Synthesis and characterization of a thermoresponsive polyoxometalate-polymer hybrid

We report the synthesis of the first organo-POM with thermoresponsive properties. Our concept will provide chemists with a new tool to design POMs whose solubility is reversibly controllable through an external stimulus. POM-polymer TBA(7)[POM]-poly(N,N-diethylacrylamide) (POM-PDEAAm), was prepared by grafting PDEAAm-NH(2) (obtained by RAFT polymerization) onto the activated Dawson acyl-POM, α(2)-[P(2)W(17)O(61)SnCH(2)CH(2)C(=O)](6-). Extensive MS analysis was used to monitor the chain-functionalization steps and to confirm the formation of the hybrid. Aqueous solutions of the (NH(4))(7)[POM-PDEAAm] exhibited a LCST of 38 °C. Thus, the solubility/aggregation of the hybrid was reversibly controlled by changing the temperature. Above 38 °C, the solution became cloudy, and cleared again upon cooling. Dynamic light scattering (DLS) revealed the formation of small aggregates in the range 100 nm. We assumed that the charged POM head units prevented the formation of the larger-scattering aggregates that are usually observed for PDEAAm, and promoted the formation of micelle-like structures. The conjugate exhibited a temperature transition, which was different from that of the polymer and depended on the counterions associated with the POM. This result demonstrates the potential for merging organic (in this case, polymer) and inorganic structures to afford materials that exhibit new properties.     

An inorganic–organic hybrid supramolecular framework based on the γ‐[Mo8O26]4− cluster and cobalt complex of aspartic acid: X‐ray structure and DFT study

A new inorganic–organic hybrid based on an aspartate functionalized polyoxomolybdate, [pentaaquacobalt(II)]‐μ‐aspartate‐[γ‐octamolybdate]‐μ‐aspartate‐[pentaaquacobalt(II)] tetrahydrate, [Co₂(C₄H₆NO₄)₂(γ‐Mo₈O₂₆)(H₂O)₁₀]·4H₂O ( 1 ), has been synthesized under hydrothermal conditions from the reaction of an Evans–Showell‐type polyoxometalate, (NH₄)₆[Co₂Mo₁₀H₄O₃₈], and l ‐aspartic acid. The complex exhibits a supramolecular three‐dimensional framework structure in the crystal lattice. Compound 1 was structurally characterized by elemental analyses, IR and UV–Vis (diffuse reflectance) spectroscopy and single‐crystal X‐ray diffraction. In this compound, aspartic acid acts as a bridge between the two Co atoms and the Mo centres, with the –CH₂COOH side chain directly linked to the Mo centre in γ‐[Mo₈O₂₆]^4? and the α‐carboxylate side chain bound to the Co centre. Commonly, the binding of transition‐metal complexes to POMs involves coordination of the metal to a terminal O atom of the POM so that 1 , with a bridging ligand between Mo and Co atoms, belongs to a separate class of hybrid materials. While the starting materials are both chiral and one might expect them to form a chiral hybrid, the decomposition of the chiral Evans–Showell‐type POM and its conversion to the centrosymmetric γ‐octamolybdate POM, plus the presence of two aspartate ligands centrosymmetrically placed on either side of the POM, leads to the formation of an achiral hybrid. We have studied energetically by means of density functional theory (DFT) calculations and using the Bader's `atoms‐in‐molecules' analysis the electrostatically enhanced hydrogen bonds (EEHBs) observed in the solid state of 1 , which are crucial for the formation of one‐dimensional supramolecular assemblies.     

