Thermodynamic characterisation of RNAase a in the presence of urea and GuHCl

It is presented a study concerning the influence of guanidinium chloride (GuHCl) and urea on thermal stability of Bovine Pancreatic Ribonuclease A (RNAase A) at differentpH values. As expected, at increasing the denaturant concentration, the protein thermostability decreases. This is shown by a decrease of both the thermodynamic parameters, temperature and heat effect, characterising the denaturation process. In order to analyse the calorimetric curves we adopt a statistical thermodynamic approach. The individual one-dimensional DSC profiles have been expanded into another dimension by varying the GuHCl concentration, so that a heat capacity surface is defined for eachpH. By means of the ICARUS program, developed in our laboratory, we accomplish a two dimensional deconvolution of the experimental data linking the binding equilibrium to the denaturation process. This analysis provides a well founded and complete statistical thermodynamic characterisation of denaturation process of RNAase A in the presence of GuHCl and allows to calculate the thermodynamic parameters associated to the binding of denaturant molecule.     

Photoinduced Double Addition of Acetylene to 3-Oxocyclopent-1-ene-1-carbonitrile or 3-oxocyclopent-1-enyl acetate leading to 2,3-dihydro-1H-inden-1-one and other rearranged products

UV Irradiation of 3-oxocyclopent-1-enyl acetate ( 17 ) and acetylene in MeCN at 0° gives, besides the product of normal enone-alkyne [2 + 2] cycloaddition (cis-4-oxobicyclo[3.2.0] hept-6-en-1-yl acetate, 18 ) and its product of oxa-di-π-methane rearrangement (5-oxotricyclo[4.1.0.0^2,7]hept-2-yl acetate, 19 ), unexpected products of further addition of a molar equivalent of acetylene. These are indanone ( = 2,3-dihydro-1H-inden-1-one, 16 ), in 21% yield, cis-1-cisoid-1,2-cis-2- ( 20 ) and cis-1-transoid-1,2-cis-2-7-oxotricyclo[4.3.0.0^2,5]non-3-en-1-yl acetate ( 21 ), 4-oxo-7-‘exo’-vinyltricyclo[3.2.0.0^2,6]hept-2-yl acetate ( 22 ), cis-4-oxo-6-‘endo’- ( 23 ) and cis-4-oxo-6-‘exo’-vinylbicyclo[3.2.0]hept-1-yl acetate ( 24 ), and cis-4-oxo-7-‘exo’-vinylbicyclo[3.2.0]hept-1-yl acetate ( 25 ). At least in part, indanone must be formed via intermediates 20 and 21 . In fact, on heating a 9:1 mixture 20/21 , indanone is obtained quantitatively. With 3-oxocyclopent-1-ene-1-carbonitrile ( 15 ) in place of 17 , indanone is formed in lower (8%) yield besides much tars.     

Oxidative Breaking of Long-Chain Acetylenic Enol Ethers of Glycerol of the Marine Sponges Raspailia pumila and of Model Compounds with Aerial Oxygen

The raspailynes (novel long-chain enol ethers of glycerol having the enol ethers double bond conjugated in sequence, to an acetylenic and an olefinic bond, isolated from the North-East-Atlantic sponges Raspailia pumila and R. ramosa) are stable under normal hydrolytic conditions for enol ethers. In contrast, when their solutions are evaporated, these lipids such as raspailyne Bl (=(?))-3-[(1Z,5Z)-(tetradeca-1,5-dien-3-ynyl)oxy]-1,2-propanediol;(?- 2 ) rapidly react with aerial O₂ under normal laboratory-daylight conditions, with rupture of the C=C enol ether bond to give 1-O-formylglycerol ( 3 ) and an aldehyde (such as tridec-4-en-2ynal( 4 ) from (?)- 2 ). This reaction must be caused by triplet O₂, since thermally generated singlet O₂ has no effect on (?)- 2 in solution. That the mere presence of an enol-ether moiety conjugated to an acetylenic group is responsible for such a behaviour is demonstrated with the model compounds 1-methoxypentadec-1-en-3-yn-5-ol ( 6a ) and its 5-O-acetyl or 5-O-tetra-hydropyranyl derivatives 6b and 6c , respectively. Resistance to both hydroytic conditions and singlet O₂ of these compounds is thought to arise from electron depletion at the enol-ether C(beta;) atom by the acetylenic group. Plausible reaction pathways for enol-ether bond rupture in these compounds by aerial O₂ are outlined.     

Syntheses of 2-hydroperoxy-and 2-hydroxy-2H-imidazoles

Oxidation of fully substituted imidazoles 1 by singlet oxygen gives in good yield fully substituted 2-hydroperoxy-2H-imidazoles 2 . Reduction of 2 by triphenylphosphine leads to 2-hydroxy-2H-irnidazoles 3 . Limitations of the methods are reported.     

Solvent-free reaction of some 1,2-diaza-1,3-butadienes with phosphites: environmentally friendly access to new diazaphospholes and E-hydrazonophosphonates

[structures: see text] The present article describes the reaction between 1,2-diaza-1,3-butadienes and trialkyl phosphites, under an atmosphere of nitrogen and under solvent-free conditions, to give alkyl 3,3-dialkoxy-2H-1,2,3lambda5-diazaphosphole-4-carboxylates that, in turn, are converted into corresponding E-hydrazonophosphonates by treatment with THF:water (95:5). These latter compounds are obtained directly by the reaction of 1,2-diaza-1,3-butadienes with trialkyl phosphites in the presence of air. These compounds are useful for the further preparation of dialkyl (5-methyl-3-oxo-2,3-dihydro-1H-4-pyrazolyl)phosphonates and 2-dialkoxyphosphoryl-1,2,3-thiadiazoles.