Nature of cationic poly(propylenimine) dendrimers in aqueous solutions as studied using versatile indicator dyes

Aqueous solutions of four cationic poly(propylenimine) low-generation dendrimers of different architecture and hydrophobicity have been examined as media for acid-base reactions of indicator dyes. The cationic dendrimers in solution can be considered as oligomers of cationic polyelectrolytes, or surfactant-like species, able to form micelles through self-association or sometimes even as unimolecular micelles. The dendrimers influence the ionization constants, tautomeric equilibria, and absorption/emission/excitation spectra of indicator dyes. The p K a values of the majority of the indicator dyes decrease in dendrimer solutions, often by 1-2 p K a units, similar to effects registered in micellar solutions of cationic surfactants. Analogously, the shifts of absorption band maxima indicate that the microenvironments of the dyes bound to the dendrimers are less polar than in water. However, some spectral effects denote the specificity of the dendrimers. The greatest difference between the dendrimers and spherical surfactant micelles is revealed by kinetic processes, especially of bromophenol blue alkaline fading in a dendrimer solution but not in a micellar surfactant solution. Within the dendrimer series, the most significant differences were observed for substances possessing n-dodecyl tails on the one hand and those without such hydrophobic portions on the other. For the last-named, the decrease in p K a's of indicators, band shifts of their anions, and in particular displacement of tautomeric equilibria compared with aqueous solutions are much smaller than for more hydrophobic dendrimers.     

Interfacial properties of cetyltrimethylammonium-coated SiO(2) nanoparticles in aqueous media as studied by using different indicator dyes

In this paper, we compare the properties of SiO(2)/water interface modified by cetyltrimethylammonium bromide (CTAB) with those of CTAB spherical micelles. The suspension of uniform silica nanoparticles coated with CTAB adlayer was investigated by using a set of acid-base indicators. The study of the colloidal system has been provided using electron microscopy and dynamic light scattering methods; the diameter of the initial SiO(2) particles in dried state was ca. 40 nm. The increase in the zeta-potential value of nanoparticles from -34 to +(37-54) mV on going from pure silica suspension to the CTAB-containing system points on the silica surface recharging and formation of surfactant bilayer (or multilayer) on the silica/water interface. To obtain further information about the interfacial surfactant adlayer, the behavior of different indicator dyes has been studied in CTAB-modified SiO(2) suspension. Comparison of the indices of apparent ionization constants, i.e., pK(a)(a) values of phenol red, bromothymol blue, and fluorescein with those determined in CTAB micellar solutions have confirmed the supposition about certain similarity between CTAB-covered silica nanoparticles and common spherical surfactant micelles. However, the experiments on kinetics of bromophenol blue fading, as well as the spectral properties of methyl orange and solvatochromic Reichardt's indicator and some other data revealed the specificity of surfactant-coated silica nanoparticles, presumably, originating from their surface morphology.     

Synthesis, structures, and photoluminescence of heteroligand complexes Ln(L)(iso-Bu2PS2)2(NO3) (Ln = Sm, Tb, Dy; L = Phen, 2,2′-Bipy)

Heteroligand complexes Ln(L)(iso-Bu₂PS₂)₂(NO₃) (Ln = Sm, Tb, Dy; L = Phen, 2,2??-Bipy) (I?CVI) are synthesized. The structure of Dy(Phen)(iso-Bu₂PS₂)₂(NO₃) (III) is determined from the data of X-ray structure analysis. The crystal structure of complex III is based on discrete mononuclear molecules in which the Dy atom has distorted dodecahedral coordination (polyhedron N₂O₂S₄). The ligands Phen, iso-Bu₂PS ₂ ^? and NO ₃ ^? are bidentate-cyclic. According to the X-ray diffraction analysis data, complexes I and II are isostructural to compound III. Complexes I?CVI have photoluminescence in the visible spectral range. The photoluminescence spectra of solid samples of compounds I?CVI exhibit bands corresponding to the radiative electron transitions of the Sm³⁺, Tb³⁺, and Dy³⁺ ions. Among the studied compounds I?CVI, the Tb(III) complexes are characterized by the most intense photoluminescence.     

Crystal structure of Sm(Phen)(i-Bu2PS2)3·MeCN and photoluminescence properties of SmL(i-Bu2PS2)3 (L = Phen, 2,2′-bipy)

It is revealed that at 300 K Sm(Phen)(i-Bu₂PS₂)₃ (I) and Sm(2,2′-Bipy)(i-Bu₂PS₂)₃ (II) complexes have photoluminescence properties typical of the Sm³⁺ ion. In the spectra, three bands are observed with 7n_max = 564 nm, 600 nm, and 645 nm. Single crystals of Sm(Phen)(i-Bu₂PS₂)₃·MeCN (III) are grown, and the structure of the compound is determined based on the X-ray diffraction data (X8 Apex diffractometer, MoK6h radiation, 7685 F _hkl, R = 0.0258). Crystals of III are triclinic, unit cell parameters are a = 11.0554(3) ?, b = 15.0446(3)?, c= 15.4849(4)?; 6h = 89.218(1)°, β = 75.555(1)°, γ = 73.484(1)°, V= 2386.6(1)?³, Z=2, ρ_calc = 1.391 g/cm³, P1 space group. The structure of III is formed from the molecules of mononuclear complex I and MeCN molecules. A coordination polyhedron of the Sm atom is an N₂S₆ tetragonal antiprism. It is shown that the structure of III includes dimeric assemblies of the molecules of complex I.     

