Positive Cooperativity Induced by Interstrand Interactions in Silver(I) Complexes with α,α'-Diimine Ligands.

The allosteric positive cooperativity accompanying the formation of compact [CuI (α,α'-diimine)2 ]+ building blocks contributed to the historically efficient synthesis of metal-containing catenates and knotted assemblies. However, its limited magnitude can easily be overcome by the negative chelate cooperativity that controls the overall formation of related polymetallic multistranded helicates and grids. Despite the more abundant use of analogous dioxygen-resistant [AgI (α,α'-diimine)2 ]+ units in modern entangled metallo-supramolecular assemblies, a related thermodynamic justification was absent. Solid-state structural characterizations show the successive formation of [AgI (α,α'-diimine)(CH3 CN)][X] and [AgI (α,α'-diimine)2 ][X] upon the stepwise reactions of α,α'-diimine=2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) derivatives with AgX (X=BF4 - , ClO4 - , PF6 - ). In room-temperature, 5-10 mM acetonitrile solutions, these cationic complexes exist as mixtures in fast exchange on the NMR timescale. Spectrophotometric titrations using the unsubstituted bpy and phen ligands point to the statistical (=non-cooperative) binding of two successive bidentate ligands around AgI , a mechanism probably driven by the formation of hydrophobic belts, that overcomes the unfavorable decrease in the positive charge borne by the metallic cation. Surprisingly, the addition of methyl groups adjacent to the nitrogen donors (6,6' positions in dmbpy; 2,9 positions in dmphen) induces positive cooperativity for the formation of [Ag(dmbpy)2 ]+ and [Ag(dmphen)2 ]+ , a trend assigned to additional stabilizing interligand interactions. Adding rigid and polarizable phenyl side arms in [Ag(Brdmbpy)2 ]+ further reinforces the positively cooperative process, while limiting the overall decrease in metal-ligand affinity.

Positive Cooperativity Induced by Interstrand Interactions in Silver(I) Complexes with α,α'-Diimine Ligands.

Invited for the cover of this issue are Davood Zare, Claude Piguet, Edwin C. Constable and co-workers at the University of Basel and the University of Geneva. The image depicts a [AgI L]+ intermediate about to catch a second α,α'-diimine ligand to form the stable [AgI L2 ]+ . Read the full text of the article at 10.1002/chem.202200912.

Synthesis, in vitro and cellular antioxidant activity evaluation of novel peptides derived from Saccharomyces cerevisiae protein hydrolysate: structure-function relationship : Antioxidant activity and synthetic peptides.

The relationship between structure and function of primary antioxidant peptide, YR-10 (YGKPVAVPAR) was considered by synthesizing three analogues including YHR-10 (YGKHVAVHAR), GA-8 (GKPVAVPA) and PAR-3 (PAR). Antioxidant activity was determined through in vitro and cellular assays. Substitution of Pro with His in the structure of YR-10 led to significant (P < 0.05) higher ABTS radical scavenging and ferric reducing activity. Following in silico simulated gastrointestinal digestion, Tyr and Arg were omitted, respectively, from N and C-terminal positions and resulted in decreasing DPPH, ABTS radical scavenging, and ferric reducing activities. PAR-3 showed the best inhibitory activity on linoleic acid oxidation. Pretreatment of Caco-2 cells with YR-10, YHR-10, and GA-8 (1000 µM) before exposure to H2O2 (160 µM) resulted in 34.10%, 39.66% and 29.159% reduction in malondialdehyde and 53.52%, 17.02% and 24.71% reduction in protein carbonyl levels. The peptide pretreatment reduced catalase level in cells and PAR-3 exhibited the most protective effects on the viability of cells exposed to oxidative stress.

Controlling Lanthanide Exchange in Triple-Stranded Helicates: A Way to Optimize Molecular Light-Upconversion.

The kinetic lability of hexadentate gallium-based tripods is sufficient to ensure thermodynamic self-assembly of luminescent heterodimetallic [GaLn(L3)3 ]6+ helicates on the hour time scale, where Ln is a trivalent 4f-block cation. The inertness is, however, large enough for preserving the triple-helical structure when [GaLn(L3)3 ]6+ is exposed to lanthanide exchange. The connection of a second gallium-based tripod further slows down the exchange processes to such an extent that spectroscopically active [CrErCr(L4)3 ]9+ can be diluted into closed-shell [GaYGa(L4)3 ]9+ matrices without metal scrambling. This feature is exploited for pushing molecular-based energy-transfer upconversion (ETU) at room temperature.

