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| 2. |
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| 3. |
- Boström, R., Eriksson, A.I., Åhlén, L., Blomberg, L., Gustafsson, G., Holback, B., Holmgren, G., Holtet, J., Jansson, S.E., Lindqvist, P.A., Lybekk, B., Mälkki, A., Riihelä, P. and Wahlund, J.E.
(författare)
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The Rosetta Dual Langmuir Probe Instrument for Measurements of Plasma Density, Temperature and Flow Velocity.
- 2001
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Ingår i: ESA SP-1165.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 4. |
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| 5. |
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| 6. |
- Bassan, Arianna, et al.
(författare)
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A Density Functional Study of a Biomimetic Non-Heme Iron Catalyst : Insights into Alkane Hydroxylation and Olefin Oxidation by a Formally HO-Fe(V)=O Oxidant
- 2004
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 11:2, s. 692-705
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Tidskriftsartikel (refereegranskat)abstract
- The reactivity of [HO(tpa)FeVO] (TPA=tris(2-pyridylmethyl)amine), derived from OO bond heterolysis of its [H2O(tpa)FeIIIOOH] precursor, was explored by means of hybrid density functional theory. The mechanism for alkane hydroxylation by the high-valent iron–oxo species invoked as an intermediate in Fe(tpa)/H2O2 catalysis was investigated. Hydroxylation of methane and propane by HOFeVO was studied by following the rebound mechanism associated with the heme center of cytochrome P450, and it is demonstrated that this species is capable of stereospecific alkane hydroxylation. The mechanism proposed for alkane hydroxylation by HOFeVO accounts for the experimentally observed incorporation of solvent water into the products. An investigation of the possible hydroxylation of acetonitrile (i.e., the solvent used in the experiments) shows that the activation energy for hydrogen-atom abstraction by HOFeVO is rather high and, in fact, rather similar to that of methane, despite the similarity of the HCH2CN bond strength to that of the secondary CH bond in propane. This result indicates that the kinetics of hydrogen-atom abstraction are strongly affected by the cyano group and rationalizes the lack of experimental evidence for solvent hydroxylation in competition with that of substrates such as cyclohexane.
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| 7. |
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| 8. |
- Bassan, Arianna, et al.
(författare)
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A Theoretical Study of the Cis-Dihydroxylation Mechanism in Naphthalene 1,2-dioxygenase
- 2004
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Ingår i: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 0949-8257 .- 1432-1327. ; 9:4, s. 439-452
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic mechanism of naphthalene 1,2-dioxygenase has been investigated by means of hybrid density functional theory. This Rieske-type enzyme, which contains an active site hosting a mononuclear non-heme iron(II) complex, uses dioxygen and two electrons provided by NADH to carry out the cis-dihydroxylation of naphthalene. Since a (hydro)peroxo-iron(III) moiety has been proposed to be involved in the catalytic cycle, it was probed whether and how this species is capable of cis-dihydroxylation of the aromatic substrate. Different oxidation and protonation states of the Fe–O2 complex were studied on the basis of the crystal structure of the enzyme with oxygen bound side-on to iron. It was found that feasible reaction pathways require a protonated peroxo ligand, FeIII–OOH; the deprotonated species, the peroxo-iron(III) complex, was found to be inert toward naphthalene. Among the different chemical patterns which have been explored, the most accessible one involves an epoxide intermediate, which may subsequently evolve toward an arene cation, and finally to the cis-diol. The possibility that an iron(V)-oxo species is formed prior to substrate hydroxylation was also examined, but found to implicate a rather high energy barrier. In contrast, a reasonably low barrier might lead to a high-valent iron-oxo species [i.e. iron(IV)-oxo] if a second external electron is supplied to the mononuclear iron center before dioxygenation.
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| 9. |
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| 10. |
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| 11. |
- Bassan, Arianna, et al.
