Carboxylate Form Research Articles

Comparative Evaluation of Different Methods of Carboxylation of Carbon Nanotubes as a Modifier of Mechanical Properties of Heat-Resistant Polyimide Based Nanocomposites

This work is a comparative evaluation of process effectiveness of multiwall carbon nanotube carboxylation in a variety of chemically active media: in concentrated and dilute nitric acid, in a mixture of nitric and sulfuric acids, in hydrogen peroxide, and in potassium permanganate. The formation of carboxylic groups on the surface of nanotubes was controlled via IR-spectroscopy, and their concentrations were determined using thermogravimetry (TG). The kinetics of increasing the concentration of carboxylic groups in the process of treating nanotubes by various methods was investigated. Nanocomposite films were prepared as a result of introducing the carboxylated nanotubes into an aromatic polyimide. The relationship between mechanical properties of films and the method of carboxylation and duration of chemical treatment was investigated. Treatment in a mixture of nitric and sulfuric acids leads to the most intense carboxylation of nanotubes. But in this environment, as in hydrogen peroxide, there is a marked degradation of nanoparticle surface. Treatment in potassium permanganate proceeds under milder conditions, does not lead to significant generation of defects on the surface of the nanotubes, but requires an increase in process duration.

Study of Hydrophilic Modification for Polyamide 6,6 and its Characterization

Polyamide 6,6 (PA 6,6) fiber is amongst the most substantial chemical fibers useful in a wide range of apparel and industrial applications. Overlooking the benefits, the poor hydrophilic nature of this fiber cause wet processing crucial and unsatisfactory ease of wearing for clothing. In this work, the surface modification of PA 6,6 fiber were studied by using Subtilisin and Alkali (NaOH). The effects of modification were investigated, including amino group determination by wool reactive dyeing, the surface morphology and chemical analysis by Scanning Electron Microscopy-Energy Dispersive Spectrometer (SEM-EDS) and Attenuated Infra-Red (ATR-IR). The dye-bath exhaustion and color strength results confirmed the increased amount of amino groups formed after modifications. The increased oxygen content in SEM-EDS results indicates the possible formation of carboxyl group after modifications. Generally, both Subtilisin and alkali treatments resulted in improvement of hydrophilicity and other properties of PA 6,6 fabrics; although Subtilisin treatment considered as clean and eco-friendly treatment in regards of environmental matters.

Diels–Alder and Dehydration Reactions of Biomass-Derived Furan and Acrylic Acid for the Synthesis of Benzoic Acid

Routes to benzoic acid starting from furan—obtained from hemicellulose in high yield—and methyl acrylate are reported. These routes involve Diels–Alder and dehydration reactions of furan and acrylic acid (or methyl acrylate) in a two-step reaction protocol that minimizes side reactions. The Diels–Alder reaction of furan and methyl acrylate (or acrylic acid) was run at 298 K and was catalyzed by Lewis acidic (Hf-, Zr-, and Sn-Beta) zeolite catalysts, and achieving a high turnover frequency (∼2 h–1) and no side reactions were observed. The oxanorbornene product was dehydrated at low temperatures (298 to 353 K) in mixtures of methanesulfonic acid and acetic anhydride in 96% yield. This is compared to an only 1.7% yield of methyl benzoate obtained for the dehydration of the oxanorbornene in neat methanesulfonic acid. The effect of oxanorbornene concentration and stereochemistry was found not to decrease the yield of aromatics, while dehydration of the carboxylic acid form of the oxanorbornene led to a decreas...

Intramolecular Lactonization of Poly(α-hydroxyacrylic acid): Kinetics and Reaction Mechanism

Poly(α-hydroxyacrylic acid), PHA, is one of the few polymers with biodegradable properties used in mechanical pulp bleaching to stabilize hydrogen peroxide. A new method for the in situ follow-up of the lactone ring formation of PHA has been developed. The results have further been applied to describe the reaction kinetics of the lactonization and hydrolysis reactions through parameter estimation. In addition, the reaction mechanism is elucidated by multivariate data analysis. Satisfactory identification and semiquantitative separation of the lactone ring as well as the acyclic (carboxyl and hydroxyl groups) forms have been established by 1H NMR in the pH range of 1–9. The lactonization reaction approaching equilibrium can be described by pseudo-first-order kinetics in the pH range of 1–6. The rate constants of the pseudo-first-order kinetic model have been estimated by nonlinear regression. Due to the very low rates of lactonization as well as the weak pH dependency of the reaction, an addition-elimination mechanism is proposed. Additionally, the presence of a transient reaction intermediate during lactonization reaction could be identified by subjecting the measurement data to multivariate data analysis (PCA, principal component analysis). A good correlation was found between the kinetic and the PCA models in terms of model validity.

