Analysis of polar compounds on PEG-40M/KF glass capillary columns

The chromatographic properties of potassium fluoride as an additive to the polyethylene glycol stationary phase were investigated. This unique base in organic chemistry was shown to succeed in yielding good results for the analysis of polar compounds, including the primary amines. Glass capillary columns of high selectivity for primary and secondary aliphatic amines were obtained by the “hexane plug” procedure by which a thin layer of KF is deposited on the inner surface of glass capillary columns. Some possible types of donor-acceptor interactions occuring within the system PEG/KF/solute were considered.     

Residual solvent content in heatset offset print

A method was developed for measuring the residual solvent content in a dried offset print. The method is based on hexane extraction. The presence of additives and resins in the printing inks necessitated purification of the extract on an aluminum oxide column. In the study concerning the effect of the heatset web offset drying process on print quality, a distinct correlation was found between the residual solvent content of the print and the drying parameters.     

Solvent Effect on the Ligand Exchange between Bis(diethyldithiocarbamato)copper(II) and Bis(diethyldiselenocarbamato)copper(II)

EPR and spectrophotometric study on the products of ligand‐exchange taking place on mixing bis(diethyldiselenocarbamato)copper(II), [Cu(Et₂dsc)₂], and bis(diethyldithiocarbamato)copper(II), [Cu(Et₂dtc)₂], solutions is reported. EPR spectra monitored at room temperature for one month period reveal a stable equilibrium among the parents (chromophores CuS₄ and CuSe₄) and the obtained mixed‐chelate [Cu(Et₂dtc)(Et₂dsc)] complex (chromophore CuS₂Se₂) in heptane, hexane, benzene, toluene, acetone, DMFA, DMSO and dichloromethane. In CCl₄ and CHCl₃ two new additional EPR spectra appear attributed to the mixed‐chelate complexes with the chromophores CuSSe₃ and CuS₃Se which are not observed with electronic spectroscopy. The intensities of all five EPR spectra decrease with the time. It is assumed that the new mixed‐chelates observed in CCl₄ and CHCl₃ are obtained in a reaction of [Cu(Et₂dtc)(Et₂dsc)] or [Cu(Et₂dtc)₂] with the ester of diselenocarbamic acid which is formed in a parallel reaction of [Cu(dsc)₂]with CCl₄ or CHCl₃.     

6-Chloro-2(2H)-pyranone: a new 2(2H)-pyranone synthon

6-Chloro-2(2H)-pyranone, which can be prepared in high yield from commercially available trans-glutaconic acid, undergoes facile Pd/Cu-catalyzed reaction with various 1-alkynes to give rise to the corresponding 6-(1-alkynyl)-2(2H)-pyranones in moderate to good yields. These last hitherto unknown compounds have been used as direct precursors to 6-alkyl- and 6-[(Z)-1-alkenyl]-2(2H)-pyranones.     

The <Emphasis Type="Italic">p</Emphasis>-(dimethylamino)benzaldehyde modification of Hantzsch reaction: Synthesis of 6-(1H-benzimidazol-2-yl)pyrido[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidino-2,4(1H, 3H)-diones

The reaction between p-(dimethylamino)benzaldehyde and 2-acylmethyl-1H-benzimidazoles and 6-amino-1,3-dimethylpyrimidino-2,4(1H,3H)-dione has given previously unknown 5-unsubstituted 6-(1H-benzimidazol-2-yl)pyrido[2,3-d]pyrimidino-2,4(1H,3H)-diones. The reaction occurs on boiling in acetic and acid and includes the formation of 1,4-dihydropyridine-bearing compounds in accordance with the Hantzsch reaction scheme and aromatization as a result of cleavage of N,N-dimethylaniline. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 585–589, April 2007.     

癸二酸—二苯并—18—冠—6共聚物的络合特性

以溶剂萃取的方法研究了癸二酸-二苯并-18-冠-6共聚物（CEP－1）的离子络合效率和选择性，测定了苦味酸盐在水与二氯甲烷中的平衡浓度，求得了草取平衡常数，并与其小分子模型物及酚醛树脂型冠醚聚合物（CEP-2）作了对比。结果表明，酮型冠醚聚合物虽然在离子萃取能力上有所下降，但其对K 却显示出更大的选择性。     

The use of large polycyclic aromatic hydrocarbons to study retention in non-aqueous reversed-phase HPLC

Summary Elution strengths of 11 common HPLC solvents on a polymeric C₁₈ phase were compared using a marker set of polycyclic aromatic hydrocarbons. Naphthalene, pyrene, benzo[ghi]perylene, and three larger naphthologues of 8, 10, and 12 rings (constituting a naphthalene zigzag series) were chosen because they span the solvent strength range up to and including the strongest solvents, tetrahydrofuran (THF) and chlorobenzene. Four pairs of similarly shaped isomers were used to probe solvent selectivity. With the exception of THF, HPLC solvent strength correlated with observed red shifts of fluorescence band maxima in each solvent. For THF, the pure solvent and blended mixtures behaved quite differently.     

