Solid-state 13C NMR Spectra Research Articles

13C NMR and structural study of solid state naphthol-1 and naphthol-2 arylazo-derivatives

Solid state 13C NMR spectra of a series of naphthol-1 and naphthol-2-arylazo-derivatives were studied and compared with respective results in solutions. Signals of carbon nuclei of naphthalene ring were assigned. Tautomeric forms of compounds were determined. It was shown that 4-(p-NO2C6H4)-azonaphthol-1 and 1-(p-NO2C6H4)-azonaphthol-2 in solid state existed exclusively in quinohydrazone form. The other two compounds—1-(C6F5)-azonaphthol-2 and 2-(p-CH2C6H4)-azonaphthol-1 in solid state were not found in the form of individual tautomeric mixtures but in respective tautomeric equilibrium form. Thus, during transition from liquid to solid state, the tautomeric equilibrium was practically unchanged. In solid state it was found that rotation around aryl-N bond was hindered in the time scale of NMR spectroscopy.

Spectroscopic investigations of humic-like acids formed via polycondensation reactions between glycine, catechol and glucose in the presence of natural zeolites

Polycondensation reactions between low-molecular-weight compounds, such as amino acids, sugars and phenols, are crucially important processes in the formation of humic substances, and clay minerals have the ability to catalyze these reactions. In the present study, catechol (CT), glycine (Gly) and glucose (Gl) were used as representative phenols, amino acids and sugars, respectively, and the effects of the catalytic activities of natural zeolites on polycondensation reactions between these compounds were investigated. The extent of polycondensation was evaluated by measuring the specific absorbance at 600 nm ( E 600) as an index of the degree of darkening. After a 3-week incubation period, the E 600 values for solutions that contained zeolite samples were 4–10 times greater than those measured in the absence of zeolite, suggesting that the zeolite had, in fact, catalyzed the polycondensation reaction. The humic-like acids (HLAs) produced in the reactions were isolated, and their elemental composition and molecular weights determined. When formed in the presence of a zeolite, the nitrogen contents and molecular weights for the HLAs were significantly higher, compared to the HLA sample formed in the absence of zeolite. In addition, solid-state CP-MAS 13C NMR spectra and carboxylic group analyses of the HLA samples indicated that the concentration of carbonyl carbon species for quinones and ketones produced in the presence of zeolite were higher than the corresponding values for samples produced in the absence of a zeolite. Carbonyl carbons in quinones and ketones indicate the nucleophilic characteristics of the samples. Therefore, a nitrogen atom in Gly, which serves as nucleophile, is incorporated into quinones and ketones in CT and Gl. The differences in the catalytic activities of the zeolite samples can be attributed to differences in their transition metal content (Fe, Mn and Ti), which function as Lewis acids.

Interlayer modification of a layered H-octosilicate (H-RUB-18) with methanol: formation of a highly ordered organosilicate nanohybrid

Highly ordered silicate–organic nanohybrids were prepared by the modification of interlayer silanol groups of a layered polysilicic acid (H-octosilicate, H-RUB-18) with methanol. The grafting reaction was performed in a Teflon-lined stainless steel autoclave at 120 °C for various reaction periods. The grafting of methoxy groups onto the interlayer surface was evidenced by the downfield chemical shifts of the methyl groups in the solid state 13C NMR spectra and the exothermic DTA peaks with substantial weight losses due to combustion of methyl groups. The degree of modification with the methoxy groups was variable in the range between 0.42 and 0.95, depending on the reaction time. The retention of the layered silicate structure was proved by XRD and 29Si HD/MAS NMR. The structure was also analyzed by molecular mechanics force field calculation and Rietveld analysis, indicating the expansion of the silicate plane composed of the 54 cage with six-membered rings in the structure. This small structural distortion, caused by repulsion between the grafted methoxy groups, resulted in transformation of the crystal system from tetragonal to monoclinic. Hydrogen molecules were sorbed into the grafted products.

