The interactions between dendrimers and different types of drugs are nowadays one of the most actively investigated areas of the pharmaceutical sciences. The interactions between dendrimers and drugs can be divided into: internal encapsulation, external electrostatic interaction, and covalent conjugation. In the present study, we investigated the potential of poly(amidoamine) (PAMAM) dendrimers for solubility of four iminodiacetic acid derivatives. We reported that PAMAM dendrimers contribute to significant solubility enhancement of iminodiacetic acid analogues. The nature of the dendrimer–drug complexes was investigated by 1H NMR and 2D-NOESY spectroscopy. The 1H NMR analysis proved that the water-soluble supramolecular structure of the complex was formed on the basis of ionic interactions between terminal amine groups of dendrimers and carboxyl groups of drug molecules, as well as internal encapsulation. The 2D-NOESY analysis revealed interactions between the primary amine groups of PAMAM dendrimers and the analogues of iminodiacetic acid. The results of solubility studies together with 1H NMR and 2D-NOESY experiments suggest that the interactions between PAMAM dendrimers of generation 1–4 and derivatives of iminodiacetic acid are based on electrostatic interactions and internal encapsulation.Electronic supplementary material The online version of this article (doi:10.1007/s10867-012-9277-5) contains supplementary material, which is available to authorized users.

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Gas-phase pyrolysis of 2-methoxy-2-methylsulfanyl-5,5-dimethyl-2,5-dihydro[1,3,4]oxadiazole (1) (also known as 2-methoxy-5,5-dimethyl-2-methylthio-2,5-dihydro[1,3,4]oxadiazole and 2-methoxy-2-methylthio-5,5-dimethyl-Δ3-l,3,4-oxadiazoline) in the source of an UV photoelectron spectrometer, by means of a CW CO2 laser as directed heat source, gave a photoelectron (PE) spectrum that included ionization bands belonging to acetone and methoxy(methylthio)carbene (3). Photoelectron spectra of authentic samples of (E)-1,2-dimethoxy-1,2-dimethyl thioethene (4), (Z)-1,2-dimethoxy-1,2-dimethylthioethene (5), S-methyl thioethanoate (6), and O-methyl ethanethioate (7), which can be derived by dimerization and rearrangement of the carbene, established that these compounds are not present in the pyrolysate. DFT calculations at the B3PW91/6-31+G(d,p) level and simulation of PE spectra at the B3LYP/6-31+G(d,p) level were instrumental in the interpretation of the experimental results. From the available experimental and calculated data, 3 is formed in a Sickle conformation upon pyrolysis of 1. Transition states for the rearrangement of 3 were examined with QTAIM. Key words: 2-methoxy-5,5-dimethyl-2-methylthio-2,5-dihydro[1,3,4]oxadiazole, pyrolysis, He(I) photoelectron spectroscopy, methoxy(methylthio)carbene, DFT calculations, QTAIM.

Reaction of ferrocene and 3,3‘,4,4‘-tetramethyl-1,1‘-diphosphaferrocene with diketene in the presence of BF3·Et2O affords the BF2 chelates of acetoacetylated metallocenes 2a,b. The crystal structures of these complexes have been determined by X-ray diffraction. When the reaction is carried out in the presence of AlCl3, metallocene 1,3-diketones 3a,b are formed.