Biomedical subjects

I Popa

Publications and source records attributed to I Popa.

At least 19 recordsLinked to original sources

PubMed2005

Structure and reactivity of surface oxides on Pt(110) during catalytic CO oxidation.

We present the first structure determination by surface x-ray diffraction during the restructuring of a model catalyst under reaction conditions, i.e., at high pressure and high temperature, and correlate the restructuring with a change in catalytic activity. We have analyzed the Pt(110) surface during CO oxidation at pressures up to 0.5 bar and temperatures up to 625 K. Depending on the pressure ratio, we find three well-defined structures: namely, (i) the bulk-terminated Pt(110) surface, (ii) a thin, commensurate oxide, and (iii) a thin, incommensurate oxide. The commensurate oxide only appears under reaction conditions, i.e., when both and CO are present and at sufficiently high temperatures. Density functional theory calculations indicate that the commensurate oxide is stabilized by carbonate ions (CO3(2-)). Both oxides have a substantially higher catalytic activity than the bulk-terminated Pt surface.

Journal Article↗

PubMed2004

Observation of coherent oscillation of a single nuclear spin and realization of a two-qubit conditional quantum gate.

Rabi nutations of a single nuclear spin in a solid have been observed. The experiments were carried out on a single electron and a single 13C nuclear spin of a single nitrogen-vacancy defect center in diamond. The system was used for implementation of quantum logical NOT and a conditional two-qubit gate (CROT). Density matrix tomography of the CROT gate shows that the gate fidelity achieved in our experiments is up to 0.9, good enough to be used in quantum algorithms.

Journal Article↗

PubMed2004

Observation of coherent oscillations in a single electron spin.

Rabi nutations and Hahn echo modulation of a single electron spin in a single defect center have been observed. The coherent evolution of the spin quantum state is followed via optical detection of the spin state. Coherence times up to several microseconds at room temperature have been measured. Optical excitation of the spin states leads to decoherence. Quantum beats between electron spin transitions in a single spin Hahn echo experiment are observed. A closer analysis reveals that beats also result from the hyperfine coupling of the electron spin to a single 14N nuclear spin. The results are analyzed in terms of a density matrix approach of an electron spin interacting with two oscillating fields.

Journal Article↗

PubMed2003

[Relationship between lipids and cutaneous immunity: example of the gangliosides].

Gangliosides are glycosphingolipids made of hydrophobic ceramides coupled to hydrophilic sialylated oligosaccharides. They belong to lipid rafts located on the outer leaflet of the plasma membrane and their oligosaccharide moieties are exposed on the cell surface. Gangliosides are shed as monomeric molecules from the plasma membrane by a largely unknown mechanism into the extracellular medium and they are synthesized de novo by the cells. The shed gangliosides bind to lipoproteins from which they are taken up by erythrocytes and leukocytes. The ganglioside enrichment of leukocytes results in an alteration in the transduction of activation signals, leading to an impaired cellular immunity.

Cytokines↗

PubMed2002

Subcellular distribution and metabolic fate of exogenous ceramides taken up by HL-60 cells.

Ceramides (Cer) are key intermediates in the metabolism of sphingomyelin and are also important second messengers. We report that natural long-chain ceramides added to the incubation medium in microgram amounts are internalized in HL-60 cells as well as the short-chain analogue C2-Cer and targeted to various subcellular compartments. No significant difference was detected in the ability of HL-60 cells to metabolize exogenous Cer containing a short (acetyl) versus long (palmitoyl or oleoyl) acyl chain. After a 2-h incubation time with [14C]-C16 ceramides, most of the cell-bound radioactivity was found in free ceramides. Sphingomyelin was the major metabolized sphingolipid containing labeled ceramides and only a small proportion of exogenous ceramides were converted to neutral glycolipids and gangliosides. Up to 20% of the exogenous ceramides taken up by the cells were recovered in mitochondria, mostly as authentic C16 ceramides and C16 sphingomyelin, along with a trace amount of labeled GM3 ganglioside. These results are consistent with the notion that exogenous natural ceramides enter cells, can be further metabolized in situ and partly targeted to mitochondria, which are known to be involved in the control of programmed cell death.

Carbon Radioisotopes↗

PubMed2001

Occurrence of ceramides and neutral glycolipids with unusual long-chain base composition in purified rat liver mitochondria.

