Green chemiluminescence from a bis-cyclometalated iridium(III) complex with an ancillary bathophenanthroline disulfonate ligand

The reaction of a fluorinated iridium complex with cerium(IV) and organic reducing agents generates an intense emission with a significant hypsochromic shift compared to contemporary chemically-initiated luminescence from metal complexes

On the characterization of NaDEHP/n-heptane nonaqueous reverse micelles: The effect of the polar solvent

The behavior of two polar solvents, ethylene glycol (EG) and dimethylformamide (DMF), entrapped in sodium bis-(2-ethylhexyl) phosphate (NaDEHP)/n-heptane reverse micelles (RMs) was investigated using dynamic light scattering (DLS), molecular probe absorption and FT-IR spectroscopy. DLS results reveal the formation of RMs containing EG and DMF as a polar component. To the best of our knowledge this is the first report where both polar solvents are entrapped by the NaDEHP surfactant to effectively create RMs. We use the solvatochromism behavior of the molecular probe, 1-methyl-8-oxyquinolinum betaine (QB), and FT-IR spectroscopy to investigate the physicochemical properties of the non-aqueous RMs. Our results demonstrate that the NaDEHP surfactant interacts through hydrogen bonds with EG at the EG/NaDEHP interface and this interaction is responsible for destroying the bulk structure of pure solvent EG when entrapped in NaDEHP RMs. On the other hand, when DMF is incorporated inside the RMs the bulk structure of DMF is destroyed upon encapsulation by the Na-DMF interaction at the DMF/NaDEHP interface. Our results are completely different than the one observed for DMF/n-heptane/AOT. Our results show how the physicochemical properties, such as micropolarity, microviscosity and hydrogen bond interaction, of nonaqueous NaDEHP/n-heptane RMs interfaces can be dramatically changed by simply using different non-aqueous polar solvents. Thus, these results can be very useful to employ these novel RMs as nanoreactors since the dimensions of the RMs are around 10 to 20 nm.Fil: Quintana Lazópulos, Silvina Soledad. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Falcone, Ruben Dario. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Chessa, Juana Josefa. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Moyano, Fernando. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Correa, Nestor Mariano. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Effect of buffer on heparin binding and sensing in competitive aqueous media

Although buffer-specific effects on molecular recognition are known in biological science, they remain rare in supramolecular chemistry. The binding between a cationic dye, Mallard Blue (MalB), and polyanionic heparin in aqueous NaCl (150 mM) is studied in three commonly-used buffers (Tris-HCl, HEPES, Phosphate, each 10 mM). Although MalB has a very similar UV-Vis spectrum in each buffer, the sensory response towards heparin was different in each case. This can be ascribed to differences in the complex formed. In Tris-HCl which has the least competitive chloride counter-anions, MalB exhibits a hypsochromic shift of 25 nm, assigned to strong binding and aggregation of the dye on heparin. In more competitive HEPES, containing a sulfonate anion, there is weaker binding and less aggregation of MalB along the heparin; the hypsochromic shift is only 15 nm. In phosphate buffer, MalB can interact quite strongly with buffer phosphate anions; although heparin binding is still observed, the hypsochromic shift associated with dye aggregation is only 5 nm. As such, specific buffer interactions with the MalB-heparin complex mediate host-guest binding and sensing. Buffer choice must be made carefully in studies of molecular recognition – we would caution against using phosphate and sulfonate containing buffers when studying electrostatic binding

Synthesis of Hydrophobically and Electrostatically Modified Polyacrylamides and Their Catalytic Effects on the Unimolecular Decarboxylation of 6-Nitrobenzisoxazole-3-carboxylate Anion

A series of hydrophobically and electrostatically modified polyacrylamides (Copol(AM-C12)) has been synthesized by radical-initiated copolymerization of acrylamide with n-dodecylmethyldiallylammonium bromide as the hydrophobe in aqueous solution using ammonium persulfate as the initiator. The formation of hydrophobic microdomains of the copolymers was revealed by large hypsochromic shifts of the longwavelength absorption band of the solvatochromic probe Methyl Orange, noncovalently bound to the macromolecule. It was found that the microdomains formed by these copolymers in aqueous solution are more hydrophobic than those of the cationic polysoaps poly(alkylmethyldiallylammonium halides) containing the same n-dodecyl groups as the side chains as a result of the reduced electrostatic repulsions at the periphery of the microdomains. The reduced cationic character of the copolymers Copol(AM-C12) most likely also accounts for the observation that the anionic dye Methyl Orange does not induce microdomain formation in aqueous solution. The effect of the hydrophobically and electrostatically modified polyacrylamides on the unimolecular decarboxylation of 6-nitrobenzisoxazole-3-carboxylate anion (6-NBIC) has been investigated in aqueous solutions at pH 11.3 and 30 °C. It is suggested that the relatively modest catalytic effects induced by Copol(AM-C12) should be ascribed to hydrogen-bond stabilization of the initial state by NH groups in the macromolecules. The decarboxylation rates of 6-NBIC at binding sites in hydrophobic microdomains increase with increasing n-dodecyl group content in the copolymers.

