Xiaomei Zhang

Tuning the morphology of self-assembled nanostructures of amphiphilic tetra(p-hydroxyphenyl)porphyrins with hydrogen bonding and metal–ligand coordination bonding

Typical amphiphilic metal-free tetrakis(4-hydroxyphenyl)porphyrin H2THPP (1) and tetrakis(4-hydroxyphenyl)porphyrinato copper complex CuTHPP (2) were fabricated into organic nanostructures by a phase-transfer method. Their self-assembly properties in aqueous solution have been comparatively studied with those of tetra(phenyl)porphyrin H2TPP (3) by electronic absorption and Fourier transform infrared (FT-IR) spectroscopy, transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), and X-ray diffraction (XRD) techniques. Experimental results reveal different molecular packing models in these aggregates, which in turn result in self-assembled nanostructures with different morphologies from nano-scale hollow spheres for 1, nanoribbons for 2, to nanobelts for 3. The present study, representing part of our continuous efforts towards understanding the relationship between synergistic interplay among noncovalent interactions such as the π–π interaction, metal–ligand coordination bonding, and hydrogen bonding in controlling and tuning the morphology of self-assembled nanostructures of tetrapyrrole derivatives, will provide information helpful for preparing self-assembled nanostructures with controlled molecular packing conformations and morphologies through molecular modification.

Morphology and chirality controlled self-assembled nanostructures of porphyrin–pentapeptide conjugate: effect of the peptide secondary conformation

An optically active porphyrin–pentapeptide conjugate 1, actually a porphyrinato zinc complex covalently linked with a glycinyl–alanyl–glycinyl–alanyl–glycine (GAGAG) peptide chain, was designed and synthesized. The self-assembly properties of this novel porphyrin–pentapeptide conjugate in THF/n-hexane and THF/water were comparatively investigated by electronic absorption, circular dichroism (CD), IR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) technique. Associated with the different secondary conformation of the pentapeptide chain covalently linked to the porphyrin ring in different solvent systems, self-assembly of conjugate 1 leads to the formation of nanofibers with right-handed helical arrangement and nanotubes with left-handed helical arrangement in a stack of porphyrin chromophores according to the CD spectroscopic result in apolar THF/n-hexane (1 : 3) and polar THF/water (1 : 3) system depending on the cooperation between intramolecular or intermolecular hydrogen bonding interaction with chiral discrimination between pentapeptide chains and porphyrin–porphyrin interactions in the direction parallel to the tetrapyrrole ring of neighboring conjugate molecules. IR spectroscopic result clearly reveals the α-helix and β-sheet secondary conformation, respectively, employed by the pentapeptide chain attached at the porphyrin core in the nanostructures formed in THF/n-hexane (1 : 3) and THF/water (1 : 3). The X-ray diffraction (XRD) result confirms that in the nanotubes, a dimeric supramolecular bilayer structure was formed through an intermolecular hydrogen bonding interaction between two conjugate molecules which, as the building block, self-assembles into the target nanostructures. These results clearly reveal the effect of a secondary conformation of pentapeptide chain in the conjugate molecule on the packing mode of porphyrin chromophore, supramolecular chirality, and morphology of the self-assembled nanostructure. The present result represents not only the first example of organic nanostructures self-assembled from a covalently linked porphyrin–pentapeptide conjugate, but more importantly the first effort towards controlling and tuning the morphology and in particular the supramolecular chirality of porphyrin nanostructures via tuning the secondary conformation of peptides in different solvent systems, which is helpful towards understanding, designing, preparing, and mimicking the structure and role of naturally occurring porphyrin–peptide conjugates. In addition, both nanofibers and nanotubes were revealed to show good semiconducting properties.

Synergistic catalysis of Au–Cu/TiO2-NB nanopaper in aerobic oxidation of benzyl alcohol

Au–Cu bimetallic nanoparticles supported on a TiO2-nanobelt (TiO2-NB) have been designed and synthesized by a one-pot photodeposition-galvanic replacement method. TEM observation revealed that small-sized metal nanoparticles (less than 2 nm) were uniformly and finely dispersed on the TiO2 nanobelt. Characterization by XRD coupled with XPS demonstrated that the Au–Cu bimetallic nanoparticles are composed of an Au-rich core/CuOx shell structure. The as-synthesized one-dimensional Au–Cu/TiO2-NB nanostructure can be easily assembled into a paper-like porous monolithic catalyst and applied in heterogeneous catalysis. The formed bimetallic nanopaper catalysts presented synergistically enhanced activity and improved stability for catalyzing the aerobic oxidation of benzyl alcohol compared to their monometallic counterparts. It is likely that the Au–CuOx heterostructure is responsible for the superior catalytic properties of the bimetallic Au–Cu/TiO2-NB catalysts, and the catalytic activity can be significantly affected by the Au/Cu ratio. The uniform and high dispersion of metal nanoparticles on TiO2 nanobelts is also believed to contribute to the stability of Au–Cu/TiO2-NB catalysts, suggesting that the one-dimensional TiO2 nanobelts are a desirable support for the preparation of nanoscale metal catalysts.

A triazine-based covalent organic framework/palladium hybrid for one-pot silicon-based cross-coupling of silanes and aryl iodides

A triazine-based covalent organic framework (COF-SDU1) was synthesized through facile solvothermal conditions and characterized by IR, solid state 13C NMR, XRD, elemental analysis and BET. By a simple solution infiltration method, Pd(II) species were successfully immobilized into COF-SDU1 due to its two-dimensional eclipsed layer-sheet structure and nitrogen-rich content. High-resolution TEM images showed the uniform loading of the Pd species into the COF-SDU1 matrix. By using this hybrid material, Pd(II)/COF-SDU1, as a sustainable and green catalyst, one-pot cross-coupling of silanes and aryl iodides was realized with high selectivity. The catalyst can be easily recovered by a simple separation process and recycled several times without obvious loss of activity and selectivity.

