| 1. |
- Kronqvist, Nina, et al.
(författare)
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Sequential pH-driven dimerization and stabilization of the N-terminal domain enables rapid spider silk formation
- 2014
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 5:1, s. 3254-
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms controlling the conversion of spider silk proteins into insoluble fibres, which happens in a fraction of a second and in a defined region of the silk glands, are still unresolved. The N-terminal domain changes conformation and forms a homodimer when pH is lowered from 7 to 6; however, the molecular details still remain to be determined. Here we investigate site-directed mutants of the N-terminal domain from Euprosthenops australis major ampullate spidroin 1 and find that the charged residues D40, R60 and K65 mediate intersubunit electrostatic interactions. Protonation of E79 and E119 is required for structural conversions of the subunits into a dimer conformation, and subsequent protonation of E84 around pH 5.7 leads to the formation of a fully stable dimer. These residues are highly conserved, indicating that the now proposed three-step mechanism prevents premature aggregation of spidroins and enables fast formation of spider silk fibres in general.
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| 2. |
- Akkuratov, Evgeny E.
(författare)
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The Biophysics of Na+,K+-ATPase in neuronal health and disease
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Na+,K+-ATPase is one of the most important proteins in the mammalian cell. It creates sodium and potassium gradients which are fundamental for the membrane potential and sodium-dependent secondary active transport. It has a second role in the cell as a receptor that by binding chemicals from the cardiotonic steroids family, the most knowledgeable of them is ouabain, triggers various signaling pathways in the cell which regulate gene activation, proliferation, apoptosis, etc. It has been shown that several severe neurological diseases are associated with mutations in the Na+,K+-ATPase encoding genes. Although Na+,K+-ATPase was discovered already in 1957 by the Danish scientist Jens Skou, the knowledge about the function of this enzyme is still not complete. In the studies included in the thesis, we have learned more about the function of Na+,K+-ATPase in different aspects of health and disease. In study I we showed a mechanism of ouabain-dependent regulation of the NMDA receptor, one of the most important receptors in the nervous system, via binding with Na+,K+-ATPase. This allows us to look at the Na+,K+-ATPase as regulator via protein-protein interaction. In study II we investigated a different aspect of Na+,K+-ATPase functioning – to look at how binding of ouabain to Na+,K+-ATPase activates a number of signaling cascades by looking at the phosphoproteome status of the cells. This allows us to see the whole picture of ouabain-mediated cascades and further characterize them. In study III we focused on the role of Na+,K+-ATPase in severe epileptic encephalopathy caused by a mutation in the ATP1A1 gene. We performed a molecular and cellular study to describe how mutations affects protein structure and function and found that this mutation converts the ion pump to a nonspecific leak channel. In study IV we performed a translational study of the most common mutation for rapid-onset dystonia-parkinsonism. We studied how this mutation affects the nervous system on the protein-, cellular-, and organism level and found that the complete absence of ultraslow afterhyperpolarization (usAHP) could explain gait disturbances found in patients. In the on-going study we showed that Na+,K+-ATPase can oligomerize and that this effect is triggered by ouabain binding to the Na+,K+-ATPase. In this study, we utilized a novel fluorescence labelling approach and used biophysical techniques with single molecule sensitivity to track Na+,K+-ATPase interactions. In summary, we applied biophysical and molecular methods to study different aspects of the function of Na+,K+-ATPase, and gained insights that could be helpful not only for answering fundamental questions about Na+,K+-ATPase but also to find a treatment for patients with diseases associated with mutations in this protein.
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| 3. |
- Bergstrand, Jan, et al.
(författare)
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Scanning inverse fluorescence correlation spectroscopy
- 2014
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 22:11, s. 13073-13090
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Tidskriftsartikel (refereegranskat)abstract
- Scanning Inverse Fluorescence Correlation Spectroscopy (siFCS) is introduced to determine the absolute size of nanodomains on surfaces. We describe here equations for obtaining the domain size from cross-and auto-correlation functions, measurement simulations which enabled testing of these equations, and measurements on model surfaces mimicking membranes containing nanodomains. Using a confocal microscope of 270 nm resolution the size of 250 nm domains were estimated by siFCS to 257 +/- 12 nm diameter, and 40 nm domains were estimated to 65 +/- 26 nm diameter. Applications of siFCS for sizing of nanodomains and protein clusters in cell membranes are discussed.
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| 4. |
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| 5. |
- Dear, Alexander J., et al.
(författare)
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Aβ Oligomer Dissociation Is Catalyzed by Fibril Surfaces
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Ingår i: ACS Chemical Neuroscience. - 1948-7193.
-
Tidskriftsartikel (refereegranskat)abstract
- Oligomeric assemblies consisting of only a few protein subunits are key species in the cytotoxicity of neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Their lifetime in solution and abundance, governed by the balance of their sources and sinks, are thus important determinants of disease. While significant advances have been made in elucidating the processes that govern oligomer production, the mechanisms behind their dissociation are still poorly understood. Here, we use chemical kinetic modeling to determine the fate of oligomers formed in vitro and discuss the implications for their abundance in vivo. We discover that oligomeric species formed predominantly on fibril surfaces, a broad class which includes the bulk of oligomers formed by the key Alzheimer's disease-associated Aβ peptides, also dissociate overwhelmingly on fibril surfaces, not in solution as had previously been assumed. We monitor this "secondary nucleation in reverse" by measuring the dissociation of Aβ42 oligomers in the presence and absence of fibrils via two distinct experimental methods. Our findings imply that drugs that bind fibril surfaces to inhibit oligomer formation may also inhibit their dissociation, with important implications for rational design of therapeutic strategies for Alzheimer's and other amyloid diseases.
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| 6. |
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| 7. |
- Gao, Yang, et al.
