Browsing by Subject "Physical Chemistry"

Sort by: Order: Results:

Now showing items 1-18 of 18
  • Isokoski, Karoliina (Helsingfors universitet, 2008)
    Rare-gas chemistry is of growing interest, and the recent advances include the 'insertion' of a Xe atom into OH and water in the rare-gas hydrides HXeO and HXeOH. The insertion of Xe atoms into the H-C bonds of hydrocarbons was also demonstrated for HXeCC, HXeCCH and HXeCCXeH, the last of which was the first rare-gas hydride containing two rare-gas atoms. We describe the preparation and characterization of a new rare-gas compound, HXeOXeH. HXeOXeH was prepared in solid xenon by photolysis of a suitable precursor, for example water, and subsequent mobilization of the photoproducts. The experimental identification was carried out by FTIR spectroscopy, isotopic substitution and by use of various precursors. The photolytical and thermal stability of the new rare-gas hydride was also studied. The experimental work was supported by extensive quantum chemical calculations provided by our co-workers. HXeOXeH forms in a cryogenic xenon matrix from neutral O and H atoms in a two-step diffusion-controlled process involving HXeO as an intermediate [reactions (1) and (2)]. This formation mechanism is unique in that a rare-gas hydride is formed from another rare-gas hydride. H + Xe + O → HXeO (1) HXeO + Xe + H → HXeOXeH (2) Similarly to other rare-gas hydrides, HXeOXeH has a strongly IR-active H-Xe stretching vibration, allowing its spectral detection at 1379.3 cm-1. HXeOXeH is a very high-energy metastable species, yet thermally more stable than many other rare-gas hydrides. The calculated bending barrier of 0.57 eV, is not enough to explain the observed stability, and HXeOXeH might be affected by additional stabilization from the solid xenon environment. Chemical bonding between xenon and environmentally abundant species like water is of particular importance due to the 'missing-xenon' problem. The relatively high thermal stability of HXeOXeH compared to other oxygen containing rare-gas compounds is relevant in this respect. Our work also raises the possibility of polymeric (–Xe–O)n networks, similarly to the computationally studied (XeCC)n polymers.
  • Arppe, Suula (Helsingfors universitet, 2012)
    Radikaalireaktiot ovat tärkeitä niin ilmakehän kuin palamisen reaktioissa. Palamisessa voi muodostua kloorimolekyylejä, minkä seurauksena polttoaineita ei voida käyttää tehokkaasti. Typpidioksidi on puolestaan olennainen osa luonnollista ilmakehää, mutta lisäksi fossiilisista polttoaineista vapautuu huomattavasti typen oksideja. Radikaalireaktioita on tässä työssä mitattu laserfotolyysi-valoionisaatiomassaspektrometrialla. Tällä herkällä menetelmällä voidaan tutkia yhtä reaktiota kerrallaan, joten suuri osa tuotteista voidaan havaita. Tuotteiden avulla voidaan saada suoraan tietoa reaktiomekanismeista. Radikaalien reaktiivisuutta voidaan selittää myös rajaorbitaaliteorian avulla: radikaalireaktioiden nopeusvakioiden ja rajaorbitaalien välinen riippuvuus antaa tietoa radikaalien reaktiivisuudesta. Tässä tutkimuksessa olemme selvittäneet kolmen kaasutilaisen alkyyliradikaalin i-C3H7, sek-C4H9 ja tert-C4H9 reaktiivisuutta Cl2:n kanssa. Tutkituilla reaktioilla on negatiivinen lämpötilariippuvuus. Mitatut reaktionopeusvakiot ovat k(i-C3H7) = (3,55 ± 0,16) · 10−11 · (T / 300 K)−2,11±0,12 cm3 molekyyli−1 s−1, k(t-C4H9) = (4,27 ± 0,39) · 10−11 · (T / 300 K)−2,70±0,25 cm3 molekyyli−1 s−1 ja k(s-C4H9) = (4,90 ± 0,45) · 10−11 · (T / 300 K)−2,01±0,27 cm3 molekyyli−1 s−1. Tulosten mukaan kloorattujen alkyyliradikaalien reagoidessa Cl2:n ja NO2:n kanssa radikaalien klooripitoisuus vaikuttaa reaktionopeuteen enemmän kuin rajaorbitaalit. Metyylillä ja metyylipohjaisilla klooratuilla radikaaleilla (CH2Cl, CHCl2 ja CCl3) on todennäköisesti eri reaktiomekanismi Cl2-reaktioissa kuin NO2-reaktioissa.
