Formation Of Coordination Bonds Research Articles

A Microbial Siderophore-Inspired Self-Gelling Hydrogel for Noninvasive Anticancer Phototherapy.

Microbial carboxyl and catechol siderophores have been shown to have natural iron-chelating abilities, suggesting that hyaluronic acid (HA) and the catechol compound, gallic acid (GA), may have iron-coordinating activities. Here, a photoresponsive self-gelling hydrogel that was both injectable and could be applied to the skin was developed on the basis of the abilities of HA and GA to form coordination bonds with ferric ions (Fe3+). The conjugate of HA and GA (HA-GA) instantly formed hydrogels in the presence of ferric ions and showed near-infrared (NIR)-responsive photothermal properties. Following their subcutaneous injection into mice, HA-GA and ferric ion formed a hydrogel, which remained at the injection site for at least 8 days. Intratumoral injection of HA-GA/Fe hydrogel into mice allowed repeated exposure of the tumor to NIR irradiation. This repeated NIR irradiation resulted in complete tumor ablation in KB carcinoma cell-xenografted mice and suppressed lung metastasis of 4T1-Luc orthotopic breast tumors. Application of HA-GA/Fe hydrogel to the skin of A375 melanoma-xenografted tumor sites, followed by NIR irradiation, also resulted in complete tumor ablation. These findings demonstrate that single applications of HA-GA/Fe hydrogel have photothermal anticancer effects against both solid tumors and skin cancers. SIGNIFICANCE: These findings provide new insights into noninvasive anticancer phototherapy using self-gelling hydrogels. Application of these hydrogels in preclinical models reduces the sizes of solid tumors and skin cancers without surgery, radiation, or chemotherapy.

Thermal Reactivity in Metal Organic Materials (MOMs): From Single-Crystal-to-Single-Crystal Reactions and Beyond.

Thermal treatment is important in the solid-state chemistry of metal organic materials (MOMs) because it can create unexpected new structures with unique properties and applications that otherwise in the solution state are very difficult or impossible to achieve. Additionally, high-temperature solid-state reactivity provide insights to better understand chemical processes taking place in the solid-state. This review article describes relevant thermally induced solid-state reactions in metal organic materials, which include metal organic frameworks (MOFs)/coordination polymers (CPs), and second coordination sphere adducts (SSCs). High temperature solid-state reactivity can occur in a single-crystal-to-single crystal manner (SCSC) usually for cases where there is small atomic motion, allowing full structural characterization by single crystal X-ray diffraction (SC-XRD) analysis. However, for the cases in which the structural transformations are severe, often the crystallinity of the metal-organic material is damaged, and this happens in a crystal-to-polycrystalline manner. For such cases, in the absence of suitable single crystals, structural characterization has to be carried out using ab initio powder X-ray diffraction analysis or pair distribution function (PDF) analysis when the product is amorphous. In this article, relevant thermally induced SCSC reactions and crystal-to-polycrystalline reactions in MOMs that involve significant structural transformations as a result of the molecular/atomic motion are described. Thermal reactivity focusing on cleavage and formation of coordination and covalent bonds, crystalline-to-amorphous-to-crystalline transformations, host–guest behavior and dehydrochlorination reactions in MOFs and SSCs will be discussed.

Raman spectroscopy along with Principal Component Analysis for the confirmation of Silver(I)-N-heterocyclic carbene complex formation.

In this study Raman spectroscopy is employed for the characterization of two different ligands called as S1 and S2 and their respective co-ordinate complexes called C1 and C2. Specific Raman spectral signatures are observed for each of these Silver(I)-N-heterocyclic carbene complexes Ag(I)-(NHCs), which can be associated with the imidazolium ring, part of both of the ligands, indicating the formation of new coordinate covalent bond. For the detailed analysis, Raman spectral data of these ligands and complexes is analyzed by multivariate data analysis technique, Principal Component Analysis (PCA) which is found very helpful to differentiate two ligands and complexes from each other. The significant Raman peaks with higher intensities in the complexes as compared to the respective ligands are associated with imidazole ring which can be attributed to the enhanced polarizability of this ring on complex formation. Moreover, the spectral features associated with (AgC) bond are observed with higher intensity at 360 in (C1) and 383 in (C2). This study indicates the potential of Raman spectroscopy for the characterization and confirmation of formation of organometallic complexes and other chemical products.

