DNA condensation and its thermal stability influenced by phospholipid bilayer and divalent cations

We studied the effect of divalent alkaline earth metal cations Ca2?, Mg2? and transition metals Co2?, Ni2?, Cu2? and Zn2? on DNA condensation and its protection against thermal denaturation in presence of dioleoylphosphatidylcholine liposomes (DOPC). Experimental results have shown that Ca2? and Mg2? as well as Zn2? mediate DNA condensation. Cu2? causes DNA double helix destabilization, and does not mediate binding between DNA and DOPC liposomes. Co2? and Ni2? can interact with DNA on both ways mentioned above. Static light scattering was use to follow the size of aggregates in DNA condensation process. Phospholipid bilayer and divalent cations protect condensed DNA against thermal destabilization. The highest stabilization effect was found in aggregates with Ca2? and Zn2?, whereas in presence of either Co2? or Ni2? some volume fraction of DNA is denatured.     

Bimodal dynamics of mechanically constrained hydrogen bonds revealed by vibrational photon echoes

We have investigated the dynamics of the hydrogen bonds that connect the components of a [2]rotaxane in solution. In this rotaxane, the amide groups in the benzylic-amide macrocycle and the succinamide thread are connected by four equivalent N-H???O=C hydrogen bonds. The fluctuations of these hydrogen bonds are mirrored by the frequency fluctuations of the NH-stretch modes, which are probed by means of three-pulse photon-echo peak shift spectroscopy. The hydrogen-bond fluctuations occur on three different time scales, with time constants of 0.1, 0.6, and ≥200 ps. Comparing these three time scales to the ones found in liquid formamide, which contains the same hydrogen-bonded amide motif but without mechanical constraints, we find that the faster two components, which are associated with small-amplitude fluctuations in the strength of the N-H???O=C hydrogen bonds, are very similar in the liquid and the rotaxane. However, the third component, which is associated with the breaking and subsequent reformation of hydrogen bonds, is found to be much slower in the rotaxane than in the liquid. It can be concluded that the mechanical bonding in a rotaxane does not influence the amplitude and time scale of the small-amplitude fluctuations of the hydrogen bonds, but strongly slows down the complete dissociation of these hydrogen bonds. This is probably because in a rotaxane breaking of the macrocycle-axle contacts is severely hindered by the mechanical constraints. The hydrogen-bond dynamics in rotaxane-based molecular machines can therefore be regarded as liquidlike on a time scale 1 ps and less, but structurally frozen on longer (up to at least 200 ps) time scales.     

Push-Pull Fluorophores Based on Imidazole-4,5-dicarbonitrile: A Comparison of Spectral Properties in Solution and Polymer Matrices

Spectral properties of novel type of fluorophores consist of a π-conjugated system end-capped with an electron-donating N,N-dimethylaminophenyl group and an electron-withdrawing imidazole-4,5-dicarbonitrile moiety were examined. An additional π-linker separating these two structural units comprises simple bond (B1P), phenyl (B2B), styryl (B3S) and ethynylphenyl (B4A) moieties. The absorption and fluorescence spectra were taken in cyclohexane, chloroform, acetonitrile, methanol and in polymer matrices such as polystyrene, poly(methyl methacrylate) and poly(vinylchloride). The longest-wavelength absorption band was observed in the range of 300 to 400 nm. Intense fluorescence with quantum yields of 0.2 to 1.0 was observed in cyclohexane, chloroform and in polymer matrices within the range of 380 to 500 nm. The fluorescence was strongly quenched in neat acetonitrile and methanol. The fluorescence lifetimes are in the range of 1–4 ns for all measured fluorophores. The large Stokes shift (4,000 to 8,000 cm⁻¹) indicates a large difference in the spatial arrangement of the chromophore in the absorbing and the emitting states. The observed fluorescence of all fluorophores in chloroform was quenched by 1-oxo-2,2,6,6-tetramethyl-4-hydroxy piperidine by the diffusion-controlled bimolecular rate (cca 2 × 10¹⁰ L mol⁻¹ s⁻¹). Polar solvents such as acetonitrile and methanol quenched the fluorescence as well but probably via a different mechanism.     

Effects of endohedral element in B24N24 clusters on hydrogenation studied by molecular orbital calculations

Possibility of hydrogen gas storage in boron nitride (BN) clusters was investigated by molecular orbital calculations. Chemisorption calculation was carried out for B₂₄N₂₄ with changing endohedral elements in BN cluster to compare the bonding energy at nitrogen and boron, which showed that Li is a suitable element for hydrogenation to B₂₄N₂₄.     

