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M Grunze

Publications and source records attributed to M Grunze.

At least 19 recordsLinked to original sources
PubMed2007

Density depletion at solid-liquid interfaces: a neutron reflectivity study.

Neutron reflectivity experiments conducted on self-assembled monolayers (SAMs) against polar (water) and nonpolar (organic) liquid phases reveal further evidence for a density reduction at hydrophobic-hydrophilic interfaces. The density depletion is found at the interface between hydrophobic dodecanethiol (C12) and hexadecanethiol (C16) SAMs and water and also between hydrophilic SAMs (C12/C11OH) and nonpolar fluids. The results show that the density deficit of a fluid in the boundary layer is not unique to aqueous solid-liquid interfaces but is more general and correlated with the affinity of the liquid to the solid surface. In water the variation of pH has only minor influence, while different electrolytes taken from the Hofmeister series seem to increase the depletion. On hydrophobic SAMs an increase in density depletion with temperature was observed, in agreement with Monte Carlo simulations performed on corresponding model systems. The increase in the water density depletion layer is governed by two effects: the surface energy difference between water and the substrate and the chemical potential of the aqueous phase.

Journal Article↗
PubMed2006

Theoretical modeling and interpretation of X-ray absorption spectra of liquid water.

We report extensive calculations to examine the capability of theory to explain the XAS spectra of liquid water. Several aspects that enter the theoretical model are addressed, such as the quantum mechanical methods, the statistics and the XAS model. As input into our quantum mechanical calculations we will use structural information on liquid water obtained from first principles and from classical molecular dynamics simulations. As XAS models, we will examine the full core hole and the half core hole approximations to transition state theory. The quantum mechanics is performed on the basis of density functional theory. We conclude from this study that recent experimental results are fully consistent with, and can be completely explained by, present day theory, in particular, the pre-edge peak is reproduced. We also find that the average bond coordination in liquid water is 3.1 and that the assertion in a recent paper that the hydrogen bond number is much less than that cannot be substantiated. Our calculations emphasize that further advances in our understanding of water can only be made by more sophisticated spectroscopy with significantly increased resolution.

Absorption↗
PubMed2006

Spectroscopic characterization of omega-substituted biphenylthiolates on gold and their use as substrates for "on-top" siloxane SAM formation.

Self-assembled monolayers (SAMs) of omega-substituted biphenylthiolates (omega-MBP) on gold were characterized by spectral ellipsometry, X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRRAS), and vibrational sum frequency generation spectroscopy (VSFG). The vibrational studies of the SAMs were supported by an ab initio frequency analysis at HF/6-31G and BP86/6-31G levels, yielding an assignment of all relevant spectral features in the range from 3500 to 1200 cm(-1). We were able to demonstrate that hydroxy-terminated MBP (HMBP) SAMs are basically featureless in the range of the CH stretching vibrations. Accordingly, the adsorption of a SAM of octadecyltrichlorosilane (OTS) on top of this model surface could be studied. A red shift of the C-O stretching vibration from 1281 to 1264 cm(-1) was observed during the chemisorption of OTS, thus allowing for a quantification of the number of OTS molecules involved in surface binding of OTS, which was found to be about 26% on average.

Journal Article↗
PubMed2005

Odd-even effects in photoemission from terphenyl-substituted alkanethiolate self-assembled monolayers.

Self-assembled monolayers (SAMs) formed from 4,4'-terphenyl-substituted alkanethiols C6H5(C6H4)2-(CH2)nSH (TPn, n = 1-6) on polycrystalline (111) gold and silver substrates have been characterized by synchrotron-based high-resolution X-ray photoelectron spectroscopy. The intensities, binding energy positions, and width of most photoemission lines exhibited pronounced odd-even effects, i.e., systematic and periodic variation, depending on either odd or even number of the methylene units in the aliphatic linker of the TPn molecules. The detailed analysis of these effects provides important information on the bonding and arrangement of the chemisorbed sulfur headgroups in the TPn films and balance of the structural forces in alkanethiolate SAMs.

Journal Article↗
PubMed2005

Interaction of self-assembled monolayers of oligo(ethylene glycol)-terminated alkanethiols with water studied by vibrational sum-frequency generation.

Vibrational sum-frequency generation (VSFG) was used to investigate the conformational changes in self-assembled monolayers (SAMs) of (1-mercaptoundec-11-yl) hexa(ethylene glycol) monomethylether (EG6-OMe) on gold when exposed to liquid water. VSFG spectra of the EG6-OMe SAMs were recorded before, during, and after exposure of the films to water and after a subsequent evacuation step. While in contact with water the entire ethylene glycol chains are found in a random, solvated state, after removal from the fluid water molecules remain absorbed only at the terminal groups of the film giving rise to distinct conformational changes. After evacuation, the structure of the EG6-OMe SAM reverts to its original state, indicating that water has been removed from the monolayer. Our findings support recent ab initio calculations and Monte Carlo simulations on the interaction of ethylene glycol-terminated monolayers with water.

