Kazuyuki Takeda

A highly integrated FPGA-based nuclear magnetic resonance spectrometer

The digital circuits required for a nuclear magnetic resonance (NMR) spectrometer, including a pulse programmer, a direct digital synthesizer, a digital receiver, and a PC interface, have been built inside a single chip of the field-programmable gate-array (FPGA). By combining the FPGA chip with peripheral analog components, a compact, laptop-sized homebuilt spectrometer has been developed, which is capable of a rf output of up to 400 MHz with amplitude-, phase-, frequency-, and pulse-modulation. The number of rf channels is extendable up to three without further increase in size.

OPENCORE NMR: open-source core modules for implementing an integrated FPGA-based NMR spectrometer.

A tool kit for implementing an integrated FPGA-based NMR spectrometer [K. Takeda, A highly integrated FPGA-based nuclear magnetic resonance spectrometer, Rev. Sci. Instrum. 78 (2007) 033103], referred to as the OPENCORE NMR spectrometer, is open to public. The system is composed of an FPGA chip and several peripheral boards for USB communication, direct-digital synthesis (DDS), RF transmission, signal acquisition, etc. Inside the FPGA chip have been implemented a number of digital modules including three pulse programmers, the digital part of DDS, a digital quadrature demodulator, dual digital low-pass filters, and a PC interface. These FPGA core modules are written in VHDL, and their source codes are available on our website. This work aims at providing sufficient information with which one can, given some facility in circuit board manufacturing, reproduce the OPENCORE NMR spectrometer presented here. Also, the users are encouraged to modify the design of spectrometer according to their own specific needs. A home-built NMR spectrometer can serve complementary roles to a sophisticated commercial spectrometer, should one comes across such new ideas that require heavy modification to hardware inside the spectrometer. This work can lower the barrier of building a handmade NMR spectrometer in the laboratory, and promote novel and exciting NMR experiments.

Solid-state NMR analysis of interaction sites of curcumin and 42-residue amyloid β-protein fibrils.

Aggregation of 42-residue amyloid β-protein (Aβ42) plays a pivotal role in the etiology of Alzheimers disease (AD). Curcumin, the yellow pigment in the rhizome of turmeric, attracts considerable attention as a food component potentially preventing the pathogenesis of AD. This is because curcumin not only inhibits the aggregation of Aβ42 but also binds to its aggregates (fibrils), resulting in disaggregation. However, the mechanism of interaction between curcumin and the Aβ42 fibrils remains unclear. In this study, we analyzed the binding mode of curcumin to the Aβ42 fibrils by solid-state NMR using dipolar-assisted rotational resonance (DARR). To improve the quality of 2D spectra, 2D DARR data were processed with the covariance NMR method, which enabled us to detect weak cross peaks between carbons of curcumin and those of the Aβ42 fibrils. The observed (13)C-(13)C cross peaks indicated that curcumin interacts with the 12th and 17-21st residues included in the β-sheet structure in the Aβ42 fibrils. Interestingly, aromatic carbons adjacent to the methoxy and/or hydroxy groups of curcumin showed clear cross peaks with the Aβ42 fibrils. This suggested that these functional groups of curcumin play an important role in its interaction with the Aβ42 fibrils.

Surface Functionalization of Silica by Si–H Activation of Hydrosilanes

Inspired by homogeneous borane catalysts that promote Si-H bond activation, we herein describe an innovative method for surface modification of silica using hydrosilanes as the modification precursor and tris(pentafluorophenyl)borane (B(C6F5)3) as the catalyst. Since the surface modification reaction between surface silanol and hydrosilane is dehydrogenative, progress and termination of the reaction can easily be confirmed by the naked eye. This new metal-free process can be performed at room temperature and requires less than 5 min to complete. Hydrosilanes bearing a range of functional groups, including alcohols and carboxylic acids, have been immobilized by this method. An excellent preservation of delicate functional groups, which are otherwise decomposed in other methods, makes this methodology appealing for versatile applications.

