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Biomedical subjects

F Hillenkamp

Publications and source records attributed to F Hillenkamp.

At least 55 records · Page 3Linked to original sources
PubMed1994

Oligosaccharides from human milk as revealed by matrix-assisted laser desorption/ionization mass spectrometry.

In this study neutral and acidic oligosaccharide fractions prepared from human milk have been investigated using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The fraction of neutral oligosaccharides was separated by gel permeation chromatography (GPC) and the resulting subfractions were analyzed by MALDI-MS using the positive ion mode. Several low-molecular-weight glycans (degree of polymerization up to 13) were observed whose structures have already been elucidated. In addition, a variety of so far unknown large-sized carbohydrates was detected whose molecular weights range from M(r) 2242 to 8000. The large-sized glycans which possess a low abundance appear to be composed of both lactosamine and fucose residues attached to the lactose unit at the reducing end of the sugar chains with a highly variable stochiometry. Following subfractionation by GPC, acidic (i.e., containing sialic acid) glycans were analyzed by MALDI-MS using both positive and negative ion mode. Because of the inferior stability of acidic glycans, various matrices were applied and compared with respect to signal intensity, resolution, and analyte stability.

Chromatography, Gel↗
PubMed1993

Microphotocoagulation: selective effects of repetitive short laser pulses.

Repetitive exposure to short laser pulses is shown to cause selective damage to absorbing structures (cells, organelles, or enzymes) with pulse energies below the threshold energy for single-pulse damage. Directly adjacent structures are spared in vivo. Additivity of (presumably nonphotochemical) subthreshold effects is demonstrated. Selective damage to the retinal pigment epithelium with sparing of the neural retina is shown (514 nm, 5 microseconds, 1-500 pulses at 500 Hz, 2- to 10-microJ pulse energy). A melanin granule model has been developed and applied to the experimental situation. Histological results as well as the basic mechanism for these effects are discussed.

Animals↗
PubMed1993

Ion stability of nucleic acids in infrared matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) with infrared laser light of a wavelength of 2.94 microns has been used for the analysis of nucleic acids. Spectra of oligodeoxynucleotides up to 26 nucleotides, oligothymidylic acids up to 100 nucleotides as well as different synthetic RNA oligomers and RNA transcripts up to 104 nucleotides are presented. A main problem in the analysis of oligodeoxynucleotides was found to be related to the loss of bases. The stability of oligothymidylic acids as opposed to oligodeoxynucleotides containing all four bases indicates that the loss of bases is correlated with A, C and G protonation which decreases the stability of the N-glycosidic bond. Experiments indicate that the breakage of the N-glycosidic bond probably occurs during the desorption process due to proton transfer from the phosphodiester groups to the ionizable bases. RNA displayed a significantly higher stability in MALDI-MS due to the presence of a 2'-OH group. Consequently, signals of RNA transcripts with a length of up to 142 nucleotides could be detected by MALDI-MS. Technical details of the method, including the distribution of positive counterions on the phosphodiester backbone, the upper mass limit and mass accuracy are discussed along with a number of potential analytical applications.

Base Sequence↗
PubMed1993

Matrix-assisted ultraviolet laser desorption/ionization mass spectrometry applied to multiple forms of lipases.

Matrix-assisted ultraviolet laser desorption/ionization mass spectrometry was used to investigate heterogeneous patterns and molecular masses of microbial lipases from Penicillium camembertii, Geotrichum candidum, and Pseudomonas sp. Mass spectral peaks of the native, glycosylated lipases from P. camembertii and G. candidum were broader than those of the corresponding deglycosylated enzymes, indicative of heterogeneous glycosylations. The broader peaks in the mass spectra were caused by an overlapping of unresolved peaks, derived from single glycoprotein species. Molecular masses determined for the deglycosylated proteins were in excellent agreement with those deduced from amino acid composition and sequence data, whereas with conventional biochemical methods (gelfiltration, sodium dodecyl sulfate-polyacrylamide gel electrophoresis) only very rough estimations of molecular masses were possible. By mass spectrometric analysis of the four fractions of chromatographically separated P. camembertii lipase molecular masses of 29,990, 34,030, 31,990, and 32,140 Da were found before and 29,960, 29,980, 29,990 and 30,010 Da, respectively, after deglycosylation. Thus from the four native fractions of P. camembertii lipase three were glycoproteins. G. candidum lipase showed an average molecular mass of 63,500 Da for the heterogeneously deglycosylated native form and a molecular mass of 59,650 Da for the deglycosylated enzyme. For the Pseudomonas lipase, which could only be isolated with lipids firmly attached, a molecular mass of 32,890 Da was determined, in close agreement with that derived from the cDNA sequence.

Bacterial Proteins↗
PubMed1992

Matrix-assisted laser desorption/ionization mass spectrometry of nucleic acids with wavelengths in the ultraviolet and infrared.

A number of different matrices have been tested and compared for ultraviolet and infrared (UV and IR) matrix-assisted laser desorption/ionization (MALDI) of oligodeoxyribonucleotides and mixtures thereof, as well as ribonucleic acids (tRNA from yeast and rRNA from E. coli). A new technique for removing alkali cations from nucleic acid samples during sample preparation on the sample support is demonstrated. The amount of oligonucleotide sample consumed during a typical measurement in IR-MALDI-MS was determined.

Angiotensin II↗
PubMed1989

Laser radiation tissue interaction.

Mechanisms of interaction between laser radiation and biological tissue are reviewed. Scattering and absorption determine the penetration of radiation into tissue; the heterogeneity of tissues prevents exact model calculations of in-depth energy deposition. The high irradiances, achievable with pulsed lasers, can induce nonlinear absorption, optical breakdown and plasma formation in tissues. Heat conduction and heat convection as well as the build-up and propagation of pressure transients damage tissue outside of the absorbing volume. The limitations to the validity of the first-order rate processes as a description for thermal tissue coagulation and the possibilities for novel photochemistry are discussed.

