Final Technical Report for DE-FG02-06ER15835: Chemical Imaging with 100nm Spatial Resolution: Combining High Resolution Flurosecence Microscopy and Ion Mobility Mass Spectrometry

We have combined, in a single instrument, high spatial resolution optical microscopy with the chemical specificity and conformational selectivity of ion mobility mass spectrometry. We discuss the design and construction of this apparatus as well as our efforts in applying this technique to thin films of molecular semiconductor materials

Time-sequenced optical nuclear magnetic resonance of gallium arsenide

A method of optical detection of nuclear magnetic resonance is demonstrated in which optical nuclear polarization, spin resonance, and optical detection are separated into distinct sequential periods and separately optimized by varying the optical, rf, and static fields. Experiments on the bulk 69Ga resonance of GaAs show that sites imperceptibly perturbed by the optically relevant defect are optically observable with the rf applied in the dark. A signal-to-noise analysis is given that relates the sensitivity to readily measured material properties and indicates applicability to dilute defects

Can nuclear magnetic resonance resolve epitaxial layers?

The recently demonstrated technique of time-sequenced optical nuclear magnetic resonance in GaAs has made possible the detection of spectra free of the line shape distortions that accompanied earlier steady-state methods with an improvement in sensitivity as well. This work examines the possibility of even higher spectral resolution by means of selective averaging with radio frequency-optical multiple-pulse techniques with the aim of isolating the site-specific changes in the spin Hamiltonian associated with excitation to localized states of the conduction band, as in quantum wells. Simulations are presented to evaluate the approach proposed. It is concluded that such experiments are capable of the sensitivity and resolution to resolve individual epitaxial layers in high-quality structures and would provide unprecedented detail on the electronic structure and its uniformity by way of the nuclear quadrupole and spin-averaged hyperfine interactions

Factors That Drive Peptide Assembly and Fibril Formation: Experimental and Theoretical Analysis of Sup35 NNQQNY Mutants

Residue mutations have substantial effects on aggregation kinetics and propensities of amyloid peptides and their aggregate morphologies. Such effects are attributed to conformational transitions accessed by various types of oligomers such as steric zipper or single β-sheet. We have studied the aggregation propensities of six NNQQNY mutants: NVVVVY, NNVVNV, NNVVNY, VIQVVY, NVVQIY, and NVQVVY in water using a combination of ion-mobility mass spectrometry, transmission electron microscopy, atomic force microscopy, and all-atom molecular dynamics simulations. Our data show a strong correlation between the tendency to form early β-sheet oligomers and the subsequent aggregation propensity. Our molecular dynamics simulations indicate that the stability of a steric zipper structure can enhance the propensity for fibril formation. Such stability can be attained by either hydrophobic interactions in the mutant peptide or polar side-chain interdigitations in the wild-type peptide. The overall results display only modest agreement with the aggregation propensity prediction methods such as PASTA, Zyggregator, and RosettaProfile, suggesting the need for better parametrization and model peptides for these algorithms

Final Technical Report for DE-FG02-06ER15835: Chemical Imaging with 100nm Spatial Resolution: Combining High Resolution Flurosecence Microscopy and Ion Mobility Mass Spectrometry

We have combined, in a single instrument, high spatial resolution optical microscopy with the chemical specificity and conformational selectivity of ion mobility mass spectrometry. We discuss the design and construction of this apparatus as well as our efforts in applying this technique to thin films of molecular semiconductor materials