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PubMed2004

Analysis of PEG 400 and 4000 in urine for gut permeability assessment using solid phase extraction and gel permeation chromatography with refractometric detection.

We developed a treatment of urine samples allowing the analysis of two intestinal permeability markers: polyethylene glycol (PEG) 400 (highly diffusible; basal permeability indicator) and PEG 4000 (poorly diffusible; indicator of an abnormal increase of permeability) by a unique gel permeation chromatography (GPC) with refractometric detection. Urinary PEG were extracted using a mixed-bed resin composed of C2 and C18 layers. Permeability mean values determined in 11 human healthy subjects were 24.20 +/- 9.30% and 0.12 +/- 0.08% for, respectively, PEG 400 and 4000. The percentage of the PEG 4000 permeability value to the one of PEG 400 corresponded to an intestinal permeability index (IPI) of 0.52 +/- 0.35 expressing a low diffusion of this poorly permeability marker.

Adult↗
PubMed2006

Determination of treosulfan in plasma and urine by HPLC with refractometric detection; pharmacokinetic studies in children undergoing myeloablative treatment prior to haematopoietic stem cell transplantation.

A direct and selective HPLC method with refractometric detection was worked out for determination of treosulfan in plasma and urine of children. Before injection onto reverse phase column plasma samples with treosulfan and barbital (I.S.) were clarified using filtration. The mobile phase was composed of phosphate buffer, pH 5 and acetonitrile. The linear range of the standard curve of treosulfan spanned concentrations of 10.0-2000.0 microg/ml and 50.0-10000.0 microg/ml in plasma and urine, respectively, and covered the levels found in biological fluids after infusion of the drug. The limit of detection amounted to 5 microg/ml for plasma and 25 microg/ml for urine. Intra- and inter-day precision and accuracy of the measurement fulfilled analytical criteria accepted in pharmacokinetic studies. Recovery of treosulfan as well as stability in biological fluids was also calculated. The validated method was successfully applied in pharmacokinetic studies of treosulfan administered to children prior to haematopoietic stem cell transplantation. Differences between pharmacokinetics of treosulfan in children and adults were also studied.

Adolescent↗
PubMed2004

Colloid-polymer mixtures in solution with refractive index matched acrylate colloids.

Colloid-polymer (CP) mixtures extend between two limiting cases, the colloid limit with the polymer coil size small compared to the colloid radius Rcol and the protein limit with the colloidal particles much smaller in size than the radius of gyration of the polymer chains Rg. In the present work, model systems are developed for the protein limit. The colloid-solvent pairs are optimized in terms of their isorefractivity in order to facilitate the characterization of large polystyrene chains in suspensions of small colloids. The degree of isorefractivity of colloidal particles was successfully evaluated in terms of a reduced scattering intensity. Two polystyrene samples with radii of gyration of Rg = 96 nm and Rg = 78 nm, respectively, are used. The radii of the colloidal particles are close to Rcol = 12 nm, leading to size ratios of Rg/Rcol = 8 and Rg/Rcol = 6.5. Four colloid solvent systems were found to be suitable for polymer characterization by light scattering, one based on silica particles and three systems with acrylate particles. The present investigation is focused on the three acrylate systems: poly(methyl methacrylate) in ethyl benzoate (ETB) at 7 degrees C, poly(ethyl methacrylate) in toluene at 7 degrees C and poly(ethyl methacrylate) in ETB at 40 degrees C. Characterization of PS chains is for the first time performed in colloid concentrations up to 2.5% by weight. In all cases, the size and shape of the polymer chains remain unchanged. A slight mismatch of the colloid scattering or a limited colloid solubility prevented investigation of PS chains at higher colloid concentration.

Acrylates↗
PubMed2005

Enzymatic degradation of model cellulose films.

Enzymatic degradation of model cellulose films prepared by a spin-coating technique was investigated by ellipsometry. The cellulose films were prior to degradation characterized by ellipsometry, contact angle measurements, ESCA (electron spectroscopy for chemical analysis) and AFM (atomic force microscopy). At enzyme addition to preformed cellulose films an initial adsorption was observed, which was followed by a total interfacial mass decrease due to enzymatic degradation of the cellulose films. The degradation rate was found to be constant during an extended time of hours, whereafter the degradation leveled off. In parallel to the decreased interfacial mass, the cellulose degradation resulted in a thinner and more dilute interfacial film. At long degradation times, however, there was an expansion of the cellulose film. The enzyme concentration affected the degradation rate significantly, with a faster degradation at a higher enzyme concentration. The effects of pH, temperature, ionic strength and stirring rate in the cuvette were also investigated.