(författare)
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Live Cell FRET Imaging Reveals Amyloid beta-Peptide Oligomerization in Hippocampal Neurons
- 2021
-
Ingår i: International Journal of Molecular Sciences. - : MDPI AG. - 1661-6596 .- 1422-0067. ; 22:9
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Tidskriftsartikel (refereegranskat)abstract
- Amyloid beta-peptide (A beta) oligomerization is believed to contribute to the neuronal dysfunction in Alzheimer disease (AD). Despite decades of research, many details of A beta oligomerization in neurons still need to be revealed. Forster resonance energy transfer (FRET) is a simple but effective way to study molecular interactions. Here, we used a confocal microscope with a sensitive Airyscan detector for FRET detection. By live cell FRET imaging, we detected A beta 42 oligomerization in primary neurons. The neurons were incubated with fluorescently labeled A beta 42 in the cell culture medium for 24 h. A beta 42 were internalized and oligomerized in the lysosomes/late endosomes in a concentration-dependent manner. Both the cellular uptake and intracellular oligomerization of A beta 42 were significantly higher than for A beta 40. These findings provide a better understanding of A beta 42 oligomerization in neurons.
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| 8. |
- Gesper, A., et al.
(författare)
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Variations in Plasma Membrane Topography Can Explain Heterogenous Diffusion Coefficients Obtained by Fluorescence Correlation Spectroscopy
- 2020
-
Ingår i: Frontiers in Cell and Developmental Biology. - : Frontiers Media SA. - 2296-634X. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Fluorescence correlation spectroscopy (FCS) is frequently used to study diffusion in cell membranes, primarily the plasma membrane. The diffusion coefficients reported in the plasma membrane of the same cell type and even within single cells typically display a large spread. We have investigated whether this spread can be explained by variations in membrane topography throughout the cell surface, that changes the amount of membrane in the FCS focal volume at different locations. Using FCS, we found that diffusion of the membrane dye DiI in the apical plasma membrane was consistently faster above the nucleus than above the cytoplasm. Using live cell scanning ion conductance microscopy (SICM) to obtain a topography map of the cell surface, we demonstrate that cell surface roughness is unevenly distributed with the plasma membrane above the nucleus being the smoothest, suggesting that the difference in diffusion observed in FCS is related to membrane topography. FCS modeled on simulated diffusion in cell surfaces obtained by SICM was consistent with the FCS data from live cells and demonstrated that topography variations can cause the appearance of anomalous diffusion in FCS measurements. Furthermore, we found that variations in the amount of the membrane marker DiD, a proxy for the membrane, but not the transmembrane protein TCRζ or the lipid-anchored protein Lck, in the FCS focal volume were related to variations in diffusion times at different positions in the plasma membrane. This relationship was seen at different positions both at the apical cell and basal cell sides. We conclude that it is crucial to consider variations in topography in the interpretation of FCS results from membranes. © Copyright © 2020 Gesper, Wennmalm, Hagemann, Eriksson, Happel and Parmryd.
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| 9. |
- Gunasekera, Sunithi, 1977-, et al.
(författare)
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Stabilized Cyclic Peptides as Scavengers of Autoantibodies : Neutralization of Anticitrullinated Protein/Peptide Antibodies in Rheumatoid Arthritis
- 2018
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Ingår i: ACS Chemical Biology. - : American Chemical Society (ACS). - 1554-8929 .- 1554-8937. ; 13:6, s. 1525-1535
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Tidskriftsartikel (refereegranskat)abstract
- The occurrence of autoantibodies is a hallmark of rheumatoid arthritis, specifically those autoantibodies targeting proteins containing the arginine-derived amino acid citrulline. There is strong evidence showing that the occurrence of anticitrullinated protein/peptide antibodies (ACPA) are involved in disease progression, and ACPA was recently shown to induce pain in animals. Here, we explore a novel concept useful for research, diagnostics, and possibly therapy of autoimmune diseases, namely, to directly target and neutralize autoantibodies using peptide binders. A high-affinity peptide-based scavenger of ACPA was developed by grafting a citrullinated epitope derived from human fibrinogen into a naturally occurring stable peptide scaffold. The best scavenger comprises the truncated epitope α-fibrinogen, [Cit573]fib(566-580), grafted into the scaffold sunflower trypsin inhibitor-1, SFTI-1. The final peptide demonstrates low nanomolar apparent affinity and superior stability.
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| 10. |
- Lakshmanan, Ramnath, et al.
(författare)
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Removal of total organic carbon from sewage wastewater using poly(ethylenimine)-functionalized magnetic nanoparticles
- 2014
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:4, s. 1036-1044
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Tidskriftsartikel (refereegranskat)abstract
- The increased levels of organic carbon in sewage wastewater during recent years impose a great challenge to the existing wastewater treatment process (WWTP). Technological innovations are therefore sought that can reduce the release of organic carbon into lakes and seas. In the present study, magnetic nanoparticles (NPs) were synthesized, functionalized with poly(ethylenimine) (PEI), and characterized using TEM (transmission electron microscopy), X-ray diffraction (XRD), FTIR (Fourier transform infrared spectroscopy), CCS (confocal correlation spectroscopy), SICS (scattering interference correlation spectroscopy), magnetism studies, and thermogravimetric analysis (TGA). The removal of total organic carbon (TOC) and other contaminants using PEI-coated magnetic nanoparticles (PEI-NPs) was tested in wastewater obtained from the Hammarby Sjöstadsverk sewage plant, Sweden. The synthesized NPs were about 12 nm in diameter and showed a homogeneous particle size distribution in dispersion by TEM and CCS analyses, respectively. The magnetization curve reveals superparamagnetic behavior, and the NPs do not reach saturation because of surface anisotropy effects. A 50% reduction in TOC was obtained in 60 min when using 20 mg/L PEI-NPs in 0.5 L of wastewater. Along with TOC, other contaminants such as turbidity (89%), color (86%), total nitrogen (24%), and microbial content (90%) were also removed without significant changes in the mineral ion composition of wastewater. We conclude that the application of PEI-NPs has the potential to reduce the processing time, complexity, sludge production, and use of additional chemicals in the WWTP.
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| 11. |
- Lizatovic, Robert, et al.