Novel Nanostructured Metal–Organic Framework-Bonded Silica Amine and Polymer: Facile Synthesis, Kinetics, Isotherms, and Thermodynamics Evaluation for Adsorption of Yttrium(III) Ions

Yttrium is a remarkable rare-earth element with multidiscipline applications, and it can be released into an aquatic system for its widespread industrial applications. The present work is devoted to evaluate the kinetics and isotherm models for adsorption of Y(III) ions by the action of a novel metal–organic framework (MOF) chemically bonded polymer with incorporated ion exchange and chelating characters. To assemble these MOFs, a number of synthetic procedures were designed and performed using microwave irradiation heating in only 12 min. (i) The selected MOFs were synthesized by the reaction of zinc acetate and glutaric to produce (ZnGA) in 3 min. (ii) Covalent bonding and coating of (ZnGA) with 3-aminopropyltrimethoxysilane were carried out to produce (ZnGA–Si–NH2) in 3 min. (iii) The polymeric compound was synthesized by coupling of p-chlorocresol with piperazine via formaldehyde to yield PC in 4 min. (iv) The final MOFs–polymer nanocomposite was synthesized by the functionalization of ZnGA–Si–NH2 with PC to assemble ZnGA–Si–NH–PC in 2 min. The impact of the polymer on stability of ZnGA–Si–NH–PC in aqueous solutions (pH 1–7) was confirmed and compared to the MOFs separately. Additionally, thermal stability and surface morphology of ZnGA–Si–NH–PC were also studied and evaluated. The metal sorption capacity values of Y(III) ions onto ZnGA–Si–NH–PC were optimized at pH 7 and established as 1175, 1925, and 4800 μmol g–1 using 0.025, 0.05, and 0.1 mol L–1 of Y(III), respectively. The interaction mechanisms for binding of Y(III) ions with ZnGA–Si–NH–PC were studied and evaluated by seven kinetics models and seven adsorption isotherm models, and the collected results confirmed that the adsorption process is well fitted with the pseudo-second-order and pore diffusion models. The collected data assured that the adsorption of Y(III) ions onto the ZnGA–Si–NH–PC nanocomposite is chemisorption (ΔH° = 42.44 kJ/mol) with the direct ion exchange mechanism of Y(III) ions with the surface hydrogen ions and coordinate bond formation mechanism with the nitrogen functional groups into the available pores of the ZnGA–Si–NH–PC nanocomposite.

Prospects of DNA Macromolecule for Corrosion Inhibitor Applications: A Mini Review

Metal deterioration inhibitors are known to be materials that have shielding power with clear manifestation that is solely focused on usage on a metallic external texture. The advancement in the utilization of metal deterioration inhibitors are now well recognised, nonetheless, majority of current inhibitors have some disadvantages. Benevolent macromolecule inhibitors with biological origins are environmentally un-harmful substances with numerous polar ends having ability to form coordination bonds. New prospects of deoxyribonucleic acid (DNA) extracted from plant species, animal species and different species of pisces used for the purpose of metal deterioration inhibition welcomes some unique research possibility for engineering applications. As a result, it is expected that DNA would have high level of effectiveness when the strains of DNA of the three species are extricated for making inhibitors due to their feasible inclusions in averting metal deterioration.