Spectroscopic and redox properties of amine-unctionalized K_2[Os-^(II)(bpy)(CN)_4] complexes

We report the first examples of amine-functionalized K_2[Os^(II)(bpy)(CN)_4] (bpy = 2,2'-bipyridine) complexes. The tetracyanoosmate complexes were prepared by UV irradiation (λ = 254 nm) of K_4[Os^(II)(CN)_6] and primary amine-functionalized bpy ligands in acidic aqueous media. The aqueous solution pH dependences of the spectroscopic and redox properties of 4,4'- and 5,5'-substituted complexes have been investigated. The pendant amine functional groups and coordinated cyanide ligands are basic sites that can be sequentially protonated, thereby allowing systematic tuning of electrochemical and optical spectroscopic properties

A study of cell membranes in nasal epithelial cells from patients with chronic rhinosinusitis with nasal polyps by means of a fluorescent probe

Aim. To assess the state of membranes in nasal epithelial cells obtained from the patients with chronic rhinosinusitis with nasal polyps (CRSwNP) with the help of the fluorescent probe 2-(2ʹ-ОН-phenyl)-5-phenyl-1,3-oxazole. Methods. The state of membrane phospholipid bilayer in suspensions of nasal epithelial cells isolated from ten patients with CRSwNP was evaluated using the fluorescent probe 2-(2ʹ-ОН-phenyl)-5-phenyl-1,3-oxazole that reacts on the physico-chemical properties of its microenvironment. Changes in fluorescence spectra were determined using a Thermo Scientific Lumina fluorescence spectrometer (Thermo Fisher Scientific) 1 hour after the addition of the probe to nasal epithelial cell suspensions. Results. CRSwNP was found to be associated with a higher rate of nasal epithelial cell membrane hydration in the region of phospholipid glycerol moiety, carbonyl groups and aliphatic chains of fatty acids attached to the carbonyl groups. Conclusion. Our findings suggest that CRSwNP is accompanied by the elevated hydration rate of the most polar region, namely polar heads of phospholipids of nasal epithelial cell membranes

Crystallographic Distinction between “Contact” and “Separated” Ion Pairs: Structural Effects on Electronic/ESR Spectra of Alkali-Metal Nitrobenzenides

The classic nitrobenzene anion-radical (NB-• or nitrobenzenide) is isolated for the first time as pure crystalline alkali-metal salts. The deliberate use of the supporting ligands 18-crown-6 and [2.2.2]cryptand allows the selective formation of contact ion pairs designated as (crown)M+NB-•, where M+ = K+, Rb+, and Cs+, as well as the separated ion pair K(cryptand)+NB-•both series of which are structurally characterized by precise low-temperature X-ray crystallography, ESR analysis, and UV−vis spectroscopy. The unusually delocalized structure of NB-• in the separated ion pair follows from the drastically shortened N−C bond and marked quinonoidal distortion of the benzenoid ring to signify complete (95%) electronic conjugation with the nitro substituent. On the other hand, the formation of contact ion pairs results in the substantial decrease of electronic conjugation in inverse order with cation size (K+ \u3e Rb+) owing to increased localization of negative charge from partial (NO2) bonding to the alkali-metal cation. Such a loss in electronic conjugation (or reverse charge transfer) may be counterintuitive, but it is in agreement with the distribution of odd-electron spin electron density from the ESR data and with the hypsochromic shift of the characteristic absorption band in the electronic spectra. Most importantly, this crystallographic study underscores the importance of ion-pair structure on the intrinsic property (and thus reactivity) of the component ions - as focused here on the nitrobenzenide anion

Identification of an Active Site-bound Nitrile Hydratase Intermediate through Single Turnover Stopped-flow Spectroscopy

Stopped-flow kinetic data were obtained for the iron-type nitrile hydratase from Rhodococcus equi TG328-2 (ReNHase) using methacrylonitrile as the substrate. Multiple turnover experiments suggest a three-step kinetic model that allows for the reversible binding of substrate, the presence of an intermediate, and the formation of product. Microscopic rate constants determined from these data are in good agreement with steady state data confirming that the stopped-flow method used was appropriate for the reaction. Single turnover stopped-flow experiments were used to identify catalytic intermediates. These data were globally fit confirming a three-step kinetic model. Independent absorption spectra acquired between 0.005 and 0.5 s of the reaction reveal a significant increase in absorbance at 375, 460, and 550 nm along with the hypsochromic shift of an Fe3+←S ligand-to-metal charge transfer band from 700 to 650 nm. The observed UV-visible absorption bands for the Fe3+-nitrile intermediate species are similar to low spin Fe3+-enzyme and model complexes bound by NO or N3−. These data provide spectroscopic evidence for the direct coordination of the nitrile substrate to the nitrile hydratase active site low spin Fe3+ center

Photochromic spiropyran monolithic polymers: Molecular photo-controllable electroosmotic pumps for micro-fluidic devices

A novel photo-controllable micro-fluidic electroosmotic pump based on spiropyran monolithic polymers is presented here for the first time. Photochromic monolithic scaffolds have been synthesised within poly(tetrafluoroethylene) coated fused silica capillaries. These monoliths have a photochromic spiropyran monomer incorporated in the bulk by thermally induced copolymerisation with a cross-linking agent (divinylbenzene) and were encased in micro-fluidic devices to function as photo-controllable electroosmotic pumps (EOPs). Due to the presence of the spiropyran the monolith can exist in two forms: a zwitterionic merocyanine (MC) form and an uncharged spiropyran (SP). As both forms bare a net overall zero charge, an acidic electrolyte was used to produce a stable anodic electroosmotic flow (EOF), while still retaining the ability to switch between the SP and the MC forms, which exhibit different charge distributions. It was confirmed that visible light, which produces the SP form, caused an increase in EOF while UV light, which generates the MC form, caused a decrease in EOF. In this way the EOF from the chip was modified by light and not by changing the electric field, temperature or buffer pH, some of the more common methods of altering the EOF