Active Amino Research Articles

Polyethyleneimine-functionalized graphene and its layer-by-layer assembly with Prussian blue

The polyethyleneimine (PEI)-functionalized graphene, which showed excellent dispersibility in water, has been simply synthesized in an alkaline solution. The graphene sheets played an important role as connector to assemble the active amino groups in PEI. This composite provided a positive environment for further functionalization. As an example, a [Prussian blue (PB)/PEI–graphene]n multilayer film has been constructed through layer-by-layer complexation method. The resulting [PB/PEI–graphene]n multilayer film demonstrated preferable electrochromic property and excellent electrocatalysis towards H2O2, which showed promising potential application in electrochemical sensing.

Enhancing antibacterial activity of surface-grafted chitosan with immobilized lysozyme on bioinspired stainless steel substrates

Bacterial infections have been widely recognized as a major cause of the failure of medical implants and devices. One promising strategy to reduce the incidence of infections is to impart the material surfaces with bactericidal function for inhibiting bacterial adhesion and biofilm formation. In this study, stainless steel (SS) surface was first activated by a biomimetic dopamine anchor to provide active amino groups, followed by covalently immobilizing chitosan (CS) with glutaraldehyde (GA) as a bifunctional linker. Hen egg white lysozyme, a natural defensive enzyme, was finally conjugated to the grafted chitosan to enhance biocidal functionality. The antibacterial assay results demonstrated substantial enhancement in bactericidal efficiency against Staphylococcus aureus (S. aureus) on the lysozyme-immobilized SS substrates under the neutral pH conditions as compared to the chitosan-grafted SS substrates. With the inherent advantages of robust anchoring ability of dopamine and specific functionality of lysozyme, the metallic substrates can be readily tailored with antibacterial property to combat biomaterial-centered infection for potential biomedical applications.

Advances in chitosan-based drug delivery vehicles

Within the past few years, chitosan-based drug delivery vehicles have become some of the most attractive to be studied. In contrast to all other polysaccharides, chitosan has demonstrated its unique characteristics for drug delivery platforms, including its active primary amino groups for chemical modification, simple and mild preparation methods for the encapsulation of biomolecules or drugs, mucoadhesion to facilitate transport across mucosal barriers and so on. In this review, an overview of the various types of chitosan-based drug delivery systems is provided, with special focus on polymeric drug conjugates and drug nanocarriers. The first part of the review is concerned with the development and applications of polymeric chitosan-drug conjugates. Then the chitosan-based nanocarrier systems as well as their preparation methods and applications are further discussed.

Synthesis, characterization, and antimicrobial activity of some new phosphorus macrocyclic compounds containing pyrazole rings

A simple synthetic method is reported for the preparation of some new phosphorus macrocycles in which the pyrazole rings are appended to a phosphorus atom. The methodology is based on the cyclocondensation reaction of bis(4-formylpyrazolyl) phosphine oxide(1a, 1b) with nitrogen nucleophiles that contain active terminal amino groups. The antimicrobial activities of the synthesized compounds were assayed.

Immobilization of β-galactosidase from Kluyveromyces lactis onto polymeric membrane surfaces: Effect of surface characteristics

The aim of this study was to investigate the effects of surface characteristics of plain and plasma modified cellulose acetate (CA) membranes on the immobilization yield of β-galactosidases from Kluyveromyces lactis (KLG) and its galacto-oligosaccharide (GOS) yield, respectively. Low pressure plasma treatments involving oxygen plasma activation, plasma polymerization (PlsP) of ethylenediamine (EDA) and PlsP of 2-mercaptoethanol were used to modify plain CA membrane surfaces. KLG enzyme was immobilized onto plain and oxygen plasma treated membrane surfaces by simple adsorption. Oxygen plasma activation increased the hydrophylicity of CA membrane surfaces and it improved the immobilization yield of the enzyme by 42%. KLG enzyme was also immobilized onto CA membrane surfaces through amino groups created by PlsP of EDA via covalent binding. Plasma action at 60W plasma power and 15min. exposure time improved the amount of membrane bounded enzyme by 3.5-fold. The enrichment of the amount of amino groups via polyethyleneimine (PEI) addition enhanced this increase from 3.5-fold to 4.5-fold. Although high enzyme loading was achived (65–83%), both of the methods dramatically decreased the enzyme activity (11–12%) and GOS yield due to probably negative effects of active amino groups. KLG enzyme was more effectively immobilized onto thiolated CA membrane surface created by PlsP of 2-mercaptoethanol with high immobilization yield (70%) and especially high enzyme activity (46%). Immobilized enzymes on the CA membranes treated by PlsP were successively reutilized for 5–8 cycles at 25°C and enzymatic derivatives retained approximately 75–80% of their initial activites at the end of the reactions.

