Measurements In Acetonitrile Research Articles

Enhanced Deoxygenation of Solvents via an Improved Inert Gas Bubbling Method with a Ventilation Pathway.

We introduce an improved inert gas bubbling method for solvent deoxygenation, featuring a ventilation path alongside the inert gas inlet to enhance the efficiency and reproducibility. While essential for life, oxygen's reactivity can disrupt scientific and industrial processes by forming unwanted intermediates and deactivating catalysts, necessitating efficient deoxygenation methods. Traditional methods like freeze-pump-thaw (FPT) are effective but time-consuming, require stringent safety measures, and have potential limitations for use with aqueous and biological samples. Our enhanced inert gas bubbling method retains the simplicity and safety of conventional bubbling while achieving FPT-like deoxygenation efficiency, demonstrated by photoluminescence intensity and lifetime measurements in acetonitrile (ACN) and toluene (TOL). Simulations using a simplified kinetic model and the Stern-Volmer equation reveal that the added ventilation pathway reduces oxygen contamination in Ar gas bubbles, improving the deoxygenation efficiency. This method is widely applicable in academic and industrial fields, requiring consistent and efficient solvent deoxygenation.

Raman spectrometer with vertical flow method for solutions containing organic solvents

The vertical flow (VF) method improves generation and collection efficiency in Raman spectroscopy. It enhances all Raman signals, including undesired signals of organic solvents having a considerably large Raman cross section. We constructed a Raman spectrometer using the VF method to overcome this drawback and introduced a spatial line rejection mask to eliminate unnecessary bands. In addition, the design of the VF unit was improved to resist organic solvents. A VF unit with a 60-µm pinhole enhanced the signal 168 times. The spatial mask effectively eliminated the large Raman bands of the solvent and enabled a longer exposure time. The increase in the dynamic range improved the signal-to-noise ratio by 10 % in methanol and acetonitrile measurements. Raman spectrometer with the VF method and spatial mask enables us to record the Raman spectrum of solute molecules without the disturbance of solvent bands.

Synthesis, Characterization, and Spectroscopic Studies of 2,6-Dimethylpyridyl-Linked Cu(I)-CNC Complexes: The Electronic Influence of Aryl Wingtips on Copper Centers.

Six new Cu(I) complexes containing pincer ligands of the type 2,6-bis(3-alkyl/arylimidazol-2-ylidene) methylpyridine I(R/R'Ar) ĈN̂C, where R = trifluoroethyl (TFE) and R' = 4-CF3, 4-NO2, 4-CN, 4-H, and 4-CH3, have been synthesized. These complexes, namely, [Cu(I(TFE)ĈN̂C)]PF6, 1-TFE; [Cu(ICF3Ar ĈN̂C]PF6, 2-CF3; [Cu(INO2Ar ĈN̂C)]PF6, 3-NO2; [Cu(ICNAr ĈN̂C]PF6, 4-CN; [Cu(IHAr ĈN̂C)]2(PF6)2, 5-H; and [Cu(ICH3Ar ĈN̂C)]2(PF6)2, 6-CH3, were fully characterized by 1H, 13C, and HMBC NMR spectroscopy, elemental analysis, electrochemical studies, and single-crystal X-ray crystallography. The crystallographic data revealed different structures and copper nuclearities for the complexes bearing aryl wingtips with electron-withdrawing (2-CF3, 3-NO2, and 4-CN) and electron-donating (5-H and 6-CH3) substituents. The solution-phase conductivity measurements in acetonitrile revealed a mix-electrolyte behavior for these complexes, supporting the presence of both mono- and binuclear forms of each complex. The fast monomer-dimer equilibrium of the Cu-CNC complexes at room temperature is reflected in their simple 1H NMR spectra in acetonitrile. However, both mono- and binuclear forms were identifiable in 1H diffusion-ordered spectroscopy (DOSY) at low temperatures. The dynamic behavior of these complexes in solution was further examined by variable-temperature 1H NMR (VT 1H NMR) experiments, and the relevant thermodynamic parameters were determined. The process was also probed by one-dimensional rotating-frame Overhauser enhancement spectroscopy (1D ROESY) experiments to elucidate the coexisting species in solution. The 2,6-dimethylpyridyl-linked Cu-CNC complexes also presented a quasi-reversible Cu(II)/Cu(I) couple in cyclic voltammetry studies, wherein a clear influence of the aryl wingtips on the E1/2 values was observed. Furthermore, the percent buried volumes (% Vbur) of the complexes were calculated, showing a similar steric hindrance around copper in all complexes. These findings support the importance of electronic effects, induced by the aryl wingtips, on the preferred coordination geometry, copper nuclearity, and redox properties of the Cu-CNC complexes.

