Two novel four-coordinated zinc(II) complexes [Zn(dmatrz)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>] and [Zn(dmatrz)<Subscript>2</Subscript>(SCN)<Subscript>2</Subscript>] exhibiting strong blue fluorescent properties

Two novel complexes, [Zn(dmatrz)₂]Cl₂ (1) and [Zn(dmatrz)₂(SCN)₂] (2), have been prepared and characterized by X-ray crystallography, absorption and luminescence spectrometries (dmatrz=3,5-dimethy-4-amino-1,2,4-triazole). The coordination environment of the zinc(II) ions in (1) and (2) has a distorted tetrahedral geometry completed via two independent nitrogen atoms of two triazole ligands and two anions, respectively. Both (1) and (2) show strong blue luminescence properties. Furthermore, (1) displays stronger blue photoluminescence than (2) as the result of different anions (Cl^- and SCN^-) coordinated to the zinc(II) ions.     

Hydrogen peroxide oxidation of di(hydroxo)platinum(II) species in carboxylic acids

A facile procedure for synthesizing the mono(hydroxo)tris(carboxylato)platinum(IV) species has been achieved. The reaction of [Pt^II(OH)₂(dmpda)] (dmpda=2,2-dimethyl-1,3-propanediamine) with a 30% aqueous solution of H₂O₂ in the presence of a carboxylic acid produces a stable [Pt^IV(OOCR)₃(OH)(dmpda)] (R=Me, Et) complex in high yield. The crystal structures of [Pt^IV(OOCMe)₃(OH)(dmpda)] . H₂O (triclinic P1 bar, a=8.761(2) Å, b=9.245(3) Å, c=10.659(2) Å, =106.25(2)°, =93.90(2)°, =98.92(2)°, V=813.1(3) ų, Z=2, R= 0.0474) and [Pt^IV(OOCEt)₃(OH)(dmpda)] (monoclinic P2₁/c, a=12.777(4) Å, b=10.514(2) Å, c=14.971(3) Å, =107.40(2)°, V=1919.2(8) ų, Z=4, R=0.0611) show that the hydroxyl group has been selectively positioned at an axial site. The intramolecular hydrogen bond between the OH and C=O moiety exists (O(H)...=C, 2.83 Å for [Pt^IV(OOCMe)₃(OH)(dmpda)] · H₂O; 2.72 Å for [Pt^IV(OOCEt)₃(OH)(dmpda)]. Formation of the axial-mono(hydroxo)tris(carboxylato)platinum(IV) species may be ascribed to a combination of `reactive-equatorial effects' with `cis-addition' in the carboxylic acid.     

Thermogravimetric study of flame-retarding properties on phosphorylated beech sawdust

Beech sawdust (S) and samples containing 1% of H₃PO₄ (SP), (NaPO₃)_n (PS), P₂O₅ (POS), NaOH/P₂O₅ (SPS), NaOH (SS) or Na₂CO₃ (CS) were analysed using dynamic and isothermal thermogravimetry (TG) in nitrogen and oxygen environments. According to the results of dynamic experiments in nitrogen, the thermal resistance at 275 °C decreased in the order: S > SS > CS > SP> SPS > PS > POS, while in oxygen the order was: S > POS > SPS=CS=PS > SP > SS. The difference in residues obtained in nitrogen in comparison to oxygen environment reaches its maximum at temperatures from 300 to 325 °C and according to the decreasing values the following order could be listed: SS (300 °C/27%) > SP (325 °C/25%) > CS (300 °C/24%) > S (325 °C/23%) > SPS (300 °C/19%) > PS (300 °C/11%) > POS (275 °C/4%). This indicates that with a decreasing difference in residues formed in oxidative and inert environments the flame-retardant effect of the sample is increasing. The calculated initial rate constants of residue formation and gasification and the corresponding activation energies of the processes in nitrogen and oxygen from the isothermal experiments gave smaller values of rate constants for SPS than for S. For the SPS sample in comparison with S the activation energy of residue formation in nitrogen decreased while the three remaining values increased. The E_r* of PS in the oxygen is the biggest from all studied samples under the conditions used, while SPS gave the biggest E_g* in the oxygen environment. The phosphorus could be washed out with water from SP and SPS, while it remained in PS and POS. These last two samples also have the best flame-retarding properties according to TG analysis.     

A new approach for the detection of carbon-centered radicals in enzymatic processes using prefluorescent probes

In this communication we propose a novel application for prefluorescent probes in the detection of free carbon-centered radicals in enzymatic processes. Prefluorescent probes combine a fluorescent moiety tethered to a paramagnetic nitroxide that acts as a fluorescence quencher. Trapping of a radical by the nitroxide group restores the fluorescence properties. The increase in fluorescence intensity with time reflects the formation and quenching of carbon-centered radicals and can be used for the quantitative evaluation of yields and kinetics. As a test system we used horseradish peroxidase, an oxidoreductase that is widely accepted to operate by a radical-mediated mechanism. We used the prefluorescent probe (quinoline-TEMPO), where a quinoline moiety has been tethered to 2,2,6,6-tetramethylpiperidin-1-oxyl.     