(författare)
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A Protein-Based Encapsulation System with Calcium-Controlled Cargo Loading and Detachment
- 2018
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Ingår i: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 57:35, s. 11334-11338
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Tidskriftsartikel (refereegranskat)abstract
- Protein-based encapsulation systems have a wide spectrum of applications in targeted delivery of cargo molecules and for chemical transformations in confined spaces. By engineering affinity between cargo and container proteins it has been possible to enable the efficient and specific encapsulation of target molecules. Missing in current approaches is the ability to turn off the interaction after encapsulation to enable the cargo to freely diffuse in the lumen of the container. Separation between cargo and container is desirable in drug delivery applications and in the use of capsids as catalytic nanoparticles. We describe an encapsulation system based on the hepatitisB virus capsid in which an engineered high-affinity interaction between cargo and capsid proteins can be modulated by Ca2+. Cargo proteins are loaded into capsids in the presence of Ca2+, while ligand removal triggers unbinding inside the container. We observe that confinement leads to hindered rotation of cargo inside the capsid. Application of the designed container for catalysis was also demonstrated by encapsulation of an enzyme with beta-glucosidase activity.
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| 12. |
- Makasewicz, Katarzyna, et al.
(författare)
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Cooperativity of alpha-Synuclein Binding to Lipid Membranes
- 2021
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Ingår i: ACS Chemical Neuroscience. - : American Chemical Society (ACS). - 1948-7193. ; 12:12, s. 2099-2109
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Tidskriftsartikel (refereegranskat)abstract
- Cooperative binding is a key feature of metabolic pathways, signaling, and transport processes. It provides tight regulation over a narrow concentration interval of a ligand, thus enabling switching to be triggered by small concentration variations. The data presented in this work reveal strong positive cooperativity of alpha-synuclein binding to phospholipid membranes. Fluorescence cross-correlation spectroscopy, confocal microscopy, and cryo-TEM results show that in excess of vesicles alpha-synuclein does not distribute randomly but binds only to a fraction of all available vesicles. Furthermore, alpha-synuclein binding to a supported lipid bilayer observed with total internal reflection fluorescence microscopy displays a much steeper dependence of bound protein on total protein concentration than expected for independent binding. The same phenomenon was observed in the case of alpha-synuclein binding to unilamellar vesicles of sizes in the nm and mu m range as well as to flat supported lipid bilayers, ruling out that nonuniform binding of the protein is governed by differences in membrane curvature. Positive cooperativity of alpha-synuclein binding to lipid membranes means that the affinity of the protein to a membrane is higher where there is already protein bound compared to a bare membrane. The phenomenon described in this work may have implications for alpha-synuclein function in synaptic transmission and other membrane remodeling events.
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| 13. |
- Makasewicz, Katarzyna, et al.
(författare)
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α-Synuclein-induced deformation of small unilamellar vesicles
- 2022
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Ingår i: QRB Discovery. - : Cambridge University Press (CUP). - 2633-2892. ; 3
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract α-Synuclein is a small neuronal protein that reversibly associates with lipid membranes. The membrane interactions are believed to be central to the healthy function of this protein involved in synaptic plasticity and neurotransmitter release. α-Synuclein has been speculated to induce vesicle fusion as well as fission, processes which are analogous to each other but proceed in different directions and involve different driving forces. In the current work, we analyse α-synuclein-induced small unilamellar vesicle deformation from a thermodynamics point of view. We show that the structures interpreted in the literature as fusion intermediates are in fact a stable deformed state and neither fusion nor vesicle clustering occurs. We speculate on the driving force for the observed deformation and put forward a hypothesis that α-synuclein self-assembly on the lipid membrane precedes and induces membrane remodelling.
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| 14. |
- Mellgren, Karin, 1962, et al.
(författare)
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Effect of nitric oxide gas on platelets during open heart operations.
- 1998
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Ingår i: The Annals of thoracic surgery. - 0003-4975. ; 65:5, s. 1335-41
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Tidskriftsartikel (refereegranskat)abstract
- The increased bleeding tendency observed after cardiopulmonary bypass is caused in part by thrombocytopenia and impaired platelet function induced by the procedure. Previous in vitro studies have shown that nitric oxide (NO) added to the oxygenator sweep gas reduces platelet activation during experimental perfusion. We evaluated the effect of 40 ppm of NO, added to the oxygenator sweep gas, on platelet consumption and activation in patients undergoing cardiopulmonary bypass.
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| 15. |
- Nagaraj, Vini, et al.
(författare)
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Elevated basal insulin secretion in type 2 diabetes caused by reduced plasma membrane cholesterol
- 2016
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Ingår i: Molecular Endocrinology. - : Endocrine Society. - 0888-8809 .- 1944-9917. ; 30:10, s. 1059-1069
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Tidskriftsartikel (refereegranskat)abstract
- Elevated basal insulin secretion under fasting conditions together with insufficient stimulated insulin release is an important hallmark of type 2 diabetes, but the mechanisms controlling basal insulin secretion remain unclear. Membrane rafts exist in pancreatic islet cells and spatially organize membrane ion channels and proteins controlling exocytosis, which may contribute to the regulation of insulin secretion. Membrane rafts (cholesterol and sphingolipid containing microdomains) were dramatically reduced in human type 2 diabetic and diabetic Goto-Kakizaki (GK) rat islets when compared with healthy islets. Oxidation of membrane cholesterol markedly reduced microdomain staining intensity in healthy human islets, but was without effect in type 2 diabetic islets. Intriguingly, oxidation of cholesterol affected glucose-stimulated insulin secretion only modestly, whereas basal insulin release was elevated. This was accompanied by increased intracellular Ca2+ spike frequency and Ca2+ influx and explained by enhanced single Ca2+ channel activity. These results suggest that the reduced presence of membrane rafts could contribute to the elevated basal insulin secretion seen in type 2 diabetes.
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| 16. |
- Navarro, Julien R. G., et al.
