Dendritic quinary PtRhMoCoFe high-entropy alloy as a robust immunosensing nanoplatform for ultrasensitive detection of biomarker.

Recently, high-entropy alloys have superior physicochemical properties as compared to conventional alloys for their glamorous "cocktail effect". Nevertheless, they are scarcely applied to electrochemical immunoassays until now. Herein, uniform PtRhMoCoFe high-entropy alloyed nanodendrites (HEANDs) were synthesized by a wet-chemical co-reduction method, where glucose and oleylamine behaved as the co-reducing agents. Then, a series of characterizations were conducted to illustrate the synergistic effect among multiple metals and fascinating structural characteristics of PtRhMoCoFe HEANDs. The obtained high-entropy alloy was adopted to build a electrochemical label-free biosensor for ultrasensitive bioassay of biomarker cTnI. In the optimized analytical system, the resultant sensor exhibited a dynamic linear range of 0.0001-200 ng mL-1 and a low detection limit of 0.0095 pg mL-1 (S/N = 3). Eventually, this sensing platform was further explored in serum samples with satisfied recovery (102.0 %). This research renders some constructive insights for synthesis of high-entropy alloys and their expanded applications in bioassays and bio-devices.

Ultrasensitive sandwich-typed electrochemical immunoassay for detection of squamous cell carcinoma antigen based on highly branched PtCo nanocrystals and dendritic mesoporous SiO2@AuPt nanoparticles.

Squamous cell carcinoma antigen (SCCA) is one of the common squamous cell carcinomas (SCC) in women, which usually works as a tumor biomarker for cervical cancer in diagnostic applications. Herein, bimetallic PtCo highly branched nanocrystals (PtCo BNCs) acted as electrode substrates to construct sandwich-typed electrochemical immunosensor for ultrasensitive detection of SCCA, by using dendritic mesoporous SiO2@AuPt nanoparticles (DM-SiO2@AuPt NPs) to adsorb electroactive thionine (Thi) as a signal label. The PtCo BNCs enlarged the loading of the primary antibody (Ab1), showing effective improvement in conductivity and sensitivity. The DM-SiO2 had abundant pores to incorporate more Thi, on which the decorated AuPt NPs created a great number of active sites to immobilize the secondary antibodies (Ab2), thereby obviously amplifying the detection signals. The prepared sensor exhibited a broader linear range (0.001-120 ng mL-1) and a lower detection limit (0.33 pg mL-1, S/N = 3), combined with high reproducibility, a low relative standard deviation (below 2.5%) and acceptable recovery (from 98.5 to 110.0%) even in diluted human serum samples. This research provides a substantial platform for clinical diagnosis of SCCA in practice.

A general strategy to prepare atomically dispersed biomimetic catalysts based on host-guest chemistry.

Herein, we report a general strategy based on host-guest interactions to fabricate atomically dispersed biomimetic catalysts, which were evaluated by diboration of phenylacetylene. The structure and function of these mimics are quite similar to those of enzymes, namely, the atomically dispersed metal serves as an active site, the external macromolecular structure plays a role as an enzyme catalytic pocket to stabilize the reaction intermediates and the interactions between the intermediates and functional groups near to the active site can reduce the reaction activation energy.

Rational Control of the Selectivity of a Ruthenium Catalyst for Hydrogenation of 4-Nitrostyrene by Strain Regulation.

Tuning the selectivity of metal catalysts is of paramount importance yet a great challenge. A new strategy to effectively control the selectivity of metal catalysts, by tuning the lattice strain, is reported. A certain amount of Co atoms is introduced into Ru catalysts to compress the Ru lattice, as confirmed by aberration-corrected high-resolution transmission electron microscopy (HRTEM) and X-ray absorption fine structure (XAFS) measurements. We discover that the lattice strain of Ru catalysts can greatly affect their selectivity, and Ru with 3 % lattice compression exhibits extremely high catalytic selectivity for hydrogenation of 4-nitrostyrene to 4-aminostyrene compared to pristine Ru (99 % vs. 66 %). Theoretical studies confirm that the optimized lateral compressive strain facilitates hydrogenation of the nitro group but impedes the hydrogenation of the vinyl group. This study provides a new guideline for designing metal catalysts with high selectivity.

