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

Porous Oxyhydroxide Derived from Metal-Organic Frameworks as Efficient Triphosphatase-like Nanozyme for Chromium(III) Ion Colorimetric Sensing

The dephosphorylation that involves the removal of a phosphate group from a substrate molecule plays a significant role in living organisms. An enzyme mimic (nanozyme) with phosphatase-like catalytic activity has recently received attention in terms of its capacity for dephosphorylation. In this study, three types of highly porous oxyhydroxide with remarkable triphosphatase-like catalytic activities, ZrOOH, GdOOH, and HfOOH, have been prepared through the transformation of metal-organic frameworks (MOFs) using a simple alkaline hydrolysis method. The triphosphatase mimetic activities of ZrOOH, GdOOH, and HfOOH were then thoroughly investigated and verified. In particular, an isotopic tracing experiment revealed that abundant surface hydroxyls could serve as nucleophilic agents to directly attack the electropositive phosphorus atom, causing the cleavage of the terminal phosphoester bonds of phosphoester substrate molecules. The kinetic analysis provided calculated values of K_m of 105.7, 90.5, and 46.1 μM, while the V_max values were 3.57, 4.76, and 2.74 × 10^-8 M s^-1 and E_a values were estimated to be 47.52, 41.15, and 52.79 kJ/mol for ZrOOH, GdOOH, and HfOOH, respectively. The chromium(III) ions acting as "poisoning" inhibitors efficiently downregulated the triphosphatase mimetic activity of GdOOH. On the basis of this effect, a colorimetric chromium(III) ion-sensing system was explored, which provided a relevant linear response range for the detection of chromium(III) ions of 5.0-200 μM and a low detection limit of 0.84 μM. This work not only shows the great potential of ZrOOH, GdOOH, and HfOOH as triphosphatase nanozymes but also deepens our understanding of the role of surface hydroxyls on phosphatase-mimicking nanozyme catalytic dephosphorization, which could be used in the rational design of phosphatase-mimicking nanozymes. Furthermore, the developed colorimetric sensing system could be applied to chromium(III) ion detection in biological systems.

Sensing Zn2+ in Aqueous Solution with a Fluorescent Scorpiand Macrocyclic Ligand Decorated with an Anthracene Bearing Tail

Synthesis of the new scorpiand ligand L composed of a [9]aneN3 macrocyclic ring bearing a CH2CH2NHCH2-anthracene tail is reported. L forms both cation (Zn2+) and anion (phosphate, benzoate) complexes. In addition, the zinc complexes of L bind these anions. The equilibrium constants for ligand protonation and complex formation were determined in 0.1 M NaCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric (pH-metric) titrations. pH Controlled coordination/detachment of the ligand tail to Zn2+ switch on and off the fluorescence emission from the anthracene fluorophore. Accordingly, L is able to sense Zn2+ in the pH range 6-10 down to nM concentrations of the metal ion. L can efficiently sense Zn2+ even in the presence of large excess of coordinating anions, such as cyanide, sulphide, phosphate and benzoate, despite their ability to bind the metal ion.

Successive outermost-to-core shell directionality of the protonation of poly(propyl ether imine) dendritic gene delivery vectors

The protonation behaviour of polycationic compounds has direct relevance to their ability to condense and deliver nucleic acids. This report pertains to a study of the protonation behaviour of polycationic poly(propyl ether imine) (PETIM) dendritic gene delivery vectors that are constituted with tertiary amine core moiety and branch sites, n-propyl ether linkages, and primary amine peripheries. The ability of this series of dendrimers to condense nucleic acids and mediate endosomal escape was studied by unravelling the protonation behaviour of the dendrimers aided by pH metric titrations and 1H and 15N NMR spectroscopies. The results demonstrate protonation of the primary and tertiary amines of outermost-to-core shells occurring in a successive stepwise fashion, in contrast to other polycationic vectors. Theoretical calculations based on the Ising model rationalize further the finer details of protonation at each shell. The protonation pattern correlates with the endosomal buffering and nucleic acid condensation properties of this PETIM-based dendritic gene delivery vectors. The study establishes that the protonation behaviour is a critical and essential parameter to assess the gene condensation and delivery vector properties of a polycationic compound.

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.