Here we demonstrate the ability to directly transfer nuclear spin polarization from highly polarized ¹²⁹Xe spins to ¹H in solution via the Spin Polarization Induced nuclear Overhauser effect (SPINOE). Experiments performed at ultra-low magnetic field enable background free detection of ¹H signal enhancements after simply bubbling hyperpolarized xenon gas in solution.

Abstract

Ultra-low field nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI) inherently suffer from a low signal-to-noise ratio due to the small thermal polarization of nuclear spins. Transfer of polarization from a pre-polarized spin system to a thermally polarized spin system via the Spin Polarization Induced Nuclear Overhauser Effect (SPINOE) could potentially be used to overcome this limitation. SPINOE is particularly advantageous at ultra-low magnetic field, where the transferred polarization can be several orders of magnitude higher than thermal polarization. Here we demonstrate direct detection of polarization transfer from highly polarized ¹²⁹Xe gas spins to ¹H spins in solution via SPINOE. At ultra-low field, where thermal nuclear spin polarization is close to background noise levels and where different nuclei can be simultaneously detected in a single spectrum, the dynamics of the polarization transfer can be observed in real time. We show that by simply bubbling hyperpolarized ¹²⁹Xe into solution, we can enhance ¹H polarization levels by a factor of up to 151-fold. While our protocol leads to lower enhancements than those previously reported under extreme Xe gas pressures, the methodology is easily repeatable and allows for on-demand enhanced spectroscopy. SPINOE at ultra-low magnetic field could also be employed to study ¹²⁹Xe interactions in solutions.

Instead of the density, the refractive index of homologues series should better be plotted versus the molar concentration of the main UV-chromophore, the C-H bond, which actually causes the refractive index changes.

Abstract

Changes of the refractive index for homologous series of hydrocarbons are usually plotted versus the density. While there is a clear linear dependence for alkanes and alkenes, the linearity deteriorates for homologous series with functional groups involving heteroatoms. The slope can even become negative, e. g., for carboxylic acids. For gaining a deeper understanding and to establish a more general correlation, we reinvestigate the corresponding theories starting with the Newton-Laplace, Gladstone-Dale and the Lorentz-Lorenz rules. We revisit the concept of molar refractivity pioneered by Landolt and Brühl and show that it is closely connected with a twin of Beer's law. We conclude that the refractive index of homologues series should better be plotted versus the molar concentration of the main UV-chromophore, the C−H bond, which actually causes the refractive index changes. This new approach is not limited to alkanes and alkenes but holds for homologous series with functional groups including heteroatoms.

Presence of water in deep eutectic solvent (DES) alters the inherent structure of DES, and hence promotes surfactant aggregation. The colloidal solution having aggregated structures of sodium N-lauroyl sarcosinate in water-diluted DES (Choline chloride :Glycerol=1: 2) acts as an ideal media to provide structural stability to Cytochrome-c, which shows enhanced enzymatic activity.

Abstract

Deep eutectic solvents (DESs) meet important requirements for green solvent technology, including non-toxicity, biodegradability, sustainability, and affordability. Despite possessing low cohesive energy density than water, DESs have been found to support the self-assembly of amphiphiles. It is very much pertinent to examine the effect of water on self-assembly of surfactants in DESs as the presence of water alters the inherent structure of DES, which is expected to affect the characteristic properties of self-assembly. Following this, we have investigated the self-assembly of amino-acid based surfactant, Sodium N-lauroyl sarcosinate (SLS), in DES-water mixtures (10, 30 and 50 w/w% of water) and explored the catalytic activity of Cytochrome-c (Cyt-c) in the formed colloidal systems. Investigations using surface tension, fluorescence, dynamic light scattering (DLS), and isothermal titration calorimetry (ITC) have shown that DES-water mixtures promote the aggregation of SLS, resulting in the lower critical aggregation concentration (cac ∼1.5–6-fold) of the surfactant as compared to water. The nanoclustering of DES at low water content and it's complete de-structuring at high water content affects the self-assembly in a contrasting manner governed by different set of interactions. Further, Cyt-c dispersed in DES-water colloidal solutions demonstrated 5-fold higher peroxidase activity than that observed in phosphate buffer.

