Venelin Enchev

Venelin Enchev
Bulgarian Academy of Sciences | BAS · Institute of General and Inorganic Chemistry

professor, DSc
Prebiotic and evolution chemistry. Modelling of chemical reactions. Sunscreens. Molecular structure.

About

126
Publications
24,029
Reads
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1,377
Citations
Citations since 2016
19 Research Items
424 Citations
20162017201820192020202120220204060
20162017201820192020202120220204060
20162017201820192020202120220204060
20162017201820192020202120220204060
Additional affiliations
February 1982 - May 2019
Bulgarian Academy of Sciences
Position
  • Professor (Full)
Education
February 1982 - February 1985
Bulgarian Academy of Sciences
Field of study
  • theoretical chemistry
January 1980 - June 1981
Sofia University "St. Kliment Ohridski"
Field of study
  • theoretical chemistry
October 1974 - September 1979
Sofia University "St. Kliment Ohridski"
Field of study
  • organic chemistry

Publications

Publications (126)
Article
Full-text available
Altogether six tautomers of cytosine and three tautomers of cytidine and deoxycytidine are studied theoretically in the gas phase and in a microhydrated environment. Their structures are optimized at MP2/6–31 + G(d,p) level. The relative energies of the isolated and the hydrated tautomers included the correction to higher correlation energy terms e...
Article
Full-text available
According to our previous investigation the total methanol extract from Graptopetalum paraguayense E. Walther demonstrates a significant inhibitory effect on herpes simplex virus type 1 (HSV-1). To clarify what causes this inhibitory activity on HSV-1, a metabolic profile of the plant was performed. Three main fractions: non-polar substances, polar...
Article
Full-text available
Abiotic synthesis of nucleobases and amino acids is of critical importance as it sheds light on potential prebiotic chemical reactions. During thermal decomposition of formamide in vacuum conditions, purine, cytosine, adenine, hypoxanthine, uracil, pterin, urea, urocanic acid, glycine, alanine and norvaline were detected. The compounds were obtaine...
Article
Full-text available
Reaction pathway of prebiotic reactions for formation of the pteridines: pterin, xanthopterine, isoxanthopterine and leucopterine, as well as the purine nucleobase guanine from pure formamide are presented. In these reactions, formamide or its tautomer, formimidic acid, play the role of proton-carrying catalyst. All required raw materials, such as...
Article
Full-text available
2-Carbamido-1,3-indandione (CAID) is a new reliable fluorescent biomarker and it exists in two tautomeric forms: 2-(hydroxyl-aminomethylidene)-indan-1,3-dione (A) and 2-carboamide-1-hydroxy-3-oxo-indan (B). The structures of the tautomers and the transition state for intramolecular proton transfer are located at MP2/6-31+G(d) level for each magnitu...
Article
Full-text available
Mechanisms of reactions for formylation of urea, leading to N,N 0-diformylurea, and for the dehydration of glycinamide and N,N 0-diformylurea, yielding hypoxanthine, are suggested. It is shown that these reactions are self-catalyzed. The first is catalyzed by formic acid, while the second is catalyzed by N,N 0-diformylurea. The suggested reaction m...
Article
Full-text available
Fluorescent and computational methods were used to elucidate the binding expedient of 2‐carbamido‐1,3‐indandione (CAID) tautomers to nucleotides. The dependence of the fluorescence emission of CAID loaded nucleic acids sequences to compound concentration, temperature and time variation was investigated. It was found that the subject compound binds...
Article
Full-text available
Complete reaction pathway of prebiotic reactions for formation of the purine nucleobases adenine, hypoxanthine, guanine, isoguanine, 2,6‐diaminopurine, and xanthine from pure formamide are presented. All reactants (hydrogen cyanide, ammonia, water, formic acid, urea) and catalysts (formamide and formimidic acid) needed in the self‐catalyzed reactio...
Conference Paper
Full-text available
Among the most common infections are those caused by human herpes viruses, including Herpes Simplex virus type 1 and type 2 (HSV-1 and HSV-2) spread worldwide. Common therapies for herpes infections employ nucleoside analogues, such as acyclovir, and target the viral DNA polymerase, essential for viral DNA replication. Systemic application of these...
Article
Full-text available
Syn- and anti-conformers of four tautomer structures of inosine were studied in gas phase and in solvent water to investigate the possibility of hydrogen bonding and of the tautomeric conversion. It was found that in the gas phase and in water solution the most stable is syn-conformer of the 6-keto tautomer followed by its anti-conformer and syn-co...
