Mladen Žinić

Intense Optical Activity from Three‐Dimensional Chiral Ordering of Plasmonic Nanoantennas

Twisting nanoparticles: Plasmonic circular dichroism was experimentally obtained in chiral 3D organizations of gold nanorods obtained by self-assembly of the nanoantennas onto a fiber template with a twisted morphology. Numerical simulations based on coupled dipoles confirm the crucial role of gold nanorods in this intense circular dichroism

Bis(Amino Acid) Oxalyl Amides as Ambidextrous Gelators of Water and Organic Solvents. Supramolecular Gels With Temperature Dependent Assembly-Dissolution Equilibrium

Bis(LeuOH) (1a), bis-(ValOH) (2a) and bis(PhgOH) (5a) (Phg denotes (R)-phenylglycine) oxalyl amides are efficient low molecular weight organic gelators of various organic solvents and their mixtures as well as water, water/DMSO, and water/DMF mixtures. The organisational motifs in aqueous gels are dominated primarily by lipophilic interactions while those in organic solvents are formed by intermolecular hydrogen bonding. Most of the gels are thermoreversible and stable for many months. However, 2a forms unstable gels with organic solvents which upon ageing transform into variety of crystalline shapes. For some 1a/alcohol gels, a linear correlation between alcohol dielectric constants (epsilon) and gel melting temperatures (Tg) was found. The 1H NMR and FTIR spectroscopic investigations of selected gels reveal the existence of temperature dependent network assembly/dissolution equilibrium. In the 1H NMR spectra of gels only the molecules dissolved in entrapped solvent could be observed. By using an internal standard, the concentration of dissolved gelator molecules could be determined. In FTIR spectra, the bands corresponding to network assembled and dissolved gelator molecules are simultaneously present. This enabled determination of the Kgel values by using both methods. From the plots of InKgel versus 1/T, the deltaHgel values of selected gels have been determined (-deltaHgel in 10-36 kJ mol(-1) range) and found to be strongly solvent dependent. The deltaHgel values determined by 1H NMR and FTIR spectroscopy are in excellent agreement. Crystal structures of 2a and rac-5a show the presence of organisational motifs and intermolecular interactions in agreement with those in gel fibres elucidated by spectroscopic methods.

Calix[4]arene Amino Acid Derivatives. Intra‐ and Intermolecular Hydrogen‐Bonded Organisation in Solution and the Solid State

Chiral calix[4]arene derivatives bearing four O-(N-acetyl-PhgOMe), (1), (Phg denotes (R)-phenylglycine) or O-(N-acetyl-LeuOMe) (2) strands have been synthesised. Both compounds in chloroform exist in stable cone conformations with non-covalently organised cavity at lower rim formed by circular interstrand amidic hydrogen bonds. Such organisation affects considerably both, the selectivity and extraction/transport properties of 1 and 2 toward metal cations. Also, the calix[4]arene derivatives with one (3) and two (5) OCH2COPhgOMe strands and the one with 1,3-OMe-2,4-(O-CH2COPhgOMe) (4) type of the substitution at lower rim have been prepared. In chloroform, derivatives 3 - 5 exist in stable conformation possessing more or less distorted calix[4]arene cone as the consequence of organisation at lower rim. For 3, NH-OH-OH-OH-OCH2, circular hydrogen bonding, for 4, two NH-OCH3 and for 5 two OH-O=CNH hydrogen bonds were found responsible for organisation at lower rim. The X-ray crystal analysis of 1, 2 and 5 showed completely different conformations and organisation than those found in solution. However, solid state and solution structures of (1, Na+) complex were identical.

A novel type of small organic gelators: bis(amino acid) oxalyl amides

Bis(S)-leucine (1) and bis-(R)-α-phenylglycine (2) oxalyl amides are discovered to be efficient small organic gelling agents capable of gelating water while their stereoisomers meso-1 and meso-2 as well as their racemates are found to be non-gelling and poorly gelling, respectively; IR, fluorescence emission spectroscopy and TEM are used to study assemblies of (S,S)-1 and (R,R)-2 in gels.

Binding of nucleotides in water by phenanthridinium bis(intercaland) receptor molecules

The bis(phenanthridinium) receptor molecules 3–5 bind nucleotides in aqueous media by stacking interactions between cis-oriented receptor units and the intercalated nucleic base part of a nucleotide with stability constants in the range 105–106 dm3 mol–1, the highest measured to date for these type of receptors and substrates.

