Proton Spin-spin Relaxation Times Research Articles

Dehydration and the ripening of ‘Hass’ avocado fruit

ABSTRACT Water loss from fruit, including avocado, has been reported to accelerate ripening. ‘Hass’ avocado fruit were imaged by MRI shortly after harvest and the proton density (PD) and spin-spin relaxation time constant T 2 data extracted for regions of interest. Water was then driven off at two rates (designated as Fast and Slow) with respiratory activity and ethylene production of the individual fruit monitored as non-destructive markers of ripening. Fruit from the Slow drying treatment ripened several days later, but with less water loss, than fruit from the Fast drying treatment. There was a correlation in the Slow drying treatment for fruit with higher PD and T 2 values to take longer to ripen. This trend was clearest for the inner mesocarp data. However, there was a weaker, inverse, relationship for fruit in the Fast drying treatment. Therefore, the relationship between water content and ripening seems to be affected by the rate of water loss. It is concluded that the capacity for water loss to accelerate avocado fruit ripening is confirmed. It also appears that MRI data collected at harvest may be indicative of the time that a fruit would naturally take to ripen.

Proton spin relaxation study with pulsed NMR on the plasticization of Na+ ion-selective electrode membranes prepared from PVCs with different degrees of polymerization.

The proton spin-spin relaxation times (T2) of ion-selective electrode membranes with differences in the polymerization degree of the incorporated poly(vinyl chloride) (PVC) polymers were investigated. T2 measurements were performed using Hahn-Echo, Solid-Echo and Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. Analyses of the T2 measurements by Hahn-Echo pulse sequences could realize the estimation of the homogeneity and compatibility for a series of ion-selective electrode membranes and reveal a relationship with the electromotive force (EMF) response in the low-concentration region of the Na+ ions. On the other hand, the normalized derivative spectra from T2 measurements by Solid-Echo and CPMG pulse sequences could approximately visualize the degree of plasticization for such potentiometric polymeric membranes. Moreover, differences in the polymerization degrees of the incorporated PVCs were scarcely found to affect the selectivity coefficients of the Na+-ISEs based on bis(12-crown-4).

Effect of Ultra-Turrax on Nanocellulose Produced by Acid Hydrolysis and Modified by Nano ZnO by Sol-Gel Method

Cellulose nanocrystals (NCC) and cellulose nanofibrils (CNF) were obtained by a single step process, with synergy between 64% sulfuric acid hydrolysis and high shear from ultra-turrax stirring, which is an advantageous process for disintegrating cellulose microcrystalline and also may improve the hydrolysis process. The surface modification on the cellulose was performed by the sol-gel process, in which the sulfate groups from hydrolysis were replaced by nanoparticles of zinc oxide, which led to the increase of up to 54°C Tonset, according to thermogravimetric analysis (TGA) results. The morphology and crystallinity degree were characterized by Helium Ion Microscopy (HIM), atomic force microscopy (AFM) and X-ray diffraction. In addition, the ZnO band was observed in Fourier transform infrared spectroscopy, furthermore, the change in the zeta potential confirmed the cellulose modification. The changes in the values of proton spin-spin relaxation time for the systems showing the confined hydrogen in the rigid domains, confirmed the results observed with the aforementioned techniques, for both cellulose after hydrolysis and ZnO modified cellulose, suggesting that ZnO disrupted crystal formation in cellulose.

Enhanced hydrolysis and acidification of cellulose at high loading for methane production via anaerobic digestion supplemented with high mobility nanobubble water

In this study, CH4 production from anaerobic digestion (AD) of refractory cellulose was investigated at a high loading of 3.5 (VScellulose/VSinoculum) under nanobubble water (NBW) addition. A longer proton spin-spin relaxation time (2611–2906 ms) of NBW during 35 days’ storage reflected its high mobility and diffusion of water molecules. Higher volatile fatty acids were yielded at the hydrolysis-acidification stage under NBW addition. Methanogenesis tests showed that Air-NBW and CO2-NBW supplementation accelerated the utilization of crystalline cellulose, achieving methane yields of 264 and 246 mL CH4/g-VSreduced, increasing by 18% and 10% compared to deionized water addition (the control), respectively. In addition, under NBW addition the cellulose crystallinity reduction was enhanced by 14–20% with microbial community being enriched with hydrolytic and methanogenic bacteria. Results from this work suggest that NBW environment with no chemical addition and relatively low energy consumption is advantageous for enhanced AD process of cellulosic biomass.

