Publications since 2004:

pH-Responsive Aminobenzocoumarins as Fluorescent Probes for Biological Acidity Schniererová K., Janeková H., Joniak J., Putala M., Štacko P., Stankovičová H. Chem. Eur. J 2024, e202400111. DOI: 10.1002/chem.202400111

Regulation of pH plays an essential role in orchestrating the delicate cellular machinery responsible for life as we know it. Its abnormal values are indicative of aberrant cellular behavior and associated with pathologies including cancer progression or solid tumors. Here, we report a series of bent and linear aminobenzocoumarins decorated with different substituents. We investigate their photophysical properties and demonstrate that the probes display strong pH-responsive fluorescence “turn on” behavior in highly acidic environments, with enhancement up to 300-fold. In combination with their low cytotoxicity, this behavior enabled their application in bioimaging of acidic lysosomes in live human cells. We believe that these molecules serve as attractive lead structures for future rational design of novel biocompatible fluorescent pH probes.

Synthesis of Unsymmetrically Substituted [5]Helicenes by Tandem Arylation of Binaphthyl by Suzuki Coupling and C–H Activation Bulko F., Cigáň M., Filo J., Putala M. Eur. J. Org. Chem. 2024, 27, e202300826. DOI: 10.1002/ejoc.202300826

We report a step-efficient approach for the synthesis of unsymmetrically substituted naphtho[1,2-g]chrysenes by tandem arylation of 2,2’-diiodo-1,1’-binaphthyl with arylboronic acids, which proceeds through Suzuki coupling followed by intramolecular arylation by C–H activation. Substrate screening examining over 30 meta- and/or para-substituted arylboronic acids showed that this approach provides the desired helicene products most effectively if arylboronic acids have a small acidifying group at the meta-position. In the case of unsymmetrically substituted arylboronic acids, the regioselectivity of C–H activation is directed by the attached group(s), its effect on the C–H acidity of the adjacent position, its coordination ability, as well as steric hindrance. Interestingly, selected [5]helicenes exhibited attractive deep blue emission with fluorescence lifetimes slightly exceeding 10 ns.

Novel low-bandgap donoracceptor thiophene-phenylene co-oligomers for light-emitting semiconductor devices Feriancová L., Balakirev D. O., Fedorenko R. S., Kuevda A. V., Trukhanov V. A., Svidchenko E. A., Surin N. M., Peregudova S. M., Dmitryakov P. V., Dubinets N. O., Fedorov Y. V., Putala M., Ponomarenko S. A., Paraschuk D. Y., Lupon Y. N. Dyes Pigm. 2023, 215, 111256. DOI: 10.1016/j.dyepig.2023.111256

Thiophene-phenylene co-oligomers (TPCOs) have shown their high potential for organic light-emitting devices because of their high luminescence and efficient charge transport. However, unsubstituted TPCOs have relatively wide optical bandgaps and the high-lying lowest unoccupied molecular orbital (LUMO) energies so that efficient electron transport is a challenge. Electron-withdrawing groups (EWGs) and fluorinated fragments embedded into the TPCO molecule structure could result in the lower LUMO energy and narrower optical bandgap. Here, we report the synthesis of two novel TPCOs series with either phenylene or perfluorinated phenylene central core and end-capped with various EWGs (aldehyde, 2-ethylhexyl cyanoacetate, hexyl rhodanine and dicyanorhodanine) and with long alkyl terminal and side chains increasing the solubility. All the oligomers synthesized were found to be thermally stable and crystalline materials with relatively low LUMO energies (down to -3.50 eV), narrow bandgaps (down to 1.9 eV), and efficient photoluminescence in the green – deep red spectral regions both in solution and solid-state. The TPCOs with 2-ethylhexyl cyanoacetate EWG were crystallized in large-area single-crystal monolayers, which showed strongly polarized photoluminescence and demonstrated their high potential as active layers in solution-processed single-layer organic light-emitting transistors.

Deracemization of binaphthyl by suzuki diarylation: the role of electronic and steric effects. Bulko F., Májek M., Putala M. J. Org. Chem. 2022, 87, 9316–9329, DOI: 10.1021/acs.joc.2c01041

We report a Suzuki 2,2′-diarylation of the racemic 2,2′-diiodo-1,1′-binaphthyl which proceeds with deracemization via a pallada(IV)cyclic intermediate, induced by a simple chiral ligand─BINAP [2,2′-bis(diphenylphosphino)-1,1′,-binaphthyl]. A systematic study of the reaction scope, using 45 arylboronic acids, reveals that the diarylated product is formed when meta- and/or para-substituted phenylboronic acids are functionalized with a substituent with the Hammett constant from −0.5 to +0.4. Multiparametric analysis accounting for the effect of geometry on the reactivity using Boltzmann-weighted Sterimol parameters and electronic effects described by Hammett descriptors shows that the enantioselectivity depends on steric effects only, with enhanced enantioselectivity observed for substituents with a larger length, wL, and reduced for substituents with a larger maximum width, wB5. We show that careful tuning of these parameters, with the aid of the presented mathematical model, can lead to excellent enantioselectivity. Additional factors that are investigated and found to affect the stereoselective course of the reaction include the reaction temperature, palladium source, palladium to ligand ratio, and the type of boronic acid derivative. During the chromatographic separation of diarylated products on an achiral silica gel, we observed a rare phenomenon: the diarylated products undergo self-disproportionation of enantiomers, with the major enantiomer being eluted first.

