Laboratory of Physical Chemistry

Helsinki, Finland

Laboratory of Physical Chemistry

Helsinki, Finland
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Bauer J.,Laboratory of Physical Chemistry | Tomisic V.,Laboratory of Physical Chemistry | Vrkljan P.B.A.,XVIII Gymnasium
Journal of Chemical Education | Year: 2012

A laboratory exercise has recently been reported in which the students use the initial rates method based on the clock reaction approach to deduce the rate law and propose a reaction mechanism for the oxidation of iodide by iron(III) ions. The same approach is used in the exercise proposed herein; the students determine the dependence of the reaction rate on ionic strength and temperature in a straightforward manner. The previously proposed mechanism is further supported by the results, the rate-determining step is identified, and the activation parameters E a, Δ†H, and Δ†S are determined for the overall reaction of the first two steps of the mechanism. The significance of such kinetic studies in elaborating reaction mechanisms is clearly demonstrated to the students. © 2012 American Chemical Society and Division of Chemical Education, Inc.

Pruyne J.G.,Trinity College at Hartford | Lee M.-T.,Paul Scherrer Institute | Lee M.-T.,University of Bern | Fabri C.,Laboratory of Physical Chemistry | And 5 more authors.
Journal of Physical Chemistry C | Year: 2014

The liquid-vapor interface is difficult to access experimentally but is of interest from a theoretical and applied point of view and has particular importance in atmospheric aerosol chemistry. Here we examine the liquid-vapor interface for mixtures of water, sodium chloride, and formic acid, an abundant chemical in the atmosphere. We compare the results of surface tension and X-ray photoelectron spectroscopy (XPS) measurements over a wide range of formic acid concentrations. Surface tension measurements provide a macroscopic characterization of solutions ranging from 0 to 3 M sodium chloride and from 0 to over 0.5 mole fraction formic acid. Sodium chloride was found to be a weak salting out agent for formic acid with surface excess depending only slightly on salt concentration. In situ XPS provides a complementary molecular level description about the liquid-vapor interface. XPS measurements over an experimental probe depth of 51 Å gave the C 1s to O 1s ratio for both total oxygen and oxygen from water. XPS also provides detailed electronic structure information that is inaccessible by surface tension. Density functional theory calculations were performed to understand the observed shift in C 1s binding energies to lower values with increasing formic acid concentration. Part of the experimental -0.2 eV shift can be assigned to the solution composition changing from predominantly monomers of formic acid to a combination of monomers and dimers; however, the lack of an appropriate reference to calibrate the absolute BE scale at high formic acid mole fraction complicates the interpretation. Our data are consistent with surface tension measurements yielding a significantly more surface sensitive measurement than XPS due to the relatively weak propensity of formic acid for the interface. A simple model allowed us to replicate the XPS results under the assumption that the surface excess was contained in the top four angstroms of solution. © 2014 American Chemical Society.

Ulvila V.,Laboratory of Physical Chemistry | Phillips C.R.,ETH Zurich | Halonen L.,Laboratory of Physical Chemistry | Vainio M.,Laboratory of Physical Chemistry | Vainio M.,Center for Metrology and Accreditation
Optics Express | Year: 2014

We demonstrate that it is possible to obtain a mid-infrared optical frequency comb (OFC) experimentally by using a continuous-wavepumped optical parametric oscillator (OPO). The comb is generated without any active modulation. It is based on cascading quadratic nonlinearities that arise from intra-cavity phase mismatched second harmonic generation of the signal wave that resonates in the OPO. The generated OFC is transferred from the signal wavelength (near-infrared) to the idler wavelength (mid-infrared) by intracavity difference frequency generation between the OPO pump wave and the signal comb. We have produced a mid-infrared frequency comb which is tunable from 3.0 to 3.4 μm with an average output power of up to 3.1 W. © 2014 Optical Society of America.

