Dinuclear Zinc(II) Complexes with Hydrogen Bond Donors as Structural and Functional Phosphatase Models

Pyridine appended pyrimidine bis hydrazone: Zn2+/ATP detection, bioimaging and functional properties of its dinuclear Zn(II) complex

A pyridine functionalized pyrimidine-based system, H2P was successfully synthesized, characterized, and evaluated for its remarkable selective characteristics towards Zn2+ and ATP ions. The chemical sensing capabilities of H2P were demonstrated through absorption, fluorescence, and NMR spectroscopic techniques. The probe exhibited outstanding sensitivity when interacting with the ions, demonstrating relatively strong association constants and impressively low detection limits. The comprehensive binding mechanism of H2P with respect to Zn2+ and ATP ions was investigated using a combination of analytical methods, including Job's plot, NMR spectroscopy, mass spectrometry, and density functional theory (DFT) experiments. The interesting sensing ability of H2P for Zn2+/ATP ions was harnessed for live cell bioimaging and other diverse on-site detection purposes, including paper strips, cotton swabs, and applications involving mung bean sprouts. Further, the fluorescent probe demonstrated its effectiveness in detecting Zn2+ and ATP within live cells, indicating its significant potential in the realm of biological imaging applications. Moreover, the molecular configuration of the zinc complex (H2P-Zn2Cl4), derived from H2P, was elucidated using X-ray crystallography. This complex exhibited intriguing multifunctional attributes, encompassing its capability for detecting picric acid and for reversible acid/base sensing responses. The enhanced conducting behavior of the complex as well as its resistance properties were investigated by performing I-V characteristics and electrochemical impedance spectroscopic (EIS) experiments respectively.

The crucial role of hydrogen bonding in shaping the structures of zinc-based coordination polymers using tridentate N, N, O donor reduced Schiff base ligands and bridging acetates

In this manuscript we report the synthesis and characterization of two new polynuclear zinc(ii) complexes, [Zn2L1(μ-OAc)3]n·H2O (1) and [Zn2L2(μ-OAc)3]n (2) using two tridentate ligands, HL1 {4-chloro-2-(((2-(methylamino)ethyl)amino)methyl)phenol} and HL2 {2,4-dibromo-6-(((3-(methylamino)propyl)amino)methyl)phenol}. The structures were confirmed by single-crystal X-ray diffraction analysis. Both complexes form 1D chains. The energy of H-bonding interaction in the solid state structures of the complexes has been estimated by DFT calculation and the crucial role of hydrogen bonding in shaping their structures has been highlighted.

Designed Metal-Containing Peptoid Membranes as Enzyme Mimetics for Catalytic Organophosphate Degradation

The detoxification of lethal organophosphate (OP) residues in the environment is crucial to prevent human exposure and protect modern society. Despite serving as excellent catalysts for OP degradation, natural enzymes require costly preparation and readily deactivate upon exposure to environmental conditions. Herein, we designed and prepared a series of phosphotriesterase mimics based on stable, self-assembled peptoid membranes to overcome these limitations of the enzymes and effectively catalyze the hydrolysis of dimethyl p-nitrophenyl phosphate (DMNP)─a nerve agent simulant. By covalently attaching metal-binding ligands to peptoid N-termini, we attained enzyme mimetics in the form of surface-functionalized crystalline nanomembranes. These nanomembranes display a precisely controlled arrangement of coordinated metal ions, which resemble the active sites found in phosphotriesterases to promote DMNP hydrolysis. Moreover, using these highly programmable peptoid nanomembranes allows for tuning the local chemical environment of the coordinated metal ion to achieve enhanced hydrolysis activity. Among the crystalline membranes that are active for DMNP degradation, those assembled from peptoids containing bis-quinoline ligands with an adjacent phenyl side chain showed the highest hydrolytic activity with a 219-fold rate acceleration over the background, demonstrating the important role of the hydrophobic environment in proximity to the active sites. Furthermore, these membranes exhibited remarkable stability and were able to retain their catalytic activity after heating to 60 °C and after multiple uses. This work provides insights into the principal features to construct a new class of biomimetic materials with high catalytic efficiency, cost-effectiveness, and reusability applied in nerve agent detoxification.