Preparation of printable double-network hydrogels with rapid self-healing and high elasticity based on hyaluronic acid for controlled drug release

On account of the features about computer-accurate control, the technology of 3D printing has a broad future for developing customized ergonomic biomedical materials. Herein, a printable dual-network hydrogel for drug delivery was designed. The acrylamide-modified hyaluronic acid was mixed with folic acid and Fe3+ at first. With the formation of metal-carboxylate coordination bonds, the first layer of physical crosslinking network (HFF) was formed, followed by performing the spectral analysis and rheology measurements to verify the bonding. The second layer of PAM network was then polymerized by ultraviolet radiation, with high elasticity and fatigue resistance to satisfy its application as a wound dressing. Furthermore, acetylsalicylic acid (Asa) was used as a drug model resulted in a pH responsiveness of the prepared hydrogels with the sustained drug releasing behavior over 300 h. These results signified the potential application of this self-healing hydrogel with good mechanical properties in regenerative medicine.

Molecular insights into the impacts of iron(III) ions on membrane fouling by alginate.

Molecular mechanisms responsible for the filtration behaviors of sodium alginate (SA) in presence of different iron(III) ion concentration were explored in this study. It was found that specific filtration resistance (SFR) of alginate mixtures (1.0 gSA/L) firstly increased and then decreased to a trough with iron(III) concentration increase from 0 to 2.5 mM. Alginate mixture interacting with 0.1 mM iron(III) possessed an SFR as high as 1.65 × 1014 m kg-1, which could be explained by Flory-Huggins lattice theory related with gel filtration. Optical observation showed significant morphology transition (from gel to granular solids) of foulant layers with iron(III) concentration increase. A series of characterizations indicated the change of microstructure, pH and surface charge of alginate mixture with iron(III) concentration. Density functional theory (DFT) simulation suggested that iron(III) ion preferentially forms coordination bonds with three terminal carboxyl groups of alginate chains, facilitating elongation and cross-linking of alginate chains. Such a coordination mode induces formation of a slime and homogeneous gel, corresponding to high SFR. Continuous increase in iron(III) concentration leads to non-terminal coordination, which makes alginate chains more clustered and coiled. This effect, together with effects of the reduced surface charge and electric double layer compression, significantly decrease SFR of alginate mixtures. This study provided deep molecular insights into effects of iron(III) ions on alginate fouling.

Silico-manganese fumes waste encapsulated cryogenic alginate beads for aqueous environment de-colorization

Safe and economical disposal of ultrafine silico-manganese fumes (SMF), a waste, generated during steel production operation is a challenge for environmental chemists. Herein, SMF waste was encapsulated into alginate, lyophilized to form cryogenic SMF beads (cSMFB). The cSMFB was characterized and its adsorptive potential was tested in the removal of methylene blue (MB), methylene green (MG), crystal violet (CV) and celestine blue (CB) from aqueous environment. The cSMFB having respective Brunauer-Emmett-Teller (BET) surface area and Barrett, Joyner, and Halenda (BJH) pore diameter of 59.88 m2/g and 18.58 Å was developed. Fourier transform infra-red (FT-IR) analysis revealed bands at 1630 and 1412 cm−1, attributed to asymmetric and symmetric stretching vibrations of carboxylate ions, characteristic of alginate (used to encapsulate SMF). Also, the bands at 1092 and 1031 cm−1 corresponding to carbohydrate rings of alginate were present. A band ascribed to metal oxides was appeared at 467 cm−1. The encapsulation of SMF waste in alginate was further confirmed by X-ray photoelectron spectroscopy (XPS) (with peaks at binding energies 34, 284.7, and 532 eV ascribed to Na 2p, C1s, and O 1s), X-ray diffraction (XRD) (with 2θ peaks at 13.5 and 22.2° for sodium alginate), and energy-dispersive X-ray (EDX) analyses. The cross-sectional image of pristine cSMFB showed highly porous rough and uneven surface. Thermogravimetric (TGA-DTA) analysis of cSMFB sample revealed the five stages total weight loss of ∼17.5% between 40 and 800 °C. Alkaline pH (pHi range: 6–8) favored the adsorption of dyes, while the equilibration time at Co: 50 mg/L was varied between 480 and 600 min. The adsorption of dyes was possibly governed through electrostatic interaction, coordinate bond formation, and cationic interchange.

