The Coiling Effect in Ether Ionic Liquids: Exploiting Acetate as a Probe for Transport Properties and Microenvironment Analysis

The inherently high viscosity of ionic liquids (ILs) can limit their potential applications. One approach to address this drawback is to modify the cation side chain with ether groups. Herein, we assessed the structure-property relationship by focusing on acetate (OAc), a strongly coordinating anion, with 1,3-dialkylimidazolium cations with different side chains, including alkyl, ether, and hydroxyl functionalized, as well as their combinations. We evaluated their viscosity, thermal stabilities, and microstructure using Raman and infrared (IR) spectroscopies, allied to density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. The viscosity data showed that the ether insertion significantly enhances the fluidity of the ILs, consistent with the coiling effect of the cation chain. Through a combined experimental and theoretical approach, we analyzed how the OAc anion interacts with ether ILs, revealing a characteristic bidentate coordination, particularly in hydroxyl functionalized ILs due to specific hydrogen bonding with the OH group. IR spectroscopy showed subtle shifts in the acidic hydrogens of imidazolium ring C(2)-H and C(4,5)-H, suggesting weaker interactions between OAc and the imidazolium ring in ether-functionalized ILs. Additionally, spatial distribution functions (SDF) and dihedral angle distribution obtained via AIMD confirmed the intramolecular hydrogen bonding due to the coiling effect of the ether side chain.

Biofragmentation of Polystyrene Microplastics: A Silent Process Performed by Chironomus sancticaroli Larvae

Polystyrene (PS) is one of the main synthetic polymers produced around the world, and it is present in the composition of a wide variety of single-use objects. When released into the environment, these materials are degraded by environmental factors, resulting in microplastics. We investigated the ability of Chironomus sancticaroli (Diptera, Chironomidae) to promote the fragmentation of PS microspheres (24.5 ± 2.9 μm) and the toxic effects associated with exposure to this polymer. C. sancticaroli larvae were exposed to 3 different concentrations of PS (67.5, 135, and 270 particles g-1 of dry sediment) for 144 h. Significant lethality was observed only at the highest concentration. A significant reduction in PS particle size as well as evidence of deterioration on the surface of the spheres, such as grooves and cracks, was observed. In addition, changes in oxidative stress biomarkers (SOD, CAT, MDA, and GST) were also observed. This is the first study to report the ability of Chironomus sp. to promote the biofragmentation of microplastics. The information obtained demonstrates that the macroinvertebrate community can play a key role in the degradation of plastic particles present in the sediment of freshwater environments and can also be threatened by such particle pollution.

Multiconfigurational Calculations and Experimental Resonant Raman/SERRS of a Donor-Acceptor Thiadiazole Dye

The resonant Raman (RR) and resonant SERS spectra of the thiadiazole-based dye dibromobenzo[c]-1,2,5-thiadiazole (DBTD) were studied through multiconfigurational XMS-CASPT2/CASSCF and experimental methods in solution. The results indicate that the S1 excited state of DBTD is described by π → π* with internal CT from the benzene ring to the thiadizole. In resonance conditions at 364 nm, the RR spectrum shows intensifications in modes that describe extensive geometrical changes at both the benzene ring and the thiadiazole region, indicating an internal CT character to the S1. The SERS spectra observed on gold and silver nanoparticles indicate different adsorption geometries, which leads to distinct enhancement patterns on the spectra with varying excitation energy. It evidences the major contribution of the chemical enhancement mechanism on the spectra from a metal → DBTD CT state, as confirmed by the simulated spectra. This theoretical approach proved strong in the prediction of the main features of the observed experimental resonant Raman and SERS spectra indicating a potential for adequate description of the chemical mechanism of SERS.