Characterization and Modeling of the Collision Induced Dissociation Patterns of Deprotonated Glycosphingolipids: Cleavage of the Glycosidic Bond.

Glycosphingolipid fragmentation behavior was investigated by combining results from analysis of a series of negative ion tandem mass spectra and molecular modeling. Fragmentation patterns extracted from 75 tandem mass spectra of mainly acidic glycosphingolipid species (gangliosides) suggest prominent cleavage of the glycosidic bonds with retention of the glycosidic oxygen atom by the species formed from the reducing end (B and Y ion formation). Dominant product ions arise from dissociation of sialic acids glycosidic bonds whereas product ions resulting from cleavage of other glycosidic bonds are less abundant. Potential energy surfaces and unimolecular reaction rates of several low-energy fragmentation pathways leading to cleavage of glycosidic bonds were estimated in order to explain observed dissociation patterns. Glycosidic bond cleavage in both neutral (unsubstituted glycosyl group) and acidic glycosphingolipids was the outcome of the charge-directed intramolecular nucleophilic substitution (SN2) mechanism. According to the suggested mechanism, the nucleophile in a form of carboxylate or oxyanion attacks the carbon at position one of the sugar ring, simultaneously breaking the glycosidic bond and yielding an epoxide. For gangliosides, unimolecular reaction rates suggest that dominant product ions related to the cleavage of sialic acid glycosidic bonds are formed via direct dissociation channels. On the other hand, low abundant product ions related to the dissociation of other glycosidic bonds are more likely to be the result of sequential dissociation. Although results from this study mainly contribute to the understanding of glycosphingolipid fragmentation chemistry, some mechanistic findings regarding cleavage of the glycosidic bond may be applicable to other glycoconjugates.

ChemInform Abstract: K3[Fe(CN)6]·3H2O Supported on Silica Gel: An Efficient and Selective Reagent for the Cleavage of Oximes to their Corresponding Carbonyl Compounds in Aqueous Medium.

K3[Fe(CN)6].3H2O supported on silica gel, a new oxidant, for efficient, simple and selective cleavage of ketoximes and aldoximes to their corresponding carbonyl compounds in aqueous medium is described. Further oxidation of aldehydes to carboxylic acid and formation of by-products were not observed. α−β unsaturated oxime was deoximated smoothly without oxidation of the double bond.

Self-defensive nano-assemblies from camptothecin-based antitumor drugs.

Camptothecin (CPT)-based drugs always undergo the reversible, pH-dependent lactone ring-opening reaction, yielding the inactive but toxic carboxylate form. Self-assembly strategy provides an effective route for preserving their bio-stability. In this article, nano-sized self-assemblies from CPT-based antitumor drugs were simply built up by directly diluting the stock dimethylsulfoxide solutions of (S)-(+)-CPT, (S)-10-hydroxyl camptothecin and carboxylic CPT with water/phosphate-buffered saline solution. Because of their different molecular structures in A-ring or modification on the 20-OH group, CPT self-assembled into helical nano-ribbons, whereas 10-hydroxycamptothecin and carboxylic CPT self-aggregated into flat nano-ribbons and cylindric nano-rods, respectively. Attractively, the self-assembly of CPT-based drugs could occur within 1 min at a low concentration of 1 × 10−5 M. Adopting the J-type self-aggregation, self-assemblies were stable in aqueous solution and could effectively protect the CPT-based drugs from hydrolysis, which thereby kept their bioactivity for tumor therapy.

Carboxylic monolayer formation for observation of intracellular structures in HeLa cells with direct electron beam excitation-assisted fluorescence microscopy.

Intracellular structures of HeLa cells are observed using a direct electron beam excitation-assisted fluorescence (D-EXA) microscope. In this microscope, a silicon nitride membrane is used as a culture plate, which typically has a low biocompatibility between the sample and the silicon nitride surface to prevent the HeLa cells from adhering strongly to the surface. In this work, the surface of silicon nitride is modified to allow strong cell attachment, which enables high-resolution observation of intracellular structures and an increased signal-to-noise ratio. In addition, the penetration depth of the electron beam is evaluated using Monte Carlo simulations. We can conclude from the results of the observations and simulations that the surface modification technique is promising for the observation of intracellular structures using the D-EXA microscope.

