Fluorescence properties and photophysics of the sulfoindocyanine Cy3 linked covalently to DNA

The sulfoindocyanine Cy3 is one of the most commonly used fluorescent dyes in the investigation of the structure and dynamics of nucleic acids by means of fluorescence methods. In this work, we report the fluorescence and photophysical properties of Cy3 attached covalently to single-stranded and duplex DNA. Steady-state and time-resolved fluorescence techniques were used to determine fluorescence quantum yields, emission lifetimes, and fluorescence anisotropy decays. The existence of a transient photoisomer was investigated by means of transient absorption techniques. The fluorescence quantum yield of Cy3 is highest when attached to the 5' terminus of single-stranded DNA (Cy3-5' ssDNA), and decreases by a factor of 2.4 when the complementary strand is annealed to form duplex DNA (Cy3-5' dsDNA). Substantial differences were also observed between the 5'-modified strands and strands modified through an internal amino-modified deoxy uridine. The fluorescence decay of Cy3 became multiexponential upon conjugation to DNA. The longest lifetime was observed for Cy3-5' ssDNA, where about 50% of the decay is dominated by a 2.0-ns lifetime. This value is more than 10 times larger than the fluorescence lifetime of the free dye in solution. These observations are interpreted in terms of a model where the molecule undergoes a trans-cis isomerization reaction from the first excited state. We observed that the activation energy for photoisomerization depends strongly on the microenvironment in which the dye is located. The unusually high activation energy measured for Cy3-5' ssDNA is an indication of dye-ssDNA interactions. In fact, the time-resolved fluorescence anisotropy decay of this sample is dominated by a 2.5-ns rotational correlation time, which evidences the lack of rotational freedom of the dye around the linker that separates it from the terminal 5' phosphate. The remarkable variations in the photophysical properties of Cy3-DNA constructs demonstrate that caution should be used when Cy3 is used in studies employing DNA conjugates.     

An end theorem for stratified spaces

We show that a manifold-stratified space X is the interior of a compact manifold-stratified space with boundary if and only if X is tame-ended and a K-theoretic obstruction γ_*(X) vanishes. The obstruction γ_*(X) is a localization of Quinn's mapping cylinder neighborhood obstruction. The main results are Theorem 1.6 and Theorem 1.7 below. In particular, this explains when a G-manifold is the interior of a compact G-manifold with boundary. One of our methods is a new transversality theorem, Theorem 1.16. Oblatum 30-VI-1996 & 21-X-1997 / Published online: 14 January 1999     

Morphology and electrical properties of pulsed-laser deposited Bi2Sr2CaCu2O8+δ films on vicinal substrates

Thin films of Bi₂Sr₂CaCu₂O_8+δ have been grown on vicinal (001) SrTiO₃ substrates by pulsed-laser deposition. Transmission electron microscopy (TEM) and X-ray diffraction reveal well ordered films with the c axis of the film parallel with the c axis of the substrate for miscut angles up to θ_S≈15°. TEM also reveals the step-like film morphology due to step-flow growth. The in-plane and out-of-plane resistivities are independent of film thickness within the range 20–300 nm and agree quite well with Bi₂Sr₂CaCu₂O_8+δ single-crystal data. Received:15 May 2000 / Accepted:17 May 2000 / Published online: 9 August 2000     

Triterpenoids

This review covers the isolation and structure determination of triterpenoids, including squalene derivatives, protostanes, lanostanes, holostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, serratanes and saponins; 305 references are cited.     

FLUORESCENCE PROPERTIES OF C-PHYCOCYANIN ISOLATED FROM A THERMOPHILIC CYANOBACTERIUM

Abstract The fluorescence lifetime of purified C-phycocyanin from the thermophilic cyanobacterium, Phormidium laminosum (strain OH-1-p. Cl 1), was measured as 1.48 ± 0.06 ns using the technique of time-correlated single-photon counting under very weak excitation pulses. The natural radiative lifetime (∼6.1 ns) of the pigment was calculated by integrating the absorption spectrum using the Strickler–Berg equation. From these two lifetimes we calculate a fluorescence quantum yield of ∼0.24 which is very close to the value ∼0.22 which we measure relative to the known value of cresyl violet in methanol. Both the fluorescence lifetime and the quantum yield of the pigment from this organism are lower than most previous values reported in the literature. We conclude that our lower values are not due to high light intensity, pH, buffer, concentration, instrumentation artifacts, aggregation effects or the thermophilic nature of the organism. Instead, we suggest that the photophysical properties of C-phycocyanin are species dependent, perhaps due to the specific molecular environment of the tetrapyrrole.     

On braid groups and right-angled Artin groups

In this article we prove a special case of a conjecture of A. Abrams and R. Ghrist about fundamental groups of certain aspherical spaces. Specifically, we show that the \(n\) -point braid group of a linear tree is a right-angled Artin group for each \(n\) .     

Systems-based decomposition schemes for the approximate solution of multi-term fractional differential equations

We give a comparison of the efficiency of three alternative decomposition schemes for the approximate solution of multi-term fractional differential equations using the Caputo form of the fractional derivative. The schemes we compare are based on conversion of the original problem into a system of equations. We review alternative approaches and consider how the most appropriate numerical scheme may be chosen to solve a particular equation.     

连续波锁模Pr3+:YLF激光器

本文报导了采用氩离子激光器来泵浦Pr³⁺:YLF晶体,应用声光调制器实现了主动锁模;同时应用振动─高反射平面镜也实现了被动锁模,两种锁模均得到了ps光脉冲.据作者了解这是这种晶体材料的第一次锁模运转.