Nuclear Magnetic Resonance Parameters Research Articles

Cation Distribution and Anion Transport in the La3Ga5-xGe1+xO14+0.5x Langasite Structure.

Exploration of compositional disorder using conventional diffraction-based techniques is challenging for systems containing isoelectronic ions possessing similar coherent neutron scattering lengths. Here, we show that a multinuclear solid-state Nuclear Magnetic Resonance (NMR) approach provides compelling insight into the Ga3+/Ge4+ cation distribution and oxygen anion transport in a family of solid electrolytes with langasite structure and La3Ga5-xGe1+xO14+0.5x composition. Ultrahigh field 71Ga Magic Angle Spinning (MAS) NMR experiments acquired at 35.2 T offer striking resolution enhancement, thereby enabling clear detection of Ga sites in different coordination environments. Three-connected GaO4, four-connected GaO4 and GaO6 polyhedra are probed for the parent La3Ga5GeO14 structure, while one additional spectral feature corresponding to the key (Ga,Ge)2O8 structural unit which forms to accommodate the interstitial oxide ions is detected for the Ge4+-doped La3Ga3.5Ge2.5O14.75 phase. The complex spectral line shapes observed in the MAS NMR spectra are reproduced very accurately by the NMR parameters computed for a symmetry-adapted configurational ensemble that comprehensively models site disorder. This approach further reveals a Ga3+/Ge4+ distribution across all Ga/Ge sites that is controlled by a kinetically governed cation diffusion process. Variable temperature 17O MAS NMR experiments up to 700 °C importantly indicate that the presence of interstitial oxide ions triggers chemical exchange between all oxygen sites, thereby enabling atomic-scale understanding of the anion diffusion mechanism underpinning the transport properties of these materials.

Molecular NMR shieldings, J-couplings, and magnetizabilities from numeric atom-centered orbital based density-functional calculations

Abstract This paper reports and benchmarks a new implementation of nuclear magnetic resonance shieldings, magnetizabilities, and J-couplings for molecules within semilocal density functional theory, based on numeric atom-centered orbital (NAO) basis sets. NAO basis sets are attractive for the calculation of these nuclear magnetic resonance (NMR) parameters because NAOs provide accurate atomic orbital representations especially near the nucleus, enabling high-quality results at modest computational cost. Moreover, NAOs are readily adaptable for linear scaling methods, enabling efficient calculations of large systems. The paper has five main parts: (1) It reviews the formalism of density functional calculations of NMR parameters in one comprehensive text to make the mathematical background available in a self-contained way. (2) The paper quantifies the attainable precision of NAO basis sets for shieldings in comparison to specialized Gaussian basis sets, showing similar performance for similar basis set size. (3) The paper quantifies the precision of calculated magnetizabilities, where the NAO basis sets appear to outperform several established Gaussian basis sets of similar size. (4) The paper quantifies the precision of computed J-couplings, for which a group of customized NAO basis sets achieves precision of ∼ Hz for smaller basis set sizes than some established Gaussian basis sets. (5) The paper demonstrates that the implementation is applicable to systems beyond 1,000 atoms in size.

Review of High Dimensional Neural Network Potentials

Over the past few years, machine learning potentials (MLPs) have been fully developed and can now be applied to a variety of large-scale atomic simulations. MLPs encompass a number of different machine learning algorithms, of which neural network potentials are the most dominant and representative, and have achieved great success. This review focuses on the second generation of neural network potentials, high-dimensional neural network potentials (HDNNPs). While HDNNP has accomplished noteworthy results in the implementation of ion diffusion, nuclear magnetic resonance parameters, defect formation, and thermal conductivity, it still encounters hurdles in the compilation of training datasets, transferability, accuracy constraints, and the management of multiple chemical species. In spite of this, HDNNP remains a highly promising methodology. Looking forward, we anticipate the development of more specialized software for HDNNP to augment research efficiency and lower the barrier to usage.

Dynamic and relativistic effects on Pt-Pt indirect spin-spin coupling in aqueous solution studied by abinitio molecular dynamics and two- vs four-component density functional NMR calculations.

