Green fluorescent protein in inertially injected aqueous nanodroplets

We inertially inject and study the contents of optically trappable aqueous nanodroplets (hydrosomes) emulsified in a perfluorinated matrix. A new piezoelectric actuated device for production of single hydrosomes on demand is introduced. Hydrosomes containing enhanced green fluorescent protein (EGFP) were injected, optically trapped, and held at the focus of an excitation laser in a confocal microscope, and single-molecule photobleaching events were observed. The rotational diffusion time of EGFP in trapped hydrosomes was measured using time-resolved fluorescence anisotropy. In free solution, the mean rotational diffusion time was determined to be 13.8 +/- 0.1 ns at 3 microM and 14.0 +/- 0.2 ns at 10 microM. In hydrosomes, the mean rotational diffusion time was similar and determined to be 12.6 +/- 1.0 ns at 3 microM and 15.5 +/- 1.6 ns at 10 microM. We conclude that the rotational motion inside the nanodroplets is consistent with rotation in free solution and that the protein therefore does not aggregate at the water-oil interface. Protein can be confined in hydrosomes with high efficiency using this technique, which provides an alternative to surface attachment or lipid encapsulation and opens up new avenues of research using single molecules contained in fluid nanovolumes.     

Matrix-assisted laser desorption/ionization mechanism study with dihydroxybenzoic acid isomers as matrices

Desorption and ionization efficiencies of matrix-assisted laser desorption/ionization (MALDI) for various biomolecules with different dihydroxybenzoic acid isomers were studied. No clear relationships were observed between MALDI biomolecule signals vs. gas-phase basicity, proton affinity and ionization potential. This indicates the the gas-phase protonation mechanism is not adequate to explain the observed results.     

Theoretical determinations of the ambient conformational distribution and unimolecular decomposition of n-propylperoxy radical

The conformational distribution and unimolecular decomposition pathways for the n-propylperoxy radical have been generated at the CBS-QB3, B3LYP/6-31+G and mPW1K/6-31+G levels of theory. At each of the theoretical levels, the 298 K Boltzmann distributions and rotational profiles indicate that all five unique rotamers of the n-propylperoxy radical can be expected to be present in significant concentrations at thermal equilibrium. At the CBS-QB3 level, the 298 K distribution of rotamers is predicted to be 28.1, 26.4, 19.6, 14.0, and 11.9% for the gG, tG, gT, gG', and tT conformations, respectively. The CBS-QB3 C-OO bond dissociation energy (DeltaH298 K) for the n-propylperoxy radical has been calculated to be 36.1 kcal/mol. The detailed CBS-QB3 potential energy surface for the unimolecular decomposition of the n-propylperoxy radical indicates that important bimolecular products could be derived from two 1,4-H transfer mechanisms available at T < 500 K, primarily via an activated n-propylperoxy adduct.     

Observation of the A-X electronic transition of the 1-C3H7O2 and 2-C3H7O2 radicals using cavity ringdown spectroscopy

Cavity ringdown spectra of the A-X electronic transition of the 1-propyl and 2-propyl peroxy radicals are reported. Spectroscopic assignments are facilitated by implementing several production mechanisms, either isomer-specific or not. Assignments of specific spectral lines to particular conformers of a given isomer are suggested. Observations on the temporal decay of the various species are reported.     

Structure and stability of self-assembled actin-lysozyme complexes in salty water

Interactions between actin, an anionic polyelectrolyte, and lysozyme, a cationic globular protein, have been examined using a combination of synchrotron small-angle x-ray scattering and molecular dynamics simulations. Lysozyme initially bridges pairs of actin filaments, which relax into hexagonally coordinated columnar complexes comprised of actin held together by incommensurate one-dimensional close-packed arrays of lysozyme macroions. These complexes are found to be stable even in the presence of significant concentrations of monovalent salt, which is quantitatively explained from a redistribution of salt between the condensed and the aqueous phases.     

MM3(96) parameterization for camptothecin analogs: An ab initio and molecular mechanics study

Torsional parameters for MM3(96) were derived for the missing atom types present in thenatural product camptothecin (CPT). Potential energy curves were calculated via ab initiocalculations on representative compounds for dihedral angles containing these missingparameters. Gaussian 92 at the restricted Hartree–Fock level of theory using thestandard 6-31G** and 4-31G** basis sets, was used for all the quantum-mechanicscalculations. Missing MM3 torsional terms were obtained by optimizing the V1, V2 and V3parameters such that MM3 could reproduce the ab initio torsional profile. MM3 calculatedmolecular structures that compare well with the ab initio results. Using the newly developedparameters, conformational analyses and QSAR studies of camptothecin analogs wereundertaken. MM3 predicts two distinct boatlike conformations for the -hydroxy lactonemoiety. The low-energy lactone conformation predicted by MM3 is in general agreement withreported X-ray crystal structures of CPT iodoacetate and 7-ethyl-10-(4-piperidino)piperidinylcarbonyloxy CPT HCl as well as the ab initio structure of a CPT-like-hydroxy lactone.     

Unified molecular picture of the surfaces of aqueous acid, base, and salt solutions

The molecular structure of the interfacial regions of aqueous electrolytes is poorly understood, despite its crucial importance in many biological, technological, and atmospheric processes. A long-term controversy pertains between the standard picture of an ion-free surface layer and the strongly ion specific behavior indicating in many cases significant propensities of simple inorganic ions for the interface. Here, we present a unified and consistent view of the structure of the air/solution interface of aqueous electrolytes containing monovalent inorganic ions. Molecular dynamics calculations show that in salt solutions and bases the positively charged ions, such as alkali cations, are repelled from the interface, whereas the anions, such as halides or hydroxide, exhibit a varying surface propensity, correlated primarily with the ion polarizability and size. The behavior of acids is different due to a significant propensity of hydronium cations for the air/solution interface. Therefore, both cations and anions exhibit enhanced concentrations at the surface and, consequently, these acids (unlike bases and salts) reduce the surface tension of water. The results of the simulations are supported by surface selective nonlinear vibrational spectroscopy, which reveals among other things that the hydronium cations are present at the air/solution interface. The ion specific propensities for the air/solution interface have important implications for a whole range of heterogeneous physical and chemical processes, including atmospheric chemistry of aerosols, corrosion processes, and bubble coalescence.