Proton Spin-lattice Relaxation Time Research Articles

Measurement of spin-lattice relaxation times in multiphase polymer systems

Solid-state Nuclear Magnetic Resonance (NMR) has emerged as a pivotal technique for unraveling the microstructure and dynamics of intricate polymer and biological materials. Within this context, site-specific proton spin–lattice relaxation times in the laboratory frame (T1) and rotating frame (T1ρ) have become indispensable tools for investigating phase separation structures and molecular dynamics in multiphase polymer systems. Notably, the site-specific measurement of proton T1 and T1ρ is usually achieved via 13C detection in polymers, where 1H polarization is typically transferred to 13C via cross polarization (CP). Nevertheless, CP relies on the 1H–13C heteronuclear dipolar couplings, and thus it does not work well for the mobile components. In this study, via the integration of CP and RINEPT (refocused insensitive nuclei enhanced by polarization transfer), we propose a robust approach for the measurement of site-specific proton T1 and T1ρ in multiphase polymers. It overcomes the limitation of CP on transferring 1H polarization to 13C in mobile components, and thus enables simultaneous determination of site-specific proton T1 and T1ρ in rigid and mobile components in multiphase polymers in a single experiment. Such experiment can also be used for dynamics-based spectral editing due to the dynamic selectivity of CP- and RINEPT-based polarization transfer process. The proposed experiments are well demonstrated on three typical multiphase polymer systems, poly(methyl methacrylate)/polybutadiene (PMMA/PB) polymer blend, polyurethane (PU) and polystyrene–polybutadiene–polystyrene (SBS) elastomers. We envisage the proposed experiments can be a universal avenue for structural and dynamic elucidation of multiphase polymers containing both rigid and mobile components.

Insights into the Improved Gas Barrier Properties of Polyurethane-Clay Nanocomposite-Coated Nylon: A Solid-State NMR Study.

Herein, the reason for the improvement in the gas barrier properties of polyurethane (PU)-clay nanocomposite-coated nylon fabric compared to unfilled PU-coated nylon fabric is investigated by probing the changes in relaxation times of PU using solid-state nuclear magnetic resonance (SS NMR) spectroscopy. The interaction of the organically modified montmorillonite (MMT) clay (Cloisite 30B) with polyurethane (PU) in PU-clay (0.5/1/2 wt %) nanocomposites was probed with respect to the change in the spin-lattice relaxation time of protons in the PU chain due to the presence of paramagnetic species in clay (T1H, para). The better the dispersion of the clay in the PU matrix, the lower the T1H, para, due to the interaction between clay and the PU matrix. 0.5 wt % PU-clay has lower T1H, para, (6.4 s) compared to 1 wt % (18.3 s) and 2 wt % (14.3 s) filled systems. The SS NMR findings are in good agreement with field-emission scanning electron microscopy (FE-SEM) analyses. In SEM microscopic images, it is observed that the PU-0.5 wt % clay has better exfoliation of clay compared to the 1 and 2 wt % PU-clay nanocomposites. This is in agreement with improved gas barrier properties of the nanocomposite coated on the nylon fabric for 0.5 wt % clay (2300 mL/m2/day) compared with 1 wt % (2500 mL/m2/day) and 2 wt % clay (2600 mL/m2/day)-incorporated PU-coated fabrics and neat PU-coated nylon fabric (4500 mL/m2/day) at 260 GSM.

Intra- and Intermolecular Hydrogen Bonding in Miscible Blends of CO2/Epoxy Cyclohexene Copolymer with Poly(Vinyl Phenol).

