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Results for “Lasers, Solid-State”

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At least 127 records · Page 7Linked to original sources

PubMed2001

Use of solid corrugated particles to enhance powder aerosol performance.

PURPOSE: To study the dispersion performance of non-porous corrugated particles, with a focus on the effect of particle surface morphology on aerosolization of bovine serum albumin (BSA) powders. METHODS: The solid-state characteristics of the spray-dried BSA powders, one consisting of smooth spherical particles and another corrugated particles, were characterized by laser diffraction, X-ray powder diffraction, scanning electron microscopy, confocal microscopy, thermogravimetric analysis, surface area analyzer, and buoyancy method. The powders were dispersed using the Rotahaler and the Dinkihaler coupled to a four-stage liquid impinger operating at 30 to 120 L/min. Fine particle fraction (FPF) was expressed as the wt. % of BSA particles of size < or =5 microm collected from the liquid impinger. RESULTS: Apart from the morphology and morphology-related properties (specific surface area, envelope density), the corrugated particles and spherical particles of BSA had very similar solid-state characteristics (particle size distribution, water content, true density, amorphous nature). Using the Dinkihaler, the FPFs of the corrugated particles were 10-20 wt. % higher than those of the smooth particles. Similar FPF differences were found for the powders dispersed by the Rotahaler, but the relative changes were larger. In addition, the differences were inversely proportional to the air flows (17.3% at 30 L/min, 25.2% at 60 L/min, 13.8% at 90, 8.5% at 120 L/min). Depending on the inhaler, capsule and device retention and impaction loss at the impinger throat were lower for the corrugated particles. CONCLUSIONS: Enhanced aerosol performance of powders can be obtained by surface modification of the particles. The surface asperities of the corrugated particles could lower the true area of contact between the particles, and thus reduce the powder cohesiveness. A distinct advantage of using corrugated particles is that the inhaler choice and air flow become less critical for these particles.

Administration, Inhalation↗

PubMed1998

Fiber bundle based scanning detection system for automated DNA sequencing.

High-throughput DNA sequencing techniques are under rapid development currently, mainly triggered by the Human Genome Project. At the present time, slab gel based automated DNA sequencing is the standard procedure, utilizing fluorophore labeling and laser-induced fluorescence detection with scanning technology. In this paper, a novel, fiber-optic bundle based detection system is introduced, where a central illuminating fiber is used for the excitation of the electrophoretically separated fluorophore-labeled DNA sequencing fragments, along with several collecting fibers disposed around the illuminating fiber to collect the emitted fluorescent signal. As a model system, Cy5-labeled DNA sequencing fragments were separated on an ultrathin polyacrylamide slab gel and detected by the fiber bundle based laser-induced fluorescence detection system. A 640-nm diode laser was used to generate the illumination beam, and the emitted light collected by the fiber bundle was detected by a solid-state avalanche photodiode.

Autoanalysis↗

PubMed1998

Surface selective 1H/29Si CP NMR by NOE enhancement from laser polarized xenon

The surface proton spin polarization created by the spin-polarization-induced nuclear Overhauser effect from optically polarized xenon can be transferred in a subsequent step by solid-state cross polarization to another nuclear spin species such as 29Si. The technique exploits the dipolar interactions of xenon nuclear spins with high gamma nuclei such as 1H, and is experimentally simpler than direct polarization transfer from 129Xe to heteronuclei such as 13C and 29Si. Copyright 1998 Academic Press.

Journal Article↗

PubMed2002

All-solid-state tunable continuous-wave ultraviolet source with high spectral purity and frequency stability.

We present a novel approach for the generation of higly frequency-stable, widely tunable, single-frequency cw UV light that is suitable for high-resolution spectroscopy. Sum-frequency generation (SFG) of two solid-state sources with a single cavity resonant for both fundamental waves is employed. Using a highly stable, narrow-linewidth frequency-doubled cw Nd:YAG laser as a master laser and slaving to it the SFG cavity and the other fundamental wave from a Ti:sapphire laser, we generate UV radiation of 33-mW output power around 313 nm. Alternatively, we use a diode laser instead of the Ti:sapphire laser and produce an output power of 2.1 mW at 313 nm. With both setups we obtain a continuous tunability of >15 GHz, short-term frequency fluctuations in the submegahertz range, a long-term frequency drift below 100 MHz/h, and stable operation for several hours. The theory of optimized doubly resonant SFG is also given.

Journal Article↗

PubMed1996

Systemic nitric oxide synthase inhibition does not affect brain oxygenation during cortical spreading depression in rats: a noninvasive near-infrared spectroscopy and laser-Doppler flowmetry study.