Dithienylnaphthalenes and quaterthiophenes substituted with electron-withdrawing groups as n-type organic semiconductors for organic field-effect transistors Feriancová L., Cigáň M., Kožíšek J., Gmucová K., Nádaždy V., Dubaj T., Sobota M., Novota M., Weis M., Putala M. J. Mater. Chem. C.  2022, 10, 10058-10074. DOI: 10.1039/d2tc01238c

We hereby report a successful design strategy for n-type semiconductor materials based on an analogy with efficient p-type semiconductors, by introducing electron-withdrawing groups while maintaining the symmetry of the molecules upon omitting one thiophene unit on each side of the oligoaryl core. Two series of dithienylnaphthalenes and quaterthiophenes substituted with various electron-withdrawing groups have been synthesised using Suzuki or Stille cross-coupling, and Knoevenagel condensation as key steps. The comparison of theoretical and experimental molecular properties related to the effect of electron-withdrawing groups is presented. Both the DFT-calculated and experimentally determined values of the energy gap between frontier orbitals have shown a decreasing trend in the order of perfluoroalkyl, acyl, perfluoroacyl, nitro, alkyldicyanovinyl and perfluoroalkyldicyanovinyl in both series. The X-ray analysis of five derivatives revealed almost planar geometry of oligoaryl core with herringbone or lamellar packing motif. The crystal structures of quaterthiophenes exhibited an s-cis conformation between the outer thiophenes in the crystals, in contrast to the theoretical prediction. Carbonyl-based compounds showed n-type behaviour as an active layer in OFET devices with electron mobility up to 0.57 cm2/Vs.

Synthesis and Effect of the Structure of Bithienyl-Terminated Surfactants for Dielectric Layer Modification in Organic Transistor Feriancová l., Kmentová I., Micjan M., Pavúk M., Weis M., Putala M. Materials 2021, 14, 6345. DOI: 10.3390/ma14216345.

A series of bithienyl-terminated surfactants with various alkyl chain lengths (from C8 to C13) and phosphono or chlorodimethylsilyl anchoring groups were synthesized by palladium catalyzed hydrophosphonation, or platinum-catalyzed hydrosilylation as a key step. Surfactants were tested in pentacene or α-sexithiophene-based organic field-effect transistors (OFETs) for the modification of the dielectric surface. The studied surfactants increased the effective mobility of the α-sexithiophene-based device by up to one order of magnitude. The length of alkyl chain showed to be significant for the pentacene-based device, as the effective mobility only increased in the case of dielectric modification with bithienylundecylphosphonic acid. AFM allowed a better understanding of the morphology of semiconductors on bare SiO2 and surfaces treated with bithienylundecylphosphonic acid.

Mild and highly efficient deacetylation of acetamido and acetoxy coumarins: A convenient and expeditious synthesis of substituted 3-aminocoumarins Krajňáková J., Joniak J., Putala M., Górová R., Jurdáková H., Stankovičová H. Synth. Commun. 2021, 51, 3277-3291. DOI: 10.1080/00397911.2021.1968904

A convenient protocol for efficient and cost-effective method for synthesis of substituted 3-aminocoumarins has been developed. The synthetic route involves expeditious and fast quantitative deacetylation of readily available acetamido derivative under anhydrous acidic conditions, employing thionyl chloride in methanol, without formation of undesired substituted 3-hydroxycoumarins. The method is suitable for derivatives bearing electron-donating as well as electron-withdrawing groups at position 7 of the coumarin scaffold. Under these conditions, a series of acetoxy substituted 3-dialkylaminocoumarins has been also successfully deacetylated to afford easily isolable corresponding hydroxy derivatives in high yields.

Effect of electron-withdrawing groups on molecular properties of naphthyl and anthryl bithiophenes as potential n-type semiconductors Feriancová L., Cigáň M., Gmucová K., Kožíšek J., Nádaždy V., Putala M. New J. Chem., 2021, 45, 9794-9804, DOI: 10.1039/D1NJ01100F

A series of ten 2-naphthyl and 2-anthrylbithiophene derivatives with electron acceptor groups were synthesised using the Negishi or Suzuki cross-coupling reaction as a key step. We present a comparison of theoretical and experimental values of the LUMO and gap energies of these derivatives and the effect of the various electron-withdrawing groups on their optical and electrochemical properties. DFT-calculated frontier orbital energy differences have shown a trend following the experimentally determined values. The participation of the electron-withdrawing group in π-conjugation decreases the LUMO level and narrows the energy gap in the order of perfluoroalkyl, acyl, perfluoroacyl, nitro ≈ dicyanovinyl in both series. TD-DFT calculations allowed better understanding of electronic transitions. X-ray structure analysis of naphthalene hexanoyl and perfluorooctanoyl derivatives revealed their herringbone or sandwich herringbone molecular packing, respectively, having a planar naphthalene-bithiophene moiety with opposite (s-trans vs. s-cis) conformation of bithiophene.

Assessing Basic Separatory Technique Skills in an Organic Experiment Based on an Incomplete Haloform Reaction
Kmentová, I., Almássy, A., Feriancová, L., Putala, M. J. Chem. Educ. 2020, 97(4), 1139–1144, DOI: 10.1021/acs.jchemed.9b01015

We present an experiment which was designed to assess the separation technique skills of the gifted high school students who attended the 50th International Chemistry Olympiad 2018. The procedure consists of two synthetic tasks and is also applicable for teaching undergraduates. The haloform reaction of 2-acetonaphthone with sodium hypochlorite in commercial bleach gave the corresponding carboxylate salt and some unreacted 2-acetonaphthone. This unreacted material is separated and then treated with in situ prepared Brady’s reagent to give a near-quantitative yield of the hydrazone, while acidification of the carboxylate salt affords the corresponding carboxylic acid. The procedure includes several separation techniques: acid–base extraction, TLC analysis, and suction filtration. The grading of the student’s work based on the combined yield of both products avoids having to account for the effects of temperature, reaction time, and reagent quality on the efficiency of the haloform reaction. The duration of the experiment is 3–4 h of working time, depending on the student’s time management skills.

