A functionalized noncovalent macrocyclic multiporphyrin assembly from a dizinc(II) bis-porphyrin receptor and a free-base dipyridylporphyrin

The bis-porphyrin system ZnP(2), in which two zinc porphyrins are connected by a phenanthroline linker in an oblique fashion, acts as a bifunctional receptor towards the complexation of free-base meso-5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin (4'-cis DPyP). In solution, NMR spectroscopy evidenced quantitative formation of the tris-porphyrin macrocyclic assembly ZnP(2)(4'-cis DPyP), in which the two fragments are held together by two axial 4'-N(pyridyl)-Zn interactions. The remarkable stability of the edifice (an association constant of about 6x10(8) M(-1) was determined by UV/Vis absorption and emission titration experiments in toluene) is due to the almost perfect geometrical match between the two interacting units. The macrocycle was crystallized and studied by X-ray diffraction, which confirmed the excellent complementarity of the two components. Photoinduced energy transfer from the singlet excited state of the zinc porphyrin chromophores to the free-base porphyrin occurs with an efficiency of 98 % (k(en)=2x10(10) s(-1) in toluene, ambient temperature) with a mechanism consistent with a dipole-dipole process with a low orientation factor.     

Variable strategy toward carbasugars and relatives. 6. Diastereoselective synthesis of 2-deoxy-2-amino-5a-carba-beta-L-mannopyranuronic acid and 2-deoxy-2-amino-5a-carba-beta-L-mannopyranose

Efficient, total syntheses of novel 2-deoxy-2-amino-5a-carba-beta-L-mannopyranuronic acid (1) and 2-deoxy-2-amino-5a-carba-beta-L-mannopyranose (2), a positional stereoisomer of validamine, have been achieved in 28% and 24% overall yields and in 12 steps and 13 steps, respectively, from 2-[(tert-butyldimethylsilyl)oxy]furan (3) and (2S)-2,3-O-isopropylideneglyceraldehyde N-benzyl imine (4) via two highly diastereoselective Mukaiyama aldol-related chemical maneuvers. The strategy, which furnishes the targeted carbasugars in enantiopure forms, allows for complete control of the configuration at all five contiguous stereocenters of the targets by utilizing the sole element of chirality present in the aldimine progenitor 4.     

Sulle funzioni fortemente continue a valori in un gruppo topologico

In una nota del 1976 C. Constantinescu [2], fa osservare che per una misura μ, definita in un δ-anelloR, a valori in un gruppo topologico e non verificante la countable chain condition, i μ-atomi non sono identificati, come nel caso classico, da particolari elementi diR ma sono parti diR godenti di opportu vista è ripreso in [3] da A. B. d’Andrea e P. de Lucia per lo studio degli atomi di una funzione finitamente addittiva in un anello. Nella presente nota si fa vedere che (n. 2), dando un’opportuna definizione di insieme μ-atomico, un μ-atomo può sempre essere individuato da un elemento diR e si stabiliscono poi (n. 3) delle relazioni fra le funzioni fortemente continue e le funzioni prive di atomi. Nel n. 4, infine, sono dimostrate alcune proprietà delle funzioni a due valori.     

Individual Reduction Potentials of the Iron Ions in Fe(2)S(2) and High-Potential Fe(4)S(4) Ferredoxins

The DelPhi program package has been used to confirm that the span in reduction potentials among high-potential Fe(4)S(4) ferredoxins must be mainly ascribed to the net protein charges arising from acidic and basic residues. Subsequently, the order of the individual reduction potentials of the iron ions in Fe(2)S(2) ferredoxins as found from NMR spectroscopy was explained mainly on the basis of different solvation contributions to the electrostatic potential. The individual reduction potentials of the iron ions in high-potential Fe(4)S(4) ferredoxins, again available from NMR spectroscopy, are only qualitatively reproduced. It is proposed that the protein triggers a distortion in the cluster which would be a further contribution to the electrochemical inequivalence of the individual iron ions.     

The transport of amino acids by 18-crown-6 through liquid membranes

The possibility of separating in cationic form some -amino acids (L-Methionine, L-Leucine, L-Isoleucine, L-Valine, L-Phenylalanine, L--Alanine and L-Cysteine) from mixtures in the presence of picrate anion has been investigated by means of active transport assisted by a pH gradient through liquid membranes. 18-Crown-6 in 1,2-dichloroethane has been used as a selective carrier. The effect of stirring rates at different volumes of the membrane, suggests a diffusional rate-limiting process of the amino acid transport.     

