The effect of the diphosphine basicity on the excited-state properties of trans-(N2)2W(R2PCH2CH2PR2)2: identification of near-degenerate, luminescent 3MLCT and 3LF terms

Absorption spectra (77 and 298 K), luminescence spectra (5-80 K), and luminescence lifetimes (5-80 K) for the title complexes have been correlated to increasing diphosphine basicity (R = 4-CF(3)-Ph < 4-H-Ph < 4-CH(3)O-Ph < Et). As a consequence, spectral peaks have been assigned to (1,3)MLCT (B(1u), W --> phosphorus) and (1,3)LF (B(2g)) terms. As the ligand basicity increases, the (3)MLCT bands observed in absorption blue-shift nearly 8000 cm(-1) and the vibrationally structured (3)LF bands observed in emission red-shift approximately 1300 cm(-1). (3)LF terms lie lowest in energy in the 4-H-Ph, 4-CH(3)O-Ph, and Et compounds, and temperature-dependent lifetime data suggest emission from each be assigned to the equilibrated, spin-orbit split levels of the (3)LF term. The (3)LF and (3)MLCT excited-state terms lie close in energy in the 4-CF(3)-Ph compound, resulting in an emission band shape that is temperature-dependent. At 77 K, the emission band is broad and structureless and is assigned to arise primarily from the (3)MLCT term. As the temperature is lowered toward 5 K, the (3)MLCT emission diminishes in intensity accompanied by the development of a vibrational structure that is characteristic of emission from the (3)LF term. These excited-state terms satisfy the requirements (different orbital origins, near-degeneracy) for separation by a Franck-Condon energy barrier, resulting in simultaneous emission from both terms between 5 and 77 K.     

Application of matrix-assisted laser desorption/ionization to on-line aerosol time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) mass spectra were obtained from single biological aerosol particles using an aerosol time-of-flight mass spectrometer (ATOFMS). The inlet to the ATOFMS was coupled with an evaporation/condensation flow cell that allowed the aerosol to be coated with matrix material as the sampled stream entered the spectrometer. Mass spectra were generated from aerosol composed either of gramicidin-S or erythromycin, two small biological molecules, or from aerosolised spores of Bacillus subtilis var niger. Three different matrices were used: 3-nitrobenzyl alcohol, picolinic acid and sinapinic acid. A spectrum of gramicidin-S was generated from approximately 250 attomoles of material using a molar ratio of 3-nitrobenzyl alcohol to analyte of approximately 20:1. A single peak, located at 1224 Da, was obtained from the bacterial spores. The washing liquid and extract solution from the spores were analyzed using electrospray mass spectrometry and subsequent MS/MS product ion experiments. This independent analysis suggests that the measured species represents part of the B. subtilis peptidoglycan. The on-line addition of matrix allows quasi-real-time chemical analysis of individual, aerodynamically sized particles, with an overall system residence time of less than 5 seconds. These results suggest that a MALDI-ATOFMS can provide nearly real-time identification of biological aerosols. Copyright 2000 John Wiley & Sons, Ltd.     

Far‐Red Emitting Fluorescent Dyes for Optical Nanoscopy: Fluorinated Silicon–Rhodamines (SiRF Dyes) and Phosphorylated Oxazines

Far‐red emitting fluorescent dyes for optical microscopy, stimulated emission depletion (STED), and ground‐state depletion (GSDIM) super‐resolution microscopy are presented. Fluorinated silicon–rhodamines (SiRF dyes) and phosphorylated oxazines have absorption and emission maxima at about λ≈660 and 680 nm, respectively, possess high photostability, and large fluorescence quantum yields in water. A high‐yielding synthetic path to introduce three aromatic fluorine atoms and unconventional conjugation/solubilization spacers into the scaffold of a silicon–rhodamine is described. The bathochromic shift in SiRF dyes is achieved without additional fused rings or double bonds. As a result, the molecular size and molecular mass stay quite small (<600 Da). The use of the λ=800 nm STED beam instead of the commonly used one at λ=750–775 nm provides excellent imaging performance and suppresses re‐excitation of SiRF and the oxazine dyes. The photophysical properties and immunofluorescence imaging performance of these new far‐red emitting dyes (photobleaching, optical resolution, and switch‐off behavior) are discussed in detail and compared with those of some well‐established fluorophores with similar spectral properties.     

