Electronic Structure of Ytterbium Bis-indenyl and -cyclopentadienyl α-Diimine Complexes: A DFT and MS-CASPT2 Investigation

The electronic structure of Yb­(Cp′)₂(N–N) complexes with Cp′ = η⁵-C₅R₅ (Cp*) or η⁵-C₉H₇ (Ind) and N–N = DAB (<i>N</i>,<i>N</i>′-<i>tert</i>-butyl-1,4-diazabutadiene), bpy (2,2′-bipyridine), and pyca ((<i>E</i>)-<i>N</i>-(pyridine-2-ylmethylene)­aniline) was investigated by means of DFT and <i>ab initio</i> (CASSCF/CASPT2) calculations. Whereas the agreement between experimental features and theory is fair for the Yb­(Ind)₂bpy molecule, the description of the electronic ground state of Yb­(Ind)₂DAB and of the Cp* complexes is more problematic. The relative energies of the closed-shell singlet, lowest open-shell singlet, and triplet were calculated for Yb­(Ind)₂DAB with various functionals at the DFT level, which overstabilize the closed-shell singlet. All functionals place the open-shell singlet energetically close to the triplet state. The best functionals (B3LYP, M06, TPSSh) estimate the singlet–triplet energy gap in the range 17–28 kJ·mol^–1, in disagreement with the experimental data. The electronic structure of the smaller and more symmetric system Yb­(η⁵-C₅H₅)₂(N–N) (N–N = DAB, bpy), for which DFT fails at describing the ground state, has been investigated by CASSCF/CASPT2 calculations. The lowest energy electronic ground state corresponds to a (4f­(Yb))²(π*_DAB)⁰-(4f­(Yb))⁰(π*_DAB)² (¹A₁) state, nearly degenerate to the triplet 4f­(Yb)¹(π*_DAB)¹ configuration according to a diradical picture

Tandem C(sp²)–OMe Activation/C(sp²)–C(sp²) Coupling in Early Transition-Metal Complexes: Aromatic C–O Activation beyond Late Transition Metals

We report on combined structural, kinetic, and computational studies unraveling the mechanism of a unique, highly selective intramolecular C­(sp²)–OMe cleavage/C­(sp²)–C­(sp²) coupling tandem reaction in group 3 metal (Y and Sc) complexes of amidine-amidopyridinate ligands. The latter process represents a rare stoichiometric model of the nonredox cleavage of inert C­(sp²)–O bonds relevant to cross-coupling reactions of aromatic ethers catalyzed by late transition metals

Tandem C(sp²)–OMe Activation/C(sp²)–C(sp²) Coupling in Early Transition-Metal Complexes: Aromatic C–O Activation beyond Late Transition Metals

We report on combined structural, kinetic, and computational studies unraveling the mechanism of a unique, highly selective intramolecular C­(sp²)–OMe cleavage/C­(sp²)–C­(sp²) coupling tandem reaction in group 3 metal (Y and Sc) complexes of amidine-amidopyridinate ligands. The latter process represents a rare stoichiometric model of the nonredox cleavage of inert C­(sp²)–O bonds relevant to cross-coupling reactions of aromatic ethers catalyzed by late transition metals

Application of the Hybridization Chain Reaction on Electrodes for the Amplified and Parallel Electrochemical Analysis of DNA

The hybridization chain reaction (HCR) is implemented for the development of amplified electrochemical DNA sensing platforms. The target analyte hybridizes with a probe oligonucleotide-functionalized electrode and triggers on the HCR process in the presence of the hairpins H_A and H_B. The formation of the analyte-triggered HCR chains is followed by Faradaic impedance spectroscopy or chronocoulometry using Fe­(CN)₆^3–/4– or Ru­(NH₃)₆³⁺ as redox labels, respectively. By using two different probe-functionalized electrodes and a mixture of four hairpins, H_A:H_B and H_C:H_D, the parallel analysis of two analytes is demonstrated. Through the structural design of the hairpin structures to include caged G-quadruplex subunits, the analyte/probe hybrid associated with the electrode triggers on the HCR process, leading to G-quadruplex-functionalized HCR chains. The association of hemin to the matrix yields electrocatalytic hemin/G-quadruplex units that provide a secondary amplification path for the detection of DNA through an electrocatalyzed reduction of H₂O₂. The system allows the detection of the analyte DNA with a detection limit corresponding to 0.2 nM

Enzyme-Capped Relay-Functionalized Mesoporous Carbon Nanoparticles: Effective Bioelectrocatalytic Matrices for Sensing and Biofuel Cell Applications