Versatile applications of transition metal incorporating quinoline Schiff base metal complexes: An overview

Since the last decade, research on quinoline Schiff base metal complexes has risen substantially due to their versatile applications across many significant fields. Schiff bases are also known as azomethines, aldimines, and imines. Quinoline Schiff base-derived metal complexes are intriguing to study topics. These complexes are employed in biological, analytical, and catalytic fields. Researchers have found that Schiff bases are more biologically active when coordinated with metal ions. Research in the biological sciences has shown that heterocyclic compounds like quinoline and its derivatives are important. Because of their broad spectrum of activity, quinoline derivatives have been discovered to be effective therapeutic agents for various disorders. Even though various classical synthetic pathways mentioned in the literature are still in use, there is an urgent need for a new, more effective method that is safer for the environment, has a higher yield, generates less hazardous waste, and is easier to use. This highlights the critical need for a safe, eco-friendly approach to quinoline scaffold synthesis. This review focuses exclusively on Schiff base metal complexes derived from quinoline, fabricated and studied in the past ten years, and having anticancer, antibacterial, antifungal, antioxidant, antidiabetic, antiproliferative, DNA-intercalation, and cytotoxic activities.

Transesterification of RNA model induced by novel dinuclear copper (II) complexes with bis-tridentate imidazole derivatives

Two novel bis-tridentate imidazole derivatives were conveniently synthesized using a 'one-pot' method. Their dinuclear (Cu₂L¹Cl₄, Cu₂L²Cl₄) and mononuclear (CuL¹Cl₂, CuL²Cl₂∙H₂O) copper (II) complexes were synthesized to comparably evaluate their reactivities in the hydrolytic cleavage of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) as a classic RNA model. Single crystals of Cu₂L¹Cl₄ and Cu₂L²Cl₄ indicate that both of them are centrosymmetric, and each central copper ion is penta-coordinated. Regarding the transesterification of HPNP, both of dinuclear ones exhibited excess one order of magnitude rate enhancement in contrast with auto-hydrolysis reaction. Under comparable conditions, dinuclear complexes displayed no more than twofold increase in activity over their mononuclear analogues, which verifies the lack of binuclear cooperation effect due to long Cu-to-Cu space.

Molecularly imprinted self-buffering double network hydrogel containing bi-amidoxime functional groups for the rapid hydrolysis of organophosphates

The development of high-performance catalyst materials with high catalytic activity for the hydrolysis of organophosphorus toxicants without additional pH buffer conditions has become an urgent need for practical application. Here, a multifunctional molecularly imprinted polymer double network hydrogel (MIP-DN) material has been prepared by integrating the first polymer network containing the functional group of bi-amidoxime as the catalytic active center and the cationic polymer polyethyleneimine (PEI) with pH buffer function as the main component of the second network. Advantageously, the resultant MIP-DN hydrogel showed excellent catalytic performance without additional pH buffer conditions, exhibiting a half-life of 25 min for the hydrolysis of paraoxon in pure water. Together with multi-functions of high catalytic activity, self-buffering function and excellent processability, the MIP-DN hydrogel prepared in this work provides a new strategy for the preparation of catalytic materials with practical application value toward toxic organophosphates.

Synthesis, characterization and computational investigation of the phosphatase activity of a dinuclear Zinc(II) complex containing a new heptadentate asymmetric ligand

We report the synthesis of a new asymmetric heptadentate ligand based on the 1,3-diaminopropan-2-ol backbone. The ligand 3-[[3-(bis-pyridin-2-ylmethyl-amino)-2-hydroxy-propyl]-(2-carbamoyl-ethyl)-amino]-propionamide (HL1) contains two amide and two pyridine groups attached to the 1,3-diaminopropan-2-ol core. Reaction between HL1 and Zn(ClO₄)₂.6H₂O resulted in the formation of the dinuclear [Zn₂(L1)(μ-OAc)](ClO₄)₂ complex, characterized by single crystal X-ray diffraction, ¹H, ¹³C and ¹⁵N NMR, ESI-(+)-MS, CHN elemental analysis as well as infrared spectroscopy. The phosphatase activity of the complex was studied in the pH range 6-11 employing pyridinium bis(2,4-dinitrophenyl)phosphate (py(BDNPP)) as substrate. The complex exhibited activity dependent on the pH, presenting an asymmetric bell shape profile with the highest activity at pH 9; at high pH ligand exchange is rate-limiting. The hydrolysis of BDNPP^- at pH 9 displayed behavior characteristic of Michaelis-Menten kinetics, with k_cat = 5.06 × 10^-3 min^-1 and K_m = 5.7 ± 1.0 mM. DFT calculations map out plausible reaction pathways and identify a terminal, Zn(II)-bound hydroxide as likely nucleophile.

