its electrochemical properties are studied. The electrochemical experiments are carried out in deaerated pH 7.0 buffer solution through cyclic voltammetry by scanning the potential from 0.1 to −0.5 V with this copper(II) complex-modified electrode as the working electrode. One redox process is observed, which could be assigned to Cu(II)/Cu(I). The formal potential E _0′ = (E _pa + E _pc)/2, where E _pa and E _pc are anodic and cathodic peak potentials, is −248 mV vs. SCE. A straight line, obtained from the plot of I _pc vs. v, indicated a surface-controlled reaction. The modified electrode is very stable and exhibits catalytic activity for oxygen reduction. The possible mechanism for the catalytic reduction of oxygen is studied by cyclic voltammetry and chronoamperometry. The results show that the dioxygen is reduced via a pathway of four-electron reduction to form water. Chronoamperometric measurements show the potentiality of the use of this working electrode as an amperometric sensor for dissolved dioxygen in aqueous media. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 8, pp. 975–979. The text was submitted by the authors in English.