Identification of functional groups and determination of carboxyl formation temperature in graphene oxide using the XPS O 1s spectrum

Experimental information on the O 1s spectra of GO by X-ray photoelectron spectrometry is limited and this will prove to be a liability when analyzing samples that have high carbon to oxygen ratios. Here, the binding energy (B.E.) information of electrons from the O 1s orbital of oxygen atoms in different functional groups were identified by characterizing GO in an in-situ heating and characterization experiment, performed in a vacuum between 473 and 573K, and chemically modified GO. The B.E.s of the O 1s electrons in hydroxyls, epoxides, carbonyls and carboxyls on GO were determined and carboxyl formation on GO was found to occur between 543 and 561K. Here, carboxyl formation is a decrease in the proportion of oxygen atoms bound to GO as hydroxyls and epoxides groups, accompanied by a greater than proportional increase in the proportion of oxygen atoms bound as carboxyls, and this results in the formation of vacancies on the graphene basal plane.

Interrelated Effects of Temperature and Environment on Wear and Tribochemistry of an Ultralow Wear PTFE Composite

A particular alumina–PTFE nanocomposite has distinguished itself with unusually large wear reductions at trace filler loadings. Recent studies have shown that the formation of carboxylic acid end groups in humid environments is a critical part of the wear reduction mechanism. This finding has significant implications for the utility of the material for space and high temperature applications. In this paper, wear rate, morphology, composition, and chemistry of the wear surfaces were characterized as a function of environmental composition and surface temperature to better understand the environmental limitations of this solid lubricating system and the associated wear resistance mechanisms. The following results were found: (1) ultralow wear rates were retained with increasing interface temperature up to 100 °C, (2) all samples ran in to low wear regardless of the environmental conditions (dry conditions caused an eventual transition to high wear), (3) carboxylates were detected after sliding in dry enviro...

Second-order calibration method applied to process three-way excitation–emission-kinetic fluorescence data: A novel tool for real-time quantitative analysis of the lactone hydrolysis of irinotecan in human plasma

Methods to monitor the metabolic transformations of pharmaceuticals in a real-time and rapid fashion are required to develop safe and effective drugs. Lactone hydrolysis is one of the most important metabolic transformations; it occurs readily in pharmaceuticals containing lactones by both enzymatic and non-enzymatic processes. In this study, a novel strategy that combines three-way excitation–emission-kinetic (EEM-kinetic) fluorescence data with second-order calibration method based on alternating normalization-weighted error (ANWE) algorithm was developed to monitor the lactone hydrolysis of irinotecan (CPT-11). Accurate real-time concentrations together with reasonable resolutions of the excitation and emission profiles could be estimated for both the lactone form (CPT-11-L) and carboxylate form (CPT-11-C) of CPT-11 during its hydrolysis, even when the fluorescence spectra of CPT-11-L and CPT-11-C seriously overlapped with each other and unknown fluorescent components coexisted in the plasma. Satisfactory results were obtained for static validation samples, spiked plasma samples, and kinetic samples. The average recoveries of CPT-11-L and CPT-11-C in three types of samples mentioned above ranged from 83.7% to 116.7%. The lactone hydrolysis of CPT-11 follows 1st-order degradation kinetics with rate constants of 0.0318±0.0031min−1 and 0.0323±0.0008min−1, and half-lives of 21.9±2.0min and 21.5±0.5min in PBS and plasma samples, respectively. The strategy described herein minimized or eliminated traditionally time-consuming sample pre-treatments and facilitated the quantification of the target drug in its native environment. This method was proved to be simple, real-time, fast, low-cost, high-efficiency and can be potentially applied to other types of dynamic systems.

Zero-valent iron doped carbons readily developed from sewage sludge for lead removal from aqueous solution

Low-cost but high-efficiency composites of iron-containing porous carbons were prepared using sewage sludge and ferric salts as raw materials. Unlike previous time- and energy-consuming manufacturing procedures, this study shows that pyrolyzing a mixture of sludge and ferric salt can produce suitable composites for lead adsorption. The specific surface area, the total pore volume and the average pore width of the optimal composite were 321m2/g, 0.25cm3/g, and 3.17nm, respectively. X-ray diffraction analysis indicated that ferric salt favored the formation of metallic iron, while Fourier transform infrared spectroscopy revealed the formation of hydroxyl and carboxylic groups. The result of batch tests indicated that the adsorption capacity of carbons activated with ferric salt could be as high as 128.9mg/g, while that of carbons without activation was 79.1mg/g. The new manufacturing procedure used in this study could save at least 19.5kJ of energy per gram of activated carbon.

