Changes in Plasma Membrane Surface Potential of PC12 Cells as Measured by Kelvin Probe Force Microscopy

The plasma membrane of a cell not only works as a physical barrier but also mediates the signal relay between the extracellular milieu and the cell interior. Various stimulants may cause the redistribution of molecules, like lipids, proteins, and polysaccharides, on the plasma membrane and change the surface potential (Φs). In this study, the Φss of PC12 cell plasma membranes were measured by atomic force microscopy in Kelvin probe mode (KPFM). The skewness values of the Φss distribution histogram were found to be mostly negative, and the incorporation of negatively charged phosphatidylserine shifted the average skewness values to positive. After being treated with H2O2, dopamine, or Zn2+, phosphatidylserine was found to be translocated to the membrane outer leaflet and the averaged skewness values were changed to positive values. These results demonstrated that KPFM can be used to monitor cell physiology status in response to various stimulants with high spatial resolution

OBSERVATION OF SUB-DOPPLER INFRARED SPECTRUM OF THE H3O+H_{3}O^{+} ION

$^{1}$ Y. T. Chen, J. M. Frye and T. Oka, J. Opt. Soc. Am. B 3, 935 (1986). $^{2}$ F. C. DeLucia, E. Herbst, G. M. Plummer and G. A. Blake, J. Chem. Phys., 78, 2312 (1983).Author Institution: Department of Chemistry and Department of Astronomy and Astrophysics, The University of ChicagoThe frequency tunable infrared source obtained by using the microwave modulation sidebands on $CO_{2}$ laser radiation is sufficiently powerful ($5 \sim 10 mWatts$) and monochromatic $(\Delta \nu \le 20 kHz)$ to conduct systematic saturation-dip spectroscopy in the $10\mu m$ region. Recently this technique was combined with the multiple reflection mirror system to increase the $sensitivity^{1}$ so that it can be applied to molecular ion spectroscopy. We report on the first successful observation of this technique applied to the $\nu_{2}$ vibration-inversion-rotation transition of $H_{3}O^{+}$ ion. The magnetic field enhanced D.C. negative glow $discharge^{2}$ of $\sim 30$ mTorr and low current produced the best result. So far the $*Q(6.6)$ transition has been observed with the signal to noise better than 10 with linewidth of $\sim 500 kHz$ (FWHM). Using the frequency stabilized $CO_{2}$ laser allows us to measure the frequency of the $H_{3}O^{+}$ transition with an absolute accuracy of $\le 300 kHz$. The measurement of more transitions and attempts at observing rotational Zeeman effect and proton hyperfine structure are in progress

STARK AND ZEEMAN EFFECT OF ETHYLENE OBSERVED BY SUB-DOPPLER INFRARED SPECTTROSCOPY

$^{1}$ Y. T. Chen, J. M. Frye and T. Oka, J. Opt. Soc. Am. B, (1986) in press Department of Chemistry and Department of Astronomy and Astrophysics, The University of Chicago, Chicago, Illinois 60637Author Institution:Recent development of sub-Doppler spectroscopy using microwave modulation sidebands of $CO_{2}$ laser radiation has enabled us to perform ultrahigh resolution tunable infrared $spectroscopy^{1}$. Using this technique we studied the small Stark and Zeeman effect of ethylene. Clear Stark splittings have been observed for several low J vibration-ratation lines of the $\nu_{7}$ band using an electric field of up to 50 KV/cm. The analysis of the Stark pattern has given the following polarizability anisotropy for the ground state: $\alpha_{zz}-\frac{\alpha_{xx}+\alpha_{yy}}{2} = 1.42(12)\AA^{3}$ $\alpha_{zz}-\alpha_{yy} = 0.27(66)\AA^{3}$ The polarizability tensor components for the $\nu_{7}$ state are considerably different from the ground state, probably because of the near degeneracy of the $\nu_{7}$ state with other vibrational states $(\nu_{4}, \nu_{8}, \nu_{10})$. More extensive analysis, as well as a study of Zeeman effect to determine the rotational g-factors, are in progress

An Isotopic Substitution Test for Orbiting H Atoms in Vibrationally Highly Excited X~1Σ+g Acetylene

International audienceA Statistical Fouurier Transform (SFT) analysis of the Stimulated Emission Pumping (SEP) spectrum of acetylene (at-26,500cm−1 above the zero-point energy of the X~1Σg state) revealed recurrences at 6 ps. A speculative assignment [J. P. Pique, M.Lombardi, Y. Chen, R. W. Field and J. L. Kinsey, Ber. Bursenges. Phys. Chem., 92, 422 (1988)] of these recurrences as a free orbiting motion of one H about CCH can be tested by isotopic substitution. We are recording SEP spectra of DCCD. Well isolated and rotationally assigned intermediate rovibronic levels for SEP have been selected from rotationally-resolved fluorescence excitation spectra (A~←X~,340) of C2D2 observed at different temperatures (−10K→400K). SEP spectra of vibrationally highly excited (>26,000cm−1 in X~1Σ+g state) C2D2 are currently being obtained through several low-J intermediate states. Each of these SEP spectra belongs to a nearly ``pure sequence'' of all rigorous quantum numbers (J. ortho/para etc.). The vibrational features in the congested spectral region sampled by SEP, however, are intrinsically unassignable in terms of the nonrigorous vibrational quantum numbers. We have applied a Statistical Fourier Tranform technique to decode the short-time (<ps.) molecular dynamical information embedded in the raw SEP spectra. The orbiting period together with the orbital radius of the hypothetical free-rotation of H/D atoms(s) in acetylene, revealed from this new statistical technique, will be discussed