Zinc(II)-Cyclen Multifunctional Complex Module-Mediated Polycation-Based High-Performance pDNA Vectors

A kind of novel multifunctional modules based on zinc(II)-coordinative cyclen has been developed, which is utilized to modify low molecular weight polyethylenimine (LMWPEI) obtaining high-performance DNA vectors. A series of in vitro experiments were carried out to explore the performance of the module in improving the key process of gene transfection, such as DNA condensation, serum resistance, cellular uptake, and endosomal escape. The results demonstrate that there is a significant synergistic effect between the functional module and PEI2.5k in the process of breaking through the key barriers of gene transfection. The optimal Zn-PCD mediates 160-fold higher gluciferase activity than commercial transfection reagents PEI25k in ADSC stem cells with more than 90% cell viability and achieves excellent transfection efficiency in diverse cell types, for instance, HepG2 cells, 293T cells, and 293F suspension cells.

Mono- and dinuclear zinc complexes bearing identical bis(thiosemicarbazone) ligand that exhibit alkaline phosphatase-like catalytic reactivity

Mono- and dinuclear zinc(II) complexes bearing bis(thiosemicarbazone) (bTSC) ligand were employed in the cleavage of phosphoester bonds. Comparative kinetic studies combined with theory suggested that the P-O bond cleavage is much accelerated by dinuclear zinc(II) complex in the presence of base. Based on the DFT-optimized structures of the proposed intermediates, it is plausible that (1) the removal of sulfur atoms of bTSC ligand from the zinc center provides two vacant sites for the binding of water (or hydroxide ion) and phosphoester and (2) the H-bonding between water (or hydroxide ion) and phosphoester, through several water molecules, may also assist the P-O bond cleavage and facilitate the nucleophilic attack. The kinetic and catalytic studies on the hydrolysis of phosphoester by dinuclear zinc complex showed a much-enhanced reactivity under basic reaction conditions, reaching over 95% conversion yield within 4 h. The currently presented compounds are arguably one of the faster synthetic Zn-based model performing phosphatase-like activity presented so far.

Ag(I) Pyridine-Amidoxime Complex as the Catalysis Activity Domain for the Rapid Hydrolysis of Organothiophosphate-Based Nerve Agents: Mechanistic Evaluation and Application

Two novel Ag(I) complexes containing synergistic pyridine and amidoxime ligands (Ag-DPAAO and Ag-PAAO) were first designed as complex monomers. Taking advantage of the molecular imprinting technique and solvothermal method, molecular imprinted porous cross-linked polymers (MIPCPs) were developed as a robust platform for the first time to incorporate Ag-PAAO into a polymer material as a recyclable catalyst. Advantageously, the observed pseudo first-order rate constant (k_obs) of MIPCP-Ag-PAAO-20% for ethyl-parathion (EP) hydrolysis is about 1.2 × 10⁴-fold higher than that of self-hydrolysis (30 °C, pH = 9). Furthermore, the reaction mechanism of the MIPCP-containing Ag-PAAO-catalyzed organothiophosphate was analyzed in detail using density functional theory and experimental spectra, indicating that the amidoxime can display dual roles for both the key coordination with the silver ion and nucleophilic attack to weaken the P-OAr bond in the catalytic active site.

