Lyotropic Aqueous 2-Picolinium Ionic Liquid Crystals and Their Shear-Induced Foams.

1-Dodecyl-2-methylpyridinium bromide ([C-2-Pic][Br]) and 1-hexadecyl-2-methylpyridinium bromide ([C-2-Pic][Br]) are two ionic liquid crystals presenting thermotropic smectic phases above 80 °C. Aiming to take advantage of the liquid crystalline properties at lower temperatures, lyotropic aqueous systems were prepared from these two organic salts. Both systems were characterized by polarized optical microscopy (POM), X-ray powder diffraction (XRD), and fast field cycling nuclear magnetic resonance (FFC-NMR) relaxometry to assess their texture, phase structure, and molecular dynamics, respectively.

Butterfly Effect in Cytarabine: Combined NMR-NQR Experiment, Solid-State Computational Modeling, Quantitative Structure-Property Relationships and Molecular Docking Study.

Cytarabine (Ara-C) is a synthetic isomer of cytidine that differs from cytidine and deoxycytidine only in the sugar. The use of arabinose instead of deoxyribose hinders the formation of phosphodiester linkages between pentoses, preventing the DNA chain from elongation and interrupting the DNA synthesis. The minor structural alteration (the inversion of hydroxyl at the 2' positions of the sugar) leads to change of the biological activity from anti-depressant and DNA/RNA block builder to powerful anti-cancer.

Elucidating the Role of Noncovalent Interactions in Favipiravir, a Drug Active against Various Human RNA Viruses; a H-N NQDR/Periodic DFT/QTAIM/RDS/3D Hirshfeld Surfaces Combined Study.

Favipiravir (6-fluoro-3-hydroxypyrazine-2-carboxamide, FPV), an active pharmaceutical component of the drug discovered and registered in March 2014 in Japan under the name Avigan, with an indication for pandemic influenza, has been studied. The study of this compound was prompted by the idea that effective processes of recognition and binding of FPV to the nucleic acid are affected predominantly by the propensity to form intra- and intermolecular interactions. Three nuclear quadrupole resonance experimental techniques, namely H-N cross-relaxation, multiple frequency sweeps, and two-frequency irradiation, followed by solid-state computational modelling (density functional theory supplemented by the quantum theory of atoms in molecules, 3D Hirshfeld Surfaces, and reduced density gradient) approaches were applied.

Observing short-range orientational order in small-molecule liquids.

Local molecular ordering in liquids has attracted a lot of interest from researchers investigating crystallization, but is still poorly understood on the molecular scale. Classical nucleation theory (CNT), a macroscopic thermodynamic description of condensation, has shortcomings when dealing with clusters consisting of tens of molecules. Cluster formation and local order fluctuations in liquid media are difficult to study due to the limited spatial resolution of electron- and photon-imaging methods.

Sensitivity of Proton NMR Relaxation and Proton NMR Diffusion Measurements to Olive Oil Adulterations with Vegetable Oils.

Olive oils and, in particular, extra-virgin olive oils (EVOOs) are one of the most frauded food. Among the different adulterations of EVOOs, the mixture of high-quality olive oils with vegetable oils is one of the most common in the market. The need for fast and cheap techniques able to detect extra-virgin olive oil adulterations was the main motivation for the present research work based on H NMR relaxation and diffusion measurements.

Analysis of Extra Virgin Olive Oils from Two Italian Regions by Means of Proton Nuclear Magnetic Resonance Relaxation and Relaxometry Measurements.

The interest in development of new non-destructive methods for characterization of extra virgin olive oils (EVOOs) has been increasing in the recent years. Among different experimental techniques, nuclear magnetic resonance (NMR) relaxation measurements are very promising in the field of food characterization and authentication. In this study, we focused on relaxation times and measured at different magnetic field strengths (namely, 2, 100, and 400 MHz) and H NMR relaxometry dispersions directly on olive oil samples without any chemical/physical treatments.

