Stabilization of Telomeric I‐Motif Structures by (2′S)‐2′‐Deoxy‐2′‐C‐Methylcytidine Residues

G‐quadruplexes and i‐motifs are tetraplex structures present in telomeres and the promoter regions of oncogenes. The possibility of producing nanodevices with pH‐sensitive functions has triggered interest in modified oligonucleotides with improved structural properties. We synthesized C‐rich oligonucleotides carrying conformationally restricted (2′S)‐2′‐deoxy‐2′‐C‐methyl‐cytidine units. The effect of this modified nucleoside on the stability of intramolecular i‐motifs from the vertebrate telomere was investigated by UV, CD, and NMR spectroscopy. The replacement of selected positions of the C‐core with C‐modified residues induced the formation of stable intercalated tetraplexes at near‐neutral pH. This study demonstrates the possibility of enhancing the stability of the i‐motif by chemical modification.     

Innate and Learned Prey-Searching Behavior in a Generalist Predator

Early colonization by Zyginidia scutellaris leafhoppers might be a key factor in the attraction and settling of generalist predators, such as Orius spp., in maize fields. In this paper, we aimed to determine whether our observations of early season increases in field populations of Orius spp. reflect a specific attraction to Z. scutellaris-induced maize volatiles, and how the responses of Orius predators to herbivore-induced volatiles (HIPVs) might be affected by previous experiences on plants infested by herbivorous prey. Therefore, we examined the innate and learned preferences of Orius majusculus toward volatiles from maize plants attacked by three potential herbivores with different feeding strategies: the leafhopper Z. scutellaris (mesophyll feeder), the lepidopteran Spodoptera littoralis (chewer), and another leafhopper Dalbulus maidis (phloem feeder). In addition, we examined the volatile profiles emitted by maize plants infested by the three herbivores. Our results show that predators exhibit a strong innate attraction to volatiles from maize plants infested with Z. scutellaris or S. littoralis. Previous predation experience in the presence of HIPVs influences the predator’s odor preferences. The innate preference for plants with cell or tissue damage may be explained by these plants releasing far more volatiles than plants infested by the phloem-sucking D. maidis. However, a predation experience on D. maidis-infested plants increased the preference for D. maidis-induced maize volatiles. After O. majusculus experienced L3-L4 larvae (too large to serve as prey) on S. littoralis-infested plants, they showed reduced attraction toward these plants and an increased attraction toward D. maidis-infested plants. When offered young larvae of S. littoralis, which are more suitable prey, preference toward HIPVs was similar to that of naive individuals. The HIPVs from plants infested by herbivores with distinctly different feeding strategies showed distinguishable quantitative differences in (Z)-3-hexenal, (E)-2-hexenal, and methyl salicylate. These compounds might serve as reliable indicators of prey presence and identity for the predator. Our results support the idea that feeding by Z. scutellaris results in the emission of maize’s HIPVs that initially recruit Orius spp. into maize fields.     

A practical approach to electrode-skin impedance unbalance measurement

Unbalance between electrode-skin impedances is a major problem in biopotential recordings, leading to increased power-line interference. This paper proposes a simple, direct method to measure that unbalance at power-line frequency (50-60 Hz), thus allowing the determination of actual recording conditions for biopotential amplifiers. The method is useful in research, amplifier testing, electrode design and teaching purposes. It has been experimentally validated by using both phantom impedances and real electrode-skin impedances.     

Dip-pen nanolithography on (bio)reactive monolayer and block-copolymer platforms: deposition of lines of single macromolecules

The application of atomic force microscopy (AFM) tip-mediated molecular transfer (dip-pen nanolithography or DPN) to fabricate nanopatterned (bio)reactive platforms based on dendrimers on reactive self-assembled monolayer (SAM) and polymer thin films is discussed. The transfer of high-molar-mass polyamidoamine (PAMAM) dendrimers (generation 5) and the rapid in situ covalent attachment of the deposited adsorbates onto reactive N-hydroxysuccinimide (NHS) terminated SAMs on gold and NHS-activated polystyrene-block-poly(tert-butyl acrylate) (PS(690)-b-PtBA(1210)) block copolymer thin films were investigated as strategies to suppress line broadening by surface diffusion in DPN. By exploiting carefully controlled environmental conditions (such as temperature and relative humidity), scan rates, and in particular the covalent attachment of the dendrimers to the reactive films, the observed line broadening and hence the lateral diffusion of dendrimers was substantially less pronounced compared to that observed with DPN of thiols on gold. By this method, high-definition patterns of dendrimers were conveniently fabricated down to 30-nm length scales. The presence of primary amino groups in the deposited dendrimers ultimately offers the possibility to anchor biochemically relevant molecules, such as proteins and polypeptides, to these nanostructured platforms for a wide range of possible applications in the life sciences and in particular for the investigation of controlled cell-surface interactions.     