The preferred reaction mechanisms of H₂ dissociation on Cu₁₃ and defective graphene-supported Cu₁₃ clusters are presented. The dissociation energy barrier, −0.31 eV, on the defective graphene-supported Cu₁₃ cluster is substantially lowered compared to that on the pure Cu₁₃ cluster at 0.30 eV, and the dissociated chemisorption strength on the defective graphene-supported Cu₁₃ cluster is also enhanced compared to the pure Cu₁₃ cluster.

Abstract

Ab initio molecular dynamics calculations were performed to study H₂ dissociation mechanisms on Cu₁₃ and defective graphene-supported Cu₁₃ clusters. The study reveals that seven types of corresponding dissociation processes are found on the two clusters. The average dissociation energy barriers are 0.51 eV on the Cu₁₃ cluster and 0.12 eV on the defective graphene-supported Cu₁₃ cluster, which are lowered by ~19 % and ~81 % compared with the pristine Cu(111) surface, respectively. Furthermore, compared with the pure Cu₁₃ cluster, the average dissociation energy barrier on the defective graphene-supported Cu₁₃ cluster is substantially reduced by about 76 %. The preferred dissociation mechanisms on the two clusters are H₂ located at a top-bridge site with the barrier heights of 0.30 eV on the Cu₁₃ cluster and −0.31 eV on the defective graphene-supported Cu₁₃ cluster_. Analysis of the H−Cu bond interactions in the transition states shows that the antibonding-orbital center shifts upward on the defective graphene-supported Cu₁₃ cluster compared with the one on the Cu₁₃ cluster, which explains the reduction of the dissociation energy barrier. The average adsorption energy of dissociated H atoms is also greatly enhanced on the defective graphene-supported Cu₁₃ cluster, about twice that on the Cu₁₃ cluster.

Pseudocapacitive charge storage properties are demonstrated for two isostructural oxides, Sr₂LaFeMnO₇ and Sr₂LaCoMnO₇, showing promising energy density, power density and stability over repeated charge-discharge cycles.

Abstract

Pseudocapacitors promise to fill the gap between traditional capacitors and batteries by delivering reasonable energy densities and power densities. In this work, pseudocapacitive charge storage properties are demonstrated for two isostructural oxides, Sr₂LaFeMnO₇ and Sr₂LaCoMnO₇. These materials comprise spatially separated bilayer stacks of corner sharing BO₆ units (B=Fe, Co or Mn). The spaces between stacks accommodate the lanthanum and strontium ions, and the remaining empty spaces are available for oxide ion intercalation, leading to pseudocapacitive charge storage. Iodometric titrations indicate that these materials do not have oxygen-vacancies. Therefore, the oxide ion intercalation becomes possible due to their structural features and the availability of interstitial sites between the octahedral stacks. Electrochemical studies reveal that both materials show promising energy density and power density values. Further experiments through fabrication of a symmetric two-electrode cell indicate that these materials retain their pseudocapacitive performance over hundreds of galvanostatic charge-discharge cycles, with little degradation even after 1000 cycles.

Oxygen or Sulfur: Three adamantyl thioethers are synthesized. Their structures and monohydrated complexes are characterized by rotational spectroscopy. Exchanging the oxygen atom by sulfur slightly distorts the molecular structure. Adducts with water are formed in a similar way with either the oxygen or the sulfur derivatives, highlighting the capability of sulfur to act as a good hydrogen bond acceptor in bulky structures of this type.

Abstract

We report on the synthesis and characterization using high-resolution rotational spectroscopy of three bulky thioethers that feature an adamantyl group connected to a sulfur atom. Detailed experimental and theoretical structures are provided and compared with the 1,1′-diadamantyl ether. In addition, we expand on previous findings concerning microsolvation of adamantyl derivatives by investigating the cluster formation between these thioethers and a water molecule. The investigation of such clusters provides valuable insights into the sulfur-centered hydrogen bonding in thioethers with increasing size and steric repulsion.