Preparation, photoluminescence and excited state properties of the homoleptic cluster cation [(W6I8)(CH3CN)6]4.

Solvated tungsten iodide cluster compounds are presented with the homoleptic cluster cation [(W6I8)(CH3CN)6]4+ and the heteroleptic [(W6I8)I(CH3CN)5]3+, synthesized from W6I22 in acetonitrile. Crystal structures were solved and refined on deep red single-crystals of [(W6I8)(CH3CN)6](I3)(BF4)3·H2O, [(W6I8)I(CH3CN)5](I3)2(BF4), and on a yellow single-crystal of [W6I8(CH3CN)6](BF4)4·2(CH3CN) on the basis of X-ray diffraction data. The structure of the homoleptic [(W6I8)(CH3CN)6]4+ cluster is based on the octahedral [W6I8]4+ tungsten iodide cluster core, coordinated by six apical acetonitrile ligands. The electron localisation function of [(W6I8)(CH3CN)6]4+ is calculated and solid-state photoluminescence and its temperature depedence are reported. Additionally, photoluminescence and transient absorption measurements in acetonitrile are shown. Results of the obtained data are compared to compounds containing [(M6I8)I6]2- and [(M6I8)L6]2- (M = Mo or W; L = ligand) clusters.

Mechanistic Impacts of Metal Site and Solvent Identities for Alkene Oxidation over Carboxylate Fe and Cr Metal–Organic Frameworks

Isolated Fe(III) and Cr(III) sites contained in nanoporous voids of isoreticular carboxylate MIL-101(Fe) and MIL-101(Cr) are interrogated for their reactivity and selectivity of liquid-phase styrene oxidation by hydrogen peroxide (H2O2). Batch kinetic measurements in acetonitrile (MeCN) at 323 K showcase that both metal-normalized oxygenate production and H2O2 consumption rates are O(101) higher for MIL-101(Fe) than MIL-101(Cr). Thermodynamically consistent reaction pathways, constructed through spiking experiments, reveal complex interconnectivities between primary (styrene oxide, benzaldehyde) and secondary (styrene glycol, benzoic acid, phenylacetaldehyde) oxygenates. Though benzaldehyde is the majority product for both MIL-101(Fe) and MIL-101(Cr), isoconversion (Xstyrene = 7%) product distributions suggest intrinsic differences in preferred reaction pathways. Apparent energy barriers for all pathways are lower over MIL-101(Fe) than for MIL-101(Cr), conferred by metal electron affinity differences for primary oxygenate selectivity, while secondary (inter)conversion rates trend with acid site densities. Fitted rate laws, radical trapping, adsorption experiments, and complementary DFT calculations indicate surface-mediated reactions by H2O2-derived surface species that outcompete bound styrene, product oxygenate, solvent, and water molecules for both MIL-101(Fe) and MIL-101(Cr) in MeCN. Extracted enthalpic and entropic effects from temperature-dependent experiments (318–328 K) in MeCN and MeOH showcase the ability of hydrogen bonding solvents in locally hydrophilic environments to selectively stabilize primary oxygenate transition states and indicate additional confinement effects from microporous substructures in MIL-101(Fe) and MIL-101(Cr). Simplified rate expressions are expanded to encompass first-order catalyst deactivation rates through temporal metal leaching experiments and assert that metal leaching dominates MIL-101(Cr) catalyst inefficiencies, while a combination of metal leaching and other (ir)reversible site changes are present for MIL-101(Fe). Overall, this work combines kinetic, spectroscopic, numerical, and computational approaches to rigorously define reaction and deactivation mechanisms for styrene oxidation by H2O2 over isoreticular MIL-101(Fe) and MIL-101(Cr).