Reversible proton-switchable fluorescence controlled by conjugation effect in an organically-functionalized polyoxometalate.

A novel monosubstituted organoimido hexamolybdate containing 6-nitroquinoline moiety has been successfully synthesized. This organically-functionalized polyoxometalate exhibits proton-induced switchable fluorescence property in aqueous acetonitrile solution at room temperature. Experimental and theoretical investigations of this reversible "on" and "off" switching mechanism have been carried out, and it is found that the protonation and deprotonation at the heterocyclic nitrogen atom within quinoline fragment leads to the breaking and reformation of the conjugation through strong d-π interaction between the hexamolybdate anionic cluster and the quinoline moiety, resulting in "on" and "off" luminescence signal.

Postfunctionalization of polyoxometalates: an efficient strategy to construct organic-inorganic zwitterions.

A class of monoorganoimido-substituted hexamolybdates containing a pyridine group have been firstly synthesized. Furthermore, a reaction protocol of alkylation based on the resulting pyridine-functionalized hexamolybdates has been developed, with which a type of zwitterionic clusters has been successfully obtained.

N-alkylation of organo-imido substituted polyoxometalates: an efficient and stoichiometric approach for the easy post-modification of polyoxometalates.

An efficient protocol for post-functionalization of organo-imido polyoxometalates is developed via creating a remote tertiary "N" atom over the surface of organo-imido hexamolybdates and subsequently post-functionalizing it with the help of allyl or alkyl halides to afford stoichiometric, "in situ" crystalline products at moderate temperatures. The parent organo-imido product 2 and post-functionalized crystalline products 3 and 4 are compared for their solid state structures. The post-functionalization protocol introduced here allows the inclusion of the desired functional groups as remote reactive organic groups over a POM's highly negative surface. The in situ crystallization of post-functionalized products further guarantees an 100% purity of final products, along with 95% yield.

Organoimido-derivatized hexamolybdates with a remote carboxyl group: syntheses and structural characterizations.

Four novel organoimido derivatives of hexamolybdate containing a remote carboxyl group have been synthesized: [Bu4N]2[Mo6O18(N-C6H4-3-COOH)] (1), [Bu4N]2[Mo6O18(N-C6H4-2-CH3-4-COOH)] (2), [Bu4N]2[Mo6O18(N-C6H4-2-CH3-5-COOH)] (3), and [Bu4N]2[Mo6O18(N-C6H4-2-CH3-3-COOH)] (4) with 3-aminobenzoic acid, 4-amino-3-methylbenzoic acid, 3-amino-4-methylbenzoic acid, and 3-amino-2-methylbenzoic acid as the imido-releasing agents, respectively. Their structures have been characterized by IR, UV-vis, (1)H NMR, ESI-MS, and single-crystal X-ray diffraction techniques. Hydrogen bonding interactions play an important role in the supramolecular assemblies of these compounds in the solid state. Although the incorporated organic ligands are similar to each other, their supramolecular assembly behaviors are quite different. For compound 1, the dimer structure is formed via hydrogen bonding between the carboxyl group and the POM cluster of two neighboring cluster anions. For compound 2, the 1D chain structure is formed via hydrogen bonding between the carboxyl groups and the POM clusters of the cluster anions. For compound 3, the 2D plane structure is formed via two types of hydrogen bonding between the aromatic rings and the POM clusters of the cluster anions. For compound 4, the 1D plus 2D structures are formed via three types of hydrogen bonding between the aromatic rings and the POM clusters of the two types of cluster anions with different orientations.

Theoretical investigation of the mechanism of primary amines reacting with hexamolybdate: an insight into the organoimido functionalization and related reactions of polyoxometalates.