In this study, we synthesized a poly(cyclohexene carbonate) (PCHC) through alternative ring-opening copolymerization of CO2 with cyclohexene oxide (CHO) mediated by a binary LZn2OAc2 catalyst at a mild temperature. A two-dimensional Fourier transform infrared (2D FTIR) spectroscopy indicated that strong intramolecular [C–H···O=C] hydrogen bonding (H-bonding) occurred in the PCHC copolymer, thereby weakening its intermolecular interactions and making it difficult to form miscible blends with other polymers. Nevertheless, blends of PCHC with poly(vinyl phenol) (PVPh), a strong hydrogen bond donor, were miscible because intermolecular H-bonding formed between the PCHC C=O units and the PVPh OH units, as evidenced through solid state NMR and one-dimensional and 2D FTIR spectroscopic analyses. Because the intermolecular H-bonding in the PCHC/PVPh binary blends were relatively weak, a negative deviation from linearity occurred in the glass transition temperatures (Tg). We measured a single proton spin-lattice relaxation time from solid state NMR spectra recorded in the rotating frame [T1ρ(H)], indicating full miscibility on the order of 2–3 nm; nevertheless, the relaxation time exhibited a positive deviation from linearity, indicating that the hydrogen bonding interactions were weak, and that the flexibility of the main chain was possibly responsible for the negative deviation in the values of Tg.

Varying the sequence distribution and hydrogen bonding strength provides highly Heat-Resistant PMMA copolymers

In this study we used free radical copolymerization of methyl methacrylate (MMA) and N-hydroxyphenylmaleimide (HPMI) to synthesize various poly(methyl methacrylate–co–N-hydroxyphenylmaleimide) (PMMA-co-PHPMI) random copolymers possessing high glass transition temperatures (Tg). FTIR and NMR spectroscopy, mass spectrometry, and differential scanning calorimetry (DSC) confirmed the chemical structures, thermal properties, hydrogen bonding interactions, and sequence distributions of these random copolymers. Because the reactivity ratio of MMA and HPMI is very different from that of MMA and maleic anhydride (MA), which prefer to form homopolymers, here we obtained partially alternating copolymers featuring strong intermolecular hydrogen bonding between the PMMA and PHPMI segments, resulting in the value of Tg increasing by up to 90 °C relative to that of the pure PMMA homopolymer. In addition, solid state NMR spectra revealed single values for the proton spin–lattice relaxation time in the rotating frame [T1ρ(H)] over all compositions of these random copolymers, with the relaxation times being shorter than the predicted average, indicating that the free volume had decreased and that the copolymers possessed rigid structures with high values of Tg.

Supramolecular Synthon Identification in Azelaic Acid – Isonicotinamide

Supramolecular synthons are the smallest structural units that contain the information inherent in building large molecular assemblies. Here, we apply solid-state NMR methods for the identification of the synthon in a cocrystal of Azelaic acid [(CH2)7(COOH)2]– Isonicotinamide [C6H6N2O]. It is observed that the spin-lattice relaxation time of protons in the cocrystal is long, implying that the choice of experiments, particularly those that involve low-sensitivity nuclei, could be time consuming. It is noticed that the two dimensional 1H double quantum (DQ) – 1H single quantum (SQ) correlation experiment at very fast MAS (60 kHz) is able to provide information on proton-proton proximities that leads to an understanding of the synthon structure. Experiments such as the CP-Reverse CP and 1H–13C HETCOR have been used to obtain spectral assignment which was additionally confirmed by first-principle GIPAW NMR chemical shift calculations. Present study indicates the basic unit to be a heterosynthon in Azelaic acid (AZA) – Isonicotinamide (INIC) cocrystal formed by two different modes of intermolecular connectivity, viz. acid–pyridine and acid–amide hydrogen bonding interactions. The presence of a CH…O type bond involving a hydrogen of INIC is also indicated from the observation of a larger chemical shift of the corresponding proton. The experimental protocol presented in this paper is expected to be a useful tool for the estimation of the basic structural arrangement of the synthons in a rapid fashion.

Developing of Nutraceuticals Systems Containing Bioactives from Salvia Hispânica Seed

This paper describes the research on the encapsulation of chia bioactives, which was derived from the extraction of Salvia hispânica seed using ethanol, employing percolation method and by Soxhlet. The obtained materials were characterized solution by nuclear magnetic resonance analysing the carbon-13 and hydrogen nuclei. The extracts were encapsulated with polycaprolactone (PCL) using nanopreciptation method. The nanoencapsulated materials were also analyses as their molecular homogeneity through low-field nuclear magnetic resonance in the time domain (NMR-DT). For that the determination of proton spin-lattice relaxation time was used to confirm the nanoencapulation. The measurements of size and zeta potential were also done employing DLS. From the results was conclude that the bioactives extracted from the seeds are associated to triacylgliceride major composed by α-linolenic acid (C18:3) and by linoleic acid (C18:2). It was also observed that the nanoencapsulation showed to be effective to produce particles with size between 203 a 430 nm, this size is appropriated to nutraceuticals formulations and/or to be added to food preparations.