Extraction and complexation of lanthanide ions by dihomooxacalix[4]arene and calix[4]arene tetraketone derivatives: An experimental and molecular dynamics investigation

Lanthanide cation binding by tetraketone derivatives of p-tert -butyldihomooxacalix[4]arene (methyl 1a , tert -butyl 1b , adamantyl 1c and phenyl 1d ) and of p-tert -butylcalix[4]arene (methyl 2a , adamantyl 2c and phenyl 2d ), in the cone conformation, was investigated. These properties were assessed by extraction experiments of the metal picrates from water to dichloromethane and by stability constant measurements in acetonitrile by UV-vis absorption spectrophotometry. Proton NMR titrations with La 3+ , Eu 3+ and Yb 3+ cations were also performed to obtain information on the binding sites. Molecular dynamics (MD) simulations and potential of mean force (PMF) free energy calculations were carried out for ligands 1d and 2d in pure solvents and at a CH 2 Cl 2 /water interface to add further information on the complexation and extraction processes. Comparison between dihomooxacalix[4]arene and calix[4]arene ketone derivatives showed that the former are better extractants, displaying the highest percentages of extraction for Gd 3+ and Yb 3+ cations. Concerning complexation, all ligands studied presented high affinities for the lanthanide ions. Ligands 1b and 1d showed preference for the light La 3+ , while 2d displayed the strongest affinity for the heavy and smaller Yb 3+ . These results were also corroborated by MD simulations, which revealed specificities of ligands 1d and 2d in the binding of lanthanide cations. L'interaction entre des cations lanthanide et des dérivés tétracétone du p - tert -butyldi-/homooxacalix[4]arène (méthyl 1a , tert -butyl 1b , adamantyl 1c et phényl 1d ) et du p - tert -butylcalix[4]arène (méthyl 2a , adamantyl 2c et phényl 2d ), en conformation cône, a été étudiée. Ces propriétés ont été évaluées par des expériences d'extraction de picrates métalliques de l'eau vers le dichlorométhane et par la détermination des constantes de stabilité dans l'acétonitrile par spectrophotométrie d'absorption dans l’UV–visible. Des titrages RMN du proton avec les cations La 3+ , Eu 3+ et Yb 3+ ont également été effectués afin d'obtenir des informations sur les sites de liaison. Des simulations en dynamique moléculaire (DM) et des calculs d'énergie libre du potentiel de force moyenne (PMF) ont été réalisés avec les ligands 1d et 2d dans les solvants purs et à l'interface CH 2 Cl 2 /eau afin d'apporter des informations complémentaires sur les processus de complexation et d'extraction. La comparaison entre les dérivés cétone du dihomooxacalix[4]arène et du calix[4]arène a montré que les premiers possèdent un meilleur pouvoir extractant, avec les pourcentages d'extraction les plus élevés pour les cations Gd 3+ et Yb 3+ . Concernant la complexation, tous les ligands étudiés présentent des affinités élevées pour les ions lanthanide. Les ligands 1b et 1d montrent une préférence pour La 3+ , cation léger, alors que 2d présente la plus forte affinité pour Yb 3+ , cation lourd et moins volumineux. Ces résultats ont également été confirmés par des simulations en DM, qui ont révélé les spécificités des ligands 1d et 2d lors de leur interaction avec les cations lanthanide.

Volatile organic compound measurements point to fog-induced biomass burning feedback to air quality in the megacity of Delhi

We report the first ambient measurements of thirteen VOCs for investigations of emissions and air quality during fog and non-fog wintertime conditions at a tower site (28.57° N, 77.11° E, 220 m amsl) in the megacity of Delhi. Measurements of acetonitrile (biomass burning (BB) tracer), isoprene (biogenic emission tracer in daytime), toluene (a traffic exhaust tracer) and benzene (emitted from BB and traffic), together with soluble and reactive oxygenated VOCs such as methanol, acetone and acetaldehyde were performed during the winters of 2015–16 and 2016–17, using proton transfer reaction mass spectrometry. Remarkably, ambient VOC composition changes during fog were not governed by solubility. Acetaldehyde, toluene, sum of C8-aromatics (e.g. xylenes), sum of C9-aromatics (e.g. trimethyl benzenes) decreased by ≥30% (>95% confidence interval), whereas acetonitrile and benzene showed significant increases by 20% (>70% confidence interval), even after accounting for boundary layer dilution. During fog, the lower temperatures appeared to induce an emissions feedback from enhanced open BB within Delhi for warming, releasing both gaseous and aerosol pollutants with consequences for fog chemistry, sustenance and intensity. The potential feedback is important to consider for improving current emission parametrizations in models used for predicting air quality and fog in such atmospheric environments.

