Multifunctions of Net Surface Charge in the Reaction on a Single Nanoparticle

Electric charge can determine where and how reaction occurs, but the relationship between net surface charge and activity is unclear because of the difficulty in simultaneously detecting charge and activity at the single nanoparticle level. In this study, we use ions as probes to detect the distribution of net surface charge and track galvanic replacement reaction on single Ag nanowire in situ and in real time by dark-field microscopy. The two ends of a single Ag nanowire are found to possess more net surface charges than the middle part. The unevenly distributed net surface charge performs multifunctions in determining the reaction activity, selectivity, and product shape. Owing to the interaction between the net surface charges and ions in solution, many clusters are generated on the Ag nanowires. The locations of generating these clusters are where faster deposition reaction happens. Furthermore, larger size Ag compounds with clear shape are produced near the two ends by attracting Ag⁺ at lower [HAuCl₄], but larger size Ag–Au alloy clusters with veiled shape are produced near the center by repelling AuCl₄^– at higher [HAuCl₄]. Given that net surface charge generally exists in nanoscience, the methodology and results obtained from this research can be widely used in other single-shaped nanomaterials

Single-Molecule Kinetics Reveals a Hidden Surface Reaction Intermediate in Single-Nanoparticle Catalysis

Detecting and characterizing reaction intermediates is not only important and powerful for elucidating reaction mechanisms but also challenging in general because of the low populations of intermediates in a reaction mixture. Studying surface reaction intermediates in heterogeneous catalysis presents additional challenges, especially the ubiquitous structural heterogeneity among the catalyst particles and the accompanying polydispersion in reaction kinetics. Here we use single-molecule fluorescence microscopy to study two complementary types of Au nanocatalystsmesoporous-silica-coated Au nanorods (i.e., Au@mSiO₂ nanorods) and bare 5.3 nm pseudospherical Au nanoparticlesat the single-particle, single-turnover resolution in catalyzing the oxidative deacetylation of amplex red by H₂O₂, a synthetically relevant and increasingly important probe reaction. For both nanocatalysts, the distributions of the microscopic reaction time from a single catalyst particle clearly reveal a kinetic intermediate, which is hidden when the data are averaged over many particles or only the time-averaged turnover rates are examined for a single particle. This intermediate is further resolvable by single-turnover kinetics at the subparticle level. Detailed single-molecule kinetic analysis leads to a quantitative reaction mechanism and supports that the intermediate is likely a surface-adsorbed one-electron-oxidized amplex red radical. The quantitation of kinetic parameters further allows for the evaluation of the large reactivity inhomogeneity among the individual nanorods and pseudospherical nanoparticles, and for Au@mSiO₂ nanorods, it uncovers their size-dependent reactivity in catalyzing the first one-electron oxidation of amplex red to the radical. Such single-particle, single-molecule kinetic studies are expected to be broadly useful for dissecting reaction kinetics and mechanisms

Relationship Between the Use of Statins and Patient Survival in Colorectal Cancer: A Systematic Review and Meta-Analysis

<div><p>Background</p><p>Studies have indicated that statins influence the risks and mortality rates of several types of solid tumors. However, the association between statin use and survival in patients with colorectal cancer (CRC) remains unclear.</p><p>Methods</p><p>We searched the PubMed and Embase databases for relevant studies published up to September 2014 that assessed statin use and CRC prognosis. The primary outcomes were overall survival (OS) and cancer-specific survival (CSS). The secondary outcomes were disease-free survival (DFS) and recurrence-free survival (RFS). Hazard ratios (HRs) and 95% confidence intervals (CIs) were extracted and pooled with Mantel–Haenszel random-effect modeling. All statistical tests were two-sided.</p><p>Results</p><p>Four studies on post-diagnosis statin therapy and five studies on pre-diagnosis statin use were included in our meta-analysis of 70,608 patients. Compared with the non-users, the patients with post-diagnosis statin use gained survival benefits for OS (HR 0.76; 95% CI: 0.68 to 0.85, P<0.001) and CSS (HR 0.70; 95% CI: 0.60 to 0.81, P<0.001). In addition, we observed that pre-diagnosis statin use prolonged the survival of patients with CRC for OS (HR 0.70; 95% CI: 0.54 to 0.91, P=0.007) and CSS (HR 0.80; 95% CI: 0.74 to 0.86, P<0.001). However, we did not observe a survival benefit for DFS (HR 1.13; 95% CI: 0.78 to 1.62, P=0.514) or RFS (HR 0.98; 95% CI: 0.36 to 2.70, P=0.975) in the CRC patients with post-diagnosis statin use.</p><p>Conclusions</p><p>Statin use before or after cancer diagnosis is related to reductions in overall and cancer-specific mortality in colorectal cancer survivors.</p></div

Fixation of Zinc(II) Ion to Dioxygen in a Highly Deformed Porphyrin: Implications for the Oxygen Carrier Mechanism of Distorted Heme

Three <i>saddle</i>-type nonplanar zinc porphyrins strapped by two short alkyl linkers have been synthesized. The deformation induced by the linkers can cause a spectral red shift of >30 nm compared with the absorption maxima of regular porphyrins and can also regulate the electronic structure of the central zinc­(II) ion. The zinc­(II) ion then complexes and activates a free dioxygen to form a superoxide group ligand by enlarging the splitting of energy levels of d orbitals under strong core deformation. The fixation of dioxygen can be reasonably explained by the Dewar–Chatt–Duncanson model. These results indicate that this type of saddle porphyrin has the potential to be used as a new model system of heme

Forest plot of statins use after diagnosis of colorectal cancer and patient survival.

<p>Forest plot of statins use after diagnosis of colorectal cancer and patient survival.</p

Baseline characteristics of included studies in the meta-analysis.

<p>Abbreviations: NR, not reported; Pre, prediagnosis; Post, postdiagnosis; S, surgery; chemo, chemotherapy; OS, overall survival; CSS, cancer-specific survival; DFS, disease-free survival; RFS, recurrence-free survival; BMI, Body Mass Index; NSAIDs; Non-steroidal anti-inflammatory drugs; AJCC, American Joint Committee on Cancer; ACEIs, angiotensin converting enzyme inhibitors;</p><p>Baseline characteristics of included studies in the meta-analysis.</p

Flowchart of study selection.

<p>Flowchart of study selection.</p

Funnel of statins use before and after diagnosis of colorectal cancer and patient survival.

<p>Funnel of statins use before and after diagnosis of colorectal cancer and patient survival.</p

Forest plot of statins use before diagnosis of colorectal cancer and patient survival.

<p>Forest plot of statins use before diagnosis of colorectal cancer and patient survival.</p

Scalable Parallel Screening of Catalyst Activity at the Single-Particle Level and Subdiffraction Resolution

High-throughput and quantitative screening of catalyst activity is crucial for guiding the work cycles of catalyst improvements and optimizations. For nanoparticle catalysts, their inherent heterogeneity makes it desirable to screen them at the single-particle level. Here, we report a single-molecule fluorescence microscopy approach that can screen the activity quantitatively of a large number of catalyst particles in parallel at the single-particle level and with subdiffraction spatial resolution. It can identify directly high activity catalyst particles and resolve subpopulations in mixtures of catalysts. It is readily scalable and broadly applicable to heterogeneous catalysts. Using ensemble measurements to establish activity correlations between different reactions, we further show that this approach can be extended to assess catalysts in reactions that do not involve fluorescent molecules. Coupled with high-throughput catalyst preparation and high-resolution structural/compositional analysis, this screening approach has promise in accelerating the development and discovery of new or better catalysts