Rapid and Sensitive Identification and Discrimination of Bound/Unbound Ligands on Colloidal Nanocrystals via Direct Analysis in Real-Time Mass Spectrometry.

Direct analysis in real-time mass spectrometry (DART-MS) has been applied to the characterization of colloidal nanocrystal surface ligands. The nanocrystals (NCs) in colloidal suspension were purified and deposited onto a solid substrate, and the solvent was allowed to evaporate. Ligand desorption was thermally stimulated using a temperature ramp from 30 °C up to 530 °C, and the desorbed ligands were introduced into a DART-MS instrument where metastable He atoms provide energy for ionization and fragmentation through the reaction with ambient vapors including O2 and H2O. The method allows the identification of ligand species with various functional groups, even in complex, mixed-ligand samples. Bound and unbound molecules can be distinguished based on the desorption temperature. In ideal cases, the desorption profile for a given molecule can be analyzed according to methods adapted from thermal desorption spectroscopy (TDS) to estimate desorption activation energy for NC-bound ligands. Results are presented and discussed for different nanocrystal and ligand types. The method is a promising complement to the range of existing tools for NC ligand analysis.

Vibronic Excitons and Conical Intersections in Semiconductor Quantum Dots.

Surface defects and organic surface-capping ligands affect the photoluminescence properties of semiconductor quantum dots (QDs) by altering the rates of competing nonradiative relaxation processes. In this study, broadband two-dimensional electronic spectroscopy reveals that absorption of light by QDs prepares vibronic excitons, excited states derived from quantum coherent mixing of the core electronic and ligand vibrational states. Rapidly damped coherent wavepacket motions of the ligands are observed during hot-carrier cooling, with vibronic coherence transferred to the photoluminescent state. These findings suggest a many-electron, molecular theory for the electronic structure of QDs, which is supported by calculations of the structures of conical intersections between the exciton potential surfaces of a small ammonia-passivated model CdSe nanoparticle.

Quenching mechanism of Zn(salicylaldimine) by nitroaromatics.

Nitroaromatics and nitroalkanes quench the fluorescence of Zn(Salophen) (H2Salophen = N,N'-phenylene-bis-(3,5-di- tert-butylsalicylideneimine); ZnL(R)) complexes. A structurally related family of ZnL(R) complexes (R = OMe, di-tBu, tBu, Cl, NO2) were prepared, and the mechanisms of fluorescence quenching by nitroaromatics were studied by a combined kinetics and spectroscopic approach. The fluorescent quantum yields for ZnL(R) were generally high (Phi approximately 0.3) with sub-nanosecond fluorescence lifetimes. The fluorescence of ZnL(R) was quenched by nitroaromatic compounds by a mixture of static and dynamic pathways, reflecting the ZnL(R) ligand bulk and reduction potential. Steady-state Stern-Volmer plots were curved for ZnL(R) with less-bulky substituents (R = OMe, NO2), suggesting that both static and dynamic pathways were important for quenching. Transient Stern-Volmer data indicated that the dynamic pathway dominated quenching for ZnL(R) with bulky substituents (R = tBu, DtBu). The quenching rate constants with varied nitroaromatics (ArNO2) followed the driving force dependence predicted for bimolecular electron transfer: ZnL* + ArNO2 --> ZnL(+) + ArNO2(-). A treatment of the diffusion-corrected quenching rates with Marcus theory yielded a modest reorganization energy (lambda = 25 kcal/mol), and a small self-exchange reorganization energy for ZnL*/ZnL(+) (ca. 20 kcal/mol) was estimated from the Marcus cross-relation, suggesting that metal phenoxyls may be robust biological redox cofactors. Electronic structure calculations indicated very small changes in bond distances for the ZnL --> ZnL(+) oxidation, suggesting that solvation was the dominant contributor to the observed reorganization energy. These mechanistic insights provide information that will be helpful to further develop ZnL(R) as sensors, as well as for potential photoinduced charge transfer chemistry.

Optic nerve head drusen and pseudotumor cerebri.

A 42-year-old woman presented with a history of headache. Results of funduscopic examination revealed elevated disc margins and bilateral optic nerve head drusen. Lumbar puncture, head computed tomography, and fluorescein fundus angiography results were consistent with the diagnosis of pseudotumor cerebri and coexistent disc drusen. Visual loss was demonstrated by formal perimetry. Headaches were unresponsive to a medical regimen that included prednisone, glycerol, acetazolamide, furosemide, and repeated lumbar punctures. A lumbar peritoneal shunt was performed, with immediate resolution of headache. Optic disc drusen can be associated with pseudotumor cerebri and can lead to diagnostic confusion.