A rapid determination of nuclear quadrupole resonance frequencies using field-cycling magnetic resonance and frequency modulated RF excitations.

A modification of Slusher-Hahn's double resonance technique is described and experimentally tested. It is based on application of multiple frequency sweeps and can be used for a rapid location of nuclear quadrupole resonance (NQR) frequencies. The resolution of the present technique is relatively low but, when the NQR frequencies are located, it is easy to use either the Slusher-Hahn's technique or pulse NQR to determine the NQR frequencies with a higher precision.

Dynamics of water and xanthan chains in hydrogels studied by NMR relaxometry and their influence on drug release.

The dynamic properties of water and polymer molecules in xanthan hydrogels at different polymer mass fractions were investigated through the combination of conventional and fast-field cycling NMR relaxation to obtain the information about dynamics in different time scales. The results showed that water dynamics were faster in diluted than in concentrated hydrogels. However, the type of polymer-chain dynamics did not change for xanthan fractions from 0.

N NQR spectroscopy reveals the proton position in N-HN bonds: a case study with proton sponges.

The position of protons in hydrogen bonds is often uncertain to some degree, as the technique most often used for structure determination, X-ray diffraction, is sensitive to electron density, which is not particularly abundant around protons. In hydrogen bonds, protons introduce an additional problem: the potential for proton motion is inherently anharmonic and thus requires the consideration of nuclear quantum effects (NQEs). Here, we demonstrate that 14N NQR spectroscopy is able to rather accurately determine proton positions in N-HN bonds, in certain cases with an accuracy comparable to that of X-ray and neutron diffraction at room temperature.

Molecular dynamics of 1-ethyl-3-methylimidazolium triflate ionic liquid studied by H and F nuclear magnetic resonances.

The molecular dynamics of an ionic liquid (IL) composed of a 1-ethyl-3-methylimidazolium cation and a triflate (trifluoromethanesulfonate) anion, abbreviated as [Emim][TfO], were studied by NMR spectroscopy. By measuring the temperature-dependent high-field 1H and F spin-lattice relaxation (SLR) rates, the frequency-dependent H and F SLR dispersion curves using fast-field-cycling relaxometry, and the temperature-dependent 1H and F diffusion constants, and by utilizing the fact that the primary NMR-active nucleus on the Emim cation is H, whereas on the TfO anion it is F, the cationic and anionic dynamics were studied separately. A single theoretical relaxation model successfully reproduced all the experimental data of both types of resonant nuclei by fitting all the data simultaneously with the same set of fit parameters.

Multifunctional Gadolinium-Doped Mesoporous TiO Nanobeads: Photoluminescence, Enhanced Spin Relaxation, and Reactive Oxygen Species Photogeneration, Beneficial for Cancer Diagnosis and Treatment.

Materials with controllable multifunctional abilities for optical imaging (OI) and magnetic resonant imaging (MRI) that also can be used in photodynamic therapy are very interesting for future applications. Mesoporous TiO sub-micrometer particles are doped with gadolinium to improve photoluminescence functionality and spin relaxation for MRI, with the added benefit of enhanced generation of reactive oxygen species (ROS). The Gd-doped TiO exhibits red emission at 637 nm that is beneficial for OI and significantly improves MRI relaxation times, with a beneficial decrease in spin-lattice and spin-spin relaxation times.

(1)H-(14)N cross-relaxation spectrum analysis in sildenafil and sildenafil citrate.

Here we describe a method for the extraction of (14)N quadrupole parameters from a (1)H-(14)N cross-relaxation spectrum by fitting the lineshapes of the (14)N quadrupole transitions. The procedures used typically to fit quadrupole lineshapes are not directly applicable to fit the (1)H-(14)N cross-relaxation spectrum, because the presence of proton homonuclear dipolar interaction broadens the lineshapes considerably and prevents a reliable determination of Cq and η from a single lineshape. Instead, one must fit two or even three lineshapes originating from the same nitrogen site simultaneously.

