Alexandru T. Balaban

Alexandru T. Balaban
Texas A&M University - Galveston | TAMUG · Department of Marine Biology

PhD

About

807
Publications
57,584
Reads
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16,946
Citations
Citations since 2017
13 Research Items
2800 Citations
20172018201920202021202220230100200300400500
20172018201920202021202220230100200300400500
20172018201920202021202220230100200300400500
20172018201920202021202220230100200300400500
Additional affiliations
January 2004 - August 2012
University of Ljubljana
Position
  • Visiting scientist for a few months per year
January 2003 - present
University of Minnesota Duluth
January 1994 - present
Texas A&M University - Galveston
Position
  • Visiting scientist,(before 2001) and between 2001 and 2013 tenured full professor. At present, after 2013, Professor Emeritus

Publications

Publications (807)
Article
Full-text available
Graph parameters and topological indices allow a discussion about hierarchical criteria for ranking monocyclic and polycyclic molecular (constitutional) chemical graphs. For brevity, chemical constitutional graphs will be referred to as CGs. These criteria include the number of vertices (graph order), cyclomatic numbers, vertex degrees (from one to...
Article
Full-text available
In this autobiographical sketch, I will present my contributions in two areas of chemistry: experimental organic and theoretical chemistries.
Article
Full-text available
The Estrada topological index EE, based on the eigenvalues of the adjacency matrix, is degenerate for cospectral graphs. By additionally considering the eigenvectors, two new topological indices are devised, which have reduced degeneracy for alkanes or cyclic graphs. Index \( RV_{a} \) shows similarity to EE in ordering of alkanes with 8–10 carbon...
Preprint
Full-text available
The Estrada topological index EE, based on the eigenvalues of the adjacency matrix, is degenerate for cospectral graphs. By additionally considering the eigenvectors, two new topological indices are devised (RV_a and RV_b), which have reduced degeneracy for alkanes or cyclic graphs. Index RV_a shows similarity to EE in ordering of alkanes with 8 to...
Article
By applying a nucleophilic aromatic substitution process (SNAr) between electrophile 4-chloro-7-nitrobenzo[c] [2.1.5]-oxadiazole 1 and mercaptoderivatives 2a-2e as nucleophilic agents (2a, 2-pyridinethiol-1-oxide; 2b, 2-pyridinethiol; 2c, 4-pyridinethiol; 2d, N-acetylcysteamine and 2e, N-acetylcysteine) were obtained the corresponding thioethers 3a...
Article
Recently assigned numerical expressions to qualitative benzenoid formulas of Clar have transformed Clar's theory into a quantitative model that allowed a structural characterization of aromaticity in benzenoid polycyclic hydrocarbons and construction of aromaticity maps for benzenoid polycyclic hydrocarbons. The key structural elements of the novel...
Chapter
Electron paramagnetic resonance spectroscopy is at present the preferred method for studying free radicals. Push–pull aminyls show exceptional stability, which is explained satisfactorily by Linnett's double-quartet theory in terms of electronic spin. Stable hydrazyls such as 2,2-diphenyl-1-picrylhydrazyl and 2,2-diphenyl-1-cyanohydrazyl can actual...
Article
The betainic title compound represents a structure with interesting physicochemical properties. These were studied by cyclic voltammetry (CV), electron paramagnetic resonance (EPR) spectroscopy, magnetic and spectral measurements. CV investigations show that the process in acetonitrile corresponds to chemically reversible one-electron reduction lea...
Article
Chemical applications of discrete mathematics and graph theory are briefly reviewed, including philosophical implications. Using the concept of dualist (inner graph-theoretical duals) it was possible to classify (cata-peri-corona classes) and enumerate benzenoid and diamondoid hydrocarbons. By associating numbers with molecular graphs, one can use...
Article
The title compound is formed by a non-trivial reaction involving two molecules of the stable free radical 2,2-diphenyl-1-picryl-hydrazyl and one molecule of
Chapter
Among the various methods for finding new medicinal drugs, the approach using molecular descriptors for quantitative structure–activity relationships (QSAR) is described in more detail, after a brief historical introduction. Starting with Corwin Hansch's observation that for many organic compounds their biological activities can often be correlated...
Article
Tension energies for acyclic and cyclic assemblies of adamantane units sharing hexagons of carbon atoms converge in a size-extensive manner for large numbers n of adamantane units. In most cases the convergence features diagrams of strain energy per adamantane unit E (n⁻¹) versus n⁻²for cyclic aggregates and versus n⁻¹ for acyclic aggregates having...
