Enhanced osteogenic activity of phosphorylated polyetheretherketone via surface-initiated grafting polymerization of vinylphosphonic acid.

Polyetheretherketone (PEEK) is considered to be a prime candidate with the potential to replace biomedical metallic materials as an orthopedic and dental implant on account of its elastic modulus similar to that of human cortical bone. Unfortunately, its biomedical application is impeded by the bioinert surface property and inferior osteogenic activity. In this work, phosphate groups were incorporated onto the PEEK surface through a single-step UV-initiated graft polymerization of vinylphosphonic acid. Diffuse reflectance Fourier transform infrared spectroscopy (DRFTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) revealed that phosphate groups were successfully introduced onto the PEEK surface without apparently altering its surface topographical feature and roughness. Water contact angle measurements diclosed the increasing hydrophilia after surface phosphonation. In vitro cell adhesion, spreading, proliferation, alkaline phosphatase activity, extracellular matrix mineralization, and real-time PCR analyses showed enhanced adhesion, spreading, proliferation and osteogenic differentiation of MC3T3-E1 osteoblast on the surface-phosphorylated PEEK. An in vivo biological evaluation in the rabbit tibiae proximal defect model by means of a histological analysis confirmed that the surface-phosphorylated PEEK had improved bone-implant contact. The obtained results indicate that enhanced osteogenic activity to surface-phosphorylated PEEK, which gives positive information of its potential applications in orthopedic and dental implants.

Ultrasonic reactivation of phosphonate poisoned calcite during crystal growth.

The effect of ultrasonic irradiation (42,150 Hz, 17 W dm(-3)/7.1 W cm(-2)) on the growth of calcite in the presence of the inhibitor nitrilotris(methylene phosphonic acid) (NTMP) was investigated at constant composition conditions. In seeded growth experiments, it was found that the inhibiting effect of NTMP on crystal growth could be seriously mitigated under influence of ultrasonic irradiation. An approximately twofold increase in volumetric growth rate was achieved during ultrasonic irradiation, and recovery of the growth rate following inhibition was strongly enhanced compared to growth experiments without ultrasonic irradiation. The results could be explained in part by the physical effect of ultrasound that causes breakage and attrition of poisoned crystals, which resulted in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that there is also a chemical effect of ultrasound that plays an important role. Several breakdown products were identified, which showed that ultrasound caused the progressive loss of phosphonate groups from NTMP, probably by means of physicochemically generated free radicals and/or pyrolysis in the hot bubble-bulk interface.

Solvent-free sonochemical preparation of alpha-aminophosphonates catalyzed by 1-hexanesulphonic acid sodium salt.

1-Hexanesulphonic acid sodium salt was found to be an efficient catalyst for the green synthesis of alpha-aminophosphonates by the coupling of aldehydes/ketone, an amine and triethyl phosphite under ultrasound irradiation at ambient temperature for appropriate time to furnish the desired product in good to excellent yield under solvent-free condition. This catalyst provides clean conversion; greater selectivity and easy workup make this protocol practical and economically attractive.

Laser photolysis of DPNI-GABA, a tool for investigating the properties and distribution of GABA receptors and for silencing neurons in situ.

Laser photolysis to release GABA at precisely defined times and locations permits investigation of the distribution of functional GABA(A) receptors in neuronal compartments, the activation kinetics and pharmacology of GABA(A) receptors in situ, and the role of individual neurons in neural circuits by selective silencing with low GABA concentrations. We describe the experimental evaluation and applications of a new nitroindoline-caged GABA, DPNI-GABA, modified to minimize the pharmacological interference commonly found with caged GABA reagents, but retaining the advantages of nitroindoline cages. Unlike the 5-methoxycarbonylmethyl-7-nitroindolinyl-GABA tested previously, DPNI-GABA inhibited GABA(A) receptors with much lower affinity, reducing peak GABA-evoked responses with an IC(50) of approximately 0.5 mM. Most importantly, the kinetics of receptor activation, determined as 10-90% rise-times, were comparable to synaptic events and were little affected by DPNI-GABA present at 1mM concentration, permitting photolysis of DPNI-GABA to mimic synaptic activation of GABA(A) receptors. With a laser spot of 1 microm applied to cerebellar molecular layer interneurons, the spatial resolution of uncaging DPNI-GABA in dendrites was estimated as 2 microm laterally and 7.5 microm focally. Finally, at low DPNI-GABA concentration, photorelease restricted to the area of the soma suppressed spiking in single Purkinje neurons or molecular layer interneurons for periods controlled by the flash intensity and duration. DPNI-GABA has properties better adapted for fast kinetic studies with laser photolysis at GABA(A) receptors than previously reported caged GABA reagents, and can be used in experiments where spatial resolution is determined by the dimensions of the laser light spot.

Optical resolution of oriented enantiomers via photodissociation: quantum model simulations for H2POSD.

We demonstrate quantum mechanically how to resolve enantiomers from an oriented racemic mixture taking advantage of photodissociation. Our approach employs a femtosecond ultraviolet (UV) laser pulse with specific linear polarization achieving selective photodissociation of one enantiomer from a mixture of L and R enantiomers. As a result, the selected enantiomer is destroyed in the electronically excited state while the opposite enantiomer is left intact in the ground state. As an example we use H2POSD which presents axial chirality. A UV pulse excites the lowest singlet excited state which has nsigma* character and is, therefore, strongly repulsive along the P-S bond. The model simulations are performed using wavepackets which propagate on two dimensional potential energy surfaces, calculated along the chirality and dissociation reaction coordinates using the CASSCF level of theory.

A plausibly prebiotic synthesis of phosphonic acids.

The insolubility of calcium phosphate in water is a significant stumbling block in the chemistry required for the origin of life. The discovery of alkyl phosphonic acids in the Murchison meteorite suggests the possibility of delivery of these water-soluble, phosphorus-containing molecules by meteorites or comets to the early Earth. This could have provided a supply of organic phosphorus for the earliest stages of chemical evolution; although probably not components of early genetic systems, phosphonic acids may have been precursors to the first nucleic acids. Here we report the synthesis of several phosphonic acids, including the most abundant found in the Murchison meteorite, by ultraviolet irradiation of orthophosphorous acid in the presence of formaldehyde, primary alcohols, or acetone. We argue that similar reactions might explain the presence of phosphonic acids in Murchison, and could also have occurred on the prebiotic Earth.