Schiff-base Coupling Research Articles

Kinetic study of electron transfer process in methyl orange decolorization by shewanella in MFCs with covalent organic frameworks modified anode

As a new electrode material for electrochemical systems, covalent organic framework (COF) materials have been gradually applied to bioelectrochemical systems. In our previous study, the COFBTA-DPPD-rGO composite was synthesized via Schiff-base coupling between benzene-1,3,5-tricarbaldehyde (BTA) and 3,8-diamino-6-phenylphenanthridine (DPPD) on reduced graphene oxide (rGO) at room temperature. Here, COFBTA-DPPD-rGO modified MFC anode was used to assist microorganisms to decolorize methyl orange (MO), and the properties of MFCs were studied. The results showed that compared to the unmodified electrode MFC (28 mA m−2, 4.20 mW m−2) the current density and maximum power density of the anode MFC modified by COFBTA-DPPD-rGO (134.5 mA m−2, 21.78 mW m−2) were increased by 380.3% and 423.6%, respectively. The transferred electron number n and charge transfer coefficient α of the modified COFBTA-DPPD-rGO anode (4 and 0.43) compared to the unmodified electrode (2.4 and 0.38) were increased by 67% and 13%, respectively. The decolorization ratio of MO could reach 90.3% at 10 h. Compared with the unmodified electrode MFC (53.0%), the decolorization ratio and kinetic constant of decolorization process were enhanced by 26% and 372%, respectively. Therefore, COFBTA-DPPD-rGO could be a new choice for applying to the MFCs.

Solvothermal synthesis of triphenylamine‐based covalent organic framework nanofibers with excellent cycle stability for supercapacitor electrodes

AbstractCovalent organic framework (COF) is a new class of porous materials used in energy storage devices. By solvothermal method, the triphenylamine‐based covalent organic framework was synthesized using Schiff base coupling reaction between tris(4‐aminophenyl) amine (TAPA) and tris(4‐formylphenyl) amine. The regular pore structure of TPA‐COFs not only exposes more active sites of triphenylamine structure to electrolyte solution during the charge–discharge process, but also accelerates the transport of ions in the active layer. At the same time, the π‐electron conjugated system and the interlayer π‐π stacking effect effectively promote the conduct of electrons in the two‐dimensional and three‐dimensional directions of COFs materials, which improves the electrochemical performance of the materials. TPA‐COFs show a higher specific capacitance of 263.1 F/g at 0.1 A/g. At the same time, TPA‐COFs materials exhibit a high specific surface area of 398.59 m2/g. After 5000 cycles of charge–discharge, the capacitance retention rate of TPA‐COFs is 111%, showing excellent cycle stability.

Erratum to: Ferrocenyl building block constructing porous organic polymer for gas capture and methyl violet adsorption

Ferrocene-based porous organic polymer (FcPOP) was constructed with ferrocene and porphyrin derivatives as building blocks via Schiff-base coupling. FcPOP was well characterized, and exhibited good thermal stability, high porosity, microporous structure, and homogeneous pore size distribution. Ferrocene blocks with highly electron-rich characteristics endowed FcPOP with excellent adsorption capacity of CO2 and methyl violet. The kinetic study indicated adsorption of methyl violet onto FcPOP mainly complied with pesudo-second order model. The maximum adsorption capacity of FcPOP derived from Langmuir isotherm model reached up to 516 mg/g. More importantly, FcPOP could be easily regenerated and repeatedly employed for removal of methyl violet with high efficiency. Overall, FcPOP in the present study highlighted prospective applications in the field of gas capture and dyeing wastewater treatment.

Characterization of Serine Protease Inhibitor from Solanum tuberosum Conjugated to Soluble Dextran and Particle Carriers.