  • Partanen, Lauri (Helsingfors universitet, 2017)
    Sulfuric acid and its gaseous hydrates play a central role in the nucleation processes of the atmosphere. In this study, the thermodynamic properties for the formation of the sulfuric acid monohydrate complex were determined from the results of accurate ab initio calculations by using statistical mechanics. Of the ab initio calculations, geometry optimizations and energy calculations were performed with the explicitly correlated CCSD(T)-F12a/VDZ-F12 method, which was shown to give results comparable to CCSD(T)/aug-cc-pVQZ level calculations. Four different stable geometries were found, and the energies of the two lowest were within 0.41 kJ mol −1 of each other. Harmonic frequencies were calculated both at the DF-SCS-LMP2/aug-cc-pVTZ level and the CCSD-F12/VDZ-F12 level. Because the harmonic approximation works badly for the high frequency OH stretches and the low frequency intermolecular large amplitude motions, some of the vibrational degrees of freedom were treated by limiting the dimensionality of the potential energy surface to small, two- or three-dimensional subspaces that contained a few strongly coupled vibrational degrees of freedom. In these anharmonic domains, the vibrational problem was solved variationally from a potential energy surface calculated at the CCSD(T)-F12a/VDZ-F12 level. Even though the subspaces are completely decoupled from the rest of the vibrational degrees of freedom, my results indicate that with a careful choice of the domains, the resulting vibrational states are accurate enough for the calculation of thermodynamic properties. It is shown that with the anharmonic domain approximation it becomes possible to incorporate quantum mechanically the presence of at least some of the other minimum energy structures into the thermodynamic properties, and that the inclusion of these is essential if accurate results are desired. Furthermore, the anharmonic domain approximation makes it relatively easy to calculate vibrational overtones which, especially for the large amplitude motions, have a major impact on the vibrational partition function. With the inclusion of the anharmonic domains, very uniform results were obtained for the thermodynamic properties with the two different methods used in the harmonic calculation. At one atmosphere and 298 K, the Gibbs free energy was found to have a value of about -8.0 kJ mol −1. The anharmonic domains used in this study had the effect of raising the zero point energy by around 1.7 kJ mol −1. Comparison with the earlier results reveals that one of the most important reasons for the differences in the Gibbs energy is the inaccurate calculation of the electronic energies of the different reaction components. Thus, we recommend that all future studies employ a higher level method for these calculations. Finally, investigations were carried out on the temperature dependence of the equilibrium constant and on the pressure and temperature dependencies of the Gibbs free energy and entropy. To this effect, the statistical thermodynamic formulae that included the anharmonic domain approximation in calculations of the thermodynamic properties were derived. The temperature dependence of both enthalpies and entropies was predicted to be rather small and, therefore, the Gibbs free energy varied almost linearly with temperature.
  • Korpinen, Markus (Helsingfors universitet, 2014)
    Intermolecular long-range interactions play an important role in several areas of modern research. In this thesis, van der Waals coefficients for different small coinage metal systems such as H2-H2, H2-Cu2, H2-Ag2, and H2-Au2 are determined from the results of accurate ab initio calculations. A four dimensional potential energy surface is computed with the coupled cluster method with a single, double and perturbative triple excitations (CCSD(T)) using a large augmented Dunning basis set. In the case of externally neutral molecules, the dominating long-range interactions are often van der Waals dispersion interactions. Many long-range pair potential models are using a pre-defined experimental or computational van der Waals C6 coefficients. To obtain the coefficients, the potential energy surface is modelled with spherical harmonic approximation together with bipolar spherical harmonics. It was noticed that the anisotropies of the potential energy surface can be described with terms which have similar angular dependencies as the electrostatic multipole-multipole interactions and the van der Waals interactions. These include, for example, quadrupole-quadrupole and quadrupole-hexadecapole interaction. Using the computed potential energy surfaces and least-squares fitting different long-range interaction models, C6 and C8 dispersion coefficients, and quadrupole and hexadecapole moments are obtained for hydrogen, copper, silver and gold dimers.
