Non-associated Molecules Research Articles

The legumin-like storage protein of Lupinus albus seeds

Legumin-like proteins of Lupinus albus seeds, consist of 12 S and 7 S species which are in part involved in an association-dissociation equilibrium that is shifted towards association by increasing the ionic strength of the medium. A consistent portion of the 7 S species does not associate to 12 S. The 12 S and the 7 S associating molecules have the same protomer composition. the 7 S non-associating molecules differ from them because they have less high M r acidic protomers. Partial proteolytic breakdown of these polypeptides appears to convert associable to non-associable molecules. The splitting protease is tightly associated to the legumin in the preparation. It is inhibited by sodium azide. The apparent M r of the heavy and the light species is 315 000 and 185 000 respectively. Also other parameters, such as diffusion coefficients, frictional ratios, Stokes' radii, are in good agreement with those of legumin-like storage proteins from other legume seeds. Binding of the purified legumin to a concanavalin A-Sepharose and incorporation of tritiated N-acetylglucosamine into legumin polypeptides during seed development have confirmed that lupin legumin is glycosylated. Only the acidic subunits appear to contain covalently linked carbohydrate.

The effect of synthesis temperature on the structure of dextran NRRL B 512F

The present study puts together the results from several types of experiments from which the effect of synthesis temperature on the primary structure and the macromolecular characteristics of native dextran NRRL B 512F has been deduced. From light-scattering measurements, it has been concluded that the average molecular weight of non-associated molecules is almost independent of synthesis temperature and much smaller than all the values reported in the literature for non-fractionated native dextran. This result was made possible due to the use of a method which does not take into account the contribution of dextran aggregates. These aggregates usually lead to an over-estimation of dextran molecular weight. By combining intrinsic viscosity measurements and hydrolysis of dextran with a glucoamylase, evidence is given that branching increases with synthesis temperature, particularly through secondary ramifications. As a result, the conformation of dextran changes from an expanded random coil type at relatively low temperature (< 20°C), to a compact solid sphere type observed at higher temperature (30°C).

Dipole moment of the intramolecular hydrogen bond. 2-Nitrophenol and its derivatives

Dipole moments of substituted 2-nitrophenols VIa-VIf and substituted 2-nitroanisoles VIIa to VIIf were measured in benzene and dioxan solutions. Infrared spectroscopy confirmed that nitrophenols VI exist either solvent and at different concentrations as non-associated molecules with an intramolecular hydrogen bond. Therefore, the difference between the experimental dipole moment and that calculated from group moments can be attributed to charge redistribution raised by the hydrogen bond. Only a minute part of it may be due to electron transfer through the ring (conjugation of the functional groups) as follows particularly from he comparison with nitroanisoles VII. Nevertheless, the charge transfer, expressed as the vector μH, amounts only 1.7 . 10-30 Cm (at an angle of 138° to the H-O bond), i.e. several times less than observed previously in compounds with more powerful hydrogen acceptors. CNDO/2 and MNDO calculations agree fairly with the gross dipole moments of the compounds investigated but are unable to predict μH, not even as far as its direction is concerned.

Rabbit MHC antigens: Occurrence of non-beta-2-microglobulin-associated class I molecules

Two monoclonal antibodies, L12/36 and L13/112, prepared from spleens of BALB/c mice immunized with extracts of the rabbit lymphoid cell line RL-5, precipitate a 42,000 mol. wt molecule from detergent lysates of this cell line. This molecule is not associated with beta-2-microglobulin (β 2m) and has been shown by sequential precipitation experiments to be antigenically distinct from the population of class I rabbit MHC (RLA) molecules that is associated with β 2m. In spite of this antigenic difference, amino acid sequence analyses indicate that the RLA heavy chain precipitated with anti-β 2m and that precipitated with the monoclonal antibodies, have identical N-terminal sequences. The sequence determined to position 36 is GSHSMRYFYTSVSRPGLGXPRFIIVGYVXXTXFVRF. The isoleucine assigned to position 24 is the first species-specific residue found for RLA class I molecules. Analysis of the β 2m associated and non-associated molecules by two-dimensional gel electrophoresis revealed no differences between the RLA heavy chains. Differences in the subcellular locations of the determinants were indicated by fluorescence microscopy and confirmed by immunoelectron microscopy. It was shown that the specificity recognized by the monoclonal antibodies is principally located on the cytoplasmic face of the plasma membrane whereas the majority of anti-β 2m reactive specificities are on the extracellular side of the cell membrane.