Mechanism Study of the Formation of Indigo Carmine-Aluminum Hydroxide Lake for Food Use.

Although aluminum lakes are widely used in food industry for dyeing demands, there is still a dearth in the understanding of the colorant lake formation mechanism. In this study, indigo carmine (IC) lake (IC-aluminum hydroxide complex), a frequently used blue lake in the food industry, was investigated in terms of kinetics, isotherms, properties of colloidal particles, infrared (IR) spectra, and titration curves. Pseudo-second-order model presented the strongest correlation with the kinetic data at all pH levels (R2 ≥0.994). In pH range from 4 to 7, the colloidal particles of aluminum hydroxide were positively charged with zeta potential around 44 mV; a further pH increase induced to a decreased zeta potential, which reached negative levels at pH 10 and beyond. Diameter maximized at pH 10 (22.47 µm) and declined when the pH was reduced. Isotherm analysis showed that the adsorption followed monolayer adsorption patterns, as described by the Langmuir isotherm model. IR spectra indicated sulfonic acid groups participated in a chemical reaction during adsorption, and the titration assay further confirmed the formation of coordination bonds between sulfonic acid groups and aluminum atoms. This study profiled the reaction responsible for the formation of the blue lake and elucidated its reaction mechanism. Furthermore, the outcome could assist in improving the production efficiency of the lake through achieving higher reaction rate and adsorption capacity. PRACTICAL APPLICATION: The study elucidated the mechanism of indigo carmine (IC)-aluminum hydroxide lake formation, including profile of the adsorption process and molecular interaction between the blue dye and the hydroxide. The outcome of this study would help to improve the production efficiency of IC-aluminum hydroxide lakes, and to decrease the content of aluminum required in the lake by optimizing the production parameters to enhance the adsorption capacity of aluminum hydroxide, which would facilitate the alleviation of the potential health hazards caused by excessive intake of aluminum through foods.

Reconstructing the Electron Density of Intermediates of the Hydrolysis of N-Acetylaspartate by Aspartoacylase

The hydrolysis of N-acetylaspartate by human aspartoacylase shows that using promolecular electron density (superpositions of the densities of spherical atoms) is insufficient for describing intermediates of reactions of enzyme catalysis. The deformation of electron density caused by the formation of covalent and coordination bonds inside a system must be considered, creating the need to develop new approaches in protein crystallography for better interpretation of observed electron density and more precise determination of the geometrical parameters of reaction intermediates.

NH2-MIL-53(Al) Metal-Organic Framework as the Smart Platform for Simultaneous High-Performance Detection and Removal of Hg2.

The worsening pollution due to mercury species makes it inevitable to explore prospective versatile materials, which not only can detect mercury ions (Hg2+) with high sensitivity but also possesses efficient capture and removal ability. In this study, a series of classic organic ligand-based luminescence MOFs materials with high oxidation state central metals (Al3+, Zr4+, Cr3+, Fe3+, and Ti4+) were synthesized and were screened to achieve simultaneously Hg2+ detection and removal through the strong coordination of amino groups or nitrogen centers with Hg2+ and the intrinsic fluorescence intensity of MOFs regulated by the ligand-to-metal charge transfer (LMCT) effect. Among these checked materials, NH2-MIL-53(Al) exhibited the excellent ability for Hg2+ detection with wide response interval (1-17.3 μM), low detection limit (0.15 μM), good selectivity, wide pH adaptation (4.0-10.0), and strong anti-interference ability. Meanwhile, the resultant NH2-MIL-53(Al) possessed an efficient removal capability toward Hg2+, accompanied by a fast uptake kinetics (within 60 min) and large loading capacity (153.85 mg g-1). Furthermore, NH2-MIL-53(Al) also displayed satisfactory stability before and after Hg2+ treatment because of the formation of strong coordination bonds between high oxidation state aluminum (Al3+) and organic carboxylate ligands. Notably, the prepared NH2-MIL-53(Al) had no significant loss of adsorption performance even after being reused four times. All of these superior properties render the smart NH2-MIL-53(Al) nanohexahedron a great potential for simultaneous Hg2+ detection and removal from water.

