Bacterial initiators form dynamic filaments on single-stranded DNA monomer by monomer.

DNA replication initiation is mediated across all domains of life by initiator proteins oligomerizing at replication origins. Recently, it was shown that initiators can directly bind single-stranded DNA (ssDNA) and thus might enhance origin melting. In this study, we used single-molecule fluorescence assays to probe the ssDNA binding mechanism of the replication initiator DnaA.

Enzymatic oxygen scavenging for photostability without pH drop in single-molecule experiments.

Over the past years, bottom-up bionanotechnology has been developed as a promising tool for future technological applications. Many of these biomolecule-based assemblies are characterized using various single-molecule techniques that require strict anaerobic conditions. The most common oxygen scavengers for single-molecule experiments are glucose oxidase and catalase (GOC) or protocatechuate dioxygenase (PCD).

Measurements of 13C multiple-quantum coherences in amyloid fibrils under magic-angle spinning.

The excitation and detection of high-order multiple quantum coherences among (13)C nuclear spins are demonstrated in the samples of [1-(13)C]-L-alanine and (13)C labeled amyloid fibrils at a spinning frequency of 20 kHz. The technique is based on the double-quantum average Hamiltonian prepared by the DRAMA-XY4 pulse sequence. Empirically, we find that multiple supercycles are required to suppress the higher-order effects for real applications.

Steric zipper formed by hydrophobic peptide fragment of Syrian hamster prion protein.

Steric zippers, where the residues of two neighboring β-sheet layers are tightly interdigitated, have been proposed as fundamental structural units of amyloid fibrils by Eisenberg and co-workers. The steric zipper formed by polypeptides containing the palindromic sequence AGAAAAGA has a distinctive feature that the distance between two interdigitated β-sheet layers is comparable to the interstrand distance of the individual β-sheet. This structural motif is of great interest in the study of prion disease because the AGAAAAGA sequence is highly conserved in prion proteins of different species.

Molecular structure of amyloid fibrils formed by residues 127 to 147 of the human prion protein.

Amyloid fibrils are filamentous and insoluble forms of peptides or proteins. Proline has long been considered to be incompatible with the cross-beta structural motif of amyloid fibrils. On the basis of solid-state NMR spectroscopy data, we present a structural model of an in-register parallel beta sheet for the amyloid fibrils formed from a human prion protein fragment, huPrP(127-47).

Pt- and Au-catalyzed oxidative cyclization of 2-ethenyl-1-(prop-2'-yn-1'-ol)benzenes to naphthyl aldehydes and ketones: catalytic oxidation of metal-alkylidene intermediates using H2O and H2O2.

2-Ethenyl-1-(prop-2'-yn-1'-ol)benzenes was cyclized through catalytic oxidation with PtCl(2)/CO/H(2)O and PEt(3)AuCl/H(2)O(2); the metal-naphthylidene intermediates were identified and oxygenated with water and H(2)O(2), respectively; for the efficiency of cyclization, the Au catalytic system is superior to that of the PtCl(2)-catalysis because of its compatibility toward diverse alcohol substrates including both internal alkynes and terminal alkynes.

Computational studies on stable triplet states of heteroacetylenes and the effects of halogen substituents.

This paper describes theoretical studies of halogen-substituted heteroacetylenes (XCMY, M = Si and Ge; X, Y = H, Cl and F) performed at the QCISD(T)/6-311G//QCISD/6-31G level of theory. The electronegative halogen substituents destabilize the singlet state such that the triplet state tends to become favorable. The triplet state has the bifunctional electronic structure of a triplet carbene joined to a heavy singlet carbene.

Metal-catalyzed chemoselective cycloisomerization of cis-2,4-dien-1-als to 3-cyclopentenones and 4-alkylidene-3,4-dihydro-2H-pyrans.

[reaction: see text] PtCl(2) (5 mol %) catalyst effected cycloisomerization of cis-2,4-dien-1-al (1) to 3-cyclopentenone (3) efficiently in hot toluene. In the presence of p-TSA, this PtCl(2) catalysis gave 2-cyclopentenone (5) exclusively because of the secondary isomerization reaction. Although the 1-2 equilibrium state greatly favors aldehyde (1), PdCl(2)(PhCN)(2) (5 mol %) catalyzed cycloisomerization of aldehyde (1) to 4,6,7,8-tetrahydro-3H-isochromene (4) smoothly in hot toluene.