Liudmil Antonov

Liudmil Antonov
Bulgarian Academy of Sciences | BAS · Emil Djakov Institute of Electronics

PhD, DSc

About

166
Publications
43,307
Reads
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3,520
Citations
Introduction
Liudmil Antonov currently works at the Institute of Electronics, Bulgarian Academy of Sciences. Liudmil does research in Analytical Chemistry, Physical Organic Chemistry and Spectroscopy. The current projects are based on the tautomerism of organic compounds. More info: http://www.tautomer.eu
Additional affiliations
July 2020 - present
Bulgarian Academy of Sciences
Position
  • Professor
May 2011 - December 2011
Tokyo Institute of Technology
Position
  • JSPS Visiting Professor
April 2007 - June 2020
Bulgarian Academy of Sciences
Position
  • Professor (Associate)
Education
September 1995 - August 1996
Tokyo Institute of Technology
Field of study
  • Theoretical Chemistry
March 1990 - September 1993
Sofia University "St. Kliment Ohridski"
Field of study
  • Molecular spectroscopy
September 1984 - September 1989
Sofia University "St. Kliment Ohridski"
Field of study
  • Organic and Analytical Chemistry

Publications

Publications (166)
Article
Two novel, 7-hydroxyquinoline based, Schiff bases have been synthesized and their spectral properties have been investigated by combined use of optical and NMR spectroscopy and theoretical DFT calculations. The results indicate that 8-((phenylimino)methyl)quinolin-7-ol exists as a mixture of enol and two keto tautomers in solution, while 8-(((penta...
Article
The reimagined concept of long-range tautomeric proton transfer using crane sub-units has been presented by designing and synthesising two new acylhydrazones containing 7-hydroxyquinoline (7-OHQ) platform. The acylhydrazone sub-units attached to the 7-OHQ at 8th position act as a crane arm for proton cargo delivery to the quinoline nitrogen. Light-...
Article
Full-text available
In this short review, we attempt to unfold various aspects of excited-state intramolecular proton transfer (ESIPT) from the studies that are available up to date. Since Weller’s discovery of ESIPT in salicylic acid (SA) and its derivative methyl salicylate (MS), numerous studies have emerged on the topic and it has become an attractive field of res...
Article
Comprehensive chemical profiling of threeRosa damascena Mill. essential oil samples and two extracts (supercritical and subcritical) was performed by means of GC/MS/FID. As a result 85 compounds, representing 87.9-99.2% of the detected compounds, were identified by GC/MS and simultaneously quantified by GC-FID.The main aroma constituents in the ess...
Article
Electronic transitions appear in the spectrum as individual bands, described by three basic parameters (position, intensity and width), which can be used for estimation of the fundamental transition characteristics as well as for quantitative analysis. The main problems concerning the mathematical resolution of overlapped individual bands in a comp...
Article
The ability of long-range proton transport by substitution of 7-hydroxyquinoline at the eighth position with sulfonamide and sulfonylhydrazone rotor units to act as a crane-arm has been studied. Different proton transport pathways triggered by different stimuli have been established depending on the structure of the crane-arms. Solvent-driven proto...
Article
The ground state tautomerism and excited state intramolecular proton transfer in two new molecular switches, namely N-(benzo[d]thiazol-2-yl)picolinamide and N-(benzo[d]thiazol-2-yl)isonicotinamide, are studied in acetonitrile by the combined use of steady state and time dependent spectroscopy and DFT calculations. Although, according to the theoret...
Article
Full-text available
The acid dissociation constant of three benzimidazoles, namely 2,2′-bibenzo[d]imidazole, 2,5′-bibenzo[d]imidazole, and 5,5′-bibenzo[d]imidazole, have been investigated by means of density functional theory calculations in gas phase and in aqueous solution. The theoretical approach was validated by the comparing of predicted and experimentally deter...
Article
Full-text available
A comprehensive chemical profiling of 1,1,1,2-tetrafluoroethane (freon R134a) subcritical extracts from the main genotypes of oil-bearing roses, was performed by gas chromatography–mass spectrometry (GC/MS) and gas chromatography with flame ionization detection (GC-FID) in order to reveal the differences in their chemical composition. One hundred a...
