Qualitative interpretation of physico-chemical and isotopic parameters in the Krka River (Croatia) assessed by multivariate statistical analysis

Multivariate statistical analyses were applied on the measured physico-chemical (Cd, Pb, Cu, Zn, Mg, Ca, O₂, alkalinity, temperature, pH, SAS, DOC and DIC) and isotopic parameters (δ¹³C and δ¹⁸O) to estimate and distinguish anthropogenic from natural influences to the water system of the Krka River. Analyses were conducted on the data collected during six years from twelve sampling sites. On the basis of orientation, positioning and grouping of parameters arranged by biplots, four main hypotheses were defined and finally statistically confirmed. Thereof, two main and distinct processes occurring in the Krka River could be highlighted: (i) upstream pollution, caused by the inflow of untreated waste-waters of city of Knin and (ii) downstream self-purification, caused by the sedimentation and/or co-precipitation of pollutants coupled by the inflow of clean subterranean water (groundwater recharge). Grouping of (i) hydrological and carbon cycle connected parameters, and (ii) anthropogenically influenced correlated parameters were proposed as a result of statistical analysis. Regarding the pH, it is shown that a stream section influenced by the subterranean inflow of Zrmanja River is statistically significantly different for all sampling campaigns during six years, being lower for about 0.5 pH unit.     

The Reaction of Methyl 2,4,6-Tri-0-benzoyl-3-0-benzyl-β-D-galactopyranoside with 1,1-Dichloromethyl Methyl Ether

When methyl 2,4,6-tri-0-benzoyl-3-0-benzyl-β-D-galacto-pyranoside (JO is treated in purified chloroform at 55-60′ with excess of dichloromethyl methyl ether in the presence of a catalytic amount of freshly fused zinc chloride for 1 h the corresponding α-glycosyl chloride 2 can be isolated by column chromatography in 75-80% yield. Compound 2 is an important intermediate in the synthesis of oligosaccharides containing a glycosyl-3-0-galactosyl sequence. Under the described reaction conditions the conversion 1 - 2 is accompanied by a slow anomerisation of 1 to give methyl 2,4,6-tri-0-benzoyl-3-0-benzyl-α-D-galactopyranoside. Prolonged treatment of 2 with the used excess of the reagent results in complete debenzylation of the substrate and the conversion of the putative 2,4,6-tri-O-benzoyl-α-D-galactopyranosyl chloride into the corresponding 3-0-formyl and 3-0-dichloromethyl derivatives.     

Low-temperature versus oxygen plasma treatment of water-based TiO2 paste for dye-sensitized solar cells

High-temperature treatment steps in fabrication process of dye sensitized solar cell (DSSC) significantly contribute to the manufacturing costs and limit the use of temperature sensitive substrates. Therefore our aim was to develop a simple method for the preparation of water-based TiO₂ paste. The paste is based on peroxotitanic acid (PTA) sol–gel matrix and commercial TiO₂ nanoparticles (P25). Two fabrication processes to decompose/transform the PTA matrix in the printed TiO₂ layer are explored and combined: annealing at temperatures up to 250 °C and/or oxygen plasma treatment. The results show that the PTA matrix in the paste converts to anatase phase and to some extent also attaches to the TiO₂ nanoparticles P25 acting as an interconnecting network within TiO₂ layer. The transformation of the PTA matrix occurs around 250 °C, but in the presence of TiO₂ nanoparticles P25 it starts already at 120 °C. In addition the results reveal that the crystallization is achievable also solely with the oxygen plasma treatment. The efficiency of the TiO₂ layers, exposed to different post-deposition treatments, is evaluated in DSSCs. The results show that oxygen plasma treatment of the TiO₂ layers could efficiently replace temperature curing at 250 °C. Within this study the DSSCs with the efficiency up to 4.2 % measured under standard test conditions (1,000 W/m², AM1.5, 25 °C) were realized.     

