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Exploring the Structure of a Hydrogen Cyanide Polymer by Electron Spin Resonance and Scanning Force Microscopy

M. P. Eastman, F. S. E. Helfrich, A. Umantsev, T. L. Porter*, R. Weber†

Departments of Chemistry, Physics and *Astronomy, Northern Arizona University, Flagstaff, Arizona, USA; †Bruker Instruments, Manning Park, Billerica, Mass., USA

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Summary: Aqueous solutions of potassium cyanide and ammonium hydroxide are known to yield a heterogeneous cyanide polymer, containing paramagnetic sites and biologically significant substructures including polypeptides. Here, such solutions were used to prepare various samples of polymer for study by X-band and W-band electron spin resonance (ESR), scanning electron microscopy (SEM), and scanning force microscopy (SFM). Elemental composition of a typical sample of the polymer was C-35.2%, N-38.47%, O-14.51%, and H- 4.13%, exposing the polymer to 6M HCl hydrolyzed portions of the polymer and released glycine and traces of other amino acids. The X-band ESR spectra consist of a single slightly asymmetric line centered at g = 2.003; spin concentration measurements made at X-band using a nitroxide radical standard yield approximate radical concentrations of 1018 spins/gm. W-band ESR indicates the presence of a single rhombic paramagnetic site with gx = 2.0025, gy = 2.0030, and gz = 2.0048 and the possibility of small 14N hyperfine splittings. The ESR spin echo studies yield a longitudinal relaxation time, T1, of 75 µS and a short-phase memory relaxation time, Tm, of about 300 nS. Scanning electron microscopy studies of the polymer show that it is made of ellipsoidal particles about one micron in size. The particles tend to clump together when suspended in aqueous solution. The particles disperse and dissolve in dimethyl sulfoxide (DMSO); when these solutions dry on microscope slides, optical microscopy shows a branched island morphology for the polymer. This morphology is reminiscent of snowflakes and is identified as dendritic. Phase contrast SFM of the dendritic arms show a striking segregation and ordering of various components of the polymer. Paramagnetic sites are conserved in the series of steps leading to dendritic structures.

Key words: cyanide, polymer, resonance, scanning force microscopy

PACS: 61.16.Ch, 76.30.-v

The authors gratefully acknowledge funding from the National Science Foundation (DMR- 00716762 and DMR-9703840). FH was supported by a grant from the NASA “Space Grant” Consortium and more recently by a Beckman Scholars Grant to Northern Arizona University from the Arnold and Mabel Beckman Foundation.