Molar Ratio Of Amino Groups Research Articles

Preparation and characterization of chitosan microparticles for immunoaffinity extraction and determination of enrofloxacin

The use of chitosan microparticles as chromatographic support has received much attention. In this study, the effects of process parameters, namely, chitosan molecular weight, chitosan concentration, molar ratio of amino group to aldehyde group, volume ratio of water to oil phase and stirring speed on the size and size distribution of chitosan microparticles and their application for immunoaffinity extraction were extensively investigated. Size distribution analysis indicated that the average diameter of the microparticles was 124μm with Span value of 1.1. The obtained microparticles exhibited low non-specific adsorption and kept stable in the pH range 4.0–10.0. Immunoaffinity chromatography (IAC) column was prepared by coupling antibody against enrofloxacin (ENR) with chitosan microparticles. Further characterization indicated that the binding capacity of the column was 4392ng ENR/mL gel and the variation of ENR extraction efficiency among columns was less than 5.2%. When challenged with ENR-fortified bovine milk samples, recoveries of ENR by immunoaffinity extraction were found to be in the range of 85.9% to 101.9%, demonstrated the feasibility of the prepared IAC columns for sample clean-up in ENR residue determination.

Synthesis of aqueous and hydroxy-terminated polyurethanes: Impacts of formulation parameters by orthogonal matrix design

Abstract Aqueous and hydroxy-terminated polyurethanes (AHPUs) were synthesized using poly(caprolactone) glycol, isophorone diisocyanate, dimethylolpropionic acid (DMPA) as main raw materials, trimethylolpropane (TMP) as crosslinking agent, ethylenediamine (EDA) as chain extender, and tris(hydroxylmethyl) aminomethane as chain terminator. The optimum synthesis condition of AHPUs was elected by L 16 (4 5 ) orthogonal experiments with the content of DMPA ( A ) and TMP ( B ), molar ratio of isocyanate to hydroxyl in the prepolymerization step ( C ) and the molar ratio of amino groups in EDA to residual isocyanate groups of prepolymerization ( D ) as factors and the transmittance, relative viscosity and particle size of dispersions as evaluation index, and the tack-free drying time, gloss, hardness, adhesion and water resistance of coatings were discussed, too. The results demonstrate that the synthetic AHPUs have good physical properties, such as relative viscosity, transmittance and particle size, what's more, the two-component films have good air-drying ability, gloss, hardness, adhesion and water resistance when synthesis parameters are A = 7.0 wt%, B = 5.0 wt%, C = 1.6 and D = 0.2.

Study on Preparation of Chitosan Microspheres Loaded with Levofloxacin

Chitosan (CS) microspheres loaded with levofloxacin (LOF) were prepared by emulsion crosslinking technique and the experimental parameters were optimized by orthogonal tests. The influences of various factors on the combination properties of chitosan microspheres were discussed. The optimal preparation condition was 98000 chitosan molecular weight, 30mg/ml chitosan concentration, 5:1 volume ratio of oil to water, 1:1 molar ratio of amino group of chitosan to aldehyde group of glutaraldehyde (GA), 1500 rpm stirring rate, 2:1 mass ratio of chitosan to levofloxacin and 1 h crosslinking time. The CS microspheres prepared under optimal parameters had spherical morphology with 1.59 μm of average geometric diameter and 0.99 of span, its loading capacity (LC) and association efficiency (AE) values were 21.71% and 80.49% respectively. In vitro release profile showed the levofloxacin released fast initially, and then slowly from the microspheres with T90 occurring at 188.5h and its delivery behavior conformed to First-Order release kinetics model.

Interactions of ε-Polylysine with Carboxymethyl Sweet Potato Starch with an Emphasis on Amino/Carboxyl Molar Ratio

The interaction between ε-polylysine (ε-PL) and anionic polysaccharides has gained considerable attention recently because of its scientific impact on the stability and appearance of liquid food systems. The purpose of this study was to characterize the interactions between ε-PL and carboxymethyl sweet potato starch (CSS) using isothermal titration calorimetry (ITC), electrical charge, and turbidity measurements. The results showed that the interaction between ε-PL and CSS was electrostatic and mainly dependent on the molar ratio of amino groups in ε-PL to carboxyl groups in CSS. Additionally, the interaction between ε-PL and CSS was also associated with pH, degree of substitution (DS) of CSS, and ionic strength of the system. For the interaction of ε-PL with high DS (>0.235) CSS, three states of the ε-PL/CSS mixture were observed as transparent, turbid, and precipitated with a successive increase in amino/carboxyl molar ratio. Distinguishingly, a transparent mixture could be obtained for CSS with low DS (0.114) at a sufficiently high amino/carboxyl molar ratio. The present study provided basic guidance in designing liquid food systems containing both ε-PL and CSS.

