13C Spin Lattice Research Articles

Single-crystal growth, crystal structure, and molecular dynamics of organic–inorganic [NH3(CH2)2NH3]CuBr4

As part of obtaining excellent properties that can be used as lead-free hybrid solar cells, the crystal growth, crystal structure, phase transition temperature, and thermal properties for [NH3(CH2)2NH3]CuBr4 were discussed. The crystal structure at 300 K was determined to be monoclinic by single-crystal X-ray diffraction (XRD) analysis. The phase transition temperatures were determined to be 447 and 473 K, and the results were consistent with the powder XRD patterns. Thermogravimetric analysis revealed thermal stability up to ~ 460 K. The continuous changes in the 1H and 13C chemical shifts and 14N static resonance frequency with increasing temperature are related to variations in the local environment and coordination geometry. The significant differences in activation energies obtained from the 1H and 13C spin–lattice relaxation times (t1ρ) at low and high temperatures were discussed. The activation energy results suggested that the energy barrier at low temperatures was related to the reorientation of the NH3 and CH2 groups around the three-fold symmetry axis, and the energy barrier at high temperatures was related to the reorientation of the [NH3(CH2)2NH3] cation. These physical properties will be provide important insights or potential applications of this crystal.Please check and confirm that the corresponding author and their respective corresponding affiliation have been correctly identified and amend if necessary.OK !

Investigation on the organic–inorganic hybrid crystal [NH2(CH3)2]2CuBr4: structure, phase transition, thermal property, structural geometry, and dynamics

Understanding the physical properties of the organic–inorganic hybrid [NH2(CH3)2]2CuBr4 is essential to expand its applications. The single [NH2(CH3)2]2CuBr4 crystals were grown and their comprehensive properties were investigated. The crystals had a monoclinic structure with the space group P21/n and lattice constants of a = 8.8651 (5) Å, b = 11.9938 (6) Å, c = 13.3559 (7) Å, and β = 91.322°. The transition temperature from phase I to phase II was determined to be 388 K. Variations in the 1H nuclear magnetic resonance chemical shifts of NH2 and 14N NMR chemical shifts according to the temperature changes in the cation were attributed to vibrations of NH2 groups at their localization sites. The 1H and 13C spin–lattice relaxation times (T1ρ) in phase II changed significantly with temperature, indicating that these values are governed by molecular motion. The T1ρ values were much longer in phase I than in phase II, which means energy transfer was difficult. Finally, the activation energies for phases I and II were considered. According to the basic mechanism of [NH2(CH3)2]2CuBr4 crystals, organic–inorganic materials may have potential applications in various fields.

Universal Dependence of Nuclear Spin Relaxation on the Concentration of Paramagnetic Centers in Nano- and Microdiamonds.

An analysis of our data on 1H and 13C spin–lattice and spin–spin relaxation times and rates in aqueous suspensions of purified nanodiamonds produced by detonation technique (DNDs), DNDs with grafted paramagnetic ions, and micro- and nanodiamonds produced by milling bulk high-temperature high-pressure diamonds is presented. It has been established that in all the studied materials, the relaxation rates depend linearly on the concentration of diamond particles in suspensions, the concentration of grafted paramagnetic ions, and surface paramagnetic defects produced by milling, while the relaxation times exhibit a hyperbolic dependence on the concentration of paramagnetic centers. This is a universal law that is valid for suspensions, gels, and solids. The results obtained will expand the understanding of the properties of nano- and microdiamonds and will be useful for their application in quantum computing, spintronics, nanophotonics, and biomedicine.

Dynamics in Flexible Pillar[n]arenes Probed by Solid-State NMR.

Pillar[n]arenes are supramolecular assemblies that can perform a range of technologically important molecular separations which are enabled by their molecular flexibility. Here, we probe dynamical behavior by performing a range of variable-temperature solid-state NMR experiments on microcrystalline perethylated pillar[n]arene (n = 5, 6) and the corresponding three pillar[6]arene xylene adducts in the 100–350 K range. This was achieved either by measuring site-selective motional averaged 13C 1H heteronuclear dipolar couplings and subsequently accessing order parameters or by determining 1H and 13C spin–lattice relaxation times and extracting correlation times based on dipolar and/or chemical shift anisotropy relaxation mechanisms. We demonstrate fast motional regimes at room temperature and highlight a significant difference in dynamics between the core of the pillar[n]arenes, the protruding flexible ethoxy groups, and the adsorbed xylene guest. Additionally, unexpected and sizable 13C 1H heteronuclear dipolar couplings for a quaternary carbon were observed for p-xylene adsorbed in pillar[6]arene only, indicating a strong host–guest interaction and establishing the p-xylene location inside the host, confirming structural refinements.