Research on the chemical mechanism in the polyacrylate latex modified cement system

In this paper, the chemical mechanism in the polyacrylate latex modified cement system was investigated by Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC) and compact pH meter. All results have shown that the chemical reactions in the polyacrylate modified system can be divided into three stages. The hydration reactions of cement can produce large amounts of Ca(OH)2 (calcium hydroxide) and lead the whole system to be alkali-rich and exothermic at the first stage. Subsequently, this environment can do great contributions to the hydrolysis of ester groups in the polyacrylate chains, resulting in the formation of carboxyl groups at the second stage. At the third stage, the final crosslinked network structure of the product was obtained by the reaction between the carboxyl groups in the polyacrylate latex chains and Ca(OH)2.

Detonation nanodiamond toxicity in human airway epithelial cells is modulated by air oxidation

Detonation nanodiamonds (DNDs), a nanomaterial with an increasing range of industrial and biomedical applications, have previously been shown to induce a pro-inflammatory response in cultured human airway epithelial cells (HAECs). We now show that surface modifications induced by air oxidation of DND (AO-DND), including an increase in oxygen content, formation of carboxylic groups associated with the appearance of high negative zeta potential and a decrease in unpaired electron content, are accompanied by a significant loss of bioactivity, as measured by levels of interleukin-8 mRNA in HAEC. These findings are relevant to the identification of chemical determinants and molecular mechanisms of the inhalational toxicity of carbonaceous nanomaterials.

Free radical grafting of gallic acid (GA) on cellulose nanocrystals (CNCS) and evaluation of antioxidant reinforced gellan gum films

Abstract Antiradical properties were introduced on cellulose nanocrystals (CNCs) by redox pair (RP) initiator and γ-radiation treatments. Different procedures were tested on CNC, first a 2 h reaction of hydrogen peroxide (H 2 O 2 )/ascorbic acid (AA) was performed on CNC solution. γ-Radiation treatment at 20 kGy dose was then applied and immediately after GA was reacted during 24 h with the pretreated CNCs, giving CNC-H 2 O 2 -AA-γ-GA. The formation of new carboxylic acids and carbonyl groups were characterized by FT-IR at 1650 and 1730 cm −1 respectively. Carboxylic acid functionalities were also analyzed by conductometric titration where an increase from 49 to 134 mmol COOH kg −1 was found from native to irradiated CNCs. A similar increase in the carboxylic acid content (132 mmol kg −1 ) was observed for CNC-H 2 O 2 -AA-γ-GA, showing the highest radical scavenging properties (8 mM Trolox eq/mg CNC). Thermogravimetric analysis confirmed the structural changes onto CNC. Film packaging containing 20% of CNC-H 2 O 2 -AA-γ-GA was then added to a gellan-based film packaging. A significant improvement ( p 2 O 2 -AA-γ-GA was added to the film packaging formulation.

Gold nanostars coated with neutral and charged polyethylene glycols: A comparative study of in-vitro biocompatibility and of their interaction with SH-SY5Y neuroblastoma cells

Gold nanostars (GNS) have been coated with four different polyethylene glycols (PEGs) equipped with a –SH function for grafting on the gold surface. These PEGs have different chain lengths with average MW=2000, 3000, 5000 and average number of –O–CH2–CH2 — units 44, 66, and 111, respectively. Two are neutral and two are terminated with –COOH and –NH2 functions, thus bearing negative and positive charges at physiological pH, thanks to the formation of carboxylate and ammonium groups. The negative charge of the GNS coated with PEG carboxylate has also been exploited to further coat the GNS with the PAH (polyallylamine hydrochloride) cationic polymer. Vitality tests have been carried out on SH-SY5Y cells treated with the five differently coated GNS for 4, 24, and 48h, at Au concentrations ranging from 1.25 to 100μg/mL. The same tests have been repeated with the pure PEGs and PAH. Excellent biocompatibility was found for all PEGs, independently on charge and chain length, both for coated GNS and for the pure polymers. On the contrary, poor biocompatibility was found for PAH overcoated GNS and for pure PAH, although the latter only at high concentrations. Exploiting the two-photon luminescence of GNS, we have found by confocal laser scanning microscopy that when GNS are coated with PEGs they do not enter SH-SY5Y cells, while when overcoated with PAH they massively penetrate into the cytoplasm. This causes cell death by dramatically changing cell morphology, as demonstrated also by atomic force microscopy.

Acceleration of Biochar Surface Oxidation during Composting?