Influence of small uncharged but amphiphilic molecules on the lower critical solution temperature of highly homogeneous N‐alkylacrylamide oligomers

The influence of small alkylamines with increasing carbon chain length (≤5) on the temperature‐induced precipitation of two N‐alkylacrylamide oligomers, poly‐N‐isopropylacrylamide [PNIPAAm; weight‐average molecular weight (M_w ) = 1600 g/mol] and poly‐N,N‐diethylacrylamide (PDEAAm; M_w = 4000 g/mol), from an aqueous solution was investigated. The alkylamines in question were too small to form micelles in the classical sense but were capable of premicellar aggregation. PNIPAAm was prepared by radical polymerization in the presence of a chain‐transfer agent and, therefore, carried a carboxylic acid end group. The structure was heterotactic. PDEAAm was prepared by anionic polymerization and, therefore, carried a butyl end group. The structure was predominately isotactic. The solubility of the oligomers was investigated by cloud‐point measurements and differential scanning calorimetry. In addition, pyrene was used as a fluorescent polarity probe. Alkylamines up to C₂ depressed the lower critical solution temperature (LCST) of PNIPAAm, whereas higher alkylamines first depressed the LCST and at higher concentrations elevated it. The LCST minimum showed a clear dependence on the alkyl chain length and structure. For PDEAAm, only pentylamine addition resulted in an LCST minimum. Otherwise, the LCST was raised. When the critical self‐association concentration (CSAC) of the alkylamines in water was compared to the critical association concentration (CAC) in aqueous oligomer solutions, PDEAAm, but not PNIPAAm, stabilized mixed aggregates (CAC < CSAC). The transition enthalpy of PNIPAAm decreased with an increasing alkylamine concentration and became 0 above the CAC. For PDEAAm, no transition endotherm could be recorded above an alkylamine concentration of 0.1 M. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4218–4229, 2000     

New Polyoxometalates Containing Hybrid Polymers and Their Potential for Nano‐Patterning

Two new polyoxometalate (POM)‐based hybrid monomers (Bu₄N)₅(H)[P₂V₃W₁₅O₅₉{(OCH₂)₃CNHCO(CH₃)C?CH₂}] ( 2 ) and (S(CH₃)₂C₆H₄OCOC(CH₃)=CH₂)₆[PVMo₁₀O₄₀] ( 5 ) were developed by grafting polymerizable organic units covalently or electrostatically onto Wells–Dawson and Keggin‐type clusters and were characterized by analytical and spectroscopic techniques including ESI‐MS and/or single‐crystal X‐ray diffraction analyses. Radical initiated polymerization of 2 and 5 with organic monomers (methacryloyloxy)phenyldimethylsulfonium triflate (MAPDST) and/or methylmethacrylate (MMA) yielded a new series of POM/polymer hybrids that were characterized by ¹H, ³¹P NMR and IR spectroscopic techniques, gel‐permeation chromatography as well as thermal analyses. Preliminary tests were conducted on these POM/polymer hybrids to evaluate their properties as photoresists using electron beam (E‐beam)/extreme ultraviolet (EUV) lithographic techniques. It was observed that the POM/polymer hybrid of 2 with MAPDST exhibited improved sensitivity under EUV lithographic conditions in comparison to the MAPDST homopolymer resist possibly due to the efficient photon harvesting by the POM clusters from the EUV source.     

Macromolecule-to-Amphiphile Conversion Process of a Polyoxometalate–Polymer Hybrid and Assembled Hybrid Vesicles

We report our findings on the macromolecule-to-amphiphile conversion process of a polyoxometalate–polymer hybrid and the assembled hybrid vesicles formed by aggregation of the hybrid amphiphile. The polyoxometalate–polymer hybrid is composed of a polyoxometalate (POM) cluster, which is covered by five tetrabutylammonium (Bu₄N⁺) countercations, and a polystyrene (PS) chain. Through a cation-exchange process the Bu₄N⁺ countercations can be replaced by protons to form a hybrid amphiphile composed of a hydrophilic, protonated POM cluster and a hydrophobic PS chain. By implementing a directed one-dimensional diffusion and analyzing the diffusion data, we confirmed that the diffusion of solvated protons rather than macromolecules or aggregates is the key factor controlling the conversion process. Once the giant hybrid amphiphiles were formed, they immediately assembled into kinetically favored vesicular aggregates. During subsequent annealing these vesicular aggregates were transformed into thermodynamically stable vesicular aggregates with a perfect vesicle structure. The success in the preparation of the POM-containing hybrid vesicles provides us with an opportunity of preparing POM-functionalized vesicles.     