Calixarene-Based lead receptors: an NMR, DFT and X-Ray synergetic approach

ABSTRACT The conformational changes of the homooxa adamantyl ketones 1 and 2, as well as of the calix[4]arene analogue derivative 3, all in the cone conformation, upon Pb2+ complexation were investigated by 1H, 13C, 207Pb NMR and proton spin-lattice relaxation times (T 1) experiments. The X-ray crystal structures of ketones 1 and 3 were determined. The inclusion of an acetonitrile molecule in the hydrophobic cavity of the ligands was observed in the solid state. In solution, inclusion was observed only in the case of Pb2+ ⊂ ketone 3 complex. DFT calculations were also performed to complement the NMR conformational analysis and to bring further insights to the cation complexation. The data confirmed the formation of 1:1 complexes between Pb2+ and the ligands, and that the cation is located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. In general, the ligand conformations became closer to a regular cone upon complexation, with the binding models found for the three ketones through the NMR studies corroborated by the DFT calculations.

Effect of Molybdenum Trioxide in the Behavior of Poly(vinyl alcohol) Nanocomposites Systems Focusing New Systems for Protection against COVID-19

The purpose of this work was to study the molecular dynamics, morphology, mechanical and thermal performance of nanomaterials formed by poly(vinyl alcohol) and molybdenum trioxide (PVA/MoO3) obtained through solution casting method, focusing new materials with therapeutic applications since the molybdenum trioxide exhibit an excellent antibacterial activity and could be a pathway to prevent viruses. The obtaining materials were characterized by conventional techniques as X-ray diffraction, thermogravimetric and dynamical-mechanical analysis. The unconventional low-field NMR relaxometry was used to evaluate the molecular dynamic and morphology of these systems. The results obtained showed that the MoO3 addition into PVA matrix promote an increase on the thermal stability at higher temperatures and a progressive increase on the rigidity of the PVA systems. Also changes in the molecular mobility of nanomaterials determined through the proton spin-lattice relaxation time showed that low proportion of molybdenum trioxide increased the intercalation of the poly(vinyl alcohol) chains between oxide lamellae while higher quantity of molybdenum trioxide caused an inverse effect on the oxide lamellae delamination. From those results the nanomaterials presented a mixed structural organization as intercalated and exfoliated morphologies. According to these first results, the nanocomposites obtained promise to be antimicrobial and antiviral agent to prevent COVID-19 and similar viruses.

Power of Aerogel Platforms to Explore Mesoscale Transport in Catalysis.

We describe the opportunity to deploy aerogels-an ultraporous nanoarchitecture with co-continuous networks of meso/macropores and covalently bonded nanoparticulates-as a platform to address the nature of the electronic, ionic, and mass transport that underlies catalytic activity. As a test case, we fabricated Au||TiO2 junctions in composite guest-host aerogels in which ∼5 nm Au nanoparticles are incorporated either directly into the anatase TiO2 network (Au "in" TiO2, AuIN-TiO2 aerogel) or deposited onto preformed TiO2 aerogel (Au "on" TiO2, AuON/TiO2 aerogel). The metal-meets-oxide nanoscale interphase as visualized by electron tomography feature extended three-dimensional (3D) interfaces, but AuIN-TiO2 aerogels impose a greater degree of Au contact with TiO2 particles than does the AuON/TiO2 form. Both aerogel variants enable transport of electrons over micrometer-scale distances across the TiO2 network to Au||TiO2 junctions, as evidenced by electron paramagnetic resonance (EPR) and ultrafast visible pump-IR probe time-resolved absorption spectroscopy. The siting of gold nanoparticles in the TiO2 network more effectively disperses trapped electrons. Density functional theory (DFT) calculations find that increased physical contact between Au and TiO2, induced by oxygen vacancies, produces increased hybridization of midgap states and quenches unpaired trapped electrons. We assign the apparent differences in electron-transport capabilities to a combination of the relatively better-wired Au||TiO2 junctions in AuIN-TiO2 aerogels, which have a greater capacity to dilute accumulated charge over a larger interfacial surface area, with an enhanced ability to discharge the accumulated electrons via catalytic reduction of adsorbed O2 to O2- at the interface. Solid-state 1H nuclear magnetic resonance experiments show that proton spin-lattice relaxation times and possibly proton diffusion are strongly coupled to Au||TiO2 interfacial design, likely through spin coupling of protons to unpaired electrons trapped at the TiO2 network. Taken together, our results show that Au||TiO2 interfacial design strongly impacts charge carrier (electron and proton) transport over mesoscale distances in catalytic aerogel architectures.