Treating 195Pt nuclear magnetic resonance parameters in solution remains a considerable challenge from a quantum chemistry point of view, requiring a high level of theory that simultaneously takes into account the relativistic effects, the dynamic treatment of the solvent-solute system, and the dynamic electron correlation. A combination of Car-Parrinello molecular dynamics (CPMD) and relativistic calculations based on two-component zeroth order regular approximation spin-orbit Kohn-Sham (2c-ZKS) and four-component Dirac-Kohn-Sham (4c-DKS) Hamiltonians is performed to address the solvent effect (water) on the conformational changes and JPtPt1 coupling. A series of bridged PtIII dinuclear complexes [L1-Pt2(NH3)4(Am)2-L2]n+ (Am = α-pyrrolidonate and pivalamidate; L = H2O, Cl-, and Br-) are studied. The computed Pt-Pt coupling is strongly dependent on the conformational dynamics of the complexes, which, in turn, is correlated with the trans influence among axial ligands and with the angle N-C-O from the bridging ligands. The J-coupling is decomposed in terms of dynamic contributions. The decomposition reveals that the vibrational and explicit solvation contributions reduce JPtPt1 of diaquo complexes (L1 = L2 = H2O) in comparison to the static gas-phase magnitude, whereas the implicit solvation and bulk contributions correspond to an increase in JPtPt1 in dihalo (L1 = L2 = X-) and aquahalo (L1 = H2O; L2 = X-) complexes. Relativistic treatment combined with CPMD shows that the 2c-ZKS Hamiltonian performs as well as 4c-DKS for the JPtPt1 coupling.

The effect of iodine on the local environment of network‐forming elements in aluminoborosilicate glasses: An NMR study

AbstractKnowledge of the structural organization of nuclear waste glasses at the atomic scale is the basis for further studies of macroscopic properties (e.g., fracture toughness, chemical durability, and leaching rate). Recent studies have focused on the iodine dissolution mechanism in oxide‐based glasses synthesized under high‐pressure conditions, but there is still a lack of key information on the extent of the modifications caused by iodine entering the glass network. We therefore decided to conduct an in‐depth study by nuclear magnetic resonance on two series of aluminoborosilicate glasses synthetized under high pressure conditions and doped with either I2 or I2O5. The obtained 11B, 23Na, and 27Al nuclear magnetic resonance (NMR) spectra were fitted and correlated with the iodine content in order to find possible relationships with the local environment change for the probed cations. These data showed that iodine has no effect on the coordination of aluminum and very little effects on that of boron. In contrast, we found an expected relationship of the I content with the 23Na NMR parameters. In comparison with previous studies on the non‐bridging oxygen (NBO) distribution in aluminoborosilicate, we suggest that Na+ is mainly scavenged from silica tetrahedra with one or two NBO ( or ) as no boron planar triangles with one NBO are expected for such compositions. From those information, we establish a model for iodine dissolution in nuclear waste glass that is consistent with previous studies.

Determination of SWCNT biosensor for bisphosphonate–2X(X = Mg2+, Ca2+, Sr2+) delivery in bone cell through electromagnetic and thermodynamic analysis using QM/MC methods

PurposeBisphosphonate (BP) medications can be applied to prohibit the damage of bone density and the remedy of bone illnesses such as osteoporosis. As the metal chelating of phosphonate groups are nearby large with six O atoms possessing the high negative charge, these compounds are active toward producing the chelated complexes through drug design method. BP agents have attracted much attention for the clinical treatment of some skeletal diseases depicted by enhancing of osteoclast-mediated bone resorption.Design/methodology/approachIn this work, it has been accomplished the CAM-B3LYP/6–311+G(d, p)/LANL2DZ to estimate the susceptibility of SWCNT for adsorbing alendronate, ibandronate, neridronate and pamidronate chelated to two metal cations of 2Mg2+, 2Ca2+, 2Sr2+ through nuclear magnetic resonance and thermodynamic parameters. Therefore, the data has explained that the feasibility of using SWCNT and BP agents becomes the norm in metal chelating of drug delivery system which has been selected through alendronate → 2X, ibandronate → 2X, neridronate → 2X and pamidronate → 2X (X = Mg2+/Ca2+/Sr2+) complexes.FindingsThe thermodynamic results have exhibited that the substitution of 2Ca2+ cation by 2Sr2+ cation in the structure of bioactive glasses can be efficient for treating vertebral complex fractures. However, it has been observed the most fluctuation in the Gibbs free energy for BPs → 2Sr2+ at 300 K. Furthermore, Monte Carlo simulation has resulted by increasing the dielectric constant in the aqueous medium can enhance the stability and efficiency of BP drugs for preventing the loss of bone density and treating the osteoporosis.Originality/valueAccording to this research, by incorporation of chelated 2Mg2+, 2Ca2+ and 2Sr2+ cations to BP drugs adsorbed onto (5, 5) armchair SWCNT, the network compaction would increase owing to the larger atomic radius of Sr2+ cation rather than Ca2+ and Mg2+, respectively.