Preparation,characterization, and electrical properties of dual‐emissive Langmuir‐Blodgett films of some europium‐substituted polyoxometalates and a platinum polyyne polymer

A new series of organometallic/inorganic composite Langmuir‐Blodgett (LB) films consisting of a rigid‐rod polyplatinyne polymer coordinated with 2,7‐bis(buta‐1,3‐diynyl)‐9,9‐dihexylfluorene (denoted as PtP) as the π‐conjugated organometallic molecule, an europium‐substituted polyoxometalate (POM; POM = Na₉EuW₁₀O₃₆, K₁₃[Eu(SiW₁₁O₃₉)₂] and K₅[Eu(SiW₁₁O₃₉)(H₂O)₂]) as the inorganic component, and an amphiphilic behenic acid (BA) as the auxiliary film‐forming agent were prepared. Structural and photophysical characterization of these LB films were achieved by π–A isotherms, absorption and photoluminescence spectra, atomic force microscopy imaging, scanning tunneling microscopy, and low‐angle X‐ray diffraction. Our experimental results indicate that stable, well‐defined, and well‐organized Langmuir and LB films are formed in pure water and POM subphases, and the presence of Eu‐based POM in the subphase causes an area expansion. It is proposed that a lamellar layered structure exists for the PtP/BA/POM LB film in which the POM and PtP molecules can lay down with the interfacial planes. Luminescence spectra of the prepared hybrid LB films show that near‐white emission spectra can be obtained due to the dual‐emissive nature of the mixed PtP/POM blends. These Pt‐polyyne‐based LB films displayed interesting electric conductivity behavior. Among them, PtP/BA/POM 13‐layer films showed a good electrical response, with the tunneling current up to ±100 nA when the voltage was monitored between ?1 and 7 V. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 879–888, 2010     

Covalent Attachment of Anderson‐Type Polyoxometalates to Single‐Walled Carbon Nanotubes Gives Enhanced Performance Electrodes for Lithium Ion Batteries

Single‐walled carbon nanotubes (SWNTs) covalently functionalized with redox‐active organo‐modified polyoxometalate (POM) clusters have been synthesized and employed as electrode materials in lithium ion batteries. The Anderson cluster [MnMo₆O₂₄]^9? is functionalized with Tris (NH₂C(CH₂OH)₃) moieties, giving the new organic–inorganic hybrid [N(nC₄H₉)₄]₃[MnMo₆O₁₈{(OCH₂)₃CNH₂}₂]. The compound is then covalently attached to carboxylic acid‐functionalized SWNTs by amide bond formation and the stability of this nanocomposite is confirmed by various spectroscopic methods. Electrochemical analyses show that the nanocomposite displays improved performance as an anode material in lithium ion batteries compared with the individual components, that is, SWNTs and/or Anderson clusters. High discharge capacities of up to 932 mAh g^?1 at a current density of 0.5 mA cm^?2 can be observed, together with high long‐term cycling stability and decreased electrochemical impedance. Chemisorption of the POM cluster on the SWNTs is shown to give better electrode performance than the purely physisorbed analogues.     

