Pulsed and cw Cr,Tm:YAG laser with simultaneous diode and flashlamp excitation

A Cr,Tm:YAG laser, under simultaneous flashlamp and diode laser excitation, was demonstrated. With respect to diode pumping a cw-output power of 35 W with a slope efficiency of 20% was achieved. With flashlamp excitation pulse energies up to 465 mJ were realised. This operation was supported by simultaneous diode pumping to bring the laser close to threshold. Repetition rates up to 10 Hz were demonstrated with this simultaneous pumping mode of the Cr,Tm:YAG laser crystal.     

The Sex Attractant Pheromone of Male Brown Rats: Identification and Field Experiment

Trapping brown rats is challenging because they avoid newly placed traps in their habitat. Herein, we report the identification of the sex pheromone produced by male brown rats and its effect on trap captures of wild female brown rats. Collecting urine‐ and feces‐soiled bedding material of laboratory‐kept rats and comparing the soiled‐bedding odorants of juvenile and adult males, as well as of adult males and females, we found nine compounds that were specific to, or most prevalent in, the odor profiles of sexually mature adult males. When we added a synthetic blend of six of these compounds (2‐heptanone, 4‐heptanone, 3‐ethyl‐2‐heptanone, 2‐octanone, 2‐nonanone, 4‐nonanone) to one of two paired food‐baited trap boxes, these boxes attracted significantly more laboratory‐strain female rats in laboratory experiments, and captured ten times more wild female rats in a field experiment than the corresponding control boxes. Our data show that the pheromone facilitates captures of wild female brown rats.     

Tailor-made poly(amidoamine)s for controlled complexation and condensation of DNA

A set of polymer carriers for DNA delivery was synthesized by combining monodisperse, sequence-defined poly(amidoamine) (PAA) segments with poly(ethylene oxide) (PEO) blocks. The precise definition of the PAA segments provides the possibility of correlating the chemical structure (monomer sequence) with the resulting biological properties. Three different PAA-PEO conjugates were synthesized by solid-phase supported synthesis, and the cationic nature of the PAA segments was systematically varied. This allows for the tailoring of interactions with double-stranded plasmid DNA (dsDNA). The potential of the PAA-PEO conjugates as non-viral vectors for gene delivery is demonstrated by investigating the dsDNA complexation and condensation properties. Depending on the applied carrier, a transition in polyplex (polymer-DNA ion complex) structures is observed. This reaches from extended ring-like structures to highly compact toroidal structures, where supercoiling of the DNA is induced. An aggregation model is proposed that is based on structural investigations of the polyplexes with atomic force microscopy (AFM) and dynamic light scattering (DLS). While the cationic PAA segment mediates primarily the contact of the carrier to the dsDNA, the PEO block stabilizes the polyplex and generates a "stealth" aggregate, as was suggested by Zeta potentials that were close to zero. The controlled aggregation leads to stable, single-plasmid complexes, and stabilizes the DNA structure itself. This is shown by ethidium bromide intercalation assays and DNase digestion assays. The presented PAA-PEO systems allow for the formation of well-defined single-plasmid polyplexes, preventing hard DNA compression and strongly polydisperse polyplexes. Moreover carrier polymers and the resulting polyplexes exhibit no cytotoxicity, as was shown by viability tests; this makes the carriers potentially suitable for in vivo delivery applications.     

Self-assembly properties of alkyloxyethyl beta-glycosides with different types of carbohydrate headgroups

The effect of alkyl chain length on micelle formation in aqueous solutions of synthetic alkyloxyethyl glycosides containing an ethyl spacer with different conformations of the disaccharide headgroups was investigated. The molecular shape was systematically changed from a wedge-shaped to a rodlike geometry by changing the type of carbohydrate headgroup. The lipophilic part consists of dodecyl or tetradecyl chains. The adsorption at the liquid-air interface was investigated by surface tension measurements. The micellar phase region (L1) was studied using small-angle neutron scattering. We have observed a strong influence of the linkage between the sugar moieties in the disaccharide headgroup and the ethyl spacer on the micellar structure: the transformation from spherical to disklike aggregates was observed for compounds with a rodlike shape, but only spherical aggregates were formed by the wedge-shaped molecules.     

