| 1. |
- Brinck, Tore, et al.
(författare)
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Solvation of sulfur-centered cations and anions in acetonitrile
- 2002
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 106:37, s. 8827-8833
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Tidskriftsartikel (refereegranskat)abstract
- The solvation of substituted phenylsulfenium ions and thiophenoxides in acetonitrile has been analyzed on the basis of experimental and theoretical data. Experimental solvation energies are obtained from previously reported oxidation and reduction potentials of the corresponding arylthiyl radicals in combination with theoretically calculated ionization potentials and electron affinities at the B3LYP/6-31+G(d) level. These calculations provide a consistent set of values in contrast to the data sets obtained in our previous paper (Larsen et al., J. Am. Chem. Soc. 2001, 123, 1723). The extracted solvation data show the expected substituent dependency for both kinds of ions, i.e., the absolute value of the solvation energy decreases as the charge becomes more delocalized. For the thiophenoxides there is good agreement between the experimental solvation energies and solvation energies computed using the polarizable continuum model (PCM). The solvation of the arylsulfenium ions, is much stronger than predicted by the PCM method. This can be attributed to the formation of a strong covalent bond of the Ritter type between the arylsulfenium ion and one molecule of acetonitrile. When this interaction is included in the solvation energy calculations by means of a combined supermolecule and PCM approach the experimental data are reproduced within a few kcal mol(-1). While the energy difference of the singlet and triplet spin states of the arylsulfenium ions is almost negligible in gas phase, the singlet cation is undoubtedly the dominating species in solution, since the triplet cation lacks the ability to form a covalent bond with acetonitrile.
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| 2. |
- Brinjikji, Waleed, et al.
(författare)
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Endotheliitis and cytokine storm as a mechanism of clot formation in COVID-19 ischemic stroke patients: A histopathologic study of retrieved clots.
- 2023
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Ingår i: Interventional neuroradiology : journal of peritherapeutic neuroradiology, surgical procedures and related neurosciences. - 2385-2011.
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Tidskriftsartikel (refereegranskat)abstract
- Studies during the COVID-19 pandemic have demonstrated an association between COVID-19 virus infection and the development of acute ischemic stroke, particularly large vessel occlusion (LVO). Studying the characteristics and immunohistochemistry of retrieved stroke emboli during mechanical thrombectomy for LVO may offer insights into the pathogenesis of LVO in COVID-19 patients. We examined retrieved COVID-19 emboli from the STRIP, EXCELLENT, and RESTORE registries and compared their characteristics to a control group.We identified COVID-positive LVO patients from the STRIP, RESTORE, and EXCELLENT studies who underwent mechanical thrombectomy. These patients were matched to a control group controlling for stroke etiology based on Trial of Org 10172 in Acute Stroke Treatment criteria. All clots were stained with Martius Scarlet Blue (MSB) along with immunohistochemistry for interleukin-6 (IL-6), C-reactive protein (CRP), von Willebrand factor (vWF), CD66b, fibrinogen, and citrullinated Histone H3. Clot composition was compared between groups.Nineteen COVID-19-positive patients and 38 controls were included. COVID-19-positive patients had a significantly higher percentage of CRP and vWF. There was no difference in IL-6, fibrin, CD66b, or citrullinated Histone H3 between groups. Based on MSB staining, there was no statistically significant difference regarding the percentage of red blood cells, white blood cells, fibrin, and platelets.Our study found higher concentrations of CRP and vWF in retrieved clots of COVID-19-positive stroke patients compared to COVID-19-negative controls. These findings support the potential role of systemic inflammation as indicated by elevated CRP and endothelial injury as indicated by elevated vWF as precipitating factors in thrombus development in these patients.
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| 3. |
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| 4. |
- Carlqvist, Peter, et al.
(författare)
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Computational study of the amination of halobenzenes and phenylpentazole. A viable route to isolate the pentazolate anion?