Animals↗
PubMed1985

Excimer laser ablation of the cornea and lens. Experimental studies.

The pulsed ultraviolet excimer laser has been used to produce tissue ablation with a high degree of precision and with minimal thermal damage to adjacent structures. In comparative studies of excimer laser ablation of the cornea and crystalline lens using 193 nm and 248 nm radiation, threshold fluence for corneal and lens ablation was higher at 248 nm than at 193 nm. Ablation of corneal stroma at 193 nm produced the most precise cuts. When examined by transmission electron microscopy, a narrow zone of damaged tissue (0.1 to 0.3 micron) was seen immediately adjacent to the tissue removed by the laser. Ablation with 248 nm radiation produced incisions with ragged edges and with a wider and more severe zone of damage in adjacent stroma. Ultraviolet spectral transmission studies of the corneal stroma showed that absorption is 10 times greater at 193 nm than at 248 nm. The excimer laser was effective in producing well controlled ablation of the crystalline lens in vitro, with effects parallel to those seen in the cornea.

Animals↗
PubMed1985

Theoretical investigations of laser thermal retinal injury.

A thermal damage model including heat conduction for retinal lesions is described to explain thermal threshold damage and compare it to experimental values in the regime of 1 ms to 300 ms. With the aid of these model calculations unspecific thermal damage (denaturation of proteins) could be separated from thermally induced damage to the photoreceptors. Furthermore, the thermal model allows an extrapolation to hazards to the fundus from intense light irradiation that have not been investigated experimentally.

Animals↗
PubMed1983

Experimental studies of laser thermal retinal injury.

In damage tests conducted on rabbit and monkey eyes, the threshold values for retinal damage resulting from different laser radiation were determined. The reproduction of the "worst-case" situation was ensured by the test apparatus. All physical parameters, such as power/energy, exposure time, and retinal spot, were carefully controlled. Probit analysis showed a very precise determination of the threshold values based on ophthalmoscopical visibility. The attempt of a simple physical interpretation of the thresholds leads to contradictions in major points, so a detailed calculation of damage functions and thermal model calculations are necessary.

Animals↗
PubMed1980

Laser-micro-mass analysis (LAMMA) of metallic and organic ions in medical samples.

Laser induced mass spectra of different ions emerging from thin sections or films of biological or organic matrices are discussed by the example of Calcium, Aluminium and Diethyl (2) hexylphthalate. Since the energy transfer of laser light induces not only certain ionization processes, but causes phase transitions and enables interactions between neighbouring atoms and molecules, the ion representative for a certain substance sometimes has to be looked for carefully. Inorganic ions not bound to organic molecules belonging to the matrix are easily detected. The same kind of bound ions can be formed by cleaving the bond to the organic molecule by the laser irradiation, but a certain amount remains with some fragments. Fragments of organic molecules are possibly formed in different ways within different matrices. The detection of the substances mentioned above can be applied to the analysis of skin of patients on chronic dialysis whose metabolism and therapeutic treatment give rise to changes in the content of several substances in different tissues.

Aluminum↗
PubMed1979

The laser microprobe mass analyzer (LAMMA): a new instrument for biomedical microprobe analysis.

After a short review of the general state of the art of microprobe analysis, recent achievements of a new system, the laser microprobe mass analyzer (LAMMA) are presented. The LAMMA-instrument, which was primarily developed for biomedical purposes, has recently been used on a large variety of specimen, biological, technical, organic and inorganic in nature. Detection limits, mass resolution and reproducibility were improved such that for many elements measurements could be extended down to the subppm range. For bulk analysis, a separate version of the LAMMA-instrument is under development. The examples of LAMMA-applications given in this paper include muscle tissue (physiological cations), uterine tissue (Fe), retina tissues (Na, Mgmg, K, Ca and Ba!), airborne particles (Pb, Fe, Al, Ti, Mn, Ca, Zn), cerebral tissue (Li), and pure cristalline organic materials.

Animals↗
PubMed1979

Minimal spot size on the retina formed by the optical system of the eye.

A knowledge of the quality of the ocular optical system is of primary importance in light- and laser-photocoagulation of the fundus. A study was therefore undertaken to determine the minimal spot size of a Helium-Neon laser focused on the retina of rabbits: freshly enucleated eyes were carefully mounted in a specially designed eye holder. A small hole was then trepanized through the sclera and neural retina in the macular region. A minimal spot was produced on the retina and the spot size was measured by scanning the intensity distribution of an enlarged image. It was shown that a diffraction limited spot size can be obtained under certain circumstances. The light scattering out of the focus, however, is about fify percent.

Animals↗
PubMed1979

Laser microprobe mass analysis: achievements and aspects.

After a short review of the general state of the art of laser microprobe analysis, recent achievements of the laser microprobe mass analyzer (LAMMA) are presented. The Lamma-instrument, which was primarily developed for biomedical purposes has been recently used on a large variety of specimens: biological, technical, organic and inorganic in nature. Detection limits, mass resolution and reproducibility have been improved so that for many elements measurements can be extended down to the subppm range. For bulk analysis a separate version of the LAMMA-instrument has been developed. The examples of LAMMA-applications given in this paper include muscle tissue (physiological cations), uterine tissue (Fe), retina tissues (Na, Mg, K, Ca and Ba), airborne particles (Pb, Fe, Al, Ti, Mn, Ca, Zn), cerebral tissue (Li), a fluorinated drug, pure crystalline organic materials (including nicotinic acid) and a selection of non biological materials (for instance thin films).

Aerosols↗