Cortical spreading depression (CSD) has been implicated in the migraine aura and in stroke. This study demonstrates near-infrared spectroscopy (NIRS) for the first time as capable of noninvasive on-line detection of CSD in the pentobarbital-anesthetized rat. CSD was accompanied by a brief and rapid increase of regional CBF (by laser-Doppler flowmetry) to 200-400% baseline. NIRS demonstrates that this hyperperfusion is associated with concentration increases of oxyhemoglobin, while deoxyhemoglobin decreases. Simultaneously, oxygen partial pressure, measured on the brain surface with a solid-state polarographic probe, was shown to be raised by at least 14 mm Hg during CSD. Oxygen-dependent phosphorescence life-time quenching measurements confirmed this finding. NIRS data on cytochrome aa3, however, showed a CSD-related shift toward a more reduced state, despite raised blood oxygenation. This may suggest either limited O2 transport from the blood to mitochondria or decreased oxygen utilization during CSD as supposed by theories about compartmentalization of energy metabolism favoring glycolytic rather than aerobic energy supply during CSD. However, the data on cytochrome aa3 warrant caution and are discussed critically. Nitric oxide synthase inhibition by systemic application of N'-nitro-L-arginine had no significant effect on the perfusion response or the tissue PO2 during CSD. During most CSD episodes, a brief decrease in MABP by 4-8 mm Hg was noted that might be caused by functional decortication during CSD.

Animals↗

PubMed2000

Expression, purification and properties of multidrug efflux proteins.

A general strategy is described for the amplified expression, purification and characterization in Escherichia coli of multidrug efflux proteins from Staphylococcus aureus, Bacillus subtilis, Methanococcus janaschii and E. coli. They all catalyse drug/H(+) antiport of substrates such as quinolones and ethidium and exemplify a family of putatively 12-helix membrane proteins. The gene for each protein was cloned downstream of the tac promoter in plasmid pTTQ18; an oligonucleotide encoding six histidine residues was added, in frame, to the C-terminus to facilitate purification. Growth conditions were optimized in 1-25-litre cultures of E. coli host strains to amplify the expression of each protein; the retention of activity was confirmed by assays of antibiotic resistance in vivo and/or assays of energized transport activity in vitro with synthetic substrates. Proteins were solubilized in dodecylmaltoside and purified to more than 90% homogeneity with Ni(2+)-nitrilotriacetate-affinity column chromography, yielding 5-25 mg per 25 litres of original culture. All the transport proteins migrated anomalously in SDS/PAGE at apparent molecular masses below those predicted from the gene sequence; identity and integrity were therefore confirmed by N-terminal amino acid sequencing and Western blotting for the C-terminal hexahistidine tag. Examination of the secondary structure of detergent-solubilized proteins by CD or Fourier-transform infrared spectroscopy following purification indicated a high content of alpha-helix (more than 75%). Matrix-assisted laser desorption ionization MS confirmed the high degree of purity and the true molecular mass. The formation of three-dimensional crystals is being attempted but crystals have yet to be grown that diffract X-rays. The growth of two-dimensional protein arrays has been more successful, with diffraction of electrons at low resolution. Proteins have been fused to green fluorescent protein or maltose-binding protein to facilitate these structural analyses. In addition, ligands for efflux proteins labelled with (13)C or (15)N have been synthesized to implement solid-state NMR studies of the ligand-binding site.

Bacillus subtilis↗

PubMed2006

Diffusion-induced Ramsey narrowing.

Diffusion-induced Ramsey narrowing is characterized and identified as a general phenomenon, in which diffusion of coherence in and out of an interaction region such as a laser beam induces spectral narrowing of the associated resonance line shape. Illustrative experiments and an intuitive analytical model are presented for this spectral narrowing effect, which occurs commonly in optically interrogated atomic systems and may also be relevant to quantum dots and other solid-state spin systems.

Journal Article↗

PubMed2002

Solid-state NMR investigations of peptide-lipid interaction and orientation of a beta-sheet antimicrobial peptide, protegrin.