Quantization of Poisson Families and of Twisted Poisson Structures

We describe a deformation quantization of a modification of Poisson geometry by a closed 3-form. Under suitable conditions, it gives rise to a stack of algebras. The basic object used for this aim is a kind of families of Poisson structures given by a Maurer–Cartan equation; they are easily quantized using Kontsevich's formality theorem. We conclude with a section on quantization of complex manifolds.     

A uniqueness result for a semilinear parabolic system

We prove that for nonnegative, continuous, bounded and nonzero initial data we have a unique solution of the reaction-diffusion system described by three differential equations with non-Lipschitz nonlinearity. We also find the set of all nonnegative solutions of the system when the initial data is zero and in the last section we briefly discuss a generalization of the theorem to a system of n equations.     

Controlled synthesis and analysis of He–H+3 in a 3.7 K ion trap

Complexes of the triatomic hydrogen ion with helium were synthesised in a low-temperature 22-pole rf ion trap at He number densities of up to 10¹⁶ cm^?3. Absolute ternary rate coefficients for sequentially attaching He atoms have been determined from the growth of complexes with increasing storage time. The number of helium-tagged ions is significantly reduced when increasing the nominal temperature from 4 to 25 K. Competition between attachment and dissociation via collisions leads to stationary He_n–H⁺₃ (n up to 9) distributions. State-specific excitation of the trapped H⁺₃ ions via IR transitions significantly reduces the formation of complexes. Tuning the laser to Δv₂ = 1 transitions in the range of 2726 cm^?1 leads to LIICG lines, i.e., to spectra caused by laser-induced inhibition of complex growth. In addition, almost 100 lines have been found between 2700 and 2765 cm^?1, which are attributed to laser-induced dissociation of the in situ formed He–H⁺₃ complex ions. These lines are not yet assigned; however, their absorption strength, statistics and predissociation lifetimes provide interesting information on both the stable complexes as well as on scattering resonances in low-energy H⁺₃+He collisions. New calculations of the potential energy surface will help to analyse the dissociation spectrum. There are some indications that para-H⁺₃ is enriched under the conditions of the present experiment.     

Equilibria, Connecting Orbits and a Priori Bounds for Semilinear Parabolic Equations with Nonlinear Boundary Conditions

We consider a semilinear parabolic equation with a nonlinear non-dissipative boundary condition. In the one-dimensional case we describe bifurcation diagrams for positive and sign-changing equilibria and connecting orbits between these equilibria. We also show that the number of sign-changing stationary solutions strongly depends on the spatial dimension. The results are based on new a priori estimates of global solutions.     

Self-assembled sensor based on boron-doped diamond and its application in voltammetric analysis of picloram

A self-assembled sensor based on a boron-doped diamond was investigated as a sensitive tool for voltammetric analysis of a member of a pyridine herbicide family - picloram. A cyclic voltammetry and a differential pulse voltammetry were applied for investigation of the voltammetric behaviour and quantification of this herbicide. Picloram yielded one well-developed irreversible oxidation signal at a very positive potential about +1.5 V vs. Ag/AgCl/3 mol L^?1 KCl electrode in an acidic medium and 1 mol L^?1 H₂SO₄ was chosen as a suitable supporting electrolyte. Operating parameters of differential pulse voltammetry were optimized and the proposed voltammetric method provided a high repeatability (a relative standard deviation of 20 repeated measurements at a concentration level of picloram of 50 µmol L^?1 equaled to 2.58%), a linear concentration range from 2.5 to 90.9 µmol L^?1 and a low limit of detection (LD = 1.64 µmol L^?1). Practical usefulness of the ‘environmentally-green’ electrochemical sensor was verified by an analysis of spiked water samples with satisfactory recoveries.     

Observations on the Preparation of β-Lactose Octaacetate

Attempts to substantially increase the relative proportion of β-lactose octaacetate in products of acetylation of α-lactose monohydrate using various acetylation protocols failed. Nevertheless, the revised protocol for isolation and crystallization, based on the classical work by Hudson and Johnson, rendered preparation of β-lactose octaacetate less labor intensive. It is proposed that the melting point and [α]_D value are not reliable criteria of purity of β-lactose octaacetate, which can be confidently determined by 1H NMR spectroscopy.