Effects of intramolecular hydrogen bonding on nuclear magnetic resonance, electron paramagnetic resonance and molecular docking studies: Mexiletine molecule.

In this study, the molecular structure of the mexiletine molecule was investigated. Since the Mexiletine molecule is a drug active ingredient, its molecular structure and spectroscopic properties are important. The effects of intramolecular hydrogen bonding on Nuclear Magnetic Resonance Parameters (NMR), Electron Paramagnetic Resonance (EPR) parameters and molecular docking studies were examined in the mexiletine molecule. The effects of intramolecular hydrogen bonding on EPR parameters and molecular docking studies are the most important steps for this study. Conformational space scanning required for molecular structure calculations was carried out with the Molecular Mechanic Force Field method. DFT method with 6-311 + + G(d,p) basis set level was used to obtain the most stable structure among the conformations. NMR parameters (1H and 13C chemical shift values) were also performed using the same basis set as the DFT method. The radicals created to calculate the Electron Paramagnetic Resonance parameters were modeled using the DFT/B3LYP/6-311 + + G(d,p) method basis set level. Molecular Docking studies were carried out with the Autodock vina program.

The Synergy between Nuclear Magnetic Resonance and Density Functional Theory Calculations.

This paper deals with the synergy between Nuclear Magnetic Resonance (NMR) spectroscopic investigations and DFT calculations, mainly of NMR parameters. Both the liquid and the solid states are discussed here. This text is a mix of published results supplemented with new findings. This paper deals with examples in which useful results could not have been obtained without combining NMR measurements and DFT calculations. Examples of such cases are tautomeric systems in which NMR data are calculated for the tautomers; hydrogen-bonded systems in which better XH bond lengths can be determined; cage compounds for which assignment cannot be made based on NMR data alone; revison of already published structures; ionic compounds for which reference data are not available; assignment of solid-state spectra and crystal forms; and the creation of libraries for biological molecules. In addition to these literature cases, a revision of a cage structure and substituent effects on pyrroles is also discussed.

NMR spectroscopy of a 18O-labeled rhodium paddlewheel complex: Isotope shifts, 103Rh-103Rh spin-spin coupling, and 103Rh singlet NMR.

Despite the importance of rhodium complexes in catalysis, and the favorable 100% natural abundance of the spin-1/2 103Rh nucleus, there are few reports of 103Rh nuclear magnetic resonance (NMR) parameters in the literature. In part, this is the consequence of the very low gyromagnetic ratio of 103Rh and its dismal NMR sensitivity. In a previous paper [Harbor-Collins et al., J. Chem. Phys. 159, 104 307 (2023)], we demonstrated an NMR methodology for 1H-enhanced 103Rh NMR and demonstrated an application to the 103Rh NMR of the dirhodium formate paddlewheel complex. In this paper, we employ selective 18O labeling to break the magnetic equivalence of the 103Rh spin pair of dirhodium formate. This allows the estimation of the 103Rh-103Rh spin-spin coupling and provides access to the 103Rh singlet state. We present the first measurement of a 18O-induced 103Rh secondary isotope shift as well as the first instance of singlet order generated in a 103Rh spin pair. The field-dependence of 103Rh singlet relaxation is measured by field-cycling NMR experiments.

Brain Structures in a Human Embryo Imaged with MR Microscopy.