Torsion and bending analysis of internal fixation techniques for femoral neck fractures: the role of implant design and bone density.

To evaluate pin/screw/plate fixation for management of femoral neck fractures, 39 proximal femora were tested in both torsion and flexion under physiological loading conditions. Three, four, or five implants of six commonly used multiple-fixation devices, and a sliding hip screw with and without an additional 6.5-mm cancellous screw were examined in paired femora. The intact and postfixation femora were initially subjected to a single applied moment, and the torsion and bending stiffness were determined from the load-deformation data. Postfixation femora were also subjected to cyclic loading in flexion at three load ranges, and fixation was judged successful if no failure occurred on or before 1,500 cycles of 667 to 2,000 N of a combined compressive force and moment. Anterior-posterior and lateral radiographs of each specimen were taken after fixation in order to evaluate Singh's index of bone density, fracture reduction, implant placement, and cross-sectional diameter of the femoral neck. Bone density was also evaluated by computed tomography (CT) and physical measurement of core samples obtained from the femoral head. The results indicate that there appears to be no justification for the use of more than three pin/screw implants for management of femoral neck fractures. Bone density was found to correlate with fracture stability and may be a useful predictor of fixation success.

Increased layer interdiffusion in polyelectrolyte films upon annealing in water and aqueous salt solutions.

As-deposited films of multilayered polyelectrolytes are considered to be non-equilibrium structures. Due to the strong attraction between oppositely charged polyions, polyelectrolyte interdiffusion is thought to be suppressed during the adsorption process. Equilibration is promoted by a decrease of the electrostatic attraction between polyion pairs. We have used neutral impact collision ion scattering spectroscopy to investigate the influence of polyelectrolyte multilayer annealing in water and aqueous 1 M NaCl solutions at different temperatures (20 and 70 degrees C) on the increase in interpenetration of a single polyelectrolyte layer throughout the whole film. The multilayers were composed of poly(4-vinylpyridinium) and poly(4-styrenesulfonate). Contrast between neighboring layers was established by labelling the layer in question with the heavy atom ruthenium. It is found that both temperature and salt increase layer interpenetration, whereas salt has a stronger influence than temperature. From numerical simulations polyelectrolyte diffusion coefficients were evaluated for the different annealing conditions. The influence of temperature and salt on the equilibration of the film is interpreted in terms of increased screening of polyion charges and binding of small counterions to polyion monomeric units.

Internal structure of polyelectrolyte multilayers probed via neutral impact collision ion scattering spectroscopy.

Layering in polyelectrolyte multilayer films has been studied by neutral impact collision ion scattering spectroscopy. The method affords a direct look at vertical ordering within these films at the nanometer scale. By labeling certain polyelectrolyte layers with heavy atom (Ru) probes, sufficient contrast has been obtained to visualize and quantify the distribution of these labeled polyelectrolytes throughout the film. The results indicate that the materials under investigation here produce linear film growth with very limited layer interpenetration. The interdigitation length between neighboring layers within the film is measured as 3.9 nm, which is approximately 1.4 times the thickness of an individual polycation/polyanion pair and is slightly less than the measured air/film roughness (4.7 nm). Detailed analysis shows that under the conditions used and at the depths probed in this study, the observed layer thickness is not significantly broadened by either instrumental or stochastic factors.

Orbital infarction syndrome after surgery for intracranial aneurysms.

BACKGROUND: Global orbital infarction results from ischemia of the intraocular and intraorbital structures due to hypoperfusion of the ophthalmic artery and its branches. PATIENTS: The authors describe six patients in whom acute proptosis, ophthalmoplegia, and blindness developed immediately after surgery for intracranial aneurysms. RESULTS: All patients underwent standard frontotemporal craniotomies to clip their aneurysms. In all patients, proptosis, ophthalmoplegia, and blindness developed in the immediate postoperative period; fundus abnormalities included retinal edema, retinal arteriolar narrowing and other vascular abnormalities, and pale optic disc swelling. Some patients had facial and corneal anesthesia. Ophthalmoplegia and facial anesthesia improved in most patients, but none regained any vision in the affected eye. CONCLUSION: Orbital infarction syndrome is a rare complication of neurosurgical procedures. Increased orbital pressure probably reduced ophthalmic artery and collateral arterial perfusion, resulting in ischemia of the intraocular and intraorbital structures. There may be multiple factors that compound the risk for orbital infarction, and patients with subarachnoid hemorrhage, increased intracranial pressure, anomalous arterial or venous circulation, or impaired orbital venous outflow seem particularly vulnerable.