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Biomedical subjects

E Lundgren

Publications and source records attributed to E Lundgren.

At least 19 recordsLinked to original sources
PubMed2006

Serum calcium is independently associated with insulin sensitivity measured with euglycaemic-hyperinsulinaemic clamp in a community-based cohort.

AIMS/HYPOTHESIS: Diabetes mellitus type 2 is associated with altered calcium metabolism. Moreover, in diseases with supranormal serum calcium levels, such as primary hyperparathyroidism, the prevalence of diabetes is increased. Relatively little is known about the relationship between serum calcium concentration and the underlying causes of diabetes-insulin resistance and defective insulin secretion-in the normocalcaemic general population. MATERIALS AND METHODS: We investigated associations between serum calcium concentration and insulin sensitivity and secretion in a population-based cohort of elderly men (Uppsala Longitudinal Study of Adult Men, n = 961). Insulin sensitivity index (M/I; glucose disposal rate [M] divided by mean insulin concentration [I]) was assessed using euglycaemic-hyperinsulinaemic clamp, and insulin secretion was estimated from the early insulin response (EIR) during an OGTT. RESULTS: In a multivariable linear regression model adjusting for BMI, physical activity, smoking, consumption of tea, alcohol, coffee and dietary calcium, serum phosphate and serum creatinine, 1 SD increase in serum calcium was associated with 0.17 mg kg(-1) min(-1) (mU/l)(-1) x 100 (0.024 mg kg(-1) min(-1) [pmol/l](-1) x 100) decrease in M/I (p = 0.01). The results remained robust in individuals with normal fasting glucose, normal glucose tolerance and serum calcium within the normal range (n = 413, regression coefficient for 1 SD increase -0.45, p = 0.001). Serum calcium was not associated with EIR. Dietary intake of calcium was not independently associated with insulin sensitivity or EIR. CONCLUSION/INTERPRETATION: Our data support the notion that endogenous calcium may be involved early in the development of diabetes and that this effect is mediated mainly through effects on insulin sensitivity rather than defective insulin secretion. Dietary intake of calcium does not seem to influence insulin sensitivity.

Aged↗
PubMed2006

Unusual process of water formation on RuO2(110) by hydrogen exposure at room temperature.

The reduction mechanism of the RuO(2)(110) surface by molecular hydrogen exposure is unraveled to an unprecedented level by a combination of temperature programmed reaction, scanning tunneling microscopy, high-resolution core level shift spectroscopy, and density functional theory calculations. We demonstrate that even at room temperature hydrogen exposure to the RuO(2)(110) surface leads to the formation of water. In a two-step process, hydrogen saturates first the bridging oxygen atoms to form (O(br)-H) species and subsequently part of these O(br)-H groups move to the undercoordinated Ru atoms where they form adsorbed water. This latter process is driven by thermodynamics leaving vacancies in the bridging O rows.

Journal Article↗
PubMed2006

Kinetics of the reduction of the Rh(111) surface oxide: linking spectroscopy and atomic-scale information.

The reduction of the surface oxide on Rh(111) by H(2) was observed in situ by scanning tunneling microscopy (STM) and high-resolution core level spectroscopy (HRCLS). At room temperature, H(2) does not adsorb on the oxide, only in reduced areas. Reduction starts in very few sites, almost exclusively in stepped areas. One can also initiate the reduction process by deliberately creating defects with the STM tip allowing us to examine the reduction kinetics in detail. Depending on the size of the reduced area and the hydrogen pressure, two growth regimes were found. At low H(2) pressures or small reduced areas, the reduction rate is limited by hydrogen adsorption on the reduced area. For large reduced areas, the reduction rate is limited by the processes at the border of the reduced area. Since a near-random distribution of the reduction nuclei was found and the reduction process at defects starts at a random time, one can use Johnson-Mehl-Avrami-Kolmogoroff (JMAK) theory to describe the process of reduction. The microscopic data from STM agree well with spatially averaged data from HRCLS measurements.

Journal Article↗
PubMed2006

Structure of Ag(111)-p(4 x 4)-O: no silver oxide.

The structure of the oxygen-induced p(4 x 4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.

Journal Article↗
PubMed2006

Positive effect of parathyroidectomy on bone mineral density in mild asymptomatic primary hyperparathyroidism.