Article
Full-text available
(Formula presented) In the 1970s the reversble spin-trapping of the biologically active nitric oxide (NO) by nitrosobenzene was discovered, and it allowed devising new NO donors from cupferron derivatives. In the present study, two ab-initio methods (Density Functional Theory and Møller-Plesset-2) were used for computing electronic properties (grou...
Article
In order to perform the screening of new potential pollution points and to estimate their impact on the environment, a quantitative structure-activity research (QSAR) modeling procedure was used to estimate possible toxicological effects of substances that were introduced into the environment. We have focused our study initially to known persistent...
Article
Tetramantanes, and all diamondoid hydrocarbons, possess carbon frameworks that are superimposable upon the cubic diamond lattice. This characteristic is invaluable in assigning their (1) H and (13) C NMR spectra because it translates into repeating structural features, such as diamond-cage isobutyl moieties with distinctively complex methine to met...
Article
Diamondoids are hydrocarbons having a carbon scaffold comprised from polymer-like composites of adamantane cages. The present paper describes computed total energies and "SWB-tension" energies (often referred to as "strain" energies) for species having $n$ adamantane or diamantane units sharing pairwise: one carbon atom (spiro-[n]adamantane or spir...
Article
In this chapter, we describe ortho-benzoquinone and its congeners where exocyclic groups are CH2, S, NH, or O. The two valence isomer forms include a bicyclo[4.2.0]octane system with an aromatic benzenoid ring fused to a four-membered ring, and a nonaromatic cyclohexadienic ring with two exocyclic double bonds. Ten types of pairs of valence isomers...
Article
The distinction between interdisciplinarity, multidisciplinarity, and transdisciplinarity is emphasized. Chemistry evolved later as a science than physics, so that in the early 19th century renowned philosophers denied the possibility of mathematics being useful for chemical problems. Later, with the advent of quantum mechanics, chemistry was viewe...
Patent
Full-text available
Methods and compositions are provided for generating and applying long-lasting therapeutic nitric oxide (NO) gas from the reaction of water-soluble chemical reactants microencapsulated in polymer matrices. In some applications the microencapsulated reactants are introduced in an aqueous gel, and in other applications they are introduced to the area...
Chapter
If an element deserves praise, then this element is carbon. Its nucleus, along with N and O, catalyzes the fusion of H into He in the sun and sun-like stars. Its minor stable isotope allows chemical structure to be elucidated by 13C-NMR, along with 1H-NMR. Its long-lived radioisotope 14C allows radiocarbon dating, and reaction mechanisms or bioacti...
Article
Diamondoid structures with shared vertices, edges, or 6-membered rings can theoretically be curved into toroidal structures whose calculated energy provides information about steric strain. Diamondoid hydrocarbons sharing one vertex between two adamantane units are called [n]spiromantanes, where n indicates the number of adamantane units. When a pa...
Chapter
This review chapter discusses oxygen and peroxides in organic chemistry. Numerous types of oxygen species are described including ions, radicals, biradicals, and zwitterionic species; examples of such species are superoxide anion (O2⋅−), dioxygenyl cation (O2⋅+), ozone (O3), oxygen oligomers (Ox), and the lowest excited singlet state of oxygen (1Δ)...
Article
The Hirsch index h measures scientific achievement or research output based on the numbers of publications and citations. The present author's index h has been considerably exceeded by the h index of one of his Ph. D. students, Claudiu Supuran, who is at present Professor at the Universita degli Studi, Florence, Italy. Professor Supuran's research...
Article
We use flag graphs to describe benzenoid and coronoid systems. Factoring out symmetries, we obtain a symmetry-type graph, which may be interpreted as a surface with boundary plus an additional combinatorial structure, which is then used to partition benzenoids into 14 classes, thereby re-interpreting in a purely combinatorial way the classification...
Article
By analogy with benzenoids, diamond hydrocarbons (diamondoids for short) can be classified according to their dualists into catamantanes with acyclic dualists, perimantanes with dualists having 6-membered rings, and coronamantanes having larger rings that are not peripheries of 6-membered ring aggregates. Coronoid diamond hydrocarbons may be either...
