Francisco Benedito Teixeira Pessine

Review: Cyclodextrin Inclusion Complexes Probed by NMR Techniques

Cyclodextrins (CDs) are cyclic oligomers of glucopyranose units that play an important role as a host in inclusion complexes, where non-covalent interactions are involved. They have been extensively studied in supramolecular chemistry. Because of its biocompatibility, relatively non-toxicity and relatively low price, CDs have been widely employed for encapsulation of several substances, being used in food, cosmetic and pharmaceutical industries. Nuclear Magnetic Resonance spectroscopy (NMR) is one of the most useful techniques to study interactions of cyclodextrins with guest compounds. It is relatively easy to apply, the experiments are fast and it is the only technique that provides information on the right orientation of the guest molecule inside the cavity and also on other important parameters related to the physico-chemical characteristics of the inclusion complexes. In this review, it will be discussed the study of inclusion complexes between drugs and cyclodextrins by different NMR techniques. Initially, a brief introduction of the properties of cyclodextrins, its importance as innovative drug carrier systems and its applicability is reviewed. Then different NMR techniques used for characterization of inclusion complexes are detailed, with examples studied in our group, which involves since simple measures of 1H-NMR spectrum to more sophisticated experiments, e.g. Diffusion Ordered SpectroscopY (DOSY), NOE methods (ROESY), T1 measure and solid NMR by 13C Cross-Polarization Magic Angle Spinning (CPMAS).

Theoretical studies of Nile Red by ab initio and semiempirical methods

Abstract Ab initio and semiempirical calculations were carried out for the Nile Red (NR) molecule to study the possible occurrence of the twisted intramolecular charge transfer process. The results showed that NR is planar in the ground state (using the CEP-31g basis set) with a high barrier to rotation of the diethylamine group by 90° (0.334 and 0.381 eV with AM1 and CEP-31g, respectively). CIS calculations showed that the charge transfer decreases after the twisting, in contrast to the TICT prediction. The solvatochromic effect was justified through the dipole moments calculated for the first excited state.

A novel sunscreen agent having antimelanoma activity.

A novel series of eight dibenzoylmethane derivatives having both sunscreen and cytotoxic activity has been obtained by derivatizing commercial dibenzoyl methanes. Four human cancer cell lines (MCF 7 (breast), NCI ADR (breast expressing the multidrug resistance phenotype), NCI 460 (lung) and UACC 62 (melanoma)) were used for the cytotoxic assay. Eight among the 19 dibenzoylmethane derivatives showed cytotoxicity against these four cell lines. Absorption spectroscopies revealed that these compounds can be used as sunscreens against UV radiation.

PARAFAC for Spectral Curve Resolution: A Case Study Using Total Luminescence in Human Dental Tartar:

Chromophore identification in biological samples often requires the physical separation of the compounds, which can be difficult. Although there are several advantages to hyphenated spectroscopic techniques for identification of substances, complex mixtures of chromophores presenting overlapped spectra cannot be identified directly through this method. This work presents an application of chemometrics to compound identification in biological samples by a spectroscopic hyphenated technique using a curve resolution method. The PARAllel FACtor analysis model (PARAFAC), which has no rotational indeterminacy, was used for curve resolution of excitation-emission spectra of human dental tartars. PARAFAC was applied under constraints (i.e., unimodality and non-negativity) and evaluated with a validation procedure. The resolved profiles are porphyrinic-like spectra presenting excitation band maxima at 407, 416, and 431 nm in the Soret band region (390–440 nm) of these substances.

Photoinactivation of different human tumor cell lines and sheep red blood cells in vitro by liposome-bound Zn(II) Phthalocyanine: Effects of cholesterol.

The in vitro photoinactivation of human tumor cell lines and sheep red blood cells (SRBC) by Zinc (II) Phthalocyanine (ZnPc) was investigated using unilamellar liposome (LUV) as delivery system, in the presence and absence of cholesterol (CHOL) in the formulation. The presence of CHOL improves the stability of the system showing to be essential for the photodynamic action of ZnPc. LUVs prepared without CHOL did not present any antiproliferative effects neither induced significant photohaemolysis. The presence of ZnPc in the culture medium caused total cell growth inhibition (TGI) only at concentrations higher than 250 micromol dm(-3). For ZnPc in LUV/CHOL (mass ratio=3:1), the mean TGI values for almost all studied cells were around 80 micromol dm(-3), and 14 micromol dm(-3) for human ovarian carcinoma (NIH: OVCAR-3) cells. The cytoplasmic components of OVCAR-3 and SRBC when irradiated in presence of ZnPc in LUV/CHOL were completely destroyed, culminating in cell swelling, lysis and death by necrosis.

