How to tune spindle size relative to cell size?

Cells need to regulate the size and shape of their organelles for proper function. For example, the mitotic spindle adapts its size to changes in cell size over several orders of magnitude, but we lack a mechanistic understanding of how this is achieved. Here, we review our current knowledge of how small and large spindles assemble and ask which microtubule-based biophysical processes (nucleation, polymerization dynamics, transport) may be responsible for spindle size regulation. Finally, we review possible cell-scale mechanisms that put spindle size under the regulation of cell size

POTENTIAL ENERGY SURFACES AND RESONANCE RAMAN EXCITATION PROFILES FOR ELECTRON DONOR/ACCEPTOR COMPLEXES

Author Institution: Department of Physics, Simon Fraser University BurnabyResonance Raman excitation profiles, absorption spectra and fluorescence spectra are calculated for a hypothetical molecule modelled after an electron donor/acceptor complex. The effects on the calculations of the shapes of the potential energy surfaces and of the different inter-nuclear distances in the two electronic states are discussed. Both the excitation profile and the fluorescence spectrum are predicted to be red shifted with respect to the absorption spectrum, consistent with the experimental results for the charge transfer transitions in complexes with tetracyanoethylene as electron acceptor and aromatic electron donors

ZEEMAN SPLITTING OF THE PHOSPHORESCENCE OF PALLADIUH-PHTHALOCYANINE IN A SHPOLSKI'I MATRIX

Author Institution: Departments of Chemistry and Physics Simon Fraser, University Burnaby British ColumbiaThe Zeeman splitting in the lowest phosphorescence state of palladium pthalocyanine in a $Shpolski’ i$ matrix of mixed $\alpha$-chloronaphthalene and n-octane at 20 K is reported. The evidence shows that this state is indeed a triplet and that in zero magnetic field the unperturbed component is about 0.7$cm^{-1}$ higher than the field sensitive degenerate pair. A g-factor of about 2.4 is calculated from the splitting which indicates that the states are not pure spin states

ELECTRONIC RELAXATION OF PtPc IN SOLID SOLUTION

Author Institution: Departments of Physics and Chemistry, Simon Fraser UniversityThe luminescence spectra, lifetimes, and quantum yields of platinum phthalocyanine (PtPc) in $\alpha$-chloronaphthalene ($\alpha$-C1N) were studied as a function of temperature (between $2^{\circ} K$ and $300^{\circ} K$) and sample preparation. At least two molecular species of PtPc (presumably differently sized aggregates) were identified. They differ in their phosphorescence spectra and lifetimes. The larger and/or chemisorbed aggregate was red-shifted vis-a-vis the smaller species and showed faster nonradiative decay. From our data we determined an activation energy of $16 + 2 cm^{-1}$ for the intersystem crossing. Activation energies of phosphorescence of the order of 10 $cm^{-1}$ were also determined. This activation energy appeared to become smaller as the aggregate became larger or chemisorbed

HIGH RESOLUTION FLUORESCENCE AND PHOSPHORESCENCE SPECTRA OF PALLADIUM PHTHALOCYANINE

$^{1}$ T.H. Huang, K.E. Rieckhoff, and E.M. Voigt, Chem. Phys. in print.Author Institution:Well resolved vibronic progressions in both the fluorescence and phosphorescence of palladium phthalocyanine (Pc), will be analyzed and compared with those of other metal Pc’ s, particularly the high-temperature and 1.5 k phosphorescences of PtPc (1). The vibronic progressions in the excitation spectra will also be discussed. [FIGURE]