Supramolecular Polymerization of C3‐Symmetric Organogelators: Cooperativity,Solvent, and Gelation Relationship

A systematic study of the influence of solvent and the size of C₃‐symmetric discotics on their supramolecular polymerization mechanism is presented. The cooperativity of the self‐assembly of the reported compounds is directly related to their gelation ability. The two series of C₃‐symmetric discotics investigated herein are based on benzene‐1,3,5‐tricarboxamides (BTAs) and oligo(phenylene ethynylene)‐based tricarboxamides (OPE? TAs) that are peripherally decorated with achiral ( 1 a and 2 a ) or chiral N‐(2‐aminoethyl)‐3,4,5‐trialkoxybenzamide units ( 1 b and 2 b ). The supramolecular polymerization of compounds 1 a , b and 2 a , b has been exhaustively investigated in a number of solvents and by using various techniques: variable‐temperature circular dichroism (VT‐CD) spectroscopy, concentration‐dependent ¹H NMR spectroscopy, and isothermal titration calorimetry (ITC). The supramolecular polymerization mechanism of compounds 2 is highly cooperative in solvents such as methylcyclohexane and toluene and is isodesmic in CHCl₃. Unexpectedly, chiral compound 1 b is practically CD‐silent, in contrast with previously reported BTAs. ITC measurements in CHCl₃ demonstrated that the supramolecular polymerization of BTA 1 a is isodesmic. These results confirm the strong influence of the π‐surface of the central aromatic core of the studied discotic and the branched nature of the peripheral side chains on the supramolecular polymerization. The gelation ability of these organogelators is negated in CHCl₃, in which the supramolecular polymerization mechanism is isodesmic.     

Controlled Click‐Assembly of Well‐Defined Hetero‐Bifunctional Cubic Silsesquioxanes and Their Application in Targeted Bioimaging

A general procedure for the assembly of hetero‐bifunctional cubic silsesquioxanes with diverse functionality and a perfectly controlled distribution of functional groups on the inorganic framework has been developed. The method is based on a two‐step sequence of mono‐ and hepta‐functionalization through the ligand‐accelerated copper(I)‐catalyzed azide–alkyne cycloaddition of a readily available octaazido cubic silsesquioxane. The stoichiometry of the reactants and the law of binomial distribution essentially determine the selectivity of the key monofunctionalization reaction when a copper catalyst with strong donor ligands is used. The methodology has been applied to the preparation of a set of bifunctional nano‐building‐blocks with orthogonal reactivity for the controlled assembly of precisely defined hybrid nanomaterials and a fluorescent multivalent probe for application in targeted cell‐imaging. The inorganic cage provides an improved photostability to the covalently attached dye as well as a convenient framework for the 3D multivalent display of the pendant epitopes. Thus, fluorescent bioprobes based on well‐defined cubic silsesquioxanes offer interesting advantages over more conventional fully organic analogues and ill‐defined hybrid nanoparticles and promise to become powerful tools for the study of cell biology and for biomedical applications.     

Dimensional Matching of Polycyclic Aromatics with Rectangular Metallacycles: Insertion Modes Determined by [C?H⋅⋅⋅π] Interactions

A family of Pd^II/Pt^II dinuclear receptors, designed to give a smooth increase in their cavity lengths (from 7.46–13.78 Å), is presented. Their inclusion complexes with a representative set of polycyclic aromatic substrates (naphthalene, carbazol, pyrene, and benzo[a]pyrene), were characterized and studied in aqueous solution and the solid state. By taking into account the dimensions of both receptors and substrates, an excellent complementarity was found between the size of the receptors and their ability to complex a given substrate. Furthermore, this dimensional matching results in specific binding modes depending on the ability of the guest to establish stabilizing [C? H???π] interactions with the host.     

Synthesis and Reactivity of Cationic Triruthenium Clusters Derived from 2‐Methyl‐ and 4‐Methylpyrimidines: From Conventional Cyclometalated Ligands to Novel Types of N‐Heterocyclic Carbenes