Absorption↗
PubMed2005

The effect of halogen substitution in self-assembled monolayers of 4-mercaptobiphenyls on noble metal substrates.

Self-assembled monolayers (SAMs) formed from 4'-substituted 4-mercaptobiphenyls X-(C6H4)2SH (X-BPT, with X = I, Cl, and F) on polycrystalline (111) gold and silver substrates have been characterized by synchrotron-based high-resolution X-ray photoelectron spectroscopy and angle-resolved near-edge X-ray absorption fine structure spectroscopy. The X-BPT molecules were found to form highly oriented and densely packed SAMs on both substrates, with a smaller molecular inclination in the case of Ag. The experimental data show clear evidence for the charge transfer between the 4'-substituent and biphenyl moieties with the direction and extent of the transfer depending on the electronegativity of the halogen substituent. At the same time, no direct evidence of the charge transfer between the 4'-substituent and the thiolate group was observed. However, the substitution of the 4'-hydrogen by a halogen atom seems to affect the detailed packing arrangements of the SAM constituents.

Halogens↗
PubMed2004

Bonding and structure of glycine on ordered Al2O3 film surfaces.

The interaction between glycine (NH2CH2COOH) layers and an ultrathin Al2O3 film grown epitaxially onto NiAl(110) was studied by temperature-programmed desorption, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, work function measurements, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. At monolayer coverages at 110 K, there are two coexisting molecular forms: the anionic (NH2CH2COO-) and the zwitterionic form (NH3+CH2COO-) of glycine. As deduced from the photoemission data, the buildup of multilayers at 110 K leads to a condensed phase predominantly in the zwitterionic state. In contrast to the monolayer at 110 K, the monolayer formed at 300 K consists primarily of glycine molecules in the anionic state. The latter species is adsorbed with the oxygen atoms of the carboxylic group pointing toward the substrate. The polarization-dependent C K- and O K-edge NEXAFS spectra indicate that the glycinate species in the monolayer at 300 K is oriented nearly perpendicular to the surface, with the amino group pointing away from the surface.

Adsorption↗
PubMed2004

Depth distribution of irradiation-induced cross-linking in aromatic self-assembled monolayers.

Pristine and strongly irradiated self-assembled monolayers of [1,1':4',1' '-terphenyl]-4,4' '-dimethanethiol (TPDMT) on Au have been characterized by near-edge X-ray absorption fine structure spectroscopy using partial electron yield acquisition mode. The TPDMT films were found to be extremely stable toward electron irradiation, which is explained by cross-linking between the aromatic backbones. In addition, we assume that a large delocalization and a strong relaxation of the initial electronic excitations in the densely packed film contributed to the film stability. The data analysis implies an inhomogeneous distribution of the irradiation-induced dehydrogenation and cross-linking of the terphenyl moieties in the TPDMT film, being most pronounced close to the film-ambient interface. The inhomogeneity was explained by quenching of the electronically excited C-H states via dipole-dipole interaction with the states' image at the metal surface, which has a reduced probability with increasing separation from the metal surface. Generally, the results suggest the importance of relaxation processes for the response of self-assembled monolayers to ionizing radiation.

Cross-Linking Reagents↗
PubMed2004

Swelling behavior of self-assembled monolayers of alkanethiol-terminated poly(ethylene glycol): a neutron reflectometry study.

The swelling behavior of alkanethiol-terminated poly(ethylene glycol) with an average molecular weight of 2180 Da (i.e., approximately 45 ethylene glycol, EG, units) in contact with water was investigated by neutron reflectometry as a function of the morphology of the PEG-SH layer. Amorphous films at a low grafting density show significant swelling with an increase of the film thickness from approximately 25 A in the dry state to approximately 70 A in contact with D2O, which corresponds to a total water uptake of approximately 38 mass %. In contrast, quasi-crystalline monolayers exhibit only a small amount of water penetrating into the film (approximately 8 mass %) with a corresponding change of the layer thickness from approximately 110 to approximately 125 A. The water uptake per EG unit corresponds to the literature value of 1.5 for the amorphous layer and to only 0.25 in the case of the quasi-crystalline film.

Letter↗
PubMed2004

Irradiation sensitivity of self-assembled monolayers with an introduced "weak link".