A serine protease inhibitor was extracted from potato tubers. The inhibitor was conjugated to soluble, prefractionated dextran and titanium dioxide and zinc oxide nanoparticles. Conjugation to dextran was achieved by periodate oxidation of the dextran, followed by Schiff base coupling to inhibitor amino groups, and finally reduction, whereas the conjugation to the oxide particles was carried out by aminosilanization and carbonyldiimidazole activation. The inhibitory effect of the conjugated inhibitor was compared to that of free inhibitor in solution and with gelatin gel as a direct substrate. A certain degree of inhibitory activity was retained for both the dextran-conjugated and particle-conjugated inhibitors. In particular, the apparent Ki value of the dextran-conjugated inhibitor was found to be in the same range as that for free inhibitor. The dextran conjugate retained a higher activity than the free inhibitor after 1 month of storage at room temperature.

Surface Confined Synthesis of Hydroxy Functionalized Two-Dimensional Polymer: The Effect of the Position of Hydroxy Groups.

We report on the on-surface synthesis of a series of two-dimensional polymers (2DPs) and macrocycles containing hydroxyl groups on a highly oriented pyrolytic graphite surface. The formed 2DPs and macrocycles were visualized through scanning tunneling microscopy. By varying the solvent and reaction temperature, structural evolution from oligomers to well-ordered 2DPs or discrete macrocycles was directly followed. In addition, we discovered that the reaction outcome can be steered from extended 2DPs to discrete macrocycles or catenular structures by exchanging the position of the hydroxyl and aldehyde group. These results indicate that the relative positions of hydroxyl and aldehyde groups on the biphenyl ring play a determining role in the control and selection of the final products of the surface-confined Schiff base coupling reaction.

Covalent organic frameworks on reduced graphene oxide with enhanced electrochemical performance

Abstract Covalent organic frameworks (COFs) are an emerging class of porous materials for energy storage devices. By using an in-situ synthesis method, the new COFBTA-DPPD-rGO composite has been synthesized via Schiff-base coupling between benzene-1,3,5-tricarbaldehyde (BTA) and 3,8-diamino-6-phenylphenanthridine (DPPD) on reduced graphene oxide (rGO) at room temperature under ambient conditions. Coupled with the improved electrical conductivity, resulting from rGO, COFBTA-DPPD-rGO showed a higher specific capacitance of 239.1 F g−1 at 0.5 A g−1, suggesting an improved electrochemical performance as electrode material for supercapacitors. Extended π-conjugation and ion conduction inside the pores throughout COFBTA-DPPD-rGO, the redox processes arising from pyridine units and electrical conductivity of rGO could be responsible for this high electrochemical performance. The electrochemical properties of COFBTA-DPPD-rGO have been investigated by various electrochemical techniques such as cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopic (EIS).

Facile Synthesis of Nitrogen-Rich Porous Organic Polymers for Latent Heat Energy Storage

The development of phase change material (PCM) composites with high latent heat of fusion and good shape-stability have received considerable attention for thermal energy engineering and management. In this work nitrogen-rich porous organic polymers (N-POPs) with high surface areas synthesized via Schiff-base coupling between 1,3,5-triformylbenzene and pararosaniline base are presented, which can take up 85 wt % of 1-octadecanol (ODA) as a PCM. The resulting ODA@N-POPs exhibit a high latent heat of fusion up to 182.7 J/g, satisfying shape-stability, and good reversibility upon 100 heating cycles, which are promising for solar thermal energy engineering and management.

Synthesis, characterization and supramolecular building motifs of substituted salphen- and thiasalphen–metal complexes

