Spatial and temporal coherence properties of single free-electron laser pulses.

The experimental characterization of the spatial and temporal coherence properties of the free-electron laser in Hamburg (FLASH) at a wavelength of 8.0 nm is presented. Double pinhole diffraction patterns of single femtosecond pulses focused to a size of about 10×10 µm(2) were measured. A transverse coherence length of 6.2 ± 0.9 µm in the horizontal and 8.7 ± 1.0 µm in the vertical direction was determined from the most coherent pulses. Using a split and delay unit the coherence time of the pulses produced in the same operation conditions of FLASH was measured to be 1.75 ± 0.01 fs. From our experiment we estimated the degeneracy parameter of the FLASH beam to be on the order of 10(10) to 10(11), which exceeds the values of this parameter at any other source in the same energy range by many orders of magnitude.

Coherence properties of individual femtosecond pulses of an x-ray free-electron laser.

Measurements of the spatial and temporal coherence of single, femtosecond x-ray pulses generated by the first hard x-ray free-electron laser, the Linac Coherent Light Source, are presented. Single-shot measurements were performed at 780 eV x-ray photon energy using apertures containing double pinholes in "diffract-and-destroy" mode. We determined a coherence length of 17 µm in the vertical direction, which is approximately the size of the focused Linac Coherent Light Source beam in the same direction. The analysis of the diffraction patterns produced by the pinholes with the largest separation yields an estimate of the temporal coherence time of 0.55 fs. We find that the total degree of transverse coherence is 56% and that the x-ray pulses are adequately described by two transverse coherent modes in each direction. This leads us to the conclusion that 78% of the total power is contained in the dominant mode.

Tunable Coherent X-rays.

A modern 1- to 2-billion-electron-volt synchrotron radiation facility (based on high-brightness electron beams and magnetic undulators) would generate coherent (laser-like) soft x-rays of wavelengths as short as 10 angstroms. The radiation would also be broadly tunable and subject to full polarization control. Radiation with these properties could be used for phase- and element-sensitive microprobing of biological assemblies and material interfaces as well as reserch on the production of electronic microstructures with features smaller than 1000 angstroms. These short wavelength capabilities, which extend to the K-absorption edges of carbon, nitrogen, and oxygen, are neither available nor projected for laboratory XUV lasers. Higher energy storage rings (5 to 6 billion electron volts) would generate significantly less coherent radiation and would be further compromised by additional x-ray thermal loading of optical components.

X-ray laser microscopy of rat sperm nuclei.

The development of high brightness and short pulse width (< 200 picoseconds) x-ray lasers now offers biologists the possibility of high-resolution imaging of specimens in an aqueous environment without the blurring effects associated with natural motions and chemical erosion. As a step toward developing the capabilities of this type of x-ray microscopy, a tantalum x-ray laser at 44.83 angstrom wavelength was used together with an x-ray zone plate lens to image both unlabeled and selectively gold-labeled dried rat sperm nuclei. The observed images show approximately 500 angstrom features, illustrate the importance of x-ray microscopy in determining chemical composition, and provide information about the uniformity of sperm chromatin organization and the extent of sperm chromatin hydration.

Transverse Coherence Limited Coherent Diffraction Imaging using a Molybdenum Soft X-ray Laser Pumped at Moderate Pump Energies.

Coherent diffraction imaging (CDI) in the extreme ultraviolet has become an important tool for nanoscale investigations. Laser-driven high harmonic generation (HHG) sources allow for lab scale applications such as cancer cell classification and phase-resolved surface studies. HHG sources exhibit excellent coherence but limited photon flux due poor conversion efficiency. In contrast, table-top soft X-ray lasers (SXRL) feature excellent temporal coherence and extraordinary high flux at limited transverse coherence. Here, the performance of a SXRL pumped at moderate pump energies is evaluated for CDI and compared to a HHG source. For CDI, a lower bound for the required mutual coherence factor of |µ 12| ≥ 0.75 is found by comparing a reconstruction with fixed support to a conventional characterization using double slits. A comparison of the captured diffraction signals suggests that SXRLs have the potential for imaging micron scale objects with sub-20 nm resolution in orders of magnitude shorter integration time compared to a conventional HHG source. Here, the low transverse coherence diameter limits the resolution to approximately 180 nm. The extraordinary high photon flux per laser shot, scalability towards higher repetition rate and capability of seeding with a high harmonic source opens a route for higher performance nanoscale imaging systems based on SXRLs.

Spatial coherence measurements of a 13.2 nm transient nickel-like cadmium soft x-ray laser pumped at grazing incidence.

