Enhancement of DNA compaction by negatively charged nanoparticles: effect of nanoparticle size and surfactant chain length

We study the compaction of genomic DNA by a series of alkyltrimethylammonium bromide surfactants having different hydrocarbon chain lengths n: dodecyl-(DTAB, n=12), tetradecyl-(TTAB, n=14) and hexadecyl-(CTAB, n=16), in the absence and in the presence of negatively charged silica nanoparticles (NPs) with a diameter in the range 15-100 nm. We show that NPs greatly enhance the ability of all cationic surfactants to induce DNA compaction and that this enhancement increases with an increase in NP diameter. In the absence of NP, the ability of cationic surfactants to induce DNA compaction increases with an increase in n. Conversely, in the presence of NPs, the enhancement of DNA compaction increases with a decrease in n. Therefore, although CTAB is the most efficient surfactant to compact DNA, maximal enhancement by NPs is obtained for the largest NP diameter (here, 100 nm) and the smallest surfactant chain length (here, DTAB). We suggest a mechanism where the preaggregation of surfactants on NP surface mediated by electrostatic interactions promotes cooperative binding to DNA and thus enhances the ability of surfactants to compact DNA. We show that the amplitude of enhancement is correlated with the difference between the surfactant concentration corresponding to aggregation on DNA alone and that corresponding to the onset of adsorption on nanoparticles.     

Synthesis and Properties of Lead(II) 1-Hydroxyethane-1,1-diphosphonate(2-) Monohydrate

Conditions for isolation of a 1-hydroxyethane-1,1-diphosphonic acid (H₄L) complex of the composition PbH₂L·H₂O from aqueous solutions of various composition are studied. The X-ray analysis of the resulting polycrystalline sample showed that it is single-phase. The IR spectrum is presented, and the solubility and thermal transformations of the sample are studied.     

2,3,5,6-Tetra(vinylthio)difluorobenzene in Reactions with Difunctional Nucleophiles

Reaction of 2,3,5,6-tetra(vinylthio)difluorobenzene with ethylene glycol affords 1,4-bis[2,3,5,6-tetra(vinylthio)-4-fluorophenoxy-1-ethyloxy-]-2,3,5,6-tetra(vinylthio)benzene, with diethylene glycol arises 2,3,5,6-tetra(vinylthio)-4-(4-hydroxyethoxyethyloxy)-1-fluorobenzene, with 1,5-diaminopentane forms 1,5-bis[2,3,5,6-tetra(vinylthio)-4-fluoroanilino]pentane; in reactions with 2-aminoethanethiol and 2-mercaptoethanol occurs substitution of two fluorine atoms by RS groups.     

Assembling of Complex Heterocyclic Ensembles, Schiff Bases, from 5-Amino-3-[2-(4,5,6,7-tetrahydroindolyl)]pyrazoles and 1-Vinyl(ethyl)-2-formylimidazoles

Condensation of 5-amino-3-(2-pyrrolyl)pyrazoles with 1-vinyl(ethyl)-2-formylimidazoles afforded complex heterocyclic ensembles: Schiff bases containing pyrrole, pyrazole, and imidazole rings. The cis,trans-orientation of CH = N and CH₂ = CH groups and E-isomeric structure of the Schiff bases under study with respect to the imine fragment, and also the presence of intra- and intermolecular hydrogen bonds were established.     

Measurement of Cross Sections for Inclusive Forward Charged Hadron Production in Carbon–Carbon Collisions at Beam Energy of 19.6 GeV per Nucleon

Physics of Atomic Nuclei - The invariant cross sections for forward charged-hadron production at zero angle in carbon–carbon collisions at a beam kinetic energy of 19.6 GeV per nucleon were...     

STRUCTURE AND COMPOSITION OF [(nacnac)MnCl]2 (nacnac = HC(C(Me)N(2.6-i-Pr2C6H3))2) PRODUCTS REDUCED BY POTASSIUM-INTERCALATED GRAPHITE IN TOLUENE AND BENZENE

Journal of Structural Chemistry - The reduction of [(nacnac)MnCl]2 (1) (nacnac = HC(C(Me)N(2.6-i-Pr2C6H3))2) by potassium intercalated graphite KC8 in toluene and benzene is...     

New Approach to the Synthesis of Strained Cyclic Systems: I. Iminocyclobutenes and Iminothietanes from 1,3-Dilithio-3-phenylpropyne and Methyl Isothiocyanate

The reaction of 1,3-dilithio-3-phenylpropyne with methyl isothiocyanate in THF-hexane at -90 to -55°C, followed by successive treatment of intermediate product with a donor of protons, superbase, and alkyl halide, yields isomeric iminocyclobutenes and iminothietanes in addition to the expected aminothiophene. The ratio of the products depends on the amount and nature of proton donor (MeOH, t-BuOH), base (MeONa, t-BuOM, M = Li, Na, K; t-AmOK), co-solvent (DMSO, HMPA), and alkyl halide (MeI, EtI, BuBr). The system t-BuOH(MeOH)-t-BuOK-DMSO is the most favorable for the formation of the corresponding iminocyclobutene.     

New results on efficient crystal extraction of protons from the 70 GeV accelerator at the Institute of High-Energy Physics

A record-high particle extraction efficiency, exceeding 40%, in agreement with theoretical predictions, is achieved using a short (5 mm long) crystal bent by 1.5 mrad. An extracted beam intensity of ∼6×10¹¹ protons per cycle is obtained. This is five to six orders of magnitude higher than previous results. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 544–548 (10 October 1998)