Surface bonding of MN4 macrocyclic metal complexes with pyridine-functionalized multi-walled carbon nanotubes for non-aqueous Li-O2 batteries.

It is essential to develop bifunctional catalysts with high activity and stability for reversible oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) in lithium-oxygen (Li-O2) batteries. In this work, pyridine (Py) functionalized multi-walled carbon nanotubes (MWCNTs) were prepared to immobilize various solid MN4 macrocyclic metal complexes (MN4-MC) as cathode electrocatalysts for Li-O2 batteries. Three types of MN4-MC molecules, including iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc) and iron protoporphyrin IX (Heme) were examined to evaluate the influence of central metal atoms and ligand substituents found in MN4-MC molecules on the electrocatalytic performance of the study samples. The order of the ORR/OER catalytic activity of the bifunctional catalysts is FePc > Heme > CoPc. The central metal atom in FePc molecule has the highest occupied molecular orbital (HOMO) energy than the corresponding metal atoms in CoPc and Heme molecules. This made the molecule to have better dioxygen-binding ability and higher catalytic activity in the ORR process; it also made it to easily lose electrons that were oxidized in the OER process. This study proposed a simplified scheme of the electrode surface route to assist in understanding the diverse ORR/OER performances of MN4-MC. It is discovered that the positive core of the MN5 coordination sphere in MN4-MC/Py/MWCNTs composite is the primary active site that can influence the formation of MN5···O2* and MN5-LOOLi cluster in the ORR process. The interfacial electron could be easily delivered between MWCNTs and MN5 active site through the Py bridge. This facilitated the formation and decomposition of MN5-LOOLi species during the ORRs/OERs, leading to the enhancement of its catalytic performance. This work provides a new insight into the effects of the molecular structure and organization of MN4-MC on the catalytic activity of O2 electrodes in Li-O2 batteries.

Effect of surface bonding of FePC with electrospun carbon nanofiber on electrocatalytic performance for aprotic Li-O2 batteries.

The bifunctional catalysts assist the complete reversible cycle of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with low polarization of a lithium-oxygen (Li-O2) battery were known to be critical cathode components. In this work, electrospun nitrogen-doped carbon nanofibers (N-CNFs) were prepared to use as supports to anchor iron phthalocyanine (FePc) bifunctional catalyst for oxygen (O2) electrode in Li-O2 batteries. By using FePc and N-CNFs, two different bonding composites were fabricated via diazonium reaction by refluxing and physical mixing methods which were resulting into covalent linkage via pyridine (Py) (denoted as FePc/Py/N-CNFs) and noncovalent interaction via π-π stacking (denoted as FePc/N-CNFs). The systematic characterizations confirmed that the spun carbon nanofibers were functionalized by pyridine and the anchored FePc molecule donated the axial ligand for the iron (Fe) center in the FePc/Py/N-CNFs composite. The FePc were embedded in the N-CNFs composites combining the electrocatalytic activity of the FePc with ORR/OER processes and N-CNFs with a three-dimensional (3D) interconnected porous network structure through a connecting link of one-dimensional (1D) porous and N-doping carbon nanofiber which exhibited a high performance when acting as the cathode in Li-O2 batteries. However, the FePc/Py/N-CNFs composite showed the higher catalytic activity and prominent structural stability due to the FePc being strongly interlinked with the N-CNFs through the Py connection, which could avoid the deformation and agglomeration of FePC molecules during cycling and thus possessed the high electrochemical performance of the composite. This study demonstrated the unique design of FePc/Py/N-CNFs composite structure in this work would be found as a promising O2 electrode material with enhanced electrochemical performance in rechargeable Li-O2 batteries.

13C NMR spectroscopy characterization of particle-size fractionated soil organic carbon in subalpine forest and grassland ecosystems.

BACKGROUND: Soil organic carbon (SOC) and carbon (C) functional groups in different particle-size fractions are important indicators of microbial activity and soil decomposition stages under wildfire disturbances. This research investigated a natural Tsuga forest and a nearby fire-induced grassland along a sampling transect in Central Taiwan with the aim to better understand the effect of forest wildfires on the change of SOC in different soil particle scales. Soil samples were separated into six particle sizes and SOC was characterized by solid-state 13C nuclear magnetic resonance spectroscopy in each fraction. RESULTS: The SOC content was higher in forest than grassland soil in the particle-size fraction samples. The O-alkyl-C content (carbohydrate-derived structures) was higher in the grassland than the forest soils, but the alkyl-C content (recalcitrant substances) was higher in forest than grassland soils, for a higher humification degree (alkyl-C/O-alkyl-C ratio) in forest soils for all the soil particle-size fractions. CONCLUSIONS: High humification degree was found in forest soils. The similar aromaticity between forest and grassland soils might be attributed to the fire-induced aromatic-C content in the grassland that offsets the original difference between the forest and grassland. High alkyl-C content and humification degree and low C/N ratios in the fine particle-size fractions implied that undecomposed recalcitrant substances tended to accumulate in the fine fractions of soils.