Integrating 31P DOSY NMR Spectroscopy and Molecular Mechanics as a Powerful Tool for Unraveling the Chemical Structures of Polyoxomolybdate‐Based Amphiphilic Nanohybrids in Aqueous Solution

Novel organic–inorganic hybrids of various sizes were generated by reaction of 1,8‐octanediphosphonic acid (ODP) and (NH₄)₆Mo₇O₂₄ in aqueous solution. The formation of rodlike hybrids with variable numbers of covalently bound ODP and polyoxomolybdate (POM) units can be tuned as a function of increasing (NH₄)₆Mo₇O₂₄ concentration at fixed ODP concentration. The chemical structure of the ODP/POM hybrids was characterized by ¹H, ³¹P, and ⁹⁵Mo NMR spectroscopy. Heteronuclear ³¹P DOSY (diffusion‐ ordered NMR spectroscopy) and molecular mechanics (MM) calculations were applied to determine the size and shape of the nanosized hybrids generated at various ODP/POM ratios. For this purpose, the structures of ODP/POM hybrids with variable numbers of ODP and POM units were optimized by MM and then approximated as cylinder‐shaped objects by using a recently described mathematical algorithm. The thus‐obtained cylinder length and diameter were further used to calculate the expected diffusion coefficients of the ODP/POM hybrids. Comparison of the calculated and experimentally determined diffusion coefficients led to the most probable ODP/POM hybrid length for each sample composition. The ³¹P DOSY results show that the length of the hybrids increases with increasing POM concentration and reaches a maximum corresponding to an average of 8 ODP/7 POM units per chain at a sample composition of 20 mM ODP and 14 mM POM. With excess POM, above the latter concentration, the formation of shorter‐chain hybrids terminated by Mo₇ clusters at one or both ends was evidenced on further increasing the POM concentration. The results demonstrate that the combination of ³¹P DOSY and MM, although virtually unexplored in POM chemistry, is a powerful innovative strategy for the detailed characterization of nanosized organic–inorganic POM‐based hybrids in solution.     

Synthesis of α‐Dawson‐Type Silicotungstate [α‐Si2W18O62]8− and Protonation and Deprotonation Inside the Aperture through Intramolecular Hydrogen Bonds

The design of structurally well‐defined anionic molecular metal–oxygen clusters, polyoxometalates (POMs), leads to inorganic receptors with unique and tunable properties. Herein, an α‐Dawson‐type silicotungstate, TBA₈[α‐Si₂W₁₈O₆₂] ? 3 H₂O ( II ) that possesses a ?8 charge was successfully synthesized by dimerization of a trivacant lacunary α‐Keggin‐type silicotungstate TBA₄H₆[α‐SiW₉O₃₄] ? 2 H₂O ( I ) in an organic solvent. POM II could be reversibly protonated (in the presence of acid) and deprotonated (in the presence of base) inside the aperture by means of intramolecular hydrogen bonds with retention of the POM structure. In contrast, the aperture of phosphorus‐centered POM TBA₆[α‐P₂W₁₈O₆₂]?H₂O ( III ) was not protonated inside the aperture. The density functional theory (DFT) calculations revealed that the basicities and charges of internal μ₃‐oxygen atoms were increased by changing the central heteroatoms from P⁵⁺ to Si⁴⁺, thereby supporting the protonation of II . Additionally, II showed much higher catalytic performance for the Knoevenagel condensation of ethyl cyanoacetate with benzaldehyde than I and III .     

Structural Characterization of the Complex between Hen Egg‐White Lysozyme and ZrIV‐Substituted Keggin Polyoxometalate as Artificial Protease

Successful co‐crystallization of a noncovalent complex between hen egg‐white lysozyme (HEWL) and the monomeric Zr^IV‐substituted Keggin polyoxometalate (POM) (Zr1 K1), (Et₂NH₂)₃[Zr(PW₁₁O₃₉)] ( 1 ), has been achieved, and its single‐crystal X‐ray structure has been determined. The dimeric Zr^IV‐substituted Keggin‐type polyoxometalate (Zr1 K2), (Et₂NH₂)₁₀[Zr(PW₁₁O₃₉)₂] ( 2 ), has been previously shown to exhibit remarkable selectivity towards HEWL hydrolysis. The reported X‐ray structure shows that the hydrolytically active Zr^IV‐substituted Keggin POM exists as a monomeric species. Prior to hydrolysis, this monomer interacts with HEWL in the vicinity of the previously identified cleavage sites found at Trp28‐Val29 and Asn44‐Arg45, through water‐mediated H‐bonding and electrostatic interactions. Three binding sites are observed at the interface of the negatively charged Keggin POM and the positively charged regions of HEWL at: 1) Gly16, Tyr20, and Arg21; 2) Asn44, Arg45, and Asn46; and 3) Arg128.     