Noninvasive MRI Native T1 Mapping Detects Response to MYCN-targeted Therapies in the Th-MYCN Model of Neuroblastoma.

Noninvasive early indicators of treatment response are crucial to the successful delivery of precision medicine in children with cancer. Neuroblastoma is a common solid tumor of young children that arises from anomalies in neural crest development. Therapeutic approaches aiming to destabilize MYCN protein, such as small-molecule inhibitors of Aurora A and mTOR, are currently being evaluated in early phase clinical trials in children with high-risk MYCN-driven disease, with limited ability to evaluate conventional pharmacodynamic biomarkers of response. T1 mapping is an MRI scan that measures the proton spin-lattice relaxation time T1. Using a multiparametric MRI-pathologic cross-correlative approach and computational pathology methodologies including a machine learning-based algorithm for the automatic detection and classification of neuroblasts, we show here that T1 mapping is sensitive to the rich histopathologic heterogeneity of neuroblastoma in the Th-MYCN transgenic model. Regions with high native T1 corresponded to regions dense in proliferative undifferentiated neuroblasts, whereas regions characterized by low T1 were rich in apoptotic or differentiating neuroblasts. Reductions in tumor-native T1 represented a sensitive biomarker of response to treatment-induced apoptosis with two MYCN-targeted small-molecule inhibitors, Aurora A kinase inhibitor alisertib (MLN8237) and mTOR inhibitor vistusertib (AZD2014). Overall, we demonstrate the potential of T1 mapping, a scan readily available on most clinical MRI scanners, to assess response to therapy and guide clinical trials for children with neuroblastoma. The study reinforces the potential role of MRI-based functional imaging in delivering precision medicine to children with neuroblastoma. SIGNIFICANCE: This study shows that MRI-based functional imaging can detect apoptotic responses to MYCN-targeted small-molecule inhibitors in a genetically engineered murine model of MYCN-driven neuroblastoma.

NMR studies of molecular ordering and molecular dynamics in a chiral liquid crystal with the SmC_{α}^{*} phase.

Molecular dynamics of the antiferroelectric liquid crystal 4'-(octyloxy)biphenyl-4-carboxylate2-fluoro-4-[(octyl-2-yloxy)carbonyl]phenyl (abbreviated as D16) was investigated using different nuclear magnetic resonance (NMR) techniques. D16 molecules form a smectic-C_{α}^{*} phase (SmC_{α}^{*}) in an extremely wide temperature range (∼10 °C). Due to a small tilt of the molecules, this phase is characterized by short switching times, important for new photonic applications. The proton spin-lattice relaxation times were measured in isotropic (Iso), smectic-A (SmA), and SmC_{α}^{*} phases over a wide frequency range of five decades, with conventional and fast field-cycling NMR techniques. This approach allowed a comparison of the essential processes of molecular dynamics taking place in these phases. On the basis of NMR relaxometry measurements, we present a description of the motional behavior of liquid crystal molecules forming SmC_{α}^{*}. Pretransitional effects were observed in wide temperature ranges in both the isotropic and SmA phases in D16. The ^{1}H fast field-cycling NMR measurements were supplemented with NMR diffusometry and ^{19}F NMR spectroscopy.