(författare)
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Oxygen Activation by Rieske Non-Heme Iron Oxygenases, a Theoretical Insight
- 2004
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:34, s. 13031-13041
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Tidskriftsartikel (refereegranskat)abstract
- The first steps of dioxygen activation in naphthalene 1,2-dioxygenase have been investigated by means of hybrid density functional theory. Reduction of molecular oxygen by this Rieske dioxygenase occurs in the catalytic domain accommodating a mononuclear non-heme iron(II) complex, and it requires two external electrons ultimately delivered by a Rieske [2Fe−2S] cluster hosted in the neighboring domain. Theoretical tools have been applied to gain insight into the O2-binding step and into the first one-electron-transfer process involving the mononuclear and the Rieske centers, and yielding an iron(II)−superoxo intermediate. The reaction, which is mimicked with a model including both metal sites, is found to be a reversible equilibrium. Although the entropic loss associated with the binding of O2 to iron(II) is not canceled by the corresponding enthalpic binding energy, it is, however, balanced by the exothermicity of the electron transfer process from the Rieske cluster to the dioxygen-bound iron(II) complex. The rationalization for the calculated energetics is related to the values of the ionization potential (IP) of the Rieske cluster and the electron affinity (EA) of the mononuclear iron complex: the latter is computed to be higher than the former, when dioxygen is bound to the metal. The possibility that a second external electron is delivered to the mononuclear site before dioxygenation of the substrate has also been examined. It is shown that, if the second electron is available in the Rieske domain, the electron transfer process is energetically favored. The results acquired with the large model comprising the two metal centers are compared to the corresponding information collected from the study of smaller models, where either the mononuclear iron complex or the Rieske cluster is included.
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| 12. |
- Bergström, L, et al.
(författare)
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Probing polymeric stabilization in nonaqueous media by direct measurements
- 2000
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Ingår i: Journal of The American Ceramic Society. - 0002-7820 .- 1551-2916. ; 83, s. 217-219
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Tidskriftsartikel (refereegranskat)abstract
- The steric repulsion induced by adsorbed layers of the commercial dispersant Hypermer KD3 has been probed by direct measurements in decalin. The forces are long range (commencing at 30-40 nm) and repulsive, and the distance dependence can be modeled with a simple scaling theory expression valid for polymer brushes. We obtain layer thicknesses on the order of L~9-15 nm for the compressed layers depending on KD3 concentration while the undisturbed layers have a thickness L~23-24 nm, independent of polymer concentration. Comparision of the measured interaction lengths of compressed and undisturbed polymer layers with previous layer thickness estimates based on rheological studies shows that the polymer layers are compressed in dense suspensions.
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| 13. |
- Blomberg, E, et al.
(författare)
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Polymer bilayer formation due to specific interactions between β-cyclodextrin and adamantane: A surface force study
- 2004
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 20, s. 10449-10454
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Tidskriftsartikel (refereegranskat)abstract
- The purposes of this study are to utilize the interactions between an adamantane end-capped poly-(ethylene oxide) (PEO) and a cationic polymer of β-cyclodextrin to build polymer bilayers on negatively charged surfaces, and to investigate the interactions between such layers. The association of this system in solution has been studied by rheology, light scattering, and fluorescence measurements. It was found that the adamantane-terminated PEO (PEO-Ad) mixed with the β-cyclodextrin polymer gives complexes where the interpolymer links are formed by specific inclusion of the adamantane groups in the β-cyclodextrin cavities. This results in a higher viscosity of the solution and growth of intermolecular clusters. The interactions between surfaces coated with a cationized β-cyclodextrin polymer across a water solution containing PEO-Ad polymers were studied by employing the interferometric surface force apparatus (SFA). In the first step, the interaction between mica surfaces coated with the cationized β-cyclodextrin polymer in pure water was investigated. It was found that the β-cyclodextrin polymer adsorbs onto mica and almost neutralizes the surface charge. The adsorbed layers of the β-cyclodextrin polymer are rather compact, with a layer thickness of about 60Å(30Å per surface). Upon separation, a very weak attractive force is observed. The β-cyclodextrin solution was then diluted by pure water by a factor of 3000 and a PEO-Ad polymer was introduced into the solution. Two different architectures of the PEO-Ad polymer were investigated: a four-arm structure and a linear structure. After the adsorption of the PEO polymer onto the β-cyclodextrin layer reached equilibrium, the forces were measured again. It was found that the weak repulsive longrange force had disappeared and an attractive force caused the surfaces to jump into contact, and that the compressed layer thickness had increased. The attractive force is interpreted as being due to a specific recognition between the hydrophobic adamantane groups on the PEO-Ad polymer and the hydrophobic cavity in the β-cyclodextrin molecules. Furthermore, the attractive force observed on separation has increased significantly, which is a further indication of a specific interaction between the β-cyclodextrin polymer and the adamantane groups
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| 14. |
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| 15. |
- Blomberg, Lars G., et al.