Nainggolan H.,Laboratory of Physical Chemistry | Nainggolan H.,University of Indonesia | Gea S.,Laboratory of Physical Chemistry | Gea S.,University of Indonesia | And 3 more authors.
Beilstein Journal of Nanotechnology | Year: 2013

The effects of the addition of fibres of bacterial cellulose (FBC) to commercial starch of Mater-Bi® have been investigated. FBC produced by cultivating Acetobacter xylinum for 21 days in glucose-based medium were purified by sodium hydroxide 2.5 wt % and sodium hypochlorite 2.5 wt % overnight, consecutively. To obtain water-free BC nanofibres, the pellicles were freeze dried at a pressure of 130 mbar at a cooling rate of 10 °C min-1. Both Mater-Bi and FBC were blended by using a mini twin-screw extruder at 160 °C for 10 min at a rotor speed of 50 rpm. Tensile tests were performed according to ASTM D638 to measure the Young's modulus, tensile strength and elongation at break. A field emission scanning electron microscope was used to observe the morphology at an accelerating voltage of 10 kV. The crystallinity (Tc) and melting temperature (Tm) were measured by DSC. Results showed a significant improvement in mechanical and thermal properties in accordance with the addition of FBC into Mater-Bi. FBC is easily incorporated in Mater-Bi matrix and produces homogeneous Mater-Bi/FBC composite. The crystallinity of the Mater-Bi/FBC composites decrease in relation to the increase in the volume fraction of FBC. © 2013 Nainggolan et al.

Dezhampanah H.,Laboratory of Physical Chemistry | Bordbar A.K.,University of Isfahan | Salimian Z.,University of Isfahan | Safaei E.,Institute for Advanced Studies in Basic Sciences
Journal of Porphyrins and Phthalocyanines | Year: 2010

The association behavior of tetrakis(N, N', N", N'"-tetramethyl tetra-2,3-pyridino)-porphyrazine copper(II) ([Cu(II) 2,3-tmtppa] 4+) was investigated in aqueous solutions at 25 °C and various ionic strengths using optical absorption and resonance light scattering (RLS) spectroscopies. The results show that [Cu(II) 2,3-tmtppa] 4+ does not have any affinity for aggregation due to increasing of salt concentration and exists as monomers even in homogeneous aqueous solutions of high ionic strengths (more than 1 M NaCl). Interaction of [Cu(II) 2,3-tmtppa] 4+ with calf thymus DNA has also been studied in 1 mM aqueous phosphate buffer of pH 7.0, by optical absorption and RLS spectroscopies, and thermal denaturation experiments. The appearance of hypochromicity of less than 10% and bathochromicity shift of δγ ≤ 2 nm in UV-vis spectra of [Cu(II) 2,3-tmtppa] 4+, increasing of thermal melting point of DNA, and no change in RLS spectra of porphyrazine due to interaction with DNA, represent the minor outside groove binding mode without any stack aggregate formation. The thermodynamic of the binding of [Cu(II) 2,3-tmtppa] 4+-DNA also has been studied. The binding constant (K) was obtained by analysis of the optical absorption spectra of the complex at various DNA concentrations using SQUAD software. The value of K was estimated to be 2.34 × 10 5 ± 0.06 M 1 at 25 °C. The thermodynamic parameters were calculated by van't Hoff equation. The enthalpy and entropy changes were 41.83 ± 3.28 kJ/mol and 242.08 ± 9.88 J/mol.K at 25 °C, respectively. The results indicate that the process is entropy-driven and suggest that hydrophobic interactions are the main driving forces for the complex formation. Increasing of the ionic strength due to addition of NaCl destabilized porphyrazine-DNA complexes, indicating the competition of Na + ions with porphyrazine complexes for occupation of minor groove binding sites. Copyright © 2010 World Scientific Publishing Company.

Vaittinen O.,Laboratory of Physical Chemistry | Metsala M.,Laboratory of Physical Chemistry | Persijn S.,VSL | Vainio M.,Laboratory of Physical Chemistry | And 2 more authors.
Applied Physics B: Lasers and Optics | Year: 2014

Adsorption of dynamically diluted ammonia at part-per-billion to low part-per-million concentrations in dry nitrogen was studied with treated and non-treated stainless steel and polymer test tubes. The treatments included electropolishing and two types of coatings based on amorphous silicon. Cavity ring-down spectroscopy with an external cavity diode laser operating in the near-infrared wavelength range was used to monitor the adsorption process in real time in continuous-flow conditions to obtain quantitative assessment of the adsorptive properties of the studied surfaces. The investigated polymers were all less adsorptive than any of the treated or non-treated stainless steel surfaces. Some of the commercial coatings reduced the adsorption loss of stainless steel by a factor of ten or more. Polyvinylidene fluoride was found to be superior (less adsorption) to the four other studied polymer coatings. The number of adsorbed ammonia molecules per surface area obtained at different ammonia gas phase concentrations was modeled with Langmuir and Freundlich isotherms. The time behavior of the adsorption-desorption process occurring in the time scale of seconds and minutes was simulated with a simple kinetic model. © 2013 Springer-Verlag Berlin Heidelberg.