Taming Lanthanide-Centered Upconversion at the Molecular Level.

Considered at the beginning of the 21th century as being incompatible with the presence of closely bound high-energy oscillators, lanthanide-centered superexcitation, which is the raising of an already excited electron to an even higher level by excited-state energy absorption, is therefore a very active topic strictly limited to the statistical doping of low-phonon bulk solids and nanoparticles. We show here that molecular lanthanide-containing coordination complexes may be judiciously tuned to overcome these limitations and to induce near-infrared (NIR)-to-visible (VIS)-light upconversion via the successive absorption of two low-energy photons using linear-optical responses. Whereas single-ion-centered excited-state absorption mechanisms remain difficult to implement in lanthanide complexes, the skillful design of intramolecular intermetallic energy-transfer processes operating in multimetallic architectures is at the origin of the recent programming of erbium-centered molecular upconversion.

Nitrate removal from industrial wastewater using six newly isolated strains of aerobic heterotrophic denitrifiers in an attached growth.

BACKGROUND: The objective of this study was to isolate specific heterotrophic aerobic denitrifying bacteria from a wastewater treatment plant and employ them in an attached growth system for wastewater denitrification. METHODS: To isolate and screen aerobic denitrifiers, Denitrifying Medium (DM) and Screen Medium (GN) were utilized. The Polymerase Chain Reaction (PCR) technique and 16S rDNA sequencing were used to identify the isolates. The formation of biofilms by selected isolates on ceramic media was examined using a Scanning Electron Microscope (SEM). This study also investigated various variables for nitrate removal, including temperature, Carbon/Nitrogen ratio (C/N), and the carbon source. A series of experiments were conducted to gauge nitrate removal under optimal variable values. RESULTS: Six purified strains exhibited the highest denitrification efficiency in less than 30 h. Pseudomonas species were chosen for additional experiments. Denitrification efficiencies ranged from a low of 71.4% (at a temperature of 30 °C, C/N ratio of 17, and citrate as the carbon source) to a high of 98.9% (at a temperature of 33 °C, C/N ratio of 8, and citrate as the carbon source). The average denitrification efficiency was 84.02%. Optimal nitrate removal occurred at temperatures around 30-31 °C and C/N ratios of approximately 5.8-6.5. CONCLUSION: This study demonstrates that aerobic denitrifying bacteria can effectively remove nitrate from aqueous solutions.

Disentangling Light- and Temperature-Induced Thermal Effects in Colloidal Au Nanoparticles.

We present temperature-dependent (from room temperature to 80 °C) absorption spectra of Au/SiO2 core-shell nanoparticles (NPs) (core diameter: ∼25 nm) in water in the range from 1.5 to 4.5 eV, which spans the localized surface plasmon resonance (LSPR) and the interband transitions. A decrease in absorption with temperature over the entire spectral range is observed, which is more prominent at the LSPR. These changes are well reproduced by theoretical calculations of the absorption spectra, based on the experimentally measured temperature-dependent real (ε1) and imaginary (ε2) parts of the dielectric constant of Au NPs and of the surrounding medium. In addition, we model the photoinduced response of the NPs over the entire spectral range. The experimental and theoretical results of the thermal heating and the simulations of the photoinduced heating are compared with the ultrafast photoinduced transient absorption (TA) spectra upon excitation of the LSPR. These show that while the latter is a reliable monitor of heating of the NP and its environment, the interband region mildly responds to heating but predominantly to the population evolution of charge carriers.

Production and characterization of poly 3-hydroxybutyrate-co-3-hydroxyvalerate in wheat starch wastewater and its potential for nanoparticle synthesis.

Polyhydroxyalkanoates (PHAs) are polymers with biodegradable and biocompatible properties accumulated in a wide variety of bacterial strains. In the present study, active sludge, wheat starch wastewater (WSW), and oil wastewater were used for the isolation and screening of PHA-accumulating bacteria. WSW was then implemented as a cheap and economical culture medium for the production of PHAs by the selected isolate. The extracted PHA was characterized, and the capability of produced biopolymer for preparing nanoparticles was evaluated. Based on the results, 96 different bacterial isolates were obtained, of which the strains isolated from WSW demonstrated the highest PHA-accumulation capability. The maximum PHA content of 3.07 g/l (59.50% of dry cell weight) was obtained by strain N6 in 21 h. The selected strain was identified by molecular approaches as Bacillus cereus. Afterward, the physicochemical characterization of an accumulated biopolymer was specified as a PHBV copolymer. Finally, spherical homogenous PHBV nanoparticles with a size of 137 nm were achieved. The PHBV nanoparticles showed a suitable small size and good zeta potential for medical applications. Hence, it can be concluded that isolated wild strain (B. cereus) has the potential exploitation capability for cost-effective PHBV production using the WSW.

