Bond-specific fragmentation of oligopeptides via electronic stopping of swift heavy ions in molecular films.

Highly bond-specific fragmentation of oligopeptides induced by swift heavy ion (SHI) irradiation was investigated by means of mass spectrometry. In pronounced contrast to measurements of samples irradiated with keV ions, oligopeptides which were exposed to 946 MeV Au ions show a high abundance of specific fragments. The highly bond-specific nature of SHI-induced fragmentation is attributed to electronic stopping as the most relevant energy loss mechanism for SHI in the oligopeptide samples in combination with the subsequent coupling between the excited electronic and the atomic subsystem. Fragmentation induced by SHI is observed to be further influenced by the structure of the oligopeptides, suggesting that electronic excitation and/or the electronic-vibrational coupling depend on the details of the molecular structure.

Towards π-wires on a semiconductor surface: Benzyne on Si(001).

Towards the goal of covalently bound molecular wires on silicon, the adsorption of benzyne on Si(001) was studied by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional calculations (DFT). The benzyne molecule is found to adsorb preferentially via the strained triple bond on one dimer of the Si(001) surface which results in an intact π system covalently bound to the surface. With increasing coverage, the molecules primarily adsorb along the dimer rows; on stepped surfaces, these molecular wires are all oriented in the same direction.

Tip-inducedß-hydrogen dissociation in an alkyl group bound on Si(001).

Atomic-scale chemical modification of surface-adsorbed ethyl groups on Si(001) was induced and studied by means of scanning tunneling microscopy. Tunneling at sample bias >+1.5 V leads to tip-induced C-H cleavage of aß-hydrogen of the covalently bound ethyl configuration. The reaction is characterized by the formation of an additional Si-H and a Si-C bond. The reaction probability shows a linear dependence on the tunneling current at 300 K; the reaction is largely suppressed at 50 K. The observed tip-induced surface reaction at room temperature is thus attributed to a one-electron excitation in combination with thermal activation.

[Long-term outcome after dialysis-dependent renal failure on the intensive care unit]. / Langzeitergebnis nach akutem dialysepflichtigem Nierenversagen auf einer internistischen Intensivstation.

BACKGROUND: Acute kidney injury (AKI) is a common and serious complication of acute life-threatening diseases. OBJECTIVES: The aim of this study was to investigate the effect of acute renal failure on mortality in intensive care patients, the need for renal replacement therapy at discharge, and the effect on long-term mortality. MATERIAL AND METHODS: Evaluation of 118 patient cases with dialysis-dependent acute renal failure between November 2016 and December 2017 admitted to a medical intensive care unit (ICU) at the University Hospital Tübingen, Germany. Dialysis at discharge and 1­year mortality were defined as the primary endpoints. The secondary endpoint was need for continuous renal replacement after 18 months. RESULTS: In 118 patients, renal replacement modality by means of hemodialysis became necessary. A mortality rate of 45.8% (54/118) was found in patients requiring dialysis. Of the 64 surviving dialysis-dependent patients, 35.9% were still dependent on renal replacement therapy at the time of discharge. The 1­year mortality rate was significantly higher in patients that still required dialysis at the time of discharge (p = 0.004). At 18-month follow-up, seven patients (10.9%) were still on renal replacement therapy. At this time, dialysis was significantly more frequent in patients with dialysis at the time of discharge than in dialysis-free patients (7.1% vs. 71.4%, p = 0.001). CONCLUSION: Severe episodes of AKI requiring renal replacement therapy in the setting of an ICU are associated with increased mortality 1 year after discharge and an increased requirement for renal replacement 18 months after discharge.

Direct Analysis of Ion-Induced Peptide Fragmentation in Secondary-Ion Mass Spectrometry.

Primary-ion-induced fragmentation in organic molecules can strongly influence the results in secondary-ion mass spectrometry (SIMS) of organic and biomolecular samples. In order to characterize this ion-induced fragmentation, oligopeptide samples irradiated in SIMS experiments were investigated by means of desorption/ionization induced by neutral SO2 clusters (DINeC). The latter is a nondestructive desorption method for mass spectrometry of biomolecules, which gives direct access to the fragments induced in the sample. Comparison of TOF-SIMS and DINeC mass spectra revealed qualitative differences between the fragments, which remain in the sample and the fragments sputtered during ion bombardment. The fragmentation strength and its spatial distribution were found to be quantitatively different for Bi1+, Bi3+, and Ar1000+ primary ions, leading to different distributions of the degree of fragmentation in the samples as directly measured by means of DINeC depth profiles.