Stabilizing a NiII-aqua complex via intramolecular hydrogen bonds: Synthesis, structure, and redox properties

Hydrogen bonds within the secondary coordination sphere are effective in controlling the chemistry of synthetic metal complexes. Coupling the capacity of hydrogen bonds with those of redox-active ligands offers a promising approach to enhance the functional properties of transition metal complexes. These qualities were successfully illustrated with the [NNN]3− pincer ligand N,N'-(azanediylbis(2,1-phenylene))bis(2,4,6-triisopropyl-benzene-sulfonamido ([ibaps]3−) through the preparation of the NiII–OH2 complex, [NiII(ibaps)(OH2)]−. The [ibaps]3− ligand contains two appended sulfonamido groups that support the formation of intramolecular hydrogen bonds. The bulky 2,4,6-triisopropylphenyl rings are necessary to ensure that only one ligand binds to a single metal ion. The molecular structure of the complex shows a square planar N3O primary coordination sphere and two intramolecular hydrogen bonds involving the aqua ligand. Electrochemical measurements in acetonitrile revealed two oxidation events at potentials below that of the ferrocenium/ferrocene couple. Oxidation with 1 equiv of ferrocenium produced the one-electron oxidized species, [Ni(ibaps)(OH2)]. Experimental and computational studies support this assignment.

T1 Population as the Driver of Excited-State Proton-Transfer in 2-Thiopyridone.

Excited‐state proton transfer (ESPT) is a fundamental process in biomolecular photochemistry, but its underlying mediators often evade direct observation. We identify a distinct pathway for ESPT in aqueous 2‐thiopyridone, by employing transient N 1s X‐ray absorption spectroscopy and multi‐configurational spectrum simulations. Photoexcitations to the singlet S2 and S4 states both relax promptly through intersystem crossing to the triplet T1 state. The T1 state, through its rapid population and near nanosecond lifetime, mediates nitrogen site deprotonation by ESPT in a secondary intersystem crossing to the S0 potential energy surface. This conclusively establishes a dominant ESPT pathway for the system in aqueous solution, which is also compatible with previous measurements in acetonitrile. Thereby, the hitherto open questions of the pathway for ESPT in the compound, including its possible dependence on excitation wavelength and choice of solvent, are resolved.

Optimized frequency dependent photothermal beam deflection spectroscopy

In the letter the optimization of the experimental setup for photothermal beam deflection spectroscopy is performed by analyzing the influence of its geometrical parameters (detector and sample position, probe beam radius and its waist position etc) on the detected signal. Furthermore, the effects of the fluid’s thermo-optical properties, for optimized geometrical configuration, on the measurement sensitivity and uncertainty determination of sample thermal properties is also studied. The examined sample is a recently developed CuFeInTe3 material. It is seen from the obtained results, that it is a complex problem to choose the proper geometrical configuration as well as sensing fluid to enhance the sensitivity of the method. A signal enhancement is observed at low modulation frequencies by placing the sample in acetonitrile (ACN), while at high modulation frequencies the sensitivity is higher for measurements made in air. For both, detection in air and acetonitrile the determination of CuFeInTe3 thermal properties is performed. The determined values of thermal diffusivity and thermal conductivity are (0.048 ± 0.002) × 10−4 m2 s−1 and 4.6 ± 0.2 W m−1 K−1 and (0.056 ± 0.005) × 10−4 m2 s−1 and 4.8 ± 0.4 W m−1 K−1 for ACN and air, respectively. It is seen, that the determined values agree well within the range of their measurement uncertainties for both cases, although the measurement uncertainty is two times lower for the measurements in ACN providing more accurate results. The analysis is performed by the use of recently developed theoretical description based on the complex geometrical optics. It is also shown, how the presented work fits into the current status of photothermal beam deflection spectroscopy.