Article
Full-text available
Тhe adequacy of chemical property predictions strongly depends on the structure representation, including the proper treatment of the tautomeric and isomeric forms. A combination of an in-house developed open-source tool for automatic generation of tautomers, Ambit-Tautomer, based on H-atom shift rules and standard quantum chemical (DFT) calculatio...
Article
A novel rotary switch, overcoming the disadvantages of the hydrazone based switches with competitive proton acceptor sub-rotors, has been designed. The new compound contains pyridyl ring and COOH group as sub-rotors, which provides engagement of the pyridyl nitrogen atom and leads to existence of a single isomer in the ground state. The availabilit...
Article
The photoinduced birefringence of two 4-substituted phthalimide 2-hydroxy Schiff bases, containing salicylic (4) and 2-hydroxy-1-naphthyl (5) moieties has been investigated in PMMA matrix. Their optical behaviour as nanocomposite films was revealed by combined use of DFT quantum chemical calculations (in ground and excited state) and experimental o...
Cover Page
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Special Issue of Molecules. The aim of this Special Issue is to collect together scientific works related to the prototropic tautomerism and proton transfer in ground and excited state in the gas phase, solution and solid state. Experimental and theoretical studies describing the structural and environmental (solvent, temperature, acidity, irradia...
Article
Full-text available
Theoretical design of conjugated proton cranes, based on 7-hydroxyquinoline as a tautomeric sub-unit, has been attempted by using ground and excited state density functional theory (DFT) calculations in various environments. The proton crane action request existence of a single enol tautomer in ground state, which under excitation goes to the excit...
Article
Two new 4-OH coumarin based rotary switches, containing fixed carbonyl groups in the rotor, have been synthesized and their properties have been studied by combined use of DFT calculations and molecular spectroscopy (UV-Vis absorbance and emission, NMR). It was found that the structure of the stator (naphthyl in 2 or quinolyl moiety in 3) and solve...
Article
Full-text available
There is no experimental information about the tautomerism of Favipiravir (T-705). Therefore, its tautomeric state was predicted by using density functional theory in gas phase and in solution (toluene, acetonitrile and water). The results have shown that, in neutral state, the enol form is strongly dominating in both gas phase and solution. The ca...
Article
The tautomerism of 8-(phenyldiazenyl)quinolin-5-ol has been studied by a combination of theoretical (DFT calculations) and experimental (UV-Vis and NMR) methods. The detailed study of neutral molecules has shown that the hydrazone tautomeric form, stabilized by an intramolecular N-H···N hydrogen bond, is solely present in most of the solvents. In s...
Article
Full-text available
The properties of several hydrazon-diketone rotary switches with OH groups in the stators (2-(2-(2-hydroxy-4-nitrophenyl)hydrazono)-1-phenylbutane-1,3-dione, 2-(2-(2-hydroxyphenyl)hydrazono)-1-phenylbutane-1,3-dione and 2-(2-(4-hydroxyphenyl)hydrazono)-1-phenylbutane-1,3-dione) were investigated by molecular spectroscopy (UV-Vis and NMR), DFT calcu...
Article
The paper presents the synthesis and characterization of two 4-substituted phthalimide 2-hydroxy-Schiff bases containing salicylic (4) and 2-hydroxy-1-naphthyl (5) moieties. The structural differences of 2-hydroxyaryl substituents, resulting in different enol/keto tautomeric behaviour, depending on the solvent environment were studied by absorption...
Article
The paper presents the synthesis and characterization of two 4-substituted phthalimide 2-hydroxy-Schiff bases containing salicylic (4) and 2-hydroxy-1-naphthyl (5) moieties. The structural differences of 2-hydroxyaryl substituents, resulting in different enol/keto tautomeric behaviour, depending on the solvent environment were studied by absorption...
Preprint
Full-text available
There is no experimental data about the tautomerism of Favipiravir (T-705). Therefore its tautomeric state was predicted by using density functional theory in gas phase and in solution (toluene, acetonitrile and water). The solvent effect was described by means of the Polarizable Continuum Model. The results have shown that the enol form is strongl...
Preprint
Full-text available
There is no experimental data about the tautomerism of Favipiravir (T-705). Therefore its tautomeric state was predicted by using density functional theory in gas phase and in solution (toluene, acetonitrile and water). The solvent effect was described by means of the Polarizable Continuum Model. The results have shown that the enol form is strongl...