SERS and resonance Raman of 5-nitroisatin on silver - The distinction between the coordination and surface complexes

Although Surface Enhanced Raman Spectroscopy (SERS) is a widespread technique with applications in several fields, the SERS effect is still not thoroughly understood due to the challenge in describing how the interaction between the analyte and the metallic surface contributes to the Raman signal enhancement. One approach to distinguish the charge transfer contribution from the metal to the molecule is the comparison of the coordination complex resonance Raman spectral features with the SERS spectra of the surface complex excited at different wavelengths. Herein, we investigated the molecule 5-nitroisatin, Nisa, its complex with a silver cation, Ag(Nisa), its anionic form, Nisa^-, and the adsorbed species over Ag colloid, Nisa/AgNP, by resonance Raman and SERS, respectively. The data show that the resonance Raman spectrum of the coordination complex Ag(Nisa) is comparable to the SERS spectrum obtained out of resonance condition. However, when the SERS spectra of Nisa/AgNP at resonance condition is obtained, quite distinct chromophores are observed. The SERS enhancement profile suggests a charge transfer from the metal to molecule in the green region of the visible spectrum and evidences the higher complexity of the electronic transitions that take place within the surface complex. To support the experimental data, DFT and TDDFT calculations were performed for Nisa, Ag(Nisa), Nisa^- and Nisa@Ag20 cluster.

Tuning the Mechanical and Thermal Properties of Hydroxypropyl Methylcellulose Cryogels with the Aid of Surfactants

The mechanical and thermal properties of cryogels depend on their microstructure. In this study, the microstructure of hydroxypropyl methylcellulose (HPMC) cryogels was modified by the addition of ionic (bis (2-ethylhexyl) sodium sulfosuccinate, AOT) and non-ionic (Kolliphor^® EL) surfactants to the precursor hydrogels (30 g/L). The surfactant concentrations varied from 0.2 mmol/L to 3.0 mmol/L. All of the hydrogels presented viscous behavior (G″ > G′). Hydrogels containing AOT (c > 2.0 mmol/L) led to cryogels with the lowest compressive modulus (13 ± 1 kPa), the highest specific surface area (2.31 m²/g), the lowest thermal conductivity (0.030 W/(m·°C)), and less hygroscopic walls. The addition of Kolliphor^® EL to the hydrogels yielded the stiffest cryogels (320 ± 32 kPa) with the lowest specific surface area (1.11 m²/g) and the highest thermal conductivity (0.055 W/(m·°C)). Density functional theory (DFT) calculations indicated an interaction energy of −31.8 kcal/mol due to the interaction between the AOT sulfonate group and the HPMC hydroxyl group and the hydrogen bond between the AOT carbonyl group and the HPMC hydroxyl group. The interaction energy between the HPMC hydroxyl group and the Kolliphor^® EL hydroxyl group was calculated as −7.91 kcal/mol. A model was proposed to describe the effects of AOT or Kolliphor^® EL on the microstructures and the mechanical/thermal properties of HPMC cryogels.

Fast, low-cost preparation of hackmanite minerals with reversible photochromic behavior using a microwave-assisted structure-conversion method

A microwave-assisted structure-conversion (MASC) method was used to obtain photochromic hackmanites (M,Na)8Al6Si6O24(Cl,S)2 (M: Li, Na, and K) in a fast (12 to 20 min) one-step process. Structural conversion from Zeolite A to hackmanite minerals has been proven to be very effective through an aluminosilicate crystalline intermediate. Photochromism is observed with both UV and X-ray (CuKα) excitation.

Marrying SPR excitation and metal-support interactions: unravelling the contribution of active surface species in plasmonic catalysis

Plasmonic catalysis takes advantage of the surface plasmon resonance (SPR) excitation to drive or accelerate chemical transformations. In addition to the plasmonic component, the control over metal-support interactions in these catalysts is expected to strongly influence the performances. For example, CeO2 has been widely employed towards oxidation reactions due to its oxygen mobility and storage properties, which allow for the formation of Ce3+ sites and adsorbed oxygen species from metal-support interactions. It is anticipated that these species may be activated by the SPR excitation and contribute to the catalytic activity of the material. Thus, a clear understanding of the role played by the SPR-mediated activation of surface oxide species at the metal-support interface is needed in order to take advantage of this phenomenon. Herein, we describe and quantify the contribution from active surface oxide species at the metal-support interface (relative to O2 from air) to the activities in green SPR-mediated oxidation reactions. We employed CeO2 decorated with Au NPs (Au/CeO2) as a model plasmonic catalyst and the oxidation of p-aminothiophenol (PATP) and aniline as proof-of-concept transformations. We compared the results with SiO2 decorated with Au NPs (Au/SiO2), in which the formation of surface oxide species at the metal-support interface is not expected. We found that the SPR-mediated activation of surface oxide species at the metal-support interface in Au/CeO2 played a pivotal role in the detected activities, being even higher than the contribution coming from the activation of O2 from air.