Designed Synthesis of Functionalized Two‐Dimensional Metal–Organic Frameworks with Preferential CO2 Capture

AbstractIn metal–organic framework (MOF) chemistry, polar functionalities greatly affect the gas adsorption properties. However, synthesis of MOFs with desired functionality is very challenging because many chemical functionalities cannot be achieved under the conditions for MOF assembly. Herein, a facile synthesis of new functionalized two‐dimensional MOFs with preferential CO2 capture is presented, which uses two successive synthesis steps: 1) rational design and template‐free synthesis of the parent MOF with designated pendant amino groups and 2) postsynthetic modification of the active amino groups with acetic acid and trimesoyl chloride functionalities. The only variation in structure arises from the functional groups of these materials. Experimental results demonstrate that the three 2D layered MOFs have remarkable thermal stability and moisture resistance, which are particularly advantageous for practical CO2 capture. Although their surface areas are moderate (270–340 m2 g−1), they still have excellent CO2 adsorption capacity (up to 2.9 mmol g−1 at 1 bar and 273 K) comparable to that of previously reported MOFs with much higher surface areas. Based on first‐principles calculations, it is shown that the acidic carbonyl functionalities in addition to the amino groups are also favorable to bind CO2 molecules. The adsorption sites generated from polar functionalities are key factors leading to high CO2 uptake.

Completely green synthesis of Ag nanoparticles stabilized by soy protein isolate under UV irradiation

A completely green pathway for the preparation of Ag nanoparticles was proposed, by using soy protein isolate (SPI) as stabilizer under UV irradiation and H2O as the environmentally benign solvent throughout the preparation. Transmission electronic microscopy (TEM) and zeta potential characterization results indicated that the Ag nanoparticles were stable and well dispersed with an average diameter about 13 nm, and X-ray diffraction (XRD) analysis of SPI/Ag composite nanoparticles confirmed the formation of metallic silver. UV-Vis spectrum showed that the Ag nanoparticles dispersion solution had the maximum absorbance at about 430 nm due to surface plasmon resonance of the Ag nanoparticles. Infrared spectroscopy confirmed that the polypeptide backbone of SPI was not cleaved during the conjugation process and that some active amino groups were oxidized. The SPI/Ag composite nanoparticles have excellent antibacterial activity against two representative bacteria, staphylococcus aureus (Gram positive) and escherichia coli (Gram negative) in the presence of SPI.

Transfer of electrolyte ions and water dissociation in anion-exchange membranes under intense current conditions

Polarization characteristics of electromembrane systems (EMS) based on the Russian commercial heterogeneous membranes MA-40 and MA-41, the anion-exchange heterogeneous membrane AMH (Mega, Czech Republic), and the modified membrane MA-40M are studied by the method of rotating membrane disk in dilute sodium chloride solutions. The effective transport numbers of ions are found; the partial voltammetric characteristics (VAC) with respect to chloride and hydroxyl ions are measured; the limiting current densities are calculated as a function of the membrane disk rotation rate. In terms of the theory of the overlimiting state of EMS, based on experimental VAC and the dependences of the effective transport numbers on the current density, the following internal parameters of systems under study are calculated: the space charge and electric field strength distribution over the diffusion layer and the membrane. It is shown that water dissociation can be virtually completely eliminated by substituting chemically stable quaternary ammonium groups inert with respect to water dissociation in the surface layer of a heterogeneous anion-exchange membrane MA-40 for the active ternary and secondary functional amino groups. The maximum electric field strength values at the membrane/solution interface, which were found in the framework of the theory of over-limiting state, turned out to be close for all anion-exchange membranes studied, namely, (7–9) × 106 V/cm. This suggests that it is the nature of ionogenic groups in the surface layer rather than the field effect that plays the decisive role in the membrane ability to accelerate the water dissociation reaction. It is proved experimentally that in highly intense current modes of the electrodialysis process, the thermal hydrolysis of quaternary ammonium bases occurs in strongly basic MA-41 and AMH membranes by the Hofmann reaction to form ternary amino groups catalytically active in water dissociation reaction. Based on the concept on the catalytic mechanism of water dissociation, the fraction of ternary amino groups formed by thermal hydrolysis in the surface layer (the space charge region) of monopolar anion-exchange membranes MA-41 and AMH is assessed quantitatively as 0.7 and 6.5%, respectively.