(författare)
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EMMA - the electric and magnetic monitor of the aurora on Astrid-2
- 2004
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 22:1, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- The Astrid-2 mission has dual primary objectives. First, it is an orbiting instrument platform for studying auroral electrodynamics. Second, it is a technology demonstration of the feasibility of using micro-satellites for innovative space plasma physics research. The EMMA instrument, which we discuss in the present paper, is designed to provide simultaneous sampling of two electric and three magnetic field components up to about 1 kHz. The spin plane components of the electric field are measured by two pairs of opposing probes extended by wire booms with a separation distance of 6.7 m. The probes have titanium nitride (TiN) surfaces. which has proved to be a material with excellent properties for providing good electrical contact between probe and plasma. The wire booms are of a new design in which the booms in the stowed position are wound around the exterior of the spacecraft body. The boom system was flown for the first time on this mission and worked flawlessly. The magnetic field is measured by a tri-axial fluxgate sensor located at the tip of a rigid. hinged boom extended along the spacecraft spin axis and facing away from the Sun. The new advanced-design fluxgate magnetometer uses digital signal processors for detection and feedback, thereby reducing the analogue circuitry to a minimum. The instrument characteristics as well as a brief review of the science accomplished and planned are presented.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Eriksson, Stefan, et al.
(författare)
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Lobe cell convection and field-aligned currents poleward of the region 1 current system
- 2002
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 107:A8
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Tidskriftsartikel (refereegranskat)abstract
- [1] We present a case and statistical study of plasma convection in the Northern Hemisphere during summer conditions using electric field, magnetic field, and particle data taken during dawn-dusk directed orbits of the FAST satellite. To our knowledge, this set provides the most comprehensive combination of data as yet presented in support of lobe cell convection from an ionospheric perspective this far from the noon sector. In particular, we study the current systems and convection patterns for all passes in July 1997 that show evidence for six large-scale field-aligned currents (FACs) rather than the usual system of four FACs associated with the region 1/region 2 current systems. A total of 71 passes out of 232 in the study had the extra pair of FACs. The extra pair of FACs in 30 of the 71 cases lies either on the dawnside or on the duskside of the noon-midnight meridian, and their position is strongly correlated with the polarity of the IMF By (negative and positive, respectively). This is consistent with the IMF dependence of a three-cell convection pattern of coexisting merging, viscous, and lobe-type convection cells. The occurrence of the asymmetric FAC pair was also strongly linked to conditions of IMF |B-y/B-z | > 1. The extra pair of FACs in these cases was clearly associated with the lobe cell of the three-cell convection system. The remaining 41 cases had the pair of FACs straddling the noon-midnight meridian. The extra pair of FACs was often (20 cases out of 30) observed at magnetic local times more than three hours away from noon, rather than being confined to regions near noon and the typical location of the cusp. Such a current system consisting of a pair of FACs poleward of the nearest region 1 current is consistent with the IMF B-y-dependent global MHD model developed by Ogino et al. [1986] for southward IMF conditions, as well as with other magnetospheric and ionospheric convection models that include the effects of merging occuring simultaneously at both low-latitude dayside and high-latitude lobe and flank magnetopause reconnection sites. Finally, the presence of the additional FACs and three-cell convection well away from noon show that the entire dayside ionosphere is affected by IMF-dependent processes, rather than only a limited region around noon.
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| 20. |
- Farouk, Salah E, et al.
(författare)
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Gamma delta T cells inhibit in vitro growth of the asexual blood stages of Plasmodium falciparum by a granule exocytosis-dependent cytotoxic pathway that requires granulysin.
