Studies on the refolding of the reduced-denatured insulin with size exclusion chromatography

The refolding of the reduced-denatured insulin from bovine pancreas was investigated with the size exclusion chromatography (SEC). It was shown that the reduced-denatured insulin originally denatured with 7.0 mol·L-1 guanidine hydrochloride (GuHCI) or 8.0 mol·L-1 urea could not be refolded with a non-oxidized mobile phase. Although the oxidized and reduced glutathione (GSSG and GSH) were employed in the oxidized mobile phase, the reduced-denatured insulin still could not be renatured. However, in the presence of 2.0 mol·L-1 urea in the oxidized mobile phase employed, the reduced-denatured insulin can be refolded with SEC, and the aggregation of denatured insulin can be diminished by urea. In addition, the disul-fide exchange of reduced-denatured insulin also can be accelerated with GSSG/GSH in the oxidized mobile phase. The three disulfide bridges of insulin were formed correctly and the reduced-unfolded insulin can be renatured completely. The results were further tested with re-versed-phase liquid chromatography (RPLC) and hydrophobic interaction chromatography (HIC).     

Water wafers: structure and melting of a hydrate inclusion compound of a neutral Pt(IV) complex with 1-methylcytosinato ligands

The characterization by X-ray analysis of the trans,trans,trans-[bis(1-methylcytosinate,N4)bis(ammine)bis(hydroxo)platinum(IV)] octahydrate complex (I) reveals an unexpected crystal packing. The neutral complex molecule is hosted by layers, totally built up by water molecules which do not exhibit a direct coordination to metal ions. These corrugated layers are made by puckered eight- and planar four-membered rings of water molecules, held together by hydrogen bonds with an ordered proton arrangement.     

The effectiveness of solvents as hydrogen bond donors

Taft and Kamlet's -scale of solvent hydrogen bond donation ability is reexamined with regard to its correlations with three widely used polarity scales: Dimroth and Reichardt's E _T (30), Kosower's Z and Mayer's A _N , as well as with the _m values of the solvents when present as monomeric solutes. The correlation with E _T serves to extend the solvent -scale according to the expression:

Hydrogen–hydrogen bonding in biphenyl revisited

The evidence for the stabilizing nature of the H–H bonding in planar biphenyl is succinctly reviewed. The stabilizing nature of the H–H bonding is revealed through a comparison of the atomic energy of every atom in planar biphenyl with the same atom in the twisted equilibrium structure. It is shown that the barrier to rotation via the planar transition state is the net resultant of a stabilisation of the four ortho-hydrogen atoms (by 8 kcal/mol each), a stabilisation of the two para-carbon atoms (by 3 kcal/mol each) and by the dominant destabilisation of the two carbon atoms joining the two rings—the two junction carbon atoms—(by 22 kcal/mol each). The energetic stabilisation of the four ortho-hydrogen atoms is further shown to be in large proportion due to the formation of the hydrogen–hydrogen interatomic surface. Furthermore, neither the “bond order” between the two junction carbon atoms nor the total electron delocalisation between the two rings exhibit a significant change in going from the planar to the twisted equilibrium geometry. These findings are in contrast with the classical view of a balance between “steric non-bonded repulsion” and better electron delocalisation as a function of the twist dihedral angle. Similar conclusions have been recently reached by Pacios and Gómez through a study of the electrostatic potential at the position of the hydrogen nuclei. We dedicate this article to Professor TM Krygowski on the occasion of his 70th birthday wishing him a long and productive life.     

Preparation and Characterization of Trimethylsilylpyridylacetylene Bridged,Dicobalt Carbonyl Complexes Containing Bis(diphenylphosphino)methylene or Bis(diphenylphosphino)ethylene Ligand

Reaction of an alkyne‐bridged dicobalt complex, [Co₂(CO)₆(μ‐Me₃SiC=Cpy)] 4 , with bis(diphenylphosphino)methylene (DPPM) or bis(diphenylphosphino)ethylene (DPPE) in THF at 55 °C yielded a DPPM or DPPE doubly bridged dicobalt compound, [{μ‐P,P‐PPh₂CH₂PPh₂}Co₂(CO)₄(μ‐Me₃SiC=Cpy)] 5 or [{μ‐P,P‐PPh₂CH₂CH₂PPh₂}Co₂(CO)₄(μ‐Me₃SiC≡Cpy)] 6 . Compound 5 and 6 were characterized by spectroscopic means as well as X‐ray crystal structure determination.     

Where are the Sn atoms in LaSb2Snx, 0.1?x?∼0.75?

The composition range and (composite modulated) structure of compounds within the wide range non-stoichiometric LaSb₂Sn_x, 0.1?x?0.75, solid solution is carefully investigated via a combined electron diffraction, XRD and electron probe microanalysis study. Evidence for metastability of the LaSb₂Sn_x phase at the low x composition end of the solid solution is presented. Direct evidence is found for a reasonably (although by no means perfectly) well ordered Sn sub-structure which is, in general, mutually incommensurable with respect to a very well ordered underlying LaSb₂ sub-structure along both a and c directions. The overall (3+2)-d superspace group symmetry is given along with a discussion of the consequences as regards the arrangement of the Sn atoms. The Sn sub-structure c-axis cell dimension shows very little variation with composition x providing direct experimental evidence of the importance of Sn-Sn metallic bonding (along one-dimensional [001] Sn strings) for the stability of the phase.     

The first structural characterization of a phosphonium amide: synthesis, isolation and molecular structure of (Ph3PEt)(NPh2)

The first isolation of a phosphonium amide, (Ph₃PEt)⁺(NPh₂)⁻, obtained via the deprotonation of a secondary amine (diphenylamine) with a phosphorus ylide (triphenylphosphonium ethylide), is described. An X-ray crystal structure provides the first observation of an essentially ion-separated Ph₂N⁻ anion in the solid state, though weak association with Ph₃PEt⁺ cations take plac through C---H…N hydrogen bonding. Cryoscopic and NMR spectroscopic data suggest that this association is not maintained in benzene solution.     