Application of a Silicon Oligomer Coating As an Alternative Treatment to Substrate Surface Activation By Etching

In order to attain adhesion of plated metals to substrates, conventionally the substrate surface roughness is increased by etching, such that deposited metal can form physical anchors into the substrate surface. Traditionally, chromic acid has been used to roughen organic resin substrates, however, due to restrictions on hexavalent chromium use, permanganate etching methods have been developed. For roughening glass and ceramic substrates, hazardous chemicals like hydrofluoric acid or molten sodium hydroxide are employed. Once surfaces have been sufficiently roughened, ionic or colloidal palladium is adsorbed onto the surface, then activated by treatment with a reducing agent, followed by electroless plating to deposit a conductive layer. With the demand for finer circuit patterns in the printed circuit board industry, smoother surfaces are needed, and due to transmission loss by the skin effect, plating adhesion to smooth surfaces is required in high frequency applications. To resolve these problems for resin substrates, UV irradiation methods and ozone treatment have been investigated where reasonable adhesion to nanometer scale roughened surfaces have been reported. An alternative method for plating on glass by coating glass with Pd catalyst containing siloxane solutions have been investigated, however instability of Pd in the presence of siloxane and other alcohol solvents stifle industrial application. Our group has been developing silicon oligomer compounds by cross-linking tetraethoxy silane with ethylene glycol (instead of water) for use in combination with acrylic resin as a coating agent for various materials with a variety of purposes such as corrosion prevention for bolts and nuts, PC case coloring, and solar panel cover glass anti-reflective coating. The cross-linking reaction is catalyzed by a metal salt, and in the ethylene glycol-silicone oligomer case, when catalyzed by PdCl2, a stable composition of Pd ion containing ethylene glycol-silicone oligomer solution was obtained. In this solution, the ethylene glycol cross-linker was believed to form coordination bonds with the Pd ion to stabilize it. However, since ethylene glycol can be oxidized to generate aldehydes, carboxylic acids and release electrons, then heating the coated film should result in reduction of the Pd ions present. Analysis of the Pd/Si-oligomer films revealed simultaneous formation of aldehydes and carboxylic acids with reduction of Pd2+ to Pd metal at 200°C. Evaluation in application to electroless Ni plating revealed no catalytic activity after the Pd/Si-oligomer films were heated at 50°C, catalytic activity but poor adhesion at 100°C, catalytic activity and sufficient adhesion at 150 and 200°C. Next, semi-additive plating and adhesion strength on glass (PD200) and glass reinforced epoxy (Ajinomoto Build-up film GX-T31) substrates according to the process illustrated in the attached figure. Stripping of the residual Pd/Si-oligomer was accomplished by dry etching followed by treatment in dilute HCl solution to remove residual Pd. On the glass substrate, a 20 mm thick copper deposits with 90° peel strength of 0.3 kN/m, and 0.5 kN/m on the epoxy substrate were attained. By adjusting the electroless plating conditions 0.5 kN/m adhesion strength was also attained for alkali-free glass and alumina ceramics. Observation of the plated film cross-section suggested the adhesion mechanism to manifest from a physical anchor effect of the plated metal film to the Pd/Si-oligomer layer. Evaluation of the insertion loss at 50 GHz1) showed no significant difference compared to the conventional dry metallization method on glass and lower loss compared to electroless plating on roughened ABF. Using the Pd/Si-oligomer as a surface activation treatment enabled plating on glass and epoxy resin with no etching or surface roughening procedure, and no requirement for chemical reduction or activation of the Pd catalyst prior to electroless plating. 1) Daisuke Sadohara, Hiroyuki Aijima, Younggun Han, Yoshihisa Katoh; 33rd Electronics Packaging Soc. Japan Spring Meeting; 2019 March 11-13th; Takushoku University, Bunkyo Campus, Tokyo Figure 1

Cobalt(ii) cation binding by proteins.

