Showing papers by "Bulgarian Academy of Sciences published in 1972"

Molecular weight determination of nucleic acids by gel electrophoresis in non-aqueous solution.

Abstract: IN most areas of research concerned with the structure, function and synthesis of nucleic acids the measurement of molecular weights plays an inescapable part. There are many instances of problems hinging on a rather precise knowledge of the molecular weight of a nucleic acid; examples of particular current interest concern both animal and viral messengers, which are larger than can be accounted for by the total protein message that they encode and ribosomal-RNA, the molecular weight of which bears on the question of the stoichiometry of ribosomal components. Unfortunately the classical methods of molecular weight determination present great difficulties. The quantities of material required are frequently outside the range of feasibility. Moreover, the non-ideality in these highly charged molecules and polydispersity1,2 resulting from contamination with minor cellular components, or commonly products of nuclease degradation (as well as the need to determine the partial specific volume), combine to make molecular weight measurement a major research undertaking. The remarkable spread of published values for widely studied RNA species reflects these problems.

Conditions of Formation of Calcite Crystals of Tabular and Acute Rhombohedral Habits

Abstract: Calcite crystals are grown under pure conditions by the method of counterdiffusion of calcium and carbonate ions in water. An extension of the diffusion method is used making possible the crystallization of calcite in a medium containing calcium or carbonate ions in excess of their stoichiometric amounts in calcite. Calcite crystals grown in the presence of an excess of Ca2+ ions exhibit an elongated habit determined by the prevailing development of some of the acute negative rhombohedra φ. {0221}, θ. {0441} or π. {0881}, whereas with an excess of CO ions the habit varies from thick -to fine-tabular due to the considerable development of the pinacoid (c {0001}). The habit of crystals grown in a medium in which both ions are approximately in stoichiometric amounts or in which the excess of one of them frequently alternates with an excess of the other, is determined by the supersaturation and varies from basic rhombohedron to acute rhombohedron m. {4041}. The results are discussed in the light of some of the existing theoretical ideas on the influence of admixtures on habit. It is shown that the order of morphological importance which can be derived on the basis of various extensions of Bravais' law agrees neither with the experimental results nor with the observations in nature. The particular habits observed in experiments, tabular and acute rhombohedral, are exactly those which Kalb had included in his morphogenetic order of calcite crystals as first and fifth habit types. Since they are the result of specific conditions in the medium they ought to deviate from the general order. The remaining three habit types, therefore, will determine the habit variations of calcite due to the decrease of supersaturation.

LCAO-HMO Study of the Bond Energy of Small Crystals

Abstract: The binding energy of one-, two- and three-dimensional crystals of primitive cubic lattices consisting of one-electron atoms are studied using the Huckel LCAO-MO method. It is shown that the average bond energy is decreased with an increase in the number of atoms in the crystal, and a trend to a constant value, different for one-, two- and three-dimensional crystals is observed. On the basis of the growth process of a one-dimensional crystal it is shown that the second atom possesses the highest bond energy. The bond energy of each subsequently added atom is smaller. However, the atom which is even forms a stronger bond than the atom which is odd by sequence of adding. The even-odd oscillations in the bonding energies are damped parallel to an increase in size of one-dimensional crystal. A comparison is made of the ratio between the experimentally obtained values for the dissociation energy of diatomic molecule and the energy per bond in an infinitely large crystal, and the ratio of the same quantities calculated by the authors. Comparison shows that in general a correlation is observed between the two ratios for these extreme cases. Die Bindungsenergie von ein-, zwei und dreidimensionalen Kristallen eines primitiven kubischen Gitters, aufgebaut aus Ein-Elektron Atomen wird unter Anwendung der LCAO-MO-Methode von Huckel untersucht. Es zeigt sich, das die mittlere Bindungsenergie mit der Zunahme der Anzahl der Atome im Kristall abnimmt. Sie nahert sich unterschiedlich fur die drei Falle einem konstanten Wert. – Am Wachstumsprozes eines eindimensionalen Kristalls erweist sich das zweite Atom als Wachstumsprozes eines eindimensionalen Kristalls erweist sich das zweite Atom als das mit der hochsten Bindungsenergie. Die Bindungsenergie jedes weiteren hinzutretenden Atoms ist kleiner. Das in der Aufeinanderfolge geradzahlige bildet eine starkere Bindung aus als das ungeradzahlige. Die Gerade-Ungerade-Schwankungen in den Bindungsenergien werden mit Zunahme der Grose des eindimensionalen Kristalls schwacher. Die Werte des Verhaltnisses zwischen experimentell ermittelten Werten fur die Dissoziationsenergie zweiatomiger Molekule und der Energie pro Bindung in einem unendlich grosen Kristall und das Verhaltnis der entsprechenden von den Autoren berechneten Grosen werden verglichen. Im allgemeinen gibt es eine Beziehung zwischen den beiden Verhaltnissen fur die genannten Extremfalle.

Inhibitory effect of N-phenyl-N'-aryl or alkylthiourea derivatives on the multiplication of some picornaviruses (Coxsackie B 1, ECHO 19, and foot-and-mouth disease virus) in cell cultures.

Abstract: The effect of eleven derivatives of N-phenyl-N'-aryl- or alkylthiourea on the multiplication of Coxsackie B1, ECHO 19 and foot-and-mouth disease viruses in cell cultures has been tested. In one-step growth cycle experiments N-phenyl-N'-4-carboxy-5-hydroxyphenylthiourea, N-phenyl-N'-3-hydroxyphenylthiourea and γ-phenylthioureidobutyric acid inhibited 99.9% of the Coxsackie B1 and ECHO 19 virus yields. N-phenyl-N'-4-hydroxyphenylthiourea suppressed 99.65% of the foot-and-mouth disease virus yield.

KOWARSKI “Protuberances” as an Example of Two-Dimensional Growth by the VLS Mechanism

Abstract: The growth kinetics of protuberances formed in the presence of water vapour at the surface of paratoluidine crystals growing from the melt was investigated. The experimental quadratic dependence of the flux of matter directed towards the droplet on its radius leads to the view that KOWARSKI's protuberances constitute an example of crystal growth by the VLS mechanism. Die Wachstumskinetik von „Protuberanzen„. die sich in Gegenwart von Wasserdampf an der Oberflache von Paratoluidin-Kristallen beim Wachstum aus der Schmelze bilden, wurde untersucht. Die experimentelle quadratische Abhangigkeit des Materialflusses zum Tropfchen in Richtung seines Radius fuhrt zu der Ansicht, das&KOWARSKI's Protuberanzen ein Beispiel fur das Kristallwachstum nach dem VLS-Mechanismus darstellen.