Femtosecond inscription of the first order Bragg gratings in pure fused silica

The fabrication of sub-micron periodic structures beyond diffraction limit is a major motivation for the present paper. We describe the fabrication of the periodic structure of 25 mm long with a pitch size of 260 nm which is less than a third of the wavelength used. This is the smallest reported period of the periodic structure inscribed by direct point-by-point method. A prototype of the add-drop filter, which utilizes such gratings, was demonstrated in one stage fabrication process of femtosecond inscription, in the bulk fused silica.

Inscription of a 300-nm-period nanostructure in a pure fused silica

Very recently, using tightly-focused femtosecond near-IR pulses, periodical sub-micron structures have been recorded [1,2]. Such microfabrication utilizes the multi-photon approach, which allows the inscription inside various non-photosensitive optical materials. The combination of multi-photon excitation with the point-by-point technique offers the great potential of creating non-uniform chirped gratings by controlling the rate of femtosecond pulses or the sample translation speed.

Point-by-point inscription of 250 nm period structure in bulk fused silica by tightly focused femtosecond UV pulses

By conducting point-by-point inscription in a continuously moving slab of pure fused silica at the optimal depth (170νm depth below the surface), we have fabricated a 250nm period nanostructure with 30nJ, 300fs, 1kHz pulses from a frequency-tripled Ti:sapphire laser. This is the smallest value for the inscribed period yet reported, and has been achieved with radical improvement in the quality of the inscribed nanostructures in comparison with previous reports.

UV femtosecond laser inscribes a 300 nm period nanostructure in a pure fused silica

We report on the first recording of a periodic structure of ~150 nm pitch in a permanently moving sample of a pure fused silica using the tightly focused, 82 nJ, 267 nm, 300 fs, 1 kHz laser pulses.

Interaction of metal salts with polyethers

The dielectric properties of pure low to medium molecular weight poly(ethylene glycol) and poly(propylene glycol) and a variety of their salt complexes have been studied through the measurement of the dielectric permittivity and dielectric loss over a range of frequency and temperature. The major proportion of this study has been concerned with the examination of the nature of the interaction between mercuric chloride and poly(propylene glycol) (PPG). Other salt-poly-ether combinations have also been considered such as cobalt chloride-PPG cadmium chloride-PPG zinc chloride-PPG and ferric chloride-PEG (polyethylene glycol). Some of this work was also supported by chemical shift and spin-lattice Nuclear Magnetic Resonance (N.M.R.) spectroscopy. The dielectric permittivity data were analysed using the Onsager relation to calculate the mean dipole moment per dipolar unit. This approach was employed in the discussion of various models proposed for the structure of salt-polyether complexes. The effect of mercuric chloride on the statistical conformations of poly(propylene-glycol) was studied in a quantitative manner using the relationships of marchal-Benoit. The dielectric relaxation activation energy and mean energy difference between gauche and trans conformations of poly(propylene glycol) in the presence of mercuric chloride, both showed a distinct minimum when the concentration of mercuric chloride was close to 5 mole %. Opposite behaviour was observed for the Cole-Cole parameter. It was concluded that the majority of the dielectric data could be rationalised in terms of a 5-membered cyclic complex formed between mercuric chloride and PPG in which the complexed segment of the polyether-(OMeCH2CH2O)- adopted either gauche or cis conformations.

Geochemistry of some sulphides and sulpho-salts from Parys Mountain, Anglesey

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Point-by-point inscription of 250-nm-period structure in bulk fused silica by tightly-focused femtosecond UV pulses: experiment and numerical modeling

By conducting point-by-point inscription in a continuously moving slab of a pure fused silica at the optimal depth (170 μm depth below the surface), we have fabricated a 250-nm-period nanostructure with 30 nJ, 300 fs, 1 kHz pulses from frequency-tripled Ti:sapphire laser. This is the smallest value for the inscribed period yet reported, and has been achieved with radical improvement in the quality of the inscribed nanostructures in comparison with previous reports. The performed numerical modeling confirms the obtained experimental results.

Micro-holographic methods for sub-micrometer grating fabrication in fused silica with UV femtosecond laser

The optical layouts incorporating binary phase diffractive grating and a standard micro-objective were used for femtosecond microfabrication of periodical structures in fused silica. Two beams, generated in Talbot type interferometer, interfered on a surface and in the bulk of the sample. The method suggested allows better control over the transverse size of the grating pitch, and thus control the reflection strength of the waveguide or fibre grating. We present the examples of direct inscription of the sub-micrometer periodical structures using a 267 nm femtosecond laser radiation.

Preparation and characterisation of amino acids based trimethoprim salts

Trimethoprim (TMP) is a dihydrofolate reductase (DHFR) inhibitor which prevents the conversion of dihydrofolic acid into tetrahydrofolic acid, resulting in the depletion of the latter and leading to bacterial death. Oral bioavailability of TMP is hindered by both its low solubility and low permeability. This study aims to prepare novel salts of TMP using anionic amino acids; aspartic and glutamic acid as counter ions in order to improve solubility and dissolution. TMP salts were prepared by lyophilisation and characterized using FT-IR spectroscopy, proton nuclear magnetic resonance (1HNMR), Differential Scanning Calorimetry (DSC) and Thermogravimetric analysis (TGA). Both the amino acids formed salts with TMP in a 1:1 molar ratio and showed a 280 fold improvement in solubility. Investigation of the microbiological activity of the prepared salts against TMP sensitive Escherichia coli showed that the new salts not only retained antibacterial activity but also exhibited higher zone of inhibition which was attributed to improved physicochemical characters such as higher solubility and dissolution. The results are an important finding that could potentially impact on faster onset of antibacterial activity and reduced therapeutic dose when administered to patients. Studies are underway investigating the effect of ion-pairing TMP with amino acids on the permeability profile of the drug.

