Browsing by Subject "kemia"

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  • Laaksonen, Tiina (Helsingin yliopisto, 2015)
    The detection of enantiomeric purity is an important part of synthetic chemistry. Especially when developing medicinal compounds the determination of the amount of enantiomeric impurities is important as one of the enantiomers may be poisonous or lethal to humans. Various methods exist for the study of enantiomeric purity and NMR spectroscopy has been intensively studied as a tool for this purpose. As NMR is fast, readily available and easy to use it provides an attractive way to study enantomeric purity. In NMR chiral discrimination is obtained by using chiral derivatising agents (CDAs) or chiral solvating agents (CSAs). CSAs have more potential in enantiomeric excess (ee) studies than CDAs as they lack of the disadvantaged of CDAs (e.g. kinetic resolution and racemisation). As chiral carboxylic acids are important in the synthesis of medicinally attractive compounds, natural products and their metabolites, CSAs which can be used for the determination of enantiomeric purity of carboxylic acids and are easily available and cheap are helpful. The present study mainly focuses on the development of CSAs suitable for the discrimination of non-ionic and ionic chiral carboxylic acids. (+)-Dehydroabietylamine was used as chiral building block for these new CSAs as it has several beneficial features such as easy availability, low price, an amenable structure for CSA construction and it is known to resolve chiral carboxylic acids via cystallisation. Three different series of non-ionic and ionic CSAs were developed from (+)-dehydroabietylamine: 1) ammonium, 2) secondary amine and 3) imidazolium based CSAs. Their enantiomeric discrimination abilities were examined with Mosher s acid and its tetrabutylammonium salt. Best resolution was obtained with non-ionic substrate and non-ionic CSA and with ionic substrate and ionic CSA. Ionic CSAs were also able to resolve non-ionic substrates but the enantiomeric resolution remained poor. The best performing CSAs were subjected for more detailed investigation. The stoichiometry of formed diastereomeric complex between the CSA and substrate was studied by titration experiment. CSA-substrate complexes were generally formed in 1:1 ratio. CSA applicability to function in ee determination was studied and they were able to detect the enantiomeric purities of samples with excellent reliability. Finally their ability to resolve various α-substituted carboxylic acids was studied showing that (+)-dehydroabietylamine based CSAs are suitable for chiral carboxylic acids containing electronegative α-substituent. Also the effect of measurement conditions and sample preparation when using cationic CSAs in enantiomeric discrimination was investigated. Lower temperatures and low polarity solvents were noticed to increase enantiomeric discrimination, among high CSA concentration. Delocalisation of negative charge in counter anion of CSA as well as the use of organic counter cation for the substrate was also notised to increase enantiomeric discrimination.
  • Johansson, Mikael (Helsingin yliopisto, 2007)
    Quantum effects are often of key importance for the function of biological systems at molecular level. Cellular respiration, where energy is extracted from the reduction of molecular oxygen to water, is no exception. In this work, the end station of the electron transport chain in mitochondria, cytochrome c oxidase, is investigated using quantum chemical methodology. Cytochrome c oxidase contains two haems, haem a and haem a3. Haem a3, with its copper companion, CuB, is involved in the final reduction of oxygen into water. This binuclear centre receives the necessary electrons from haem a. Haem a, in turn, receives its electrons from a copper ion pair in the vicinity, called CuA. Density functional theory (DFT) has been used to clarify the charge and spin distributions of haem a, as well as changes in these during redox activity. Upon reduction, the added electron is shown to be evenly distributed over the entire haem structure, important for the accommodation of the prosthetic group within the protein. At the same time, the spin distribution of the open-shell oxidised state is more localised to the central iron. The exact spin density distribution has been disputed in the literature, however, different experiments indicating different distributions of the unpaired electron. The apparent contradiction is shown to be due to the false assumption of a unit amount of unpaired electron density; in fact, the oxidised state has about 1.3 unpaired electrons. The validity of the DFT results have been corroborated by wave function based coupled cluster calculations. Point charges, for use in classical force field based simulations, have been parameterised for the four metal centres, using a newly developed methodology. In the procedure, the subsystem for which point charges are to be obtained, is surrounded by an outer region, with the purpose of stabilising the inner region, both electronically and structurally. Finally, the possibility of vibrational promotion of the electron transfer step between haem a and a3 has been investigated. Calculating the full vibrational spectra, at DFT level, of a combined model of the two haems, revealed several normal modes that do shift electron density between the haems. The magnitude of the shift was found to be moderate, at most. The proposed mechanism could have an assisting role in the electron transfer, which still seems to be dominated by electron tunnelling.
