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Dive into the research topics where Tomislav Jednačak is active.

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Featured researches published by Tomislav Jednačak.


RSC Advances | 2014

Pyridoxal hydrazonato molybdenum(VI) complexes: assembly, structure and epoxidation (pre)catalyst testing under solvent-free conditions

Jana Pisk; Biserka Prugovečki; Dubravka Matković-Čalogović; Tomislav Jednačak; Predrag Novak; Dominique Agustin; Višnja Vrdoljak

Pyridoxal hydrazonato molybdenum(VI) complexes were prepared by the reaction of the corresponding hydrazone (H2L1 = pyridoxal isonicotinic acid hydrazone, H2L2 = pyridoxal benzhydrazone, H2L3 = pyridoxal 4-hydroxy benzhydrazone) and [MoO2(acac)2] under appropriate conditions. The complexes can be classified into three categories: mononuclear [MoO2(L1–3)(MeOH)], polynuclear [MoO2(L1–3)]n and hybrid organic–inorganic compounds with the Lindqvist polyoxomolybdate [MoO2(HL1–3)]2Mo6O19. A unique example of a cationic polymer assembly with Lindqvist anions is reported herein for the first time. The compounds were characterised by elemental, TG and DSC analyses and by spectroscopic (IR, UV-Vis, 1H, 13C NMR) techniques. The crystal and molecular structure of the pyridoxal benzhydrazone H2L2, three mononuclear complexes [MoO2(L1–3)(MeOH)], and the Lindqvist-containing compounds [MoO2(HL2)]2Mo6O19·2MeCN and (H4L1)Mo6O19 were determined by single crystal X-ray diffraction. All complexes were tested as (pre)catalysts for the epoxidation of cyclooctene under solvent-free conditions with the use of aqueous TBHP (TBHP = tert-butylhydroperoxyde) as an oxidant. Optimal results in terms of conversion, selectivity, TOF and TON were obtained at very low (pre)catalyst loadings (0.05% [Mo] vs. substrate). The influence of the Linqvist anion on catalytic performance is discussed.


Journal of Pharmaceutical and Biomedical Analysis | 2011

In-line reaction monitoring of entacapone synthesis by Raman spectroscopy and multivariate analysis.

Predrag Novak; Andrea Kišić; Tomica Hrenar; Tomislav Jednačak; Snežana Miljanić; Gordana Verbanec

In-line Raman spectroscopy and multivariate analysis were used to monitor Knoevenagel condensation reaction, the final step in preparation of drug entacapone. By applying a fiber optical Raman probe immersed into a reaction vessel Raman spectra of the reaction mixture were recorded in situ during the entacapone synthesis in toluene, heptane and isobutyl acetate. Due to the complexity of the measured spectra, the obtained data were analyzed and interpreted by means of principal component analysis. It has been shown that progress of this reaction can be monitored in real-time and reaction end points can be determined in different solvents. The reaction was found to be the fastest in heptane due to the lower loss of the catalyst. For a comparison the reaction was independently monitored by off-line Raman spectroscopy and liquid chromatography which confirmed the results obtained in-line. The results presented here have shown that this in-line approach can be used as a fast, non destructive and reliable method to monitor the Knoevenagel reaction in real time. The knowledge gained in this study can further be exploited for the industrial process control.


Acta Pharmaceutica | 2014

Fast real-time monitoring of entacapone crystallization and characterization of polymorphs via Raman spectroscopy, statistics and SWAXS

Tomislav Jednačak; Aden Hodzic; Otto Scheibelhofer; Marijan Marijan; Johannes G. Khinast; Predrag Novak

Abstract Crystallization of the drug entacapone from binary solvent mixtures was monitored in situ using a Raman optical probe. The recorded Raman spectra and statistical analysis, which included the principal components method and indirect hard modeling made it possible to estimate the starting point of crystallization, to assess crystallization temperatures and to provide information on the polymorphic content of the mixture. It was established that crystallization temperatures were proportional to the volume content of the solvent in mixtures. The samples were also evaluated off-line via Raman spectroscopy and SWAXS. The collected data showed the presence of forms b and g in all solvent mixtures. In a toluene/methanol 30:70 mixture, in addition to forms b and g, at least one of the forms A, D or a was also indicated by SWAXS. The results have shown that the presence of a particular polymorph is strongly dependent on the nature and portion of the solvent in the binary solvent mixture.


Journal of Molecular Structure | 2015

Intra- and intermolecular hydrogen bonding in acetylacetone and benzoylacetone derived enaminone derivatives

Vedrana Lazić; Mihaela Jurković; Tomislav Jednačak; Tomica Hrenar; Jelena Parlov Vuković; Predrag Novak


Croatica Chemica Acta | 2011

Bioactive Phenylenediamine Derivatives of Dehydroacetic Acid: Synthesis, Structural Characterization and Deuterium Isotope Effects

Tomislav Jednačak; Predrag Novak; Krunoslav Užarević; Igor Bratoš; Jelena Marković; Marina Cindrić


Crystal Growth & Design | 2014

Multiple solid forms of 1, 5-bis(salicylidene)carbohydrazide : polymorph-modulated thermal reactivity

Mirta Rubčić; Nives Galić; Ivan Halasz; Tomislav Jednačak; Nenad Judaš; Janez Plavec; Primož Šket; Predrag Novak


Croatica Chemica Acta | 2012

Synthesis, Structural Characterization and Hydrogen Bonding of Mono(salicylidene)carbohydrazide

Predrag Novak; Tomislav Jednačak; Jelena Parlov Vuković; Klaus Zangger; Mirta Rubčić; Nives Galić; Tomica Hrenar


Organic Process Research & Development | 2016

Monitoring and Quantification of Omeprazole Synthesis Reaction by In-Line Raman Spectroscopy and Characterization of the Reaction Components

Damir Šahnić; Ernest Meštrović; Tomislav Jednačak; Iva Habinovec; Jelena Parlov Vuković; Predrag Novak


Archive | 2012

NMR Spectroscopy for Studying Interactions of Bioactive Molecules

Predrag Novak; Tomislav Jednačak


Polyhedron | 2017

Intriguing binding modes of tetradentate pyridoxal derivatives to molybdenum centre

Jana Pisk; Biserka Prugovečki; Tomislav Jednačak; Predrag Novak; Višnja Vrdoljak

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