Determining the structure and mode of action of microbisporicin, a potent lantibiotic active against multiresistant pathogens

Antibiotics blocking bacterial cell wall assembly (beta-lactams and glycopeptides) are facing a challenge from the progressive spread of resistant pathogens. Lantibiotics are promising candidates to alleviate this problem. Microbisporicin, the most potent antibacterial among known comparable lantibiotics, was discovered during a screening applied to uncommon actinomycetes. It is produced by Microbispora sp. as two similarly active and structurally related polypeptides (A1, 2246-Da and A2, 2230-Da) of 24 amino acids linked by 5 intramolecular thioether bridges. Microbisporicin contains two posttranslational modifications that have never been reported previously in lantibiotics: 5-chloro-trypthopan and mono- (in A2) or bis-hydroxylated (in A1) proline. Consistent with screening criteria, microbisporicin selectively blocks peptidoglycan biosynthesis, causing cytoplasmic UDP-linked precursor accumulation. Considering its spectrum of activity and its efficacy in vivo, microbisporicin represents a promising antibiotic to treat emerging infections.     

High throughput synthesis of polyesters using entropically driven ring-opening polymerizations

Copolyesters were synthesized in a high throughput (HT) manner and in high yield on ca. a 90 mg scale using entropically driven ring-opening polymerizations (ED-ROPs). This synthetic approach is a valuable addition to the HT polymer synthesis arsenal in that it allows condensation-type polymers with relatively large repeat units, such as those in poly(ethylene terephthalate) and poly(butylene terephthalate), to be obtained easily. The synthetic procedure involved taking mixtures of the appropriate macrocyclic oligoesters and heating them together under neat conditions at 250-300 degrees C for 2 h in the presence of 0.1 mol % of di- n-butyltin oxide or tetra- n-butylammonium tetrafluoroborate. In most cases Mw values were >25,000 and, as expected for ED-ROPs, the polydispersity indices were close to 2.0. Higher molecular weights could be obtained by using longer reaction times, but this might lead to product decomposition. The method worked well for esters formally derived from aliphatic or aromatic acids and alcohols, but less well for esters derived from phenols. Attempts were also made to synthesize copolymers by mixing together the two homopolymers and heating with a catalyst. These reactions were successful in a few instances, but generally, they were not. This is probably because the homopolymers did not mix well. An aluminum reaction block with 36 wells lined with Teflon cups, that fitted snugly in a cylindrical Buchi oven, was the most successful method for carrying out syntheses in an HT manner.     

A bifurcated pathway to thiazoles and imidazoles using a modular flow microreactor

A scalable method for the preparation of 4,5-disubstituted thiazoles and imidazoles as distinct regioisomeric products using a modular flow microreactor has been devised. The process makes use of microfluidic reaction chips and packed immobilized-reagent columns to effect bifurcation of the reaction pathway.     

Phototoxicity and cytotoxicity of chlorophyll a/cyclodextrins complexes on Jurkat cells

The aggregation status of chlorophyll a (Chl a) and the ability of four cyclodextrins, hydroxypropyl-beta-cyclodextrin (HP-beta-CD), hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD), heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DIMEB), and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TRIMEB), to solubilize the pigment in the complete cellular medium RPMI 1640 was estimated by means of UV-Vis absorption and static resonance light scattering (RLS) measurements. The results indicate that the pigment interacts with cyclodextrins in the cellular medium differently to that observed in water. The cytotoxic and phototoxic activity of these complexes towards human leukemia T-lymphocytes (Jurkat cells) was tested by means of experiments aimed to discriminate between the intrinsic toxicity and the toxicity induced by light. The overall data indicate that the HP-beta-CD is the cyclodextrins having the best characteristics to form with Chl a a potential supramolecular system for the photodynamic therapy.     

Mentha pulegium L.: A Plant Underestimated for Its Toxicity to Be Recovered from the Perspective of the Circular Economy

The aim of the study was to investigate the micromorphology of Mentha pulegium leaves and flowers harvested in three different Sicilian (Italy) areas with peculiar pedo-climatic conditions, and to characterize the phytochemical profile, the phytotoxic activity, and the eco-compatibility of their essential oils (EOs) for potential use as safe bioherbicides. Light microscopy (LM) and scanning electron microscopy (SEM) highlighted that M. pulegium indumentum consists of non-glandular and glandular trichomes of different types. Peltate trichomes of plants from the different sites showed few significant differences in dimension and abundance, but they were characterized by a surprisingly high number of secretory cells both in leaves and flowers. Phytochemical analyses showed that oxygenated monoterpenes were the most abundant class in all the EOs investigated (92.2–97.7%), but two different chemotypes, pulegone/isomenthone and piperitone/isomenthone, were found. The complex of morphological and phytochemical data indicates that soil salinity strongly affects the expression of the toxic metabolite pulegone, rather than the EO yield. Phytotoxicity tests showed a moderate activity of EOs against the selected species as confirmed by α-amylase assay. Moreover, the low toxicity on brine shrimp provided a rationale for the possible use of investigated EOs as eco-friendly herbicides.