Fabrication of bacterial cellulose-based wound dressings with improved performance by impregnation with alginate.

Bacterial cellulose (BC) hydrogels are among the most efficient materials already being used for the treatment of complex wounds. The moist environment provided by the BC dressing is a key feature assuring efficient wound recovery. Improving the dressings´ moisture-holding ability facilitates its application and leads to an economically preferable extended wear time. To produce materials with reduced moisture loss, BC dressings were impregnated with a secondary hydrophilic component: alginate. The feasibility of an industrial fabrication of this composite was evaluated on pilot scale equipment. It was shown that the procedure can easily be scaled up without significantly increasing the manufacturing time. The resultant composite possessed improved water-retention properties, providing a smooth dressing exchange as demonstrated by a wound-imitating model. The new materials were moreover shown to be compatible with an antimicrobially active compound, which assures their efficiency in the treatment of highly colonized wounds.

Photodependent Melting of Unmodified DNA Using a Photosensitive Intercalator: A New and Generic Tool for Photoreversible Assembly of DNA Nanostructures at Constant Temperature.

External control of DNA melting and hybridization, a key step in bio- and DNA nanotechnology, is commonly achieved with temperature. The use of light to direct this process is a challenging alternative, which has been only possible with a DNA modification, such as covalent grafting or mismatch introduction, so far. Here we describe the first photocontrol of DNA melting that relies on the addition of a molecule that noncovalently interacts with unmodified DNA and affects its melting properties in a photoreversible and highly robust manner, without any prerequisite in the length or sequence of the target DNA molecule. We synthesize azobenzene-containing guanidinium derivatives and show that a bivalent molecule with a conformation-dependent binding mode, AzoDiGua, strongly increases the melting temperature (Tm) of DNA under dark conditions because its trans isomer intercalates in the DNA double helix. Upon UV irradiation at 365 nm, the trans-cis isomerization induced the ejection of AzoDiGua from the intercalation binding sites, resulting in a decrease in Tm up to 18 °C. This illumination-dependent Tm shift is observed on many types of DNA, from self-complementary single-stranded or double-stranded oligonucleotides to long genomic duplex DNA molecules. Finally, we show that simply adding AzoDiGua allows us to photoreversibly control the assembly/disassembly of a DNA nanostructure at constant temperature, as demonstrated here with a self-hybridized DNA hairpin. We anticipate that this strategy will be the key ingredient in a new and generic way of placing DNA-based bio- and nanotechnologies under dynamic control by light.

Selective stabilization of abasic site-containing DNA by insertion of sterically demanding biaryl ligands.

Biaryl derivatives that consist of one DNA-intercalating unit and a sterically demanding component exhibit a specific behavior towards abasic site-containing DNA (AP-DNA) as determined by thermal DNA denaturation experiments, spectrometric titrations and CD spectroscopic analysis. Specifically, these ligands strongly stabilize AP-DNA towards dissociation, whereas they do not or only marginally affect the melting temperature of regular duplex DNA.

Photosensitive polyamines for high-performance photocontrol of DNA higher-order structure.

Polyamines are small, ubiquitous, positively charged molecules that play an essential role in numerous biological processes such as DNA packaging, gene regulation, neuron activity, and cell proliferation. Here, we synthesize the first series of photosensitive polyamines (PPAs) and demonstrate their ability to photoreversibly control nanoscale DNA higher-order structure with high efficiency. We show with fluorescence microscopy imaging that the efficiency of the PPAs as DNA-compacting agents is directly correlated to their molecular charge. Micromolar concentration of the most efficient molecule described here, a PPA containing three charges at neutral pH, compacts DNA molecules from a few kilobase pairs to a few hundred kilobase pairs, while subsequent 3 min UV illuminations at 365 nm triggers complete unfolding of DNA molecules. Additional application of blue light (440 nm for 3 min) induces the refolding of DNA into the compact state. Atomic force microscopy reveals that the compaction involves a global folding of the whole DNA molecule, whereas UV-induced unfolding is a modification initiated from the periphery of the compacted DNA, resulting in the occurrence of intermediate flower-like structures prior to the fully unfolded state.

Studies of the solvatochromic emission properties of N-aroylurea derivatives II: influence of hydrogen-bonding interactions.

The solvatochromic emission properties of five naphthoylurea derivatives with different substitution patterns at the naphthoylurea functionality were investigated, with a particular focus on the influence of inter- and intramolecular H-bonding interactions. The bathochromic shifts of the emission maxima correlate well with the acceptor number or Catalán's acidity of the solvent (Δλ = 47-86 nm), indicating an excited species with a pronounced negative charge that is stabilized by H-bond donating (HBD) solvents. In media with restricted free volume the formation of the charged species is not favored, because the required conformational change to establish an intramolecular charge transfer (ICT) between the fluorophore and the acylurea substituent is hindered, and the emission mainly originates from the locally excited state. This relationship between the alignment of the naphthoyl carbonyl functionality relative to the naphthyl ring and the spectroscopic shift was confirmed by the comparison of the ground state conformation and the emission spectra of the naphthoylurea derivatives in the solid state. Time-resolved experiments revealed different excited entities, whose lifetimes are significantly influenced by the HBD properties and the temperature of the environment. With few exceptions the naphthoylurea derivatives exhibit only two emissive species in the nanosecond range. All experimental data point to conformational relaxation and solvent reorganization leading to the cis and trans isomers of one preferential conformer with respect to the acylurea unit. The structure of the preferred conformation is mainly determined by the possible inter- or intramolecular H-bonds and is therefore also strongly influenced by the HBD and H-bond accepting (HBA) properties of the polar solvents. As the NH groups of the acylurea functionality contribute mainly to the entire inter- and intramolecular H-bond arrangement the variation of the substitution pattern of the urea unit, specifically the presence and position of the NH groups, leads to derivatives with significantly different steady-state and time-resolved emission properties.