Modulatory resonance recoupling of heteronuclear dipolar interactions under magic angle spinning

Abstract A new solid-state NMR technique for recoupling heteronuclear dipolar interactions under magic angle spinning is proposed. In this method, the recoupling is achieved by interference between two non-commutable time-dependent Hamiltonians in the doubly rotating frame: one is the heteronuclear dipolar interaction modulated by MAS and the other is the rf interaction whose amplitude is modulated. When the two modulation frequencies are matched to each other, the cross term between the two interactions becomes time-independent. Since the recoupling condition does not include the intensity of the rf field, this recoupling method is insensitive to inhomogeneity of the rf field. This new recoupling method is demonstrated for 2- 13 C/ 15 N doubly labeled glycine.

Dynamic Nuclear Polarization by Electron Spins in the Photoexcited Triplet State: I. Attainment of Proton Polarization of 0.7 at 105 K in Naphthalene

A high 1 H polarization of 0.7 is attained at 105 K in a 0.32 T field by dynamic nuclear polarization using electron spins in the photoexcited triplet state. In a single crystal sample of 0.018 mol...

Newly Designed 3 T MRI Magnet Wound With Bi-2223 Tape Conductors

We have designed and fabricated a 3T magnetic resonance imaging magnet system for the human brain, which was wound with Bi-2223 tape conductors. Cooled by a Gifford-McMahon cryocooler, it was operated at 20 K with a stored energy of 2.3 MJ. A magnetic-field homogeneity of 5 ppm was attained at 1.5 T, which was our target value. Using this Bi-2223 high-temperature superconducting magnet, we obtained magnetic resonance images in 1.5 T at 8.5 K. The system was successfully magnetized to 3 T, which is the final target field in our project. This work demonstrates the potential of the high-temperature superconducting magnet for use in human magnetic resonance imaging experiments.

Reduction on reactive pore surfaces as a versatile approach to synthesize monolith-supported metal alloy nanoparticles and their catalytic applications

Supported metal alloy nanoparticles demonstrate high potential in designing heterogeneous catalysts for organic syntheses, pollution control and fuel cells. However, requirements of high temperature and multistep processes remain standing problems in traditional synthetic strategies. We herein present a low-temperature, single-step, liquid-phase methodology for designing monolith-supported metal alloy nanoparticles with high physicochemical stability and accessibility. Metal ions in aqueous solutions are reduced to form their corresponding metal alloy nanoparticles within hierarchically porous hydrogen silsesquioxane (HSQ, HSiO1.5) monoliths bearing well-defined macro- and mesopores and exhibiting high surface redox activity due to the presence of abundant Si–H groups. Supported bi-, tri- and tetrametallic nanoparticles have been synthesized with controlled compositions and loadings, and characterized in detail by microscopy and spectroscopy techniques. Examination of these supported metal alloy nanoparticles in catalytic reduction of 4-nitrophenol shows high catalytic activities depending on their compositions. Their recyclability and potential application in continuous flow reactors are also demonstrated.

Optimization of 1H spin density for dynamic nuclear polarization using photo-excited triplet electron spins.

In dynamic nuclear polarization (DNP) using photo-excited triplet electron spins, known as Microwave-Induced Optical Nuclear Polarization (MIONP), the attainable (1)H polarization is determined by the ratio of the buildup rate and the spin-lattice relaxation rate, in turn depend on the (1)H spin density. It is shown that the final (1)H polarization can be enhanced by diluting the (1)H spins with partial deuteration. The DNP experiments are demonstrated in 0.05 mol% pentacene-doped p-terphenyl for various (1)H abundances. It is also shown that the (1)H spin diffusion coefficient can be determined by examining the initial buildup rate of (1)H polarization for various repetition rates of the DNP sequence.

Dynamic nuclear polarization by photoexcited-triplet electron spins in polycrystalline samples

Abstract It is shown that the large electron spin polarization created in the photoexcited triplet species can be transferred to the nuclear spins even in a polycrystalline sample by utilizing a partial area of the extremely broad ESR powder spectrum for cross polarization (CP). The proton polarization 3160 times as large as the thermal equilibrium value was obtained in 0.018 mol% pentacene-doped naphthalene at 100 K in a field of 0.319 T. The influence of the proton spin–lattice relaxation and the sample thickness on the attained polarization is discussed.