Study on multimers and their structures in molecular association mixture

Self-association system of(R)-1,3-butanediol in dilute carbon tetrachloride(CCl4)solution is studied as a model of molecular association mixture.Analysis methods including FSMWEFA(fixed-size moving window evolving factor analysis)combined with PCA(principal component analysis),SIMPLISMA (simple-to-use interactive self-modeling mixture analysis),and ITTFA(iterative target transformation factor analysis)are adopted to resolve infrared spectra of(R)-1,3-butanediol solution.Association number and equilibrium constant are computed.(R)-1,3-butanediol in dilute inert solution is determined as a monomer-trimer equilibrium system.Theoretical investigation of trimer structures is carried out with DFT(density functional theory),and structural factors are analyzed.     

<Emphasis Type="Italic">Brønsted</Emphasis> Acids in Ionic Liquids: Fundamentals,Organic Reactions,and Comparisons

Summary. A background for studying acids in various solvents is developed, emphasizing the importance of knowing to what extent a solvent conducts electricity and is therefore ionized, the dissociation equilibria of common molecular solvents and the acidic and basic species generated by solvent leveling. Acidity measurements in the atypical solvent water are discussed and the common method of expressing acidity in other systems – by Hammett values – is introduced. Representative examples of reactions involving Br?nsted acids in ionic liquids are presented and attention paid to the questions of speciation and acidity values. It is found that the gas phase proton affinity of a base is often a better guide to the acidity of its conjugate acid in an ionic liquid than is the dissociation constant of the said acid in water.     

Phenanthroline complexes bearing diamide-anion recognition sites

The synthesis and anion binding properties of new ruthenium(II) and cobalt(II) phenanthroline complexes, containing two amide subunits are described. Evidence for anion binding in dimethyl sulfoxide (DMSO) solution was obtained from u.v.–vis titration experiments. Results indicated that these receptors showed strong affinity for F⁻ and AcO⁻, and showed weak affinity for OH⁻ and H₂PO ₄ ⁻ , and showed no affinity for Cl⁻, Br⁻, I⁻. These receptors interacted with various anions examined through hydrogen-bond formation.     

Sensitively probing the cofactor redox species and photo-induced electron transfer of wild-type and pheophytin-replaced photosynthetic proteins reconstituted in self-assembled monolayers

An ultrathin, ordered, and packed protein film, consisting of the 2-mercaptoacetic acid (MAA), polydimethyldiallylammonium chloride (PDDA), and wild-type (WT) photosynthetic reaction center (RC; termed as WT-RC) or its pheophytin (Phe)-replaced counterpart (termed as Phe-RC), was fabricated by self-assembling technique onto gold electrode for facilitating the electron transfer (ET) between RC and the electrode surface. Near-infrared (NIR)-visible (Vis) absorption and fluorescence (FL) emission spectra revealed the influence of pigment substitution on the cofactors arrangement and excitation relaxation of the proteins, respectively. Square wave voltammetry (SWV) and photoelectric tests were employed to systematically address the differences between the WT-RC films and mutant ones on the direct and photo-induced ET. The electrochemical results demonstrated that ET initiated by the oxidation of the primary donor (P) was obviously slowed down, and the formed P⁺ had more population as well as more positive redox potential in the Phe-RC films compared with those in the WT ones. The photoelectrochemical results displayed the dramatically enhanced photoelectric performances of the mutant ones, further suggesting the slow-down formation of final charge-separated state in Phe-RC. The functionalized protein films introduced in this paper provided an efficient approach to sensitively probe the redox cofactors and ET differences resulting from only minor changes in pigment arrangement in the pigment–protein complex. The favored ET process observed for the membrane proteins RC was potentially valuable for a deep understanding of the multi-step biological ET process and development of versatile bioelectronic devices.     

Development of a non-invasive method for the determination of the macroscopic neutron cross sections of a sample matrix in large-sample prompt-gamma neutron activation analysis

In order to correct for neutron self-shielding in large-sample prompt gamma NAA, a method has been developed to determine the macroscopic scattering and absorption cross sections, i.e., Σ _a and Σ _s, using four Cu flux monitors placed around the sample. With Monte Carlo computations, the neutron densities throughout the sample and the resulting and the corresponding self-shielding factor as calculated from the Σ _a and Σ _s as obtained through the Cu monitors were compared to the true values. The derived Σ _a and Σ _s were found to be sufficiently accurate as long as Σ _t = Σ _a + Σ _s was less than 0.6 cm⁻¹ and Σ _s/Σ _t was greater than 0.1.     

Thermal analysis and microscopical characterization of cholesterol in gallstones

Summary Cholesterol constitutes the major component of most gallstones. It was identified and determined in gallstones by thermal analysis technique (DSC and TG-DTA), mainly by the use of the melting temperature (T_onset=145°C and T_max=149°C) and by DTG peak decomposition (T_max=364°C). Cholesterol anhydrous (ChA), which showed endothermic polymorphic peak, T_max=40°C, without mass loss, was differentiated from cholesterol monohydrate (ChH), which showed a broad endothermic peak, T_max=59°C, attributed to loss of water of crystallization (theoretical 4.45%). Morphological studies of gallstones were performed by optical microscopy and scanning electron microscopy (SEM). The stones consisted of a pigmented core with a variably-sized irregular central cavity, surrounded by a radially arranged deposits of plate-like ChH. The outer part of the stones showed ChA crystal arborescences. X-ray microanalysis gave a typical spectrum rich in C and O, and in some instances the presence of P, which was attributed to the presence of phospholipids. CaCO₃ was easily characterized by TG with the use of DTG decomposition peak at 674°C.