Suzuki coupling reaction catalyzed heterogeneously by Pd(salen)/polyoxometalate compound: another example for synergistic effect of organic/inorganic hybrid

A hybrid compound consisting of palladium(salen) [salen = N,N′‐bis(salicylidene)ethylenediamine] complex covalently linked to a lacunary Keggin‐type polyoxometalate, K₈[SiW₁₁O₃₉](POM), was synthesized and characterized by FT‐IR, elemental analysis, inductively coupled plasma and diffuse reflectance UV–visible spectroscopic methods. The hybrid, [Pd(salen)–POM], was investigated in the Suzuki cross‐coupling in EtOH/H₂O under mild reaction conditions. In comparison to the corresponding organic and inorganic moiety, the hybrid has shown greatly improved catalytic activity, and much higher yields toward coupling products were obtained with a low catalyst loading for various aryl halides, including unreactive and sterically hindered ones. The catalyst also exhibited prominent recyclable performance and no obvious loss of activity was observed after six consecutive runs. Copyright © 2013 John Wiley & Sons, Ltd.     

Epoxidation of cyclohexene with H2O2 over efficient water‐tolerant heterogeneous catalysts composed of mono‐substituted phosphotungstic acid on co‐functionalized SBA‐15

A series of Keggin‐type heteropolyacid‐based heterogeneous catalysts (Co‐/Fe‐/Cu‐POM‐octyl‐NH₃‐SBA‐15) were synthesized via immobilized transition metal mono‐ substituted phosphotungstic acids (Co‐/Fe‐/Cu‐POM) on octyl‐amino‐co‐functionalized mesoporous silica SBA‐15 (octyl‐NH₂‐SBA‐15). Characterization results indicated that Co‐/Fe‐/Cu‐POM units were highly dispersed in mesochannels of SBA‐15, and both types of Brønsted and Lewis acid sites existed in Co‐/Fe‐/Cu‐POM‐octyl‐NH₃‐SBA‐15 catalysts. Co‐POM‐octyl‐NH₃‐SBA‐15 catalyst showed excellent catalytic performance in H₂O₂‐mediated cyclohexene epoxidation with 83.8% of cyclohexene conversion, 92.8% of cyclohexene oxide selectivity, and 98/2 of epoxidation/allylic oxidation selectivity. The order of catalytic activity was Co‐POM‐octyl‐NH₃‐SBA‐15 > Fe‐POM‐octyl‐NH₃‐SBA‐15 > Cu‐POM‐octyl‐NH₃‐SBA‐15. In order to obtain insights into the role of ‐octyl moieties during catalysis, an octyl‐free catalyst (Co‐POM‐NH₃‐SBA‐15) was also synthesized. In comparison with Co‐POM‐NH₃‐SBA‐15, Co‐POM‐octyl‐NH₃‐SBA‐15 showed enhanced catalytic properties (viz. activity and selectivity) in cyclohexene epoxidation. Strong chemical bonding between ‐NH₃⁺ anchored on the surface of SBA‐15 and heteropolyanions resulted in excellent stability of Co‐POM‐octyl‐NH₃‐SBA‐15 catalyst, and it could be reused six times without considerable loss of activity.     