- 2004
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 69:9, s. 3222-3225
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Tidskriftsartikel (refereegranskat)abstract
- Amination of halobenzenes, which proceeds via the benzyne intermediate (1), has been studied using quantum chemical methods. The computational data are in agreement with experimentally observed trends in reactivity and provide a qualitative explanation for the observed hydrogen isotope effects. To investigate if this is a viable way to isolate the pentazolate anion (2), the reactivities of the halobenzenes have been compared to phenylpentazole (3). The reaction energetics for phenylpentazole become favorable after complexation with Zn2+.
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| 5. |
- Carlqvist, Per, et al.
(författare)
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Formation of Twisted Elephant Trunks in the Rosette Nebula
- 2002
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Ingår i: Astrophysics and Space Science. - 0004-640X .- 1572-946X. ; 280:4, s. 405-412
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Tidskriftsartikel (refereegranskat)abstract
- New observations show that dark elephant trunks in the Rosette nebula are often built up by thin filaments. In several of the trunks the filaments seem to form a twisted pattern. This pattern is hard to reconcile with current theory. We propose a new model for the formation of twisted elephant trunks in which electromagnetic forces play an important role. The model considers the behaviour of a twisted magnetic filament in a molecular cloud, where a cluster of hot stars has been recently born. As a result of stellar winds, and radiation pressure, electromagnetic forces, and inertia forces part of the filament can develop into a double helix pointing towards the stars. The double helix represents the twisted elephant trunk. A simple analogy experiment visualizes and supports the trunk model.
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| 6. |
- Carlqvist, Peter, et al.
(författare)
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The stability of arylpentazoles
- 2004
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:36, s. 7463-7467
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Tidskriftsartikel (refereegranskat)abstract
- The stability of phenylpentazole along with para-substituted and ortho,para-substituted arylpentazoles have been studied using high-level density functional theory (DFT). The decomposition of arylpentazoles to N-2 and the corresponding azide is a first-order reaction, where the breaking of the N1-N2 bond is concomitant with cleavage of the N3-N4 bond. Calculations confirm that the stability of arylpentazoles increases with electron-donating groups and decreases with electron-withdrawing groups, in the para position, as found in experiments. The stabilizing effect of the electron-donating groups is shown to be due to a resonance interaction with the electron-withdrawing pentazole ring. Addition of solvation effects, using the polarizable continuum model to simulate the polar solvent methanol, increases the stability of arylpentazoles. This is due to a more polar ground state than transition state. The calculated free energies of activation for the arylpentazoles agree well with experimental results. From the calculations, the electron-withdrawing effect of the pentazole group is found to be similar to that of cyanide (-CN). Some new arylpentazoles with hydroxyl groups in the ortho position are proposed. These are predicted to be more stable than all previously synthesized neutral arylpentazoles.
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| 7. |
- Carlqvist, Per, et al.
(författare)
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Theory of Twisted Trunks
- 2003
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 403, s. 399-412
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Tidskriftsartikel (refereegranskat)abstract
- Using the 2.6 m Nordic Optical Telescope we have observed a large number of elephant trunks in several regions. Here, we present a small selection of this material consisting of a few large, well-developed trunks, and some smaller ones. We find that: (i) the well-developed trunks are made up of dark filaments and knots which show evidence of twisted structures, (ii) the trunks are connected with essentially two filamentary legs running in V-shape, and (iii) all trunks have the maximum extinction in their heads. We advance a theory of twisted elephant trunks which is based on the presence of magnetic flux ropes in molecular clouds where hot OB stars are formed. If the rope contains a local condensation it may adopt a V-shape as the region around the hot stars expands. If, in addition, the magnetic field in the rope is sufficiently twisted, the rope may form a double helix at the apex of the V. The double helix is identified with the twisted elephant trunks. In order to illustrate the mechanisms behind the double helix we have constructed a mechanical analogy model of the magnetic flux rope in which the rope has been replaced by a bundle of elastic strings loaded by a weight. Experiments with the model clearly show that part of the bundle will transform into a double helix when the twist of the bundle is sufficiently large. We have also worked out a simple theoretical model of a mass-loaded magnetic flux rope. Numerical calculations show that a double helix will indeed form when the twist of the rope exceeds a certain critical limit. Numerical model calculations are applied to both the analogy model experiments and one of the well-developed elephant trunks. On the basis of our model we also suggest a new interpretation of the so called EGGs. The double helix mechanism is quite general, and should be active also in other suitable environments. One such environment may be the shell of supernova remnants. Another example is the expanding bubble outlined by the North Celestial Pole Loop.