Article
Full-text available
Graptopetalum paraguayense E. Walther (GP) belongs to the Crassulaceae family and has several health benefits. In the present study we evaluated the cytotoxic, anti-Herpes Simplex virus (HSV) and antibacterial activities of a total methanol/water GP extract. The results from the cytotoxicity investigation of the tested extract showed a high cell to...
Article
Full-text available
Cytotoxicity assay of 2-carbamido-1,3-indandione (CAID) has been performed by means of the validated Balb/c 3T3 Neutral Red Uptake Test. In addition, the intracellular localization of CAID in murine embryonic fibroblasts, studied by fluorescence microscopy, is reported. The results indicate complete absence of toxicity of CAID to immortalized norma...
Article
Full-text available
The synthesis and structure elucidation of two new compounds, 2-(methylthio)-1,3-diazaspiro[4.4]non-2-ene-4-one (1) and 2-(methylthio)-1,3-diazaspiro[4.4]non-2-ene-4-thione (2), are presented. Both compounds crystalized in monoclinic crystal system. Compound 1 formed plate-like colorless crystals, while compound 2 gave yellow needles. The structura...
Article
A series of symmetric and unsymmetric monomethine azacyanine dyes (monomethine azacyanine and merocyanine sulfobetaines) were synthesized with moderate to high yields via a novel method using microwave irradiation. The compounds are derived from a condensation reaction between 2-thiomethylbenzotiazolium salts and 2-imino-3-methylbenzothiazolines pr...
Article
Full-text available
To provide an in-depth insight into the molecular basis of spontaneous tautomerism in DNA and RNA base pairs, a hybrid Monte Carlo (MC)–quantum chemical (QC) methodology is implemented to map two-dimensional potential energy surfaces along the reaction coordinates of solvent-assisted proton transfer processes in guanosine and its analog acyclovir i...
Article
Full-text available
New insight of the formation mechanism of chalcones is presented in the current study. Ab initio calculations were applied in studying the mechanistic pathways for the base-catalyzed Claisen–Schmidt condensation for obtaining chalcones (1,3-diphenyl-2-propen-1-ons). The energies of the stationary points along the reaction coordinate were obtained a...
Article
Full-text available
The aim of this preliminary study is to test the anti-conjunctivitis properties of xGraptoveria (Crassulaceae) and to identify its bioactive constituents. Fresh watery juice of leaves of xGraptoveria was extracted with n-butanol and the extract was analyzed by GC/MS. The ethnobotanical appraisal of the anti-conjunctivitis properties of xGraptoveri...
Article
Full-text available
The present work reports theoretical and experimental studies on the photophysical properties of two tautomeric forms of 2-carbamido-1,3-indandione (CAID). By means of UV-vis, steady-state and time-dependent fluorescence spectroscopy it is shown that both enol forms, 2-(hydroxylaminomethylidene)-indan-1,3-dione and 2-carboamide-1-hydroxy-3-oxo-inda...
Article
Full-text available
A hybrid statistical physics – quantum-chemical methodology was implemented to study the water-assisted intramolecular proton-transfer processes in 5- and 6-azauracils in aqueous solutions. The solvent effects were included in the model by explicit inclusion of two pairs of water molecules, which model the relevant part of the first hydration shell...
Conference Paper
Full-text available
Ab initio quantum chemical investigations on the tautomeric equilibrium in 5- and 6-azauracils in water were performed. The solvent effects were considered by explicit inclusion of two pairs of water molecules, which model a first hydration shell around the solute. The effects of the water as solvent were introduced at two different levels - using...
Article
Full-text available
The structure of 2-(4-hydroxyphenyl)-substituted indan-1,3-dione and phenalene-1,3-dione is investigated using a combination of solid-state NMR, single crystal X-ray analyses and quantum chemical calculations. It is shown that 2-(4-hydroxyphenyl)-1,3-indandione exists as a diketo tautomer while 2-(4-hydroxy-phenyl)-1,3-phenalenedione exists in the...
Article
Full-text available
The synthesis of two novel compounds, 1-amino-3',4'-dihydro-2H,2'H,5H-spiro[imidazolidine-4,1'-naphthalene]-2,5-dione and 1,3-bis(hydroxymethyl)-3',4'-dihydro-2H,2'H,5H-spiro[imidazolidine-4,1'-naphthalene]-2,5-dione, was re-ported. The structures of the compounds were verified by 1 H, 13 C NMR and IR spectroscopy and quantum-chemical cal-culations...
