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Biomedical subjects

L Hellner

Publications and source records attributed to L Hellner.

At least 19 recordsLinked to original sources
PubMed2005

Picometer-scale electronic control of molecular dynamics inside a single molecule.

Tunneling electrons from a low-temperature (5 kelvin) scanning tunneling microscope were used to control, through resonant electronic excitation, the molecular dynamics of an individual biphenyl molecule adsorbed on a silicon(100) surface. Different reversible molecular movements were selectively activated by tuning the electron energy and by selecting precise locations for the excitation inside the molecule. Both the spatial selectivity and energy dependence of the electronic control are supported by spectroscopic measurements with the scanning tunneling microscope. These experiments demonstrate the feasibility of controlling the molecular dynamics of a single molecule through the localization of the electronic excitation inside the molecule.

Journal Article↗
PubMed2004

Atomic-scale STM experiments on semiconductor surfaces: towards molecular nanomachines.

The electronic or quantum control of individual molecules with the scanning tunnelling microscope offers exciting perspectives on operating molecular nanomachines. This implies the use of semiconductor surfaces rather than metallic surfaces which would rapidly quench the electronic excitations. We review recent results illustrating the state of the art and the main problems which need to be solved: the choice, design and properties of functionalized organic molecules on semiconductor surfaces; the control of the inelastic electronic channels through a single molecule; and the search for well-controlled atomic-scale wide-band-gap semiconductor surfaces.

Journal Article↗
PubMed2001

Electronic structure of partially hydrogenated Si(100)-( 2 x 1) surfaces prepared by thermal and nonthermal desorption.

The electronic structure of partially hydrogenated Si(100)- (2 x 1) surfaces, prepared by controlled thermal annealing and nonthermal photon stimulated desorption of fully hydrogenated Si(100) surfaces, has been investigated by using valence band photoemission. Thermal and nonthermal desorption are found to produce very specific electronic surface structures. This led us to the discovery of two specific surface states having binding energies of 1.0 and 0.7 eV associated with the isolated Si dimers and single Si dangling bonds, respectively.

Journal Article↗
PubMed2000

Selective photon-stimulated desorption of hydrogen from GaAs surfaces.

Photon-stimulated desorption of H(+) from hydrogenated GaAs (110) and (100) surfaces was studied as a function of photon energy. Distinct peaks, observed around As 3d core-level binding energy for desorption from the GaAs (100) surface and in the As 3d and Ga 3p region for desorption from the GaAs (110) surface, show a striking similarity with the fine structure (spin-orbit splitting) measured in the photoemission from As 3d and Ga 3p levels. These results provide clear evidence for direct desorption processes and represent a basis for selective modification of hydrogenated GaAs surfaces.

Journal Article↗
PubMed1988

The intragastric milieu during gastric ulcer treatment with pirenzepine 50 mg b.i.d. or cimetidine 400 mg b.i.d.

In a double-blind randomised four-center trial 43 patients with gastric ulcer (20 men, 23 women; mean age 52.2 years) were treated with either pirenzepine (P) 50 mg b.i.d. (n = 24) or cimetidine (C) 400 mg b.i.d. (n = 19) during six weeks. In ten patients gastric juice was examined before and at the end of the treatment for concentration and type of the microbial flora, and for nitrite concentration. After six weeks 83% of the patients in both groups were either symptom-free or clearly improved. In 15/24 patients on P (62.6%) and in 13/18 on C (72.2%) the ulcer(s) were healed at the time of control endoscopy. In the ten patients investigated, intragastric concentrations of fungi, bacteria, and nitrite were not significantly changed by the treatment. In gastric ulcer, treatment with pirenzepine 50 mg b.i.d. or cimetidine 400 mg b.i.d. during six weeks does not result in significant microbial overgrowth or generation of nitrite.

Adult↗
PubMed1985

Pirenzepine versus cimetidine in duodenal ulcer treatment. A clinical and microbiological study.

The therapeutic efficacy of pirenzepine (PIR) and cimetidine (CIM) in duodenal ulcer and their effects on the intragastric milieu have been studied in a double-blind multicentre trial. Seventy-nine patients with endoscopically proven duodenal ulcer were randomly allocated to 4 weeks' treatment with either 50 mg PIR twice daily or 400 mg CIM twice daily. In addition to clinical and endoscopic evaluation and registration of side effects and laboratory test results, endoscopically obtained gastric juice was cultured and its nitrite concentration was measured before and at the end of the treatment. Seventy-five patients completed the study. The treatment groups were comparable with regard to age, sex, smoking habits, and consumption of coffee and alcohol. After 4 weeks, 27 of 37 patients (73%) in the PIR group were completely healed, compared with 29 of 38 (76%) in the CIM group (NS). The number of patients with side effects was similar in both groups, but side effects of antimuscarinic type were more frequently reported by patients in the PIR group. Intragastric microbial concentrations increased significantly during treatment in both groups but remained well within normal limits. No single nitrite concentration before or after treatment exceeded the normal range. In conclusion, the two drugs were about equally effective in the short-term treatment of duodenal ulcer disease. In the doses given they did not adversely affect the intragastric milieu.

Aged↗
PubMed1984

Intragastric bacteria and nitrite after short-term treatment with different doses of antimuscarinic drugs.

In 11 volunteers gastric acid secretion was measured under basal conditions and after modified sham-feeding after 4 1/2 days' treatment with placebo tablets twice daily (placebo), pirenzepine, 50 mg twice daily (pirenzepine), benzilonium bromide, 17.5 mg twice daily (benzilonium 35), or benzilonium bromide, 35 mg twice daily (benzilonium 70), respectively. The first basal portion of gastric fluid was cultured aerobically and anaerobically, and its nitrite concentrations were measured by a colorimetric technique. Basal acid output was reduced 40% by pirenzepine, 71% by benzilonium 35, and 84% by benzilonium 70. Reduction of the stimulated acid output was 47%, 57%, and 74%, respectively. Mean bacterial count (in log10/ml gastric juice) after placebo was 3.50 +/- 0.81 (SEM). Only the treatment with benzilonium 70 gave significantly increased bacterial counts (6.41 +/- 0.68; p less than 0.01). Mean nitrite concentrations (in mumol/l) after placebo, pirenzepine, benzilonium 35, and benzilonium 70 were 2.90 +/- 1.26 (SEM), 3.90 +/- 1.17, 11.36 +/- 7.24, and 18.81 +/- 5.71, respectively. The last value was significantly different from that after placebo (p less than 0.025). Bacterial counts were negatively correlated to basal acid output (p less than 0.001) but not to stimulated acid output. Nitrite was directly correlated to bacterial counts and inversely correlated to basal and stimulated acid output. Even a short-lasting but strong inhibition of gastric acid output by antimuscarinics can change the intragastric milieu significantly. No significant changes occur after moderate reduction of gastric acid output.

Adult↗