Article
The E/Z switching mechanism of the rotary switch ethyl-2-(2-(quinolin-8-yl)hydrazono)-2-(pyridin-2-yl)acetate was studied by NMR, UV–Vis, and ultrafast spectroscopy and modeled by advanced quantum-chemical calculations. Three possible mechanisms were considered theoretically: out-of-plane rotation, in-plane inversion and proton transfer. Neither of...
Article
Complexation reactions of polyether ionophorous antibiotic Monensin A with divalent metal ions were studied in methanolic solutions by means of synchrotron radiation circular dichroism (SRCD) spectroscopy. Data showed that in the presence of organic base (Et4NOH) Monensin A forms two types of metal complexes depending on metal-to-ligand molar ratio...
Article
Full-text available
Two novel pinene-type ligands have been synthesized and their tautomeric and self-associating behavior studied in solution and in the solid state. The first ligand, an acetylated derivative of 5,6-pinene-bipyridine, displays keto-enol tautomerism in solution. This tautomeric equilibrium was studied by NMR and UV-Vis spectroscopy in various solvents...
Article
Full-text available
Raman spectroscopy, being able to provide rich information about the chemical composition of the sample, is gaining an increasing interest in the applications of food. Raman spectroscopy was used to analyze a set of wine samples (red and white) sourced from rarely studied traditional Bulgarian wines. One of the objectives of this study was to attem...
Cover Page
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Article
Full-text available
The concept for sensing systems using the tautomerism as elementary signaling process has been further developed by synthesizing a ligand containing 4-(phenyldiazenyl)naphthalene-1-ol as a tautomeric block and an amide group as metal capturing antenna. Although it has been expected that the intramolecular hydrogen bonding (between the tautomeric hy...
Article
We present a combined theoretical and experimental study on the UV-Vis spectra of enol-keto (EK) and keto-keto (KK) tautomeric forms of curcumin dissolved in aqueous solution. Solvent effects have been investigated by resorting to the implicit Polarizable Continuum Model (QM/PCM) and non-polarizable and fully polarizable QM/MM approaches, the latte...
Article
Full-text available
The performance of 26 hybrid density functionals was tested against a tautomeric dataset (TautData), containing experimental information for the keto-enol tautomeric equilibrium in 16 tautomeric azodyes and Schiff bases in cyclohexane, carbon tetrachloride and acetonitrile. The results have shown that MN12-SX, BHandH and M06-2X can be used to descr...
Article
Full-text available
A comprehensive study was performed for the first time to compare two structurally related substance classes, namely indazole-5-carboxamides (11-16) and (indazole-5-yl)methanimines (17-22). Both chemical entities are potent, selective and reversible MAO-B inhibitors and, therefore, may serve as promising lead structures for the development of drug...
Preprint
Full-text available
The concept for sensing systems using the tautomerism as elementary signaling process has been further developed by synthesizing a ligand containing 4-(phenyldiazenyl)naphthalene-1-ol as a tautomeric block and an amide group as metal capturing antenna. Although it has been expected, that the intramolecular hydrogen bonding (between the tautomeric h...
Article
The title compound potentially can exist as four isomers in solution. Recently Lycka has proposed a protocol for distinguishing two of them based on 15N NMR. This approach has been confirmed theoretically, in the current study, and further developed into a logical scheme that allows the existence of each of the isomers to be proven in solution. The...
Article
In order to meet the need for NMR reference compounds in the study of tautomeric azo dyes, two series of azo dyes, derived from 3-methyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-amine and 5-methyl-2-phenyl-4-(2-phenylhydrazono)-2,4-dihydro-3H-pyrazol-3-one, have been studied by using molecular spectroscopy (UV–Vis and NMR) and quantum-chemical calc...
Article
The tautomeric optical sensors based on 4-(phenyldiazenyl)naphthalen-1-ol exist in their pure enol tautomeric form as free ligands, while the addition of metal ion fully shifts the equilibrium towards the keto tautomer allowing a red shift in the measured absorbance. This effect is achieved when a side ionophore group is connected to a tautomeric b...
Article
Full-text available
The possibility of applying near-infrared (NIR) spectroscopy to monitor 13 active components (phenolic acids, flavonoids, and sesquiterpene lactones) in Arnicae flos was studied. The preprocessing of the spectra were performed by using the conventional Golay-Savitzky procedure and the newly developed step-by-step filter. The results obtained show t...
