Biomedical subjects

Shawn D Wettig

Publications and source records attributed to Shawn D Wettig.

7 recordsLinked to original sources

PubMed2005

M-DNA: A novel metal ion complex of DNA studied by fluorescence techniques.

M-DNA, a complex formed in solution between divalent metal ions (M) and duplex DNA, has been studied extensively using fluorescence quenching. This review examines the methods used to examine the formation of M-DNA, and its ability to serve as a pathway for electron transfer between donor and acceptor chromaphores. A mass action model for M-DNA formation is presented based upon the results of fluorescence quenching studies using fluorescein/QSY-7 labeled duplexes. From the mass action analysis, it was determined that approximately 1.4 protons are released per base pair, with k(eq) on the order of 10(-8), indicative of a strong interaction. As resonance energy transfer is shown to be unlikely over the distances involved in this work, the observed quenching in M-DNA is discussed in terms of an electron hopping mechanism for electron transfer, with k(hop)=2.5 x 10(11)s(-1).

Animals↗

PubMed2005

Synthesis and solution properties of gemini surfactants containing oleyl chains.

Gemini surfactants 18:1-s-18:1, where s = 2, 3, and 6 methylene groups and 18:1 refers to oleyl carbon chains, have been synthesized, characterized and a number of micelle solution properties measured by using electrical conductance, fluorescence probe emission, light scattering (DLS), surface tension and isothermal titration calorimetry (ITC) methods at 25 degrees C. The cmc values of 18:1-2-18:1, 18:1-3-18:1, and 18:1-6-18:1 were found to be 26.9, 23.4, and 18.0 microM, respectively, using the electrical conductance method. Surface tension results suggest that in 0.01 N NaCl solutions, the s = 2 and 3 members of the series form multilayer rather than monolayer structures, while the s = 6 homologue adopts a close-packed arrangement. This is consistent with DLS and EM measurements which show vesicle formation for the s = 2 and 3 compounds, and micelle formation for the s = 6 compound. The enthalpies of micellization (deltaH degrees (M)) are more exothermic for the 18:1-s-18:1 series of surfactants, than for the 12-s-12 series. The differences are rationalized in terms of steric and configurational contributions to deltaH degrees (M) arising from difficulties associated with packing of the bulky cis-9-octadecene tails.

Alkenes↗

PubMed2005

Isothermal titration calorimetry and dynamic light scattering studies of interactions between gemini surfactants of different structure and Pluronic block copolymers.

The interactions between triblock copolymers of poly(ethylene oxide) and poly(propylene oxide), P103 and F108, EO(n)PO(m)EO(n), m=56 and n=17 and 132, respectively, and m-s-m type gemini surfactants, m=8, 10, 12, and 18, and s = 3, 6, 12, and 16, have been studied in aqueous solution using isothermal titration calorimetry and dynamic light scattering techniques. The enthalpograms of F108 as a function of surfactant concentration show one broad peak at polymer concentrations C(p) < or = 0.50 wt%, below the cmc of the copolymer at 25 degrees C. It is attributed to interactions between the surfactant and the triblock copolymer monomer. DLS results show hydrodynamic radii (R(h)) initially consistent with copolymer monomers that change to values consistent with gemini surfactant micelles as the surfactant concentration is increased. In P103 solutions at C(p) > or = 0.05 wt%, two peaks appear in the enthalpograms, and they are attributed to the interactions between the gemini surfactant and the micelle or monomer forms of the copolymer. An origin-based nonlinear fitting program was employed to deconvolute the two peaks and to obtain estimates of peak properties. An estimate of the fraction of copolymer in aggregated form was also obtained. The enthalpy change due to interactions between the surfactants and P103 aggregates is very large compared to values obtained for traditional surfactants. This suggests that extensive reorganization of copolymer aggregates and surrounding solvent occurs during the interaction. DLS results for the P103 systems containing C(p) > or = 0.05% show evidence of very large aggregates in solution, likely P103 micelle clusters. The transitions observed in the hydrodynamic radii are consistent with a breakdown of micelle clusters with addition of gemini surfactant, followed by mixed micelle formation and/or deaggregation into monomer P103. This is followed by interactions similar to those typically observed in surfactant-nonionic polymer systems. Mechanisms for the interaction and the observed structural changes are discussed.

Biophysics↗

PubMed2004

Interactions between 12-EOx-12 gemini surfactants and pluronic ABA block copolymers (F108 and P103) studied by isothermal titration calorimetry.