OBJECTIVES: Patients with mild primary hyperparathyroidism (pHPT) often appear asymptomatic, and have previously been regarded as not requiring treatment. However, increased cardiovascular morbidity and dyslipidaemia have also been recognized in mild pHPT, which also seem to be normalized after parathyroidectomy. The present study explores whether postmenopausal women with mild pHPT have decreased bone mineral density (BMD) compared with age-matched healthy controls, and the effects on BMD of parathyroidectomy. DESIGN, SUBJECTS AND INTERVENTION: A population-based health screening of 5202 postmenopausal women identified 87 overtly asymptomatic patients with mild pHPT as well as age-matched healthy controls. A 5-year follow-up included 49 cases who had undergone parathyroidectomy. BMD was measured with DXA at the femoral neck, the lumbar spine and the total body. RESULTS: At study entry, BMD was 5-6% lower in the lumbar spine (L2-L4) and femoral neck in cases compared with matched controls. After the 5-year follow-up, BMD increased in L2-L4 by 2.9% (P = 0.002) in the parathyroidectomized cases and remained stable in the femoral neck. However, femoral neck BMD increased 4.1% (P = 0.013) for cases <67 years old (50% of the cohort). CONCLUSION: In accordance with recent NIH guidelines for pHPT treatment, the level of BMD per se in the investigated group of patients justifies parathyroidectomy in almost half of the cases with mild pHPT. Surgery could be expected to increase BMD in L2-L4 to the level of the controls, to increase femoral neck BMD in patients <67 years of age and to preserve femoral neck BMD in the elderly population.

Absorptiometry, Photon↗
PubMed2005

One-dimensional PtO2 at Pt steps: formation and reaction with CO.

Using core-level spectroscopy and density functional theory we show that a one-dimensional (1D) oxide structure forms at the steps of the Pt(332) surface after exposure. The 1D oxide is found to be stable in an oxygen pressure range, where bulk oxides are only metastable, and is therefore argued to be a precursor to the Pt oxidation. As an example of the consequences of such a precursor exclusively present at the steps, we investigate the reaction of CO with oxygen covered Pt(332). Albeit more strongly bound, the oxidic oxygen is found to react more easily with CO than oxygen chemisorbed on the Pt terraces.

Journal Article↗
PubMed2005

Ru(0001) model catalyst under oxidizing and reducing reaction conditions: in-situ high-pressure surface X-ray diffraction study.

With surface X-ray diffraction (SXRD) using a high-pressure reaction chamber we investigated in-situ the oxidation of the Ru(0001) model catalyst under various reaction conditions, starting from a strongly oxidizing environment to reaction conditions typical for CO oxidation. With a mixture of O(2) and CO (stoichiometry, 2:1) the partial pressure of oxygen has to be increased to 20 mbar to form the catalytically active RuO(2)(110) oxide film, while in pure oxygen environment a pressure of 10(-5) mbar is already sufficient to oxidize the Ru(0001) surface. For preparation temperatures in the range of 550-630 K a self-limiting RuO(2)(110) film is produced with a thickness of 1.6 nm. The RuO(2)(110) film grows self-acceleratedly after an induction period. The RuO(2) films on Ru(0001) can readily be reduced by H(2) and CO exposures at 415 K, without an induction period.

Journal Article↗
PubMed2005

A surface x-ray study of the structure and morphology of the oxidized Pd001 surface.

The oxidation of Pd(100) and the formation of PdO was studied in situ using surface x-ray diffraction. A bulklike, epitaxial PdO film is formed at oxygen partial pressures beyond 1 mbar and sample temperatures exceeding 650 K. The main orientation is PdO(001)/Pd(001), based upon bulk reflections from the PdO film. By comparing with measurements from the Pd crystal truncation rods, we estimate an rms surface roughness of 6 A, in good agreement with previous high pressure scanning tunneling microscopy measurements. Finally, we observed the transformation from the (radical5 x radical5) surface oxide to PdO bulk oxide at 675 K and 50 mbar O(2) pressure.

Journal Article↗
PubMed2004

High-coverage oxygen structures on Rh111: adsorbate repulsion and site preference is not enough.

A new O induced structure on Rh(111) displaying a (2 sqaureroot[3] x 2sqaureroot[3])R30 degrees periodicity with an oxygen coverage of 2/3 has been studied by high resolution core level spectroscopy, scanning tunneling microscopy, and density functional theory. Although O favors fcc hollow sites in all other known phases, it occupies both fcc and hcp sites in this structure, which cannot be explained by pairwise adsorbate repulsion only. Both the (2sqaureroot[3] x 2sqaureroot[3])R30 degrees and (2 x 2)-3O structures also exemplify that density-of-states contrast can lead to oxygen adatoms appearing as protrusions in scanning tunneling microscopy images.

Journal Article↗
PubMed2004

Self-limited growth of a thin oxide layer on Rh(111).

The oxidation of the Rh(111) surface at oxygen pressures from 10(-10) mbar to 0.5 bar and temperatures between 300 and 900 K has been studied on the atomic scale using a multimethod approach of experimental and theoretical techniques. Oxidation starts at the steps, resulting in a trilayer O-Rh-O surface oxide which, although not thermodynamically stable, prevents further oxidation at intermediate pressures. A thick corundum like Rh2O3 bulk oxide is formed only at significantly higher pressures and temperatures.

