Binding of cationic and neutral phenanthridine intercalators to a DNA oligomer is controlled by dispersion energy: quantum chemical calculations and molecular mechanics simulations

Correlated ab initio as well as semiempirical quantum chemical calculations and molecular dynamics simulations were used to study the intercalation of cationic ethidium, cationic 5-ethyl-6-phenylphenanthridinium and uncharged 3,8-diamino-6-phenylphenanthridine to DNA. The stabilization energy of the cationic intercalators is considerably larger than that of the uncharged one. The dominant energy contribution with all intercalators is represented by dispersion energy. In the case of the cationic intercalators, the electrostatic and charge-transfer terms are also important. The DeltaG of ethidium intercalation to DNA was estimated at -4.5 kcal mol(-1) and this value agrees well with the experimental result. Of six contributions to the final free energy, the interaction energy value is crucial. The intercalation process is governed by the non-covalent stacking (including charge-transfer) interaction while the hydrogen bonding between the ethidium amino groups and the DNA backbone is less important. This is confirmed by the evaluation of the interaction energy as well as by the calculation of the free energy change. The intercalation affects the macroscopic properties of DNA in terms of its flexibility. This explains the easier entry of another intercalator molecule in the vicinity of an existing intercalation site.     

Separation and investigation of structure-mobility relationships of insect oostatic peptides by capillary zone electrophoresis

Capillary zone electrophoresis (CZE) has been applied to qualitative analysis, separation, and physicochemical characterization of synthetic insect oostatic peptides (IOPs) and their derivatives and fragments. Series of homologous IOPs were separated in three acidic background electrolytes (BGEs; pH 2.25, 2.30, 2.40) and an alkaline BGE (pH 8.1). Best separation was achieved in acid BGE composed of 100 mM H3PO4, 50 mM Tris, pH 2.25. The effective electrophoretic mobilities, mu(ep), of all IOPs in four BGEs were determined and several semiempirical models correlating effective mobility with charge-to-size ratio (mu(ep) versus q/Mr k) were tested to describe the migration behavior of IOP in CZE. None of models was found to be unambiguously applicable for the whole set of 20 IOPs differing in size (dipeptide - decapeptide) and charge (-2 to +0.77 elementary charges). However, a high coefficient of correlation, 0.9993, was found for the subset of homologous series of IOPs with decreasing number of proline residues at C-terminus, H-Tyr-Asp-Pro-Ala-Prox-OH, x = 6 - 0, for the dependence of mu(ep) on q/Mr k with k = 0.5 for IOPs as anions in alkaline BGE and with k = 2/3 for IOPs as cations in optimized acidic Tris-phosphate BGE. From these dependences the probable structure of IOPs in solution could be predicted.     

Correlated ab initio study of nucleic acid bases and their tautomers in the gas phase,in a microhydrated environment and in aqueous solution. guanine: surprising stabilization of rare tautomers in aqueous solution

Altogether eight keto and enol tautomers of guanine were studied theoretically in the gas phase, in a microhydrated environment (1 and 2 water molecules) and in bulk water. The structures of isolated, as well as mono- and dihydrated tautomers were determined by means of the RI-MP2 method using the extended TZVPP (5s3p2d1f/3s2p1d) basis set. The relative energies of isolated tautomers included the correction to higher correlation energy terms evaluated at the CCSD(T)/aug-cc-pVDZ level. The relative enthalpies at 0 K and relative free energies at 298 K were based on the above-mentioned relative energies and zero-point vibration energies, temperature-dependent enthalpy terms and entropies evaluated at the MP2/6-31G level. The keto form having hydrogen atom at N7 is the global minimum while the canonical form having hydrogen atom at N9 represents the first local minimum at all theoretical levels in vacuo and in the presence of 1 and 2 water molecules. All three unusual rare tautomers having hydrogens at N3 and N7, at N3 and N9, and also at N9 and N7 are systematically considerably less stable and can be hardly detected in the gas phase. The theoretical predictions fully agree with existing theoretical as well as experimental results. The effect of bulk solvent on the relative stability of guanine tautomers was studied by self-consistent reaction field and molecular dynamics free energy calculations using the thermodynamic integration method. Bulk solvent, surprisingly, strongly favored these three rare tautomers over all remaining low-energy tautomers and probably only these forms can exist in water phase. The global minimum (tautomer with hydrogens at N3 and N7) is by 13 kcal/mol more stable than the canonical form (3rd local minimum). Addition of one or two water molecules does not change the relative stability order of isolated guanine tautomers but the respective trend clearly supports the surprising stabilization of three rare forms.     

Polarographic determination of methyl methacrylate

The permanganate oxidation of methyl methacrylate in weakly acidic solution yields methyl pyruvate. Hydroxylamine hydrochloride is used for destroying the excess of permanganate. At the same time it is consumed for oximation of the pyruvate, and the resulting oxime is determined polarographically. The reaction scheme of permanganate oxidation of methyl methacrylate is suggested and optimum working conditions are found both for permanganate oxidation and for polarographic determination. The method is used for the determination of vapours of methyl methacrylate in the air, for industrial hygiene purposes.     