The spatial coherence of a 13.2 nm transient collisional Ni-like Cd soft X-ray laser pumped at 23 degrees grazing incidence was measured in a series of Young's double-slit experiments. We observed pronounced fringe visibility variations associated with microstructures in the beam's intensity profile. The transverse coherence length was measured to be about 1/20 of the beam diameter and did not significantly improve with longer plasma columns. The equivalent incoherent source size is determined to be 10 mum and the laser's peak spectral brightness ~ 3 x 10(23) photons/sec/mm(2)/mrad(2) within less than 0.01% spectral bandwidth.

The interior of a whole and unmodified biological object--the zymogen granule--viewed with a high-resolution X-ray microscope.

We report the ability of focused soft X-rays to visualize at spatial resolution well beyond that of the optical microscope (less than 100 nm) the interior of a small, whole biological object without fixation, staining, dehydration or sectioning. Quantitative estimation of its protein content with unique femtogram sensitivity is also reported. The present results represent a significant step towards the goals of natural imaging and chemical mapping of biological structures with soft X-rays.

Reflection mode imaging with nanoscale resolution using a compact extreme ultraviolet laser.

We report the demonstration of reflection mode imaging of 100 nm-scale features using 46.9 nm light from a compact capillary-discharge laser. Our imaging system employs a Sc/Si multilayer coated Schwarzschild condenser and a freestanding zone plate objective. The reported results advance the development of practical and readily available surface and nanostructure imaging tools based on the use of compact sources of extreme ultraviolet light.

Physicochemical consequences of the perdeuteriation of glutathione S-transferase from S. japonicum.

Glutathione S:-transferase (GST) from Schistosoma japonicum has been prepared in both normal protiated (pGST) and fully deuteriated (dGST) form by recombinant DNA technology. Electrospray mass spectrometry showed that the level of deuteriation in dGST was 96% and was homogeneous across the sample. This result is attributed to the use of a deuterium-tolerant host Escherichia coli strain in the preparation of the protein. 10 heteroatom-bound deuteriums (in addition to the carbon-bound deuteriums) were resistant to exchange when dGST was incubated in protiated buffer. The physicochemical and biological properties of the two proteins were compared. dGST was relatively less stable to heat denaturation and to proteolytic cleavage than was pGST. The midpoint transition temperature for pGST was 54.9 degrees C, whereas that for dGST was 51.0 degrees C. Static light-scattering measurements revealed that the association behavior of dGST is also different from that of pGST. The perdeuteriated enzyme shows a tendency to associate into dimers of the fundamental dimer. This is in contrast with results that have been obtained for other perdeuteriated proteins in which perdeuteriation has been shown to promote dissociation of aggregates. dGST showed a similar K(m) to pGST; similar results had been obtained previously with bacterial alkaline phosphatase. However, whereas the alkaline phosphatase showed a reduced rate of catalysis on deuteriation, dGST exhibited a slightly higher rate of catalysis than pGST. It is clear that the bulk substitution of deuterium for protium has significant effects on the properties of proteins. Until many more examples have been studied, it will be difficult to predict these effects for any given protein. Nevertheless, deuteriation represents an intriguing method of preparing functional analogs of recombinant proteins.

Preparation and characterization of poly(epsilon-caprolactone) polymer blends for the delivery of proteins.

A series of ternary blend matrices, based on high- and low-molecular-weight poly(epsilon-caprolactone) (PCL) and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer (Synperonic L61), has been developed for the delivery of proteins. The inclusion of Synperonic L61 served to enhance the water content of the matrix available for protein diffusion. Blends comprising high-molecular-weight PCL (PCLH) and Synperonic L61 alone were found by scanning electron microscopy to be incompatible over a wide composition range. The addition of a low-molecular-weight PCL (PCLL) enhanced compatibility of the polymeric components. Analysis of the dynamic mechanical and thermal properties of these blends showed a significant shift in the glass transition temperature of the material (-38 to -55 degrees C), as the weight fraction of Synperonic L61 increased to 30 wt%, indicative of limited miscibility of the components in the non-crystalline phase. All ternary blended matrices showed a higher degree of hydration relative to homogeneous PCLH. The maximum water content could be modified by adjusting the weight fraction of Synperonic L61 in the blend. The rate of release of a model protein, bovine serum albumin (BSA), from matrices containing Synperonic L61 was considerably higher than that from PCLH and PCLH/PCLL alone. Analysis of the release mechanisms of BSA from these matrices suggested that, whilst diffusion was the predominant mode of protein transport, the elution of Synperonic L61 from blended matrices during the dissolution caused a notable deviation from Fickian control.

An investigation of the parameters influencing the bioadhesive properties of Myverol 18-99/water gels.

