Preface

O’Connor, Desmond; Phillips, David

doi:10.1016/b978-0-12-524140-3.50003-4

Cited by 531 publications

(696 citation statements)

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“…The decay parameters were recovered using a nonlinear least squares iterative fitting procedure based on the Marquardt algorithm (Bevington, 1969). The program also includes statistical and plotting subroutine packages (O'Connor & Phillips, 1984). The goodness of the fit of a given set of observed data and the chosen function was evaluated by the reduced 2 ratio, the weighted residuals (Lampert et al, 1983), and the autocorrelation function of the weighted residuals (Grinvald & Steinberg, 1974).…”

Section: Methodsmentioning

confidence: 99%

Membrane Organization at Low Cholesterol Concentrations: A Study Using 7-Nitrobenz-2-oxa-1,3-diazol-4-yl-Labeled Cholesterol

1996

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Cholesterol is most often found distributed nonrandomly in the plane of the bilayer, giving rise to cholesterol-rich and -poor domains. Many of these domains are thought to be crucial for the maintenance of membrane structure and function. However, such well-characterized domains generally occur in the membranes that contain relatively large amounts of cholesterol. Cholesterol organization in membranes containing very low amounts of cholesterol has not been investigated extensively. Recent evidence from differential-scanning calorimetric studies suggests that cholesterol may not form uniform monodisperse solutions, as assumed earlier, in the membranes even at very low concentrations. Fluorescent cholesterol analogues, when chosen carefully, offer a powerful approach for studying the distribution and organization of cholesterol in membranes at low concentrations. In this paper, we have studied the organization of cholesterol in membranes at very low concentrations (up to 5 mol % of the total lipid) using a fluorescent cholesterol analogue (NBD-cholesterol) which is labeled with the 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) group at the flexible acyl chain, without any alteration in the structural features necessary for proper membrane incorporation. Our results show that NBD-cholesterol exhibits local organization even at very low concentrations. This is consistent with the recently suggested model of cholesterol organization in membranes at low concentrations, involving the formation of transbilayer, tail-to-tail dimers The fluid mosaic model for biological membranes defines the membrane as an oriented, two-dimensional, viscous solution of proteins and lipids in instantaneous thermodynamic equilibrium (Singer & Nicolson, 1972). Although the basic tenets of this model have stood the test of time, one of its implicit assumptions, that the lipid molecules merely provide the milieu for the membrane proteins and that they are distributed uniformly throughout the bilayer, has been found to be not quite true. In fact, current evidence points out that both transverse and lateral regionalization, which can be described in terms of micro-and macrodomains, are common features of many biological membranes (Curtain et al., 1988;Edidin, 1992;Tocanne, 1992;Glaser, 1993;Jacobson et al., 1995).Cholesterol is one of the membrane components that is found, more often than not, distributed nonrandomly in structural and kinetic domains or pools in both biological and model membranes (Yeagle, 1985;Gennis, 1989;Schroeder et al., 1991;Liscum & Underwood, 1995). The reason for this lies in the rather unusual chemical structure of cholesterol that can by no means be considered a representative component of the "bulk" membrane (see Figure 1). The unusual shape of cholesterol also causes a phase separation in membranes at relatively high concentrations, resulting in the formation of cholesterol-rich and -poor domains that are structurally and compositionally so distinct that they can be observed histochemically and isolated physical...

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Section: Methodsmentioning

confidence: 99%

Membrane Organization at Low Cholesterol Concentrations: A Study Using 7-Nitrobenz-2-oxa-1,3-diazol-4-yl-Labeled Cholesterol

1996

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“…A Hamamatsu multichannel plate photomultiplier tube is used as a photon counter. With this setup it is possible to measure spectra by scanning the monochromator and to measure decay curves of emitters at particular emission frequencies by time correlated single photon counting [21]. This technique measures the time between the arrival of an emitted photon (start) and the laser pulse (stop) with ps resolution.…”

Section: Optical Detectionmentioning

confidence: 99%

Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

et al. 2009

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We study experimentally time-resolved emission of CdSe quantum dots in an environment with a controlled local density of states (LDOS). The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS, allowing us to determine the size-dependent quantum efficiency and oscillator strength. We find that the quantum efficiency decreases with increasing emission energy mostly due to an increase in nonradiative decay. For the first time, we manage to obtain the oscillator strength of the important class of CdSe quantum dots. The oscillator strength varies weakly with frequency in agreement with behavior of quantum dots in the strong confinement limit. Surprisingly, the measured absolute values are a factor of 5 below theoretically calculated values. Our results are relevant for applications of CdSe quantum dots in spontaneous emission control and cavity quantum electrodynamics. * URL: www.photonicbandgaps.com arXiv:0808.3191v1 [physics.optics]

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“…Nanosecond lifetime measurements were made using the time correlated single photon counting ͑TCSPC͒ technique. 14 The synchrotron radiation 15 generated from the DORIS III storage ring at HASYLAB/DESY has a temporal profile of 120 ps ͑FWHM͒, and when provided in ''5 Bunch Mode,'' at a repetition rate of 5.208 MHz, decay times of up to 10 s can be measured with TCSPC. Decay times were extracted by fitting trial functions, single, double or triple exponential functions, convoluted with the temporal profile of the SR excitation pulse, to the recorded decay profiles.…”

Section: Methodsmentioning

confidence: 99%

A synchrotron radiation study of high-lying excited states of matrix-isolated atomic magnesium

Kerins

Healy

McCaffrey

2000

Low Temperature Physics

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Previous steady-state and time-resolved luminescence spectroscopy of 3p 1 P 1 atomic magnesium, isolated in thin film samples of the solid rare gases, is extended to include the higher energy 4p 1 P 1 excitation. Well-resolved site splittings are recorded in Mg/Ar samples for excitation to the 4p 1 P 1 level. A small red shift in the absorption energy to the 4p 1 P 1 level for Mg/Ar contrasts with a small blue shift on absorption to the 3p 1 P 1 level. Direct emission from the 4p 1 P 1 level is not observed in any of the rare gas matrices; instead, intense emission from the low energy 3p 1 P 1 level is. Measurements of the emission decay curves in Mg/Ar have revealed slow rates in the steps feeding the 3p 1 P 1 level following 4p 1 P 1 excitation. The reason for the differential shifting of the 4p 1 P 1 and 3p 1 P 1 levels as well as the lack of direct 4p 1 P 1 emission is thought to be related to the strong binding interaction between Mg in the 4p 1 P 1 state and the rare gases.

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Preface

Cited by 531 publications

References 0 publications

Membrane Organization at Low Cholesterol Concentrations: A Study Using 7-Nitrobenz-2-oxa-1,3-diazol-4-yl-Labeled Cholesterol

Membrane Organization at Low Cholesterol Concentrations: A Study Using 7-Nitrobenz-2-oxa-1,3-diazol-4-yl-Labeled Cholesterol

Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

A synchrotron radiation study of high-lying excited states of matrix-isolated atomic magnesium

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