The functionalization of polyoxometalates (POMs), especially with an amino group to yield organonitrogenous derivatives of POMs, is an efficient approach to the enrichment of their structures and the diversification of their properties for various applications. The mechanism for the formation of organonitrogenous-derivatized hexamolybdates was explored by investigating the monofunctionalization of the [Mo(6)O(19)](2-) ion with methylamine using the density functional theory (DFT) method. The calculations show that the direct imidoylization of hexamolybdate with methylamine is both kinetically and thermodynamically unfavorable. However, this imidoylization was found to take place readily in the presence of dimethylcarbodiimide (DMC), for which the free-energy barrier was calculated to be +32.5 kcal mol(-1) in acetonitrile. Moreover, various factors controlling the efficiency of the imidoylization were examined. The calculations show that [W(5)MoO(19)](2-) has a relatively lower reactivity than [Mo(6)O(19)](2-), and that the imidoylization of [W(6)O(19)](2-) is an unfavorable process. With respect to the effect of carbodiimides, it is found that the catalytic activity is directly proportional to the electron-withdrawing effects of the substituents. As to the reactivity of R-NH(2) , the computation results indicate that the free-energy barriers of the substitution reactions are linearly correlated with the basicity constants (pK(b)) of the amino groups. It is noteworthy that the introduction of the proton dramatically decreases the free-energy barrier of the imidoylization of [Mo(6)O(19)](2-) catalyzed by DMC to 24.3 kcal mol(-1) in acetonitrile.

Syntheses and structural characterizations of di-substituted alkylimido hexamolybdates: an insight on bi-alkylimido functionalization.

Bi-alkylimido functionalization of hexamolybdates has been developed and several novel di-substituted alkylimido hexamolybdates with n-butyl, cyclohexyl and tert-butylamines as the imido-releasing reagents have been synthesized in reasonable yields. Their structures have been characterized by elemental analysis, IR, UV-Vis, and ESI mass spectrometry. Moreover, the structures of [Mo(6)O(17)(NCy)(2)](2-) and [Mo(6)O(17)(NCMe(3))(2)](2) have been determined by single-crystal X-ray diffraction techniques. It is notable that the compound (Bu(4)N)(2)[Mo(6)O(17)(NCy)(2)] crystallizes in polar space group Fdd2 with potential ferroelectricity. In addition, theoretical investigation of the reactivity and regioselectivity of bi-alkylimido functionalization has also been conducted. The calculation results show that more energy is required for the bi-functionalization process than for the mono-substitution process, and that the cis-bi-functionalization is the kinetically favored process while trans-[Mo(6)O(17)(NR)(2)](2-) is the thermodynamically favored product.

χ-Octamolybdate [Mo(V)4Mo(VI)4O24](4-): an unusual small polyoxometalate in partially reduced form from nonaqueous solvent reduction.

The first mixed-valent octamolybdate anion [Mo(V)(4)Mo(VI)(4)O(24)](4-), termed χ-octamolybdate due to its shape, was obtained by partial reduction of α-(Bu(4)N)(4)-[Mo(8)O(26)] in dry acetonitrile. Single-crystal X-ray structure analysis revealed that the anion includes an unusual Mo(V)(4)O(8) cubane-like cluster core, whose four side faces are capped by four MoO(4) units to form a crosslike cluster. X-ray photoelectron spectroscopy (XPS) and bond valence sum (BVS) calculations were carried out to validate the presence of mixed-valent Mo centers.

Polyoxometalatocyclophanes: controlled assembly of polyoxometalate-based chiral metallamacrocycles from achiral building blocks.

The first polyoxometalatocyclophanes have been synthesized by the covalent linkage of a hexamolybdate cluster and bisarylimido ligands containing flexible chains. These metallamacrocycles are chiral, and some of them can undergo spontaneous resolution. The work provides a new protocol for preparing chiral polyoxometalates (POMs) and chiral metallamacrocycles from achiral building blocks by fastening both ends of a flexible chain onto an achiral POM to remove the symmetric center and mirror.