- 2004
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Ingår i: European Journal of Immunology. - : Wiley. - 0014-2980 .- 1521-4141. ; 34:8, s. 2248-56
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Tidskriftsartikel (refereegranskat)abstract
- Several reports have stated the ability of gamma delta T cells to inhibit the growth of the asexual blood stages of Plasmodium falciparum in vitro. However, little information is available about the mechanisms involved. In this study, in vitro systems were used to study the role of the granule exocytosis-dependent cytotoxic pathway in the growth inhibition/killing of P. falciparum by human gamma delta T cells. Our results show that the inhibition requires cell-to-cell contact and that gamma delta T cells kill the asexual blood stages of P. falciparum through a granule exocytosis-dependent cytotoxic pathway after recognition of certain ligands or molecules expressed on the surface of infected erythrocytes or merozoites. The in vitro inhibitory capacity of gamma delta T cells was strongly correlated with the expression of granulysin in the cytotoxic granules, while non-inhibitory CD4+ and CD8+ T cells expressed very little, implicating a role for granulysin in parasite inhibition. This was further suggested by the addition of neutralizing anti-granulysin antibodies, which abrogated the parasite inhibitory capacity of the gamma delta T cells. Taken together, our results suggest that the capacity of gamma delta T cells for inhibition/killing of P. falciparum is based on the granule exocytosis-dependent cytotoxic pathway and that the presence of granulysin is essential to maintain efficient killing.
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| 21. |
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| 22. |
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| 23. |
- Grunnesjö, Marie I., et al.
(författare)
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A randomized controlled clinical trial of stay-active care versus manual therapy in addition to stay-active care : functional variables and pain.
- 2004
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Ingår i: Journal of Manipulative and Physiological Therapeutics. - : Elsevier BV. - 0161-4754 .- 1532-6586. ; 27:7, s. 431-441
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES To compare the effect of manual therapy in addition to the stay-active concept versus the stay-active concept only in low back pain patients. STUDY DESIGN A randomized, controlled trial during 10 weeks. METHODS One hundred sixty outpatients with acute or subacute low back pain were recruited from a geographically defined area. They were randomly allocated to a reference group treated with the stay-active concept and, in some cases, muscle stretching and an experimental group receiving manual therapy and, in some cases, steroid injections in addition to the stay-active concept. Pain and disability rating index were used as outcome measures. RESULTS At baseline, the experimental group had somewhat more pain, a higher disability rating index, and more herniated disks than the reference group. After 5 and 10 weeks, the experimental group had less pain and a lower disability rating index than the reference group. CONCLUSIONS The manual treatment concept used in this study in low back pain patients appears to reduce pain and disability rating better than the traditional stay-active concept.
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| 24. |
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| 25. |
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| 26. |
- Himo, Fahmi, et al.
(författare)
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Relative acidities of ortho-substituted phenols, as models for modified tyrosines in proteins
- 2002
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 106:37, s. 8757-8761
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Tidskriftsartikel (refereegranskat)abstract
- The effects of a variety of ortho-substituents (CH3, OH, OCH3, SH, SCH3, NH2, NO2, F, Cl, CN, and imidazole) on the acidity of phenol are investigated using hybrid density functional theory. Substitutions are made at the ortho-position to model modified tyrosine residues found in enzymes. Although the experimental trends are reproduced, the calculations tend to exaggerate the substituent effects. It is shown that the cysteine cross-link to tyrosine, present in the radical enzyme galactose oxidase, has a small effect on the pK(a) of the residue. The histidine cross-link present in cytochrome c oxidase, on the other hand, will contribute more to. lower the pKa. Comparing the substituent effects on the O-H bond strengths and the acidities, no simple correlation is found between the two.
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| 27. |
- Himo, Fahmi, et al.
(författare)
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Substituent effects on OH bond strength and hyperfine properties of phenol, as model for modified tyrosyl radicals in proteins
- 2000
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Ingår i: International Journal of Quantum Chemistry. - 0020-7608 .- 1097-461X. ; 76:6, s. 714-723
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory is used to investigate the effects of a variety of substituents (CH3, OH, OCH3, SH, SCH3, NH2, NMe2, NO2, F, Cl, CN, and imidazole) on the phenol O-H bond dissociation energy (BDE) and phenoxyl radical hyperfine properties. Substitutions are made at the ortho position to model modified tyrosine residues found in enzymes. The calculations show that besides the electronic effects of the substituents, intramolecular hydrogen bonds between OH and the substituents will contribute considerably to stabilize the parent species. Substituent effects on anisole O-Me bond strengths can thus not correctly describe the effects on ortho-substituted phenol O-H bond strengths, as previously proposed. This fact is supported by a series of calculations on o-substituted anisoles. The odd-alternant spin pattern of the phenoxyl radical is conserved for most of the substitutions. In particular, it is predicted that the cysteine crosslink to tyrosine, present in the radical enzyme galactose oxidase, and the histidine crosslink, present in cytochrome-c oxidase, will only have minor effects on the BDE and the radical hyperfine coupling constants and spin distribution of the tyrosyl radical.
