Next Generation Access Network Deployment in Croatia: Optical Access Networks and Current IoT/5G Status

This paper gives an overview and background of optical access network deployment in Croatia. Optical access network development in Croatia has been put into a global as well as in the European Union context. All the challenges and the driving factors for optical access networks deployment are considered. Optical access network architectures that have been deployed by most of the investors in Croatian telecommunication market are presented, as well as the architectures that are in early phase of deployment. Finally, an overview on current status of mobile networks of the fifth generation and Internet of Things is given.     

Optimisation of FIA system for detection of organophosphorus and carbamate pesticides based on cholinesterase inhibition

The sensitivity of the bioanalytical FIA system containing different immobilised cholinesterases (AChEs from electric eel, human erythrocytes, bovine erythrocytes and BuChE from horse serum) for determination of organophosphorus and carbamate pesticides was tested. Responses to some frequently used organophosphorus (paraoxon, oxydemeton-methyl, triazophos) and carbamate (carbofuran, propoxur) pesticides were found to be dependent on the origin of cholinesterases. The highest sensitivity was obtained by bioanalytical columns prepared with electric eel AChE while the lowest sensitivity was shown by the bioanalytical columns prepared with horse serum BuChE. The differences in responses for different enzymes were found to be less pronounced when the contact time between the enzyme and the pesticide is long enough (low flow rates). The optimal flow rate was chosen as a compromise between the duration of analysis and reasonably low limits of detection.     

Hydrogen Bonding and Solvent Effects on Complexation of Alkali Metal Cations by Lower Rim Calix[4]arene Tetra(O-[N -acetyl-D -phenylglycine methyl ester]) Derivative

Complexation of alkali metal cations with 5,11,17,23-tetra-tert-butyl-26,28,25,27-tetrakis(O-methyl-D-α-phenylglycylcarbonylmethoxy)calix[4]arene (L) was studied by means of spectrophotometric, conductometric and potentiometric titrations at 25 °C. The solvent effect on the binding ability of L was examined by using two solvents with different affinities for hydrogen bonding, viz. methanol and acetonitrile. Despite the presence of intramolecular NH···O=C hydrogen bonds in L, which need to be disrupted to allow metal ion binding, this calix[4]arene amino acid derivative was shown to be an efficient binder for smaller Li⁺ and Na⁺ cations in acetonitrile (lg K_LiL > 5, lg K_NaL = 7.66), moderately efficient for K⁺ (lg K_KL = 4.62), whereas larger Rb⁺ and Cs⁺ did not fit in its hydrophilic cavity. The complex stabilities in methanol were significantly lower (lg K_NaL = 4.45, lg K_KL = 2.48). That could be explained by different solvation of the cations and by competition between the cations and methanol molecules (via hydrogen bonds) for amide carbonyl oxygens. The influence of cation solvation on complex stability was most pronounced in the case of Li⁺ for which, contrary to the quite stable LiL⁺ complex in acetonitrile, no complexation was observed in methanol under the conditions used.     

Photoinduced gelation by stilbene oxalyl amide compounds

Oxalyl amide derivatives bearing 4-dodecyloxy-stilbene as a cis-trans photoisomerizing unit were synthesized. The trans derivative acted as a versatile gelator of various organic solvents, whereas the corresponding cis derivative showed a poor gelation ability or none at all. In diluted solution (c = 2.0 x10(-5) mol dm(-3), ethanol), the cis isomer was photochemically converted into the trans isomer within 4 min. Depending on the radiation wavelength, the trans isomer was stable or liable to photodecomposition. When exposed to irradiation, a concentrated solution of the cis isomer (c = 2.0 x 10(-2) mol dm(-3), ethanol) turned into a gel. The FT-Raman, FT-IR, and 1H NMR spectra demonstrated that the gelation process occurred because of a rapid cis --> trans photoisomerization followed by a self-assembly of the trans molecules. Apart from the formation of hydrogen bonding between the oxalyl amide parts of the molecules, confirmed by FT-IR spectroscopy, it was assumed that the pi-pi stacking between the trans-stilbene units of the molecule and a lipophilic interaction between long alkyl chains were the interactions responsible for gelation.     

Validation of different commercially available cholinesterases for pesticide toxicity test

A systematic study of different commercially available cholinesterases (AChEs from electric eel, human erythrocytes, bovine erythrocytes and BuChE from horse serum) for the FIA determination of some frequently used organophosphate (paraoxon, oxydemeton-methyl, triazophos, diazionon) and carbamate (carbofuran, propoxur) pesticides was carried out. Responses of the previously developed photothermal FIA system were found to be dependent on the origin of cholinesterases and properties of tested pesticides. The highest sensitivity was obtained with electric eel AChE and the lowest sensitivity with horse serum BuChE. The LOD values for investigated pesticides correlate with acute toxicities expressed as LD50 (oral, rat). The presented FIA system could serve as an alternative screening test to evaluate the toxicity of different environmental samples, new cholinesterase inhibiting pesticides or other products (e.g. nerve gases).     

