
Agnes Buvári-BarczaEötvös Loránd University · Institute of Chemistry
Agnes Buvári-Barcza
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Publications (43)
Stability constants for the complexes of anionic, neutral (zwitterionic) and protonated forms of l- and d-enantiomers of eight amino acids with β-cyclodextrin and the positively charged quaternary ammonium β-cyclodextrin (QA-β-CD, DS = 3.6 ± 0.3) have been determined by spectrophotometric and pH-potentiometric methods. The highest stability constan...
Complex formation reactions of phenylboronic, phenylphosphonic, phenylarsonic and 4-aminophenyl arsonic acids with β-cyclodextrin (cycloheptaamylose, β-CD) and some simple carbohydrates (mannitol, sorbitol, glucose) have been studied using spectrophotometric, potentiometric methods and solubility measurements, supplemented with HPLC and IR analyses...
In spite of the fact that cyclodextrins are mentioned often as enzyme mimicing agents (being really very good and relatively simple model molecules) and the changes in physical and chemical properties of guests (solubility, volatility, light-sensitivity, etc.) during the complex formation are of primary interest for practical purposes (and mainly t...
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The poor water solubility of the free base and the high dissociation constant (K(a)) hinder mainly the assay of alkaloid salts. We have elaborated an environment friendly method that can be carried out in aqueous media. The stability difference of the cyclodextrin (CD) complexes of free and protonated bases were used for this purpose. The base is i...
The use and importance of formic acid and acetic anhydride (Ac2O) is increasing in nonaqueous acid-base titrations, but their interaction with the solutes is poorly understood. This paper attempts to clarify the effect of the solvents; NMR and spectrophotometric investigations were done to reveal the interactions between some bases and the mentione...
Most phenomena (like promoting and leveling as well as differentiating effects) of common nonaqueous titrations can be explained by the Brönsted's concept combined with the hydrogen bond theory but some open problems are shown in connection with the use of formic acid and/or acetic anhydride.
A relatively high and unexpected increase of inclusion complex stabilities could be detected in some half dissociated dicarboxylic acids (HA− ions) with intramolecular H-bonding. The intermolecular hydrogen bonds between the protruding functional groups of the guest and the hydroxy groups of the host are known to enhance the stability of the cyclod...
The acid–base determination of different substances by nonaqueous titrations is highly preferred in pharmaceutical analyses since the method is quantitative, exact, and reproducible. The modern interpretation of the reactions in nonaqueous solvents started in the last century, but several inconsistencies and unsolved problems can be found in the li...
Two guests reacting with cyclodextrins (CDs) may form ternary complexes, in addition to the common competition of 1:1 complexes. One of the guests can really be included into the cavity of the CD, while the second guest molecule is either inserted close to the first one or attached to the outer surface of the supramolecule by H-bonding. There is a...
Natural and substituted cyclodextrins (CDs), as well as some calixarenes, have been investigated with respect to their solubilization of C60 in water. Underivatized γ-CD is proved to have unique solubilizing power among the possible complexing agents as it produces stable solutions and solids containing real 1∶2 complexes. The differences in the ap...
The most common native host molecule, -cyclodextrin (cycloheptaamylose) is able toform inclusion complexes with a large variety of guestmolecules (or ions) of different size and shape. Theproperties of the included guest molecule are highlyinfluenced by the host-guest interaction, and thepractical usefulness of -cyclodextrin isdependent on these ef...
The stability of inclusion complexes (i.e. the measure of molecular recognition between a guest and (beta-cyclodextrin, CD) is highly influenced by the fit of the guest into the cavity of the host and by secondary bonds among the functional groups getting in close connection. The guests themselves influence these interactions by their sizes, shapes...
To clarify the complexation behaviour of the less studied maltosyl--cyclodextrin, its interactions with some characteristic guests such as phenolphthalein and p-nitrophenol have been studied. The results show that similar types of inclusion complexes are formed as in the case of the unsubstituted -cyclodextrin. In addition to the formation of inclu...
The interaction of the p-nitrophenol/p-nitrophenolate conjugate has been investigated with different 2-hydroxypropyl--cyclodextrin hosts. The measured values for stability constants attain a maximum as a function of increasing average degree of substitution. The quotients of constants, characterizing the inclusion of p-nitrophenolate and p-nitroph...
Capillary zone electrophoresis method has been developed for the separation (and determination) of monoand dimaltosyl-β-cyclodextrins
using indirect UV absorbance detection. The separation is based on inclusion complex formation with benzoate ion which is
used as background electrolyte and absorbance provider simultaneously. Good resolution of cycl...
The highly alkaline aluminate lye, which is produced in the first step of Bayer process, is characterized by low water activity and strong competition for water molecules. The consequence of these effects is that two (or more) negatively charged species can be brought together and stabilized in the form of anionic hydrogen bonded complexes. Dependi...
Phenolphthalein forms stable and colourless complexes with cyclodextrins and the hydroxypropylation does not hinder this molecular recognition. The interaction can be easily followed by spectrophotometry, but the Benesi-Hildebrand method can not be recommended for the calculation of formation constants because the concentration of the complex is re...
During the past few years many papers were published on the gamma-cyclodextrin—C60 interaction. These described different procedures for the synthesis of a 2:1 inclusion complex, which can be prepared in solid form and exists in solution only in the presence of high cyclo-dextrin excess as a magenta coloured solution or as a yellowish brown colloid...
Some inclusion complexes ofß-cyclodextrin (cyclomaltoheptaose) have been investigated, particularly with respect to their solubility. The mathematical characterization of the equilibrated host-guest system containing both solid and solution phases is discussed (first of all those, which contain 1:1 or 1:1 + 2:1 species) and demonstrated by differen...