Detection of a Transient Intermediate in a Rapid Protein Folding Process by Solid-State Nuclear Magnetic Resonance

We describe the use of solid-state NMR spectroscopy to characterize a partially folded state of the 35-residue helical protein HP35 created by rapid freeze-quenching from a thermally unfolded state on the 10-20 micros time scale. Two-dimensional solid-state (13)C NMR spectra of (13)C-labeled HP35 in frozen glycerol/water solution exhibit two sets of signals, one corresponding to strongly unfolded protein molecules and the other to an ensemble of molecules having native helical secondary structure but incomplete tertiary structure. The NMR data indicate that secondary structure forms within the freeze-quenching time scale but that full folding involves a slower phase of structural annealing. The approximately 5 micros folding time observed in earlier studies of HP35 by time-resolved optical techniques may not represent the time scale for full folding.

Organic geochemistry of resins from modern Agathis australis and Eocene resins from New Zealand: Diagenetic and taxonomic implications

Abstract A maturation series of resins and fossil resins from New Zealand, ranging in age from Modern to Eocene and ranging from uncoalified to high volatile C bituminous coal, were analyzed by elemental, pyrolysis-gas chromatography (Py-GC), Fourier Transform infrared (FTir), and solid-state 13C nuclear magnetic resonance (13C NMR) techniques. For comparison, four resin samples from the Latrobe Valley, Australia, were analyzed. All of the resins and fossil resins of this study show very high H/C atomic ratios, and are characterized by dominant peaks in the 10–60 ppm range of solid-state 13C NMR spectra and prominent bands in the aliphatic stretching region (2800–3000 cm− 1) of FTir spectra, all indicating a highly aliphatic molecular structure. The 13C NMR and FTir data indicate a diterpenoid structure for these resins. There is an abrupt loss of oxygen that occurs at the Lignite A/Subbituminous C stage, which is attributed to a dramatic loss of carboxyl (COOH) from the diterpenoid molecule. This is a new finding in the diagenesis of resins. This important loss in oxygenated functional groups is attributed to a maturation change. Also, there is a progressive loss of exomethylene (CH2) groups with increasing degree of maturation, as shown by both 13C NMR and FTir data. This change has been noted by previous investigators. Exomethylene is absent in the fossil resins from the Eocene high volatile C bituminous coals. This progressive loss is characteristic of Class I resinites. FTir data indicate that the oxygenated functional groups are strong in all the resin samples except the fossil resin from high volatile C bituminous coal. This important change in oxygenated functional groups is attributed to maturation changes. The 13C NMR and FTir data indicate there are minor changes in the Agathis australis resin from the living tree and soil, which suggests that alteration of A. australis resins begins shortly after deposition in the soil for as little as 1000 years. The Morwell and Yallourn fossil resins from brown coal (lignite B) Australia do not have some of the FTir characteristics of the New Zealand resins, which most likely indicates they have a different plant source because different degrees of oxidation and weathering and changes due to fires (i.e., charring) can be ruled out. Our results have implications for studies of the maturation, provenance, and botanical sources of fossil resins and resinites in Eocene and Miocene coals and sediments of New Zealand and Australia.

Single-crystal and powder X-ray diffraction and solid-state 13C NMR of p-nitrophenyl glycopyranosides, the derivatives of d-galactose, d-glucose, and d-mannose

The X-ray diffraction patterns, 13C CP MAS NMR spectra, and powder X-ray diffraction analyses were obtained for selected p-nitrophenyl glycosides: α- and β- d-galactopyranosides ( 1 and 2), α- and β- d-glucopyranosides ( 3 and 4), and α- and β- d-mannopyranosides ( 5 and 6). In X-ray diffraction analysis of 1 and 2, characteristic shortening and lengthening of selected bonds were observed in the molecules of 1 due to anomeric effect, and in the crystal lattice of 1 and 2, hydrogen bonds of complex network were detected. In the crystal asymmetric unit of 1 there were two independent molecules, whereas in 2 there was one molecule. For 1 and 3– 6 the number of resonances in solid-state 13C NMR spectra exceeded the number of the carbon atoms in the molecules, while for 2 there were distinct singlet resonances in its solid-state NMR spectrum. Furthermore, the powder X-ray diffraction (PXRD) performed for 1– 3 and 5 revealed that 1, 3, and 5 existed as single polymorphs proving that the doublets observed in appropriate solid-state NMR spectra were connected with two non-equivalent molecules in the crystal asymmetric unit. On the other hand 2 existed as a mixture of two polymorphs, one of them was almost in agreement with the calculated pattern obtained from XRD (the difference in volumes of the unit cells), and the subsequent unknown polymorph existed in small amounts and therefore it was not observed in solid-state NMR measurements.