Synthesis, characterization and properties of TAP-6FDA hyperbranched polyimides with different branching degrees

A series of hyperbranched polyimides were successfully synthesized by condensation polymerization of A2-type dianhydride monomer 2,2-bis(3,4-dicarboxylphenyl) hexafluoropropane dianhydride (6FDA) and B′B2-type triamine monomer 2,4,6-triaminopyrimidine (TAP). Polymers with different branching degrees (DB) and terminated groups were obtained by changing the monomer addition order and the monomer molar ratio. Fourier transform infrared spectroscopy and 1H NMR were used to verify the structure of the prepared polyimides, which indicated that the amino group still existed in all the products. The DB of the polymers indicated by 1H NMR increased from 30% to 79% with the molar ratio of TAP:6FDA decreasing from 1:1 to 1:2. The absolute molecular weights were measured by size-exclusion chromatography with multi-angle laser light-scattering detection, which suggested that the highest molecular weight would be obtained when the molar ratio of amino groups:anhydride groups of the monomers was 3:3.2. With the DB increasing, the d-spacing values indicated by wide angle X-ray diffraction increased from 5.15 Å to 5.68 Å and the UV − visible spectra of the polymers exhibited decreasing cut-off wavelengths. The 5% weight loss temperature in nitrogen increased with decreasing content of TAP monomer, and the glass transition temperatures of the obtained polyimides decreased from 282 °C to 258 °C with increasing DB. © 2013 Society of Chemical Industry

Palladium Supported on Functionalized Mesoporous Silica as an Efficient Catalyst for Suzuki–Miyaura Coupling Reaction

Mesoporous SBA-15 was modified with organic functional groups by co-condensation method. The functionalized mesoporous silica can be loaded with palladium and the resulting material used as a catalyst for the Suzuki–Miyaura coupling reactions. Highly dispersed and uniform palladium nanoparticles could be detected using transmission electron microscopy. The Pd-SBA-15 nanocomposite with controlled molar ratio of amino groups to palladium exhibits an excellent catalytic activity and low Pd leaching for the Suzuki–Miyaura coupling reaction. The catalyst can also be reused at least six recycles in air with only a minor loss of activity. Mesoporous SBA-15 was modified with organic functional groups by co-condensation method. The functionalized mesoporous silica can be loaded with palladium and the resulting material used as a catalyst for the Suzuki–Miyaura coupling reactions. Highly dispersed and uniform palladium nanoparticles could be detected using transmission electron microscopy. The Pd-SBA-15 nanocomposite with controlled molar ratio of amino groups to palladium exhibits an excellent catalytic activity and low Pd leaching for the Suzuki–Miyaura coupling reaction. The catalyst can also be reused at least six recycles in air with only a minor loss of activity.

Preparation of Iminoacetic Acid-type Composite Chelating Material IAA-PEI/SiO2 and Preliminary Studies on Chelating Adsorption Property towards Heavy Metal Ions

Polyamine polyethyleneimine (PEI) was first grafted on the surfaces of micro-sized silica gel particles in the manner of the coupling graft (the manner of “grafting to”), forming the grafting particles PEI/SiO2. Subsequently, via a polymer reaction, the nucleophilic substitution reaction between the primary and secondary amino groups of the grafted PEI macromolecule and chloroactic acid (CAA), iminoacetic acid groups were bonded onto the grafted PEI chains, and an iminoacetic acid (IAA)-type composite chelating material, IAA-PEI/SiO2, was formed. In this work, the preparation process of IAA-PEI/SiO2 particles was mainly researched, and the effects of the main factors on the polymer reaction, i.e., the nucleophilic substitution reaction, were examined emphatically. The adsorption behavior of IAA-PEI/SiO2 particles towards several kinds of heavy metal ions was preliminarily evaluated. The experiments results show that it is feasible to introduce IAA groups onto PEI/SiO2 particles via the substitution reaction between CAA and the amino groups of the grafted PEI. The reaction rate is affected greatly by the feed ratio of the amino group of PEI to CAA, so the substitution reaction between CAA and the amino groups of the grafted PEI is a bimolecular nucleophilic substitution reaction (SN2). The reaction temperature and the used amount of acid-acceptor NaHCO3 affect the bonding rate of IAA groups greatly. The fitting temperature was 60°C, and 1:1 of the molar ratio of NaHCO3 to CAA was an appropriate amount of acid-acceptor NaHCO3. Under the above optimal reaction conditions and with 3:1 molar ratio of amino group of PEI to CAA, 72% of the IAA group bonding rate (it is based on the hydrogen atoms in the primary and secondary amino groups of the grafted PEI) in 8 h can be reached. The composite chelating material IAA-PEI/SiO2 possesses a strong chelating adsorption ability for heavy metal ions because of the increase of the ligands and formation of stable five-membered chelate rings.