The SALSAC approach: comparing the reactivity of solvent-dispersed nanoparticles with nanoparticulate surfaces.

We demonstrate that the 'surface-as-ligand, surface-as-complex' (SALSAC) approach that we have established for annealed nanoparticulate TiO2 surfaces can be successfully applied to nanoparticles (NPs) dispersed in solution. Commercial TiO2 NPs have been activated by initial treatment with aqueous HNO3 followed by dispersion in water and heating under microwave conditions. We have functionalized the activated NPs with anchoring ligands 1-4; 1-3 contain one or two phosphonic acid anchoring groups and 4 has two carboxylic acid anchors; ligands 1, 2 and 4 contain 6,6'-dimethyl-2,2'-bipyridine (Me2bpy) metal binding domains and 3 contains a 2,2':6',2''-terpyridine (tpy) unit. Ligand functionalization of the activated NPs has been validated using infrared and 1H NMR spectroscopies, and thermogravimetric analysis. NPs functionalized with 1, 2 and 4 react with [Cu(MeCN)4][PF6] and those with 3 react with FeCl2·4H2O; metal binding has been investigated using solid-state absorption spectroscopy and scanning electron microscopy (SEM). Competitive binding of ligands 1-4 to TiO2 NPs has been investigated and shows preferential binding of phosphonic acid over carboxylic acid anchors. For the phosphonic acids, the binding orders are 3 > 1 > 2 which is rationalized in terms of relative pK a values (phosphonic acid and [HMe2bpy]+ or [Htpy]+) and the number of anchoring groups in the ligands. Ligand exchange between ligand-functionalized NPs and homoleptic metal complexes gives NPs functionalized with heteroleptic copper(i) or iron(ii) complexes.

Screening of carbon and nitrogen sources using mixture analysis designs for carotenoid production by Blakeslea trispora.

The production of many secondary metabolites such as carotenoids is influenced by the type of carbon and nitrogen sources and C:N ratio applied in culture medium. The present study discusses the role of C:N ratio and screening of carbon and nitrogen sources using mixture analysis design in carotenoids production by Blakeslea trispora. The C:N ratios of 20, 40, and 60 with six nitrogen sources were evaluated. Results indicated that limitation of nitrogen source (C:N of 60) could improve carotenoids production. Six nitrogen and carbon sources were then screened using mixture analysis design. The most effective nitrogen and carbon sources were soybean powder and glucose, respectively. The productivity of carotenoids (983.8 ± 31.5 mg/L) based on consumed nitrogen and carbon source was 189.10 mg/g soybean powder and 19.66 mg/g glucose. Mixture analysis design indicated single carbon and nitrogen source were more effective than a mixture of sources for carotenoids production.

Isolation and purification of rat islet cells by flow cytometry.

Flow cytometry has been employed as a method to study homogeneity of isolated islet subpopulations. After collagenase digestion of rat pancreas and elutriation of tissue fragments, islets were isolated and dissociated, and cells were analyzed and sorted according to their low forward angle light scattering properties by using automated flow cytometry. A standardized procedure was developed for the preparation of rat islet cell grafts for purification of islet cells. In this process, after collagenase digestion of pancreas, islets were isolated, dissociated, identification by dithizone method and then with enzymatic procedure by DNase and trypsin, the islet cells changed into single cells and beta cells were identified by immunofluorescence method and then assayed by flow cytometry. Methods have been developed for the preparation of suspension of viable rat pancreatic islet cells and their analysis and sorting in the fluorescence activated cell sorter (FACC IV, Becton Dickinson, Sunnyvale, Ca). Flow cytometry of these cells indicated that there were 91% of beta cells in cell suspension. Most of the exocrine particles were lost during digestion. Purified endocrine islet cell grafts were prepared by pure beta-cells, without endocrine non-beta cells. The purified aggregates were devoid of endocrine non-beta cells and damaged cells.

Assessing the quality of sardine based on biogenic amines using a fuzzy logic model.

