Effect of gelation conditions on the gel structure and resolving power of agarose-based DNA sequencing gels

A Percolation Approach for Investigating the Sol-Gel Phase Transition of κ-Carrageenan: A Steady-State Fluorescence Study

A steady-state fluorescence technique was employed to study sol-gel transitions in K-carrageenan systems at various carrageenan concentrations. Scattered light, Isc, and fluorescence intensity, I, were monitored against temperature to determine critical phase transition temperatures and exponents. Pyranine was used as a fluorescence probe to monitor these phase transitions. It was observed that coil-to-helix (sol-gel) transition temperatures, Tch, strongly correlated with carrageenan concentration. The weight average degree of polymerization, DPw and gel fraction G, exponents (γ and β) were measured and found to be in accord with the classical Flory-Stockmayer model.

Hysteresis During Sol-Gel and Gel-Sol Phase Transitions of k-Carrageenan: A Photon Transmission Study

Photon transmission techniques were used to study sol-gel and gel-sol transitions in k-carrageenan-water systems with various carrageenan contents. The photon transmission intensity, Itr was monitored against temperature to determine critical phase transition temperatures and transition rates. It was observed that the sol-gel transition temperatures, Tsg, were found much lower than the gel-sol, Tgs, transition temperatures based on the hysteresis of the phase transition loops. Sol-gel and gel-sol activation energies were determined and it was found that a carrageenan-water system required less energy for the gel-sol transition than for the sol-gel transition.

4-Perfluoroalkylbutoxybenzene derivatives as liquid crystalline organogelators based on phase-selective gelators

4-Perfluoroalkylbutoxybenzene derivatives as a smart soft material show efficient and rapid phase-selective gelation ability from water at extremes of pH.

NMR analysis of weak molecular interactions using slice-selective experiments via study of concentration gradients in agar gels

Weak molecular interactions can be localized and quantified using a single NMR experiment analysing concentration gradients generated in agar gels.

Application of pulsed field gel electrophoresis to type Campylobacter jejuni

Pulsed field gel electrophoresis (PFGE) is generally accepted as one of the most discriminatory methods available for genotyping Campylobacter jejuni. PFGE has been extensively used in epidemiological studies, including outbreak investigation, persistence of genotypes in a human population, environmental diversity of sporadic infection isolates, dissemination of antibiotic-resistant strains, and comparison of genotypes within and between hosts. The main purpose of this chapter is to present a working PFGE protocol for those interested in incorporating this technique in their laboratories.

Photon Transmission Study on Conformational Ordering of Iota-Carrageenan in CaCl2 Solution

Coil-to-double helix (c-h) and double helix-to-dimer (h-d) phase transitions of iota-carrageenan in CaCl(2) solution upon cooling were studied using photon transmission technique. Photon transmission intensity, I(tr) was monitored against temperature to determine the (c-h) and (h-d) transition temperatures (T(ch) and T(hd)) and activation energies (DeltaE(ch) and DeltaE(hd)). An extra dimer-to-dimer (d-d) transition was also observed during cooling at low temperature region. However, upon heating dimers disappear to double helices by making dimer-to-double helix (d-h) transition. Further heating resulted double helix-to-coil (h-c) transition at high temperature region. T(dh) and T(ch) temperatures and DeltaE(dh) and DeltaE(hc) activation energies were also determined. It was observed that T(hc) and T(ch) temperatures and DeltaE(dh) and DeltaE(hd) activation energies do not effected by carrageenan content. However, T(hd), T(dh) and T(dd) temperatures and DeltaE(ch) and DeltaE(hc) activation energies were found to be strongly correlated to the carrageenan content in the system.