The porous high surface area and conducting properties of mesoporous carbon nanoparticles, CNPs (<500 nm diameter of NPs, pore dimensions ∼6.3 nm), are implemented to design electrically contacted enzyme electrodes for biosensing and biofuel cell applications. The relay units ferrocene methanol, Fc-MeOH, methylene blue, MB⁺, and 2,2′-azino­bis(3-ethyl­benzo­thiazoline-6-sulfonic acid), ABTS^2–, are loaded in the pores of the mesoporous CNPs, and the pores are capped with glucose oxidase, GOx, horseradish peroxidase, HRP, or bilirubin oxidase, BOD, respectively. The resulting relay/enzyme-functionalized CNPs are immobilized on glassy carbon electrodes, and the relays encapsulated in the pores are sufficiently free to electrically contact the different enzymes with the bulk electrode supports. The Fc-MeOH/GOx CNP-functionalized electrode is implemented for the bio­electro­catalyzed sensing of glucose, and the MB⁺/HRP-modified CNPs are applied for the electrochemical sensing of H₂O₂. The ABTS^2–/BOD-modified CNPs provide an effective electrically contacted material for the bio­electro­catalyzed reduction of O₂ (<i>k</i>_cat = 94 electrons·s^–1). Integration of the Fc-MeOH/GOx CNP electrode and of the electrically wired ABTS^2–/BOD CNP electrode as anode and cathode, respectively, yields a biofuel cell revealing a power output of ∼95 μW·cm^–2

Integration of Switchable DNA-Based Hydrogels with Surfaces by the Hybridization Chain Reaction

A novel method to assemble acrylamide/acrydite DNA copolymer hydrogels on surfaces, specifically gold-coated surfaces, is introduced. The method involves the synthesis of two different copolymer chains consisting of hairpin A, H_A, modified acrylamide copolymer and hairpin B, H_B, acrylamide copolymer. In the presence of a nucleic acid promoter monolayer associated with the surface, the hybridization chain reaction between the two hairpin-modified polymer chains is initiated, giving rise to the cross-opening of hairpins H_A and H_B and the formation of a cross-linked hydrogel on the surface. By the cofunctionalization of the H_A- and H_B-modified polymer chains with G-rich DNA tethers that include the G-quadruplex subunits, hydrogels of switchable stiffness are generated. In the presence of K⁺-ions, the hydrogel associated with the surface is cooperatively cross-linked by duplex units of H_A and H_B, and K⁺-ion-stabilized G-quadruplex units, giving rise to a stiff hydrogel. The 18-crown-6-ether-stimulated elimination of the K⁺-ions dissociates the bridging G-quadruplex units, resulting in a hydrogel of reduced stiffness. The duplex/G-quadruplex cooperatively stabilized hydrogel associated with the surface reveals switchable electrocatalytic properties. The incorporation of hemin into the G-quadruplex units electrocatalyzes the reduction of H₂O₂. The 18-crown-6-ether stimulated dissociation of the hemin/G-quadruplex bridging units leads to a catalytically inactive hydrogel

Gossypol-Capped Mitoxantrone-Loaded Mesoporous SiO₂ NPs for the Cooperative Controlled Release of Two Anti-Cancer Drugs

Mesoporous SiO₂ nanoparticles, MP-SiO₂ NPs, are functionalized with the boronic acid ligand units. The pores of the MP-SiO₂ NPs are loaded with the anticancer drug mitoxantrone, and the pores are capped with the anticancer drug gossypol. The resulting two-drug-functionalized MP-SiO₂ NPs provide a potential stimuli-responsive anticancer drug carrier for cooperative chemotherapeutic treatment. In vitro experiments reveal that the MP-SiO₂ NPs are unlocked under environmental conditions present in cancer cells, e.g., acidic pH and lactic acid overexpressed in cancer cells. The effective unlocking of the capping units under these conditions is attributed to the acidic hydrolysis of the boronate ester capping units and to the cooperative separation of the boronate ester bridges by the lactate ligand. The gossypol-capped mitoxantrone-loaded MP-SiO₂ NPs reveals preferential cytotoxicity toward cancer cells and cooperative chemotherapeutic activities toward the cancer cells. The MCF-10A epithelial breast cells and the malignant MDA-MB-231 breast cancer cells treated with the gossypol-capped mitoxantrone-loaded MP-SiO₂ NPs revealed after a time-interval of 5 days a cell death of ca. 8% and 60%, respectively. Also, the gossypol-capped mitoxantrone-loaded MP-SiO₂ NPs revealed superior cancer-cell death (ca. 60%) as compared to control carriers consisting of β-cyclodextrin-capped mitoxantrone-loaded (ca. 40%) under similar loading of the mitoxantrone drug. The drugs-loaded MP-SiO₂ NPs reveal impressive long-term stabilities