Thermodynamic Parameters of Complexation Calixpyrrole Derivative with Lanthanides Cations (Lu3, Ho3, Eu3+ and Pr3+) in Nonaquoeus Media

Calix [4] pyrrole derivative was used to target lanthanide cations. Meso tetramethyl-tetrakis-[(4-N, N-diethylacetamide) phenoxymethyl] calix [4] pyrrole, L2 was synthesised. This receptor constituted of hard donor atoms at the lower rim which interact with lanthanide cations being hard cations. 1H NMR investigations showed that both, the pyrrolic N and the acetamide arm group provide sites for interaction with lanthanide metal cations. These findings are verified by conductance measurements in acetonitrile, plots of molar conductance against the ligand/metal cation ratio reveal the formation of 1:2 complexes between this ligand with lanthanide metal cations. Standard thermodynamics parameters of complexation (log Ks, ΔHᵒc, ΔSᵒc, ΔGᵒc) of L2 with lanthanide cations in acetonitrile were determined using the Nano ITC (isothermal titration calorimetry). The complexation process between these metal cations and the receptor L2 was enthalpically controlled.

Fundamental Studies of Synthesizing Novel Calix[4]arene Derivative as Host for Treatment of Toxic Metal Cations (Hg2+, Cd2+, Pb2+ and Ag+)

Novel calix[4]arene derivative containing mixed pendant arms in its lower rim, 25, 27- bis (diethylamino) ethoxy- 26, 28- (bis-methoxyethoxy) calix[4]arene, L3, has been synthesized to target the heavy metal cations. 1H NMR investigations seems to indicate that the receptor L3 interacts preferentially with Hg2+, Cd2+, Pb2+ and Ag+ in acetonitrile. Complexation studies in acetonitrile show that the lower rim groups of the receptor L3 are the active sites of its interaction with metal ions. These findings are corroborated by conductance measurements in acetonitrile, plots of molar conductance against the ligand/metal cation ratio reveal the formation of 1:1 complexes between this ligand with these cations. Standard thermodynamics parameters of complexation (log Ks, ΔHAiµ’ c, ΔSAiµ’ c, ΔGAiµ’ c) of L3 with Hg2+, Cd2+, Pb2+ and Ag+ in acetonitrile were determined using the Nano ITC (isothermal titration calorimetry). For all the systems investigated, the complexation process between these metal cations and the receptor L3 was enthalpically controlled. The enthalpic and entropic contributions to the Gibbs energy associated with these processes are analysed.

Conversion of electrodeposited Co(OH)2 to CoOOH and Co3O4, and comparison of their catalytic activity for the oxygen evolution reaction

Cobalt hydroxide, β-Co(OH)2, was electrodeposited cathodically from an alkaline solution of tris(ethylenediamine)cobalt(III). The Co(OH)2 crystals grew into a microcone morphology and the surface became CoOOH at anodic potentials. The Co(OH)2 film was fully converted to CoOOH by electrochemical oxidation at 95°C in 1M KOH and to Co3O4 by thermal decomposition at 300°C in air. The Co(OH)2 and CoOOH films grew with a [001] orientation on Au(111), and the converted Co3O4 films had a [111] orientation. The overall morphology was retained upon conversion. However, an increase in roughness was observed on the surface of the CoOOH and Co3O4 microcones. The electrochemically active area of the films was estimated from double layer capacitance measurements in acetonitrile with tetrabutylammonium hexafluorophosphate electrolyte. The CoOOH had a roughness factor of 9.4, and the Co3O4 had a roughness factor of 63.6. The catalytic activities of the films for the oxygen evolution reaction (OER) were compared by Tafel analysis in an O2 saturated 1M KOH at room temperature. The CoOOH and Co3O4 films appeared to exhibit different Tafel behavior with Co3O4 being the superior catalyst when the geometric area was used in the Tafel analysis. However, when the observed current densities were corrected for the measured electrochemically active areas, the linear regions of the two Tafel plots fell on the same line. The results suggest that the active species, likely Co(IV), for the OER is the same on both materials. Both CoOOH and Co3O4 had a Tafel slope of 60mV dec−1 and an exchange current density of 6.1×10−11 A cm−2. The conversion method outlined in the paper provides a means to produce Co3O4 with a large electrochemically-active area.