(författare)
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Luminescent Nanocellulose Platform : From Controlled Graft Block Copolymerization to Biomarker Sensing
- 2016
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 17:3, s. 1101-1109
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Tidskriftsartikel (refereegranskat)abstract
- A strategy is devised for the conversion of cellulose nanofibrils (CNF) into fluorescently labeled probes involving the synthesis of CNF-based macroinitiators that initiate radical polymerilation of methyl acrylate and acrylic acid N-hydroxysuccinimide ester producing a graft block copolymer modified CNF. Finally, a luminescent probe (Lucifer yellow derivative) was labeled onto the modified CNF through an amidation reaction. The surface modification steps were :verified with solid-state C-13 nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy. Fluorescence correlation spectroscopy (FCS) confirmed the successful labeling of the CNF; the CNF have a hydrodynamic radius of about 700 nm with an average number of dye molecules per fibril of at least 6600. The modified CNF was also imaged with confocal laser scanning microscopy. Luminescent CNF proved to be viable biomarkers and allow for fluorescence-based optical detection of CNF uptake and distribution in organisms such as crustaceans. The luminescent CNF were exposed to live juvenile daphnids and microscopy analysis revealed the presence of the luminescent CNF all over D. magna's alimentary canal tissues without any toxicity effect leading to the death of the specimen.
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| 17. |
- Nordahl, Linnea, et al.
(författare)
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Detection and quantification of Na,K-ATPase dimers in the plasma membrane of living cells by FRET-FCS
- 2024
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Ingår i: Biochimica et Biophysica Acta - General Subjects. - : Elsevier BV. - 0304-4165 .- 1872-8006. ; 1868:7
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Tidskriftsartikel (refereegranskat)abstract
- The sodium potassium pump, Na,K-ATPase (NKA), is an integral plasma membrane protein, expressed in all eukaryotic cells. It is responsible for maintaining the transmembrane Na+ gradient and is the major determinant of the membrane potential. Self-interaction and oligomerization of NKA in cell membranes has been proposed and discussed but is still an open question. Here, we have used a combination of FRET and Fluorescence Correlation Spectroscopy, FRET-FCS, to analyze NKA in the plasma membrane of living cells. Click chemistry was used to conjugate the fluorescent labels Alexa 488 and Alexa 647 to non-canonical amino acids introduced in the NKA α1 and β1 subunits. We demonstrate that FRET-FCS can detect an order of magnitude lower concentration of green-red labeled protein pairs in a single-labeled red and green background than what is possible with cross-correlation (FCCS). We show that a significant fraction of NKA is expressed as a dimer in the plasma membrane. We also introduce a method to estimate not only the number of single and double labeled NKA, but the number of unlabeled, endogenous NKA and estimate the density of endogenous NKA at the plasma membrane to 1400 ± 800 enzymes/μm2.
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| 18. |
- Nordahl, Linnea, et al.
(författare)
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Direct Observation of Na,K‐ATPase Oligomers in The Plasma Membrane of Living Cells by FRET‐FCS
- 2022
-
Ingår i: The FASEB Journal. - : Wiley. - 0892-6638 .- 1530-6860. ; 36:S1
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Tidskriftsartikel (refereegranskat)abstract
- The sodium pump, Na,K-ATPase, is an integral plasma membrane protein, expressed in all eukaryotic cells. Na,K-ATPase transforms chemical energy from ATP into a gradient of Na+ and K+ over the plasma membrane by actively exporting three Na+ ions and importing two K+ ions for each hydrolyzed ATP. It is responsible for maintenance of the transmembrane Na+ gradient and is the major determinant of the membrane potential. It provides the driving force for all Na+-coupled transport processes, thereby controlling essential functions in the cell. Na,K-ATPase is formed by three subunits alpha/beta/FXYD, where alpha is the catalytic ion-transporting subunit, beta is a regulatory subunit and FXYD is accessory.Self-interaction and oligomerization of the Na,K-ATPase alpha/beta heterodimer in cell membranes has been proposed and discussed for a long time but is still an open question.Here we have used a combination of FRET and Fluorescence Correlation Spectroscopy, FRET-FCS, in order to detect oligomers of Na,K-ATPase. Compared to conventional cross-correlation FCCS, FRET-FCS is one to two orders of magnitude more sensitive when detecting oligomers. Moreover, FRET-FCS is inherently insensitive to unbalanced labeling, which is a great advantage during live cell measurements.We hypothesized that Na,K-ATPase can exist in a higher order oligomeric state and demonstrate the use of FRET-FCS to test this hypothesisWe have introduced fluorescent labels by using expression of non-canonical amino acid modified beta subunits. The FRET pair Alexa488 and Alexa647 was directly conjugated to the beta subunits using selective click chemistry. Conventional FCS measurements of labeled cells revealed the absolute density of labeled and unlabeled Na,K-ATPase. With FRET-FCS we could observe FRET signals and FCS curves demonstrating the existence of oligomers. Positive controls for the FRET-FCS measurements were constructed by labeling alpha subunits with Alexa488 and beta subunits with Alexa647.Furthermore, we performed Monte Carlo simulations of Na,K-ATPase, as monomer and as oligomer of increasing order, together with its ligands in a picket and fence diffusion model of the plasma membrane. The simulations suggest that oligomerization can have an impact on the net efficiency of the Na,K-ATPase measured as ATP turnover.In conclusion we find that Na,K-ATPase can be found in the plasma membrane as oligomers. Further we discuss the consequences of oligomerization and propose that it can have a regulatory effect for the Na,K-ATPase net efficiency.
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| 19. |
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| 20. |
- Nordenström, Malin, et al.
(författare)
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The structure of cellulose nanofibril networks at low concentrations and their stabilizing action on colloidal particles
- 2022
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 297, s. 120046-
-
Tidskriftsartikel (refereegranskat)abstract
- The structure and dynamics of networks formed by rod-shaped particles can be indirectly investigated by measuring the diffusion of spherical tracer particles. This method was used to characterize cellulose nanofibril (CNF) networks in both dispersed and arrested states, the results of which were compared with coarse-grained Brownian dynamics simulations. At a CNF concentration of 0.2 wt% a transition was observed where, below this concentration tracer diffusion is governed by the increasing macroscopic viscosity of the dispersion. Above 0.2 wt%, the diffusion of small particles (20-40 nm) remains viscosity controlled, while particles (100-500 nm) become trapped in the CNF network. Sedimentation of silica microparticles (1-5 mu m) in CNF dispersions was also determined, showing that sedimentation of larger particles is significantly affected by the presence of CNF. At concentrations of 0.2 wt%, the sedimentation velocity of 5 mu m particles was reduced by 99 % compared to pure water.
