Papers by Mihaela Hillebrand
Molecules, Jun 1, 2010
The interactions of 3-carboxyphenoxathiin with Bovine Serum Albumin (BSA) and Human Serum Albumin... more The interactions of 3-carboxyphenoxathiin with Bovine Serum Albumin (BSA) and Human Serum Albumin (HSA) have been studied by fluorescence and circular dichroism spectroscopy. The binding of 3-carboxyphenoxathiin quenches the BSA and HSA fluorescence, revealing a 1:1 interaction with a binding constant of about 10 5 M-1. In addition, according to the synchronous fluorescence spectra of BSA and HSA in presence of 3-carboxyphenoxathiin, the tryptophan residues of the proteins are most perturbed by the binding process. Finally, the distance between the acceptor, 3-carboxyphenoxathiin, and the donor, BSA or HSA, was estimated on the basis of the Förster resonance energy transfer (FRET). The fluorescence results are correlated with those obtained from the circular dichroism spectra, which reveal the change of the albumin conformation during the interaction process.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2012
The association process of a host-guest system, cyclodextrins (CyD) - 3-carboxycoumarin acid (3CC... more The association process of a host-guest system, cyclodextrins (CyD) - 3-carboxycoumarin acid (3CCA) was followed by means of UV-vis, circular dichroism and steady-state fluorescence spectroscopies in buffer solution at pH=1. The experimental data were analyzed in order to get information on the stoichiometry, the equilibrium constants and the geometry of the inclusion complexes. In the circular dichroism spectra, a positive induced signal was obtained reflecting that the guest penetrates the cavity in such a way that the transition moment of the electronic band is quasi parallel to the host main axis. The experimental data are supported by the DFT and TDDFT (B3LYP/6-31G) calculations performed on the isolated ligand and by TDDFT (ZINDO) calculations carried out on the supramolecular ligand-cyclodextrin system.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2012
The experimental induced circular dichroism (ICD) and absorption spectra of the achiral flavonoid... more The experimental induced circular dichroism (ICD) and absorption spectra of the achiral flavonoid kaempferol upon binding to human serum albumin (HSA) were correlated to electronic CD and UV-vis spectra theoretically predicted by time-dependent density functional theory (TDDFT). The neutral and four anionic species of kaempferol in various conformations were considered in the calculations. The appearance of the experimental ICD signal was rationalized in terms of kaempferol binding to HSA in a distorted, chiral, rigid conformation. The comparison between the experimental and simulated spectra allowed for the identification of the kaempferol species that binds to HSA, namely the anion generated by deprotonation of the hydroxyl group in position 7. This approach constitutes a convenient method for evidencing the binding species and for determining its conformation in the binding pocket of the protein. Its main advantage over the UV-vis absorption method lays in the fact that only the bound ligand species gives an ICD signal.
Canadian Journal of Chemistry, 2002
The photochemical and thermal behavior of maleic anhydride 1a and dichloromaleic anhydride 1b, in... more The photochemical and thermal behavior of maleic anhydride 1a and dichloromaleic anhydride 1b, in cryogenic matrix were investigated by means of FT-IR spectroscopy. The ketenylcarbenes represent the key intermediate in the decomposition processes of the anhydrides, even if they were not observed experimentally. The yields of the different products depend on the thermal or photochemical reaction conditions. The main photochemical products obtained from 1a were cyclopropenone and acetylene, whereas the major products from 1b were dichlorocyclopropenone and dichloroacetylene, along with small quantities of dichloropropadienone. The thermal reaction leads to dichloro propa dienone, CO, and CO2. MO calculations performed at the HF/6-31G*//HF/6-31G* level support the experimental mechanisms.Key words: photolysis, thermolysis, ab initio calculations, cryogenic matrix, ketenylcarbenes.