The Use of Spray-Dried Mn3O4/C Composites as Electrocatalysts for Li-O2 Batteries.

The electrocatalytic activities of Mn3O4/C composites are studied in lithium-oxygen (Li-O2) batteries as cathode catalysts. The Mn3O4/C composites are fabricated using ultrasonic spray pyrolysis (USP) with organic surfactants as the carbon sources. The physical and electrochemical performance of the composites is characterized by X-ray diffraction, scanning electron microscopy, particle size analysis, Brunauer-Emmett-Teller (BET) measurements, elemental analysis, galvanostatic charge-discharge methods and rotating ring-disk electrode (RRDE) measurements. The electrochemical tests demonstrate that the Mn3O4/C composite that is prepared using Trition X-114 (TX114) surfactant has higher activity as a bi-functional catalyst and delivers better oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic performance in Li-O2 batteries because there is a larger surface area and particles are homogeneous with a meso/macro porous structure. The rate constant (kf) for the production of superoxide radical (O2•-) and the propylene carbonate (PC)-electrolyte decomposition rate constant (k) for M3O4/C and Super P electrodes are measured using RRDE experiments and analysis in the 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6)/PC electrolyte. The results show that TX114 has higher electrocatalytic activity for the first step of ORR to generate O2•- and produces a faster PC-electrolyte decomposition rate.

Investigation of MnO2 and Ordered Mesoporous Carbon Composites as Electrocatalysts for Li-O2 Battery Applications.

The electrocatalytic activities of the MnO2/C composites are examined in Li-O2 cells as the cathode catalysts. Hierarchically mesoporous carbon-supported manganese oxide (MnO2/C) composites are prepared using a combination of soft template and hydrothermal methods. The composites are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, small angle X-ray scattering, The Brunauer-Emmett-Teller (BET) measurements, galvanostatic charge-discharge methods, and rotating ring-disk electrode (RRDE) measurements. The electrochemical tests indicate that the MnO2/C composites have excellent catalytic activity towards oxygen reduction reactions (ORRs) due to the larger surface area of ordered mesoporous carbon and higher catalytic activity of MnO2. The O2 solubility, diffusion rates of O2 and O2•- coefficients (DO2 and DO-2), the rate constant (kf) for producing O2•-, and the propylene carbonate (PC)-electrolyte decomposition rate constant (k) of the MnO2/C material were measured by RRDE experiments in the 0.1 M TBAPF6/PC electrolyte. The values of kf and k for MnO2/C are 4.29 × 10-2 cm·s-1 and 2.6 s-1, respectively. The results indicate that the MnO2/C cathode catalyst has higher electrocatalytic activity for the first step of ORR to produce O2•- and achieves a faster PC-electrolyte decomposition rate.

Characterization of soil organic matter in perhumid natural cypress forest: comparison of humification in different particle-size fractions.

BACKGROUND: The Chamaecyparis forest is a valuable natural resource in eastern Asia. The characteristics of soil humic substances and the influence of environmental factors in natural Chamaecyparis forests in subtropical mountain regions are poorly understood. The study site of a perhumid Chamaecyparis forest is in the Yuanyang Lake Preserved Area in northcentral Taiwan. We collected samples from organic horizons (Oi, Oe and Oa) and from the surface horizon (O/A horizon) at the summit, footslope and lakeshore to characterize the composition of the soil organic matter. Samples of organic horizons were dried and ground, and those of the O/A horizon were passed through wet sieving for different particle-size fractions before analysis. The C chemical structure in the samples was determined with CP/MAS 13C NMR spectra. RESULTS: The ratios of alkyl-C/O-alkyl-C and aromaticity increased with decomposition of litter from the Oi, Oe, to Oa horizon. The ratio of alkyl-C/O-alkyl-C also increased from coarse (> 250 µm) to very fine (< 2 µm) particle fractions, which indicates increased humification of soil organic matter (SOM) in the fine-sized fractions. However, aromaticity tended to decrease with decreasing particle size, so it may not be useful in evaluating SOM humification of different particle-size fractions. CONCLUSIONS: The humification degree of the samples from O horizons and different particle-size fractions of the O/A horizon showed no gradient change with change in topography. This prevalent slow decomposition of organic matter in these perhumid climate conditions may narrow the difference in humification from the summit to lakeshore.