Hydrothermal Dehydration for the “Green” Reduction of Exfoliated Graphene Oxide to Graphene and Demonstration of Tunable Optical Limiting Properties

This work reports a simple, clean, and controlled hydrothermal dehydration route to convert graphene oxide (GO) to stable graphene solution. The hydrothermally treated GO was characterized using UV−visible absorption spectroscopy, atomic force microscopy, Raman spectroscopy, X-ray photoemission spectroscopy, and solid state 13C NMR spectra. Compared to chemical reduction processes using hydrazine, the present “water-only” route has the combined advantages of removing oxygen functional groups from GO and repairing the aromatic structures. By controlling the hydrothermal temperatures, we can modify the physical properties of GO and obtain tunable optical limiting performance.

A humic-acid-like polycondensate produced with no use of catalyst

The synthesis and physicochemical characterization of a water soluble humic-acid-like polycondensate (HALP), which mimics fundamental physicochemical and spectroscopic properties of natural humic acids is presented. The polymer can be synthesized under ambient O 2 by oxidative co-polymerization of gallic (GA) and protocatechuic (PA) acid at pH >9, with no need for a catalyst. Solid state 13C NMR spectra for GA-PA-HALP show that ring-opening reactions of GA, PA monomers are involved in GA-PA-HALP formation. EPR spectroscopy shows that GA-PA-HALP contains stable phenol-based radicals, with pH-dependent concentration. The H-binding profile of GA-PA-HALP follows the NICA-Donnan model, with two sets of distributed p K a values in the range 4–6 corresponding to carboxyl groups, and 7–9 corresponding to phenolic groups, as in natural HA. GA-PA-HALP bears a permanent negative charge Q 0 = −2.3 equiv kg −1 which is higher than the literature Q 0 values of −1 to −2 equiv kg −1 observed for natural HAs. A critical comparison of the present data with literature data is provided.

Alpha cellulose from industrial and agricultural renewable sources like short flax fibres, ears of corn and wheat-straw and its transformation into cellulose acetates

Cellulose with high content of alpha cellulose (ca. 98%, named CF) was extracted from short flax fibres following a free chloride procedure based on a two-step oxidative approach. The same procedure provided celluloses with alpha cellulose content around 83% from ears of corn (CC) and wheat straw (CW). CF can be used for the preparation of cellulose triacetate (CTA) and diacetate (CA), while both CC and CW can be used for the preparation of CA. The polymerisation degree (DP), dynamic light scattering (DLS) measurements, solution 13C NMR and solid state (CP MAS) 13C NMR spectra were properly used to characterise the extracted celluloses CF, CC, CW as well as their acetylated derivatives CTA and CA. Commercial alpha cellulose and CA samples were characterised in the same way and compared with CF, CC, CW and CTA, CA, respectively. From these comparisons, they all appeared to be cellulose materials suitable for industrial developments.

Structure and interactions of ulvan in the cell wall of the marine green algae Ulva rotundata (Ulvales, Chlorophyceae)

Ulvan, the sulfated cell-wall polysaccharides from green seaweeds ( Ulva species), presents structural and functional properties of interest for different applications. Its extraction yield in water varies depending on the species, the period of collect and the mode of conservation of algae. To identify limits of extraction, the structure and interactions of ulvan in the cell wall of Ulva were investigated following a sequential solvent extraction. Hot sodium oxalate and hot dilute HCl were the two major extracts. Other solvents affecting protein structure or low hydrogen bonded polymers yielded minor ulvan fractions but affected solid state 13C NMR spectra indicating that proteins likely contributed to cross-link and/or to entrap Ulva cell wall polysaccharides. Ulvan-lyase degradation showed that ulvan consisted in a wide continuum of related polysaccharides differing in the extent and type of fine structural characteristics. Besides solvent acidity, particle size of seaweeds was an important parameter controlling the ulvan extraction efficiency. Major ulvan cell wall interactions were discussed with regard to ionic interactions, covalent linkages and peculiar solution behavior of ulvan in various physicochemical environments.