NMR and NQR study of polymorphism in carbamazepine

Four polymorphic forms of carbamazepine have been simultaneously investigated by 1H NMR and 14N NQR. The results show that the proton spin-lattice relaxation time and the 14N NQR spectra can be used to differentiate between various polymorphic forms. Spontaneous transformations from Form II to Form III and from Form IV to Form III have been investigated through their influence on the 14N NQR spectrum and the proton NMR signal and spin-lattice relaxation. The 14N NQR spectra prove that in the observed polymorphic forms of carbamazepine the hydrogen bonded dimers of carbamazepine molecules are the basic elements of the crystal structure. The dimers are centrosymmetric in Forms III and IV and in metastable polymorphic form occurring during the transformation of Form IV to Form III. Two non-equivalent molecular positions are observed in Form II with the occupation ratio 1:1 and in Form I with the occupation ratio either 2:1 or 3:1. The 14N NQR data are related to the published crystal structures. Possible reasons for the mismatch of the X-ray and NQR data for Forms I and II are discussed.

Nanoscale rotational dynamics of four independent rotators confined in crowded crystalline layers.

We report a study where Car-Parrinello molecular dynamics simulations and variable-temperature (30-300 K) 1H spin-lattice relaxation time experiments nicely complement each other to characterize the dynamics within a set of four crystalline 1,4-diethynylbicyclo[2.2.2]octane (BCO) rotors assembled in the metal-organic rotor, {Li+4(-CO2-Ph-BCO-py)4(H2O)8}·2DMF. The remarkable finding of this work is that, despite the individual rotational barriers of four rotors being indiscernible and superimposed in a broad relaxation process, we were able to unravel a strongly interrelated series of rotational motions involving disrotatory and conrotatory motions in pairs as well as rotational steps of single rotators, all three processes with similar, sizeable rotational barriers of 6 kcal mol-1. It is noteworthy that DFT molecular dynamics simulations and variable-temperature (30-300 K) proton spin-lattice relaxation time experiments deliver the same high value for the rotational barriers stressing the potential of the combined use of the two techniques in understanding rotational motion at the nanoscale.

Phase Behavior of Amorphous Solid Dispersions of Felodipine: Homogeneity and Drug-Polymer Interactions.

In the current investigation, the role of drug-polymer hydrogen bonding (H-bonding) with respect to the phase behavior of amorphous solid dispersions (ASDs) is studied in depth on a nanometer level. Melt-quenched dispersions of felodipine (FEL) with poly(vinylpyrrolidone), or PVP, poly(vinylpyrrolidone-co-vinylacetate), or PVP/VA, and poly(vinylacetate), or PVAc, were prepared at drug loadings of 50-90% w/w. Modulated differential scanning calorimetry (MDSC) was used to detect microscopic homogeneity for each set of ASDs. A single composition dependent glass transition temperature (Tg) was observed over the entire composition range in MDSC data for each set of ASDs; however some samples within each set of ASDs showed a crystallization exotherm and corresponding melting endotherm in the first heating scan. Solid-state nuclear magnetic resonance spectroscopy (SSNMR) was further employed to understand phase homogeneity in these systems. The proton spin-lattice relaxation times in the laboratory and rotating frame (1H T1 and T1ρ) for the drug and individual polymer for each set of ASDs were measured to evaluate phase homogeneity. On the basis of proton relaxation measurements, it was revealed that FEL:PVP and FEL:PVP/VA ASDs exhibited better compositional homogeneity than FEL:PVAc ASDs. The strength and the extent of H-bonding were studied by using 13C SSNMR spectra. In addition, deconvolution of the carbonyl region of amorphous FEL revealed that 40% of amorphous FEL molecules were hydrogen bonded (H-bonded) through dimers and the remaining 60% were free/non H-bonded. The dimer fraction decreased as the polymer content increased for each set of ASDs, while the free fraction increased. This indicated that the polymers containing hydrogen bond acceptor groups disrupted dimers and formed intermolecular H-bonding interactions with FEL. The strength and extent of FEL:polymer H-bonding was rank ordered as PVP > PVP/VA > PVAc. These findings were also confirmed through DFT calculations on these systems. Our results suggest that drug-polymer H-bonding interaction may impact the phase homogeneity in ASDs formulated by a specific method. The data from the current study further demonstrate that SSNMR is a powerful tool for characterizing phase homogeneity in ASDs with sub-50 nm resolution. In addition, SSNMR can provide insights into drug-polymer interactions and speciation in ASDs.