  • Partanen, Lauri (Helsingin yliopisto, 2017)
    Sulfuric and hydrochloric acids participate in several important chemical processes occurring in the atmosphere. Due to its tendency to react with water molecules, sulfuric acid is an important factor in cloud formation and related phenomena. Hydrochloric acid is heavily implicated in stratospheric ozone depletion because of its role as a temporary reservoir for chlorine radicals. In this thesis, the thermodynamics and dynamics of these two acids are investigated. The dynamic part focuses on the chemical processes following collision of HCl on water and amorphous ice surfaces at different temperatures. By utilizing ab initio molecular dynamics, it is observed that the surface temperature and the initial kinetic energy of the HCl molecule have important and not wholly overlapping effects on its ionization behaviour. The results add to the understanding of hydrochloric acid dissociation on water surfaces in various parts of the atmosphere, potentially illuminating new pathways for related chemical reactions, such as the formation of ClNO on amorphous ice surfaces. The thermodynamic studies revolve around the impact of multiple low-lying stable conformers, or global anharmonicity, on the thermodynamic properties. The studies for this part focus on complexes of sulfuric acid, especially sulfuric acid monohydrate. Due to the relatively small size of the monohydrate, high-level ab initio methods can be employed to obtain accurate values for its thermodynamic properties, thus providing a reliable basis for comparison with less accurate approaches. New ways of accounting for global anharmonicity are developed both for small- and medium-sized clusters. For small clusters, an approximation is presented where the large amplitude motions connecting different conformers are treated separately from the rest of the vibrations, resulting in direct quantum mechanical accounting of the different conformers. In the case of medium-sized clusters, an equation based on statistical mechanics is derived to replace the erroneous Boltzmann averaging formula that has seen wide use in the literature.
  • Parviainen, Arno (Helsingin yliopisto, 2016)
    As the consumption of natural resources increase with the exponential world population growth, the food industry needs to answer the demand. This means that farming has to be increased and optimized from its current level. The problem is summoned from the fact that the amount of arable land is decreasing. This eventually leads to prioritizing the land for food crops and the downscaling the production of i.e. palm oil and cotton. Cotton is ~90% pure cellulose and is used for textile commodities for its properties over synthetic fibers. The same cellulose can be found all around in nature, from the structure of trees to algae. Cellulose is the world s most commonly found polymer and it is generated annually in nature enough to stop cotton farming altogether. The problem is the low solubility of cellulose to commonly used solvents. The extensive hydrogen bonding network of cellulose gives this biopolymer its strong features. The structure of cellulose and the chemical features has been known for a century and a half to this date, but solubilization of cellulose has evaded a more systemic, yet pragmatic approach. There have been introductions of various types of solvent systems for cellulose dissolution, from which ionic liquids have been the most successful class of solvents. The research performed in this thesis has been focusing on the research and development of new cellulose dissolving ionic liquids. A class of imidazolium based ionic liquids was used as the starting point for the development, since they exhibit high dissolutive power and relatively low viscosities. The chemical stability of the solvent system needs to sustain various kinds of chemical and physical stress without compromising process safety, ecology or economy. Our research indicated that the acidity-basicity of the ionic liquid components was correlating with the chemical-physical stability of the solvents. The higher the basicity was the less stable the ionic liquid become and in the same time it was found out that the ionic liquids that were synthesized from less basic components were not able to dissolve cellulose in the first place. We calculated the gas-phase basicities (proton affinity) of various types and strengths of bases by using simple and efficient computational method. After the calculations were done, we combined the bases with acetic acid to form acetate ionic liquids and with propionic acid for propionates correspondingly. After the examination of the cellulose dissolution capability we discovered a threshold basicity where the cellulose dissolution capability was introduced. In a collaboration with Aalto University, we developed an ionic liquid that could be used in industrial scale production of cellulose fibers. The research was steered towards investigation of the chemical stability and recyclability of this new ionic liquid.
