Jukka Jokisaari

Quadratic response calculations of the electronic spin-orbit contribution to nuclear shielding tensors

The electronic spin-orbit contribution to nuclear magnetic shielding tensors, which causes the heavy-atom chemical shift of the shielding of light nuclei in the vicinity of heavy elements, is calculated as a sum of analytical quadratic response functions. We include both the one- and two-electron parts of the spin-orbit Hamiltonian and consider the interaction with both the Fermi contact and the spin-dipolar mechanisms. Ab initio calculations at the SCF and MCSCF levels are presented for the 1H and 13C shielding tensors in the hydrogen and methyl halides. The applicability of different approximations to the full spin-orbit correction is discussed, and the calculated results are compared with experimental data, where available.

Solute molecular structure determination by N.M.R.

The apparent variation of the HCH bond angle in methyl iodide and of the ratios of internuclear H-H distances in benzene was studied in several thermotropic liquid crystals and in their mixtures. In each case, 13C-methane was used as an internal ‘deformation reference’ and also as a 1H chemical shift reference for the determination of chemical shift anisotropies. The results show that structures in agreement with microwave studies are obtained in liquid crystal mixtures in which the dipolar C-H coupling constant of methane vanishes. The 1H chemical shift anisotropy, ΔσH, of methyl iodide was determined by the gradient method in the mixture of two thermotropic liquid crystals, ZLI 1167 and Phase IV. The variation of the relative concentrations of the components led to a wide range of ΔσH values: from 1·7 p.p.m. to 7·7 p.p.m. when going from Phase IV to ZLI 1167. Also a new means to determine 1H chemical shift anisotropies is proposed. For methyl iodide and benzene, this method predicts the ΔσH values of 8·...

Microfluidic Gas‐Flow Imaging Utilizing Parahydrogen‐Induced Polarization and Remote‐Detection NMR

Microfluidics is the science and technology of systems that process or manipulate small amounts of fluids using channels with dimensions of less than one millimeter. Fluid transport in microfluidic devices is usually monitored by optical detection methods, such as laser-induced fluorescence. Even though they are very useful in many cases, these methods set a limit to the manufacturing material of the chip under study, which must be optically transparent. Furthermore, optical methods generally require addition of markers, which can alter the hydrodynamic properties of the system. Nuclear magnetic resonance (NMR) has several advantages compared with optical methods in microfluidic flow profiling, because it does not require the use of markers, it allows versatile experiments providing image, dynamic, and spectroscopic information, and radiofrequency (RF) waves can penetrate opaque materials. However, conventional NMR measurements using a large coil around the microfluidic device are very challenging or even impossible because of low sensitivity resulting from the low filling factor of the coil (typically on the order of 10 5 to 10 ) and the low sensitivity of large coils. The issue is even worse when gases, whose molecular number density is about three orders of magnitude lower than in liquid, are investigated. Herein, we overcome the sensitivity issue for microfluidic gas flow by combining remote-detection (RD) magnetic resonance imaging (MRI) and parahydrogen-induced polarization (PHIP) techniques. In RD MRI, spatial information is encoded into fluid spins by magnetic field gradients and a large RF coil around the microfluidic device, corresponding to the phase encoding in a conventional MRI experiment. Thereafter, the spin coherences are stored as a longitudinal magnetization, and the amplitude of the magnetization is detected by an ultrasensitive solenoid microcoil outside the device. As the fluid molecules flow from the encoding region to the detector, RD MRI provides time-offlight (TOF) information, making it possible to obtain threedimensional TOF images of fluid flow in the device. In our setup (Figure 1b and Supporting Information), the encoding

Vapor‐phase far‐infrared spectrum and double minimum potential function of trimethylene oxide

The far‐infrared spectrum of trimethylene oxide has been investigated with high resolution and accuracy. A good agreement between the observed and the calculated origins of the ring‐puckering vibration bands was achieved with the potential function V(ξ) = 60 (−0.3235ξ2 + 0.1010ξ4 + 1.45 × 10−4 ξ6) cm−1 in the harmonic oscillator representation.

Twist-bend nematic phase of the liquid crystal dimer CB7CB: orientational order and conical angle determined by 129Xe and 2H NMR spectroscopy

The liquid crystal dimer 1ʺ,7ʺ-bis(4-cyanobiphenyl-4ʹ-yl) heptane (CB7CB) has been shown to possess a nematic–nematic phase transition at 376 K. The phase below this temperature has been identified as a globally uniaxial twist-bend nematic phase, NTB. Within the temperature range 376–388 K, a classic uniaxial nematic phase, N, appears. The NTB phase has a helical structure and the liquid crystal director, n, is tilted with respect to the helix axis; these are formed into a conglomerate of degenerate domains having opposite handedness. In a magnetic field, the helix axis orients along the field. In the present studies, the properties of CB7CB are investigated using 129Xe NMR spectroscopy of dissolved xenon and 2H NMR of CB7CB-d4 and the probe 4-octyl-4ʹ-cyanobiphenyl-d2 also dissolved in CB7CB. In a uniaxial liquid crystalline environment, the 129Xe shielding tensor is cylindrically symmetric due to the deformation of the electron cloud by anisotropic forces associated with the director. The anisotropic part of the shielding tensor depends upon the orientational order parameter of the liquid crystal with respect to the applied magnetic field and the conical (aka tilt) angle of the director. The temperature dependence of the orientational order parameter and of the conical angle has been determined independently from 129Xe and previous 2H NMR experiments. In the NTB phase, the averaged Saupe ordering matrix contains three off-diagonal elements. The temperature dependence of one of these, resulting from the phase chirality, has been determined from the 2H quadrupolar splittings.