The perturbation of the three-site interaction of phenolphthalein on complexation with different cyclodextrins (CDs) has been investigated as a function of the type and degree of substitution of the CD. The UV visible spectra are practically identical, while the circular dichroism spectra change dramatically both in intensities and signs. Parallel...
The hydroxypropylation of β-cyclodextrin does not change the essential nature of its interaction with phenolphthalein but the pattern and degree of substitution do alter both the stability constant of the inclusion complex and its induced circular dichroism spectrum. The reason for this phenomenon is that substitution of the hydroxy groups (especia...
The phenomena have been investigated using phenolphthalein because it proved to be an excellent model for inclusion complex formation as a relatively large guest molecule and its interaction with β-cyclodextrin is known rather well. The average degree of substitution (DS) of hydroxypropyl-β-cyclodextrin samples ranged between (0.0) — 2.9 -16.0 and...
The p-nitrophenol/phenolate conjugate has been investigated as the model of small guest molecules with respect to inclusion complex formation with different hydroxypropyl-β-cyclodextrin hosts. The stability constants measured seem to pass a maximum in function of increasing average degree of substitution.
It has been shown that the solid-solid mechanochemical reaction between crystalline buckminsterfullerene and gamma cyclodextrin at room temperature yields an inclusion complex of more intact nature than the procedure previously suggested by Swedish researchers. Experimental evidence suggests that the reaction proceeds via the mechanochemical amorph...
γ-Cyclodextrin appears to catalyze the reaction of C60 with water during reflux and in addition to the water soluble 1:1 and 2:1 complexes (whose stability constants could be estimated as ≥ 4 × 10 and ≥ 4 × 10, respectively) some (complexed) fullerene derivatives are also formed.
The stability constants of the inclusion complexes between 2-hydroxypropyl--cyclodextrin and phenolphthalein have been found to decrease with increasing degree of substitution; the hydroxypropylation of the primary rim has a relatively higher effect. The change of specific rotations seems to support this finding. The decrease can be explained by th...
The interactions of cyclomalto-octaose (γ-cyclodextrin) with some phthalein-type acid—base indicators have been investigated photometrically. Bromine substituents enhance the formation of complexes and tetrabromophenolphthalein [3,3-bis(3,5-dibromo-4-hydroxyphenyl)-3H-isobenzofuran-1-one] forms the most stable complex (K 6.0 × 103). This stability...
Complex formation of methyl orange and some other azobenzene derivatives with cyclodextrins has been studied in acidic and alkaline solutions by a spectrophotometric method. A correlation has been established between the stability constants of the complexes, the spectral changes accompanying complex formation and a tautomeric equilibrium between pr...
The interactions between some alkali halides, perchlorates and sulfates and-cyclodextrin (cycloheptaamylose, CD) have been investigated by solubility, spectrophotometric, thermoanalytical and preparative methods. The main conclusions are as follows. (i) The most pronounced interaction occurs with the anions; in dilute solutions this can be characte...
The interactions of phenol, aniline, and their nitro derivatives with -cyclodextrin (cyclohepta-amylose) have been studied by a spectrophotometric method. The complex formation constants have been determined for both the conjugate acid and base forms. The para isomer of nitrophenol is the only case when a more stable complex is formed with the ioni...
The complex formation of phenolphthalein and β-cyclodextrin (cyclohepta-amylose) has been investigated by spectrophotometric, c.d., and potentiometric methods. It has been shown that complexes are formed with the protonated and dissociated forms of phenolphthalein as well; the dianion is complexed in alkaline solution in a colourless form. The comp...
The complex formation of B-cyclodextrin with short chain aliphatic alcohols has been studied. The stability constants of 1:1 complexes, determined spectrophotometrically, increase monotonically in the series of normal alcohols, while branching in the chain results in a further increase in stability. With smaller monoalcohols, complexes containing m...
Based on solubility measurements the existence of a complex containing two
molecules of benzoic acid for one molecule of cyclodextrin has been proved in which
the second acid is assumed to be bound by hydrogen bridge. The formation constants
of the 1 : 1 and 1 : 2 complexes have been determined.
The solubility of benzoic acid in water is increased by the presence of β-cyclodextrin. The solubility vs. cyclodextrin concentration plots are practically linear but the slope is >1, suggesting that not only simple binary but also ternary complexes are formed.
The solubility of benzoic acid was measured in solutions of β-CD and β-CD-benzoic acid c...
The cis–trans isomerization of 4-dimethylamino-azobenzene has been investigated spectrophotometrically in benzene solutions in the presence of some carboxylic acids, phenol and i-propanol. It has been established that proton donors increase the rate of the cis –trans reaction. The catalytic effect can be attributed to a hydrogen bridged interaction...
The solubility of water in benzene containing benzoic acid has been measured and the concentration of the dissolved water found increasing parallel with the acid concentration. According to these results, in benzene solutions containing water, the formation of monomer monohydrate, monomer dihydrate, dimer monohydrate and dimer dihydrate, too, have...
The partition of benzoic acid has been measured between water and benzene in the presence of sodium benzoate, at 25 °C temperature. We have to consider not only the dimerization in benzene, but H+, A -, HA, HA2-and H2A2 species in the aqueous phase as well. By computerised evaluation, the corresponding formation constants: β11= (8.527 ± 0.066) · 10...
ESCA investigations of transition metal complexes of salicylaldoxime and its derivatives were used to demonstrate how the electron binding energies of the donor atoms and central atoms are affected by complex formation, by the stabilities of the resulting complexes, by substituents changing the electron densities of the donor atoms, and by cis-tran...