Gibbs monolayers at the air/water interface: surface partitioning and lateral mobility of an electrochemically active surfactant

Monolayer films of a water-soluble surfactant, 4-octaneamido-2,2,6,6-tetramethyl-1-piperidinyloxy (C8-TEMPO) were investigated at the air/water interface. An electrochemical, horizontal touch method was developed to measure the equilibrium surface concentrations (gamma) of C8TEMPO. The dependence of gamma on the solution concentration followed a Langmuir isotherm and yielded the partition constant K = (2.3+/-0.2) x 10(4) M(-1). These results were verified by surface tension measurements and Brewster angle microscopy. Within experimental error, the same K values were obtained. The lateral diffusion constants vs surface concentration of this molecule were measured by 2D voltammetry. In these experiments, the component of the oxidation current due to C8TEMPO in the bulk of the solution was subtracted from the total measured current to obtain the component due to the lateral surface diffusion. In the ange of mean molecular areas from 120 to 400 A2/molecule, the lateral diffusion constant of C8TEMPO increased from 1.0 x 10(-6) to 1.0 x 10(-5) cm2/s. The latter value is about 2.5 times larger than the C8TEMPO diffusion constant in bulk water. Comparison of the lateral mobilities of C8TEMPO and two longer alkane chain, water-insoluble homologues, C14TEMPO and C18TEMPO, showed no statistically significant differences.     

Nickel-catalyzed cycloaddition of alkynes and isocyanates

A mild and general route for preparing 2-pyridones from isocyanates and diynes is described. Ni imidazolyidene complexes were used to mediate cyclizations between both internal and terminal diynes with aryl and alkyl isocyanates. In addition, the efficacy of this protocol allows for the preparation of a fused seven-membered pyridone and for three component cyclizations.     

Rapid antibody conformational screening by matrix-assisted laser desorption/ionization hydrogen-deuterium exchange mass spectrometry

Recent advances in the field of cancer biology have accelerated the discovery and development of novel biopharmaceuticals. At the forefront of these drug development efforts are high-throughput screening, compressed timelines, and limited sample quantities, all characteristic of the discovery space. To meet program targets, large numbers of protein variants must be produced, screened, and characterized, presenting a daunting analytical challenge. Additionally, the higher-order structure is paramount for protein function and must be monitored as a critical quality attribute. Matrix-assisted laser desorption/ionization mass spectrometry has been utilized as an ultra-fast, automatable, sample-sparing analytical tool for biomolecules. Our group has published applications integrating hydrogen-deuterium exchange mass spectrometry with matrix-assisted laser desorption/ionization mass spectrometry for the rapid conformational characterization of small proteins, the current work expands this application to monoclonal and bi-specific antibodies. This study demonstrates the ability of the methodology, matrix-assisted laser desorption/ionization hydrogen-deuterium exchange mass spectrometry, to detect conformational differences between bi-specific antibodies from different expression hosts. These conformational differences were validated by orthogonal techniques including circular dichroism, nuclear magnetic resonance, and size-exclusion chromatography hydrogen-deuterium exchange mass spectrometry. This work demonstrates the utility of applying the developed methodology as a rapid conformational screening tool to triage samples for further analytical characterization.     

Comparative study of polymeric stabilizers for magnetite nanoparticles using ATRP

A series of polyelectrolytes with controlled molecular weight, a narrow chain-length distribution, and systematic structural differences were synthesized using atom-transfer radical polymerization and investigated as stabilizers for magnetite nanoparticles in aqueous suspensions. Structural differences include the degree of polymerization, the chain architecture, and the identity of the charged functional unit. The synthesized polymers are sulfonated poly(2-hydroxyethyl methacrylate), a block copolymer of the former with poly(n-butyl methacrylate), poly(sodium styrene sulfonate), poly(sodium acrylate), and poly(sodium vinylphosphonate). The colloidal stability is assessed by measuring the fraction of particles, based on turbidity, that sediment after a period of time at increasing ionic strength. Sedimentation results are complimented by dynamic light scattering determinations of the hydrodynamic diameter of the particles that remain suspended. When adsorption and sedimentation are conducted at high pH, poly(sodium acrylate) and poly(sodium vinylphosphonate) yield the most stable suspensions because of their strong coordinative interactions with the iron oxide surface. At low pH, the polymers that retain pendant negative charges (each of the sulfonated polymers) yield high stable fractions at all ionic strengths investigated up to 100 mM (NaCl), whereas polyelectrolytes that become protonated with decreasing pH, poly(sodium acrylate) and poly(sodium vinylphosphonate), lose their stabilizing capacity even at low ionic strengths. The chain-length distribution profoundly alters a polymer's stabilization tendencies. Two poly(sodium acrylate) samples with the same number-average molecular weight but widely different chain-length distributions proved to have opposite tendencies, with the polydisperse sample being a good stabilizer and the low polydispersity one being a strong flocculant. This investigation provides guidelines for the design of polymeric stabilizers for magnetite nanoparticles according to the pH and ionic strength of the intended application.