Spontaneous knotting-from oligoamide threads to trefoil knots.
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Amides↗
Biomedical subjects
Wolfgang Lindner
Publications and source records attributed to Wolfgang Lindner.
Oxygenation and ventilation in spontaneously breathing very preterm infants with nasopharyngeal CPAP in the delivery room.
AIM: To provide data on ventilation, oxygenation and acid-base state from birth to 48 h in very preterm infants treated with lung recruitment manoeuvre and nasopharyngeal continuous positive airway pressure in the delivery room. METHODS: Subjects of this prospective observational cohort study were 48 of 61 infants enrolled in a randomised controlled trial to test two lung recruitment manoeuvres after birth. The infants had received an arterial line in the delivery room. The outcome measures were data on oxygenation, ventilation and acid-base state during spontaneous breathing. RESULTS: Data are presented as (n [%]; median [minimum-maximum]). 22 of 48 (46%) infants (gestational age, 26.4 [25.0-28.9] weeks; birth weight 870 [540-1310] g) were never intubated during the study. The FiO(2) of these infants was low (0.4 [0.21-0.45] at 45 min and 0.21 [0.21-0.5] at 48 h). PCO(2) reached its maximum at 24 (11-44) min (8 [6.4-10.8] kPa) and decreased below 6.7 kPa (median) within 3 h. The incidence of intracranial haemorrhage/periventricular leukomalacia did not increase with hypercapnia (pCO(2) > 8 kPa). CONCLUSION: A transient period of hypercapnia after birth may occur in spontaneously breathing very preterm infants supported with nasopharyngeal continuous positive airway pressure in the delivery room. The incidence of cerebral damage was not increased in infants with hypercapnia.
Acid-Base Equilibrium↗
Comprehensive analysis of branched aliphatic D-amino acids in mammals using an integrated multi-loop two-dimensional column-switching high-performance liquid chromatographic system combining reversed-phase and enantioselective columns.
A validated two-dimensional HPLC method for the comprehensive analysis of small quantities of branched aliphatic D-amino acids in the presence of large amounts of their L-congeners in mammalian tissues and physiological fluids is described. The quantitative analysis of these aliphatic amino acids (Val, allo-Ile, Ile, and Leu) is important for the diagnosis of various inherent metabolic disorders of amino acids, and the D-enantiomers are expected to be of particular interest from a pharmacological point of view. Target analytes were determined as their fluorescent derivatives, pre-column labeled with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), using an automated two-dimensional column-switching high-performance liquid chromatographic system combining a narrow bore reversed-phase column and an enantioselective column connected with an integrated multi-loop peak fraction storage device. The described two-dimensional analysis concept proved to be successful for the given task in biological samples taken from mammals. Total analysis time for the reversed-phase separation of the four target NBD-amino acids is 60 min, and the integrated enantiomer separation of each of the four analytes is completed in approximately 5 min. In the rat, significant amounts of D-Leu were found in all tissues and physiological fluids tested (trace-1.3 nmol/g tissue), and in the urine, the presence of high amounts of D-allo-Ile (D-isomer of a non-proteinogenic amino acid, 22.2 nmol/ml) was demonstrated. D-allo-Ile was also found in the urine of dog and mouse, which indicates the ubiquitous presence of this unusual D-amino acid and the potential need to clarify its unique metabolism in mammals.
Amino Acids↗
Investigation of the lactosylation of whey proteins by liquid chromatography-mass spectrometry.
Heat treatment of milk induces a reaction between the milk proteins and lactose, resulting in lactosylated protein species. The lactosylation of the two major whey proteins alpha-lactalbumin and beta-lactoglobulin was investigated by reversed phase liquid chromatography-mass spectrometry (LC-MS). Three sample series, consisting of aqueous model solutions of each whey protein separately and in mixture and whole milk, were heated for different time periods, and the progression of the lactosylation reaction was monitored. The observed degrees of lactosylation and the reaction kinetics showed that the lactosylation of beta-lactoglobulin was not influenced by the presence of other components, whereas the lactosylation of alpha-lactalbumin was enhanced in whole milk compared to the aqueous model systems. An in-depth evaluation of the LC-MS data yielded information regarding changes of physicochemical properties of the whey proteins upon lactosylation. Whereas retention time shifts indicated changes in hydrophobicity for both alpha-lactalbumin and beta-lactoglobulin, changes in the charge state distribution denoting conformational alterations were observed only for beta-lactoglobulin. The analysis of different liquid and solid milk products showed that the lactosylation patterns of the whey proteins can be used as indicators for the extent of heat treatment.