An in vitro assessment was undertaken of the parameters influencing the bioadhesive strength of lyotropic liquid crystalline gels formed by the monoglyceride blend Myverol 18-99 and water. The gels were found to bind more strongly to a dry Perspex surface than to moist mucosal tissue and were shown to be weaker bioadhesives than Carbopol 934P and sodium alginate. The works of adhesion and forces of detachment were independent of contact time, were reduced by the presence of surface water and increased with an increase in the compression force, suggesting that interpenetration was not the mechanism of bioadhesion. The bioadhesion of Myverol 18-99/water gels appeared to be due to secondary chemical bonds, such as van der Waals forces, but was limited by their cohesive strength. An in vivo gel retention assessment by gamma scintigraphy showed that the gels were retained within the vaginal cavity for a period of at least 6 h.

A DSC study of the miscibility of poly(ethylene oxide)-block-poly(DL-lactide) copolymers with poly(DL-lactide).

The purpose of this study was to examine the miscibility of poly(ethylene oxide)-block-poly(DL-lactide) copolymers with poly (DL-lactide). The copolymers L7E73L7 and L17E78L17 (L = carbonyloxymethylmethylene unit, OCOCH(CH3); E = oxyethylene unit, OCH2CH2) were synthesised by non-catalysed anionic polymerisation and characterised by gel permeation chromatography and 13C NMR. Blends of each of the copolymers with poly(DL-lactide) with compositions over the range from 10 to 90 wt% copolymer were cast as thin films and examined by differential scanning calorimetry (DSC) to determine glass transition temperatures (Tg) and melting temperatures (Tm). The phase diagram showed a region of miscibility above the melting point of the copolymer in the system (approx. 35-40 degrees C). Within this region the system was glassy at low mass fractions of oxyethylene in the copolymer (wE < or = 0.1) and rubbery at higher mass fractions. Below Tm a mechanically compatible glassy blend existed at low wE whilst quenching of systems of higher wE led to phase separation, the biphasic region consisting of crystalline Em-sequences of copolymer separated from non-crystalline poly(DL-lactide). The phase diagram resulting from this study provides the means for the design of drug delivery systems based on blends of poly(DL-lactide) and poly(ethylene oxide)-containing components. The crystal melt boundary can be lowered by the use of block copolymers with short poly(ethylene oxide) blocks permitting the preparation of blends which are miscible at room temperature and rubbery or glassy according to composition.

Oral sustained delivery of theophylline using in-situ gelation of sodium alginate.

Gels formed in situ following oral administration of aqueous solutions of sodium alginate (1.0-2.0%w/v) to rats were evaluated as sustained release vehicles for the delivery of theophylline. The liquid formulation contained calcium ions in complexed form, the release of which in the acidic environment of the stomach caused gelation of the alginate. Bioavailability of theophylline from alginate gels formed by in situ gelation in the rat stomach was increased by 1.3-2-fold in rats for alginate concentrations of 2.0 to 1.0%w/v respectively compared with that from a proprietary oral sustained release formulation containing an identical drug concentration. There was no significant difference in the mean residence times of theophylline when administered by these two vehicles.

In vitro release of cytarabine from swellable matrices of CnEmCn triblock copolymers.

Matrices loaded with cytarabine were prepared by compression of the tailor made triblock copolymers C17E227C17 and C17E454C17 (where C=methylene and E=oxyethylene). Observations of the swelling characteristics of copolymer matrices on immersion in distilled water indicated an increase in the thickness of the gel layer around the matrices following ingress of water into the matrices. The in vitro release of cytarabine was characterised from matrices of different molar mass and with different known drug loadings. The release of cytarabine from the copolymer matrices was predominantly by a Fickian diffusion mechanism; the release rate was dependent on drug loading and independent of copolymer molar mass.

In situ-gelling gellan formulations as vehicles for oral drug delivery.

Gels formed in situ following oral administration of 1% (w/v) aqueous solutions of gellan to rats and rabbits were evaluated as sustained-release vehicles. The formulation contained calcium ions in complexed form, the release of which in the acidic environment of the stomach caused gelation of the gellan gum. The in vitro release of theophylline from the rigid gellan gels followed root-time kinetics over a period of 6 h. Plasma levels of theophylline after oral administration of gellan solutions and a commercial oral sustained-release liquid dosage form containing an identical drug concentration were compared in both rats and rabbits. Bioavailability of theophylline from gellan gels formed by in situ gelation in the animal stomach was increased by four-fivefold in rats and threefold in rabbits compared with that from the commercial oral formulation. There was no significant difference in the mean residence times of theophylline when administered by these two vehicles.

Thermally reversible xyloglucan gels as vehicles for rectal drug delivery.