MCM-41 and Na-magadiite silicates internal voids probed by pyrene fluorescence spectroscopy

Investigation of the properties of two different silicate materials, namely MCM-41, with one-dimensional, cylindrical pores (4.04 nm diameter), and Na-magadiite, with a bidimensional, layered structure (1.67 nm between layers) was carried out. These materials may be used as sorbents, and their polarity is determinative to the kind of applications they may be employed at. Pyrene, which presents a vibronically resolved emission spectrum, was used as a fluorescent probe to give information on the polarity of these silicates voids. The ratio of band intensity at 383 nm (band 3) to that at 373 nm (band 1) is known to diminish as the polarity of the medium increases. Pristine sorbents and pyrene-adsorbed ones were characterized by thermogravimetric analysis and X-ray diffraction. UV-VIS emission spectra of included pyrene were recorded at temperatures ranging from 10 to 300 K, and from comparing the I(3) : I(1) ratio it was found that Na-magadiite internal sites correspond to a less polar medium than those in MCM-41. This is in accordance with the thermogravimetric data, which shows that a larger amount of pyrene was included in Na-magadiite, despite its smaller dimensions. Yet, excimer emission, usually a concentration dependent phenomenon, was mainly observed for the MCM-41 samples. Upon temperature lowering, pyrene molecules move to other sites of different polarities, towards an intermediary value for both materials.

Fluorescence Piroxicam Study in the Presence of Cyclodextrins by Using the PARAFAC Method

The nonsteroidal anti-inflammatory drug Piroxicam is of interest not only in pharmacology and therapeutics but also in structural dynamics. This drug in solution presents several equilibria that depend on its conformational structure and the medium. Piroxicam was studied by total fluorescence by using a chemometric method (parallel factor analysis or PARAFAC) to resolve its spectra. The addition of cyclodextrins can promote the encapsulation of some preferred Piroxicam species and more easily affect the spectral de-convolution. Because each species has a distinct spectrum as a function of the degree of encapsulation, a factorial fractional design (face-centered fractional cubic with a central sample) was considered for different cyclodextrins solutions. It was possible to identify a correlation between some spectra and the isomers and to reach some understanding of the spectroscopic behavior of the drug in cyclodextrin-containing hydrophilic solvents.

Lipid membrane with low proton permeability

This work reports the production of a liposomal formulation, having a lipidic membrane with known chemical composition and a low proton permeability, as confirmed by physicochemical characterization of the maintenance of a transmembranic pH gradient. These liposomes consist of DSPC, DSPE-PEG, DSPG and cholesterol, with low internal pH. To verify the low proton permeability of these liposomal bilayers, a study of proton migration according to the fluorescence quenching of 9-aminoacridine (9AA), as well as CPT-11 encapsulation, were used to monitor the acidification of the intravesicular space. Both experiments showed that this liposomal formulation is able to maintain a transmembranic proton gradient.

Preparation and characterisation of 5–fluorouracil containing PLGA nanospheres coated with chitosan, for drug delivery

The aim of this study was to design a new Drug Delivery System (DDS) based on poly (lactide–co–glycolide) (PLGA) biodegradable nanospheres (NS) coated with Chitosan (CTS), in order to prolong its residence time and to deliver the nanoparticles more specifically to cancer cells. We have tried three methods of incorporation of Chitosan in the nanoparticles, but only one was efficient. The first method is named entanglement of chains, the second method is known as single adsorption and, in the third, we prior linked covalently Chitosan to the polymer and then prepared the nanoparticles. After selected the best method, it was monitored the stability following the temporal variation of diameter, polydispersity and zeta potential of particles prepared using different percentages of CTS and pH values, using a pre–optimised formulation of 5–fluorouracil containing PLGA NS.

Spectrofluorimetry and chemometrics for investigation of norfloxacin distribution in multilamellar liposomes.

Norfloxacin (NFX), a fluoroquinolone, was encapsulated in multi-lamellar liposomes (MLV) of soy-bean phosphatidylcholine at pH 7.0. The observed affinity of this class of drugs for hydrophobic environments, such as phospholipid bilayers, could lead to a better understanding of the mechanism of uptake in bacteria. The fluorescent properties of NFX were examined both free in solution and in MLV, using anisotropy and fluorescence quenching measurements. The latter data was treated with a chemometric method to deconvolute the overlapped spectra of zwitterionic and neutral species of NFX in equilibrium at this pH. The results show that NFX incorporates into the lipidic bilayers with two different distributions of species: the zwitterionic form in the lipid/aqueous interface, and the neutral one, more towards the center of the bilayer.