Search results for "circular"
showing 10 items of 856 documents
Protein aggregation/crystallization and minor structural changes: universal versus specific aspects.
2007
AbstractProtein association covers wide interests in biophysics, protein science, and biotechnologies, and it is often viewed as governed by conformation details. More recently, the existence of a universal physical principle governing aggregation/crystallization processes has been suggested by a series of experiments and shown to be linked to the universal scaling properties of concentration fluctuations occurring in the proximity of a phase transition (spinodal demixing in the specific case). Such properties have provided a quantitative basis for capturing kinetic association data on a universal master curve, ruled by the normalized distance of the state of the system from its instability…
Innovation strategies geared toward the circular economy: A case study of the organic olive-oil industry
2018
Circular Economy (CE) focuses on the (re)design of processes and products aiming to minimize negative environmental impact, by reducing the use of non-renewable resources, increasing products durability, improving waste management and enhancing the market for secondary raw materials. In the management field very few contributions deal with the topic of CE as a model that firms can implement from a business model perspective. The aim of the present study is to describe, by using a case study in olive oil industry, how firms in practice adapt their business model towards CE paradigm and the influence of personal drivers and stakeholders in this adaptation. The findings reveal that circular ec…
Synthesis and Characterization of Adducts Derived from the syn-Diastereomer of Benzo[a]pyrene 7,8-Dihydrodiol 9,10-Epoxide and the 5‘-d(CCTATAGATATCC…
1996
5'-d(CCTATAGATATCC) was reacted with each syn-enantiomer of trans-7,8-dihydroxy 9,10-epoxy 7,8,9,10-tetrahydrobenzo[a]pyrene (syn-BPDE). The (-)-enantiomer yielded one dominating adduct, whereas the (+)-enantiomer resulted in two major adducts. As indicated by optical spectroscopic methods, the major adduct derived from both (-)- and (+)-syn-BPDE involves cis addition of the C-10 position of the diol epoxide to the exocyclic amino group of deoxyguanosine [(-)-syn-BPDEc-N2-dG and (+)-syn-BPDEc-N2-dG, respectively], whereas the minor (+)-syn-BPDE adduct is identical to a trans adduct [(+)-syn-BPDEt-N2-dG]. The cis adducts as well as the (+)-syn-BPDEt-N2-dG adduct are chemically stable for sev…
Assignment of the Absolute Configuration and Total Synthesis of (+)-Caripyrin
2014
The antifungal secondary metabolite (+)-caripyrin was studied by vibrational circular dichroism spectroscopy. Analysis of the recorded data, with the Boltzmann weighted-average of the spectra calculated at the B3LYP/6-311G(d,p) level of theory for all relevant conformers, unequivocally proved the (R,R)-configuration for the dextrorotatory natural product. Based on this finding, a short enantioselective synthesis of (+)-caripyrin was developed.
DNA interaction of CuII, NiII and ZnII functionalized salphen complexes: studies by linear dichroism, gel electrophoresis and PCR.
2013
The interaction of salphen-type NiII, CuII and ZnII complexes with native DNA was investigated by exploiting linear dichroism experiments. The NiII complex behaves as a typical intercalator, binding strongly and stiffening and unwinding the DNA. The strength of the DNA interaction is slightly weaker for the copper complex and much weaker for the zinc complex. Plasmid-DNA gel electrophoresis experiments indicated that while CuII and ZnII complexes do not induce the unwinding of supercoiled DNA, the NiII complex has a nuclease activity without the addition of external agents. On the other hand, as shown in the PCR assays, we demonstrate that, at the used concentrations, only the CuII complex …
Flipping Motion To Bias the Organized Supramolecular Polymerization of N-Heterotriangulenes
2019
Synergistic experimental and theoretical studies have allowed the disentangling of the possible pathways for the supramolecular polymerization of a series of dicyanovinyl-bridged N-heterotriangulene (NHT) derivatives bearing benzamide units with achiral (1a) and chiral (1b,c) side chains. The synthesis of these bowl-shaped, self-assembling units yields a mixture of monomeric species with C3- and C1-symmetry. Both monomeric species are able to self-assemble into different supramolecular aggregates with sufficient stability to coexist in freshly prepared solutions. The dissimilar ratio of the aggregates initially generated results in different spectroscopic features and, more specifically, in…
Structure elucidation of the adducts formed by fjord region Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxides with deoxyguanosine.
