Biomedical subjects

István Lukovits

Publications and source records attributed to István Lukovits.

4 recordsLinked to original sources

PubMedDate not supplied

Nanotubes: number of Kekulé structures and aromaticity.

Carbon nanotubes (CNTs) are composed of cylindrical graphite sheets consisting of sp(2) carbons. Due to their structure CNTs are considered to be aromatic systems. In this work the number of Kekulé structures (K) in "armchair" CNTs was estimated by using the transfer matrix technique. All Kekulé structures of the cyclic variants of naphthalene and benzo[c]phenanthrene have been generated and the basic patterns have been obtained. From this information the elements of the transfer matrix were derived. The results obtained indicate that K (and the resonance energy) is greater if tubulenes are extended in the vertical than in the horizontal direction. Tubulenes are therefore more stabile than cyclic strips. An illustration, obtained by using scanning probe microscope, has been attached to affirm the existence of thin CNTs.

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PubMedDate not supplied

Atomic walk counts of negative order.

Atomic walk counts (awc's) of order k (k > or = 1) are the number of all possible walks of length k which start at a specified vertex (atom) i and end at any vertex j separated by m (0 < or = m < or = k) edges from vertex i. The sum of atomic walk counts of order k is the molecular walk count (mwc) of order k. The concept of atomic and molecular walk counts was extended to zero and negative orders by using a backward algorithm based on the usual procedure used to obtain the values of mwc's. The procedure can also be used in cases in which the adjacency matrix A related to the actual structure is singular and therefore A(-1) does not exist. awc's and mwc's of negative order may assume noninteger and even negative values. If matrix A is singular, atomic walk counts of zero order may not be equal to one.

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PubMedDate not supplied

Enumeration of conjugated circuits in nanotubes.

The resonance energy of (1,1)n "armchair" carbon nanotubes and (n,n)1 nanoribbons was determined by enumerating the conjugated circuits (CC) and the Kekulé structures. The lower indices denote the number of hexagon layers. It was found that the resonance energy per carbon atom is equal to 0.160 eV in (1,1)n tubes and 0.142 eV in (n,n)1 tubes.

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PubMedDate not supplied

Resonance energy in graphite.

According to Zhu et al. the resonance energy/electron (REPE) in infinite graphite sheets is equal to 0.17 eV. In the present work the REPE was calculated for parallelogram-shaped graphite sheets (PSGSs). The number of Kekulé structures and contributions of benzene-like and naphthalene-like conjugated circuits were taken into account. Analogously to polyacenes, it was found that REPE = 0.00 eV in PSGSs. The convergence is slow. These results indicate that PSGS is less "aromatic" than its infinite counterpart. Therefore addition reactions are expected to be less difficult to carry out in PSGSs than in infinite or rectangular graphite sheets.

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