pH-responsive microgels containing hydrophilic crosslinking co-monomers: shell-exploding microgels through design

pH-responsive microgels are crosslinked polymer colloids that swell when the pH approaches the pK _a of the particles. They have potential application for injectable gels for tissue repair and drug delivery systems. This study focuses on the pH-triggered gelation behaviour of a series of poly (EA/MAA/X) microgels. EA and MAA are ethylacrylate and methacrylic acid. Here, we investigate the effect of crosslinking monomer type (X) on microgel properties. The crosslinking monomers used were poly (ethyleneglycol) dimethacrylate (PEGD), ethyleneglycol dimethacrylate (EGD) and butanediol diacrylate (BDD). The microgel containing PEGD (m-PEGD) is a new system. The microgel containing BDD (m-BDD) was used as a control system. The concentrated microgel dispersions formed physical gels when the pH was increased to 5.3?C6.7, and the polymer volume fractions (? _p ) were above about 0.05. Evidence from photon correlation spectroscopy (PCS) and dynamic rheology was presented for abrupt pH-triggered increases, and then decreases of the hydrodynamic diameters for m-PEGD and the microgel prepared using EGD (m-EGD). This appears to be tuneable through crosslinker structure. An unexpected gelation behaviour, which may involve a new gel state for microgels, was found for m-PEGD dispersions. Uniquely, those dispersions formed gels at pH values less than the microgel's pK _a . This behaviour was linked to an outer-shell electrostatic repulsive interaction. The data point to a phenomenon, whereby the m-PEGD shells appear to explode at pH values above 7.0. The control microgel prepared, using BDD (m-BDD), did not show any evidence of shell fragmentation at any pH. That microgel has potential as a model pH-responsive microgel system in that the properties measured by PCS and rheology agreed well. To probe that system in more detail, the rheological data for m-BDD was analysed using scaling theory. The variation of the storage modulus (G') with ? _p gave a scaling exponent of 2.0.     

On-line reaction monitoring by extractive electrospray ionisation

The design and development of a novel extractive electrospray ionisation (EESI) device for on-line reaction monitoring is described. The EESI apparatus uses a secondary, grounded nebuliser to produce an analyte aerosol and a Venturi pump is then used to transfer a sample of the aerosol to an electrospray source where it is ionised. The EESI apparatus was then tested with a variety of small, organic molecules to assess sensitivity, linearity and dynamic range. The performance of the technique will depend on the mass spectrometer used for the experiments; in the configurations used here it has a usable dynamic range of around 3.5 orders of magnitude with a linear range of around 2.5 orders of magnitude and is capable of analysing species present down to low μg/mL with signal-to-noise ratio greater than 2.5. The use of EESI for reaction monitoring was validated using a series of mock reaction mixtures and then used to monitor the base hydrolysis of ethyl salicylate to salicylic acid.     

From {Bi22O26} to chiral ligand-protected {Bi38O45}-based bismuth oxido clusters

The reaction of [Bi(22)O(26)(OSiMe(2)tBu)(14)] (1) in THF with salicylic acid gave [Bi(22)O(24)(HSal)(14)] (2) first, which was converted into [Bi(38)O(45)(HSal)(22)(OH)(2)(DMSO)(16.5)]·DMSO·H(2)O (3·DMSO·H(2)O) after dissolution and crystallization from DMSO. Single-crystal X-ray diffraction analysis and ESI mass spectrometry associated with infrared multi-photon dissociation (IRMPD) tandem MS experiments confirm the formation of the large and quite stable bismuth oxido cluster 3. The reaction of compound 2 with the butoxycarbonyl(BOC)-protected amino acids phenylalanine and valine (BOC-PheOH and BOC-ValOH), respectively, resulted in the formation of chiral [Bi(38)O(45)(BOC-AA)(22)(OH)(2)] (AA=deprotonated amino acid), as shown by a combination of different analytical techniques such as elemental analysis, dynamic light scattering, circular dichroism spectroscopy, and ESI mass spectrometry.     