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.

Multinuclear solid-state NMR of complex nitrogen-rich polymeric microcapsules: Weight fractions, spectral editing, component mixing, and persistent radicals

The molecular structure of a crosslinked nitrogen-rich resin made from melamine, urea, and aldehydes, and of microcapsules made from the reactive resin with multiple polymeric components in aqueous dispersion, has been analyzed by 13C, 13C{1H}, 1H–13C, 1H, 13C{14N}, and 15N solid-state NMR without isotopic enrichment. Quantitative 13C NMR spectra of the microcapsules and three precursor materials enable determination of the fractions of different components. Spectral editing of non-protonated carbons by recoupled dipolar dephasing, of CH by dipolar DEPT, and of C–N by 13C{14N} SPIDER resolves peak overlap and helps with peak assignment. It reveals that the N- and O-rich resin “imitates” the spectrum of polysaccharides such as chitin, cellulose, or Ambergum to an astonishing degree. 15N NMR can distinguish melamine from urea and guanazole, NC=O from COO, and primary from secondary amines. Such a comprehensive and quantitative analysis enables prediction of the elemental composition of the resin, to be compared with combustion analysis for validation. It also provides a reliable reference for iterative simulations of 13C NMR spectra from structural models. The conversion from quantitative NMR peak areas of structural components to the weight fractions of interest in industrial practice is derived and demonstrated. Upon microcapsule formation, 15N and 13C NMR consistently show loss of urea and aldehyde and an increase in primary amines while melamine is retained. NMR also made unexpected findings, such as imbedded crystallites in one of the resins, as well as persistent radicals in the microcapsules. The crystallites produce distinct sharp lines and are distinguished from liquid-like components by their strong dipolar couplings, resulting in fast dipolar dephasing. Fast 1H spin–lattice relaxation on the 35-ms time scale and characteristically non-exponential 13C spin–lattice relaxation indicate persistent radicals, confirmed by EPR. Through 1H spin diffusion, the mixing of components on the 5-nm scale was documented.

Effects of sorbitol and formamide plasticizers on molecular motion in corn starch studied using NMR and DMTA

ABSTRACTMechanical and thermal properties of composite polymer materials strongly depend on their local structure and molecular dynamics which can be effectively studied by the solid‐state nuclear magnetic resonance (NMR) techniques. In the present paper, the influence of formamide (F) and sorbitol (S) plasticizers on molecular motion in thermoplastic starch (TPS) was studied using solid‐state NMR spectroscopy and dynamic mechanical thermal analysis (DMTA). DMTA measurements carried out for formamide‐ (F‐TPS) and sorbitol‐plasticized (S‐TPS) corn starches indicated heterogeneous plasticizer distribution of plasticizer‐rich and starch‐rich phases within the samples. The single pulse and cross‐polarization13C NMR spectra measured for both plasticized starches confirmed the amorphous character of their structure and distinctly different chain mobility supported by the values of13C spin–lattice relaxation times. The results of the analysis of broad line and magic angle spinning1H NMR spectra are in accordance with the results of DMTA measurements, revealing lower mobility of starch chains within S‐TPS in comparison to F‐TPS. Crosslinking of the starch chains with sorbitol molecules was suggested as being responsible for the lower mobility of the starch chains in S‐TPS. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48964.

Determination of the correlation between the structure and dynamics of deflazacort by solid state NMR measurements

The correlation between the structure and dynamics of glucocorticoid deflazacort is determined by a 2DPASS CP-MAS SSNMR experiment and 13C spin–lattice relaxation time by a Torchia CP experiment.

Influence of Diffusion Time on the Diffusion Coefficients of Gases in Polymers Determined by Pulsed Gradient Spin Echo NMR

The diffusive behavior of pure and mixed 13CO2, methane, and ethylene in poly(4,4′-hexafluoroisopropylidene diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine) membranes is investigated using a pulsed gradient spin echo NMR method. Also, proton and 13C spin–lattice and spin–spin relaxation times are measured. In all cases, the relaxation times of sorbed gases are well described assuming a single component, indicating that gas molecules in the membrane recognize one environment. If there is more than one, they are in fast exchange between them, and average values of relaxation times are observed. The diffusion coefficient of 13CO2 is independent of the diffusion time, exhibiting a Fickian behavior in all cases. Meanwhile, those of methane and ethylene vary with the diffusion time, and data analysis was performed considering their non-Fickian behavior. The diffusion coefficient of methane increases in the presence of 13CO2 and ethylene, suggesting that the sieving properties of the glassy polyimi...