Nanoporous palladium catalyzed silicon-based one-pot cross-coupling reaction of aryl iodides with organosilanes

One-pot cross-coupling of aryl iodides with organosilanes is realized in excellent yield by utilizing dealloyed nanoporous palladium as a sustainable and heterogeneous catalyst. The reaction is completed under mild conditions and the catalyst can be reused several times without evident loss of its catalytic activity.

Oxidation of Organosilanes with Nanoporous Copper as a Sustainable Non‐Noble‐Metal Catalyst

Although many noble-metal catalysts have been used for the oxidation of organosilanes, there has been less success with non-noble-metal catalysts. Here, unsupported nanoporous copper (np-Cu) is used to catalyze the oxidation of organosilanes under mild conditions. It is the first time that this reaction has been achieved with a heterogeneous copper catalyst with high activity and selectivity. Both water and alcohols are used as oxidants and the corresponding organosilanols and organosilyl ethers are obtained in high yield. The possible mechanism was obtained by kinetic studies. The catalyst could be reused at least five times without evident loss of activity. As a novel green catalyst np-Cu should play a unique role in organic synthesis.

Helical self-assembly and nonlinear optical properties of optically active phthalocyanine derivatives bearing eight optically active diethyleneglycol mono-(S)-2-methylbutyl ether moieties on the β-position of the phthalocyanine ring

Two phthalocyanine derivatives with eight peripheral chiral diethyleneglycol mono-(S)-2-methylbutyl ether moieties on the β-position of the phthalocyanine ring were prepared from the tetramerization of corresponding phthalonitriles, promoted by organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The self-assembly behavior of metal free phthalocyanine 1 and its copper congener 2 have been comparatively investigated by electronic absorption and circular dichroism (CD) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The metal free phthalocyanine 1 self-assembles into the right-handed screw-like aggregates (ca. 10 μm length, 6 μm width, and 1.5 μm helical pitch), while, phthalocyaninato copper 2 self-assembled into left-handed fibrous aggregates (ca. 25 μm length, 1 μm width, and 0.7 μm helical pitch). These results indicated the effect of metal-coordination bonds on the morphology and handedness of the self-assembled nanostructures. Further, excellent nonlinear optical (NLO) properties of both compounds were also revealed by a Z-scan experiment, which expand their applications in nonlinear optics.

Novel imine-linked porphyrin covalent organic frameworks with good adsorption removing properties of RhB

A new imine-linked porphyrin covalent organic framework (COF) CuP-DMNDA-COF with a large surface area was constructed from the condensation between 5,10,15,20-tetra(p-amino-phenyl)porphyrinatocopper(II) (CuTAPP) and 2,6-dimethoxynaphthalene-1,5-dicarbaldehyde (DMNDA) under solvothermal conditions. Simple treatment of CuP-DMNDA-COF with iron(III) in acetone led to the formation of the Fe-coordinated COF material CuP-DMNDA-COF/Fe, which exhibits superior adsorption performance for Rhodamine B (RhB) with easy recyclability and sustainability, indicating its good application potential for wastewater treatment.

Self-assembly and nonlinear optical properties of (μ-oxo)bis[meso-tetrakis(p-bromophenyl-porphyrinato)iron(III)]

A sandwich-type dimer, namely (μ-oxo)bis[tetrakis(p-bromophenyl-porphyrinato)iron(III)], [(TBPP)Fe]2O, was prepared under solvothermal conditions and structurally characterized for the first time. Its self-assembly behavior has been comparatively investigated with the monomer [(TBPP)Fe]Cl by electronic absorption spectroscopy, scanning electron microscopy (SEM), and powder X-ray diffraction (PXRD) with the help of single crystal analysis. The optical properties of both compounds were studied by an open aperture Z-scan technique, revealing their good third-order nonlinear optical (NLO) properties. In particular, the μ-oxo dimer shows an about one order of magnitude larger two-photon absorption (TPA) cross-section (σ) value than the monomer due to its more extended conjugated electronic structure.

Facile one-pot synthesis of a porphyrin-based hydrophilic porous organic polymer and application as recyclable absorbent for selective separation of methylene blue

With the development of dye production and printing industry, dyes wastewater has increased dramatically. The resulting environmental pollution problem is increasing seriously. In the present work, a porphyrin-based porous organic polymer (PPOPs-OH) was synthesized by using pyrrole and 2,6-dihydroxynaphthalene-1,5-dicarbaldehyde (DHNDA) as basic building block in situ. This method was cost- and time-efficient, without the participation of metal catalysts. Further reaction of PPOPs-OH with chlorosulfonic acid, a new sulfonic acid functional material (PPOPs-SO3H) was obtained with the increasing electronegativity and hydrophilicity. PPOPs-SO3H exhibit good adsorption capacity for methylene blue (MB) from water (980.4 mg g-1) and excellent selectivity for MB in the present of rhodamine B (RhB) and methyl orange (MO). Mechanism investigation revealed that electrostatic in comparison with π-π interaction is the prominent force in the absorption process. Recycling experiments found the absorption properties of PPOPs-SO3H did not reduce significantly after several cycles. As a consequence, our findings highlight an appealing opportunities for covalent organic polymers with their potential application as high-efficiency and robust adsorbents for pollutants removal and environmental protection.