THE EFFECT OF MERCURIC IONS ON THE EXCITED STATES OF DNA-INTERCALATED ETHIDIUM BROMIDE

The first excited triplet state of DNA-intercalated ethidium bromide is produced with a quantum yield of 0.010.002 on irradiation at 532 nm. A difference extinction coefficient of 1.50.210³ m² mol^?1 is measured for the triplet state at 380 nm. Mercuric ions quench the first excited singlet state of DNA-intercalated ethidium bromide via induced spin orbit coupling to give an increased yield of ethidium triplet states. The same mercuric ion that quenches the singlet state then quenches the triplet state, via the same mechanism, with a rate constant of ca 3.510³ s^?1. An upper limit for the rate of detachment of Hg²⁺ from its binding site in DNA may be fixed at ca 10³ s^?1.     

Optical coherence refractometry

We introduce a novel approach to refractometry using a low coherence interferometer at multiple angles of incidence. We show that for plane parallel samples it is possible to measure their phase refractive index rather than the group index that is usually measured by interferometric methods. This is a significant development because it enables bulk refractive index measurement of scattering and soft samples, not relying on surface measurements that can be prone to error. Our technique is also noncontact and compatible with in situ refractive index measurements. Here, we demonstrate this new technique on a pure silica test piece and a highly scattering resin slab, comparing the results with standard critical angle refractometry.     

Self-organized domain formation in low-dislocation-density GaN

The growth of high-quality GaN layers on a wafer size appropriate for device applications is based on heteroepitaxy on foreign substrates. Heteroepitaxial GaN layers with low densities (below 10⁶ cm⁻²) of extended structural defects can be achieved by lateral overgrowth of mask-patterned templates or by the growth of extremely thick GaN layers as a route towards free-standing GaN-pseudosubstrates. We present the microscopic analysis of such low-dislocation-density GaN layers by means of scanning cathodoluminescence microscopy (CL). Several state-of-the-art concepts of lateral overgrowth are compared, including two-step epitaxial lateral overgrowth of stripe masks (ELO), multi-stack ELO comprising several mask layers as well as an alternative approach involving in situ SiN nano-masks. The self-organized formation of typical microscopic growth domains with characteristic optical properties is evidenced by CL for all lateral overgrowth techniques. This behavior directly fingerprints the different growth rates and the specific impurity incorporation on non-equivalent GaN facets, e.g. (0001), or , always present during lateral overgrowth and closely related to the mask geometry. Accordingly, characteristic CL line shapes found in ELO on periodic, micrometer scale mask patterns are also detected for GaN on in situ SiN nano-masks and clearly reveal the individual facet structure during overgrowth. For thick GaN layers, CL is used to detect the spontaneous appearance of inclined facets inside inverted pyramidal defects. Optimized, thick GaN layers exclusively formed by (0001)-growth are proven to be laterally homogeneous despite periodically varying residual stress and dislocation density of the underlying ELO template.     

Extraction and characterisation of anti-oestradiol immunoglobulins from human serum by high-performance liquid chromatography

Summary Immunoglobulins have been extracted from human and rabbit serum by size exclusion high performance liquid chromatography. In the case of rabbit immunized against ethinyl-oestradiol and woman having arterial thrombosis in the course of oral contraceptive use, the extracted immunoglobulins present a very high affinity for 17 -oestradiol sulphate. The measurement of affinity to this compound of different extracted immunoglobulins allows a quantitative determination of these specific proteins. Comparative studies with radioimmunoassays are in good agreement.Presented at the 14th International Symposium on Chromatography London, September, 1982