Two new series of substituted salphen-metal complexes and thiasalphen–metal complexes have been synthesized. The fluorine substituted salphen-metal complexes (5, 6 and 7) were prepared by the coordination of ligand 4 (obtained by the reaction of 4,5-difluorosalicylaldehyde with o-phenylenediamine) with Ni(II), Cu(II) and Zn(II) ions, respectively. The thiasalphen–metal complexes (8, 9 and 10) were prepared strategically following the unique route of the in situ reduction of bis(o-formylphenyl)disulfide to mercaptobenzaldehyde then complexation with Ni(II), Cu(II) and Zn(II) ions, followed by Schiff base coupling with o-phenylenediamine, in a single pot. The products were characterized by elemental analysis, ESI-MS, FT-IR and 1H/13C NMR spectroscopy. The structures of 4, 5, 6, 9 and 10 were established by single crystal X-ray analysis. The various non-bonding interactions resulted in fascinating supramolecular building motifs. The photophysical and electrochemical properties (band gaps, HOMO−LUMO energies) of all the six complexes were studied by UV–Vis spectroscopy and cyclic voltammetry. The optical band gaps were found to be in the range 2.31–2.79eV.

Surface−Enhanced Polymerization via Schiff-Base Coupling at the Solid–Water Interface under pH Control

On-surface polymerization realized at the solid–liquid interface represents a promising route to obtain stable and conductive organic layers with tunable properties. We present here spectroscopic evidence of π-conjugated polymer formation at the interface between an iodine-modified Au(111) and an aqueous solution. Schiff-base coupling has been used to drive the reaction by changing the pH. Scanning tunneling microscopy (STM) investigations show that the substrate acts as a template driving the formation of 1D ordered nanostructures. All the chemical states of the molecules on the surface have been identified and their evolution as a function of the pH has been monitored by synchrotron radiation X-ray photoelectron spectroscopy (XPS), demonstrating that two polymeric phases, undistinguishable by STM, exist on the surface: intermediate state and π-conjugated final product. The I/Au(111) substrate enhances the formation of π-conjugated polymers, as established comparing their production on the surface and in...

Side-functionalized two-dimensional polymers synthesized via on-surface Schiff-base coupling

An imine-based 2D polymer side-functionalized with o-hydroxyl group was designed in regard to its potential ability to serve as a chelating agent and synthesized on a highly oriented pyrolytic graphite surface with a relatively low annealing temperature. When annealed to a higher temperature the o-hydroxyl group reacts further with the imine group, leading to the formation of oxazoline, which causes significant distortion to the network. The formation of oxazoline was further confirmed by ATR-FTIR.

Fluorescent Amphiphilic PEG‐Peptide‐PEG Triblock Conjugate Micelles for Cell Imaging

A fluorescent amphiphilic poly(ethylene glycol)-peptide-fluorophore-peptide-poly(ethylene glycol) (PEG-Pep-F-Pep-PEG) triblock conjugate with a hydrophobic fluorophore moiety at the centre of the chain is synthesized by "grafting to" technique based on Schiff-base coupling chemistry. The conjugate is characterized by nuclear magnetic resonance (NMR), circular dichroism (CD), and fluorescence spectroscopy techniques. The aqueous solution of the triblock conjugate emits blue light and exhibits a fluorescence emission band at 430 nm. The amphiphilic conjugate molecules undergo self-assembly into micelles (D ≈ 15-20 nm) in aqueous solution as confirmed from transmission electron microscopy (TEM) and dynamic light scattering (DLS). The critical aggregation concentration is determined by pyrene fluorescence assay and is found to be 0.051 mg mL(-1) . The highly stable and low toxic fluorescent PEG-Pep-F-Pep-PEG conjugate micelles are used for imaging of HeLa cells.

In Situ STM Investigation of Aromatic Poly(azomethine) Arrays Constructed by “On-Site” Equilibrium Polymerization