The inclusion complexes of the carboxylate forms of 3-carboxy-(I) and 2-carboxy-phenoxathiin (II)... more The inclusion complexes of the carboxylate forms of 3-carboxy-(I) and 2-carboxy-phenoxathiin (II) with β-cyclodextrin were studied by both one-and two-dimensional NMR spectroscopy. The analysis of the induced chemical shifts of the guests in the presence of different amounts of the host indicates the formation of complexes with 1:1 stoichiometry and association averaged pK values of 3.75 (I) and 4.4 (II). The qualitative analysis of cross peaks in the ROESY spectra support the inclusion of the guests in the cavity with the substituted phenyl ring, the COO − group being in the proximity of the primary rim.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2008
and-conditions-of-access.pdf This article may be used for research, teaching and private study pu... more and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution , reselling , loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
Revue Roumaine de Chimie
Experimental induced circular dichroism spectra of the achiral isoflavone genistein upon binding ... more Experimental induced circular dichroism spectra of the achiral isoflavone genistein upon binding to human serum albumin were correlated with theoretical spectra obtained by time-dependent density functional theory calculations on the neutral and three anionic species of genistein in several conformations. Coupling these methods allowed us to identify the mechanism responsible for chirality induction in genistein upon binding, namely the distortion of the molecular conformation of the ligand upon inclusion into the sterically-restricted protein binding pocket. The bound genistein species and its conformation were identified and the binding parameters were estimated.
Electrochimica Acta, 2006
The redox behaviour of four arylidene substituted derivatives of dibenz-[b, e]-thiepin-5, 5-dioxi... more The redox behaviour of four arylidene substituted derivatives of dibenz-[b, e]-thiepin-5, 5-dioxide-11-one was investigated in aprotic media by cyclic voltammetry coupled with spectral EPR and UV–vis–absorption techniques. The results point out that the ...
The inclusion complexes of many organic ligands, drugs or metal ions, in cyclodextrins (CDs) repr... more The inclusion complexes of many organic ligands, drugs or metal ions, in cyclodextrins (CDs) represent a class of the simplest supramolecular systems widely studied for the last several decades. The increasing interest for their investigation arises from both a theoretical and an applicative points of view. Considering the first one, their study contributes to the understanding of the molecular recognition and molecular interactions, emphasizing the role of different structural factors. From a more practical purpose, the encapsulation of different drugs in the CD cavity produces an increase in the solubility (Brewster & Loftsson, 2007) and allows for a more controlled oral, parental, ocular, nasal or rectal drug release (Challa et al., 2005). A special interest resides in the CDs potential as alternatives for conventional anti-obesity medications (Grunberger et al., 2007). The same goal is also realized using the supramolecular systems, such as hydrogels, obtained by the selfassembl...
Journal of Photochemistry and Photobiology A: …, 2007
... The experimental data were rationalized in terms of the Marcus theory on the electron transfe... more ... The experimental data were rationalized in terms of the Marcus theory on the electron transfer reactions. The bimolecular quenching constants and the free energy change estimated by the RehmWeller relationship fit well the data for other coumarinamine systems. ...
Molecules, 2009
Binding of a newly synthesized indanedione derivative, 2-(2-hydroxy-3ethoxybenzylidene)-1,3-indan... more Binding of a newly synthesized indanedione derivative, 2-(2-hydroxy-3ethoxybenzylidene)-1,3-indanedione (HEBID), to human and bovine serum albumins (HSA and BSA), under simulated physiological conditions was monitored by fluorescence spectroscopy. The binding parameters (binding constants and number of binding sites) and quenching constants were determined according to literature models. The quenching mechanism was assigned to a Förster non-radiative energy transfer due to the HEBID-SA complex formation. A slightly increased affinity of HEBID for HSA was found, while the number of binding sites is approximately one for both albumins. The molecular distance between donor (albumin) and acceptor (HEBID) and the energy transfer efficiency were estimated, in the view of Förster's theory. The effect of HEBID on the protein conformation was investigated using circular dichroism and synchronous fluorescence spectroscopies. The results revealed partial unfolding in the albumins upon interaction, as well as changes in the local polarity around the tryptophan residues.
Molecules, 2010
The interactions of 3-carboxyphenoxathiin with Bovine Serum Albumin (BSA) and Human Serum Albumin... more The interactions of 3-carboxyphenoxathiin with Bovine Serum Albumin (BSA) and Human Serum Albumin (HSA) have been studied by fluorescence and circular dichroism spectroscopy. The binding of 3-carboxyphenoxathiin quenches the BSA and HSA fluorescence, revealing a 1:1 interaction with a binding constant of about 10 5 M-1. In addition, according to the synchronous fluorescence spectra of BSA and HSA in presence of 3-carboxyphenoxathiin, the tryptophan residues of the proteins are most perturbed by the binding process. Finally, the distance between the acceptor, 3-carboxyphenoxathiin, and the donor, BSA or HSA, was estimated on the basis of the Förster resonance energy transfer (FRET). The fluorescence results are correlated with those obtained from the circular dichroism spectra, which reveal the change of the albumin conformation during the interaction process.