Dead biomass of Amazon yeast: A new insight into bioremediation and recovery of silver by intracellular synthesis of nanoparticles

This investigation was undertaken to describe a natural process for the removal of silver and the simultaneous recovery of Ag/Ag₂O nanoparticles by dead biomass of the yeast Rhodotorula mucilaginosa. The removal of silver ions from aqueous solution and the synthesis of Ag/Ag₂O nanoparticles were analyzed based on physicochemical factors and equilibrium concentration, combined with transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (FTIR). A successful process for the synthesis of Ag/Ag₂O nanoparticles was obtained, following the Langmuir isotherm model, showing a high biosorption capacity of silver (49.0 mg g^-1). The nanoparticles were spherical, had an average size of 11.0 nm, were synthesized intracellularly and capped by yeast proteins. This sustainable protocol is an attractive platform for the industrial-scale production of silver nanoparticles and of a silver nanobiosorbent.

The thermochromic behavior of aromatic amine-SO2 charge transfer complexes

The distinct thermochromism observed in solutions containing N,N-dimethylaniline (DMA) and N,N-diethylaniline (DEA) and SO₂ was investigated by resonance Raman spectroscopy in a wide range of temperatures. The results indicate in addition to the charge transfer (CT) complexes DMA-SO₂ and DEA-SO₂, the presence of collision complexes involving the CT complexes and excess DMA and DEA molecules. The latter in fact is the chromophore responsible for the long wavelength absorption originating the color. The Raman signature of the collision complex was attributed to the distinct enhancement of a band at 1140cm^-1 assigned to ν_s(SO₂), in contrast to the same mode in the 1:1 complex at 1115cm^-1. The intensity of such band, assigned to the collision complex is favored at high temperatures and depends on the steric hindrance associated to amines, as well as the SO₂ molar fraction. Quantum chemical calculations based on time-dependent density functional theory (TDDFT) support the proposed interpretation.

Probing the solvation structure and dynamics in ionic liquids by time-resolved infrared spectroscopy of 4-(dimethylamino)benzonitrile

In this work we demonstrate the use of the push–pull model system 4-(dimethylamino)benzonitrile (DMABN) as a convenient molecular probe to investigate the local solvation structure and dynamics by means of time-resolved infrared spectroscopy (TRIR).

Molecular dynamics and a spectroscopic study of sulfur dioxide absorption by an ionic liquid and its mixtures with PEO

An investigation comprising experimental techniques (absorption capacity of SO₂ and vibrational spectroscopy) and molecular simulations (thermodynamics, structure, and dynamics) has been performed for the polymer poly(ethylene oxide) (PEO), the ionic liquid butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N₄₁₁₁][Tf₂N]) and their mixtures as sulfur dioxide (SO₂) absorbing materials. The polymer PEO has higher capacity to absorb SO₂ than the neat ionic liquid, whereas the mixtures presented intermediary absorption capacities. The band assigned to the symmetric stretching band of SO₂ at ca. 1140 cm^-1, which is considered a spectroscopic probe for the strength of SO₂ interactions with its neighborhood, shifts to lower wavenumbers as more negative total interaction energy values of SO₂ were evaluated from the simulations. The solvation free energy of SO₂, ΔG_sol, correlates linearly with the absorption capacity of SO₂. The negative values of ΔG_sol are due to negative and positive values of enthalpy and entropy, respectively. In the ionic liquid, SO₂ weakens the cation-anion interactions, whereas in the mixture with a high content of PEO these interactions are slightly increased. Such effects were correlated with the relative population of cisoid and transoid conformers of Tf₂N anions as revealed by Raman spectroscopy. Moreover, the presence of SO₂ in the systems provokes the increase of diffusion coefficients of the absorbing species in comparison with the systems without the gas. Proper to the slow dynamics of the polymer, the diffusion coefficient of ions and SO₂ diminishes with the increase of the PEO content.