Two-dimensional (2D) arrays of π-conjugated aromatic polymers produced by surface-selective Schiff base coupling reactions between an aromatic diamine and an aromatic dialdehyde were investigated in detail using in situ scanning tunneling microscopy. Surface-selective coupling was achieved for almost all diamine/dialdehyde combinations attempted, although several combinations did not proceed even in homogeneous aqueous alkaline solution. Most of the combinations of an aromatic diamine and a dialdehyde, except the combinations of 4,4'-azodianiline with mono/bithiophenedicarboxaldehyde, formed highly ordered π-conjugated polymer arrays on an iodine-modified Au(111) surface in aqueous solution at a suitable pH. The simplest polymer of the various combinations tested, obtained from the combination of 1,4-diaminobenzene with terephthaldicarboxaldehyde, gave a 2D array consisting of linearly connected benzene units. Poly(azomethine) adlayers caused a positive shift in the electrochemical potential of the butterfly shaped oxidative adsorption and reductive desorption of iodine. The acceleration of the reductive desorption of iodine suggests the existence of a weak interaction between the polymer layer and iodine. Not only the first polymer adlayers but also partially adsorbed secondary adlayers with "on-top" epitaxial behavior were frequently observed for all polymer systems. The alignment of the polymer chains in the adlayers possessed a certain regularity in terms of a regular interval between polymer chains because of repulsive interpolymer interactions.

Towards a fully optimised organic LED device: Analysis of surface synthesis using coupling reactions by ToF-SIMS

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and polarisation–modulation reflection–absorption infrared spectroscopy (PM-RAIRS) have been used to monitor the surface synthesis of self-assembled aromatic π-conjugated molecular wires on gold substrates as a step towards a novel structure for organic electroluminescent devices (OLEDs). The wires have been synthesised using a series of Schiff's base coupling reactions in solution on a self-assembled monolayer of an aromatic thiolate anchor. ToF-SIMS and PM-RAIRS measurements have demonstrated that: (i) the anchor molecules self-assemble at the gold surface, (ii) the anchor molecules selectively react through imino coupling reactions with additional wire units with high efficiency and (iii) the wire-like structure is predominantly orientated normal to the surface.

Bioreactive Surfaces Prepared via the Self-Assembly of Dendron Thiols and Subsequent Dendrimer Bridging Reactions

Here, we report a novel route to prepare bioreactive surfaces on gold by the self-assembly of generation-three hydroxyl-terminated dendron thiols (G3-OH) and subsequent bridging reactions using generation-two amine-terminated dendrimers (G2-NH(2)). It has been shown that G3-OH dendron thiols form a stable and uniform self-assembled monolayer on gold, which can be activated by the homobifunctional cross-linker N,N-disuccinimidyl carbonate (DSC). Subsequent derivatization of the activated monolayer via dendrimer bridging reactions with G2-NH(2) enhances the stability, reactivity, and versatility of the prepared surface. Each step of the surface formation reaction has been monitored, and the resulting surface has been characterized by wetting, electrochemistry, scanning tunneling microscopy (STM), and infrared (IR) spectroscopy measurements. The reactivity of this surface was demonstrated by a Schiff base coupling reaction with 4-cyanobenzaldehyde, by immobilizing biotin molecules onto the peripheral amine groups using one of the conjugation methods, and by further binding avidin onto the biotinylated surface. We believe that the prepared bioreactive surface with a high density of amine groups will be useful for the immobilization of biological macromolecules for various biosensor applications, such as the fabrication of DNA microarrays and protein chips.

Synthesis and characteristics of the human serum albumin-triazine chiral stationary phase.

Human serum albumin (HSA) was successfully bonded to silica with s-triazine as activator. The coupling reaction by this method was rapid and effective. The triazine-activated silica is relatively stable and can be installed for at least 1 month without obvious loss of reactivity when stored below 30 degrees C, pH below 7. It was observed that the amount of bound HSA reached 120 mg/g silica calculated from the UV absorbance difference of the HSA solution. d, l-tryptophan was selected as the probe solute to characterize the properties of HSA bonded s-triazine chiral stationary phase, and separation factor of 9.4 was obtained for d,l-tryptophan. Furthermore, the amount of effective HSA on silica was measured by high-performance frontal analysis, and only 16.8 mg/g silica was responsible for the resolution of d,l-tryptophan. These results indicate that the amount of both the bound and effective HSA on silica with triazine as activator was much higher than those by the Schiff base coupling method. Different kinds of enantiomers were resolved successfully on the aminopropylsilica-bonded HSA s-triazine chiral stationary phase.