1999
Model adducts to be used in the identification of biologically formed adducts were synthesized by reaction of fjord-region dibenzo[a,l]pyrene 11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE) and deoxyadenosine (dA). The (+/-)-anti-DB[a,l]PDE was reacted with dA in dimethylformamide at 100 degrees C for 30 min to give four DB[a, l]PDE-14-N(6)dA adducts: (-)-anti-trans (26%), (+)-anti-trans (26%), (-)-anti-cis (17%), and (+)-anti-cis (17%). The (+/-)-syn-DB[a,l]PDE was reacted with dA under the same conditions to yield four DB[a, l]PDE-14-N(6)dA adducts and one N7Ade adduct: (+)-syn-cis (19%), (+)-syn-trans (13%), (-)-syn-cis (19%), (-)-syn-trans (13%), and (+/-)-syn-DB[a,l]PDE-14-N7Ade (22%). T…
Bis- and Trisamides Derived From 1′-Aminoferrocene-1-carboxylic Acid and α-Amino Acids: Synthesis and Conformational Analysis
2009
Ferrocene derivatives with one or two achiral and chiral arms based on α-amino acids (Gly, l-Ala, l-Val) attached to the cyclopentadienyl rings were prepared by solution-phase peptide synthesis from N-acetyl- and N-Boc-protected 1′-aminoferrocene-1-carboxylic acids (Boc = tert-butoxycarbonyl). The conformational preference in the solid state of selected examples was elucidated by X-ray crystallography. The chiroptical properties of chiral bis- and trisamides were investigated by circular dichroism (CD) spectroscopy in solution. The conformational preference was studied by NMR and IR spectroscopy, as well as by molecular modeling (DFT). For the bisamides, a conformational library is observed…
(Strept)avidin as host for biotinylated coordination complexes: stability, chiral discrimination, and cooperativity
2005
Incorporation of a biotinylated ruthenium tris(bipyridine) [Ru(bpy)₂(Biot-bpy)]²⁺ (1) in either avidin or streptavidin-(strept)avidin-can be conveniently followed by circular dichroism spectroscopy. To determine the stepwise association constants, cooperativity, and chiral discrimination properties, diastereopure (Λ and δ)-1 species were synthesized and incorporated in tetrameric (strept)avidin to afford (δ-[Ru(bpy)₂(Biot-bpy)]²⁺)x⊂avidin, (Λ- [Ru(bpy)₂(Biot-bpy)]²⁺)x⊂avidin, (δ-[Ru(bpy)₂(Biot- bpy)]²⁺)x⊂streptavidin, and (Λ-[Ru(bpy)₂(Biot-bpy)]²⁺) x⊂streptavidin (x = 1-4) For these four systems, the overall stability constants are log β₄ = 28.6, 30.3, 36.2, and 36.4, respectively. Critical…
A Stereochemically Driven Supramolecular Polymerisation
2018
Anthracyclines self-assemble in water into dimers. In the presence of sufficiently high salt (NaCl) concentrations, solutions of the antibiotic doxorubicin, but not those of the closely related molecules daunomycin and epirubicin, turn into gels barely compatible with the presence of small oligomers. The use of spectroscopic, scattering, imaging and computational techniques, allowed light to be shed on the self-assembly process that triggered doxorubicin gelification. A complex picture emerged, with doxorubicin molecules assembled into long, highly chiral, supramolecular aggregates made of hundreds of units, showing redshifted fluorescence spectra, very short fluorescence lifetimes and smal…