Multi‐Pathway Excited State Relaxation of Adenine Oligomers in Aqueous Solution: A Joint Theoretical and Experimental Study

The singlet excited states of adenine oligomers, model systems widely used for the understanding of the interaction of ultraviolet radiation with DNA, are investigated by fluorescence spectroscopy and time‐dependent (TD) DFT calculations. Fluorescence decays, fluorescence anisotropy decays, and time‐resolved fluorescence spectra are recorded from the femtosecond to the nanosecond timescales for single strand (dA)₂₀ in aqueous solution. These experimental observations and, in particular, the comparison of the fluorescence behavior upon UVC and UVA excitation allow the identification of various types of electronic transitions with different energy and polarization. Calculations performed for up to five stacked 9‐methyladenines, taking into account the solvent, show that different excited states are responsible for the absorption in the UVC and UVA spectral domains. Independently of the number of bases, bright excitons may evolve toward two types of excited dimers having π–π* or charge‐transfer character, each one distinguished by its own geometry and spectroscopic signature. According to the picture arising from the joint experimental and theoretical investigation, UVC‐induced fluorescence contains contribution from 1) exciton states with a different degree of localization, decaying within a few ps, 2) “neutral” excited dimers decaying on the sub‐nanosecond timescale, being the dominant species, and 3) charge‐transfer states decaying on the nanosecond timescale. The majority of the photons emitted upon UVA excitation are related to charge‐transfer states.     

Kinetic Study on Models of the Noncatalyzed Reaction Between α, ω -Dicarboxypolyamide-11 and α, ω -Dihydroxypolyoxyalkylenes

The kinetics of the noncatalyzed reaction between α, ω -dicarboxypoly-amide-11 and α, ω -dihydroxypolyoxyalkylenes is investigated by using the reactions of 11-dodecylamidoundecanoic acid with 1-dodecanol, 2-tridecanol, α-dodecyl-ω-hydroxypolyoxyethylene or α-dodecyl-ω;-hydroxypolyoxypropylene as models. Kinetic data fit a 3rd overall order (2 in acid and 1 in alcohol). Rate constants and activation parameters are determined and compared.     

An Efficient Acylation of Free Glycosylamines for the Synthesis of N-Glycosyl Amino Acids and N-Glycosidic Surfactants for Membrane Studies

Abstract

Treatment of free glycosylamines with 3-acyl-5-methyl-1,3,4-thiadiazole-2 (3H)-thiones 6 or with acids and 5-methyl-2-thioxo-1,3,4-thiadiazole-3(2H)-carbothioic acid S-(5-methyl-1,3,4-thiadiazol-2-yl) ester 7 in hydroorganic media afforded N-acylglycosylamines in high yields and without any competitive deglycosylation. This reaction found applications in the synthesis of N-glycopeptide building blocks and of glycosidic non ionic surfactants. Results concerning surface activities of two N-acylglycosylamines are reported. The new non ionic N-octanoyl-β-D-glucosylamine surfactant exhibited efficacy and selectivity in the extraction of membrane proteins, enhanced the activity of a membrane succinate dehydrogenase and proved thus useful for membrane studies.     

Liquid–liquid miscibility and volumetric properties of aqueous solutions of ionic liquids as a function of temperature

The volumetric properties of seven {water + ionic liquid} binary mixtures have been studied as a function of temperature from (293 to 343) K. The phase behaviour of the systems was first investigated using a nephelometric method and excess molar volumes were calculated from densities measured using an Anton Paar densimeter and fitted using a Redlich–Kister type equation. Two ionic liquids fully miscible with water (1-butyl-3-methylimidazolium tetrafluoroborate ([C₁C₄Im][BF₄]) and 1-ethyl-3-methylimidazolium ethylsulfate ([C₁C₂Im][EtSO₄])) and five ionic liquids only partially miscible with water (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₁C₂Im][NTf₂]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₁C₄Im][NTf₂]), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₁C₄Im][PF₆]), 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C₁C₄Pyrro][NTf₂]), and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N₄₁₁₁][NTf₂])) were chosen. Small excess volumes (less than 0.5 cm³ · mol^?1 at 298 K) are obtained compared with the molar volumes of the pure components (less than 0.3% of the molar volume of the pure ionic liquid). For all the considered systems, except for {[C₁C₂Im][EtSO₄] + water}, positive excess molar volumes were calculated. Finally, an increase of the non-ideality character is observed for all the systems as temperature increases.     

