Reversible light switch for macrocycle mobility in a DNA rotaxane

A recent trend in DNA nanotechnology consists of the assembly of architectures with dynamic properties that can be regulated by employing external stimuli. Reversible processes are important for implementing molecular motion into DNA architectures as they allow for the regeneration of the original state. Here we describe two different approaches for the reversible switching of a double-stranded DNA rotaxane architecture from a stationary pseudorotaxane mode into a state with movable components. Both states only marginally differ in their respective topologies but their mechanical properties are fundamentally different. In the two approaches, the switching operation is based on strand-displacement reactions. One of them employs toehold-extended oligodeoxynucleotides whereas in the other one the switching is achieved by light-irradiation. In both cases, multiple back and forth switching between the stationary and the mobile states was achieved in nearly quantitative fashion. The ability to reversibly operate mechanical motion in an interlocked DNA nanostructure opens exciting new avenues in DNA nanotechnology.     

Multiple positive solutions of non-local initial value problems for first order differential systems

The paper gives a new and natural method for the existence of multiple positive solutions for first order differential systems with non-local initial value conditions involving linear functionals. The case of higher order differential equations is also considered. The results are accompanied by numerical examples confirming the theory and proving for practice the importance of the bounds in solution localization.     

Antioxidant potential and authenticity of some commercial fruit juices studied by EPR and IRMS

Antioxidant status of foods, plant, or fruit products is generally characterized by means of spectroscopic methods. Methods like HPLC, UV-VIS, or MS spectroscopy are used to understand the chemical and physical properties of different samples, and also EPR spectroscopy seems to be a valuable tool to characterize antioxidant activity of juice beverages. In this technique, certain antioxidants present in fruit juices interact with free radicals interrupting the chain reaction that can possibly damage essential molecules. Recording the EPR signal decay caused by the reaction with a natural or artificial reducing agent, it is possible to draw conclusions about the antioxidant capability of materials. IRMS is a powerful tool to distinguish between an authentic fruit juice and a juice obtained by concentrate dilution. This technique allows also the detection of commercial C₄ cane or corn derived sugar syrups in C₃ fruit juices. In the present study, four commercial fruit juices were investigated using stable isotope measurements (oxygen, hydrogen, and carbon) and EPR measurements in order to check the correct labeling in the Romanian markets and to compare antioxidant activity of the studied juices and the reference. It was proven that the number of paramagnetic species decreases in time with different reaction rates and this was correlated with the antioxidant activity of the studied juices. Stable isotope ratio measurements have demonstrated that the fruit juices studied were reconstructed from concentrates with tap water, according to their label.     

Floer–Novikov homology and applications to Lagrangian submanifolds

We use a non-Hamiltonian version of Lagrangian Floer homology to prove that an exact Lagrangian submanifold in the cotangent bundle of the 3-torus T ³ must be diffeomorphic to T ³. This improves a previous result of Fukaya, Seidel and Smith.     

Mechanism of atmospheric CO2 fixation in the cavities of a dinuclear cryptate

Using density functional theory (DFT) methods, we have investigated two possible mechanisms for atmospheric CO(2) fixation in the cavity of the dinuclear zinc(II) octa-azacryptate, and the subsequent reaction with methanol whereby this latter reaction transforms the (essentially) chemically inert CO(2) into useful products. The first mechanism (I) was proposed by Chen et al. [Chem.-Asian J. 2007, 2, 710], and involves the attachment of one CO(2) molecule onto the hydroxyl-cryptate form, resulting in the formation of a bicarbonate-cryptate species and subsequent reaction with one methanol molecule. In addition, we suggest another mechanism that is initiated via the attachment of a methanol molecule onto one of the Zn-centers, yielding a methoxy-cryptate species. The product is used to activate a CO(2) molecule and generate a methoxycarbonate-cryptate. The energy profiles of both mechanisms were determined, and we conclude that, while both mechanisms are energetically feasible, free energy profiles suggest that the scheme proposed by Chen et al. is most likely.     