To delineate brain microstructures in human embryos during the formation of the various major primordia by MR microscopy, with different contrasts appropriate for each target. We focused mainly on the internal structures in the cerebral cortex and the accessory nerves of the brain. To find appropriate sequence parameters, we measured nuclear magnetic resonance (NMR) parameters and created kernel density plots of T1 and T2 values. We performed T1-weighted gradient echo imaging with parameters similar to those used in the previous studies. We performed T2*-weighted gradient echo imaging to delineate the target structures with the appropriate sequence parameters according to the NMR parameter and flip angle measurements. We also performed high-resolution imaging with both T1- and T2*-weighted sequences. T1, T2, and T2* values of the target tissues were positively correlated and shorter than those of the surrounding tissues. In T1-weighted images with a voxel size of (30 µm)3 and (20 µm)3, various organs and tissues and the agarose gel were differentiated as in previous studies, and the structure of approximately 40 µm in size was depicted, but the detailed structures within the cerebral cortex and the accessory nerves were not delineated. In T2*-weighted images with a voxel size of (30 µm)3, the layered structure within the cerebral cortex and the accessory nerves were clearly visualized. Overall, T1-weighted images provided more information than T2*-weighted images, but important internal brain structures of interest were visible only in T2*-weighted images. Therefore, it is essential to perform MR microscopy with different contrasts. We have visualized brain structures in a human embryo that had not previously been delineated by MR microscopy. We discussed pulse sequences appropriate for the structures of interest. This methodology would provide a way to visualize crucial embryological information about the anatomical structure of human embryos.

Electron Spin Resonance Spectrum Simulations of Possible Radicals of the Ketoprofen Molecule

In this study, the molecular structure of Ketoprofen molecule, which is the drug active ingredient , was revealed by using the Density Functional Theory method and the Molecular Mechanical Force Field method. First of all, conformational space scanning in the Ketoprofen molecule was performed by the Molecular Mechanical Force Field method. The most stable structure of the ketoprofen molecule was found with the help of the Density Functional Theory method. The geometry parameters of the ketoprofen molecule and the Nuclear Magnetic Resonance parameters were calculated with the help of the Density Functional Theory method. Possible radicals were modeled using the most stable structure of the ketoprofen molecule. Electron Spin Resonance parameters of these possible radicals were calculated with the Density Functions Theory method. The calculated Electron Spin Resonance parameters were used in the JEOL IsoSimu/Fa Version 2.2.0 simulation program and theoretical Electron Spin Resonance spectra of possible radicals were obtained.

Predicting 51V nuclear magnetic resonance observables in molecular crystals.

Solid-state nuclear magnetic resonance (NMR) spectroscopy and quantum chemical density functional theory (DFT) calculations are widely used to characterize vanadium centers in biological and pharmaceutically relevant compounds. Several techniques have been recently developed to improve the accuracy of predicted NMR parameters obtained from DFT. Fragment-based and planewave-corrected methods employing hybrid density functionals are particularly effective tools for solid-state applications. A recent benchmark study involving molecular crystal compounds found that fragment-based NMR calculations using hybrid density functionals improve the accuracy of predicted 51V chemical shieldings by 20% relative to traditional planewave methods. This work extends the previous study, including a careful analysis of 51V chemical shift anisotropy, electric field gradient calculations, and a more extensive test set. The accuracy of planewave-corrected techniques and recently developed fragment-based methods using electrostatic embedding based on the polarized continuum model (PCM) are found to be highly competitive with previous methods. Planewave-corrected methods achieve a 34% improvement in the errors of predicted 51V chemical shieldings relative to planewave. Additionally, planewave-corrected and fragment-based calculations were performed using PCM embedding, improving the accuracy of predicted 51V chemical shielding (CS) tensor principal values by 30% and values by 15% relative to traditional planewave methods. The performance of these methods is further examined using a redox-active oxovandium complex and a common 51V NMR reference compound.

Can simple 'molecular' corrections outperform projector augmented-wave density functional theory in the prediction of 35 Cl electric field gradient tensor parameters for chlorine-containing crystalline systems?

Many-body expansion (MBE) fragment approaches have been applied to accurately compute nuclear magnetic resonance (NMR) parameters in crystalline systems. Recent examples demonstrate that electric field gradient (EFG) tensor parameters can be accurately calculated for 14 N and 17 O. A key additional development is the simple molecular correction (SMC) approach, which uses two one-body fragment (i.e., isolated molecule) calculations to adjust NMR parameter values established using 'benchmark' projector augmented-wave (PAW) density functional theory (DFT) values. Here, we apply a SMC using the hybrid PBE0 exchange-correlation (XC) functional to see if this can improve the accuracy of calculated 35 Cl EFG tensor parameters. We selected eight organic and two inorganic crystal structures and considered 15 chlorine sites. We find that this SMC improves the accuracy of computed values for both the 35 Cl quadrupolar coupling constant (CQ ) and the asymmetry parameter ( ) by approximately 30% compared with benchmark PAW DFT values. We also assessed a SMC that offers local improvements not only in terms of the quality of the XC functional but simultaneously in the quality of the description of relativistic effects via the inclusion of spin-orbit effects. As the inorganic systems considered contain heavy atoms bonded to the chlorine atoms, we find further improvements in the accuracy of calculated 35 Cl EFG tensor parameters when both a hybrid functional and spin-orbit effects are included in the SMC. On the contrary, for chlorine-containing organics, the inclusion of spin-orbit relativistic effects using a SMC does not improve the accuracy of computed 35 Cl EFG tensor parameters.