The effect of lipids on the sorption of diuron and phenanthrene in soils

The influence of lipids on the sorption of diuron and phenanthrene to soils was investigated. Accelerated solvent extraction (ASE) was used to extract lipids from twelve soil horizons. Extractable lipids accounted for 3–13% of organic C. The organic carbon-normalized sorption coefficients ( K OC) for diuron and phenanthrene were consistently higher for the lipid-extracted soils than for the whole soils (average of 31% for diuron and 29% for phenanthrene), indicating that lipids compete for or block sorption sites on the organic matter. Sorption experiments on one pair of HF-treated soils indicated that the blocking effects of minerals and lipids are independent, since lipid extraction and HF-treatment combined increased K OC by more than either treatment alone. Lipids extracted from whole and HF-treated soils were very similar in composition, consisting predominantly of long-chain polymethylene structures. K OC of the lipid itself was lower than for any of the whole soils and soil fractions (lipid extracted and HF-treated) for diuron, but higher for phenanthrene. Solid-state 13C NMR spectra of the HF-treated soils before and after lipid extraction indicated that 15–20% of alkyl C was removed by ASE and that no other structures were affected.

Azelastine Hydrochloride: A Powder Diffraction and 13C CPMAS NMR Study of Its Anhydrous and Solvated Forms

Azelastine, a widely commercialized drug for the treatment of allergic asthma and rhinitis, has been commonly used as anhydrous hydrochloride salt, but it was found to form also hydrates or solvates upon recrystallization. The anhydrous form can be isolated also by precipitation from CH3CN solution or quantitatively generated from the hydrated form by heating it near 180 °C. The crystal structures of the anhydrous and of the three different solvated species have been determined by unconventional ab initio powder diffraction methods using laboratory data only, supported by solid state 13C NMR spectra and thermal analyses. Crystals of the anhydrous form are monoclinic, P21/n, a = 13.7858(9) A, b = 16.3911(9) A, c = 9.4085(5) A, β = 97.540(4)°, V = 2107.6(2) A3, Z = 4; the hydrated form crystallizes in the triclinic P1 space group, a = 9.5594(8) A, b = 9.8208(8) A, c = 14.644(1) A, α = 86.726(5)°, β = 109.511(5)°, γ = 119.176(5)°, V = 1122.1(2) A3, Z = 2. The stability of the two systems, in comparison with...

Synthesis and properties of conducting organic/inorganic polyurethane hybrids

A series of polyurethane/polyaniline/silica organic/inorganic hybrids were synthesized via the conventional polyurethane (PU) prepolymer technique. Amine-endcapped polyaniline (PANI) with low molecular weight and higher solubility was firstly synthesized. This PANI oligomer was then used together with nano-silica bearing silanol groups as chain extenders to prepare the conducting polyurethane hybrids. The polyurethane hybrids were designated as PU- xPANI- ySiO 2 ( x + y = 1). For comparison, the urethane-aniline block copolymer and the PU/silica hybrid were designated as PU-PANI and PU-SiO 2, respectively. The structures of PU-PANI, PU-SiO 2 and conducting polyurethane hybrids were confirmed by FT-IR, solid-state 13C, and 29Si NMR spectra. In nano-silica containing organic/inorganic conducting polyurethane hybrids, UV–vis spectra revealed the maximum absorption bands similar to that of PU-PANI. X-ray diffraction patterns indicated that these samples are typical of semicrystalline/amorphous materials. SEM image of PU-0.5PANI-0.5SiO 2 showed that PANI was dispersed homogeneously and interconnected continuously in the insulating PU-silica matrix. TGA results of the polymer hybrids exhibited higher thermal stabilities and lower decomposition rates than that of PU-PANI both in nitrogen and air. Differential scanning calorimetry (DSC) studies indicated that the polyurethane hybrids had higher glass-transition temperatures (T g) with the increase of PANI, but lower than that of PU-PANI. Stress–strain curves for all of the polyurethane hybrids showed the elastomeric behavior of typical polyurethanes. The surface resistivity values of all hybrids were about 10 8 ∼ 10 10 Ω/sq. and might meet the requirement of the anti-electrostatic materials.