Gas Chromatography-Mass Spectrometry↗
Validated method for the determination of the ethanol consumption markers ethyl glucuronide, ethyl phosphate, and ethyl sulfate in human urine by reversed-phase/weak anion exchange liquid chromatography-tandem mass spectrometry.
A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of the ethanol consumption markers ethyl glucuronide (EtG), ethyl phosphate (EtP), and ethyl sulfate (EtS) in human urine was developed. A reversed-phase/weak anion exchange type stationary phase demonstrated particular suitability for the analysis of these highly polar acids. Sample preparation was minimized to centrifugation and dilution of urine prior to injection. The method was validated in the range of 5-750 microg.L(-1) with 1:20 and 1:1000 diluted urine, which corresponds to actual concentration ranges of 0.1-15 and 5-750 mg.L(-1) in undiluted samples. Method validation was carried out using six different lots of human urine. Over the entire calibration range intraday and interday precision (each n = 5, three concentration levels per dilution factor) adopted values between 0.6 and 4.7% and 0.8 and 12.1%, relative standard deviation, respectively. Corresponding accuracy values ranged between 94.2 and 113.5% and 86.6 and 110.9%, respectively. Matrix effects (absolute/relative) were found to be present in minor extent (approximately -30% to +15% MS/MS signal alterations) and were well corrected by the employed isotopically labeled internal standards. The validated assay was applied to urine samples of a drinking study as well as postmortem specimens. It was possible to assess the principal potential of EtP as ethanol consumption marker. Elevated concentration levels were found in real samples; however, EtP seems to be less sensitive compared to the previously known ethanol phase II conjugates EtG and EtS.
Adult↗
Changes in peptic digestibility of bovine beta-lactoglobulin as a result of food processing studied by capillary electrophoresis and immunochemical methods.
Digestion studies constitute a functional tool for allergen characterisation. This strategy for investigating allergenic proteins relates to the observation of increased proteolytic resistance of some proteins recognised to exhibit allergenic potential. beta-Lactoglobulin (betaLG) is one of the major whey proteins, a potent milk allergen and shows a high stability against peptic hydrolysis in its native form. In order to study the impact of milk fermentation process on its digestibility, two complementary analytical methods were applied: capillary zone electrophoresis (CZE) to quantitatively study proteolytic degradation of betaLG isolated from different fermented bovine milk products, and enzyme linked immunosorbent assay (ELISA) to assess differences in immunoreactivity. betaLG, isolated from either raw or pasteurised cow's milk (CM), as expected, showed only minimal digestibility (less than 10% in 2 h). However, when raw milk or pasteurised milk was fermented, the rate of peptic digestion of the protein significantly increased (up to 45% in 2 h). In accordance with changes in digestibility, the immunochemical response for all fermented samples was lower than that of non-fermented references. Raw and pasteurised milk "naturally" fermented in our laboratory only resulted in a slight reduction (betaLG detected is still in the range of milligrams per gram sample), whereas the industrially manufactured sour milk as well as the "Acidophilus milk" reflected a remarkably lower level of immunoreactivity (55-56 microg/g sample).
Animals↗
Survival and major neonatal complications in infants born between 22 0/7 and 24 6/7 weeks of gestation (1999-2003).
OBJECTIVE: This study was undertaken to compare survival and morbidity until discharge in infants born after 22-23 versus 24 weeks' gestational age (GA). STUDY DESIGN: Cohort study of all infants 25 weeks or less, born in 3 tertiary perinatal centers (1999-2003). RESULTS: Of a total of 336 infants, 133 (40%) died before or immediately after birth without the provision of life support, 203 (60%) received active neonatal treatment. Infants with life support (n = 82 at 22 to 23 weeks, n = 121 at 24 weeks) differed with respect to antenatal steroid prophylaxis (44% vs 62%) and cesarean section rate (51% vs 71%). Survival was 67% compared with 82% (P = .016). The incidence of intraventricular hemorrhage III or greater or periventricular leukomalacia (15/15%), severe retinopathy of prematurity (18/15%), and chronic lung disease (40/47%) was similar in both GA groups. CONCLUSIONS: The provision of life support for extremely preterm infants increases their chance of survival without more neonatal morbidity.
Cause of Death↗
CNS-manifestation of aspergillosis in an extremely low-birth-weight infant.
