Structural change in a B-DNA helix with hydrostatic pressure

Study of the effects of pressure on macromolecular structure improves our understanding of the forces governing structure, provides details on the relevance of cavities and packing in structure, increases our understanding of hydration and provides a basis to understand the biology of high-pressure organisms. A study of DNA, in particular, helps us to understand how pressure can affect gene activity. Here we present the first high-resolution experimental study of B-DNA structure at high pressure, using NMR data acquired at pressures up to 200 MPa (2 kbar). The structure of DNA compresses very little, but is distorted so as to widen the minor groove, and to compress hydrogen bonds, with AT pairs compressing more than GC pairs. The minor groove changes are suggested to lead to a compression of the hydration water in the minor groove

Viscosity Measurement in a Lubricant Film Using an Ultrasonically Resonating Matching Layer

A novel ultrasonic viscometer intended for in-situ applications in lubricated components is presented. The concept is based on the reflection of a shear wave at a solid-liquid boundary that depends on the viscosity of the liquid and the acoustic properties of the solid. Very little ultrasound energy can propagate into the oil at a metal-oil interface because the acoustic mismatch is great, and this leads to large measurement errors. The method described in this paper overcomes this limitation by placing a thin intermediate matching layer between the metal and the lubricant. Results obtained with this technique are in excellent agreement with expected values from conventional viscometers when Newtonian mineral oils are analysed. When complex non-Newtonian mixtures are tested, the viscosity measurement is frequency dependent. At high ultrasonic frequencies, over 1 MHz, it is possible to shear only the base oil, while to obtain the viscosity of the mixture it is necessary to choose a lower excitation frequency to match the dispersed polymer relaxation time

High-resolution ultrasonic spectroscopy

High-resolution ultrasonic spectroscopy (HR-US) is an analytical technique for direct and non-destructive monitoring of molecular and micro-structural transformations in liquids and semi-solid materials. It is based on precision measurements of ultrasonic velocity and attenuation in analysed samples. The application areas of HR-US in research, product development, and quality and process control include analysis of conformational transitions of polymers, ligand binding, molecular self-assembly and aggregation, crystallisation, gelation, characterisation of phase transitions and phase diagrams, and monitoring of chemical and biochemical reactions. The technique does not require optical markers or optical transparency. The HR-US measurements can be performed in small sample volumes (down to droplet size), over broad temperature range, at ambient and elevated pressures, and in various measuring regimes such as automatic temperature ramps, titrations and measurements in flow

Excited state complex formation between 3-aminophthalhydrazide and DNA: A fluorescence quenching reaction

Fluorescence quenching reaction of 3-aminophthalhyrdazide (luminol) due to the interaction with short DNA fragments has been studied employing steady-state and time correlated single photon counting techniques. The interaction of luminol with DNA in the excited state has also been analyzed using Stern-Volmer (S-V) mechanism. A very weak ground state interaction is proposed to explain the higher values of the quenching rate constant and is consistent with positive curvatures in the S-V plots. A plausible explanation of the quenching mechanism has been discussed on the basis of hydrogen bonding interaction between luminol and DNA fragment. It is proposed that the phosphate backbone present in DNA is responsible for the interaction with luminol.</p