Protegrin-1 (PG-1) is a broad-spectrum beta-sheet antimicrobial peptide found in porcine leukocytes. The mechanism of action and the orientation of PG-1 in lipid bilayers are here investigated using (2)H, (31)P, (13)C, and (15)N solid-state NMR spectroscopy. (2)H spectra of mechanically aligned and chain-perdeuterated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) bilayers indicate that PG-1 at high concentrations destroys the orientational order of the aligned lamellar bilayer. The conformation of the lipid headgroups in the unoriented region is significantly altered, as seen from the (31)P spectra of POPC and the (2)H spectra of headgroup-deuterated 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine. These observations indicate that PG-1 disrupts microbial membranes by breaking the extended bilayer into smaller disks, where a significant fraction of lipids is located in the edges of the disks with a distribution of orientations. These edges allow the lipid bilayer to bend back on itself as in toroidal pores. Interestingly, this loss of bilayer orientation occurs only in long-chain lipids such as POPC and not in shorter chain lipids such as 1,2-dilauroyl-sn-glycero-3-phosphatidylcholine (DLPC). To understand the mode of binding of PG-1 to the lipid bilayer, we determined the orientation of PG-1 in DLPC bilayers. The (13)CO and (15)N chemical shifts of Val-16 labeled PG-1 indicate that the beta-strand axis is tilted by 55 degrees +/- 5 degrees from the bilayer normal while the normal of the beta-sheet plane is 48 degrees +/- 5 degrees from the bilayer normal. This orientation favors interaction of the hydrophobic backbone of the peptide with the hydrophobic core of the bilayer and positions the cationic Arg side chains to interact with the anionic phosphate groups. This is the first time that the orientation of a disulfide-stabilized beta-sheet membrane peptide has been determined by solid-state NMR.

Amino Acid Sequence↗

PubMed1999

Detection of nonthermal melting by ultrafast X-ray diffraction.

Using ultrafast, time-resolved, 1.54 angstrom x-ray diffraction, thermal and ultrafast nonthermal melting of germanium, involving passage through nonequilibrium extreme states of matter, was observed. Such ultrafast, optical-pump, x-ray diffraction probe measurements provide a way to study many other transient processes in physics, chemistry, and biology, including direct observation of the atomic motion by which many solid-state processes and chemical and biochemical reactions take place.

Biochemistry↗

PubMed1997

Protein stability and conformational rearrangements in lipid bilayers: linear gramicidin, a model system.

The replacement of four tryptophans in gramicidin A by four phenylalanines (gramicidin M) causes no change in the molecular fold of this dimeric peptide in a low dielectric isotropic organic solvent, but the molecular folds are dramatically different in a lipid bilayer environment. The indoles of gramicidin A interact with the anisotropic bilayer environment to induce a change in the molecular fold. The double-helical fold of gramicidin M, as opposed to the single-stranded structure of gramicidin A, is not compatible with ion conductance. Gramicidin A/gramicidin M hybrid structures have also been prepared, and like gramicidin M homodimers, these dimeric hybrids appear to have a double-helical fold, suggesting that a couple of indoles are being buried in the bilayer interstices. To achieve this equilibrium structure (i.e., minimum energy conformation), incubation at 68 degrees C for 2 days is required. Kinetically trapped metastable structures may be more common in lipid bilayers than in an aqueous isotropic environment. Structural characterizations in the bilayers were achieved with solid-state NMR-derived orientational constraints from uniformly aligned lipid bilayer samples, and characterizations in organic solvents were accomplished by solution NMR.

Dimerization↗

PubMed1998

Consideration of conformational transitions and racemization during process development of recombinant glucagon-like peptide-1.

Physicochemical characterization of dry, excipient-free recombinant glucagon-like peptide-1 (rGLP-1) indicates the conformation and purity of the bulk peptide is dependent on the purification scheme and the in-process storage and handling. The recombinant peptide preparations were highly pure and consistent with the expected primary structure and bioactivity. However, variations in solubility were observed for preparations processed by different methods. The differences in solubility were shown to be due to conformational differences induced during purification. A processing scheme was identified to produce rGLP-1 in its native, soluble form, which exhibits FT-IR spectra, consistent with glucagon-like peptide-1 synthesized by solid-state peptide synthesis. rGLP-1 was also found to undergo base-catalyzed amino acid racemization. Racemization can impact the yield and impurity profile of bulk rGLP-1, since the peptide is exposed to alkali during its purification. A combination of enzymatic digestion using leucine aminopeptidase (which cleaves N-terminal L-amino acids >> D-amino acids) and matrix-assisted laser desorption ionization mass spectrometry was used to identify racemization as a degradation pathway. The racemization rate increased with increasing temperature and base concentration, but decreased with increasing peptide concentration. The racemized peptides were shown to be less bioactive than rGLP-1.

Chemical Precipitation↗

PubMed1997

Long-lifetime metal-ligand pH probe.