Phosphorus hydrazides as building blocks for potential photoaffinity labels. Synthesis and co-ordination chemistry of perfluoroaryl azide conjugates of phenylphosphonothioic dihydrazide

The phosphorus hydrazide PhP(S)(NMeNH2)21 reacted with the azido functionalized aldehyde 4-N3C6F4CHO to give a mixture of Schiff-base adducts with one or two perfluoroaryl azido substituents on 1. However, the reaction with R′CHO (R = 4-O2NC6H4, 3-O2NC6H4 or 2,4-Me2C6H3) resulted in a considerable selectivity of incorporating one aromatic substituent in the terminal hydrazide unit of 1via Schiff-base coupling to produce PhP(S)(NMeNH2)(NMeNCHR′)(R′= 4-O2NC6H43, 3-O2NC6H44 or 2,4-Me2C6H35). These mono-Schiff-base adducts 3–5 undergo further Schiff-base coupling with azidotetrafluorobenzaldehyde to produce the azido-functionalized phosphorus hydrazides PhP(S)-(NMeNCHC6F4N3)(NMeNCHR′)(R′= 4-O2NC6H47, 3-O2NC6H48 or 2,4-Me2C6H39). The ligating properties of the representative phosphorus hydrazides 2 and 9 with palladium (II) were investigated. The crystal structure of the complex [PdCl2{PhP(S)(NMeNH2)(NMeNCHC6F4N3-4)}] reveals that the palladium(II) is bound in a chelating cis arrangement to the phosphorus chalcogenide and the hydrazine nitrogen via a five-membered metallacyclic framework: monoclinic, space group P21/n, a= 7.826(10), b= 18.051 (20), c= 18.330(3)A, β= 98.196(7)°, Z= 4, R= 0.038 and R′= 0.053.

Internalization and delivery to lysosomes of hydrazide horseradish peroxidase, a covalent membrane probe.

Hydrazide horseradish peroxidase, (hydHRP), a hydrazide derivative of the common cytochemical tracer HRP, was covalently coupled to the surface of periodate-treated Chinese hamster ovary (CHO) cells and used to study the distribution and internalization of plasma membrane glycoconjugates. The Schiff-base coupling of hydHRP to the cell surface at 4 degrees C had little effect on cell viability. After coupling, cells were washed at 4 degrees C and the subcellular distribution of hydHRP was determined immediately or after incubation at 37 degrees C. Within 1 hr, hydHRP was observed to cap over pseudopodal-like extensions and then accumulate over a 2.5 h period in a punctate to perinuclear staining pattern over the cell body. By electron microscopy, the pseudopodal-like regions were found to be areas of extensive cell surface invaginations, rich in microfilaments. HydHRP internalized over a 2.5 to 18 hr period was observed in smooth vesicles resembling pinosomes/endosomes, multivesicular bodies (lysosomes), and small perinuclear vesicles. Little, if any, hydHRP activity was detected in association with elements of Golgi apparatus. By cell fractionation in 10% Percoll gradients, hydHRP was found to have accumulated in prelysosomal endocytic vesicles and lysosomes. For cells that were first surface labeled with 125I at 4 degrees C and then conjugated with hydHRP, little, if any, cotransport of the 125I label with hydHRP was observed. Over the entire capping and internalization period, most hydHRP activity remained membrane associated. Overall, these results indicate that the dominant intracellular transport route for a covalent membrane probe, hydHRP glycoconjugate, is similar if not identical to that previously reported for the solute probe native HRP (16) in CHO cells. HydHRP internalization provides further evidence for the independent sorting of proteins in endocytic transport.

Schiff base coupling of cyclic and high-polymeric phosphazenes to aldehydes and amines: chemotherapeutic models

Schiff base coupling of cyclic and high-polymeric phosphazenes to aldehydes and amines: chemotherapeutic models