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| 8. |
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| 9. |
- Holm, A. H., et al.
(författare)
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Thermochemistry of arylselanyl radicals and the pertinent ions in acetonitrile
- 2003
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 125:8, s. 2148-2157
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Tidskriftsartikel (refereegranskat)abstract
- Reduction and oxidation potentials of a series of parasubstituted phenylselanyl radicals, XC6H4Se*, have been measured using photomodulated voltammetry in acetonitrile. The thermodynamic significance of these data was substantiated through a study of the oxidation process of the pertinent selenolates in linear sweep voltammetry. Both the reduction and the oxidation potentials correlate linearly with the Hammett substituent coefficients sigma and sigma(+) leading in the latter case to slopes, rho(+), of 2.5 and 3.8, respectively. Through comparison of these slopes with those published previously for the O- and S-centered analogues, it is revealed that the pi-interaction becomes progressively smaller as the size of the radical center increases in the order O, S, and Se. Solvation energies of the pertinent selenolates and selanylium ions have been extracted from thermochemical cycles incorporating the measured electrode potentials for XC6H4Se* as well as electron affinities and ionization potentials obtained from theoretical calculations at the B3LYP/6-31+G(d) level. The extracted data show the expected overall substituent dependency for both kinds of ions; that is, the absolute value of the solvation energy decreases as the charge becomes more delocalized. The data have also been compared with solvation energies computed using the polarizable continuum model (PCM). Interestingly, we find that, while the model seems to work well for selenolates, it underestimates the solvation of selanylium ions in acetonitrile by as much as 25 kcal mol(-1). These large deviations are ascribed to the fact that the PCM method does not take specific solvent effects into account as it treats the solvent as a continuum described solely by its dielectric constant. Gas-phase calculations show that the arylselanylium ions can coordinate covalently to one or two molecules of acetonitrile in strong Ritter-type adducts. When this strong interaction is included in the solvation energy calculations by means of a combined supermolecule and PCM approach, the experimental data are reproduced within a few kcal mol-1. Although the energy difference of the singlet and triplet spin states of the arylselanylium ions is small for the gas-phase structures, the singlet cation is undoubtedly the dominating species in solution because the triplet cation lacks the ability to form covalent bonds.
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| 10. |
- Ristow, M, et al.
(författare)
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Deficiency of phosphofructo-1-kinase/muscle subtype in humans is associated with impairment of insulin secretory oscillations
- 1999
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 48:8, s. 1557-1561
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Tidskriftsartikel (refereegranskat)abstract
- In healthy humans, insulin is secreted in an oscillatory manner. While the underlying mechanisms generating these oscillations are not fully established, increasing evidence suggests a central role for phosphofructo-1-kinase/muscle subtype (PFK1-M), which also serves as the predominantly active PFK1 subtype in the pancreatic beta-cell. The fact that normal oscillatory secretion is impaired in subjects with impaired glucose tolerance and healthy relatives of patients with type 2 diabetes suggests that this defect may be involved in the secretory dysfunction. To evaluate a possible link between inherited PFK1-M deficiency in humans (Tarui's disease or glycogenosis type VII) and altered insulin oscillations, in vivo studies were performed. We determined basal insulin oscillations during 2 h of frequent plasma sampling in two related teen-aged individuals with homozygous and heterozygous PFK1-M deficiency compared with nondeficient, unrelated control subjects. As predicted by the underlying hypothesis, normal oscillations in insulin secretion were completely abolished in the individual with homozygous deficiency of PFK1-M and significantly impaired in the heterozygous individual, as shown by spectral density and autocorrelation analyses. Thus, deficiency of PFK1-M subtype in humans appears to be associated with an impaired oscillatory insulin secretion pattern and may contribute to the commonly observed secretion defects occurring in type 2 diabetes.
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