Facile synthesis of high-molecular-weight acid-labile polypeptides using urethane derivatives

Polypeptides have received noticeable attention in the biomedical field due to their structural versatility and biomimetic properties. Particularly, polypeptides that are responsive to biological stimuli, such as mildly acidic extracellular and intracellular conditions, have great potential as delivery carriers for therapeutics. However, synthesis of high-molecular-weight acid-labile peptides is often daunting due to highly restrictive polymerization conditions and limitations in preserving acid-degradable functional groups. For instance, the popular N-carboxyanhydride (NCA) ring-opening polymerization (ROP) is efficient, but acid-labile NCA monomers are difficult to synthesize and store. In this study, acid-labile polypeptides with high molecular weights were synthesized under mild, permissive conditions using carboxylated urethane derivative monomers which are stable for ease of handling. The polymerization was successful in various organic solvents at room temperature, and did not require additional energy or initiation to drive the formation of NCA intermediates. The polymerization was also rapid enough to be independent of inert atmosphere. The strategy explored here to synthesize high-molecular-weight acid-labile polypeptides offers significant advantages including facile synthesis of acid-labile urethane derivative monomers that are stable, even in contact with moisture, and fast polymerization under easily achievable conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 280–286     

Selective enzymatic labeling to detect packing-induced denaturation of double-stranded DNA at interfaces

The adsorption of DNA on surfaces is a widespread procedure and is a common way for fabrication of biosensors, DNA chips, and nanoelectronic devices. Although the biologically relevant and prevailing in vivo structure of DNA is its double-stranded (dsDNA) conformation, the characterization of DNA on surfaces has mainly focused on single-stranded DNA (ssDNA). Studying the structure of dsDNA on surfaces is of invaluable importance to microarray performance since their effectiveness relies on the ability of two DNA molecules to hybridize and remain stable. In addition, many of the enzymatic transactions performed on DNA require dsDNA, rather than ssDNA, as a substrate. However, it is not established that adsorbed dsDNA remains in its structure and does not denature. Here, two methodologies have been developed for distinguishing between surface-adsorbed single- and double-stranded DNA. We demonstrate that, upon formation of a dense monolayer, the nonthiolated strand comprising the dsDNA is released and the monolayer consists of mostly ssDNA. The fraction of dsDNA within the ssDNA monolayer depends on the length of the oligomers. A likely mechanism leading to this rearrangement is discussed.     

Structure Elucidation of a Complex Faldaprevir‐(±)‐α‐Tocopherol Addition Product Reveals Reactivity of Common Excipient Vitamin E‐TPGS

Vitamin E‐TPGS (d ‐α‐tocopheryl polyethylene glycol succinate) is a common excipient used in drug formulations. This excipient is formed by esterification of Vitamin E succinate with polyethylene glycol. As part of an oral formulation for active pharmaceutical ingredient (API) Faldaprevir, Vitamin E‐TPGS was found to decompose under ambient conditions producing free (±)‐α‐Tocopherol which subsequently formed an adduct composed of α‐Tocopherol and the API. The addition product was isolated using liquid chromatography with collections onto solid‐phase extraction cartridges, and full structure elucidation was achieved using mass spectrometry and nuclear magnetic resonance spectroscopy. The results revealed a regioselective addition of α‐Tocopherol to the API that likely occurs through the formation of a stabilized ortho‐quinone methide intermediate. This finding demonstrates the propensity of the common excipient (Vitamin E‐TPGS) to generate chemically active intermediates that may react with formulation ingredients.     

Asymptotic behavior of the p-torsion functions as p goes to 1

Let \({\Omega}\) be a Lipschitz bounded domain of \({\mathbb{R}^N}\), \({N\geq2}\), and let \({u_p\in W_0^{1,p}(\Omega)}\) denote the p-torsion function of \({\Omega}\), p > 1. It is observed that the value 1 for the Cheeger constant \({h(\Omega)}\) is threshold with respect to the asymptotic behavior of u_p, as \({p\rightarrow 1^+}\), in the following sense: when \({h(\Omega) > 1}\), one has \({\lim_{p\rightarrow 1^+}\left\|u_{p}\right\| _{L^\infty(\Omega)}=0}\), and when \({h(\Omega) < 1}\), one has \({\lim_{p\rightarrow 1^+}\left\|u_p\right\| _{L^\infty(\Omega)}=\infty}\). In the case \({h(\Omega)=1}\), it is proved that \({\limsup_{p\rightarrow1^+}\left\|u_p\right\|_{L^\infty(\Omega)}<\infty}\). For a radial annulus \({\Omega_{a,b}}\), with inner radius a and outer radius b, it is proved that \({\lim_{p\rightarrow 1^+}\left\|u_p\right\| _{L^\infty(\Omega_{a,b})}=0}\) when \({h(\Omega_{a,b})=1}\).     

Sizing large proteins and protein complexes by electrospray ionization mass spectrometry and ion mobility

Mass spectrometry (MS) and ion mobility with electrospray ionization (ESI) have the capability to measure and detect large noncovalent protein-ligand and protein-protein complexes. Using an ion mobility method of gas-phase electrophoretic mobility molecular analysis (GEMMA), protein particles representing a range of sizes can be separated by their electrophoretic mobility in air. Highly charged particles produced from a protein complex solution using electrospray can be manipulated to produce singly charged ions, which can be separated and quantified by their electrophoretic mobility. Results from ESI-GEMMA analysis from our laboratory and others were compared with other experimental and theoretically determined parameters, such as molecular mass and cryoelectron microscopy and X-ray crystal structure dimensions. There is a strong correlation between the electrophoretic mobility diameter determined from GEMMA analysis and the molecular mass for protein complexes up to 12 MDa, including the 93 kDa enolase dimer, the 480 kDa ferritin 24-mer complex, the 4.6 MDa cowpea chlorotic mottle virus (CCMV), and the 9 MDa MVP-vault assembly. ESI-GEMMA is used to differentiate a number of similarly sized vault complexes that are composed of different N-terminal protein tags on the MVP subunit. The average effective density of the proteins and protein complexes studied was 0.6 g/cm(3). Moreover, there is evidence that proteins and protein complexes collapse or become more compact in the gas phase in the absence of water.     

Estimating rate constants in a convection-diffusion system with a boundary reaction

While performing biomolecular interaction analysis (BIA), scientistsoften use surface plasmon resonance (SPR) to measure rate constantsof the associated reactions. A mathematical model of a BIAcore^TM,a common SPR device, consists of a convection-diffusion equationin a channel with a reacting surface at the channel ceiling.Asymptotic and singular perturbation techniques are used toanalyse the concentration of the reacting species in two cases:when the reaction occurs much more slowly than diffusion, andwhen the reaction occurs on the same time-scale as diffusion.Linear and nonlinear integral equations result from the analysis;explicit and asymptotic solutions are constructed for physicallyrealizable cases. These expressions provide a direct way toestimate the rate constants from raw data.