Dynamics of Alanine Methyl Groups in Alanine Oligopeptides and Spider Dragline Silks with Different Packing Structures As Studied by 13C Solid-State NMR Relaxation

The dynamics of alanine methyl groups in alanine oligopeptides and polyalanine regions in Nephila clavata dragline and recombinant silks changed remarkably depending on the different packing arrangements. In particular, a notable difference in the 13C spin–lattice relaxation time T1 of Ala Cβ peaks was observed in the solid-state NMR between (Ala)6 and (Ala)7, which have rectangular and staggered packing arrangements, respectively. Moreover, the remarkably longer T1 value of the lowest field peak in Ala Cβ carbons clearly indicated the presence of staggered packing structure. Then, the relaxation behavior of polyalanine regions in spider dragline silks with mixed packing arrangements were clarified in both dry and hydrated states. The partial appearance of the staggered packing structure in (Ala)6 with rectangular packing structure was detected from the changes in line shapes of Ala 13Cβ peaks for the three kinds of 13C single-labeled (Ala)6 samples together with the change in their relaxation behavior.

Solid state 13C‐NMR study of a plasticized PLA/PHB polymer blend

ABSTRACTHigh‐resolution solid‐state 13C nuclear magnetic resonance spectra and 13C spin–lattice relaxation times T1(13C) are used to characterize the structure of a polymer blend prepared from poly(lactic acid) (85 wt %) and poly(3‐hydroxybutyrate) (15 wt %) and the effect of the plasticizer triacetine on the structure and molecular dynamics of the blend. Single‐pulse and cross‐polarization magic angle spinning 13C nuclear magnetic resonance spectra indicate that the nonplasticized polymer blend consists of semicrystalline poly(3‐hydroxybutyrate) domains built into an amorphous poly(lactic acid) matrix. Triacetine supports formation of the crystalline regions within both polymer components in the blend. Spin–lattice relaxation times of carbonyl carbons indicate that the nonplasticized polymer blend consists of noninteracting chains of blended polymers and plasticization of the polymer blend increases the relaxation rate. The glass transition, cold crystallization, and melting processes of the nonplasticized and plasticized blends were also studied using differential scanning calorimetry methods. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46296.

Effect of isopropyl-substituent introduction into tetraethylenepentamine-based solid sorbents for CO2 capture

Chemical modification of the amino functional groups of amine-impregnated solid sorbents is an effective strategy for drastically improving the regeneration performance for CO2 capture. In this study, isopropyl groups were introduced into tetraethylenepentamine (TEPA) to obtain N-(isopropyl)-TEPA (IP-TEPA), which was impregnated in mesocellular silica foam (MSU-F). The obtained solid sorbent enabled low-temperature regeneration with a low regeneration energy. To clarify the role of the IP groups, experimental and computational methods were used to compare the IP-TEPA/MSU-F sorbent with TEPA/MSU-F in terms of CO2 working capacity, reaction product stability, self-diffusion coefficient, 13C spin–lattice relaxation time, and CO2 capture performance in steam-aided vacuum swing adsorption.

Effect of magic angle spinning on 13C spin–lattice and spin–spin relaxation in nanodiamonds

We report on 13C spin–lattice (R1) and spin–spin (R2) relaxation rate dependence on magic-angle-spinning (MAS) rate in highly purified synthetic nanodiamonds. Noticeable slowdown of both relaxation processes and reduction of nuclear spin diffusion coefficient D with increasing MAS rate was obtained. This effect is attributed to suppression of nuclear spin diffusion by MAS. We developed a theoretical approach that describes the MAS rate dependence of R1, R2 and D, allows quantitative analysis of the data and shows good compliance with the experiment.

Anomalous role change of tertiary amino and ester groups as hydrogen acceptors in eudragit E based solid dispersion depending on the concentration of naproxen.

Eudragit E (EGE) is a basic polymer incorporating tertiary amino and ester groups. The role of the functional groups of EGE in the formation of solid dispersion (SD) with Naproxen (NAP) was investigated. The glass transition temperature (Tg) of EGE decreased with the plasticizing effect of NAP up to 20% weight ratio. Addition of NAP at over 30% induced a rise in Tg, with the maximum value being reached at 60% NAP. Further addition of NAP led to a rapid drop of the Tg. A dramatic difference of physical stability between the SDs including 60 and 70% NAP was confirmed. The SD including 70% NAP rapidly crystallized at 40 °C with 75% relative humidity, while the amorphous state could be maintained over 6 months in the SD with 60% NAP. The infrared and (13)C solid state-NMR spectra of the SDs suggested a formation of ionic interaction between the carboxylic acid of NAP and the amino group of EGE. The SD with 20% NAP raised the (13)C spin-lattice relaxation (T1) of the amino group, but it decreased with over 30% NAP. The change in the (13)C-T1 disappeared with 70% NAP. The (13)C-T1 of the ester group rose depending on the amount of NAP. From these findings, we concluded that the role as hydrogen acceptor shifted from the amine to the ester group with an increase in amount of NAP. Furthermore, the amino group of EGE did not contribute to the interaction at over 70% NAP. These phenomena could be strongly correlated with Tg and stability.

