Protonated Amine Groups Research Articles

The adsorption behavior and mechanism of Cr(VI) on facile synthesized mesoporous NH-SiO2.

An efficient Cr(VI) adsorbent, mesoporous amine-functionalized silica (NH-SiO2), was successfully synthesized within 2h by a facile one-step route under room temperature and aqueous solution. The structure properties of the obtained materials were characterized by N2 adsorption-desorption isotherm, XRD, TEM, and FT-IR. The Cr(VI) removal performance was investigated by batch experiment. It was found that Cr(VI) removal performance was dependent on solution pH, and the removal efficiency is above 90% for initial pH in the range of 1.0-4.0. The adsorption process was obeyed by pseudo-second-order model, and the equilibrium adsorption data were fitted well by Langmuir model. The maximum monolayer adsorption capacity was 205.76mg/g at pH2.0, which was larger than that of traditional two-step tri-amine-functionalized MCM-41. Additionally, high selectivity was exhibited in NH-SiO2 for removal Cr(VI) from co-presence anions Cl-, NO3-, PO43-, SO42-, and SiO32-. Furthermore, the spent NH-SiO2 could be regenerated by 0.005M NaOH, and Cr(VI) removal is above 92% after NH-SiO2 recycled four. From the analyzed results of adsorption energy, FT-IR, and XPS, the electrostatic attraction between protonated amine group and HCrO4- was the mainly adsorption mechanism. And then some adsorbed Cr(VI) was reduced to low toxicity Cr(III) on the adsorbent surface by electron transfer from nitrogen in -NBr group to Cr(VI).

Amine Resin by Chromium (III)‐Fibrous Protein for Enhanced Removal of Two Reactive Anionic Dyes

Amine resin (ACrFP) based on chromium (III)‐fibrous protein (CrFP) was synthesized by solvothermal reaction using tetraethylenepentamine, and its utilization in removing two kinds of anionic dyes (reactive brilliant red X‐3B and K‐2BP) was investigated. This adsorbent with protonated amine groups was characterized by SEM‐EDS, zeta potential, FTIR, Raman, and XPS. EDS analysis illustrated that the nitrogen content of ACrFP increased 6.40% compared with CrFP, suggesting grafting of amine groups into the framework of CrFP. Raman analysis of anionic dyes in solution and the ACrFP resin which has adsorbed dyes suggested that X‐3B and K‐2BP in solution have been loaded on solid, and XPS measurement of ACrFP, X‐3B‐ACrFP, and K‐2BP‐ACrFPfurther affirmed the results of Raman. Both sorption isotherms of X‐3B and K‐2BP were favored in lower temperature. About 0.1 mol/L of HCl could desorb reactive red dyes from ACrFP and the regenerated adsorbent could reuse several cycles. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S196–S204, 2019

Negative Surface Shielded Polymeric Micelles with Colloidal Stability for Intracellular Endosomal/Lysosomal Escape.

The critical process and step in achieving effective antitumor therapies is facilitating endosomal escape, which can enhance the intracellular target delivery of therapeutics. However, the normally adopted approaches tend to result in colloidal instability as a result of the inevitable interactions between the resulting positively charged surfaces of micelles and proteins in vivo. Herein, negatively charged surface shielded polymeric micelles, consisting of polymethylacrylamide derivatives and hydrophilic chitosan ( Mw = 18.8 kDa) linked by 3,3'-dithiodipropionic, are constructed. Until the pH decreases to less than 4.5, the DOX-loaded polymeric micelles (CSO-SS-PDPA/DOX) retain a negative surface charge as a result of the abundant amide groups, which could resist formation of the protein "corona" as visualized by transmission electron microscopy. Robust endosomal escape within tens of minutes due to protonated amine groups and specific redox-responsive drug release is visualized by confocal microscopy. The superior therapeutic efficacy in both 3D tumor spheroids and MCF-7 bearing mice further suggested that the prepared CSO-SS-PDPA/DOX is a promising approach for maintaining colloidal stability while achieving intracellular endosomal/lysosomal escape, which opens new opportunities for drug delivery.