Herein, a set of non-homologous proteins (238) that could bind the cobalt(ii) cations was selected from all the available Protein Data Bank structures with Co2+ cations. The secondary structure motifs around the amino acid residues that most frequently bind the Co2+ cations (His, Asp, and Glu) as well as the amino acid contents of the inner and outer spheres of complexes were studied. The residues forming coordination bonds to Co2+ (from the inner spheres of the complexes) are overrepresented in the regions of random coil between two β strands, between a β strand and α helix, and in all types of β strands, except that situated between an α helix and β strand. The residues situated at a distance of less than 5 Å from the Co2+ cations, but unable to form coordination bond to them (from the outer spheres of the complexes), are overrepresented in the regions of coil between the β strand and α helix and between two β strands. The data obtained for the Co2+ binding sites was compared with the data obtained for the Mg2+ and Mn2+ binding sites. Although the preferable motifs of the secondary structure for Co2+ binding (beta strand-loop-beta strand and beta strand-loop-alpha helix) are the same as those for Mg2+ and Mn2+, there are some differences in the amino acid contents of the inner and outer spheres of these complexes. The Co2+ cations are preferably coordinated by a combination of His and Glu residues, whereas the Mn2+ and Mg2+ cations prefer a combination of His and Asp and just Asp residues, respectively. As a result, two computer algorithms were developed that could evaluate the possibility of Mg2+ and Mn2+ replacement by the Co2+ cations (chemres.bsmu.by). These algorithms should help to investigate the pathogenesis of cobalt intoxication occurring in patients with cobalt-containing artificial joints.

Enhancing the surface affinity with silver nano-particles for antibacterial cotton fabric by coating carboxymethyl chitosan and l-cysteine

This study evaluates the durability and antibacterial function of silver nanoparticle (SP) coatings on natural cotton fabrics via a combination of carboxymethyl chitosan (CMCS) and l-cysteine (Cys). Surface modification is accomplished by grafting CMCS on the cotton fabric followed by immobilizing SP via amidation reaction with Cys. The X-ray photoelectron spectroscopic (XPS) results show that the amine and thiol groups of Cys form coordination bonds with SP. Durability experiments show that the antibacterial function of the modified fabrics is sustained even after 180 cycles of washing with bacterial reduction rates (BR) >97% for Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Surface characterization results reveal that the combination of the two binders (CMCS and Cys) allows for a stable dispersion of SP on the modified fiber surfaces with >89% of the silver coating layer preserved after 180 rounds of washing. Moreover, cytotoxicity assays performed on the leachate of the modified fabric show insignificant effects on human immortalized keratinocyte (Hacat) cells indicating that the material is safe to wear against human skin. The results collectively demonstrate that the modified fabric has great potential for use in textile applications.

Computer-aided discovery of connected metal-organic frameworks

Composite metal-organic frameworks (MOFs) tend to possess complex interfaces that prevent facile and rational design. Here we present a joint computational/experimental workflow that screens thousands of MOFs and identifies the optimal MOF pairs that can seamlessly connect to one another by taking advantage of the fact that the metal nodes of one MOF can form coordination bonds with the linkers of the second MOF. Six MOF pairs (HKUST-1@MOF-5, HKUST-1@IRMOF-18, UiO-67@HKUST-1, PCN-68@MOF-5, UiO-66@MIL-88B(Fe) and UiO-67@MIL-88C(Fe)) yielded from our theoretical predictions were successfully synthesized, leading to clean single crystalline MOF@MOF, demonstrating the power of our joint workflow. Our work can serve as a starting point to accelerate the discovery of novel MOF composites that can potentially be used for many different applications.

Solid-Gas Phase Synthesis of Coordination Networks by Using Redox-Active Ligands and Elucidation of Their Oxidation Reaction.