Journal Article↗
PubMed2004

Visualization of atomic processes on ruthenium dioxide using scanning tunneling microscopy.

The visualization of surface reactions on the atomic scale provides direct insight into the microscopic reaction steps taking place in a catalytic reaction at a (model) catalyst's surface. Employing the technique of scanning tunneling microscopy (STM), we investigated the CO oxidation reaction over the RuO2(110) and RuO2(100) surfaces. For both surfaces the protruding bridging O atoms are imaged in STM as bright features. The reaction mechanism is identical on both orientations of RuO2. CO molecules adsorb on the undercoordinated surface Ru atoms from where they recombine with undercoordinated O atoms to form CO2 at the oxide surface. In contrast to the RuO2(110) surface, the RuO2(100) surface stabilizes also a catalytically inactive c(2 x 2) surface phase onto which CO is not able to adsorb above 100 K. We argue that this inactive RuO2(100)-c(2 x 2) phase may play an important role in the deactivation of RuO2 catalysts in the electrochemical Cl2 evolution and other heterogeneous reactions.

Journal Article↗
PubMed2004

Kinetic hindrance during the initial oxidation of Pd(100) at ambient pressures.

The oxidation of the Pd(100) surface at oxygen pressures in the 10(-6) to 10(3) mbar range and temperatures up to 1000 K has been studied in situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions, we observe either a thin (sqrt[5]xsqrt[5])R27 degrees surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K.

Journal Article↗
PubMed2003

Identification of step atoms by high resolution core level spectroscopy.

Vicinal Rh(111) surfaces are studied with high resolution core level photoemission. We demonstrate the possibility to distinguish between the different kinds of surface atoms on these surfaces by virtue of their 3d core level binding energies. In particular, the low coordinated step atoms are found to exhibit a clear fingerprint in Rh 3d spectra. We demonstrate how this may be used to show that initial oxygen adsorption occurs on the steps and not on the terraces of the vicinal surfaces.

Journal Article↗
PubMed2002

Two-dimensional oxide on Pd(111).

The oxidation of Pd(111) leads to an incommensurate surface oxide, which was studied by the use of scanning tunneling microscopy, surface x-ray diffraction, high resolution core level spectroscopy, and density functional calculations. A combination of these methods reveals a two-dimensional structure having no resemblance to bulk oxides of Pd. Our study also demonstrates how the atomic arrangement of a nontrivial incommensurate surface can be solved by molecular dynamics in a case where experimental techniques alone give no solution.

Journal Article↗
PubMed2002

Geometry of the valence transition induced surface reconstruction of Sm(0001).

We present a structural determination of the surface reconstruction of the Sm(0001) surface using surface x-ray diffraction, scanning tunneling microscopy, and ab initio calculations. The reconstruction is associated with a large (22%) expansion of the atomic radius for the top monolayer surface Sm atoms. The mechanism driving the surface reconstruction in Sm is unique among all elements and is connected to the strong correlations of the 4f electrons in Sm and the intermediate valence observed in certain Sm compounds. The atoms constituting the top monolayer of Sm(0001) have vastly different chemical properties compared to the layer underneath and behave as if they were an adsorbate of a different chemical species.

Journal Article↗
PubMed2001

Capture of a dimeric intermediate during transthyretin amyloid formation.

Point mutations in the human plasma protein transthyretin are associated with the neurological disorder familial amyloidosis with polyneuropathy type 1. The disease is characterized by amyloid fibril deposits causing damage at the site of deposition. Substitution of two amino acids in the hydrophobic core of transthyretin lead to a mutant that was very prone to form amyloid. In addition, this mutant has also been shown to induce a toxic response on a neuroblastoma cell line. Renaturation of the transthyretin mutant at low temperature facilitated the isolation of an amyloid-forming intermediate state having the apparent size of a dimer. Increasing the temperature effectively enhanced the rate of interconversion from a partly denatured protein to mature amyloid. Using circular dichroism the beta-sheet content of the formed mature fibrils was significantly lower than that of the native fold of transthyretin. Morphology studies using electron microscopy also indicated a temperature-dependent transformation from amorphous aggregates toward mature amyloid fibrils. In addition, 1-anilino-8-naphtalenesulfonate fluorescence studies suggested the loss of the thyroxin-binding channel within both the isolated intermediate and the mature fibrils.

Amyloid↗
PubMed2001

Adsorption sites and ligand effect for CO on an alloy surface: a direct view.

CO adsorption on a PtCo(111) surface was studied by scanning tunneling microscopy. Comparison of images with chemical contrast of Pt and Co and images showing the CO molecules indicates that CO resides exclusively on top of Pt sites and never on Co. CO bonding is highly sensitive to the chemical environment. The probability to find CO on a Pt atom increases drastically with the number of its Co nearest neighbors. Ab initio calculations show that this ligand effect is due to different positions of the center of the Pt d band.

Journal Article↗