Danijela Vojta | Universität Koblenz (original) (raw)

Papers by Danijela Vojta

Research paper thumbnail of Medical Diary for the ensuing Week

Research paper thumbnail of The diversity in thermal behavior of novel catanionic cholates: The dominant effect of quaternary ammonium centers

ABSTRACT The thermal behavior of novel catanionic compounds based on cholate anion was examined. ... more ABSTRACT The thermal behavior of novel catanionic compounds based on cholate anion was examined. The study explains the effect of the raising dodecyl chain number, as well as of the raising headgroup number in quaternary ammonium salts on their physico-chemical properties. The examined samples are crystal smectic phases at room temperature. Their rich and diverse thermal behavior is seen through polymorphic phase transitions, thermotropic mesomorphism of smectic nature and in some cases, kinetically managed crystallization that lasts in days. The changes of the cholates keto-enol isomer balance during thermal treatment are obtained. For both groups of samples temperatures of isotropisation and the thermodynamic parameters follow polynomial regression. Introduction of the new dodecyl chain leads to more ordered structure, while implementation the new headgroup leads to advanced polymer-like structure. The obtained results demonstrate an effort for getting and controlling the regularity of the physico-chemical and thermotropic properties for new compounds by systematic changing of cationic part of the molecule. These informations could provide in the future the easiest way for selection of potentially new and targeted applicable materials.

Research paper thumbnail of Intramolecular couplings and the secondary structure of CC stretching bands

Research paper thumbnail of Ionic strength and composition govern the elasticity of biological membranes. A study of model DMPC bilayers by force- and transmission IR spectroscopy

Chemistry and Physics of Lipids, 2015

A B S T R A C T Infrared (IR) spectroscopy was used to quantify the ion mixture effect of seawate... more A B S T R A C T Infrared (IR) spectroscopy was used to quantify the ion mixture effect of seawater (SW), particularly the contribution of Mg 2+ and Ca 2+ as dominant divalent cations, on the thermotropic phase behaviour of 1,2dimyristoyl-sn-glycero-3-posphocholine (DMPC) bilayers. The changed character of the main transition at 24 C from sharp to gradual in films and the 1 C shift of the main transition temperature in dispersions reflect the interactions of lipid headgroups with the ions in SW. Force spectroscopy was used to quantify the nanomechanical hardness of a DMPC supported lipid bilayer (SLB). Considering the electrostatic and ion binding equilibrium contributions while systematically probing the SLB in various salt solutions, we showed that ionic strength had a decisive influence on its nanomechanics. The mechanical hardness of DMPC SLBs in the liquid crystalline phase linearly increases with the increasing fraction of all ion-bound lipids in a series of monovalent salt solutions. It also linearly increases in the gel phase but almost three times faster (the corresponding slopes are 4.9 nN/100 mM and 13.32 nN/100 mM, respectively). We also showed that in the presence of divalent ions (Ca 2+ and Mg 2+ ) the bilayer mechanical hardness was unproportionally increased, and that was accompanied with the decrease of Na + ion and increase of Cl À ion bound lipids. The underlying process is a cooperative and competitive ion binding in both the gel and the liquid crystalline phase. Bilayer hardness thus turned out to be very sensitive to ionic strength as well as to ionic composition of the surrounding medium. In particular, the indicated correlation helped us to emphasize the colligative properties of SW as a naturally occurring complex ion mixture.

Research paper thumbnail of Intramolecular couplings and the secondary structure of CC stretching bands

Vibrational Spectroscopy, 2010

Research paper thumbnail of The study of secondary effects in vibrational and hydrogen bonding properties of 2- and 3-ethynylpyridine and ethynylbenzene by IR spectroscopy

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014

Research paper thumbnail of The study of hydrogen bonding and π⋯π interactions in phenol⋯ethynylbenzene complex by IR spectroscopy

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014

Research paper thumbnail of The exploration of hydrogen bonding properties of 2,6- and 3,5-diethynylpyridine by IR spectroscopy

Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, 2014

Hydrogen bonding properties of 2,6- and 3,5-diethynylpyridine were analyzed by exploring of their... more Hydrogen bonding properties of 2,6- and 3,5-diethynylpyridine were analyzed by exploring of their interactions with trimethylphosphate, as hydrogen bond acceptor, or phenol, as hydrogen bond donor, in tetrachloroethene C2Cl4. The employment of IR spectroscopy enabled unravelling of their interaction pattern as well as the determination of their association constants (Kc) and standard reaction enthalpies (ΔrH(⦵)). The association of diethynylpyridines with trimethylphosphate in stoichiometry 1:1 is established through CH⋯O hydrogen bond, accompanied by the secondary interaction between CC moiety and CH3 group of trimethylphosphate. In the complexes with phenol, along with the expected OH⋯N interaction, CC⋯HO interaction is revealed. In contrast to 2,6-diethynylpyridine where the spatial arrangement of hydrogen bond accepting groups enables the simultaneous involvement of phenol OH group in both OH⋯N and OH⋯CC hydrogen bond, in the complex between phenol and 3,5-diethynylpyridine this...

