Publications by authors named "Dean Markovic"

Amino acids (AAs) have broad nutritional, therapeutic, and medical significance and thus are one of the most common active ingredients of nutritional supplements. Analytical strategies for determining AAs are high-priced and often limited to methods that require modification of AA polarity or incorporation of an aromatic moiety. The aim of this work was to develop a new method for the determination of L-arginine, L-ornithine, and L-lysine on low-cost microchip electrophoresis instrumentation conjugated with capacitively coupled contactless conductivity detection.

View Article and Find Full Text PDF

The analysis of dietary supplements is far less regulated than pharmaceuticals, leading to potential quality issues. Considering their positive effect, many athletes consume supplements containing L-histidine and β-alanine. A new microfluidic method for the determination of L-histidine and β-alanine in dietary supplement formulations has been developed.

View Article and Find Full Text PDF

Background: While granulatamides A and B have been previously isolated, their biological activities have been only partially examined. The aim of this study was to synthesize granulatamide B (4b), a tryptamine-derivative naturally occurring in coral species, using the well-known procedure of Sun and Fürstner and its 12 structural analogues by modifying the side chain, which differs in length, degree of saturation as well as number and conjugation of double bonds.

Methods: The prepared library of compounds underwent comprehensive assessment for their biological activities, encompassing antioxidative, antiproliferative, and antibacterial properties, in addition to toxicity evaluation using a Zebrafish model.

View Article and Find Full Text PDF

The health supplement industry is one of the fastest growing industries in the world, but there is a lack of suitable analytical methods for the determination of active compounds in health supplements such as peptides. The present work describes an implementation of contactless conductivity detection on microchip technology as a new strategy for the electrophoretic determination of L-carnosine in complex health supplement formulations without pre-concentration and derivatization steps. The best results were obtained in the case of +1.

View Article and Find Full Text PDF

Beneficial effects of a natural zeolite clinoptilolite in vivo on mammals, including humans, have been empirically observed and documented in literature. The positive biological activities have been associated to its detoxifying and antioxidative properties, and its immunostimulative and adsorption properties. Herein, we present the in vitro and in vivo study of clinoptilolite zeolite materials adsorption properties for d-glucose.

View Article and Find Full Text PDF

The behavior of a new 1,3-dioctadecyl-1-imidazol-3-ium tetraphenylborate (DODI-TPB) surfactant sensor was studied in single and complex mixtures of technical grade QACs-benzalkonium chloride (BAC), -didecyl--dimethylammonium chloride (DDAC), and -dioctyl--dimethylammonium chloride (DOAC) usually used in COVID-19 disinfecting agents formulations. The results obtained with the new DODI-TPB sensor were in good agreement with data measured by a 1,3-dihexadecyl-1-benzo[]imidazol-3-ium-tetraphenylborate (DMI-TPB) surfactant sensor, as well as two-phase titration used as a reference method. The quantitative titrations of a two-component mixture of the cationic homologs (a) DDAC and DOAC; and (b) BAC and DOAC showed that the new DODI-TPB surfactant sensor can clearly distinguish two separate mixture components in a single potentiometric titration curve with two characteristic inflexion points.

View Article and Find Full Text PDF

A low-cost and fast potentiometric surfactant sensor for cationic surfactants, based on the new ion-pair 1,3-dioctadecyl-1-imidazol-3-ium-tetraphenylborate (DODI-TPB), is presented. The new cationic surfactant DODI-Br was synthesized and characterized by NMR, LC-MS, and elemental analysis, and was used for synthesis of the DODI-TPB ionophore. The DODI-TPB surfactant sensor was obtained by implementation of the ionophore in PVC.

View Article and Find Full Text PDF

Since the middle of the last century, marine organisms have been identified as producers of chemically and biologically diverse secondary metabolites which have exerted various biological activities including anticancer, anti-inflammatory, antioxidant, antimicrobial, antifouling and others. This review primarily focuses on the marine phenolic compounds and their derivatives with potent anticancer activity, isolated and/or modified in the last decade. Reports on the elucidation of their structures as well as biosynthetic studies and total synthesis are also covered.

