Biophysical modeling of photosynthetic electron transfer and practical applications to cyanobacteria

Siirretty Doriast

Impact of Surface-Active Guanidinium-, Tetramethylguanidinium-, and Cholinium-Based Ionic Liquids on Vibrio Fischeri Cells and Dipalmitoylphosphatidylcholine Liposomes

We investigated the toxicological effect of seven novel cholinium, guanidinium, and tetramethylguanidinium carboxylate ionic liquids (ILs) from an ecotoxicological point of view. The emphasis was on the potential structure-toxicity dependency of these surface-active ILs in aqueous environment. The median effective concentrations (EC50) were defined for each IL using Vibrio (Aliivibrio) fischeri marine bacteria. Dipalmitoylphosphatidylcholine (DPPC) liposomes were used as biomimetic lipid membranes to study the interactions between the surface-active ILs and the liposomes. The interactions were investigated by following the change in the DPPC phase transition behaviour using differential scanning calorimetry (DSC). Critical micelle concentrations for the ILs were determined to clarify the analysis of the toxicity and the interaction results. Increasing anion alkyl chain length increased the toxicity, whereas branching of the chain decreased the toxicity of the ILs. The toxicity of the ILs in this study was mainly determined by the surface-active anions, while cations induced a minor impact on the toxicity. In the DSC experiments the same trend was observed for all the studied anions, whereas the cations seemed to induce more variable impact on the phase transition behaviour. Toxicity measurements combined with liposome interaction studies can provide a valuable tool for assessing the mechanism of toxicity.Peer reviewe

Immobilization of natural lipid biomembranes and their interactions with choline carboxylates : A Nanoplasmonic sensing study

The cell membrane is mainly composed of lipid bilayers with inserted proteins and carbohydrates. Lipid bilayers made of purified or synthetic lipids are widely used for estimating the effect of target compounds on cell membranes. However, the composition of such biomimetic membranes is much simpler than the composition of biological membranes. Interactions between compounds and simple composition biomimetic membranes might not demonstrate the effect of target compounds as precisely as membranes with compositions close to real organisms. Therefore, the aim of our study is to construct biomimetic membrane closely mimicking the state of natural membranes. Liposomes were prepared from lipids extracted from L-alpha-phosphatidylcholine, Escherichia coli, yeast (Saccharomyces cerevisiae) and bovine liver cells through agitation and sonication. They were immobilized onto silicon dioxide (SiO2) sensor surfaces using N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid buffer with calcium chloride. The biomimetic membranes were successfully immobilized onto the SiO2 sensor surface and detected by nanoplasmonic sensing. The immobilized membranes were exposed to choline carboxylates. The membrane disruption effect was, as expected, more pronounced with increasing carbohydrate chain length of the carboxylates. The results correlated with the toxicity values determined using Vibrio fischeri bacteria. The yeast extracted lipid membranes had the strongest response to introduction of choline laurate while the bovine liver lipid extracted liposomes were the most sensitive towards the shorter choline carboxylates. This implies that the composition of the cell membrane plays a crucial role upon interaction with choline carboxylates, and underlines the necessity of testing membrane systems of different origin to obtain an overall image of such interactions.Peer reviewe

Interactions of Ionic Liquids and Spirocyclic Compounds with Liposome Model Membranes. A Steady-State Fluorescence Anisotropy Study

Understanding the toxicity of ionic liquids (ILs) is crucial in the search of greener chemicals. By comparing in vivo toxicity and in vitro interactions determined between compounds and biomimetic lipid membranes, more detailed toxicity vs. structure relation can be obtained. However, determining the interactions between non-surface-active compounds and liposomes has been a challenging task. Organisational changes induced by ILs and IL-like spirocyclic compounds within 1,6-diphenyl-1,3,5-hexatriene-doped biomimetic liposomes was studied by steady-state fluorescence anisotropy technique. The extent of organisational changes detected within the liposome bilayers were compared to the toxicity of the compounds determined using Vibrio Fischeri bacteria. Four liposome compositions made of pure 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocoline (POPC) and mixtures of POPC, 1-palmitoyl-2-oleyl-sn-glycero-3-phosphoserine (POPS), and cholesterol (Chol) were tested as biomimetic models. Changes observed within the POPC/POPS/Chol 55:20:25 bilayers correlated the best with the toxicity results: ten out of twelve compounds followed the trend of increasing bilayer disorder - increasing toxicity. The study suggests that the toxicity of non-surface-active compounds is dependent on their ability to diffuse into the bilayers. The extent of bilayer's organisational changes correlates rather well with the toxicity of the compounds. Highly sensitive technique, such as fluorescence anisotropy measurements, is needed for detecting subtle changes within the bilayer structures.Peer reviewe