The irradiation sensitivity of n-alkanethiolate SAMs can be enhanced by the incorporation of an irradiation-sensitive functionality as a predetermined breaking point into the alkyl chain. Following this general strategy, several different sulfur-derived functional entities with a variable position in the alkyl chain were tested. In some cases, the incorporation of these entities resulted in a noticeable enhancement of the irradiation-induced desorption (by about 30%), even though the chains were not exclusively cut at the position of the incorporated group, but the scission events related to the "weak links" were just added to those in the alkyl matrix. The position of the incorporated group along the alkyl chain was found to be most essential for its performance as a weak link; the enhancement of irradiation-induced desorption was observed only when the groups were placed close to the SAM-ambient interface.

Journal Article↗
PubMed2003

Multimode detection of hydrogen gas using palladium-covered silicon micro-channels.

Palladium was electrodeposited onto lithographically patterned Si(100) "micro-channels" with dimensions of 2 microm (width) x 100 microm (length). The properties of these Pd-covered Si micro-channels for detecting dihydrogen gas were then evaluated. Pd electrodeposition was carried out under conditions favoring an instantaneous nucleation and growth mechanism. This strategy produced size-similar Pd particles at a coverage of (4-6) x 10(9) cm(-2) within the confines of the Si micro-channel. When the mean particle radius, ro, was smaller than a critical value (ro < rc = 70-85 nm), each Pd particle was well separated on the surface from adjacent particles, on average, and no response to H2 gas attributable to the micro-channel was observed. As Pd particles were grown larger, to a mean radius of ro approximately equal to rc, adjacent particles on the surface touched and the electrical resistance of the micro-channel dropped by several orders of magnitude. These "type 2" H2 sensors exhibited a rapid (< 1 s), reversible decrease in their resistance in response to exposure to H2 above 0.5%, but a minimum resistance was observed at 1-2%, and a resistance increase was seen at higher H2 concentration. This complex behavior resulted from the existence of three mechanisms for charge transport across the micro-channel. If still larger quantities of Pd were deposited, the Pd particle ensemble coalesced into an electrically continuous film. These "type 3" sensors became more resistive in the presence of H2, not more conductive as seen for sensors of types 1 and 2, but the amplitude of this response was smaller than seen for type 2 sensors.

Journal Article↗
PubMed2002

Optimization of the low energy electron point source microscope: imaging of macromolecules.

Optimal conditions for low energy electron point source microscopy are investigated by the simulation and numerical reconstruction of holograms of phthalocyaninato polysiloxane, PcPS, a rod-like macromolecule. The effects of the electron energy, width of the electron beam and the detector size on the spatial resolution in the reconstructed images are modeled. We find that for electron energies around 200eV, with the specimen 0.1 microm from the source, a screen recording the image in a cone of at least 15 degrees half angle (7 cm lateral dimension at 10 cm from the source) with at least 512 x 512 pixel and 8-bit resolution will result in near atomic resolution.

Journal Article↗
PubMed2000

Detection of molecular alignment in confined films

Optical second harmonic generation was used to study the in-plane alignment of self-assembled silane monolayers attached to a glass surface under mechanical loading. The measurements allow correlation of the macroscopic forces acting on the monolayer with the average orientation and the azimuthal molecular alignment of the terminal molecular entity. Compression and shear forces lead to an alignment of the initially randomly oriented molecules on a macroscopic length scale. The change in azimuthal alignment of molecules under mechanical stress was found to be irreversible on the time scale of 12 hours, whereas changes of the molecular tilt angle were reversible.

Journal Article↗
PubMed1998

Plasma Protein Adsorption and Platelet Adhesion on Poly

In this work we describe experiments designed to understand the blood compatibility and resistance to platelet adhesion of poly[bis(trifluoroethoxy)phosphazene] (Acta Polymerica 36, 627 (1985)) (PTFEP) coated surfaces. We compare quantitative in vitro protein adsorption measurements using enzyme linked immunosorbent assays (ELISA) and platelet adherence tests on PTFEP with other organic surfaces and hydroxylated glass. Compared to some materials of medical interest (polymethylmethacrylate and silicone) and other materials (hydroxylated glass, aldehyde-, alkyl-, or amino-terminated surfaces) exhibiting a wide range of physical properties, PTFEP showed the highest human serum albumin adsorption and the lowest adsorption of fibrinogen and fibronectin. These proteins are related to thrombus formation and cellular attachment, respectively. Coagulation-stimulating proteins are predominantly bound reversibly on PTFEP and do not appear to denaturate to the extent found on the other surfaces. Copyright 1998 Academic Press. Copyright 1998Academic Press

Journal Article↗
PubMed1998

Reduced pulmonary function in patients with spinal osteoporotic fractures.

