SERS Investigation on Oligopeptides Used as Biomimetic Coatings for Medical Devices.

The surface-enhanced Raman scattering (SERS) spectra of three amphiphilic oligopeptides derived from EAK16 (AEAEAKAK)2 were examined to study systematic amino acid substitution effects on the corresponding interaction with Ag colloidal nanoparticles. Such self-assembling molecular systems, known as "molecular Lego", are of particular interest for their uses in tissue engineering and as biomimetic coatings for medical devices because they can form insoluble macroscopic membranes under physiological conditions. Spectra were collected for both native and gamma-irradiated samples. Quantum mechanical data on two of the examined oligopeptides were also obtained to clarify the assignment of the prominent significative bands observed in the spectra. In general, the peptide-nanoparticles interaction occurs through the COO- groups, with the amide bond and the aliphatic chain close to the colloid surface. After gamma irradiation, mimicking a free oxidative radical attack, the SERS spectra of the biomaterials show that COO- groups still provide the main peptide-nanoparticle interactions. However, the spatial arrangement of the peptides is different, exhibiting a systematic decrease in the distance between aliphatic chains and colloid nanoparticles.

Cyclodextrin-based nanocarriers containing a synergic drug combination: A potential formulation for pulmonary administration of antitubercular drugs.

Tuberculosis (TB) remains a major global health problem. The use of ethionamide (ETH), a main second line drug, is associated to severe toxic side-effects due to its low therapeutic index. In this challenging context, "booster" molecules have been synthetized to increase the efficacy of ETH. However, the administration of ETH/booster pair is mostly hampered by the low solubility of these drugs and the tendency of ETH to crystallize. Here, ETH and a poorly water-soluble booster, so-called BDM43266, were simultaneously loaded in polymeric ß-cyclodextrin nanoparticles (pßCyD NPs) following a "green" protocol. The interaction of ETH and BDM43266 with pßCyD NPs was investigated by complementary techniques. Remarkably, the inclusion of ETH and BDM43266 pßCyD NPs led to an increase of their apparent solubility in water of 10- and 90-fold, respectively. Competition studies of ETH and BDM43266 for the CyD cavities of pßCyD NPs corroborated the fact that the drugs did not compete with each other, confirming the possibility to simultaneously co-incorporate them in NPs. The drug-loaded NP suspensions could be filtered through 0.22µm filters. Finally, the drug-loaded NPs were passed through a Microsprayer® to evaluate the feasibility to administer pßCyD NPs by pulmonary route. Each spray delivered a constant amount of both drugs and the NPs were totally recovered after passage through the Microsprayer®. These promising results pave the way for a future use of pßCyD NPs for the pulmonary delivery of the ETH/BDM43266 pair.

Complexes of the antitumoral drugs Doxorubicin and Sabarubicin with telomeric G-quadruplex in basket conformation: ground and excited state properties.

We studied the binding of two anthracycline drugs, Doxorubicin and Sabarubicin, to a model telomeric sequence 5'-d[GGG(TTAGGG)(3)]-3' (21-mer), assuming the basket G-quadruplex (G4) conformation in Na(+)-rich aqueous solution. We used an approach that combines spectroscopic and microcalorimetric techniques to obtain information about ground and excited state properties of the most stable complexes. Both drugs bind to the 21-mer in basket conformation and complexes of 1:1 and 2:1 drug : 21-mer stoichiometry coexist in solution. Binding constants were determined from fluorescence and isothermal titration calorimetry experiments. For both drugs association is driven by enthalpy and disfavoured by entropy in the case of two sequential binding events to different sites. The drug fluorescence is completely quenched in the 1:1 complex, most likely by electron transfer from the guanine system to the anthraquinone moiety, while part of the emission survives in the 2:1 complex. Circular dichroism (CD) of the individual complexes is dominated by the G-quadruplex signal in the UV and by the anthracycline signal in the near-UV and Vis region. The experimental CD spectra combined with conformational calculations at MM level and quantum mechanical calculation of the rotational strength of the electronic transitions afforded information on the binding geometries.

Chiral recognition of 2-(3-benzoylphenyl)propionic acid (ketoprofen) by serum albumin: an investigation with microcalorimetry, circular dichroism and molecular modelling.

The interaction of enantiomeric ketoprofen (KP) with BSA and HSA was studied by isothermal titration calorimetry (ITC). Affinity constants and thermodynamic parameters for complexation in two main protein sites were determined. Affinity constants for both proteins are generally lower for S(+)- than for R(-)-KP. Large enthalpic contributions to Gibbs free energy are compensated by large negative entropic terms for S(+) in the BSA-subdomain IIIA and HSA-subdomain IIA. The lowest energy BSA complexes of both enantiomers were structurally characterized by combining molecular mechanics (MM) and molecular dynamics (MD) with circular dichroism (CD). Comparison of quantum mechanically calculated rotational strengths with the CD signals of the complexes supported the structures. These allowed to identify the main interactions of the KP enantiomers with surrounding amino acids at short distances, that limit significantly KP mobility in both sites. In the primary binding site S(+) is close to Tyr 409 in subdomain IIIA (Sudlow site II), and R(-) is close to Trp 212 and His 240 in subdomain IIA (Sudlow site I). The same sites are involved in the formation of 2:1 complexes. The equilibrium structures are characterized by marked geometrical distortion of KP.

Licochalcone A bound to bovine serum albumin: a spectroscopic, photophysical and structural study.

The interaction of Licochalcone A (LA) with bovine serum albumin (BSA) was studied by circular dichroism (CD), UV-Vis absorption, fluorescence and laser flash photolysis. The most stable 1 : 1 and 2 : 1 LA : BSA complexes were spectroscopically characterized. Two protein sites of similar affinity are involved in the LA association with both stoichiometries. The fluorescence quantum yield was found to be higher by ca. one order of magnitude for bound LA than for the free molecule. The emission lifetime strongly depended on the protein site. Binding induced an increase in the radiative rate constant for one location and a decrease of the non-radiative rate in the other location. Two LA triplets were evidenced in the protein environment, the first one shorter-lived and the second one longer-lived than in buffer. The BSA fluorescence was quenched in the complexes. FRET was found to be inefficient. Molecular mechanics (MM), molecular dynamics (MD) and quantum mechanical calculations of rotational strength combined with CD data afforded the likely structures of the complexes. One, involving the interaction of LA with Trp212 in domain II, was able to account for most of the observed photophysical effects. MM and MD calculations also showed LA associates in domain III, the lowest energy complex being one with the drug close to Tyr409.