A specific tumor-targeting magnetofluorescent nanoprobe for dual-modality molecular imaging.

Poly(acrylic acid) was decorated onto Fe(3)O(4) resulting in a highly water-soluble superparamagnetic iron oxide. The Poly(acrylic acid) iron oxide (PAAIO) complexes possess specific magnetic properties in the presence of an external magnetic field and are attractive contrast agents for magnetic resonance imaging (MRI). The free carboxylic groups of PAAIO exposed on the surface allow for covalent attachment of a fluorescent dye, Rhodamine 123 (Rh123) to form PAAIO-Rh123, which permits applications in fluorescence imaging. PAAIO-Rh123 is therefore a dual-modality molecular probe. In order to endow specific properties to compounds that target cancer cells and to prevent recognition by the reticuloendothelial system (RES), folic acid-linked poly(ethylene glycol) (FA-PEG) was further conjugated onto PAAIO-Rh123. The amounts of Rh123 and FA-PEG on the modified iron oxides were quantitatively determined by elemental analysis. The iron content was determined by inductively coupled plasma-optical emission spectrometer (ICP-OES). The particle diameters were characterized by dynamic light scattering (DLS) and transmission electron microscope (TEM). Superparamagnetism was confirmed by the superconducting quantum interference device (SQUID) magnetometer. The cellular internalization efficacy of the modified iron oxides was realized in folate-overexpressed FR(+) and folate-deficient FR(-) KB cells by flow cytometry and confocal laser scanning microscopy (CLSM). The quantitative amount of iron internalized into different harvested KB cells was measured by ICP-OES. The T(2)-weighted MR images were tested in FR(+) KB cells.

Folic acid-Pluronic F127 magnetic nanoparticle clusters for combined targeting, diagnosis, and therapy applications.

Superparamagnetic iron oxides possess specific magnetic properties in the presence of an external magnetic field, which make them an attractive platform as contrast agents for magnetic resonance imaging (MRI) and as carriers for drug delivery. In this study, we investigate the drug delivery and the MRI properties of folate-mediated water-soluble iron oxide incorporated into micelles. Pluronic F127 (PF127), which can be self-assembled into micelles upon increasing concentration or raising temperatures, is used to decorate water-soluble polyacrylic acid-bound iron oxides (PAAIO) via a chemical reaction. Next, the hydrophobic dye Nile red is encapsulated into the hydrophobic poly(propylene oxide) compartment of PF127 as a model drug and as a fluorescent agent. Upon encapsulation, PAAIO retains its superparamagnetic characteristics, and thus can be used for MR imaging. A tumor-specific targeting ligand, folic acid (FA), is conjugated onto PF127-PAAIO to produce a multifunctional superparamagnetic iron oxide, FA-PF127-PAAIO. FA-PF127-PAAIO can be simultaneously applied as a diagnostic and therapeutic agent that specifically targets cancer cells that overexpress folate receptors in their cell membranes. PF127-PAAIO is used as a reference group. Based on FTIR and UV-vis absorbance spectra, the successful synthesis of PF127-PAAIO and FA-PF127-PAAIO is realized. The magnetic nanoparticle clusters of PF127-PAAIO and FA-PF127-PAAIO are visualized by transmission electron microscope (TEM). FA-PF127-PAAIO, together with a targeting ligand, displays a higher intracellular uptake into KB cells. This result is confirmed by laser confocal scanning microscopy (CLSM), flow cytometry, and atomic absorption spectroscopy (AAS) studies. The hysteresis curves, generated by using a superconducting quantum interference device (SQUID) magnetometer analysis, demonstrate that the magnetic nanoparticles are superparamagnetic with insignificant hysteresis. The MTT assay explains the negligible cell cytotoxicity of PF127-PAAIO and FA-PF127-PAAIO. In KB cells, the in vitro MRI study indicates the better T(2)-weighted images in FA-PF127-PAAIO than in PF127-PAAIO.

Biodegradable amphiphilic copolymers based on poly(epsilon-caprolactone)-graft chondroitin sulfate as drug carriers.