Vertebral deformation in spinal osteoporosis results in spinal and thoracic deformation, causing pain, disability and an overall decrease in quality of life. We sought to determine whether thoracic spinal deformation may lead to impaired pulmonary function. We studied expiratory relaxed vital capacity (VC) and forced expiratory volume in 1 s (FEV1) in 34 patients with spinal osteoporotic fractures and 51 patients with chronic low back pain (CLBP) due to reasons other than osteoporosis. Measurements of pulmonary function tests were calculated as a percentage of the normal range adjusting for age, sex, and height using the equations for normal values of the EKGS (Europäische Gesellschaft für Kohle und Stahl). Severity of osteoporosis was determined by calculation of the spine deformity index (SDI-total and SDI-anterior) on lateral radiographs of the spine and clinical measures of body stature (height reduction, distance from lowest ribs to iliac crest and distance from the occiput to the wall). Patients with osteoporosis had a lower vital capacity (%VC of the reference value) than patients with CLBP. The differences were more prominent (p < 0.05) when the previous body height, at age 25 years, was used as reference for calculation of VC (mean +/- SD: 93.6% +/- 15.3% in patients with osteoporosis v 105.6% +/- 15.1% in patients with CLBP). FEV1 was significantly (p < 0.05) lower in patients with osteoporosis when previous body height was considered, in comparison with patients with CLBP (mean +/- SD: 85.0% +/- 14.2% in patients with osteoporosis v 92.4% +/- 13.6% in patients with CLBP). In patients with osteoporosis VC (standardized on previous body height) was significantly negatively correlated with SDI-anterior (r = -0.4, p < 0.03). Furthermore, VC standardized on previous body height showed a weak but significant negative correlation with some clinical measures of osteoporosis (height reduction vs %VC: r = -0.34, p < 0.05; distance from the lowest ribs to iliac crest vs %VC: r = 0.35, p < 0.04). In conclusion, we found that pulmonary function is significantly diminished in patients with spinal osteoporotic fractures as compared with CLBP patients without evidence of manifest osteoporosis. Reduction of pulmonary function is correlated significantly with clinical and radiological measures of severity of spinal deformation due to osteoporotic fractures.

Aged↗
PubMed1997

On-line detection of nonspecific protein adsorption at artificial surfaces.

A detailed understanding of the interaction of proteins with artificial surfaces is essential for many applications in medicine and biochemistry. The affinity of surfaces toward proteins may, for instance, remove pharmacological proteins from media or control the adherence of pathogenic bacteria to protheses. Only a few analytical techniques now exist that can be used to study the binding process in real time, using unlabeled proteins. By investigating the adsorption kinetics of fibrinogen at differently terminated self-assembled monolayers (SAMs) of alkanethiols on thin gold films, it is demonstrated that acoustic plate-mode sensors are a promising analytical tool for studying the adsorption of proteins. In agreement with previous studies for fibrinogen, it is shown in situ that hexa(ethylene glycol)-terminated SAMs (HS(CH2)11 (OCH2CH2)6OH) exhibit very low protein adsorption and that methyl-terminated SAMs (HS(CH2)11CH3) tend to absorb large amounts of protein nonspecifically. The observed adsorption kinetics deviate from classical Langmuir behavior; these kinetics are compatible with a mechanism that involves an unfolding of fibrinogen after adsorption. Film quality is controlled by IR, XPS, and contact angle measurements.

Adsorption↗
PubMed1996

Multifrequency evaluation of different immunosorbents on acoustic plate mode sensors.

Previous studies of acoustic plate modes on ZX-LiNbO3 have indicated that practical mass-sensitive immunosensors can be implemented by using devices with higher frequencies of operation and/or by improving techniques for the immobilization of antibodies. However, it is also known from these studies that the viscoelastic properties of aminosilane films, used for the covalent immobilization of antibodies on the crystal surface, cannot be ignored in the sensor response. In the present work, in an attempt to study the effect of viscoelasticity of the binding film, three different films with different viscoelasticity and binding capacities, an aminosilane, a dextran, and a poly-(etherurethane)-based immunosorbent (XP-5), were prepared on the sensor surface for the immobilization of antibodies. Immunochemical reactions were monitored by the acoustic plate mode sensor at three different frequencies, thus allowing the direct observation of the frequency dependence of mass sensitivity with different films. Depending on the type of immunosorbent, the sensitivity at the third harmonic was enhanced by a factor of 2-5 with respect to the fundamental response. A third acoustic mode at a closely spaced frequency to the third harmonic yielded lower sensitivity values, which indicates that sensitivity depends not only on the frequency of device operation but also on particle displacement amplitude and components of the selected wave. Since antigen binding capacities of the different immunosorbents were determined independently by a modified ELISA test, sensor responses can also be correlated to the immunosorbent structure, and hence the viscoelastic properties. A dual delay line configuration was used which compensates for second-order effects such as temperature variations and nonspecific adsorption.

Antibodies↗