Article
Full-text available
A theoretical and experimental study on the absorption and fluorescence properties of a newly synthesized compound 3,6-bis(4,5-dihydroxyoxazo-2-yl)benzene-1,2-diol in ethanol is reported. Evidence suggesting intramolecular proton transfer in the excited singlet state is presented. All possible tautomeric forms are studied by means of TDDFT B3LYP/6-...
Article
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a b s t r a c t A new model tautomeric system with intramolecular hydrogen bonding is proposed. Geometry optimi-zations are performed at HF and MP2 levels and absorption spectra are simulated at TDDFT level. The MP2 level of theory was chosen for studying the effect of the external electric static field (EF) on the molecular electronic structure. T...
Article
Full-text available
Abstract NMR spectroscopy and quantum chemical calculations were applied for structural characterization and determination of the preferred stereochemical sequence distribution of the monomer units in the homopolymer chains of poly(butyl-a-cyanoacrylate) nanoparticles. The stereochemical sequence distribution of the monomer units was defined by ana...
Article
Antioxidants could be promising agents for management of oxidative stress-related diseases. New biologically active compounds, belonging to a rare class of natural lignans with antiangiogenic, antitumoral and DNA intercalating properties, have been recently synthesized. These compounds are benzo[kl]xanthene lignans (1,2) and dihydrobenzofuran neoli...
Presentation
Full-text available
The Nobel laureates in chemistry for the period 1901-2010 are presented.
Article
The structure of 2-carboxyindan-1,3-dione was investigated using a combination of quantum-chemical calculations and solid-state NMR and IR spectroscopy. Due to poor solubility of the compound in different solvents, no single crystals could be obtained. Two dimeric structures formed from the tautomers of 2-carboxyindan-1,3-dione are likely to coexis...
Article
Full-text available
It has long been postulated that rare tautomeric or ionized forms of nucleic acid bases may play a role in mispair formation. Therefore, ab initio quantum chemical investigations on the tautomeric equilibrium in 5-fluorouracil (5FU) and its anions (deprotonated from N1, AN1, and from N3, AN3) and their tautomeric forms in water were performed. The...
Conference Paper
Full-text available
The structure of metal complexes of Cu(II), Zn(II), Co(II), Ni(II) and Fe(III) with 2-carboxamide-indan-1,3-dione was investigated in gas phase by means of quantum-chemical calculations at ab initio level. It was found that the ferric complex is octahedral, Zn(II) and Co(II) are tetrahedral, Cu(II) has distorted tetrahedral structure and Ni(II) is...
Article
Full-text available
Detailed investigation of the tautomerism of oxadiazoles, thiadiazoles, and selenadiazoles containing hydroxy, mercapto, or selenyl groups in position 2 and 5 of the five-membered ring was carried out at MP2, MP4, and CCSD(T) levels of theory. The relative stabilities of the tautomers of the heterocycles were investigated in gas phase. It is found...
Article
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a b s t r a c t The pH influence on the cis–trans isomerization of the Valine-Proline dipeptide was investigated by means of NMR spectral techniques and quantum chemical calculations at different computational levels. It was found that the process of isomerization is strongly pH dependent. The trans-isomer of Val-Pro is the more abundant isomer whe...
Article
Full-text available
Two new platinum(IV) complexes of 3-aminocyclohexanespiro-5-hydantoin (achsh) and 3-aminocycloheptanespiro-5-hydantoin (achpsh) were prepared and characterized. Ab initio calculation of the structure and the measurements of IR and NMR spectra of complexes were also performed. The complex-es were evaluated for in vitro cytotoxicity in murine erythro...
Article
Full-text available
The structure and relative stabilities of the tautomers and isomers of 4-nitroso-pyrazolones were investigated at HF, DFT and MPn (n = 2, 4) quantum chemical levels. The effect of the medium on the relative stabilities of the different structures of the studied compounds was estimated using the polarizable continuum model. 1H, 13C and 15N NMR chemi...
Article
Full-text available
The design, preparation and characterization of poly(butylcyanoacrylate) nanoparticles as a drug-delivery system for daunorubicin is reported. A range of light scattering [photon correlation spectroscopy (PCS)], spectroscopic [(1)H nuclear magnetic resonance ((1)H NMR), Fourier transform infrared (FTIR), chromatographic [gel permeation chromatograp...
Article
Full-text available
The structures of N-(4-benzalaniline)-15-crown-5 and N-(4’-benzalaniline)-15-crown-5 and their Li+, Na+, K+, Be2+, Mg2+, Ca2+, Sr2+ and Ba2+ complexes are optimized using ab initio and DFT methods. It was found that in all cases the Mn+–N distances (n = 1, 2) are longer than the average Mn+–O ones in the corresponding complexes and the metal– nitro...