Plasmonic Nanorattles as Next-Generation Catalysts for Surface Plasmon Resonance-Mediated Oxidations Promoted by Activated Oxygen

Nanorattles, comprised of a nanosphere inside a nanoshell, were employed as the next generation of plasmonic catalysts for oxidations promoted by activated O2 . After investigating how the presence of a nanosphere inside a nanoshell affected the electric-field enhancements in the nanorattle relative to a nanoshell and a nanosphere, the SPR-mediated oxidation of p-aminothiophenol (PATP) functionalized at their surface was investigated to benchmark how these different electric-field intensities affected the performances of Au@AgAu nanorattles, AgAu nanoshells and Au nanoparticles having similar sizes. The high performance of the nanorattles enabled the visible-light driven synthesis of azobenzene from aniline under ambient conditions. As the nanorattles allow the formation of electromagnetic hot spots without relying on the uncontrolled aggregation of nanostructures, it enables their application as catalysts in liquid phase under mild conditions using visible light as the main energy input.

The Fault in Their Shapes: Investigating the Surface-Plasmon-Resonance-Mediated Catalytic Activities of Silver Quasi-Spheres, Cubes, Triangular Prisms, and Wires

The surface-plasmon-resonance (SPR)-mediated catalytic activities of Ag and Au nanoparticles have emerged a relatively new frontier in catalysis in which visible light can be employed as an eco-friendly energy input to drive chemical reactions. Although this phenomenon has been reported for a variety of transformations, the effect of the nanoparticle shape and crystalline structure on the activities remains unclear. In this paper, we investigated the SPR-mediated catalytic activity of Ag quasi-spheres, cubes, triangular prisms, and wires toward the oxidation of p-aminothiophenol to p,p'-dimercaptoazobenzene by activated O2. The activities at 632.8 nm excitation followed the order triangular prisms and quasi-spheres > wires ≫ cubes. These results indicated that the shape, optical properties, and crystal structure played an important role in the detected SPR-mediated activities.

Unraveling the nature of Turkevich gold nanoparticles: the unexpected role of the dicarboxyketone species

In this paper we show how surface coordination chemistry can elucidate one of the reproducibility issues related to the classical synthesis of gold nanoparticles by the Turkevich method.

Bioremediation from wastewater and extracellular synthesis of copper nanoparticles by the fungus Trichoderma koningiopsis

This is the first study describing the rapid extracellular production of copper nanoparticles by dead biomass of Trichoderma koningiopsis. The production and uptake of copper nanoparticles by dead biomass of Trichoderma koningiopsis were characterized by investigating physicochemical factors, equilibrium concentrations and biosorption kinetics, combined with scanning electron microscopy (SEM), energy dispersive X-ray (EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). A successful route for the metallic copper nanoparticles synthesis was achieved, and followed a Langmuir isotherm where a high biosorption capacity was observed, 21.1 mg g(-1). The kinetic analysis showed that copper biosorption followed a pseudo-second-order model. The nanoparticles mainly exhibited a spherical shape, with an average size of 87.5 nm, and were synthesized extracellularly. The presence of proteins as stabilizing agents of the nanoparticles was demonstrated. The extracellular biosynthesis and uptake of copper nanoparticles using dead fungal biomass is a low-cost green processes, and bioremediation of impacted local.

Intracellular biosynthesis and removal of copper nanoparticles by dead biomass of yeast isolated from the wastewater of a mine in the Brazilian Amazonia

In this study was developed a natural process using a biological system for the biosynthesis of nanoparticles (NPs) and possible removal of copper from wastewater by dead biomass of the yeast Rhodotorula mucilaginosa. Dead and live biomass of Rhodotorula mucilaginosa was used to analyze the equilibrium and kinetics of copper biosorption by the yeast in function of the initial metal concentration, contact time, pH, temperature, agitation and inoculum volume. Dead biomass exhibited the highest biosorption capacity of copper, 26.2 mg g(-1), which was achieved within 60 min of contact, at pH 5.0, temperature of 30°C, and agitation speed of 150 rpm. The equilibrium data were best described by the Langmuir isotherm and Kinetic analysis indicated a pseudo-second-order model. The average size, morphology and location of NPs biosynthesized by the yeast were determined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The shape of the intracellularly synthesized NPs was mainly spherical, with an average size of 10.5 nm. The X-ray photoelectron spectroscopy (XPS) analysis of the copper NPs confirmed the formation of metallic copper. The dead biomass of Rhodotorula mucilaginosa may be considered an efficiently bioprocess, being fast and low-cost to production of copper nanoparticles and also a probably nano-adsorbent of this metal ion in wastewater in bioremediation process.