Peltola J.,VTT Technical Research Center of Finland | Peltola J.,Laboratory of Physical Chemistry | Hieta T.,VTT Technical Research Center of Finland | Vainio M.,VTT Technical Research Center of Finland | Vainio M.,Laboratory of Physical Chemistry
Optics Letters | Year: 2015

We present a simple and highly sensitive cantileverenhanced photo-acoustic sensor for detection of nitrogen dioxide. A noise equivalent detection limit of 50 parts-per-trillion in 1 s is demonstrated. The limit was reached with an average optical power of 4.7 W using a continuous-wave laser at 532 nm. The achieved normalized noise equivalent absorption coefficient was 2.6 10-10 Wcm1 Hz12. © 2015 Optical Society of America.

Primorac E.,Laboratory of Physical Chemistry | Dapic I.,Laboratory of Physical Chemistry | Strbe N.,Laboratory of Physical Chemistry | Kovacevic D.,Laboratory of Physical Chemistry
Colloids and Surfaces B: Biointerfaces | Year: 2010

The method of stagnation point optical reflectometry was applied for investigation of adsorption of bovine serum albumin (BSA) on previously formed poly(allylamine hydrochloride)/poly(sodium 4-styrenesulphonate) (PAH/PSS) multilayer with PAH being a terminal layer. The solid substrate was silica in the form of silicon wafers carrying an oxide layer. In order to interpret the adsorption of BSA, the build-up mechanism of PAH/PSS multilayers was examined with special emphasis on the effect of electrolyte concentration, pH of solution, and the anchoring (precursor) layer on that process. Additionally, the effect of BSA concentration and of the anchoring layer on BSA adsorption was investigated. It was shown that in all investigated systems the adsorption of BSA depends on conditions under which the multilayer was formed (ionic strength, pH and presence of an anchoring layer), as well as on BSA concentration. It follows that adsorption of BSA could be controlled not only by choosing suitable BSA concentration, but also by modifying the preformed multilayer. © 2009 Elsevier B.V. All rights reserved.

Yulikov M.,Laboratory of Physical Chemistry
Electron Paramagnetic Resonance | Year: 2015

Essential details of two techniques for distance measurements between non-identical spin labels are summarized. One technique is based on double electron-electron resonance (DEER) between Gd(III) ions and nitroxide radicals. The other technique is based on indirect measurements of stochastic dipolar interaction between Ln(III) ions and organic radicals via the change of longitudinal relaxation of the latter species. Combination of these techniques with double electron-electron resonance in pairs of identical spin labels (nitroxide-nitroxide or Gd(III)-Gd(III)) allows to suggest a new experimental strategy for multiple distance measurements in orthogonally-labelled samples. General discussion of advantages and disadvantages of the new strategy for studies of biomacromolecules and their complexes is given along with illustrative experimental examples. In particular, performance of Gd(III)-nitroxide DEER is compared to other possible combinations of nonidentical spin label pairs, while relaxation enhancement in pairs Fe(III)-organic radical is compared to the case of Dy(III)-nitroxide pairs. © The Royal Society of Chemistry 2015.

Preocanin T.,Laboratory of Physical Chemistry | Selmani A.,Laboratory of Physical Chemistry | Mazur D.,Laboratory of Physical Chemistry | Kallay N.,Laboratory of Physical Chemistry
Applied Surface Science | Year: 2010

The method for evaluation of surface potential from the electrode potential of single crystal electrodes is refined. The effect of NaCl and LiCl concentrations on the dependency of the surface potential of TiO2 on pH was examined. The point of zero potential was shifted to lower pH values in the presence of NaCl and to higher pH values in the presence of LiCl. The interpretation of the data based on the Surface Complexation Model suggested that at 0 0 1 crystal plane of rutile, sodium ions as counterions have more pronounced affinity for association with negatively charged surface groups with respect to the lithium ions. © 2010 Elsevier B.V. All rights reserved.

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