The unusual binding abilities of the His-analogue of Arg-vasopressin towards Cu2+

A new vasopressin analogue, [His(1,6)]AVP, was synthesized and characterized by potentiometric measurements as well as by UV-Vis, CD and EPR spectroscopy. At the physiological pH the peptide forms a stable complex with Cu(2+) ions which is characterized by the {NH(2), N(Im), N(Im(macrochelate))} binding mode. The replacement of both Cys by His residues in the vasopressin sequence results in a very significant increase in the efficiency of Cu(2+) binding.     

Liquid-vapor equilibrium of the systems butylmethylimidazolium nitrate-CO2 and hydroxypropylmethylimidazolium nitrate-CO2 at high pressure: influence of water on the phase behavior

Ionic liquids (IL) are receiving increasing attention due to their potential as "green" solvents, especially when used in combination with SC-CO2. In this work liquid-vapor equilibria of binary mixtures of CO2 with two imidazolium-based ionic liquids (IL) with a nitrate anion have been experimentally determined: butylmethylimidazolium nitrate (BMImNO3) and hydroxypropylmethylimidazolium nitrate (HOPMImNO3), using a Cailletet apparatus that operates according to the synthetic method. CO2 concentrations from 5 up to 30 mol % were investigated. It was found that CO2 is substantially less soluble in HOPMImNO3 than in BMImNO3. Since these ILs are very hygroscopic, water easily can be a major contaminant, causing changes in the phase behavior. In case these Ils are to be used in practical applications, for instance, together with CO2 as a medium in supercritical enzymatic reactions, it is very important to have quantitative information on how the water content will affect the phase behavior. This work presents the first systematic study on the influence of water on the solubility of carbon dioxide in hygroscopic ILs. It was observed that the presence of water reduces the absolute solubility of CO2. However, at fixed ratios of CO2/IL, the bubble point pressure remains almost unchanged with increasing water content. In order to explain the experimental results, the densities of aqueous mixtures of both ILs were determined experimentally and the excess molar volumes calculated.     

De novo refolding and aggregation of insulin in a nonaqueous environment: an inside out protein remake

While thermodynamic penalties associated with protein-water interactions are the key driving force of folding, perturbed hydration of destabilized protein molecules may trigger aggregation, which in vivo often causes cellular and histological damage. Here we show, that the denatured state of an alpha-helical protein, insulin, converts to a non-native beta-sheet-rich structure upon de novo "refolding" in an anhydrous environment. The beta-pleated conformer precipitates from solutions of DMSO-denatured insulin upon dilution with chloroform. DMSO destroys hydrogen bond network of the native protein acting as a strong acceptor of main chain hydrogen bonds. Upon the addition of chloroform, which is a weak hydrogen bond donor per se, competitive hydrogen bonds between DMSO and chloroform are formed. This leads to the release of unfolded insulin molecules. In the absence of water, the imminent saturation of polypeptide's dandling hydrogen bonds does not produce the native and predominantly alpha-helical state but a beta-sheet-rich structure, which is morphologically and spectrally distinct from insulin amyloid fibrils. Unlike insulin fibrils, the beta-sheet conformer is metastable and refolds spontaneously to the native form in an aqueous environment. This implies that "folding" in the absence of water results in inefficient burial of hydrophobic side-chains, and thermodynamic frustration at the water-protein interface.     

Equilateral triangles on a Jordan curve and a generalization of a theorem of Dold

Let be a Jordan curve in the plane. It is a simple topological riddle to determine if there is an equilateral triangle with vertices on γ. By reformulating this question in the paradigm of configuration spaces and test maps, we can solve this riddle using a Borsuk-Ulam type theorem obtained using equivariant methods.     

Synthetic studies directed toward dideoxy lomaiviticinone lead to unexpected 1,2-oxazepine and isoxazole formation

In the course of studies directed toward the synthesis of dideoxy lomaiviticinone, 3-(nitromethyl)cyclohexenones 2a (X = H) and 2b (X = I) were prepared. The corresponding enolates were reacted with naphthazarin (1) and unexpectedly afforded 1,2-oxazepine 3 and isoxazole 4, respectively. Rationale for their formation is proposed.     

Controlling the macrocycle size by the stoichiometry of the applied template ion

Reaction of 4-tert-butyl-2,6-diformylphenol with (1R,2R)- or (1S,2S)-1,2-diaminocyclohexane in the presence of 1 equivalent of Zn(2+) ions leads to selective formation of a chiral 2+2 macrocycle. Application of 0.5 equivalent of Zn(2+) ions under the same conditions leads to selective formation of a chiral 3+3 macrocycle, which forms a cavitand-shaped trinuclear double-decker complex with Zn(II).     

Thermochromic discotic 6-oxoverdazyls

6-Oxoverdazyls 1b[n], substituted with three 3,4,5-trialkoxyphenyl groups (n = 8 and 10), exhibit a columnar hexagonal phase (Col(h)) below 130 °C. They display reversible color change from red to green at the transition to the isotropic phase. XRD and magnetization data do not support dimerization of the radicals in the mesophase.     

The synthesis of opiorphin and studies on its binding ability toward Cu(II)

Opiorphin (OPI) is an endogenous pentapeptide isolated from human saliva. A characteristic feature of this peptide is the presence of an N-terminal Gln residue. The synthesis and binding abilities of opiorphin toward Cu(II) ions are described. The use of potentiometric and spectroscopic methods allows us to propose the binding mode of the formed complexes.