A re-investigation of [Fe(L-cysteinate)2(CO)2]2-: an example of non-heme CO coordination of possible relevance to CO binding to ion channel receptors

[Fe(L-cysteinate)(2)(CO)(2)](2-) is a CO releasing molecule which has low cytotoxicity to RAW264.7 macrophages. It provides an example of CO binding using ligands available to ion channels which use CO as a signalling molecule in the absence of heme. Previous work has shown that this compound consists of five isomers and it was proposed that the two isomers with trans-dicarbonyls are dominant. In this work the isomers are re-assigned and shown to be capable of releasing CO, albeit too slowly to act as a signalling receptor. It is shown that by linking the two L-cysteines together to form [Fe(SCH(2)CH{CO(2)H}NHCH(2))(2)(CO)(2)], only one isomer is isolated.     

Radical conversion and migration in electron capture dissociation

Electron capture dissociation (ECD) is an important analytical technique which is used frequently in proteomics experiments to reveal information about both primary sequence and post-translational modifications. Although the utility of ECD is unquestioned, the underlying chemistry which leads to the observed fragmentation is still under debate. Backbone dissociation is frequently the exclusive focus when mechanistic questions about ECD are posed, despite the fact that numerous other abundant dissociation channels exist. Herein, the focus is shifted to side chain loss and other dissociation channels which offer clues about the underlying mechanism(s). It is found that the initially formed hydrogen abundant radicals in ECD can convert quickly to hydrogen deficient radicals via a variety of pathways. Dissociation which occurs subsequent to this conversion is mediated by hydrogen deficient radical chemistry, which has been the subject of extensive study in experiments which are independent from ECD. Statistical analysis of fragments observed in ECD is in excellent agreement with predictions made by an understanding of hydrogen deficient radical chemistry. Furthermore, hydrogen deficient radical mediated dissociation likely contributes to observed ECD fragmentation patterns in unexpected ways, such as the selective dissociation observed at disulfide bonds. Many aspects of dissociation observed in ECD are easily reproduced in well-controlled experiments examining hydrogen deficient radicals generated by non-ECD methods. All of these observations indicate that when considering the means by which electron capture leads to dissociation, hydrogen deficient radical chemistry must be given careful consideration.     

Comparison of UPLC and HPLC for Analysis of Dietary Folates

Ultra performance liquid chromatography (UPLC) using small sub-2 ??m particles and high performance liquid chromatography (HPLC) were compared for separation and determination of the most common dietary folates; 5-methyltetrahydrofolate, tetrahydrofolate, 5-formyltetrahydrofolate, 10-formylfolic acid and folic acid. Two UPLC columns??Acquity BEH C₁₈ and Acquity HSS T3, and two HPLC columns with similar surface chemistry??Xbridge C₁₈ and Atlantis d18 were tested. When using UPLC, the signal-to-noise ratio could be improved by a factor of 2?C50 for different folate derivatives and the run time could be reduced fourfold without sacrificing separation efficiency. The applicability of UPLC to real food samples was demonstrated.     

Real-time monitoring of nanomolar binding to a cyclodextrin monolayer immobilized on a Si/SiO2/novolac surface using white light reflectance spectroscopy: the case of triclosan

The monitoring of the antibacterial agent triclosan binding at nanomolar concentration from an aqueous solution by employing a well-packed monolayer with a predetermined single orientation made of specifically synthesized 2,3-dimethyl-6-(undec-10-enamide)-6-deoxy-β-cyclodextrin (DMBUA) on a silicon wafer (Si/SiO(2)) coated with a novolac resin is reported. A white light reflectance spectroscopy (WLRS) setup was used for the real-time monitoring of the DMBUA deposition and triclosan binding processes. Film thicknesses obtained by WLRS were in very good agreement with the ones measured by X-ray reflectivity (XRR) experiments. Triclosan binds strongly to the DMBUA monolayer (logK(assoc)=6.68). NMR studies in aqueous solution indicated that the chlorophenolyl ring rather than the dichlorophenyl ring is preferentially inserted into DMBUA cups. The current detecting system that requires no tedious surface chemistry, no thiolated cyclodextrins, no gold surfaces, and no expensive equipment may be useful in capturing small molecules and may permit various applications, e.g., preparation of antimicrobial surfaces.     

