Adsorption and Thermal Decomposition of Triphenyl Bismuth on Silicon (001)

We investigate the adsorption and thermal decomposition of triphenyl bismuth (TPB) on the silicon (001) surface using atomic-resolution scanning tunneling microscopy, synchrotron-based X-ray photoelectron spectroscopy, and density functional theory calculations. Our results show that the adsorption of TPB at room temperature creates both bismuth–silicon and phenyl–silicon bonds. Annealing above room temperature leads to increased chemical interactions between the phenyl groups and the silicon surface, followed by phenyl detachment and bismuth subsurface migration. The thermal decomposition of the carbon fragments leads to the formation of silicon carbide at the surface. This chemical understanding of the process allows for controlled bismuth introduction into the near surface of silicon and opens pathways for ultra-shallow doping approaches

Structural characterization of anti-inflammatory Immunoglobulin G Fc proteins

Immunoglobulin G (IgG) is a central mediator of host defense due to its ability to recognize and eliminate pathogens. The recognition and effector responses are encoded on distinct regions of IgGs. The diversity of the antigen recognition Fab domains accounts for IgG’s ability to bind with high specificity to essentially any antigen. Recent studies have indicated that the Fc effector domain also displays considerable heterogeneity, accounting for its complex effector functions of inflammation, modulation and immune suppression. Therapeutic anti-tumor antibodies, for example, require the pro-inflammatory properties of the IgG Fc to eliminate tumor cells, while the anti-inflammatory activity of Intravenous Immunoglobulin G (IVIG) requires specific Fc glycans for activity. In particular, the anti-inflammatory activity of IVIG is ascribed to a small population of IgGs in which the Asn297-linked complex N-glycans attached to each Fc C_H2 domain include terminal α2,6-linked sialic acids. We used chemoenzymatic glycoengineering to prepare fully di-sialylated IgG Fc and solved its crystal structure. Comparison of the structures of asialylated Fc, sialylated Fc, and F241A Fc, a mutant that displays increased glycan sialylation, suggests that increased conformational flexibility of the C_H2 domain is associated with the switch from pro- to anti-inflammatory activity of the Fc

Dehydrohalogenation Condensation Reaction of Phenylhydrazine with Cl-Terminated Si(111) Surfaces

Formation of stable organic–inorganic contacts with silicon often requires oxygen- and carbon-free interfaces. Some of the general approaches to create such interfaces rely on the formation of a Si–N bond. A reaction of dehydrohalogenation condensation of Cl-terminated Si(111) surface with phenylhydrazine is investigated as a means to introduce a simple function to the surface using a −NH-NH₂ moiety as opposed to previously investigated approaches. The use of substituted hydrazine allows for the formation of a stable structure that is less strained compared to the previously investigated primary amines and leads to minimal surface oxidation. The process is confirmed by a combination of infrared studies, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry investigations. Density functional theory is utilized to yield a plausible surface reaction mechanism and provide a set of experimental observables to compare with these data

Reaction of Hydrazine with a Chlorine-Terminated Si(111) Surface

Interaction of hydrazine with Cl-terminated Si(111) surface was explored in order to understand the pathways for obtaining a reactive functionalized silicon surface that is oxygen-free. Hydrazine-functionalized Si(111) surface with Si–NH–NH–Si species was prepared starting with Cl-terminated Si(111) surface in a reaction with anhydrous hydrazine at 35 °C. This process was followed by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry to characterize the modified surface. DFT calculations were performed to supplement the analysis, to identify major surface species resulting from this reaction, and to provide a mechanistic insight into the initial stages of modification. This work provides a new pathway to obtain a well-defined functionalized silicon surface with a Si–N interface that is oxygen- and carbon-free and that can be used for further functionalization or deposition schemes