Synthesis and Structural Characterization of a New Hydrogen-bonded Polyrotaxane of [Co(H2O)6]2+ with 1,1''-(Propane-1,3-diyl)dipyridinium-4-carboxylate

A new double betaine 1,1 '-(propane-1,3-diyl)dipyridinium-4-carboxylate L has been synthesized. Reaction of 1,1'-(propane-1,3-diyl)dipyridinium-4-carboxylate tetrahydrate 1 With Co(ClO4)2·6H2O leads to the formation of a new Co(Ⅱ) coordination compound,namely [Co(H2O)6]·2H2O·2L·2ClO4 2.The crystal structures of 1 and 2 have been determined by single-crystal X-ray diffraction method. Crystal data for 1: monoclinic, space group C2/c, a =18.945(4), b = 7.700(2), c = 11.888(2) (A), β = 101.67(3)°, V = 1698.3(6) (A)3, Z = 4, F(000) =760.0, Dc = 1.402 g/cm3, the final R = 0.0607 and wR = 0.1607 for 950 observed reflections (I ＞2σ(I)); and those for 2: monoclinic, space group P21/c, a = 17.982(1), b = 15.879 (1), c = 7.0716(5) (A), β = 100.675(1)°, V = 1984.3(3) (A)3, Z = 4, F(000) = 1010.0, Dc = 1.631 g/cm3, the final R = 0.0316 and wR = 0.0896 for 3784 observed reflections (I ＞2σ(I)). Crystal structure analysis indicates that in 1, molecules of L in a "V-shaped" conformation are linked to chains sustained by O-H…O hydrogen bonds between carboxylate groups and solvent water molecules.The chains are joined by O-H…O and C-H…O hydrogen bonds to further expand into a three-dimensional structure. For 2, molecules of L in a "Z-shaped" conformation are linked by hydrogen bonds between carboxylate groups and aqua ligands to form a chain of loops running down the b axis. The (2D→2D) polythreading in compound 2 represents the mode of parallel interpenetration of 2D sheets, having polyrotaxane character.     

Infrared and ab initio studies of hydrogen bonding and proton transfer in the complexes formed by pyrazoles

The results of experimental studies and quantum mechanical calculations of vibrational spectra and structure of hydrogen bonded complexes formed by pyrazole (P) and 3,5-dimethylpyrazole (DMP) are presented. IR spectra of pyrazoles in solutions, gas phase, and solid state have been investigated in wide range of concentrations and temperatures. It has been found that in the gas phase both P and DMP reveal the equilibrium between monomers, dimers, and trimers. In solutions the equilibrium between monomers and trimers dominates, no bands, which can be attributed to dimers were detected. DMP retains the trimer structure in solid state, while in the case of pyrazole P, formation of the crystal provides another type of association. Geometrical and spectral characteristics of dimers and trimers, obtained by ab initio calculations, are presented and compared with experimental data.

IR spectra of solutions containing P and DMP with a number of acids (acetic and trifluoroacetic acids, pentachlorophenol, HBr) have been studied in parallel with ab initio calculations. It has been found that pentachlorophenol forms with pyrazoles complexes with one strong hydrogen bond O–HN, while NH pyrazole group remains unbonded. With carboxylic acids DMP forms 1:1 cyclic complexes with two hydrogen bonds. In the case of acetic acid, the complex in CH₂Cl₂ solution reveals molecular structure with OHN and C=OHN bonds, in accordance with results of the calculations. For trifluoroacetic acid, the calculations predict the molecular structure to be energetically more stable in the case of the isolated binary complex (in gas phase), while the experimental spectrum of CH₂Cl₂ solution gives an evidence of the proton transfer with formation of the cyclic ionic pair with two NH⁺O⁻ bonds. The agreement with experimental results can be improved by taking into account the influence of environment in the framework of Onsager or Tomasi models. The shape of proton potential function of the complexes and medium effect on its parameters, resulted from experimental data and calculations, are discussed. It has been found that the number of potential minima and their relative depth depend strongly on the method of calculations and the basic set. Under excess of trifluoroacetic acid, the formation of 2:1 acid–DMP complex has been detected. Spectral characteristics and results of calculations point to the cyclic structure of this complex, which includes homoconjugated bis-trifluoroacetate anion and DMPH⁺ cation. With HBr both studied pyrazoles were found to form ionic complexes including one or two pyrazole molecules per one acid molecule and correspondingly monocation or homoconjugated cation BHB⁺.     

Mutual Solubilities of Water and Alkanes

Summary.  The evaluation of mutual solubility data for systems water with n-alkanes, isoalkanes, and cycloalkanes along the three phase line is reported and a formula for the prediction of solubility of alkanes in water is developed. Then a cubic equation of state with an added term, which accounts for hydrogen bonding is used for correlation of liquid–liquid equilibrium data and for prediction of solubility of water in hydrocarbons using alkane in water solubility data. Comparison of the predicted and experimental solubilities is performed using all accessible experimental data. With this approach it is possible to predict the solubilities of water in alkanes with good accuracy over the temperature range up to about 20 K below critical temperature. Solubility of alkanes in water can also be calculated using experimental data for solubility of water in alkanes but results of these calculations are more sensitive to experimental errors of the data. Corresponding author: E-mail: macz@ichf.edu.pl Received August 5, 2002; accepted (revised) September 13, 2002 Published online March 13, 2003 RID="a" ID="a" Dedicated to Prof. Dr. H. Gamsj?ger on the occasion of his 70^th birthday anniversary