Water Behavior of Aerogels Obtained from Chemically Modified Potato Starches during Hydration

Aerogels are highly porous materials that are prepared by removing water held within a hydrogel in a manner that maintains the three-dimensional structure of the gel. Recently, there has been much interest in the preparation of aerogels from biopolymers, including starch. The applicability of native starches in the food industry is partially limited; therefore, the functional properties of starch are often improved by means of physical and/or chemical modification. The aim of the work was the analysis of molecular dynamics and the transport of water in aerogels obtained from native and chemically modified potato starches of the normal and waxy variety. Chemical modification with OSA (E 1450) as well as cross-linking with adipic anhydrite and acetylation (E 1422) had no significant impact on the hydration of potato starch aerogels as well as equilibrium water activity. The introduction of chemical moieties into starch macromolecules led to the improved binding of water by the biopolymer matrix; this was especially evident in the case of waxy starch derivatives. A increase in the amylopectin-to-amylose ratio of starch used for production of aerogels resulted in a decrease of equilibrium water activity along with spin-lattice relaxation time.

Synthesis of a New Polyanion Possessing Dense 1,2,3-Triazole Backbone

Polyanions are an important class of water-soluble polymers because polyanions are utilized in a wide range of industrial fields. It is thus a great challenge to develop polyanions with novel structures to make their applications broader. In this study, a new polyanion with a dense 1,2,3-triazole backbone, poly(4-azido-5-hexanoic acid) (poly(AH)), was synthesized by copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) polymerization of t-butyl 4-azido-5-hexanoate followed by hydrolysis of the t-butyl ester groups. Turbidimetric and potentiometric titration data indicated that poly(AH) was well soluble in water under basic conditions (pH < 7) and a weaker polyanion (apparent pKa = 5.4) than polyacrylic acid (apparent pKa = 4.5). Adsorption tests exhibited that sodium salt of poly(AH) (poly(AH)Na) adsorbed most preferably Fe3+ among the four metal ions examined, i.e., Cu2+, Pb2+, Li+, and Fe3+. 1H spin-lattice relaxation time measurements indicated that Fe3+ ions were adsorbed favorably onto the 1,2,3-triazole residues.

Room temperature coherent control of spin defects in hexagonal boron nitride

Optically active spin defects are promising candidates for solid-state quantum information and sensing applications. To use these defects in quantum applications coherent manipulation of their spin state is required. Here, we realize coherent control of ensembles of boron vacancy centers in hexagonal boron nitride (hBN). Specifically, by applying pulsed spin resonance protocols, we measure a spin-lattice relaxation time of 18 microseconds and a spin coherence time of 2 microseconds at room temperature. The spin-lattice relaxation time increases by three orders of magnitude at cryogenic temperature. By applying a method to decouple the spin state from its inhomogeneous nuclear environment the optically detected magnetic resonance linewidth is substantially reduced to several tens of kilohertz. Our results are important for the employment of van der Waals materials for quantum technologies, specifically in the context of high resolution quantum sensing of two-dimensional heterostructures, nanoscale devices, and emerging atomically thin magnets.

Study the Structure and Dynamics of Antifungal Agent Ketoconazole by CSA and Site-Specific Spin-Lattice Relaxation Time Measurements