Article
Full-text available
The dualist of an [n]diamondoid consists of vertices situated in the centers of each of the n adamantane units, and of edges connecting vertices corresponding to units sharing a chair-shaped hexagon of carbon atoms. Since the polycyclic structure of diamondoids is rather complex, so is their nomenclature. For specifying chemical constitution or iso...
Article
The development of chemical applications of graph theory is reviewed from a personal perspective. Graph-theoretical methods for finding all graphs fulfilling certain mathematical conditions followed by eliminating chemically impossible solutions are equivalent to the 'Sherlock Holmes principle'.For molecular graphs, this is illustrated by monocycli...
Article
[n]Diamondoids are hydrocarbons whose carbon skeleton is a portion of the diamond lattice, and contains n adamantane cells (or units) sharing chair-shaped hexagons of carbon atoms. When centers of these adamantane units are connected by lines, the resulting construction is called the dualist of the diamondoid, and it also is similar to a portion of...
Chapter
Among the two long-known allotropic forms of carbon, sp2-hybridized multilamellar graphite is the thermodynamic stable form at normal temperature and pressure, whereas the denser sp3-hybridized diamond becomes favored at very high pressures. Portions of graphene sheets with dangling bonds connected with hydrogen atoms are planar polycyclic benzenoi...
Article
By analogy with the Stone–Wales rearrangement in sp2-hybridized carbon allotropes that involves turning one CC bond by 90° in a graphene sheet and reconnecting it cross-wise with two carbon atoms, the similar rearrangement for the diamond lattice was called connected exchange. In this case one C–C bond in the diamond lattice involving sp3-hybridize...
Article
Full-text available
2-Mercaptobenzothiazole (1) reacts with halo-nitro-aromatics (2a-2g) by nucleophilic substitution yielding crystalline sulfides (3a-3g). The following halo-nitro-aromatics were employed: 2a, 4-chloro-7-nitrobenzofurazan or NBD-Cl; 2b, picryl chloride; 2c, 1-fluoro-2,4-dinitrobenzene; 2d, 2-chloro- 3,5-dinitropyridine; 2e, 1,5-difluoro-2,4-dinitrobe...
Article
Isomeric diamondoids with the same number $n$ of adamantane units (or cells), which share the same molecular formula $\text{ C}_\mathrm{Q}(\text{ CH})_\mathrm{T}(\text{ CH}_{2})_\mathrm{S}$ , can be divided into valence isomers by partitioning the number $C $ of their carbon atoms according to whether they are Quaternary, Tertiary, or Seconda...
Article
A partial distance-weighted variable anti-connectivity topological index was introduced for modelling pK (a) values of 31 aliphatic carboxylic acids and haloalkyl-carboxylic acids. The partial distance-weighted variable anti-connectivity index showed superior modelling capabilities compared with the index calculated from the complete graph, because...
Article
We explore the possibility of using selective invariants of a novel distance matrix D max of graphs to discriminate between graphs. The D max matrix contains information only on dominant distances of a graph, which are defined as those entries in a distance matrix that are the largest in any row or a column. For a test we selected a set of the smal...
Article
Isomeric diamond hydrocarbons (diamondoids or polymantanes) with the same number n of adamantane units share the same molecular formula C(Q)(CH)(T)(CH(2))(S) and can be divided into valence isomers (denoted as Q-T-S) by partitioning the number C = Q + T + S of their carbon atoms according to whether they are quaternary, tertiary, or secondary. Vert...
Article
The Hirsch citation index h is nowadays the most frequently used numerical indicator for the performance of scientists as reflected in their output and in the reaction of the scientific community reflected in citations of individual contributions. A few of the possible improvements of h are briefly reviewed. Garfield’s journal impact factor (IF) ch...
Article
There is current interest, both for basic science and technological applications, in fluorocarbons such as CF4 and the related molecules. Here we first report a Hartree–Fock calculation of the ground-state electron density in the octahedral molecule SF6 using the experimentally determined bond length. From this density, the number of electrons lyin...
Article
We report on calculated CC bond currents for a dozen derivatives of hexabenzocoroenene in which one or more proximal carbon atoms at the molecular periphery have been bridged. The approach that we use is graph-theoretical in nature, following our outline of this method in 2003, which is based on finding all conjugated circuits in all Kekulé valence...
Article
Flag graphs have been used in the past for describing maps on closed surfaces. In this paper we use them for the first time in mathematical chemistry for describing benzenoids and some other similar structures. Examples include catacondensed and pericondensed benzenoids. Several theorems are included. Symmetries of benzenoid systems, flag graphs, a...