Highly Photoluminescent Nitrogen- and Zinc-Doped Carbon Dots for Efficient Delivery of CRISPR/Cas9 and mRNA

Safe and efficient delivery of CRISPR/Cas9 systems is still a challenge. Here we report the development of fluorescent nitrogen- and zinc-doped carbon dots (N-Zn-doped CDs) using one-step microwave-aided pyrolysis based on citric acid, branched PEI_25k, and different zinc salts. These versatile nanovectors with a quantum yield of around 60% could not only transfect large CRISPR plasmids (∼9 kb) with higher efficiency (80%) compared to PEI_25k and lipofectamine 2000 (Lipo 2K), but they also delivered mRNA into HEK 293T cells with the efficiency 20 times greater than and equal to that of PEI_25k and Lipo 2K, respectively. Unlike PEI_25k, N-Zn-doped CDs exhibited good transfection efficiency even at low plasmid doses and in the presence of 10% fetal bovine serum (FBS). Moreover, these nanovectors demonstrated excellent efficiency in GFP gene disruption by transferring plasmid encoding Cas9 and sgRNA targeting GFP as well as Cas9/sgRNA ribonucleoproteins into HEK 293T-GFP cells. Hence, N-Zn-doped CDs with remarkable photoluminescence properties and high transfection efficiency in the delivery of both CRISPR complexes and mRNA provide a promising platform for developing safe, efficient, and traceable delivery systems for biological research.

Dicyanamide-intertwined assembly of two new Zn complexes based on N2O4-type pro-ligand: Synthesis, crystal networks, spectroscopic insights, and selective nitroaromatic turn-off fluorescence sensing

Two new dicyanamide bridged multinuclear Zn complexes, [Zn₂(L¹)(µ_1,5-dca)₂(µ₁-dca)]_n (1) and [Zn₂(L²)(µ_1,5-dca)₂(µ₁-dca)]_n (2) have been synthesized using N₂O₄-based pro-ligands (H₂L¹ = N,N'-bis(5-bromo-3-methoxysalicylidenimino)-1,3-diaminopropane, H₂L² = N,N'-bis(3-ethoxysalicylidene)-2,2-dimethyl-1,3-propanediamine) and characterized by microanalytical and spectroscopic techniques. Both complexes are stable in solution and solid-state. Thermogravimetric analysis (TGA) findings showed that complexes are stable at room temperature. Single-crystal X-ray diffraction (SCXRD) has proven that complexes are identical structures where two zinc metal ions are crystallographically independent. The directional properties of dicyanamide co-ligands via µ_1,5 bridging have resulted in different connectivity of zinc metal ions leading to 1D templates. SCXRD revealed some notable non-covalent interactions (π⋯π, C-H····π, and H-bonding) in their solid-state crystal structures. 1-2 have strong fluorescence behaviour over pro-ligands, which may be quenched in the presence of various electron-deficient explosive nitroaromatic compounds (epNACs). Complex 2 fluorescence intensity is sharper than 1; hence the former retained high sensitivity and selectivity for trinitrophenol (TNP). The enhancement of fluorescence mechanism, detection limit (LOD), and the quenching constant (K_SV) have been calculated using the Stern-Volmer equation (SV), where the K_SV value for TNP is found to be 1.542 × 10⁴ M^-1. The solution phase quenching mechanism has been rationalized by (a) electrostatic interactions through charge-transfer complex, (b) photo-induced electron transfer (PET) by the HOMO-LUMO energy gap via DFT, and (c) fluorescence resonance energy transfer (FRET). Finally, complex 2 is applied as a sensor by turn-off fluorescence response to detecting TNP nitroaromatics in the DMF medium.

Zn(ii)-Dipicolylamine analogues with amphiphilic side chains endow low molecular weight PEI with high transfection performance

To investigate the effect of amphiphilic balance of Zn(ii)-dipicolylamine analogues on the transfection process, we fabricated a series of Zn(ii)-dipicolylamine functional modules (DDAC-Rs) with different hydrophilic-phobic side chains to modify low molecular weight PEI (Zn-DP-Rs) by the Michael addition reaction. Zn-DP-Rs with hydrophilic terminal hydroxy group side chains demonstrate superior overall performance compared to those of hydrophobic alkyl side chains. In terms of the influence of the chain lengths in DDAC-Rs, from Zn-DP-A/OH-3 to Zn-DP-A/OH-5, the corresponding transfection efficiency shows an upward trend as the lengths increase. However, decreasing efficacy is observed with further increase in the length of side chains. In addition, the Zn-DP-Rs with amphiphilic side chains show prominent performance in every respect, highlighting the significance of balance in the amphipathy of side chains in DDAC-Rs. This work is of great significance for the development of polycationic gene carrier materials with excellent performance.