Cation effect on thermal transition of ι-carrageenan: a photon transmission study

Coil-to-double helix (c-h) and double helix-to-dimer (h-d) phase transitions of iota-carrageenan in various cation (CaCl2) solutions upon heating and cooling were studied using the photon transmission technique. Photon transmission intensity, Itr, was monitored against temperature to determine the (c-h) and (h-d) transition temperatures (Tch and Thd) and activation energies (DeltaEch and DeltaEhd). An extra dimer-to-dimer (d-d) transition was observed during cooling at low temperature region. However, upon heating dimers directly decompose into double helices by making dimer-to-double helix (d-h) transition. Further heating results in double helix-to-coil (h-c) transition at high temperature region. Tdh and Thc temperatures and Delta Edh and DeltaEhc activation energies were determined. It was observed that Thc and Tch temperatures and DeltaEch and DeltaEhc activation energies were found to be strongly correlated to the CaCl2 content in the system.

Small Molecule Diffusion into Swelling Iota-Carrageenan Gels: A Fluorescence Study

Small molecule diffusion into Iota-Carrageenan gel was studied by using steady-state fluorescence (SSF) technique. Pyranine, dissolved in water was used as fluorescence probe. Fluorescence emission intensity, I(p), and scattered light intensity, I(sc), were monitored to study diffusion and swelling processes at various temperatures respectively. Fickian and Li-Tanaka models were elaborated to produce diffusion, D, and collective diffusion, D(0), coefficients. Diffusion and swelling activation energies were also obtained and found to be 20.5 kj mol(-1) and 28.2 kj mol(-1), respectively.

Force of an actin spring

Cellular movements are produced by forces. Typically, cytoskeletal proteins such as microtubules and actin filaments generate forces via polymerization or in conjunction with molecular motors. However, the fertilization of a Limulus polyphemus egg involves a third type of actin-based cellular engine--a biological spring. During the acrosome reaction, a 60-microm long coiled and twisted bundle of actin filaments straightens and extends from a sperm cell, penetrating the vitelline layer surrounding the egg. A subtle overtwist of 0.2 degrees /subunit underlies the mechanochemical basis for the extension of this actin spring. Upon calcium activation, this conformational strain energy is converted to mechanical work, generating the force required to extend the bundle through the vitelline layer. In this article, we stall the extension of the acrosome bundle in agarose gels of different concentrations. From the stall forces, we estimate a maximum force of 2 nN and a puncturing pressure of 1.6 MPa. We show the maximum force of extension is three times larger than the force required to puncture the vitelline layer. Thus, the elastic strain energy stored in the acrosome bundle is more than sufficient to power the acrosome reaction through the egg envelope.

A fluorescence study on the gel-to-sol transition of κ-carrageenan

The fluorescence technique was employed to study gel-to-sol transitions in kappa-carrageenan systems with various carrageenan contents. Pyranine was used as a fluorescence probe for monitoring these transitions. Fluorescence, Ip and scattered light, Isc intensities were measured against temperature to determine critical phase transition temperatures and exponents. It was observed that gel-to-sol transition temperatures, Tgs are found to be dependent to the carrageenan content. The measured critical exponents gamma' and beta' were found to be very close to the weight average degree of polymerization, DPw and gel fraction G, exponents (gamma and beta) of the classical Percolation Model.

Cation effects on sol-gel and gel-sol phase transitions of kappa-carrageenan-water system

Sol-gel and gel-sol phase transitions of kappa-carrageenan in pure water and in KCl solution were studied using photon transmission technique. Photon transmission intensity, I(tr), was monitored against temperature to determine the sol-gel and gel-sol temperatures (T(sg) and T(gs)) and activation energies (deltaH(sg) and deltaH(gs)). It was observed that T(gs) was notably higher than T(sg) due to the hysteresis on the phase transition loops. T(gs) and deltaH(gs) values were also higher for gels containing KCl than for those without KCl. The increase in carrageenan content caused an increase in both critical temperatures and activation energies for the gels prepared in pure water and in KCl solution. Increases in the KCl/carrageenan ratio, raised both T(gs) and T(sg). Similarly deltaH(sg) was elevated by the increase in cation content of the gel. These results were interpreted as the formation of stronger gels in the presence of KCl in water.