Novel highly substituted thiophene-based n-type organic semiconductor: structural study, optical anisotropy and molecular control
Hagara J., Mrkyvkova N., Feriancová L., Putala M., Nádaždy P.,  Hodas M., Shaji A., Nádaždy V., Huss-Hansen M.K., Knaapila M., Hagenlocher J., Russegger N., Zwadlo M.,  Merten L.,  Sojková M., Hulman M., Vlad A., Pandit P., Roth S., Jergel M., Majková E., Hinderhofer A., Siffalovic P., Schreiber F.  Cryst. Eng. Comm. 2020, 22, 7095-7103. DOI: 10.1039/D0CE01171A

Oligothiophenes and their functionalized derivatives have been shown to be a viable option for high-performance organic electronic devices. The functionalization of oligothiophene-based materials allows further tailoring of their properties for specific applications. We have synthesized a new thiophene-based molecule 1-[5′-(2-naphthyl)-2,2′-bithiophen-5-yl]hexan-1-one (NCOH), and we have studied the optical and structural properties of NCOH thin films. NCOH is a highly substituted member of the oligothiophene family, designed to improve its molecular stacking, where the presence of an electron-withdrawing group enhances its electron transport capabilities. Employing in situ and time-resolved grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements, we determined the NCOH thin film crystallographic structure and its evolution starting from the early stages of the film growth. We observed strong optical anisotropy resulting from a highly oriented crystallographic structure. Additionally, we investigated the substrate-induced changes of the molecular orientation utilizing the few-layer MoS2 with different orientations of the atomic layers. This study, with its primary focus on the fundamentally important n-type molecular semiconductor, contributes to the field of organic-based (opto-)electronics.

Celebrating the Golden Jubilee of the International Chemistry Olympiad: Back to Where It All Began
Fung F. M., Putala M., Holzhauser P., Somsook E., Hernandez C., Chang I-J. J. Chem. Educ. 2018, 95, 193−196. DOI: 10.1021/acs.jchemed.7b00640


The International Chemistry Olympiad (IChO) is celebrating its 50th anniversary in 2018. Since 1968, 30 countries have hosted this prestigious event for preuniversity students, and 83 countries have participated in this annual tournament. The aim of the IChO includes promoting students’ interest in science, in particular, popularization of chemistry. For the jubilee celebration, IChO is returning to its birthplace, Czech Republic and Slovakia

Effect of alkyl side chains on properties and organic transistor performance of 2,6-bis(2,2′-bithiophen-5-yl)naphthalene
Mišicák R., Novota M., Weis M., Cigáň M., Šiffalovič P., Nádaždy P., Kožíšek J., Kožíšková J., Pavúk M., Putala M., Synth. Met. 2017, 233, 1-14. DOI: 10.1016/j.synthmet.2017.08.010

Herein we report the synthesis and characterization of C2-symmetric 2,6-bis(5′-alkyl-2,2′-bithiophen-5-yl)naphthalene derivatives with alkyl side chains of various length and shape, including even the less commonly examined cyclohexyl and cyclohexylalkyl groups. By investigation of how these side chains influence solubility, self-assembly and charge mobility, we aimed to extend the knowledge of structure-function property relationship of the oligothiophene compounds. Charge mobilities observed in this study ranged from 10− 3 to 10− 1 cm2 V− 1 s− 1. The highest values referred to thin layers of derivatives end-capped with linear alkyl chains. XRD methods uncovered OFET-favorable layering of tilted molecular arrangement with the molecular long axes in the out of plane direction. Although the charge mobilities showed variation of as much as two orders of magnitude, XRD measurements of these derivatives revealed similar packing and self-assembly behavior. Hence, the charge mobility differences are more a result of the naturally diverse spatial demands of the tested alkyl groups, with the linear alkyl chains offering the tightest close packing of the π-conjugated backbone. On the other hand, the bulky 2-hexyldecyl group turned out to be the only group that made it possible to avoid insolubility of these derivatives and provided excellent solubility (23 mg/mL of chloroform), while the charge mobility remained acceptable even of the spin-coated thin layers.

Charge transport in 2,6-bis(5′-hexyl-2,2′-bithiophene-5-yl)naphthalene-based organic devices Filo J., Putala M., Gmucova K., Jakabovic J., Weis M., Synth. Met. 2016, 211, 84-88. DOI: 10.1016/j.synthmet.2015.10.027

Organic semiconductor 2,6-bis(5′-hexyl-2,2′-bithiophene-5-yl)naphthalene (H2T26N) is employed as an active layer in organic field-effect transistors (OFETs) or as a hole-transport layer in organic light-emitting diodes (OLEDs). In OFET device the p-type conductivity is confirmed and the hole mobility as high as 0.34 cm2/V s is achieved. The emission spectrum of ITO/H2T26N/tris(8-quinolinolato) aluminum (Alq3)/Ca OLED shows emission peaks which cannot be ascribed to either the H2T26N or Alq3 layer. Through studies of photoluminescence spectra and electrochemical properties we demonstrate that the additional feature results from an exciplex at the H2T26N/Alq3 bilayer interface.