We describe the synthesis and fluorescence spectral characterization of a pH-sensitive metal-ligand complex, [Ru(deabpy)(bpy)2]2., where deabpy is 4,4'-diethylaminomethyl-2,2'-bipyridine. This metal-ligand complex (MLC) was found to display pH-dependent intensities, emission spectra, and decay times, with the changes centered near the physiological useful pH value of 7.5. The apparent pKa values were not found to be dependent on ionic strength. The compound was found to be useful for lifetime-based sensing by phase-modulation fluorometry. Global analysis of the intensity decays over a range of pH values revealed two decay times of 235 and 380 ns, associated with the protonated and unprotonated forms, respectively. Because of its long decay time, optical pH measurements could be accomplished by phase-modulation fluorometry with a conveniently low modulation frequency of 700 kHz. The lifetime data were obtained with either a amplitude-modulated laser or with an amplitude-modulated blue-light-emitting diode. This pH-sensitive complex also displays a modest spectral shift with change in pH, allowing its use as a wavelength-ratiometric MLC probe. One can imagine lifetime sensors for a variety of blood cations and point-of-care assays based on long-lifetime metal-ligand complexes and simple solid-state light sources and detectors.

2,2'-Dipyridyl↗

PubMedDate not supplied

A new method for characterizing beta-ray ophthalmic applicator sources.

A technique is described which enables one to obtain detailed dose characteristics of 90Sr beta-ray ophthalmic applicators. A radiochromic radiation detector which is a solid-state solution of hexahydroxyethyl pararosaniline cyanide in a nylon polymer (i.e., thin foil), has been used to determine the surface dose rate and dose distribution of these sources. The detectors are rugged, easily handled, have an equivalent response (optical density per unit absorbed dose) to photons and electrons, and produce high-resolution images. They have been found useful for this application due to the high surface dose rates [0.10-1.0 Gy (H2O)/s] and their low sensitivity (approximately 10(4) Gy for an optical density of 1.0). The foils have been evaluated on a He-Ne scanning laser densitometer with a resolution of 0.3 mum. Comparison with NIST (formerly NBS) extrapolation ionization chamber measurements indicates surface dose-rate agreement within 6%. Spectral dosimetric characteristics are presented and discussed.

Beta Particles↗

PubMed1989

Transition dipole orientations in the early photolysis intermediates of rhodopsin.

The linear dichroism spectrum of rhodopsin in sonicated bovine disk membranes was measured 30, 60, 170, and 600 ns after room temperature photolysis with a linearly polarized, 7-ns laser pulse (lambda = 355 or 477 nm). A global exponential fitting procedure based on singular value decomposition was used to fit the linear dichroism data to two exponential processes which differed spectrally from one another and whose lifetimes were 42 +/- 7 ns and 225 +/- 40 ns. These results are interpreted in terms of a sequential model where bathorhodopsin (BATHO, lambda max = 543 nm) decays toward equilibrium with a blue shifted intermediate (BSI, lambda max = 478 nm). BSI then decays to lumirhodopsin (LUMI, lambda max = 492 nm). It has been suggested that two bathorhodopsins decay in parallel to their products. However, a Monte Carlo simulation of partial photolysis of solid-state visual pigment samples shows that one mechanism which creates populations of BATHO having different photolysis rates at 77 K may not be responsible for the two decay rates reported here at room temperature. The angle between the cis band and 498-nm band transition dipoles of rhodopsin is determined to be 38 degrees. The angles between both these transition dipoles and those of the long-wave-length bands of BATHO, BSI, and LUMI are also determined. It is shown that when BATHO is formed its transition dipole moves away from the original cis band transition dipole direction. The transition dipole then moves roughly twice as much towards the original cis band direction when BSI appears. Production of LUMI is associated with return of the transition dipole almost to the original orientation relative to the cis band, but with some displacement normal to the plane which contains the previous motions. The correlation between the lambda max of an intermediate and its transition dipole direction is discussed.

Animals↗

PubMed2001

Infrared and EPR Spectroscopic Studies of 2-C(2)H(2)F and 1-C(2)H(2)F Radicals Isolated in Solid Argon.

