Search PubMed⌕ Search

Biomedical subjects

S Bahr

Publications and source records attributed to S Bahr.

9 recordsLinked to original sources
PubMed2006

Interaction of NaI with solid water and methanol.

The interaction of NaI with amorphous solid water (ASW) and methanol (MeOH) has been investigated with metastable impact electron spectroscopy (MIES), UPS(HeI), and temperature programmed desorption (TPD). We have studied the electron emission from the ionization of the highest-lying states of H(2)O, CH(3)OH, and of 5pI. We have prepared NaI layers on ASW (MeOH) films at about 105 K and annealed them up to about 200 K. Surface segregation of iodide is observed in ASW, as predicted for NaI aqueous solutions. On the other hand, surface segregation is not observed in MeOH, again as predicted for the interaction of NaI with liquid methanol. Electronic properties (ionization potentials, optical band gaps) and water binding energies are reported and are analyzed on the basis of available DFT results for hydrated NaI clusters.

Methanol↗
PubMed2006

Electronic structure of the surface of the ionic liquid [EMIM][Tf(2)N] studied by metastable impact electron spectroscopy (MIES), UPS, and XPS.

The near-surface electronic structure of the room-temperature ionic liquid (RT-IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf(2)N]) has been investigated with the combination of the electron spectroscopies metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS (HeI and HeII)), and monochromatized X-ray photoelectron spectroscopy (XPS). We find that the top of the valence band states originates from states of the cation (see also ref 1). The ultimately surface-sensitive technique MIES proves that the surface layer consists of both cations and anions. The temperature dependence of the spectra has been measured between about 160 and 610 K. Information on the glass transition and the possibility for low-temperature distillation of [EMIM][Tf(2)N] at reduced pressures is derived from the present results.

Journal Article↗
PubMed2006

Acetic acid-water interaction in solid interfaces.

The adsorption of acetic acid on a proton-ordered water ice surface is modeled using periodic plane-waves density-functional theory. The structures of acetic acid adsorbed as a monomer or oligomers, hydrated or not, are calculated through gradient optimization. The resulting quantum electronic density of states are compared to metastable impact electron spectroscopy (MIES) results and lead to selection of the most plausible structures of acetic acid on water ice. Hypotheses are formulated for the structure of the acid film growing on the ice surface including mainly cyclic dimers and hydrated forms. Adsorptions of single water molecules on acetic acid crystal surfaces are also studied after optimization of the acetic acid crystal bulk and surface structure. More comparisons with spectroscopic studies are proposed in the accompanying paper.

Journal Article↗
PubMed2006

Interaction of acetic acid with solid water.

The interaction of acetic acid (AA, CH(3)COOH), with solid water, deposited on metals, tungsten and gold, at 80 K, was investigated. We have prepared acid/water interfaces at 80 K, namely, acid layers on thin films of solid water and H(2)O adlayers on thin acid films; they were annealed between 80 and 200 K. Metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy UPS(HeII) were utilized to obtain information on the electronic structure of the outermost surface from the study of the electron emission from the weakest bound MOs of the acids, and of the molecular water. Temperature-programmed desorption (TPD) provided information on the desorption kinetics, and Fourier-transformed infrared spectroscopy (FTIR) provided information on the identification of the adsorbed species as well as on the water and acid crystallization. The results are compatible with the finding of ref 1 (preceding paper), made on the basis of DFT calculations, that AA adsorbs on ice as cyclic dimers. Above 120 K, a rearrangement of the AA dimers is suggested by a sharpening of the spectral features in the IR spectra and by spectral changes in MIES and UPS; this is attributed to the glass transition in AA around 130 K. Above 150 K the spectra transform into those characteristic for polycrystalline polymer chains. This structure is stable up to about 180 K; desorption of water takes place from underneath the AA film, and practically all water has desorbed through the AA film before AA desorption starts. There is no indication of water-induced deprotonation of the acid molecules. For the interaction of H(2)O molecules adsorbed on amorphous AA films, the comparison of MIES with the DFT results of ref 1 shows that the initial phase of exposure does not lead to the formation of a top-adsorbed closed water film at 80 K. Rather, the H(2)O molecules become attached to or incorporated into the preexisting AA network by H bonding; no water network is formed in the initial stage of the water adsorption. Also under these conditions no deprotonation of the acid can be detected.

Journal Article↗
PubMed2005

Interaction of formic acid with solid water.