Article
Comparison is made between three different indices that characterise the individual rings of a wide range of condensed benzenoid hydrocarbons. Two of these ("pi-electron partitions" and the six-centre delocalisation-indices that have been called "Delta(6)-values") have been introduced only recently as potential indicators of what might be called "l...
Article
After recalling that art and science belong to Snow's 'two cultures', a brief mention is made of the 'stimulus package' proposed by Vannevar Bush for basic science in USA. Common traits are shared by artists and scientists, especially when the latter ones also create their objects of study (invention versus discovery). A few personal contributions...
Article
Full-text available
In a quest for novel persistent free radicals, two products were obtained from the reaction between 1,1-diphenylhydrazine and 4-chloro-7- nitrobenzofurazan: the expected 1-(4-nitrobenzofurazan-7-yl)-2,2-diphenyl- hydrazine 3 formed via an S NAr process, and the unexpected 4,7-benzofurazandione-(bis-1,1-diphenylhydrazone) 4 formed from 3 by a furthe...
Article
Full-text available
AbstractEarlier studies revealed that the effect of benzo-annelation on cyclic conjugation in the central ring of a polycyclic conjugated molecule obeys certain general regularities. We now elaborate quantitative models of this effect, showing that the main factors that need to be taken into account are the numbers of angularly, linearly, and gemin...
Article
We revisited the π-electron ring partitions in catacondensed benzenoids and re-examined structural regularities reported for the ring partitions in these compounds, seeking the origin of the observed regularities. We examined the distribution of the π-electron ring partitions by counting the contributions arising from benzene rings having different...
Article
Full-text available
The effects of benzo- and benzocyclobutadieno-(BCBD-)annelation on the local aromaticity of the central ring (X) of phenanthrene were examined. The local aromaticity of the ring X was estimated using a graph-theory-based index and two geometry-based indices. DFT calculations of phenanthrene congeners showed that many of these molecules are nonplana...
Article
We consider the aromaticity of biphenylene and structurally related linear or angular [n]phenylenes for which the direct application of the model of conjugated circuits does not offer valid expressions for resonance energy and aromaticity. We located the cause of this problem as being due to Kekulé valence structures in which neighboring benzenoid...
Article
After a brief history of the aromaticity concept, the use of Clar sextet circles is reviewed for explaining various aspects of planar aromatic systems (benzenoids, heterocycles) and of tridimensional carbon aggregates. When folding a graphene sheet for obtaining nanotubes, nanotori, or nanocones, the congruence of Clar sextet circles allows the cla...
Article
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Article
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This review discusses from a qualitative viewpoint three-dimensional structures (hydrocarbons and carbon allo-tropes) that can be obtained from the 4,6,12-archimedean tiling of the Euclidean plane (graphenylene net) or that are related to subgraphs derived from the graphenylene net, insisting on helical structures called [n]heliphenes with alternat...
Chapter
After an introductory brief discussion of the important and much debated concept of aromaticity, we elaborate on a recently proposed scheme for the partition of π-electrons of Kekuléan polycyclic conjugated hydrocarbons to individual rings, so that by summing π-electrons within individual rings of polycyclic conjugated hydrocarbons one obtains the...
Article
Full-text available
Abstract Considerations based on the energetics of cyclic conjugation in individual rings indicate that benzocyclobutadieno-annelation has the opposite effect on local aromaticity in benzenoid hydrocarbons to benzo-annelation. This finding is now tested and corroborated by density functional theory (DFT) calculations of the geometry of all benzo- a...
Article
Full-text available
Earlier studies revealed that benzo-annelation has a peculiar effect on the intensity of cyclic conjugation in the five-membered ring of fluoranthene congeners. Now, the analogous effect of benzocyclobutadieno-annelation was examined and it was found show it is opposite to the effect of benzo-annelation: a benzocyclobutadiene fragment in angular (r...
Article
Full-text available
Starting from the Kryptofix 22 azacrown compound, mono-and di-branched derivatives have been synthesized, by coupling with one or two 4-chloro-3,5-dinitrobenzoyl chloride units and then substituting the chlorine(s) on the aromatic ring(s) with methoxyamine. The two new compounds were characterized by IR, NMR, and UV-Vis spectra; they are soluble in...