The phase instability and critical point in a liquid mixture of an associating and inert component

The problem of phase instability in a binary mixture of an associating component with an inert component is analyzed from the standpoint of the theory of association equilibria. It is demonstrated that conditions of the spinodal and critical point for such a binary system are equivalent to those of the spinodal and critical point of a multicomponent mixture consisting of complex species arising by association (including nonassociated molecules). These conditions are formulated so as if species in this mixture did not participate in association and dissociation processes; configurational terms expressing changes in the content of the individual complexes depending on changes in total composition are included implicitly.

Association of Synthetic Polymers

Abstract The methods available for a quantitative evaluation of solutions of associating macro-molecules are reviewed. Association is defined as a rapid equilibrium between unimers (non-associated molecules) and multimers (associated molecules) in homogeneous solutions. It can be subdivided into open and closed associations. Open associations are consecutive processes. Closed associations represent all-or-none processes. Both types of associations can be of either the end-to-end type (number of associogenic sites independent of molecular weight) or the segment-to-segment type (number of associogenic sites increasing with molecular weight in a polymerhomologue series). Relations between the polymolecularity of the unimers and the polydispersity of the multimers are given. Viscometry is shown to be no reliable method for the investigation of association if used alone without the knowledge of thermodynamic data. The equilibrium constants of macromolecules seem to be higher than those of low molecular weight ...

Untersuchungen zur Ermittlung von Assoziationskonstanten aus infrarotspektroskopischen Messungen an Alkoholen

Infrared-spectroscopic measurements on the free OH absorption band of isopropanol, t-butanol and t-pentanol using various concentrations in CCl 4 and various temperatures, showed that the fraction α of the non-associated alcohol molecules was dependent on the concentration. Five different association models were used for calculating the formation constants of the single species. Within the limits of the accuracy of the measurements the values of α found as a function of concentration at various temperatures may be described by several contradictory models. Agreement between experiment and model may thus be accidental. Many errors and disagreements in the interpretation of association published in former studies, are comprehensible for this reason. In addition to the dimer absorption band near 3500 cm −1, these results support the view that with alcohols only a general association model with all species present is correct up to a definite maximum magnitude, and that special hypotheses concerning the value of the single formation constants may at best be considered as rough approximations.

High-resolution Raman spectroscopy in the red and near infrared—II: Vibrational frequencies and molecular interactions of halogens and diatomic interhalogens

The Raman frequencies of a series of diatomic halogen and interhalogen molecules in the liquid state and in different solvents are reported. The measurements were carried out on spectra excited in the red and near-infrared spectral range by helium or rubidium radiations, and photographed under high or medium dispersion. The results are tabulated together with the values Δ G 1 2 as obtained from band spectra for the isolated molecules and with available data from infrared absorption measurements and from simultaneous transitions. In comparison to the frequencies to be expected for the non-associated molecules, the observed values show a marked decrease, due to interactions between identical molecular species, or to solute-solvent interactions. Interactions of the latter kind lead, in some cases, to the formation of loose charge-transfer complexes with the solvent acting as donor, and, consequently, to a more pronounced change of frequency of the accepting halogen. The origin of still larger effects, observed on solutions in pyridine, is discussed.

THE ULTRAVIOLET ABSORPTION SPECTRA OF NITRIC ACID SOLUTIONS

The ultraviolet absorption spectra of binary mixtures of nitric acid, water, acetic acid, acetic anhydride, and nitrogen pentoxide have been investigated over the ranges of concentration in which the systems exhibit sufficient chemical stability. The variations in the spectra are considered in relation to the other physical properties of the systems, as reported in the literature. The ultraviolet spectrum of nitric acid in the presence both of nitrogen pentoxide and water is interpreted in terms of a series of equilibria which involve the nitrate (NO3−) and nitronium (NO2+) ions and associated and nonassociated neutral molecules. The specific gravities of anhydrous nitric acid solutions of ammonium nitrate, potassium nitrate, ammonium acetate, acetic acid at 20 ± 0.1 °C. and of nitrogen pentoxide at 25 ± 0.1 °C. are also reported.

THE MOLECULAR DIAMETER OF DEUTERIUM AS DETERMINED BY VISCOSITY MEASUREMENTS

The viscosities of deuterium over the range 23 to −183 °C. have been measured. The viscosities of the two-component system deuterium-hydrogen have been measured over the whole concentration range at 22 °C. The results show that the deuterium molecule has the same diameter as the hydrogen molecule. The interest attached to the viscosity results for the two-component system are pointed out. The difference between the molecular volume of liquid deuterium oxide and that of liquid water is attributed by the authors to a difference in equilibrium between associated and non-associated molecules in the respective systems.