Step-by-step from amorphous phosphate to nano-structured calcium hydroxyapatite: monitoring by solid-state H and P NMR and spin dynamics.

The solid-state H, P NMR spectra and cross-polarization (CP MAS) kinetics in the series of samples containing amorphous phosphate phase (AMP), composite of AMP + nano-structured calcium hydroxyapatite (nano-CaHA) and high-crystalline nano-CaHA were studied under moderate spinning rates (5-30 kHz). The combined analysis of the solid-state H and P NMR spectra provides the possibility to determine the hydration numbers of the components and the phase composition index. A broad set of spin dynamics models (isotropic/anisotropic, relaxing/non-relaxing, secular/semi-non-secular) was applied and fitted to the experimental CP MAS data.

Synthesis, structural and luminescent properties of Mn-doped calcium pyrophosphate (CaPO) polymorphs.

In the present work, three different Mn-doped calcium pyrophosphate (CPP, CaPO) polymorphs were synthesized by wet co-precipitation method followed by annealing at different temperatures. The crystal structure and purity were studied by powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR), solid-state nuclear magnetic resonance (SS-NMR), and electron paramagnetic resonance (EPR) spectroscopies. Scanning electron microscopy (SEM) was used to investigate the morphological features of the synthesized products.

Structural Features of the [C4mim][Cl] Ionic Liquid and Its Mixtures with Water: Insight from a H NMR Experimental and QM/MD Study.

The H NMR chemical shift of water exhibits non-monotonic dependence on the composition of an aqueous mixture of 1-butyl-3-methylimidazolium chloride, [C4mim][Cl], ionic liquid (IL). A clear minimum is observed for the H NMR chemical shift at a molar fraction of the IL of 0.34.

Solid-State NMR and Impedance Spectroscopy Study of Spin Dynamics in Proton-Conducting Polymers: An Application of Anisotropic Relaxing Model.

The H-C cross-polarization (CP) kinetics in poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) was studied under moderate (10 kHz) magic-angle spinning (MAS). To elucidate the role of adsorbed water in spin diffusion and proton conductivity, PMETAC was degassed under vacuum. The CP MAS results were processed by applying the anisotropic Naito and McDowell spin dynamics model, which includes the complete scheme of the rotating frame spin-lattice relaxation pathways.

Computational NMR Study of Ion Pairing of 1-Decyl-3-methyl-imidazolium Chloride in Molecular Solvents.

The H NMR spectra of 10 mole fraction solutions of 1-decyl-3-methyl-imidazolium chloride ionic liquid in water, acetonitrile, and dichloromethane have been measured. The chemical shift of the proton at position 2 in the imidazolium ring of 1-decyl-3-methyl-imidazolium (H2) is rather different for all three samples, reflecting the shifting equilibrium between the contact pairs and free fully solvated ions. Classical molecular dynamics simulations of the 1-decyl-3-methyl-imidazolium chloride contact ion pair as well as of free ions in water, acetonitrile, and dichloromethane have been conducted, and the quantum mechanics/molecular mechanics methods have been applied to predict NMR chemical shifts for the H2 proton.

Excitation quenching in chlorophyll-carotenoid antenna systems: 'coherent' or 'incoherent'.

Plants possess an essential ability to rapidly down-regulate light-harvesting in response to high light. This photoprotective process involves the formation of energy-quenching interactions between the chlorophyll and carotenoid pigments within the antenna of Photosystem II (PSII). The nature of these interactions is currently debated, with, among others, 'incoherent' or 'coherent' quenching models (or a combination of the two) suggested by a range of time-resolved spectroscopic measurements.

CP MAS kinetics in soft matter: Spin diffusion, local disorder and thermal equilibration in poly(2-hydroxyethyl methacrylate).

The H-C cross-polarization magic angle spinning kinetics was studied in poly(2-hydroxyethyl methacrylate) (pHEMA), i.e. a soft material with high degrees of internal freedom and molecular disorder, having the purpose to track the influence of increasing local incoherent contributions to the effects of coherent nature in the open quantum spin systems.

How carotenoid distortions may determine optical properties: lessons from the Orange Carotenoid Protein.

Carotenoids in photosynthetic proteins carry out the dual function of harvesting light and defending against photo-damage by quenching excess energy. The latter involves the low-lying, dark, excited state labelled S1. Here "dark" means optically-forbidden, a property that is often attributed to molecular symmetry, which leads to speculation that its optical properties may be strongly-perturbed by structural distortions.

