Mechanistic understanding of N2 activation: a comparison of unsupported and supported Ru catalysts.

N2 dissociative adsorption is commonly the rate-determining step in thermal ammonia synthesis. Herein, we performed density functional theory (DFT) calculations to understand the N2 dissociation mechanism on models of unsupported Ru(0001) terraces, Ru B5 sites, and polar MgO(111)-supported Ru8 cluster mimicking a B5 site geometry, denoted (Ru8(B5-like)/MgO(111)). The activation energy of N2 dissociative adsorption on the Ru8(B5-like)/MgO(111) model (Ea = 0.33 eV) is much lower than that on the unsupported Ru(0001) terrace (Ea = 1.74 eV) and Ru B5 (Ea = 0.62 eV) models. The lower N2 dissociation barrier on Ru B5 sites is facilitated by the enhanced σ donation and π* back-donation between N2(σ, π*) and Ru(d) orbitals resulting in the stronger activation of the molecular side-on N2* dissociation precursor. The Ru8(B5-like)/MgO(111) also exhibits enhanced σ donation because of the B5-like cluster geometry. Furthermore, the Ru cluster of the bare Ru8(B5-like)/MgO(111) model is positively charged. This induced an unusual π donation from N2(π) to Ru(d) orbitals as revealed by analyses of the density of states and partial charge densities. The combined σ and π donation resulted in an increased synergistic π* back-donation. The total interactions between N2(σ, π, π*) and Ru(d) resulted in an overall electron transfer to the adsorbed N2 from the Ru atoms in the B5-like site with no direct involvement of the MgO(111) substrate. Analyses of bond stretching vibrations and bond lengths show that the N2(σ, π, π*) and Ru(d) interactions lead to a weaker N-N bond and stronger Ru-N bonds. These correspond to a lower barrier of N2 dissociation on the Ru8(B5-like)/MgO(111) model, where the highest red-shift of N-N vibration and the longest N-N bond length were observed after side-on N2* adsorption. These results demonstrate that an electron-deficient Ru catalyst are not always inhibited from donating electrons to adsorbed N2. Rather, this study shows that the electron deficiency of Ru can promote π* back-donation and N2 activation. These new insights may therefore open new avenues to design supported Ru catalysts for nitrogen activation.

Mini-LEDs with Diffuse Reflection Cavity Arrays and Quantum Dot Film for Thin, Large-Area, High-Luminance Flat Light Source.

Mini-light-emitting diodes (mini-LEDs) were combined with multiple three-dimensional (3D) diffuse reflection cavity arrays (DRCAs) to produce thin, large-area, high-brightness, flat light source modules. The curvature of the 3D free-form DRCA was optimized to control its light path; this increased the distance between light sources and reduced the number of light sources used. Experiments with a 12.3-inch prototype indicated that 216 mini-LEDs were required for a 6 mm optical mixing distance to achieve a thin, large-area surface with high brightness, uniformity, and color saturation of 23,044 cd/m2, 90.13%, and 119.2, respectively. This module can serve as the local dimming backlight in next generation automotive displays.

From mono-PEGylation towards anti-nonspecific protein interaction: comparison of dihydrolipoic acid versus glutathione-capped fluorescent gold nanoclusters using gel electrophoresis.

Ultrafine fluorescent gold nanoclusters (AuNCs) have emerged as biocompatible nanoprobes for biomedical imaging in vivo, and the precision surface chemistry of AuNCs is the key for attaining their clinical application. Comparison of two promising candidates for future nanomedicine, i.e. dihydrolipoic acid- versus glutathione-capped AuNCs (AuNC@DHLA vs. AuNC@GSH), was conducted for the first time to clarify their polyethylene glycol-related bioconjugate chemistry (PEGylation) and protein interactions. Gel electrophoresis was performed to separate the number of AuNCs PEGylation, and the molecular weight of the PEG spacer dominated the resolution of the separation in the gel. We have engineered and isolated the mono-PEGylated AuNCs either from the indirect carbodiimide bioconjugate chemistry or the direct Au-S binding. One-pot synthesis showed great efficiency for isolating mono-PEGylated AuNC@GSH from the tailored controlled aggregation of Au(i)-thiolate complexes on in situ generated Au(0) cores. Post-PEGylation of AuNC@GSH was also feasible using monodendate thiol-terminated PEG, but bidendate ligands of AuNC@DHLA exhibited low PEGylated efficiency by Au-S binding. In addition, mono-PEGylated AuNC@GSH significantly enhanced the ability of anti-nonspecific protein adsorption, but mono-PEGylated AuNC@DHLA cannot avoid the nonspecific binding with serum albumin. In addition, specific nano-assembly involving mono-biotinylated AuNCs with streptavidin were also compared using gel electrophoresis. These results provide key insights into the selection, preparation and design of functional AuNCs as nanoprobes for versatile biomedical applications.

Ulcerative keratitis caused by Haemophilus influenzae.

PURPOSE: To report the clinical course, treatments, antibiotic sensitivities, and visual outcomes for eyes with ulcerative keratitis caused by Haemophlilus influenzae. METHODS: The medical records of 10 patients with culture-proven H. influenzae-associated corneal ulcer in a tertiary referral center in a 5-year period (1998-2003) were retrospectively reviewed. RESULTS: The median age was 61 years (range, 2-83 years). The mean follow-up time was 9.4 months (range, 2-31 months). Risk factors such as previous surgeries (5), herpes simplex keratitis (2), leukoma adherens with calcification (1), and exposure keratitis (1) were identified in 9 patients. In vitro testing of the H. influenzae isolates showed that 6 of 10 were resistant to ampicillin; all were sensitive to amoxicillin/clavulanic acid, ceftriaxone, and cefuroxime. All cases responded well to medical antibiotic treatment. Final best spectacle-corrected visual acuity ranged from no light perception to 20/30. CONCLUSION: H. influenzae is a rare cause of corneal ulceration. Predisposing factors for infection are usually present. Accurate diagnosis and treatment may preserve ocular integrity and visual acuity.

Mycobacterium keratitis after laser in situ keratomileusis.

PURPOSE: We present a case of Mycobacterium keratitis after laser in situ keratomileusis (LASIK). METHOD: A retrospective case report. RESULTS: A 40-year-old woman developed Mycobacterium chelonae keratitis in the right eye 2 weeks after bilateral LASIK. The diagnosis was made by acid-fast staining of corneal scrapings on admission and confirmed by culture results 2 weeks later. Intensive treatment with topical amikacin (25 mg/mL) and ciprofloxacin and partial excision of the flap led to resolution of the infection after 2 months of therapy. In addition, topical methylprednisolone (1 mg/mL) was necessary to control inflammation and pain. No recurrence was found during the 1-year follow-up period. The final uncorrected and corrected visual acuity in the right eye was 20/25 and 20/20, respectively. CONCLUSION: Mycobacterium keratitis is a potentially vision-threatening complication after LASIK. Early recognition of the organisms and aggressive treatment if infection develops may improve the outcome. When surgery is indicated, partial flap amputation, which may help to resolve the infection and preserve better vision, may be considered.

Idiopathic subconjunctival abscess.

Subconjunctival abscess is a relatively rare cause of ocular infection. It is usually associated with predisposing factors such as previous trauma or surgery. We report a case of subconjunctival abscess in a 61-year-old woman with no known risk factors. The subconjunctival abscess resolved completely after surgical excision and treatment with topical ciprofloxacin. The final vision preserved 20/20.