Contour Temperature Programmed Desorption for Monitoring Multiple Chemical Reaction Products

A simple method for obtaining a comprehensive overview of major compounds desorbing from the surface during temperature programmed desorption (TPD) experiments is outlined. Standard commercially available equipment is used to perform the experiment. The method is particularly valuable when high molecular mass compounds are being studied. The acquisition of contour temperature programmed desorption (CTPD) spectra, sampling 50-dalton mass ranges at a time in the thermal desorption experiments, is described and demonstrated for the interaction of benzotriazole adsorbed on a Ni(111) surface. Conventional two-dimensional TPD spectra can be extracted from the CTPD by taking vertical slices of the contour

Cytotoxicity in the Age of Nano: The Role of Fourth Period Transition Metal Oxide Nanoparticle Physicochemical Properties

A clear understanding of physicochemical factors governing nanoparticle toxicity is still in its infancy. We used a systematic approach to delineate physicochemical properties of nanoparticles that govern cytotoxicity. The cytotoxicity of fourth period metal oxide nanoparticles (NPs): TiO2, Cr2O3, Mn2O3, Fe2O3, NiO, CuO, and ZnO increases with the atomic number of the transition metal oxide. This trend was not cell-type specific, as observed in non-transformed human lung cells (BEAS-2B) and human bronchoalveolar carcinoma-derived cells (A549). Addition of NPs to the cell culture medium did not significantly alter pH. Physiochemical properties were assessed to discover the determinants of cytotoxicity: (1) point-of-zero charge (PZC) (i.e., isoelectric point) described the surface charge of NPs in cytosolic and lysosomal compartments; (2) relative number of available binding sites on the NP surface quantified by X-ray photoelectron spectroscopy was used to estimate the probability of biomolecular interactions on the particle surface; (3) band-gap energy measurements to predict electron abstraction from NPs which might lead to oxidative stress and subsequent cell death; and (4) ion dissolution. Our results indicate that cytotoxicity is a function of particle surface charge, the relative number of available surface binding sites, and metal ion dissolution from NPs. These findings provide a physicochemical basis for both risk assessment and the design of safer nanomaterials

Nontoxic Carbon Dots Potently Inhibit Human Insulin Fibrillation

One prevention and therapeutic strategy for diseases associated with peptide or protein fibrillation is to inhibit or delay the fibrillation process. Carbon dots (C–Dots) have recently emerged as benign nanoparticles to replace toxic quantum dots and have attracted great attention because of their unique optical properties and potential applications in biological systems. However, the effect of C-Dots on peptide or protein fibrillation has not been explored. In this in vitro study, human insulin was selected as a model to investigate the effect of C-Dots on insulin fibrillation. Water-soluble fluorescent C-Dots with sizes less than 6 nm were prepared from carbon powder and characterized by UV–vis spectroscopy, fluorescence, Fourier transform infrared spectrophotometry, X-ray photoelectron spectrometry, transmission electron microscopy, and atomic force microscopy. These C-Dotswere able to efficiently inhibit insulin fibrillation in a concentration-dependent manner. Theinhibiting effect of C-Dots was even observed at 0.2 μg/mL. Importantly, 40 μg/mL of C-Dots prevent 0.2 mg/mL of human insulin from fibrillation for 5 days under 65 °C, whereas insulin denatures in 3 h under the same conditions without C-Dots. The inhibiting effect is likely due to the interaction between C-Dots and insulin species before elongation. Cytotoxicity study shows that these C-Dots have very low cytotoxicity. Therefore, these C-Dots have the potential to inhibit insulin fibrillation in biological systems and in the pharmaceutical industry for the processing and formulation of insulin

Liquid Reaction Apparatus for Surface Analysis

A design for a liquid reaction apparatus is described which allows surfaces prepared in ultrahigh vacuum (UHV) to be reacted with solutions of a wide pH range under dry nitrogen atmosphere and subsequently returned to UHV for surface analysis

