Complexation of Cu(II) Ions with the Lowest Generation Poly(amido-amine)-OH Dendrimers: A Molecular Simulation Study

Ratiometric pH Sensing, Photophysics, and Cell Imaging of Nonaromatic Light-Emitting Polymers

Here, four nontraditional fluorescent polymers (NTFPs) of varying N,N-dimethyl-2-propenamide (DMPA) and butyl prop-2-enoate (BPE) mole ratios, i.e., 2:1 (NTFP1), 4:1 (NTFP2), 8:1 (NTFP3), and 16:1 (NTFP4), are prepared via random polymerization in water. The maximum fluorescence enhancement of NTFP3 makes it suitable for ratiometric pH sensing, Cu(II) sensing, and pH-dependent cell imaging of Madin-Darby canine kidney (MDCK) cells. The oxygen donor functionalities of NTFP3 involved in binding and sensing with Cu(II) ions are studied by absorption, emission, electron paramagnetic resonance, Fourier transform infrared (FTIR), and O1s/Cu2p X-ray photoelectron spectroscopies (XPS). The spectral responses of the ratiometric pH sensor within 1.5-11.5 confirm 22 and 44 nm red shifts in absorption and ratiometric emission, respectively. The striking color changes from blue (436 nm) to green (480 nm) via an increase in pH are thought to be the stabilization of the charged canonical form of tertiary amide, i.e., -C(O^-)═N⁺(CH₃)₂, realized from the changes in the absorption/fluorescence spectra and XPS/FTIR analyses. The through-space n-π* interactions in the NTFP3 aggregate, N-branching-associated rigidity, and nonconventional intramolecular hydrogen bondings of adjacent NTFP3 moieties in the NTFP3 aggregate contribute to aggregation-enhanced emissions (AEEs). Here, structures of NTFP3, NTFP3 aggregate, and Cu(II)-NTFP3; absorption; n-π* interactions; hydrogen bondings; AEEs; and binding with Cu(II) are ascertained by density functional theory, time-dependent density functional theory, and reduced density gradient calculations. The excellent limits of detection and Stern-Volmer constants of NTFP3 are 2.24 nM/0.14234 ppb and 4.26 × 10³ M^-1 at pH = 6.5 and 0.95 nM/0.06037 ppb and 4.90 × 10³ M^-1 at pH = 8.0, respectively. Additionally, the Stokes shift and binding energy of NTFP3 are 13,636 cm^-1/1.69 eV and -4.64 eV, respectively. The pH-dependent MDCK cell imaging ability of noncytotoxic NTFP3 is supported via fluorescence imaging and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

Toxic metal sequential sequestration in water using new amido-aminoacid ligand as a model for the interaction with polyamidoamines

Polyamidoamines are low cost and easily synthesized materials that may find applications in cations sequestration and water treatment. In this paper a new amido-aminoacid ligand containing methionine has been designed as a monomeric model of the corresponding polyamidoamine. The amido-aminoacid ligand has been synthesized in high yield, by reacting acrylamide and methionine via aza-Michael addition in water and mild temperature conditions. The reaction has been monitored by NMR and Raman spectroscopies and the crystal structure has been determined by X-ray diffraction analysis. The coordination ability of the ligand towards Cu²⁺ cations in water, as well as its affinity for Ni²⁺ and Co²⁺ has been studied by potentiometric and spectrophotometric techniques. The divalent metal cations sequestration from water may occur with sequential selection by changing the pH of the solution. The copper complex with two coordinated ligands has been fully characterized in the solid state by single crystal X-ray diffraction. The results are discussed with a view to use these materials in the treatment of water contaminated by toxic transition metal ions.