Adsorption↗
PubMed2006

Protein diffusion in agarose hydrogel in situ measured by improved refractive index method.

The accurate knowledge of the diffusion behavior of protein within biomimetic hydrogel matrix at body temperature has a great implication for the design of efficient controlled release protein-base drug delivery devices. In this paper, we improved our previous in situ refractive index method with great temperature-controlled capability. For the first time, this newly improved method was employed to study the diffusion of protein (bovine serum albumin (BSA) and lysozyme) in agarose hydrogel at body temperature (37 degrees C). The change of the gel refractive index caused by the change of the diffusing protein concentration within the gel during the diffusion process enables the effective diffusion coefficients of protein to be estimated. The diffusion coefficients of proteins decrease with the increase of the concentration of agarose and the solute molecular size. At the considered range of agarose concentration (0.5-3.0 wt.%), the diffusion coefficients range from 4.98 to 8.21 x 10(-7) cm(2)/s for BSA and 1.15 to 1.56 x 10(-6) cm(2)/s for lysozyme, respectively. Temperature dependence of diffusivity of BSA in agarose hydrogel was also investigated. Furthermore, the retardance effect of polymer volume fraction on the diffusivity of both BSA and lysozyme in agarose hydrogels was analyzed with three models, Amsden's, Clauge and Philips', and Ogsten's model.

Algorithms↗
PubMed2005

Imaging quality of intraocular lenses.

PURPOSE: To compare the imaging quality of several commercially available intraocular lenses (IOLs) using the modulation transfer function (MTF) method according to the requirements of the International Standard European Industrial Norm/International Organization for Standardization 11979. SETTING: Universitat für Technik der Informationsverarbeitung, Universität Karlsruhe, Karlsruhe and Universitäts Augenklinik, Ulm, Ulm, Germany. METHODS: Two refractive powers (+13 diopter [D] and +26 D) of each IOL type were tested. The imaging quality of all tested IOLs was measured before the injection test and in 5-minute intervals after the injection for 40 minutes. The measurement data were analyzed according to 2 quality criteria, Strehl ratio and the ISO condition. For analysis of the type of optical design, SEM images of the central cross section were taken of each IOL. Basic terms in optics such as MTF, resolution, and optical aberration are introduced, and their relevance for ophthalmology is discussed in detail. This paper represents an extensive study comparing the imaging quality of various IOLs including the comparison of measurements before and after injection through a cartridge as used for state-of-the-art implantation techniques. All measurements were performed using an MTF measurement system using a 546 nm optimized laser source and an effective aperture of 3.0 mm on the IOL according to ISO standard. An ISO standard eye model using an artificial cornea (spherical design) and a watery solution to simulate in vivo conditions was used. RESULTS: All IOLs apart from 1 +26 D lens complied with ISO standard requirements. However, the imaging quality varied up to 49% depending on the optical design and the manufacturing quality. CONCLUSION: When the methods and materials recommended by the manufacturer for IOL injection through a cartridge were used, no long-term effect on the imaging quality of the IOLs was observed. However, the basic imaging quality of different designs and different manufacturers varied significantly (up to 50% at +26 D) IOLs and should be considered when choosing an IOL.

Contrast Sensitivity↗
PubMed2006

Corneal elevation indices in normal and keratoconic eyes.