Dry-cured ham tissue characterization by fast field cycling NMR relaxometry and quantitative magnetization transfer.

Fast field cycling (FFC) and quantitative magnetization transfer (qMT) NMR methods are two powerful tools in NMR analysis of biological tissues. The qMT method is well established in biomedical NMR applications, while the FFC method is often used in investigations of molecular dynamics on which longitudinal NMR relaxation times of the investigated material critically depend. Despite their proven analytical potential, these two methods were rarely used in NMR studies of food, especially when combined together.

(1)H NMR Relaxometric Study of Molecular Dynamics in a "de Vries" Liquid Crystal.

Liquid crystals that exhibit de Vries smectic A phases are promising materials for new generations of ferroelectric liquid crystal displays and other electro-optical devices. We investigated the molecular dynamic properties of a rod-like de Vries liquid crystal compound, namely the 9HL, a (S)-hexyl lactate derivative, in the whole mesophasic range. This is the first molecular dynamics' investigation on a de Vries phase, and the interest of this system is related to the understanding of the structural and supramolecular organization of de Vries SmA phases, which has been a subject of a broad scientific debate in the last years.

Polymorphism and disorder in natural active ingredients. Low and high-temperature phases of anhydrous caffeine: Spectroscopic ((1)H-(14)N NMR-NQR/(14)N NQR) and solid-state computational modelling (DFT/QTAIM/RDS) study.

The polymorphism of anhydrous caffeine (1,3,7-trimethylxanthine; 1,3,7-trimethyl-1H-purine-2,6-(3H,7H)-dione) has been studied by (1)H-(14)N NMR-NQR (Nuclear Magnetic Resonance-Nuclear Quadrupole Resonance) double resonance and pure (14)N NQR (Nuclear Quadrupole Resonance) followed by computational modelling (Density Functional Theory, supplemented Quantum Theory of Atoms in Molecules with Reduced Density Gradient) in solid state. For two stable (phase II, form β) and metastable (phase I, form α) polymorphs the complete NQR spectra consisting of 12 lines were recorded. The assignment of signals detected in experiment to particular nitrogen sites was verified with the help of DFT.

¹H-²H cross-relaxation study in a partially deuterated nematic liquid crystal.

A detailed study of the cross-relaxation effects between the ¹H and ²H spins systems is presented in the nematic phase of a 5-cyanobiphenyl (5CB) liquid crystal, partially deuterated at α position (5CB-αd₂). The proton spin-lattice relaxation time was measured at a frequency range from 5 kHz to 100 MHz at a temperature 5 K below the nematic-isotropic phase transition. In the low frequency domain, the spin-lattice relaxation rate (T₁⁻¹) dispersion clearly differs from that of the fully protonated 5CB homologue.

WURST-QCPMG sequence and "spin-lock" in ¹⁴N nuclear quadrupole resonance.

¹⁴N nuclear quadrupole resonance (NQR) is a promising method for the analysis of pharmaceuticals or for the detection of nitrogen based illicit compounds, but so far, the technique is still not widely used, mostly due to the very low sensitivity. This problem is already acute in the preliminary NQR stage, when a compound is being examined for the first time and the NQR frequencies are being searched for, by scanning a wide frequency range step-by-step. In the present work, we experimentally show how to increase the efficiency of this initial stage by using a combination of a wideband excitation achieved with frequency swept pulses (WURST) and a "spin-lock" state obtained with a quadrupolar-CPMG (QCPMG) sequence.

Phase transition and ring-puckering motion in a metal-organic perovskite [(CH2)3NH2][Zn(HCOO)3].

Phase transitions in a metal-organic perovskite with an azetidinium cation, which exhibits giant polarizability, were investigated using differential scanning calorimetry (DSC) and (1)H nuclear magnetic resonance (NMR) measurements. The DSC results indicated successive phase transitions at 254 and 299 K. The temperature dependence of the spin-lattice relaxation time T(1) determined by NMR indicated that the activation energy for cation ring-puckering motion was 25 kJ mol(-1) in phase I (T > 299 K).