The interactions between triblock copolymers of poly(ethylene oxide) and poly(propylene oxide), P103 and F108, EO(n)PO(m)EO(n), m = 56 and n = 17 and 132, respectively, and gemini surfactants (oligooxa)-alkanediyl-alpha,omega-bis(dimethyldodecylammonium bromide) (12-EO(x)-12), x = 0-3, have been studied in aqueous solution using isothermal titration calorimetry. The thermograms of F108 as a function of surfactant concentration show one broad peak at polymer concentrations, Cp, < or =0.50 wt %, below the critical micelle concentration (cmc) of the copolymer at 25 degrees C. It is attributed to interactions between the surfactant and the triblock copolymer monomer. The critical aggregation concentration (cac) remains constant while deltaHmax2 and the saturation concentration, C2, increase with increasing copolymer concentration. Analysis of the cac data offers semiquantitative support that the degree of ionization of the surfactant aggregates bound to polymers is likely to be larger than that at the surfactant cmc. In P103 solutions at Cp > or = 0.05 wt %, two peaks appear in the thermograms and they are attributed to the interactions between the gemini surfactant and the micelle or monomeric forms of the copolymer. An origin-based nonlinear fitting program was employed to deconvolute the two peaks and to obtain estimates of peak properties. An estimate of the fraction of copolymer in aggregated form was also obtained. The enthalpy change due to interactions between the surfactants and P103 aggregates is very large compared to values obtained for traditional surfactants. This suggests that extensive reorganization of copolymer aggregates and surrounding solvent occurs during the interaction. Dehydration of the copolymers by the surfactant may also play an important step in the interaction. The endothermic enthalpy change reflecting interactions between the surfactant and polymer decreases more rapidly as the length and hydrophilic character of the spacer increases, suggesting that more favorable interactions occur with the P103 monomers having shorter PEO segments.

Journal Article↗

PubMed2003

Thermodynamic investigation of M-DNA: a novel metal ion-DNA complex.

The thermodynamics of formation of a novel divalent metal ion-DNA complex known as M-DNA have been investigated using an ethidium bromide (EB) fluorescence assay, and with isothermal titration calorimetry. The process of M-DNA formation was observed from the EB assay to be strongly temperature-dependent. The binding of Zn(2+) to calf thymus (42% GC content) and Escherichia coli (50% GC content) DNA at pH 8.5 exhibited an endothermic cooperative binding process at Zn(2+) concentrations of approximately 0.1 mM, indicating an entropy driven process. This binding process is consistent with a site-specific binding interaction, similar in nature to Z-DNA formation; however, the interaction occurs at much lower metal ion concentrations. The enthalpy of M-DNA formation for calf thymus DNA was determined to be 10.5+/-0.7 and 9+/-2 kJ/mbp at DNA concentrations of 100 and 50 microg ml(-1), respectively. An enthalpy of 13+/-3 kJ/mbp was obtained for M-DNA formation for 50 microg ml(-1) E. coli DNA. No evidence of M-DNA formation was observed in either DNA at pH 7.5 with Zn(2+) or at either pH 7.5 or 8.5 with Mg(2+).

DNA↗

PubMed2003

M-DNA: a self-assembling molecular wire for nanoelectronics and biosensing.

M-DNA is a complex between divalent metal ions such as Zn2+ and duplex DNA which forms at pH 8.5. Unlike B-DNA, M-DNA does not bind ethidium so that M-DNA formation can be monitored conveniently by an ethidium fluorescence assay. M-DNA was shown to be a better conductor than B-DNA by fluorometric measurements of electron transport in donor-acceptor labelled duplexes; by direct conductivity measurements of M-DNA bound between gold electrodes and by cyclic voltammetric studies on ferrocene labelled duplexes attached to gold microelectrodes. As is the case with B-DNA, M-DNA can self-assemble into a variety of structures and is anticipated to find widespread use in nanoelectronics and biosensing.

Biosensing Techniques↗

PubMed2002

Long range molecular wire behaviour in a metal complex of DNA.

M-DNA is a complex of metal ions such as Zn(2+) with duplex DNA. Previous results showed that the fluorescence of a donor fluorophore was quenched when an acceptor fluorophore was placed at the opposite end of a short M-DNA duplex. In order to investigate further the molecular wire behaviour of M-DNA, 30-mer duplexes were constructed with fluorescein as donor and rhodamine, pyrene and the cyanine dyes, Cy5 and Cy5.5 as acceptors. Good quenching was observed in all cases even though the efficiency of resonance energy transfer was calculated to be < 5%. The distance dependence of quenching was investigated by preparing doubly-labelled duplexes ranging in length from 20 to 1,000 base pairs. Upon formation of M-DNA significant quenching of the fluorescence of the donor fluorophore was observed in duplexes up to 500 base pairs in length. The amount of quenching decreased with increasing length of the duplexes with a shallow distance dependence. The results are consistent with an electron transfer mechanism in which the electron hops between metal centers. This process can occur efficiently over long distances.

Base Sequence↗