Easily oxidizable triarylamine materials with naphthalene and binaphthalene core: structure–properties relationship
Kerner L., Gmucová K., Kožíšek J., Petříček V., Putala M. Tetrahedron, 2016, 72(44), 7081-7092. DOI: 10.1016/j.tet.2016.09.063

We devised and synthesized a series of electron-rich compounds featuring diphenylamine, carbazole or dibenzo[c,g]carbazole connected via phenylacetylene linkers to an aromatic central unit. The key synthetic step was a high yielding cross coupling reaction between halogenated (bi)naphthalene and organometallic reagents prepared in situ from terminal alkynes (side-arms). By masking one of the iodo functions with a diethyltriazenyl group in the side-arm precursors, we efficiently circumvented the formation of doubly aminated by-products. Although one step longer, this approach led to higher yields of terminal alkynes than the direct coupling route. Spectroscopic and electrochemical measurements supported by computational evidence revealed that conjugation in the 1,4-disubstituted naphthalene backbone is superior to the 1,5 or 2,6 substituted cores. The diphenylamine derivative gets oxidized more readily when compared to its carbazole analogs. Expanding the core to binaphthalene did not alter electronic properties, but influenced the physical characteristics significantly.

Effect of the ethynylene linker on the properties and carrier mobility of naphthalene derivatives with hexylbithienyl arms Mišicák R., Stříteský S., Vala M., Weiter M., Cigáň M., Gmucová K., Végsö K., Weis M., Kožíšek J., Pavúk M., Putala M. Synth. Met. 2016, 217, 156-171. DOI: 10.1016/j.synthmet.2016.03.034

A series of new naphthalene derivatives with (5′-hexyl-2,2′-bithiophene-5-yl)ethynyl side arms attached to the central naphthalene core at positions 1 and 4 (H2TA14N), 1 and 5 (H2TA15N), and 2 and 6 (H2TA26N) were synthesized by a sequencing of alkynylations performed according to a Negishi cross-coupling protocol. This synthetic approach provides higher yields compared to Sonogashira-based alkynylations, particularly when aryl bromides are used as starting materials. Compared to the analogous derivatives with hexylbithienyl arms directly attached to the naphthalene core (H2T14N, H2T15N, and H2T26N), an ethynylene linker ensures the planarity of the molecules, causing a change in the order of derivatives by intramolecular conjugation from H2T15N < H2T14N < H2T26N to H2TA15N ≈ H2TA26N < H2TA14N, as can be seen from the solution, and thin film optical and electrochemical properties as well. However, the order of derivatives by the hole mobility in a field effect transistor remains unaltered by an ethynylene linker (H2TA14N < H2TA15N < H2TA26N). The tendency in charge mobility can be explained by different packing motifs affected by molecular symmetry and was revealed by single crystal X-ray analysis and 2D X-ray GIWAXS and AFM characterization of the thin films.

Fluxional Pd(II) NHC complexes - Synthesis, structure elucidation and catalytic studies Dangalov M., Stoyanova M., Petrov P., Putala M., Vassileva N.G. J. Organomet. Chem. 2016, 817, 1-14. DOI: 10.1016/j.jorganchem.2016.05.002

Four catalytically relevant Pd(II) complexes involving N-heterocyclic carbenes (NHCs) and bidentate N- and P-donor ligands were synthesized and characterized. The structures and conformations of the complexes were elucidated on the basis of combination of dynamic NMR and DFT studies. Conformational studies in respect to hindered rotation around C-Ndonor and Pd-CNHC bonds were performed resulting in surprisingly good agreement between the calculated and the experimental results. The results from dynamic NMR and DFT studies confirm hindered rotation around the C-N bond in 1,3-disubstituted imidazole complexes. The fluxional behavior of P-donor ligands includes exchange between left-handed and right-handed phosphine propellers. The catalytic studies of 1,3-disubstituted 4,5-fused imidazole complexes produced excellent activities in Suzuki–Miyaura Reaction.

Atropisomerism of 2,2′-Diaryl-1,1′-binaphthalenes Containing Three Stereogenic Axes: Experimental and Computational Study Ehn M., Vassilev N. G., Pašteka L. F., Dangalov M., Putala M. Eur. J. Org. Chem. 2015, DOI: 10.1002/ejoc.201500840

The rotational barriers of four 2,2′-diaryl-1,1′-binaphthalenes have been determined on the basis of peak volume integration in variable-temperature 1H EXSY NMR spectra. They were consistent with those determined at higher temperatures by complete line shape analysis. DFT calculations at the B2-PLYP//B3LYP-D3/6-311++G(d,p) level provided relative enthalpy values in very good agreement with the experimentally measured data both for particular atropisomers and for transition states. Calculations showed that the simultaneous rotation of both aryl groups has a much higher barrier than the individual rotations. The tendency of the atropisomerization barriers to increase for the first three derivatives correlates with the sizes of the substituents in the ortho positions of the phenyl rings (methoxy < dimethylamino < methyl), whereas the barriers for the derivative bearing isopropyl groups are, surprisingly, in the same range as for that bearing methyl substituents. We assume that in the latter case tilting of the binaphthalene moiety is responsible for the lowering of rotational barriers.

Elucidation of Photoisomerization-Related Structural Changes in an Acrylamide-Bridged Binaphthalene-Diazene Macrocyclic Chiroptical Switch by Experimental Electronic Circular Dichroism Spectra Simulation: Role of Dispersion Corrections Kerner L., Kicková A., Filo J., Kedžuch S., Putala M. J. Phys. Chem. A 2015, 119, 32, 8588–8598. DOI: 10.1021/acs.jpca.5b03474