The 103Rh NMR spectroscopy and relaxometry of the rhodium formate paddlewheel complex.

The nuclear magnetic resonance (NMR) spectroscopy of spin-1/2 nuclei with low gyromagnetic ratio is challenging due to the low NMR signal strength. Methodology for the rapid acquisition of 103Rh NMR parameters is demonstrated for the case of the rhodium formate "paddlewheel" complex Rh2(HCO2)4. A scheme is described for enhancing the 103Rh signal strength by polarization transfer from 1H nuclei, which also greatly reduces the interference from ringing artifacts, a common hurdle for the direct observation of low-γ nuclei. The 103Rh relaxation time constants T1 and T2 are measured within 20minby using 1H-detected experiments. The field dependence of the 103Rh T1 is measured. The high-field relaxation is dominated by the chemical shift anisotropy mechanism. The 103Rh shielding anisotropy is found to be very large: |Δσ| = 9900 ± 540ppm. This estimate is compared with density functional theory calculations.

Coordination of Mercury(II) in Water Promoted over Hydrolysis in Solvated Clusters [Hg(H2O)1-6](aq)2+: Insights from Relativistic Effects and Free Energy Analysis.

Understanding the nature of the interaction between mercury(II) ions, Hg2+, and water molecules is crucial to describe the stability and chemical behavior of structures formed during solvation, as well as the conditions that favor the Hg2+ coordination or inducing water hydrolysis. In our study, we explored exhaustively the potential energy surface of Hg2+ with up to six water molecules. We analyzed electronic and Gibbs free energies, binding, and nuclear magnetic resonance parameters. We used the zeroth-order regular approximation Hamiltonian, including scalar and spin-orbit relativistic corrections for free energy calculations and geometry optimizations to explore the interplay between electron correlation and relativistic effects. We analyzed intermolecular interactions with energy decomposition analysis, quantum theory of atoms in molecules, and natural bond orbital. Additionally, we used the four-component Dirac Hamiltonian to compute solvent effect on the magnetic shielding and J-coupling constants. Our results revealed that the water hydrolysis by Hg2+ requires a minimum of three water molecules. We found that the interaction between Hg2+ and water molecules is an orbital interaction due to relativistic effects and the most stable structures are opened-shape clusters, reducing the number of oxygen-mercury contacts and maximizing the formation of hydrogen bonds among water molecules. In these types of clusters, Hg2+ promotes the water hydrolysis over coordination with oxygen atoms. However, when we considered the change associated with the transfer of a cluster from the ideal gas to a solvated system, our solvation free energy analysis revealed that closed-shape clusters are more favorable, maximizing the number of oxygen-mercury contacts and reducing the formation of hydrogen bonds among water molecules. This finding suggests that, under room conditions, the coordination of Hg2+ is more favorable than hydrolysis. Our results have significant implications for understanding Hg2+ behavior in water, helping to develop targeted strategies for mercury remediation and management, and contributing to advancements in the broader field of environmental chemistry.

Logging evaluation of pore structure and reservoir quality in shale oil reservoir: The Fengcheng Formation in Mahu Sag, Junggar Basin, China