  • Rauhalahti, Markus (Helsingin yliopisto, 2018)
    The development of new energy sources for the replacement of fossil fuels is an important task in chemistry. Artificial photosynthesis is a viable option for the generation of fuels. In it, water molecules are oxidized and the resulting protons are reduced to hydrogen, or further combined with carbon dioxide to form carbon fuels. The processes are powered by solar energy. Water oxidation is the bottleneck in the process, as the reaction requires the breaking of four O-H bonds, formation of a O-O bond, and the dissociation of the formed oxygen molecule. Research in past decades has resulted in transition metal complexes, mostly with ruthenium and iridium metal centers, which catalyze oxidation of water with moderate turnover frequencies and numbers. In order for the artificial photosynthesis to be a viable source of energy, catalysts using cheaper and more abundant first row transition metals and having better performance are needed. The the theory section the relevant inorganic and quantum chemistry and the used computational methods are presented. In the literature section, biological photosynthesis and the modular artificial photosynthetic system are presented and the most important water oxidation catalysts are highlighted. In the research section, an efficient water oxidation catalyst by the group of Sun is studied computationally. The coordination geometries and spin-state energetics of the catalyst were studied using Ru, Fe, and Os metal centers at different stages of the catalytic cycle. The Fe catalyst was a high-spin complex with weakened metal-ligand bonding due to the occupation of antibonding metal-ligand orbitals. The modification of the ligand framework with substituents was also studied. Substitution did not have a major effect in charge distributions or coordination geometries, implying that the differences in reactivities observed experimentally are due to environmental effects.
  • Dimitrova, Maria (Helsingfors universitet, 2016)
    Ionic liquids are chemical compounds with low symmetry, which is manifested by the existence of the liquid phase below room temperature. A common class of ionic liquids is based on the imidazolium cation and an inorganic anion. The specific structure gives rise to some peculiar properties, including low vapour pressure, thermal and chemical stability, electrical conductivity, catalytic activity, and good solvation ability for both polar and non-polar compounds. The complex non-covalent interactions between the ions give rise to an internal structure with specific distribution of the polar and non-polar moieties. Of particular interest is the cage-like structure suggested by 129Xe NMR spectroscopy, and confirmed by molecular dynamics simulations, as small molecules or noble gas atoms can be embedded in these cavities. Computational studies on ionic liquids can be performed at different levels of theory using a multiscale approach. Molecular dynamics can give the distribution of ion pairs in the bulk structure. Density functional theory allows evaluations of the intermolecular interactions in small clusters. High-level ab initio methods are suitable for calculating thermodynamic properties and interaction energies. In this work, the ionic liquid 1-butyl-3-methylimidazolium chloride and its interactions with xenon have been investigated using density functional theory calculations. Studies on an isolated pair provided geometrical parameters, and revealed a favourable interaction with a xenon atom. The calculation on a system consisting of four ion pairs showed that the properties of ionic liquids have to be investigated on larger systems in order to avoid artificial interactions. A cluster consisting of 32 ion pairs was optimized at the PBEh-3c/def2-mSVP level of theory. The interaction energy with xenon was found to be 5.4 kcal/mol, which confirms the experimentally observed ability of imidazolium-based ionic liquids to dissolve the noble gas.
  • Rajala, Taneli (Helsingfors universitet, 2014)
    Enhancement of polymer electrolyte fuel cell tolerance to CO impurities would allow the use of lower quality hydrogen, thus reducing the costs without compromising fuel cell performance. In this work, the effect of carbon monoxide is mitigated by combining different methods, including air bleed, varying the anode flow rate and using a state-of-the-art Pt-Ru catalyst at two operating temperatures. The tolerance was investigated by feeding a novel arrangement of segmented cells with hydrogen containing carbon monoxide less than 20 ppm. Anode exhaust gas was constantly analysed using a gas chromatograph. It was discovered that increasing the volumetric flow rate of hydrogen and especially utilising ruthenium in the catalyst enhance the carbon monoxide tolerance. When applying the air bleed, an oxygen/CO molar ratio of at least 117 was required to stop the poisoning with a platinum catalyst. Approximately a fifth of the air bleed needed with platinum was enough with Pt-Ru. The results also suggest that when applying air bleed at elevated temperatures, it is beneficial to lower the cell temperature for the duration of the air bleed.
