Search results for "amine"

Design of chiral magnets: Cyanide-bridged bimetallic assemblies based on cyclohexane-1,2-diamine

2003

Abstract Four magnetic compounds based on chiral ligands trans-(1S,2S)-chxn and trans-(1R,2R)-chxn (chxn: cyclohexane-1,2-diamine), [Ni(trans-(1S,2S)-chxn)2]3[Fe(CN)6]2·2H2O (1), [Ni(trans-(1R,2R)-chxn)2]3[Fe(CN)6]2·2H2O (2), [Cu(trans-(1S,2S)-chxn)2]3[Fe(CN)6]2·4.5H2O (3) and [Cu(trans-(1R,2R)-chxn)2]3[Fe(CN)6]2·4.5H2O (4), are reported. The four compounds are chiral, as confirmed by X-ray analyses and circular dichroism measurements. From the magnetic point of view, 1 and 2 behave as ferromagnets, whereas 3 and 4 show a paramagnetic behavior.

VCD studies on cyclic peptides assembled from L-α-amino acids and a trans-2-aminocyclopentane- or trans-2-aminocyclohexane carboxylic acid.

2010

The increasing interest in peptidomimetics of biological relevance prompted us to synthesize a series of cyclic peptides comprising trans-2-aminocyclohexane carboxylic acid (Achc) or trans-2-aminocyclopentane carboxylic acid (Acpc). NMR experiments in combination with MD calculations were performed to investigate the three-dimensional structure of the cyclic peptides. These data were compared to the conformational information obtained by electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopy. Experimental VCD spectra were compared to theoretical VCD spectra computed quantum chemically at B3LYP/6-31G(d) density functional theory (DFT) level. The good agreem…

Core Histones Are Glutaminyl Substrates for Tissue Transglutaminase

1996

Chicken erythrocyte core histones are glutaminyl substrates in the transglutaminase (TGase) reaction with monodansylcadaverine (DNC) as donor amine. The modification is very fast when compared with that of many native substrates of TGase. Out of the 18 glutamines of the four histones, nine (namely glutamine 95 of H2B; glutamines 5, 19, and 125 of H3; glutamines 27 and 93 of H4; and glutamines 24, 104, and 112 of H2A) are the amine acceptors in free histones. The use of Gln112 of H2A requires a temperature-dependent partial unfolding of the histone, showing that structural determinants are decisive for the glutamine specificity. The structures of H2A and H2B do not appreciably change upon mo…

Separation, isolation and stereochemical assignment of imazalil enantiomers and their quantitation in an in vitro toxicity test

2016

A simple method for the separation of the enantiomers of the fungicide imazalil was developed. Racemic imazalil was separated into its enantiomers with an enantiomeric purity of 99% using HPLC-UV with an enantioselective column (permethylated cyclodextrin) operated in reversed phase mode (water with 0.2% trimethylamine and 0.08% acetic acid and methanol). The absolute configuration of the separated enantiomers was assigned and unequivocally confirmed by optical rotation as well as by vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) combined with ab-initio calculations. The same enantioselective column was also used to develop an HPLC-MS/MS method for the quantifi…

Structural characterisation of the natural membrane-bound state of melittin: a fluorescence study of a dansylated analogue

1997

Abstract The binding of a dansylated analogue of melittin (DNC–melittin) to natural membranes is described. The cytolytic peptide from honey bee venom melittin was enzymatically labelled in its glutamine-25 with the fluorescent probe monodansylcadaverine using guinea pig liver transglutaminase. The labelled peptide was characterised functionally in cytolytic assays, and spectroscopically by circular dichroism and fluorescence. The behaviour of DNC–melittin was, in all respects, indistinguishable from that of the naturally occurring peptide. We used resonance energy transfer to measure the state of aggregation of melittin on the membrane plane in synthetic and natural lipid bilayers. When bo…

Another step toward DNA selective targeting: NiII and CuII complexes of a Schiff base ligand able to bind gene promoter G-quadruplexes

2016

DNA G-rich sequences are able to form four-stranded structures organized in stacked guanine tetrads. These structures, called G-quadruplexes, were found to have an important role in the regulation of oncogenes expression and became, for such a reason, appealing targets for anticancer drugs. Aiming at finding selective G-quadruplex binders, we have designed, synthesized and characterized a new water soluble Salen-like Schiff base ligand and its NiII and CuII metal complexes. UV-Vis, circular dichroism and FRET measurements indicated that the nickel complex can stabilize oncogene promoter G-quadruplexes with high selectivity, presenting no interactions with duplex DNA at all. The same compoun…

Subcomponent self‐assembly of a cyclic tetranuclear Fe(II) helicate in a highly diastereoselective self‐sorting manner

2019

Abstract An enantiomerically pure diamine based on the 4,15‐difunctionalized [2.2]paracyclophane scaffold and 2‐formylpyridine self‐assemble into an optically pure cyclic metallosupramolecular Fe4L6 helicate upon mixing with iron(II) ions in a diastereoselective subcomponent self‐assembly process. The cyclic assembly results from steric strain that prevents the formation of a smaller linear dinuclear triple‐stranded helicate, and hence, leads to the larger strain‐free assembly that fulfils the maximum occupancy rule. Interestingly, use of the racemic diamine also leads to a racemic mixture of the homochiral cyclic helicates as the major product in a highly diastereoselective narcissistic ch…

Thiourea Organocatalysts as Emerging Chiral Pollutants: En Route to Porphyrin-Based (Chir)Optical Sensing

2021

Environmental pollution with chiral organic compounds is an emerging problem requiring innovative sensing methods. Amino-functionalized thioureas, such as 2-(dimethylamino)cyclohexyl-(3,5-bis(trifluoromethyl)phenyl)thiourea (Takemoto’s catalyst), are widely used organocatalysts with virtually unknown environmental safety data. Ecotoxicity studies based on the Vibrio fischeri luminescence inhibition test reveal significant toxicity of Takemoto’s catalyst (EC50 = 7.9 mg/L) and its NH2-substituted analog (EC50 = 7.2–7.4 mg/L). The observed toxic effect was pronounced by the influence of the trifluoromethyl moiety. En route to the porphyrin-based chemosensing of Takemoto-type thioureas, their s…

1981

The interaction of poly(L-glutamic acid) with 3,6-dioxaoctamethylenediamine was studied by circular dichroism spectroscopy under different conditions. In aqueous solution at pH 5,6 and in aqueous 1,4-dioxane (30–50 vol.-%) at pH 7,3 the conformation of poly(L-glutamic acid) was completely changed from α-helical to random coil in the presence of an excess of the diamine.

Reframing Climate Justice : A Three-dimensional View on Just Climate Negotiations

2016

This article proposes reframing the justice discourse in climate negotiations. In so doing, it makes two claims. First, global climate negotiations deserve to be addressed as an issue of justice on their own due to their peculiar characteristics. Second, a multidimensional theory of justice is superior to distributional theories for this task. To support these arguments, I apply the multidimensional theory of justice to global climate negotiations. This analysis reveals that injustice in the negotiations is multidimensional and irreducible to distributional questions. Furthermore, it shows how promoting justice in this broad sense would have significant effect on the negotiation procedures …