Surface characterizations of spin-coated films of ethylcellulose and hydroxypropyl methylcellulose blends

Films of pure ethylcellulose (EC) and hydroxypropyl methylcellulose (HPMC) polymers and EC/HPMC blends were prepared from solutions by spin coating where isopropyl alcohol (IPA), water, and IPA/water cosolvent were used as solvents. Surface structures of the films were investigated using optical microscopy, atomic force microscopy (AFM), and Raman mapping and spectroscopy. For the films prepared from EC/HPMC blend solutions using the IPA/water cosolvent, different domain structures such as islands or pits and phase separation between EC and HPMC were observed by optical microscopy and AFM. The nature of the polymer components on the surface of the films was identified by Raman mapping and spectroscopy. Experimental results also indicated that polymer composition, solvent, and temperature during spin coating had significant impacts on surface structures of the films.     

A Retro-Diels Alder route to Tetramethyldisilene Me2Si=SiMe2 revisited: Flow Pyrolysis of 1,1,2,2-Tetramethyl-1,2-disilacyclohex-4-ene

Reinvestigation of the flow pyrolysis of 1,1,2,2-tetramethyl-1,2-disilacyclohex-4-ene did not identify conditions under which the retro-Diels Alder reaction was the exclusive process. Extrusion of Me₂Si=SiMe₂was confirmed, but dimerization of directly extruded Me₂Si: contributes significantly to its formation. Rearrangement of 1,1,2,2-tetramethyl-1,2-disilacyclohex-4-ene to 1,1,3,3-tetramethyl-1,3-disilacyclohex-4-ene is a major process under a variety of conditions. Computational studies reduced the number of viable pathways. Both experimental and computational results point to stepwise extrusion of Me₂Si=SiMe₂ via a diradical intermediate and to linkage by one or more common intermediates of the extrusion pathway and the pathway leading to rearranged disilacyclohexene. Such a mechanism receives support from the formation of 1,2- and 1,3-disilacyclohex-4-enes, that is both the Diels-Alder product and the rearrangement product, in the addition of Me₂Si=SiMe₂ to butadiene. Dedicated to Professor Mitsuo Kira on the occasion of his being honored for his inspiring work as the recipient of the 2005 Wacker Silicon Award.     

Charge carrier field emission determines the number of charges on native state proteins in electrospray ionization

Although multiple charging in electrospray ionization (ESI) is essential to protein mass spectrometry, the underlying mechanism of multiple charging has not been explicated. Here, we present a new theory to describe ESI of native-state proteins and predict the number of excess charges on proteins in ESI. The theory proposes that proteins are ionized as charged residues in ESI, as they retain residual excess charges after solvent evaporation and do not desorb from charged ESI droplets. However, their charge state is not determined by the Rayleigh limit of a droplet of similar size to the protein; rather, their final charge state is determined by the electric field-induced emission of small charged solute ions and clusters from protein-containing ESI droplets. This theory predicts that the number of charges on a protein in ESI should be directly proportional to the square of the gas-phase protein diameter and to E*, the critical electric field strength at which ion emission from droplets occurs. This critical field strength is determined by the properties of the excess charge carriers (i.e., the solute) in droplets. Charge-state measurements of native-state proteins with molecular masses in the 5-76 kDa range in ammonium acetate and triethylammonium bicarbonate are in excellent agreement with theoretical predictions and strongly support the mechanism of protein ESI proposed here.