PURPOSE: To determine an index that distinguishes keratoconus and keratoconus-suspect eyes from normal eyes with Orbscan (Bausch & Lomb) corneal elevation maps. SETTING: Department of Ophthalmology, Tan Tock Seng Hospital, Singapore, and iLaser Centre, Island Hospital, Penang, Malaysia. METHODS: In this initial phase of this multicenter nonrandomized retrospective study, 1 eye of 166 normal subjects, 15 keratoconus patients, and 11 keratoconus suspects was examined at 1 clinic. The anterior best-fit sphere (BFS), posterior BFS, anterior elevation, posterior elevation, and maximum and minimum keratometries were analyzed. Two indices with the highest sensitivity and specificity classifying these conditions were identified using receiver operating characteristic curves. These 2 indices were evaluated in a subsequent validation study using 1 eye of 221 normal subjects, 43 keratoconus patients, and 23 keratoconus suspects from another clinic. RESULTS: The anterior elevation and anterior elevation ratio (anterior elevation ratio = anterior elevation/anterior BFS) best classified the different groups. An anterior elevation ratio of 0.5122 mm or less had 99% sensitivity and 95.2% specificity while a ratio 16.5 mum or less had 80.1% sensitivity and 80.8% specificity in discriminating normal eyes from keratoconus and keratoconus suspects. The results were similar in the validation study. In addition, these anterior elevation and anterior elevation ratio cutoff values had high sensitivity and specificity in identifying keratoconus suspects from normal eyes in the validation study. CONCLUSION: Anterior corneal elevation parameters are clinically relevant measures for detecting keratoconus and suspected keratoconus eyes.

Adult↗
PubMed2006

Comparative assessment of contrast with spherical and aspherical intraocular lenses.

PURPOSE: To analyze the contrast differences between spherical and aspherical intraocular lenses (IOLs) using polychromatic modulation transfer function (MTF) computations. SETTING: Oto-Neuro-Ophthalmological Department, Eye Institute, University of Florence, Florence, Italy. METHODS: A questionnaire evaluating patients' subjective perception of halos, glare, and contrast sensitivity in different lighting conditions was administered to 2 groups of pseudophakic patients. In the first group, a spherical IOL (AR40e, AMO) had been implanted and in the second group, an aspherical IOL (Tecnis Z9000, AMO). The optical performances of the 2 IOLs were analyzed with ray-tracing software. The overall MTF of an electro-optical system and the polychromatic MTF were evaluated. RESULTS: The questionnaire analysis, confirmed with ray-tracing analysis, showed that patients with an aspherical IOL do not present with all the expected advantages. Even if there are differences in the monochromatic MTF curve computation, there is not a significant difference in the results obtained in the polychromatic MTF computation. CONCLUSION: The aspherical IOL anterior surface resolved the spherical aberration problem, but the longitudinal chromatic aberration must still be resolved.

Aged↗
PubMed2006

Diffraction-like phenomena in a periodic magnetization distribution at 1.5 T using the distant dipolar field (DDF).

In the CRAZED experiment (COSY revamped by asymmetric Z-gradient echo detection, Warren et al.), a spatially anisotropic magnetization distribution is created by application of a magnetic field gradient (strength G, duration tau) which in turn generates a response called the distant dipolar field (DDF). The DDF is a source of intermolecular multiple-quantum coherences (iMQC) which contain information on the distance d=pi/(gammaGtau) between pairs of dipolar-coupled spins. Diffraction-like phenomena may result for periodically structured samples. In this study, we report the observation of diffraction owing to the DDF at 1.5 T using a clinical whole-body tomograph. Based on the semi-classical treatment of the problem by Robyr and Bowtell, diffraction conditions were obtained for a CRAZED-type pulse sequence that selects iMQC of order N. The predicted distinct difference in N=2 and N not equal2 coherences, i.e., a dominant continuous course as a function of tau (N=2) and prominent diffraction peaks otherwise, could be verified in CRAZED experiments in a periodically structured sample selecting coherence orders N=2 and N=3. The diffractive signal component contains information on the geometric structure of the sample. Applications of this technique may permit the detection of changes in composition and geometry of periodic structures.

Computer Simulation↗
PubMed2004

A selective and sensitive assay of berberine using total internal reflected resonance light scattering technique with fluorescein at the water/1,2-dichloroethane interface.

An assay of berberine (BE) was developed with good selectivity and sensitivity based on the total internal reflected resonance light scattering (TIR-RLS) signals from water/1,2-dichloroethane (H(2)O/DCE) interface. Under optimal conditions, amphiphilic complex formed by BE and fluorescein (Flu) was adsorbed to H(2)O/DCE interface, resulting in good separation of BE from the coexisting foreign substances in aqueous phase and significant enrichment of BE at the interface. This enriched species at the interface was found corresponding to enhanced TIR-RLS signals located at 370.0 nm. Proportional relationships were established between the enhanced TIR-RLS intensity and the BE in the range of 3.2 x 10(-9) to 3.2 x 10(-6) mol l(-1) with the limit of detections (3sigma) being 1.3 ng ml(-1). Favorable sensitivity of TIR-RLS technique was demonstrated superior to that of high-performance liquid-chromatography (HPLC) method. The feasibility of the proposed technique was validated by the satisfactory performance of intra-assay and inter-assay BE in tablets.