Synthesis and characterization of self‐catalyzed imide‐containing pthalonitrile resins

AbstractSome new amino‐ and imide‐containing phthalonitrile compounds with 1:1 molar ratio of amino group to pthalonitrile unit were successfully synthesized. The molecular structures were characterized by spectroscopic techniques. They were thermally polymerized under nitrogen/air, even in the absence of curing additives. The thermal properties of the cured products were characterized by thermogravimetric analysis and differential scanning calorimetry. The 5% weight loss temperatures ranged from 525 to 528 °C and 513 to 520 °C under nitrogen and air, respectively. Char yields (900 °C) were in the range of 62–70%. Rheometric measurements showed that the rate of the cure reaction differs for all the three monomers. The glass transition temperature advances with increasing extent of cure and disappears on postcure at 375 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

A new multifunctional polymer: Synthesis and characterization of mPEG-b-PAA-grafted chitosan copolymer

A new multifunctional mPEG-b-PAA-grafted chitosan copolymer possessing amino and carboxyl groups, mPEG-b-PAA-g-CHI (compound 6), was designed for a potential application in gene/drug delivery and synthesized by the methods of reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylic acid (AA) and grafting reaction of a biodegradable chitosan (CHI) derivative. Completion of the reactions and characterization of the resulting compounds were demonstrated by 1H NMR, FTIR and gel permeation chtomatography (GPC) studies. The results show that the molar ratio of amino groups to carboxyl groups in the copolymer (compound 6) is 0.41:0.59.

Palladium supported on functionalized mesoporous silica as an efficient catalyst for Heck reaction

Pd nanoparticles supported in functionalized mesoporous silica were prepared. Mesoporous silica support was modified with [3-(2-aminoethyl aminopropyl)] trimethoxysilane. Palladium ions were grafted onto the functionalized mesoporous silica and reduced with hydrazine hydrate to obtain the Pd nanoparticles supported on functionalized mesoporous silica. The Pd loading in the nanocomposite of Pd supported on the functionalized mesoporous silica is 4.30 wt%. CO chemisorption analysis on the nanocomposite shows a Pd dispersion as high as 35% and a Pd surface area of 156 m 2/g. The surface area, pore size, and pore volume decrease slightly with the incorporation of the Pd nanoparticles into the functionalized mesoporous silica. Pd supported on the functionalized mesoporous silica with controlled molar ratio of amino groups to palladium exhibits an excellent catalytic activity and low Pd leaching for the Heck carbon–carbon coupling reaction. The catalyst can be reused for at least six recycles in air with only a minor loss of activity.

Preparation and characterization of uniform-sized chitosan microspheres containing insulin by membrane emulsification and a two-step solidification process

Chitosan microsphere has important application in controlled release of protein and peptide drug, because it shows excellent mucoadhesive and permeation enhancing effect across the biological surfaces. In the conventional preparation methods of chitosan microsphere, the W/O emulsion was usually prepared by mechanical stirring method, and then the droplets were solidified by glutaraldehyde. There existed limitation and shortage such as broad size distribution, de-activity of bio-drug and difficulty in drug release because protein and peptide drug have the same amino group as chitosan. In this study, we established a method to prepare uniform-sized microsphere, and solve above problems by combining a special membrane emulsification technique and a step-wise crosslinking method. That is, the chitosan/acetic acid aqueous solution was pressed through the uniform pores of a porous glass membrane into a paraffin/petroleum ether mixture containing PO-500 emulsifier, to form a W/O emulsion with uniform droplet size. Then, the uniform droplets were solidified by a two-step crosslinking method. At the first step, tripolyphosphate (TPP) solution was dropped gradually in the emulsion, TPP diffused into the droplet to crosslink chitosan by an ionic linkage, generating a microgel. At the second step, an adequate amount of glutaraldehyde was added. The solidification conditions of the two-step process were optimized by investigating the effects of solidification conditions on morphology of microspheres, encapsulation efficiency (EE), drug activity and release profile in vitro. The suitable preparative conditions were determined as follows: pH value of aqueous phase and TPP solution was 3.5–4.0, the molar ratio of amino group of chitosan to aldehyde group of glutaraldehyde was 1:1 and the crosslinking time of glutaraldehyde was 60 min.

Some Aspects of the Reaction between Chitosan and Formaldehyde

Abstract Reactions of chitosan (degree of deacetylation 67%, weight-average molecular weight 850,000) with formaldehyde were performed in a dilute aqueous acetic acid solution at a molar ratio of amino groups of the polymer to HCHO of 0.06:O.1 mol/L and at different temperatures (45, 60, and 75°C). In each case the pH of the reaction mixtures was 3.4 during the experiments. The process was investigated by measuring the kinetic changes of the free formaldehyde concentration and the sum of free formaldehyde and methylol groups produced. No gelation of the reaction product was observed. The experimental results led to the conclusion that the methylol groups formed by the addition of HCHO to chitosan functions take part in some intramolecular reactions with amino and/or hydroxyl groups of chitosan. Initially, the concentration of the resultant methylene bridges grows rapidly and then drops again until an equilibrium is established. This rather unusual decomposition of the methylene links once formed without changing the reaction conditions is accompanied by a substantial growth of the amount of methylol derivative whose concentration at the beginning of the process increased rather slowly.