Search

Long-duration gamma-ray bursts (GRBs) are powerful cosmic explosions, signaling the death of massive stars. Among them, GRB 221009A is by far the brightest burst ever observed. Because of its enormous energy ( E iso ≈ 10 55 erg) and proximity ( z ≈ 0.15), GRB 221009A is an exceptionally rare event that pushes the limits of our theories. We present multiwavelength observations covering the first 3 months of its afterglow evolution. The x-ray brightness decays as a power law with slope ≈ t -1.66 , which is not consistent with standard predictions for jetted emission. We attribute this behavior to a shallow energy profile of the relativistic jet. A similar trend is observed in other energetic GRBs, suggesting that the most extreme explosions may be powered by structured jets launched by a common central engine.

The highly organized spatial structure of proteins' polar groups results in the existence of a permanent intraprotein electric field and in protein's weak dielectric response, i.e. its low dielectric constant. The first factor affects equilibrium free energy gap of a charge-transfer reaction, the second (medium polarization effect) influences both equilibrium and non-equilibrium (reorganization) energies, decreasing the latter substantially. In the framework of the rigorous 'fixed-charge-density' formalism, the medium polarization component of the reaction activation energy has been calculated, both for the activation energy of the elementary act proper, and the effective activation energy accounting for the charges' transfer from water into a low-dielectric structureless medium. In all typical cases of reactions, the energy spent for charge transfer from water into structureless 'protein' is larger than the gain in activation energy due to the protein's low reorganization energy. Therefore, the low dielectric constant of proteins is not sufficient to ensure their high catalytic activity, and an additional effect of the pre-existing intraprotein electric field, compensating for an excessive charging energy, is necessary. Only a combined action of low reorganization energy and pre-existing electric field provides proteins with their high catalytic activity. The dependence of activation energy on the globule geometry has been analyzed. It is shown that, for each reaction, an optimum set of geometric parameters exists. For five hydrolytic enzymes, the optimum globule radii have been calculated using the experimental geometry of their active sites. The calculated radii agree satisfactorily with the real sizes of these macromolecules, both by absolute and by relative values.

A method for measuring the adsorption of dimethyl sulfoxide on native and denatured trypsin and albumin was developed. On native proteins, no positive adsorption was registered, and a slight negative adsorption within the limits of experimental error was observed. It was shown that the properties of denatured proteins depend on the mode and conditions of denaturation. On one of denatured trypsin specimens, positive adsorption of dimethyl sulfoxide was registered, on other specimens no adsorption was observed. The reason for this behavior lies in the hydrophobic nature of adsorption of dimethyl sulfoxide at the interface, while the surface of native protein globules and, probably, most denatured protein specimens is hydrophilic.

Electrokinetic behaviour of human lymphocytes was studied by photon correlation spectroscopy technique on laser IR-spectrometer. The electrophoretic mobilities (EPMs) were measured for peripheral blood lymphocytes (PBL) and CEM-C12 T cell line in 1:1 electrolyte at 22 degrees C. Plots of mobility vs ionic strength in the range 0.001-0.1 M were compared with theoretical curves calculated from (i) the Smoluchowsky formula, (ii) the simplified form of the Dukhin-Deryaguin equation which takes into account the fact that the mobility decreases due to the relaxation effect and (iii) the equation suggested by Donath and Pastushenko, which takes into account the influence of cell glycoprotein layer (GPL) on the EPM values. It has been found that the first two equations describe the experimental data with the assumption that surface charge density (sigma) decreases and width of the hydrodynamically immobile layer (L) increases with decreasing ionic strength; the relaxation effect turns out to be insignificant for the cell charges and sizes under consideration. In agreement with these findings, the third equation is approximately consistent with experimental data on the condition that GPL is allowed to expand with decreasing ionic strength, with simultaneous decrease of its full charge density (sigma(f)). The results are compared with relevant evidence for erythrocytes. The possible applications of the inferences arrived at in electrophoretic studies of cell behaviour are also discussed.

The influence of polarization of surrounding medium on the intraglobular electric field of the alpha-chymotrypsin molecule is considered. The polarization is taken into account by the image charges method, the proper approximations for calculation of the fields due to intraglobular and surface charges are suggested. The polarization of surroundings does not change the qualitative picture of the electric field in the active center of the alpha-chymotrypsin molecule set up by protein dipoles, but reduces almost to zero the intraglobular field set up by surface ions.

The dissociation of the ionogenic groups of the active centre of alpha-chymotrypsin is considered taking into account effects of short- and long-range solvation and intraglobular electric field. The ionic pair Asp102-CO2-. His57-ImH+ is shown to be the most probable state of the neutral active centre of alpha-chymotrypsin, this ionic pair being stabilized substantially through electrostatic interaction of the ions. The pair dissociates releasing the proton from the N epsilon 2 atom of His57 and forming a catalytically active group Asp102-CO2-. His57-Im. The pK value approximately 7 characteristic of this acid-base equilibrium pertains to the active centre as a whole rather than to the isolated imidazolium ion. The approach developed by the authors is compared with other works in this area.

The electric field set up by the dipoles of peptide groups ad other dipoles at the atoms of substrate and catalytic groups of alpha-chymotrypsin is considered. It is shown that substantial electric potentials reaching some tenths of volts exist in the active center of the enzyme, the fact which must influence significantly the reactivity of corresponding groups. In contrast to low molecular weight liquids, the contribution to the total potential of dipoles located at different distances from the point under consideration often changes nonmonotonically with the distance, sometimes the predominant influence being exerted not by the nearest polar groups but by the more distant ones. The existence of electric fields having a complex spatial configuration determined by the protein structure can be defined as the effect of the polar medium preorganization. Emphasis is placed on the necessity of taking into account the polarization of the external medium by charges of protein atoms and ions (the difference of primary and secondary electric fields).

Factors determining the change of dissociation constants of ionogenic groups upon their transfer from water into a protein globule are considered. The change of the short-range interaction is simulated with the aid of two model solvents: dimethylformamide (DMF) and formamide (FA). The change of Bornian solvation energy is calculated taking into account the interaction of ions situated inside a protein globule with the surrounding electrolyte solution. The change of ion energy due to the intraglobular electric field preexisting in the enzyme molecule is calculated. Each of the factors listed above gives a large contribution into the ion energy in the case of Asp-102 these contributions compensate each other to a great extent.