Singular values of the Dirac operator in dense QCD-like theories

We study the singular values of the Dirac operator in dense QCD-like theories at zero temperature. The Dirac singular values are real and nonnegative at any nonzero quark density. The scale of their spectrum is set by the diquark condensate, in contrast to the complex Dirac eigenvalues whose scale is set by the chiral condensate at low density and by the BCS gap at high density. We identify three different low-energy effective theories with diquark sources applicable at low, intermediate, and high density, together with their overlapping domains of validity. We derive a number of exact formulas for the Dirac singular values, including Banks-Casher-type relations for the diquark condensate, Smilga-Stern-type relations for the slope of the singular value density, and Leutwyler-Smilga-type sum rules for the inverse singular values. We construct random matrix theories and determine the form of the microscopic spectral correlation functions of the singular values for all nonzero quark densities. We also derive a rigorous index theorem for non-Hermitian Dirac operators. Our results can in principle be tested in lattice simulations.Comment: 3 references added, version published in JHE

Charge Transport in DNA-Based Devices

Charge migration along DNA molecules has attracted scientific interest for over half a century. Reports on possible high rates of charge transfer between donor and acceptor through the DNA, obtained in the last decade from solution chemistry experiments on large numbers of molecules, triggered a series of direct electrical transport measurements through DNA single molecules, bundles and networks. These measurements are reviewed and presented here. From these experiments we conclude that electrical transport is feasible in short DNA molecules, in bundles and networks, but blocked in long single molecules that are attached to surfaces. The experimental background is complemented by an account of the theoretical/computational schemes that are applied to study the electronic and transport properties of DNA-based nanowires. Examples of selected applications are given, to show the capabilities and limits of current theoretical approaches to accurately describe the wires, interpret the transport measurements, and predict suitable strategies to enhance the conductivity of DNA nanostructures.Comment: A single pdf file of 52 pages, containing the text and 23 figures. Review about direct measurements of DNA conductivity and related theoretical studies. For higher-resolution figures contact the authors or retrieve the original publications cited in the caption

Fluorescence-based techniques to assess the miscibility and physical stability of a drug-lipid complex

The objective of this study was to evaluate the feasibility of using fluorescence-based techniques to assess the miscibility and physical stability of a drug-lipid complex pharmaceutical dosage form under a solvent-free condition. An indomethacin-phospholipid complex (IDM-PLC) was used as model complex for this study. The miscibility of indomethacin within the phospholipid was assessed by fluorescence spectroscopy, fluorescence microscopy and infrared spectroscopy. The miscibility limit of the complex system was determined by fluorescence to be 20-30% drug loading content, showing good correlation with infrared spectroscopy. The physical stability of the indomethacin-phospholipid complex stored at 40â was evaluated by fluorescence microscopy. Indomethacin formulated in the lipid complex with an indomethacin loading not more than 30% remained in an amorphous state within a period of 21 days, while the samples with a drug loading over 30% started to crystallize earlier with increasing drug content. IDM-PLC having higher miscibilities were found to be more resistant to recrystallization under heating, thus having better physical stability. Fluorescence-based techniques showed convenience and promise in characterizing drug-lipid miscibility and predicting storage stability under a solvent-free condition.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Solution structure of a DNA double helix with consecutive metal-mediated base pairs

Metal-mediated base pairs represent a powerful tool for the site-specific functionlization of nucleic acids with metal ions. The development of applications of the metal-modified nucleic acids will depend on the availability of structural information on these double helices. We present here the NMR solution structure of a self-complementary DNA oligonucleotide with three consecutive imidazole nucleotides in its centre. In the absence of transition-metal ions, a hairpin structure is adopted with the artifical nucleotides forming the loop. In the presence of Ag(I) ions, a duplex comprising three imidazole-Ag+-imidazole base pairs is formed. Direct proof for the formation of metal-mediated base pairs was obtained from (1)J(N-15,Ag-107/109) couplings upon incorporation of N-15-labelled imidazole. The duplex adopts a B-type conformation with only minor deviations in the region of the artifical bases. This work represents the first structural characterization of a metal-modified nucleic acid with a continuous stretch of metal-mediated base pairs