Analysis of single, cisplatin-induced DNA bends by atomic force microscopy and simulations.

Bent DNA, or DNA that is locally more flexible, is a recognition motif for many DNA binding proteins. These DNA conformational properties can thus influence many cellular processes, such as replication, transcription, and DNA repair. The importance of these DNA conformational properties is juxtaposed to the experimental difficulty to accurately determine small bends, locally more flexible DNA, or a combination of both (bends with increased flexibility). In essence, many current bulk methods use average quantities, such as the average end-to-end distance, to extract DNA conformational properties; they cannot access the additional information that is contained in the end-to-end distance distributions. We developed a method that exploits this additional information to determine DNA conformational parameters. The method is based on matching end-to-end distance distributions obtained experimentally by atomic force microscopy imaging to distributions obtained from simulations. We applied this method to investigate cisplatin GG biadducts. We found that cisplatin induces a bend angle of 36° and softens the DNA locally around the bend.

Determination of sulfur in biodiesel microemulsions using the summation of the intensities of multiple emission lines.

A method for the determination of sulfur in biodiesel samples by inductively coupled plasma optical emission spectrometry which uses microemulsion for sample preparation and the summation of the intensities of multiple emission lines has been developed. Microemulsions were prepared using 0.5 mL of 20% v/v HNO(3), 0.5 mL of Triton X-100, 2-3 mL of biodiesel sample, and diluted with n-propanol to a final volume of 10 mL. Summation of the emission intensities of multiple sulfur lines allowed for increased accuracy and sensitivity. The amounts of sulfur determined experimentally were between 2 and 7 mg L(-1), well below legislative standards for many countries. Recoveries obtained ranged from 72 to 119%, and recoveries obtained for the 182.562 nm line were slightly lower. This is most likely due to its lower sensitivity. Using microemulsion for sample preparation and the summation of the intensities of multiple emission lines for the successful determination of sulfur in biodiesel has been demonstrated.

Continuum source tungsten coil atomic fluorescence spectrometry.

A simple continuum source tungsten coil atomic fluorescence spectrometer is constructed and evaluated. The heart of the system is the atomizer: a low-cost tungsten filament extracted from a 150 W light bulb. The filament is resistively heated with a small, solid-state, constant-current power supply. The atomizer is housed in a glass chamber and purged with a 1 L/min flow of a conventional welding gas mixture: 10% H(2)/Ar. A 25 µL sample aliquot is pipetted onto the tungsten coil, the liquid is dried at low current, and then the atomic vapor is produced by applying a current in the range 3.5-5.5 A. The atomization current does not produce temperatures high enough to excite atomic emission. Radiation from a 300 W xenon lamp is focused through the atomic vapor, exciting atomic fluorescence. Fluorescence signals are collected using a hand-held charge-coupled device (CCD) spectrometer. Simultaneous determination of ten elements (Ag, Bi, Cr, Cu, Ga, In, Mg, Mn, and Tl) results in detection limits in the range 0.3 to 10 ng. The application of higher atomization currents (10 A) leads to straightforward detection of atomic emission signals with no modifications to the instrument.