Article
Full-text available
The structures of some 2-substituted indan-1,3-diones are investigated in the gas phase and solution using quantum chemical calculations and spectral (NMR, IR, and UV) measurements. The influence of the substituent at the 2-position on the tautomeric equilibrium of 2-substituted indan-1,3-diones in solvents with different polarity is evaluated. It...
Article
Full-text available
The tautomeric equilibria of formamide, thioformamide, selenoformamide, 2-amino-4- oxo-oxazoline, 2-amino-4-oxo-thiazoline and 5-fluorouracil are studied in gas phase and in water solution using post-Hartree-Fock (MPn) and DFT quantum chemical calculations. The values of the proton transfer barriers in isolated, mono- and polyhydrated tautomers of...
Article
Full-text available
Intramolecular hydrogen bonding (IHB) interactions and molecular structures of 2-nitrosophenol, nitrosonaphthols, and their quinone-monooxime tautomers were investigated at ab initio and density functional theory (DFT) levels. The geometry optimization of the structures studied was performed without any geometrical restrictions. Possible conformati...
Article
Full-text available
The composition, some spectral characteristics, and thermal decomposition of solid lanthanide–titanium (lanthanide (Ln) = Y, La, Ce) and lanthanide–titanium citrates (CA) and tartrates (TA) have been studied. The com-plexes have been prepared in ethylene glycol medium at conditions modeling those of the polymerized-complex method applied for Ln 2 T...
Article
Full-text available
Cerium(III/IV) and Ce(IV)–Ti(IV) citric complexes were synthesized in ethylene glycol medium under conditions similar to those of the polymerized complex method (PCM). Solution phase 1H, 13C NMR, solid state 13C CP MAS NMR and IR spectroscopy, and X-ray powder diffractometry were used to characterize the composition and structure of the synthesized...
Thesis
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The DSc thesis is in the field of theoretical chemistry. The tautomerism of five-membered heterocyclic compounds with two heteroatoms in the ring, as well as nitroso-oxime tautomerism in cyclic compounds, is studied. It is found that the semi-empirical MNDO, AM1 and PM3 quantum-chemical methods are not appropriate for studying this type of compoun...
Article
The title compounds were synthesized starting from homophthalic anhydride and an imine. The amides obtained showed unexpected values for 3J3,4 that cannot be used to deduce their configuration and conformation. This problem was resolved for one representative compound (the 4-(pyrrolidinylcarbonyl) derivative) by means of detailed NMR studies, X-ray...
Article
Full-text available
The relative stabilities of the tautomers of 2-aminothiazolidine-4-one and 4-aminothiazolidine-2-one were calculated at the MP2/6-31+G(d,p) level by considering their mono- and trihydrated complexes. Single-point calculations at the MP4/6-31+G(d,p)//MP2/6-31+G(d,p) level of theory were performed to obtain more accurate energies. The values of proto...
Conference Paper
Full-text available
Isomerisation processes of ground and excited states of three compounds were studied quantum-chemically in order to find explanation for their photostability.
Article
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The structure of 2-carboxamide-indan-1,3-dione was investigated in gas phase, solution and solid states using a combination of quantum-chemical calculations, NMR spectroscopy and X-ray crystallography. Quantum-chemical calculations indicate that two tautomeric forms, 2-(hydroxyaminomethylidene)-indan-1,3-dione (A) and 2-carboamide-1-hydroxy-3-oxo-i...
Article
Full-text available
Post-Hartree-Fock ab initio quantum chemical calculations were performed for 5-fluorouracil in the gas phase and in a three-water cluster. Full geometry optimizations of the 5-fluorouracil-water complexes were carried out at the MP2/6-31+G(d,p) level of theory. MP4/6-31+G(d,p)//MP2/6-31+G(d,p) and MP4/6-31++G(d,p)//MP2/6-31+G(d,p) single-point calc...
Article
Full-text available
Dithioanalogues of cycloalkanespiro-5-hydantoins were prepared by reaction of the respective spirohydantoins with Lawesson's reagent or P 4 S 10 . Cycloalkanespiro-5-(2-thiohydantoins) and cycloalkanespiro-5-(4-hydantoins) were also synthesized from cycloalkanespiro-5-(2,4-dithio-hydantoins) via different reaction pathways. The structures of the co...
Article
Full-text available
The relative stabilities of the tautomers of pseudothiohydantoin were calculated at MP2/6-31+G(d,p) level by considering isolated molecules and their trihydrated complexes. Single-point calculations at MP4/6-31+G(d,p)//MP2/6-31+G(d,p) level of theory were performed to obtain more accurate energies. The theoretical IR spectra of the tautomers of pse...