Application of the Floquet theory to multiple quantum NMR of dipolar-coupled multi-spin systems under magic angle spinning

A new analytical Liouville-space representation of the time-propagator under magic angle spinning (MAS) is introduced using the formalized quantum Floquet theory. This approach has the advantage that it is applicable to the analysis of any type of NMR experiment where MAS is combined with multiple-pulse excitation. General relationships describing the spectral parameters in multiple-quantum (MQ) MAS spectra are derived in this representation. Their use is illustrated with an application to double-quantum (DQ) NMR spectra of dipolar-coupled multi-spin systems. Corresponding to the separation of the MAS time-propagator into a rotor modulated and a dephasing component, two distinct mechanisms for DQ excitation are identified. One of them exploits the rotor-modulated component to excite DQ coherences through dipolar-recoupling techniques, which are familiar for spin pairs. Analytical expressions of the integral intensities and linewidths in the resulting DQ sideband pattern are derived in the form of power series expansions of the inverse rotor frequency, of which coefficients depend on structural parameters. In a multi-spin system they can most reliably be extracted in the fast spinning regime. The other mechanism exploits the dephasing component, which is characteristic to multi-spin systems only. This is shown to give rise to DQ coherences by free evolution at full rotor periods. The possibility to exploit it for selective excitation of higher order MQ coherences is discussed. In either case, the dephasing component also leads to residual broadening. The main results of the theoretical developments are demonstrated experimentally on adamantane.     

A mathematical model of aging-related and cortisol induced hippocampal dysfunction

Background  

The hippocampus is essential for declarative memory synthesis and is a core pathological substrate for Alzheimer's disease (AD), the most common aging-related dementing disease. Acute increases in plasma cortisol are associated with transient hippocampal inhibition and retrograde amnesia, while chronic cortisol elevation is associated with hippocampal atrophy. Thus, cortisol levels could be monitored and managed in older people, to decrease their risk of AD type hippocampal dysfunction. We generated an in silicomodel of the chronic effects of elevated plasma cortisol on hippocampal activity and atrophy, using the systems biology mark-up language (SBML). We further challenged the model with biologically based interventions to ascertain if cortisol associated hippocampal dysfunction could be abrogated.     

A comparative pilot study on ultraviolet-induced skin changes assessed by noninvasive imaging techniques in vivo

The effects of acute and chronic ultraviolet (UV) on the morphology of human skin have been extensively studied ex vivo by means of histological investigations. However, innovative skin imaging techniques enable visualization of micromorphological structures in vivo. We aimed to perform a correlation study evaluating in vivo dose and time dependent skin changes following solar-simulated irradiation using noninvasive techniques such as optical coherence tomography (OCT) and confocal laser scanning microscopy (CLSM). The forearms of 10 healthy subjects were exposed to 1 minimal erythema dose (MED) and 3 MED of solar-simulated radiation. Noninvasive measurements were performed before and 24 h and 72 h after UV exposures. We demonstrate definite OCT and CLSM findings obtained from UV-exposed skin, including an increase in epidermal thickness (hyperproliferation, acanthosis), a reduction in dermal reflectivity (dermal edema), an increase in brightness of the basal layer (pigmentation), and an increase in vessel diameter within the dermal papillae (vasodilatation). A moderate to strong linear association between the methods employed was observed. In conclusion, noninvasive high-resolution imaging techniques such as OCT and CLSM may be promising tools for photobiological studies aimed at assessing photoadaptive and/or phototoxic processes in vivo. However, larger studies are needed to demonstrate the applicability of the findings presented in this pilot study.