Bifunctional Mixed-Lanthanide Cyano-Bridged Coordination Polymers Ln_0.5Ln′_0.5(H₂O)₅[W(CN)₈] (Ln/Ln′ = Eu³⁺/Tb³⁺, Eu³⁺/Gd³⁺, Tb³⁺/Sm³⁺)

A new family of mixed-lanthanide cyano-bridged coordination polymers Ln_0.5Ln′_0.5(H₂O)₅[W­(CN)₈] (where Ln/Ln′ = Eu³⁺/Tb³⁺, Eu³⁺/Gd³⁺, and Tb³⁺/Sm³⁺) containing two lanthanide and one transition metal ions were obtained and characterized by X-ray diffraction, photoluminescence spectroscopy, magnetic analyses, and theoretical computation. These compounds are isotypical and crystallize in the tetragonal system <i>P</i>4<i>/nmm</i> forming two-dimensional grid-like networks. They present a magnetic ordering at low temperature and display the red Eu³⁺ (⁵D₀ → ⁷F_0–4) and green Tb³⁺ (⁵D₄ → ⁷F_6–2) characteristic photoluminescence. The Tb_0.5Eu_0.5(H₂O)₅[W­(CN)₈] compound presents therefore green and red emission and shows Tb³⁺-to-Eu³⁺ energy transfer

Investigation on NMR Relaxivity of Nano-Sized Cyano-Bridged Coordination Polymers

We present the first comparative investigation of the Nuclear Magnetic Resonance (NMR) relaxivity of a series of nanosized cyano-bridged coordination networks stabilized in aqueous solution. These Ln³⁺/[Fe­(CN)₆]^3‑ (Ln = Gd, Tb, Y) and M²⁺/[Fe­(CN)₆]^3‑ (M = Ni, Cu, Fe) nanoparticles with sizes ranging from 1.4 to 5.5 nm are stabilized by polyethylene glycols (MW = 400 or 1000), polyethylene glycol functionalized with amine groups (MW = 1500), or by N-acetyl-d-glucosamine. The evaluation of NMR relaxivity allowed estimation of the Magnetic Resonance Imaging (MRI) contrast efficiency of our systems. The results demonstrate that Gd³⁺/[Fe­(CN)₆]^3‑ nanoparticles have <i>r</i>_1p and <i>r</i>_2p relaxivities about four times higher than the values observed in the same conditions for the commercial Contrast Agents (CAs) ProHance or Omniscan, regardless of the stabilizing agent used, while nanoparticles of Prussian blue and its analogues M²⁺/[Fe­(CN)₆]^3‑ (M = Ni, Cu, Fe) present relatively modest values. The influence of the chemical composition of the nanoparticles, their crystal structure, spin values of lanthanide and transition metal ions, and stabilizing agent on the relaxivity values are investigated and discussed

Investigation on NMR Relaxivity of Nano-Sized Cyano-Bridged Coordination Polymers

We present the first comparative investigation of the Nuclear Magnetic Resonance (NMR) relaxivity of a series of nanosized cyano-bridged coordination networks stabilized in aqueous solution. These Ln³⁺/[Fe­(CN)₆]^3‑ (Ln = Gd, Tb, Y) and M²⁺/[Fe­(CN)₆]^3‑ (M = Ni, Cu, Fe) nanoparticles with sizes ranging from 1.4 to 5.5 nm are stabilized by polyethylene glycols (MW = 400 or 1000), polyethylene glycol functionalized with amine groups (MW = 1500), or by N-acetyl-d-glucosamine. The evaluation of NMR relaxivity allowed estimation of the Magnetic Resonance Imaging (MRI) contrast efficiency of our systems. The results demonstrate that Gd³⁺/[Fe­(CN)₆]^3‑ nanoparticles have <i>r</i>_1p and <i>r</i>_2p relaxivities about four times higher than the values observed in the same conditions for the commercial Contrast Agents (CAs) ProHance or Omniscan, regardless of the stabilizing agent used, while nanoparticles of Prussian blue and its analogues M²⁺/[Fe­(CN)₆]^3‑ (M = Ni, Cu, Fe) present relatively modest values. The influence of the chemical composition of the nanoparticles, their crystal structure, spin values of lanthanide and transition metal ions, and stabilizing agent on the relaxivity values are investigated and discussed