Charge transfer in graphene/polymer interfaces for CO2 detection

Understanding charge transfer processes between graphene and functional materials is crucial from the perspectives of fundamental sciences and potential applications, including electronic devices, photonic devices, and sensors. In this study, we present the charge transfer behavior of graphene and amine-rich polyethyleneimine (PEI) upon CO2 exposure, which was significantly improved after introduction of hygroscopic polyethylene glycol (PEG) in humid air. By blending PEI and PEG, the number of protonated amine groups in PEI was remarkably increased in the presence of water molecules, leading to a strong electron doping effect on graphene. The presence of CO2 gas resulted in a large change in the resistance of PEI/PEG-co-functionalized graphene because of the dramatic reduction of said doping effect, reaching a maximum sensitivity of 32% at 5,000 ppm CO2 and an applied bias of 0.1 V in air with 60% relative humidity at room temperature. This charge transfer correlation will facilitate the development of portable graphene-based sensors for real-time gas detection and the extension of the applications of graphene-based electronic and photonic devices.

Biopolymer-layered polysilicate micro/nanocomposite based on chitosan intercalated in magadiite

On the basis of their high adsorption and cation exchange capacity, swelling potential and low toxicity, layered sodium silicate magadiite (Na–magadiite) is an attractive solid for intercalation of polymers. This study envisages the intercalation of cationic biopolymer chitosan (Chit) in Na–magadiite to prepare a Chit/magadiite micro/nanocomposite. Characterisation of starting-magadiite, pure chitosan and Chit/magadiite were investigated using powder X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and thermal analysis. XRD confirmed that the chitosan had been intercalated into the interlayer space of magadiite by increasing the basal spacing, d001 from 15.6 A to 21.45 A. The presence of characteristic bands of biopolymer and layered silicate in Chit/magadiite were confirmed by FTIR analysis. The thermal stability of micro/nanocomposite was evaluated by thermogravimetry analysis. The results suggested the formation of electrostatic interactions by protonated amine groups with the negatively charged magadiite surface as well as intercalation in the form of a predominant monolayer arrangement of chitosan chains in layered silicate magadiite.

Improved removal of hexavalent chromium from 10 mg/L solution by new micron sized polymer clusters of aniline formaldehyde condensate

Removal of hexavalent chromium by aniline-formaldehyde condensate polymer coated on silica gel, in the past, showed poor removal at low concentration range with high adsorbent dose (∼30% removal at 10 mg/L with a adsorbent dose of 8 g/L). We have now synthesized a new form of the support less polymer which brings down residual concentration to less than 1 mg/L with a 2 g/L dose. The maximum removal of total chromium was observed between pH 3–8 (94–98% removal at 2 g/L dose). Removal is susceptible to processing of the polymer and batch to batch variation has been observed. Field emission scanning Electron microscope (FESEM) showed polymer consists of micron-sized (1–2 µm diameter) clusters. Phosphate and nitrate strongly inhibited total chromium uptake while effect of sulphate and chloride were less. Desorption was 86% with 1 N HCl and reuse of the micron sized AFC was possible for four cycles. Ion exchange as well as redox interaction between chromate ion and protonated amine group of polymer was found to be the key factor for adsorption.

Influence of copper(II) ions on the noncovalent interactions between cytidine-5′-diphosphate or cytidine-5′-triphosphate and biogenic amines putrescine or spermidine

Potentiometric and NMR spectroscopic studies of the nucleotide (NucP)/polyamine (PA) system (where NucP = CDP, CTP, PA = putrescine or spermidine) revealed the formation of molecular complexes (NucP)(Hx+y)(PA) (where Hx+y = number of protons; x - from NucP and y - from PA). Their thermodynamic parameters were determined and the modes of their interactions were proposed. The main reaction centers were found to be the protonated amine groups of polyamine (positive centers) and phosphate groups of nucleotide (negative centers). The pH ranges in which the complex occurs correspond to those of amine protonation and -PO3x- group deprotonation, which unambiguously confirms the dipole-dipole type of interaction. In the pH range of total deprotonation of NHx+ groups from the polyamine, the molecular complexes disappear. The equilibrium and spectroscopic studies of the ternary systems Cu(II)/NucP/PA evidenced the formation of Cu(NucP)Hx+y(PA) type coordination compounds and Cu(NucP)⋯(PA)(Hx) type molecular complexes with polyamine in the outer coordination sphere. The main sites of metal ion bonding in the latter species are the phosphate groups of the nucleotide, while in the coordination compounds – besides the phosphate groups – also the donor nitrogen atoms from the polyamines. In this paper we have also quantitatively calculated the effect of metal ions on the formation of the molecular complexes.