Berberine↗
PubMed2005

Determination of surface-bound hydroxypropylcellulose (HPC) on drug particles in colloidal dispersions using size exclusion chromatography: a comparison of ELS and RI detection.

Evaporative light scattering (ELS) and refractive index (RI) detection methods were evaluated for the determination of surface-bound hydroxypropylcellulose (HPC) on drug particles in colloidal dispersions. Size exclusion chromatography (SEC) was used to separate HPC from other components of the dispersions. The instrumental parameters of the ELS detector were optimized to obtain maximum peak intensity, adequate peak shape and minimal baseline noise by varying the mobile phase flow rate, nebulizer temperature, and evaporation temperature. The chromatographic method was validated using both detectors. The ELS detector response exhibited second order polynomial and linear double logarithmic correlation with concentration over a 10-300% range while the RI response was linear. The double logarithmic correlation simplified the calculation compared to using the polynomial fit, and it provided more accurate results compared to the linear fit approach. Total HPC was obtained by solubilizing all components of the dispersion and analyzing for HPC. Non-bound HPC was obtained by ultracentrifuging the dispersion and analyzing the supernatant for HPC concentration. Analysis for total- and non-bound HPC in a representative colloidal dispersion gave method precisions with R.S.D.s of 2.5 and 2.2% for ELS, and 4.5 and 2.4% for RI (n=4). HPC bound to the surface of the drug particles was determined by difference: % bound HPC=100%-% non-bound HPC. Resultant % bound HPC values ranged from 22.1 to 25.4% of available HPC. Both ELS and RI are satisfactory detection techniques for HPC quantitation and for determination of the proportion of HPC bound to drug colloid particles, and the assay results are comparable.

Algorithms↗
PubMed2004

Propagation of electromagnetic radiation in mitochondria?

Mitochondria are the main source of ultra-weak chemiluminescence generated by reactive oxygen species, which are continuously formed during the mitochondrial oxidative metabolism. Vertebrate cells show typically filamentous mitochondria associated with the microtubules of the cytoskeleton, forming together a continuous network (mitochondrial reticulum). The refractive index of both mitochondria and microtubules is higher than the surrounding cytoplasm, which results that the mitochondrial reticulum can act as an optical waveguide, i.e. electromagnetic radiation can propagate within the network. A detailed analysis of the inner structure of mitochondria shows, that they can be optically modelled as a multi-layer system with alternating indices of refraction. The parameters of this multi-layer system are dependent on the physiologic state of the mitochondria. The effect of the multi-layer system on electromagnetic radiation propagating along the mitochondrial reticulum is analysed by the transfer-matrix method. If induced light emission could take place in mitochondria, the multi-layer system could lead to lasing action like it has been realized in technical distributed feedback laser. Based on former reports about the influence of external illumination on the physiology of mitochondria it is speculated whether there exists some kind of long-range interaction between individual mitochondria mediated by electromagnetic radiation.

Animals↗
PubMed2006

Computational determination of refractive index distribution in the crystalline cones of the compound eye of Antarctic krill (Euphausia superba).

In order to understand how a compound eye channels light to the retina and forms an image, one needs to know the refractive index distribution in the crystalline cones. Direct measurements of the refractive indices require sections of fresh, unfixed tissue and the use of an interference microscope, but frequently neither is available. Using the eye of the Antarctic krill Euphausia superba (the main food of baleen whales) we developed a computational method to predict a likely refractive index distribution non-invasively from sections of fixed material without the need of an interference microscope. We used a computer model of the eye and calculated the most realistic spatial distribution of the refractive index gradient in the crystalline cone that would enable the eye to produce a sharp image on the retina. The animals are known to see well and on the basis of our computations we predict that for the eyes of the adult a maximum refractive index of 1.45-1.50 in the centre of the cone yields a better angular sensitivity and light absorption in a target receptor of the retina than if N(max) were 1.55. In juveniles with a narrower spatial separation between dioptric structures and retina, however, an N(max) of 1.50-1.55 gives a superior result. Our method to determine the most likely refractive index distribution in the cone without the need of fresh material and an interference microscope could be useful in the study of other invertebrate eyes that are known to possess good resolving power, but for a variety of reasons are not suitable for or will not permit direct refractive index measurements of their dioptric tissues to be taken.