The Permian Fengcheng Formation in the Mahu Sag of the Junggar Basin is characterized by frequent changes of mineral compositions and lamina structure. The alkali lacustrine shale reservoir shows strong heterogeneity and anisotropy, it is particularly important to clarify the relationship between pore structure and reservoir quality. The pore characteristics were investigated by using thin sections, Scanning Electron Microscope (SEM), and Nuclear Magnetic Resonance (NMR) analyses. The pore types are mainly composed of inorganic pores, organic pores, and microfractures. The storage space is dominated by inorganic pores and microfractures. The pore structure was divided into four types by NMR parameters including T2 spectral morphology, T2gm, total porosity, and movable fluid porosity. Combined with core NMR experiments and two-dimensional (2D) NMR logs, 21 ms was adopted as the T2cutoff value to represent the demarcation between movable and bound fluids. From Type I to Type IV, the energy clusters reflect the movable fluids including movable oil and movable water gradually decreasing in the upper right corner. The energy clusters reflect the bound fluids including clay-bound water and bitumen gradually increasing in the lower left corner in the T1-T2 map. The results show that the heterogeneity of mineral compositions and lamina structures are the key factors directly leading to the complexity and distribution of pore structure. Quartz with strong compaction resistance helps keep a large number of primary interparticle pores, and feldspar dissolution pores caused by organic acids are present. Dolomite intercrystalline pores and dissolution pores provide a large amount of storage space for the shale, while the cementation of calcite reduces pore spaces. The increase of felsic mineral content is conducive to improving the pore structure and oil-bearing potential of oil shale reservoir, while clay minerals and calcite are contrary. There are abundant primary interparticle pores and dissolution pores in the layered siliceous (felsic) shales, and they consist of the upper sweet spot in the Fengcheng Formation. The longitudinal time (T1) and transverse time (T2) spectra are bimodal with high total porosity and movable oil content, reflecting high reservoir quality and oil-bearing property. Laminated dolomite shales contain dolomite intercrystalline pores and dissolution pores, and they consist of the lower sweet spot in the Fengcheng Formation. The results above provide a new perspective on the evaluation of pore structure and reservoir quality of shales in the context of an alkaline lake.

Carbon Nanotubes as Biosensors for Releasing Conjugated Bisphosphonates–Metal Ions in Bone Tissue: Targeted Drug Delivery through the DFT Method

Bisphosphonate (BP) agents have attracted much attention for their precise therapy in some skeletal maladies demonstrated by enhancing osteoclast-mediated bone resorption. In this work, the use of CAM-B3LYP/6-311+G(d,p)/LANL2DZ to estimate the susceptibility of single-walled carbon nanotube (SWCNT) for adsorbing alendronate, ibandronate, neridronate, and pamidronate chelated to two metal cations of 2Mg2+, 2Ca2+, and 2Sr2+ through nuclear magnetic resonance and thermodynamic parameters has been accomplished. For most biological medications, oral bioavailability is too low to reach a therapeutic level, and advanced delivery systems such as formulations including permeation enhancers or enzyme inhibitors, lipid-based nanocarriers, and microneedles will likely increase the oral bioavailability of these medications properly. Therefore, the measurements have described that the eventuality of using SWCNT and BP agents becomes the norm in metal chelating of the drug delivery system, which has been selected through (alendronate, ibandronate, neridronate, pamidronate) → 2X (X = Mg2+/Ca2+/Sr2+) complexes. The NMR results of chelated alendronate, ibandronate, neridronate, and pamidronate complexes adsorbed onto (5,5) armchair SWCNT have remarked the location of active sites of tagged nitrogen (N), phosphorus (S), oxygen (O), and metal cations of magnesium (Mg2+), calcium (Ca2+), and strontium (Sr2+) in these molecules which replace the movement of the charge electron transfer in polar bisphosphonates (BPs) toward (5,5) armchair carbon nanotube (CNT). The thermodynamic results have exhibited that the substitution of 2Ca2+ cation by 2Sr2+ cation in the compound of the bioactive glasses can be efficient for treating vertebral complex fractures. However, the most fluctuation in the Gibbs free energy for BPs → 2Sr2+ has been observed at 300 K. This manuscript aimed to show that (5,5) armchair SWCNT can easily penetrate in the bone cells, delivering chelated BP–cations directly to the bone tissue. Drug delivery systems can improve the pharmacological profile, therapeutic profile, and efficacy of BP drugs and lower the occurrence of off-targets.