Biosynthesis and uptake of copper nanoparticles by dead biomass of Hypocrea lixii isolated from the metal mine in the Brazilian Amazon Region

A biological system for the biosynthesis of nanoparticles (NPs) and uptake of copper from wastewater, using dead biomass of Hypocrea lixii was analyzed and described for the first time. The equilibrium and kinetics investigation of the biosorption of copper onto dead, dried and live biomass of fungus were performed as a function of initial metal concentration, pH, temperature, agitation and inoculum volume. The high biosorption capacity was observed for dead biomass, completed within 60 min of contact, at pH 5.0, temperature of 40°C and agitation speed of 150 rpm with a maximum copper biosorption of 19.0 mg g⁻¹. The equilibrium data were better described using the Langmuir isotherm and kinetic analysis indicated that copper biosorption follows a pseudo-second-order model. The average size, morphology and location of NPs biosynthesized by the fungus were determined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). NPs were mainly spherical, with an average size of 24.5 nm, and were synthesized extracellularly. The X-ray diffraction (XRD) analysis confirms the presence of metallic copper particles. Infrared spectroscopy (FTIR) study revealed that the amide groups interact with the particles, which was accountable for the stability of NPs. This method further confirmed the presence of proteins as stabilizing and capping agents surrounding the copper NPs. These studies demonstrate that dead biomass of Hypocrea lixii provides an economic and technically feasible option for bioremediation of wastewater and is a potential candidate for industrial-scale production of copper NPs.

L-diphenylalanine microtubes as a potential drug-delivery system: characterization, release kinetics, and cytotoxicity

Microtubes obtained from the self-assembly of L-diphenylalanine (FF-MTs) were evaluated as potential vehicles for drug delivery. The biological marker Rhodamine B (RhB) was chosen as a model drug and conjugated to the peptide arrays during self-organization in the liquid phase. Microscopy and X-ray studies were performed to provide morphological and structural information. The data revealed that the cargo was distributed either in small aggregates at the hydrophobic surface of the FF-MTs or homogeneously embedded in the structure, presumably anchored at polar sites in the matrix. Raman spectroscopy revealed notable shifts of the characteristic RhB resonance peaks, demonstrating the successful conjugation of the fluorophore and peptide assemblies. In vitro assays were conducted in erythrocytes and fibroblast cells. Interestingly, FF-MTs were found to modulate the release of the load. The release of RhB from the FF-MTs followed first-order kinetics with a steady-state profile, demonstrating the potential of these carriers to deliver drugs at constant rates in the body. Cytotoxicity investigations revealed high cell viability up to concentrations of 5 mg mL(-1), demonstrating the low toxicity of the FF-MTs.

A facile approach to TiO2 colloidal spheres decorated with Au nanoparticles displaying well-defined sizes and uniform dispersion

This paper describes a straightforward approach for the synthesis of hybrid materials composed of titanium dioxide (TiO(2)) colloidal spheres decorated with gold nanoparticles (Au NPs). In the reported method, monodisperse TiO(2) colloidal spheres (∼220 nm in diameter) could be directly employed as templates for the nucleation and growth of Au NPs over their surface using AuCl(4)(-)(aq) as the Au precursor, ascorbic acid as the reducing agent, PVP as the stabilizer, and water as the solvent. The Au NPs presented a uniform distribution over the TiO(2) surface. Interestingly, the size of the Au NPs could be controlled by performing sequential reduction steps with AuCl(4)(-)(aq). This method could also be adapted for the production of TiO(2) colloidal spheres decorated with other metal NPs including silver (Ag), palladium (Pd), and platinum (Pt). The catalytic activities of the TiO(2)-Au materials as a function of composition and NPs size were investigated toward the reduction of 4-nitrophenol to 4-aminophenol under ambient conditions. An increase of up to 10.3-fold was observed for TiO(2)-Au relative to TiO(2). A surface-enhanced Raman scattering application for TiO(2)-Au was also demonstrated employing 4-mercaptopyridine as the probe molecule. The results presented herein indicate that our approach may serve as a platform for the synthesis of hybrid materials containing TiO(2) and metal NPs displaying well-defined morphologies, compositions, and sizes. This can have important implications for the design of TiO(2)-based materials with improved performances for photocatalysis and photovoltaic applications.