Effect of autoclaving on the mechanical properties and structure of the giant squid hydrolysate‐polysaccharide gel

Fish hydrolysates are an attractive option for preparing composite gel foods. However, not much is known regarding their gel properties. Here, we investigated the effect of the autoclaving treatment (121°C, 10 min) on the microstructure and properties of the giant squid hydrolysate-konjac glucomannan-κ-carrageenan-locust bean gum gel (GSH-P gel). The nuclear magnetic resonance proton spin-spin relaxation time (T2 ) measurements indicated that autoclaving led to stronger water-binding ability of the GSH-P gel. The rheological measurements indicated that autoclaving led to significantly higher viscoelastic modulus and gel strength. The results of confocal laser scanning microscopy and small-angle X-ray scattering indicated that the phase separation of polysaccharides and proteins/peptides was enhanced by autoclaving, and the polysaccharides swelled better, resulting in less, but ordered, network structures. Autoclaving had a similar, but insignificant, positive effect on the polysaccharide (P) gel. Thus, GSH seems to play an important role in the process of polysaccharide gelation. This study shows that autoclaving can alter the structure and improve the properties of the GSH-P gel.

Synthesis of Various Glycopolymers Bearing Sialyllactose and the Effect of Their Molecular Mobility on Interaction with the Influenza Virus.

Synthetic glyco-ligands are promising candidates for effective nanomedicines against pathogens. Glycopolymers bearing sialyl-oligosaccharides interact with hemagglutinin present on the surface of influenza viruses. In designing new glycopolymers that further enhance the interaction with viruses, both static and dynamic properties of the glycopolymers should be considered. In this report, we evaluated the correlation between dynamic properties of glycopolymers and their interaction with the influenza virus. Glycopolymers with pendant sialyllactoses and various linker structures were synthesized, and their molecular mobility was determined by proton spin-spin relaxation time measurements. The molecular mobility of the glycounits increased as the length of the linker structures increased. Interestingly, glycopolymers with the medium-length linker structure exhibited the strongest interaction with the influenza virus, suggesting that optimal molecular mobility is required for maximizing multivalent interactions with the target.

Water immobilization by glass microspheres affects biological activity

We recently reported that the water holding capacity of myofibrillar protein hydrogels could be increased upon addition of small amounts of microparticles, particularly glass microspheres. Glass microspheres were found to decrease the spin-spin relaxation time (T2) of water protons in the gels, which was interpreted as enhanced water binding by the glass. We were thus interested in determining whether the observed effects on water proton relaxation were a direct consequence of water-glass interactions. Here we show how glass microspheres reduce the mobility of pure water, reflected in large decreases in the T2 of water protons, decreases in the self-diffusion coefficient of water molecules, a lower water activity, and strengthening of O-H bonds. Even though glass is considered an inert material, glass microspheres were shown to inhibit the growth of human embryonic kidney cells, and stimulate or inhibit the growth of leukemia and monocytic lymphoma cells in vitro, depending on dose and time. The germination of alfalfa seeds and the growth of E.coli cells were also inhibited upon exposure to glass microspheres. This work indicates that the properties and behavior of materials, even ones considered inert, can be affected by their size. These observations suggest possible toxicological consequences of exposure to microparticles, but also open us possibilities to affect cellular/organism function via modulation of macromolecular hydration.

Complexation of κ-carrageenan with gelatin in the aqueous phase analysed by 1H NMR kinetics and relaxation

The 1H NMR spectroscopy is used to study the kinetics of gelation in the aqueous mixtures of κ-carrageenan with gelatin. The time dependence of NMR signals intensities shows that the kinetics of gel formation consists of classical ‘fast’ (rate constant k≈6h−1) and ‘slow’ (k≈1h−1) periods, corresponding to a coil→helix transition and subsequent aggregation of helices. Upon increase of the κ-carrageenan/gelatin (w/w) ratio Z the rate of the fast process slows down by a factor of 1.6–2.4. Further analysis was done by studying the dependence of spin-spin relaxation times of protons of gelatin on Z in the aqueous phase. A qualitative scheme describing hydrogel formation in the complex solution is given. It is hypothesized that at higher concentration of PECs the hydrogel structure network is stabilized by three types of nodes: triple helices of gelatin and intra-/inter-molecular double helices of κ-carrageenan.