Chirality of Alanine Molecules in Water Solvent: A Theoretical Perspective

Sequential quantum mechanics/molecular mechanics (QM/MM) calculations combining the average solvent electrostatic configuration (ASEC) and the free energy gradient method are employed to locate minimum structures of α- and β-alanine in a water environment. Herein, we study the solvation effects in the nuclear magnetic resonance (NMR) spectroscopy, vibrational circular dichroism (VCD) spectroscopy, and electronic circular dichroism (ECD) spectroscopy of dl-α-alanine and β-alanine molecules. Our results point out that the ASEC-FEG (average solvent electrostatic configuration with the free energy gradient) method is a suitable approach for finding equilibrium structures of the alanine molecules in aqueous solution. Its accuracy is checked by comparing the optimized structures with those reached by the polarizable continuum model (PCM) and via experimental data. NMR parameters and vibrational and electronic UV-vis spectra are computed with a remarkable agreement with their corresponding experimental values.

Properties of 3-fluoroprop-2-enoic acids, chemical shifts and indirect spin-spin coupling constants: A DFT study

Nuclear magnetic resonance (NMR) parameters, shielding constants, and indirect spin-spin coupling constants (SSCC) in a large set of model compounds were calculated using the combination of the B3PW91, B3LYP, and BHandH functionals with the 6-311+(d,p), 6-311++G(d,p), 6-311++G(2d,p), and 6-311++G(3df, 3pd) basis sets, in order to verify the most appropriate methods for calculating these parameters. Selected methods were applied to calculate the NMR parameters in (2E)- and (2Z)-3-fluoroprop-2-enoic acids. Optimization of structures revealed four stable rotamers of each isomer, E and Z, of 3-fluoroprop-2-enoic acid. The internal molecular energy of s-cis and s-trans syn rotamers indicated that they are favorable in solution. All rotamers of 3-fluoroprop-2-enoic acid are coplanar except E s-trans anti, which has a "twisted" structure due to repulsion between hydrogen atoms CFH and HO. Topological analysis of the electronic structure of molecules including properties of critical points revealed noncovalent F...OH and F...HO bonds in Z s-trans syn and anti rotamers, respectively. The molecules of acid tend to form dimers and trimers in solution via hydrogen bonds O...H, CH...O, and CH...F, with binding energies ranging from a few to over a dozen kcal per mol. Theoretical chemical shifts and SSCCs were analyzed in detail to find a dependence on the geometry of individual rotameters. Calculations revealed a 5J(F,H) of -31 Hz in Z s-trans-anti rotamer containing the F...HO hydrogen bond, while this SSCC ranges from -1.9 to 1.4 Hz in the remaining rotamers. Intermolecular SSCCs across hydrogen bonds range from -3 to 7 Hz in dimers and trimers. Theoretical NMR parameters were compared with available experimental data.

Isolation and quantification of a 17-epi-dammarane triterpenoid rhuslactone from roots of Rhus chinensis and its preventive effects on coronary heart disease and thrombosis in zebrafish

Based on mass spectrometry(MS)-guided separation strategy, compound 1 was obtained from the roots of Rhus chinensis. By comprehensive analysis of high resolution-electrospray ionization-mass spectrometry(HR-ESI-MS), nuclear magnetic resonance(NMR) data, and quantum chemical calculation of NMR(qcc-NMR) parameters, compound 1 was elucidated as rhuslactone, a 17-epi-dammarane triterpenoid with a rare 17α-side chain. An HPLC-ELSD method for its quantification in R. chinensis was established and adopted for the quantification of rhuslactone in different batches of R. chinensis. Rhuslactone displayed a good linear relationship within the range of 0.021 3-1.07 μmol·mL~(-1 )(r=0.997 6), and the average recovery was 99.34% [relative standard deviation(RSD) 2.9%). Moreover, the results of the evaluation test of the preventive effects of rhusalctone on coronary heart disease(CHD) and thrombosis showed that rhuslactone(0.11 nmol·mL~(-1)) significantly alleviated heart enlargement and venous congestion and increased cardiac output(CO), blood flow velocity(BFV), and heart rate, thereby reducing thrombus formation in zebrafish with CHD. The effects of rhuslactone on CO and BFV were superior to that of digoxin(1.02 nmol·mL~(-1)), and its effect on improving heart rate was comparable to that of digoxin. This study provides experimental references for the isolation, identification, quality control, and application of rhuslactone from R. chinensis against CHD. It is worth mentioning that this study has discussed some omissions in the determination of the stereochemistry of C-17 in dammarane triterpenoids in the present coursebook Chemistry of Chinese Medicine and some research papers, that is, the compound may be 17-epi-dammarane triterpenoid. This paper has also proposed steps for the establishment of C-17 stereochemistry.