Metal Coordination Properties of a Chromophoric Desferrioxamine (DFO) Derivative: Insight on the Coordination Stoichiometry and Thermodynamic Stability of Zr4+ Complexes

Desferrioxamine (DFO) is the current “gold standard” chelator for ⁸⁹Zr⁴⁺, which is used to label monoclonal antibodies for applications in immunopositron emission tomography. Recently, controversial data have been reported regarding the speciation and the stability of the complexes formed by DFO with Zr⁴⁺ in solution. To shed some light on this point, we studied the coordination properties in solution ofa chromophoric DFO derivative bearing a substituted pyrimidine residue (DFO–Pm) toward several metal ions (Zr⁴⁺, Cu²⁺, Zn²⁺, Mg²⁺, Ca²⁺, Na⁺, K⁺). Potentiometric titrations showed that DFO–Pm and pristine DFO form complexes with very similar stoichiometry and stability. DFO–Pm, which can consequently be taken as a model system for DFO, provides a photochemical response to metal coordination that can be used to further define the complexes formed. In the critical case of Zr⁴⁺, spectrophotometric measurements allowed the verification of the formation of 1:1 and 2:3 complexes that, together with 2:2 complexes form the coordination model that was obtained through the use of our potentiometric measurements. Additionally, mass spectrometry measurements verified the formation of 1:1 and 2:3 complexes and showed that 1:2 species can be easily generated through the fragmentation of the 2:3 species. In conclusion, the results obtained with DFO–Pm validate the complexation model of Zr⁴⁺/DFO composed of 1:1, 2:2, and 2:3 metal-to-ligand complexes. Convergences and conflicts with other works are addressed.     

The conductivity of dilute electrolyte solutions: Expanded lee and wheaton equation for symmetrical,unsymmetrical and mixed electrolytes

The conductivity equation of Lee and Wheaton is expanded in a power series in the ionic strength I. Different levels of approximation are analyzed and it is shown that for unsymmetrical electrolytes it is necessary to keep the terms I^3/2lnI and I² to maintain the performance of the full equation.     

Conformational energy contribution to the heat of solution in polymer–solvent systems. Part II. Experimental results

Heats of solution (ΔH_exp) in solvents of increasing thermodynamic power have been measured for four polymers: polystyrene (PS), poly(vinyl acetate) (PVAc), polyisobutylene (PIB) and polydimethylsiloxane (PDMS). After subtraction from ΔH_exp of an interaction term (calculated by the Hildebrand treatment based on solubility parameters) and the excess volume term, the quantity remaining is interpreted as the conformational energy contribution (ΔU_conf) to the heat of solution. ΔU_conf appears to correlate well with some basic conformational properties of the chain, such as the sign of the temperature coefficient of unperturbed dimensions derived from solution properties, and shows a monotonic behavior with α, the expansion coefficient of the polymer coil in the final solution. Numerical values of ΔU_conf, at least for those cases in which polymer solubility parameters are known with some certainty, are much larger than those evaluated from rubber elasticity experiments (through the experimentally accessible value of the energy component of the force of retraction im simple elongation).     

Electroproduction of hadrons in nuclei

Recent results from HERMES and expectations from Jlab in the hadron leptoproduction of nuclei are presented. The possible interpretations in terms of medium modifications of the parton fragmentation function and the implications on the parton energy loss are discussed.     

2-Isoxazoline derivatives. Part I. A base-promoted fragmentation of 2-isoxazolines

The action of bases on 3-aryl (or alkyl)-5-acyl-2-isoxazolines has been shown to give rise to the corresponding aromatic (or aliphatic) nitriles and α-diketones by cleavage of the O-N and C₃? C₄ bonds of the heterocyclic ring. This fragmentation reaction has been extended to other 2-isoxazolines substituted in the 5-position with electron-attracting groups.     

Transfer reaction and molecular weight distribution in the anionic polymerization of formaldehyde

The anhydrous formaldehyde polymerization is examined. The influence of initiator and monomer concentration on the molecular weight and molecular weight distribution are emphasized. A mechanism for the transfer to the monomer is introduced. This mechanism is confirmed by experimental results and leads to the formation of formyl end groups. The influence of various initiators on the transfer reaction also is evaluated.     

Influence of environmental factors on composition of volatile constituents and biological activity of Helichrysum italicum (Roth) Don (Asteraceae)

The biovariability of Helichrysum italicum (Roth) Don grown wild in Calabria and Sardinia (Italy) was reported. This species has been characterized through the detection, isolation and quantitative evaluation of chemical markers (alpha-terpinolene, trans-cariophyllene and neryl acetate) by GC and GC-MS. Antioxidant activity of the methanolic H. italicum extracts using DPPH and beta-carotene bleaching test showed that the Calabrian samples were more active than those from Sardinia. The antibacterial activity of all extracts evidenced the best performance on the Gram positive bacteria particularly on Micrococcus luteus. Moreover, antifungal activity of all extracts was also tested evidencing important results particularly on the phytopathogene fungus Pythium ultimum. In general, as regards the antifungal activity, the extracts from Sardinia were more active than those from Calabria. The phytochemical analysis and the biological activity data suggested a possible use of these plant matrices in alimentary, cosmetic and pharmaceutical fields.     

Solid-phase convergent synthesis of a benzimidazolone library via the combination of two smaller arrays of carboxylic acids and secondary amines

The concept of convergent synthesis can be extended to combinatorial chemistry in order to obtain collections of products characterized by considerable chemical diversity and a certain molecular complexity. In this work, a library consisting of three carboxylic acids containing a benzimidazolonic functionality with variations at two positions was synthesized on solid phase. After cleavage, this library was combined with a second library consisting of 16 solid-supported amines containing two points of variation. IRORI technology was used for the split-and-mix synthesis of the final 48 members library.