Natural proteins are good candidates for producing food packaging films due to their excellent functional properties. However, some deficiencies as their poor water resistance need to be addressed ...before films can be used in daily applications. This article explores the use of a low-cost plant-derived phenolic compound, tannic acid, as crosslinking agent for producing plasticized casein films. FTIR, high-resolution NMR, and rheological measurements confirmed the crosslinking reaction between casein amine groups and tannic acid. The influence of crosslinking agent concentration on the mechanical and viscoelastic properties, thermal stability, swelling behavior, water vapor permeability, cytotoxicity and degradation in composting conditions were investigated. The obtained results showed that tannic acid was an effective crosslinking agent for casein protein, so the yielded films which exhibit improved physicochemical properties, can be employed for food packaging applications.
Display omitted
•Tannic acid, a low-cost plant-derived phenolic compound was employed to crosslink casein films.•Functional properties of the films were significantly improved by the tannic acid crosslinking.•Casein films resulted non-cytotoxic for food packaging applications.•Biodegradation of casein films could be controlled by the tannic acid concentration in the protein matrix.
Antiprotozoal tinidazole (TNZ) exhibits low aqueous solubility (Sw) and poor photochemical stability. In this work, TNZ was used to form cocrystals and eutectics with the aim of enhancing its ...solubility and physical stability. The choice of coformers was based on a crystal engineering strategy focused on the success rate of supramolecular heterosynthon formation between azoles and carboxylic acids. By liquid-assisted grinding, three cocrystals with p-aminobenzoic acid (PABA), citric acid (CA), and salicylic acid (SA) and two eutectics with nicotinamide and succinic acid were obtained and characterized using powder X-ray diffraction, 13C solid-state nuclear magnetic resonance, infrared spectroscopy, differential scanning calorimetry, thermogravimetry, and hot-stage microscopy. The crystal structures of TNZ-PABA and TNZ-SA were resolved by means of single-crystal X-ray diffraction, which revealed that they are a solvated and an unsolvated cocrystal, respectively. The Sw values of the obtained samples were determined at 37 °C, with the outcome that only the TNZ-CA cocrystal had a slightly higher Sw than pure TNZ. A physical stability study was also performed under UV–visible irradiation, and it was found that the three cocrystals showed better photostability when compared to TNZ, the two eutectics, and each respective physical mixture, a finding that could be relevant from the pharmacotechnical point of view.
Phosphoric acid (PA) confined in a commercial mesoporous silica (CARIACT G) with porous size in the range of 3 to 10 nm was studied in relation to its coordination with the silanol groups on the ...silica surface as a function of temperature, up to 180 °C, using 31P and 29Si MAS NMR spectroscopy. As the temperature increases, the coordination of Si and P in the mesopores depends on the pore size, that is, on the area/volume ratio of the silica matrix. In the mesoporous silica with the higher pore size (10 nm), a considerable fraction of PA is nonbonded to the silanol groups on the surface, and it seems to be responsible for its higher conductivity at temperatures above 120 °C as compared to the samples with a smaller pore size. The electrical conductivity of the functionalized mesoporous silica was higher than that reported for other silico-phosphoric composites synthesized by sol–gel methods using soft templates, which require high-temperature calcination and high-cost reagents and are close to that of the best PA-doped polybenzimidazole membranes used in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). The rate of PA release from the mesoporous silica matrix when the system is exposed to water has been measured, and it was found to be strongly dependent on the pore size. The low cost and simplicity of the PA-functionalized mesoporous silica preparation method makes this material a promising candidate to be used as an electrolyte in HT-PEMFCs.
Solid state nuclear magnetic resonance of polymers Monti, Gustavo Alberto; Acosta, Rodolfo Héctor; Chattah, Ana Karina ...
Journal of Magnetic Resonance Open,
December 2023, 2023-12-00, 2023-12-01, Letnik:
16-17
Journal Article
Odprti dostop
•We present a review of solid-state NMR studies applied to characterization of polymers.•An order parameter that condensates the elastic response within the theoretical framework of the entangled ...phantom theory for rubber elasticity was identified.•Time−temperature superposition (TTS) was employed to expand the characteristic time scales of NMR exploration by about 2 orders of magnitude in PDMS.
The development of Solid-State Nuclear Magnetic Resonance (SSNMR) in Argentina took a great buster at the beginning of the 1990s along with the acquisition of many “state-of-the-art” high-field NMR spectrometers, two of them multipurpose solid-liquid spectrometers. From then to nowadays, the study of solid samples, including polymers, has been a current topic at the NMR group of the Facultad de Matemática, Astronomía, Física y Computación of Universidad Nacional de Córdoba, in Argentina. In this work, we propose a review approach of several research works on solid polymers performed in our group, covering low-field relaxation studies and high-resolution SSNMR.