Biochar composting experiments were performed to determine whether composting is a suitable method to accelerate biochar surface oxidation for increasing its reactivity. To assess the results, surface properties of Terra Preta (Brazil) and ancient charcoal pit (Northern Italy) biochars were additionally investigated. Calculation of O/C ratios by energy-dispersive X-ray spectroscopy demonstrated the anticipated increasing values from fresh biochars (0.13) to composted biochars (0.40), and finally charcoal pit biochars (0.54) and ancient Terra Preta biochars (0.64). By means of Fourier transformation infrared microscopy, formation of carboxylic and phenolic groups on biochars surface could be detected. Carboxylic acids of three composted biochars increased up to 14%, whereas one composted biochar showed a 21% lower proportion of carboxylic acids compared to the corresponding fresh biochar. Phenolic groups increased by 23% for the last mentioned biochar, and on all other biochars phenolic groups decreased up to 22%. Results showed that biochar surface oxidation can be accelerated through composting but still far away from ancient biochars.

Urinary excretion and metabolism of the α-pyrrolidinophenone designer drug 1-phenyl-2-(pyrrolidin-1-yl)octan-1-one (PV9) in humans

1-Phenyl-2-(pyrrolidin-1-yl)octan-1-one (PV9) and 16 metabolites, including diastereomers and conjugates, were identified or tentatively detected in human urine by gas chromatography–mass spectrometry and liquid chromatography–high-resolution tandem mass spectrometry. These urinary metabolites indicated that the metabolic pathways of PV9 include: (1) the reduction of ketone groups to their corresponding alcohols; (2) oxidation of the pyrrolidine ring to the corresponding pyrrolidone; (3) aliphatic oxidation of the terminal carbon atom to the corresponding carboxylate form, possibly through an alcohol intermediate (not detected); and (4) hydroxylation at the penultimate carbon atom to the corresponding alcohols followed by further oxidation to ketones, and combinations of these steps. In addition, results from the quantitative analyses of five phase-I metabolites using newly synthesized authentic standards suggested that the main metabolic pathway includes the aliphatic oxidation of terminal and/or penultimate carbons. Human metabolism of PV9 differed significantly from those of α-pyrrolidinovalerophenone and α-pyrrolidinobutiophenone, suggesting that the main metabolic pathways of α-pyrrolidinophenones significantly change depending on the alkyl chain length of the parent molecule.

Semi-quantitative determination of monocarboxylate forms of ginkgolide B in plasma by UPLC-MS.

Ginkgolide B (GB) has a unique structure incorporating three γ-lactones that may be hydrolyzed in aquae as carboxylate forms. However, the determinations of them are challenging because there is no way to prepare the standards of any hydrolyzed products of GB in the solid state. In this report, a semi-quantitative method was developed to determine the monocarboxylate forms of GB in plasma. UPLC coupled with selected ion monitoring (SIR) of m/z 423 and m/z 441 were employed to detect the trilactone and monocarboxylates in assistances with the frozen method and the recovered method, which were, respectively, used to stabilize the hydrolyzed states and fully recover the monocarboxylates as the trilactone in samples. Two monocarboxylates were detected in pH 7.4 potassium phosphate buffers (PPB) after incubations, while only one was found in plasma in vitro and in vivo. The identifications of them require further studies. Following the bioanalytical validation of the trilactone, critical issues of the relative responses of the monocarboxylates in contrast to the trilactone, matrix effects, and stabilities were carefully investigated with subtly designed measures. The validation results supported the quantifications of monocarboxylates in PPB or plasma directly by using the corresponding calibration curve of the trilactone. The applications of this method presented a clear disparity between the hydrolysis kinetics of GB in plasma and PPB. Based on the quantification results and method applications, it was concluded that the present method was suitable to study the complex hydrolysis mechanisms of GB in vitro and in vivo.

Synthesis, crystal structure and thermochemical study on a novel ternary coordination compound [Bi(C7H5O3)3C12H8N2

A new ternary bismuth complex [Bi(C7H5O3)3C12H8N2] (C7H6O3, o-hydroxybenzoic acid; C12H8N2, 1,10-phenanthroline monohydrate) and its crystal were prepared and characterized. The results showed that the crystal is triclinic, space group P ī with a = 10.184(2) A, b = 11.807(2) A, c = 12.893(3) A, α = 76.81(3)°, β = 68.79(3)°, γ = 80.85(3)°, Z = 2, Dc = 1.891 g cm−3, F(000) = 776. The crystal contains a mononuclear molecule. Bi3+ is eight-coordinated by three bidentate chelating carboxylic groups and one o-phenanthroline molecule; C7H6O3 coordinated with Bi3+ in the form of carboxylate; the two nitrogen atoms of C12H8N2 are bidentate-coordinated with Bi3+ forming a chelate ring. At 298.15 K, the standard molar enthalpy of formation of the title complex was estimated to be ΔfHmΘ[Bi(C7H5O3)3C12H8N2 (s), 298.15 K] = −(303.99 ± 4.95) kJ mol−1.