Fluorescent carbon nanodots conjugated with folic acid for distinguishing folate-receptor-positive cancer cells from normal cells

In this work, an efficient approach for targeting and detecting cancer cells has been developed through the design of the assembly of fluorescent carbon nanodots and folic acid (C-dots–FA), which is endocytosible by the overexpressed folate receptor (FR) molecule. The fluorescent C-dots were prepared by a facile microwave pyrolysis method, but their surfaces were passivated with 4,7,10-trioxa-1,13-tridecanediamine, so that active amino groups could be engineered for the further conjugation with FA. The uptake of the designed C-dots–FA by HeLa cancer cells, as revealed by confocal laser scanning microscopy, is via receptor-mediated endocytosis, which is further confirmed by competition experiments as well as a comparative study with FR-negative MCF-7 cells. The proposed method shows excellent biocompatibility, and, most notably, its applicability to discriminating FR-positive cancer cells from normal cells has been successfully demonstrated by culturing and analyzing the first model cell mixture of NIH-3T3 and HeLa cells, which makes it of great potential for cancer diagnosis studies.

Functionalization of two-component molecular networks: recognition of Fe3+

Two-component supramolecular networks have been constructed with a symmetric triphenylene derivative with three carboxyl groups (sym-TTT) and melamine. Two kinds of hydrogen bonds with different strength are involved in the multi-component self-assembly, one is H-bond between carboxyl group of sym-TTT and melamine, the other is intermolecular H-bond between melamine molecules. These interactions drive a structural transformation from close-packed network to hexagonal network with active amino groups inside of the cavity. Scanning tunneling microscopy (STM) measurements reveal that the functionalized network of sym-TTT/melamine could recognise Fe(3+). These results could be helpful for designing functionalized molecular networks by multi-component self-assembling strategy.

Fluorescent organic–inorganic hybrid polyphosphazene microspheres for the trace detection of nitroaromatic explosives

Highly cross-linked, intrinsically fluorescent organic–inorganic hybrid polymer microspheres bearing primary amine groups on the surface have been successfully prepared through a one-pot polycondensation of hexachlorocyclotriphosphazene with benzidine. Just by the single-step introduction of plentiful π-conjugated benzidine units in the structure, the resulting microspheres easily obtain both the luminescence and abundant active amino groups, with no need for more modification. Thus further using the microspheres as fluorescence-based nitroaromatic sensor, 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, and picric acid can be effectively and sensitively detected. Because the nitroaromatic analytes can be effectively enriched on the surface of the microspheres by the charge-transfer complexing interaction between electron-deficient aromatic rings and electron-rich amino groups, which facilitates the electron transfer and energy transfer from microspheres to nitroaromatics, and finally leads to a significant and sensitive fluorescence quenching response. Moreover, the microspheres also exhibit remarkable thermal stability, photobleaching stability, and solvent resistance and dispersion ability in various solvents including both aqueous and organic media, owing to the highly cross-linked and organic–inorganic hybrid structure.