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| 28. |
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| 29. |
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| 30. |
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| 31. |
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| 32. |
- Johansson, M, et al.
(författare)
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A phoneme recognizer for the hearing impaired
- 2002
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Konferensbidrag (refereegranskat)abstract
- This paper describes an automatic speech recognition system designed to investigate the use of phoneme recognition as a hearing aid in telephone communication. The system was tested in two experiments. The first involved 19 normal hearing subjects with a simulated severe hearing impairment. The second involved 5 hearing impaired subjects. In both studies we used a procedure called Speech Tracking to measure the effective communication speed between two persons. A substantial improvement was found in both cases.
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| 33. |
- Le Berre, F, et al.
(författare)
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Interfacial properties of a model polyampholyte studied by surface force measurements, ESCA, and ellipsometry
- 2001
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 17, s. 699-704
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of a model polyampholyte, i.e. [acryl amide]-[sodium 2-(acrylamido)-2-methylpropanesulfonate]-[2-(methacryloyloxy)-ethyltrimethyl-ammmonium chloride] ([AM]-[NaAMPS]-[MADQUAT]) at mica and silica surfaces was investigated by surface force measurements, electron spectroscopy for chemical analysis (ESCA), and ellipsometry. It was found that the adsorption isotherm of this polyampholyte on mica was of the high affinity type, yielding an adsorbed amount at saturation of 5.5 ± 0.5 mg/m2. From ellipsometry studies with silica, it was found that the adsorption was relatively fast, reaching saturation after about 1000 s on adsorption from a 20 ppm solution. From both ellipsometry and ESCA it was found that the effect of electrolyte on the adsorbed amount of pre-adsorbed polyampholyte is relatively minor at concentrations up to 10 mM. At higher electrolyte concentrations, however, some desorption of the polyampholyte occurs. Surface force measurements showed that the extension of the polymer layer normal to the mica surface was small compared to the radius of gyration of the polymer in bulk. Upon addition of electrolyte the adsorbed layer was found to contract.
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| 34. |
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| 35. |
- Lundberg, Marcus, 1974-, et al.
(författare)
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Density functional models of the mechanism for decarboxylation in orotidine decarboxylase
- 2002
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Ingår i: Journal of Molecular Modeling. - : Springer Science and Business Media LLC. - 1610-2940 .- 0948-5023. ; 8:4, s. 119-130
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of orotidine 5-monophosphate decarboxylase (ODCase) has been modeled using hybrid Density Functional Theory (B3LYP functional). The main goal of the present study was to investigate if much larger quantum chemical models of the active site than previously used could shed new light on the mechanism. The models used include the five conserved amino acids expected to be the most important ones for catalysis. One result of this model is that a mechanism involving a direct cleavage of the C-C bond followed by a protonation of C6 by Lys93 appears unlikely, with a barrier for decarboxylation 20 kcal mol(-1) too high. Additional effects like electrostatic stress and ground-state destabilization have been estimated to have only a minor influence on the reaction barrier. The conclusion from the calculations is that the negative charge developing on the substrate during decarboxylation must be stabilized by a protonation of the carbonyl O2 of the substrate. For this mechanism, the addition of the catalytic amino acids decreases the reaction barrier by 25 kcal mol(-1), but full agreement with experimental results has still not been reached. Further modifications of this mechanism are discussed.
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| 36. |
- Lundberg, Marcus, et al.