The interaction of formic acid (HCOOH) with solid water, deposited on tungsten at 80 K, was investigated. We have prepared and annealed formic acid (FA)/water interfaces (FA layers on thin films of solid water and H(2)O adlayers on thin FA films). Metastable impact electron spectroscopy and ultraviolet photoemission spectroscopy (He I and II) were utilized to study the electron emission from the 10a' to 6a' molecular orbitals (MOs) of FA, and the 1b(1), 3a(1), and 1b(2) MOs of H(2)O. These spectra were compared with results of density-functional theory calculations on FA-H(2)O complexes reported in Ref. 14 [A. Allouche, J. Chem. Phys. 122, 234703(2005), (preceding paper)]. Temperature programmed desorption was applied for information on the desorption kinetics. Initially, FA is adsorbed on top of the water film. The FA spectra are distorted with respect to those from FA monomers; it is concluded that a strong interaction exists between the adsorbates. Even though partial solvation of FA species takes place during annealing, FA remains in the top layer up to the desorption of the water film. When H(2)O molecules are offered to FA films at 80 K, no water network is formed during the initial stage of water exposure; H(2)O molecules interact individually via H bonds with the formic acid network. Experiment and theory agree that no water-induced deprotonation of the formic acid molecules takes place.

Journal Article↗
PubMed2002

Use of 2% 2-phenoxyethanol and 0.1% octenidine as antiseptic in premature newborn infants of 23-26 weeks gestation.

In preterm newborn infants, topical iodine-containing antiseptics disturb thyroid hormone regulation while alcohol-based disinfectants may cause local burns. We therefore investigated the use of an aqueous solution containing 0.1% octenidine and 2% 2-phenoxyethanol for skin disinfection during the first seven days of life in premature newborns with a gestational age <27 weeks who were consecutively admitted to our level III neonatal intensive care unit between November 1, 2000 and December 31, 2001 (N=24). In boys. (N=13) the renal excretion of absorbed 2-phenoxyethanol and its metabolite 2-phenoxyacetic acid was quantitated by high-pressure liquid chromatography. In the most immature newborn (gestational age 23 6/7 weeks), a transient erythematous reaction was observed following application of the octenidine/phenoxyethanol solution prior to umbilical vessel catheterization. No other local reactions were observed. The urinary concentration of 2-phenoxyethanol was <2 ppm in all samples, while urinary 2-phenoxyacetic acid concentrations reached 5-95 ppm (median 24 ppm). One infant had a culture-proven septicaemia (Bacillus species) during the first seven days of life. We conclude that, in contrast to alcohol-based antiseptics, an aqueous solution of 0.1% octenidine and 2-phenoxyethanol does not cause major skin damage in premature newborn infants <27 weeks' gestation. 2-Phenoxyethanol is readily absorbed by the newborn's skin but apparently undergoes extensive oxidative metabolization to 2-phenoxyacetic acid.

Anti-Infective Agents, Local↗
PubMed1997

In vitro activities of the biguanide PS-15 and its metabolite, WR99210, against cycloguanil-resistant Plasmodium falciparum isolates from Thailand.

The in vitro activities of the new biguanide PS-15 and its putative active metabolite, WR99210, were determined against seven different isolates or clones of Plasmodium falciparum. The mean 50% inhibitory concentrations of PS-15 and WR99210 were 1,015 and 0.06 ng/ml, respectively. WR99210 was up to 363 times more potent than cycloguanil, the active metabolite of proguanil, against cycloguanil-resistant parasites. The pronounced activity of WR99210 against multidrug-resistant P. falciparum indicates that further studies are required to determine the value of the prodrug, PS-15, as an antimalarial agent.

Animals↗
PubMed1993

[Follow-up angiography after balloon dilatation of aortic isthmus stenoses in adults].

Between May 1985 and April 1991, 30 patients (seven females and 23 males) 14 to 54 years old (median, 25 years) underwent balloon angioplasty for unoperated native (n = 26) or recurrent postoperative (n = 4) coarctation of the aorta. 28/30 patients had systemic hypertension (RR > 140/90 mmHg). Dilatation of the stenotic segment could be achieved in 28/30 patients. The residual pressure gradient was > 30 mmHg in six patients. In 2/4 patients with recurrent coarctation the balloon had ruptured, while dilatation was successful in the other two patients. The mean diameter of the stenotic segment increased from 5.8 +/- 2.7 mm to 11.9 +/- 2.5 mm and the peak pressure gradient decreased from 61 +/- 18 mmHg to 20 +/- 13 mmHg. Complications were a small hemorrhagic pleural effusion in one patient and a groin hematoma in another patient. Clinical follow-up studies with retrograde catheterization of the aorta and angiography were performed in all 28 patients with dilated coarctation, 6 months to 6 years after the procedure, representing a total follow-up time of 72 (average, 2.6) patient-years. Multiple follow-up studies (n = 2-4) were performed in 17/28 patients. In one patient the first angiogram revealed aneurysm formation while a small bulge was seen in two others. Intra-aortic pressure measurements revealed a peak gradient of < 30 mmHg in 24/28 patients with a mean of 14 +/- 10 mmHg. The blood pressure was normal in 23/28 patients. In the other five patients whose pressure gradients were 7, 30, 30, 35, and 60 mmHg moderate hypertension persisted.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