View Article and Find Full Text PDF

Due to sedentary lifestyle and harsh environmental conditions, gorgonian coral extracts are recognized as a rich source of novel compounds with various biological activities, of interest to the pharmaceutical and cosmetic industries. The presented study aimed to perform chemical screening of organic extracts and semi-purified fractions obtained from the common Adriatic gorgonian, sea fan, (Koch, 1887) and explore its abilities to exert different biological effects in vitro. Qualitative chemical evaluation revealed the presence of several classes of secondary metabolites extended with mass spectrometry analysis and tentative dereplication by using Global Natural Product Social Molecular Networking online platform (GNPS).

View Article and Find Full Text PDF

A 1,3-dihexadecyl-1-benzo[]imidazol-3-ium-tetraphenylborate (DHBI-TPB) ion-pair implemented in DHBI-TPB surfactant sensor was used for the potentiometric quantification of anionic surfactants in detergents and commercial household care products. The DHBI-TPB ion-pair was characterized by FTIR spectroscopy and computational analysis which revealed a crucial contribution of the C-H∙∙∙π contacts for the optimal complex formation. The DHBI-TPB sensor potentiometric response showed excellent analytical properties and Nernstian slope for SDS (60.

View Article and Find Full Text PDF

A novel, simple, low-cost, and user-friendly potentiometric surfactant sensor based on the new 1,3-dihexadecyl-1-benzo[]imidazol-3-ium-tetraphenylborate (DHBI-TPB) ion-pair for the detection of cationic surfactants in personal care products and disinfectants is presented here. The new cationic surfactant DHBI-Br was successfully synthesized and characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectrometry, liquid chromatography-mass spectrometry (LC-MS) and elemental analysis and was further employed for DHBI-TPB ion-pair preparation. The sensor gave excellent response characteristics for CTAB, CPC and Hyamine with a Nernstian slope (57.

View Article and Find Full Text PDF

This study describes a straightforward preparation of hybrid organic-inorganic thin films containing a stable 'sandwich'-like structure of two atomic layer deposited (ALD) ZnO layers separated by a thin organosilane phase, which is built from a single organic component (3-mercaptopropyl)trimethoxysilane (MPTMS). Grafting of MPTMS on the first ALD ZnO layer was performed in solution and driven by the strong affinity of the terminal thiol functionality (-SH) towards ZnO. We demonstrate that under different reaction conditions, either MPTMS monolayers are prepared or a 5 nm thick cross-linked polymeric network is formed due to the self-condensation of silane, which covers the ALD ZnO surface.

View Article and Find Full Text PDF

This review covers recent literature from 2012-2019 concerning 170 marine natural products and their semisynthetic analogues with strong anticancer biological activities. Reports that shed light on cellular and molecular mechanisms and biological functions of these compounds, thus advancing the understanding in cancer biology are also included. Biosynthetic studies and total syntheses, which have provided access to derivatives and have contributed to the proper structure or stereochemistry elucidation or revision are mentioned.

View Article and Find Full Text PDF

Gorgonian corals, which belong to the genus , are known as natural sources of diverse compounds with unique structural characteristics and interesting bioactivities both in vitro and in vivo. This review is focused primarily on the secondary metabolites isolated from various species. The chemical structures of 64 compounds were divided into three main groups and comprehensively presented: a) terpenoids, b) sterols, and c) alkaloids and nucleosides.

View Article and Find Full Text PDF

The present work shows a surface-induced preparation of sub-100 nm organosilica nanohemispheres on atomic layer deposited (ALD) AlO thin films, which was achieved by cooperative condensation/hydrolysis and thiol-ene click chemical reactions. The two-step synthetic approach consists of an initial silanization of the AlO film with vinyltrimethoxysilane (VTMS), followed by a photo-promoted growth of surface-bound nanoparticles in the presence of (3-mercaptopropyl)trimethoxysilane (MPTMS). Characterization by means of FE-SEM, XPS and EDS points towards the growth of the nanohemispherical structures being governed by an initial nucleation of thiolated organosilica seeds in solution as a result of self-condensation of MPTMS and oxidation of thiols to disulfides.

