Feature weighting in "chick-a-dee" call notes of Poecile atricapillus

Artificial neural networks were trained to discriminate between different note types from the black-capped chickadee (Poecile atricapillus) "chick-a-dee" call. Each individual note was represented as a vector of summary features taken from note spectrograms and networks were trained to respond to exemplar notes of one type and to fail to respond to exemplar notes of another type. Following initial network training, the network was presented novel notes in which individual acoustic features had been modified. The strength of the response of the network to each novel and shifted note was recorded. When network responses were plotted as a function of the degree of acoustic feature modification and training context, it became clear that modifications of some acoustic features had significant effects on network responses, while others did not. Moreover, the training context of the network also played a role in the responses of networks to manipulated test notes. The implications of using artificial neural networks to generate testable hypotheses for animal research and the role of context are discussed.     

Comparison of Plackett-Burman and supersaturated designs in robustness testing

An optimized FIA assay of L-N-monomethylarginine (LNMMA) was validated. The linearity, precision, accuracy and range of the analytical method were evaluated and robustness testing was performed. Several experimental designs for robustness testing containing different numbers of experiments (N) were compared. Both Plackett-Burman (N=8 or 12) and supersaturated designs (N=6) were examined. The latter design results were analyzed with the Fixing Effects and Adding Rows (FEAR) method, based on the initial addition of zero effect rows to the model matrix, which then are iteratively replaced by fixed effects. It was evaluated whether by reducing the number of experiments from 12 to 8 or 6, similar effects are estimated and considered (non-)significant. The FIA method was found linear in a range of 70-130% of the LNMMA concentration in the samples, and precise and accurate in a range of 80-120%. The estimated factor effects and the critical effects were found comparable for all examined designs, though there also are some indications that some from the supersaturated designs tend to be overestimated. The method was considered robust, since no significant effects occurred for the response describing the quantitative aspect of the method. For other responses, such as peak height and residence time, significant effects occur. However, only the most important effects are found with all designs. The effects reported from a supersaturated design based on the FEAR method still can be subject of further research.     

In-situ infrared spectroscopy of buried organic monolayers: influence of the substrate on titanium reactivity with a Langmuir-Blodgett film

The reactivity of metals vapor deposited onto organic monolayers has historically been correlated to the metal/terminal organic group chemistry. Here we demonstrate that the chemical composition of the substrate unexpectedly plays a significant role as well. In particular, the reactivity of evaporated titanium toward a cadmium stearate Langmuir-Blodgett (LB) film was found to depend on the substrate upon which the LB film was deposited. Infrared spectra taken in a modified ATR (Kretschmann) geometry with a thin Au substrate showed large changes in peak shape, peak position, and peak width in the C-H stretching region, indicating titanium penetration into the LB film and decomposition of the original well-packed monolayer structure. LB monolayers formed on a platinum oxide (PtO(x)) surface showed remarkably small changes after Ti deposition, indicating only a slight increase in disorder and no significant metal penetration into the film. Films on SiO2 substrates showed reactivity between that of Au and PtO(x). These differences in reactivity can be correlated primarily with the amount of available oxygen associated with each substrate, including surface oxide layers and water incorporated within the LB film.     

Phosphate vibrations probe local electric fields and hydration in biomolecules

The role of electric fields in important biological processes such as binding and catalysis has been studied almost exclusively by computational methods. Experimental measurements of the local electric field in macromolecules are possible using suitably calibrated vibrational probes. Here we demonstrate that the vibrational transitions of phosphate groups are highly sensitive to an electric field and show how that sensitivity can be quantified, allowing electric field measurements to be made in phosphate-containing biological systems without chemical modification.     

Nuclear spin dependence of the reaction of H(3)+ with H2. II. Experimental measurements

The nuclear spin dependence of the chemical reaction H(3)(+)+ H(2) → H(2)?+ H(3)(+) has been studied in a hollow cathode plasma cell. Multipass infrared direct absorption spectroscopy has been employed to monitor the populations of several low-energy rotational levels of ortho- and para-H(3)(+) (o-H(3)(+) and p-H(3)(+)) in hydrogenic plasmas of varying para-H(2) (p-H(2)) enrichment. The ratio of the rates of the proton hop (k(H)) and hydrogen exchange (k(E)) reactions α ≡ k(H)/k(E) is inferred from the observed p-H(3)(+) fraction as a function of p-H(2) fraction using steady-state chemical models. Measurements have been performed both in uncooled (T(kin) ～ 350 K) and in liquid-nitrogen-cooled (T(kin) ～ 135 K) plasmas, marking the first time this reaction has been studied at low temperature. The value of α has been found to decrease from 1.6 ± 0.1 at 350 K to 0.5 ± 0.1 at 135 K.     

Methodology for porting retention prediction data from old to new columns and from conventional-scale to miniaturised ion chromatography systems

Several procedures are available for simulating and optimising separations in ion chromatography (IC), based on the application of retention models to an extensive database of analyte retention times on a wide range of columns. These procedures are subject to errors arising from batch-to-batch variability in the synthesis of stationary phases, or when using a column having a different diameter to that used when the database was acquired originally. Approaches are described in which the retention database can be recalibrated to accommodate changes in the stationary phase (ion-exchange selectivity coefficient and ion-exchange capacity) or in the column diameter which lead to changes in phase ratio. The entire database can be recalibrated for all analytes on a particular column by performing three isocratic separations with two analyte ions. The retention data so obtained are then used to derive a "porting" equation which is employed to generate the required simulated separation. Accurate prediction of retention times is demonstrated for both anions and cations on 2mm and 0.4mm diameter columns under elution conditions which consist of up to five sequential isocratic or linear gradient elution steps. The proposed approach gives average errors in retention time prediction of less than 3% and the correlation coefficient was 0.9849 between predicted and observed retention times for 344 data points comprising 33 anionic or cationic analytes, 5 column internal diameters and 8 complex elution profiles.     