Anionic layered networks reconstructed from [Cd(SCN)3]infinity(-) chains in pseudo one-dimensional conducting salts of halogenated tetrathiafulvalenes

The electrocrystallization of diiodo- and dibromo-ethylenedithiotetrathiafuvalene (EDT-TTFI2 and EDT-TTFBr2) in the presence of the polymeric 1D [Et4N][Cd(SCN)3] as an electrolyte affords two different salts, formulated as [EDT-TTF-I2]4[Cd3(NCS)8] x CH3CN x H2O (1) and [EDT-TTF-Br2]10[Cd5(SCN)14] x 2 TCE (2), characterized by a two-dimensional segregation of the partially oxidized donor molecules and the polymeric anionic network incorporating embedded solvent molecules. Both salts exhibit a partial charge transfer, that is, rho = 0.5 in 1 and an unconventional rho = 0.4 in 2. They behave as semiconductors with sigma RT = 0.67 and 33 S cm(-1) and activation energies of 330 and 370 K for 1 and 2, respectively. Compared with a 1:3 Cd/SCN ratio of the starting electrolyte, the reconstructed, thiocyanate (SCN)-deficient motifs [Cd3(NCS)8](2-) and [Cd5(SCN)14](4-) organize into layered hollow structures with cavities filled by solvent molecules, halogen-bonded to the halogenated TTF molecules, through a C(TTF)-I...N[triple bond]C-CH3 interaction in 1, through a type II C(TTF)-Br...Cl-C(TCE) halogen/halogen interaction in 2. Band structure and Fermi surface calculations for the two salts indicate a two-dimensional character, while the semiconducting properties of the salts are attributed to an efficient nesting of the hidden 1D Fermi surfaces.     

Modulating the framework negative charge density in the system [BDT-TTP*+]/[Re6S5Cl9(1-)]/[Re6(S/Se)6Cl8(2-)]/[Re6S7Cl7(3-)]: templating by isosteric cluster anions of identical symmetry and shape, variations of incommensurate band filling, and electronic structure in 2D metals

A series of 2D metals, beta-(BDT-TTP)6[Re6Se6Cl8] x (CHCl2-CHCl2)2, 2; beta-(ST-TTP)6[Re6S6Cl8] x (CH2Cl-CHCl2)2, 3; beta-(BDT-TTP)7[Re6S6Cl8]0.5[Re6S7Cl7]0.5 x (CH2Cl2), 4; beta-(BDT-TTP)7[Re6Se6Cl8]0.5[Re6S7Cl7]0.5 x (CH2Cl2), 5; beta-(BDT-TTP)8[Re6S7Cl7] x (CH2Cl2)4, 6 (BDT-TTP and ST-TTP are 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene and 2-(1,3-diselenol-2-ylidene)-5(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, respectively) is reported to have one single beta-slab layered topology despite successive increases of the cluster anion negative charge. The charge density within the templating composite inorganic-neutral molecule slab is shown to remain above a threshold of ca. one negative charge per square nanometer, that is, for cluster anions with two negative charges and higher. Conversely, discrete stacks are shown to be stabilized instead in the semiconducting salts (BDT-TTP)2[Re6S5Cl9], 1 where the cluster anion bears one negative charge only. The electronic structure of salts 2-6 is shown to be very stable and kept almost intact across the series. The templating strategy is shown to fulfill its anticipated potential for deliberate installment of incommensurate band fillings in molecular metals. The deliberate admixture of the 6:1 and 8:1 structures yields novel phases with a 7:1 stoichiometry with the anticipated crystal and electronic structures. The action at the organic-inorganic interface triggered by changing the anion charge yet keeping its shape and volume identical, which ultimately governs the shape of the unit cell, is of paramount importance in defining the Fermi surface of these metallic salts. The present BDT-TTP salts thus provide a series of materials with strongly related but subtly different Fermi surfaces worthy of many physical studies. Shubnikov-de Haas measurements are expected to be particularly interesting since they are especially sensitive to the details of the Fermi surface.     

Ultrafast dynamics of acetylacetone (2,4-pentanedione) in the S2 state

The dynamics of the enolic form of acetylacetone (E-AcAc) was investigated using a femtosecond pump-probe experiment. The pump at 266 nm excited E-AcAc in the first bright state, S2(pi pi*). The resulting dynamics was probed by multiphoton ionization at 800 nm. It was investigated for 80 ps on the S2(pi pi*) and S1(n pi*) potential energy surfaces. An important step is the transfer from S2 to S1 that occurs with a time constant of 1.4 +/- 0.2 ps. Before, the system had left the excitation region in 70 +/- 10 fs. An intermediate step was identified when E-AcAc traveled on the S2 surface. Likely, it corresponds to an accidental resonance in the detection scheme that is met along this path. More importantly, some clues are given that an intramolecular vibrational energy relaxation is observed, which transfers excess vibrational energy from the enolic group O-H to the other modes of the molecule. The present multistep evolution of excited E-AcAc probably also describes, at least qualitatively, the dynamics of other electronically excited beta-diketones.     

