Fluorescence Dynamics of Coumarin C522 as a Function of Micelle Confinement along with Cyclodextrin Supramolecular Complex Formation

Our aim is to doubly confine a molecule of coumarin C522 in a host–guest supramolecular complex with β‐cyclodextrin in a reverse sodium dioctyl sulfosuccinate (AOT) micelle using nonpolar n‐heptane and polar water solvents. Varying the volumes of coumarin C522 and β‐cyclodextrin dissolved in water allows us to control the water‐pool diameters of the reverse micelle in n‐heptane with values of w=3, 5, 10, 20, and 40, where w is the ratio of water concentration to AOT concentration in n‐heptane. To study the fluorescence dynamics of coumarin C522, the spectral steady‐state and time‐resolved dependences are compared for the two systems coumarin C522(water)/AOT(n‐heptane), denoted C522/micelle, and coumarin C522/β‐cyclodextrin(water)/AOT(n‐heptane), referred to as C522/CD/micelle. The formation of the supramolecular host–guest complex CD–C522 is indicated by a blue shift, but in the micelle, the shift is red. However, the values of the fluorescence maxima at 520 and 515 nm are still way below the value of 535 nm representing bulk water. The interpretation of the red shift is based on two complementary processes. The first one is the confinement of CD and C522 by the micelle water pool and the second is the perturbation of the micelle by CD and C522, resulting in an increase of the water polarity. The fluorescence spectra of the C522/micelle and C522/CD/micelle systems have maxima and shoulders. The shoulder intensities at 440 nm, representing the C522 at n‐heptane/AOT interface, decrease as the w values decrease. This intensity shift suggests that the small micelle provides a stronger confinement, and the presence of CD shifts the equilibrium from n‐heptane towards the water pool even more. The fluorescence emission maxima of the C522/micelle and C522/CD/micelle systems for all w values clearly differentiate two trends for w=3–5, and w=10–40, suggesting different interaction in the small and large micelles. Moreover, these fluorescence maxima result in 7 and 13 nm differences for w=3 and w=5, respectively, and provide the spectral evidence to differentiate the C522 confinement in the C522/micelle and C522/CD/micelle systems as an effect of the CD molecule, which might be interpreted as a double confinement of C522 in CD within the micelle. The ultrafast decay in the case of w=3 ranges from 9.5 to 16 ps, with an average of 12.6 ps, in the case of the C522/micelle system. For C522/CD/micelle, the ultrafast decay at w=3 ranges from 9 to 14.5 ps, with an average of 11.8 ps. Increasing w values (from 10 to 40) result in a decrease of the ultrafast decay values in both cases to an average value of about 6.5 ps. The ultrafast decays of 12.6 and 11.8 ps for C522/micelle and C522/CD/micelle, respectively, are in the agreement with the observed red shift, supporting a double confinement in the C522/CD/micelle(w=3) system. The dynamics in the small and large micelles clearly show two different trends. Two slopes in the data are observed for w values of 3–5 and 10–40 in the steady‐state and time‐resolved data. The average ultrafast lifetimes are determined to be 12.6 and 6.5 ps for the small (w=3) and the large (w=40) micelles, respectively. To interpret the experimental solvation dynamics, a simplified model is proposed, and although the model involves a number of parameters, it satisfactory fits the dynamics and provides the gradient of permittivity in the ideal micelle for free water located in the centre (60–80) and for bound water (25–60). An attempt to map the fluorescence dynamics of the doubly confined C522/CD/micelle system is presented for the first time.     

Catalytic Conversion of Simulated Biogas Mixtures to Synthesis Gas in a Fluidized Bed Reactor Supported by a DBD

The catalytic conversion of methane and carbon dioxide was studied in a fluidized bed reactor supported by a 13.56?Hz driven coaxial DBD-reactor. Palladium or cupper catalyst which are covered on Al₂O₃ particles were used. The goal was to test whether biogas can be used for the production of synthesis gas. The influences of discharge power, catalysts and temperature of the catalyst bed on the product yield were studied. The starting material and product stream was analyzed by quadrupole mass spectrometry and infrared spectroscopy. H₂/CO ratios can be adjusted in a range between 0.65 (without a catalyst) and 1.75 (using a copper catalyst). The process is highly selective for hydrogen production (up to 83%, using a Palladium catalyst). A copper catalyst increases the H₂/CO ratio can from 1.04 to 1.16 and the palladium catalyst from 1.11 to 1.43 by heating the catalyst to a temperature of 250°C.     