Copper, nickel, and zinc cyclam-amino acid and cyclam-peptide complexes may be synthesized with "click" chemistry and are noncytotoxic

We describe the synthesis of cyclam metal complexes derivatized with amino acids or a tripeptide using a copper(I)-catalyzed Huisgen "click" reaction. The linker triazole formed during the synthesis plays an active coordinating role in the complexes. The reaction conditions do not racemize the amino acid stereocenters. However, a methylene group adjacent to the triazole is susceptible to H/D exchange under ambient conditions, an observation which has potentially important implications for structures involving stereocenters adjacent to triazoles in click-derived structures. The successful incorporation of several amino acids is described, including reactive tryptophan and cysteine side chains. All complexes are formed rapidly upon introduction of the relevant metal salt, including synthetically convenient cases where trifluoroacetate salts of cyclam derivatives are used directly in the metalation. None of the metal complexes displayed any cytotoxicity to mammalian cells, suggesting that the attachment of such complexes to amino acids and peptides does not induce toxicity, further supporting their potential suitability for labeling/imaging studies. One Cu(II)-cyclam-triazole-cysteine disulfide complex displayed moderate activity against MCF-10A breast nontumorigenic epithelial cells.     

Synthesis, structure, aggregation-induced emission, self-assembly, and electron mobility of 2,5-bis(triphenylsilylethynyl)-3,4-diphenylsiloles

2,5-Bis(triphenylsilylethynyl)-3,4-diphenylsiloles with different 1,1-substituents [XYSi(CPh)(2) (C-C≡C-SiPh(3))(2)] (Ph=phenyl) were synthesized in high yields by the Sonogashira coupling of 2,5-dibromo-3,4-diphenylsiloles with triphenylsilylacetylene, and two of these were characterized crystallographically. Crystal structures and theoretical calculations showed that the new silole molecules had higher conjugation than 2,5-diarylsiloles. They possessed low HOMO and LUMO energy levels due to the electron-withdrawing effect of the triphenylsilylethynyl groups. Cyclic voltammetry analysis revealed low electron affinities, which were comparable to those of perfluoroarylsiloles. B3LYP/6-31* calculations demonstrated that the new siloles possessed large reorganization energies for electron and hole transfers and high electron mobilities. A mobility of up to 1.2×10(-5) cm(2) V(-1) s(-1) was obtained by the transient electroluminescence method, which was about fivefold higher than that of tris(8-hydroxyquinolinato)aluminum, a widely used electron-transport material, under the same conditions. All of the silole molecules possessed high thermal stability. Although, their solutions were weakly emissive, their nanoparticle suspensions and thin films emitted intense blue-green light upon photoexcitation, demonstrating a novel feature of aggregation-induced emission (AIE). Polarized emissions were observed in the silole crystals. The addition of solvents, which did not dissolve the silole molecules, into silole-containing solutions caused self-assembly of the molecules, which produced macroscopic fibrils with strong light emissions.     

A potent antimalarial trichothecene from hyphomycete species

Antimalarial screening of diverse fungal samples resulted in the isolation and identification of a new sesquiterpene, trichothecinol D (1), which exhibited potent in vitro activity against Plasmodium falciparum with a 200-fold selectivity for parasite versus mammalian cytotoxicity. Trichothecinol D was obtained by bioassay-guided fractionation of two hyphomycete species. Its chemical characterization was performed by detailed NMR spectroscopy and high resolution mass spectrometry. The absolute configuration of trichothecinol D was determined by X-ray crystallography.     

Oxide and carbide formation at titanium/organic monolayer interfaces

X-ray photoelectron spectra (XPS) are reported from a series of buried titanium/organic monolayer interfaces accessed through sample delamination in ultrahigh vacuum (UHV). Conventional characterization of such buried interfaces requires ion-mill depth profiling, an energetic process that frequently destroys bonding information by chemically reducing the milled material. In contrast, we show that delaminating the samples at the metal/organic interface in vacuum yields sharp, nonreduced spectra that allow quantitative analysis of the buried interface chemistry. Using this UHV delamination XPS, we examine titanium vapor deposited onto a C18 cadmium stearate Langmuir-Blodgett monolayer supported on Au, SiO2, or PtO2 substrates. Titanium is widely used as an adhesion layer in organic thick film metallization as well as a top metal contact for molecular monolayer junctions, where it has been assumed to form a few-atoms-thick Ti carbide overlayer. We establish here that under many conditions the titanium instead forms a few-nanometers-thick Ti oxide overlayer. Both TiO2 and reduced TiOx species exist, with the relative proportion depending on oxygen availability. Oxygen is gettered during deposition from the ambient, from the organic film, and remarkably, from the substrate itself, producing substrate-dependent amounts of Ti oxide and Ti carbide "damage". On Au substrates, up to 20% of the molecular-monolayer carbon formed titanium carbide, SiO2 substrates approximately 15%, and PtO2 substrates <5%. Titanium oxide formation is also strongly dependent on the deposition rate and chamber pressure.