Исследование молекулярной подвижности протонов воды при взаимодействии с химически модифицированными крахмалами методами ДСК и ЯМР-релаксации, "Химическая физика"

The change of water protons mobility in the system chemically modified starches – water were investigated by DSC and NMR-relaxation methods. The amount of unfrozen water at subzero temperature as well as additional unfrozen water which appears after gelatinization have lower values for chemically modified starches in comparison with the native starch. The proton spin-spin relaxation time Т2 for chemically modified starch samples, conventionally referred to the fraction of water inside the starch granules, are monotonically decreasing at heating, while for the native starch this dependence has extreme character. The study of dispersion of 7% gels, characterizing the rate of chemical exchange of water protons with the protons of hydroxyl groups of polysaccharides, demonstrated the absence of such dependence for chemically modified starches at the operating frequency of measuring device 20 МHz. Received data suggest considerable destructive changes in chemically modified starches structure.

The Influence of Organo-Clay Ratio in the HIPS-OMMT Nanocomposites Analyzed by Proton Spin-Lattice and Spin-Spin Relaxation Times

Spin-lattice and spin-spin relaxation times are one of the most attractive tools in the solid-state nuclear magnetic resonance spectroscopy to evaluate the level of clay dispersion in the nanocomposite matrices. The efficiency of the relaxation processes can be used to evaluate the nanoparticles intermolecular interactions and, consequently, the dispersion of them in the polymer matrix, the molecular dynamic of the hybrid compounds, as well as the molecular domains formation in an organic material. The determination of relaxation parameters was carried out to evaluate the organoclay exfoliation and intercalation process in the polymeric matrix, in addition to their dispersion and distribution in the matrix. The proton NMR relaxation data showed that the polymeric nanomaterials investigated presented good intermolecular interaction that promoted good nanoparticles dispersion and distribution in the hybrid materials. The proportion of 2% clay promoted a greater heterogeneity in the matrix compared to other ratios; 1% clay influenced only to the higher molecular rigidity phase; and 3% clay had a decrease in heterogeneity compared to 2% though still influenced the matrix as a whole. These results prove the efficiency of NMR technique in the evaluation of nanofillers interaction with polymer matrices, as well as their dispersion and distribution.

Rapid Method Based on Proton Spin-Spin Relaxation Time for Evaluation of Freezing Damage in Frozen Fruit and Vegetable

This study proposed the use of nuclear magnetic resonance (NMR) technique based on proton spin–spin relaxation time (T2) of water to indicate freezing damage in frozen fruit and vegetable. T2 value can be used to indicate water content in the cells of samples. The results showed that T2 values of frozen-thawed samples were lower than those of fresh (undamaged) samples. This is because of the cell membrane damage due to the formation of ice crystals, leading to leakage of water. The microstructural changes of frozen-thawed barley coleoptile tissue and apple parenchyma tissue were evident when observed using a high-resolution three-dimensional X-ray microscope and an optical microscope, respectively. Changes in the T2 value could be related directly to the microstructural changes of barley coleoptile tissue and apple parenchyma tissue. T2 value can be measured in far less time than conventional methods and is considered a rapid and effective method to indicate freezing damage in frozen foods. Practical Applications Freezing damage (e.g., cell shrinkage, membrane damage and loss of water holding capacity) caused by ice crystal formation affects the quality of frozen food products after thawing. This study proposed an alternative nuclear magnetic resonance (NMR) technique based on proton spin–spin relaxation time (T2) of water to indicate freezing damage in frozen fruit and vegetable. NMR measurement of T2 value can be performed in far less time than conventional freezing damage measurements (e.g., electrical conductivity and microscopy) and thus can be used as a rapid and reliable technique for determination of water in food samples and subsequently can be used to indicate freezing damage caused by ice crystal formation.

Functional, histological and biomechanical characterization of wheat water-mutant leaves.

A wheat (Triticum turgidum subsp. durum) mutant, generated with sodium azide from wild-type (WT) cv. 'Trinakria', differs in its water affinity of dry leaves, and was designated as a water-mutant. Compared with the WT, water-mutant leaves have lower rates of water uptake, while stomatal and cuticular transpiration do not differ. The nuclear magnetic resonance proton signals used for image reconstruction of leaf cross sections showed differences between these genotypes for the T1 proton spin-density and the T2 proton spin-spin relaxation time. Structural and histochemical analyses at midrib level showed that the water-mutant has thinner leaves, with more and smaller cells per unit area of mesophyll and sclerenchyma, and has altered staining patterns of lignin and pectin-like substances. Stress-strain curves to examine the rheological properties of the leaves showed a biphasic trend, which reveals that the tensile strength at break load and the elastic modulus of the second phase of the water-mutant are significantly higher than for the WT. These data support the proposal of interrelationships among local biophysical properties of the leaf, the microscopic water structure, the rheological properties and the water flux rate across the leaf. This water-mutant can be used for analysis of the genetic basis of these differences, and for identification of gene(s) that govern these traits.