  • Karhu, Juho (Helsingfors universitet, 2014)
    Optical parametric oscillators (OPO) are sources of coherent light, often used to produce laser like light in wavelength regions where ordinary laser operation is challenging. In terms of chemistry, most attractive such a region is in mid-infrared, where strong fundamental vibrational transitions occur. OPOs are based on nonlinear polarization, which some materials exhibit when radiated with strong coherent light and effectively allow transferring optical power from one wavelength region to another. Even a simple OPO setup can offer watt-level of continuous-wave power in mid-infrared. There are ongoing challenges with the stability of OPO output frequency and continuous tuning of the wavelength, both of which are important for a light source used in high-resolution molecular spectroscopy. Theory and literature part of this thesis first covers the fundamentals of the theory behind OPO, centering on a continuous-wave single resonant operation. Afterwards, we look into the more well-known features affecting the stability of the OPO, as well as some common schemes used to combat the instabilities. In the experimental part, we measure and attempt to characterize some features of instabilities we have previously noticed that are not readily explained by known instability sources. The OPO's output wavelength occasionally changes in discrete jumps known as mode hops. There appear to be some preferences to the magnitude of these jumps that do not seem to fit in the current understanding of OPO operation. We followed the frequency changes of a typical singly resonant continuous-wave OPO for longer time periods and offered some possible explanations for the observations. We utilize a few methods to increase the number of mode hops to produce meaningful statistical data.
  • Toivanen, Elias Akseli (Helsingfors universitet, 2014)
    Two-electron integrals, which arise in the quantum mechanical description of electron-electron repulsion, are needed in electronic structure calculations. In this thesis, a fully numerical scheme for computing them has been developed and implemented. The accuracy and performance of the scheme is also demonstrated with proof-of-concept calculations. The work in this thesis is a part of the ongoing efforts aiming at a fully numerical electronic structure code for massively parallel computer architectures. The power of these emerging computational resources can be seized only if all computational tasks are divided to small and independent parts that are then processed concurrently. Such a divide and conquer approach is indeed the main characteristic of the present integration scheme. The scheme is a variant of the Fast Multipole Method (FMM) that is an algorithm originally designed for rapid evaluation of electrostatic and gravitational potential fields in point particle simulations. Since the two-electron integrals can be formulated as a problem in electrostatics involving electrostatic potentials and continuous charge densities, the FMM algorithm is also applicable for tackling them. The basic idea in the present scheme is to decompose the computational domain to sub-domains in which the electron densities and electrostatic potentials are further decomposed to finite element functions. The two-electron integrals are then computed as a sum of contributions from each sub-domain. As the current scheme performs all integrals on real-space grids, it has been titled as the Grid-based Fast Multipole Method (GB-FMM). Its computational cost scales linearly with respect to the number of sub-domains. The thesis consists of two parts – a literature review discussing the key features of electronic structure calculations at the Hartree-Fock level of theory and a documentation of the GB-FMM. The results of the proof-of-concept calculations are encouraging. The GB-FMM scheme can achieve parts per billion accuracy. In addition, an analysis of its performance in a single-core environment indicates that the computational cost of the GB-FMM scheme has a rather big prefactor but a favorable scaling with respect to system size. However, as the GB-FMM algorithm has been designed with parallel execution in mind, its full power is predicted to become evident only when massively parallel computers will become commonplace.
  • Pekkanen, Timo Theodor (Helsingfors universitet, 2016)
    The oxygen reactions of hydrocarbon radicals are important both in combustion and atmospheric chemistry. In this thesis I have studied the oxygen reactions of propagyl-type radicals (propargyl, 1-methylpropargyl, 3-methylpropargyl and 3-ethylpropargyl). Propargyl radical (2-propyn-1-yl) is an alkyl radical with the structure H3C≡C–CH2● . Because these radicals are resonance stabilised, their oxygen reactions are relatively slow. This means that in a combustion environment they might reach an high enough concentration for their self-reactions to become important. The self-reactions of unsaturated radicals are the first step in the formation of polyaromatic hydrocarbons. I measured the rate coefficients and equilibrium constants for the oxygen reactions of 3-methylpropargly and 3-ethylpropargly at low pressures (0.2 – 3 Torr) using a tubular flow reactor coupled to a resonance-gas-discharge-lamp photoionisation mass spectrometer (PIMS). Laser photolysis was used to generate the radicals. I have compared my experimental results to previous studies done for the propargyl + O2 and 1-methylpropargyl + O2 reactions. I reanalysed the equilibrium data from these previous studies with an improved kinetic mechanism. At temperatures below 500 K the reactions were found to be dependent on bath gas pressure and they also had negative temperature dependence. The reactivity order was found to be 3-ethylpropargyl > 3-methylpropargyl ≈ 1-methylpropargyl > propargyl. Standard reaction enthalpies and entropies are reported for all four reactions. The experimental results were combined with quantum chemical computations.