UNLABELLED: Invasive aspergillosis is a rare condition in term and preterm infants. We present here the fatal case of a 28-week gestational age preterm baby who developed pulmonary, hepatic and central nervous system aspergillosis during the first days of life. A hyperechogenic lesion adjacent to the lateral ventricle was diagnosed by ultrasound and initially considered to represent periventricular leukomalacia. Within several days the lesion increased in size and was then falsely considered to be an intraventricular haemorrhage. Aspergillus fumigatus was ultimately isolated in the tracheal aspirates, ascites and in material recovered by open brain biopsy. Despite treatment with conventional and liposomal amphotericin B the infant patient died. CONCLUSION: Invasive aspergillosis has to be considered in the differential diagnosis of an unusual hyperechogenic brain lesion in very low-birth-weight infants with persistent symptoms and signs of systemic infection despite broad-spectrum antibacterial therapy. Consideration of this diagnosis should result in an aggressive diagnostic work-up to allow early initiation of an appropriate treatment.
Antifungal Agents↗
Chiral recognition mass spectrometry: remarkable effects observed from the relative ion abundances of ternary diastereomeric complexes using electrospray ionization.
The relative abundances of ternary diastereomeric complexes (composed each from a cinchonane-type chiral selector, a model chiral acid, and an alkali cation) are shown to change remarkably and fortuitously with variation in concentration and type of alkali metal using electrospray ionization-mass spectrometry and competitive binding analysis.
Journal Article↗
Monolithic silica-based capillary column with strong chiral cation-exchange type surface modification for enantioselective non-aqueous capillary electrochromatography.
A silica-based monolithic stationary phase prepared by the sol-gel process in a 100 microm I.D. fused-silica (FS) capillary has been modified chemically with 3-mercaptopropyl trimethoxysilane followed by immobilization of a strong cation-exchange (SCX) type chiral selector, (S)-N-(4-allyloxy-3,5-dichlorobenzoyl)-2-amino-3,3-dimethylbutane phosphonic acid, by radical addition reaction onto the reactive sulfhydryl surface. After a fine-tuning of the mobile phase composition, the enantioselective capillary column was evaluated for the separation of various chiral basic drugs by enantioselective non-aqueous capillary electrochromatography (CEC), in comparison to capillary column analogs packed with 3.5 microm silica particles having attached the same selector. The performance of the monolithic silica column was further compared to corresponding polymethacrylate-based organic polymer monoliths. The study indicated that strong counter-ions such as 2-aminobutanol or N,N,N',N'-tetramethylethylenediamine are needed, although they reduce the electroosmotic flow velocity and separation factors in comparison to less efficient counter-ions, in order to allow the elution of the oppositely charged solutes in the ion-exchange retention mode within reasonable run time and as sharp zones. In contrast, weak counter-ions such as N,N-diisopropylethylamine (Huenig base) provided stronger electroosmotic flow and much better separation factors, but relatively poor peak efficiencies. Overall, with the chemically functionalized monolithic silica column the high quality separations of packed column analogs could be approximated, with regards to both separation factors and peak performances. On the other hand, the monolithic capillary column certainly outperformed the packed column in terms of system robustness under capillary electrochromatography conditions and showed excellent column longevity. The enantioselective strong cation-exchange-type monolithic silica column performed also well in comparison to the organic polymer monolith.
Cation Exchange Resins↗
Determination of ethyl sulfate--a marker for recent ethanol consumption--in human urine by CE with indirect UV detection.
A CE method for the determination of the ethanol consumption marker ethyl sulfate (EtS) in human urine was developed. Analysis was performed in negative polarity mode with a background electrolyte composed of 15 mM maleic acid, 1 mM phthalic acid, and 0.05 mM cetyltrimethylammonium bromide (CTAB) at pH 2.5 and indirect UV detection at 220 nm (300 nm reference wavelength). This buffer system provided selective separation conditions for EtS and vinylsulfonic acid, employed as internal standard, from urine matrix components. Sample pretreatment of urine was minimized to a 1:5 dilution with water. The optimized CE method was validated in the range of 5-700 mg/L using seven lots of urine. Intra- and inter-day precision and accuracy values, determined at 5, 60, and 700 mg/L with each lot of urine, fulfilled the requirements according to common guidelines for bioanalytical method validation. The application to forensic urine samples collected at autopsies as well as a successful cross-validation with a LC-MS/MS-based method confirmed the overall validity and real-world suitability of the developed expeditious CE assay (sample throughput 130 per day).
Adult↗
Stereoselective separations of chiral phosphinic acid pseudodipeptides by CEC using silica monoliths modified with an anion-exchange-type chiral selector.