Investigations of the <italic>T</italic>1 Temperature Dependence of Protons in Water and Contrast Agents Using a High-<italic>T</italic>c DC-SQUID-Based ULF NMR System

The temperature dependence of proton's spin-lattice relaxation time T 1 in water samples and Gd-based contrast agents with a measurement field of 72 μ T was systematically studied by dc-SQUID-based ultralow field (ULF) nuclear magnetic resonance (NMR) spectrometer. The temperature of samples was controlled by a thermostatic bath and the standard error of T 1 was around 0.01 s within five different groups, the results showed that T 1 had a similar linear temperature dependence when it was compared to conventional NMR data and varied with the purity of the water samples. Then, the relaxivity r 1 of Gd-based metal-organic frameworks (MOFs) and Gd-DTPA (where DTPA is diethylene triamine pentaacetate) were also studied. Both of them had a much higher r 1 in ULF NMR than conventional NMR, which was around 45 mM−1·s−1 and 98 mM−1·s−1, respectively; however, the T 1 of Gd-based contrast agents did not follow the linear temperature dependence, and the relaxivity r 1 would not be influenced by temperature, which implies Gd-MOFs and Gd-DTPA are also high performance T 1 contrast agents in ULF NMR and MRI.

Tunable ionization degree in cationic polyurethanes and effects on phase separation

A linear non-ionic hard-soft segmented polyurethane (PU0) was prepared by the prepolymer synthesis method. The isocyanate terminated prepolymer, formed by a short and rigid aromatic diisocyanate and a long flexible poly(tetramethylene oxide) (PTMO), was chain extended with a piperazine (PIP) diol derivative. The non-ionic polyurethane was then ionized by a post-modification method, i.e. alkylation of the piperazine nitrogen atoms, thus obtaining cationomers with three different ionization degrees, named PU10, PU50, PU80. The polymers were characterized by means of FT-IR spectroscopy, solution and solid state Nuclear Magnetic Resonance (NMR) spectroscopies, Differential Scanning Calorimetry (DSC) and ThermoGravimetric Analysis (TGA). The chemical structure of the obtained polymers and their cationic content was confirmed by solution state 1H NMR. It was found that the methylation occurs quantitatively up to 50% of the PIP nitrogen atoms and that, even if a large excess of methylating agent is used, in our operating conditions a maximum of 80% of the PIP nitrogen atoms are ionized. All the characterization techniques used suggested that an increasing ionization degree induces a better phase separation between hard and soft domains, with a lower amount of diisocyanate units dispersed in the soft phase. In particular, FT-IR showed that the introduction of ionic sites modifies the hydrogen bond network and induces a better aggregation of the rigid units. In addition, DSC showed that (i) the glass transition temperature values of the polymers decrease and tend to that measured for pure PTMO upon increasing ionization; (ii) a crystalline phase due to PTMO packing in ordered structures appears at the highest ionization degrees, similarly to pure PTMO. 1H Time-Domain NMR and 13C solid state NMR revealed an increase in PTMO mobility with increasing ionic content, in agreement with DSC results.The measurements of proton spin lattice relaxation times in both the laboratory (T1) and rotating (T1ρ) frames allowed limits on the size of the hard domains to be estimated. T1ρ data hint at a phase demixing effect upon increasing the ionization degree.

The “Wine-T1” NMR experiment for novel wine-metabolome fingerprinting with nuclear-spin relaxation