Studies of the solvatochromic emission properties of N-aroylurea derivatives I: Influence of the substitution pattern.

The influence of the substituent of the N-aroylurea functionality on the solvatochromic properties of this class of compounds was investigated with eight examples. The absorption spectra of these compounds exhibit the characteristic spectroscopic properties of the corresponding arene fragment and are only slightly dependent on the solvent. In contrast, all investigated aroylurea derivatives exhibit a strong solvatochromism with a good linear correlation between the emission energy and the acceptor numbers (AN) of the solvents; that is, the emission maximum shifts bathochromically (Δλ = 50-93 nm) with increasing AN. Furthermore, in media with increasing viscosity, as established in glycerol or ethanol solutions with decreasing temperature, the emission maxima are significantly shifted to shorter wavelengths and the full width at half maximum (FWHM) changes. All experimental data point to two emitting states, namely the locally excited (LE) state and the charge-transfer (CT) state. Thus, after initial photoexcitation to the LE state an internal charge transfer (ICT) takes place due to the donor-acceptor interplay between the arene unit and the N-acylureido functionality, mainly assisted by the intramolecular hydrogen bond between the terminal NH group and the aryl-substituted carbonyl functionality, hence interconverting the latter to a stronger acceptor. In the polarized CT state the acylurea unit develops a negative charge, which, after solvent relaxation, is stabilized by solvents with high acceptor number. Time-resolved emission spectroscopy revealed additional conformational changes in the excited state. Two emissive species were identified at room temperature, whose lifetimes depend strongly on the chemical environment. In addition, time-resolved emission spectra (TRES) showed red-shifted emission bands at longer delays after the excitation pulse in polar solvents. These findings are rationalized by the presence of two different emitting rotational conformers.

Water-soluble, pH-sensitive fluorescent probes on the basis of acridizinium ions.

The acridizinium fluorophore was employed as water-soluble substitute for anthracene in PET probes and donor-pi-acceptor systems that may be used as fluorescent light-up probes and ratiometric probes in aqueous media.

Relationship between the structure and the DNA binding properties of diazoniapolycyclic duplex- and triplex-DNA binders: efficiency, selectivity, and binding mode.

The association of dicationic polycyclic ligands, namely, four diazoniapentaphene derivatives, three diazoniaanthra[1,2-a]anthracenes, diazoniahexaphene, and a partly saturated hydroxy-substituted diazoniapentaphene with double-stranded and triple-helical DNA, was investigated by spectrophotometric and viscosimetric titrations, CD and LD spectroscopy, DNA melting experiments, and molecular modeling studies. All experimental and theoretical data reveal an intercalative DNA-binding mode of the diazoniapentaphenes and diazoniaanthra[1,2-a]anthracenes; the latter have approximately 10-fold higher affinity for the DNA duplex. CD spectroscopic investigations and molecular modeling studies show that only one azonianaphthalene part of the ligand is intercalated between the DNA base pairs, whereas the remaining part of the ligand points outside the intercalation pocket. In contrast, the diazoniahexaphene is a DNA groove binder, which binds selectively to [poly(dAdT)]2. At low ligand-to-DNA ratios (r < 0.15), the diazoniahexaphene also behaves as an intercalator; however, all spectroscopic and viscosimetric data are consistent with significant groove binding of this ligand at r > 0.2. Studies of the interaction of diazoniapolycyclic ions with triplex DNA reveal a preferential binding of both diazoniapentaphenes and diazoniaanthra[1,2-a]anthracenes to the triplex and stabilization thereof. These properties are more pronounced in the case of the hexacyclic diazoniaanthra[1,2-a]anthracenes; however, the diazoniahexaphene shows no preferential binding to the triplex. The DNA binding properties of the diazoniapentaphene derivatives remain essentially the same upon variation of the positions of nitrogen atoms or substitution with methyl groups. In contrast, the interactions of the diazoniaanthra[1,2-a]anthracence isomers with triplex DNA are slightly different. Notably, the 14a,16a-diazoniaanthra[1,2-a]anthracene is among the most efficient triplex stabilizers, with a 9-fold larger binding affinity for the triplex than for the DNA duplex. Moreover, the diazoniapentaphene and diazoniaanthra[1,2-a]anthracene derivatives represent the first examples of triplex-DNA binders that do not require additional aminoalkyl side chains for efficient triplex stabilization.

Functional analysis of self-injurious behavior in an adult with Lesch-Nyhan syndrome.

A three-phase functional analysis was conducted to discover controlling variables of self-injury in a 28-year-old individual with Lesch-Nyhan syndrome. Experimental verification followed information-gathering and interpretive phases. Self-injurious responses were blocked to prevent harm to the participant; therefore, responses measured were precursors to self-injury. A multielement experimental design included four assessment conditions: social attention contingent on precursory behavior, attention contingent on behavior incompatible with precursory behavior, continuous attention and minimal attention. Highest rates of precursory behavior occurred during continuous attention and when incompatible behavior was reinforced. Social attention appeared to act as a discriminative stimulus for self-injurious behavior in this participant.