Cluster-induced desorption investigated by means of molecular dynamics simulations-Microsolvation in clusters of polar and non-polar constituents.

The desorption of surface-adsorbed molecules induced by cluster-surface collisions of neutral molecular clusters, in particular, SO2 clusters, was investigated by means of molecular dynamics simulations. The desorption efficiency was found to be in general much higher for clusters of polar molecules when compared to nonpolar cluster constituents, for both nonpolar and polar adsorbates. In all cases, desorption is shown to proceed via dissolvation of the analyte in the cluster. In systems with nonpolar cluster constituents, the process is mainly driven by the increase in the entropy of the dissolved analyte in a larger cluster fragment. The latter process is enhanced by polar cluster constituents since the respective clusters show lower fragmentation at comparable kinetic energy and thus provide in average larger cluster fragments for the analytes to be dissolved in. In systems with clusters of polar constituents and polar adsorbates, the process is most efficient due to the additional energetic stabilization of the desorbed molecule in the solvation shell formed in the cluster fragment.

Dynamics of proton transfer reactions on silicon surfaces: OH-dissociation of methanol and water on Si(001).

The reaction dynamics of methanol and water on Si(001) were investigated by means of molecular beam techniques. The initial sticking probability s0 was determined as a function of the kinetic energy of the incoming molecules, Ekin, and surface temperature, Ts. For both, methanol and water, a nonactivated reactional channel was observed; the dynamics were found to be determined by the reaction into the datively bonded intermediate state. A low conversion barrier was deduced for the conversion from this intermediate into the final state. It is attributed to the reaction mechanism, which proceeds via proton transfer from the OH-group of the datively bonded molecules to a Si surface atom. Despite this low conversion barrier, adsorption into the intermediate and further reaction via proton transfer were found to be largely decoupled.

Formation of Si/organic interfaces using alkyne-functionalized cyclooctynes-precursor-mediated adsorption of linear alkynes versus direct adsorption of cyclooctyne on Si(0 0 1).

Adsorption of ethynyl-cyclopropyl-cyclooctyne (ECCO), an alkyne-functionalized cyclooctyne, on Si(0 0 1) was studied by means of x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Together, XPS and STM results clearly indicate chemoselective adsorption of ECCO on Si(0 0 1) via a [2+2] cycloaddition of the strained triple bond of cyclooctyne without reaction of the ethynyl group. The results are compared to the adsorption of acetylene on Si(0 0 1): C2H2 adsorbs on Si(0 0 1) via a precursor-mediated reaction channel as it was shown by means of temperature dependent measurements of the sticking probability as well as by means of STM experiments at variable temperature. On the other hand, cyclooctyne adsorbs on Si(0 0 1) via a direct reaction channel. This qualitative difference in the reaction pathways of the two functionalities leads to the observed chemoselective adsorption of ECCO via the strained triple bond of cyclooctyne. As the ethynyl group stays intact, monolayers of ECCO on Si(0 0 1) form a well defined interface between the silicon substrate and further organic molecular layers which can be attached to the ethynyl functionality.

Second-harmonic generation as a probe for structural and electronic properties of buried GaP/Si(0 0 1) interfaces.

Optical second-harmonic generation is demonstrated to be a sensitive probe of the buried interface between the lattice-matched semiconductors gallium phosphide and silicon with (0 0 1) orientation. Ex situ rotational anisotropy measurements on GaP/Si heterostructures show a strong isotropic component of the second-harmonic response not present for pure Si(0 0 1) or GaP(0 0 1). The strength of the overlaying anisotropic response directly correlates with the quality of the interface as determined by atomically resolved scanning transmission electron microscopy. Systematic comparison of samples fabricated under different growth conditions in metal-organic vapor phase epitaxy reveals that the anisotropy for different polarization combinations can be used as a selective fingerprint for the occurrence of anti-phase domains and twins. This all-optical technique can be applied as an in situ and non-invasive monitor even during growth.

Electron microscopy of polyoxometalate ions on graphene by electrospray ion beam deposition.

Aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM) has enabled atomically resolved imaging of molecules adsorbed on low-dimensional materials like carbon nanotubes, graphene oxide and few-layer-graphene. However, conventional methods for depositing molecules onto such supports lack selectivity and specificity. Here, we describe the chemically selective preparation and deposition of molecules-like polyoxometalate (POM) anions [PW12O40]3- using electrospray ion-beam deposition (ES-IBD) along with high-resolution TEM imaging. This approach provides access to sub-monolayer coatings of intact molecules on freestanding graphene, which enables their atomically resolved ex situ characterization by low-voltage AC-HRTEM. The capability to tune the deposition parameters in either soft or reactive landing mode, combined with the well-defined high-vacuum deposition conditions, renders the ES-IBD based method advantageous over alternative methods such as drop-casting. Furthermore, it might be expanded towards depositing and imaging large and nonvolatile molecules with complex structures.

Late Conversion to Belatacept After Kidney Transplantation: Outcome and Prognostic Factors.

BACKGROUND: Conversion to belatacept at a later point after kidney transplantation (KT) as a rescue therapy has been shown to be beneficiary in an increasing number of patients, but prognostic factors for a favorable outcome have never been investigated. METHODS: The present study analyzed all KT patients after late conversion to belatacept in a single center regarding graft survival and changes in estimated glomerular filtration rate (eGFR), proteinuria, and mean fluorescence intensity (MFI) of donor-specific antibodies (DSA). RESULTS: A total of 69 KT patients were converted to belatacept. eGFR increased from 28.9 ± 18.2 mL/min/1.73 m2 at time of conversion to 34.8 ± 20.1 mL/min/1.73 m2 after 18 months (P = .025). After conversion, 26/69 patients (37.7%) showed a sustained increase in eGFR of >5 mL/min/1.73 m2 after 12 months and were defined as responders. All other patients (43/69, 62.3%) were defined as nonresponders. In multivariate analysis, nonresponders presented with significantly higher proteinuria (552 ± 690 vs 165 ± 158 mg/L; P = .004) at the time of conversion. Changes of eGFR from before conversion and the time of conversion were similar in both subgroups (-5.7 ± 9.2 and 29.2 ± 17.3 mL/min/1.73 m2 in responders and -4.6 ± 10.7 and 28.7 ± 19.0 mL/min/1.73 m2 in nonresponders). HLA antibody panel reactivity did not change after conversion. DSA-MFI was higher in nonresponders (7,155 ± 6,785) than in responders (2,336 ± 2,173; P = .001). One patient (1/69, 1.4%) developed de novo DSA after conversion, and no antibody-mediated rejection was diagnosed within 1,540 treatment months. CONCLUSIONS: Late conversion to belatacept is beneficiary for a subgroup of patients, with lower proteinuria at the time of conversion being an indicator for a favorable outcome.

Extended-Spectrum Beta-Lactamase-Producing Enterobacteriaceae-Related Urinary Tract Infection in Kidney Transplant Recipients: Risk Factors, Treatment, and Long-Term Outcome.

BACKGROUND: Prevalence of extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBL-E) has risen in kidney transplant (KT) patients, with no long-term data so far on graft function or survival. METHODS: KT patients with ESBL-E-positive urine culture were retrospectively analyzed regarding initial adequate antimicrobial therapy, recurrent infection, transplant function, and survival compared with an ESBL-E-negative KT control cohort. RESULTS: ESBL-E-positive KT patients (n = 93) were older (55.5 ± 16.1 vs 49.5 ± 16.8 y; P = .001), presented with higher trough levels of cyclosporine and tacrolimus (121 ± 71 vs 102 ± 32 ng/mL [P = .04]; and 7.9 ± 3.3 vs 7.0 ± 2.3 ng/mL [P = .04], respectively), higher dosages of mycophenolate (1,533 ± 670 vs 1,493 ± 436; P = .001), and more acute rejection episodes within 3 months before diagnosis (12.9% vs 0.8%; P < .0001) compared with control subjects (n = 591). Five-year patient survival was superior in control subjects compared with ESBL-E-positive patients (91.2% vs 83.5%; P = .034) but long-term graft function was similar. Hospitalization rates were higher in patients presenting with ESBL-E-related urinary tract infection (UTI) compared with control subjects with ESBL-E-negative UTI (60.3% vs 31.3%; P = .002) but 5-year graft survival was superior in patients presenting with ESBL-E-related UTI (88.6% vs 69.8%; P = .035) compared with control subjects with ESBL-E-negative UTI. Recurrence rates were similar in patients with or without ESBL-E-related UTI. Initial antibiotic treatment was adequate in 41.2% of patients presenting with ESBL-E-related urosepsis, resulting in a reevaluation of antibiotic stewardship in our clinic. CONCLUSIONS: ESBL-E detection in general was associated with higher mortality, but graft survival in patients with ESBL-E-related UTI was significantly better compared with ESBL-E-negative UTI.