The conversion of carbon dioxide (CO2) into more valuable chemical compounds represents a critical objective for addressing environmental challenges and advancing sustainable energy sources. The CO2 reduction reaction (CO2RR) holds promise for transforming CO2 into versatile feedstock materials and fuels. Leveraging first-principles methodologies provides a robust approach to evaluate catalysts and steer experimental efforts. In this study, we examine the CO2RR process using a diverse array of representative cluster models derived from X-MOF-74 (where X encompasses Mg, Mn, Fe, Co, Ni, Cu, or Zn) through first-principles methods. Notably, our investigation highlights the Fe-MOF-74 cluster's unique attributes, including favorable CO2 binding and the lowest limiting potential of the studied clusters for converting CO2 to methane (CH4) at 0.32 eV. Our analysis identified critical factors driving the selective CO2RR pathway, enabling the formation CH4 on the Fe-MOF-74 cluster. These factors involve less favorable reduction of hydrogen to H2 and strong binding affinities between the Fe open-metal site and reduction intermediates, effectively curtailing desorption processes of closed-shell intermediates such as formic acid (HCOOH), formaldehyde (CH2O), and methanol (CH3OH), to lead to selective CH4 formation.

Polyimide is a potential material for high-performance printed circuit boards because of its chemical stability and excellent thermal and mechanical properties. Flexible printed circuit boards must have a low static dielectric constant and dielectric loss to reduce signal loss in high-speed communication devices. Engineering the molecular structure of polyimides with large pendant groups is a strategy to reduce their dielectric constant. However, there is no systematic study on how the large pendant groups influence electrical energy loss. We integrated all-atomic molecular dynamics and semi-empirical quantum mechanical calculations to examine the influence of pendant groups on polymer chain anisotropy and electrical energy loss at high frequencies. We analyzed the radius of gyration, relative shape anisotropy, dipole moment, and degree of polarization of the selected polyimides (TPAHF, TmBPHF, TpBPHF, MPDA, TriPMPDA, m-PDA, and m-TFPDA). The simulation results show that anisotropy perpendicular to chain direction and local chain rigidity correlate to electrical energy loss rather than dipole moment magnitudes. Polyimides with anisotropic pendant groups and significant local chain rigidity reduce electrical energy loss. The degree of polarization correlated well with the dielectric loss with a moderate computational cost, and difficulties in directly calculating the dielectric loss were circumvented.

Oxidative lesions in DNA model systems, induced by OH⋅, have been structurally characterized by infrared multiple photon dissociation spectroscopy and density functional theory calculations. The addition of one oxygen atom occurs on the nucleobase moiety.

Abstract

OH⋅-induced oxidation products of DNA nucleosides and nucleotides have been structurally characterized by collision-induced dissociation tandem mass spectrometry (CID-MS²) and Infrared Multiple Photon Dissociation (IRMPD) spectroscopy. CID-MS² results have shown that the addition of one oxygen atom occurs on the nucleobase moiety. The gas-phase geometries of +16 mass increment products of 2’-deoxyadenosine (dA(O)H⁺), 2’-deoxyadenosine 5’-monophosphate (dAMP(O)H⁺), 2’-deoxycytidine (dC(O)H⁺), and 2’-deoxycytidine 5’-monophosphate (dCMP(O)H⁺) are extensively investigated by IRMPD spectroscopy and quantum-chemical calculations. We show that a carbonyl group is formed at the C8 position after oxidation of 2’-deoxyadenosine and its monophosphate derivative. For 2’-deoxycytidine and its monophosphate derivative, the oxygen atom is added to the C5 position to form a C−OH group. IRMPD spectroscopy has been employed for the first time to provide direct structural information on oxidative lesions in DNA model systems.

Quantum-mechanical investigations in endofullerenes: the effect of uniaxial distortion on quantized states of the nanoconfined water molecule

Abstract

A water molecule confined inside the C₇₀ fullerene was quantum-mechanically described using a computational approach within the MCTDH framework. Such procedure involves the development of a full-dimensional coupled hamiltonian, with an exact kinetic energy operator, including all rotational, translational and vibrational degrees of freedom of the endofullerene system. In turn, through an effective pairwise potential model, the ground and rotationally excited states of the encapsulated H₂O inside the C₇₀ cage were calculated, and traced back to the isotropic case of the H₂O@C₆₀ endofullerene in order to understand the nature and physical origin of the symmetry breaking observed experimentally in the latter system. Moreover, the computational scheme used here allows to study the quantization of the translational movement of the encapsulated water molecule inside the C₇₀ fullerene, and to investigate the confinement effects in the vibrational energy levels of the H₂O@C₇₀ system.