New AlIIIZnII and AlIIICuII dinuclear complexes: Phosphatase-like activity and cytotoxicity

Herein, we report the synthesis and characterization of the first two Al^III(μ-OH)M^II (M = Zn (1) and Cu (2)) complexes with the unsymmetrical ligand H₂L{2-[[(2-hydroxybenzyl)(2-pyridylmethyl)]aminomethyl]-6-bis(pyridylmethyl)aminomethyl}-4-methylphenol. The complexes were characterized through elemental analysis, X-ray crystallography, IR spectroscopy, mass spectrometry and potentiometric titration. In addition, complex 2 was characterized by electronic spectroscopy. Kinetics studies on the hydrolysis of the model substrate bis(2,4-dinitrophenyl)phosphate by 1 and 2 show Michaelis-Menten behavior, with 1 being slightly more active (8.31%) than 2 (at pH 7.0). The antimicrobial effect of the compounds was studied using four bacterial strains (Staphylococcus aureus, Pseudomonas aeuruginosa, Shigella sonnei and Shigella dysenteriae) and for both complexes the inhibition of bacterial growth was superior to that caused by sulfapyridine, but inferior to that of tetracycline. The dark cytotoxicity and photocytotoxicity (under UV-A light) of the complexes in a chronic myelogenous leukemia cell line were investigated. Complexes 1 and 2 exhibited significant cytotoxic activity against K562 cells, which undergoes a 2-fold increase on applying 5 min of irradiation with UV-A light. Complex 2 was more effective and a good correlation between cytotoxicity and intracellular concentration was observed, the intracellular copper concentration required to inhibit 50% of cell growth being 3.5 × 10^-15 mol cell^-1.

A long-term stable paper-based glucose sensor using a glucose oxidase-loaded, Mn2BPMP-conjugated nanocarrier with a smartphone readout

A simple paper-based analytical device (PAD) for the one-pot detection of glucose was developed herein using an artificial peroxidase-functionalized and glucose oxidase (GOx)-loaded pluronic-based nanocarrier (PNC). Mn₂BPMP (BPMP; 2,6-bis[(bis(2-pyridylmethyl)amino)-methyl]-4-methylphenolate), an artificial peroxidase, was conjugated to PNC, allowing GOx to be loaded with a very high encapsulation efficiency. In solution, Mn₂BPMP-PNC showed higher peroxidase-like catalytic efficiency than did Mn₂BPMP at physiological pH. In addition, glucose detection via enzyme cascade reaction between GOx and Mn₂BPMP in the GOx loaded-Mn₂BPMP-PNC was more sensitive than the simple combination of Mn₂BPMP and GOx with excellent selectivity. Subsequently, a PAD was fabricated using a laser printer with an assay substance containing GOx loaded-Mn₂BPMP-PNC and peroxidase chromogenic substrate. The prepared Mn₂BPMP-PNC-based PAD quantitatively measured glucose in human serum ranging from normal levels to those typical for diabetics as well as in buffer by obtaining RGB (red, green, and blue) color values through smartphone readout or the naked eye. Importantly, the present PNC-based PAD maintained the detection efficiency during storage at room temperature for 6 weeks in contrast to the rapid decrease in detection efficiency obtained for PAD containing Mn₂BPMP and GOx without PNC.

Recent Advances in Heterogeneous Catalytic Systems Containing Metal Ions for Phosphate Ester Hydrolysis

Organophosphates are a class of organic compounds that are important for living organisms, forming the building blocks for DNA, RNA, and some essential cofactors. Furthermore, non-natural organophosphates are widely used in industrial applications, including as pesticides; in laundry detergents; and, unfortunately, as chemical weapons agents. In some cases, the natural degradation of organophosphates can take thousands of years; this longevity creates problems associated with handling and the storage of waste generated by such phosphate esters, in particular. Efforts to develop new catalysts for the cleavage of phosphate esters have progressed in recent decades, mainly in the area of homogeneous catalysis. In contrast, the development of heterogeneous catalysts for the hydrolysis of organophosphates has not been as prominent. Herein, examples of heterogeneous systems are described and the importance of the development of heterogeneous catalysts applicable to organophosphate hydrolysis is highlighted, shedding light on recent advances related to different solid matrices that have been employed.