Synthesis, characterization, and in vitro antimicrobial and antitumor activities of some tetraphenylstibonium(V) carboxylates

Several hitherto unreported pentacoordinated tetraphenylstibonium(V) carboxylates of general formula (C6H5)4SbL, where L = o-OHC6H5COO, (C6H5)2C(OH)COO, 2-(6-OCH3C10H6)CH(CH3)COO, ArCH(OH)COO (Ar = C6H5, p-CF3C6H4, and pOCH3C6H4), have been prepared and characterized by elemental analysis, solid state IR, 1H NMR, and 13C NMR spectra, conductivity, and molecular weight measurements. Spectroscopic data together with solution phase studies conform to the requirement of triagonal-bipyramidal configuration for these compounds. They were tested for in vitro antifungal (against Aspergillus flavus and Aspergillus niger) and antibacterial (against Staphylococcus aureus and Klebsiella pneumoniae) activities. The in vitro antitumor activity of all stibonium carboxylates was examined against MCF-7 cell line. A few of them were found to exhibit moderate to significant biological activity. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:688–693, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20498

Solid-state 13C NMR and SAXS characterization of the amorphous phase in low-molecular weight poly(ethylene oxide)s

Low-molecular weight poly(ethylene oxide)s (PEO) with extended, once or twice folded chains (as characterized by SAXS), were investigated by solid-state 13C NMR spectra measured under conditions to detect only the signal of the narrow line component. The direct detection and integrated intensities of the signals from hydroxy-terminated chain-end units in these spectra confirm that the narrow line component corresponds to the noncrystalline (amorphous) phase. The NMR line of PEO carbons adjacent to the hydroxy end-groups was used as an intensity standard to obtain information on the mean number of carbons per chain contributing to the amorphous phase. Assuming that amorphous phase is formed by chain ends (cilia) and folds it follows from the spectra that the length of folds is 6–7 monomer units; cilia are 2–3 monomer units long.

Crystallization of Polyethylenes Containing Chlorines: Precise vs Random Placement

The crystallization behavior and crystalline structure of a series of chlorine-containing polyethylenes (PEs) with either a random or a precise placement of the Cl atom on each and every 21st, 19th, 15th, and 9th backbone carbon have been studied by DSC, NMR, Raman spectroscopy, WAXD, SAXS and AFM in samples cooled from the melt at 1 °C/min. All precision Cl-substituted PEs crystallize as homopolymers based on their DD/MAS solid-state 13C NMR spectra that reveal a uniform distribution of the content of halogen between crystalline and noncrystalline regions. In addition, unique WAXD crystallographic patterns that differ from those of the linear PE and random polymers, relatively large crystal thicknesses, and sharp crystallization and melting peaks also support this homopolymer pattern in precision systems. In contrast, a high concentration of Cl in the noncrystalline regions in the case of the random systems suggest that the crystallization process for randomly substituted samples is being led by the selection of the most crystalline sequences, resulting in broad thermal transitions and lower crystallinities. Increasing chlorine content in both precision and random systems decreases crystallinity, melting temperature, heat of fusion, and crystallite thicknesses suggesting that Cl atoms are defects that hinder the crystallization of these polyolefins. Both systems are found to exhibit a lamellar crystalline morphology. Precision substituted polyethylenes form long, straight, and stacked lamellae with axialitic (PE21Cl, PE19Cl, and PE15Cl) or spherulitic (PE9Cl) organization as typical of homopolymers of similar molar mass. In contrast, the lamellae of random analogs are curved and more segmented as found in other PE random copolymers. The distribution of Cl within the crystalline regions of systems with precision substitution is strongly affected by the sequence length of the methylene groups. Packing around the substitution point of PE21Cl, PE19Cl, and PE15Cl render nearly all-trans conformations and asymmetric Cl distribution, while close staggering of Cl atoms in the crystals of PE9Cl exert conformational distortions as observed by a strong increase of TG conformers in the Raman spectra.

Hydrothermal Syntheses of Colloidal Carbon Spheres from Cyclodextrins

Colloidal carbon spheres have been prepared from aqueous α-, β-, and γ-cyclodextrin (CD) solutions in closed systems under hydrothermal conditions at 160 °C. Both liquid and solid-state 13C NMR spectra taken for samples at different reaction times have been used to monitor the dehydration and carbonization pathways. CD slowly hydrolyzes to glucose and forms 5-hydroxymethyl furfural (HMF) followed by carbonization into colloidal carbon spheres. The isolated carbon spheres are 70−150 nm in diameter, exhibit a core−shell structure, and are comprised of a condensed core (C═C) peppered with resident chemical functionalities including carboxylate and hydroxyl groups. Evidence from 13C solid-state NMR and FT-IR spectra reveal that the evolving carbon spheres show a gradual increase in the amount of aromatic carbon as a function of reaction time and that the carbon spheres generated from γ-CD contain significantly higher aromatic carbon than those derived from α- and β-CD.