A nonaqueous CEC method for the simultaneous separation of the four stereoisomers of the N-benzyloxycarbonyl phosphinic pseudodipeptide methyl ester benzyloxycarbonyl-homophenylalanine Z-hPhepsi(PO2HCH2)Phe-OCH3 as well as of the corresponding N-2,4-dinitrophenyl (DNP)-derivative with free C-terminal carboxylic group DNP-hPhepsi(PO2HCH2)Phe-OH was developed. For this purpose, a monolithic silica capillary column modified with a cinchona alkaloid-derived anion-exchange-type chiral selector, namely O-9-(tert-butylcarbamoyl)quinidine (tBuCQD) was prepared. The mobile phase composition (ACN/methanol ratio, counterion type) was thoroughly optimized to end up with baseline resolution of all four stereoisomers with critical resolution of as high as about 2. The CEC method proved to be superior over the corresponding HPLC separations primarily due to significantly enhanced plate numbers (between 200,000 and 600,000 m(-1) in CEC). Diastereoselectivity contributions arising from electrophoretic mobility differences of the diastereomers facilitated the separation of the later eluted diastereomeric peak pair (peaks III and IV), but had a negative influence on the selectivity of the earlier eluted diastereomeric peak pair (peaks I and II). The stereoselective CEC assay allowed the assessment of the stereoisomeric purity of the individual isomers which were obtained by preparative HPLC on a CHIRALPAK QD-AX column that is based on the same tBuCQD selector. The present study demonstrates that there exist problems which are hard to solve by HPLC, yet can be conveniently solved by CEC. Moreover, it was intended to prove by this practical application that CEC with monolithic columns is robust enough to be used for solving real-life problems.
Anion Exchange Resins↗
Derivatisation of arginine residues with malondialdehyde for the analysis of peptides and protein digests by LC-ESI-MS/MS.
In this study a selective tagging strategy for the derivatisation of arginine residues in peptides is presented. It is based on the reaction of the guanidine group of the arginine side-chain with malondialdehyde (MDA) under strongly acidic conditions, in which a stable pyrimidine ring is formed. The reaction conditions have been optimised so that quantitative modification can be achieved for a variety of peptides. The label has a strong influence on the polarity and basicity of the arginine side-chain and thus on the chromatographic and mass spectrometric properties of arginine-containing peptides. For example, retention, particularly of small and polar peptides as well as arginine-rich peptides, is significantly increased by derivatisation, and therefore sensitivity is also enhanced in liquid chromatography-mass spectrometry (LC-MS). The arginine side-chain also has a strong impact on the fragmentation behaviour of peptides in tandem mass spectrometry. This has been investigated for standard peptides for which, in some cases, significantly more fragment ions were formed after derivatisation. Finally, the method was tested for tryptic digests of standard proteins to demonstrate how the tagging strategy can give improved or complementary information for protein identification.
Acids↗
Deuterium isotope effects observed during competitive binding chiral recognition electrospray ionization--mass spectrometry of cinchona alkaloid-based systems.
Deuterium isotope effects are reported for binding between tert-butylcarbamoyl-quinine/quinidine chiral selectors and isotopomeric quasienantiomers of N-(3,5-dinitrobenzoyl)leucine measured using electrospray ionization-mass spectrometry (ESI-MS) and competitive binding. Evaluation of mixtures of each selector with one labeled and one unlabeled enantiomeric selectand of identical configuration showed a significant difference in measured ion abundances of diastereomeric complexes between the selector and each selectand. It was found that in some cases, the complex containing the nondeuterated selectand was 15% more abundant than its deuterated counterpart. On the basis of an assessment of solution- and gas-phase isotope effects reported in the literature, a series of control experiments were performed to study the origin of the effects. On the basis of these measurements, our preliminary conclusion is that the differing gas-phase physicochemical nature of the deuterated versus nondeuterated selectand represents the strongest contribution to the observed effect in this chiral molecular recognition system.
Binding, Competitive↗
Silica-based monolithic columns with mixed-mode reversed-phase/weak anion-exchange selectivity principle for high-performance liquid chromatography.