Nondestructive readout of light-driven molecular memory devices can be achieved by monitoring the alterations in the chiroptical properties of 1,1′-binaphthalene as a conformationally responsive chiral group. In our system, this signaling unit is connected via acrylamide linkers to the receiving diphenyldiazene fragment, which undergoes significant geometrical changes upon (E)/(Z)-photoisomerization. The compound functions as a stable photochromic switch by alternating irradiation at 365/465 nm, with fully reversible modulation of circular dichroism (CD) signal intensity (up to 1:3) and extended thermal stability of the (Z)-isomer. According to molecular modeling, the acrylamide spacers are due to the imposed cyclic strain upon photoisomerization forced to switch amide conformations, which is markedly reflected in the CD spectra, whereas binaphthalene conformational changes are mostly neglected both by theory and by experiment. In CD simulation by TD-DFT, CAM-B3LYP outperforms B3LYP and M06 by means of similarity analysis, whereas the last mentioned functional also delivers satisfactory performance qualitatively. The inclusion of dispersion corrections during geometry optimization was crucial to retain consistency with the measured spectra. By carefully considering all relevant conformations of this 20-membered macrocycle, reasonable agreement with the experiment is reached not only for the CD simulation of the individual conformers but also of the photoisomerization process of their admixture.

Oligothiophenes with the naphthalene core for organic thin-film transistors: Variation in positions of bithiophenyl attachment to the naphthalene
Filo J., Mišicák R., Cigáň M., Weis M., Jakabovič J., Gmucová K., Pavúk M., Dobročka E., Putala M. Synth. Met. 2015, 202, 73-81. DOI: 10.1016/j.synthmet.2015.01.020

Relationship between molecular structure of organic material and its semiconducting properties is far from being trivial. Hence, a complex study based on systematic variation of molecular structure can contribute to understanding of this relationship. Herein we describe the synthesis, characterization and field-effect transistor (OFET) properties of a consistent series of naphthalene derivatives with hexylbithiophenyl chains attached at positions 1 and 4 (H2T14N), 1 and 5 (H2T15N), and 2 and 6 (H2T26N). The almost planar derivative H2T26N with the narrowest HOMO-LUMO band gap has good film forming ability, resulting in the remarkably high hole mobility (0.12 cm2 V−1 s−1). Although both the H2T14N and H2T15N derivatives have almost the same twist of thiophene unit from the naphthalene plane, the latter has weaker conjugation between the bithiophenyl arms but exhibited higher charge mobility (0.016 cm2 V−1 s−1). Apparently, a proper combination of molecular structure prerequisites and film-forming properties of semiconducting molecular material is essential for good OFET performance. It has been shown that also molecular symmetry can play an important role for effective two-dimensional molecular packing of the organic material.

Radical scavenging capacity of n-(2-mercapto-2-methylpropionyl)-l-cysteine: Design and synthesis of its derivative with enhanced potential to scavenge hypochlorite Baňasová M., Kerner L., Juránek I., Putala M., Valachová K., Šoltés L.  J. Information, Intelligence and Knowledge 2014,  6(4), 453-470. DOI: 10.1201/b18153-12 (Book Chapter - Physical Chemistry Research for Engineering and Applied Sciences, Volume 1: Principles and Technological Implications, Part of DOI: 10.1201/b18153)

High-molar-mass hyaluronan (HA) – glycosaminoglycan composed of repeating disaccharide units of N-acetyl-d-glucosamine and d-glucuronic acid linked by β-(1→4) and β-(1→3) glycoside bonds – is an essential component of the extracellular matrix in many tissues. It is rather susceptible to free-radical mediated degradation resulting in various physiological and pathological consequences. In the present study, we investigated the effect of N-(2-mercapto-2-methylpropionyl)-l-cysteine against free-radical degradation of highmolar-mass HA. We applied rotational viscometry to record time-dependent changes of the dynamic viscosity of HA solutions, which reflected a decrease of HA molar-mass and thereby its fragmentation. The oxidative degradation of high-molar-mass hyaluronan was evoked by the Weissberger biogenic oxidative system comprising Cu(II) and ascorbate. Previously, we proved that stage I of oxidative HA degradation was mediated predominantly by hydroxyl radicals while stage II by peroxyl-type radicals. To determine the scavenging activity of the compound tested, ABTS and DPPH assays were used. Oximetry was used to monitor the consumption of oxygen by the treated HA solutions.

Bioactive carbocyclic nucleoside analogues - Syntheses and properties of entecavir
Campian M., Putala M., Sebesta R. Curr. Org. Chem. 2014, 18(22), DOI : 10.2174/1385272819666140929200719

Carbocyclic nucleoside analogs are highly biologically relevant compounds. A large variety of them already serve as drugs or are investigated with this aim in mind. This review analyses syntheses of major types of carbocyclic nucleoside derivatives including those of pharmacological interest. The emphasis of this review is on entecavir, a derivative exhibiting selective activity at nanomolar level against hepatitis B virus. The first subject of this review is the summary of nucleoside analogs, mainly classification and synthetic strategies employed for the preparation of these derivatives. The second part focuses on the recent developments in the field of enanti oselective approaches of synthesis of entecavir and related compounds. This paper covers the literature from 1992 to 2013.

New phenanthrene-based organic semiconductor material for electronic devices Novota M., Micjan M., Nevrela J., Flickyngerová S., Juhász P., Mišicák R., Putala M., Jakabovic J., Weis M. The Tenth International Conference on Advanced Semiconductor Devices and Microsystems, 2014, 1-4, DOI: 10.1109/ASDAM.2014.6998655

This work describes the thin-film fabrication technology and characterization of devices based on organic semiconductor 3,6-bis(5`-hexyl-2,2`-bithiophen-5-yl)phenanthrene (H2T36Phen). The surface morphology, optical, and electrical properties are investigated for thin organic films. It demonstrates that the solution-based depositions require different substrate surface treatment than the evaporation-based deposition.