The methylation of the uncoordinated nitrogen atom of the cyclometalated triruthenium cluster complexes [Ru₃(μ‐H)(μ‐κ²N¹,C⁶‐2‐Mepyr)(CO)₁₀] ( 1 ; 2‐MepyrH=2‐methylpyrimidine) and [Ru₃(μ‐H)(μ‐κ²N¹,C⁶‐4‐Mepyr)(CO)₁₀] ( 9 ; 4‐MepyrH=4‐methylpyrimidine) gives two similar cationic complexes, [Ru₃(μ‐H)(μ‐κ²N¹,C⁶‐2,3‐Me₂pyr)(CO)₁₀]⁺( 2 ⁺) and [Ru₃(μ‐H)(μ‐κ²N¹,C⁶‐3,4‐Me₂pyr)(CO)₁₀]⁺ ( 9 ⁺), respectively, whose heterocyclic ligands belong to a novel type of N‐heterocyclic carbenes (NHCs) that have the C_carbene atom in 6‐position of a pyrimidine framework. The position of the C‐methyl group in the ligands of complexes 2 ⁺ (on C²) and 9 ⁺ (on C⁴) is of key importance for the outcome of their reactions with K[N(SiMe₃)₂], K‐selectride, and cobaltocene. Although these reagents react with 2 ⁺ to give [Ru₃(μ‐H)(μ‐κ²N¹,C⁶‐2‐CH₂‐3‐Mepyr)(CO)₁₀] ( 3 ; deprotonation of the C²‐Me group), [Ru₃(μ‐H)(μ₃‐κ³N¹,C⁵,C⁶‐4‐H‐2,3‐Me₂pyr)(CO)₉] ( 4 ; hydride addition at C⁴), and [Ru₆(μ‐H)₂{μ₆‐κ⁶N¹,N^1′,C⁵,C^5′,C⁶,C^6′‐4,4′‐bis(2,3‐Me₂pyr)}(CO)₁₈] ( 5 ; reductive dimerization at C⁴), respectively, similar reactions with 9 ⁺ have only allowed the isolation of [Ru₃(μ‐H)(μ₃‐κ²N¹,C⁶‐2‐H‐3,4‐Me₂pyr)(CO)₉] ( 11 ; hydride addition at C²). Compounds 3 and 11 also contain novel six‐membered ring NHC ligands. Theoretical studies have established that the deprotonation of 2 ⁺ and 9 ⁺ (that have ligand‐based LUMOs) are charge‐controlled processes and that both the composition of the LUMOs of these cationic complexes and the steric protection of their ligand ring atoms govern the regioselectivity of their nucleophilic addition and reduction reactions.     

Heterobimetallic Cuprates Consisting of a Redox‐Switchable,Silicon‐Based Metalloligand: Synthesis,Structures, and Electronic Properties

A series of bimetallic silyl halido cuprates consisting of the new tripodal silicon‐based metalloligand [κ³N‐Si(3,5‐Me₂pz)₃Mo(CO)₃]^? is presented (pz=pyrazolyl). This metalloligand is straightforwardly accessible by reacting the ambidentate ligand tris(3,5‐dimethylpyrazolyl)silanide ({Si(3,5‐Me₂pz)₃}^?) with [Mo(CO)₃(η⁶‐toluene)]. The compound features a fac‐coordinated tripodal chelating ligand and an outward pointing, “free” pyramidal silyl donor, which is easily accessible for a secondary coordination to other metal centers. Several bimetallic silyl halido cuprates of the general formula [CuX{μ‐κ¹Si:κ³N‐Si(3,5‐Me₂pz)₃Mo(CO)₃}]^? (X=Cl, Br, I) have been synthesized. The electronic and structural properties of these complexes were probed in detail by X‐ray diffraction analysis, electrospray mass spectrometry, infrared‐induced multiphoton dissociation studies, cyclic voltammetry, spectroelectrochemistry, gas‐phase photoelectron spectroscopy, as well as UV/Vis and fluorescence spectroscopy. The heterobimetallic complexes contain linear two‐coordinate copper(I) entities with the shortest silicon–copper distances reported so far. Oxidation of the anionic complexes in methylene chloride and acetonitrile solutions at ${E{{0\hfill \atop 1/2\hfill}}}$ =?0.60 and ?0.44 V (vs. ferrocene/ferrocenium (Fc/Fc⁺)), respectively, shows substantial reversibility. Based on various results obtained from different characterization methods, as well as density functional theory calculations, these oxidation events were attributed to the Mo⁰/Mo^I redox couple.