Study of Solvent Effects on the Protonation of Functional Group of Disubstituted Anilines: Factor Analysis Applied to the Correlation between Protonation Constants and Solvatochromic Parameters in Ethanol–Water Mixtures

Summary. The stoichiometric protonation constants (log β) of some disubstituted aniline derivatives in ethanol–water mixtures (0–90% ethanol by volume) at 25.0 ± 0.1°C were firstly submitted to factor analysis in order to obtain the number factors which affect the variation of the whole data sets and, afterwards, submitted to target factor analysis to identify these factors. The influence of solvatochromic parameters in the interactions between aniline derivatives and the solvent studied was identified and quantified. The general equation of Kamlet and Taft was reduced for these mixtures to two terms using combined factor analysis (FA) and target factor analysis (TFA): the independent term and the hydrogen-bond donating ability, α (HBD), solvatochromic parameters. Further, the quasi-lattice quasi-chemical (QLQC) theory of preferential solvation has been applied to quantify the preferential solvation by water of electrolytes in ethanol–water mixtures. The effects of the substituents on the protonation constants, the additivities of these effects, and the applicability of the Hammett equation to the behavior of substituents are also discussed. Further, Hammett’s reaction constant for the protonation of disubstituted anilines has been obtained for all the solvent mixtures and correlates well with α (HBD) of the solvent.     

Molecular modeling of a putative antagonist binding site on helix III of the β-adrenoceptor

Summary In recent biochemical studies it was demonstrated that residue Asp¹¹³ of the-adrenoceptor (-AR) is an indispensable amino acid for the binding of-AR antagonists. Earlier fluorescence studies showed that a tryptophan-rich region of the-AR is involved in the binding of propranolol, the prototype-AR antagonist. Bearing these two biochemical findings in mind, we explored the-AR part containing Asp¹¹³, for an energetically favorable antagonist binding site. This was done by performing molecular docking studies with the antagonist propranolol and a specific-AR peptide which included, besides Asp¹¹³, two possibly relevant tryptophan residues. In the docking calculations, the propranolol molecule was allowed to vary all its internal torsional angles. The receptor peptide was kept in an-helix conformation, while side chains relevant to ligand binding were flexible to enable optimal adaptations to the ligand's binding conformation. By means of force-field calculations the total energy was minimized, consisting of the intramolecular energies of both ligand and receptor peptide, and the intermolecular energy. We found an antagonist binding site, consisting of amino acids Asp¹¹³ and Trp¹⁰⁹, which enabled energetically favorable interactions with the receptor-binding groups of propranolol. According to these results, binding involves three main interaction points: (i) a reinforced ionic bond; (ii) a hydrogen bond; and (iii) a hydrophobic/charge transfer interaction. The deduced binding site shows a difference in affinity between the levo- and dextrorotatory isomers of propranolol caused by a difference in ability to form a hydrogen bond, which is in conformity with the experimentally observed stereoselectivity. Moreover, it also provides an explanation for the ₁-selectivity ofp-phenyl substituted phenoxypropanolamines like betaxolol. Thep-phenyl substituent of betaxolol was shown to be sterically hindered upon binding to the ₂-AR peptide, whereas this hindrance is very likely to be much less with the ₁-AR peptide. Finally, the proposed antagonist binding site is discussed in the light of some recent biochemical findings and theories.Abbreviations -AR -adrenergic receptor - cDNA complementary DNA - H-bond hydrogen bond - VdW van der Waals - QSAR quantitative structure-activity relationship - ¹²⁵I-pBABC p-(bromoacetamido)benzyl-1-[¹²⁵I]iodocarazol     

Solvent effects on the electronic absorption spectrum of formamide studied by a sequential Monte Carlo/quantum mechanical approach

Sequential Monte Carlo/quantum mechanical calculations are performed to study the solvent effects on the electronic absorption spectrum of formamide (FMA) in aqueous solution, varying from hydrogen bonds to the outer solvation shells. Full quantum-mechanical intermediate neglect of differential overlap/singly excited configuration interaction calculations are performed in the supermolecular structures generated by the Monte Carlo simulation. The largest calculation involves the ensemble average of 75 statistically uncorrelated quantum mechanical results obtained with the FMA solute surrounded by 150 water solvent molecules. We find that the n → π* transition suffers a blueshift of 1,600 cm⁻¹ upon solvation and the π → π* transition undergoes a redshift of 800 cm⁻¹. On average, 1.5 hydrogen bonds are formed between FMA and water and these contribute with about 20% and about 30% of the total solvation shifts of the n → π* and π → π* transitions, respectively. The autocorrelation function of the energy is used to sample configurations from the Monte Carlo simulation, and the solvation shifts are shown to be converged values. Received: 14 March 2002 / Accepted: 3 April 2002 / Published online: 24 June 2002