2-fluorovinyl radicals were generated in solid argon by solid-state chemical reactions of mobile F atoms with acetylene and its deuterated analogues. Highly resolved EPR spectra of the stabilized radicals CHF&dbond;(*)CH, CDF&dbond;(*)CD, CHF&dbond;(*)CD, and CDF&dbond;(*)CH were obtained for the first time. The observed spectra were assigned to cis-2-fluorovinyl radical based on excellent agreement between the measured (a(F) = 6.50, a(betaH) = 3.86, a(alphaH) = 0.25 mT) hyperfine constants and those calculated using density functional (B3LYP) theory. Analogous experiments carried out using infrared spectroscopy yielded a complete assignment of the vibrational frequencies. An unusual reversible photochemical conversion is observed in which cis-2-fluorovinyl radicals can be partially converted to 1-fluorovinyl radicals by pulsed laser photolysis at 532 nm. Photolysis at 355 nm converts 1-fluorovinyl back to cis-2-fluorovinyl. High-resolution EPR and infrared spectra of 1-fluorovinyl were obtained for the first time. The measured hyperfine constants (a(F) = 13.71, a(H1) = 4.21, a(H2) = 1.16 mT) are in good agreement with calculated values. Copyright 2001 Academic Press.

Journal Article↗

PubMed1992

A new endoscope for ophthalmic microsurgery.

We present an endoscope designed for ophthalmic microsurgery. The handpiece contains a charge-coupled device, a solid-state imager (250,000 pixels), and a probe (either 0.89 or 1.5 mm in diameter), including the light guide. The light source is a halogen lamp. The clear views the instrument provides of the ciliary sulcus and ciliary body behind the iris make it useful in secondary posterior chamber intraocular lens implantation using the ciliary sulcus suturing technique, and in endolaser photocoagulation of the ciliary body in end-stage glaucoma. It also is useful in performing vitrectomy in cases in which visualization is difficult because of corneal opacification or fluid-gas exchange.

Cataract Extraction↗

PubMed2003

Use of confocal microscopy to follow the development of penetrative hyphae during growth of Rhizopus oligosporus in an artificial solid-state fermentation system.

Two methods were compared for determining the concentration of penetrative biomass during growth of Rhizopus oligosporus on an artificial solid substrate consisting of an inert gel and starch as the sole source of carbon and energy. The first method was based on the use of a hand microtome to make sections of approximately 0.2- to 0.4-mm thickness parallel to the substrate surface and the determination of the glucosamine content in each slice. Use of glucosamine measurements to estimate biomass concentrations was shown to be problematic due to the large variations in glucosamine content with mycelial age. The second method was a novel method based on the use of confocal scanning laser microscopy to estimate the fractional volume occupied by the biomass. Although it is not simple to translate fractional volumes into dry weights of hyphae due to the lack of experimentally determined conversion factors, measurement of the fractional volumes in themselves is useful for characterizing fungal penetration into the substrate. Growth of penetrative biomass in the artificial model substrate showed two forms of growth with an indistinct mass in the region close to the substrate surface and a few hyphae penetrating perpendicularly to the surface in regions further away from the substrate surface. The biomass profiles against depth obtained from the confocal microscopy showed two linear regions on log-linear plots, which are possibly related to different oxygen availability at different depths within the substrate. Confocal microscopy has the potential to be a powerful tool in the investigation of fungal growth mechanisms in solid-state fermentation.

Biofilms↗

PubMed2001

A nifedipine coground mixture with sodium deoxycholate. I. Colloidal particle formation and solid-state analysis.

Sodium deoxycholate (DCNa) is a bile salt that forms multimolecular inclusion compounds with a variety of organic substances. In this study, complex formulation of DCNa with nifedipine, a poorly water soluble drug, by grinding was investigated. The coground mixture was prepared with a vibration rod mill, and its solid state was characterized using powder X-ray diffraction, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. A laser diffraction particle size analyzer was also used to determine the particle size distribution curve in solution. When a nifedipine-DCNa (1:2 w/w) mixture coground for 30 min was dispersed into water and a pH 6.8 buffer solution, a semitransparent colloidal solution occurred immediately; 90% of the total particles formed in solution had a diameter less than 600 nm. Both powder X-ray diffraction peaks and DSC endothermic peak of nifedipine crystals were not found for the coground mixture, whereas a new exothermic peak was observed on DSC thermograms. The magnitude of this exothermic peak depended on the weight fraction of DCNa and the grinding time, indicating that nifedipine crystals changed into an amorphous state by complex formation with DCNa during the grinding process. In the FTIR spectrum of the coground mixture, the peaks of aromatic CH out-of-plane bend and dihydropyridine NH stretch of nifedipine were considerably weakened, suggesting that van der Waals interaction may be present between the drug and DCNa molecules. From these results, it is clear that the cogrinding method with DCNa is very useful for the formation of amorphous nifedipine in the solid state and the production of colloidal particles of the drug in solution.

Buffers↗