There is an increasing concern about the quality and quality assessment procedures of seafood. In the present study, a model to assess fish quality based on biogenic amine contents using fuzzy logic model (FLM) is proposed. The fish used was sardine (Sardinella sp.) where the production of eight biogenic amines was monitored over fifteen days of storage at 0, 3 and 10°C. Based on the results, histamine, putrescine and cadaverine were selected as input variables and twelve quality grades were considered for quality of fish as output variables for the FLM. Input data were processed by rules established in the model and were then defuzzified according to defined output variables. Finally, the quality of fish was evaluated using the designed model and Pearson correlation between storage times with quality of fish showed r=0.97, 0.95 and 1 for fish stored at 0, 3 and 10°C, respectively.

CrIII as an alternative to RuII in metallo-supramolecular chemistry.

Compared to divalent ruthenium coordination complexes, which are widely exploited as parts of multi-component photonic devices, optically active trivalent chromium complexes are under-represented in multi-metallic supramolecular architectures performing energy conversion mainly because of the tricky preparation of stable heteroleptic CrIII building blocks. We herein propose some improvements with the synthesis of a novel family of kinetically inert heteroleptic bis-terdentate mononuclear complexes, which can be incorporated into dinuclear rod-like dyads as a proof-of-concept. The mechanism and magnitude of intermetallic CrCr communication have been unraveled by a combination of magnetic, photophysical and thermodynamic investigations. Alternated aromatic/alkyne connectors provided by Sonogashira coupling reactions emerge as the most efficient wires for long-distance communication between two chromium centres bridged by Janus-type back-to-back bis-terdentate receptors.

Determination of trans- and cis-urocanic acid in relation to histamine, putrescine, and cadaverine contents in tuna (Auxis Thazard) at different storage temperatures.

Scombroid fish poisoning is usually associated with consumption of fish containing high levels of histamine. However, reports indicate that some cases have responded to antihistamine therapy while ingested histamine levels in these cases were low. Potentiation of histamine toxicity by some biogenic amines, and release of endogenous histamine by other compounds such as cis-urocanic acid (UCA) are some hypotheses that have been put forth to explain this anomaly. Very little is known about the effects of storage conditions on the production of both UCA isomers and biogenic amines in tuna. Thus, the production of trans- and cis-UCA, histamine, putrescine, and cadaverine in tuna during 15 d of storage at 0, 3, and 10 °C and 2 d storage at ambient temperature were monitored. The initial trans- and cis-UCA contents in fresh tuna were 2.90 and 1.47 mg/kg, respectively, whereas the levels of putrescine and cadaverine were less than 2 mg/kg, and histamine was not detected. The highest levels of trans- and cis-UCA were obtained during 15 d storage at 3 °C (23.74 and 21.79 mg/kg, respectively) while the highest concentrations of histamine (2796 mg/kg), putrescine (220.32 mg/kg) and cadaverine (1045.20 mg/kg) were obtained during storage at room temperature, 10 and 10 °C, respectively. Histamine content increased considerably during storage at 10 °C whereas trans- and cis-UCA contents changed slightly. The initial trans-UCA content decreased during storage at ambient temperature. Thus, unlike histamine, concentrations of trans- and cis-UCA did not result in elevated levels during storage of tuna.

Smaller than a nanoparticle with the design of discrete polynuclear molecular complexes displaying near-infrared to visible upconversion.

This work shows that the operation of near-infrared to visible light-upconversion in a discrete molecule is not limited to non-linear optical processes, but may result from superexcitation processes using linear optics. The design of nine-coordinate metallic sites made up of neutral N-heterocyclic donor atoms in kinetically inert dinuclear [GaEr(L1)(3)](6+) and trinuclear [GaErGa(L2)(3)](9+) helicates leads to [ErN(9)] chromophores displaying unprecedented dual visible nanosecond Er((4)S(3/2)→(4)I15/2) and near-infrared microsecond Er((4)I(13/2)→(4)I1(5/2)) emissive components. Attempts to induce one ion excited-state absorption (ESA) upconversion upon near-infrared excitation of these complexes failed because of the too-faint Er-centred absorption cross sections. The replacement of the trivalent gallium cation with a photophysically-tailored pseudo-octahedral [CrN(6)] chromophore working as a sensitizer for trivalent erbium in [CrEr(L1)(3)](6+) improves the near-infrared excitation efficiency, leading to the observation of a weak energy transfer upconversion (ETU). The connection of a second sensitizer in [CrErCr(L2)(3)](9+) generates a novel mechanism for upconversion, in which the superexcitation process is based on the Cr(III)-sensitizers. Two successive Cr→Er energy transfer processes (concerted-ETU) compete with a standard Er-centred ETU, and a gain in upconverted luminescence by a factor larger than statistical values is predicted and observed.