Formation of coordination networks is a complex process affected by a multitude of factors. Many synthetic strategies have been developed that attempt to control these factors and direct the structure of the final product. Coordination bond formation and structural assembly processes, however, typically take place either in the solution or solid states. In comparison, gas-phase network synthesis remains largely unexplored. Herein, two new two-dimensional coordination networks are obtained from the solid-gas phase reaction between ZnX2 (X=I, Br) and the redox-active 2,5,8-tri(4-pyridyl)1,3-diazaphenalene (HTPDAP) ligand. Their structures were solved by ab initio powder X-ray diffraction analysis and feature a novel Zn halide trimeric cluster. This strategy is contrasted with a conventional solvothermal synthesis, which led to a one-dimensional coordination polymer instead. The intrinsic electroactive properties of these materials were probed by solid-state cyclic voltammetry measurements, which revealed the presence of HTPDAP and halide-based processes. Chemical oxidation of the two-dimensional networks by using NOPF6 agent, unexpectedly, led to the formation of a nitrated analog of HTPDAP, the PF6 - salt of diprotonated 4,6,7,9-tetranitro-2,5,8-tris(4-pyridyl)diazaphenalene cation (denoted N-TPDAP), which was isolated and characterized. These results provide deeper insights into the oxidation process of HTPDAP-containing networks and uncover unique redox-induced chemical transformations.

Synthesis and structures of N-(4-picolyl)azacalix[4]arene and its bridged derivatives

Azacalixarenes have side arms (N-substituents) on the nitrogen atoms in their macrocyclic ring systems; thus, a variety of molecular designs are possible by modifying these side arms. This is a special feature of azacalixarene system which is not available in calix[n]arenes. In this paper, we used azacalix[3.1.3.1] and [3.1.1.1]arenes because these compounds have concave cavities. The cavity size of the azacalix[3.1.1.1] structure is small like the calix[4]arenes, but, supramolecular systems can be designed in which two or three azacalix units are connected by covalent or coordination bonds. Previously reported compounds, N-(4-picolyl)-[3.1.3.1] or [3.1.1.1]arenes, can be applied for this purpose. The 4-picolyl group can form covalent bonds with alkylation and form coordination bonds with a variety of transition metal ions. By using these bonds, we extend the cavity size of the azacalixarenes and construct newly designed supramolecular structures. We expected that these molecules would form larger molecular cavities upon side arm modification, and inclusion abilities of these cavities can be extended compared to the azacalixarenes of small cavity sizes. However, most of these molecular structures could not be determined, and none showed inclusion phenomena contrary to our expectations. Only the molecular structure of a p-xylylene-bridged molecule was confirmed, which possessed a self-inclusion structure in which the bridging unit (p-xylylene) was encapsulated by two azacalixarene cavities. Additionally, it was found that p-methyl-N-(4-picolyl)azacalix[3.1.1.1]arene 1 formed two molecular packing modes depending on the recrystallizing solvents. One is stacked structure by π–π interactions, and another is capsule type structure in which two solvent molecules were encapsulated. A self-inclusion type cage molecule was obtained by connecting N-(4-picolyl)azacalix[3.1.1.1]arene with a p-xylylene unit.

Metallo-Supramolecular Hydrogels from the Copolymers of Acrylic Acid and 4-(2,2':6',2″-terpyridin-4'-yl)styrene.

Hydrophilic copolymers containing 2,2′:6′,2″-terpyridine moieties and acrylic acid (AA) units poly (acrylic acid-co-4-(2,2′:6′,2″-terpyridin-4′-yl)styrene) (P(AA-co-TPY)) were synthesized and characterized. Coordinated with different transition metal ions, the dilute aqueous solution of the copolymers exhibited red-shifted UV-vis absorption peaks of π-π* transition from 317 to 340 nm. Further, interacting with iron ions, the copolymer showed new absorption peaks at a longer wavelength region (570 nm) and the absorption intensity enhanced with increase of the ion concentration. When enough ions were added to coordinate with the 2,2′:6′,2″-terpyridine moieties, novel metallo-supramolecular hydrogels were obtained due to the formation of metal coordination bonds between polymer back bones and transition metal ions (Ni2+, Zn2+, Cd2+, Fe2+ and Cu2+), which acted as self-assembly crosslinking structures. The mechanical strength and morphology of the resulting metallo-supramolecular hydrogels have been investigated.