Synthesis, Conformational Studies, X-ray Structures, and Complexation Properties of Semirigid Macrocyclic Phosphonamides

The semirigid phosphonamide ligands 1-5 have been synthesized from the macrocyclic precursors 6-9 by reaction with 1,3-propanediol ditosylate or 1,2-dichloroethane. For the thiophosphoryl compounds 1 and 2, and the phosphoryl derivative 5, the reactions were carried out in biphasic aqueous NaOH solutions. The phosphoryl derivatives 3 and 4 were better obtained from NaH in anhydrous tetrahydrofuran. The conformations of the hosts in solution were deduced from low-temperature NMR and NOE difference experiments. Conformational equilibria between exo and endo forms are observed for the 18-membered macrocycles 1 and 3. The exo conformer predominates in solution for the 21-membered macrocycle 2, whereas 4 exists as rapidly exchanging conformers. The X-ray crystal structures of macrocycles 1, 2, and 5 have been determined as well as the complexes 1.Hg(SCN)(2) and 5.LiNO(3). In the Hg(2+) complex the metal ion is located out of the macrocyclic cavity and is coordinated to the thiophosphoryl unit. In 5.LiNO(3)()()the Li(+) cation is located inside the macrocyclic cavity and is coordinated to a tetrahedral array of oxygen donors. Free energies of complexation (DeltaG degrees ) of the phosphorylated ligands 3-5 with alkali metal and ammonium cations were determined in CHCl(3) saturated with H(2)O by picrate extraction experiments. The -DeltaG degrees values are greatest for 4 complexing K(+) and NH(4)(+) (7.3 and 8.0 kcal/mol, respectively). The relationships between structure and binding are discussed.     

Synthesis,Crystal Structure and IR Spectra of Complexes of Mn(II) by Indole-2-Carboxylic or Isoquinoline-1-Carboxylic Acids and 1,10-Phenanthroline

Abstract  

Two ternary complexes of manganese(II) indole-2-carboxylate (2-IC⁻) or isoquinolinecarboxylate (IQC⁻) with 1,10-phenanthroline (phen) in methanol or in dimethylacetamide (DMA) were synthesized and studied by X-ray diffraction and IR spectra. [Mn(C₉H₆NO₂)₂(C₁₂H₈N₂)₂]·CH₄O (1) crystallizes in the triclinic space group P-1 with cell parameters of a = 10.548(2) ?, b = 14.168(3) ?, c = 14.580(3) ?, α = 62.35(2)°, β = 69.16(2)°, γ = 78.61(2)°, V = 1802.4(6) ?³ and Z = 2; [Mn(C₁₀H₆NO₂)₂(C₁₂H₈N₂)].C₄H₉NO (2) crystallizes in the monoclinic space group P2₁/a with cell parameters of a = 15.304(5) ?, b = 12.871(5) ?, c = 17.421(5) ?, β = 114.39(1), V = 3125(2) ?³ and Z = 4. In 1, Mn is six-coordinate by two bidentate phen ligands and two 2-IC⁻ ligands and exhibits a very distorted octahedral geometry. This complex is solvated by methanol involved in hydrogen bonding. In 2, Mn atom is surrounded by one bidentate phen ligand and two bidentate IQC⁻ ligands. The complex exhibits a distorted octahedral geometry around the Mn^II atom. The crystal structure is completed by a disordered DMA solvate molecule. The IR spectra of both compounds are slightly different in the range 4000–2400 cm⁻¹ which may be attributed to hydrogen bond lack in 2.     

Embedding of Biological Regulatory Networks and Property Preservation

In the course of understanding biological regulatory networks (BRN), scientists usually start by studying small BRNs that they believe to be of particular importance to represent a biological function, and then, embed them in a larger network. Such a reduction can lead to neglect relevant regulations and to study a network whose properties can be very different from the properties of this network viewed as a part of the whole. In this paper we study, from a logical point of view, on which conditions concerning both networks, properties can be inherited by BRNs from sub-BRNs. We give some conditions on the nature of the network embeddings ensuring that dynamic properties on the embedded sub-BRNs are preserved at the level of the whole BRN.