Research paper thumbnail of Medical Diary for the ensuing Week

Research paper thumbnail of The diversity in thermal behavior of novel catanionic cholates: The dominant effect of quaternary ammonium centers

ABSTRACT The thermal behavior of novel catanionic compounds based on cholate anion was examined. ... more ABSTRACT The thermal behavior of novel catanionic compounds based on cholate anion was examined. The study explains the effect of the raising dodecyl chain number, as well as of the raising headgroup number in quaternary ammonium salts on their physico-chemical properties. The examined samples are crystal smectic phases at room temperature. Their rich and diverse thermal behavior is seen through polymorphic phase transitions, thermotropic mesomorphism of smectic nature and in some cases, kinetically managed crystallization that lasts in days. The changes of the cholates keto-enol isomer balance during thermal treatment are obtained. For both groups of samples temperatures of isotropisation and the thermodynamic parameters follow polynomial regression. Introduction of the new dodecyl chain leads to more ordered structure, while implementation the new headgroup leads to advanced polymer-like structure. The obtained results demonstrate an effort for getting and controlling the regularity of the physico-chemical and thermotropic properties for new compounds by systematic changing of cationic part of the molecule. These informations could provide in the future the easiest way for selection of potentially new and targeted applicable materials.

Research paper thumbnail of Intramolecular couplings and the secondary structure of CC stretching bands

Research paper thumbnail of Ionic strength and composition govern the elasticity of biological membranes. A study of model DMPC bilayers by force- and transmission IR spectroscopy

Chemistry and Physics of Lipids, 2015

A B S T R A C T Infrared (IR) spectroscopy was used to quantify the ion mixture effect of seawate... more A B S T R A C T Infrared (IR) spectroscopy was used to quantify the ion mixture effect of seawater (SW), particularly the contribution of Mg 2+ and Ca 2+ as dominant divalent cations, on the thermotropic phase behaviour of 1,2dimyristoyl-sn-glycero-3-posphocholine (DMPC) bilayers. The changed character of the main transition at 24 C from sharp to gradual in films and the 1 C shift of the main transition temperature in dispersions reflect the interactions of lipid headgroups with the ions in SW. Force spectroscopy was used to quantify the nanomechanical hardness of a DMPC supported lipid bilayer (SLB). Considering the electrostatic and ion binding equilibrium contributions while systematically probing the SLB in various salt solutions, we showed that ionic strength had a decisive influence on its nanomechanics. The mechanical hardness of DMPC SLBs in the liquid crystalline phase linearly increases with the increasing fraction of all ion-bound lipids in a series of monovalent salt solutions. It also linearly increases in the gel phase but almost three times faster (the corresponding slopes are 4.9 nN/100 mM and 13.32 nN/100 mM, respectively). We also showed that in the presence of divalent ions (Ca 2+ and Mg 2+ ) the bilayer mechanical hardness was unproportionally increased, and that was accompanied with the decrease of Na + ion and increase of Cl À ion bound lipids. The underlying process is a cooperative and competitive ion binding in both the gel and the liquid crystalline phase. Bilayer hardness thus turned out to be very sensitive to ionic strength as well as to ionic composition of the surrounding medium. In particular, the indicated correlation helped us to emphasize the colligative properties of SW as a naturally occurring complex ion mixture.

Research paper thumbnail of Intramolecular couplings and the secondary structure of CC stretching bands

Vibrational Spectroscopy, 2010

Research paper thumbnail of The study of secondary effects in vibrational and hydrogen bonding properties of 2- and 3-ethynylpyridine and ethynylbenzene by IR spectroscopy

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014

Research paper thumbnail of The study of hydrogen bonding and π⋯π interactions in phenol⋯ethynylbenzene complex by IR spectroscopy

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014

Research paper thumbnail of The exploration of hydrogen bonding properties of 2,6- and 3,5-diethynylpyridine by IR spectroscopy

Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, 2014

Hydrogen bonding properties of 2,6- and 3,5-diethynylpyridine were analyzed by exploring of their... more Hydrogen bonding properties of 2,6- and 3,5-diethynylpyridine were analyzed by exploring of their interactions with trimethylphosphate, as hydrogen bond acceptor, or phenol, as hydrogen bond donor, in tetrachloroethene C2Cl4. The employment of IR spectroscopy enabled unravelling of their interaction pattern as well as the determination of their association constants (Kc) and standard reaction enthalpies (ΔrH(⦵)). The association of diethynylpyridines with trimethylphosphate in stoichiometry 1:1 is established through CH⋯O hydrogen bond, accompanied by the secondary interaction between CC moiety and CH3 group of trimethylphosphate. In the complexes with phenol, along with the expected OH⋯N interaction, CC⋯HO interaction is revealed. In contrast to 2,6-diethynylpyridine where the spatial arrangement of hydrogen bond accepting groups enables the simultaneous involvement of phenol OH group in both OH⋯N and OH⋯CC hydrogen bond, in the complex between phenol and 3,5-diethynylpyridine this...