This article describes the synthesis, chromatographic characterization, and performance evaluation of analytical (100 x 4.6 mm id) and semipreparative (100 x 10 mm id) monolithic silica columns with mixed-mode RP/weak anion-exchange (RP/WAX) surface modification. The monolithic RP/WAX columns were obtained by immobilization of N-(10-undecenoyl)-3-aminoquinuclidine onto thiol-modified monolithic silica columns (Chromolith) by a radical addition reaction. Their chromatographic characterization by Engelhardt and Tanaka tests revealed slightly lower hydrophobic selectivities than C-8 phases, as well as higher polarity and also improved shape selectivity than RP-18e silica rods. The surface modification enabled separation by both RP and anion-exchange chromatography principles, and thus showed complementary selectivities to the RP-18e monoliths. The mixed-mode monoliths have been tested for the separation of peptides and turned out to be particularly useful for hydrophilic acidic peptides, which are usually insufficiently retained on RP-18e monolithic columns. Compared to a corresponding particulate RP/WAX column (5 microm, 10 nm pore diameter), the analytical RP/WAX monolith caused lower system pressure drops and showed, as expected, higher efficiency (e.g. by a factor of about 2.5 lower C-term for a tetrapeptide). The upscaling from the analytical to semipreparative column dimension was also successful.
Anions↗
Quinine carbamate chiral stationary phases: systematic optimization of steric selector-selectand binding increments and enantioselectivity by quantitative structure-enantioselectivity relationship studies.
A series of quinine carbamate-based chiral stationary phases (CSPs) differing solely in the carbamate residue have been devised and a congeneric set of N-3,5-dinitrobenzoyl (DNB) amino acids (AAs) was separated into enantiomers on these CSPs by HPLC using a buffered hydro-organic mobile phase. Some details on retention and chiral recognition mechanisms have been investigated by application of quantitative structure-property relationship (QSPR) studies using the linear free energy relationship methodology, i.e., the extrathermodynamic approach. Retention factors of the high affinity enantiomer (log k2) and enantioselectivities (log alpha) were correlated with Taft's steric parameter as structural descriptor for the variability in the carbamate and AA residues, and statistically significant QSPR models could be obtained. They confirmed that the variance in the dependent variable (log k2, log alpha) is mainly associated with the steric bulkiness of the selectors' carbamate and of the AA residues. The retention factor of the second eluted enantiomers and the enantioselectivity first increased with steric bulkiness of the carbamate and AA residues, which may be explained by stronger dispersive interactions. After reaching an optimum, the dependent variable, however, declined with further increase of the steric bulkiness of the substituents, probably because of steric hindrance. The variability of the retention factors of the first eluted enantiomer could not be explained by steric descriptors. Instead, it has become obvious that the retention arises mainly from interactions of the DNB-AA and the quinine carbamate backbone, as it turned out to be more or less constant and solely to a minute amount modulated by the carbamate residue and the AA side chain. The QSPR models were fully in agreement with an earlier postulated chromatographically and spectroscopically derived hypothetical selector-selectand binding model.
Amino Acids↗
Chemistry meets proteomics: the use of chemical tagging reactions for MS-based proteomics.
As proteomics matures from a purely descriptive to a function-oriented discipline of the life sciences, there is strong demand for novel methodologies that increase the depth of information that can be obtained from proteomic studies. MS has long played a central role for protein identification and characterization, often in combination with dedicated chemical modification reactions. Today, chemistry is helping to advance the field of proteomics in numerous ways. In this review, we focus on those methodologies that have a significant impact for the large-scale study of proteins and peptides. This includes approaches that allow the introduction of affinity tags for the enrichment of subclasses of peptides or proteins and strategies for in vitro stable isotope labeling for quantification purposes, among others. Particular attention is given to the study of PTMs where recent advancements have been promising, but many interesting targets are not yet being addressed.
Animals↗
Identification of marker proteins for the adulteration of meat products with soybean proteins by multidimensional liquid chromatography-tandem mass spectrometry.
Soybean proteins are frequently added to processed meat products for economic reasons and to improve their functional properties. Monitoring of the addition of soybean protein to meat products is of high interest due to the existence of regulations forbidding or limiting the amount of soybean proteins that can be added during the processing of meat products. We have used chromatographic prefractionation on the protein level by perfusion liquid chromatography to isolate peaks of interest from extracts of soybean protein isolate (SPI) and of meat products containing SPI. After enzymatic digestion using trypsin, the collected fractions were analyzed by nanoflow liquid chromatography-tandem mass spectrometry. Several variants and subunits of the major seed proteins, glycinin and beta-conglycinin, were identified in SPI, along with two other proteins. In soybean-protein-containing meat samples, different glycinin A subunits could be identified from the peak discriminating between samples with and without soybean proteins added. Among those, glycinin G4 subunit A4 was consistently found in all samples. Consequently, this protein (subunit) can be used as a target for new analytical techniques in the course of identifying the addition of soybean protein to meat products.
Animals↗