Computational calculation identified optimal binding sites in nano-sized magnetic-cored dendrimer

Magnetic-cored dendrimers (MDs) with amino groups were prepared with the formation of poly(amidoamine) dendrimer on the surface of magnetite nanoparticles (MNPs). The experiment involved the binding of four different heavy metal ions including Pb (II), Cu (II), Zn (II), and Cr (VI). Density functional theory (DFT) calculation was applied to the experimental results to determine the optimal configurations between the heavy metal species and generation 1 amino (NH₂) functionalized MD (G1-NH₂-MD). Different binding configurations among the possible binding positions of inner and outer G1-NH₂-MD were determined with the ionic radius and coordination number of each heavy metal ion. Although Pb²⁺ and Zn²⁺ were stable in the terminal positions, Cu²⁺ was the most stable in the internal position. The oxygen and hydrogen atoms of HCrO₄^- formed a hydrogen bond with the NH₂ groups, and thus dipole-nonpolar molecular interaction occurred with the CH₂ groups of G1-NH₂-MD. Specific binding positions and energies of different heavy metal species were identified through the DFT calculation in the study. The DFT calculation results also contributed to an understanding of the binding priority of each metal ions in the mixed solution. Furthermore, Pb²⁺ was preferably adsorbed in the mixed solution of Pb²⁺, Cu²⁺, and Zn²⁺.

Raman and NMR kinetics study of the formation of amidoamines containing N-hydroxyethyl groups and investigations on their Cu(II) complexes in water

Three amidoamines containing the N-hydroxyethyl group (^HOEt), namely (^HOEt)₂N(CH₂)₂C(O)NH₂ (1), [(^HOEt)₂N(CH₂)₂C(O)NH]₂CH₂ (2) and ^HOEtN[(CH₂)₂C(O)NH₂]₂ (3) have been synthesized by reacting diethanolamine ^HOEt₂NH with acrylamide and N,N'-methylenebisacrylamide (respectively 1 and 2) and ethanolamine ^HOEtNH₂ with acrylamide (3). Four other compounds corresponding to 1 and 2, but derived from sec-amines Me₂NH (4 and 5) and Et₂NH (6 and 7) have been prepared for the sake of comparison of the spectroscopic features. All compounds have been obtained by the well-known aza-Michael addition between an N-nucleophile and an activated vinyl group. The reaction in water between diethanolamine and acrylamide leading to 1 has been monitored in situ by Raman and NMR spectroscopy, both techniques confirming second order kinetics and giving values for kinetic constants in excellent agreement. The coordination ability of 1 and 2 towards Cu²⁺ in water has been studied by the Job's plot method. Spectroscopic data indicate that ligand 1 prevalently forms a 4:1 Ligand/Metal complex with a (N,O₃) coordination set on the equatorial plane of Cu²⁺, whereas ligand 2, containing two amide functionalities bridged by a methylene group, appears able to form a 1:1 Ligand/Metal chelate species, again with a (N,O₃) donor set around copper.

Anionic sulfonated and carboxylated PPI dendrimers with the EDA core: synthesis and characterization of selective metal complexing agents

Herein we describe the synthesis and characterization of new sulfonated and carboxylated poly(propyleneimino) (PPI) dendrimers with the ethylenediamino (EDA) core, at generations 1, 2 and 3. By means of UV-Vis and EPR spectroscopy, using Cu(2+) as a probe, we concluded that these dendrimers show a specific pattern in the coordination of metal ions. In agreement with the UV-Vis studies, EPR spectra of carboxylated compounds are constituted by 3 different signals which appear and then disappear with increasing copper concentration, corresponding to the saturation of different copper complexation sites. At the lowest copper concentration up to a 1:1 molar ratio between Cu(II) and the dendrimer, the spectrum is characteristic of a CuN2O2 coordination at the core of the dendrimer. The spectrum appearing at higher Cu(II) concentrations indicates a peripheral location of the ions coordinating one nitrogen and 3 oxygen atoms in a square planar geometry in restricted mobility conditions. For the highest concentrations tested, copper ions are confined at the external dendrimer surface with CuO4 coordination. For sulfonate systems, the EPR results are in line with a weaker interaction of Cu(II) with the nitrogen sites and a stronger interaction with the oxygen (SO3(-)) groups with respect to the interactions measured by EPR for carboxylate systems.