Numerical investigation of the effect of the temporal pulse shape on modification of fused silica by femtosecond pulses

We report the results of numerical studies of the impact of asymmetric femtosecond pulses focused in the bulk of the material on the femtosecond modification of fused silica. It is shown that such pulses lead to localisation of absorption in the process of femtosecond modification and to a decrease in the threshold energy of modification. It is found that the optimal asymmetry parameters for reaching the maximum plasma density in the focusing region depend on the pulse energy: at an initial energy of about 100 nJ, it is preferable to use pulses with positive TOD; however, when the energy is increased, it is preferable to use pulses with negative TOD. This is explained by differences in the dynamics of the processes of absorption of energy of a pulse propagating in the material.

Amino acids in oral drug delivery:salts, ion-pairs and transcriptomics

Oral drug delivery is considered the most popular route of delivery because of the ease of administration, availability of a wide range of dosage forms and the large surface area for drug absorption via the intestinal membrane. However, besides the unfavourable biopharmaceutical properties of the therapeutic agents, efflux transporters such as Pglycoprotein (P-gp) and multiple resistance proteins (MRP) decrease the overall drug uptake by extruding the drug from the cells. Although, prodrugs have been investigated to improve drug partitioning by masking the polar groups covalently with pre-moieties promoting increased uptake, they present significant challenges including reduced solubility and increased toxicity. The current work investigates the use of amino acids as ion-pairs for three model drugs: indomethacin (weak acid), trimethoprim (weak base) and ciprofloxacin (zwitter ion) in an attempt to improve both solubility and uptake. Solubility was studied by salt formation while creating new routes for uptake across the membranes via amino acids transporter proteins or dipeptidyl transporters was the rationale to enhance absorption. New salts were prepared for the model drugs and the oppositely charged amino acids by freeze drying and they were characterised using FTIR, 1HNMR, DSC, SEM, pH solubility profile, solubility and dissolution. Permeability profiles were assessed using an in vitro cell based method; Caco-2 cells and the genetic changes occurring across the transporter genes and various pathways involved in the cellular activities were studied using DNA microarrays. Solubility data showed a significant increase in drug solubility upon preparing the new salts with the oppositely charged counter ions (ciprofloxacin glutamate salt exhibiting 2.9x103 fold enhancement when compared to the free drug). Moreover, permeability studies showed a 3 fold increase in trimethoprim and indomethacin permeabilities upon ion-pairing with amino acids and more than 10 fold when the zwitter ionic drug was paired with glutamic acid. Microarray data revealed that trimethoprim was absorbed actively via OCTN1 transporters while MRP7 is the main transporter gene that mediates its efflux. The absorption of trimethoprim from trimethoprim glutamic acid ion-paired formulations was affected by the ratio of glutamic acid in the formulation which was inversely proportional to the degree of expression of OCTN1. Interestingly, ciprofloxacin glutamic acid ion-pairs were found to decrease the up-regulation of ciprofloxacin efflux proteins (P-gp and MRP4) and over-express two solute carrier transporters; (PEPT2 and SLCO1A2) suggesting that a high aqueous binding constant (K11aq) enables the ion-paired formulations to be absorbed as one entity. In conclusion, formation of ion-pairs with amino acids can influence in a positive way solubility, transfer and gene expression effects of drugs.

Impact of the counterion on the solubility and physicochemical properties of salts of carboxylic acid drugs

Aim: Salt formation is a widely used approach to improve the physicochemical and solid state properties of an active pharmaceutical ingredient. In order to better understand the relationships between the active drug, the selected counterion and the resultant salt form, crystalline salts were formed using four different carboxylic acid drugs and a closely related series of amine counterions. Thirty-six related crystalline salts were prepared, characterized and the relationship between solubility and dissolution behaviour and other properties of the salt and the counterion studied. Methods: Salts of four model acid drugs, gemfibrozil, flurbiprofen, ibuprofen and etodolac were prepared using the counterions butylamine, hexylamine, octylamine, benzylamine, cyclohexylamine, tert-butylamine, 2-amino-2-methylpropan-1-ol, 2-amino-2-methylpropan-1,3-diol andtris(hydroxymethyl)aminomethane. Salt formation was confirmed, the salts were characterized and their corresponding solubilities determined and rationalized with respect to the counterions' properties. Results and conclusion: The properties of the salt highly dependent on the nature of the counterion and, although there is considerable variation, some general conclusion can be drawn. For the alkyl amines series, increasing chain length leads to a reduction in solubility across all the acidic drugs studied and a reduction in melting point, thus contradicting simplistic relationships between solubility and melting point. Small, compact counterions consistently produce crystalline salts with high melting point accompanied with a modest improvement in solubility and the nature of hydrogen bonding between the ions has a major impact on the solubility. © 2012 Informa Healthcare USA, Inc.

The pyrolysis of plastics in molten salts

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Modelling of femtosecond inscription in fused silica

We present theoretical and numerical analysis of the femtosecond processing of silica by laser beam with power below self-focusing threshold. © 2006 IEEE.