Todor Nikolov

An effective method for bioconversion of delignified waste-cellulose fibers from the paper industry with a cellulase complex.

Abstract An effective method for production of glucose was developed using enzymatic hydrolysis of waste-cellulose fibers by the cellulase complex from Trichoderma reesei . However, these cellulosic materials are strongly resistant to direct enzymatic hydrolysis (the degree of degradation after 48 h of enzyme treatment did not exceed 14%) apparently due to the presence of various chemical substances used in the process of paper production. This adhesive “envelope” around the cellulose fibers was effectively pretreated with 0.25% H 3 PO 4 and after that the free cellulose mass was extensively hydrolyzed by the cellulase complex (degree of degradation more than 80%). The HPLC analyses of the enzyme hydrolysates revealed glucose as the main component as well as some cellobiose and xylose.

Séquences de dépôt à l'articulation plate-forme urgonienne–bassin (intervalle Barrémien–Albien) dans le Prébalkan occidental (Bulgarie du Nord-Ouest)

Abstract In the western Fore-Balkan (northwest Bulgaria), the characterization of numerous depositional sequences within the Barremian–Albian interval allows us to reconstruct from southeast to northwest the successive palaeogeographies of this part of the north Tethyan margin: two carbonate (Urgonian) platforms flanking a central terrigenous basin during the Barremian; a single centrifugal terrigenous basin (Aptian) marked, along its axis, by an olistostrome and siliciclastic turbidites; a single Albian basin characterized by the stacking of glauconite-rich condensation sections and anoxic black marls.

Géométrie des formations et des séquences de dépôt éocrétacées (intervalle Hauterivien-Aptien) de Bulgarie nord-orientale

Abstract The study, in terms of sequence stratigraphy (with ammonite zone control), of numerous cross-sections of Lower Cretaceous (Hauterivian to Aptian) series cropping out along two transects A-B (Fore Balkan and southern part of the Moesian Platform) and C-D (northeastern part of the Moesian Platform) shows the eastwards extension of the North-Tethyan palaeogeographic pattern platform-basin-platform, previously established in central Bulgaria. However, the two boundaryplatforms are strongly assymetrical, this assymetry being revealed by the importance, to the south, of the relative lowstand prograding siliciclastic bodies (supplied by continental erosions linked to extensional tectonics) during the synrift phase (not marked to the north) and by the age, the facies (oolitic to the north, Urgonian to the south) and the number of the calcareous tongues interpreted as the transgressive systems tracts of backstepping depositional sequences, well-marked at the shelf/basin transition.

Enregistrement sédimentaire de la tectonique extensive et de l'eustatisme dans le Jurassique terminal et le Crétacé basal du Prébalkan central et oriental (Bulgarie)

Abstract The thick (2 000 m) siliciclastic-dominated synrifi series, which fills up most of the internal troughs of the Central Fore Balkan from Uppermost Tithonian to Valanginian, is subdivided into ten tectono- eustatic depositional sequences. The sequences consist of a coarse and voluminous low stand wedge (block complex, canyon-cone conglomerates, megaslumps, calcareous breccias, etc.) induced by extensional tectonics; and above, a pelite-dominated high stand wedge, of eustatic origin, which contains most of the zonal and subzonal Ammonites allowing datations and correlations. To the NE, towards the Moesian Platform, only the high stand wedges (with or without the transgressive system tracts) of the successive sequences overflow the troughs and become richer in carbonates to the top of the parasequences.

Kinetics of enzymatic hydrolysis of sodium carboxymethylcellulose with different degrees of polymerization by cellulase

AbstractThe reaction cellulase (EC 3.2.1.4)—sodium carboxymethylcellulose (Na-CMC) with different degrees of polymerization (n=140, 640 and 900) was investigated by the use of a modifiedMichaelis-Menten equation, valid for enzymatic hydrolysis of linear homopolymers. TheMichaelis-Menten constant [Km′ (M)=6.31·10−2mol/dm3] and the reaction rate constant (k′+2=4.07·10−6s−1), which correspond to the enzymatic hydrolysis of a single bond in the homopolymer substrates are determined. The free energy (Δ

Le Cretace inferieur en Bulgarie

G^{ = |}

Outline of the Jurassic and early Cretaceous tectonic evolution in Bulgaria

=101 kJ/mol), which corresponds to the degradation and formation of a single bond in the enzyme—polymer substrate is also estimated. This energy expressed in electronvolt units is Δ