Synergic effect in gelation by two-component mixture of chiral gelators

Observation of the synergic gelation effect (SGE) in two-component gels is reported. An equimolar mixture of (S,S)-bis(LeuOH) oxalamide [(S,S)-1] and (S,S)-bis(leucinol) oxalamide [(S,S)-2] is able to gel up to 7 times larger a volume of p-xylene than an equal mass of each component and up to 5 times larger a volume than an equal mass of the (S,S)-1 + (R,R)-2 or (S,S)-1 + rac-2 equimolar mixtures. The homochiral (S,S)-1 + (S,S)-2 combination of gelators is capable of hardening a volumes up to 5 times larger of certain solvents than the heterochiral (S,S)-1 + (R,R)-2 combination. Experimental evidence provided by determination of gelation efficiency, by 1H NMR, TEM and XRD studies, by determination of phase transition diagrams and calculations of thermodynamic parameters for gel melting processes shows that synergism depends on the chirality of the components, on the solvent properties and on the gel morphology. It was found that each component tends to form reversed bilayers in lipophilic solvents which then interact and organize into gel unit fibers. The unit fibers formed by interaction of the (S,S)-1 and (S,S)-2 bilayers and of the (S,S)-1 and (R,R)-2 bilayers are distereoisomeric. In certain solvents, such diastereomeric unit fibers give different gel morphologies which in turn results by different thermal stabilities of the gels, and in some cases by dramatically different gelling efficiencies of gelator mixtures. The latter observation is denoted as the synergic gelation effect (SGE).

In vitro cytotoxicity of three 4,9-diazapyrenium hydrogensulfate derivatives on different human tumor cell lines.

DNA intercalating agents interfere with DNA’s role as a template in replication and transcription by inserting an intercalator molecule between adjacent base pairs. We synthesized three potential novel intercalators, 4,9-diazapyrenium hydrogensulfate derivatives: 5,10-diphenyl-4,9-dimethyl-4,9-diazapyrenium hydrogensulfate (FDAP), 4,9-dimethyl-4,9-diazapyrenium hydrogensulfate (GDAP) and 2,4,7,9-tetramethyl-4,9-diazapyrenium hydrogensulfate (MDAP) and tested their biological effects in vitro on four human tumor cell lines (SKBr3: breast carcinoma, HeLa: cervical carcinoma, CaCo2: colon carcinoma and SW620: poorly differentiated cells from lymph node metastasis of colon carcinoma). Cytotoxic effects on cell growth and viability were determined using tetrazolium dye (MTT) assay. DNA synthesis and proliferation of treated cells were studied by the [3H]-thymidine incorporation test. DNA fragmentation was analyzed by agarose gel electrophoresis. The growth inhibitory effect was cell-specific and dose-dependent. The most pronounced antiproliferative effect was observed on SKBr3 cells for FDAP (10–5 M) 91.8%, for MDAP (10–5 M) 85.3% and on SW620 cells for GDAP (10–5 M) 65.3%. The DNA ladder fragmentation of treated HeLa and SKBr3 cells, as a hallmark of apoptosis, was observed. Based on specific DNA fragmentation, morphological changes (reduced cell volume, round cell shape, condensed chromatin) and growth inhibition of treated human tumor cells we conclude that tested substances induced apoptotic cell death.

Lipophilic derivative of rhodamine 19: characterization and spectroscopic properties

A new octadecylamide derivative of rhodamine 19 was synthesized by reaction of rhodamine 19 ethyl ester (rhodamine 6 G) with octadecylamine. This lipophilic dye exists in two forms: as a cationic species containing a secondary amide group and as an electrically neutral molecule containing an additional ring closed between the oxygen of the amide group and the central carbon of the xanthene part. Both forms were isolated and characterized in detail by means of elemental analysis, mass spectrometry, IR, NMR and UV–VIS spectroscopy. Depending on the hydrogen ion activity in solution and the availability of solvent hydrogen for hydrogen bond formation, the cationic form easily converted into a neutral one and vice versa. On the basis of absorption and emission UV–VIS spectroscopic data, the equilibrium of the two forms was studied in various solvents. An increase in dye concentration in acidified methanol/water mixture (volume fraction of water, ϕ=80%) led to aggregation of the cationic molecules. Using the UV–VIS absorption data, a corresponding dimerization constant was evaluated.

Fluoride-responsive organogelator based on oxalamide-derived anthraquinone

Anthraquinone derived oxalamide gelator 1 forms with aromatic solvents and alcohols very stable gels which selectively respond to the presence of fluoride anion by colour change and/or gel-to-sol transition.

The Formation of CuCl2‐Specific Metallogels of Pyridyloxalamide Derivatives in Alcohols

Isomeric pyridyloxalamide derivatives 1-3, which differed in the position of the nitrogen atom on the pyridyl ring, showed remarkably different gel-forming aptitudes in the presence of CuCl2 salt in alcohols. Whilst derivatives 1 and 3 formed a soluble complex and a solid precipitate, respectively, ligand 2 generated a remarkably metal- and anion-specific metallogel.