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A study on the silk fibroin sol-gel transitions is conducted by monitoring the process under various physicochemical conditions with optical spectroscopy at 550 nm. No detectable changes in the protein secondary structure are found up to about 15% gelation, indicating that these early stages of gelation are not accompanied by the formation of [beta]-sheets.

Two efficient routes to the C1-C22 subunits of halichondrin B are described. The cage ketal, which contains 11 asymmetric centers embedded within the ABCDEF-ring framework, is assembled from (+)-conduritol E (27) in 18 steps and 4% overall yield.

A method that manipulates the alignment director of a liquid crystalline sample to obtain anistropic magnetic interaction parameters, such as dipolar coupling, in an oriented liquid crystalline sample is described. Using a complex switched angle spinning (SAS) method that involves three changes in spinning axis, the solidlike spinning sideband pattern are correlated with the isotropic chemical shifts in a 2D experiment.

Matrix-assisted laser desorption/ionization mass spectrometry (MALI)I-MS) requires cocrystallization of analyte with a large excess of matrix, which must be mutually soluble in a solvent that encourages crystal growth upon evaporation. MALDI-MS of hydrophobic proteins can be difficult, because they tend to aggregate in polar solutions. High concentrations of denaturants and salts are often employed to combat protein aggregation, but this can result in signal suppression. By using various organic cosolvent systems and matrixes at different protein:matrix ratios, we were able to use MALDI-TOFMS to detect four bacterially expressed hydrophobic proteins comprising alanine-rich mutants of the basic region/leucine zipper protein (bZIP) GCN4. By manipulating sample temperature, we were able to maintain protein solubility. Protein aggregation was suppressed when mixing the protein and matrix solutions at 4 [degrees] C prior to warming to 37 [degrees] C, following the temperature-leap technique described by Xie and Wetlaufer (Protein Sci. 1996, 5, 517-523), who used this method to renature bovine carbonic anhydrase II. Manipulation of temperature encouraged our hydrophobic proteins to adopt conformations leading to the nonaggregating state, and solubility was maintained even when the concentration of denaturant was reduced from 4 M to 400 mM. The temperature-leap tactic was critical for maintaining protein solubility, preventing signal suppression normally seen with higher concentrations of salts, allowing for generation of superior spectra, and should prove applicable to other systems prone to aggregation.

The characteristic of the triple bonding between gallium (Ga) atoms was determined through a theoretical analysis of a gallyne complex's model electronic structure and related molecules. The existence of the triple bond was doubted since the bond length was shorter than known Ga-Ga single bonds. It was observed that bent structures of model molecules contained triple bonds composed of two dative and a pi bond although the dative bonds in the molecules were weak. The nature of the chemical bond was determined mainly by the electronic structure and not by the molecular geometry.

Ab initio quantum mechanical techniques were employed in the study of M2(GaH)3 (M = Li,Na,K) compounds, which are models for the newly synthesized class of Ga3 three-membered -ring cyclogallene compounds. The experimental (X-ray) structures were in close agreement with theory. While Na2(GaH)3 has C3 symmetry, the remaining two compounds are C3h symmetric. The parent neutral three-membered-ring structure (GaH)3 is not stable as the imaginary vibrational frequencies of (GaH)3 lead to Ga-Ga bond breaking.

H NMR spectroscopy facilitated the estimation of electron self-exchange constants for copper I/II macrocyclic tetrathiaether complexes, in the presence of D2O. Activation factors for copper-cyclic tetrathiaethers (14)aneS4 and (15)aneS4 systems are similar, but self-exchange constant rates vary. This may be due to the sharing of one pathway by two systems and the affinity of a second pathway to copper-cyclic tetrathiaether (15)aneS4 system.

Two-directional arborols with spirane or biphenyl cores were studied in order to determine the effect of core shape and thickness on assembly process. Results suggested that the steric energies of the aggregate molecules are comparable to other gel-forming systems. There was a correlation between steric energies of values greater than -50 kcal/mol and their tendency to gel in aqueous medium. This led to the conclusion that positive steric energy values may be used to predict the gel-forming tendenciesof the arborol.

The aryl group directs thestereochemical course of the electrophile-induced cyclization of substituted 6-aryl-5-hexen-2-ols into C-aryl glycopyranosides. Initial studies using beta-lactam hexenols show that the stereochemistry also depends on the electrophile and the reaction conditions. Kinetic control leads to trans-2,6-disubstituted pyrans while thermodynamic control favors the more stable cis-2,6 pyrans. The mechanism involves an antiperiplanar addition of oxygen and electrophile across the olefin via a transition state where the cis-forms possess a higher energy than the trans-forms.

The first anionic N-heterocyclic dicarbene containing both normal (C2) and abnormal carbene (C4) centers in the same five-membered imidazole ring (III) is prepared by lithiation of the imidazole monocarbene. The dicarbene nature is shown by the formation of the group 13 Lewis acid adducts.

Potassium graphite reduction of L:Ga(Mes)[Cl.sub.2] [L: = :C[{(i-Pr)NC[(Me)}.sub.2], Mes = 2,4,6-[Me.sub.3][c.sub.6][H.sub.2]] in hexane has produced the organogallium dimer L:(Mes)(Cl)Ga-Ga(Cl)(Mes):L. Potassium reduction of L:Ga(Mes)[Cl.sub.2] in toluene has produced the neutral aromatic [Ga.sub.6] octahedron L:Ga[[Ga.sub.4][Mes.sub.4]]Ga:L.

The syntheses, structures and computations of N-heterocyclic carbene (NHC, L:) stabilized [P.sub.2] molecules are described. These compounds have displayed a unique bis-phosphinidene structure, containing two phosphinidene units, each with two lone pairs of electrons, bridged by a phosphorus-phosphorus single bond.

The conformational variations of neutral diborenes in the solid state are described. The polymorphic structures of diborene are attributed to a combination of inter alia, packing effects in the crystal, crystallizing-solvent polarity and intramolecular ligand steric effects.

The synthesis and molecular structure of the first isoelectronic gallepin are described along with its nature of bonding and aromaticity. This compound has displayed the aromatic 6[pi]-electron structure.

The synthesis and characterization of the first stable neutral diborene compound with double boron-boron (B=B) bond are presented.

An investigation was conducted on the energy transfer from rhodobacter sphaeroides light-harvesting complex I (LHI) to the reaction center (RC) with steady state and time-resolved fluorescence spectroscopy. According to Forster energy transfer theory, the acceleration of energy transfer was consistent with the increase in the energy transfer rate estimated from the spectral overlap between the RC absorbance and the LHI fluorescence.