Unusual multi-step sequential Au(III)/Au(II) processes of gold(III) quinoxalinoporphyrins in acidic non-aqueous media

The electrochemistry of gold(III) mono- and bis-quinoxalinoporphyrins was examined in CH(2)Cl(2) or PhCN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) before and after the addition of trifluoroacetic acid to solution. The investigated porphyrins are represented as Au(PQ)PF(6) and Au(QPQ)PF(6), where P is the dianion of the 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin and Q is a quinoxaline group fused to a β,β'-pyrrolic position of the porphyrin macrocycle; in Au(QPQ)PF(6) there is a linear arrangement where the quinoxalines are fused to pyrrolic positions that are opposite each other. The porphyrin without the fused quinoxaline groups, Au(P)PF(6), was also investigated under the same solution conditions. In the absence of acid, all three gold(III) porphyrins undergo a single reversible Au(III)/Au(II) process leading to the formation of a Au(II) porphyrin which can be further reduced at more negative potentials to give stepwise the Au(II) porphyrin π-anion radical and dianion, respectively. However, in the presence of acid, the initial Au(III)/Au(II) processes of Au(PQ)PF(6) and Au(QPQ)PF(6) are followed by an internal electron transfer and protonation to regenerate new Au(III) porphyrins assigned as Au(III)(PQH)(+) and Au(III)(QPQH)(+). Both protonated gold(III) quinoxalinoporphyrins then undergo a second Au(III)/Au(II) process at more negative potentials. The electrogenerated monoprotonated monoquinoxalinoporphyrin, Au(II)(PQH), is then further reduced to its π-anion radical and dianion forms, but this is not the case for the monoprotonated bis-quinoxalinoporphyrin, Au(II)(QPQH), which accepts a second proton and is rapidly converted to Au(III)(HQPQH)(+) before undergoing a third Au(III)/Au(II) process to produce Au(II)(HQPQH) as a final product. Thus, Au(P)PF(6) undergoes one metal-centered reduction while Au(PQ)PF(6) and Au(QPQ)PF(6) exhibit two and three Au(III)/Au(II) processes, respectively. These unusual multistep sequential Au(III)/Au(II) processes were monitored by thin-layer spectroelectrochemistry and a reduction/oxidation mechanism for Au(PQ)PF(6) and Au(QPQ)PF(6) in acidic media is proposed.     

Further studies of intramolecular Michael reactions of nitrosoalkenes for construction of functionalized bridged ring systems

A wide variety of stabilized carbanions have been found to participate as nucleophiles in intramolecular Michael-type conjugate additions to in situ generated nitrosoalkenes to form bridged carbocyclic systems. The vinylnitroso platforms for these cyclizations have been prepared via two key steps involving ring-closing metathesis of vinyl chlorides and regioselective conversion of vinyl chlorides to α-chloroketones with sodium hypochlorite in glacial acetic acid/acetone. An alternative approach to preparation of some cyclization substrates has involved use of more reactive enol ethers as precursors to the requisite α-chloroketones. A sulfonamide anion has also been found to be an effective nucleophile in this type of reaction, leading to formation of a 6-azabicyclo[3.2.1]octane.     

An OFF-ON fluorescent probe for Zn2+ based on a GFP-inspired imidazolone derivative attached to a 1,10-phenanthroline moiety

A green fluorescent protein chromophore inspired chemosenor for Zn(2+) was designed and synthesized. A Zn(2+) specific fluorescence enhancement was observed due to restricted rotation between the 1,10-phenanthroline and imidazolone moieties.