Pt-like Hydrogen Evolution Electrocatalysis on PANI/CoP Hybrid Nanowires by Weakening the Shackles of Hydrogen Ions on the Surfaces of Catalysts.

The search for high active, stable, and cost-efficient hydrogen evolution reaction (HER) electrocatalysts for water electrolysis has attracted great interest. The coordinated water molecules in the hydronium ions will obviously reduce the positive charge density of H+ and hamper the ability of H+ to receive electrons from the cathode, leading to large overpotential of HER on nonprecious metal catalysts. Here we realize Pt-like hydrogen evolution electrocatalysis on polyaniline (PANI) nanodots (NDs)-decorated CoP hybrid nanowires (HNWs) supported on carbon fibers (CFs) (PANI/CoP HNWs-CFs) as PANI can effectively capture H+ from hydronium ions to form protonated amine groups that have higher positive charge density than those of hydronium ions and can be electro-reduced easily. The PANI/CoP HNWs-CFs as low-cost electrocatalysts show excellent catalytic performance toward HER in acidic solution, such as super high catalytic activity, small Tafel slope, and superior stability.

Promising sub-100 nm tailor made hollow chitosan/poly(acrylic acid) nanocapsules for antibiotic therapy

Herein, we report on the preparation of ultra-low sized (<100 nm in diameter) biodegradable polymeric capsules for potential applications as nanocontainers in antibiotic therapy. Hollow nanospheres based on the chitosan/poly(acrylic acid) pair are elaborated via (i) the layer-by-layer technique using gold nanoparticles (20 and 60 nm in size) as sacrificial templates, (ii) loading with amoxicillin, a betalactam antibiotic, and (iii) removal of the gold core via cyanide-assisted hydrolysis. Size, dispersity and concentration of the resulting nanocapsules are easily tuned by the nanoparticle templates, while wall thickness is controlled by the number of polyelectrolyte bilayers. Electrostatic interactions between the protonated amine groups of chitosan and the carboxyl groups of poly(acrylic acid) act as the driving attraction force allowing easy and fast design of robust and well-ordered multilayer films. Successful hydrolysis of the gold core is evidenced by time-dependent monitoring of the gold spectroscopic signature (absorbance at 519 nm and 539 nm for the gold nanoparticles with 20 and 60 nm, respectively). Crosslinked capsules are also prepared through crosslinking of the chitosan chains with glutaraldehyde. Chitosan-based nanocapsules are finally evidenced to be promising drug delivery vehicles of amoxicillin trihydrate with tuneable properties such as entrapment efficiency in the range of 62–75% and 3.5–5.5% concerning the drug loading.

Adsorption of hexavalent chromium by polyacrylonitrile-based porous carbon from aqueous solution.

Owing to the unique microporous structure and high specific surface area, porous carbon could act as a good carrier for functional materials. In this paper, polyacrylonitrile (PAN)-based porous carbon materials (PPC-0.6-600, PPC-0.8-600, PPC-0.6-800 and PPC-0.8-800) were prepared by heating KOH at 600°C and 800oC for the removal of Cr(VI) from aqueous solution. The adsorbent was characterized by the techniques of Fourier transform infrared spectroscopy (FT-IR), elementary analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and N2 adsorption techniques. The results showed that the adsorption capacity increased with decreasing pH value of the initial solution. The adsorption capacity of Cr(VI) on PPC-0.8-800 was much greater than that on other materials, and maximum adsorption capacity were calculated to be 374.90 mg g−1. Moreover, PPC-0.8-800 had superior recyclability for the removal of Cr(VI) from wastewater, about 82% of its initial adsorption capacity was retained even after five cycles. The result of kinetic simulation showed that the adsorption of Cr(VI) on the PAN-based porous carbon could be described by pseudo-second-order kinetics. The adsorption process was the ionic interaction between protonated amine groups of PPC and HCrO4- ions.