Self-assembly of Arg-Phe nanostructures via the solid-vapor phase method

We report for the first time on the self-assembly of nanostructures composed exclusively of alternating positively charged and hydrophobic amino acids. A novel arginine/phenylalanine octapeptide, RF8, was synthesized. Because the low hydrophobicity of this sequence makes its spontaneous ordering through solution-based methods difficult, a recently proposed solid-vapor approach was used to obtain nanometric architectures on ITO/PET substrates. The formation of the nanostructures was investigated under different preparation conditions, specifically, under different gas-phase solvents (aniline, water, and dichloromethane), different peptide concentrations in the precursor solution, and different incubation times. The stability of the assemblies was experimentally studied by electron microscopy and thermogravimetric analysis coupled with mass spectrometry. The secondary structure was assessed by infrared and Raman spectroscopy, and the arrays were found to assume an antiparallel β-sheet conformation. FEG-SEM images clearly reveal the appearance of fibrillar structures that form extensive homogeneously distributed networks. A close relationship between the morphology and preparation parameters was found, and a concentration-triggered mechanism was suggested. Molecular dynamics simulations were performed to address the thermal stability and nature of intermolecular interactions of the putative assembly structure. Results obtained when water is considered as solvent shows that a stable lamellar structure is formed containing a thin layer of water in between the RF8 peptides that is stabilized by H-bonding.

Adsorption of caffeic acid on titanium dioxide: a spectroscopic study

Caffeic acid is an ortho-phenol found in vegetable tissues presenting important properties such as carcinogenesis inhibitor, anti-oxidant, anti-viral, anti-inflammatory and anti-rheumatic actions. It was observed that caffeic acid was not degraded in daylight during the adsorption on TiO(2) at pH 4.8. The adsorption fit very well to a Brunauer-Emmett-Teller isotherm equation with a monolayer coverage of 68.15 mg(CA)g(-1)(TiO2 and saturation coverage of 195.4 mg(CA)g(-1)(TiO2). A strong adsorption of caffeic acid was verified on TiO(2) for the dry solid obtained from the mixture. The Raman and IR spectroscopies revealed that the adsorption should occur through the interaction of the diphenol oxygens with contribution of CC double bond of the acrylic group, however, the carboxylic acid group did not have participation in the adsorption.

Raman, IR, UV-vis and EPR characterization of two copper dioxolene complexes derived from L-dopa and dopamine

The anionic complexes [Cu(L(1-))3](1-), L(-)=dopasemiquinone or L-dopasemiquinone, were prepared and characterized. The complexes are stable in aqueous solution showing intense absorption bands at ca. 605 nm for Cu(II)-L-dopasemiquinone and at ca. 595 nm for Cu(II)-dopasemiquinone in the UV-vis spectra, that can be assigned to intraligand transitions. Noradrenaline and adrenaline, under the same reaction conditions, did not yield Cu-complexes, despite the bands in the UV region showing that noradrenaline and adrenaline were oxidized during the process. The complexes display a resonance Raman effect, and the most enhanced bands involve ring modes and particularly the nuCC+nuCO stretching mode at ca. 1384 cm(-1). The free radical nature of the ligands and the oxidation state of the Cu(II) were confirmed by the EPR spectra that display absorptions assigned to organic radicals with g=2.0005 and g=2.0923, and for Cu(II) with g=2.008 and g=2.0897 for L-dopasemiquinone and dopasemiquinone, respectively. The possibility that dopamine and L-dopa can form stable and aqueous-soluble copper complexes at neutral pH, whereas noradrenaline and adrenaline cannot, may be important in understanding how Cu(II)-dopamine crosses the cellular membrane as proposed in the literature to explain the role of copper in Wilson disease.