Binuclear metal complexes with a novel hexadentate imidazole derivative for the cleavage of phosphate diesters and biomolecules: distinguishable mechanisms

Oxidative cleavage of phosphate diesters (HPNP, BNPP) is highly faster than the hydrolytic one by binuclear metal complexes with novel imidazole derivative, producing a non-lactone phosphate monoester due to the direct attack of free radicals.

Synthesis and redox reactions of binuclear zinc(ii)–thiolate complexes with elemental sulfur

The synthesis, characterization and reactivity of a series of binuclear zinc(ii) complexes are described featuring the redox reaction of coordinated thiolates with elemental sulfur.

A Series of Manganese(III) Salen Complexes as a Result of Team-Based Inquiry in a Transnational Education Programme

The development of a team-based approach to research-led transnational practical chemistry teaching is described in which a team of five Chinese students on an articulated transnational degree programme, supported by a team of academic and technical staff, carried out a study examining the structural chemistry of a series of manganese(III) salen complexes. A series of four crystallographically characterized manganese(III) salen complexes with ancillary carboxylate ligands are reported here. The carboxylate coordination modes range from the bridging syn-anti μ² -κO : κO' mode observed in the predominant cyclohexanoate and isobutyrate species, to a capping terminal monodentate mode for the adamantanoate species, and an unusual mixture of bridging and terminal coordination modes observed in a second minor phase of the cyclohexanoate species. The variation on extended structures based on the weakly interacting aliphatic backbones may provide a useful basis for further structural studies.

Mechanistic Studies of Homo- and Heterodinuclear Zinc Phosphoesterase Mimics: What Has Been Learned?

Phosphoesterases hydrolyze the phosphorus oxygen bond of phosphomono-, di- or triesters and are involved in various important biological processes. Carboxylate and/or hydroxido-bridged dizinc(II) sites are a widespread structural motif in this enzyme class. Much effort has been invested to unravel the mechanistic features that provide the enormous rate accelerations observed for enzymatic phosphate ester hydrolysis and much has been learned by using simple low-molecular-weight model systems for the biological dizinc(II) sites. This review summarizes the knowledge and mechanistic understanding of phosphoesterases that has been gained from biomimetic dizinc(II) complexes, showing the power as well as the limitations of model studies.

Insights into Second-Sphere Effects on Redox Potentials, Spectroscopic Properties, and Superoxide Dismutase Activity of Manganese Complexes with Schiff-Base Ligands

Six Mn-Schiff base complexes, [Mn(X-salpn)]0/+ (salpn = 1,3-bis(sal-ic-ylidenamino)propane, X = H [1], 5-Cl [2], 2,5-F2 [3], 3,5-Cl2 [4], 5-NO2 [5], 3,5-(NO2)2 [6]), were synthesized and characterized in solution, and second-sphere effects on their electrochemical and spectroscopic properties were analyzed. The six complexes catalyze the dismutation of superoxide with catalytic rate constants in the range 0.65 to 1.54 × 106 M-1 s-1 obtained through the nitro blue tetrazolium photoreduction inhibition superoxide dismutases assay, in aqueous medium of pH 7.8. In solution, these compounds possess two labile solvent molecules in the axial positions favoring coordination of the highly nucleophilic O2 •- to the metal center. Even complex 5, [Mn(5-(NO2)salpn) (OAc) (H2O)], with an axial acetate in the solid state, behaves as a 1:1 electrolyte in methanolic solution. Electron paramagnetic resonance and UV-vis monitoring of the reaction of [Mn(X-salpn)]0/+ with KO2 demonstrates that in diluted solutions these complexes behave as catalysts supporting several additions of excess O2 •-, but at high complex concentrations (≥0.75 mM) catalyst self-inhibition occurs by the formation of a catalytically inactive dimer. The correlation of spectroscopic, electrochemical, and kinetics data suggest that second-sphere effects control the oxidation states of Mn involved in the O2 •- dismutation cycle catalyzed by complexes 1-6 and modulate the strength of the Mn-substrate adduct for electron-transfer through an inner-sphere mechanism.

