Licesio J. Rodriguez

Complexation of the Non-steroidal Anti-inflammatory Drug Nabumetone with Modified and Unmodified Cyclodextrins

The inclusion of the anti-inflammatory drug, Nabumetone, in α-, β- and hydroxypropyl-β-cyclodextrin (CDs) is studied using UV-VIS absorption and steady-state fluorescence emission. Binding constants and thermodynamic parameters of complex formation are determined by spectrofluorimetry. The inclusion phenomena of Nabumetone with the three cyclodextrins is compared with that of the well known similar anti-inflammatory drug Naproxen. In the case of Nabumetone pronounced differences are observed in the complexation process with each cyclodextrin whereas the respective Naproxen complexes are nearly identical. 1H-NMR experiments show that the inclusion process in Nabumetone can occur either through the substituents in the -2 (butanone) or -6 (methoxy) positions in the naphthalene ring.

New Insight into the Structure of CTAB Micelles in the Presence of Cyclodextrins, Using Non-Steroidic Anti-Inflammatory Agents – Nabumetone, Naproxen – as Fluorescent Probes

The structure of CTAB micelles in the presence of α-, β- and hydroxypropyl-β-cyclodextrin has been investigated by means of conductivity and spectroscopic measurements – absorption and steady state fluorescence – using Naproxen, Nabumetone and pyrene as probes. In the presence of the three cyclodextrins, two types of micelles have been detected. The first type is a pure surfactant micelle, while the other is formed by surfactant monomers complexed with cyclodextrins. The presence of cyclodextrins produces a decrease in the cmc of the pure micelle. The second type of micelle is formed at higher cmc* values, 25.6 × 10-4 M, 27.8 × 10-4 M and 38.9 × 10-4 M for α-, β-, and HPβCD respectively. A significant increase in the ionisation degree has been detected. The aggregation number is strongly increased, being 92 ± 3 , 97 ± 3 and 80 ± 2 for for α-, β-, and HPβCD respectively. The polarity of this micelle decreases, indicating that it becomes tighter and its hydrophobic region becomes less polar.

Hydrogen bonding in a non-steroidal anti-inflammatory drug—Naproxen

Photophysical properties of a non-steroidal anti-inflammatory drug, Naproxen (6-methoxy alpha-methyl-2-naphthalene acetic acid sodium salt), were investigated in solvents of different polarity, hydrogen donor ability and also in cyclodextrins. The results indicate that in all cases the emitting state is the 1L(b) singlet. In alcoholic solvents, an intermolecular hydrogen bond is responsible for the observed photophysical behaviour of the probe whereas in non-protic solvents (polar and weakly polar) an intramolecular hydrogen bond type is postulated to rationalize the data found. In water, the non-radiative rate constant has a value similar to those found in aqueous solutions of alpha- and beta-cyclodextrins where the probe form complexes. The behaviour in water is explained by a water-structure enforced hydrophobic effect. The spectroscopic results are interpreted on the basis of a multiple-parameter model that considers specific solute-solvent interactions. These were also observed in the ground state and detected by Fourier transform infrared spectroscopy. Molecular mechanics (MM) and molecular orbital (AM1) calculations also support the existence of two conformations (rotamers) in Naproxen with non-equivalent intramolecular hydrogen bond-like formation.

Complexes of molybdenum(V) and molybdenum(IV) with dithiocarbamates derived from α-amino acids. Reaction kinetics in organic solvents

Abstract The reaction between dithiocarbamate derivatives of α-amino acids (glycine, alanine, α-amino-butyric acid, norvaline, valine, norleucine, leucine and isoleucine) and sodium molybdate in acid medium leads to the formation of molybdenum(V) complexes with the general formula [Mo 2 O 3 )dtc a.a.) 4 ]·2H 2 O (a.a = amino acid). The complexes were characterized by elemental analysis, FT-IR and uv-vis spectroscopies and XPS. They are binuclear complexes with a linear oxygen bridge, the dithiocarbamate moiety acting as a bidentate ligand and thus yielding a distorted octahedral coordination for the metal cation. In organic solvents, these compounds undergo a chemical transformation, yielding complexes with the general formula [MoO(dtc a.a.) 2 ], whose synthesis is also described. These complexes were characterized using the same experimental techniques as above. The kinetics of transformation in organic media were studied, proposing a multi-step reaction mechanism, and the rate constants have also been determined.

Lithium ion complexation kinetics by cyclic and acyclic polyethers

Results of the ultrasonic absorption relaxation and nuclear magnetic resonance studies of the kinetics of alkali metal cation complexation by macrocycl ic 1 igands in a variety of nonaqueous solvents are reviewed. The effects of a competition between low permittivity solvent molecules, anions, and neutral macrocycles for the first coordination sphere of the lithium cation are clearly evident. utility of the Eigen-Winkler reaction mechanism for describing the ultrasonic absorption results is pointed out. techniques are used to explore the kinetics of lithium ion complexation by acyclic polyethers such as poly(ethy1ene oxide) in acetonitrile a striking insight emerges: The complexation kinetics reflect a localized cation- polyether interaction that is independent of the 1 ength of the polyether chain as one proceeds from triglyme to a poly(ethy1ene oxide) of 15,000 average molar w eight. complexation kinetic studies in neat 1 iquid poly(ethy1ene oxides) is discussed and possible applications of the results in developing an understanding of polymeric electrolytes in 1 ithium batteries is out1 ined. The When the same ultrasonic

Dithiocarbamates derived from aspartic and glutamic acids as chelating agents

Dithiocarbamates (dtcs) derived from aspartic (asp) and glutamic (glu) acids have been synthesized and characterized. Their Ba salts are of the general formula Ba3(dtc–aa)2, where aa = amino acid. The dithiocarbamates react with NiII salts to yield square-planar complexes, [Ni(dtc–aa)2]. Complexes with PbII and CdII, with formula [M3(dtc–aa)2], are insoluble in water, and for CdII a second compound can be isolated in an acidic medium for the glutamic acid derivative, with formula [Cd(dtc–glu)]. Conductivity measurements indicate an appreciable affinity of the dithiocarbamates for these metal ions, with an almost quantitative scavenging ability.

Molecular dynamics of macrocycle-metal ion complexes involving heteronuclear binding atoms

Combination of ultrasonic absorption relaxation spectra with infrared absorption spectra yields a clearer picture of the mechanism of complexation of metal ions by macrocycles in nonaqueous solutions. The Eigen-Winkler multistep reaction mechanism has consistently provided a suitable fit of the ultrasonic absorption data for systems such as monovalent sodium cation reacting with 18-crown-6 in acetonitrile. A macrocycle such as Kryptofix 22 having two nitrogen atoms in the ring experiences an exo-exo

Solubility of diazepam and prazepam in aqueous non-ionic surfactants

exo-endo ;ft endo-endo change in conformation readily detected by ultrasonic techniques. Differences in complexation-decomplexation mechanisms deduced from ultrasonic and NMR data can be rationalized in terms of the limitations of the experimental techniques.

An equilibrium and kinetic investigation of salt-cycloamylose complexes

The solubility of diazepam and prazepam in aqueous polyoxyethylen‐10‐dodecanol, polyoxyethylen‐23‐dodecanol and polyoxyethylen‐20‐hexadecanol, has been determined at 25.0°C. Diazepam seems to achieve a higher micellar penetration than prazepam, in spite of an expected smaller hydrophobic character. Thermodynamic interpretation of the micellar solutions is carried out using the regular solutions approach. A surfactant‐independent relation between solubilities of both drugs has been derived.