Glycol-based sol-gel process for the fabrication of ferroelectric PZT thin films

A new sol-gel system using ethylene glycol was developed for the fabrication of PZT thin films with compositions near the morphotropic phase boundary Pb(Zr_0.52Ti_0.48)O₃. Ethylene glycol was used as both a chelating agent and a solvent to replace the highly toxic methoxyethanol used in previous formulations. Thin films were deposited by spin coating the solutions onto platinized silicon substrates. Films were completely crystallized by about 600°C and contained the ferroelectric perovskite phase. A dielectric constant of about 750–800 at 1 KHz was obtained for thin films of 0.3 µm thickness. The hysteresis measurements revealed a remanent polarization of 15 mC/cm² with a coercive field of 60 kV/cm.     

Metalations—XVI : Polylithiation at benzylic positions

Metalation of mesitylene with butyllithium in hexane in the presence of tetramethylethylenediamine yields mono-, di- and trilithiated benzylic compounds (1–5), characterized as their silylated derivatives. Dilithiation occurred partly at the same but preferentially at different methyls. The symmetrical tris-1,3,5-(lithiomethylene)benzene was the main product. Similar metalation occurred with m-xylene. o-Xylene gave also dilithiated products, but at a slower rate, and p-xylene gave slowly and exclusively the gem-dilithio-derivative.The results were explained by greater stabilization of polylithio derivatives with charges all on the starred carbons of the conjugated system, rather than those with charges uniformly dispersed on all carbons. CNDO/2 calculations of the energy of the anions account only partially for the order of stability of most of the studied compounds, but a good correlation between this experimental order and the energies of the lithium compounds was found.     

A NEW FLUORESCENT PHOTOPRODUCT OF TRYPTOPHAN EVIDENCED BY LONG WAVELENGTH EXCITATION OF FLUORESCENCE

Abstract— Besides the normal tryptophan (Trp) fluorescence in aqueous solution (emission maximum at 350 nm), a new emission, peaking around 380 nm, appears by long wavelength excitation. Its fluorescence yield (φ_s 0.24) is higher than that of tryptophan (φ_Trp= 0.13). The growth of this emission is observed under different experimental conditions, mainly under UV anaerobic irradiation. To explain this observation, the formation of a C₃-hydroxylated derivative is tentatively suggested.     

ROTATIONAL DIFFUSION OF RHODAMINE 6G IN HUMAN BLOOD SERUM

Abstract —The time-dependent rotational relaxation of Rhodamine 6G in fresh and dried human blood serum was investigated using picosecond phasefluorometry. Measurements were also carried out in aqueous solutions of amino acids, glucose, urea, and bovine serum albumin to evaluate our model for the interactions. It is shown that the distribution of Rhodamine 6G between the aqueous and the protein phase of the blood serum strongly depends on protein concentration and temperature.     

Theorems for carbon cages

New theorems are established for cages (or polyhedra) with trivalent vertices. One theorem says that all such cages have at least three Kekulé structures (or perfect matchings). Thence, resonance generally appears as a possibility. Another theorem says that for every even vertex count >70 there is at least one cage of a preferable subclass, while for vertex count <70 the sole preferable cage is that of the truncated icosahedron. Thence, the unique role of the buckminsterfullerene structure for C₆₀ is mathematically indicated.[/p]Work supported by the Welch Foundation of Houston, Texas.     

Studies on substituted lactams (I)

Syntheses and reactions of 4-carboxy-2-pyrrolidone, 6,6-dimethyl-4-carboxy-2-piperidone, and 5,5-dimethyl-4-carboxy-2-pyrrolidone are described. Whereas 4-carboxy-2-pyrrolidone polymerizes upon heating to form a polyimide, the two lactams containing geminal dimethyl groups undergo isomerization. The 6,6-dimethyl-4-carboxy-2-piperidone isomerizes to 5,5-dimethyl-3-carboxymethyl-2-pyrrolidone, and 5,5-dimethyl-4-carboxy-2-pyrrolidone affords isopropylidene succinimide. Possible mechanisms for these reactions are discussed.     

Synthesis of 2′,3′-dihydrospiro[benzofuran-2(3H),4′(1′-H)isoquinoline]s. A novel heterocyclic ring system

The synthesis of a novel 2′,3′-dihydrospiro(benzofuran-2(3H),4′(1′H)isoquinoline] ring system ( IV ) by a nucleophilic aromatic fluoride displacement-cyclization is described. Preparation of various derivatives of IV as well as the precursor 4-(2-fluorobenzyl)-1,2,3,4-tetrahydro-4-isoquinolinols is also described.