View Article and Find Full Text PDF

The transamidation reactions of unprotected mono- and disaccharidic carboxamides with various primary and secondary arylic, heterocyclic or aliphatic amines are described. This new method is green and atom efficient and gives good to high yields. Notably, the conditions do not require either a solvent or a catalyst and give ammonia as a single by-product.

View Article and Find Full Text PDF

Trimethylsilyl, triethylsilyl, tert-butyldimethylsilyl, and triisopropylsilyl 2-methylprop-2-ene-1-sulfinates were prepared through (CuOTf)2⋅C6H6-catalyzed sila-ene reactions of the corresponding methallylsilanes with SO2 at 50 °C. Sterically hindered, epimerizable, and base-sensitive alcohols gave the corresponding silyl ethers in high yields and purities at room temperature and under neutral conditions. As the byproducts of the silylation reaction (SO2 +isobutylene) are volatile, the workup was simplified to solvent evaporation.

View Article and Find Full Text PDF

The neodolastane diterpenoids comprise a group of 44 compounds including guanacastepenes, heptemerones, plicatilisins, radianspenes, 2,15-epoxy-5,13-dihydroxyneodolast-3-en-14-one and sphaerostanol. These fungal and marine natural products are characterized by a tricyclic neodolastane skeleton that consists of fused five-, seven- and six-membered rings. Their reported antibiotic activities against antibiotic-resistant bacteria together with strong antifungal and anticancer activities and their novel structures render these compounds interesting synthetic targets.

View Article and Find Full Text PDF

A practical method for the synthesis of three novel 3-C-nitromethyl-hexofuranoses is reported. The Henry reaction on a 1,2:5,6-di-O-isopropylidene-α-d-gulofuranose-derived ketone provided a 3-C-branched gulo-isomer as the sole reaction product. The dehydration-rehydration of the latter yielded an isopropylidene-protected 3-C-nitromethyl-galactofuranose.

View Article and Find Full Text PDF

Mild and chemoselective opening of lactones with sodium trimethylsilanolate in high yields and aprotic solvents is described. Kinetic studies demonstrate that the B(Ac)2 mechanistic pathway is followed. Nucleophilic attack of silanolate onto the carbonyl of the lactone moiety is the rate-determining step.

View Article and Find Full Text PDF

An efficient method has been developed for the preparation of yet unknown acyclic mixed anhydrides of carboxylic and sulfinic acids. Sterically hindered 2-methylbut-3-ene-2-sulfinyl carboxylates add primary and secondary amines preferentially onto the carbonyl moieties realizing a new method for the one-pot preparation of carboxamides. It uses 1:1 mixtures of carboxylic acids and amines without a base, requires no excess of reagents, and liberates only volatile coproducts.

View Article and Find Full Text PDF

We report a series of palladium diarylamido complexes containing a cyclometalated phosphine ligand and a coordinated THF that form enamine products from migratory insertion of ethylene and octene into the metal-nitrogen bond. The reactions of these complexes were sensitive to the electronic properties of the diarylamido group. The complex with the more electron-donating amido ligand reacted nearly 2 orders of magnitude faster than the complex with the least electron-donating amido group.

View Article and Find Full Text PDF

The first ene reactions of SO(2) and unfunctionalized alkenes are reported. Calculations suggest that the endergonic ene reactions of SO(2) with alkenes can be used to generate beta,gamma-unsaturated sulfinyl and sulfonyl compounds. Indeed, in the presence of one equivalent of BCl(3), the unstable sulfinic acid form stable sulfinic acid.

View Article and Find Full Text PDF