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| 21. |
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| 22. |
- Paulraj, Thomas, et al.
(författare)
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Porous Cellulose Nanofiber-Based Microcapsules for Biomolecular Sensing
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:48, s. 41146-41154
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanofibers (CNFs) have recently attracted a lot of attention in sensing because of their multifunctional character and properties such as renewability, nontoxicity, biodegradability, printability, and optical transparency in addition to unique physicochemical, barrier, and mechanical properties. However, the focus has exclusively been devoted toward developing two-dimensional sensing platforms in the form of nanopaper or nanocellulose-based hydrogels. To improve the flexibility and sensing performance in situ, for example, to detect biomarkers in vivo for early disease diagnostics, more advanced CNF-based structures are needed. Here, we developed porous and hollow, yet robust, CNF-based microcapsules using only the primary plant cell wall components, CNF, pectin, and xyloglucan, to assemble the capsule wall. The fluorescein isothiocyanate-labeled dextrans with M-w of 70 and 2000 kDa could enter the hollow capsules at a rate of 0.13 +/- 0.04 and 0.014 +/- 0.009 s(-1), respectively. This property is very attractive because it minimizes the influence of mass transport through the capsule wall on the response time. As a proof of concept, glucose oxidase (GOx) enzyme was loaded (and cross-linked) in the microcapsule interior with an encapsulation efficiency of 68 +/- 2%. The GOx-loaded microcapsules were immobilized on a variety of surfaces (here, inside a flow channel, on a carbon-coated sensor or a graphite rod) and glucose concentrations up to 10 mM could successfully be measured. The present concept offers new opportunities in the development of simple, more efficient, and disposable nanocellulose-based analytical devices for several sensing applications including environmental monitoring, healthcare, and diagnostics.
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| 23. |
- Paulraj, Thomas, et al.
(författare)
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Primary cell wall inspired micro containers as a step towards a synthetic plant cell
- 2020
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Ingår i: Nature Communications. - : Nature Research. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The structural integrity of living plant cells heavily relies on the plant cell wall containing a nanofibrous cellulose skeleton. Hence, if synthetic plant cells consist of such a cell wall, they would allow for manipulation into more complex synthetic plant structures. Herein, we have overcome the fundamental difficulties associated with assembling lipid vesicles with cellulosic nanofibers (CNFs). We prepare plantosomes with an outer shell of CNF and pectin, and beneath this, a thin layer of lipids (oleic acid and phospholipids) that surrounds a water core. By exploiting the phase behavior of the lipids, regulated by pH and Mg2+ ions, we form vesicle-crowded interiors that change the outer dimension of the plantosomes, mimicking the expansion in real plant cells during, e.g., growth. The internal pressure enables growth of lipid tubules through the plantosome cell wall, which paves the way to the development of hierarchical plant structures and advanced synthetic plant cell mimics. © 2020, The Author(s).
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| 24. |
- Petersen, Julian, et al.
(författare)
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Agonist-induced dimer dissociation as a macromolecular step in G protein-coupled receptor signaling
- 2017
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 8:1
-
Tidskriftsartikel (refereegranskat)abstract
- G protein-coupled receptors (GPCRs) constitute the largest family of cell surface receptors. They can exist and act as dimers, but the requirement of dimers for agonist-induced signal initiation and structural dynamics remains largely unknown. Frizzled 6 (FZD6) is a member of Class F GPCRs, which bind WNT proteins to initiate signaling. Here, we show that FZD6 dimerizes and that the dimer interface of FZD6 is formed by the transmembrane a-helices four and five. Most importantly, we present the agonist-induced dissociation/re-association of a GPCR dimer through the use of live cell imaging techniques. Further analysis of a dimerization-impaired FZD6 mutant indicates that dimer dissociation is an integral part of FZD6 signaling to extracellular signal-regulated kinases1/2. The discovery of agonistdependent dynamics of dimers as an intrinsic process of receptor activation extends our understanding of Class F and other dimerizing GPCRs, offering novel targets for dimerinterfering small molecules.
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| 25. |
- Pettersson, Pontus, et al.
(författare)
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Soluble TatA forms oligomers that interact with membranes : Structure and insertion studies of a versatile protein transporter
- 2021
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736 .- 1879-2642. ; 1863:2
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Tidskriftsartikel (refereegranskat)abstract
- The twin-arginine translocase (Tat) mediates the transport of already-folded proteins across membranes in bacteria, plants and archaea. TatA is a small, dynamic subunit of the Tat-system that is believed to be the active component during target protein translocation. TatA is foremost characterized as a bitopic membrane protein, but has also been found to partition into a soluble, oligomeric structure of yet unknown function. To elucidate the interplay between the membrane-bound and soluble forms we have investigated the oligomers formed by Arabidopsis thaliana TatA. We used several biophysical techniques to study the oligomeric structure in solution, the conversion that takes place upon interaction with membrane models of different compositions, and the effect on bilayer integrity upon insertion. Our results demonstrate that in solution TatA oligomerizes into large objects with a high degree of ordered structure. Upon interaction with lipids, conformational changes take place and TatA disintegrates into lower order oligomers. The insertion of TatA into lipid bilayers causes a temporary leakage of small molecules across the bilayer. The disruptive effect on the membrane is dependent on the liposome's negative surface charge density, with more leakage observed for purely zwitterionic bilayers. Overall, our findings indicate that A. thaliana TatA forms oligomers in solution that insert into bilayers, a process that involves reorganization of the protein oligomer.
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| 26. |
- Rabasovic, M. D., et al.
(författare)
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Label-Free Fluctuation Spectroscopy Based on Coherent Anti-Stokes Raman Scattering from Bulk Water Molecules
- 2016
-
Ingår i: ChemPhysChem. - : John Wiley & Sons. - 1439-4235 .- 1439-7641. ; 17:7, s. 1025-1033
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Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles (NPs) and molecules can be analyzed by inverse fluorescence correlation spectroscopy (iFCS) as they pass through an open detection volume, displacing fractions of the fluorescence-emitting solution in which they are dissolved. iFCS does not require the NPs or molecules to be labeled. However, fluorophores in m-mm concentrations are needed for the solution signal. Here, we instead use coherent anti-Stokes Raman scattering (CARS) from plain water molecules as the signal from the solution. By this fully label-free approach, termed inverse CARS-based correlation spectroscopy (iCARS-CS), NPs that are a few tenths of nm in diameter and at pM concentrations can be analyzed, and their absolute volumes/concentrations can be determined. Likewise, lipid vesicles can be analyzed as they diffuse/flow through the detection volume by using CARS fluctuations from the surrounding water molecules. iCARS-CS could likely offer a broadly applicable, label-free characterization technique of, for example, NPs, small lipid exosomes, or microparticles in biomolecular diagnostics and screening, and can also utilize CARS signals from biologically relevant media other than water.