Article
Hydrazones are popular building blocks in the development of functional materials because of their simple structure, straightforward synthesis, hydrolytic stability and tunable properties. Although a significant body of experimental information has been accumulated on the hydrazone-based rotary switches, mechanistic studies are still scarce. The ef...
Article
Full-text available
DEVELOPMENT OF NEW HIGHLY POTENT DRUG LEADS FOR DISORDERS OF THE CENTRAL NERVOUS SYSTEM NTZ Lab Ltd. has developed new promising brain-penetrant compounds, the discovery of which is described in our latest publication in the European Journal of Medicinal Chemistry. We develop a series of promising BBB permeable derivatives combining both high pot...
Article
Recently a useful paper of Muelleman and Glaser has been published in this Journal demonstrating how Microsoft Excel can be applied for band decomposition in IR and UV–vis spectroscopy. With this communication, I intend to update the provided information, stressing the physical meaning of the results and defining some of the terms used.
Article
Full-text available
The ability of oxime-containing acetylcholinesterase reactivators BT-07 (K005), BT-08 (K033), BT-07-4M (K074), and obidoxime (H 2 LX 2, X = Cl⁻ , Br⁻) to bind palladium(II) or platinum(II) cations was evaluated in aqueous solutions (pH 7.4) at metal-to-ligand molar ratio varying from 1:10 to 10:1. Spectral changes were monitored within a week after...
Article
A series of aryl azo derivatives of naphthols (1–3) were studied by means of UV–Vis and NMR spectroscopy in different solvents as well as by quantum chemical calculations and X-ray analysis. Previous studies have shown that Sudan I (1) exists as a tautomeric mixture. The effect of the solvents is minimized by the existing intramolecular hydrogen bo...
Article
Rosa damascena Mill. is one of the most important plants from Rosaceae family, with a long historical use in the traditional medicine and as a valuable oil bearing plant. The rose scent derived as oil, concrete or absolute, is one of the world most sought-after products and the development of reliable analytical methods for the origin assessment an...
Article
Full-text available
Pharmacological and physicochemical studies of N-unsubstituted indazole-5-carboxamides (subclass I) and their structurally optimised N1-methylated analogues (subclass II), initially developed as drug and radioligand candidates for the treatment and diagnosis of Parkinson’s disease (PD), are presented. The compounds are highly brain permeable, selec...
Article
The ground state tautomerism and excited state intramolecular proton transfer (ESIPT) of 10-hydroxybenzo[h]quinoline (HBQ) and its nitro derivatives, 7-nitrobenzo[h]quinolin-10-ol (2) and 7,9-dinitrobenzo[h]quinolin-10-ol (3), has been studied in acetonitrile by steady state as well as time dependent spectroscopy and quantum-chemical calculations....
Article
The effect of the complex formation with calix[4]arene on the tautomerism of curcumin was studied in water by means of theoretical calculations at M062X/6-31G(d,p) level of theory. The results show that both tautomeric forms can enter and leave the host cavity without sterical problems. The binding of the diketo tautomeric form was found to be more...
Article
The tautomeric properties of an N-(3,4-dichlorophenyl)-1H-indazole-5-carboxamide (NTZ-1006, 2) derivative, developed as highly potent, reversible and selective MAO-B inhibitor useful for the treatment of Parkinson's disease (PD) and other neurological disorders, have been studied both experimentally and theoretically. The theoretical data (M06–2X,...
Article
Full-text available
The use of spectral measurements using either UV, visible (VIS), or near-infrared (NIR) spectroscopy to characterize wines or to predict wine chemical composition has been extensively reported. However, little is known about the effect of path length on the UV, VIS, and NIR spectrum of wine and the subsequent effect on the performance of calibratio...
Article
The title compound is potentially tautomeric and its tautomerism was studied by means of molecular spectroscopy (1H and 13C NMR and UV-Vis) in DMSO as well as by quantum chemical calculations (M06-2X/TZVP). The detailed assignment of the NMR signals supported by the theoretical calculations clearly shows that the previous interpretation, available...