Highly sterically hindered binaphthalene-based monophosphane ligands: Synthesis and application in stereoselective Suzuki-Miyaura reactions Mešková M., Putala M. Tetrahedron Asymmetry 2013, 24(15–16), 894-902. DOI: 10.1016/j.tetasy.2013.06.007

A series of new sterically hindered (R)-(2′-aryl-1,1′-binaphthalene-2-yl)phosphanes with ortho-substituted phenyls as aryl groups were prepared via Negishi monoarylation of enantiopure 2,2′-dibromo-1,1′-binaphthalene followed by lithiation and quenching with diphenylphosphanyl or dicyclohexylphosphanyl chloride. These ligands were applied to the stereoselective Suzuki–Miyaura coupling for the preparation of substituted biaryls. The enantioselectivity correlated positively when increasing the hindrance of the 2′-aryl group of the ligand. Using the best performing diphenylphosphane ligand with a 2,6-dimethoxyphenyl aryl group, various arylnaphthalenes were prepared in high to excellent yields (68–99%) with low to good ee (12–75% ee), the latter being comparable to the best values reported when using other chiral monophosphane ligands.

Stereostructure and thermodynamic stability of atropisomers of ortho-substituted 2,2′-diaryl-1,1′-binaphthalenes Ehn M., Vassilev N. G., Kasák P., Horváth B., Filo J., Mereiter K., Rakovský E., Putala M. Tetrahedron: Asymmetry 2013, 24 (20), 1303-1311. DOI: 10.1016/j.tetasy.2013.09.005

A series of ortho-substituted 2,2′-aryl-1,1′-binaphthalenes were prepared via Negishi arylation of 2,2′-diiodo-1,1′-binaphthalene in good to high yields (65–95%) as an equilibrium mixtures of up to three atropisomers (unlike,unlike, like,unlike, and like,like). Thermodynamic stability parameters of the atropisomers were evaluated from VT NMR spectra by regression analysis. The DFT parameters calculated using CAM-B3LYP functional comprising solvent permittivity were, apart from the toluene solution, which was expected to interact with the aromatic solute, in qualitative agreement with the experimental values. In the case of the ditolyl derivative, the population of the atropisomers was confirmed by CD spectroscopy via comparison with the population-weighted averaged spectrum computed using the M06 functional. X-ray structure analyses of particular atropisomers of the dianisyl, dianilinyl, and dinaphthyl derivatives are also presented and discussed.

Synthesis and properties of macrocyclic diazene switch with binaphthalene unit attached via acrylamide linkers Kicková A., Horváth B.,Kerner L., Putala M. Chem. Papers, 2013, 67, 101-109. DOI: 10.2478/s11696-012-0247-y

2,2′-Diiodo-1,1′-binaphthalene undergoes a tandem Heck reaction with methyl acrylate to afford methyl 2-(7H-dibenzo[c,g]fluoren-7-ylidene)acetate. As a consequence, the target macrocyclic diazene with binaphthalene unit attached via acrylamide linker was prepared by the stepwise building of acrylamide at a binaphthalene moiety, including the Doebner modification of the Knoevenagel condensation, and completed by oxidative macrocyclisation of aniline end-groups. Despite being an equimolar mixture of monomer and dimer, it exhibited remarkable changes in CD spectra due to reversible (E/Z) isomerisation of N=N diazene bonds upon irradiation at 365/465 nm. Although the dimer isomerises from (E) to (Z) isomer 7.4 times faster than the monomer, the latter’s contribution to the change in ellipticity at 307 nm in the photostationary state is 2.4 times greater.


Spectral properties of binaphthalene-coumarins interconnected through hydrazone linkage Cigáň M., Filo J., Stankovičová H., Gáplovský A., Putala M. Spectrochim. Acta A: Mol. Biomol. Spectrosc. 2012,  89, 276-83. DOI: 10.1016/j.saa.2012.01.010

Photophysical properties of new coumarin-3-carbaldehyde (dihydrodinaphtho[2,1-c:1',2'-e]azepin-N-yl)imines bearing dimethylamino and methoxy groups at position 7 of coumarin were investigated. Dimethylamino derivative exhibits different solvent polarity dependence of fluorescent characteristics for nonpolar, medium polar and highly polar solvents. This effect can be rationalized by diverse charge distribution in the singlet excited state due to its different stabilization by solvation in the solvents of particular group. While 2-fold higher values of Stokes shift were observed for methoxy derivative, its quantum yield of fluorescence is much lower due to high nonradiative decay rate constant of the excited state.

The development of an approach toward sterically-hindered chiral 2′-aryl-1,1′-binaphthalenes functionalized at position 2 Mešková M., Putala M. Tetrahedron Letters 2011, 52 (41), 5379-5383 DOI: 10.1016/j.tetlet.2011.08.046

Several approaches were examined for the preparation of 1,1′-binaphthalene derivatives bearing sterically demanding ortho-substituted aryl at position 2′ which are suitable for further functionalization at position 2. Steric hindrance of ortho-substituted aryl groups was critical for the approach through BINOL monotriflate. Among variations of cross-coupling reactions of 2,2′-dihalo-1,1′-binaphthalenes, Negishi arylation of an enantiopure 2,2′-dibromide was found to be the method of choice for regioselective and stereoconservative preparation of the target 2′-monoarylated precursor. Functionalization of the latter at position 2 was demonstrated by bromine substitution via lithiation followed by the reaction with several electrophiles.

