How accurate are electronic structure methods for actinoid chemistry?

The CASPT2, CCSD, and CCSD(T) levels of wave function theory and seven density functionals were tested against experiment for predicting the ionization potentials and bond dissociation energies of actinoid monoxides and dioxides with their cations. The goal is to guide future work by enabling the choice of an appropriate method when performing calculations on actinoid-containing systems. We found that four density functionals, namely MPW3LYP, B3LYP, M05, and M06, and three levels of wave function theory, namely CASPT2, CCSD, and CCSD(T), give similar mean unsigned errors for actinoid?Coxygen bond energies and for ionization potentials of actinoid oxides and their cations.     

Impact of Gd3+ on DNP of [1-13C]pyruvate doped with trityl OX063, BDPA, or 4-oxo-TEMPO

Hyperpolarized [1-(13)C]pyruvate has become an important diagnostic tracer of normal and aberrant cellular metabolism for in vitro and in vivo NMR spectroscopy (MRS) and imaging (MRI). In pursuit of achieving high NMR signal enhancements in dynamic nuclear polarization (DNP) experiments, we have performed an extensive investigation of the influence of Gd(3+) doping, a parameter previously reported to improve hyperpolarized NMR signals, on the DNP of this compound. [1-(13)C]Pyruvate samples were doped with varying amounts of Gd(3+) and fixed optimal concentrations of free radical polarizing agents commonly used in fast dissolution DNP: trityl OX063 (15 mM), 4-oxo-TEMPO (40 mM), and BDPA (40 mM). In general, we have observed three regions of interest, namely, (i) a monotonic increase in DNP-enhanced nuclear polarization P(dnp) upon increasing the Gd(3+) concentration until a certain threshold concentration c(1) (1-2 mM) is reached, (ii) a region of roughly constant maximum P(dnp) from c(1) until a concentration threshold c(2) (4-5 mM), and (iii) a monotonic decrease in P(dnp) at Gd(3+) concentration c > c(2). Of the three free radical polarizing agents used, trityl OX063 gave the best response to Gd(3+) doping, with a 300% increase in the solid-state nuclear polarization, whereas addition of the optimum Gd(3+) concentration on BDPA and 4-oxo-TEMPO-doped samples only yielded a relatively modest 5-20% increase in the base DNP-enhanced polarization. The increase in P(dnp) due to Gd(3+) doping is ascribed to the decrease in the electronic spin-lattice relaxation T(1e) of the free radical electrons, which plays a role in achieving lower spin temperature T(s) of the nuclear Zeeman system. These results are discussed qualitatively in terms of the spin temperature model of DNP.     

An algorithm for the calculation of the net induction energy and induced multipole tensors in a set of charge distributions with non-linear contributions of all potentials of external fields and both permanent and induced multipoles

This algorithm for the calculation of the induced multipole tensors in a set of charge distributions includes the contributions of partial derivatives of arbitrary order of the potentials defined by both induced and permanent multipoles as well as non-uniform external fields of arbitrary strength. Specific equations are given for both systems with and without translational order. The algorithm, which is based on the Maxwell invariant form, uses direct extensions of algorithms previously developed and tested for the calculation of permanent multipole energies and induced dipole vectors (when the non-uniformity of the field is neglected). The induced tensor components are calculated iteratively. The first approximation, which gives the components as the solution of a set of simultaneous linear equations, includes all nonlinear, non-uniform contributions of permanent multipoles and external fields as well as all contributions linear in derivatives of the induced potentials. The induced tensor components are then used to calculate the net induction energy. The general relations between the polarizability tensors with respect to a centre and the moments of the polarizability densities about the centre are derived.     

Bi-exponential diffusion signal decay in normal appearing white matter of multiple sclerosis

Purpose

Our aim was to characterize bi-exponential diffusion signal changes in normal appearing white matter of multiple sclerosis (MS) patients.

Methods

Diffusion parameters were measured using mono-exponential (0–1000 s/mm²) and bi-exponential (0–5000 s/mm²) approaches from 14 relapsing-remitting subtype of MS patients and 14 age- and sex-matched controls after acquiring diffusion-weighted images on a 3T MRI system. The results were analyzed using parametric or nonparametric tests and multiple linear regression models.

Results

Mono-exponential apparent diffusion coefficient (ADC) slightly increased in controls (P=.09), but decreased significantly in MS as a function of age, nonetheless an elevated ADC was observed with increasing lesion number in patients. Bi-exponential analyses showed that the increased ADC is the result of decreased relative volume fraction of slow diffusing component (f_s). However, the fast and slow diffusion components (ADC_f, ADC_s) did not change as a function of either age in controls or lesion number and age in MS patients.