  • Laakia, Jaakko (Helsingin yliopisto, 2017)
    This thesis covers two aspects of utilisation of advanced separation technology together with mass spectrometry: 1. Drift tube ion mobility spectrometry mass spectrometry (IMS-MS) studies of the behaviour of ions in the gas phase and 2. Comprehensive two dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOF-MS) studies for characterization of crude oil samples. In IMS studies, the focus was on the separation of isomeric compounds. For example, [M-H]- ions of 2,4-di-tert-butylphenol (2,4-DtBPh) and 2,6-di-tert-butylphenol (2,6-DtBPh) were separated. It was also observed that shielding of the charge site by the functional groups of a molecule has a large effect on the separation of the isomeric compounds. For example, amines with a shielded charge site were separated from those with a more open charge site, while some of the isomeric amines studied were not separated. Different kinds of adduct ions were observed for some of the analytes. Dioxygen adducts were seen for 2,4-DtBPh [M+O2]-, 2,6-di-tert-butylpyridine (2,6-DtBPyr) [M+O2]+· and 2,6-di-tert-butyl-4-methylpyridine (2,6-DtB-4MPyr) [M+O2]+·. The adduct formation increases the total mass of the analyte ion, and therefore, for example the 2,4-DtBPh [M+O2]- ion could be separated from its isomeric compound 2,6-DtBPh [M-H]-, which did not from the dioxygen adduct ion. In the case of 2,6-DtBPyr and 2,6-DtB-4MPyr, the [M]+ ions formed dioxygen adduct [M+O2]+· ions. The both ions, [M]+ and [M+O2]+·, shared the same drift time which was longer than their [M+H]+ ion species. This work demonstrates that measuring with IMS the mobility of different ion structures of the same molecule, especially dioxygen adducts, results in a better understanding of the role of adduct ions in the IMS-separation process. In GC×GC-TOF-MS studies, the focus was on detailed characterization of crude oil samples. For instance, oils from the Recôncavo Basin were classified to two different groups by using minor oil components. The GC×GC-TOF-MS data showed the correlation between 2D retention time and the number of carbons in a ring for several hydrocarbons as known from the literature. This information was used to achieve more structural information about eight new tetracyclic compounds, some of them similar to nor-steranes, detected during analysis. Some of these new compounds could be used as maturity indicators. This study demonstrated how GC×GC-TOF-MS can be used to separate geochemically interested isomers, identify minor geochemical differences between oils and achieve structural information about unknown biomarkers.
  • Salmi, Leo (Helsingin yliopisto, 2020)
    Inorganic–organic hybrids represent a class of materials consisting of inorganic and organic components mixed at the molecular level. This offers not only the possibility to combine material properties of the constituents, but also to discover completely new characteristics. Because of this, hybrid materials have become an important part of materials research. Atomic layer deposition (ALD) is a gas phase thin film deposition method with the ability to deposit conformal films with good control over film thickness and composition. Furthermore, ALD offers large-area uniformity and perfect step-coverage. Molecular layer deposition (MLD), used for depositing organic polymers, is a method derived directly from ALD. The combination of ALD and MLD offers a convenient way of depositing inorganic–organic hybrid material thin films for applications, such as electronics and optics, where ultimate precision is needed. In this thesis, ALD/MLD was used to deposit hybrid nanolaminates, metal–organic frameworks, and zinc glutarate. Nanolaminates of Ta2O5 and polyimide were deposited using tantalum ethoxide, water, pyromellitic dianhydride, and diaminohexane as the precursors. The leakage currents could be greatly reduced compared to the bare Ta2O5 and polyimide by layering of the materials. It was also shown that the mechanical properties could be improved by introduction of the organic layers. MOF-5 and IRMOF-8 thin films were deposited using zinc acetate, 1,4-benzenedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid as the precursors. The deposition process included ALD/MLD combined with a two-step post-deposition crystallization in moist air and in an autoclave with dimethylformamide. Despite the need for a liquid-phase crystallization, the conformality and continuity of the films could be preserved. ALD/MLD of zinc glutarate thin films was shown for the first time ever using zinc acetate and glutaric acid as the precursors. The films were crystalline as-deposited with a structure matching to zinc glutarate. Catalytic activity of the films was demonstrated by polymerizing propylene oxide and CO2 in the presence of zinc glutarate coated glass wool and steel mesh.