Temperature-Responsive Polyoxometalate Catalysts for DBT Desulfurization in One-Pot Oxidation Combined with Extraction

Intelligent thermo-responsive catalysts [C₁₆H₃₃N(CH₃)₃]₃[PO₄{MO(O₂)₂}₄]/poly(N-isopropylacrylamide) (M = Mo and W, abbreviated as C₁₆PM(O₂)₂/PNIPAM) have been prepared using thermo-responsive polymer PNIPAM as a support. The thermo-responsive hybrids exhibit novel switchable property based on the change of temperature, while its solubility in organic solvent is reversibly controllable through an external temperature stimulus linking the gap between heterogeneous catalysis and homogeneous one. Moreover, non-polar organic substrates are accumulated around the catalytic sites by two synergistic effects of amphiphilic POM molecules and the existence of PNIPAM. Therefore, this solid hybrid has been successfully used in catalyzing the oxidation of refractory sulfur-containing compound dibenzothiophene into its corresponding sulfone with high selectivity in the presence of H₂O₂. Application of this catalyst brings about an efficient, useful and green process in desulfurization through extraction and oxidation simultaneously.     

Keggin‐Type Polyoxometalate‐Based Metal–Organic Networks for Photocatalytic Dye Degradation

The reaction of Keggin‐type polyoxometalate (POM) units, transition‐metal (TM) ions, and a rigid bis(imidazole) ligand (1,4‐bis(1‐imidazolyl)benzene (bimb)) in a hydrothermal environment led to the isolation of four new POM‐based metal–organic networks, [H₂L][CuL][SiW₁₂O₄₀]?2 H₂O ( 1 ), [H₂L]₂[Co(H₂O)₃L][SiW₁₁CoO₃₉]?6 H₂O ( 2 ), KH[CuL]₂[SiW₁₁CoO₃₉(H₂O)]?2 H₂O ( 3 ), and [CuL]₄[GeW₁₂O₄₀]?H₂O ( 4 ; L=bimb). All four compounds were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction, and single‐crystal X‐ray diffraction. Compounds 1 and 3 are new 3D networks with 1D channels. Compounds 2 and 4 contain 2D networks, which further stack into 3D supramolecular networks. The contributions of pH value, the negative charge of the POM, and the TM coordination modes to the construction of 3D networks were elucidated by comparing the synthetic conditions and structures of compounds 1 – 4 . The photocatalytic properties of compounds 1 – 4 were investigated using methylene blue (MB) degradation under UV light. All compounds showed good catalytic activity and structural stability. The possible catalytic mechanism was discussed on the basis of active‐species trapping experiments. The different photocatalytic activities of compounds 1 – 4 were explained by comparison of the band gaps of different POM species and different packing modes of POM units in these hybrid compounds.     

Polyisobutylene‐b‐Poly(N,N‐diethylacrylamide) well‐defined amphiphilic diblock copolymer: Synthesis and thermo‐responsive phase behavior

Polyisobutylene‐b‐poly(N,N‐diethylacrylamide) (PIB‐b‐PDEAAm) well‐defined amphiphilic diblock copolymers were synthesized by sequential living carbocationic polymerization and reversible addition‐fragmentation chain transfer (RAFT) polymerization. The hydrophobic polyisobutylene segment was first built by living carbocationic polymerization of isobutylene at ?70 ° C followed by multistep transformations to give a well‐defined (M_w/M_n = 1.22) macromolecular chain transfer agent, PIB‐CTA. The hydrophilic poly(N,N‐diethylacrylamide) block was constructed by PIB‐CTA mediated RAFT polymerization of N,N‐diethylacrylamide at 60 ° C to afford the desired well‐defined PIB‐b‐PDEAAm diblock copolymers with narrow molecular weight distributions (M_w/M_n ≤1.26). Fluorescence spectroscopy, transmission electron microscope, and dynamic light scattering (DLS) were employed to investigate the self‐assembly behavior of PIB‐b‐PDEAAm amphiphilic diblock copolymers in aqueous media. These diblock copolymers also exhibited thermo‐responsive phase behavior, which was confirmed by UV‐Vis and DLS measurements. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1143–1150     

