Structural evolution of environmentally responsive cationic liposome-DNA complexes with a reducible lipid linker

Environmentally responsive materials (i.e., materials that respond to changes in their environment with a change in their properties or structure) are attracting increasing amounts of interest. We recently designed and synthesized a series of cleavable multivalent lipids (CMVLn, with n = 2-5 being the number of positive headgroup charges at full protonation) with a disulfide bond in the linker between their cationic headgroup and hydrophobic tails. The self-assembled complexes of the CMVLs and DNA are a prototypical environmentally responsive material, undergoing extensive structural rearrangement when exposed to reducing agents. We investigated the structural evolution of CMVL-DNA complexes at varied complex composition, temperature, and incubation time using small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). A related lipid with a stable linker, TMVL4, was used as a control. In a nonreducing environment, CMVL-DNA complexes form the lamellar (L(α)(C)) phase, with DNA rods sandwiched between lipid bilayers. However, new self-assembled phases form when the disulfide linker is cleaved by dithiothreitol or the biologically relevant reducing agent glutathione. The released DNA and cleaved CMVL headgroups form a loosely organized phase, giving rise to a characteristic broad SAXS correlation profile. CMVLs with high headgroup charge also form condensed DNA bundles. Intriguingly, the cleaved hydrophobic tails of the CMVLs reassemble into tilted chain-ordered L(β') phases upon incubation at physiological temperature (37 °C), as indicated by characteristic WAXS peaks. X-ray scattering further reveals that two of the three phases (L(βF), L(βL), and L(βI)) constituting the L(β') phase coexist in these samples. The described system may have applications in lipid-based nanotechnologies.     

Efficient adsorption of anionic dyes onto magnetic graphene oxide coated with polyethylenimine: Kinetic,isotherm, and thermodynamic studies

Research on Chemical Intermediates - The removal efficiency of two anionic dyes, namely direct red 81 (DR 81) and reactive blue 19 (RB 19), from aqueous solution was investigated through batch...     

Adsorptive removal of mercury (II), copper (II), and lead (II) ions from aqueous solutions using glutathione-functionalized NiFe2O4/graphene oxide composite

Research on Chemical Intermediates - The aim of the present study was to develop a novel adsorbent through decorating the surface of graphene oxide (GO) nanosheets with nickel ferrite (NiFe2O4)...     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

Synthesis and antimicrobial activity of novel oxysterols from lanosterol

Chemically diverse oxysterols and their synthetic manipulations were carried out from variety of Δ⁸⁽⁹⁾-lanosterol derivatives and evaluated for their in vitro antimicrobial activities. Most of the synthesized oxysterols exhibited significant antifungal activity against the tested strains.     

Linear cavity Brillouin fiber laser with improved characteristics

A configuration for linear cavity Brillouin fiber laser (BFL) generation is demonstrated using a standard single-mode fiber, two optical circulators, a 3 dB coupler, and a 95/5 coupler to allow high efficiency. With a Brillouin pump (BP) power of 13 dBm, the laser peak power is 12.3 dB higher than a conventional linear cavity BFL at an upshifted wavelength of 0.086 nm from the BP wavelength. In addition, it is revealed that the BFL peak power can be higher than the transmitted BP peak power when the BP power exceeds the second Brillouin Stokes threshold power.     

Beitrag zur pr?parativen Fraktionierung von Block- und statistischen Copolymeren

Zusammenfassung Mit Hilfe der Gelpermeations-Chromatographie, der Makro--Backer-Williams-Kolonne und der Dreieckfällungsfraktionierungs-Methode nach Meyerhoff wurden Block- und statistische Styrol-Butadien-Copolymere präparativ vergleichend fraktioniert. Die so erhaltenen Fraktionen wurden teilweise durch Absolutmethoden charakterisiert. Die Molekulargewichtsbestimmung bzw. die Molekulargewichtsverteilung der aus den drei Methoden erhaltenen Fraktionen wurde mit Hilfe der GPC überprüft, und mit Hilfe eines Computerprogramms aus den GPC-Chromatogrammen berechnet. Es zeigte sich, daß die Polydispersität der Fraktionen im Bereich von 1,15 bis 1,80 variiert und die Fraktionierungsmethode spezifisch ist. Die erhaltenen Fraktionen waren in ihrer chemischen Zusammensetzung zufriedenstellend einheitlich.

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Contribution to the preparative fractionation of block and statistical copolymers

Summary With the aid of gel permeation chromatography, the macro-Backar-Williams column and the triangle precipitation fractionation method according to Meyerhoff, block and statistical styrene-butadiene copolymers were separated into single fractions. The fractions thus obtained were partly characterized by absolute methods. The molecular weight determination or the molecular weight distribution of the fractions were calculated from the GPC chromatograms with the aid of computer programs. The polydispersity of the fractions varied in the region of 1.15 to 1.80, and was specific for the fractionation method. However, the fractions obtained were sufficiently uniform in relation to their chemical composition.

     

Determination of chemical heterogeneity of copolymers by gel-permeation chromatography

Summary The determination of the chemical heterogeneity of copolymers has been carried out by means of gel-permeation chromatography (GPC). Consequently mixtures of different homopolymers with the same relative molecular masses have been fractionated. Although maximum chemical non-uniformity appears, non-uniform effects obtained from the GPC are negligible. It is seen that for copolymers a GPC separation only occurs when the chemical composition of the copolymer changes simultaneously with the degree of polymerisation. We have established that, in a few cases, minute chemical heterogeneity is evident from the GPC curves, but not in the bulk which obeys the kinetics of copolymerisation.