  • Carlberg, J. J. (Suomen metsätieteellinen seura, 1935)
  • Holopainen, Jani (Helsingin yliopisto, 2017)
    Bone is a fibrous nanocomposite material with a complex hierarchical system of different macro-, micro- and nanostructures. The structure elegantly supports the bone cell functions and facilitates bone remodeling by cellular activity. Injuries and diseases, e.g. osteoporosis, can cause bone fractures and loss that need to be treated with orthopedic implants. The global orthopedic market was estimated at $30 500 000 000 in 2012 and predicted to grow rapidly. A substantial amount of this goes to revision surgery due to implant failures. This not only causes unnecessary costs and work but reduces the quality of life for patients. The key for improving the performance of current implants lies in optimizing both the surface chemistry and structure from macro- to nanoscale. At best bone defects can be treated with bone scaffolds that induce formation of new bone via cellular functions and are degraded by the body thus evading the need for implant removal surgery. However, combining the favorable mechanical, structural and chemical properties poses challenges for the design and preparation methods used for bone implants and scaffolds. The aim of this work was to investigate the preparation of thin film and fibrous biomaterials for bone implants and scaffolds. New processes were developed for various biomaterials and their properties were thoroughly characterized. A method to convert CaCO3 nanostructures to nanocrystalline hydroxyapatite (HA) by treatment in phosphate solution was used to prepare HA thin films and fibers from atomic layer deposited (ALD) and electrospun CaCO3, respectively. HA fibers were also fabricated conventionally by annealing electrospun composite fibers that incorporated Ca and P precursors. Biocomposite fibers of HA nanoparticles and polylactic acid (nHA/PLA) were directly electrospun. These different nanofibers are highly interesting for bone scaffolds owing to their high surface area and the structural similarity to the fibrous nanostructure found in bone. However, conventional electrospinning is limited by its modest production rate. A needleless twisted wire electrospinning (NTWE) setup was developed to increase the production rate and was studied for the preparation of HA fibers for the bone scaffolds. Solution blow spinning (SBS) and electroblowing (EB) of HA were studied as other upscaling alternatives. Promising results were obtained in cell culture studies with the different materials. The electrospun materials could find use in fibrous bone scaffolds. The HA fibers were found out to be very interesting from a biological standpoint, but the fragility of the fibers limits their usability as such and therefore methods to incorporate bioceramic fibers into more rigid support structures should be developed. The method to prepare nanocrystalline HA by the conversion of CaCO3 proved to be highly conformal as evidenced by its ability to preserve the original shape of the ALD films and electrospun fibers. NTWE and EB were shown to be capable of producing high quality nanofibers and to provide a viable upscaling route to conventional electrospinning. In contrast, the quality of the SBS fibers needs improvement. Further work would be required to conclude if EB and NTWE are upscalable to industrial scale production levels.
  • Hakola, Maija (Helsingin yliopisto, 2013)
    There is nowadays a strong concern about decreasing oil supplies and global warming leading to ever increasing interest in biobased fuels and chemical production. The utilization of lignocellulosic raw materials for liquid biofuels and chemicals is a challenging task due to raw materials rigid structure which is resistant towards any actions to break it. Thus the raw materials should be pretreated to reach an economically vital process. Catalytic and alkaline oxidation presented here are novel, highly selective and effective methods to separate carbohydrates from lignin in different lignocellulosic materials. Both pretreatment methods are carried out at 120 140 ˚C for 4 20 hours under 10 bar oxygen pressure and in alkaline water solution. In catalytic oxidation also copper(II) phenanthroline catalyst is used. The obtained carbohydrate rich fraction is remarkably easy to hydrolyze with enzymes to corresponding sugars. The carbohydrate rich material from catalytic oxidation is nearly quantitatively converted into corresponding monohydrates in 24 hours by enzymatic hydrolysis. The enzyme loading can also be significantly decreased compared to standard methods, which helps to decrease the total costs of the process. Catalytic and alkaline oxidation pretreatment methods can be applied also to chromated copper arsenite treated waste wood, which is considered as hazardous waste. When combined with very mild sulfuric acid extraction and enzymatic hydrolysis 90 % sugar yield is obtained from the carbohydrate material. The sugars can be further utilized in chemical industry, which makes this method an interesting way to recycle hazardous waste. In a process turning lignocellulosic materials into sugars hydrolysis plays the key role. The hydrolysis is usually carried out enzymatically or with acids. They both have their disadvantages, such as long reaction times, poor yields or corrosive effect. As an alternative to traditional acid hydrolysis a microwave assisted mild acid hydrolysis is presented here. It can be applied to xylan, which is converted to xylose quantitatively in just one minute with 2 wt-% hydrochloric acid. When applied to milled birch wood 70 % yield of xylose is obtained. Subjecting alkaline oxidation pretreated birch to a three-step reaction, all the xylan and 66 % of the cellulose is hydrolyzed to corresponding sugars.
  • Granström, Mari (Helsingin yliopisto, 2009)
    Even though cellulose is the most abundant polymer on Earth, its utilisation has some limitations regarding its efficient use in the production of bio-based materials. It is quite clear from statistics that only a relatively small fraction of cellulose is used for the production of commodity materials and chemicals. This fact was the driving force in our research into understanding, designing, synthesising and finding new alternative applications for this well-known but underused biomaterial. This thesis focuses on the developing advanced materials and products from cellulose by using novel approaches. The aim of this study was to investigate and explore the versatility of cellulose as a starting material for the synthesis of cellulose-based materials, to introduce new synthetic methods for cellulose modification, and to widen the already existing synthetic approaches. Due to the insolubility of cellulose in organic solvents and in water, ionic liquids were applied extensively as the reaction media in the modification reactions. Cellulose derivatives were designed and fine-tuned to obtain desired properties. This was done by altering the inherent hydrogen bond network by introducing different substituents. These substituents either prevented spontaneous formation of hydrogen bonding completely or created new interactions between the cellulose chains. This enabled spontaneous self-assembly leading to supramolecular structures. It was also demonstrated that the material properties of cellulose can be modified even those molecules with a low degree of substitution when highly hydrophobic films and aerogels were prepared from fatty acid derivatives of nanocellulose. Development towards advanced cellulose-based materials was demostrated by synthesising chlorophyllcellulose derivatives that showed potential in photocurrent generation systems. In addition, liquid crystalline cellulose derivatives prepared in this study, showed to function as UV-absorbers in paper.