  • Arppe, Teemu (Helsingfors universitet, 2012)
    Jalokaasu ksenonin yhdisteitä tunnetaan satamäärin, mutta vieläkään ei tiedetä tarkasti, kuinka ksenon sitoutuu maankuoressa tai ihmisessä. Uusien ksenonyhdisteiden valmistaminen voi siten hyödyttää kemian ohella esimerkiksi geologian tai lääketieteen tutkimusta. Tässä tutkielmassa kuvaan, miten valmistimme matriisi-isolaation avulla halogenoidut ksenonsyanidimolekyylit ClXeCN, ClXeNC ja BrXeCN. Molekyylit muodostuivat, kun ksenonmatriisiin, jossa oli kloorisyaania (ClCN) tai bromisyaania (BrCN), kohdistettiin ultraviolettisäteilyä. Molekyylien määrä kasvoi matriisia lämmittämällä. Tulosten vahvistamiseksi kokeita toistettiin hiili-13-isotooppia sisältäneellä kloorisyaanilla. Tutkittavien molekyylien valinta ja infrapunaspektroskopialla tehty tunnistaminen tukeutuivat kvanttikemiallisiin tiheysfunktionaalilaskuihin. Tutkimuksen tulokset vahvistavat tietojamme siitä, milloin laskennallisesti vakaa jalokaasumolekyyli pystytään valmistamaan matriisi-isolaatiolla ja miten laskennallisten värähtelytaajuuksien avulla voidaan tulkita matriisissa mitattuja spektrejä. Tutkimuksen pohjalta voidaan hahmotella muutamia ehdokkaita seuraaviksi jalokaasusyanideiksi.
  • Myllys, Nanna (Helsingfors universitet, 2015)
    Ilmakehässä tapahtuva hiukkasmuodostus on tärkeä tutkimuskohde, sillä muodostuvat sekundäärihiukkaset vaikuttavat ihmisten terveyteen ja maapallon säteilytasapainoon. Hiukkasmuodostuksen ensiaskeleista ei ole toistaiseksi tarkkaa tietoa, mutta laskennallisten ja kokeellisten tutkimusten avulla on selvitetty, että rikkihappo on keskeisessä roolissa uusien hiukkasten muodostumisessa. Se ei kuitenkaan yksin tai edes veden kanssa riitä selittämään kaikkia havaittuja muodostumistapahtumia. Ilmakehässä on useita erilaisia tiivistymiskykyisiä molekyylejä, joista tässä tutkielmassa keskityttiin ammoniakkiin ja dimetyyliamiiniin. Tutkimuksessa laskettiin kvanttikemiallisin menetelmin erilaisten rikkihappoa ja emästä sisältävien klustereiden Gibbsin vapaat muodostumisenergiat, joiden avulla muodostettiin klustereiden kokojakaumat ilmakehän klusteridynamiikkakoodilla (ACDC). Saatuja kokojakaumia verrattiin alemmalla kvanttikemiallisella menetelmällä laskettuihin tuloksiin ja havaittiin, että ACDC on herkkä käytetylle laskennalliselle tasolle. Tutkielmassa on esitelty myös kattavasti erilaiset likimääräismenetelmät Schrödingerin yhtälön ratkaisuun ja pohdittu, kuinka tutkittavalle ongelmalle valitaan sopiva menetelmän ja kantajoukon yhdistelmä. Tutkielman on tarkoitus tukea samankaltaisten laskennallisten systeemien ratkaisemista.