A chiroptical binaphthopyran switch: Amplified CD response in a polystyrene film Kicková A., Donovalová J., Kasák P., Putala M.  New J. Chem. 2010 DOI: 10.1039/c0nj00102c

Enantiopure 10,10′-bi(naphtho[2,3-b]pyran) (5a) has been prepared from (R)-BINOL by using the attachment of 1,1-diphenylallyl alcohol to positions 3 and 3′ of the binaphthalene via Heck coupling as a key step. The irradiation of 5a in solution with UV light at 313 nm caused photochemical opening of only one of the pyran rings, accompanied by minor changes in the CD spectrum. Thermal ring closure occurred spontaneously with an activation barrier of 74 kJ mol−1. When 5a was immobilised in a polystyrene film, an improved switching performance, both in terms of fatigue resistance (>10 cycles) and CD signal amplitude (>100 mdeg, >6 : 1 signal ratio of open/closed forms), was observed.

Bisphenylene homologues of BINOL-based phosphoramidites: synthesis, stereostructure, and application in catalysis Miklášová N., Julínek O., Mešková M., Setnička V., Urbanová M., Putala M. Tetrahedron Lett. 2010, 51(15), 1966-1970. DOI: 10.1016/j.tetlet.2010.02.041

Bis-ortho- and bis-meta-phenylene homologues of BINOL-based N,N-dimethylphosphoramidites were prepared from the corresponding diols by treatment with hexamethyltriaminophosphane. Phosphoramidites derived from bulkier secondary amines were synthesized by 5-phenyl-1H-tetrazole-promoted amine exchange. All the phosphoramidites were obtained as single diastereomers. Their configurations at the C(naphthyl)–C(phenyl) axes were determined by vibrational circular dichroism (VCD) spectroscopy. Preliminary testing of the ligands in copper-catalyzed conjugate addition of diethylzinc to acyclic enones and nitrostyrene gave the corresponding products in up to 74% ee.

Semiconducting organic molecular materials Filo J., Putala M. Journal of Electrical Engineering 2010, 61(5), 314-320. DOI: 10.2478/v10187-010-0050-3

This feature article gives an overview of recent advances in development of high performance molecular organic semiconductors for field-effect transistors with emphasis on the structure of molecular materials and requirements for high-performance.

Determination of molecular structure of bisphenylene homologues of binol-based phosphoramidites by chiroptical methods Julínek O., Setnička V., Miklášová N., Putala M., Ruud K., Urbanová M. J. Phys. Chem. A 2009, 113(40), 10717-10725. DOI: 10.1021/jp906724f

Vibrational (VCD), electronic circular dichroism (ECD), and IR absorption spectra together with transparent spectral region optical rotation (OR) of two derivatives of bisphenylene 1,1'-binaphthyl-based phosphoramidites containing three stereogenic axes were measured and the results were compared with simulated data obtained by ab initio calculations with density functional theory. An excellent agreement between experimental and predicted B3LYP/6-31G** and BPW91/6-31G** VCD spectra enabled the assignment of all VCD bands in the experimental spectra, while the Gibbs free energy of all the conformers allowed the determination of their relative populations. The calculation of ECD spectra showed that CAM-B3LYP/6-311G** provided results superior to those of B3LYP/6-311G**. The theoretical results for the OR at the B3LYP/6-311G** and CAM-B3LYP/6-311G** levels were in good agreement with experimental optical rotations, but exhibited lower sensitivity in determining particular conformers than VCD and ECD. By a careful comparison of experimental VCD, IR, and ECD spectra and OR with calculated data, it was possible to assign the absolute configuration of all three stereogenic axes and to determine the molecular structure of the studied bisphenylene 1,1'-binaphthyl-based phosphoramidites in solution with a high degree of confidence.

Fluoride anion sensing using colorimetric reagents containing binaphthyl moiety and urea binding site Mikláš R., Kasák P., Devínsky F., Putala M.  Chem. Pap 2009, 63 (6), 709-715. DOI: 10.2478/s11696-009-0079-6

Four 1,1-binaphthalene based bis-urea derivatives bearing aryl groups at end-on nitrogen atoms IIIa–d were synthesized as potential sensor molecules. These receptors show characteristic UV-VIS spectral changes on complexation with anions and they exhibit selective recognition of F− over other halide anions. Interaction of a fluoride anion with urea NH groups was confirmed by 1H NMR data. The presence of an electron-withdrawing nitro group in N -aryls (receptors IIIa and IIIb) appeared to be necessary for naked-eye colorimetric detection. These receptors show dramatic color change from light-yellow to orange (IIIa) or to orange-red (IIIb) in the presence of guest fluoride anions already at concentrations of 10−5 mol dm−3 of the receptor and host.

Suzuki cross-coupling at the chiral groove of 1,1′-binaphthyl: Stereoconservation versus deracemization pathway Brath H., Mešková M., Putala M. Eur. J. Org. Chem. 2009, 3315–3318. DOI: 10.1002/ejoc.200900071

The use of monophos as a ligand in the palladium-catalyzed Suzuki diarylation of 2,2′-diiodo-1,1′-binaphthyl under optimized conditions followed a stereoconservative course. However, some chiral P ligands were found to be capable of inducing stereogenic information during this coupling, regardless of the configuration of the starting diiodide. Among those ligands tested in the deracemization approach, binap exhibited the highest level of asymmetric induction, yielding diarylated product in 83 % ee starting from racemic diiodide.