Structure of [Dy(Phen)(C4H8NCS2)3]·3CH2Cl2 solvate. Magnetic properties and photoluminiscence of [Ln(Phen)(C4H8NCS2)3] (Ln = Sm,Eu, Tb,Dy, Tm) complexes

It is found that diffraction patterns of complexes I–V of the composition [Ln(Phen)(C₄H₈NCS₂)₃] (Ln = Sm, Eu, Tb, Dy, and Tm respectively) are similar. Single crystals of [Dy(Phen)(C₄H₈NCS₂)₃]·3CH₂Cl₂ (VI) obtained are. According to the X-ray crystallographic data, in the structure of VI the unit cell contains two crystallographically independent molecules of the [Dy(Phen)(C₄H₈NCS₂)₃] complex and six CH₂Cl₂ molecules. The N₂S₆ coordination polyhedron of the Dy atom is a distorted square antiprism. In the range of 2–300 K the magnetic properties of complexes I–V are studied. It is found that complex III passes to the magnetically ordered state; the spontaneous magnetization at 2 K is 24 600 G·cm³/mol. At 300 K compounds I–IV exhibit photoluminescence in the visible spectral range. It is found that the photoluminescence intensity of complex I is several times higher than the photoluminescence intensity of complexes II–IV.     

Coordination polymer [Sm(Biq)(iso-Bu2PS2)3] n : Synthesis,structure, and photoluminescence

A heteroligand complex [Sm(Biq)(iso-Bu₂PS₂)₃] _n (Biq = 6,6′-biquinoline) is synthesized. According to the X-ray diffraction data, the complex is one-dimensional coordination polymer. The crystal structure is built of chains consisting of fragments Sm(iso-Bu₂PS₂)₃ and molecules of the bidentate-bridging ligand Biq. The coordination polyhedron N₂S₆ of the Sm atom is a distorted tetragonal antiprism. The complex exhibits red photoluminescence (λ_max = 562, 598, 642, and 703 nm).     

The distribution of the anion and zwitterion forms of methyl orange between the disperse microemulsion pseudophase and continuous water phase

A procedure is suggested for determining the distribution constants of methyl orange dye between water and direct microemulsion droplets (N-cetylpyridinium chloride + 1-pentanol + benzene in water) as the disperse phase, which allows one to circumvent difficulties associated with the formation of low-solubility salts and premicellar associates. Within the framework of the pseudophase model of equilibria, the distribution constants of the yellow monoanion and red zwitterion methyl orange forms between microscopic droplets and the continuous phase at an ionic strength of 0.2 mol/l (NaCl + HCl) were determined from the dependence of the apparent ionization constant of the indicator on the volume fraction of the disperse pseudophase. The constants on the molar concentration scale were \(P_{B^ - }^ \otimes \) = (253 ± 0.08) × 10⁵ and \(P_{^ + HB^ - }^ \otimes \) = (1.7 ± 0.4) × 10².     

Surface Modification of Aminopropylated Silica Gel with Tetraphosphorylated bis-Methoxycarbonylmethoxycalix[4]Arenes for Effective Europium(Iii) Sorption

Theoretical and Experimental Chemistry - bis-Methoxycarbonylmethoxy derivatives capable of reacting with the surface of aminopropylated silica gel with the formation of chemically and thermally...     

Copper(II) Complexes with Chiral Ligands Containing Fragments of Monoterpenoids and Amino Acid Esters

Complexes [CuL¹Cl₂] (I), [CuL²Cl₂] · EtOH (II), and Cu₂L³Cl₄ (III) containing esters of the N-derivatives of optically active amino acids based on (+)-3-carene (L¹, L²) and (?)-α-pinene (L³) are synthesized. The crystal and molecular structures of compounds I and II are determined by X-ray diffraction analyses (CIF files CCDC nos. 1560071 (I), 1560072 (II)). The crystal structure of compound I consists of mononuclear complex molecules. In the structure of compound II, the unit cell contains two crystallographically independent molecules of mononuclear complex [CuL²Cl₂] and two EtOH molecules. Ligands L¹ and L² perform the tridentate-chelating function by the N atoms of the NH and NOH groups and by the O atom of the C=O group. In compounds I and II, the coordination polyhedra Cl₂N₂O of the Cu atoms are trigonal bipyramid. According to the data of IR and electronic spectroscopy, binuclear complex III has similar coordination polyhedra. The experimental values of μ_eff for compounds I, II, and III at 300 K are 1.93, 1.88, and 2.71 μB. For complex III, the μ_eff(T) dependence in a range of 2–300 K indicates a weak ferromagnetic exchange interaction.