Conclusions

These data demonstrated that the myelin content of the white matter affects diffusion in relapsing-remitting subtype of multiple sclerosis that is possibly a consequence of the shift between different water fractions.     

Fast Dissolution Dynamic Nuclear Polarization NMR of 13C-Enriched 89Y-DOTA Complex: Experimental and Theoretical Considerations

The yttrium complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra(1′-¹³C-acetic acid) [¹³C]DOTA was synthesized. Fast dissolution dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) studies revealed that the ⁸⁹Y, ¹³C, and ¹⁵N nuclei present in the complex could be co-polarized at the same optimum microwave irradiation frequency. The liquid-state spin–lattice relaxation time T ₁ of these nuclei were found to be reasonably long to preserve some or most of the DNP-enhanced polarization after dissolution. The hyperpolarized ¹³C and ⁸⁹Y NMR signals were optimized in different glassing mixtures. The overall results are discussed in light of the thermal mixing model of DNP.     

Thermal effusivity investigations of solid materials by using the thermal-wave-resonator-cavity (TWRC) configuration. Theory and mathematical simulations

An alternative photopyroelectric (PPE) technique that combines the front detection configuration (FPPE) with the thermal-wave-resonator-cavity (TWRC) method is proposed. The theoretical analysis of the phase of the FPPE signal indicates that the configuration offers information about both fluid sample and backing material. The backing independent values of the normalized PPE phase give the possibility to calculate fluid’s thermal diffusivity. By monitoring the thickness of a fluid with well known properties, the thermal effusivity of a solid sample (backing material) can be measured.     

Characteristics of Volcanic Tuff from Macicasu (Romania) and Its Capacity to Remove Ammonia from Contaminated Air

In the present work, the capability of the volcanic tuff from Macicasu (Romania) to remove ammonia (NH₃) from air with different contamination levels during 24 h of adsorption experiments was investigated. The natural zeolitic volcanic tuff was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), the Brunauer–Emmett–Teller (BET) method, inductively coupled plasma optical emission spectrometry (ICP-OES), and thermogravimetric analysis (TGA). The adsorption capacities varied between 0.022 mg NH₃ g⁻¹ zeolite and 0.282 mg NH₃ g⁻¹ zeolite, depending on the NH₃ concentrations in the air and at the contact time. The nonlinear forms of the Langmuir and Freundlich isotherm models were used to fit the experimental data. Additionally, the adsorption of NH₃ was studied using nonlinear pseudo-first-order (PFO), pseudo-second-order (PSO), and Elovich kinetic model. Based on the total volume of pores of used volcanic tuff, the NH₃ was removed from the air both due to the physical adsorption of NH₃ gas and the ion exchange of NH₄⁺ (resulted from a reaction between NH₃ and H₂O adsorbed by the zeolite). Depending on the initial NH₃ concentration and the amount of volcanic tuff, the NH₃ concentrations can be reduced below the threshold of this contaminant in the air. The adsorption capacity of NH₃ per unit of zeolite (1 g) varied in the range of 0.022–0.282 mg NH₃ g⁻¹ depending on the NH₃ concentration in the air.     

Magnetic properties of TlCaBaCuO4.5 compounds prepared from different starting materials

It has been shown, that different starting materials result in Tl–Ca–Ba–Cu–O superconductors of different type even at the same heat treatment process. This manifests itself in the developing structure, in the number, share-rate and superconducting properties of the occurring phases as well. Microcrystals, phase-compositions, crystallinities, unit cells, onset and critical temperatures, magnetic flux exclusions, critical currents, magnetizations and critical magnetic fields essentially unlike from each other have been observed, depending on the starting materials. The presence of a starting compound having low melting point, as Ba(NO₃)₂ can cause a more compact, better superconducting final product, implying better connection between the grains.     

Polynomial path for the calculation of liquid state free energies from computer simulations tested on liquid water

The polynomial path is introduced for the calculation of liquid state free energies. The well-characterized SPC, TIP4P, and MCY water models were used to demonstrate its efficiency, as well as its range of applicability in conjunction with Monte Carlo computer simulations using thermodynamic integration based on Gaussian quadratures. The technique employed is compared with the slow-growth method (another variant of thermodynamic integration), the perturbation method, and the use of the grand-canonical ensemble.