  • Cáceres-Jensen, Lizethly; Rodríguez-Becerra, Jorge; Jorquera-Moreno, Bárbara; Escudey, Mauricio; Druker-Ibañez, Sofía; Hernández-Ramos, José; Díaz-Arce, Tatiana; Pernaa, Johannes; Aksela, Maija (2021)
    Teaching the fundamentals of chemical kinetics on the college level is challenging to teachers and students alike due to its abstract nature of concepts and limited connection with real context applications. This study consisted of two phases starting with designing a chemistry education for the sustainable development-based learning environment of reaction kinetics, followed by a case study in which students' perceptions toward learning chemistry by solving a real environmental problem using digital resources, spreadsheets, and an active learning environment, were explored. First, we designed a Socio-Scientific Environmental Chemistry module centered on the sorption kinetic processes of herbicides in volcanic ash derived soils (VADS) and their potential to pollute groundwater. The objective of the learning module was to contribute to the development of sustainability skills, to promote learning of contextualized chemistry knowledge, and to develop scientific skills. This module employs spreadsheets as computational tools in chemistry to model real sorption kinetic data of herbicides in VADS. The learning module was designed for one section of two Analytical Chemistry courses and one Physical Chemistry course of an undergraduate chemistry teacher-training program. After the design phase, the learning module was implemented in each course, and students' perceptions were gathered using the focus group technique. The sample was of 22 students distributed into three focus groups. The data collected were analyzed and categorized through qualitative content analysis using the Technological Pedagogical Science Knowledge (TPASK) framework. On the basis of our findings, the students acquired contextualized chemistry knowledge and develop skills and knowledge related to using digital resources and spreadsheets in a scientific context. Besides, the preservice chemistry teachers' knowledge of pedagogy allowed them to develop some elements of their pedagogical science knowledge and TPASK. This case study shows that the problem-based learning approach offers great potential in supporting a learning environment suitable to working with spreadsheets to solve real-environment problems in chemistry education.
  • Roslund, Kajsa (Helsingfors universitet, 2017)
    This thesis aims to introduce and describe the importance of small molecule volatiles as biomarkers, and both their present and future roles in disease diagnostics and basic research. A few examples of these molecules are introduced in more detail, including the medical conditions they are related to, as well as the advantages and challenges concerning their analysis. The biomarkers discussed in this thesis are hydrogen cyanide (HCN), ammonia (NH3), nitric oxide (NO), hydrogen sulfide (H2S), acetone (C3H6O) and methane (CH4). The volatility of these molecules makes them suitable for breath analysis, which is described thoroughly in this thesis. The diagnostic potential of breath analysis, as well as its comparability to traditional analysis techniques, such as blood and urine analysis, are also discussed. Measurement of small-molecule volatiles from the headspace of bacterial cultures is also introduced and described in detail, and its importance considering the understanding of bacterial activity and metabolism discussed further. Volatile biomarkers in human breath and produced by bacteria are thus the main themes of this work. This thesis also describes a laser based, cavity-enhanced absorption technique that can be used to measure volatile, small-molecule biomarkers, such as those mentioned above. The measurement technique in question is cavity ring-down spectroscopy (CRDS), and its main features, as well as its advantages and limitations are discussed in detail, with special emphasis on features advantageous in breath analysis and bacterial headspace measurements. Sampling of the bacterial headspace and breath gas are introduced thoroughly. Special emphasis is given to the custom-built sampling line constructed in our laboratory, and it is used as a descriptive example when discussing the handling of gaseous samples. The measurement setups developed in our laboratory for the headspace measurements of both aerobic and anaerobic bacteria are also introduced in more detail. The experimental part of this thesis describes the bacterial headspace measurements done with the custom built CRDS instrument and sampling setup constructed in our laboratory. The aim of this experimental demonstration was to investigate, whether some oral bacteria are able to produce detectable amounts of HCN in vitro, identify these bacteria, and monitor their HCN production as thoroughly as possible. Oral bacteria capable of producing HCN could possibly affect the concentrations measured from human exhaled breath, and this should be taken into account in the HCN breath analysis. In the future, HCN could also be considered a possible biomarker for oral pathogenic bacteria responsible for periodontal diseases, if these bacteria are able to produce HCN in detectable amounts. Another aim of this experimental demonstration was to prove that our suggested measurement setup is suitable for both anaerobic and aerobic bacterial headspace measurement, and that it offers reliable, consistent and reproducible results. We were able to prove that certain oral anaerobes from Porphyromonas, Prevotella and Fusobacterium genera can produce detectable levels of HCN in vitro, which is a novel finding. We also observed a strong correlation between the HCN and carbon dioxide (CO2) productions of Porphyromonas gingivalis, which indicates a connection between bacterial metabolic activity and HCN production. Measurements done for the positive control produced similar results to those observed in previous studies, which demonstrates that our proposed system can be applied in the screening and evaluation of HCN production by both aerobic and anaerobic bacteria. In addition, results from duplicate and triplicate measurements were consistent with each other, further indicating that our proposed measurement and sampling setup are valid.