Modeling the formation of ordered nano-assemblies comprised by dendrimers and linear polyelectrolytes: the role of Coulombic interactions

Models of mixtures of peripherally charged dendrimers with oppositely charged linear polyelectrolytes in the presence of explicit solvent are studied by means of molecular dynamics simulations. Under the influence of varying strength of electrostatic interactions, these systems appear to form dynamically arrested film-like interconnected structures in the polymer-rich phase. Acting like a pseudo-thermodynamic inverse temperature, the increase of the strength of the Coulombic interactions drive the polymeric constituents of the mixture to a gradual dynamic freezing-in. The timescale of the average density fluctuations of the formed complexes initially increases in the weak electrostatic regime reaching a finite limit as the strength of electrostatic interactions grow. Although the models are overall electrically neutral, during this process the dendrimer/linear complexes develop a polar character with an excess charge mainly close to the periphery of the dendrimers. The morphological characteristics of the resulted pattern are found to depend on the size of the polymer chains on account of the distinct conformational features assumed by the complexed linear polyelectrolytes of different length. In addition, the length of the polymer chain appears to affect the dynamics of the counterions, thus affecting the ionic transport properties of the system. It appears, therefore, that the strength of electrostatic interactions together with the length of the linear polyelectrolytes are parameters to which these systems are particularly responsive, offering thus the possibility for a better control of the resulted structure and the electric properties of these soft-colloidal systems.

Water-soluble anionic POSS-core dendrimer: synthesis and copper(II) complexes in aqueous solution

A carboxylic acid-terminated polyhedral oligosilsesquioxane (POSS)-core dendrimer (POSS-CO2H) was synthesized from octa(3-ammoniumpropyl)octasilsesquioxane octachloride (POSS-NH3+) via a t-butyl ester-terminated POSS-core dendrimer that was prepared from neutralized POSS-NH3+ and t-butyl acrylate. Complexing properties of the sodium salts of POSS-CO2H (POSS-CO2Na) with Cu2+ were studied in comparison with those of the G1.5 poly(amidoamine) (PAMAM) dendrimer (G1.5-CO2Na) by spectroscopic approach and isothermal titration calorimetry. In the case of G1.5-CO2Na, Cu2+-N4 and Cu2+-N2O2 complexes are possible coordination modes, and only a Cu2+-N2O2 complex can be formed for POSS-CO2Na. In the case of POSS-CO2Na, upon increasing the concentration of Cu2+, the values of the binding constants decreased. However, the values of binding constants in the regions of the Cu2+-N2O2 coordination mode for G1.5-CO2Na increased with increasing concentration of Cu2+. This observation suggests that the uptake of Cu2+ is inhibited by increasing binding numbers of Cu2+ due to the rigid structure of the POSS-core dendrimer.

Dendrimer-Tetrachloroplatinate Precursor Interactions. 2. Noncovalent Binding in PAMAM Outer Pockets

Density functional theory is used to investigate the complexation ability of dendrimer outer pockets--in both tertiary amine protonated and unprotonated scenarios--toward molecular guests, particularly tetrachloroplatinate(II) and its mono- and diaquated derivatives as well as competing counterions. The effect of the outer pocket (host) on the binding affinity of guest molecules is analyzed and it is found that is more feasible for the host to accept species, particularly charged ones, inside an unprotonated pocket rather than outside; unlike the protonated pocket where the opposite is more likely to occur. Conformational changes triggered by the hosting of particular guests can have an impact in the global configuration of the larger dendrimer the pockets are part of.

Dendrimer−Tetrachloroplatinate Precursor Interactions. 1. Hydration of Pt(II) Species and PAMAM Outer Pockets

Density functional theory is used to investigate the structure and energetics of the tetrachloroplatinate anion and its hydrolysis products at several degrees of hydration, as well as those of outer dendrimer pockets hosting such species. The number of water molecules able to saturate an unprotonated outer dendrimer pocket is found to be two, as inferred from calculated thermodynamic data. However, such a number could not be established for a protonated pocket where the dendrimer adopts a more open configuration. An analysis of possible pocket configurations is done on the basis of the orientations of the amide O atoms in the outer pockets. The effect of explicit water on the infrared spectra of the dendrimer pockets is reported and compared to experimental values.