Interactions of ionic liquids with polysaccharides. VI. Pure cellulose nanoparticles from trimethylsilyl cellulose synthesized in ionic liquids

Trimethylsilyl cellulose (TMSC) can be efficiently synthesized with 1,1,1,3,3,3‐hexamethyldisilazane (HMDS) by applying the ionic liquids (ILs) 1‐ethyl‐3‐methylimidazolium acetate, 1‐ethyl‐3‐methylimidazolium chloride, and 1‐butyl‐3‐methylimidazolium chloride as reaction medium, yielding pure biopolymer derivatives with degrees of substitution (DS) up to 2.89. Cosolvents, for example, chloroform, could be used to adjust the viscosity of the system and to achieve the miscibility of the components. During the synthesis of highly functionalized derivatives precipitation of the TMSC occurred, which simplifies the recycling of the IL. The high tendency of TMSC toward the formation of supermolecular structures was exploited for the formation of nanoparticles studying a simple dialysis process. Amazingly, pure cellulose nanoparticles can be obtained by dissolving TMSC in tetrahydrofurane or N,N‐dimethyl acetamide and dialysis against water. FTIR spectroscopy confirmed the complete removal of the TMS functions during this process. Scanning electron microscopy, dynamic light scattering, atomic force microscopy, and particle size distribution analysis showed that cellulose particles down to a size of 170 nm are accessible in this simple manner. The nanoparticle suspensions exhibit viscosities in the range of water. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4070–4080, 2008     

A quantitative analytical model for static dipolar disorder broadening of the density of states at organic heterointerfaces

Understanding the electronic structure of organic-organic heterointerfaces is crucial for many device applications of organic semiconductors. Here we have developed a simple analytical model to describe the effect of static dipolar disorder in a polymer dielectric on the density of states of an adjacent organic semiconductor. The degree of energetic disorder varies strongly with distance from the interface. Using a simple mobility model, we have been able to explain quantitatively both the magnitude as well as the gate voltage dependence of the field-effect mobility for polymer gate dielectrics with different dielectric constants.     

Isolation of two-dimensional 2:1 cation-ordered perovskite units by anion vacancy ordering in Ba6Na2Nb2P2O17

A new six-layer perovskite-related structure Ba 6Na 2Nb 2M 2O 17 (M = P, V), which consists of cubic (c) BaO 3 layers and oxygen-deficient pseudocubic (c') BaO 2 layers stacked in the sequence c'ccccc, is presented. In Ba 6Na 2Nb 2M 2O 17, two-dimensional slabs of the well-known 2:1 octahedral cation-ordered perovskite motif are isolated between layers of tetrahedral units formed by anion vacancy ordering: two consecutive NbO 6 octahedral layers are sandwiched by two single NaO 6 octahedral layers, which, in turn, connect with two isolated MO 4 tetrahedral layers. Both oxides are derived from the 2:1 ordered perovskite structure (e.g., Ba 3ZnTa 2O 9) by ordered removal of O atoms in every sixth BaO 3 layer. Both materials exhibit a relative permittivity of approximately 20-23, Q x f 0 values of approximately 7800-10600 GHz, and negative temperature coefficients of the resonant frequency of approximately -23 to -7 ppm/ degrees C.     

An adaptive tissue characterization network for model-free visualization of dynamic contrast-enhanced magnetic resonance image data

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has become an important source of information to aid cancer diagnosis. Nevertheless, due to the multi-temporal nature of the three-dimensional volume data obtained from DCE-MRI, evaluation of the image data is a challenging task and tools are required to support the human expert. We investigate an approach for automatic localization and characterization of suspicious lesions in DCE-MRI data. It applies an artificial neural network (ANN) architecture which combines unsupervised and supervised techniques for voxel-by-voxel classification of temporal kinetic signals. The algorithm is easy to implement, allows for fast training and application even for huge data sets and can be directly used to augment the display of DCE-MRI data. To demonstrate that the system provides a reasonable assessment of kinetic signals, the outcome is compared with the results obtained from the model-based three-time-points (3TP) technique which represents a clinical standard protocol for analysing breast cancer lesions. The evaluation based on the DCE-MRI data of 12 cases indicates that, although the ANN is trained with imprecisely labeled data, the approach leads to an outcome conforming with 3TP without presupposing an explicit model of the underlying physiological process.     