Direct Determination of Equilibrium Potentials for Hydrogen Oxidation/Production by Open Circuit Potential Measurements in Acetonitrile

Open circuit potentials were measured for acetonitrile solutions of a variety of acids and their conjugate bases under 1 atm H2. Acids examined were triethylammonium, dimethylformamidium, 2,6-dichloroanilinium, 4-cyanoanilinium, 4-bromoanilinium, and 4-anisidinium salts. These potentials, along with the pKa values of the acids, establish the value of the standard hydrogen electrode (SHE) potential in acetonitrile as -0.028(4) V vs the ferrocenium/ferrocene couple. Dimethylformamidium forms homoconjugates and other aggregates with dimethylformamide; open circuit potentials (OCPs) were used to quantify the extent of these reactions. Overpotentials for electrocatalytic hydrogen production and oxidation were determined from open circuit potentials and voltammograms of acidic or basic catalyst solutions under H2. For these solutions, agreement between OCP values and potentials calculated using the Nernst equation is within 12 mV. Use of the measured equilibrium potential allows direct comparison of catalytic systems in different media; it requires neither pKa values, homoconjugation constants, nor the SHE potential.

Complexation and DFT studies of lower rim hexahomotrioxacalix[3]arene derivatives bearing pyridyl groups with transition and heavy metal cations. Cone versus partial cone conformation

The binding of representative alkali, alkaline earth, transition and heavy metal cations by 2-pyridylmethoxy derivatives (1b, in cone and partial cone conformations) of p-tert-butylhexahomotrioxacalix[3]arene was studied. Binding was assessed by extraction studies of the metal picrates from water into dichloromethane and by stability constant measurements in acetonitrile and methanol, using spectrophotometric and potentiometric techniques. Microcalorimetric studies of some selected complexes in acetonitrile were performed, as well as proton NMR titrations. Computational methods (density functional theory calculations) were also employed to complement the NMR data. The results are compared with those obtained with the dihomooxacalix[4]arene 2b and the calix[4]arene 3b derivative analogues. Partial cone-1b is the best extractant for transition and heavy metal cations. Both conformers of 1b exhibit very high stability constants for soft and intermediate cations Pb2+, Cd2+, Hg2+, Zn2+ and Ni2+, with cone-1b the strongest binder (ML, log β ≥ 7) and partial cone-1b the most selective. Both derivatives show a slight preference for Na+. Besides the formation of ML complexes, ML2 and M2L species were also observed. The former complexes were, in general, formed with the transition and heavy metal cations, whereas the latter were obtained with Ag+ and Hg2+ and partial cone-1b. In most cases, these species were corroborated by the proton NMR and density functional theory studies. Copyright © 2013 John Wiley & Sons, Ltd.

Viscosity and Thermodynamic Properties of Alkali Metal Bromides in the Presence of Acetonitrile, 3-Hydroxypropionitrile and Acetonitrile + 3-Hydroxypropionitrile Mixture at Various Temperatures

Excess molar volume Vm E , energy of activation Ev , Gibbs energy change G and entropy change S have been investigated for this study density and viscosity measurements of Acetonitrile (AN), 3-hydroxypropionitrile (3-HPN) and 50% mixture of AN + 3-HPN and alkali metal bromides (Li,Na,K,Rb and Cs)Br in AN, 3-HPN and 50%AN+3-HPN over the concentration range (0.01 - 0.05 mol.dm -3 ) at temperature range (298 to 323 K) were used. On the basis of Jones-Dole Equation the viscosity B-coefficient and the thermodynamic, activation parameters for viscous flow of solutions have been evaluated. The B-coefficient values of LiBr, NaBr , KBr, RbBr and CsBr are positive and decreases by increasing the temperature. The B-coefficient values are positive in protic and aprotic solvents. The positive values reveal that electrolytes behave as structure maker. data of densities and viscosities of alkali metal bromides in AN, 3-HPN and in a 50% AN +3-HPN mixture at different temperatures to determine the activation and thermodynamic parameters like energy of activationEv , Gibbs energy changeG and entropy changeS. Results are discussed in terms of intermolecular interactions (13). The excess molar volume is also reported for the binary solvent system.