  • Kuutti, Lauri (Helsingin yliopisto, 2013)
    Despite the similarity of their structural basic units, cellulose- and starch-based materials behave differently in many industrial applications. In this thesis, the structure and properties of these polysaccharides and their selected derivatives were studied by means of five comprehensive examples. In the first investigation, highly crystalline cellulose was identified from Valonia macrophysa vesicles by atomic force microscopy. The role of water as a possible modifier on the surface of cellulose was found to be very important. The monoclinic phases were found on the cellulose surfaces with a lateral resolution of about 4 Å, indicating that water molecules cannot penetrate and thus disturb the surface structure of monoclinic cellulose. On the other hand, the absence of triclinic phases was explained by the used measuring geometry without liquid cell. The ageing of metastable oat and barley thermoplastic starch films was followed by frictional imaging. As a consequence of the ageing, the films lose some of their mechanical properties. In the oat films, glycerol used as a plasticiser diffused from the starch-glycerol-water matrix to the surface of thermoplastic starch, resulting in areas with low friction. In the case of barley starch films, the ageing first resulted in short range reorientation of polymers and finally slow crystallization of amylopectin branches. Solution precipitation techniques were applied to produce ideally spherical starch ester particles (with a diameter about half the wavelength of visible light), suitable for fillers in paper coatings in the third study. Particles assume their shape and size spontaneously when solvated starch polymer is mixed with non-solvent, due to the free mobility of the modified starch chains. Starch pigment has improved affinity to paper surface and it can be used as such or mixed with other pigments to enhance the optical or printing properties of paper. Starch-based pigmenting materials with improved optical performance were prepared in the laboratory by the complexation approach. Analytical results indicated that the complexation of carboxymethyl starch and inorganics strongly depends on the carboxymethyl group in the starch-based hybrid pigmented materials. The formed insoluble hybrids were mostly amorphous and the crystalline contribution of the inorganic component was not evident. The resulting precipitates exhibited composite structures. Finally, three starch-based and two cellulose-based polymers were selected for flocculation and filtration tests. In shearless dewatering conditions, the retention and dewatering properties of the starch-based polymers were similar to those of commercial polyacrylamide-based polymers. The flow studies in higher shear conditions showed that with the studied dosages the starch-based polymers could not reach the flocculation levels needed to maintain sufficient retention properties. The performance of the cellulose-based polymers as flocculating agents was less efficient. The reasons for the more limited performance of the polysaccharide-based flocculants were too low molecular weight and the charge density distribution. Better understanding of how to improve the hydrodynamic properties of bio-based polymers will be essential when planning new bio-based flocculants. The deeper understanding of the relationships between the desired structures and properties of polysaccharides helps to utilize them more effectively. In this way it is possible to obtain better bio-based and environmentally sustainable products in the competition with the current products based on conventional petrochemistry.