  • Zhu, Cheng (Helsingin yliopisto, 2016)
    Noble-gas chemistry was started in 1962 when Neil Bartlett reported the first noble-gas compound, xenon hexafluoroplatinate. This discovery was followed by successful synthesis of many other noble-gas compounds. Matrix-isolation infrared spectroscopy has been an important tool in noble-gas chemistry. In 1995, noble-gas hydrides HNgY (Ng is a noble-gas atom and Y is an electronegative fragment) were characterized by using this method. To date, a substantial number of noble-gas hydrides have been identified including the first neutral ground-state Ar compound, HArF. A few noble-gas compounds of the YNgY’ type (Y and Y’ are electronegative fragments) have also been prepared in matrices. This thesis consists of two parts. In the first part, two new HNgY compounds (HKrCCCl and HXeCCCl) and three new YNgY’ compounds (FKrCN, FXeCN, and FXeNC) are described. These molecules are prepared in noble-gas matrices (Kr and Xe) by ultraviolet photolysis of the precursors and subsequent annealing and characterized by infrared spectroscopy. The assignments are supported by ab initio calculations at the MP2(full) and CCSD(T) levels of theory. The precursors HCCCl and FCN are synthesized using a microwave discharge of HClC=CCl2/Ng and (FCN)3/Ng gaseous mixtures, respectively. The infrared spectrum of CCCl radical is also reported. In the second part, the complexation effect on HXeI and the matrix effect on HXeI and HXeH are studied. Two new complexes (HXeI···HCl and HXeI···HCCH) are prepared in a Xe matrix and assigned based on the ab initio calculations at the MP2(full) and CCSD(T) levels of theory. Similarly to the previously studied systems, the H–Xe stretching mode of HXeI in these complexes show substantial blue shifts. The decomposition of the HXeI complexes (including known HXeI···HBr and HXeI···HI) by broadband IR radiation of the spectrometer slows down as the H–Xe stretching frequency increases. HXeI and HXeH are studied in Ar, Kr, and Xe matrices. The order of the H–Xe stretching frequency of HXeH in these matrices (ν(Xe) < ν(Kr) < ν(Ar)) is the same as that of previously studied HXeCl, HXeBr, and HXeCCH. For HXeI, the frequency order is diffe rent: ν(Xe) < ν(Ar) < ν(Kr), which is a remarkable observation. The experimental results are successfully simulated using the hybrid quantum-classical calculations.
  • Laiho, Satu (Helsingfors universitet, 2017)
    Uloshengityksen on jo kauan tiedetty kertovan hengittäjän terveydestä. Hengityksessä onkin arvioitu olevan tuhansia pelkästään endogeenista alkuperää olevia yhdisteitä, mutta vain muutamia niistä on tutkittu riittävästi, jotta niiden käyttäminen kliinisessä diagnostiikassa on tullut mahdolliseksi. Hengitysanalyysin potentiaali on siis edelleen laajalti hyödyntämättä, vaikka sen edut esimerkiksi verianalyysiin nähden ovat ilmeiset. Uloshengitys on näytematriisina yksinkertainen ja sen kerääminen on nopeaa, kivutonta sekä helppoa, ja näytteet on mahdollista analysoida vain muutamissa minuuteissa. Hengitysanalyysin potentiaali diagnostisena menetelmänä perustuu keuhkorakkuloiden ja verenkieron väliseen ohueen kapillaarikalvoon, jonka läpi monet verenkierron yhdisteet pääsevät haihtumaan suoraan uloshengitykseen. Monilla yhdisteillä hengityksessä esiintyvät pitoisuudet heijastavat siis suoraan veren yhdistepitoisuuksia. Yksi kiinnostusta herättänyt potentiaalinen biomerkkiaine on ammoniakki, joka on yhdistetty muun muassa