Biomedical subjects

Ralf Moritz

Publications and source records attributed to Ralf Moritz.

5 recordsLinked to original sources

PubMed2005

Structure elucidation of degradation products of the antibiotic amoxicillin with ion trap MS(n) and accurate mass determination by ESI TOF.

Today, it is necessary to identify relevant compounds appearing in discovery and development of new drug substances in the pharmaceutical industry. For that purpose, the measurement of accurate molecular mass and empirical formula calculation is very important for structure elucidation in addition to other available analytical methods. In this work, the identification and confirmation of degradation products in a finished dosage form of the antibiotic drug amoxicillin obtained under stress conditions will be demonstrated. Structure elucidation is performed utilizing liquid chromatography (LC) ion trap MS/MS and MS3 together with accurate mass measurement of the molecular ions and of the collision induced dissociation (CID) fragments by liquid chromatography electro spray ionization time-of-flight mass spectrometry (LC/ESI-TOF).

Algorithms↗

PubMed2004

Instrumentation for advanced microseparations in pharmaceutical analysis and proteomics.

Small-volume chromatographic columns are only able to generate narrow peaks when flow rates, injection volume and instrument components, such as detector, connecting tubing and fittings, are matched to the peak dispersion from the column. Criteria for the proper design of chromatographic instrumentation are therefore derived from a general model on total dispersion. The performance of such a system is then experimentally evaluated from applications run on narrow-bore, small-volume columns. In order to achieve flow rates that match the dimensions of such columns, a new concept for electronic flow control (EFC) is introduced. A theoretical optimization of column efficiency and throughput is discussed and the results verified with practical examples on short, narrow-bore columns packed with small, porous and superficially porous particles. For complex sample mixtures, the concept of peak capacity is introduced and applied to orthogonal separation principles in multiple chromatographic dimensions through column switching techniques.

Chromatography, High Pressure Liquid↗

PubMed2003

Mass-based fraction collection of crude synthetic peptides in analytical and preparative scale.

Synthetic peptides become more and more important as drug candidates in the treatment of a variety of diseases. A particular therapeutic focus for synthetic peptides is cancer treatment.1,2 In order to keep pace with the growing number of newly synthesized peptides, peptide purification should not represent the bottleneck in the drug discovery process. Since the target masses of synthetic peptides are well known, mass-based fraction collection represents an efficient technique for their purification. In contrast to fraction triggering with less specific detectors, employing a mass selective detector leads in each run only to the purification of the target mass. Consequently, it is not necessary to pick the compound of interest out of a series of redundant fractions. In this article we demonstrate mass-based purification of a variety of crude synthetic peptides by reversed phase high-performance liquid chromatography. The peptides were in the mass range from less than 1 kDa to more than 10 kDa and covered a pI range from 4 to 13. We particularly focused on some technical aspects of the system that were prerequisite for reliable compound purification with high recoveries.

Muramidase↗

PubMed2002

Impact of four (13)C-proline isotope labels on the infrared spectra of ribonuclease T1.

Ribonuclease T1 was biosynthesized, with all four prolines (13)C-labeled in the peptide C[double bond]O bond, using a proline auxotrophic yeast strain of Saccharomyces cerevisiae. The (13)C- and (12)C-proline isotopomers of ribonuclease T1 were investigated by infrared spectroscopy in the thermally unfolded and natively folded state at 80 and 20 degrees C, respectively. In the thermally unfolded state, both proteins established almost indistinguishable spectral features in the secondary structure sensitive amide I region. In contrast, the spectra measured at 20 degrees C revealed substantial qualitative and quantitative differences, though parallel analysis by circular dichroism suggested identical native folds for both isotopomers. Major spectral differences in the infrared spectra were detected at 1626 and 1679 cm(-1), which are diagnostic marker bands for antiparallel beta-sheets in ribonuclease T1 and at 1645 cm(-1), a region that is characteristic for the infrared absorption of irregular structures. Starting with the known three-dimensional structure of ribonuclease T1, the observed effects of the isotope labeling are discussed on the basis of transition dipole coupling between the (12)C[double bond]O and (13)C[double bond]O groups. The experimental results were confirmed by transition dipole coupling calculations of the amide I manifold of the labeled and unlabeled variant.

Aspergillus oryzae↗

PubMed2002

Time-resolved FTIR difference spectroscopy as tool for investigating refolding reactions of ribonuclease T1 synchronized with trans --> cis prolyl isomerization.

The structurally well-characterized enzyme ribonuclease T1 was used as a model protein to further evaluate time-resolved Fourier transform IR difference spectroscopy in conjunction with temperature-jump techniques as a useful detection technique for protein folding studies. Compared to the wild-type protein, it was confirmed that the lack of one cis-proline bond at position 55 of the S54G/P55N variant is sufficient to significantly simplify and accelerate the refolding process. This result was sustained by the characterization of the early refolding events that occurred within the experimental dead time.

Kinetics↗