Enhancement of temporal periodicity cues in cochlear implants: effects on prosodic perception and vowel identification

Standard continuous interleaved sampling processing, and a modified processing strategy designed to enhance temporal cues to voice pitch, were compared on tests of intonation perception, and vowel perception, both in implant users and in acoustic simulations. In standard processing, 400 Hz low-pass envelopes modulated either pulse trains (implant users) or noise carriers (simulations). In the modified strategy, slow-rate envelope modulations, which convey dynamic spectral variation crucial for speech understanding, were extracted by low-pass filtering (32 Hz). In addition, during voiced speech, higher-rate temporal modulation in each channel was provided by 100% amplitude-modulation by a sawtooth-like wave form whose periodicity followed the fundamental frequency (F0) of the input. Channel levels were determined by the product of the lower- and higher-rate modulation components. Both in acoustic simulations and in implant users, the ability to use intonation information to identify sentences as question or statement was significantly better with modified processing. However, while there was no difference in vowel recognition in the acoustic simulation, implant users performed worse with modified processing both in vowel recognition and in formant frequency discrimination. It appears that, while enhancing pitch perception, modified processing harmed the transmission of spectral information.     

Structure elucidation of a novel family of mycolactone toxins from the frog pathogen Mycobacterium sp. MU128FXT by mass spectrometry

Structures are proposed, based on LC-ion trap MSn analysis and high-resolution FTICR MS/MS analysis, for a novel family of mycolactone toxins isolated from the frog pathogen MU128FXT and differing from those produced by the human pathogen M. ulcerans MUAgy99 in having an altered polyketide side chain.     

Synthetic Wisdom: The Design of a Mixed-Mode Modelling System for Organizational Decision Making

This paper discusses some of the early thinking about the development of a conference-based decision support system. It presents a scheme for the practical development of the mapping of argumentation (‘cognitive mapping’), particularly in the field of strategic planning. The objective is to redesign software (COPE) so that it may become both an effective conferencing system for the collection of ‘synthetic wisdom’ and yet also facilitate the analysis of the qualitative and quantitative features of the models so constructed. It stresses the need for the system to be able to cope with both the political and the behavioural aspects of the decision-making arena.     

Inelastic hadron-nucleus interactions at 20 and 37 GeV/c

The experiment studies charged particle production for π^?, K^?, and $\text{p}$ interactions on nuclei at 20 and 37 GeV/c at the CERN SPS. A non-magnetic detector, consisting of CsI(Tl) scintillation and lucite ?erenkov counters, distinguishes between fast particles, mainly pions, and slow particles, mainly nucleons, with a cut at velocity β ≈ 0.7. Angular distributions, multiplicity distributions and correlations of slow and fast particles were analysed. It is shown that the measurement of the correlations can provide a critical test for different theoretical models of the hadron-nucleus interaction. At the energies studied so far a systematic deviation from KNO scaling is observed. This gives further support to the “standard picture” of the hadron-nucleus interaction and it contrasts with predictions of the coherent-tube model. The regularity observed for the angular distribution of fast secondaries as a function of the number of slow particles can only be explained by combining features predicted by different models.     

Supramolecular Copolymerization as a Strategy to Control the Stability of Self‐Assembled Nanofibers

A major challenge in supramolecular polymerization is controlling the stability of the polymers formed, that is, controlling the rate of monomer exchange in the equilibrium between monomer and polymer. The exchange dynamics of supramolecular polymers based on benzene‐1,3,5‐tricarboxamide (BTA) can be regulated by copolymerizing molecules with dendronized (dBTA) and linear (nBTA) ethylene glycol‐based water‐soluble side chains. Whereas nBTAs form long nanofibers in water, dBTAs do not polymerize, forming instead small spherical aggregates. The copolymerization of the two BTAs results in long nanofibers. The exchange dynamics of both the BTA monomers in the copolymer are significantly slowed down in the mixed systems, leading to a more stable copolymer, while the morphology and spectroscopic signature of the copolymers are identical to that of nBTA homopolymer. This copolymerization is the supramolecular counterpart of styrene/ maleic anhydride copolymerization.     

A Redox‐Activated G‐Quadruplex DNA Binder Based on a Platinum(IV)–Salphen Complex

There has been increasing interest in the development of small molecules that can selectively bind to G‐quadruplex DNA structures. The latter have been associated with a number of key biological processes and therefore are proposed to be potential targets for drug development. Herein, we report the first example of a reduction‐activated G‐quadruplex DNA binder. We show that a new octahedral platinum(IV)–salphen complex does not interact with DNA in aqueous media at pH 7.4; however, upon addition of bioreductants such as ascorbic acid or glutathione, the compound is readily reduced to the corresponding square planar platinum(II) complex. In contrast to the parent platinum(IV) complex, the in situ generated platinum(II) complex has good affinity for G‐quadruplex DNA.