The goal of this study was to develop a new type of core-shell micelles based on biocompatible and biodegradable amphiphilic copolymers, named PCL-CS, using chondroitin sulfate (CS) as a hydrophilic segment and poly(epsilon-caprolactone) (PCL) as a hydrophobic segment. The copolymers, prepared from the various compositions between CS and PCL, were characterized by Fourier transform infrared spectrometer, proton nuclear magnetic resonance spectrometer, and differential scanning calorimeter. The PCL-CS copolymers could be assembled into micelles using a simple emulsion. With the fluorescent probe technique, the critical micelle concentrations were obtained in the range of 1.26 x 10(-3)-8.86 x 10(-3) mg/mL. The spherical images of micelles were visualized in the presence of polyvinyl alcohol (PVA) with the use of the transmission electron microscope. The particle sizes of micelles were all smaller than 300 nm, neither aggregate nor change in hydrodynamic sizes after 15 days staying in solutions containing salts or PVA by dynamic light scattering. The intracellular uptake of KB cells incubated with PCL-CS micelles was evidenced by confocal laser scanning microscope upon loading fluorescein isothiocyanate labeled bovine serum albumin as a probe.

Characterization of hydrogels prepared from copolymerization of the different degrees of methacrylate-grafted chondroitin sulfate macromers and acrylic acid.

Different degrees (between 20 and 75%) of methacrylate-grafted chondroitin sulfate (CS-MA) were synthesized. These CS-MA macromers were further copolymerized with acrylic acid (AA) at the molar ratio of 1 to 5 to form hydrogels. The sol percents of these CS-MA-AA hydrogels decreased and the cross-linking densities were studied with respect to the degrees of MA substitution onto CS-MA. The cytotoxicity with the increase in degree of MA substitution (DS) onto CS-MA as well as their hydrogels prepared from the corresponding macromers was tested using 293T cells. The cell viability of human dermal fibroblast and mescenchymal stem cells was further tested upon exposure to 75% CS-MA for 1-, 3-, and 7-day incubation period. The hydrogels maintained degradability for long periods of time as evidenced by SEM. A model protein, BSA, demonstrated the prolong-release behaviors of these hydrogels in simulated gastric fluids and pH 7.4 phosphate buffer solutions and a faster release rate in the presence of chondroitinase and esterase at pH 7.4.

Controlled immobilization of chondroitin sulfate in polyacrylic acid networks.

Novel semi-interpenetrating polymer networks (semi-IPNs) of chondroitin sulfate (ChS) and acrylic acid (AA) were prepared with the aim of obtaining a hydrogel for use as a colon-specific drug carrier. By controlling the concentrations of cross-linking agent, diethylene glycol dimethacrylate (DEGDA), as well as the reaction solvent, high swelling percentages were obtained (approx. 1600%). However, the highest sol percent obtained for these hydrogels was approx. 70%, and most of the chondroitin sulfate remained soluble and could be extracted. Therefore, an alternative approach was adopted: methacrylate-grafted ChS (ChSMA) was synthesized and then co-polymerized with acrylic acid (AA) at a molar ratio of 1:5 with various concentrations of AA. The sol content of these ChSMA-AA hydrogels was reduced to approx. 20%, and the cross-linking densities were almost 100-fold higher than those of the semi-IPNs. FT-IR spectra showed that the H-bonding interactions between ChS and PAA and the spectra of the semi-IPNs were similar to that of PAA itself after sol extraction. In contrast, the FT-IR spectra of ChSMA-AA remained intact after sol extraction. Ketoprofen was used as a model drug to test the sustained release behavior of these hydrogels.

Characterization of chondroitin sulfate and its interpenetrating polymer network hydrogels for sustained-drug release.

The goal of this work was to utilize the chondroitin sulfate (CS) based hydrogels for a drug delivery matrix. CS is a good structure/disease-modifying anti-osteroarthritis drug (S/DMOAD). However, the readily water-soluble nature limits its application as a solid-state drug-delivery vehicle. In this study, two methods were used to prepare CS hydrogels: directly crosslinking CS with poly(ethylene glycol) diglycidyl ether (EX-810) abbreviated as CS-EX or forming an interpenetrating polymer network named CS-EX-IPN. The CS-EX-IPN hydrogel was carried out by sequentially crosslinking reaction between CS and EX-810 in one phase and acrylic acid and di(ethylene glycol) diacrylate (DEGDA) as a counter phase. The swelling percent, cross-section morphology, and effective crosslinking density of hydrogels were characterized. The values of compression modulus and effective crosslinking density of CS-EX-IPN were approximately 3.6-fold higher than CS-EX. We also characterized the release of a model drug, diclofenac sodium (DS) and a model protein, bovine serum albumin (BSA), from CS-EX and CS-EX-IPN. The similar release profiles of DS were observed in the both hydrogels but slower release rate of BSA occurred in CS-EX-IPN. The release profiles of the two model drugs fit in a diffusion-controlled mechanism. The D(eff) values are in the order of 10(-5) for DS and 10(-7) for BSA.