Translational Diffusion in a Set of Imidazolium-Based Ionic Liquids [bmim]A and Their Mixtures with Water.

As the development of the work ( (10), 2362-2372), we have investigated the translational mobility in the same set of dried imidazolium-based ionic liquids (ILs) [bmim]A (A = BF, NO, TfO, I, Br, and Cl) in a wide temperature range using the NMR technique. It is shown that for the [bmim] cation, the temperature dependencies of product η do not follow the Stokes-Einstein relation for most systems studied, that is, the so-called "diffusion-viscosity decoupling" was realized. The correlation between local and translational mobility in pure IL of the [bmim][A] type was investigated using the data on NMR relaxation rates and diffusion coefficients.

The full dynamics of energy relaxation in large organic molecules: from photo-excitation to solvent heating.

In some molecular systems, such as nucleobases, polyenes or the active ingredients of sunscreens, substantial amounts of photo-excitation energy are dissipated on a sub-picosecond time scale, raising questions such as: where does this energy go or among which degrees of freedom it is being distributed at such early times? Here we use transient absorption spectroscopy to track excitation energy dispersing from the optically accessible vibronic subsystem into the remaining vibrational subsystem of the solute and solvent. Monitoring the flow of energy during vibrational redistribution enables quantification of local molecular heating. Subsequent heat dissipation away from the solute molecule is characterized by classical thermodynamics and molecular dynamics simulations.

Molecular Mobility in a Set of Imidazolium-Based Ionic Liquids [bmim]A by the NMR-Relaxation Method.

The detailed investigation of the local mobility in a set of dried imidazolium-based ionic liquids (1-butyl-3-methylimidazolium) in a wide temperature range and varying anions (BF, I, Cl, Br, NO, TfO) is presented. The measurements of temperature dependencies of the spin-lattice relaxation times of H and C nuclei are motivated by the need to obtain a fundamental characterization of molecular mobility of the substances under study, namely, to estimate the correlation times, τ, for the motion of individual molecular groups. In particular, it follows from obtained results that the mobility of the hydrocarbon "tail" is higher (smaller τ) than that of the imidazole ring, and this expected tendency is quantified.

Quasi-Equilibria and Polarization Transfer Between Adjacent and Remote Spins: H-C CP MAS Kinetics in Glycine.

The H-C CP MAS kinetic curves were measured in glycine powder sample at the MAS rates of 7, 10, and 12 kHz. Each experimental curve contained up to 1000 equidistant points over the whole contact time range of 10 μs - 10 ms. The CP kinetic data for CH group, i.

NMR and XRD Study of Hydrogen Bonding in Picolinic Acid N-Oxide in Crystalline State and Solutions: Media and Temperature Effects on Potential Energy Surface.

Solvent and temperature effects on H-bonding in crystalline picolinic acid N-oxide (PANO) and in solutions were studied by NMR (H MAS and H-C CP/MAS) and X-ray diffraction (XRD) methods. The single-crystal XRD experiments on β-polymorph were carried out at 105 and 299 K. C chemical shifts of PANO pyridine ring carbons were chosen as an effective diagnostic tool for the H-bond sensing.

A possible molecular basis for photoprotection in the minor antenna proteins of plants.

The bioenergetics of light-harvesting by photosynthetic antenna proteins in higher plants is well understood. However, investigation into the regulatory non-photochemical quenching (NPQ) mechanism, which dissipates excess energy in high light, has led to several conflicting models. It is generally accepted that the major photosystem II antenna protein, LHCII, is the site of NPQ, although the minor antenna complexes (CP24/26/29) are also proposed as alternative/additional NPQ sites.

NMR, Raman, and DFT Study of Lyotropic Chromonic Liquid Crystals of Biomedical Interest: Tautomeric Equilibrium and Slow Self-Assembling in Sunset Yellow Aqueous Solutions.

Temperature and composition effects in Sunset Yellow FCF (SSY) aqueous solutions were studied by the H, N NMR as well as Raman spectroscopy passing through all phase transitions between isotropic phase (I) and chromonic phases-nematic (N) and columnar (M). It was shown that the tautomeric equilibrium in SSY is strongly shifted toward the hydrazone form. The corresponding equilibrium constant p K = 2.

Fine control of chlorophyll-carotenoid interactions defines the functionality of light-harvesting proteins in plants.

