Chapter 5: Ring-Opening Metathesis Polymerization with an Ultrafast-initiating

Ring-opening metathesis polymerization (ROMP) is one of the most widely used polymerizations. With the development of well-defined catalysts, such as (t-BuO)2(ArN)-Mo=CH(t-Bu) (1), Cl2(PCy3)2Ru=CHPh (2), and Cl2(PCy3)(IMesH2)Ru=CHPh (3), more controlled polymer structures have been obtained by either living polymerization or chain transfer induced polymerization. However, these catalysts suffer from a number of limitations. This chapter describes ROMP with the recently developed catalyst 4 which solves many problems of catalysts 1-3. The first is described the living polymerization of norbornene and norbornene derivatives by catalyst 4 to produce polymers with very narrow polydispersity index (PDI) and good molecular weight control. It also promotes living ROMP of several monomers that previous catalysts had problems with. Lastly, syntheses of block copolymers are also described. In the second half of the chapter, ROMP of more challenging protic monomers are demonstrated. Amphiphilic block copolymers have been prepared by catalyst 4 which spontaneously undergo self-assembly into stable nanoparticles (10- 50 nm in radius) in non-hydrogen bonding solvents such as CH2Cl2 and CHCl3. Polymeric nanoparticles are characterized by NMR, GPC, DLS and SEM. 102 Background Ring-opening metathesis polymerization (ROMP) is one of the most used and studied chain growth polymerizations. 1 Unlike the step growth olefin polymerization, acyclic diene metathesis polymerization (ADMET), 2 ROMP is highly efficient for strained cycloalkenes because the metathesis equilibrium is shifted highly toward the ring opening process in order to release the ring stain. Over the last fifteen years, chemists have expanded the utility of ROMP by developing well-defined catalysts whose initiation and propagation can be controlled to produce well-define polymers. 3 With the discovery of living polymerization of norborenes to produce polymers with good molecular weight control and narrow PDI (eq 1), 4 ROMP was applied to many areas including electronic materials, electroluminescent material, packaging, solid support, and bioactive polymers.

BRIEF NOTES SUBSTRUCTURE OF MICROTUBULES IN BRAIN NERVE

INTRODUCTION out according to the method of Luft (9). The fixative The presence of neurotubules with a diameter of available in the present study was 1.25 % glutaraldehyde containing 5 % sucrose and 500 ppm ruthenium about 200-250 A was first described in nervous red, and buffered with 0.1 M cacodylate at pH 7.4

- 10OOC temperature range in different crystallographic directions arc also described for this high temperature semiconductor. Substantial is observed.

n attractive high temperature properties. of the present study was to obtain much larger samples and characterize the material. The original phase diagram can be found in [4] and fig. 1 represents the more recently assessed diagram redrawn from [5]. While the is a congruently melting line compound, decomposes at a temperature of 1470C. Growth from the melt of can be achieved next to this temperature by crystallizationof slightly solutions (see an arrow in the insert, for example). However, the published data did not precise the composition for the end of the plateau. details 2,1. Synthesis and crystal growth. and samples weighing 2g synthesized in graphite crucibles with lids under Ar flow using an induction furnace. temperature was controlled by an optical pyrometer within After 30 minutes at the melts were quickly cooled down by shutting off the furnace power. Characterization of the resulting samples was

Acknowledgements

iii i

Standing Calcium Gradients in Olfactory Receptor Neurons Can Be Abolished

ABSTRACT Digital imaging and the patch clamp technique were used to investigate the intracellular calcium concentration in olfactory receptor neurons using the Ca 2+ indicator dyes fura-2 and fura-2/AM. The spatial distribution of Ca 2+ as well as its modification by the drugs Amiloride and Ruthenium Red were studied. Resting calcium concentrations in cells loaded with fura-2/AM were between 10 and 200 nM. In cells that were loaded with the pentapotassium salt of fura-2 through the patch pipette, calcium concentrations were in the same range if ATP was added to the pipette solution. Otherwise, Ca 2+ reached concentrations of ~ 500 nM. Most of the observed cells showed a standing gradient of calcium, the calcium concentrations in the distal dendritic end of the cell being higher than in the soma. In some cells, the gradient was markedly reduced or abolished by adding either Amiloride or Ruthenium Red to the bath solution. In a few cells, neither drug had any effect upon the gradient. It is suggested that the inhomogenous spatial distribution of intracellular calcium in olfactory cells of Xenopus laevis is brought about by an influx of calcium ions through two different calcium permeable conductances in the peripheral compartments of the cells. The fact that only either Ruthenium Red or Amiloride abolished the standing calcium gradient further suggested that the two conductances blocked were presumably not coexpressed in the same cells

OH

The Mitsunobu reaction is one of the most extensively used coupling reactions in organic synthesis and typically employs azodicarboxylate reagents such as DEAD or DIAD. However, these reagents have drawbacks such as low room-temperature stability and difficulty in removing the hydrazine byproducts. Professor Bruce Lipshutz and co-workers have developed an attractive alternative to the existing reagents: di(4-chlorobenzyl) DEAD: 94% azodicarboxylate (DCAD). DIAD: 89% DCAD is a stable solid that has an activity comparable to those of DEAD and DIAD in typical Mitsunobu reactions such as substitutions, esterifications, and etherifications. However, unlike the standard reagents, the hydrazine byproduct can be removed by simple precipitation directly from the reaction mixture, and is easily recycled in high yield to regenerate DCAD. Lipshutz, B. H. et al. Org. Lett. 2006, 8, 5069. Di(4-chlorobenzyl) azodicarboxylat

The Effect of Dye Density on the Efficiency of Photosensitization of TiO2 Films: Light-Harvesting by Phenothiazine-Labelled

molecule

Recyclable Metathesis Catalyst

molecule

S

[Chem. Eur. J. 10, 3331–3340 (2004)] A novel 3,8-bis-terthiophenyl-(1,10-phenanthroline) coordinated to [Ru(bpy)2] was synthesized and characterized by electrochemical and spectroscopic techniques, and shown to be a suitable starting material for the electrodeposition of functionalized molecular wires in between nano-gap electrodes, generating stable molecular nano-devices. Temperature dependent nonlinear I-V curves were obtained in the 80 to 300 K range. The material can be deposited on ITO also, forming compact electrochromic films at surface concentrations lower than about 1 × 10 –8 mol·cm 2, but a more loosely bond fibrous form is preferentially deposited at higher surface concentrations