  • Aurela, Minna (Helsingin yliopisto, 2016)
    Atmospheric aerosols have a significant effect on people and the environment. They cause adverse health effects especially for cardiorespiratory patients. Atmospheric aerosols also affect the Earth s climate directly by scattering and absorbing solar radiation and indirectly by modifying amounts and properties of clouds. Reliable characterisation and quantification of airborne particles and their sources are essential for developing control strategies for atmospheric pollution and decreasing the uncertainties of estimating particles effects on climate change. Aerosols can be divided into fine and coarse particles based on their size. This thesis concentrated on fine particles, which are either directly emitted into the atmosphere (primary particles) or formed in the atmosphere through gas-to-particle conversion (secondary particles). The main sources of atmospheric fine particles are natural and anthropogenic combustion, industry and secondary aerosol formation (biogenic and anthropogenic). The overall objective of this thesis was to investigate the chemical composition of fine particles with different temporal and seasonal time-scales. For this purpose, a variety of different sampling techniques, off-line analytical methods and on-line instruments were used to characterise the main chemical species of fine particles in simultaneous and independent campaigns at several sites mainly in southern Finland but also in South Africa. More specific objectives were to investigate the dominant sources of particulate organic matter in the Helsinki area and chemically characterise the fine particles originating from biomass burning. Determining the effect of air mass origin on the chemical composition and concentration of fine particles was also one of the specific aims. In this thesis, it was found that the chemical composition of fine particles had strong spatial and temporal variation, although on average the mass concentrations of fine particles were quite similar between different sites. The main components in fine particulate matter in southern Finland was particulate organic matter (POM), followed by sulphate, whereas sulphate had the highest contribution to particulate mass in South Africa. Source apportionment analysis of POM revealed clear primary sources from traffic and from biomass burning. However, the secondary organic aerosol had the largest contribution of POM, even though the campaigns were conducted in specific environments such as residential areas where biomass combustion is commonly used or traffic environments. Occasionally, the contribution of biomass burning organic aerosol increased substantially as ambient air temperature decreased. Additionally, simultaneous measurements pointed out a high contribution of common regional or long-range transported sources over large areas of southern Finland. Similarly, the air mass passing over either clean or polluted areas showed a significant effect on the mass concentrations in Finland and South Africa.
  • Oksanen, Ilona (University of Helsinki, 2000)
  • Virtanen, Tommi (Helsingin yliopisto, 2014)
    The aim of this thesis was to combine several advanced nuclear magnetic resonance (NMR) spectroscopic techniques for studying the cellulose in materials still possessing, at least partly, the original complexity of wood fiber. The NMR spectroscopic approaches can be roughly divided into two classes: First, solid state NMR methods were used to characterize cellulose and its response to various treatments directly. This approach was used to characterize cellulose fibril aggregation in kraft pulps with different physical properties, and to characterize microcrystalline cellulose manufactured from various unconventional sources. Second approach involves utilization of molecular probes, namely solvent components and water, to provide information about interactions between solvent species and cellulose in pulp fibers, and about effect of certain reactivity enhancing pretreatments on cellulose accessibility and fiber wall structures up to micrometer size scale. The solvent molecules were studied during dissolution process using high resolution magic angle spinning (HR-MAS) NMR technique, which is capable of yielding a high resolution NMR spectrum from an inhomogeneous sample. Other approaches to observe the structural changes in pulp involved NMR diffusometry, studies of magnetization cross relaxation between water and cellulose, and quantitation of the amount of nonfreezing water in fiber wall using a proton NMR experiment. When comparing the different approaches, it was observed that the often used quantity, cellulose crystallinity, turned out to be a rather poor indicator for changes taking place in complex cellulose systems, as its value remained mostly inert while the other techniques already revealed changes in specific surface area of the fibers, average pore size at a size scale of ten nanometers, and in accessibility of chemicals through the fiber wall and to the cellulose fibrils. This shows the importance of combination of different type of NMR experiments when studying materials with considerable complexity.
  • Ikäläinen, Suvi (Helsingin yliopisto, 2012)
    Theoretical examination of traditional nuclear magnetic resonance (NMR) parameters as well as novel quantities related to magneto-optic phenomena is carried out in this thesis for a collection of organic molecules. Electronic structure methods are employed, and reliable calculations involving large molecules and computationally demanding properties are made feasible through the use of completeness-optimized basis sets. In addition to introducing the foundations of NMR, a theory for the nuclear spin-induced optical rotation (NSOR) is formulated. In the NSOR, the plane of polarization of linearly polarized light is rotated by spin-polarized nuclei in an NMR sample as predicted by the Faraday effect. It has been hypothesized that this could be an advantageous alternative to traditional NMR detection. The opposite phenomenon, i.e., the laser-induced NMR splitting, is also investigated. Computational methods are discussed, including the method of completeness optimization. Nuclear shielding and spin-spin coupling are evaluated for hydrocarbon systems that simulate graphene nanoflakes, while the laser-induced NMR splitting is studied for hydrocarbons of increasing size in order to find molecules that may potentially interest the experimentalist. The NSOR is calculated for small organic systems with inequivalent nuclei to prove the existence of an optical chemical shift. The existence of the optical shift is verified in a combined experimental and computational study. Finally, relativistic effects on the size of the optical rotation are evaluated for xenon, and they are found to be significant. Completeness-optimized basis sets are used in all cases, and extensive analysis regarding the accuracy of results is made.