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| 27. |
- Sandén, Tor, et al.
(författare)
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A Zeptoliter Volume Meter for Analysis of Single Protein Molecules
- 2012
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 12:1, s. 370-375
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Tidskriftsartikel (refereegranskat)abstract
- A central goal in bioanalytics is to determine the concentration of and interactions between biomolecules. Nanotechnology allows performing such analyses in a highly parallel, low-cost, and miniaturized fashion. Here we report on label-free volume, concentration, and mobility analysis of single protein molecules and nanoparticles during their diffusion through a subattoliter detection volume, confined by a 100 nm aperture in a thin gold film. A high concentration of small fluorescent molecules renders the aqueous solution in the aperture brightly fluorescent. Nonfluorescent analytes diffusing into the aperture displace the fluorescent molecules in the solution, leading to a decrease of the detected fluorescence signal, while analytes diffusing out of the aperture return the fluorescence level. The resulting fluorescence fluctuations provide direct information on the volume, concentration, and mobility of the nonfluorescent analytes through fluctuation analysis in both time and amplitude.
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| 28. |
- Shelke, Ganesh V, 1986, et al.
(författare)
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Endosomal signalling via exosome surface TGF beta-1
- 2019
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Ingår i: Journal of Extracellular Vesicles. - : Wiley. - 2001-3078. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Extracellular vesicles such as exosomes convey biological messages between cells, either by surface-to-surface interaction or by shuttling of bioactive molecules to a recipient cell's cytoplasm. Here we show that exosomes released by mast cells harbour both active and latent transforming growth factor beta-1 (TGF beta-1) on their surfaces. The latent form of TGF beta-1 is associated with the exosomes via heparinase-II and pH-sensitive elements. These vesicles traffic to the endocytic compartment of recipient human mesenchymal stem cells (MSCs) within 60 min of exposure. Further, the exosomes-associated TGF beta-1 is retained within the endosomal compartments at the time of signalling, which results in prolonged cellular signalling compared to free-TGF beta-1. These exosomes induce a migratory phenotype in primary MSCs involving SMAD-dependent pathways. Our results show that mast cell-derived exosomes are decorated with latent TGF beta-1 and are retained in recipient MSC endosomes, influencing recipient cell migratory phenotype. We conclude that exosomes can convey signalling within endosomes by delivering bioactive surface ligands to this intracellular compartment.
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| 29. |
- Villamil Giraldo, Ana-Maria, 1973-, et al.
(författare)
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Interactions of the lysosomotropic detergent omethyl-serine dodecylamide hydrochloride (Msdh) with lipid bilayer membranes-implications for cell toxicity
- 2020
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Ingår i: International Journal of Molecular Sciences. - : MDPI AG. - 1661-6596 .- 1422-0067. ; 21:9
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Tidskriftsartikel (refereegranskat)abstract
- O-methyl-serine dodecylamine hydrochloride (MSDH) is a detergent that accumulates selectively in lysosomes, a so-called lysosomotropic detergent, with unexpected chemical properties. At physiological pH, it spontaneously forms vesicles, which disassemble into small aggregates (probably micelles) below pH 6.4. In this study, we characterize the interaction between MSDH and liposomes at different pH and correlate the findings to toxicity in human fibroblasts. We find that the effect of MSDH on lipid membranes is highly pH-dependent. At neutral pH, the partitioning of MSDH into the liposome membrane is immediate and causes the leakage of small fluorophores, unless the ratio between MSDH and lipids is kept low. At pH 5, the partitioning of MSDH into the membrane is kinetically impeded since MSDH is charged and a high ratio between MSDH and the lipids is required to permeabilize the membrane. When transferred to cell culture conditions, the ratio between MSDH and plasma membrane lipids must therefore be low, at physiological pH, to maintain plasma membrane integrity. Transmission electron microscopy suggests that MSDH vesicles are taken up by endocytosis. As the pH of the endosomal compartment progressively drops, MSDH vesicles disassemble, leading to a high concentration of increasingly charged MSDH in small aggregates inside the lysosomes. At sufficiently high MSDH concentrations, the lysosome is permeabilized, the proteolytic content released to the cytosol and apoptotic cell death is induced.
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| 30. |
- Villamil Giraldo, Ana Maria, et al.
(författare)
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Spontaneous Vesiculation and pH-Induced Disassembly of a Lysosomotropic Detergent : Impacts on Lysosomotropism and Lysosomal Delivery
- 2016
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Ingår i: LANGMUIR. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 32:50, s. 13566-13575
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Tidskriftsartikel (refereegranskat)abstract
- Lysosomotropic detergents (LDs) selectively rupture lysosomal membranes through mechanisms that have yet to be characterized. A consensus view, currently, holds that LDs, which are weakly basic, diffuse across cellular membranes as monomers in an uncharged state, and via protonation in the acidic lysosomal compartment, they become trapped, accumulate, and subsequently solubilize the membrane and induce lysosomal membrane permeabilization. Here we demonstrate that the lysosomotropic detergent O-methyl-serine dodecylamide hydrochloride (MSDH) spontaneously assembles into vesicles at, and above, cytosolic pH, and that the vesicles disassemble as the pH reaches 6.4 or lower. The aggregation commences at concentrations below the range of those used in cell studies. Assembly and disassembly of the vesicles was studied via dynamic light scattering, zeta potential measurements, cryo-TEM, and fluorescence correlation spectroscopy and was found to be reversible via control of the pH. Aggregation of MSDH into closed vesicles under cytosolic conditions is at variance with the commonly held view of LD behavior, and we propose that endocytotic pathways should be considered as possible routes of LD entry into lysosomes. We further demonstrate that MSDH vesicles can be loaded with fluorophores via a solution transition from low to high pH, for subsequent release when the pH is lowered again. The ability to encapsulate molecular cargo into MSDH vesicles together with its ability to disaggregate at low pH and to permeabilize the lysosomal membrane presents an intriguing possibility to use MSDH as a delivery system.