Spectroscopic investigation of conjugated polymers derived from nitroanilines

For the first time, the resonance Raman spectroscopy was used to characterize polymers derived from meta- and para-nitroanilines. In order to improve the polymer structure analysis, other techniques were also used such as FTIR, UV-vis, XRD, XPS, EPR and N K-XANES. The insertion of strong electron-withdrawing groups (NO2) in polyaniline (PANI)-like backbone causes drastic changes in the lower energy charge transfer states, related to the polymer effective conjugation length. The resonance Raman data show that the NO2 moiety has a minor contribution on the CT state in poly(meta-nitroaniline), PMN, while in the poly(para-nitroaniline), PPN, the quinoid structure induced by para-substitution increases the charge density of NO2 groups, causing a more localized chromophore. The characterization of the imine nitrogen and of the protonated segments was done by XPS, N K-XANES and EPR spectroscopies and the lower polymerization degree of PPN, in comparison to PMN, is confirmed by XRD and TG data.

Saturation of the Electron-Withdrawing Capability of the NO2Group in Nitroaromatic Anions: Spectroscopic and Quantum-Chemical Evidence

The electronic (UV-vis) and resonance Raman (RR) spectra of the anionic species derived from 4-nitrophenol (pNP) and 4-nitroaniline (pNA) are reported. The interpretation of the electronic transitions in the visible, near-UV region was supported by quantum-mechanical calculations, allowing a consistent analysis of the enhancement patterns observed in the RR spectra, which show substantial differences in relation to those observed for the neutral species. The removal of the proton of the donor groups (OH and NH2) leads to additional charge density at the oxygen atoms of the electron-withdrawing group (NO2). On the other hand, when the RR spectra of [pNP]- and [pNA]- are compared, a drastic difference concerning the enhancement of modes related to the NO2 moiety is noticed. In particular, in the case of [pNA]-, the RR enhancement pattern involving the NO2 moiety is at variance with those observed for nitroaromatics in general, because the corresponding normal modes involve a more complex composition. Such results are in accordance with the quantum-chemical calculations, which indicate, in the case of [pNA]-, a saturation of the charge density at the N-O bonds, even in the ground state (i.e., the charge density is very similar in the ground and excited-state, which precludes large geometric variations of the NO2 moiety in the two electronic states). Conversely, in this case the most enhanced bands have significant participation of ring modes, which suggests that the charge in the excited-state is now much more distributed in the molecule as a whole.

The Sulfur Dioxide−1-Butyl-3-Methylimidazolium Bromide Interaction: Drastic Changes in Structural and Physical Properties

The contact between minor amounts of SO2 and crystalline 1-butyl-3-methyl-imidazolium bromide (BMIBr) causes the almost immediate melting of the ionic liquid (mp 45 degrees C) as well as a dramatic decrease in its viscosity in comparison to the pure molten phase. The same behavior was observed for other halide ionic liquids of higher melting points (70, 135, and 220 degrees C). The Raman spectrum of BMIBr-SO2 clearly indicates a specific charge transfer interaction involving SO2 and the halide. The measurements of ionic conductivity and diffusion coefficients obtained for the neat BMIBr (molten phase) and for the BMIBr-SO2 strongly suggest a higher degree of ionic association in the presence of SO2. Molecular dynamic simulations indicate that although the cation-anion distance is preserved in the short range, there is a variation in the interionic distances in the second shell, leading to a less organized structure in the long range. The modulation of the structural and physical properties of ionic liquids by SO2 and the convenient choice of the ions for gas absorption are suggested.