The synthesis and characterization of a bis-oxime functionalized binucleating macrocycle and its polynuclear complexes

Summary A novel tetraoxime containing a substituted twofold macrocycle, 6,6-spirobi[1,12-di(hydroxyimino)-2,39,10-dibenzo-1, 11-diaza-4,8-dithiacyclotridecane] (5), has been synthesized from 6,6-bis(5-amino-3,4-benzo-2-thiapentyl)-1, 11-diamino-2, 39, 10-dibenzo-4,8-dithiaundecane (3), which was itself prepared from the potassium salt of 2-aminothiophenol (2), pentaerythrityltetrabromide (1) and cyanogendi-N-oxide (4). A polymeric Co^III complex of (5) containing a 11 metalligand ratio has been isolated. The template synthesis of a new Co^III complex containing bridging BF₂ groups was achieved using the hydrogen-bridged Co^III complex. The hetero-polynuclear complex of (5) was prepared by reacting the BF _inf2 ^sup– -capped polymeric Co^III complex with bis(benzonitrile)Pd^IIchloride. The structure of the ligand and its complexes are in accord to elemental analyses, ¹H- and ¹³C-n.m.r., i.r. and mass spectral data.     

Molecular recognition of cyclic-nucleotides and current sensors for their detection

This work briefly describes available sensors for cAMP and cGMP. Many sensors are based on derivatization of naturally occurring products such as immunoglobulins, protein kinases, etc. Only a few published works deal with chemosensors, which are built up by "total" chemical synthesis. This field stays opened for combinatorial chemist. The best sensors are protein kinases genetically modified with mutants of green fluorescent protein, which allow screening of entire cell cultures.     

Copper(II)–manganese(II) complexes of 3,3′-(1,3-propanediyldiimine)bis-(3-methyl-2-butanone)dioxime with superoxide dismutase-like activity

Novel mononuclear [Cu(HPnAO)H₂O]ClO₄ (2), homodinuclear [Cu(PnAO)Cu(phen)(H₂O)₂](ClO₄)₂ (3), homotrinuclear [Cu₃(PnAO)₂(H₂O)₂](ClO₄)₂ (4) and heterodinuclear [Cu(PnAO)Mn(phen)₂(H₂O)](ClO₄)₂ (5) complexes have been prepared from 3,3-(1,3-propanediyldiimine)bis-(3-methyl-2-butanone)dioxime (H₂PnAO) and characterized by elemental analyses, magnetic moments, i.r., u.v.–vis., and by mass spectral studies. The geometry of the metal chelates is discussed with the help of magnetic and spectroscopic measurements. I.r. spectra show that the ligand acts in a tetradentate manner and coordinates through the (C=N) and (N—H) groups. The elemental analyses, stoichiometry and the spectroscopic data of the complexes indicate that the copper(II) ions are coordinated by the ligand dianion. The heterodinuclear complex (5) displays in vitro ability to scavenge superoxide radicals produced by the xanthine–xanthine oxidase (XXO) system, using nitroblue tetrazolium as an indicator. The complex also supports aerobic growth of Escherichia coli (sodA ^– sodB ^–) in vivo in minimal media, indicating that complex (5) is a speculative potent SOD-mimic.     

An innovative silicon photomultiplier digitizing camera for gamma-ray astronomy

The single-mirror small-size telescope (SST-1M) is one of the three proposed designs for the small-size telescopes (SSTs) of the Cherenkov Telescope Array (CTA) project. The SST-1M will be equipped with a 4 m-diameter segmented reflector dish and an innovative fully digital camera based on silicon photo-multipliers. Since the SST sub-array will consist of up to 70 telescopes, the challenge is not only to build telescopes with excellent performance, but also to design them so that their components can be commissioned, assembled and tested by industry. In this paper we review the basic steps that led to the design concepts for the SST-1M camera and the ongoing realization of the first prototype, with focus on the innovative solutions adopted for the photodetector plane and the readout and trigger parts of the camera. In addition, we report on results of laboratory measurements on real scale elements that validate the camera design and show that it is capable of matching the CTA requirements of operating up to high moonlight background conditions.     

The Influence of Polysaccharides/TiO2 on the Model Membranes of Dipalmitoylphosphatidylglycerol and Bacterial Lipids

The aim of the study was to determine the bactericidal properties of popular medical, pharmaceutical, and cosmetic ingredients, namely chitosan (Ch), hyaluronic acid (HA), and titanium dioxide (TiO₂). The characteristics presented in this paper are based on the Langmuir monolayer studies of the model biological membranes formed on subphases with these compounds or their mixtures. To prepare the Langmuir film, 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DPPG) phospholipid, which is the component of most bacterial membranes, as well as biological material-lipids isolated from bacteria Escherichia coli and Staphylococcus aureus were used. The analysis of the surface pressure-mean molecular area (π-A) isotherms, compression modulus as a function of surface pressure, C_S⁻¹ = f(π), relative surface pressure as a function of time, π/π₀ = f(t), hysteresis loops, as well as structure visualized using a Brewster angle microscope (BAM) shows clearly that Ch, HA, and TiO₂ have antibacterial properties. Ch and TiO₂ mostly affect S. aureus monolayer structure during compression. They can enhance the permeability of biological membranes leading to the bacteria cell death. In turn, HA has a greater impact on the thickness of E. coli film.     

Modelling and numerical simulation of martensitic transformation in shape memory alloys

We consider the evolution of martensitic fine structures in shape memory alloys which undergo an isothermal phase-transformation. This process is modelled on a microscopical, continuum-mechanical level by partial differential equations. Here a homogeneous degree-1 dissipation potential is involved which can reflect specific energies needed for rate-independent phase transformations. An interface energy is incorporated by a nonlocal term, and hard-device loading is considered. After setting up the model and specifying its energy balance properties, three-dimensional numerical experiments for the cubic-to-tetragonal transformation in an InTl single crystal are presented which demonstrate geometrical/material interactions under tensile and shear loading.Received: 27 June 2002, Accepted: 18 March 2003, Published online: 27 June 2003PACS: 81.30Kf