Oligonucleotide fingerprinting of arrayed genomic DNA sequences using LNA-modified hybridization probes

Recently, we established a robust method for the detection of hybridization events using a DNA microarray deposited on a nanoporous membrane. Here, in a follow-up study, we demonstrate the performance of this approach on a larger set of LNA-modified oligoprobes and genomic DNA sequences. Twenty-six different LNA-modified 7-mer oligoprobes were hybridized to a set of 66 randomly selected human genomic DNA clones spotted on a nanoporous membrane slide. Subsequently, assay sensitivity analysis was performed using receiver operating characteristic (ROC) curves. Comparison of LNA-modified heptamers and DNA heptamers revealed that the LNA modification clearly improved sensitivity and specificity of hybridization experiment. Clustering analysis was applied in order to test practical performance of hybridization experiments with LNA-modified oligoprobes in recognizing similarity of genomic DNA sequences. Comparing the results with the theoretical sequence clusters, we conclude that the application of LNA-modified oligoprobes allows for reliable clustering of DNA sequences which reflects the underlying sequence homology. Our results show that LNA-modified oligoprobes can be used effectively to unravel sequence similarity of DNA sequences and thus, to characterize the content of unknown DNA libraries.     

A Carbene-Stabilized Boryl-Phosphinidene

Herein, the synthesis and characterization of the carbene-stabilized boryl phosphinidenes 1 – 3 are reported. Compounds 1 – 3 are obtained by reacting Me-cAAC=PK (Me₂-cAAC=dimethyl cyclic(alkyl)(amino)carbene) and dihaloaryl borane in toluene. All three compounds were characterized by X-ray crystallography. Quantum mechanical studies indicated that these compounds have two lone pairs on the P center viz., an σ-type lone pair and a “hidden” π-type lone pair. Hence, these compounds can act as double Lewis bases, and the basicity of the π-type lone pair is higher than the σ-type lone pair.     

Thermal degradation behaviors of a novel nanocomposite based on polypropylene and Co-Al layered double hydroxide

The thermal degradation behaviors of a novel nanocomposite based on polypropylene and organic Co/Al layered double hydroxide (PP/CoAl-LDH) were studied via thermogravimetric analysis (TGA) in the present work. The thermal degradation activation energies of the PP/CoAl-LDH nanocomposite were determined via Friedman and Flynn-Wall-Ozawa methods, and were compared with those of neat PP. The relationship between the organic CoAl-LDH concentration and the activation energies in PP/CoAl-LDH nanocomposite also has been investigated. An internal reason and an outer reason leading to high fire retardancy of PP/CoAl-LDH nanocomposite were proposed. The presence of CoAl-LDH tended to increase significantly the decomposition activation energy of nanocomposite at full-scale temperature and had an important influence on both of internal and outer reasons.     

Oscillatory forces of nanoparticle suspensions confined between rough surfaces modified with polyelectrolytes via the layer-by-layer technique

This paper addresses the systematic study of surface roughness effects on the internal structuring of silica nanoparticle suspensions under confinement. The confining surfaces are modified by physisorption of layers of oppositely charged polyelectrolytes with the so-called layer-by-layer technique. The layer-by-layer technique modifies the surface roughness without changing the surface potential of a multilayer with the same outermost layer, by increasing the number of constituent layers and ionic strength of the polyelectrolyte solutions and by selecting an appropriate pair of polyelectrolytes. The oscillatory forces of nanoparticle suspensions with a particle diameter of 26 nm are measured by a colloidal-probe atomic force microscope (CP-AFM). The characteristic lengths of the oscillatory force, i.e., wavelength, which indicates interparticle distance, and decay length, or particle correlation length, are not affected by the surface roughness. The corresponding reduction in the oscillatory amplitude and the shift in the phase correlate with an increase in surface roughness. Increasing surface roughness further induces a disappearance of the oscillations, and both confining surfaces contribute to the effect of surface roughness on the force reduction. In order to show an oscillatory force, the particles have to show positional correlation over a reasonably long range perpendicular to the surface, and the correlation function should be the same over a larger lateral area. This requires that both the particles and the surfaces have a high degree of order or symmetry; otherwise, the oscillation does not occur. A roughness of a few nanometers on a single surface, which corresponds to about 10% of the nanoparticle diameter, is sufficient to eliminate the oscillatory force.