Changes in urocanic acid, histamine, putrescine and cadaverine levels in Indian mackerel (Rastrelliger kanagurta) during storage at different temperatures.

Histamine, putrescine cadaverine and cis-urocanic acid (UCA) have all been implicated or suggested in scombroid fish poisoning. However, there is little information on UCA especially during storage. Changes in their contents during storage of whole Indian mackerel at 0, 3±1, 10±1 for up to 15 days and 23±2°C for up to 2 days were monitored. Fresh muscles contained 14.83 mg/kg trans-UCA, 2.23 mg/kg cis-UCA and 1.86 mg/kg cadaverine. Histamine and putrescine were not detected. After 15 days at 0 and 3°C, trans-UCA content increased to 52.83 and 189.51 mg/kg, respectively, and decreased to <2 mg/kg at the other two temperatures. Storage at 10°C also resulted in an increase in trans-UCA after 3 days, only to decrease after 6 days. The concentration of cis-UCA increased nearly 13-fold after 15 days at 0 and 3°C, decreased at 10°C and remained unchanged at 23°C. Histamine, putrescine and cadaverine levels increased significantly (P value<0.05) at all temperatures especially at 23°C.

A rapid biosynthesis route for the preparation of gold nanoparticles by aqueous extract of cypress leaves at room temperature.

In the present study, green synthesis of gold nanoparticles was reported using the aqueous extract of cypress leaves. The reduction of gold salt with the extract of cypress leaves resulted in the formation of gold nanoparticles. Effects of extract concentration and extract pH were investigated on the size of the nanoparticles. It was found that the average particle size of synthesized gold nanoparticles depends strongly on extract concentration and extract pH. FT-IR spectroscopy showed that bioorganic capping molecules were bound to the surface of particles. X-ray techniques confirmed the formation of gold nanoparticles and their crystalline structure. The inductively coupled plasma atomic emission spectroscopy analysis displayed that the reaction progress is higher than 90% at room temperature. Gold nanoparticles were mostly spherical in shape along with some irregular shapes. Cypress is an evergreen plant and its leaves are easily available in all four seasons. Also, the rate of the reaction was high and it was completed in only 10min. For these reasons, this method is cost-effective and environmentally friendly. Thus, it can be used in the synthesis of gold nanoparticles instead of chemical methods and other biosynthesis approaches.

Development and validation of an ion-pair chromatographic method for simultaneous determination of trans- and cis-urocanic acid in fish samples.

Urocanic acid (UCA) has been reported to be a mast cell degranulator and has also been suggested as a complementary agent in implicated scombroid fish poisoning. In this research, a new method is described to extract, clean up and perform simultaneous ion-pair chromatographic analysis of trans- and cis-urocanic acid (UCA) in fish samples. UCA was extracted using 0.05 M HCl and protein was removed from the extract by precipitation with 10% trisodium citrate and 10% citric acid. The HPLC method that is developed showed a rapid, precise and sensitive method with short retention time for simultaneous separation of UCA isomers in fish samples. Estimation of trans- and cis-UCA in the muscle of Indian mackerel, tuna and sardine showed that, as expected, no cis-UCA existed in fish muscles and the highest concentration of trans-UCA was found in Indian mackerel with 118.8 mg kg(-1) while the highest concentrations of trans-UCA in tuna and sardine were 12.1 and 17.5 mg kg(-1), respectively.

Rapid green synthesis of gold nanoparticles using Rosa hybrida petal extract at room temperature.

This study reports a green method for the synthesis of gold nanoparticles using the aqueous extract of rose petals. The effects of gold salt concentration, extract concentration and extract quantity were investigated on nanoparticles synthesis. Gold nanoparticles were characterized with different techniques such as UV-vis spectroscopy, FT-IR spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, dynamic light scattering and transmission electron microscopy. Transmission electron microscopy experiments showed that these nanoparticles are formed with various shapes. FT-IR spectroscopy revealed that gold nanoparticles were functionalized with biomolecules that have primary amine group (-NH2), carbonyl group, -OH groups and other stabilizing functional groups. X-ray diffraction pattern showed high purity and face centered cubic structure of gold nanoparticles. Dynamic light scattering technique was used for particle size measurement, and it was found to be about 10nm. The rate of the reaction was high and it was completed within 5 min.