The r ∞-structure of thiophene in various liquid crystals with 13C-methane as an internal reference

The r ∞-structure of thiophene was studied in thermotropic liquid crystals and in their mixtures. In each case, 13C-enriched methane was added to the sample to serve as an internal ‘deformation reference’. The results indicate that the structure of thiophene is very sensitive to the liquid crystal environment. The structure obtained for thiophene in such liquid crystal mixtures in which the D CH of methane is vanishingly small is in agreement with the microwave structure. The best agreement, however, is obtained in the mixture of MBBA and ZLI 1167 where the D CH of methane is c. 2 Hz.

Spectral density analysis of nuclear spin-spin coupling: I. A Hulthén potential LCAO model for JX-H in hydrides XH4

Abstract A spectral density function has been calculated for the indirect nuclear spin-spin coupling in hydrides XH 4 , using a simple LCAO model for the X-H fragment. The basis consists of bound and continuum solutions is a Hulthen screened Coulomb potential, and a hydrogen atomic orbital. The reduced coupling constant, K , is an integral over all momenta, k , of this spectral density function. The calculated values of K are about half from the experimental ones, but the 23-fold increase of K from C-H to Pb-H is successfully interpreted by the model. The “high-energy tail” contribution to K from k > 10 2 au is found to be of the relative order of 10 −4 for all systems considered.

Moisture in softwoods: fiber saturation point, hydroxyl site content, and the amount of micropores as determined from NMR relaxation time distributions

Abstract Distributions of nuclear magnetic resonance (NMR) relaxation times provide detailed information about the moisture absorbed in wood. In this work, T2*, T2, and T1 distributions were recorded from fresh sapwood and heartwood samples of pine (Pinus sylvestris) and spruce (Picea abies) at various temperatures. Below the melting point of bulk water, free water is frozen and its signal disappears from the distributions. Then, the low-temperature distributions of the unfrozen bound water contain more information about its components, because the large free water peaks hiding some smaller bound water peaks are absent and the exchange between free and bound water is prevented. Comparison of the total moisture signal integrals above and below the bulk melting point enables the determination of fiber saturation point (FSP), which, in this context, denotes the total water capacity of cell wall. T2*, T2, and T1 distributions offer different kinds of information about moisture components. All the peaks in the distributions were assigned, and it was demonstrated that the accessible hydroxyl site content and the amount of micropores can be estimated based on the peak integrals.

Proton, carbon-13 and mercury-199 N.M.R. studies on dimethyl mercury in isotropic and anisotropic phases

The solvent dependence of the indirect Hg-H, Hg-C and C-H coupling constants in dimethyl mercury has been studied. The measurements show an increase of about 2 per cent in the absolute values of the Hg-H and Hg-C coupling constants on passing from neat dimethyl mercury to a solution in deuterated acetone. Solvent dependence is also observable in comparing the values of the coupling constants in different thermotropic nematogens. This study shows, in accordance with earlier works, that the indirect contribution to the Hg-H coupling is negligible, while the Hg-C coupling is more anisotropic than was earlier predicted. Substituting 13C for 12C causes a downfield isotope shift of about 7 Hz in the 199Hg chemical shifts.

Calculation of binary magnetic properties and potential energy curve in xenon dimer: Second virial coefficient of 129Xe nuclear shielding

Quantum chemical calculations of the nuclear shielding tensor, the nuclear quadrupole coupling tensor, and the spin-rotation tensor are reported for the Xe dimer using ab initio quantum chemical methods. The binary chemical shift delta, the anisotropy of the shielding tensor Delta sigma, the nuclear quadrupole coupling tensor component along the internuclear axis chi( parallel ), and the spin-rotation constant C( perpendicular ) are presented as a function of internuclear distance. The basis set superposition error is approximately corrected for by using the counterpoise correction (CP) method. Electron correlation effects are systematically studied via the Hartree-Fock, complete active space self-consistent field, second-order Møller-Plesset many-body perturbation, and coupled-cluster singles and doubles (CCSD) theories, the last one without and with noniterative triples, at the nonrelativistic all-electron level. We also report a high-quality theoretical interatomic potential for the Xe dimer, gained using the relativistic effective potential/core polarization potential scheme. These calculations used valence basis set of cc-pVQZ quality supplemented with a set of midbond functions. The second virial coefficient of Xe nuclear shielding, which is probably the experimentally best-characterized intermolecular interaction effect in nuclear magnetic resonance spectroscopy, is computed as a function of temperature, and compared to experiment and earlier theoretical results. The best results for the second virial coefficient, obtained using the CCSD(CP) binary chemical shift curve and either our best theoretical potential or the empirical potentials from the literature, are in good agreement with experiment. Zero-point vibrational corrections of delta, Delta sigma, chi (parallel), and C (perpendicular) in the nu=0, J=0 rovibrational ground state of the xenon dimer are also reported.