Photophysical properties of biologically compatible CdSe quantum dot structures

The photophysical properties of CdSe and ZnS(CdSe) semiconductor quantum dots in nonpolar and aqueous solutions were examined with steady-state (absorption and emission) and time-resolved (time-correlated single-photon-counting) spectroscopy. The CdSe structures were prepared from a single CdSe synthesis, a portion of which were ZnS-capped, thus any differences observed in the spectral behavior between the two preparations were due to changes in the molecular shell. Quantum dots in nonpolar solvents were surrounded with a trioctylphosphine oxide (TOPO) coating from the initial synthesis solution. ZnS-capped CdSe were initially brighter than bare uncapped CdSe and had overall faster emission decays. The dynamics did not vary when the solvent was changed from hexane to dichloromethane; however, replacement of the TOPO cap by pyridine affected CdSe but not ZnS(CdSe). CdSe was then solubilized in water with mercapto-acetic acid or dihydrolipoic acid, whereas ZnS(CdSe) could be solubilized only with dihydrolipoic acid. Both solubilization agents quenched the nanocrystal emission, though with CdSe the quenching was nearly complete. Additional quenching of the remaining emission was observed when the redox-active molecule adenine was conjugated to the water-soluble CdSe but was not seen with ZnS(CdSe). The emission of aqueous CdSe could be enhanced under prolonged exposure to room light and resulted in a substantial increase of the emission lifetimes; however, the enhancement occurred concurrently with precipitation of the nanocrystals, which was possibly caused by photocatalytic destruction of the mercaptoacetic acid coating. These results are the first presented on aqueous CdSe quantum dot structures and are presented in the context of designing better, more stable biological probes.     

CLEARANCE TIMES OF PORPHYRIN DERIVATIVES FROM MICE AS MEASURED BY in vivo FLUORESCENCE SPECTROSCOPY

The clearance times of 17 different porphyrin derivatives from SKH:HR-1 mice have been measured using the technique of in vivo fluorescence spectroscopy. This technique monitors the in vivo porphyrin fluorescence observed from the external skin surface. Most hydrophilic porphyrin derivatives show relatively short clearance times, in the order of 2.5-6 h. The dicarboxylic acid porphyrins, proto-, hydroxyethylvinyldeutero- and hematoporphyrin IX have clearance times of 7.8, 12.2 and 14.7 h respectively. The mixture hematoporphyrin derivative has an intermediate clearance time of 12.6 h. N-methylated porphyrins show clearance times in the vicinity of 15-22 h. Monoaspartyl chlorin e6 shows the longest clearance time of all porphyrin derivatives measured (30.3 h).     

A chiral cyclohexanone linked to polystyrene for solid-phase synthesis of chiral alpha-carbonyls

Two chiral cyclohexanones were linked to polystyrene resin. The polymer-bound auxiliaries were subjected to a sequence of four reactions, the last of which cleaves the desired alpha-chiral carbonyl compound off the resin, concurrently regenerating the resin-bound auxiliary in its original form. The resin can then be reused.     

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Interference of transverse rings in multifilamentation of powerful femtosecond laser pulses in air

We observe multiple filaments and interference of their ring structures in the propagation of 14 mJ, 45 fs infrared laser pulse in air. We suggest a simple physical model describing the formation and the interference of rings as the result of superposition of the background field of the whole beam and the fields that diverge from the filaments due to the defocusing in the laser-produced plasma. The size and the number of maxima in the interference pattern depend on the position of the filament formation along the direction of propagation. The simulated picture of the ring structure interference is in qualitative agreement with the one obtained from the experiment.     

Neptunium(III) application in extraction chromatography

This paper describes a novel strategy for actinide separation by extraction chromatography with Np(III) valence adjustment. Neptunium(IV) was reduced to Np(III) using Cr(II) and then selectively separated from uranium (IV) on a TEVA resin. After elution, Np(III) was retained on a DGA resin in order to remove any detrimental chromium impurities. Neptunium(III) formation was demonstrated by the complete and selective elution of Np from TEVA resin (99 ± 7%) in less than 12 mL of 9 M HCl from U(IV) (0.7 ± 0.7%). It was determined by UV–visible and kinetic studies that Cr(II) was the only species responsible for the elution of Np(IV) as Np(III) and that the Cr(II) solution could be prepared from 2 to 30 min before its use without the need of complex degassing systems to prevent the oxidation of Np(III) by oxygen. The methodology proposed here with TEVA/DGA resins provides removal of Cr(III) impurities produced at high decontamination factors (2.8 × 10³ and 7.3 × 10⁴ respectively).     

Anatomy of the thyroarytenoid branch of the recurrent laryngeal nerve.

OBJECTIVE: To determine the position and anatomic variability of the thyroarytenoid (TA) branch of the recurrent laryngeal nerve (RLN). METHODS: The RLN on 13 human cadaver specimens (24 sides) was dissected to the termination of the TA branch in the TA muscle. A pin was placed at the inferior aspect of the thyroid cartilage at the inferior tubercle. Using a caliper, the distance from the pin to the TA branch of the RLN was measured. The direction of the nerve and number of branches were recorded. RESULTS: The average distance to the TA branch of the RLN is 4.23 mm with a standard deviation of 2.86 mm. The median distance is 3.75 mm. Most of the specimens fell in a range of 1 to 4 mm. Overall, 54% of the nerves traveled in a horizontal direction, but vertical and oblique orientations were observed. About 20% of specimens demonstrated branching of the TA nerve. CONCLUSION: Measuring 4 mm from the inferior tubercle along a perpendicular line from the thyroid tubercle on the inferior border of the thyroid cartilage provides a good estimate of the location of the TA branch of the RLN. This information is useful when creating a posterior thyrotomy for TA neurectomy for patients with adductor spasmodic dysphonia. Knowledge of the course and possible branching of the nerve, will aid in localizing the nerve as well as ensuring adequate resection.