Novel poly(2-oxazoline) block copolymer with aromatic heterocyclic side chains as a drug delivery platform

Here we report a novel poly(2-oxazoline)-based block copolymer with the aromatic heterocyclic side chains in one block, poly(2-methyl-2-oxazoline)-b-poly(2-N,N-dimethyl-1,3,5-triazine-2,4-diamine-6-ethyl-2-oxazoline) (PMeOx-PcBOx), and demonstrate its potential application as a drug delivery platform. The copolymer was synthesized via the condensation of N,N-dimethylbiguanide with the methyl ester side chain in poly(2-methoxycarboxyethyl-2-oxazoline) block (PMestOx) of the PMeOx-PMestOx diblock copolymer. We confirmed the N,N-dimethylbiguanide condensation with PMestOx and the complete conversion of the side chain to the N,N-dimethyl-1,3,5-triazine-2,4-diamine-6-ethyl moiety by NMR spectroscopy, MALDI-TOF mass spectroscopy, UV–Vis spectroscopy, and titration analysis. The PMeOx-PcBOx copolymer self-assemble into polymeric micelles in aqueous solution. Successful encapsulation into these micelles has been demonstrated for 1) several poorly soluble drugs, such as bruceantin and LY2109761, and 2) dichloro(1,2-diaminocyclohexane)platinum(II) (DachPt). The first class of drugs is incorporated possibly via hydrogen bonding and pi-pi interactions with the PcBOx side groups, while the second one is likely forms coordination bonds with the same side groups. The capability of this new copolymer to solubilize a uniquely diverse set of active pharmaceutical ingredients suggests potential applications in drug delivery.

A nanoscale photothermal agent based on a metal-organic coordination polymer as a drug-loading framework for effective combination therapy

Metallic materials are widely emerging as photothermal agents owing to their superior photothermal transduction efficiency and satisfactory photostability. In this study, an iron-based coordination polymer (Fe-CNP) loaded with doxorubicin (DOX) was assessed as a dual-function agent for photothermal therapy (PTT) and tumor-targeted chemotherapy. Fe-CNPs were synthesized by a one-step coordination reaction between Fe3+, hydrocaffeic acid, and dopamine-modified hyaluronic acid. A drug-loading method was developed to entrap DOX within Fe-CNPs through the formation of coordination bonds by Fe3+ and DOX (Scheme 1). DOX release was rapidly triggered in the cellular acidic environment and further enhanced by hyperpyrexia in the part of tumor, which will kill the remaining tumor cells after PTT. Animal experiments demonstrated complete inhibition of tumor growth without recurrence in 21 days after injection of DOX@Fe-CNPs with NIR laser irradiation. These results confirmed the enhanced anti-tumor efficiency of the chemo-photothermal nanosystem. Our work may reveal a photothermal coordination polymer as a drug-loading framework and highlight the development of metal-organic materials in combined chemo-photothermal therapy. Statement of SignificancePhotothermal therapy (PTT), which could directly act on tumors, has been considered as a promising treatment method for cancer. The combination of PTT with chemotherapy is attracting tremendous attention because such advanced application can achieve personalized precise medicine. Unfortunately, most PTT materials have photobleaching property, which results in reduced photothermal efficiency. Furthermore, their clinical applications also suffer from low loading capacity of chemotherapeutic drugs or nonbiodegradability in the biological system. In this study, we hypothesized that iron-based coordination polymers (Fe-CNPs) could function dually as agents to deliver both PTT and tumor-targeted chemotherapy by coordination loading of the chemotherapeutic drug doxorubicin (DOX). Our work may open up new avenues to rationally design versatile platforms for photothermal–chemotherapy to obtain synergistically enhanced therapeutic efficacy.