Fluorescent properties of novel dendrimer dyes based on thiazole orange

In this paper, polyamidoamine (PAMAM) dendrimers with active amino group of some generations ( G=0.5–2) were prepared from commercial aminoacetaldehyde diethyl acetal by the divergent method. After that, thiazole orange (TO) with –COOH was incorporated with dendrimers of G=1 and 2 to afford novel dendrimer-TO dyes. The fluorescent properties studies showed that the fluorescent intensity of the same concentration of dendrimer-TO ( G=2) was higher than that of the dendrimer-TO ( G=1), and both of them were much stronger than free TO with –COOH. There was a fluorescent enhancement of the dendrimer dyes compared with free dye. The dendrimer dyes were of well-defined chemical structure,with little aggregation and self-quenching as well as good fluorescence properties of good stability, high intensity and sensitivity, which could be used in labeling cancer cells and further in diagnosis and detection of early-stage tumors.

Immobilization of Glucose Oxidase on L-lysine Modifided Chitosan

A L-lysine modified semi-crosslinked chitosan (LMCCT) beads was synthesized and demonstrated to be an excellent enzyme support by studying the enzymatic properties of glucose oxidases (GODs) immobilized on it. The prepared LMCCT beads have very larger BET specific surface ( 403 m2/g) and excellent chemical stability due to the semi-crosslinking of chitosan backbones. The insertion of the flexible L-lysine spacers between chitosan backbone and the active amino groups increases the activity of immobilized GODs (I-GODs) and improves the affinity of I-GODs towards the substrate, which was testified by the smaller Michaealis constant, Km and larger reactive rate, Vm of I-GODs on LMCCT than that on crosslinked chitosan. Further studies of I-GOD activity at varied temperature and pH also indicated that I-GOD on LMCCT has an excellent stability.

Fluorescent quantification of amino groups on silica nanoparticle surfaces

Functionalization of the surfaces of silica particles is often the first step in their various applications. An improved heterogeneous Fmoc-Cl fluorescent assay using an aqueous solution was developed to detect the number of amino groups on solid-phase supports. The fluorescent Fmoc-Cl method is 50-fold more sensitive than the current UV assay using an organic solvent. This method, together with the homogeneous fluorescamine and OPA assays, is used to detect amino groups on the silica particle surface. The accuracy and effect factors of these methods were examined and the assays were optimized. The results showed that the amine groups on silica particles can produce stronger fluorescence than small amine molecules in solution, because the porous structure of the particle surface is a more hydrophobic environment. The number of active amino groups that can be conjugated with biomolecules is much less than the total number of amino groups on the silica particle. Compared with physical methods, chemical assays involving direct reaction with amino groups would furnish the closest result to the number of active amino groups on the particle surface.

Synthesis of sorption-active polyfunctional derivatives of polycaproamide and polyglycidyl methacrylate graft copolymers

The kinetic and thermodynamic parameters of polymer-analog conversion of the graft copolymer of polycaproamide and polyglycidyl methacrylate with sulfamic acid (initial rate, duration, and effective activation energy) were determined. It was shown that the values of the initial rates correlate well with the concentration of the sulfamic acid reaction solution. The formation of a new derivative of the PCA—PGMA graft copolymer containing functionally active amino and sulfo acid groups was confirmed by the data from chemical and analytical analysis and IR spectroscopy. A method was developed for obtaining a sorption-active fibrous polyampholyte containing functionally active amino and sulfo acid groups with SECHCl = SECNaOH = 0.895 mmole/g.

Electrochemical Evaluation of Protein-Ligand Binding Using an Electrode Covered with Chitin-Chitosan Film

An electrode covered with chitin-chitosan composite film was constructed to monitor binding between protein and ligand. Chitin, which is one of the extracellular matrixes, was dissolved in an organic solvent of N,N-dimethylacetoamide and 1-methyl-2-pyrrolidone. Because chitosan powder remained undissolved, it was considered to be a reaction field of biomolecule interactions. To examine whether the film was powerful, avidin and biotin were selected as a model of a protein and its ligand. Biotin moieties were introduced to active amino groups of the chitosan with a biotinylation reagent. To evaluate the binding on the film, biotin labeled with an electroactive daunomycin was used as a probe. As a result, an oxidation peak of the labeled biotin decreased. This was because the labeled biotin was held in the binding sites of avidin for biotin not used to be immobilized on a biotin-modified chitosan particle. Consequently, the binding could be monitored on the chitin-chitosan film with high biocompatibility. The procedure becomes a new method to evaluate binding between protein and ligand.

