18 research outputs found
Supramolecular and Biomacromolecular Enhancement of Metal-Free Magnetic Resonance Imaging Contrast Agents
Many contrast agents for magnetic resonance imaging are based on gadolinium, however side effects limit their use in some patients. Organic radical contrast agents (ORCAs) are potential alternatives, but are reduced rapidly in physiological conditions and have low relaxivities as single molecule contrast agents. Herein, we use a supramolecular strategy where cucurbit[8]uril binds with nanomolar affinities to ORCAs and protects them against biological reductants to create a stable radical in vivo. We further over came the weak contrast by conjugating this complex on the surface of a self-assembled biomacromolecule derived from the tobacco mosaic virus.</div
Influence of <sup>13</sup>C Isotopic Labeling Location on Dynamic Nuclear Polarization of Acetate
Dynamic
nuclear polarization (DNP) via the dissolution method has
alleviated the insensitivity problem in liquid-state nuclear magnetic
resonance (NMR) spectroscopy by amplifying the signals by several
thousand-fold. This NMR signal amplification process emanates from
the microwave-mediated transfer of high electron spin alignment to
the nuclear spins at high magnetic field and cryogenic temperature.
Since the interplay between the electrons and nuclei is crucial, the
chemical composition of a DNP sample such as the type of free radical
used, glassing solvents, or the nature of the target nuclei can significantly
affect the NMR signal enhancement levels that can be attained with
DNP. Herein, we have investigated the influence of <sup>13</sup>C
isotopic labeling location on the DNP of a model <sup>13</sup>C compound,
sodium acetate, at 3.35 T and 1.4 K using the narrow electron spin
resonance (ESR) line width free radical trityl OX063. Our results
show that the carboxyl <sup>13</sup>C spins yielded about twice the
polarization produced in methyl <sup>13</sup>C spins. Deuteration
of the methyl <sup>13</sup>C group, while proven beneficial in the
liquid-state, did not produce an improvement in the <sup>13</sup>C
polarization level at cryogenic conditions. In fact, a slight reduction
of the solid-state <sup>13</sup>C polarization was observed when <sup>2</sup>H spins are present in the methyl group. Furthermore, our
data reveal that there is a close correlation between the solid-state <sup>13</sup>C <i>T</i><sub>1</sub> relaxation times of these
samples and the relative <sup>13</sup>C polarization levels. The overall
results suggest the achievable solid-state polarization of <sup>13</sup>C acetate is directly affected by the location of the <sup>13</sup>C isotopic labeling via the possible interplay of nuclear relaxation
leakage factor and cross-talks between nuclear Zeeman reservoirs in
DNP
BDPA: An Efficient Polarizing Agent for Fast Dissolution Dynamic Nuclear Polarization NMR Spectroscopy
1H and 195Pt NMR Study of the Parallel Two-Chain Compound Per2[Pt(mnt)2]
1H and 195Pt NMR are used to probe the spin ½ anion chain in the quasi-one-dimensional conductor Per2[Pt(mnt)2], which exhibits nearly simultaneous charge density wave (CDW) and spin-Peierls (SP) transitions at low temperatures (Tc ~ 8 K). Below Tc the [Pt(mnt)2] chain forms a spin-singlet state that is evident in 1H NMR spectra and spin relaxation (1/T1) rates; however minority unpaired Pt spins may remain in the SP ground state. With increasing magnetic field, the SP and CDW order parameters decrease in unison, indicating they are coupled up to a critical field Bc ~ 20 T. Above Bc, the spin singlet evolves into a spin-polarized configuration. The 195Pt NMR signals vanish as either Tc or Bc are approached from within the SP ground state, suggesting the hyperfine field of the Pt nucleus is significantly stronger than at the proton sites. Simulations yield a consistent picture of the angular, temperature, and magnetic field-dependent spectral features
Single-walled carbon nanotube buckypaper and mesophase pitch carbon/carbon composites
Carbon/carbon composites consisting of single-walled carbon nanotube (SWCNT) buckypaper (BP) and mesophase pitch resin have been produced through impregnation of BP with pitch using toluene as a solvent. Drying, stabilization and carbonization processes were performed sequentially, and repeated to increase the pitch content. Voids in the carbon/carbon composite samples decreased with increasing impregnation process cycles. Electrical conductivity and density of the composites increased with carbonization by two to three times that of pristine BP. These results indicate that discontinuity and intertube contact barriers of SWCNTs in the BP are partially overcome by the carbonization process of pitch. The temperature dependence of the Raman shift shows that mechanical strain is increased since carbonized pitch matrix surrounds the nanotubes.close
Enhanced Efficiency of <sup>13</sup>C Dynamic Nuclear Polarization by Superparamagnetic Iron Oxide Nanoparticle Doping
The
attainment of high NMR signal enhancements is crucial to the
success of in vitro or in vivo hyperpolarized NMR or imaging (MRI)
experiments. In this work, we report on the use of a superparamagnetic
iron oxide nanoparticle (SPION) MRI contrast agent Feraheme (ferumoxytol)
as a beneficial additive in <sup>13</sup>C samples for dissolution
dynamic nuclear polarization (DNP). Our DNP data at 3.35 T and 1.2
K reveal that the addition of 11 mM elemental iron concentration of
Feraheme in trityl OX063-doped 3 M [1-<sup>13</sup>C] acetate samples
resulted in a substantial improvement of <sup>13</sup>C DNP signal
by a factor of almost three-fold. Concomitant with the large DNP signal
increase is the narrowing of the <sup>13</sup>C microwave DNP spectra
for samples doped with SPION. W-band electron paramagnetic resonance
(EPR) spectroscopy data suggest that these two prominent effects of
SPION doping on <sup>13</sup>C DNP can be ascribed to the shortening
of trityl OX063 electron <i>T</i><sub>1</sub>, as explained
within the thermal mixing DNP model. Liquid-state <sup>13</sup>C NMR
signal enhancements as high as 20,000-fold for SPION-doped samples
were recorded after dissolution at 9.4 T and 297 K, which is about
three times the liquid-state NMR signal enhancement of the control
sample. While the presence of SPION in hyperpolarized solution drastically
reduces <sup>13</sup>C <i>T</i><sub>1</sub>, this can be
mitigated by polarizing smaller aliquots of DNP samples. Moreover,
we have shown that Feraheme nanoparticles (∼30 nm in size)
can be easily and effectively removed from the hyperpolarized liquid
by simple mechanical filtration, and thus one can potentially incorporate
an in-line filtration for these SPIONS along the dissolution pathway
of the hyperpolarizer, a significant advantage over other DNP enhancers
such as the lanthanide complexes. The overall results suggest that
the commercially available and FDA-approved Feraheme is a highly efficient
DNP enhancer that could be readily translated for use in clinical
applications of dissolution DNP