A series of trinuclear zinc(ii) complexes with reduced Schiff base ligands: turn-off fluorescent chemosensors with high selectivity for nitroaromatics

A series of trinuclear zinc(ii) complexes have been synthesized and characterized by X-ray crystallography. The ability of the complexes to act as sensors for the detection of nitroaromatics in DMF has been assessed.

Phosphatase-mimicking activity of a unique penta-nuclear zinc(ii) complex with a reduced Schiff base ligand: assessment of its ability to sense nitroaromatics

A penta-nuclear zinc(ii) complex has been synthesized and characterized. The complex has shown good phosphatase-mimicking activity, which has been evaluated spectrophotometrically. The complex also behaves as a sensor for the detection of nitroaromatics via turn-off fluorescence response.

Zinc Coordination Substitute Amine: A Noncationic Platform for Efficient and Safe Gene Delivery

Amines have been extensively involved in vector design thus far, however, their clinical translation has been impeded by several obstacles: cytotoxicity, polyplex serum instability and low efficacy in vivo. In pursuit of functional groups to substitute amines in vector design to address these disadvantages is of great significance. Herein, we report well-tailored noncationic copolymers that contain hydrophilic, hydrophobic, and zinc coordinative moieties through reversible addition-fragmentation chain transfer (RAFT) polymerization for efficient and safe gene delivery. These polymers are capable of condensing DNA, enabling the formation of uncharged polyplexes. Especially, the zinc coordinative ligand can simultaneously benefit strong DNA binding, robust cellular uptake, efficacious endosomal destabilization, low cytotoxicity, and avoidance of serum protein adsorption. The coordinative module holds great promise to substitute amines and inspires the development of next-generation gene vectors. More importantly, the coordinative copolymers illuminate the possibility and potential of noncationic gene delivery systems for clinical applications.

Phosphodiester models for cleavage of nucleic acids

Nucleic acids that store and transfer biological information are polymeric diesters of phosphoric acid. Cleavage of the phosphodiester linkages by protein enzymes, nucleases, is one of the underlying biological processes. The remarkable catalytic efficiency of nucleases, together with the ability of ribonucleic acids to serve sometimes as nucleases, has made the cleavage of phosphodiesters a subject of intensive mechanistic studies. In addition to studies of nucleases by pH-rate dependency, X-ray crystallography, amino acid/nucleotide substitution and computational approaches, experimental and theoretical studies with small molecular model compounds still play a role. With small molecules, the importance of various elementary processes, such as proton transfer and metal ion binding, for stabilization of transition states may be elucidated and systematic variation of the basicity of the entering or departing nucleophile enables determination of the position of the transition state on the reaction coordinate. Such data is important on analyzing enzyme mechanisms based on synergistic participation of several catalytic entities. Many nucleases are metalloenzymes and small molecular models offer an excellent tool to construct models for their catalytic centers. The present review tends to be an up to date summary of what has been achieved by mechanistic studies with small molecular phosphodiesters.

Dinuclear metal(ii)-acetato complexes based on bicompartmental 4-chlorophenolate: syntheses, structures, magnetic properties, DNA interactions and phosphodiester hydrolysis