The hydroxyl radical scavenging activity of chitosan, hyaluronan, starch and their O-carboxymethylated derivatives

In order to study the effect of active hydroxyl and amino groups on scavenging activity against hydroxyl radicals of polysaccharides, three kinds of carboxymethylated polysaccharides (carboxymethyl chitosan (O-CM-chitosan), carboxymethyl hyaluronan (CMHA), and carboxymethyl starch (CMS)) were prepared and their antioxidant activities against hydroxyl radicals were assessed, respectively. Results showed that O-CM-chitosan had lower scavenging ability on hydroxyl radicals than chitosan. CMHA and CMS had the same tendency. For the three kinds of polysaccharides, scavenging ability on hydroxyl radicals was found to be in the order of chitosan > HA > starch. The scavenging ability of carboxymethylated polysaccharides had the same order as related to its corresponding polysaccharides at higher concentrations (≧0.8 mg/ml). There were not only hydroxyl groups but also amino or acetamino (CH 3CONH–) groups in the molecules of chitosan and HA, but only hydroxyl group for starch. It was suggested that the sequence influence the scavenging activity against hydroxyl radicals might be amino group > acetamide group > hydroxyl group.

Multifunctional nanocomposites of superparamagnetic (Fe3O4) and NIR-responsive rare earth-doped up-conversion fluorescent (NaYF4 : Yb,Er) nanoparticles and their applications in biolabeling and fluorescent imaging of cancer cells

A new kind of magnetic/luminescent multifunctional nanoparticles was synthesized by covalently linking multiple carboxyl-functionalized superparamagnetic Fe(3)O(4) nanoparticles and individual amino-functionalized silica-coated fluorescent NaYF(4) : Yb,Er up-conversion nanoparticles (UCNPs). The resultant nanocomposites bear active carboxylic and amino groups on the surface that were proved to be chemically active and useful for further facile bioconjugation with biomolecules. The UCNPs in the nanocomposite particles can emit visible light in response to the irradiation by near infrared (NIR) light, enabling the application of the nanocomposites in bioimaging. X-Ray diffraction, infrared spectroscopy, transmission electron microscopy, luminescence spectroscopy, and magnetometry were applied to characterize the multifunctional nanocomposites. The nanocomposites exhibited good superparamagnetic and excellent green up-conversion photoluminescent properties that can be exploited in magnetic separation and guiding as well as bioimaging. Due to the presence of active functional groups on the nanocomposite surface, the Fe(3)O(4)/NaYF(4) : Yb,Er magnetic/luminescent nanocomposites were successfully conjugated with a protein called transferrin, which specifically recognizes the transferrin receptors overexpressed on HeLa cells, and can be employed for biolabeling and fluorescent imaging of HeLa cells. Because NIR light can penetrate biological samples with good depth without damaging them and can avoid autofluorescence from them, the presence of both NIR-responsive UCNPs and superparamagnetic nanoparticles in the nanocomposite particles will enable the practical application of the nanocomposites in bioimaging and separation.

Silver‐Mediated Direct Amination of Benzoxazoles: Tuning the Amino Group Source from Formamides to Parent Amines

Going to the source: Formamides or parent amines were used as an amino group source for the silver-mediated amination of benzoxazoles. Although reactions with formamides proceeded at high temperatures, the direct amination with amines took place under much milder conditions (see scheme). Optically active amino groups could also be installed without racemization.

Water-Soluble Graphene Covalently Functionalized by Biocompatible Poly-l-lysine

Graphene sheets functionalized covalently with biocompatible poly-l-lysine (PLL) were first synthesized in an alkaline solution. PLL-functionalized graphene is water-soluble and biocompatible, which makes it a novel material promising for biological applications. Graphene sheets played an important role as connectors to assemble these active amino groups of poly-l-lysine, which provided a very biocompatible environment for further functionalization, such as attaching bioactive molecules. As an example, an amplified biosensor toward H(2)O(2) based on linking peroxidase onto PLL-functionalized graphene was investigated.