Ionic Dynamics in [C4mim]NTf2 in the Glassy and Liquid States: Results from 13C and 1H NMR Spectroscopy.

The ionic dynamics of the room temperature ionic liquid 1-butyl-3-methylimdiazolium bis((trifluoromethyl)sulfonyl)amide ([C(4)mim]NTf(2)) is studied using (13)C and (1)H nuclear magnetic resonance (NMR) spectroscopy over a wide temperature range encompassing the glassy and liquid states. The temperature dependence of the (13)C spin-lattice relaxation time is analyzed with four different models to derive the rotational dynamics of the RTIL in the nano to picosecond range. It was found that the extended model-free approach bridges the data obtained from the BPP and DC models, and describes ion dynamics of the RTIL well. Three different motions are observed based on the approach: an overall ion rotation, a slow and a fast local rotational motion. The time scale of the slow local rotational motion, particularly of the imidazolium ring carbons, is strongly coupled to the time scale of the overall ion rotation, above the melting point. Below the melting point these two time scales show strong decoupling and the local rotation displays nanosecond dynamics in the glassy state. The analyses of the second moment (M(2)) of the (1)H and (13)C nuclides indicate that, in addition to the axial rotations of the two methyl groups (cation) and the CF(3) group (anion), all (13)C sites including the imidazolium ring carbon and CF(3) show evidence of mobility, even in the glassy state.

Roles of chemically inequivalent N(CH3)4 ions in phase transition temperatures in [N(CH3)4]2CoCl4 by single-crystal NMR and MAS NMR

The temperature dependences of the 1H and 13C spin–lattice relaxation time in the laboratory frame, T1, and in the rotating frame, T1ρ, in [N(CH3)4]2CoCl4 were measured by static nuclear magnetic resonance (NMR) and magic angle spinning (MAS) NMR. In the ferroelastic phase, 1H T1ρ underwent molecular motion according to the Bloembergen–Purcell–Pound theory. Two inequivalent ions, a-N(CH3)4 and b-N(CH3)4, were identified by 13C cross polarization (CP)/MAS NMR. On the basis of the 13C NMR results, the existence of two chemically inequivalent a-N(CH3)4 and b-N(CH3)4 ions in the ferroelectric phase and the existence of the ferroelastic twin structure of the N(CH3)4 ions in the ferroelastic phase were discussed.

A Stable Amorphous Statin: Solid-State NMR and Dielectric Studies on Dynamic Heterogeneity of Simvastatin

Statins have been widely used as cholesterol-lowering agents. However, low aqueous solubility of crystalline statins and, consequently, reduced biovailability require seeking for alternative forms and formulations to ensure an accurate therapeutic window. The objective of the present study was to evaluate the stability of amorphous simvastatin by probing molecular dynamics using two nondestructive techniques: solid-state NMR and dielectric relaxation spectroscopy. Glassy simvastatin was obtained by the melt quench technique. (13)C cross-polarization/magic-angle-spinning (CP/MAS) NMR spectra and (1)H MAS NMR spectra were obtained from 293 K up to 333 K (Tg ≈ 302 K). The (13)C spin-lattice relaxation times in the rotating frame, T1ρ, were measured as a function of temperature, and the correlation time and activation energy data obtained for local motions in different frequency scales revealed strong dynamic heterogeneity, which appears to be essential for the stability of the amorphous form of simvastatin. In addition, the (1)H MAS measurements presented evidence for mobility of the hydrogen atoms in hydroxyl groups which was assigned to noncooperative secondary relaxations. The complex dielectric permittivity of simvastatin was monitored in isochronal mode at five frequencies (from 0.1 to 1000 kHz), by carrying out a heating/cooling cycle allowing to obtain simvastatin in the supercooled and glassy states. The results showed that no dipolar moment was lost due to immobilization, thus confirming that no crystallization had taken place. Complementarily, the present study focused on the thermal stability of simvastatin using thermogravimetric analysis while the thermal events were followed up by differential scanning calorimetry and dielectric relaxation spectroscopy. Overall, the results confirm that the simvastatin in the glass form reveals a potential use in the solid phase formulation on the pharmaceutical industry.