alpha-phenylpropionic acid derivatives. Synthesis and dethiation of 5-benzoylbenzo[b]thiophene-3-carboxylic acid

The total synthesis of the title compound 8 started with p-thiocresol which was acylated with oxalyl chloride to give compound 1 . This product underwent a condensation reaction with chloroacetic acid under basic conditions yielding compound 2 . Two different synthetic pathways were used to convert compound 2 into the title compound 8 . The first consisted in decarboxylation of 2 to 3 , which was then converted to the ester 4 , which was brominated and the product 5 was subjected to a Friedel-Craft's reaction with benzene. The resulting benzyl derivative 6 was oxidized to the benzoyl stage i.e. compound 7 , which was finally hydrolyzed to 8 . The second pathway was similar to the first one so that the steps of esterification, bromination, Friedel-Craft's alkylation and oxidation started with the dicarboxylic acid 2 . Thus compounds 12–16 were obtained, and the last product was decarboxylated to 8 . The yields in both procedures were similar. Finally, the dethiation of compound 8 with Raney nickel afforded compounds 18, 19 and 20 .     

CELLULAR DELIVERY AND RETENTION OF PHOTOFRIN: III. ROLE OF PLASMA PROTEINS IN PHOTOSENSITIZER CLEARANCE FROM CELLS

Abstract— Human plasma proteins, albumin, globulins and low density (LDL), high density (HDL) and very low density (VLDL) lipoproteins were tested for their effects on retention of Photofrin and three other photosensitizers in cultured cells. This was assessed by incubating the cells, subsequent to the exposure to Photofrin, in the photo-sensitizer-free medium containing various concentrations of different plasma proteins. Photofrin clearance levels differed with individual plasma proteins and also were dependent on concentration of these proteins in the incubation medium. All of the proteins except VLDL promoted clearance of Photofrin taken up by the cells in the presence of 5% human serum. Subsequent to some Photofrin exposure conditions (in the presence of 5% fetal bovine serum, or in protein-free medium), albumin, in contrast to LDL, HDL and globulins, exhibited decreased capacity for promoting the photosensitizer clearance from the cells. The VLDL showed very little or no effect in promoting cellular clearance of Photofrin, tetraphenyl porphine tetrasulfonate (TPPS₄), and di- and tetrasulfonated chloroaluminum phthalocy-anine (AlPcS₂ and AlPcS₄, respectively). The LDL seem to be particularly effective in promoting clearance of Photofrin and AlPcS₂ from the cells, whereas albumin and globulins were shown to be more effective than LDL and HDL in promoting the cellular clearance of TPPS₄.     

Chiral bis(amino alcohol)oxalamide gelators-gelation properties and supramolecular organization: racemate versus pure enantiomer gelation

Four new chiral bis(amino alcohol)oxalamides (1-4: amino alcohol=leucinol, valinol, phenylglycinol, and phenylalaninol, respectively) have been prepared as low-molecular-weight organic gelators. Their gelation properties towards various organic solvents and mixtures were determined and these were then compared to related bis(amino acid) oxalamide gelators. Spectroscopic (FTIR, (1)H NMR) and X-ray diffraction studies revealed that the primary organization motif of (S,S)-1 and racemate 1 (rac-1) in lipophilic solvents involved the formation of inverse bilayers. The X-ray crystal structure of (S,S)-1 also shows this type of bilayer organization. The crystal structure of rac-2 reveals meso bilayers of hydrogen-bonded aggregates. Within the bilayers formed, the gelator molecules are connected by cooperative hydrogen bonding between oxalamide units and OH groups, while the interbilayer interactions are realized through lipophilic interactions between the iBu groups of leucinol. Oxalamide meso-1 lacks any gelation ability and crystallizes in monolayers. In dichloromethane rac-1 forms an unstable gel; this is prone to crystallization as a result of the formation of symmetrical meso bilayers. In contrast, in aromatic solvents rac-1 forms stable gels; this indicates that enantiomeric bilayers are formed. Oxalamide rac-1 is capable of gelling a volume of toluene three times larger than (S,S)-1. A tranmission electron microscopy investigation of rac-1 and (S,S)-1 toluene gels reveals the presence of thinner fibers in the former gel, and, hence, a more compact network that is capable of immobilizing a larger volume of the solvent. The self-assembly of these types of gelator molecules into bilayers and subsequent formation of fibrous aggregates can be explained by considering the strength and direction of aggregate forces (supramolecular vectors) in three-dimensional space.     

THE EFFECTS OF LOW DENSITY LIPOPROTEINS ON UPTAKE OF PHOTOFRIN II

The cellular uptake of Photofrin II (PII) was studied using fluorescence imaging and chemical extraction. The influence of serum and low density lipoproteins (LDL) was examined under a variety of experimental conditions employing cultured human cells of different origins as well as a subcutaneously SMT-F tumor implanted in mice. Results showed that serum inhibited PII uptake. In general, LDL also inhibits PII uptake with the exception of an initial increase in the first 10-30 min when the cellular concentration of PII was measured by fluorescence imaging instead of chemical extraction. Our results suggest a possible de-aggregation process occurring upon internalization or binding of PII to LDL.