Hierarchical Analysis of Self‐Assembled PEGylated Hexaphenylalanine Photoluminescent Nanostructures

Despite the growing literature about diphenylalanine‐based peptide materials, it still remains a challenge to delineate the theoretical insight into peptide nanostructure formation and the structural features that could permit materials with enhanced properties to be engineered. Herein, we report the synthesis of a novel peptide building block composed of six phenylalanine residues and eight PEG units, PEG₈‐F6. This aromatic peptide self‐assembles in water in stable and well‐ordered nanostructures with optoelectronic properties. A variety of techniques, such as fluorescence, FTIR, CD, DLS, SEM, SAXS, and WAXS allowed us to correlate the photoluminescence properties of the self‐assembled nanostructures with the structural organization of the peptide building block at the micro‐ and nanoscale. Finally, a model of hexaphenylalanine in aqueous solution by molecular dynamics simulations is presented to suggest structural and energetic factors controlling the formation of nanostructures.     

A Convenient ar-SE Laboratory Experiment Avoiding the Use of Sulfuric Acid: the Nitration of Diphenylmethane in Ch2Cl2

The nitration of diphenylmethane to three main isomeric dinitro derivatives, performed with nitric acid in dichloromethane, is proposed as an organic laboratory experiment showing a number of advantages over typical aromatic nitrations in sulfuric acid.     

Coordinating properties of C2-symmetric chiral bis(oxazolinylpyridinyl)dioxolane ligands

Metal complexes of general formula M(L)X₂ and M(L)X₃ [L = (4S,5S)-2,2-dimethyl-4,5-bis{6-[(4,5-dihydro-4-(S)-(1-methylethyl)oxazol-2-yl)pyridin-2-yl]}-1,3-dioxolane] were obtained by reacting, respectively, Co^II, Cu^II, Ni^II, and Zn^II nitrate salts and the Rh^III chloride salt, with a chiral C₂-symmetric bis(oxazolinylpyridinyl)dioxolane (L) ligand, in MeOH/CHCl₃ solution. A single crystal X-ray analysis was carried out on [Ni(L)(OH₂)₂](NO₃)₂ · 2H₂O and the molecular structure of L was also determined. In the free ligand the two symmetric arms are essentially planar and oriented nearly perpendicular to the dioxolane average plane. In the Ni complex one seven-membered and two five-membered chelation rings are formed. The metal atom also lies on the C₂ axis, and two symmetry-related water molecules complete the octahedral coordination environment. Both compounds crystallize in chiral space groups; the ligand crystallizes in orthorhombic system, space group C 2 2 2₁, Z = 4; the nickel complex crystallizes in tetragonal system, space group P 4₃ 2₁ 2, Z = 4.     

Silver(I) and copper(I) complexes supported by fully fluorinated 1,3,5-triazapentadienyl ligands

Synthesis of the perfluorinated 1,3,5-triazapentadiene [N{(CF(3))C(C(6)F(5))N}(2)]H and the use of its conjugate base as a supporting ligand for the isolation of silver(i) and copper(i) complexes are reported. Some of the related chemistry involving [N{(C(3)F(7))C(C(6)F(5))N}(2)](-) (that has bulkier -C(3)F(7) groups on the 1,3,5-triazapentadienyl ligand backbone) is also presented. X-ray crystallographic data show a wide variety of structures ranging from intermolecular, hydrogen-bonded chain structure for [N{(CF(3))C(C(6)F(5))N}(2)]H with a twisted W-shaped N(3)C(2) core, monomeric [N{(CF(3))C(C(6)F(5))N}(2)]Ag(CN(t)Bu)(2) and [N{(C(3)F(7))C(C(6)F(5))N}(2)]Ag(CN(t)Bu)(2) where the κ(1)-bonded triazapentadienyl ligand bonding to the metal fragment via the central nitrogen atom, monomeric [N{(CF(3))C(C(6)F(5))N}(2)]Ag(PPh(3))(2) and [N{(C(3)F(7))C(C(6)F(5))N}(2)]Ag(PPh(3))(2) that feature κ(1)-bonded triazapentadienyl ligand bonding to the metal fragment via one of the terminal nitrogen atoms, to that of the monomeric [N{(CF(3))C(C(6)F(5))N}(2)]Cu(CN(t)Bu)(2) containing a κ(2)-bonded triazapentadienyl ligand and a U-shaped NCNCN ligand backbone. The isocyanide adducts show relatively high ν(CN) values in the IR spectra.     

