Influence of compatibilizing agent molecular structure on the mechanical properties of phosphate glass fiber‐reinforced PLA composites

Eight compatibilizing agents were studied to investigate their effect on the quality of the interface between a phosphate glass fiber and a poly(lactic acid) (PLA) matrix. After application of the agents via dip‐coating, the fibers were Soxhlet extracted to remove any unreacted compatibilizer. To assess the interface quality, single fiber tensile tests of treated fibers and interfacial shear strengths (IFSS) of single fiber composites (SFC) were assessed. Of the agents tested, Glycerol‐2‐phosphate disodium pentahydrate (GP) and low molecular weight PLA with a sodium salt terminal group (PLA‐Na) showed the highest IFSS values, which were significantly higher than those of the control. Oligomeric PLA with a carboxylic acid end group and alendronate sodium trihydrate also showed an improvement over the control fibers. The hydrolytic degradation of these single fiber composites was studied over 7 days in water at 37 °C and a significant decrease in IFSS was observed in all cases, with the treated samples dropping to the level of the control. TGA and XPS analysis of the sized fibers showed that GP and PLA‐Na had been applied successfully to the fiber surface. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3082–3094, 2010     

A microfluidic reactor for rapid,low‐pressure proteolysis with on‐chip electrospray ionization

A microfluidic reactor that enables rapid digestion of proteins prior to on‐line analysis by electrospray ionization mass spectrometry (ESI‐MS) is introduced. The device incorporates a wide (1.5 cm), shallow (10 µm) reactor ‘well’ that is functionalized with pepsin‐agarose, a design that facilitates low‐pressure operation and high clogging resistance. Electrospray ionization is carried out directly from a short metal capillary integrated into the chip outlet. Fabrication, involving laser ablation of polymethyl methacrylate (PMMA), is exceedingly straightforward and inexpensive. High sequence coverage spectra of myoglobin (Mb), ubiquitin (Ub) and bovine serum albumin (BSA) digests were obtained after <4 s of residence time in the reactor. Stress testing showed little loss of performance over ～2 h continuous use at high flow rates (30 µL/min). The device provides a convenient platform for a range of applications in proteomics and structural biology, i.e. to enable high‐throughput workflows or to limit back‐exchange in spatially resolved hydrogen/deuterium exchange (HDX) experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

Scope and limitations of the base-catalyzed phospha-peterson P=C bond-forming reaction

Phosphaalkenes (MesP=CRR': R = R' = Ph (1a); R = R' = 4-FC6H4 (1b); R = Ph, R' = 4-FC6H4 (1c); R = R' = 4-OMeC6H4 (1d); R = Ph, R' = 4-OMeC6H4 (1e); R = Ph, R' = 2-pyridyl (1f)) are prepared from the reaction of MesP(SiMe3)2 and O=CRR' in the presence of a trace of KOH or NaOH. The base-catalyzed phospha-Peterson reaction is quantitated by NMR spectroscopy, and isolated yields of phosphaalkene between 40 and 70% are obtained after vacuum distillation and/or recrystallization. The asymmetrically substituted phosphaalkenes (1c, 1e, 1f) form as 1:1 mixtures of E and Z isomers; however, X-ray crystallography reveals that the E isomers crystallize preferentially. Interestingly, E-1e and E-1f readily isomerize in solution in the dark, although the rate of isomerization is much faster when samples are exposed to light. X-ray crystal structures of 1b, E-1e, and E-1f reveal that the P=C bond lengths (average of 1.70 A) are in the long end of the range typically found in phosphaalkenes (1.61-1.71 A). Attempts to prepare isolable P-adamantyl phosphaalkenes following this route were unsuccessful. Although AdP=CPh2 (2a) is detected by 31P NMR spectroscopy, attempts to isolate this species afforded the 1,2-diphosphetane (AdPCPh2)2 (3a), which was characterized by X-ray crystallography.     

Friction and forces between cellulose model surfaces: a comparison

Four different cellulose model surfaces, and one silica surface, have been studied by means of atomic force microscopy (AFM). The normal interactions have been found to consist of a longer range double layer force with a short range steric interaction, the nature of which is extensively discussed. Both the surface charge and range of the steric force depend on the type of cellulose substrate used, as does the magnitude of the adhesion. Studies of friction reveal that surface roughness is the determining factor for the friction coefficient, with which it increases monotonically. The absolute value, however, is determined by the surface chemistry. All studied cellulose surfaces show similar behavior in response to xyloglucan addition.     

