TY - JOUR
T1 - Electrochemical Preparation and EPR Studies of Lithium Phthalocyanine
T2 - Evaluation of the Nucleation and Growth Mechanism and Evidence for Potential-Dependent Phase Formation
AU - Ilangovan, Govindasamy
AU - Zweier, Jay L.
AU - Kuppusamy, Periannan
PY - 2000/5/4
Y1 - 2000/5/4
N2 - A very reliable and reproducible electrochemical preparative procedure to obtain oxygen-sensitive lithium phthalocyanine (LiPc) microcrystalline powder, a critical material for in vivo application of electron paramagnetic resonance (EPR) oximetry to measure the partial pressure of molecular oxygen pO2, is described. Important issues including the effect of preparative conditions on the resulting material and the influence of the deposition mechanism on crystal structure are investigated using cyclic voltammetry, chronoamperometry, X-ray diffraction (XRD), and high- and low-frequency EPR measurements. The electrochemical measurements reveal that electrodeposition of LiPc follows a nucleation pathway. Detailed electrocrystallization studies show that the nucleation mechanism is instantaneous and the three-dimensional growth is controlled by the diffusion of the reactant from the bulk solution. Critical evidence, for deposition potential-dependent electrochemical phase formation, is presented. The XRD studies indicate that, in certain deposition conditions, namely, deposition at potentials +0.1 and +0.2 V (Ag/AgCl), the β structure of LiPc, which is insensitive to molecular oxygen in terms of EPR oximetry, is formed in higher fraction. On the other hand, at deposition potentials +0.4 and +0.7 V, exclusively the oxygen-sensitive x form is obtained. A rapidity test showed that while at deposition potentials +0.4 and +0.7 V only the x form is obtained, the +0.4 V sample responds more quickly to oxygen than the +0.7 V sample. From the present work, a variety of LiPc microparticles, suitable for in vivo EPR oximetry applications, can be prepared.
AB - A very reliable and reproducible electrochemical preparative procedure to obtain oxygen-sensitive lithium phthalocyanine (LiPc) microcrystalline powder, a critical material for in vivo application of electron paramagnetic resonance (EPR) oximetry to measure the partial pressure of molecular oxygen pO2, is described. Important issues including the effect of preparative conditions on the resulting material and the influence of the deposition mechanism on crystal structure are investigated using cyclic voltammetry, chronoamperometry, X-ray diffraction (XRD), and high- and low-frequency EPR measurements. The electrochemical measurements reveal that electrodeposition of LiPc follows a nucleation pathway. Detailed electrocrystallization studies show that the nucleation mechanism is instantaneous and the three-dimensional growth is controlled by the diffusion of the reactant from the bulk solution. Critical evidence, for deposition potential-dependent electrochemical phase formation, is presented. The XRD studies indicate that, in certain deposition conditions, namely, deposition at potentials +0.1 and +0.2 V (Ag/AgCl), the β structure of LiPc, which is insensitive to molecular oxygen in terms of EPR oximetry, is formed in higher fraction. On the other hand, at deposition potentials +0.4 and +0.7 V, exclusively the oxygen-sensitive x form is obtained. A rapidity test showed that while at deposition potentials +0.4 and +0.7 V only the x form is obtained, the +0.4 V sample responds more quickly to oxygen than the +0.7 V sample. From the present work, a variety of LiPc microparticles, suitable for in vivo EPR oximetry applications, can be prepared.
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M3 - Article
AN - SCOPUS:0001167984
SN - 1089-5647
VL - 104
SP - 4047
EP - 4059
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 17
ER -