In agreement with the draft resolution OENO-SCMA 17-618 at step 5 “Quantitation of glucose, malic acid, acetic acid, fumaric acid, shikimic acid and sorbic acid in wine using proton nuclear magnetic resonance spectroscopy(1H NMR)” said technique has been recently accepted within the OIV chair as a primary quantitative analytical technique for beverage analysis such as wine. However, poor chemical shift dispersion in1H NMR spectra severely penalizes quantification within overlapped or crowded regions. To outflank said penalization and quantify metabolites in signal overcrowding situations, the novel “Wine-T1” experiment is proposed. The novel scheme comprises the addition of a second dimension, wherein the proton spin-lattice relaxation times (T1-{1H}) of each metabolite's spin-system is correlated to a chemical-shift dimension. The new experiment includes a water and ethanol signal pre-saturation module, prior to the T1saturation-inversion recovery dimension in order to maximize signal-to-noise ratio of wine metabolome NMR spectra. “Wine-T1” pulse sequence can be adapted to all commercial spectrometers (Bruker, Varian/Agilent, Jeol) and with acquisition times in the order of minutes, it should be considered as a fast repetition method to produce a robust metabolome fingerprint that has not been described before, to the best of our knowledge.

Reduction of the 13C cross-polarization experimental time for pharmaceutical samples with long T1 by ball milling in solid-state NMR

Many pharmaceutical samples have notably long 1H T1 (proton spin-lattice relaxation time), leading to lengthy experiments lasting several days in solid-state NMR studies. In this work, we propose the use of ball milling on the pharmaceutical samples to reduce the 1H T1, which also leads to enhanced sensitivity in {1H}-13C Cross-Polarization (CP) experiments due to reduced particle sizes and increased surface areas of the samples. Experimentally, we determined that depending on the substrates and milling time, the signal-to-noise ratio (S/N) of a 1D 13C CP spectrum can be increased by a factor of 3–6, which means that the experimental time can be shortened by a factor of 9–36. Furthermore, the application of simple ball-milling within a short time avoids the amorphization of the studied samples such that no signal due to amorphous state is observed in the 13C CP spectrum. This simple ball milling method used for sensitivity enhancement can be further applied in the SS-NMR studies of pharmaceutical samples.

A New High-Performance Gadonanotube-Polymer Hybrid Material for Stem Cell Labeling and Tracking by MRI.

A gentle, rapid method has been developed to introduce a polyacrylic acid (PAA) polymer coating on the surface of gadonanotubes (GNTs) which significantly increases their dispersibility in water without the need of a surfactant. As a result, the polymer, with its many carboxylic acid groups, coats the surface of the GNTs to form a new GNT-polymer hybrid material (PAA-GNT) which can be highly dispersed in water (ca. 20 mg·mL−1) at physiological pH. When dispersed in water, the new PAA-GNT material is a powerful MRI contrast agent with an extremely short water proton spin-lattice relaxation time (T 1) which results in a T 1-weighted relaxivity of 150 mM−1·s−1 per Gd3+ ion at 1.5 T. Furthermore, the PAA-GNTs have been used to safely label porcine bone-marrow-derived mesenchymal stem cells for magnetic resonance imaging. The labeled cells display excellent image contrast in phantom imaging experiments, and transmission electron microscopy images of the labeled cells reveal the presence of highly dispersed PAA-GNTs within the cytoplasm with 1014 Gd3+ ions per cell.

The effect of modified cellulose particles on morphology and properties ethylene vinyl acetate copolymer

More ecofriendly packaging can be obtained with the use of cellulose as a reinforcement and barrier. For this work, cellulose particles were incorporated in EVA matrix to obtain transparent EVA composite films with cellulose particles at different concentrations focusing on the improvement of the barrier properties. The films were obtained by solution casting. Commercial microcrystalline cellulose (MCC) was modified with glacial acetic acid, reducing the particle size. These modifications were monitored by FTIR, XRD, NMR and SEM. The composites formed by EVA/MCC were characterized by XRD, thermogravimetric analysis and mechanical properties to understand the influence of these particles on the displacement of the crystalline planes of the polymer matrix. The degree of crystallinity was also altered as larger concentrations of cellulose were added to EVA. TGA results showed no significant changes in the thermal degradation temperature of the material and, from DSC, it was seen that cellulose did not behave as a nucleating agent in EVA. The storage modulus obtained from the DMA analysis was inversely proportional to the cellulose content, indicating that there was an increase in the rigidity of the material caused by the dispersion of cellulose, which acts as a material reinforcement. These data were corroborated by the increase in the proton spin-lattice relaxation time values determined by NMR relaxometry technique, which provides information on sample molecular behavior, confirming the molecular interaction between material components.