Article
Full-text available
Detailed investigation of the tautomerism of oxazolidines, thiazolidines and selenazolidines substituted at positions 2 and 4 by hydroxy and amino groups was carried out by calculations at HF and MP2 levels of theory and NMR spectroscopy. The relative stabilities of the tautomers of the heterocycles were calculated in gas phase and in solvents CHCl...
Article
Full-text available
La-, Ti-and La–Ti-citrates, prepared in ethylene glycol medium (at conditions similar to those used in the polymerized complex method) and isolated as solid substances, have been studied by 13 C-solid state NMR analysis, XPS, SEM and EDAX. The obtained results, together with data from elemental, thermogravimetric, IR, 13 C-and 1 H-NMR (in solution)...
Article
Full-text available
The tautomeric equilibria of formamide, thioformamide and selenoformamide were studied in the gas phase and in water solution using ab initio quantum chemical calculations. The solvent effects were considered by explicit inclusion of three water molecules, which model a first hydration shell around the solute. Full geometry optimizations of these c...
Article
Full-text available
An ab initio HF and MP2 study of the static (hyper)polarizabilities of 2,4-substituted imidazoles and thiazoles is presented. The comparison of the two types of five-membered heterocycles suggests, that the exocyclic heteroatoms have much more influence upon the calculated hyperpolarizabilities, than the ring heteroatoms. It has been found, that ad...
Article
Full-text available
The FTIR spectra of 4-dimethylamino pyridinium-betaine of squaric acid in 4000– 100 cm 21 frequency region in solid state were measured. In addition, the structure and harmonic vibrational frequencies of this molecule were theoretically evaluated using restricted Hartree – Fock and B3LYP density functional methods. The computed vibrational frequenc...
Article
Full-text available
The possible involvement of 5-fluorouracil (5FU) in the initiation process of the polymerization of n-butylcyanoacrylate monomer during nanoparticle formation was investigated. 5FU in acidic solution (pH 2-3) may interfere in the initiation process through its amino groups via the formation of zwitterions. The proposed zwitterionic mechanism of ini...
Article
Full-text available
The tautomeric and conformational equilibrium of 2-nitrosophenol and 9,10-phenanthrenequinonemonooxime was studied by ab initio methods. The geometry optimizations of the structures investigated were done without any geometrical restrictions at HF/6-31G** and MP2/6-31G** levels of theory. The transition structures for tautomeric and rotameric conve...
Conference Paper
Full-text available
2-Acetylindane-1,3-dione as new component in sunscreens: The spectral properties and photostability of 2-acetylindane-1,3-dione (2AID) in different solvents and cosmetic cream are reported. Comparison is made with the photostability of two commercially sunscreens: benzophenone-3 and octylmethoxycinnamate. 2AID is shown to exhibiting a higher photos...
Conference Paper
Full-text available
Ab initio quantum chemical calculations were performed for 5-fluorouracil in the gas phase and in water solution. The solvent effects were modeled by explicit inclusion of three water molecules, which creates the first hydration shell around the solute. Full geometry optimizations without any constrains of the 5-fluorouracil-water complexes were ca...
Article
Full-text available
Poly(butylcyanoacrylate) nanoparticles (PBCN) as a drug carrier of 5-fluorouracil (5FU) intended for topical treatment of skin lesia were investigated. The presence of 5FU (as saline solution, pH 10-11) in the polymerization medium affected the polymerization as well as the nanoparticle formation by influencing the initiation of the polymerization...
Article
Full-text available
The structure of the product of the condensation reaction between 2-acetylindan-1,3-dione and aniline has been investigated in the gas phase, solution and solid state using a combination of quantum-chemical calculations, NMR and IR spectroscopies, and X-ray crystallography. Energetics of both isomers and all tautomers of the product of the reaction...
Article
Full-text available
Two anionic complexes of Au(III) with the bioligand biuret, cis-[Au(Biu)X2] (BiuH2=biuret, X=Cl, Br), have been synthesized and characterized. The molecular structure of cis-[Au(Biu)Br2]PPh4 has been determined by X-ray diffraction analysis. The complex anion has square-planar geometry with one deprotonated biuret dianion coordinated bidentately to...
Article
Full-text available
Ab initio (HF and MP2 level) and semiempirical (AM1, PM3, MNDO) calculations on the relative stabilities and structures of the potential tautomeric forms of rhodanine, isorhodanine, thiazolidine-2,4-dione, and thiorhodanine are reported. Ab initio calculations predict that the thiooxo, oxothio, dioxo, and dithio tautomers are the most stable. These...