Controlling dispersion and migration of particulate additives with block copolymers and Diels-Alder chemistry

Reversible Diels-Alder chemistry was exploited to develop thermo-responsive polymer films. Here, low molecular weight poly(styrene) (PS) and poly(ethylene glycol) (PEG) were prepared with furyl and maleimido chain ends, respectively. These polymers were then tethered together to form a thiol-terminated PEG-b-PS diblock copolymer ligand via a Diels-Alder linkage and were employed to randomly disperse 10 nm diameter Au nanoparticles within a matrix of PEG. Thermal treatment caused the Diels-Alder linkages between the polymer blocks to be severed, resulting in controllable surface functionalization due to phase separation. Migration of the Au nanoparticles to the surface of the films was characterized by Rutherford backscattering spectroscopy, small-angle X-ray scattering, contact angle measurements, and atomic force microscopy.     

Fuzzy ternary particle systems by surface-initiated atom transfer radical polymerization from layer-by-layer colloidal core-shell macroinitiator particles

We report the synthesis of ternary polymer particle material systems composed of (a) a spherical colloidal particle core, coated with (b) a polyelectrolyte intermediate shell, and followed by (c) a grafted polymer brush prepared by surface-initiated polymerization as the outer shell. The layer-by-layer (LbL) deposition process was utilized to create a functional intermediate shell of poly(diallyl-dimethylammonium chloride)/poly(acrylic acid) multilayers on the colloid template with the final layer containing an atom transfer radical polymerization (ATRP) macroinitiator polyelectrolyte. The intermediate core-shell architecture was analyzed with FT-IR, electrophoretic mobililty (zeta-potential) measurements, atomic force microscopy, and transmission electron microscopy (TEM) techniques. The particles were then utilized as macroinitiators for the surface-initiated ATRP grafting process for poly(methyl methacrylate) polymer brush. The polymer grafting was confirmed with thermo gravimetric analysis, FT-IR, and TEM. The polymer brush formed the outermost shell for a ternary colloidal particle system. By combining the LbL and surface-initiated ATRP methods to produce controllable multidomain core-shell architectures, interesting functional properties should be obtainable based on independent polyelectrolyte and polymer brush behavior.     

Temporary anion states and dissociative electron attachment in diphenyl disulfide

The temporary anion states of gas-phase diphenyl disulfide are characterized by means of electron transmission (ET) and dissociative electron attachment (DEA) spectroscopies. The measured energies of vertical electron attachment are compared to the virtual orbital energies of the neutral state molecule supplied by MP2 and B3LYP calculations with the 6-31G basis set. The calculated energies, scaled with empirical equations, reproduce satisfactorily the attachment energies measured in the ET spectrum. The first anion state of diphenyl disulfide is stable, thus escaping detection in ETS. The vertical and adiabatic electron affinities, evaluated with B3LYP/6-31+G calculations as the energy difference between the neutral and anion states, are predicted to be 0.37 and 1.38 eV, respectively. The anion current displayed in the DEA spectrum has a sharp and intense peak at zero energy, essentially due to the C6H5S- negative fragment. In agreement, according to the calculations, the localization properties of the first anion state are strongly S-S antibonding, and the energetic requirement for its dissociation along the S-S bond is fulfilled even at zero energy.     

Model studies of the Cu(B) site of cytochrome c oxidase utilizing a Zn(II) complex containing an imidazole-phenol cross-linked ligand

Cytochrome c oxidase, the enzyme complex responsible for the four-electron reduction of O2 to H2O, contains an unusual histidine-tyrosine cross-link in its bimetallic heme a3-CuB active site. We have synthesised an unhindered, tripodal chelating ligand, BPAIP, containing the unusual ortho-imidazole-phenol linkage, which mimics the coordination environment of the CuB center. The ligand was used to investigate the physicochemical (pKa, oxidation potential) and coordination properties of the imidazole-phenol linkage when bound to a dication. Zn(II) coordination lowers the pKa of the phenol by 0.6 log units, and increases the potential of the phenolate/phenoxyl radical couple by approximately 50 mV. These results are consistent with inductive withdrawal of electron density from the phenolic ring. Spectroscopic data and theoretical calculations (DFT) were used to establish that the cationic complex [Zn(BPAIP)Br]+ has an axially distorted trigonal bipyramidal structure, with three coordinating nitrogen ligands (two pyridine and one imidazole) occupying the equatorial plane and the bromide and the tertiary amine nitrogen of the tripod in the axial positions. Interestingly, the Zn-Namine bonding interaction is weak or absent in [Zn(BPAIP)Br]+ and the complex gains stability in basic solutions, as indicated by 1H NMR spectroscopy. These observations are supported by theoretical calculations (DFT), which suggest that the electron-donating capacity of the equatorial imidazole ligand can be varied by modulation of the protonation and/or redox state of the cross-linked phenol. Deprotonation of the phenol makes the equatorial imidazole a stronger sigma-donor, resulting in an increased Zn-Nimd interaction and thereby leading to distortion of the axial ligand axis toward a more tetrahedral geometry.