Efficient sequence-specific purification of Listeria innocua mRNA species by triplex affinity capture with parallel tail-clamps

Parallel clamps can interact in a sequence-specific manner with homopyrimidine DNA and RNA oligonucleotides to form triplexes. For longer nucleic acids, we have previously demonstrated the inhibitory effect of DNA-target secondary structures on triplex formation. We further designed a modification of these molecules-that is, tail-clamps formed by addition of a tail sequence to the parallel clamp-and proved efficient binding of the molecules with structured single-stranded DNA targets. Here we explore the possible application of the tail-clamp strategy for triplex formation with RNA targets, which are typically found as strongly folded single-stranded molecules. Efficient and specific binding of a tail-clamp designed to form a parallel triplex with Listeria innocua iap mRNA sequences has been verified by UV melting curves and triplex affinity capture techniques. Furthermore, we show for the first time the formation of stable complexes of mRNA with tail-clamps not only under acidic but also under neutral and slightly basic pH conditions. These results signify a further step towards the possible applications of triplexes with mRNA molecules; research, analytical, and therapeutic uses can be envisaged. As an example, our tail-clamp-based triplex affinity capture assay allowed the specific capture and recovery of iap mRNA molecules from an L. innocua total RNA solution with 45 % yield.     

Increasing robustness against changes in the interferent structure by incorporating prior information in the augmented classical least-squares framework

A class of multivariate calibration methods called augmented classical least squares (ACLS) has been proposed which combines an explicit linear additive model with the predictive power of inverse models, such as principal component regression (PCR) and partial least squares (PLS). Because of its use of the explicit linear additive model, ACLS provides an interesting framework to incorporate different sources of prior information, such as measured pure component spectra, in the model. In this study, the predictive power of ACLS models incorporating different amounts of prior information has been compared to that of PCR and PLS using two examples, a designed experiment and one with biological samples. In both cases, the ACLS models showed predictive power comparable to PLS under idealized validation conditions. When a different interferent structure was present in the validation samples, the predictive power of the inverse models (PCR and PLS) dramatically decreased, with an increase in root-mean-squared error of prediction by a factor of 3.5 for the first example and a factor of 2 in the second example. The incorporation of prior information in the ACLS framework was found to considerably reduce or even completely remove these dramatic effects, especially when the pure component contributions for the interferents were taken into account.     

A Fast and Reliable UHPLC-PDA Method for Determination of Patulin in Apple Food Products Using QuEChERS Extraction

A fast and reliable method for the quantification of patulin using ultra high performance liquid chromatography coupled to a photodiode array detector was developed and validated for the analysis of several apple-based foodstuffs. Sample preparation was based on the QuEChERS procedure. Samples were extracted with acetonitrile and partitioned with a mixture of sodium citrate, NaCl, and Mg₂SO₄. The cleanup step was performed using dispersive SPE mixed with Mg₂SO₄ and PSA. This step was carried out twice in order to improve chromatographic results. The method was validated in spiked cloudy apple juice, apple puree, apple yogurt, beer with apple juice, and cider and applied to 24 commercial samples. The limits of detection and limits of quantification were ≥0.4 and ≥2 ng/g, respectively. Both were below the maximum legal limit established by the European Union. Recoveries for all the matrices were between 78.4 and 94.7 % while relative standard deviations were between 3.8 and 10.4 %. Patulin was detected on four apple juices from concentrate, one cloudy apple juice from an eco-store, and one beer. Nevertheless, the highest concentration found was 25.4 ng/g.     

Highly linear wide‐swing continuous tuning of CMOS transconductors

A technique to improve the input and output range of CMOS transconductors with resistive current division for continuous tuning is presented. Using it, a tunable transconductor is proposed which features high linearity over a wide input range and simplicity. Measurement results of the transconductor, fabricated in a 0.5 µm CMOS process, show an IM3 of ?66 dB for a ±1.65 V supply and two input tones centered at 1 MHz of 1 V_pp each, and only 0.7 mW of power consumption. This represents an improvement of 13 dB versus the same transconductor using conventional current division. Copyright © 2013 John Wiley & Sons, Ltd.