  • Vänskä, Tommy (Helsingin yliopisto, 2011)
    This thesis presents ab initio studies of two kinds of physical systems, quantum dots and bosons, using two program packages of which the bosonic one has mainly been developed by the author. The implemented models, \emph{i.e.}, configuration interaction (CI) and coupled cluster (CC) take the correlated motion of the particles into account, and provide a hierarchy of computational schemes, on top of which the exact solution, within the limit of the single-particle basis set, is obtained. The theory underlying the models is presented in some detail, in order to provide insight into the approximations made and the circumstances under which they hold. Some of the computational methods are also highlighted. In the final sections the results are summarized. The CI and CC calculations on multiexciton complexes in self-assembled semiconductor quantum dots are presented and compared, along with radiative and non-radiative transition rates. Full CI calculations on quantum rings and double quantum rings are also presented. In the latter case, experimental and theoretical results from the literature are re-examined and an alternative explanation for the reported photoluminescence spectra is found. The boson program is first applied on a fictitious model system consisting of bosonic electrons in a central Coulomb field for which CI at the singles and doubles level is found to account for almost all of the correlation energy. Finally, the boson program is employed to study Bose-Einstein condensates confined in different anisotropic trap potentials. The effects of the anisotropy on the relative correlation energy is examined, as well as the effect of varying the interaction potential.}
  • Lin, Ying-Chan (Helsingin yliopisto, 2008)
    The chemical and physical properties of bimetallic clusters have attracted considerable attention due to the potential technological applications of mixed-metal systems. It is of fundamental interests to study clusters because they are the link between atomic surface and bulk properties. More information of metal-metal bond in small clusters can be hence released. The studies in my thesis mainly focus on the two different kinds of bimetallic clusters: the clusters consisting of extraordinary shaped all metal four-membered rings and a series of sodium auride clusters. As described in most general organic chemistry books nowadays, a group of compounds are classified as aromatic compounds because of their remarkable stabilities, particular geometrical and energetic properties and so on. The notation of aromaticity is essentially qualitative. More recently, the connection has been made between aromaticity and energetic and magnetic properties. Also, the discussions of the aromatic nature of molecular rings are no longer limited to organic compounds obeying the Hückel’s rule. In our research, we mainly applied the GIMIC method to several bimetallic clusters at the CCSD level, and compared the results with those obtained by using chemical shift based methods. The magnetically induced ring currents can be generated easily by employing GIMIC method, and the nature of aromaticity for each system can be therefore clarified. We performed intensive quantum chemical calculations to explore the characters of the anionic sodium auride clusters and the corresponding neutral clusters since it has been fascinating in investigating molecules with gold atom involved due to its distinctive physical and chemical properties. As small gold clusters, the sodium auride clusters seem to form planar structures. With the addition of a negative charge, the gold atom in anionic clusters prefers to carry the charge and orients itself away from other gold atoms. As a result, the energetically lowest isomer for an anionic cluster is distinguished from the one for the corresponding neutral cluster. Mostly importantly, we presented a comprehensive strategy of ab initio applications to computationally implement the experimental photoelectron spectra.
  • Zaleski-Ejgierd, Patryk (Helsingin yliopisto, 2009)
    There is intense activity in the area of theoretical chemistry of gold. It is now possible to predict new molecular species, and more recently, solids by combining relativistic methodology with isoelectronic thinking. In this thesis we predict a series of solid sheet-type crystals for Group-11 cyanides, MCN (M=Cu, Ag, Au), and Group-2 and 12 carbides MC2 (M=Be-Ba, Zn-Hg). The idea of sheets is then extended to nanostrips which can be bent to nanorings. The bending energies and deformation frequencies can be systematized by treating these molecules as an elastic bodies. In these species Au atoms act as an 'intermolecular glue'. Further suggested molecular species are the new uncongested aurocarbons, and the neutral Au_nHg_m clusters. Many of the suggested species are expected to be stabilized by aurophilic interactions. We also estimate the MP2 basis-set limit of the aurophilicity for the model compounds [ClAuPH_3]_2 and [P(AuPH_3)_4]^+. Beside investigating the size of the basis-set applied, our research confirms that the 19-VE TZVP+2f level, used a decade ago, already produced 74 % of the present aurophilic attraction energy for the [ClAuPH_3]_2 dimer. Likewise we verify the preferred C4v structure for the [P(AuPH_3)_4]^+ cation at the MP2 level. We also perform the first calculation on model aurophilic systems using the SCS-MP2 method and compare the results to high-accuracy CCSD(T) ones. The recently obtained high-resolution microwave spectra on MCN molecules (M=Cu, Ag, Au) provide an excellent testing ground for quantum chemistry. MP2 or CCSD(T) calculations, correlating all 19 valence electrons of Au and including BSSE and SO corrections, are able to give bond lengths to 0.6 pm, or better. Our calculated vibrational frequencies are expected to be better than the currently available experimental estimates. Qualitative evidence for multiple Au-C bonding in triatomic AuCN is also found.
