Christopher A. Klug

Fluorescent PLLA-nanodiamond composites for bone tissue engineering.

Superior mechanical properties, rich surface chemistry, and good biocompatibility of diamond nanoparticles make them attractive in biomaterial applications. A multifunctional fluorescent composite bone scaffold material has been produced utilizing a biodegradable polymer, poly(l-lactic acid) (PLLA), and octadecylamine-functionalized nanodiamond (ND-ODA). The uniform dispersion of nanoparticles in the polymer led to significant increase in hardness and Youngs modulus of the composites. Addition of 10%wt of ND-ODA resulted in more than 200% increase in Youngs modulus and 800% increase in hardness, bringing the nanocomposite properties close to that of the human cortical bone. Testing of ND-ODA/PLLA as a matrix supporting murine osteoblast (7F2) cell growth for up to 1 week showed that the addition of ND-ODA had no negative effects on cell proliferation. ND-ODA serves as a multifunctional additive providing improved mechanical properties, bright fluorescence, and options for drug loading and delivery via surface modification. Thus ND-ODA/PLLA composites open up numerous avenues for their use as components of bone scaffolds and smart surgical tools such as fixation devices in musculoskeletal tissue engineering and regenerative medicine. Intense fluorescence of ND-ODA/PLLA scaffolds can be used to monitor bone re-growth replacing the implant in vivo.

Using quaternions to design composite pulses for spin-1 NQR

The fictitious spin-1/2 operators are well known to describe the evolution of a pure nuclear quadrupole resonance (NQR) system; particularly, the application of a radio-frequency pulse at one of the NQR transition frequencies is equivalent to a three-dimensional rotation in a space defined by the corresponding fictitious spin-1/2 operators. We demonstrate, theoretically and experimentally, that consecutive noncommuting rotations applied at the same transition frequency are well described by a single rotation given by quaternion parameterization of the rotations in ficitious spin-1/2 operator space. This new route could greatly save computing time and efforts. We extend this approach to design composite pulses that compensate for the effects of the radio-frequency field inhomogeneity for a powder sample of spin-1 nuclei.

Distance between phosphine-sulfide sidechains of a disubstituted peptide by DRAMA 31P NMR.

Dipolar restoration at the magic angle (DRAMA) has been used to measure the 31P-31P internuclear distance between phosphine-sulfide substituted sidechanins on the fourth and eighth residues of a 12-residue helical peptide. The 7.4 A distance is the same for the peptide lyophilized in bulk or isolated in a cryo- and lyoprotected matrix of poly(ethylene glycol) and sucrose. However, the 31P linewidth for the undiluted peptide is an order of magnitude greater than for the matrix-isolated peptide indicating charge and hydration heterogeneity in the bulk state.

Automated detection of broad NMR spectra: 19 F NMR of paramagnetic UF 4 and 195 Pt NMR of supported Pt catalysts

The automated detection of broad NMR spectra via the controlled stepwise motion of the NMR probe along the field axis of the superconducting solenoid is demonstrated for the detection of 19F NMR of paramagnetic UF4 and 195Pt NMR of supported metal catalysts. The sensitivity advantages of performing these measurements at 2.3 T are discussed with reference to applying this methodology to room temperature in situ electrochemical 195Pt NMR.

Investigations of Uranyl Fluoride Sesquihydrate (UO2F2·1.57H2O): Combining 19F Solid-State MAS NMR Spectroscopy and GIPAW Chemical Shift Calculations

High-resolution 19F magic-angle spinning (MAS) NMR spectra were obtained for the uranium-bearing solid uranyl fluoride sesquihydrate (UO2F2·1.57H2O). While there are seven distinct crystallographic fluorine sites, the 19F NMR spectrum reveals six peaks at -33.3, 9.1, 25.7, 33.0, 39.0, and 48.2 ppm, with the peak at 33.0 ppm twice the intensity of all the others and therefore corresponding to two sites. To assign the peaks in the experimental spectra to crystallographic sites, 19F chemical shifts were calculated using the gauge including projector augmented waves (GIPAW) plane-wave pseudopotential approach for a DFT-optimized crystal structure. The peak assignments from DFT are consistent with two-dimensional double-quantum 19F MAS NMR experiments.