Display omitted
► Enalapril maleate:β-cyclodextrin complexation in solid state was studied. ► The complex particles were characterized by SSNMR, SEM and XRPD. ► Results of solid-state analysis revealed that the ...complex is a new amorphous solid. ► The compatibility between enalapril maleate with magnesium stearate was evaluated. ► Enalapril maleate in the complex form was more stable than the drug alone.
Complexation of enalapril maleate with β-cyclodextrin was used to overcome the known enalapril maleate–excipient interaction in solid state. The complex formation was characterized by 13C solid state nuclear magnetic resonance, X-ray powder diffraction and scanning electron microscopy. Additionally, thermogravimetric analysis (TGA) was used to evaluate the compatibility between magnesium stearate with enalapril maleate alone or in the complex form. Degradation of the drug at 40°C/75% relative humidity in the presence of magnesium stearate was monitored by high performance liquid chromatography (HPLC). Enalapril maleate in the complex form was more stable than the drug alone, with the drug recovery after 6 month being: 95±1% and 82.1±0.5%, respectively. This satisfactory high stability of the enalapril:β-CD complex will be potentially useful for its application as solid pharmaceutical dosage products.
The complex chemical functionalization of aldehyde moieties in Cu(ii)- and Co(ii)-pyridinecarboxaldehyde complexes was studied. X-ray studies demonstrated that the aldehyde group (R
HO) of the four ...pyridine molecules is converted to dihydrogen
ester (R
(OCH
)(OH)
) and hemiacetal (R
H(OH)(OCH
)) moieties in both 4-pyridinecarboxaldehyde copper and cobalt complexes. In contrast, the aldehyde group is retained when the 3-pyridinecarboxaldehyde ligand is complexed with cobalt. In the different copper complexes, similar paramagnetic
H resonance lines were obtained in the solid state; however, the connectivity with the carbon structure and the
H vicinities were done with 2D
H-
C HETCOR,
H-
H SQ/DQ and proton spin diffusion (PSD) experiments. The strong paramagnetic effect exerted by the cobalt center prevented the observation of
C NMR signals and chemical information could only be obtained from X-ray experiments. 2D PSD experiments in the solid state were useful for the proton assignments in both Cu(ii) complexes. The combination of X-ray crystallography experiments with DFT calculations together with the experimental results obtained from EPR and solid-state NMR allowed the assignment of NMR signals in pyridinecarboxaldehyde ligands coordinated with copper ions. In cases where the crystallographic information was not available, as in the case of the 3-pyridinecarboxaldehyde Cu(ii) complex, the combination of these techniques allowed not only the assignment of NMR signals but also the study of the functionalization of the substituent group.
The interactions between pilocarpine (PIL) and the anionic polyelectrolyte carbomer (CBR) were investigated. The effects of the chemical interactions on the chemical stability of the drug also were ...evaluated. The binary system was characterized by nuclear magnetic resonance techniques, Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction, scanning electron microscopy (SEM) and thermal analysis. The experiments showed that the complex, prepared by freeze-drying, is a solid amorphous form different from its precursors, thereby offering an interesting alternative for the preparation of extended release matrices. The solution stability of PIL was studied at pH 7 and 8, at 70°C. The PIL solution stability was evaluated alone and in the presence of CBR. Results indicated that the drug in the presence of the polymer is 3.3 and 3.5 times more stable, at pH 7 and pH 8, respectively, than the drug without CBR. The activation energy and the frequency factor, according to Arrhenius plot, were estimated to be 13.9±0.4 and 14.8±0.5kcalmol−1, and 6.1±0.3 and 7.6±0.3, with and without the polymer, respectively.
One of the key parameters in assessing the production potential of unconventional oil and gas reservoirs is the quantification of organic matter, which is generally determined by pyrolysis. ...Laboratory nuclear magnetic resonance (NMR) is widely used in the oil industry; being a nondestructive method, it enables the possibility to perform several analyses on the same sample, which is desirable due to the heterogeneity of these types of geological formations. 13C spectra provide much information, from speciation to maturity determination. The main drawback of this technique is the inherently low signal obtained for these nuclei, rendering extremely long experimental times. A solution is using cross-polarization schemes that transfer the high polarization of nearby 1H nuclei to 13C ones, with the penalty that quantification is a priori not feasible. In this work, we analyze the cross-polarization evolution and conclude that quantifying the total organic content (TOC) is possible for a wide range of organic matter content and maturities for rock samples corresponding to the Neuquén and Cuyo basins in Argentina.
PDF