munuaisten vajaatoimintaan ja veren kohonneisiin ureapitoisuuksiin. Poikkeuksellisen emäsluonteensa takia, hengityksen ammoniakin erittymismekanismin on kuitenkin arveltu poikkeavan muista endogeenisista yhdisteistä, ja yhdisteen on epäilty päätyvän hengitykseen veren sijasta syljestä haihtumalla. Epäselvyys ammoniakin tuottomekanismista onkin pitkään hidastanut yhdisteen analyysinpotentiaalin ymmärtämistä. Hengityksen lisäksi myös sylkianalyysit ovat herättäneet huomioita syljen helpon kerättävyyden ja erityisen koostumuksen ansiosta. Erityisesti syljen ureapitoisuudet on yhdistetty hengityksen ammoniakin tapaan veren ureapitoisuuksiin ja munuaisten toimintaan, minkä takia myös syljen ureaa on pidetty potentiaalisena biomerkkiaine. Tutkielmassa käsitellään hengityksen ammoniakin sekä syljen ammoniakin ja urean muodostumista sekä arvioidaan niiden yhteyttä elimistön ammoniakki- ja ureapitoisuuksiin. Lisäksi tutkielma käsittelee hengityksen ja syljen mittauksessa huomioon otettavia asioita sekä itse mittauksien suoritusta. Tutkielman tutkimusosuutta varten 12:sta dialyysiin osallistuvalta munuaisten vajaatoimintapotilaalta mitattiin hengityksen ja syljen ammoniakkipitoisuutta sekä veren ja syljen ureapitoisuutta hoidon ajan. Tuloksien perusteella pyrittiin arvioimaan hengityksen ammoniakin alkuperää sekä syljen urean ja hengityksen ammoniakin kykyä mitata munuaisten vajaatoimintapotilaiden ureemista tilaa sekä dialyysihoidon tehoa.
  • Skyttä, Mirva (Helsingfors universitet, 2013)
    Tutkielman kirjallisuusosassa tarkastellaan yleisellä tasolla hengitysanalyysin apuna käytettyjä mittalaitteita sekä hengitysnäytteenotossa huomioitavia asioita. Lisäksi käydään lyhyesti läpi erityyppisten kaasujen vaihtoon liittyviä tekijöitä keuhkorakkuloiden ilman ja veren välisellä pinnalla. Myös jo kliiniseen käyttöön vakiintuneita uloshengitysilman testejä tarkastellaan mittalaitteiden näkökulmasta. Tutkielman kokeellisessa osassa mitattiin diabeetikoiden ja terveiden ihmisten uloshengitysilman vetysyanidipitoisuuksia itserakennetulla ontelovaimenemisspektrometrillä. Ontelovaimenemisspektroskopia on ontelovahvisteinen muunnos tavallisesta laserabsorptiospektroskopiasta. Diabetes on puolestaan aineenvaihdunnallinen häiriö, jossa sokeriaineenvaihdunnassa tarvittavan insuliinin toiminta on joko kokonaan lakkautunut tai osittain häiriintynyt. Diabetes voi etenkin hoitamattomana johtaa lukuisiin komplikaatioihin. Diabetes mainitaan esimerkiksi Pseudomonas aeruginosa -bakteerin aiheuttamien infektioiden riskitekijäksi. Joidenkin Pseudomonas aeruginosa -viljelmien yläpuolisesta höyrytilasta on mitattu vetysyanidia, mikä antoi motivaation tälle tutkimukselle. Mittaukset tehtiin yhteistyössä Helsingin yliopiston FinnDiane-projektin kanssa. FinnDiane-projektin tavoitteena on etsiä geneettisiä riskitekijöitä diabeteskomplikaatioille. Osalla tutkimuksen diabeetikoista oli jonkin asteinen munuaisvaurio, johon saattaa liittyä Pseudomonas aeruginosan aiheuttama infektio. Mittauksissa ei vielä havaittu merkittävää eroa diabeetikoiden ja terveiden ihmisten vetysyanidipitoisuuksien välillä. Lopullista johtopäätöstä vetysyanidin soveltuvuudesta Pseudomonas aeruginosa -bakteerin infektoiman diabeetikon tunnistamiseksi ei kuitenkaan voida vielä tehdä, sillä kontrolliryhmässä oli paljon nuorempia henkilöitä kuin diabeetikoiden ryhmässä. Siksi diabeetikoita ja vanhempia kontrollihenkilöitä on vielä mitattava lisää ennen lopullisen johtopäätöksen tekemistä.