A deep investigation into the structure of carbon dots

Since their discovery, carbon dots (CDs) have been a promising nanomaterial in a variety of fields including nanomedicine. Despite their potential in this area, there are many obstacles to overcome for CDs to be approved for biomedical use. One major hindrance to CDs’ approval is related to their poorly defined structure. Herein a structural study of CDs is presented in order to rectify this shortcoming. The properties of three CDs which have significant promise in biomedical applications, black CDs (B-CDs), carbon nitride dots (CNDs), and yellow CDs (Y-CDs), are compared in order to develop a coherent structural model for each nanosystem. Absorption coefficients were measured for each system and this data gave insight on the level of disorder in each system. Furthermore, extensive structural characterization has been performed in order to derive structural information for each system. This data showed that B-CDs and CNDs are functionalized to a greater degree and are also more disordered and amorphous than Y-CDs. These techniques were used to develop a structural model consistent with the obtained data and what is known for carbonic nanostructures. These models can be used to analyze CD emission properties and to better understand the structure-property relationship in CDs

Solid-liquid Adsorption of Calcium Phosphate on TiO₂

Calcium phosphate (CP) in aqueous solution was exposed to thin-film TiO2 surfaces at predetermined times ranging from 10 min to 20 h using a liquid reaction apparatus (LRA). Surface analysis was then performed using X-ray photoelectron (XPS) and Auger electron (AES) spectroscopies and time-of-flight secondary ion mass spectrometry (ToF-SIMS) with polyatomic primary ions. XPS revealed that CP nucleated and grew on the TiO2 surface, with phosphate groups growing on top of an initial 2-dimensional (2D) Ca-rich layer. AES depth profiling of a 4-h solution exposure complemented this finding and gave additional evidence for 3-dimensional (3D) phosphate islands forming on top of the calcium. ToF-SIMS analysis of CP adsorbed on the surface indicated that the predominant phase on the surface was brushite, CaHPO4· 2H2O. A model for Ca2+ cation bridging at the oxide interface is proposed. © 1999 American Chemical Society

Comparing the Chelating Abilities of EDTA, N-acetylcysteine (NAC) and N-acetylcysteine Amide (NACA) to Pb(II) by X-Ray Photoelectron (XPS) and UV-vis Spectroscopies

Prior in vivo studies on the treatment of lead poisoning using EDTA, penicillinamine (Pen), selenocysteine (Sel), Succimer, N-acetylcysteine (NAC) and N-acetylcysteine amide (NACA) as chelators showed differences in their ability to decrease both Pb(II) levels and oxidative stress. This present study, performed in vitro, was undertaken to further delineate the chelating abilities of these antioxidants. UV-vis spectroscopy was used to measure binding constants of the antioxidant-Pb complexes. X-ray photoelectron spectroscopy (XPS) was adopted as a rapid and direct method to quantify the degree of binding of these antioxidants to Pb(II). Pb-antioxidant complexations were performed at 0–10⁰C, dissolving antioxidant and Pb acetate in the distilled water. NACA was found to have the highest degree of chelation of the antioxidants in the series as demonstrated by its high binding constant from the UV data. Deconvolution of the Pb 4f orbitals showed greater amounts of Pb(II) precipitates accompanying Pb-NACA complexation as compared to the formation of Pb-NAC and Pb-EDTA, providing corroborating data showing NACA to have the highest affinity for the metal

Characterizing the Chemical Nature of a Sorbed Amine on Indoor Surfaces Using ATR-FTIR

Sorptive interactions with indoor surfaces strongly influence indoor exposure to organic pollutants. Thus, we develop a better understanding of intermolecular interactions between an aliphatic amine and indoor surfaces using ATR-FTIR spectroscopy. The measurements are conducted at high relative humidity in the presence of CO2 and NH3, a gaseous acid and base found in indoor air. The spectral features of an amine sorbed on mineral and polyethylene surfaces are indicative of a protonated species. An amine may chemisorb to either dry surface sites or an adsorbed water surface. These contrast with the spectra of an amine sorbed on latex paint under an NH3 stream in which the peaks assigned to protonation are not observed