Vapor-Liquid Equilibrium of Ionic Liquid 7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium Acetate and Its Mixtures with Water

Ionic liquids have the potential to be used for extracting valuable chemicals from raw materials. These processes often involve water, and after extraction, the water or other chemicals must be removed from the ionic liquid, so it can be reused. To help in designing such processes, we present data on the vapor-liquid equilibrium of the system containing protic ionic liquid 7-methyl-1,5,7-triazabicyclo [ 4.4.0 ] dec-5-enium acetate, water, acetic acid, and 7-methyl-1,5,7-triazabicyclo [4.4.0] dec-5-ene. Earlier studies have only focused on mixtures of water and an ionic liquid with a stoichiometric ratio of the ions. Here, we also investigated mixtures containing an excess of the acid or base component because in real systems with protic ionic liquids, the amount of acid and base in the mixture can vary. We modeled the data using both the ePC-SAFT and NRTL models, and we compared the performance of different modeling strategies. We also experimentally determined the vapor composition for a few of the samples, but none of the modeling strategies tested could accurately predict the concentration of the acid and base components in the vapor phase.Peer reviewe

Recycling of Superbase-Based Ionic Liquid Solvents for the Production of Textile-Grade Regenerated Cellulose Fibers in the Lyocell Process

This article has a correction concerning the authors: We regret that there is an error with the author list in our original article. The authors Jussi Helminen, Paulus Hyväri, and Ilkka Kilpeläinen, all with the Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland, were mistakenly omitted. The author list should be as shown above in this Addition and Correction. DOI 10.1021/acssuschemeng.0c07773Ioncell is a Lyocell based technology for the production of manmade cellulose fibers. This technology exploits the intrinsic dissolution power of superbase-based ionic liquids (ILs) toward cellulose and the ability to form spinnable cellulose solutions. The regenerated fibers are produced via a dry-jet wet spinning process in which the cellulose filaments are stretched in an air gap before regenerating in an aqueous coagulation medium. For the commercialization of this process, it is essential to demonstrate the quantitative recovery of the solvent from the coagulation bath without impairing its solvation power. This study reports on the spinnability and recyclability of the IL 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate ([mTBDH][OAc]) over five cycles in comparison to 1,5-diaza-bicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]). The aqueous IL solutions were recovered from the coagulation bath by successive thermal treatments under reduced pressure. Accordingly, the recycled ILs were utilized to dissolve 13 wt % cellulose pulp in each cycle without the addition of make-up IL. While using [mTBDH][OAc], the pulp was completely dissolved and processed into easily spinnable cellulose solutions during all five cycles, whereas the ability to dissolve pulp was completely lost after the first recovery cycle when using [DBNH][OAc]. The composition of the recovered ILs and extent of side-products generated in the adopted process was analyzed in detail. This includes characterization of the rheological properties of the solutions as well as the macromolecular and mechanical properties of the regenerated fibers. In addition, we review the toxicity of both solvents using Vibrio fischeri bacteria. Finally, the spun fibers from all [mTBDH][OAc] spinning trials were combined to produce a demonstration dress (Paju), designed and sewn by Marimekko Design House in Finland.Peer reviewe

Correlation between Ionic Liquid Cytotoxicity and Liposome-Ionic Liquid Interactions

This study aims at extending the understanding of the toxicity mechanism of ionic liquids (ILs) using various analytical methods and cytotoxicity assays. The cytotoxicity of eight ILs and one zwitterionic compound was determined using mammalian and bacterial cells. The time dependency of the IL toxicity was assessed using human corneal epithelial cells. Hemolysis was performed using human red blood cells and the results were compared with destabilization data of synthetic liposomes upon addition of ILs. The effect of the ILs on the size and zeta potential of liposomes revealed information on changes in the lipid bilayer. Differential scanning calorimetry was used to study the penetration of the ILs into the lipid bilayer. Pulsed field gradient nuclear magnetic resonance spectroscopy was used to determine whether the ILs occurred as unimers, micelles, or if they were bound to liposomes. The results show that the investigated ILs can be divided into three groups based on the cytotoxicity mechanism: cell wall disrupting ILs, ILs exerting toxicity through both cell wall penetration and metabolic alteration, and ILs affecting solely on cell metabolism.Peer reviewe