Coordination chemistry of 4-methyl-2,6,7-trioxa-1-phosphabicyclo[2,2,1]heptane: preparation and characterization of Ru(II) complexes

The complexes TpRu[P(OCH(2))(2)(OCCH(3)](PPh(3))Cl (2) [Tp = hydridotris(pyrazolyl)borate; P(OCH(2))(2)(OCCH(3)) (1) = (4-methyl-2,6,7-trioxa-1-phosphabicyclo[2,2,1]heptane] and TpRu(L)(PPh(3))Cl [L = P(OCH(2))(3)CEt (3), PMe(3) (4) or P(OMe)(3) (5)], (η(6)-C(6)H(6))Ru(L)Cl(2) [L = PPh(3) (6), P(OMe)(3) (7), PMe(3) (8), P(OCH(2))(3)CEt (9), CO (10) or P(OCH(2))(2)(OCCH(3)) (11)] and (η(6)-p-cymene)Ru(L)Cl(2) [L = P(OCH(2))(3)CEt (12), P(OCH(2))(2)(OCCH(3))P(OCH(2))(2)(OCCH(3)) (13), P(OMe)(3) (14) or PPh(3) (15)] have been synthesized, isolated, and characterized by NMR spectroscopy, cyclic voltammetry, mass spectrometry, and, for some complexes, single crystal X-ray diffraction. Data from cyclic voltammetry and solid-state structures have been used to compare the properties of (1) with other phosphorus-based ligands as well as carbon monoxide. Data from the solid-state structures of Ru(II) complexes show that P(OCH(2))(2)(OCCH(3)) has a cone angle of 104°. Cyclic voltammetry data reveal that the Ru(II) complexes bearing P(OCH(2))(2)(OCCH(3)) have more positive Ru(III/II) redox potentials than analogous complexes with the other phosphorus ligands; however, the Ru(III/II) potential for (η(6)-C(6)H(6))Ru[P(OCH(2))(2)(OCCH(3))]Cl(2) is more negative compared to the Ru(III/II) potential for the CO complex (η(6)-C(6)H(6))Ru(CO)Cl(2). For the Ru(II) complexes studied herein, these data are consistent with the overall donor ability of 1 being less than other common phosphines (e.g., PMe(3) or PPh(3)) or phosphites [e.g., P(OCH(2))(3)CEt or P(OMe)(3)] but greater than carbon monoxide.     

Mechanistic insight from activation parameters for the reaction of a ruthenium hydride complex with CO2 in conventional solvents and an ionic liquid

Detailed kinetic studies were performed on the reaction of [Ru(II)(terpy)(bpy)H](+) (terpy = 2,2',6',2″-terpyridine; bpy = 2,2'-bipyridine) with CO(2) in conventional solvents (water, methanol, and ethanol) and in the ionic liquid [emim][NTf(2)] ([emim] = 1-ethyl-3-methyl-imidazolium; [NTf(2)] = bistrifluoromethylsulfonylamide). Second-order rate constants and activation parameters (ΔH(?), ΔS(?), and ΔV(?)) were determined for the reaction in all solvents. The second-order rate constants correlate with the acceptor number of the solvent, whereas the activation parameters support the associative nature of the reaction. The results in water, especially the activation entropy (+14 ± 2 J K(-1) mol(-1)) and activation volume (-5.9 ± 0.6 cm(3) mol(-1)), differ significantly from those found for the other solvents.     