Influence of the cluster constituents' reactivity on the desorption/ionization process induced by neutral SO2 clusters.

The influence of the chemical nature of the cluster constituents on the desorption/ionization process was investigated for desorption/ionization induced by neutral SO2 clusters (DINeC). The polar clusters act as a transient matrix in which the desorbed analyte molecules are dissolved during the desorption process. For drop-cast samples, the desorption/ionization efficiency was found to be largely independent of the pH value of the initial solution the samples were prepared from; positive ions were almost always dominant and no multiply charged negative ions were observed. The results were traced back to the interaction of SO2 with water present in the samples. Both H/D exchange experiments and surface charge measurements showed that SO2 from the cluster beam interacts with water on and in the sample forming sulfurous acid. The latter then acts as an efficient proton supply leading to an enhanced ionization efficiency. The results demonstrate the possibility to control the ionization efficiency when using reactive cluster constituents in desorption-based ionization methods such as DINeC and cluster-based secondary ion mass spectrometry.

Characterization of the Aerosol-Based Synthesis of Uranium Particles as a Potential Reference Material for Microanalytical Methods.

A process for production of micrometer-sized particles composed of uranium oxide using aerosol spray pyrolysis is characterized with respect to the various production parameters. The aerosol is generated using a vibrating orifice aerosol generator providing monodisperse droplets, which are oxidized in a subsequent heat treatment. The final particles are characterized with microanalytical methods to determine size, shape, internal morphology, and chemical and structural properties in order to assess the suitability of the produced particles as a reference material for microanalytical methods, in particular, for mass spectrometry. It is demonstrated that physicochemical processes during particle formation and the heat treatment to chemically transform particles into an oxide strongly influence the particle shape and the internal morphology. Synchrotron µ-X-ray based techniques combined with µ-Raman spectroscopy have been applied to demonstrate that the obtained microparticles consist of a triuranium octoxide phase. Our studies demonstrate that the process is capable of delivering spherical particles with determined uniform size and elemental as well as chemical composition. The particles therefore represent a suitable base material to fulfill the homogeneity and stability requirements of a reference material for microanalytical methods applied in, for example, international safeguards or nuclear forensics.

Risk Evaluation and Outcome of Pneumocystis jirovecii Pneumonia in Kidney Transplant Patients.

Pneumocystis jirovecii pneumonia (PJP) affects immunocompromised patients. As a result of effective prophylaxis in the 1st months after kidney transplantation, PJP is increasingly diagnosed in the long term after transplantation. The present study evaluates course and outcome of PJP in a single transplant center from 2010 to 2015. Twenty-three patients presented with PJP at a mean of 53.7 ± 50.2 months after transplantation. Of these, 3 patients underwent ABO-incompatible (ABO-i) living-donor transplantation and 3 patients were treated with the use of belatacept. For risk estimation, 3 control cohorts were defined: a control group of all kidney transplant patients presenting for routine follow up (n = 575), all patients transplanted in an ABO-i setting (n = 45), and all patients treated with belatacept in our clinic (n = 69). Mortality in patients with PJP was 3/23 (13%) and graft loss after PJP was 3/23 (13%) resulting in patient and graft survivals of 87% and 73.9%, respectively. All patients were without PJP prophylaxis at time of diagnosis. Five of the 23 PJP patients received rejection therapy or dose escalation of immunosuppression 6 months before PJP infection, and 1 patient experienced acute rejection within 6 months after PJP treatment. In the course of PJP, 8 patients developed acute respiratory insufficiency. At time of PJP diagnosis, patients presented with severe lymphopenia (mean ± SD lymphocyte count, 0.64 ± 0.27/nL; normal range: 1.5-3/nL). Patients after ABO-i transplantation, as well as patients treated with belatacept, showed an increased risk for PJP (7.3% and 4.3%, respectively); however, in belatacept patients, other risk factors, such as age, low estimated glomerular filtration rate (eGFR), and lymphopenia seemed to contribute to this increased risk.

[Immunosuppression and its use in kidney transplantation]. / Immunsuppression und Ergebnisse in der Nierentransplantation.