(författare)
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Developing active site models of ODCase : from large quantum models to a QM/MM approach
- 2004
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Ingår i: Topics in current chemistry. - Berlin : Springer. - 0340-1022 .- 1436-5049. - 3540205667 ; 238, s. 79-112
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic mechanism of orotidine monophosphate decarboxylase (ODCase) has been modeled using density functional theory with the B3LYP functional. Barriers for three different mechanisms have been calculated using large QM and QM/MM models. A concerted protonation mechanism where TS stabilization is provided only by the positive Lys93 has a high barrier around 35 kcal/mol. QM/MM calculations confirm the results obtained using QM models. For a base protonation mechanism, 02 protonation gives a barrier for decarboxylation of 26 kcal/mol. Extensions to this QM model indicate that the cost of protonation may be inderestimated and the support for the base protonation mechanism is uncertain. An initial QM/MM investigation of a stepwise mechanism, where water molecules seem to play an important role for TS stabilization, gives the most promising results with an estimated barrier of 22 kcal/mol.
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| 37. |
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| 38. |
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| 39. |
- Lundberg, Marcus, 1974-, et al.
(författare)
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Modeling water exchange on monomeric and dimeric Mn centers
- 2003
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Ingår i: Theoretical Chemistry accounts. - : Springer Science and Business Media LLC. - 1432-881X .- 1432-2234. ; 110:3, s. 130-143
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Tidskriftsartikel (refereegranskat)abstract
- Water exchange on Mn centers in proteins has been modeled with density functional theory using the B3LYP functional. The reaction barrier for dissociative water exchange on [Mn-IV(H2O)(2)(OH)(4)] is only 9.6 kcal mol(-1), corresponding to a rate of 6 x 10(5) s(-1). It has also been investigated how modifications of the model complex change the exchange rate. Three cases of water exchange on Mn dimers have been modeled. The reaction barrier for dissociative exchange of a terminal water ligand on [(H2O)(2)(OH)(2)Mn-IV(mu-O)(2)Mn-IV(H2O)(2) (OH)(2)] is 8.6 kcal mol(-1), while the bridging oxo group exchange with a ring-opening mechanism has a barrier of 19.2 kcal mol(-1). These results are intended for interpretations of measurements of water exchange for the oxygen evolving complex of photosystem II. Finally, a tautomerization mechanism for exchange of a terminal oxyl radical has been modeled for the synthetic 02 catalyst [(terpy)(H2O)Mn-IV(mu-O)(2)Mn-IV(O.)(terpy)](3+) (terpy=2,2':6,2"-terpyridine). The calculated reaction barrier is 14.7 kcal mol(-1).
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| 40. |
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| 41. |
- Lundberg, Marcus, 1974-, et al.
(författare)
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Oxyl radical required for O-O bond formation in synthetic Mn-catalyst
- 2004
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 43:1, s. 264-274
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Tidskriftsartikel (refereegranskat)abstract
- DFT calculations using the B3LYP functional support the suggestion that the [(terpy)(H2O)Mn-IV(mu-O)(2)Mn-III(H2O)-(terpy)](3+) (terpy=2,2':6,2"-terpyridine) complex functions as a synthetic O-2 catalyst. The calculated barrier for O-O bond formation with water is 23 kcal/mol. In this complex, as well as in models of the oxygen evolving complex in PSII, the active species is a Mn-IV-oxyl radical. From comparisons with inactive Mn-V-oxo complexes, it is proposed that radical formation is actually a requirement for O-2 formation activity in Mn-complexes.
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| 42. |
- Naver, Lars, et al.
(författare)
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Broad spectrum of time of detection, primary symptoms and disease progression in infants with HIV-1 infection
- 2001
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Ingår i: European Journal of Clinical Microbiology and Infectious Diseases. - : Springer Science and Business Media LLC. - 0934-9723 .- 1435-4373. ; 20:3, s. 159-166
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between time of HIV-1 detection, appearance of symptoms and disease progression was studied in all 24 HIV-1-infected infants from a cohort of 117 children who were born to HIV-1-infected mothers and monitored from birth. HIV isolation from plasma and mononuclear cells, HIV-1 DNA PCR (polymerase chain reaction) and, retrospectively, a quantitative assay for HIV-1 RNA were used for virus detection. Two infants possibly exhibited a symptomatic primary HIV infection. More children with than without symptoms during the first year of life progressed to immunological class 3 (P=0.013) and to AIDS or death (P=0.003) during follow-up. HIV-1 was detected within 4 days of age in 4 of 16 infants: 3 of them became symptomatic within 1 year, as did 6 of the remaining 12 infants (not statistically significant). All four infants in whom virus was detected within 4 days of age progressed to severe immunosuppression, compared to 6 of 14 in whom the virus detection test was initially negative prior to the first positive result (n.s.). Two children with previous repeatedly negative HIV detection tests were diagnosed with HIV-1 infection at 8 and 9 months, respectively. Repeated blood sampling is needed for the diagnosis of HIV-1 infection in perinatally exposed infants, and virus detection tests for exclusion of HIV-1 infection must be used with caution.