Highly correlated calculations using optimized virtual orbital space with controlled accuracy. Application to counterpoise corrected interaction energy calculations

In this work, we investigate the correlation between error introduced by truncation of optimized virtual orbital space (OVOS) on the MP2 level (Y_MP2) with the error of the post‐MP2 contributions, such as the CCSD‐MP2 (i.e., Y_ΔCCSD), CCSD(T)‐MP2 (i.e., Y_ΔCCSD(T)), or the (T) separately. We found a correlation between the Y_MP2 and several other quantities, such as the percent of recovered optimization functional value in the truncated OVOS (OF%), or the aforementioned Y_ΔCCSD, Y_ΔCCSD(T), Y_(T), which is to good approximation linear in the logarithmic scale. These correlations open a possibility to control the accuracy of the post‐MP2 calculations in the truncated OVOS, because the Y_MP2 and the OF% are easily obtained, almost as a byproduct of the virtual orbital optimization. According to the results present in this work, knowledge of the Y_MP2 or the OF% allows us to safely estimate the order of magnitude of the error of the post‐MP2 corrections. To keep the accuracy of, for instance, CCSD(T) correlation energy calculated in the truncated OVOS within 1.10^?5 ? 1.10^?6 Hartree error bars, we can typically reduce only a few percent of the OVOS, although this value increases slightly with enlarging the atomic orbital (AO) basis set and the number of inactive occupied orbitals. Still, even such a modest reduction can save more then a half of the computation time, compared with calculations in the full VOS. The situation is, however, much more favourable in case of counterpoise (CP) corrected calculations of interaction energy, where this methodology enables safe truncation of significant part of OVOS of monomers, resulting from the presence of the ghost AO. Dimension of such truncated OVOS essentially corresponds to CP‐uncorrected calculations, thus leads to more than an order of magnitude speedup of calculation of monomers. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Modified Riemschneider Reaction of 3‐Thiocyanatoquinolinediones

The Riemschneider reaction of 3‐thiocyanatoquinoline‐2,4(1H,3H)‐diones with conc. H₂SO₄ was investigated. Using different reaction conditions, 13 types of reaction products were isolated. Compounds bearing a Me, Et, or Bu group at C(3) afforded mainly [1,3]thiazolo[5,4‐c]quinoline‐2,4‐diones and 1,9b‐dihydro‐9b‐hydroxythiazolo[5,4‐c]quinoline‐2,4‐diones. In the case of the 3‐Bu derivatives of the starting compounds, C‐debutylation was also observed. If a Bn group is present at C(3), rapid C‐debenzylation of the starting thiocyanates occurred, yielding [1,3]oxathiolo[4,5‐c]quinoline‐2,4‐diones, and mixtures of mono‐, di‐, and trisulfides derived from 4‐hydroxy‐3‐sulfanylquinoline‐2‐ones. The reaction mechanism of all of the transformations is discussed. All new compounds were characterized by IR, ¹H‐ and ¹³C‐NMR, and EI and ESI mass spectra, and in some cases, ¹⁵N‐NMR spectra were also used to characterize new compounds.     

Preparation of samarium(II) iodide: quantitative evaluation of the effect of water, oxygen, and peroxide content, preparative methods, and the activation of samarium metal

Samarium(II) iodide (SmI(2)) is one of the most important reducing agents in organic synthesis. Synthetic chemistry promoted by SmI(2) depends on the efficient and reliable preparation of the reagent. Unfortunately, users can experience difficulties preparing the reagent, and this has prevented realization of the full synthetic potential of SmI(2). To provide synthetic chemists with general and reliable methods for the preparation of SmI(2), a systematic evaluation of the factors involved in its synthesis has been carried out. Our studies confirm that SmI(2) is a user-friendly reagent. Factors such as water, oxygen, and peroxide content in THF have little influence on the synthesis of SmI(2). In addition, the use of specialized glovebox equipment or Schlenk techniques is not required for the preparation of SmI(2). However, our studies suggest that the quality of samarium metal is an important factor and that the use of low quality metal is the main cause of failed preparations of the reagent. Accordingly, we report a straightforward method for activation of "inactive" samarium metal and demonstrate the broad utility of this protocol through the electron transfer reductions of a range of substrates using SmI(2) prepared from otherwise "inactive" metal. An investigation into the stability of SmI(2) solutions and an evaluation of commercially available solutions of the reagent is also reported.