Photosynthetic antenna proteins can be thought of as "programmed solvents", which bind pigments at specific mutual orientations, thus tuning the overall energetic landscape and ensuring highly efficient light-harvesting. While positioning of chlorophyll cofactors is well understood and rationalized by the principle of an "energy funnel", the carotenoids still pose many open questions. Particularly, their short excited state lifetime (<25 ps) renders them potential energy sinks able to compete with the reaction centers and drastically undermine light-harvesting efficiency.

The carotenoid pathway: what is important for excitation quenching in plant antenna complexes?

Plant light-harvesting is regulated by the Non-Photochemical Quenching (NPQ) mechanism involving the reversible formation of excitation quenching sites in the Photosystem II (PSII) antenna in response to high light. While the major antenna complex, LHCII, is known to be a site of NPQ, the precise mechanism of excitation quenching is not clearly understood. A preliminary model of the quenched crystal structure of LHCII implied that quenching arises from slow energy capture by Car pigments.

Effects of tunable excitation in carotenoids explained by the vibrational energy relaxation approach.

Carotenoids are fundamental building blocks of natural light harvesters with convoluted and ultrafast energy deactivation networks. In order to disentangle such complex relaxation dynamics, several studies focused on transient absorption measurements and their dependence on the pump wavelength. However, such findings are inconclusive and sometimes contradictory.

A Unified Picture of S* in Carotenoids.

In π-conjugated chain molecules such as carotenoids, coupling between electronic and vibrational degrees of freedom is of central importance. It governs both dynamic and static properties, such as the time scales of excited state relaxation as well as absorption spectra. In this work, we treat vibronic dynamics in carotenoids on four electronic states (|S0⟩, |S1⟩, |S2⟩, and |Sn⟩) in a physically rigorous framework.

Vibronic energy relaxation approach highlighting deactivation pathways in carotenoids.

Energy relaxation between two electronic states of a molecule is mediated by a set of relevant vibrational states. We describe this fundamental process in a fully quantum mechanical framework based on first principles. This approach explains population transfer rates as well as describes the entire transient absorption signal as vibronic transitions between electronic states.

Very short NMR relaxation times of anions in ionic liquids: new pulse sequence to eliminate the acoustic ringing.

NMR relaxation processes of anions were studied in two neat imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride. The spin-lattice and spin-spin relaxations of 81Br and 35Cl nuclei were found to be extremely fast due to very strong quadrupolar interactions. The determined relaxation rates are comparable with those observed in the solids or in some critical organic solute/water/salt systems.

NMR and Raman spectroscopy monitoring of proton/deuteron exchange in aqueous solutions of ionic liquids forming hydrogen bond: a role of anions, self-aggregation, and mesophase formation.

The H/D exchange process in the imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride ([C10mim][Br] and [C10mim][Cl]) in D2O solutions of various concentrations was studied applying (1)H, (13)C NMR, and Raman spectroscopy. The time dependencies of integral intensities in NMR spectra indicate that the H/D exchange in [C10mim][Br] at very high dilution (10(-4) mole fraction of RTIL) runs only slightly faster than in [C10mim][Cl]. The kinetics of this process drastically changes above critical aggregation concentration (CAC).

Hydrogen bonding in pyridine N-oxide/acid systems: proton transfer and fine details revealed by FTIR, NMR, and X-ray diffraction.

The H-bonded complexes of pyridine N-oxide (PyO) with H(2)O, acetic, cyanoacetic, propiolic, tribromoacetic, trichloroacetic, trifluoroacetic, hydrochloric, and methanesulfonic acids have been studied by FTIR and NMR spectroscopy, X-ray diffraction, and quantum chemical DFT calculations. Correlations between vibrational frequencies of the NO stretching and PyO ring modes and geometric parameters of the H-bond have been established. FTIR experiments show and DFT calculations confirm that definite discontinuity is present in the vicinity of the midpoint in the proton transfer pathway.

1H, 13C NMR and DFT Study of Hydrogen Bonding in Imidazolium-based Ionic Liquids.

The ionic liquid 1-decyl-3-methyl-imidazolium bromide [C10mim][Br], the neat material, and also dissolved (~0.01 mole fraction) in various dielectric media (acetonitrile, benzene, chloroform, dichloromethane, methanol, 2-butanol and H2O) was studied using 1H and 13C NMR spectroscopy. The most important interaction in this compound is considered to be the Br-.