Animals↗
PubMed2003

Plasmon-waveguide resonance spectroscopy: a new tool for investigating signal transduction by G-protein coupled receptors.

Plasmon-waveguide resonance (PWR) spectroscopy provides a highly sensitive method for characterizing the kinetics, affinities and conformational changes involved in ligand binding to G-protein coupled receptors, without the need for radioactive or other labeling strategies. In the case of the cloned delta-opioid receptor from human brain incorporated into a lipid bilayer, we have shown that affinities determined in this way are consistent with those measured by standard binding procedures using membranes or whole cells containing the receptors, and that the spectral and kinetic properties of the binding processes allow facile distinction between agonist, inverse agonist, and antagonist ligands. We have also shown by direct measurements that G-protein binding affinities and the ability to undergo GTP/GDP exchange are dependent upon the type of ligand pre-bound to the receptor. PWR spectroscopy thus provides a powerful new approach to investigating signal transduction in biological membrane systems.

Humans↗
PubMed2004

Amino acid contents along the visual and equatorial axes of a pig lens by Raman spectroscopy.

Using near infrared Raman microspectroscopy with laser light of 830 nm, the distribution of amino acids along the visual and equatorial axes of a normal pig lens was studied. The classification of pig lens Raman spectra in these axes was performed using principal component analysis and linear discriminant analysis. The analysis of the scattered light selectively collected from point to point, along the visual axis, indicated that the tyrosine and tryptophan increases and then, at approximately 4 mm position, decreases. Moreover, in the equatorial plane, the nuclear part has the highest concentration of these amino acids. However, the phenylalanine content increases from anterior to posterior cortex of the lens as long as in the equatorial axis it slightly increases and then at approximately 2-2.3 mm position, decreases. The changes in amino acid conformation along the visual axis, similarly to the changes in protein conformation, may explain the refractive gradient of the lens.

Amino Acids↗
PubMed2006

Optical constants, dielectric constants, molar absorption coefficients, molar polarizability, vibrational assignment and transition moments of liquid iodobenzene between 4000 and 400 cm(-1) at 25 degrees C.

This paper reports the complex refractive index, molar absorption coefficient and imaginary molar polarizability spectra of liquid iodobenzene at 25 degrees C. The imaginary molar polarizability spectrum was fitted with 184 classical damped harmonic bands to determine the integrated intensity of the individual transitions. The standard deviation of the fitted spectrum from the experimental spectrum is 0.024 cm(3) mol(-1), and the R(2) value of the fit is 0.9968 indicating that the fitted spectrum is an accurate representation of the experimental spectrum. The dipole moment derivatives with respect to the normal coordinates and transition moments were determined for 26 of the 30 fundamentals. The total intensities of the in-plane and out-of-plane fundamentals were compared to benzene and other monosubstituted benzene derivatives using the F-sum rule. It was found that the total intensity of the out-of-plane fundamentals is essentially the same for the different compounds while the total intensities for the in-plane fundamentals varies according to the electronegativities of the substituents.

Iodobenzenes↗
PubMed2006

Multistate/multifunctional switches based on photochromic Schiff base.

The salicylidene Schiff base derivative, namely, N-salicylidene-(S)-alpha-naphthylethylamine (SNEA) has been synthesized to study the characterization of multistate/multifunctional switches. Upon the stimulations of optical inputs (UV light and visible light) and chemical inputs (pH and Zn(2+)), SNEA undergoes reversible photochromism, deprotonation and complexation reactions. In this case, four chemical species are involved. These interconversions of SNEA between four states have been systematically investigated by the absorption and the emission spectra. Spectroscopic studies indicate that the photochromic switch, pH switch and fluorescent switch can be realized using the single molecular entity of SNEA.

Cations, Divalent↗