Polyarginine nanocapsules: a new platform for intracellular drug delivery

This report describes the development of a new nanocarrier, named as polyarginine (PArg) nanocapsules, specifically designed for overcoming cellular barriers. These nanocapsules are composed of an oily core and a PArg corona. The attachment of the PArg corona was mediated by its interaction with the oily core, which was conveniently stabilized with phosphatidylcholine. Hybrid PArg/PEG nanocapsules could also be obtained by introducing PEG-stearate in the nanocapsules formation process. The nanocapsules had an average size in the range of 120–160 nm, and a positive surface charge, which varied between +56 and +28 mV for PArg and PArg/PEG nanocapsules, respectively. They could accommodate significant amounts of lipophilic drugs, i.e., docetaxel, in their core, and also polar negatively charged molecules, i.e., plasmid DNA, on their coating. As a preliminary proof-of-principle, we explored the ability of these nanocarriers to enter cancer cells and to inhibit proliferation in the non-small cell lung cancer NCI-H460 cell line, using flow cytometry and confocal microscopy analysis. The results indicated that PArg nanocapsules are rapidly and massively accumulated into the NCI-H460 cells and that the PArg shell plays a critical role in the internalization process. Moreover, the incubation with docetaxel-loaded nanocapsules with NCI-H460 cells led to an enhanced inhibition of their proliferation, as compared to the free drug. Overall, this is the first report of the potential of PArg nanocapsules as intracellular drug delivery vehicles.

     

In Situ Vesicle Formation by Native Chemical Ligation

Phospholipid vesicles are of intense fundamental and practical interest, yet methods for their de novo generation from reactive precursors are limited. A non‐enzymatic and chemoselective method to spontaneously generate phospholipid membranes from water‐soluble starting materials would be a powerful tool for generating vesicles and studying lipid membranes. Here we describe the use of native chemical ligation (NCL) to rapidly prepare phospholipids spontaneously from thioesters. While NCL is one of the most popular tools for synthesizing proteins and nucleic acids, to our knowledge this is the first example of using NCL to generate phospholipids de novo. The lipids are capable of in situ synthesis and self‐assembly into vesicles that can grow to several microns in diameter. The selectivity of the NCL reaction makes in situ membrane formation compatible with biological materials such as proteins. This work expands the application of NCL to the formation of phospholipid membranes.     

Spontaneous Reconstitution of Functional Transmembrane Proteins During Bioorthogonal Phospholipid Membrane Synthesis

Transmembrane proteins are critical for signaling, transport, and metabolism, yet their reconstitution in synthetic membranes is often challenging. Non‐enzymatic and chemoselective methods to generate phospholipid membranes in situ would be powerful tools for the incorporation of membrane proteins. Herein, the spontaneous reconstitution of functional integral membrane proteins during the de novo synthesis of biomimetic phospholipid bilayers is described. The approach takes advantage of bioorthogonal coupling reactions to generate proteoliposomes from micelle‐solubilized proteins. This method was successfully used to reconstitute three different transmembrane proteins into synthetic membranes. This is the first example of the use of non‐enzymatic chemical synthesis of phospholipids to prepare proteoliposomes.     

Why Is the Spontaneous Deprotonation of [Cu(uracil)2]2+ Complexes Accompanied by Enolization of the System?

The reaction‐force formalism is applied to carry out a detailed analysis of the mechanisms behind the enolization processes undergone by the complexes formed on interaction of uracil dimers with Cu²⁺ ions after spontaneous deprotonation of the resulting complexes. These enolization processes apparently involve a single proton transfer (PT) from an NH group to a carbonyl group of the same uracil moiety, which should involve a rather high activation barrier that prevents the process occurring. However, the reaction‐force, chemical‐potential, and electronic‐flux profiles unambiguously indicate that the actual mechanism involves three low‐barrier elementary steps, and this explains why enolization of the [Cu(uracil?H)(uracil)]⁺ complexes is a highly facile, assisted PT process. All of the observed PT processes show a typical profile for both the chemical potential and the electronic flux associated with the bond‐breaking and the bond‐formation processes.     