Chondroitin sulfate-based anti-inflammatory macromolecular prodrugs.

Macromolecular prodrugs of three non-steroidal anti-inflammatory drugs (NSAIDs), ibuprofen, ketoprofen, and naproxen, were prepared by the covalent attachment of the drugs onto chondroitin sulfate (ChS) using PEG 1000 as a spacer. Drug-PEG adducts were synthesized using 1,1'-carbonyl diimidazole as a coupling agent in dimethyl sulfoxide, followed by the reaction with ChS in highly dilute aqueous solution at pH 6.8 via N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDAC) as a conjugation agent. The drug-ChS conjugates were confirmed by FTIR, 1H NMR and 13C NMR and the molar percent of drug substitution onto ChS was characterized by 1H NMR using the peak areas of the three protons of -PhiCHCH3 on the drugs to those of -NHCOCH3 on ChS. All drug-ChS conjugates are water-soluble. The release amounts of the free drugs from their corresponding drug-ChS conjugates were evaluated in the presence or absence of either esterase or chondroitinase, and the both enzymes in pH 7.4 Tris-buffer solutions at 37 degrees C by high performance liquid chromatography (HPLC). Keto-ChS conjugates released approximately 100% ketoprofen within 12h in the presence of esterase, but the combination with chondroitinase did not accelerate the release rate. The degradation of Keto-ChS conjugates by chondroitinase was confirmed by gel permeation chromatography (GPC). The Keto-ChS conjugates still retained the enzymatic recognition even at the substitution of ketoprofen as high as 56 mol%. The inhibition percent of carrageenan-induced edema of Keto-ChS-56 was comparable to that of a simple blend of ChS and ketoprofen, suggesting that biologically active ChS and ketoprofen could be liberated from the conjugate.

Characterization of polyelectrolyte complexes between chondroitin sulfate and chitosan in the solid state.

Chondroitin sulfate (ChS) was used to form polyelectrolyte complexes with chitosan (ChI), and its potential as a colon-targeted drug carrier was investigated. In order to determine the optimal conditions for the formation of a stable polyelectrolyte complex, the formation of ChS/ChI complexes was examined at two different pH values with various weight ratios, or at a fixed molar ratio of ChS/ChI of 1/2 under various pH conditions. The molar compositions of the various ChS/ChI complexes were quantitated with the use of solid-state 13C CP MAS NMR. The equivalent molar ratios of the complexes ranged from 0.47 to 0.54, in agreement with the data determined by elemental analysis. The fact that these values were close to 0.5 suggests that most of the --OSO3- and the --COO- groups on ChS formed strong electrostatic interactions with the --NH3+ groups on ChI, obeying a simple stoichiometric reaction between two oppositely charged moieties. Similar compositions of the complexes were obtained under most conditions tested; however, different strengths of the interactions between the two polysaccharides were noted from measurements of the water-associated transition and thermal degradation temperatures and the degree of ChS dissolution. FTIR and 13C NMR clearly showed H-bond formation at low pH, indicating that in addition to the varying degrees of electrostatic interaction, H bonding may be involved in complex formation. The highest degradation temperature, as determined by thermal gravimetric analysis, and the lowest ChS sol fraction, as measured by gel permeation chromatography, were observed with the complex prepared at pH 5, with a 1:1 mole ratio of the two opposite charges in feed. This complex also exhibited the highest water-associated transition temperature, as determined by differential scanning calorimetry. Furthermore, the swelling behavior of these complexes was pH dependent; this is a property that can potentially be exploited to control drug release from these complexes under specific pH conditions.

New approach to IR study of monomer-dimer self-association: 2,2-dimethyl-3-ethyl-3-pentanol in tetrachloroethylene as an example.

The dimerization of 2,2-dimethyl-3-ethyl-3-pentanol in tetrachloroethylene in the diluted region has been studied at four temperatures by IR spectroscopy. The aforementioned solute compound is chosen because self-association beyond dimerization is hampered by the steric hindrance generated by the bulky sidechains. The integrated absorbances of the monomer bands were treated based on Eq. (9) to obtain its molar absorptivity and dimerization constant. The same dimerization constant as well as the molar absorptivity of dimer band can be obtained based on Eq. (13) from the data treatment of the integrated absorbances of the dimer band. The disparity between two values of dimerization constant determined by two independent sources offers an opportunity to check the consistency of the determination. The standard enthalpy and entropy of dimerization have also been calculated by means of van't Hoff plot, respectively, from the data of temperature-dependent dimerization constants obtained from the monomer bands and dimer bands.