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| 43. |
- Pelmenschikov, Vladimir, et al.
(författare)
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A Mechanism from Quantum Chemical Studies for Methane Formation in Methanogenesis
- 2002
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 124:15, s. 4039-4049
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism for methane formation in methyl-coenzyme M reductase (MCR) has been investigated using the B3LYP hybrid density functional method and chemical models consisting of 107 atoms. The experimental X-ray crystal structure of the enzyme in the inactive MCRox1-silent state was used to set up the initial model structure. The calculations suggest a mechanism not previously proposed, in which the most remarkable feature is the formation of an essentially free methyl radical at the transition state. The reaction cycle suggested starts from a Michaelis complex with CoB and methyl-CoM coenzymes bound and with a squareplanar coordination of the Ni(I) center in the tetrapyrrole F430 prosthetic group. In the rate-limiting step the methyl radical is released from methyl-CoM, induced by the attack of Ni(I) on the methyl-CoM thioether sulfur. In this step, the metal center is oxidized from Ni(I) to Ni(II). The resulting methyl radical is rapidly quenched by hydrogen-atom transfer from the CoB thiol group, yielding the methane molecule and the CoB radical. The estimated activation energy is around 20 kcal/mol, which includes a significant contribution from entropy due to the formation of the free methyl. The mechanism implies an inversion of configuration at the reactive carbon. The size of the inversion barrier is used to explain the fact that CF3−S−CoM is an inactive substrate. Heterodisulfide CoB−S−S−CoM formation is proposed in the final step in which nickel is reduced back to Ni(I). The suggested mechanism agrees well with experimental observations.
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| 44. |
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| 45. |
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| 46. |
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| 47. |
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| 48. |
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| 49. |
- Sydbom, A, et al.
(författare)
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Health effects of diesel exhaust emissions
- 2001
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Ingår i: European Respiratory Journal. - : European Respiratory Society (ERS). - 0903-1936 .- 1399-3003. ; 17:4, s. 733-746
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Tidskriftsartikel (refereegranskat)abstract
- Epidemiological studies have demonstrated an association between different levels of air pollution and various health outcomes including mortality, exacerbation of asthma, chronic bronchitis, respiratory tract infections, ischaemic heart disease and stroke. Of the motor vehicle generated air pollutants, diesel exhaust particles account for a highly significant percentage of the particles emitted in many towns and cities. This review is therefore focused on the health effects of diesel exhaust, and especially the particular matter components. Acute effects of diesel exhaust exposure include irritation of the nose and eyes, lung function changes, respiratory changes, headache, fatigue and nausea. Chronic exposures are associated with cough, sputum production and lung function decrements. In addition to symptoms, exposure studies in healthy humans have documented a number of profound inflammatory changes in the airways, notably, before changes in pulmonary function can be detected. It is likely that such effects may be even more detrimental in asthmatics and other subjects with compromised pulmonary function. There are also observations supporting the hypothesis that diesel exhaust is one important factor contributing to the allergy pandemic. For example, in many experimental systems, diesel exhaust particles can be shown to act as adjuvants to allergen and hence increase the sensitization response. Much of the research on adverse effects of diesel exhaust, both in vivo and in vitro, has however been conducted in animals. Questions remain concerning the relevance of exposure levels and whether findings in such models can be extrapolated into humans. It is therefore imperative to further assess acute and chronic effects of diesel exhaust in mechanistic studies with careful consideration of exposure levels. Whenever possible and ethically justified, studies should be carried out in humans.
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