Structural studies of 4,5,6,7-tetrabromobenzimidazole derivatives by means of solid-state 13C, 15N NMR spectroscopy and DFT calculations

Tetrabromobenzimidazole derivatives containing sulfur or nitrogen atom in a five- or six-membered saturated ring were synthesized as potential ligands of casein kinase (CK2). Structural data of these compounds are crucial for understanding their inhibitory activity as inhibitors. Solution and solid-state 13C NMR spectra were recorded for six compounds, and 15N MAS spectra – for two of them. 13C CPMAS spectra were assigned by comparison with solution data and with the aid of dipolar dephasing and variable contact time experiments. The correctness of assignments of 13C and 15N chemical shifts was verified by GIAO DFT calculations of shielding constants. The differences between the solution and solid-state chemical shift values were explained in terms of intermolecular interactions. The doublet resonances occurring in the solid-state 13C and 15N NMR spectra of N 1, N 2-propylene-2-amino-4,5,6,7-tetrabromobenzimidazole indicate the presence of two molecules in crystallographic unit cell. Shielding constants calculated for a dimer with two N1′ H…N3 hydrogen bonds suggest that the association type does not influence carbon shielding. The coexistence of two tautomers with N1′ H and N3 H is less probable.

Framework Functionalization of Periodic Mesoporous Organosilica with 1,2-bis[3-(triethoxysilylpropyl)ureido] cyclohexane Function via Basic Co-condensation Self-Assembly

The synthesized bis silylated long alkyl chain containing organosilicate precursor, 1,2-bis(3-(triethoxysilylpropyl)ureido)cyclohexane (BSPUCh) has been used as co-precursor with 1,2-bis (triethoxysilyl)ethane (BTSE) for the preparation of functional periodic mesoporous organosilicas (PMOs) via surfactant-mediated basic co-condensation self-assembly method. The various characterization techniques such as X-ray diffraction patterns (XRD), transmission electron microscope (TEM), N2 adsorption-desorption isotherms (BET), FT-IR, and 13C and 29Si CPMAS NMR spectroscopies were used to characterize the resulting structure of functionalized PMO mesostructures. Results obtained from XRD, TEM, and BET analysis clearly showed that the structural and pore arrangement of the functionalized PMOs were found to be dependent on the used concentration of BSPUCh. The functional PMOs showed well ordered mesophases when BSPUCh concentration was < or = 9 wt% in the initial mixtures, whereas higher concentration of the BSPUCh always produced disordered hierarchical mesostructures with bimodal pore size distributions. The incorporation of BSPUCh also reduces the surface area, pore volume, pore size, and pore wall thickness of the functionalized nanostructures, indicating that the BSPUCh is incorporated in the pore channels of the PMOs. The solid-state 13C and 29Si NMR spectra showed that the BSPUCh organosilicate with non-hydrolyzable bridging ligands propylureidocyclohexane has been successfully covalently linked in the framework of the resulting functional PMOs.

Preparation, characterization, and properties of new crosslinked proton-conducting membranes with polyoxyalkylene moieties

A new class of crosslinked proton-conducting membranes (CPMs) with polyoxyalkylene moieties was designed and prepared based on poly(styrene-co-maleic anhydride) modified with 2-aminoethanesulfonic acid sodium salt (AESA-Na) and polyoxyalkylenediamines (PEGDAs). The number density of the pendant of sulfonate group was controlled by the ratio of AESA-Na to PEGDA. The resulted membranes possess good mechanical strength and excellent flexibility. The structural characterizations of these membranes were confirmed by FT-IR and solid-state 13C NMR spectra. All these membranes exhibit a wholly amorphous morphology, and show a one-step weight loss from 350°C, indicating their good thermal stability. The CPM sample with 1.25mequiv SO3H per gram reaches the proton conductivity of 0.21Scm−1 at 30°C and 0.49Scm−1 at 95°C, respectively. Moreover, these protonated membranes show adequate oxidative stability in Fenton's reagent at 30°C.