Manipulation of charge states of biopolymer ions by atmospheric pressure ion/molecule reactions implemented in an extractive electrospray ionization source.

A home-made extractive electrospray ionization source is coupled to an linear quadrupole ion trap mass spectrometer to investigate ion/molecule reactions of biopolymers at ambient pressure. Multiply charged biopolymers such as peptides and proteins generated in an electrospray are easily reduced to a low charge state by the atmospheric pressure ion/molecule reactions occurring between the multiply charged ions and a strong basic reagent sprayed in neutral form into the electrospray plume. The charge state of the biopolymer ions can be manipulated by controlling the amount of the basic reagent. The production of biopolymer ions with low charge states results in a substantial improvement of sensitivity and reduced spectral congestion in ESI-MS. This is of importance for biopolymer mixture analysis and could have promising applications in proteomics.

Unusual cold crystallization behavior in physically aged poly(L-lactide).

A comparative study of cold crystallization behavior in poly(L-lactide) (PLLA) annealed below and just above the glass transition temperature (T(g)) has been conducted. Annealing benefits the generation of local order and the subsequent cold crystallization process, which becomes significant in PLLA annealed just above T(g). Surprisingly, morphological observation reveals high density nuclei in PLLA annealed below T(g), contrary to its relatively slow crystallization kinetics. This unusual crystallization behavior in physically aged PLLA arises from the retarded crystal growth rate because of incomplete recovery of reduced segmental mobility above T(g). In contrast, annealing just above T(g) has little influence on the crystal growth rate, and the increased nucleation density alone accounts for the accelerated crystallization rate.

Self-assembled micellar nanoparticles of a novel star copolymer for thermo and pH dual-responsive drug release.

An amphiphilic star block copolymer comprised of a hydrophobic PMMA block and a hydrophilic tri-arm poly(NIPAAm-co-DMAEMA) block was synthesized by copolymerization of NIPAAm and DMAEMA, with Ce(4+) ions and tris(hydroxymethyl)methylamine as a redox initiatory system. The star copolymer undergoes self-assembly to the micellar nanoparticles with a core-shell structure and the thermo/pH dual-response, originated from the thermo-sensitivity of PNIPAAm and the pH-sensitivity of PDMAEMA. A fluorescence probe study showed the pH-dependent low CMCs (7.5 to 11.2 mg/L) of the micelles, confirming the formation of stable micelles. Morphological investigations showed that the blank and drug-loaded micelles both had spherical and uniform shapes. The sizes of the blank and drug-loaded nanoparticles were between 80 and 120 nm, depending on the given pH. The LCSTs of the star copolymer were determined to be 32 degrees C, 36.6 degrees C and 39.5 degrees C, corresponding to pH 5, pH 7.4 and pH 9, respectively, demonstrating a pH-dependent thermo-response. As a drug delivery, the micellar nanoparticles showed the dual-responsive release profiles in vitro, which were confirmed by the drug release studies. The obtained results showed the thermo-triggered accelerated release at pH 7.4, and the pH-triggered accelerated release at 37 degrees C, indicating the micelles nanoparticles would be a promising site-specific drug delivery for enhancing the accumulation of drug in targeting pathological areas.

[Enrichment of nicotine in plasma with three-phase hollow fiber based liquid phase microextraction].

A novel method for fast determination of nicotine in plasma was established by using high performance liquid chromatography (HPLC) coupled with a three-phase hollow fiber based liquid phase microextraction (TP-HF-LPME) technique for sample preparation. The microextraction was mediated by the pH difference between the environment inside and outside of an organic phase immobilized in the pores formed in the wall of a polypropylene hollow fiber. The pH value of the medium outside the organic phase was adjusted by adding a dilute KOH solution to form a basic donor phase while the pH value of the inner media was set to pH 3 to form an acceptor phase using a 10 mmol/L KH2PO4 solution. On working conditions, neutral nicotine molecules were firstly extracted from the original sample solution to the organic phase, and then the analyte was extracted from the organic phase to the acceptor phase. After described extraction time, 4 microL of acceptor phase was withdrawn and directly injected into HPLC system for analysis. Parameters related to TP-HF-LPME (organic solvent, pH of acceptor and donor phase, stirring rate, salt effect, methanol content in acceptor phase and extraction time) were also optimized experimentally. The proposed method integrates extraction, enrichment and clean-up into a single step, dramatically simplifying the traditional procedure to prepare a liquid sample with complex matrices such as plasma. It has been demonstrated to be a very fast, effective and virtually "green" sample preparation technique, which provided a good linear range (0.1 - 50 mg/L) with Nu of 0.999 6, a low detection limit (0.05 mg/L, S/N = 3) and a satisfactory relative standard deviation (< 5%).