K. Jurga

High homogeneity B1 30.2 MHz Nuclear Magnetic Resonance Probe for off-resonance relaxation times measurements

This paper reports on design and construction of a double coil high-homogeneity ensuring Nuclear Magnetic Resonance Probe for off-resonance relaxation time measurements. NMR off-resonance experiments pose unique technical problems. Long irradiation can overheat the sample, dephase the spins because of B(1) field inhomogeneity and degrade the signal received by requiring the receiver bandwidth to be broader than that needed for normal experiment. The probe proposed solves these problems by introducing a separate off-resonance irradiation coil which is larger than the receiver coil and is wound up on the dewar tube that separates it from the receiver coil thus also thermally protects the sample from overheating. Large size of the irradiation coil also improves the field homogeneity because as a ratio of the sample diameter to the magnet (coil) diameter increases, the field inhomogeneity also increases (Blümich et al., 2008) [1]. The small receiver coil offers maximization of the filling factor and a high signal to the noise ratio.

Molecular dynamics of poly(ethylene 2,6-naphthalate)-polycarbonate composite by nuclear magnetic resonance

The aim of the work was to examine molecular dynamics of a series of poly(ethylene 2,6-naphthalate)-polycarbonate blends with changing weight ratio of copolymers by off-resonance nuclear magnetic resonance technique. It was shown that this technique provides information about the correlation times of the internal motions. The spectral density function amplitudes were estimated on the basis of the dispersion of the spin-lattice relaxation time off-resonanceTlpoff. The measurements were performed for two series of blends which had been injection moulded with and without compatibilizer. The new polymer materials were also characterized using differential scanning calorimetry. Samples obtained after injection moulding and annealing became amorphous, which indicates that a reaction of transesterification process between the two polymers occurred.

Methodology for solid state NMR off-resonance study of molecular dynamics in heteronuclear systems

Methodology for the study of dynamics in heteronuclear systems in the laboratory frame was described in the previous paper [1]. Now the methodology for the study of molecular dynamics in the solid state heteronuclear systems in the rotating frame is presented. The solid state NMR off-resonance experiments were carried out on a homemade pulse spectrometer operating at the frequency of 30.2 MHz for protons. This spectrometer includes a specially designed probe which contains two independently tuned and electrically isolated coils installed in the coaxial position on the dewar. A unique probe design allows working at three slightly differing frequencies off and on resonance for protons and at the frequency of 28.411 MHz for fluorine nuclei with complete absence of their electrical interference. The probe allows simultaneously creating rf magnetic fields at off-resonance frequencies within the range of 30.2-30.6 MHz and at the frequency of 28.411 MHz. Presented heteronuclear cross-relaxation off-resonance experiments in the rotating frame provide information about molecular dynamics.

Adiabatic fast passage application in solid state NMR study of cross relaxation and molecular dynamics in heteronuclear systems.

The paper presents the benefits of using fast adiabatic passage for the study of molecular dynamics in the solid state heteronuclear systems in the laboratory frame. A homemade pulse spectrometer operating at the frequency of 30.2MHz and 28.411MHz for protons and fluorines, respectively, has been enhanced with microcontroller direct digital synthesizer DDS controller [1-4]. This work briefly describes how to construct a low-cost and easy-to-assemble adiabatic extension set for homemade and commercial spectrometers based on recently very popular Arduino shields. The described set was designed for fast adiabatic generation. Timing and synchronization problems are discussed. The cross-relaxation experiments with different initial states of the two spin systems have been performed. Contrary to our previous work [5] where the steady-state NOE experiments were conducted now proton spins (1)H are polarized in the magnetic field B0 while fluorine spins (19)F are perturbed by selective saturation for a short time and then the system is allowed to evolve for a period in the absence of a saturating field. The adiabatic passage application leads to a reversal of magnetization of fluorine spins and increases the amplitude of the signal.

Local motions in poly(ethylene-co-norbornene) studied by 1H NMR relaxometry

Molecular motions in poly(ethylene-co-norbornene) were studied in a temperature range well below its glass transition point by a few techniques based on the NMR phenomenon. Temperature dependencies of proton spin-lattice relaxation times T1 (at 200 MHz and at 30.2 MHz), proton spin-lattice relaxation time in the rotating frame T1ρ (at 68 kHz) and frequency dispersion of proton spin-lattice off-resonance relaxation times in the rotating frame T1ρ(off) were determined for the copolymer. Analysis of (1)H NMR relaxation data permitted characterization of local motions occurring in the copolymer i.e. rotation of methyl groups around C3 axes, reorientations of methylene groups and motions of segments of polymer chains including norbornene groups.

A Proton NMR Study of n-Decylammonium Chain Dynamics in the Perovskite-type Layered Compound (C10H21NH3)2CdCl4

Abstract A detailed proton second moment and spin-lattice relaxation time investigation of the bilayered compound (C10H21NH3)2 CdCl4 is reported. In the low temperature phase the methyl group exe-cutes a classical threefold reorientation, while the NH3 group is involved in a similar reorientation in an asymmetric potential well. Evidence for defect chain motions in this phase has been found, and infomation regarding the potential wells associated with these motions has been extracted from the data. In the high temperature phase, slow chain defect motions and fast fourfold reorientations of chains about their long axes, parallel to the normal to the bilayer, have been observed.

Internal Dynamics of Norethisterone by NMR, IINS and QC Methods

The low-temperature inelastic incoherent neutron scattering spectrum of norethisterone was compared with that calculated by the density functional theory method. The quantum chemical calculations permitted proposing the assignment of the vibrational modes. In particular, the dynamics of the methyl group substituted at C(13) of the steroid skeleton was analysed on the basis of the neutron scattering spectra and temperature dependence of the spin-lattice relaxation time (1H NMR).

Proton relaxation studies of 17α hydroxy- and 21 hydroxy-progesterones by1H NMR

Proton spin-lattice relaxation timesT1 in 17α hydroxy- and 21 hydroxy-progesterones have been performed in the temperature range from 100 to 400 K at the frequencies of 30 and 90 MHz. The dynamic processes involving the methyl group reorientation about the threefold symmetry axis of the C−C bond are separated, and their activation parameters are determined.