Quantitative Spectroscopic Study of Equilibrium in CO2-Loaded Aqueous 2-(Ethylamino)ethanol Solutions

The chemical absorption of CO2 in aqueous solutions of 2-(ethylamino)ethanol at 313 K was investigated by nuclear magnetic resonance (NMR) spectroscopy. Accurate 13C NMR quantitation by inverse-gated decoupling was achieved on the basis of 13C spin–lattice relaxation time measurements for all species in the system. The concentration of carbonate species (HCO3–/CO32–) monotonically increased with increasing CO2 loading, whereas that of carbamate anion [CH3CH2N(CH2CH2OH)COO–] showed a peak around 0.5 mol of CO2/mol of amine. Furthermore, we found that alkyl carbonate species (CH3CH2NHCH2CH2OCOO–) formed in the high-CO2 loading range, which was confirmed by 2D NMR spectroscopy and density functional theory calculations with a dielectric continuum solvation model at the B3LYP/aug-cc-pVDZ//B3LYP/6-311++G(d,p) level.

Characterization of a Water–Solid Interaction in a Partially Ordered System

GNE068-PC, a developmental compound, was previously characterized to be mesomorphous, i.e. having long-range order associated with significant local molecular disorder (Chakravarty et. al., Mol. Pharmaceutics, accepted). The compound was exposed to moisture under different relative humidity conditions ranging from 11% to 60% RH at room temperature (RT) for 7 days, and the resultant product phases were characterized. The partially ordered sample progressively lost crystallinity (long-range order) and birefringence (orientational order) upon exposure to increasing RH conditions, leading to the formation of a completely disordered amorphous phase at 60% RH (RT). Long-range positional order was irrecoverable even after moisture removal from the sample exposed to 60% RH. This was attributed to replacement of residual ethyl acetate by water, the former being critical for maintenance of long-range order in the material. In addition, water sorption appeared to irreversibly alter the molecular orientation, thereby affecting sample birefringence. Solid-state NMR revealed increases in (1)H and (13)C spin-lattice relaxation times (T1) going from the mesomorphous phase to the fully amorphous phase. This was indicative of reduction in lattice mobility, likely due to the decreased motion of the aromatic portions of the molecule, in particular C17, which showed the most dramatic increase in (13)C T1. This is likely due to decrease in available free volume upon water sorption. Drying of the hydrated disordered phase showed somewhat greater mobility than the hydrated phase, likely due to increased relative free volume through removal of water. A water-solid interaction therefore irreversibly changed the solid-state makeup of GNE068-PC.

The interplay between the solid effect and the cross effect mechanisms in solid state 13C DNP at 95 GHz using trityl radicals

The 13C solid state Dynamic Nuclear Polarization (DNP) mechanism using trityl radicals (OX63) as polarizers was investigated in the temperature range of 10–60K. The solutions used were 6M 13C urea in DMSO/H2O (50% v/v) with 15mM and 30mM OX63. The measurements were carried out at ∼3.5T, which corresponds to Larmor frequencies of 95GHz and 36MHz for the OX63 and the 13C nuclei, respectively. Measurements of the 13C signal intensity as a function of the microwave (MW) irradiation frequency yielded 13C DNP spectra with temperature dependent lineshapes for both samples. The maximum enhancement for the 30mM sample was reached at 40K, while that of the 15mM sample at 20–30K. Furthermore, the lineshapes observed showed that both the cross effect (CE) and the solid effect (SE) DNP mechanisms are active in this temperature range and that their relative contribution is temperature dependent. Simulations of the spectra with the relative contributions of the CE and SE mechanisms as a fit parameter revealed that for both samples the CE contribution decreases with decreasing temperature while the SE contribution increases. In addition, for the 15mM sample the contributions of the two mechanisms are comparable from 20K to 60K while for the 30mM the CE dominates in this range, as expected from the higher concentration. The steep decrease of the CE contribution towards low temperatures is however unexpected. The temperature dependence of the OX63 longitudinal relaxation, DNP buildup times and 13C spin lattice relaxation times did not reveal any obvious correlation with the DNP temperature dependence. A similar behavior of the CE and SE mechanism was observed for 1H DNP with the nitroxide radical TEMPOL as a polarizer. This suggests that this effect is a general phenomenon involving a temperature dependent competition between the CE and SE mechanisms, the source of which is, however, still unknown.