Article
Full-text available
The molecular structure of any system may be unambiguously described by its adjacency matrix, A, in which bonds are assigned entry a(ij) = 1 and non-bonded pairs of atoms entry a(ij) = 0. For π-electron-containing conjugated hydrocarbons, this matrix may be modified in order to represent one of the possible Kekulé structures by assigning entry 1 to...
Article
Laser action is demonstrated to occur in seven pyrylium salts between 4100 and 5100 Å with quantum yields extending from 4% to 12%. Theoretical calculations of the energy and oscillator strength of S0 → Sn transitions confirm band assignments deduced from experimental results. These results allow detection of a weak hidden transition in the 2,6-dim...
Article
Two new radical-cations (as crystalline perchlorates) 1 and 2 were synthesized from the respective amines 3 and 4, and 2,4,6-trimethylpyrylium perchlorate 5. The properties and spectra of the new radical-cation perchlorates (which may be recrystallized from ethanol or from water) are described.
Article
Full-text available
The effects of tritiated water on derivatives of benzene and pyridine in the presence of aluminum chloride were investigated. The specific activities obtained reflect the order of decreasing reactivity towards electrophilic substitution: benzene approximates fluorobenzene> chlorobenzene) 2,4,6- collidine> 2,6-lutidine > pyridine> nitrobenzene. (...
Article
In a quest for novel persistent free radicals, two products were obtained from the reaction between 1,1-diphenylhydrazine and 4-chloro-7-nitrobenzofurazan: the expected 1-(4- nitrobenzofurazan-7-yl)-2,2-diphenyl-hydrazine 3 formed via an SNAr process, and the unexpected 4,7-benzofurazandione-(bis-1,1-diphenylhydrazone) 4 formed from 3 by a further...
Article
Full-text available
Axial chirality is present in many interesting structures. Some predicted helical structures may be stabilized by inter-or intra-molecular hydrogen bridges.
Article
Full-text available
In a series of earlier studies, it was established that benzo-annelation in the angular (resp. linear) position relative to a ring R of a polycyclic conjugated pi-electron system, increases (resp. decreases) the intensity of the cyclic conjugation in the ring R. Herein, it is shown how this regularity can be explained by means of a simple, Kekule-s...
Article
In continuation of previous investigations, it is now shown that for catafuscnes the Hückel π-electron energy is correlated excellently with two simple descriptors (small integers), namely the number h of benzenoid rings and the number n of zeros in the code of their dualists, i.e. the number of linearly fused rings. On the other hand, several bulk...
Article
Aromaticity is regarded as the cornerstone of heterocyclic chemistry. It is largely multidimensional and scale dependent. It is noted that five and six-membered aromatic heterocycles can accommodate a π-electron sextet without appreciable strain. This chapter describes how a planar two-dimensional symmetry, with molecules, having sp²-hybridization,...
Article
Molecular insights into cationic lipid assemblies are relatively hard to reveal due to intrinsic mobility of the structural elements, hydration of the polar head and counterion, etc. Using X-ray diffraction of 4,6-dimethyl-2-tetradecyl-1-(2-tetradecanoyloxyethyl)pyridinium hexafluorophosphate (1) single crystals we succeeded in visualizing the mole...
Article
A synthetic design was devised for preparing primary amines related to anticancer drugs clomiphene and tamoxifen on the basis of key intermediates with a phenolic group, to which a side chain (omega-aminoethoxy or omega-aminopropoxy) was attached. These compounds were then reacted with 2,4,6-trimethyl- or 2,4,6-triphenylpyrylium salts. This afforde...
Article
Starting from 4-chloro-3,5-dinitrobenzoic acid 1, compounds 2–10 (N-alkoxy-3,5-dinitro-4-aminobenzoic acid esters where alkoxy stands for methoxy, carboxymethoxy, triphenylmethoxy, or corresponding amides) have been obtained, from which compounds 3–5 and 7–10 are new, and for the known compounds 2 and 6 the synthetic procedure has been improved. Th...
Article
N-Phenylaza-15-crown-5 3 reacts with phenothiazine 1a, 2-chlorophenothiazine 1b, or phenoxazine 1c in the presence of mild oxidizing agents (I2, Fe 3+ or Cu 2+ ) affording new Wurster aza-crown-ethers 4a–4c. Homolytic processes for the formation of compounds 4a-4c were discussed. Redox properties of these compounds were investigated by cyclic volta...

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