Fast field-cycling NMR relaxometry study of chiral and nonchiral nematic liquid crystals.

We present a proton NMR relaxometry study of the molecular dynamics in three liquid crystalline systems: 4'-n-pentyl-4-cyanobiphenyl (5CB), (S)-4'-(3-methylpentyl)-4-cyanobiphenyl (5CB*), and a 12% weight mixture of 5CB* in 5CB. The proton spin-lattice relaxation time (T1) was measured as a function of temperature and Larmor frequency in the isotropic, nematic, chiral nematic (N*), and smectic A phases of these liquid crystalline systems. A unified relaxation model was used to analyze the molecular dynamics, considering local molecular rotations/reorientations, translational self-diffusion, and collective motions as the relaxation mechanisms that contribute most effectively to the T1(-1) relaxation.

Capacitor-based detection of nuclear magnetization: nuclear quadrupole resonance of surfaces.

We demonstrate excitation and detection of nuclear magnetization in a nuclear quadrupole resonance (NQR) experiment with a parallel plate capacitor, where the sample is located between the two capacitor plates and not in a coil as usually. While the sensitivity of this capacitor-based detection is found lower compared to an optimal coil-based detection of the same amount of sample, it becomes comparable in the case of very thin samples and even advantageous in the proximity of conducting bodies. This capacitor-based setup may find its application in acquisition of NQR signals from the surface layers on conducting bodies or in a portable tightly integrated nuclear magnetic resonance sensor.

1H NMR relaxometry study of a rod-like chiral liquid crystal in its isotropic, cholesteric, TGBA*, and TGBC* phases.

The molecular dynamics of a chiral liquid crystal showing a rich variety of frustrated mesophases has been investigated by means of 1H NMR relaxometry. The interest in this lactate derivative, HZL 7/*, is related to a large range of thermal stabilities of the twist grain boundary (TGB) phases. Dispersions of the 1H spin-lattice relaxation times, T1, in the frequency range from 300 MHz to 5 kHz were measured and consistently analyzed in the isotropic, chiral nematic, TGBA*, and two TGBC* phases.

Aplicability of TNT "super-Q detection" to multipulse sequences.

The use of high-Q probes to increase the sensitivity in NMR and NQR is a well-known technique, however very high Q values are associated with several limitations. This paper explores the (14)N NQR multipulse detection of trinitrotoluene (TNT) signal-to-noise ratio as a function of the pickup coil Q factor, with a particular emphasis on the "super-Q" regime, where probe bandwidth becomes narrower than the NQR linewidths. We have used a mixed experimental-theoretical approach to find the TNT Q-dependent signal-to-noise value which avoided the inconvenient construction of a probe at every Q.

Improving 14N nuclear quadrupole resonance detection of trinitrotoluene using off-resonance effects.

The off-resonance dependence of the amplitudes of the six dominant (14)N nuclear quadrupole resonance (NQR) lines in commercial polymorphic trinitrotoluene (TNT) sample were experimentally determined for a wide range of experimental parameters when irradiated with the spin-lock spin-echo (SLSE) pulse sequence. We find that the amplitudes off-resonance dependence follows a sinc-like function with an additional modulation due to the spacing between the RF pulses. This dependence can be very well modeled with expressions we have derived for a single site (14)N NQR in paranitrotoluene (PNT).

TNT detection with 14N NQR: multipulse sequences and matched filter.

Nuclear quadrupole resonance (NQR) has a distinct potential to verify the presence of nitrogen bearing substances based on the unequivocal signatures of their spectra. Therefore, this technique is especially suitable for remote detection of illicit substances and explosives. Unfortunately, the inherent signal-to-noise of the most abundant explosive trinitrotoluene (TNT) is very low.