Yritysjärjestelyt ja omaisuuslajisiirrot

Opinnäytetyön tarkoituksena oli tehdä uutta opintomateriaalia Oulun ammattikorkeakouluun yritysverotuksen erityiskysymyksiä opintojaksolle yritysjärjestelyjen, yksityiskäytön sekä tulolähde- ja omaisuuslajisiirtojen osioon. Opintojakso kuuluu taloushallinnon opintosuuntauksen vapaa valintaisiin ammattiopintoihin. Opintomateriaalin päivittäminen edellä mainitun osion osalta oli ajankohtaista, sillä yhteisöjen tulolähdejaottelua on uudistettu ja näitä uudistuksia tullaan soveltamaan verotukseen ensimmäisen kerran vuoden 2020 verotusta toimitettaessa. Opinnäytetyö on toiminnallinen ja se koostuu raporttiosasta ja opintomateriaalista eli tuotoksesta. Tietoperustassa on kerrottu tulolähde-, omaisuuslajijaottelun, yksityiskäytön ja erilaisten yritysjärjestelyjen perusteet sekä se miten yhteisöjen tulolähdejaottelun uudistus vaikuttaa näihin. Opinnäytetyössä vastataan kysymyksiin siitä, mitä ovat tulolähde ja omaisuuslajisiirtojen verovaikutukset, miten yhteisöjen tulolähdejaon uudistus vaikuttaa verotukseen ja minkälainen on erilaisten yritysjärjestelyjen verovaikutus. Tietoperusta pohjautuu verolakeihin, hallituksen esityksiin, verohallinnon ohjeistuksiin ja aihetta käsitelevään kirjallisuuteen sekä artikkeleihin. Opinnäytetyön toiminnallisessa osassa on kerrottu, miten opinnäytetyöprosessi eteni ja miten opintomateriaali tehtiin. Opintomateriaali sisältää selventäviä esimerkkejä tietotoperustassa käsitellyistä aihepiireistä ja sen on tarkoitus toimia opiskelun tukena opintojaksolla. Valmis opintomateriaali on opinnäytetyön lopussa liitteenä

Connectivity of Photosystem II Is the Physical Basis of Retrapping in Photosynthetic Thermoluminescence

Energy transfer between photosystem II (PSII) centers is known from previous fluorescence studies. We have studied the theoretical consequences of energetic connectivity of PSII centers on photosynthetic thermoluminescence (TL) and predict that connectivity affects the TL Q band. First, connectivity is expected to make the Q band wider and more symmetric than an ideal first-order TL band. Second, the presence of closed PSII centers in an energetically connected group of PSII centers is expected to lower the probability that an exciton originating in a recombination reaction becomes retrapped. The latter effect would shift the Q band toward lower temperature, and the shift would be greater the higher the percentage of closed PSII centers at the beginning of the measurement. These effects can be generalized as second-order effects, as they make the Q band resemble the second-order TL bands obtained from semiconducting solids. We applied the connected-units model of chlorophyll fluorescence to derive equations for quantifying the second-order effects in TL. To test the effect of the initial proportion of closed reaction centers, we measured the Q band with different intensities of the excitation flash and found that the peak position changed by 2.5°C toward higher temperature when the flash intensity was lowered from saturating to 0.39% of saturating. The result shows that energy transfer between reaction centers of PSII forms the physical basis of retrapping in photosynthetic TL. The second-order effects partially explain the deviation of the form of the Q band from ideal first-order TL

Impact of different group 2 sigma factors on light use efficiency and high salt stress in the cyanobacterium Synechocystis sp. PCC 6803.

Sigma factors of RNA polymerase recognize promoters and have a central role in controlling transcription initiation and acclimation to changing environmental conditions. The cyanobacterium Synechocystis sp. PCC 6803 encodes four non-essential group 2 sigma factors, SigB, SigC, SigD and SigE that closely resemble the essential SigA factor. Three out of four group 2 sigma factors were simultaneously inactivated and acclimation responses of the triple inactivation strains were studied. All triple inactivation strains grew slowly in low light, and our analysis suggests that the reason is a reduced capacity to adjust the perception of light. Simultaneous inactivation of SigB and SigD hampered growth also in high light. SigB is the most important group 2 sigma factor for salt acclimation, and elimination of all the other group 2 sigma factors slightly improved the salt tolerance of Synechocystis. Presence of only SigE allowed full salt acclimation including up-regulation of hspA and ggpS genes, but more slowly than SigB. Cells with only SigD acclimated to high salt but the acclimation processes differed from those of the control strain. Presence of only SigC prevented salt acclimation