Metal Ion Binding by a G-2 Poly(ethylene imine) Dendrimer. Ion-Directed Self-Assembling of Hierarchical Mono- and Two-Dimensional Nanostructured Materials

Dendrimers as efficient nanocarriers for the protection and delivery of bioactive phytochemicals

The genesis of dendrimers can be considered as a revolution in nano-scaled bioactive delivery systems. These structures possess a unique potential in encapsulating/entrapping bioactive ingredients due to their tree-like nature. Therefore, they could swiftly obtain a valuable statue in nutraceutical, pharmaceutical and medical sciences. Phytochemicals, as a large proportion of bioactives, have been studied and used by scholars in several fields of pharmacology, medical, food, and cosmetic for many years. But, the solubility, stability, and bioavailability issues have always been recognized as limiting factors in their application. Therefore, the main aim of this study is representing the use of dendrimers as novel nanocarriers for phytochemical bioactive compounds to deal with these problems. Hence, after a brief review of phytochemical ingredients, the text is commenced with a detailed explanation of dendrimers, including definitions, types, generations, synthesizing methods, and safety issues; then is continued with demonstration of their applications in encapsulation of phytochemical bioactive compounds and their active/passive delivery by dendrimers. Dendrimers provide a vast and appropriate surface to entrap the targeted phytochemical bioactive ingredients. Several parameters can affect the yield of nanoencapsulation by dendrimers, including their generation, type of end groups, surface charge, core structure, pH, and ambient factors. Another important issue of dendrimers is related to their toxicity. Cationic dendrimers, particularly PAMAM can be toxic to body cells through attaching to the cell membranes and disturbing their functions. However, a number of solutions have been suggested to decrease their toxicity.

Solution Studies and Crystal Structures of Heteropolynuclear Potassium/Copper Complexes with Phytate and Aromatic Polyamines: Self-Assembly through Coordinative and Supramolecular Interactions

Phytate (L^12- ) is a relevant natural product. It interacts strongly with biologically relevant cations, due to the high negative charge exhibited in a wide pH range. The synthesis and crystal structures of the mixed-ligand Cu(II) polynuclear complexes K(H₂ tptz)_0.5 [Cu(H₈ L)(tptz)] ⋅ 3.6H₂ O (1), K(H₂ O)₃ {[Cu(H₂ O)(bpca)]₃ (H₈ L)} ⋅ 1.75H₂ O (2), and K_1.5 (H₂ O)₂ [Cu(bpca)](H_9.5 L) ⋅ 8H₂ O (3) (tptz=2,4,6-tri(pyridin-2-yl)-1,3,5-triazine; Hbpca=bis(2-pyridylcarbonyl) amine) are reported herein. They were obtained by the use of an aromatic rigid amine, which satisfies some of the metal coordination sites and promotes the hierarchical assembly of 2D polymeric structures. Speciation of phytate-Cu(II)-Hbpca system and determination of complex stability constants were performed by means of potentiometric titrations, in 0.15 M NMe₄ Cl at 37.0 °C, showing that, even in solution, this system is able to produce highly aggregated complexes, such as [Cu₃ (bpca)₃ (H₇ L)]^2- . Furthermore, the Cu(II)-mediated tptz hydrolysis was studied by UV-vis spectroscopy at room temperature in 0.15 M NMe₄ Cl. Based on the equilibrium results and with the aid of molecular modelling tools, a plausible self-assembly process for 2 and 3 could be proposed.

A diglycolamide-functionalized TREN-based dendrimer with a ‘crab-like’ grip for the complexation of actinides and lanthanides

TREN-G1-DGA, a multiple DGA ligand, was synthesized and evaluated for the extraction of actinides and fission product ions.

HBPEI-grafted carbon nanotubes for the effective retention of Pd2+ and Pt2+ through complexation

Using the complexing properties of HBPEIs for the effective retention of Pd and Pt on MWCNT.

