Spectroscopic study of proflavine adsorption on the carbon nanotube surface

The present paper sheds light on one of the possible mechanisms of interaction between the typical aromatic dye proflavine and the carbon nanotube surface, namely, π-stacking between aromatic rings of these compounds. To investigate such a complexation, a qualitative analysis was performed by means of ultraviolet visible, infrared, and nuclear magnetic resonance spectroscopy. The data obtained suggest that π-stacking brings the major contribution to the stabilization of the complex between proflavine and the carbon nanotub

The Use of the Statistical Entropy in Some New Approaches for the Description of Biosystems

Some problems of describing biological systems with the use of entropy as a measure of the complexity of these systems are considered. Entropy is studied both for the organism as a whole and for its parts down to the molecular level. Correlation of actions of various parts of the whole organism, intercellular interactions and control, as well as cooperativity on the microlevel lead to a more complex structure and lower statistical entropy. For a multicellular organism, entropy is much lower than entropy for the same mass of a colony of unicellular organisms. Cooperativity always reduces the entropy of the system; a simple example of ligand binding to a macromolecule carrying two reaction centers shows how entropy is consistent with the ambiguity of the result in the Bernoulli test scheme. Particular attention is paid to the qualitative and quantitative relationship between the entropy of the system and the cooperativity of ligand binding to macromolecules. A kinetic model of metabolism. corresponding to Schrödinger’s concept of the maintenance biosystems by “negentropy feeding”, is proposed. This model allows calculating the nonequilibrium local entropy and comparing it with the local equilibrium entropy inherent in non-living matter

Shape-independent model (SHIM) approach for studying aggregation by NMR diffusometry

NMR diffusometry has been gaining wide popularity in various areas of applied chemistry for investigating diffusion and complexation processes in solid and aqueous phases. To date, the application of this method to study aggregation phenomena proceeding beyond the dimer stage of assembly has been restricted by the need for a priori knowledge of the aggregates’ shape, commonly difficult to know in practice. We describe here a comprehensive analysis of aggregation parameter-dependency on the type and shape selected for modeling assembly processes, and report for the first time a shape-independent model (designated the SHIM-model), which may be used as an alternative in cases when information on aggregates’ shapes are unavailable. The model can be used for determining equilibrium aggregation parameters from self-diffusion NMR data including equilibrium self-association constant and changes in enthalpy, ΔH, and entropy, ΔS

A New Model of Hemoglobin Oxygenation

The study of hemoglobin oxygenation, starting from the classical works of Hill, has laid the foundation for molecular biophysics. The cooperative nature of oxygen binding to hemoglobin has been variously described in different models. In the Adair model, which better fits the experimental data, the constants of oxygen binding at various stages differ. However, the physical meaning of the parameters in this model remains unclear. In this work, we applied Hill’s approach, extending its interpretation; we obtained a good agreement between the theory and the experiment. The equation in which the Hill coefficient is modulated by the Lorentz distribution for oxygen partial pressure approximates the experimental data better than not only the classical Hill equation, but also the Adair equation

C60 fullerene aggregation in aqueous solution

In the present work we develop a novel approach for quantification of the energetics of C-60 fullerene aggregation in aqueous media in terms of equilibrium aggregation constant K-F. In particular, it is shown that the experimental determination of the magnitude of K-F is possible only within the framework of the 'up-scaled aggregation model', considering the C60 fullerene water solution as a solution of fullerene clusters. Using dynamic light scattering (DLS) data we report the value, K-F = 56 000 M-1, which is in good agreement with existing theoretical estimates and the results of energetic analyses. It is suggested that the proposed 'up-scaled model' may be used in any instances of non-specific aggregation resulting in formation of large spherical particles. The measurement of the translational diffusion coefficient and the dimensions of the light scattering particles using a DLS approach with respect to C-60 fullerene aggregates is found to contain significant systematic errors originating from the interaction effect that is well-known for micellar solutions. As a result, corrections to the equations associated with DLS data are proposed