Relationship between hexamerization and ssDNA binding affinity in the uvsY recombination protein of bacteriophage T4

In bacteriophage T4, homologous genetic recombination events are catalyzed by a presynaptic filament containing stoichiometric quantities of the T4 uvsX recombinase bound cooperatively to single-stranded DNA (ssDNA). The formation of this filament requires the displacement of cooperatively bound gp32 (the T4 ssDNA-binding protein) from the ssDNA, a thermodynamically unfavorable reaction. This displacement is mediated by the T4 uvsY protein (15.8 kDa, 137 amino acids), which interacts with both uvsX- and gp32-ssDNA complexes and modulates their properties. Previously, we showed that uvsY exists as a hexamer under physiological conditions and that uvsY hexamers bind noncooperatively but with high affinity to ssDNA. We also showed that a fusion protein containing the N-terminal 101 amino acid residues of uvsY lacks interactions with uvsX and gp32 but retains both weak ssDNA-binding activity and a residual ability to stimulate uvsX-catalyzed recombination functions. Here, we present quantitative data on the oligomeric structure and ssDNA-binding properties of a closely related fusion protein designated uvsY. Sedimentation velocity and equilibrium results establish that uvsY, unlike native uvsY, behaves as a monomer in solution (M(app) = 14.2 kDa, = 2.1). Like native uvsY, uvsY binds noncooperatively to an etheno-DNA (epsilonDNA) lattice with a binding site size of 4 nucleotides/monomer; however at physiological ionic strength, the association constant for uvsY-epsilonDNA is decreased 10(4)-fold relative to native uvsY. Nevertheless, the magnitude of the salt effect on the association constant (K) is essentially unchanged between uvsY and uvsY, indicating that disruption of the C-terminus does not disrupt the electrostatic ssDNA-binding determinants found within each protomer of uvsY. Instead, the large difference in ssDNA-binding affinities reflects the loss of hexamerization ability by uvsY, suggesting that a form of intrahexamer synergism or cooperativity between binding sites within the uvsY hexamer leads to its high observed affinity for ssDNA.

Single-stranded DNA binding properties of the UvsX recombinase of bacteriophage T4: binding parameters and effects of nucleotides

Bacteriophage T4 provides an important model for the biochemistry and genetics of DNA metabolism. Phage-encoded proteins conduct all essential steps of T4 DNA replication, repair, and recombination. Central to these three processes is the T4 UvsX protein, a member of the filamentous, ATP-dependent class of general recombination enzymes typified by the Escherichia coli RecA protein. Like RecA, UvsX forms presynaptic filaments on single-stranded (ss) DNA, which are the obligatory nucleoprotein intermediates in recombination. Aspects of the T4 presynaptic filament are explored by quantitative characterization of the UvsX-ssDNA interaction using an etheno-derivitized single-stranded DNA molecule, epsilonDNA, whose fluorescence is enhanced by UvsX binding. Studies with this model lattice show that UvsX exhibits a moderate level of cooperativity (omega=100) when binding to epsilonDNA with a binding-site size (n) equal to four nucleotide residues. Salt-stability studies of this complex reveal that the non-hydrolyzable ATP analog, ATPgammaS, induces a high-affinity binding mode that is distinguishable from complexes formed with ADP or in the absence of a nucleotide cofactor. With this new information, both functional relationships between the UvsX and RecA recombinases, and implications for UvsX interactions with the other proteins of the T4 presynaptic filament (UvsY and gp32) may be further explored.

Genetic analysis of a large kindred exhibiting type I protein C deficiency and associated thrombosis

A previously described large Vermont kindred possessing a high incidence of venous thromboembolism with associated Type I protein C deficiency (1) has been genetically analyzed. All nine exons of the protein C gene, including both coding and non-coding regions, have been amplified from blood cell genomic DNA using the Tag DNA polymerase chain reaction (PCR) and primers corresponding to flanking intronic regions, and the products directly sequenced. An initial mutation (C-->T) resulting in Thr298-->Met was observed in one arm of the family exhibiting a history of thrombosis and protein C deficiency and was designated protein CVERMONT IIa. However, examination of the kindred member parent (male) of this arm and members of other arms of the kindred demonstrated that the mutation entered the arm via the genetically unrelated spouse. Further analysis of the father and members of other arms of the kindred revealed a different mutation (C insertion: CAT-->CCAT), resulting in a frameshift beginning at amino acid #107 (His-->Pro) and truncation of the protein at codon #119 of the mature protein. This mutation, called protein CVERMONT IIb, is associated with protein C deficiency and thrombosis throughout the kindred.