Cation, Anion and Ion-Pair Complexes with a G-3 Poly(ethylene imine) Dendrimer in Aqueous Solution

The G-3 poly(ethylene imine) ligand L2 shows a multifaceted coordination ability, being able to bind metal cations, anions and ion-pairs. The equilibrium constants for the formation of metal (Cu²⁺, Zn²⁺), anion (SO₄^2-) and ion-pair (Cu²⁺/SO₄^2-) complexes were determined in 0.1 M Me₄NCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric titrations. Thanks to its dendrimeric nature, L2 can form highly nucleated metal complexes, such as Cu₅L2¹⁰⁺ and Zn₄L2⁸⁺, in successive and well-defined complexation steps. Protonated forms of L2 give rise to relatively weak anion complexes with SO₄^2-, but the addition of Cu²⁺ significantly enhances the binding ability of the ligand toward this anion below pH 9. In more alkaline solutions, an opposite trend is observed. The coordination properties of L2 are discussed with the support of modelling calculations. According to results, L2 is a promising molecule for the preparation of solid supported materials for the recovery of cations and anions from aqueous media and/or for applications in heterogeneous catalysis.

Surface Decoration of Amino-Functionalized Metal-Organic Framework/Graphene Oxide Composite onto Polydopamine-Coated Membrane Substrate for Highly Efficient Heavy Metal Removal

A new metal-organic framework/graphene oxide composite (IRMOF-3/GO) with high adsorption capacity of copper(II) (maximal adsorption amount = 254.14 mg/g at pH 5.0 and 25 °C) was prepared. Novel and highly efficient nanofiltration (NF) membrane can be facilely fabricated via surface decoration of IRMOF-3/GO onto polydopamine (PDA)-coated polysulfone (PSF) substrate. After decoration of IRMOF-3/GO, membrane surface potential increased from 6.7 to 13.1 mV at pH 5.0 and 25 °C. Due to the adsorption effect of IRMOF-3/GO and the enhancement of membrane surface potential, the prepared NF membrane (the loading amount of IRMOF-3/GO is ca. 13.6 g/m²) exhibits a highly efficient rejection of copper(II). The copper(II) rejection reaches up to ∼90%, while maintaining a relatively high flux of ∼31 L/m²/h at the pressure of 0.7 MPa and pH 5.0. Moreover, the membrane also presents an outstanding stability throughout the 2000 min NF testing period. Thus, the newly developed NF membrane shows a promising potential for water cleaning. This work provides a worthy reference for designing highly efficient NF membranes modified by metal-organic framework (MOF) relevant materials.

Diglycolamide-functionalized poly(propylene imine) diaminobutane dendrimers for sequestration of trivalent f-elements: synthesis, extraction and complexation

Three generations of diglycolamide-functionalized poly(propylene imine)diaminobutane dendrimers were synthesized and evaluated for their complexation ability towards trivalent actinides/lanthanides.

Anion Complexes with Tetrazine-Based Ligands: Formation of Strong Anion-π Interactions in Solution and in the Solid State

Ligands L1 and L2, consisting of a tetrazine ring decorated with two morpholine pendants of different lengths, show peculiar anion-binding behaviors. In several cases, even the neutral ligands, in addition to their protonated HL(+) and H2L(2+) (L = L1 and L2) forms, bind anions such as F(-), NO3(-), PF6(-), ClO4(-), and SO4(2-) to form stable complexes in water. The crystal structures of H2L1(PF6)2·2H2O, H2L1(ClO4)2·2H2O, H2L2(NO3)2, H2L2(PF6)2·H2O, and H2L2(ClO4)2·H2O show that anion-π interactions are pivotal for the formation of these complexes, although other weak forces may contribute to their stability. Complex stability constants were determined by means of potentiometric titration in aqueous solution at 298.1 K, while dissection of the free-energy change of association (ΔG°) into its enthalpic (ΔH°) and entropic (TΔS°) components was accomplished by means of isothermal titration calorimetry measurements. Stability constants are poorly regulated by anion-ligand charge-charge attraction. Thermodynamic data show that the formation of complexes with neutral ligands, which are principally stabilized by anion-π interactions, is enthalpically favorable (-ΔG°, 11.1-17.5 kJ/mol; ΔH°, -2.3 to -0.5 kJ/mol; TΔS°, 9.0-17.0 kJ/mol), while for charged ligands, enthalpy changes are mostly unfavorable. Complexation reactions are invariably promoted by large and favorable entropic contributions. The importance of desolvation phenomena manifested by such thermodynamic data was confirmed by the hydrodynamic results obtained by means of diffusion NMR spectroscopy. In the case of L2, complexation equilibria were also studied in a 80:20 (v/v) water/ethanol mixture. In this mixed solvent of lower dielectric constant than water, the stability of anion complexes decreases, relative to water. Solvation effects, mostly involving the ligand, are thought to be responsible for this peculiar behavior.