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| 31. |
- Vogel, H., et al.
(författare)
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Probing bio-molecular interactions in attoliter volumes
- 2014
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Ingår i: Optical Sensors, 2014. - Washington, D.C. : OSA. - 9781557528209
-
Konferensbidrag (refereegranskat)abstract
- We report on label-free volume, concentration, and mobility analysis of single protein molecules and nanoparticles during their diffusion through a subattoliter detection volume, confined by a 100 nm aperture in a thin gold film. A high concentration of small fluorescent molecules renders the aqueous solution in the aperture brightly fluorescent. Nonfluorescent analytes diffusing into the aperture displace the fluorescent molecules in the solution, leading to a decrease of the detected fluorescence signal, while analytes diffusing out of the aperture return the fluorescence level. The resulting fluorescence fluctuations provide direct information on the volume, concentration, and mobility of the nonfluorescent analytes through fluctuation analysis in both time and amplitude.
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| 32. |
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| 33. |
- Wennmalm, Stefan
(författare)
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Detecting the dynamics of single biomolecules
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is concerned with the detection of single biomolecules. Through detection of individual molecules it can be clarified whether a behavior which has been observed in a population is representative for all molecules. For detection confocal fluorescence microscopy was used, in particular Fluorescence Correlation Spectroscopy (FCS). Complexes of a 217 base-pairs DNA and the fluorescent molecule TMR were immobilized at low concentration on glass coverslips. Through an automatic search single complexes were positioned into the open laser excitation volume (1 [my]m). The detected fluctuating fluorescence intensity of the single molecules was interpreted as association / dissociation of TMR to the nucleotide guanosine. Within the limiting survival time of the fluorophores, the fluctuation rates of the DNA-TMR molecules were found to be heterogeneously distributed. From an analysis of non-fluctuating DNA-TMR complexes an exponential distribution of survival time and number of detected photons was found. Enzymatic activity of horseradish peroxidase (HRP) and of ribonuclease T1 (RNase T1) was analyzed by FCS. For RNase T1, enzyme (~ fM conc.) mediated release of surface immobilized DNA was demonstrated. In the case of HRP, the enzymes were immobilized. The analyzed enzymatic cycle involved formation of a fluorescent enzyme-product complex. It was found that the rate with which the enzyme-product complex was formed was widely distributed. An FCS-setup for ultraviolet excitation and emission was built. With UV-excitation the fluorescence of certain nucleotides and aminoacids can be used. In particular biomolecular dynamics in which such fluorophores are involved could be analyzed. The modified nucleotide 2-aminopurine (2-AP) was used as fluorophore. The diffusion and triplet state dynamics of 2-AP were analyzed. The dynamics of voltage gated ion channels in cell membranes were measured. The voltage- sensing segment S4 of the Shaker potassium channel was labeled with TMR. A combination of the patch-clamp technique and FCS was used. In an allopen or all-closed measurement, correlation between ion current through the channels and fluorescence change generated by S4's conformational rearrangement was observed. This indicates that cross-correlation of the same signals during spontaneous millisecond opening and closing should be detectable.
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| 34. |
- Wennmalm, Stefan, et al.
(författare)
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Highly Sensitive FRET-FCS Detects Amyloid beta-Peptide Oligomers in Solution at Physiological Concentrations
- 2015
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 87:23, s. 11700-11705
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Tidskriftsartikel (refereegranskat)abstract
- Oligomers formed by the amyloid beta-peptide (A beta) are pathogens in Alzheimers disease. Increased knowledge on the oligomerization process is crucial for understanding the disease and for finding treatments. Ideally, A beta oligomerization should be studied in solution and at physiologically relevant concentrations, but most popular techniques of today are not capable of such analyses. We demonstrate here that the combination of FOrster Resonance Energy Transfer and Fluorescence Correlation Spectroscopy (FRET-FCS) has a unique ability to detect small subpopulations of FRET-active molecules and oligomers. FRET-FCS could readily detect a FRET-active oligonucleotide present at levels as low as 0.5% compared to FRET-inactive dye molecules. In contrast, three established fluorescence fluctuation techniques (FCS, FCCS, and PCH) required fractions between 7 and 11%. When applied to the analysis of A beta, FRET-FCS detected oligomers consisting of less than 10 A beta molecules, which coexisted with the monomers at fractions as low as 2 +/- 2%. Thus, we demonstrate for the first time direct detection of small fractions of A beta oligomers in solution at physiological concentrations. This ability of FRET-FCS could be an indispensable tool for studying biological oligomerization processes, in general, and for finding therapeutically useful oligomerization inhibitors.
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| 35. |
- Wennmalm, Stefan, et al.
(författare)
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Interferometry and fluorescence detection for simultaneous analysis of labeled and unlabeled nanoparticles in solution
- 2012
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 134:48, s. 19516-19519
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Tidskriftsartikel (refereegranskat)abstract
- A novel fluctuation spectroscopy technique based on interferometry is described. The technique, termed scattering interference correlation spectroscopy (SICS), autocorrelates the signals from the forward-scattered and transmitted laser light from nanoparticles (NPs) in solution. SICS has two important features: First, for unlabeled NPs with known refractive index, it analyzes not only the diffusion coefficient but also the effective cross section and concentration in a single measurement. Second, it can be combined with fluorescence correlation spectroscopy (FCS) for simultaneous analysis of labeled and unlabeled NPs. SICS is here demonstrated on unlabeled M13 phages and on unlabeled NPs with diameters of 210 nm down to 26 nm. It is also shown how the combination of SICS and FCS can be used to determine the fraction of fluorescent NPs in a mixture and estimate Kd from a single binding measurement.
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| 36. |
- Wennmalm, Stefan, et al.