Photophysical parameters and fluorescence quenching of 7-diethylaminocoumarin (DEAC) laser dye

The optical properties including electronic absorption spectrum, emission spectrum, fluorescence quantum yield, and dipole moment of electronic transition of 7-diethylaminocoumarin (DEAC) laser dye have been measured in different solvents. Both electronic absorption and fluorescence spectra are red shifted as the polarity of the medium increases, indicating that the dipole moment of molecule increases on excitation. The fluorescence quantum yield of DEAC decreases as the polarity of solvent increases, a result of the role of solvent polarity in stabilization of the twisting of the intramolecular charge transfer (TICT) in excited state, which is a non-emissive state, as well as hydrogen bonding with the hetero-atom of dye. The emission spectrum of DEAC has also been measured in cationic (CTAC) and anionic (SDS) micelles, the intensity increases as the concentration of surfactant increases, and an abrupt change in emission intensity is observed at critical micelle concentration (CMC) of surfactant. 2×10 −3 mol dm −3 of DEAC gives laser emission in the blue region on pumping with nitrogen laser ( λ ex=337.1 nm). The laser parameters such as tuning range, gain coefficient ( α), emission cross section ( σ e), and half-life energy have been calculated in different solvents, namely acetone, dioxane , ethanol, and dimethyforamide (DMF). The photoreactivity of DEAC has been studied in CCl 4 at a wavelength of 366 nm. The values of photochemical yield ( ϕ c) and rate constant ( k) are determined. The interaction of organic acceptors such as picric acid (PA), tetracyanoethylene (TCNE), and 7,7,8,8-tetracynoquinonedimethane (TCNQ) with DEAC is also studied using fluorescence measurements in acetonitrile (CH 3CN); from fluorescence quenching study we assume the possible electron transfer from excited donor DEAC to organic acceptor forming non-emissive exciplex.

7 Diethylaminocoumarin (DEAC) 레이져 염료의 광물리적 파라미터, 광분해, 형광 소광 및 Convolutive Voltammetry

7 diethylaminocoumarin (DEAC) 레이저 염료의 광물리적 특성들을 다양한 용매에서 측정하였다. DEAC의 방출 스펙트럼은 양이온성(CTAC) 미셀과 음이온성(SDS) 미셀에서 측정하였고, 레이저 파라미터는 아세톤, 다이옥산, 에탄올 및 dimethylforamide (DMF)과 같은 여러 가지 용매에 대하여 계산하였다. DEAC의 광반응성은 366 nm 빛을 사용하여 <TEX>$CCl_4$</TEX> 용매에서 연구하였고, 광화학 수득률 (<TEX>${\Phi}_c$</TEX>)과 속도 상수(k)도 결정하였다. picric acid (PA), tetracyanoethylene (TCNE), 7,7,8,8-tetracynoquinonedimethane (TCNQ)등의 유기 수용체와 DEAC의 상호 작용에 대한 연구는 acetonitrile (<TEX>$CH_3CN$</TEX>) 용액에서 형광을 측정하므로 써 수행하였다. DEAC의 전기화학적 연구는 백금 전극을 사용하여 0.1 mol/L tetrabutyl ammonium perchlorate (TBAP)/<TEX>$CH_3CN$</TEX> 용액에서 순환 전류-전압법, convolutive voltammetry 및 디지털 시뮬레이션을 조합하여 수행하였고, 전기화학 파라미터도 결정하였다. The photophysical properties of 7-diethylaminocoumarin (DEAC) laser dye have been measured in different solvents. The emission spectrum of DEAC has also been measured in cationic (CTAC) and anionic (SDS) micelles. The laser parameters have been calculated in different solvents namely acetone, dioxane, ethanol and dimethylforamide(DMF). The photoreactivity of DEAC has been studied in <TEX>$CCl_4$</TEX> solvent using 366 nm light. The values of photochemical yield (<TEX>${\Phi}_c$</TEX>) and rate constant (k) are determined. The interaction of organic acceptors such as picric acid (PA), tetracyanoethylene (TCNE) and 7,7,8,8-tetracynoquinonedimethane (TCNQ) with DEAC are also studied using fluorescence measurements in acetonitrile (<TEX>$CH_3CN$</TEX>). The electrochemical investigation of (DEAC) has been carried out using cyclic voltammetry and convolutive voltammetry combined with digital simulation technique at a platinum electrode in 0.1 mol <TEX>$L^{-1}$</TEX> tetrabutyl ammonium perchlorate (TBAP) in <TEX>$CH_3CN$</TEX> solvent. The electrochemical parameters of the investigated compound were determined using cyclic and convolutive voltammetry. The extracted electrochemical parameters were verified and confirmed via digital simulation method.