Improved Hydrogen‐Storage Thermodynamics and Kinetics for an RbF‐Doped Mg(NH2)2–2 LiH System

The introduction of RbF into the Mg(NH₂)₂–2 LiH system significantly decreased its (de‐)hydrogenation temperatures and enhanced its hydrogen‐storage kinetics. The Mg(NH₂)₂–2 LiH–0.08 RbF composite exhibits the optimal hydrogen‐storage properties as it could reversibly store approximately 4.76 wt % hydrogen through a two‐stage reaction with the onset temperatures of 80 °C for dehydrogenation and 55 °C for hydrogenation. At 130 °C, approximately 70 % of hydrogen was rapidly released from the 0.08 RbF‐doped sample within 180 min, and the fully dehydrogenated sample could absorb approximately 4.8 wt % of hydrogen at 120 °C. Structural analyses revealed that RbF reacted readily with LiH to convert to RbH and LiF owing to the favorable thermodynamics during ball‐milling. The newly generated RbH participated in the following dehydrogenation reaction, consequently resulting in a decrease in the reaction enthalpy change and activation energy.     

Thermo‐ and pH‐Responsive Micelles of Poly(acrylic acid)‐block‐Poly(N,N‐diethylacrylamide)

Summary: The bis‐hydrophilic block copolymer, poly(acrylic acid)₄₅‐block‐poly(N,N‐diethylacrylamide)₃₆₀, was obtained after hydrolysis of poly(tert‐butyl acrylate)₄₅‐block‐poly(N,N‐diethylacrylamide)₃₆₀, synthesized by sequential anionic polymerization of tert‐butyl acrylate (tBA) and N,N‐diethylacrylamide (DEAAm) in the presence of Et₃Al. The polymer is stimuli‐sensitive with respect to both pH and temperature in aqueous solution, reversibly forming spherical crew‐cut micelles with PDEAAm‐core (〈R_h〉_z = 21.5 nm) under alkaline conditions for T > 35 °C as well as inverse star‐like micelles with an expanded PAA‐core (〈R_h〉_z = 43.8 nm) under acidic conditions for T < 35 °C, as indicated by dynamic light scattering.

Modes of micelle formation for poly(acrylic acid)₄₅‐block‐poly(N,N‐diethylacrylamide)₃₆₀ in aqueous solution depending on the pH and temperature.     

POM‐Catalyzed In Situ Ligand Synthesis for the Construction of Metal Complexes and Their Use in the Formation of Coordination Polymers

Six organic–inorganic hybrid materials were synthesized by the in situ oxidation of neocuproine by using MoO₃/Na₂MoO₄ as the catalyst in the presence of Cu(NO₃)₂. The crystal structures of Mo8‐Cu4‐PHEN and Mo8‐Cu2‐5(2PIC) are composed of [Mo₈O₂₆]^4? polyoxometalate (POM) units, whereas the crystal structure of Mo6‐Cu‐COPHEN is composed of a [Mo₆O₁₉]^2? POM unit; both POM units could be considered as the active form of the catalyst. Reaction of the hybrid materials with 1,3,5‐benzenetricarboxylic acid (BTC) resulted in the formation of two different coordination polymers (CPs) under different reaction conditions. These CPs, depending on their structural attributes, exhibit distinct differences in the adsorption of H₂, CO₂, and water. The use of 2‐methylpyridine instead of neocuproine does not give any oxidation products under the same reaction conditions due to the incorrect positioning of the methyl group with respect to the Cu^II center.     