BACKGROUND: Current immunosuppressive protocols effectively prevent acute rejection of renal allografts. Extensive drug toxicity and the deleterious effects of long-term immunosuppression are associated with significant morbidity and mortality. OBJECTIVES: The purpose of this article is to provide an overview over modern immunosuppressants and their unwanted side effects and to discuss strategies for improved long-term transplant survival. METHODS: Review of the current topic-related literature and discussion of our own experience. RESULTS: The use of antibody induction together with an initial combination therapy of calcineurin inhibitors, mycophenolate and steroids is recommended and results in excellent early outcomes. Detrimental effects include an increased incidence of infections, malignomas, and cardiovascular diseases. Long-term transplant survival is impaired by extensive drug toxicity and the frequent development of donor specific antibodies. Reduction of overall cumulative exposure to immunosuppressants or the reduction of specific toxic drugs such as calcineurin inhibitors and steroids may improve long-term results. Alternative immunosuppressants like mTOR inhibitors and belatacept appear to be effective and safe but their long-term effects on patient and allograft survival needs to be established in clinical trials. CONCLUSIONS: Current immunosuppressants provide effective protection from renal allograft rejection. However, their use is complicated by serious side effects. In the future, development of novel immunosuppressants and optimization of minimization strategies may help to improve long-term success after kidney transplantation.

New perspectives of immunosuppression.

Efficient rejection prophylaxis and excellent short-term results in organ transplantation can not obscure the fact that long-term outcomes have not improved substantially over the last decade with rather constant graft attrition rates beyond the first year. There remains an unmet medical need for new immunosuppressive regimens to improve long-term graft and patient survival while carrying a low side effect burden. Several trials in renal transplant recipients are in the planning stages. In general there are two major strategies to improve outcomes: (a) the constant evolution of new immunosuppressive regimens with the currently approved immunosuppressants, and/or (b) the use of novel immunosuppressants. In this review, we give an overview of the most recent developments of novel immunosuppressive regimes. We show promising new immunosuppressive drugs and new immunosuppressive strategies serving as potential alternative's for calcineurin inhibitor-based regimens. Such regimens should provide similar efficacy and eventually better tolerability or a different side-effect profile with clinical benefits.

Quantification of the ionization probability during desorption/ionization of oligopeptides induced by neutral cluster impact.

RATIONALE: Desorption-and-ionization induced by neutral cluster impact is a soft and matrix-free method, which leads to the formation of free ions of oligopeptides and smaller proteins without fragmentation. As a prerequisite for its successful application in bioanalytics, especially with respect to sensitivity, the ionization efficiency, i.e., the ion-to-neutral ratio of the desorbing molecules, was determined. METHODS: Neutral SO2 clusters of 10(3) to 10(4) molecules in size were seeded in a pulsed He beam and used to desorb and ionize oligopeptides by means of cluster surface impact. The samples were prepared by drop casting a well-defined amount of substance on the substrate surface; the desorbing ions were identified by means of time-of-flight mass spectrometry. Furthermore, the ion current leaving the surface was determined for positive ions, which predominate in the investigated oligopeptides. RESULTS: For angiotensin II, bradykinin (1-7), and adrenocorticotropic hormone (34-39), the number of ions desorbed from the respective samples was compared with the amount of substance applied on the substrate. Assuming that all biomolecules were desorbed during the experiment, the ion-to-neutral ratio or ionization efficiency η was determined. For the tested molecules, values of η between 0.5% and 3% were observed; the substrate material and the total amount of substance applied were shown to have a minor effect on the results. CONCLUSIONS: The ion-to-neutral ratio in desorption/ionization of oligopeptides induced by neutral cluster impact was determined to be of the order of 10(-3) to 10(-2). The soft and matrix-free nature of the method in combination with this value of η might be interesting for applications in bioanalytics.

Adsorption dynamics of ethylene on Si(001).

The dynamics of ethylene adsorption on the Si(001) surface was investigated by means of molecular beam techniques. A constant decrease of initial sticking probability s(0) was observed with increasing kinetic energy indicating a non-activated adsorption channel. With increasing surface temperature, s(0) decreases as well, pointing towards adsorption via a precursor state. Quantitative evaluation of the temperature dependence of s(0) via the Kisliuk model was possible for surface temperatures above 250 K; below that value, the temperature dependence is dominated by the adsorption dynamics into the precursor state. Maximum surface coverage was found to be reduced with increasing surface temperature, which is discussed on the basis of a long lifetime of the precursor state at low temperatures.