Effects of external electromagnetic fields on the conformational sampling of a short alanine peptide

Non‐equilibrium molecular dynamics simulations of a solvated 21‐residue polyalanine (A21) peptide, featuring a high propensity for helix formation, have been performed at 300 K and 1 bar in the presence of external electromagnetic (e/m) fields in the microwave region (2.45 GHz) and an r.m.s. electric field intensity range of 0.01–0.05 V/Å. To investigate how the field presence affects transitions between the conformational states of a protein, we report 16 independent 40 ns‐trajectories of A21 starting from both extended and fully folded states. We observe folding‐behavior of the peptide consistent with prior simulation and experimental studies. The peptide displays a natural tendency to form stable elements of secondary structure which are stabilized by tertiary interactions with proximate regions of the peptide. Consistent with our earlier work, the presence of external e/m fields disrupts this behavior, involving a mechanism of localized dipolar alignment which serves to enhance intra‐protein perturbations in hydrogen bonds (English, et al., J. Chem. Phys. 2010 , 133, 091105), leading to more frequent transitions between shorter‐lifetime states. © 2012 Wiley Periodicals, Inc.     

Designing a Useful Lipid Raft Model Membrane for Electrochemical and Surface Analytical Studies

A model biomimetic system for the study of protein reconstitution or drug interactions should include lipid rafts in the mixed lipid monolayer, since they are usually the domains embedding membrane proteins and peptides. Four model lipid films composed of three components: 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), cholesterol (Chol) and sphingomyelin (SM) mixed in different molar ratios were proposed and investigated using surface pressure measurements and thermodynamic analysis of the monolayers at the air–water interface and imaged by Brewster angle microscopy. The ternary monolayers were transferred from the air–water onto the gold electrodes to form bilayer films and were studied for the first time by electrochemical methods: alternative current voltammetry and electrochemical impedance spectroscopy and imaged by atomic force microscopy. In excess of DOPC, the ternary systems remained too liquid for the raft region to be stable, while in the excess of cholesterol the layers were too solid. The layers with SM in excess lead to the formation of Chol:SM complexes but the amount of the fluid matrix was very low. The equimolar content of the three components lead to the formation of a stable and well-organized assembly with well-developed raft microdomains of larger thickness, surrounded by the more fluid part of the bilayer. The latter is proposed as a convenient raft model membrane for further physicochemical studies of interactions with drugs or pollutants or incorporation of membrane proteins.     

A fixed point formula of Lefschetz type in Arakelov geometry I: statement and proof

We consider arithmetic varieties endowed with an action of the group scheme of n-th roots of unity and we define equivariant arithmetic K ₀-theory for these varieties. We use the equivariant analytic torsion to define direct image maps in this context and we prove a Riemann-Roch theorem for the natural transformation of equivariant arithmetic K ₀-theory induced by the restriction to the fixed point scheme; this theorem can be viewed as an analog, in the context of Arakelov geometry, of the regular case of the theorem proved by P. Baum, W. Fulton and G. Quart in [BaFQ]. We show that it implies an equivariant refinement of the arithmetic Riemann-Roch theorem, in a form conjectured by J.-M. Bismut (cf. [B2, Par. (l), p. 353] and also Ch. Soulé’s question in [SABK, 1.5, p. 162]). Oblatum 22-I-1999 & 20-II-2001?Published online: 4 May 2001     

Biogenic Synthesis of CuO,ZnO, and CuO–ZnO Nanoparticles Using Leaf Extracts of Dovyalis caffra and Their Biological Properties

Biogenic metal oxide nanoparticles (NPs) have emerged as a useful tool in biology due to their biocompatibility properties with most biological systems. In this study, we report the synthesis of copper oxide (CuO), zinc oxide (ZnO) nanoparticles (NPs), and their nanocomposite (CuO–ZnO) prepared using the phytochemical extracts from the leaves of Dovyalis caffra (kei apple). The physicochemical properties of these nanomaterials were established using some characterization techniques including X-ray diffraction analysis (XRD), ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The XRD result confirmed the presence of a monoclinic CuO (Tenorite), and a hexagonal ZnO (Zincite) nanoparticles phase, which were both confirmed in the CuO–ZnO composite. The electron microscopy of the CuO–ZnO, CuO, and ZnO NPs showed a mixture of nano-scale sizes and spherical/short-rod morphologies, with some agglomeration. In the constituent’s analysis (EDX), no unwanted peak was found, which showed the absence of impurities. Antioxidant properties of the nanoparticles was studied, which confirmed that CuO–ZnO nanocomposite exhibited better scavenging potential than the individual metal oxide nanoparticles (CuO, and ZnO), and ascorbic acid with respect to their minimum inhibitory concentration (IC₅₀) values. Similarly, the in vitro anticancer studies using MCF7 breast cancer cell lines indicated a concentration-dependent profile with the CuO–ZnO nanocomposite having the best activity over the respective metal oxides, but slightly lower than the standard 5-Fluorouracil drug.