Strong Solid‐state Luminescence Enhancement in Supramolecular Assemblies of Polyoxometalate and “Aggregation‐Induced Emission”‐active Phospholium

Two new supramolecular fluorescent hybrid materials, combining for the first time [M₆O₁₉]^2? (M=Mo, W) polyoxometalates (POMs) and aggregation‐induced emission (AIE)‐active 1‐methyl‐1,2,3,4,5‐pentaphenyl‐phospholium ( 1⁺ ), were successfully synthesized. This novel molecular self‐assembling strategy allows designing efficient solid‐state emitters, such as (1)₂[W₆O₁₉] , by directing favorably the balance between the AIE and aggregation‐caused quenching (ACQ) effects using both anion‐π⁺ and H‐bonding interactions in the solid state. Combined single‐crystal X‐ray diffraction, Raman, UV‐vis and photoluminescence analyses highlighted that the nucleophilic oxygen‐enriched POM surfaces strengthened the rigidity of the phospholium via strong C?H???O contacts, thereby exalting its solid‐state luminescence. Besides, the bulky POM anions prevented π–π stacking interactions between the luminophores, blocking detrimental self‐quenching effects.     

The Synthesis and Characterization of Aromatic Hybrid Anderson–Evans POMs and their Serum Albumin Interactions: The Shift from Polar to Hydrophobic Interactions

Four aromatic hybrid Anderson polyoxomolybdates with Fe³⁺ or Mn³⁺ as the central heteroatom have been synthesized by using a pre‐functionalization protocol and characterized by using single‐crystal X‐ray diffraction, FTIR, ESI‐MS, ¹H NMR spectroscopy, and elemental analysis. Structural analysis revealed the formation of (TBA)₃[FeMo₆O₁₈{(OCH₂)₃CNHCOC₆H₅}₂] ? 3.5 ACN ( TBA‐FeMo₆‐bzn ; TBA=tetrabutylammonium, ACN=acetonitrile, bzn=TRIS‐benzoic acid alkanolamide, TRIS?R=(HOCH₂)₃C?R)), (TBA)₃[FeMo₆O₁₈{(OCH₂)₃CNHCOC₈H₇}₂] ? 2.5 ACN ( TBA‐FeMo₆‐cin ; cin=TRIS‐cinnamic acid alkanolamide), (TBA)₃[MnMo₆O₁₈{(OCH₂)₃CNHCOC₆H₅}₂] ? 3.5 ACN ( TBA‐MnMo₆‐bzn ), and (TBA)₃[MnMo₆O₁₈{(OCH₂)₃CNHCOC₈H₇}₂] ? 2.5 ACN ( TBA‐MnMo₆‐cin ). To make these four compounds applicable in biological systems, an ion exchange was performed that gave the water‐soluble (up to 80 mM ) sodium salts Na₃[FeMo₆O₁₈{(OCH₂)₃CNHCOC₆H₅}₂] ( Na‐FeMo₆‐bzn ), Na₃[FeMo₆O₁₈{(OCH₂)₃CNHCOC₈H₇}₂] ( Na‐FeMo₆‐cin ), Na₃[MnMo₆O₁₈{(OCH₂)₃CNHCOC₆H₅}₂] ( Na‐MnMo₆‐bzn ), and Na₃[MnMo₆O₁₈{(OCH₂)₃CNHCOC₈H₇}₂] ( Na‐MnMo₆‐cin ). The hydrolytic stability of the sodium salts was examined by applying ESI‐MS in the pH range of 4 to 9. Sodium dodecylsulfate–polyacrylamide gel electrophoresis (SDS‐PAGE) showed that human and bovine serum albumin (HSA and BSA) remain intact in solutions that contain up to 100 equivalents of the sodium salts over more than 4 d at 20 °C. Tryptophan (Trp) fluorescence quenching was applied to study the interactions between the sodium salts and HSA and BSA at pH 5.5 and 7.4. The quenching constants were extracted by using Stern–Volmer analysis, which suggested the formation of a 1:1 POM–protein complex in all samples. It is suggested that the aromatic hybrid POM approaches subdomain IIA of HSA and exhibits hydrophobic interactions with its hydrophobic tails, whereas the Anderson core is stabilized through electrostatic interactions with polar amino acid side chains from, for example, subdomain IB.