A study on the inclusion complexation of 3,4,5-trihydroxybenzoic acid with β-cyclodextrin at different pH

Complexation of Cyclodextrins with Benzoic Acid in Water-Organic Solvents: A Solvation-Thermodynamic Approach

The aim of this research is to obtain new data about the complexation between β-cyclodextrin (β-CD) and benzoic acid (BA) as a model reaction of the complex formation of hydrophobic molecules with cyclodextrins (CDs) in various media. This research may help developing cyclodextrin-based pharmaceutical formulations through the choice of the appropriate solvent mixture that may be employed in the industrial application aiming to control the reactions/processes in liquid phase. In this paper, NMR results for the molecular complex formation between BA and β-CD ([BA⊂β-CD]) in D₂O-DMSO-d₆ and in D₂O-EtOH have shown that the stability of the complex in the H₂O-DMSO-d₆ varies within the experimental error, while decreases in H₂O-EtOH. Changes in the Gibbs energy of BA resolvation in water and water–dimethylsulfoxide mixtures have been obtained and have been used in the analysis of the reagent solvation contributions into the Gibbs energy changes of the [BA⊂β-CD] molecular complex formation. Quantum chemical calculations of the interaction energy between β-CD and BA as well as the structure of the [BA⊂β-CD] complex and the energy of β-CD and BA interaction in vacuum and in the medium of water, methanol and dimethylsulfoxide solvents are carried out. The stability of [BA⊂β-CD] complex in H₂O-EtOH and H₂O-DMSO solvents, obtained by different methods, are compared. The thermodynamic parameters of the [BA⊂β-CD] molecular complexation as well as the reagent solvation contributions in H₂O-EtOH and H₂O-DMSO mixtures were analyzed by the solvation-thermodynamic approach.

Spectral and molecular modeling investigations of supramolecular complexes of mefenamic acid and aceclofenac with α- and β-cyclodextrin

Inclusion complexes of mefenamic acid (MFA) and aceclofenac (ALF) with α- and β-cyclodextrins (CDs) in aqueous medium were investigated by absorption, fluorescence, time-resolved fluorescence methods. The solid inclusion complexes between drugs and CDs were characterized by SEM, TEM, FT-IR, ¹H NMR, DSC and powder XRD techniques. Spectral studies indicated that both CDs form 1:1 inclusion complex with MFA and ALF. The experimental results revealed that the inclusion process is a spontaneous process. Time-resolved fluorescence studies suggested that ALF exhibited biexponential decay in aqueous and triexponential decay in CD whereas significant enhancement of lifetime of decay components of MFA was observed. Morphologies of drug-CD complexes observed by TEM demonstrate that self-aggregates of MFA/α-CD, ALF/α-CD and ALF/β-CD were nano-sized particles while vesicles were observed for MFA/β-CD. A spatial arrangement of inclusion complex is proposed based on ¹H NMR and PM3 results. Investigations of thermodynamic and electronic properties confirmed the stability of the inclusion complex.

Micrometer size rod formed by secondary self assembly of omeprazole with α- and β-cyclodextrins

Self assembly of α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) micro rods induced by omeprazole (OMP) were observed by SEM and TEM. OMP/CD inclusion complexes have formed the secondary self assembly micro meter size rod like structure. This structure was driven by the intermolecular hydrogen bonding as well as van der Waals forces. Both forces induced the ordered assembly and arrangement of OMP/CD inclusion complexes, whereas CD molecules acted as molecular bricks. The OMP/CD inclusion complexes primary assembled form individual nanorods and then secondary self aggregate nanorods were form a micro meter rod structure. The results indicate that inter-nanotubular hydrogen bonding plays a crucial role in the formation of the self assembled micro rods. The inclusion complexes were also characterized using FT-IR, DSC, powder XRD, (1)H NMR, absorption, fluorescence, life time measurements and molecular modeling methods.

Encapsulation of 4-hydroxy-3-methoxy benzoic acid and 4-hydroxy-3,5-dimethoxy benzoic acid with native and modified cyclodextrins

Inclusion complex formation of 4-hydroxy-3-methoxybenzoic acid (HMBA) and 4-hydroxy-3,5-dimethoxybenzoic acid (HDMBA) with α-CD, β-CD, HP-α-CD and HP-β-CD were studied by absorption, steady state fluorescence, time resolved fluorescence, FT-IR, (1)H NMR and molecular modeling methods. The effect of the CDs with HMBA and HDMBA were studied in pH∼1, pH∼7 and pH∼10 buffer solutions. The study revealed that both hydroxybenzoic acids formed 1:1 complex with the four CDs. The theoretical values suggest that both guests are partially encapsulated into the CDs cavity. The hydroxy group is present in the interior part of the CD cavity and carboxyl group is present in the hydrophilic part of the CD cavity. Molecular modeling studies proved that (i) the negative Gibbs energy and enthalpy changes for the inclusion complexes indicated that the formation of these complexes were spontaneous and exothermic, (ii) hydrogen bonding interactions played a major role in the inclusion process, (iii) the dipole moment values for guests increased when they entered into the CDs cavities which is an indication of the increase of the polarity and the formation of complex and (iv) differences in binding energy and enthalpy change suggest that the β-CD formed more stable complex than α-CD.

Spectral and molecular modeling studies on hydroxybenzaldehydes with native and modified cyclodextrins

The inclusion complexation of 2-hydroxy-3-methoxybenzaldehyde (2HMB), 4-hydroxy-3-methoxybenzaldehyde (4HMB), 3,4-dimethoxybenzaldehyde (DMB) and 4-hydroxy-3,5-dimethoxybenzaldehyde (HDMB) with α-CD, β-CD, HP-α-CD and HP-β-CD were carried out by UV-Visible, steady-state and time-resolved fluorescence and PM3 methods. All the benzaldehydes shows dual fluorescence in aqueous and CD mediums and 1:1 inclusion complexes were formed with CDs. PM3 geometry optimizations results indicate that the HDMB/CD complex is significantly more favorable than the other complexes. The negative enthalpy changes suggest that the inclusion complexation processes are spontaneous. The geometry of the most stable complex shows that methoxy/OH group of HMBs is entrapped in the less polar CD cavities, while the aldehyde group present in the upper part of the CDs cavities.