(författare)
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Inverse-Fluorescence Correlation Spectroscopy
- 2009
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 81:22, s. 9209-9215
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Tidskriftsartikel (refereegranskat)abstract
- An alternative version of fluorescence correlation spectroscopy is presented, where the signal from a medium surrounding the particles of interest is analyzed, as opposed to a signal from the particles themselves. Ibis allows for analysis of unlabeled particles and potentially of biomolecules. Here, the concept together with principal experiments on polystyrene beads of 100, 200, 400, and 800 nm diameter in an aqueous solution of alexa 488-fluorophores are presented. The use of photo detectors allowing higher photon fluxes, or of reduced detection volumes, should enable analysis of significantly smaller particles or even biomolecules.
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| 37. |
- Wennmalm, Stefan, 1970-, et al.
(författare)
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Inverse-fluorescence correlation spectroscopy: more information and less labeling
- 2011
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Ingår i: Frontiers in Bioscience. - : Frontiers in Bioscience. - 1093-9946 .- 1093-4715 .- 1945-0516 .- 1945-0524. ; s3, s. 385-392
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Tidskriftsartikel (refereegranskat)abstract
- Inverse-Fluorescence Correlation Spectroscopy(iFCS) is a recently developed modification of standardFCS that allows analysis of particles and biomoleculeswithout labeling. The particles generate no signal; insteadthe signal is generated by a surrounding medium. Particlesdiffusing through the FCS-detection volume displace afraction of the surrounding medium, causing transient dipsin the detected signal. These give information about themobility and concentration of the analyzed particles. Alsolabeled particles can be analyzed, whereby their signal iscross-correlated with that from the surrounding medium(iFCCS). This can give information about the volume of thelabeled particles, or alternatively about the size of thedetection volume. Also the interaction of unlabeledparticles with small, labeled ligands can be analyzed withiFCCS. This allows using cross-correlation as a sensitiveindication of binding, even though only one binding-partneris labeled. This review describes the principles of iFCS andiFCCS and measurements of microspheres dissolved in asurrounding medium containing alexa 488. We also discusspractical considerations, and future possibilities foranalyses of biomolecules.
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| 38. |
- Wennmalm, Stefan, et al.
(författare)
-
Inverse-Fluorescence Cross-Correlation Spectroscopy
- 2010
-
Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 82:13, s. 5646-5651
-
Tidskriftsartikel (refereegranskat)abstract
- Inverse-fluorescence correlation spectroscopy (iFCS) was recently introduced as an alternative version of FCS that does not require labeling of the analyzed particles or biomolecules. In iFCS, the signal from a medium surrounding the particles is analyzed, as opposed to a signal from the studied particles themselves. As unlabeled particles diffuse through the detection volume, they displace a fraction of the fluorescent medium, causing transient dips in the detected signal which give information about the mobility and concentration of the analyzed particles. Here inverse-fluorescence cross-correlation spectroscopy (iFCCS) is introduced as an extension of iFCS. In iFCCS, labeled particles/biomolecules are analyzed and their fluorescence signal is cross-correlated with the signal from the surrounding medium. When labeled particles are analyzed, a direct estimate of the volume of the particles is obtained or, alternatively, an estimate of the size of the detection volume. Another possibility is to analyze the interaction of small, labeled molecules with unlabeled particles, resulting in cross-correlation as an indication of binding, even though only one binding partner is labeled. This also enables accurate estimation of the degree of labeling, since the amounts of labeled and unlabeled particles are estimated independently.
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| 39. |
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| 40. |
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| 41. |
- Wennmalm, Stefan, 1970-
(författare)
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Potentials and pitfalls of inverse fluorescence correlation spectroscopy
- 2018
-
Ingår i: Methods. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 1046-2023 .- 1095-9130. ; 140, s. 23-31
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Tidskriftsartikel (refereegranskat)abstract
- Inverse Fluorescence Correlation Spectroscopy (iFCS) is a variant of FCS where unlabeled particles in solution, or domains in membranes, displace their surrounding, signal-generating molecules and thereby generate fluctuations. iFCS has to date been applied to unlabeled as well as labeled particles and protein molecules, using fluorescence as well as Raman scattering as a signal source, in diffraction-limited detection volumes as well as in nano-wells, and on fixed surfaces as well as in lipid bilayers. This review describes these applications and discusses the potentials and pitfalls when using iFCS.
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| 42. |
- Wennmalm, Stefan, 1970-, et al.
(författare)
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Studying Individual Events in Biology
- 2007
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Ingår i: Annual Review of Biochemistry. - : Annual Reviews. - 0066-4154 .- 1545-4509. ; 76, s. 419-446
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Tidskriftsartikel (refereegranskat)abstract
- Studying the properties of individual events and molecules offers a host of advantages over taking only macroscopic measurements of populations. Here we review such advantages, as well as some pitfalls, focusing on examples from biological imaging. Examples include single proteins, their interactions in cells, organelles, and their interactions both with each other and with parts of the cell. Additionally, we discuss constraints that limit the study of single events, along with the criteria that must be fulfilled to determine whether single molecules or events are being detected.
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| 43. |
- Wennmalm, Stefan, et al.
(författare)
-
UV-Fluorescence Correlation Spectroscopy of 2-Aminopurine
- 2001
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Ingår i: Biological chemistry (Print). - 1431-6730 .- 1437-4315. ; 382:3, s. 393-397
-
Tidskriftsartikel (refereegranskat)abstract
- We have built a fluorescence correlation spectroscopy (FCS) microscope for ultraviolet excitation (280 300 nm) and emission. With UV excitation the fluorescence of natural fluorophores such as the modified nucleotide 2-aminopurine can be analyzed. The sensitivity of a natural fluorophore toward conformational changes can reveal dynamics in biomolecules. UVFCS is well suited for detection of intensity fluctuations related to such conformational dynamics. Here we show UVFCS measured on pQuarterphenyl and on 2-aminopurine (2-AP). The triplet state rate constants and the excitation cross section for 2- AP were estimated to k[23]=1 x 10[6] s[-1], k[31]=3 x 10[5] s[-1], and σ=2 x 10[-17] cm[2].
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| 44. |
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