Pedro Berci Filho

Photophysical characterization of a 1,4,5,8-naphthalenediimide derivative

Abstract The photophysical properties of N , N -dibutyl-1,4,5,8-naphthalenediimide ( 1 , Scheme 1) were studied using absorption and fluorescence spectroscopy. The absorption and emission spectra of 1 are mirror images and show resolved vibrational structure indicating that 1 is a rigid molecule which does not relax substantially from the initially formed Franck-Condon state. The fluorescence of 1 is rather weak (quantum yield, approximately 0.002), supposedly due to fast intersystem crossing to a close-lying triplet level. Diimide 1 aggregates in acetonitrile and in aqueous medium, but aggregation is prevented by the presence of α-cyclodextrin (α-CD) due to complex formation between α-CD and the butyl substituents of 1 . Diimide 1 displays unusual spectral characteristics in aromatic hydrocarbon solvents, which can be attributed to ground state complex formation between 1 and the aromatic compound. The addition of benzene, toluene and p -xylene to an acetonitrile solution of 1 was followed by fluorescence spectroscopy, and the data obtained were treated as simple 1 : 1 equilibria. Association constants were calculated for the complexes between 1 and the aromatic compounds. The magnitude of the constants suggests that these ground state complexes are basically of the π-stacking type, with no charge transfer character. In the excited state, however, the complexes show polar character, suggesting that electron transfer occurs following excitation.

Efficient Sonochemical Synthesis of 3‐ and 4‐Electron Withdrawing Ring Substituted N‐Alkyl‐1,8‐naphthalimides from the Related Anhydrides

Abstract 1,8‐N‐alkyl‐naphthalimides substituted with electron withdrawing groups were readily prepared in high yields using ultrasound in aqueous media.

Effect of dialkyldimethylammonium vesicles on the thiolysis of p-nitrophenyl acetate

Abstract Cationic surfactant vesicles, prepared by an alcohol injection technique and characterized by gel filtration, are extremely effective at increasing the rate of ester thiolysis at near neutral pH.

Synthesis, characterization and interaction with ionic micelles of tetraacetylated dipyridamole

Abstract Tetraacetylated dipyridamole (Ac-DIP) was synthesized by reaction of dipyridamole (DIP) with acetic anhydride in a quantitative yield. Infrared and NMR spectra showed that the acetylation was complete, yielding the expected new bands and the disappearance of hydroxyl bands in the IR and NMR spectra. Tetraacetylated DIP was analyzed by electronic absorption and fluorescence emission in different solvents. The solubility of Ac-DIP in water is considerably lower than that of DIP, and both the absorption and emission are shifted to the blue denoting a less efficient relaxation to the solvent. Extinction coefficients and quantum yields in ethanol, chloroform and dimethyl sulfoxide are very similar for Ac-DIP and DIP. 1 H and 13 C NMR spectra were obtained in deuterated chloroform and dimethyl sulfoxide and a complete assignment of peaks was obtained. In order to obtain more insight into the properties of Ac-DIP, the interaction of DIP and Ac-DIP with cationic cetyltrimethylammonium chloride (CTAC) and anionic sodium dodecyl sulfate (SDS) micelles was studied. In the presence of micelles the p K a of DIP changes considerably from its value in water: from 5.8 to 4.3 in CTAC and to 7.3 in SDS indicating a considerable interaction with micelles. The p K a of Ac-DIP in SDS is 5.8. For both compounds the interaction with micelles is predominantly hydrophobic in nature but for Ac-DIP it is less sensitive to the charge on the micelle and the degree of ionization of the drug. All the results suggest that Ac-DIP is significantly more hydrophobic than DIP, being probably quite efficient in the interaction with membrane systems. This could be quite relevant for its effect at the cellular level.

Synthesis and Properties of New Paramagnetic Hybrid Bayerite from Al(0)/Naphthalene Dianhydride Reaction

The reaction of Naphthalene 1,4,5,8-dianhydride (NTCDA) with elemental aluminum(0) powder is studied in an aqueous alcoholic KOH mixture to search for the NTCDA anion and dianion electron-adducts. After analyzing various reaction conditions it was found that the reaction yielded a greenish precipitate in 3:1 (v:v) ethanol:water mixture. This powder is composed mainly of aluminum trihydroxide crystallites of bayerite [α-Al(OH3)(s)] and the organic content is approximately 6%. This hybrid material proved to be paramagnetic even after exposure to air for one year and at temperatures up to 200 oC. Typical carbonylic bound to metal IR bands and reflectance UV-VIS spectra demonstrate the entrapment of NTCDA radical anion into the aluminum trihydroxide, hence rendering its green color and a paramagnetic behavior. Thus, besides the understanding of an aluminum reaction in suspension, the entrapment of an organic material (NTCDA) that stays stable as the corresponding radical can provide an interesting option for the synthesis of aluminum trihydroxide composites.