From 0D dimer to 2D network-supramolecular assembly of organic derivatized polyoxometalates with remote hydroxyl via hydrogen bonding.

A series of remote hydroxyl functionalized organoimido derivatives of hexamolybdate, (Bu(4)N)(2)[Mo(6)O(18)(Cres)] (1) (Cres = 4-amino-m-cresol), (Bu(4)N)(2)[Mo(6)O(17)(Cres)(2)] x H(2)O (2), (Bu(4)N)(2)[Mo(6)O(18)(Phen)] x i-PrOH (Phen = p-aminophenol)(3), (Bu(4)N)(2)[Mo(6)O(18)(Phen)] x EtOH (4), (Bu(4)N)(2)[Mo(6)O(17)(Phen)(2)] (5), (Bu(4)N)(2)[Mo(6)O(18)(Naph)] (Naph = 5-amino-1-napheynyl) (6), and (Bu(4)N)(2)[Mo(6)O(18)(Chex)] x 1.5 H(2)O (Chex = trans-4-aminocyclohexanol) (7) were synthesized and characterized by single crystal X-ray diffraction, FT-IR spectra, UV-vis spectra, elemental analysis, (1)H NMR, and cyclic voltammetry. X-ray structural study reveals that intermolecular and intramolecular hydrogen bonding plays an important role in their supramolecular assembly; it is found that (i) bridged oxo ligands of hexamolybdate cluster are more inclined to form hydrogen bonds as acceptors than terminal oxo ligands in this system; (ii) small solvent molecules with hydrogen bonding donor and acceptor, such as water, i-PrOH, and EtOH, usually act as hydrogen bonding bridge in their supramolecular assembly; (iii) hydrogen bonding has an important influence on their anion conformation besides cell packing; (iv) the hydrogen bonding supramolecular assembly of compounds 1-7 demonstrate an interesting change from dimer (3), to 1D infinite single chain (4), to 1D infinite double chain (2), and to 2D network (1, 5, 6, and 7) owing to the alteration of the grafting organic ligand, the substituted number, and the crystallized solvent molecule. To explore their potential application in conductivity, the optical band gap of compounds 1-7 were determined upon their solid state reflectance spectra. Our current study not only surveys systematically hydrogen bonding interaction and supramolecular assembly of remote hydroxyl functionalized organoimido-derivatized hexamolybdates but also provides some available precursors for further modification including esterification.

Theoretical investigation of N-nitrosodimethylamine formation from dimethylamine nitrosation catalyzed by carbonyl compounds.

The carbonyl-compound-catalyzed nitrosation of amines to form carcinogenic nitrosamines under nonacidic condition is different from the classic nitrosation via acidification of nitrite anion. The mechanistic pathways of N-nitrosodimethylamine (NDMA) formation by the reactions of dimethylamine (DMA) with the nitrite anion catalyzed by carbonyl compounds have been investigated using the DFT/B3LYP method at the 6-311+G(d,p) level. The computational results show that the energy barriers of the nucleophilic addition reaction, which were calculated as 27-40 kcal/mol, increase significantly with methylation but vary slightly with chloromethylation on the carbonyl group. Comparison of energy barriers of this nucleophilic addition reaction and the electrophilic substitution reaction indicates that the former is the rate-determining step, from which the order of the catalytic activity is obtained as formaldehyde > chloral > acetaldehyde > acetone. Furthermore, analysis of electronic and steric effects on catalytic activity reveals that electron-withdrawing substituents decrease the energy barrier but electron-donating substituents and steric hindrance will block this catalytic reaction. Based on this discovery, fluoral is proposed as a good catalyst for the nitrosation of DMA by nitrite anion, which has a calculated energy barrier of about 26 kcal/mol. The results obtained in this work will help elucidate the mechanisms of formation of nitrosamines.