Hydroxyapatite-chitosan based bioactive hybrid biomaterials with improved mechanical strength

Composites consisting of hydroxyapatite (HA) and chitosan (CTS) have recently been intensively studied. In this work, a novel inorganic-organic (I/O) HA/CTS materials in the form of granules were prepared through a simple solution-based chemical method. During the synthesis of these hybrids, the electrostatic complexes between positively charged, protonated amine groups of chitosan and the negative phosphate species (HPO42− and H2PO4−) were formed. Our biocomposites belong to the class I of hybrids, which was confirmed by FTIR studies. XRD analysis revealed that the obtained materials consisted of hydroxyapatite as the only crystalline phase. Homogeneous dispersion of the components in HA/CTS composites was confirmed. The use of 17wt% and 23wt% of chitosan resulted in approximately 12-fold and 16-fold increase in the compressive strength of HA/CTS as compared to the non-modified HA material. During incubation of the studied materials in SBF, pH of the solution remained close to the physiological one. Formation of apatite layer on their surfaces indicated bioactive nature of the developed biomaterials.

FTIR spectroscopy studies on the spontaneous neutralization of chitosan acetate films by moisture conditioning

The influence of moisture ambiance on the spontaneous neutralization of amorphous chitosan acetate films during storage at 30°C and water activities (aw) in the range of 0.11 to 0.84 is studied by Fourier transform infrared (FTIR) spectroscopy. Three ranges of relative humidity affecting the chitosan acetate films are identified: i) 0.11≤aw≤0.32, produces dehydration and partial neutralization; ii) aw=0.44 and 0.55, spontaneous neutralization and rearrangement of OH bonds; iii) 0.64≤aw≤0.85, prevalence of films in the acetate form and moisture absorption. Acetate content of films as function of water activity and storage time is assessed from the band accounting for the electrostatic interaction of protonated amine groups (–NH3+) in chitosan and carboxylate ions (–COO−) of acetic acid. FTIR spectroscopy results are correlated with the equilibrium properties determined from moisture sorption isotherm. The simple method presented may help to produce chitosan acetate films with tuned protonation degree that are relevant in many applications such as biomedical, food, cosmetics, and pharmaceutical.

Efficient removal of hexavalent chromium from water and soil using magnetic ceramsite coated by functionalized nano carbon spheres

A magnetic ceramsite (MC) coated by nano carbon spheres (MCCS) was fabricated, and then the MCCS was stabilized and functionalized by polyethylenimine (PEI) to obtain a nanocomposite named as MCCSP. The nano carbon spheres (NCS) possessed plenty of amino and oxygen-containing groups (OH, COOH) and distributed homogeneously on the surface of MC, meanwhile the size and dispersion of these NCS could be conveniently adjusted. MCCSP demonstrated a high adsorption capacity for Cr(VI) which could be then reduced to low toxic trivalent chromium (Cr(III)), and the obtained Cr(III) could be chelated on the surface of MCCSP by protonated amine groups. Importantly, the resulting MCCSP-Cr could be conveniently collected from water and soil by a magnetic separation system (MSS). Therefore, this work provides a promising approach to remediate Cr(VI)-contaminated water and soil and may have a high application value.

