Ligated aluminum cluster anions, LAl ( = 1-14, L = N[Si(Me)]).

A wide range of low oxidation state aluminum-containing cluster anions, LAln- (n = 1-14, L = N[Si(Me)3]2), were produced via reactions between aluminum cluster anions and hexamethyldisilazane (HMDS). These clusters were identified by mass spectrometry, with a few of them (n = 4, 6, and 7) further characterized by a synergy of anion photoelectron spectroscopy and density functional theory (DFT) based calculations. As compared to a previously reported method which reacts anionic aluminum hydrides with ligands, the direct reactions between aluminum cluster anions and ligands promise a more general synthetic scheme for preparing low oxidation state, ligated aluminum clusters over a large size range.

Low oxidation state aluminum-containing cluster anions: Cp(∗)AlnH(-), n = 1-3.

Three new, low oxidation state, aluminum-containing cluster anions, Cp*AlnH(-), n = 1-3, were prepared via reactions between aluminum hydride cluster anions, AlnHm (-), and Cp*H ligands. These were characterized by mass spectrometry, anion photoelectron spectroscopy, and density functional theory based calculations. Agreement between the experimentally and theoretically determined vertical detachment energies and adiabatic detachment energies validated the computed geometrical structures.

The thiourea group modulates the fluorescence emission decay of fluorescein-labeled molecules.

We have investigated the spectral properties and emission characteristics of fluorescein-5-thiocarbamoyl-N,N'-caproate (FITC-ACA) to examine the origin of the complex emission decay often observed in fluorescein-labeled molecules. The covalent attachment of fluorescein to epsilon-amino-n-caproic acid does not perturb the prototropic transitions of the chromophore or the general fluorescence characteristics of the various prototropic forms. However, both the monoanion and dianion forms of FITC-ACA are quenched relative to free fluorescein and exhibit a complex emission decay that is described by two discrete lifetimes.

Unfolding of class A amphipathic peptides on a lipid surface.

The folding of polypeptides associated with biomembranes is a ubiquitous phenomenon, yet the thermodynamics underlying the process are poorly understood. In the present work we examine the unfolding of a series of alpha-helical amphipathic membrane-associated peptides using guanidine hydrochloride as a denaturant. The peptides are based on the class A amphipathic helix motif, and each contains a single tryptophan at sequence position 2, 3, 7, 12, or 14.

Site-specific tryptophan fluorescence spectroscopy as a probe of membrane peptide structure and dynamics.

The fluorescence from tryptophan contains valuable information about the environment local to the indole side-chain. This environment sensitivity coupled with the ability to synthetically or genetically incorporate a single tryptophan residue at specific sites in a polypeptide sequence has provided the membrane biophysicist with powerful tools for examining the structure and dynamics of membrane peptides and proteins. Here we briefly review the use of site-specific tryptophan fluorescence spectroscopy to probe aspects of peptide orientation, structure, and dynamics in lipid bilayers, focusing on recent developments in the literature.

The central domain of Escherichia coli TyrR is responsible for hexamerization associated with tyrosine-mediated repression of gene expression.

TyrR from Escherichia coli regulates the expression of genes for aromatic amino acid uptake and biosynthesis. Its central ATP-hydrolyzing domain is similar to conserved domains of bacterial regulatory proteins that interact with RNA polymerase holoenzyme associated with the alternative sigma factor, sigma(54). It is also related to the common module of the AAA+ superfamily of proteins that is involved in a wide range of cellular activities.