The aim of this study was to investigate the potential application of thermoreversible gels formed by a xyloglucan polysaccharide derived from tamarind seed for rectal drug delivery. Xyloglucan that had been partially degraded by beta-galactosidase to eliminate 44% of galactose residues formed gels at concentrations of between 1 to 2% w/w at gelation temperatures decreasing over the range 27 to 22 degreesC with increasing concentration. The in vitro release of indomethacin and diltiazem from the enzyme-degraded xyloglucan gels followed root-time kinetics over a period of 5 h at 37 degreesC; the diffusion coefficients increasing with temperature increase between 10 and 37 degreesC. The in vitro release of indomethacin from the gels was significantly more sustained than from commercial suppositories. Measurement of plasma levels of indomethacin after rectal administration to rabbits of the gels and commercial suppositories containing an identical drug concentration indicated a broader absorption peak following administration of the gels, and a longer residence time. There was no significant difference in bioavailability of indomethacin when administered by these two vehicles. Morphological studies of rectal mucosa following a single administration of the gels showed no evidence of tissue damage. The results of this study suggest the potential of the enzyme-degraded xyloglucan gels as vehicles for rectal delivery of drugs.

The effect of fluoridation on the dental health of urban Scottish Schoolchildren.

A comparison was made of the dental health of children aged 4-5 and 9-10 in two Scottish towns, one with fluoridated drinking water and the other without. Striking differences were observed. A 44% reduction in decayed, missing, and filled deciduous teeth was found in 4-5 year-olds in the fluoridated compared with the non-fluoridated town and a 50% reduction in decayed, missing, and filled permanent teeth was recorded for the 9-10-year-olds. Larger percentage differences were found for the anterior teeth: a 65% reduction in deciduous incisors and canines, and an 81% reduction in permanent incisors and canines. Fluoridation of public water supplies in urban areas of Scotland would be a safe and effective way of dramatically improving dental health.

Adsorption of an amphiphilic penicillin onto human serum albumin: characterisation of the complex.

The complex formed by the interaction of the amphiphilic penicillin drug nafcillin and human serum albumin (HSA) in water at 25 degrees C has been characterised using a range of physicochemical techniques. Measurements of the solution conductivity and the electrophoretic mobility of the complexes have shown an ionic adsorption of the drug on the protein surface leading to a surface saturation at a nafcillin concentration of 0.012 mmol kg(-1) and subsequent formation of drug micelles in solutions of higher nafcillin concentration. Measurements of the size of the complex and the thickness of the adsorbed layer by static and dynamic light scattering have shown a gradual change in hydrodynamic radius of the complex with increasing drug concentration typical of a saturation rather than a denaturation process, the magnitude of the change being insufficient to account for any appreciable extension or unfolding of the HSA molecule. The interaction potential between the HSA/nafcillin complexes, and the stability of the complexes were determined from the dependence of diffusion coefficients on protein concentration by application of the DLVO colloidal stability theory. The results indicate decreasing stability of the colloidal dispersion of the drug/protein complexes with an increase in the concentration of added drug.

Do triglycerides modulate the effectiveness of clozapine?

We describe a case in which a patient's clinical response to clozapine appears to correlate positively with his serum triglyceride concentrations. We propose that the observed clinical response may partly be the result of the physical interaction of clozapine with the very low-density lipoproteins. We base this supposition on our previous in-vitro study showing that the plasma distribution of clozapine is significantly altered by increases in plasma triglyceride concentrations. Although this case only represents one patient, it highlights the possibility that serum lipids may be potential contributors to the clinical effectiveness of clozapine.

Aggregation of antihistamines in aqueous solution: effect of counterions on self-association of pyridine derivatives.

The effects of electrolytes on the self-association of the antihistaminic drugs, tripelennamine hydrochloride, thenyldiamine hydrochloride, pyrilamine maleate, pheniramine maleate, chlorpheniramine maleate, and brompheniramine maleate, in aqueous solution were examined by light-scattering from tripelennamine bydrochloride and thenyldiamine hydrochloride in 0.154 mole of sodium chloride/kg and 0.150 mole of sodium maleate/kg indicated a micellar pattern of aggregation. Higher aggregation numbers and lower CMC's were determined in the presence of the maleate ion. No significant discontinuity in the concentration dependence of the light scattering of the remaining compounds in either of the two electrolytes was evident, and the aggregation of these compounds was treated using a stepwise association model. Values of the association constants and the limiting number of associating species were, in general, increased by the addition of electrolyte in the order water less than sodium chloride less than sodium maleate. An apparently nonmicellar pattern of aggregation could be induced by chemically changing the counterion from chloride to maleate.