Copper(II) ions interactions in the systems with triamines and ATP. Potentiometric and spectroscopic studies

The mode of interaction and thermodynamic stability of complexes formed in binary and ternary Cu(II)/ATP/triamines systems were studied using potentiometric and spectroscopic (NMR, EPR, UV–Vis) methods. It was found that in binary metal-free systems ATP/HxPA species are formed (PA: Spd=spermidine or 3,3-tri=1,7-diamino-4-azaheptane) where the phosphate groups from nucleotides are preferred negative centers and protonated amine groups of amines are positive centers of reaction. In the ternary systems Cu/ATP/Hx(PA) as well as Cu/(ATP)(PA) species are formed. The type of the formed Cu(II) complexes depends on pH of the solution. For a low pH value the complexation appears between Cu(II) and ATP molecules via oxygen atoms of phosphate groups. For a very high pH value, where ATP is hydrolyzed, the Cu(II) ions are bound to the nitrogen atoms of polyamine molecules. We did not detect any direct coordination of the N7 nitrogen atom of adenosine to Cu(II) ions. It means that the CuN7 interaction is an indirect type and can be due to noncovalent interplay including water molecule. EPR studies were performed at glassy state (77K) after a fast freezing both for binary and ternary systems. The glassy state EPR spectra do not reflect species identified in titration studies indicating significant effect of rapid temperature decrease on equilibrium of Cu(II) complexes. We propose the molecular structure of all the studied complexes at the glassy state deduced from EPR and optical spectroscopy results.

Mechanistic understanding of crystal violet dye sorption by woody biochar: implications for wastewater treatment.

Dye-based industries, particularly small and medium scale, discharge their effluents into waterways without treatment due to cost considerations. We investigated the use of biochars produced from the woody tree Gliricidia sepium at 300°C (GBC300) and 500°C (GBC500) in the laboratory and at 700°C from a dendro bioenergy industry (GBC700), to evaluate their potential for sorption of crystal violet (CV) dye. Experiments were conducted to assess the effect of pH reaction time and CV loading on the adsorption process. The equilibrium adsorption capacity was higher with GBC700 (7.9mgg-1) than GBC500 (4.9mgg-1) and GBC300 (4.4mgg-1), at pH 8. The CV sorption process was dependent on the pH, surface area and pore volume of biochar (GBC). Both Freundlich and Hill isotherm models fitted best to the equilibrium isotherm data suggesting cooperative interactions via physisorption and chemisorption mechanisms for CV sorption. The highest Hill sorption capacity of 125.5mgg-1 was given by GBC700 at pH 8. Kinetic data followed the pseudo-second-order model, suggesting that the sorption process is more inclined toward the chemisorption mechanism. Pore diffusion, π-π electron donor-acceptor interaction and H-bonding were postulated to be involved in physisorption, whereas electrostatic interactions of protonated amine group of CV and negatively charged GBC surface led to a chemisorption type of adsorption. Overall, GBC produced as a by-product of the dendro industry could be a promising remedy for CV removal from an aqueous environment.

Salt Promotes Protonation of Amine Groups at Air/Water Interface.

Interfacial water reorientation caused by charged Langmuir monolayers consisting of primary fatty amine (ODA) and cationic lipid having quaternary amine headgroup (DPTAP) were investigated by interface-selective vibrational sum-frequency generation spectroscopy. For DPTAP monolayer, initially large sum-frequency intensity from interfacial water OH band decreased steadily by increasing monovalent salt (NaCl, NaI) concentration due to counterion adsorption. On the other hand, ODA/water exhibited significantly smaller sum-frequency intensity than DPTAP/water, implying only small portion of protonated amine group (-NH3+) initially existed. By increasing the ionic strength, however, SF intensity of water OH band was enhanced markedly up to ∼1 mM, and then decreased in both NaCl and NaI solutions. By measuring the phase of the sum-frequency spectra, it was found that water dipoles under the ODA headgroup point downward, indicating that the surfaces were always positively charged. This demonstrated that increasing ionic strength facilitates protonation of primary amine headgroups. A simple model based on Poisson-Boltzmann (PB) theory explained this protonation behavior of primary amines.

Side-chain effects on the structures of protonated amino acid dimers: A gas-phase infrared spectroscopy study

A protonated amino acid can interact in several ways with another uncharged amino acid molecule to form a protonated dimer. In case of amino acids that do not have basic or acidic side chains, the most likely protonation site is the amino group and the then protonated amine can be involved in a pairwise interaction with a neutral amine, a carboxylic acid, a carboxylate group and/or the sidechain of the partner amino acid. Here, we employ gas-phase infrared spectroscopy and density functional theory to identify these pairwise interactions in protonated homodimers of serine, isoleucine, phenylalanine and tyrosine. The results show the influence of the different side-chains on the respective interactions. A charge-solvated structure with pairwise interaction between a protonated amine and a neutral amine is preferred if the side chain can provide additional stabilizing interaction with the positive charge. In contrast, for amino acids where the side chain only interacts weakly with the protonated amine group, a protonated dimer is formed by an interaction between the protonated amine and the neutral carboxylic acid of the second amino acid.