Chiral binaphthalenes bearing two pyridine ligands attached via acetylene spacers. Synthesis and coordination study  Kasák P., Brath H., Krascsenicsová-Poláková K., Kicková A., Moldovan N., Putala M. Collect. Czech. Chem. Commun. 2007, 72(8), 1139–1157. DOI: 10.1135/cccc20071139

An effective methodology has been developed for the synthesis of enantiopure 2,2′-dialkynylated 1,1′-binaphthalene derivatives. Enantiopure 2,2′-diiodo-1,1′-binaphthalene (10) provided 2,2′-diethynyl-1,1′-binaphthalene (16) in the Negishi alkyn  ylation supported by microwave irradiation in a very good yield with conservation of stereochemical information. The Stephen–Castro alkynylation of 10 afforded products in lower yields; however, in stereoconservative manner as well. Terminal diacetylene 16 served as precursor in the Sonogashira cross-coupling reaction to give new bispyridine derivatives 7–9 as potential ligands in moderate to high yields. Coordination of bispyridines with Zn2+ and Ag+ ions was observed by NMR and CD spectroscopy. The coordination ability of bis(2-pyridylethynyl) derivative 7 to palladium cation was determined by X-ray structure analysis.


Potential 1,1′-binaphthyl NLO-phores with extended conjugation between positions 2 and 6, and 2′ and 6 Juríček M., Kasák P., Stach M., Putala M. Tetrahedron Lett. 2007, 48(50), 8869-8873. DOI: 10.1016/j.tetlet.2007.10.044

A synthetic approach is reported which allows independent introduction of alkynyl groups to positions 2,2′ and then to 6,6′ of binaphthyls. The approach is based on the high selectivity of the Stephens–Castro alkynylation of 6,6′-dibromo-2,2′-diiodo-1,1′-binaphthyl. The tetraalkynylated derivatives exhibit extended conjugation between groups at positions 2 and 6, and 2′ and 6′, achieved by overcoming steric hindrance at positions 2 and 2′ by using alkynyl spacers.

Study on the electronic effects on stereoconservativity of Suzuki coupling in chiral groove of binaphthyl. Juríček M., Brath H., Kasák P., Putala M. J. Organomet. Chem. 2007, 692(23), 5279-5284. DOI: 10.1016/j.jorganchem.2007.08.010

Racemization during Suzuki diarylation of enantiopure 2,2′-diiodo-1,1′-binaphthyl was found to be suppressed by electronic factors which control the rate of oxidative addition (especially to presumptive undesired Pd(IV)-intermediate): either by use of palladium complex with phosphane ligand of moderate donating ability or utilizing 2,2′-dibromo-1,1′-binaphthyl as a substrate.

Elaboration of a novel effective approach to enantiopure functionalised 2,2′-dialkyl-1,1′-binaphthyls by stereoconservative cross-couplings at positions 2 and 2′. Kasák P., Putala M. Tetrahedron Lett. 2004 , 45, 5279–5282. DOI: 10.1016/j.tetlet.2004.05.016

The yield and the stereochemical outcome of methylations of 1,10-binaphthyl-2,20-dielectrophiles (ditriflate and diiodide)clearly depend on the reactivity of the organometallics used. It was found that only the Negishi reaction of a diiodide allows directeffective synthesis of non-racemic functionalisedC2-symmetric 2,20-dialkyl-1,10-binaphthyls.

Suzuki arylation at positions 2 and 2’ of 1,1’-binaphthyls: stereochemical result depending on the sense of polarity of substrates Kasák P., Brath H., Dubovská M., Juríček M., Putala M. Tetrahedron Lett. 2004, 45, 791-794. DOI: 10.1016/j.tetlet.2003.11.017

The first preparation of enantiomerically pure 1,1-binaphthyl-2,2-diboronic acid (by resolution) is reported. Optimization of the cross-coupling conditions was found to be crucial to achieve good yields in Suzuki arylation in approaches from both 2,2-diiodide or 2,2-diboronic acid (52–56%, with model p-tolyl reagents). Stereochemical results in these reactions were dramatically different: almost complete racemization starting from the 2,2-diiodide versus complete conservation of stereogenic information from the 2,2-diboronic acid. This novel synthetic approach, a stereoconservative Suzuki arylation of the diboronic acid, should be a valuable method for the synthesis of a new group of 2,2-diarylated (including functionalized) binaphthyl derivatives.

Novel route to enantiopure 2,2’-diaryl-1,1’-binaphthalenes by stereoconservative Suzuki arylation at positions 2 and 2’ Brath H., Dubovská M., Juríček M., Kasák P., Putala M. Collect. Czech. Chem. Commun. 2004, 69, 1517-1536. DOI: 10.1135/cccc20041517

The Suzuki arylation of enantiopure 2,2'-diiodo-1,1'-binaphthalene affords the 2,2'-diarylated products in considerable yields (up to 52%), however, significantly racemized. The reversed-polarity approach, using novel enantiopure 1,1'-binaphthalene-2,2'-diyldiboronic acid, prepared either by resolution or by stereoconservative boronation, allowed, after optimization of coupling conditions, to obtain the model 2,2'-ditolylated product in good yield (56%) as well, but in addition, without impairing of enantiomeric purity (i.e. stereoconservatively). The developed synthetic approach was found to be an expedient method for the synthesis of enantiopure 2,2'-diaryl-1,1'-binaphthalenes, especially for those with electron-neutral and electron-deficient poor aryl groups. Observing that the diboronic acid decomposes by hydrodeboronation under the reaction conditions, 2-aryl-1,1'-binaphthalenes were isolated as the main products from the reaction with less reactive electron-rich aryl iodides.

Stereoconservative Negishi arylation and alkynylation as an efficient approach to enantiopure 2,2’-diarylated 1,1’-binaphthyls Krascsenicsová K., Walla P., Kasák P., Uray G., Kappe O. C., Putala M. Chem. Commun. 2004, 2606-2607. DOI: 10.1039/B410185E

Negishi arylation and alkynylation of easily synthesized chiral 2,2′-diodo-1,1′-binaphthyl rapidly proceeds in refluxing THF utilizing controlled microwave irradiation, affording enantiopure 2,2′-diarylated 1,1′-binaphthyls in good to excellent yields.