Satisfactory Linear Correlation Research Articles

Determination and Correlation of the Water Activity of Cheese Whey Solutions

ABSTRACTThis work reports on the experimental determination (and correlation) of water activity (aw) in cheese whey solutions of varying total solids content (up to about 50% solids). It was shown that a satisfactory linear correlation between aw and solids (given as g of solids/100g of water) of whey existed. The aw of whey solutions was close to but always below that of lactose, which indicated that other nonlactose constituents also contributed to aw lowering.

Wavenumbers of C=O valence vibrations of endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximides

Wavenumbers of symmetrical and antisymmetrical C=O valence vibrations of 50 derivatives of endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide have been measured in tetrachloromethane and chloroform. A satisfactory linear correlation between νs(C=O) and νas(C=O) has been found for 98 experimental points obtained in the two solvents. The anomalous low slope value ρ = 0.43 of this dependence can be used as evidence for endo configuration of the bicyclic 2,3-dicarboximides. The results are discussed in comparison with analogous relations found for other five-membered cyclic dicarboximides.

15N NMR spectra of nitrogen-containing polyfluoroaromatic compounds

1. According to15N NMR data, nitrogen-containing polyfluoroaromatic compounds have a more highly screened nitrogen atom in comparison with the situation in the hydrocarbon analogues and derivatives in which the nitrogen atom is directly bonded to the polyfluoroaryl ring. The screening of the15N depends on the electric fields of the O atoms of fluorine and also on the electronic influence of the pentafluorophenyl group. 2. A satisfactory linear correlation has been found between the15N chemical shifts in a series of polyfluoroaromatic compounds and the charge density on this atom is calculated by the CNDO/2 method.

Macrocyclic Enzyme Model Systems. Catalytic Activity of Cyclic Peptides Involving Hydrophobic Segments

Abstract In order to develop an effective hydrolase model, BCP-1 was synthesized and its kinetic behavior investigated. The corresponding linear hexapeptide was prepared by the solid phase method and subjected to cyclization by the azide method. BCP-1 enhanced the hydrolysis of p-nitrophenyl carboxylates bearing a long alkyl chain. The pH-rate profile for the hydrolysis of p-nitrophenyl hexadecanoate (PNPP) as effected by BCP-1 was not of a bell-shaped type but a sigmoid, from which the kinetic pKa value was estimated as 12.3. The initial reaction rate was found to level off beyond a certain range of substrate concentration (saturation-type kinetics), the kinetic data being analyzed on the basis of Michaelis-Menten scheme. The large hydrophobic binding ability of BCP-1 toward PNPP (Km(app) \simeq10−6M) was attributed to its double-layered bicyclic structure. The Hammett plot for the hydrolysis of substituted phenyl hexadecanoates gave a satisfactory linear correlation. Consequently, the acyl transfer from the bound substrate to the imidazole anion of the histidyl residue of BCP-1 was referred to the rate-determining step. The large negative entropy change for the acyl transfer step seems to indicate that the Michaelis complex does not have a conformation favorable for such acyl transfer process. The catalytic effectiveness (kcat⁄Km(app)) for the BCP-1 catalysis in PNPP hydrolysis is comparable to that for enzymatic hydrolysis.

PMR spectra and electronic structures of the neutral bases and cations of thiazolo [3,2-a] -benzimidazole and its methyl derivatives

The PMR spectra of the neutral bases and cations of methyl derivatives of thiazolo[3,2-a]-benzimidazole were studied. The dependence of the chemical shifts on the acid concentration was examined. The investigated system is protonated and N-methylated at the N9 atom. The structure of the conjugated cation corresponds to considerable delocalization of the effective positive charge to the heteroatoms of the thiazole ring. A satisfactory linear correlation between the corrected chemical shifts and the π-electron densities, calculated by the simple MO LCAO method using a coulombic integral for the sulfur atom, hS=0.9, and the parameters of the Pullman system for the remaining heteroatoms, was observed.

Strontium 90 fallout distribution at middle latitudes of the Northern and Southern Hemispheres and its relation to precipitation

The dependence of 90Sr deposition on precipitation within each 10° latitude belt is investigated. No satisfactory linear correlation is found for undifferentiated measurements obtained under different climatic conditions. Regions in which the data deviate systematically from the general trend of results in each latitude belt are singled out. A satisfactory linear correlation for most of the data has been obtained for four seasons of the year between 50 and 60°N and for the first and second quarters between 30 and 40°N and 40 and 50°N. In the latter cases, the third quarter is characterized by the largest deviations of the results from a linear dependence. The regression equations for the dependence of 90Sr deposition on precipitation in each latitude belt are given.

Substituent effects on the addition of alcohols and anilines to organic isothiocyanates

The addition reactions of alcohols, ROH (R = CH 3, C 2H 5 n-C 3H 7, i-C 3H 7 and t-C 4H 9), to p-bromophenylisothiocyanate show that the rates decrease in the order, CH 3OH > C 2H 5OH > n-C 3H 7OH > i-C 3H 7OH > t-C 4H 9OH, although the basicities of the alcohols vary in the reverse order. The results indicate the greater importance of steric factors as compared with polar factors. Evidence is also presented for the formation of a complex between the isothiocyanate and the alcohol in the first stage of the addition reaction. In the addition of aniline to substituted phenylisothiocyanates the rate data give a satisfactory linear correlation with Hammett σ constants and the results clearly show that electron-withdrawing groups favour the addition reaction. The addition of aniline to alkyl isothiocyanates have been studied in order to find out the nature of alkyl group interaction in these derivatives. Kinetic studies on the addition of substituted anilines to phenylisothiocyanate show that the rate of reaction increases with the electron-donating ability of the substituents on the aniline as also the basicity of the aniline.

Mechanism of the addition of alcohols to substituted phenylisothiocyanates : Electrical effects of the substituents on the reaction

The addition reaction of alcohols to substituted phenylisothiocyanates is found to be a second-order reaction. The reaction is catalysed by triethylamine. First-order rate constants of the addition reaction have been determined in excess of ethanol, for a number of substituted phenylisothiocyanates and the rate data give a satisfactory linear correlation with Hammett σ constants of groups. While the energies of activation vary randomly with substitution, the entropies of activation bear a linear relationship to the energies of activation. Infra-red spectra indicate that the thiourethanes which are the products of the addition reaction exist in the thioamide form. The most prominent resonance form which can satisfactorily explain both the kinetic and infrared data, has been suggested.