The Use of Solid State NMR to Evaluate EVA/Silica FILMs

Nanocomposites based on ethylene-co-vinyl acetate (EVA) and silica oxide (SiO2), with nanometric size (40nm) were prepared by solution process, employing chloroform as solvent. The nanocomposites were mainly characterized by solid state nuclear magnetic resonance spectroscopy (NMR). From the methodology employed polymer matrix was evaluated by the determination of proton nuclear spin-lattice relaxation time (T1H) and spin-spin relaxation time (T2H) employing low field NMR spectrometer and also applying carbon-13 (13C) solid-state NMR techniques and proton spin-lattice relaxation time in the rotating frame (T1pH) by high field NMR. The nanoparticle, silica oxide, was analyzed by silicon-29 (29Si) NMR MAS spectrum. The evaluation of relaxation time showed an increase in the proton spin-lattice relaxation time, because of silicon nucleus interaction with polymer chains promoting an increase in the sample rigidity, which is a result of good silica oxide dispersion in the polymeric matrix. The nanomaterial with 5% of SiO2presented good dispersion of silica oxide in the polymeric matrix, because of the formation of strong intermolecular interaction.

Effect of electrization on molecular mobility in gold nanocomposites based on arabinogalactan

A correlation is found between the proton spin-spin relaxation times in gold nanocomposites based on arabinogalactan in aqueous solutions and the maximum conducting layer thicknesses of films cast from solutions of composites. The obtained correlation is considered from the viewpoint of electrization’s effect on the mobility of macromolecules of the investigated polymer nanocomposites. The dependence of arabinogalactan mobility on the type of solvent (H2O or D2O) is established, and a conclusion is drawn as to the effect of the hydrogen bonds of arabinogalactan with solvent on polymer mobility in solutions.

Stability and Cytotoxicity of Well-Dispersed Magnetite Nanoparticles Prepared by Hydrothermal Method

A preparation of well-dispersed magnetite nanoparticles was demonstrated in this study. Magnetite nanoparticles (MNPs) were synthesized by a hydrothermal method using aloe vera extract and serial centrifugation was employed to separate the sizes of well-dispersed particles. Well-dispersed MNPs with average sizes of 241, 227, 195, 165, 141 and 93 nm were obtained. They were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and vibrating sample magnetometry (VSM). XRD results indicated the MNPs were Fe3O4. Magnetic hysteresis loop measurements of the samples showed superparamagnetic properties. Pulsed nuclear magnetic resonance (NMR) showed stable proton (1H) spin-spin relaxation time (T2) values of water with suspended magnetite nanoparticles over a time course of 20 min, suggesting they were well-dispersed. The synthesized magnetite nanoparticles showed low cytotoxicity to NIH 3T3 cells at concentrations of 1-10%.

INTERACTION BETWEEN DRUGS AND BIOMEDICAL MATERIALS I: BINDING POSITION OF BEZAFIBRATE TO HUMAN SERUM ALUBMIN

The interaction between bezafibrate (BZF) and human serum albumin (HSA) was investigated by equilibrium dialysis. Since the binding constant of BZF to HSA was independent of ionic strength and decreased with the addition of fatty acid, the interaction between BZF and HSA was considered to be due to hydrophobic mechanism. Chemical shifts in 1H-NMR spectra of BZF were independent of the concentration of BZF and addition of HSA. Spin-lattice relaxation time (T1) and spin-spin relaxation time (T2) of respective protons of BZF were independent of the concentration, but depended on the concentration of HSA added. The binding position of BZF to HSA was considered to involve the hydrophobic aromatic moiety of BZF from the ratio of spin-spin relaxation rates (1/T2) of BZF bound to HSA and free BZF.