  • Ahmad, Jahir Uddin (Helsingin yliopisto, 2012)
    The oxidation of alcohols to the corresponding carbonyl compounds is a key reaction in the synthesis of organic chemicals. Consequently, a vast number of diverse methods based on copper that accomplish this functional group transformation are reviewed in this work. A successful development from pressurized oxygen to open air and from organic to environmentally friendly water solvent in oxidation of alcohols to the corresponding carbonyl compounds catalyzed by copper is presented. The first direct organocatalytic oxidation of alcohols to aldehydes with O2 in alkaline water was developed. One of the effects metal ions on the reaction was that the Cu ion is the most beneficial recipient of quantitative oxidation. Thus aerobic oxidation of alcohols to the corresponding carbonyl compounds catalyzed by TEMPO/Cu 2 N arylpyrrolecarbaldimine in alkaline water was discovered. The solid and solution structures of sterically hindered salicylaldimine and cis trans isomers of the corresponding Cu(II) complexes are discussed. High yield synthetic routes for mixed ligand Cu(II) complexes derived from salicylaldehyde and the corresponding salicylaldimine were developed. New crystal structures of the above compounds were determined by X ray crystallography. The catalytic property of homo and heteroligated bis(phenoxidoyimino)Cu(II)complexes toward oxidation reactions were investigated. Accordingly, facile base free aerobic oxidations of alcohols to aldehydes and ketones in toluene using low loading of both TEMPO and catalysts under mild conditions were introduced. In addition to the aerobic catalytic methods, oxidation of alcohols to the corresponding carbonyl compounds with H2O2 as an end oxidant in pure water using simple CuSO4 as a catalyst is presented. The effect of various additives, such as acids or bases, radical scavengers and N containing ligands, on the efficiency/selectivity of the catalyst system was studied as well. Finally, highly efficient open air oxidation of alcohols in water catalyzed by in situ made Cu(II) phenoxyimine complexes without additional auxiliarities such as base or co solvent are described.
  • Berg, Mika (Helsingin yliopisto, 2021)
    The metabolic disorder type 2 diabetes characterized by insulin resistance and a reduced production of insulin is one of the fastest growing health and economic menaces for the society. Although, the increasing number of individuals suffering from type 2 diabetes and insulin resistance may have different diabetic characteristics and therefore a risk of severe diabetic complications such as diabetic kidney disease, most individuals still undergo the same forms of treatment and medication. Usually, the first line therapy option is the drug metformin. However, the use of metformin is contraindicated in many cases especially when kidney function declines. Apart from metformin the only insulin sensitizer available on the market is pioglitazone but its risks involving cardiovascular effects are highly debated. More recently, several alternative drugs with different drug targets have been introduced. However, they may possess poor efficiency or safety or are expensive. Consequently, new alternative and more individualized forms of treatment are desperately needed. The SH2-domain containing inositol 5´-phosphatase 2 (SHIP2) is a little studied target for the treatment of type 2 diabetes and insulin resistance. The study presented in this thesis mainly focuses on the design and synthesis of novel blood glucose lowering agents that potentially act as SHIP2 inhibitors and insulin sensitizers. In an in silico screening a group of compounds that bind to SHIP2 were found and were biologically validated in vitro by showing their inhibition of SHIP2. Interestingly, one of the compounds was the most widely used anti-diabetic drug metformin. Additionally, completely novel compounds that significantly inhibited SHIP2 were found. Based on these findings two sets of sulfonanilides were designed and synthesized and their biological efficacy was validated by a functionalized glucose uptake assay. Our best candidates were non-toxic and increased the glucose uptake into cells at lower concentrations than metformin. This indicates that our sulfonanilides can lower the blood glucose levels. We also provide insights into the protein-ligand interactions that may have some impact for future SHIP2 drug design. Large molecular libraries around the most promising candidate from the screening were designed and synthesized. In these sets of 181 molecules many compounds significantly increased the glucose uptake into cells. The druglike properties and in vitro efficacy of the top six compounds were investigated more closely. All compounds were non-toxic and soluble at the effective concentrations. However, some additional modifications and improvements are needed to optimize the metabolic stability of these compounds. Our aim in the future is also to show that these compounds protect podocytes from apoptosis which is an important factor considering the severe diabetic complication, diabetic kidney disease. In view of a huge unmet medical need, we aim to patent the specific new chemical entities after optimization of the metabolic stability properties. Our findings confirm that SHIP2 is an interesting alternative target that may be used for designing novel treatments for type 2 diabetes and insulin resistance. In addition, we have also shown the potential of our compounds for increasing the glucose uptake into cells thus lowering the blood glucose levels.