Photo‐responsive amphiphilic poly(α‐hydroxy acids) with pendent o‐nitrobenzyl ester constructed via copper‐catalyzed azide‐alkyne cycloaddition reaction

Photo‐responsive block copolymer mPEG‐b‐poly(Tyr)‐g‐NB was prepared by introduction of o‐nitrobenzyl ester group into the side chain of amphiphilic poly(ethylene glycol)‐b‐poly(α‐hydroxy acids) (mPEG‐b‐poly(Tyr)) containing pendent alkynyl group via copper‐catalyzed azide‐alkyne cycloaddition reaction. The amphiphilic mPEG‐b‐poly(Tyr) was synthesized via the ring‐opening polymerization of O‐carboxyanhydrides, with monomethoxy poly(ethylene glycol) (mPEG) as macroinitiator. The molecular structure, self‐assembly, and photo‐controlled release of the obtained mPEG‐b‐poly(Tyr)‐g‐NB were thoroughly investigated. mPEG‐b‐poly(Tyr)‐g‐NB could self‐assemble into spherical micelles in water and showed disassembly under UV light irradiation, which was demonstrated by means of UV‐vis spectroscopy, scan electron microscopes, and dynamic light scattering measurement. Fluorescence emission measurements demonstrated that Nile red, encapsulated by micelles, can be released upon UV irradiation. This study provides a convenient way to construct smart poly(α‐hydroxy acids)‐based nanocarriers for controlled release of hydrophobic drugs. Copyright © 2015 John Wiley & Sons, Ltd.     

Tutorial review on validation of liquid chromatography–mass spectrometry methods: Part I

This is the part I of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS) and discuss specific issues that arise with MS (and MS/MS) detection in LC (as opposed to the “conventional” detectors). The Part I briefly introduces the principles of operation of LC–MS (emphasizing the aspects important from the validation point of view, in particular the ionization process and ionization suppression/enhancement); reviews the main validation guideline documents and discusses in detail the following performance parameters: selectivity/specificity/identity, ruggedness/robustness, limit of detection, limit of quantification, decision limit and detection capability. With every method performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to determine it, specifically in the case of LC–MS methods.     

Low‐Temperature Synthesis of Thermoresponsive Diblock Copolymer Nano‐Objects via Aqueous Photoinitiated Polymerization‐Induced Self‐Assembly (Photo‐PISA) using Thermoresponsive Macro‐RAFT Agents

Photoinitiated reversible addition‐fragmentation chain transfer (RAFT) dispersion polymerization of 2‐hydroxypropyl methacrylate is conducted in water at low temperature using thermoresponsive copolymers of 2‐(2‐methoxyethoxy) ethyl methacrylate and oligo(ethylene glycol) methacrylate (M_n = 475 g mol⁻¹) as the macro‐RAFT agent. Kinetic studies confirm that quantitative monomer conversion is achieved within 15 min of visible‐light irradiation (405 nm, 0.5 mW cm⁻²), and good control is maintained during the polymerization. The polymerization can be temporally controlled by a simple “ON/OFF” switch of the light source. Finally, thermoresponsive diblock copolymer nano‐objects with a diverse set of complex morphologies (spheres, worms, and vesicles) are prepared using this particular formulation.

     

Amphiphilic Imbalance and Stabilization of Block Copolymer Micelles on‐Demand through Combinational Photo‐Cleavage and Photo‐Crosslinking

An amphiphilic block copolymer of poly(ethylene oxide)‐b‐poly((N‐methacryloxy phthalimide)‐co‐(7‐(4‐vinyl‐benzyloxyl)‐4‐methylcoumarin)) (PEO₄₅‐b‐P(MAPI₃₆‐co‐VBC₄)) is designed to improve the micellar stability during the photo‐triggered release of hydrophobic cargoes. Analysis of absorption and emission spectra, solution transmittance, dynamic light scattering, and transmission electron microscopy supports that polymer micelles of PEO₄₅‐b‐P(MAPI₃₆‐co‐VBC₄) upon the combinational irradiation of 365 and 254 nm light can be solubilized through the photolysis of phthalimide esters and simultaneously crosslinked via the partially reversible photo‐dimerization of coumarins. The photo‐triggered release experiment shows that the leakage of doxorubicin molecules from crosslinked micelles can be predictably regulated by controlling the irradiation time of 365 and 254 nm light.

     

Chiral separation of novel diazenes on a polysaccharide‐based stationary phase in the reversed‐phase mode

Chiral high‐performance liquid chromatography separation of two recently synthesized liquid crystalline materials C1 and C2 was studied in the reversed‐phase mode. Both materials have an azo‐moiety and one chiral center in their molecular structures. They were available in racemic and pure S forms. For the enantiomeric separations, a Chiralpak AY‐RH stationary phase based on amylose tris(5‐chloro‐2‐methylphenylcarbamate) coated on 5 μm silica was used. The compounds were analyzed in both of their possible forms, the more thermodynamically stable E form and the labile Z form. The conditions and time scale of the UV‐induced E to Z transition were briefly evaluated. Under the optimized conditions, we were able to baseline separate S and R enantiomers of both of the studied materials not only in their E forms, but also in their Z forms. In comparison to the separation in the normal‐phase mode, which we have reported recently, the resolution in the reversed‐phase mode is significantly better. Interestingly, peak reversal was noticed for the S and R enantiomers when the separation was carried out with E versus Z forms of both compounds.     

1,5‐Diphenyl‐1,4‐diyn‐3‐one: A highly efficient photoinitiator

In a continuation of our research on new chromophores for photoinitiators (PIs), we investigated a triple‐bond‐containing benzophenone derivative. 1,5‐Diphenyl‐1,4‐pentadiyn‐3‐one ( 2 ) was prepared from phenylacetylene and ethyl formate by a one‐pot reaction. Differential scanning photocalorimetry experiments in lauryl acrylate of 2 showed surprisingly high activity for the double‐bond conversion and rate of polymerization at the lowest PI concentrations and even without any coinitiator. By the application of monomers with abstractable hydrogens, significant improvement in the photoreactivity was observed. Ultraviolet–visible spectroscopy revealed strong absorption up to 350 nm. Steady‐state photolysis experiments proved that the photochemistry of this compound was faster than that of benzophenone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 101–111, 2005     

γ-poly(glutamic acid) as an initiator of cationic polymerization of N-vinylcarbazole and N-vinyl-2-pyrrolidone

The cationic polymerization of vinyl monomers initiated by biosynthesized γ-poly(glutamic acid) (γ-PGA) powder surface was carried out in a heterogeneous system. It was found that the polymerization of N-vinylcarbazole (NVC) and N-vinyl-2-pyrrolidone (NVPD) is initiated by γ-PGA powder. The grafting of polymers onto γ-PGA surface was scarcely observed. The apparent activation energy of the polymerization of NVC and NVPD was estimated to be 20.2 and 24.8 kJ/mol, respectively. The polymerization was totally inhibited by the addition of triethylamine and pyridine, but not hydroquinone. The polymerization rate in nitrobenzene was larger than that in toluene. These results indicated the cationic nature of the polymerization. γ-PGA treated with KOH did not show the initiating activity of the polymerization. Therefore, carboxyl groups on γ-PGA powder surface play an important role in the initiation of the polymerization. It may be suggested that the polymerization is initiated by proton addition to monomer from carboxyl groups on γ-PGA powder surface and the propagation proceeds with carboxylate anion on the surface as counter ion. © 1993 John Wiley & Sons, Inc.