Engineering Cooperative Nanosytems

Our laboratory is interested in engineering tools and systems using nanoparticle scaffolds to transform the diagnosis and treatment of cancer. We aim to integrate nanomaterials with enhanced nanoscale properties and bioresponsive functionalities with our knowledge of the tumor microenvironment to explore this paradigm. Towards this end, we have developed and investigated nanoparticle conjugates based on three nanoparticle cores that harness features of the nanoscale: semiconductor quantum dots that exhibit size-based optical properties, dextran-coated iron oxide particles whose assembly alters the spin-spin relaxation time of hydrogen protons on magnetic resonance imaging, and polymer-coated gold nanorods that interact resonantly with near-infrared light. Our studies have shown how these nanoparticles specifically designed to enhance their interaction with the biological environment can help achieve targeting, triggered self-assembly, remote actuation with radiofrequency fields, sensing of kinase activity, and delivery of short interfering RNAs. In collaboration with Erkki Ruoslahti (Burnham Institute), we have explored how decorating the surface with peptides obtained from in vivo phage display can alter the properties of these nanoparticles and control their trafficking. To increase the accumulation of the nanoparticles at the tumor site we are exploring in vivo self-assembly of these particles. Our approach is inspired by platelets_natural microparticles that normally circulate in a latent form but can home to sites of injury and transform to an activated state, whereby they adhere and recruit more platelets. This results in assemblies of magnetic nanoparticles that may then acquire emergent properties, allowing either their enhanced visualization or remote actuation of drug delivery. More recently, we have also emulated biological systems where biological components remotely communicate via biological intermediates. The resultant nanoparticle formulations then act as a “system” to produce emergent behaviors for enhancing diagnosis and therapy.

Water mobility within arabinoxylan and β-glucan films studied by NMR and dynamic vapour sorption

The main purpose of this research was to determine the impact of the structure and organisation of polysaccharides on the hydration properties of the cell walls of cereal grains. In order to remodel the lamellar assembly of arabinoxylan (AX) and (1 → 3)(1 → 4)-β-D-glucan (BG) within the endosperm cell walls, films were prepared and analysed using dynamic vapour sorption and time domain nuclear magnetic resonance spectroscopy. The water diffusivities within the AX and BG films were measured at 20 °C by observing the water sorption kinetics within a mathematical model based on Fick's second law. The evolution of spin-spin relaxation times of water protons measured by increasing the temperature is explained by the additional contributions of motion of the protons of polysaccharides and/or rapid chemical exchanges of protons between water and hydroxyl groups of polysaccharides. The difference between patterns of water behaviour within the AX and BG films can be related to the difference in their nanostructures. The smaller nanopores of the BG films cause their nanostructure to be more compact.

Determining the sizes of micropores in activated charcoals by the pulsed NMR method

The pulsed NMR method was used to measure the nuclear spin-spin relaxation of protons of water adsorbed in micropores of activated charcoal (AC) samples with different porous structures. A correlation was found between the spin-spin relaxation time of water protons in AC with completely filled micropores and the volume density of water primary adsorption centers in the AC samples. An equation for approximating obtained dependences is proposed that allows us to determine the volume of micropores in AC.

Effect of chain rigidity on block copolymer micelle formation and dissolution as observed by 1H-NMR spectroscopy

Amphiphilic copolymers poly(methyl methacrylate-b-acrylic acid), poly(methyl methacrylate-b-methacrylic acid), poly(methyl acrylate-b-acrylic acid) and poly(methyl acrylate-b-methacrylic acid) were prepared by reversible addition fragmentation chain-transfer (RAFT) polymerization. The hydrophilic polyacid blocks were either synthesized directly or formed by the hydrolysis of poly(tert-butyl acrylate) or poly(tert-butyl methacrylate) blocks. The hydrophobic blocks consisted of either the more rigid, high glass transition temperature (Tg) poly(methyl methacrylate) or more flexible, low Tg poly(methyl acrylate) material. The hydrophilic blocks were either poly(methacrylic acid) (rigid, high Tg) or poly(acrylic acid) (flexible, low Tg). The micellization behavior of the polymers was studied by proton nuclear magnetic resonance (1H-NMR) spectroscopy in mixtures of 1,4-dioxane-d8 and D2O. All four polymers were soluble in neat dioxane. In solutions of higher water content, the polymers with the more rigid hydrophobic blocks formed into micelles as was evidenced by broadening of the resonances resulting from the protons in those blocks. At moderate water concentration (25–50%), dissolution of the micelles was observed upon heating the solution. No micellization was observed in polymers containing the less rigid poly(methyl acrylate) hydrophobic block regardless of the identity of the hydrophilic block. As further evidence of micellization formation and dissolution, the spin-lattice (T1) and spin-spin (T2) relaxation times of protons in the hydrophobic and hydrophilic blocks were measured. Significant differences in the relaxation times as functions of temperature and solvent concentration were observed between the hydrophilic and hydrophobic blocks of the micelle-forming polymers.