On-chip pre-concentration and complexation of [¹⁸F]fluoride ions via regenerable anion exchange particles for radiochemical synthesis of Positron Emission Tomography tracers

Microfluidic approaches have demonstrated a relevant impact on radiochemical reactions involving Positron Emission Tomography (PET) nuclides, due to shorter reaction times and smaller precursor quantities. However, little attention has been given to the integration of the initial pre-concentration and drying of radioactive [(18)F]fluoride ions, required for the labeling of radiotracer compounds. In this work we report the design, fabrication and implementation of a glass microfluidic device filled with recyclable anion exchange particles for the repeated recovery of [(18)F] and [(19)F]fluoride ions. The device was first tested with non radioactive [(19)F]fluoride ions and it was shown to repeatedly trap and elute >95% fluoride over 40 successive experimental runs with no decrease in efficiency. The same device was then tested for the trapping and release of [(18)F]fluoride ions over 20 experiments with no measurable decrease in performance. Finally, the [(18)F]fluoride ions were eluted as a K(18)F/K2.2.2 complex, dried by repeated dissolution in acetonitrile and evaporation of residual water, and reacted with ethyl ditosylate (EtDT) leading to the desired product ([(18)F]fluoroethyltosylate) with 96 ± 3% yield (RCY). The overall time needed for conditioning, trapping, elution and regeneration was less than 6 min. This approach will be of great benefit towards an integrated platform able to perform faster and safer radiochemical synthesis on the micro-scale.     

The synthesis and application of polyamino polycarboxylic bifunctional chelating agents

Bifunctional chelating agents (BFCAs) are molecules which contain two different moieties: a strong metal chelating unit and a reactive functional group. The latter is directed to react with amines, thiols, alcohols or other reactive molecules to form stable covalent bonds while the chelating moiety is able to strongly coordinate a metal ion. In this way, it is possible to label a molecule of interest (e.g. an antibody or a peptide) with a metal or a radioactive metal ion. Of all the ligands reported so far, those based on a polyamino polycarboxylic structure are most efficient and are widely employed for the chelation of metal ions. The resulting metal complexes have found a broad range of applications in chemistry, biology and medicine. Diagnostic imaging (MRI, SPECT, PET), molecular imaging, tumour therapy and luminescent materials are only a few examples. The present critical review gives an overview of the syntheses and most important applications of polyamino polycarboxylic BFCAs (334 references).     

A molecular clip throws new light on the complexes formed by a family of cyclam-cored dendrimers with Zn(II) ions. Efficient energy transfer in the heteroleptic complexes

Complexation of Zn(II) ions by cyclam cored dendrimers appended with four (G0), eight (G1) and 16 naphthyl chromophores (G2) at the periphery have been investigated in CH?CN-CH?Cl? 1?:?1 (v/v) solution by absorption and emission, ESI-mass and 1H NMR spectroscopy. The results obtained can be interpreted by the formation of complexes of 2?:?1 dendrimer to metal stoichiometry, at low metal ion concentration, and 1?:?1 complexes upon further addition of Zn(II) ions, for all the dendrimer generations. Upon addition of a molecular clip C2? consisting of two anthracene sidewalls bridged by a benzene group with two sulfate substituents in the para positions, heteroleptic complexes of general formula [GnZnC] are formed. Interestingly, in these complexes, a very efficient quenching (practically 100%) of the dendrimer naphthyl luminescence and sensitization (ca. 90%) of the clip anthracene emission take place. The complex [G2ZnC] exhibits a very high molar absorption coefficient in the UV spectral region owing to the 16 naphthyl chromophores of the dendrimer and the two anthracene units of the clip (ε = 1.7 × 10? M?1 cm?1 at 263 nm). Furthermore, the excitation energy absorbed by the naphthyl chromophores is efficiently funneled to the two anthracene units of the clip, which emits in the blue spectral region.     

Asymmetric Synthesis in the Presence of Cyclodextrins

Oxidative couplings of 2-naphthol, 6-bromo-2-naphthol and2-naphthylamine were achieved at room temperature in the presence of H₂O₂, horseradish peroxidase and a suitable cyclodextrin.2-Thionaphthol behaved differently, yielding the corresponding disulfide. Yields of binaphthyl derivatives were generally excellent, and a fairly good enantiomeric excess was observed. Under similar reaction conditions methyl 2-(6-methoxy-2-naphthyl) propanoate, when treated with esterase in the presence of cyclodextrin, yielded naproxen (a well-known anti-inflammatory drug) with a good enantiomeric excess. No reaction product was detected in the absence of cyclodextrin. Cyclodextrins do not act as simple transfer agents.     

12-Acylindolo[1,2-c]quinazolines by palladium-catalyzed cyclocarbonylation of o-alkynyltrifluoroacetanilides

6-Trifluoromethyl-12-acylindolo[1,2-c]quinazolines are prepared in high yield through the palladium-catalyzed reaction of bis(o-trifluoroacetamidophenyl)acetylene with aryl or vinyl halides and triflates. The reaction, which tolerates a variety of important functional groups, probably involves the formation of a 3-acyl-2-(o-trifluoroacetamidophenyl)indole intermediate, followed by its cyclization to the indoloquinazoline product. [reaction: see text]