An azole antifungal agent, ketoconazole, is widely used in the treatment of mucosal fungal infections related to AIDS immunosuppression, organ transplantation, and cancer chemotherapy. The structure and dynamics of ketoconazole are thoroughly studied by chemical shift anisotropy tensor and site-specific spin-lattice relaxation time measurements. The molecular correlation time at crystallographically different carbon sites is calculated by considering that the spin-lattice relaxation mechanism for the 13C nucleus is mainly governed by chemical shift anisotropy interaction and hetero-nuclear dipole-dipole coupling. The CSA parameters at the crystallographically distinct sites of ketoconazole are determined by two-dimensional phase adjusted spinning sideband (2D PASS) cross-polarization magic angle spinning (CP-MAS) solid-state NMR experiment. The site-specific spin-lattice relaxation time is measured by the Torchia CP experiment. The spin-lattice relaxation rate is slow for all the carbon nuclei sites except C2, C3, C4, C5, and C26 carbon nuclei reside on the piperazine ring and the methyl group. It suggests the close-pack arrangement of the molecule due to π-π stacking interaction. The molecular correlation time of all the carbon atoms reside on the benzene ring, 1,3-dioxolane ring, imidazole ring, and the 2,4-dichlorobenzene ring is of the order of 10-4 s, while it is of the order of 10-7 s for carbon atoms reside on the piperazine ring. The CSA parameters of the carbon nuclei on the piperazine ring (C2, C3, C4, C5), and the methyl group (C26) are very low compared to other carbon nuclei. The CSA parameters are very high for carbon nuclei reside on the benzene ring, imidazole ring, and the 2,4-dichlorobenzene ring due to the presence of π-electrons. A huge variation of the spin-lattice relaxation time and the molecular correlation time are observed for numerous carbon nuclei situated on the side-chain of ketoconazole. The spin-lattice relaxation time varies from 500 s to 8 s, and the molecular correlation time varies in the range of 10-4s to 10-7s. These types of investigations portrayed the correlation between the structure and dynamics of the antifungal drug ketoconazole, which will help to develop the advanced antifungal drugs. Additionally, the CSA information of the drug molecules will be immensely useful for NMR crystallography.

A Solid-State NMR Study of the Antibacterial Drug Cefpodoxime Proxetil

The structure-activity relationship of various molecular moieties of cefpodoxime proxetil is described by measuring Chemical shift anisotropy (CSA) tensor, spin-lattice relaxation time and molecular correlation time at twenty one crystallographically different carbon nuclei sites. Cefpodoxime proxetil molecule is associated with three rings, the aminothiazole ring, β-lactam ring, and the dihydrothiazine ring, which provide stability to the drug molecule towards β-lactamases and increase the affinity of the drug to PBPs receptors. A large variation of CSA parameters and motional degrees of freedom are observed among carbon nuclei reside on these three rings, which implies that the electronic environment, molecular conformation, and molecular dynamics are altered substantially within the ring. The substitution at the C7 position of the β-lactam ring (like acyl side chain, oxime group, and aminothiazole ring) is responsible for semi-synthetic incorporation. It also influences the antibacterial activity and the binding affinity of the drug with β-lactamase. A huge variation of the spin-lattice relaxation time and molecular correlation time is observed in this region. These types of description of the structure-activity relationship of the antibacterial drug cefpodoxime proxetil will be beneficial for developing the advanced antibacterial drugs, and it will also be useful in NMR crystallography.

The Role of Titanium Dioxide on the Hydration of Portland Cement: A Combined NMR and Ultrasonic Study

Titanium dioxide (TiO2) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO2 influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO2 were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO2 enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin–lattice relaxation time T1 results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T1 values and large capillary pores with long T1 values. During early hydration times, TiO2 is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO2 appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results.

Rapid mono and biexponential 3D-T1ρ mapping of knee cartilage using variational networks

In this study we use undersampled MRI acquisition methods to obtain accelerated 3D mono and biexponential spin–lattice relaxation time in the rotating frame (T1ρ) mapping of knee cartilage, reducing the usual long scan time. We compare the accelerated T1ρ maps obtained by deep learning-based variational network (VN) and compressed sensing (CS). Both methods were compared with spatial (S) and spatio-temporal (ST) filters. Complex-valued fitting was used for T1ρ parameters estimation. We tested with seven in vivo and six synthetic datasets, with acceleration factors (AF) from 2 to 10. Median normalized absolute deviation (MNAD), analysis of variance (ANOVA), and coefficient of variation (CV) were used for analysis. The methods CS-ST, VN-S, and VN-ST performed well for accelerating monoexponential T1ρ mapping, with MNAD around 5% for AF = 2, which increases almost linearly with the AF to an MNAD of 13% for AF = 8, with all methods. For biexponential mapping, the VN-ST was the best method starting with MNAD of 7.4% for AF = 2 and reaching MNAD of 13.1% for AF = 8. The VN was able to produce 3D-T1ρ mapping of knee cartilage with lower error than CS. The best results were obtained by VN-ST, improving CS-ST method by nearly 7.5%.