ATP dephosphorylation can be either enhanced or inhibited by pH-controlled interaction with a dendrimer molecule

Synthetic polyammonium/polyamine receptors are known to enhance ATP dephosphorylation in solution. ATP interaction with a G-3 poly(ethylene imine) dendrimer shows an unprecedented behaviour, the dendrimer catalyst being able to enhance or inhibit dephosphorylation of the nucleotide depending on the solution pH.

Directional supracolloidal self-assembly via dynamic covalent bonds and metal coordination

An emerging strategy towards the sophistication of supramolecular nanomaterials is the use of supracolloidal self-assembly, in which micelles or colloids are used as building blocks. Binding directionality can produce nanostructures with attractive properties. Herein, we present a new directional supracolloidal self-assembly by virtue of dynamic covalent bonds and metal coordination in water. Conjugation of a ligand precursor to a water-soluble block copolymer through dynamic covalent bonds leads to the dehydration and micellization of the functionalized polymer. Reversible reaction facilitates the permeation of metal ions into core-shell interfaces. Conversely, metal-coordination promotes reaction over the interfaces. Cu(ii)-coordination occurs overwhelmingly inside each isolated micelle. However, Zn(ii)-coordination induced a directional self-assembly whose nanostructures evolve stepwise from nanorods, nanowires, necklaces, and finally to supracolloidal networks scaling-up to several tens of micrometres. Post-reactions of simultaneous dynamic covalent bond conversion and Zn(ii)-coordination over the core-shell interfaces endow these supracolloidal networks with a huge specific surface area for hydrophobic dative metal centres accessible to substrates in water. Water-soluble shells play important roles in directional supracolloidal assembly and in the stabilization of nanostructures. Thus the directional self-assembly provides a versatile platform to produce metallo-hybridized nanomaterials that are promising as enzyme-inspired aqueous catalysts.

Inorganic mercury sequestration by a poly(ethylene imine) dendrimer in aqueous solution

The interaction of the G-2 poly(ethylene imine) dendrimer L, derived from ammonia as initiating core, with Hg(II) and HgCl42- was studied in aqueous solution by means of potentiometric (pH-metric) measurements. Speciation of these complex systems showed that L is able to form a wide variety of complexes including 1:1, 2:1, 3:1 and 3:2 metal-to-ligand species, of different protonation states, as well as the anion complexes [(H7L)HgCl4]5+ and [(H8L)HgCl4]6+. The stability of the metal complexes is very high, making L an excellent sequestering agent for Hg(II), over a large pH range, and a promising ligand for the preparation of functionalized activated carbons to be employed in the remediation and the prevention of environmental problems.

Reversible magnetic mercury extraction from water

Magnetic carbon-coated cobalt nanoparticles functionalized with polyethyleneimine proved to be highly effective and selective for the detoxification of mercury ions from aqueous solutions.

Binding and removal of octahedral, tetrahedral, square planar and linear anions in water by means of activated carbon functionalized with a pyrimidine-based anion receptor

Enhanced anion recovery from water is achieved upon functionalization of activated carbon with polyamine groups.

A dodecanuclear copper(ii) cage self-assembled from six dicopper building units

Sandwich capping of two {Cu₃(μ₃-NO₃)}⁵⁻ triangles over a hydroxido-bridged {Cu₆} hexagon, supported by six ligands resulted in a novel Cu₁₂ cage in a flattened cuboctahedral topology.