Emission and chemistry of organic carbon in the gas and aerosol phase at a sub-urban site near Mexico City in March 2006 during the MILAGRO study

Abstract. Volatile organic compounds (VOCs) and carbonaceous aerosol were measured at a sub-urban site near Mexico City in March of 2006 during the MILAGRO study (Megacity Initiative: Local and Global Research Objectives). Diurnal variations of hydrocarbons, elemental carbon (EC) and hydrocarbon-like organic aerosol (HOA) were dominated by a high peak in the early morning when local emissions accumulated in a shallow boundary layer, and a minimum in the afternoon when the emissions were diluted in a significantly expanded boundary layer and, in case of the reactive gases, removed by OH. In comparison, diurnal variations of species with secondary sources such as the aldehydes, ketones, oxygenated organic aerosol (OOA) and water-soluble organic carbon (WSOC) stayed relatively high in the afternoon indicating strong photochemical formation. Emission ratios of many hydrocarbon species relative to CO were higher in Mexico City than in the U.S., but we found similar emission ratios for most oxygenated VOCs and organic aerosol. Secondary formation of acetone may be more efficient in Mexico City than in the U.S., due to higher emissions of alkane precursors from the use of liquefied petroleum gas. Secondary formation of organic aerosol was similar between Mexico City and the U.S. Combining the data for all measured gas and aerosol species, we describe the budget of total observed organic carbon (TOOC), and find that the enhancement ratio of TOOC relative to CO is conserved between the early morning and mid afternoon despite large compositional changes. Finally, the influence of biomass burning is investigated using the measurements of acetonitrile, which was found to correlate with levoglucosan in the particle phase. Diurnal variations of acetonitrile indicate a contribution from local burning sources. Scatter plots of acetonitrile versus CO suggest that the contribution of biomass burning to the enhancement of most gas and aerosol species was not dominant and perhaps not dissimilar from observations in the U.S.

A thermodynamic study of complexation of 18-crown-6 with Zn2+, Tl+, Hg2+ and $$ {\text{UO}}^{{{\text{2 + }}}}_{{\text{2}}} $$ cations in acetonitrile-dimethylformamide binary media and study the effect of anion on the stability constant of (18C6-Na+) complex in methanol solutions

The equilibrium constants and thermodynamic parameters for complex formation of 18-crown-6(18C6) with Zn2+, Tl+, Hg2+ and \( {\text{UO}}^{{{\text{2 + }}}}_{{\text{2}}} \) cations have been determined by conductivity measurements in acetonitrile(AN)-dimethylformamide(DMF) binary solutions. 18-crown-6 forms 1:1 complexes [M:L] with Zn2+, Hg2+ and \( {\text{UO}}^{{{\text{2 + }}}}_{{\text{2}}} \) cations, but in the case of Tl+ cation, a 1:2 [M:L2] complex is formed in most binary solutions. The thermodynamic parameters (\( \Delta {\text{H}}^{ \circ }_{{\text{c}}} \) and \( \Delta {\text{S}}^{ \circ }_{{\text{c}}} \)) which were obtained from temperature dependence of the equilibrium constants show that in most cases, the complexes are enthalpy destabilized but entropy stabilized and a non-monotonic behaviour is observed for variations of standard enthalpy and entropy changes versus the composition of AN/DMF binary mixed solvents. The obtained results show that the order of selectivity of 18C6 ligand for these cations changes with the composition of the mixed solvent. A non-linear relationship was observed between the stability constants (logKf) of these complexes with the composition of AN/DMF binary solutions. The influence of the \( {\text{ClO}}^{ - }_{{\text{4}}} \), \( {\text{NO}}^{ - }_{{\text{3}}} \) and \( {\text{Cl}}^{ - } \) anions on the stability constant of (18C6-Na+) complex in methanol (MeOH) solutions was also studied by potentiometry method. The results show that the stability of (18C6-Na+) complex in the presence of the anions increases in order: \( {\text{ClO}}^{ - }_{{\text{4}}} \) > \( {\text{NO}}^{ - }_{{\text{3}}} \) > \( {\text{Cl}}^{ - } \).