Synthesis of novel chromene scaffolds for adenosine receptors

A one-pot procedure was developed for the synthesis of novel 3-[amino(methoxy)methylene]-2-oxo-3,4-dihydro-2H-chromen-4-yl)-3-cyanoacetamides and chromeno[3,4-c]pyridine-1-carbonitriles from the reaction of 2-oxo-2H-chromene-3-carbonitriles and cyanoacetamides. These chromene derivatives were identified as new scaffolds for adenosine receptors and the hits 3a, 3c, 5a, and 5b were found.     

Theoretical study of methoxy group influence in the gas‐phase elimination kinetics of methoxyalkyl chlorides

The unimolecular gas‐phase elimination kinetics of 2‐methoxy‐1‐chloroethane, 3‐methoxy‐1‐chloropropane, and 4‐methoxyl‐1‐chloroburane has been studied by using density functional theory (DFT) methods to propose the most reasonable mechanisms of decomposition of the aforementioned compounds. Calculation results of 2‐methoxy‐1‐chloroethane and 3‐methoxy‐1‐chloropropane suggest dehydrochlorination through a concerted nonsynchronous four‐centered cyclic transition state (TS) to give the corresponding olefin. In the case of 4‐methoxyl‐1‐chloroburane, in addition to the 1,2‐elimination mechanism, the anchimeric assistance by the methoxy group, through a polar five‐centered cyclic TS, provides additional pathways to give 4‐methoxy‐butene, tetrahydrofuran and chloromethane. The bond polarization of the C? Cl, in the direction of C^δ+ ··· Cl^δ?, is the limiting step of these elimination reactions. The significant increase in rate together with the formation of a cyclic product tetrahydrofuran in the gas‐phase elimination of 4‐methoxyl‐1‐chloroburane is attributed to neighboring group participation of the oxygen of the methoxy group in the TS. The theoretical calculations show a good agreement with the reported experimental results. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Combating small molecule environmental contaminants: detection and sequestration using functional nucleic acids

Small molecule contaminants pose a significant threat to the environment and human health. While regulations are in place for allowed limits in many countries, detection and remediation of contaminants in more resource-limited settings and everyday environmental sources remains a challenge. Functional nucleic acids, including aptamers and DNA enzymes, have emerged as powerful options for addressing this challenge due to their ability to non-covalently interact with small molecule targets. The goal of this perspective is to outline recent efforts toward the selection of aptamers for small molecules and describe their subsequent implementation for environmental applications. Finally, we provide an outlook that addresses barriers that hinder these technologies from being widely adopted in field friendly settings and propose a path forward toward addressing these challenges.

Small molecule contaminants pose a significant threat to the environment and human health.     

Rapid Formation of Non-canonical Phospholipid Membranes by Chemoselective Amide-Forming Ligations with Hydroxylamines**

There has been increasing interest in methods to generate synthetic lipid membranes as key constituents of artificial cells or to develop new tools for remodeling membranes in living cells. However, the biosynthesis of phospholipids involves elaborate enzymatic pathways that are challenging to reconstitute in vitro. An alternative approach is to use chemical reactions to non-enzymatically generate natural or non-canonical phospholipids de novo. Previous reports have shown that synthetic lipid membranes can be formed in situ using various ligation chemistries, but these methods lack biocompatibility and/or suffer from slow kinetics at physiological pH. Thus, it would be valuable to develop chemoselective strategies for synthesizing phospholipids from water-soluble precursors that are compatible with synthetic or living cells Here, we demonstrate that amide-forming ligations between lipid precursors bearing hydroxylamines and α-ketoacids (KAs) or potassium acyltrifluoroborates (KATs) can be used to prepare non-canonical phospholipids at physiological pH conditions. The generated amide-linked phospholipids spontaneously self-assemble into cell-like micron-sized vesicles similar to natural phospholipid membranes. We show that lipid synthesis using KAT ligation proceeds extremely rapidly, and the high selectivity and biocompatibility of the approach facilitates the in situ synthesis of phospholipids and associated membranes in living cells.