A series of dinuclear metal(ii)-acetato complexes: [Ni2(μ-L(Cl)O)(μ2-OAc)2](PF6)·3H2O (1), [Ni2(μ-L(Cl)O)(μ2-OAc)2](ClO4)·CH3COCH3 (2), [Cu2(μ-L(Cl)O)(μ2-OAc)(ClO4)](ClO4) (3), [Cu2(μ-L(Cl)O)(OAc)2](PF6)·H2O (4), [Zn2(μ-L(Cl)O)(μ2-OAc)2](PF6) (5) and [Mn2(L(Cl)-O)(μ2-OAc)2](ClO4)·H2O (6), where L(Cl)O(-) = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-chlorophenolate, were synthesized. The complexes were structurally characterized by spectroscopic techniques and single crystal X-ray crystallography. Six-coordinate geometries with doubly bridged acetato ligands were found in Ni(ii), Zn(ii) and Mn(ii) complexes 1, 2, 5 and 6, whereas with Cu(ii) complexes a five-coordinate species was obtained with 4, and mixed five- and six-coordinate geometries with a doubly bridged dimetal core were observed in 3. The magnetic properties of complexes 1-4 and 6 were studied at variable temperatures and revealed weak to very weak antiferromagnetic interactions in 1, 2, 4 and 6 (J = -0.55 to -9.4 cm(-1)) and ferromagnetic coupling in 3 (J = 15.4 cm(-1)). These results are consistent with DFT calculations performed at the B3LYP/def2-TZVP(-f) level of theory. Under physiological conditions, the interaction of the dinculear complexes 1-5 with supercoiled plasmid ds-DNA did not show any pronounced nuclease activity, but Ni(ii) complexes 1 and 2 revealed a strong ability to unwind the supercoiled conformation of ds-DNA. The mechanistic studies performed on the interaction of the Ni(ii) complexes with DNA demonstrated the important impact of the nickel(ii) ion in the unwinding process. In combination with the DNA study, the phosphatase activity of complexes 1, 3, and 5 was examined by the phosphodiester hydrolysis of bis(2,4-dinitrophenol)phosphate (BDNPP) in the pH range of 5.5-10.5 at 25 °C. The Michaelis-Menten kinetics performed at pH 7 and 10.7 showed that catalytic efficiencies kcat/KM (kcat = catalytic rate constant, KM = substrate binding constant) decrease in the order: Ni(ii), 1 > Zn(ii), 5 > Cu(ii), 3. A similar trend was also observed with the turnover numbers at pH = 7. The results are discussed in relation to the coordination geometry and nature of the metal center as well as the steric environment imposed by the compartmental phenoxido ligand.

Zinc(ii) complexes with uncommon aminal and hemiaminal ether derivatives: synthesis, structure, phosphatase activity and theoretical rationalization of ligand and complex formation

Zinc(ii)-mediated and anion-controlled unusual Aminal and Hemiaminal Ether Derivative complex formations verified experimentally and rationalized by DFT calculations.

Metal complexes of a novel heterocyclic benzimidazole ligand formed by rearrangement-cyclization of the corresponding Schiff base. Electrosynthesis, structural characterization and antimicrobial activity

One-pot electrochemical synthesis of metal complexes containing a novel heterocyclic benzimidazole ligand is reported and characterized.

Portraying the role of halo ligands and the auxiliary part of ligands of mononuclear manganese(iii)-Schiff base complexes in catalyzing phospho–ester bond hydrolysis

The influences of the auxiliary part of ligands and halo ligands have been explored towards phosphatase like activity using a series of manganese(iii)-Schiff base complexes as catalysts.

Thiocyanate mediated structural diversity in phenol based "end-off" compartmental ligand complexes of group 12 metal ions: Studies on their photophysical properties and phosphatase like activity

The reaction of a pentadentate compartmental ligand LH, namely 4-tert-Butyl-2,6-bis-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol, with group 12 metal ions (Zn^II, Cd^II, Hg^II) followed by addition of NaSCN afforded one discrete dinuclear complex [Zn₂(L)(SCN)₃](1), and two polymeric 1D species [Cd_2.5(L)(SCN)₃(AcO)]_n (2) and [Hg₂(L)(SCN)₃]_n (3). All the complexes have been structurally characterized by single crystal X-ray diffraction. The crystal structure of the complexes reveals different coordination modes of thiocyanate anion that affect the different topology detected in the compounds: the anions are μ¹-NCS and μ^1,1-NCS connected in complex 1, while μ^1,3-NCS bridging mode is observed in 2, and μ¹-SCN and μ^1,3-NCS in 3. The polymeric Hg complex of the bicompartmental ligand system here reported is unprecedented. Detail study of their photophysical properties including the phosphorescence spectra at 77K has been done. Phosphatase like activity of all the three complexes has been performed in DMSO-H₂O medium and their activity follows the order of 1>2>>3.