The course of the hydrolysis and the reaction kinetics of AlN powder in diluted aqueous suspensions

The reactivity of AlN powder in diluted aqueous suspensions in the temperature range 22–90 °C was investigated in order to better understand and control the process of hydrolysis. The hydrolysis exhibits three interdependent stages: during the induction period (first stage) amorphous aluminum hydroxide gel is formed, followed by the crystallization of boehmite (second stage) and bayerite (third stage). The hydrolysis rate significantly increased with higher starting temperatures of the suspension, but was independent of the starting pH value; however, the pH value of 10 caused the disappearance of the induction period. The kinetics was described using un-reacted-core model, and the chemical reaction at the product-layer/un-reacted-core interface was the rate-controlling step for the second stage of the hydrolysis in the temperature range 22–70 °C, for which the calculated activation energy is 101 kJ/mol; whereas at 90 °C, the diffusion through the product layer became the rate-controlling step.     

Chemical aspects of wear of alumina ceramics

In our investigation, the effects of the tribochemically-induced dissolution of alumina ceramics and modulation of near-surface forces (surface charge) within the tribocontact were studied. The wear and friction behaviors of alumina were investigated using a reciprocating sliding test in different chemical environments. The samples for the tests were hemispherical pins and plates of polished alumina, both prepared by a near-net-shaping method.

The sliding tests were conducted in water-based liquids with different pH values or with the addition of a polyelectrolyte to control the surface charge at solid surfaces. The coefficient of friction was continuously recorded during the tests and the wear-loss was subsequently determined for all samples. The results show a significant effect of the chemical agents on the coefficient of friction as well as on the material-removal rate in different aqueous media. The results are discussed in terms of the chemical and electrochemical properties of the materials in the tribocontact.     

Synthesis of bioactive β-TCP coatings with tailored physico-chemical properties on zirconia bioceramics

The objective of this work was to develop a synthesis procedure for the deposition of β-TCP coatings with tailored physico-chemical properties on zirconia bioceramics. The synthesis procedure involved two steps: (i) a rapid wet-chemical deposition of a biomimetic CaP coating and (ii) a subsequent post-deposition processing of the biomimetic CaP coating, which included a heat treatment between 800 and 1200 °C, followed by a short sonication in a water bath. By regulating the heating temperature the topography of the β-TCP coatings could be controlled. The average surface roughness (R_a) ranged from 42 nm for the coating that was heated at 900 °C (TCP-900) to 630 nm for the TCP-1200 coating. Moreover, the heating temperature also affected the dissolution rate of the coatings in a physiological solution, their protein-adsorption capacity and their bioactivity in a simulated body fluid.     

Synthetic Neoglycoconjugates of Hepta- and Nonamannoside Ligands for Eliciting Oligomannose-Specific HIV-1-Neutralizing Antibodies

Oligomannose-type glycans on the spike protein of HIV-1 constitute relevant epitopes to elicit broadly neutralizing antibodies (bnAbs). Herein we describe an improved synthesis of α- and β-linked hepta- and nonamannosyl ligands that were subsequently converted into BSA and CRM₁₉₇ neoglycoconjugates. We assembled the ligands from anomeric 3-azidopropyl spacer glycosides from select 3-O-protected thiocresyl mannoside donors. Chain extensions were achieved using [4+3] or [4+5] block synthesis of thiocresyl and trichloroacetimidate glycosyl donors. Subsequent global deprotection generated the 3-aminopropyl oligosaccharide ligands. ELISA binding data obtained with the β-anomeric hepta- and nonamannosyl conjugates with a selection of HIV-1 bnAbs showed comparable binding of both mannosyl ligands by Fab fragments yet lesser binding of the nonasaccharide conjugate by the corresponding IgG antibodies. These results support previous observations that a complete Man₉ structure might not be the preferred antigenic binding motif for some oligomannose-specific antibodies, and have implications for glycoside designs to elicit oligomannose-targeted HIV-1-neutralizing antibodies.