Article
In two consecutive studies the tautomerism in 4-((2-hydroxynaphthalen-1-yl)diazenyl)-3,5-dinitrobenzoic acid and the structurally similar 1-((2-nitrophenyl)diazenyl)naphthalen-2-ol has been considered from viewpoint of theoretical chemistry, UV-Vis spectroscopy and NMR. Although the theoretical data (at M062X level) show that both compounds exist o...
Article
The solvent dependent excited state dynamics of 4-hydroxy-3-(piperidin-1-ylmethyl)-1-naphthaldehyde (compound 2), a candidate for a molecular switch based on intramolecular proton transfer, was investigated by ultrafast spectroscopy and quantum-chemical calculations. In acetonitrile a mixture of molecules in the enol and zwitterionic proton transfe...
Article
Savitzky-Golay differentiation procedure is a commonly used pre-processing technique in the near infrared spectroscopy being implemented in the instrumental or specialized data processing software. However, the spectra can be recorded linearly to the wavelength or energy scale depending on the available instrument, which leads to different derivati...
Article
The pharmacological and physicochemical analysis of structurally optimized N-alkyl-substituted indazole-5-carboxamides, developed as potential drug and radioligand candidates for the treatment and diagnosis of Parkinson's disease (PD) and other neurological disorders, is reported. Recent efforts have been focused on the development of subnanomolar...
Article
The tautomeric structures of 4-((2-hydroxynaphthalen-1-yl)diazenyl)-3,5-dinitrobenzoic acid have been revised by using quantum chemical (M06-2X/TZVP) calculations showing that the previously suggested structures are incorrect. By using theoretically predicted relative energies and Uv–Vis spectral analysis of a structurally similar compound (1-((2-n...
Article
The tobacco absolute usually obtained from tobacco waste, generated at various stages of post-harvest processing of the tobacco leaves and the cigarettes production, can be an important source of natural additives for tobacco compositions and cosmetics. Therefore, the chemical profile of Bulgarian tobacco absolutes derived from the three main type...
Article
A simple approach for the synthesis of multifunctionalized N1-alkyl 7-amino-6-azaoxindole derivatives was developed and investigated. Formation of 5-amino- and 7-amino-6-aza-2-oxindoles 12a and 13a, respectively, was achieved using an intramolecular reductive cyclization as a key step. Subsequent alkylation of the pyrrole N1 atom in 12a led to the...
Book
Full-text available
Reflecting the substantially increased interest in tautomerism, this book demonstrates the transformation of fundamental knowledge into novel concepts and the latest applications. Each chapter introduces the theoretical background, before reviewing and critically discussing the experimental techniques and corresponding applications. Special emphasi...
Chapter
“N-Type” and “C-type” tautomerism and their features are considered in this chapter.
Chapter
Some interesting examples of tautomeric systems are considered in this chapter in order to create a background for deeper experimental and theoretical interpretation.
Chapter
This chapter will consider most interesting and promising systems, where controlled shift in the position of tautomeric equilibrium can be achieved in solution upon protonation or complex formation. Advantages and disadvantages of the described systems will be discussed in order to provide further ideas for development.
Article
Proton transfer in 10-hydroxybenzo[h]quinoline (HBQ) and structurally modified compounds was investigated experimentally (steady state UV-Vis absorption and emission spectroscopy, NMR and advanced chemometric techniques) and theoretically (DFT and TD-DFT M06-2X/TZVP calculations) in the ground and excited singlet state. We observed that the incorpo...
Article
State of the art Density Functional Theory approaches have been employed to provide an accurate description of the photophysical properties of azodyes and Schiff bases displaying intramolecular hydrogen bonding features . These compounds exist as tautomeric mixtures at the ground state and, upon excitation, in the case of Schiff bases, an excited s...
Article
Full-text available
The conformational behaviour of 3-methyl-4-(4-methylbenzoyl)-1-phenyl-pyrazol-5-one was studied using a combination of X-ray diffraction, NMR spectroscopy in solution and solid state, and DFT calculations in the gas phase. The compound can adopt four different tautomers, determined by the combination of the keto–enol tautomerism of pyrazolone and t...
Article
The paper mentioned in the title contains inaccuracies and misleading interpretations that seriously misrepresent basic knowledge about tautomerism in azo dyes. Therefore, we aim in this Letter to correct the most obvious mistakes, to address the misrepresentation of the main issues of tautomerism, and to give a better understanding of the basic pr...