Experimental and theoretical results are presented on increases in the rate of electrochemical re... more Experimental and theoretical results are presented on increases in the rate of electrochemical reactions, which are achieved by replacing a small fraction of the original anions in solution with more inhibiting ones. The rate of the electrochemical oxidation of formic acid was substantially increased by replacing a small amount of the supporting electrolyte, perchloric acid, with either sulfuric acid or tetrafluoroboric acid. The largest increases were achieved by substituting mixtures of the last two acids. A theoretical analysis of an electrochemical reaction coupled to anion adsorption is presented. The analysis reveals that, if repulsive forces of appropriate strength form between unlike surface anions, replacing a fraction of the original anions in solution with one or two kinds of more inhibiting anions can increase the rate of reaction.
Analytica Chimica Acta, 2000
ABSTRACT Phenyl-beta-naphthylamine (PBN) used as rubber antioxidant was found to have native fluo... more ABSTRACT Phenyl-beta-naphthylamine (PBN) used as rubber antioxidant was found to have native fluorescence. A spectrofluorimetric method for determination of PBN in multicomponent mixtures of polymer additives is described. The apparent excitation and fluorescence wavelengths used are 348 and 413.5 nm, respectively. Maximum fluorescence intensity is obtained by irradiating PBN dissolved in ethanol, at room temperature. The fluorescence varies linearly with the concentration of PBN in the range of 0.04-4 microg mL(-1). The accuracy and precision of the method are reported.
Analytica Chimica Acta, 2000
ABSTRACT Phenyl-beta-naphthylamine (PBN) used as rubber antioxidant was found to have native fluo... more ABSTRACT Phenyl-beta-naphthylamine (PBN) used as rubber antioxidant was found to have native fluorescence. A spectrofluorimetric method for determination of PBN in multicomponent mixtures of polymer additives is described. The apparent excitation and fluorescence wavelengths used are 348 and 413.5 nm, respectively. Maximum fluorescence intensity is obtained by irradiating PBN dissolved in ethanol, at room temperature. The fluorescence varies linearly with the concentration of PBN in the range of 0.04-4 microg mL(-1). The accuracy and precision of the method are reported.
Central European Journal of Chemistry, 2011
Fluorescence spectroscopy and circular dichroism (CD) spectroscopy were used to investigate the i... more Fluorescence spectroscopy and circular dichroism (CD) spectroscopy were used to investigate the interaction of coumarin-3-carboxylic acid with human serum albumin (HSA) and bovine serum albumin (BSA) under physiological conditions in a buffer solution of pH 7.4. Quenching constants were determined using the Lineweaver-Burk equation to provide a measure of the binding affinity of coumarin-3-carboxylic acid to HSA/BSA. Binding studies concerning
Central European Journal of Chemistry, 2011
Fluorescence spectroscopy and circular dichroism (CD) spectroscopy were used to investigate the i... more Fluorescence spectroscopy and circular dichroism (CD) spectroscopy were used to investigate the interaction of coumarin-3-carboxylic acid with human serum albumin (HSA) and bovine serum albumin (BSA) under physiological conditions in a buffer solution of pH 7.4. Quenching constants were determined using the Lineweaver-Burk equation to provide a measure of the binding affinity of coumarin-3-carboxylic acid to HSA/BSA. Binding studies concerning
... Aura Tintaru, Daniela Gavriliu, § Ovidiu Maior, § and Mihaela Hillebrand* . ... For all th... more ... Aura Tintaru, Daniela Gavriliu, § Ovidiu Maior, § and Mihaela Hillebrand* . ... For all the compounds the best fit to the experimental data was obtained for 1:1 stoichiometry and points out association constants in the range 5000−7000 M -1 , for 1, 2, and 3b and 1770 M -1 for 3a. ...
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Papers by Mihaela Hillebrand