The free ceramide content of rat liver mitochondria was found to be 1.7 nmol/mg protein and outer membranes contained a three-fold higher concentration than inner membranes. The mitochondrial content in neutral glycolipids was 0.6 nmol/mg protein. The long-chain bases found in free ceramides were d18:1 sphingosine, d18:0 3-ketosphinganine and t21:1 phytosphingosine in increasing order. In contrast, 3-ketosphinganine was the only base of glucosylceramide and lactosylceramide of inner membranes, whereas d18:1 sphingosine was the major long-chain base of glucosylceramide of outer membranes.

Animals↗

PubMed1997

Cystic fibrosis mutations in Romania.

UNLABELLED: We have investigated the genotype in 32 children with cystic fibrosis from Romania. The diagnosis of cystic fibrosis was made on the basis of typical clinical findings and sweat electrolyte levels using the pilocarpine iontophoresis method. CONCLUSION: Genetic analysis of 32 children with cystic fibrosis from Romania showed a 25% incidence of DeltaF508 mutation and a 64.5% incidence of unknown mutations, 5 other known mutations and 1 new mutation 1,717-2(A > G).

Blood Proteins↗

PubMed1996

Biological activity of maleic anhydride copolymers. I. Biocompatibility and antitumoural effects of maleic anhydride-vinyl acetate, maleic anhydride-methyl methacrylate and maleic anhydride-styrene copolymers.

A series of maleic anhydride (MA)-vinyl acetate (VA), MA-methyl methacrylate (MM), and MA-styrene (S) copolymers were prepared and characterized. On employing various amounts of initiator, maleic anhydride-vinyl acetate, methyl methacrylate, and styrene copolymers with molecular weights ranging between 18,000 and 200,000 have been obtained. The in vivo and in vitro tests performed on K562 cellular cultures (human chronic myeloid leukemia) have shown that, as a function of the molecular weight, the synthesized copolymers demonstrate a 50% in vitro cytotoxicity and an average tumour regression of maximum 68%.

Animals↗

PubMed1996

Glucoamylase absorption and desorption process.

This paper reports the study of glucoamylase absorption and desorption processes on spherical particles constituting acrylic supports. The kinetic (reaction order, half-life of the reaction, reaction rate constant), and thermodynamic parameters (activation energy, pre-exponential factor) of the glucoamylase immobilization reaction dynamics inside the acrylic supports have been studied. Hindrance of the penetrants (protein molecules), which defeats the polymer's cohesive forces and passes through the diffusional barriers towards the sites available to receive it, denotes the influence of the diffusion phenomena, and might be expressed by the values of the effective diffusion coefficient and of the energetic parameters, as well. The desorption dynamics of glucoamylase in specific buffer concentration gradients and temperature are dependent on the eluent volume and on the protein eluate.

Absorption↗

PubMed1995

Identification of the low density lipoprotein receptor-related protein (LRP) as an endocytic receptor for thrombospondin-1.

Thrombospondin-1 (TSP1) has potent biological effects on vasculature smooth muscle cells (SMCs) and endothelial cells. The regulation of extracellular accumulation of TSP1 is mediated by a previously obscure process of endocytosis which leads to its lysosomal degradation. Since members of the low density lipoprotein receptor (LDLR) family have been found to mediate endocytosis which leads to degradation of a diverse array of ligands, we evaluated their possible role in the uptake and degradation of TSP1 by vascular SMCs, endothelial-cells and fibroblasts. 125I-TSP1 was found to be internalized and degraded lysosomally by all these cell types. Both the internalization and degradation of 125I-TSP1 could be inhibited by a specific antagonist of the LDLR family, the 39-kD receptor-associated protein (RAP). Antibodies to the LDLR-related protein (LRP) completely blocked the uptake and degradation of 125I-TSP1 in SMCs and fibroblasts but not endothelial cells. Solid-phase binding assays confirmed that LRP bound to TSP1 and that the interaction was of high affinity (Kd = 5 nM). Neither RAP nor LRP antibodies inhibited the binding of 125I-TSP1 to surfaces of SMCs. However, cell surface binding, as well as, endocytosis and degradation could be blocked by heparin or by pre-treatment of the cells with either heparitinase, chondroitinase or beta-D-xyloside. The data indicates that cell surface proteoglycans are involved in the LRP-mediated clearance of TSP1. A model for the clearance of TSP1 by these cells is that TSP1 bound to proteoglycans is presented to LRP for endocytosis. In endothelial cells, however, the internalization of TSP1 was not mediated by LRP but since RAP inhibited TSP1 uptake and degradation, we postulate that another member of the LDLR family is likely to be involved.

Binding, Competitive↗

PubMed1983