Binding efficacy and kinetics of chitosan with DNA duplex: The effects of deacetylation degree and nucleotide sequences

The binding process of DNA duplex with various types of chitosan polymers were studied at atomic level through molecular dynamics simulations. The interaction kinetics and binding strength, complex morphology and DNA structure evolution were systematically accessed. The binding efficacy of chitosan to DNA reduces (both in complexation speed and binding strength) when deacetylation degree is decreased, because protonated amine groups on chitosan backbone are more prone to bind with DNA, especially the phosphate oxygen, through coulomb interaction. The Watson Crick hydrogen bonds of A-T base pairs are more easily to break because chitosan is capable to form competitive hydrogen bonds with them. It is surprising to find that the G-C nucleotides have highly restrained kinetic motion than that of A-T nucleotides, which would be important for DNA-chitosan complexation and condensation to happen at the microscopic level. From our current results, the degree of chitosan deacetylation is found to play a certain role in regulating the DNA-chitosan complexation process, but is not as important as being believed before. Other types of chemical functionalization that can tune the chitosan’s hydrophobicity should deserve more attentions in the experiment.

Self-catalytic Synthesis of ZnO Nanoparticles@SiO2 Composites with Controllable Fluorescence

ZnO nanoparticles@SiO2 (ZnO NPs@SiO2) composites have been prepared by a self-catalytic approach in a water–ethanol solution at near neutral conditions. A multifunctional precursor combining not only a silicon alkoxide and a metal carboxylate group, but also a protonated amine group was designed. The intramolecular protonated amine groups could act as catalytic sites for the hydrolysis and condensation of silicon alkoxides. Thus self-catalytic reactions would proceed spontaneously without the addition of any other catalyst. By adjusting the manner of adding the silica source, ZnO NPs with an average diameter of 2.61, 4.00, and 5.72 nm for ZnO NPs@SiO2 composites could be controllably synthesized. Accordingly, the different ZnO NPs@SiO2 composites displayed blue, green, and yellow three emission under ultraviolet light.

Novel doxorubicin loaded PEGylated cuprous telluride nanocrystals for combined photothermal-chemo cancer treatment

Recently, combined photothermal-chemo therapy has attracted great attention due to its enhanced anti-tumor efficiency via synergistic effects. Herein, PEGylated cuprous telluride nanocrystals (PEGylated Cu2Te NCs) were developed as novel drug nanocarriers for combined photothermal-chemo treatment of cancer cells. PEGylated Cu2Te NCs were fabricated through a simple two-step process, comprised of hot injection and thin-film hydration. The as-prepared PEGylated Cu2Te NCs (average diameter of 5.21±1.05nm) showed a noticeable photothermal conversion efficiency of 33.1% and good capacity to load hydrophobic anti-cancer drug. Due to the protonated amine group at low pH, the doxorubicin (DOX)-loaded PEGylated Cu2Te NCs (PEGylated Cu2Te-DOX NCs) exhibited an acidic pH promoted drug release profile. Moreover, a three-parameter model, which considers the effects of drug-carrier interactions on the initial burst release and the sustained release of drug from micro- and nano-sized carriers, was used to gain insight into how pH and laser irradiation affect drug release from PEGylated Cu2Te-DOX NCs. Based on the results from in vitro cell study, PEGylated Cu2Te-DOX NCs revealed remarkably photothermal-chemo synergistic effect to HeLa cells, attributed to both the PEGylated Cu2Te NCs mediated photothermal ablation and enhanced cellular uptake of the drug. Thus, our results encourage the usage of Cu2Te-DOX drug nanocarriers for enhanced treatment of cancer cells by combined photothermal-chemo therapy.