Intermolecular Clamping by Hydrogen Bonds: 2-Pyridone center dot NH3

A combined spectroscopic and ab initio theoretical study of the doubly hydrogen-bonded complex of 2-pyridone (2PY) with NH3 has been performed. The S-1 <- S-0 spectrum extends up to approximate to 1200 cm(-1) above the 0(0)(0) band, close to twice the range observed for 2PY. The S-1 state nonradiative decay for vibrations above approximate to 300 cm(-1) in the NH3 complex is dramatically slowed down relative to bare 2PY. Also, the Delta v=2,4,... overtone bands of the v(1)' and v(2)' out-of-plane vibrations that dominate the low-energy spectral region of 2PY are much weaker or missing for 2PY center dot NH3, which implies that the bridging (2PY)NH center dot center dot center dot NH3 and H2NH center dot center dot center dot O=C H-bonds clamp the 2PY at a planar geometry in the S-1 state. The mass-resolved UV vibronic spectra of jet-cooled 2PY center dot NH3 and its H/D mixed isotopomers are measured using two-color resonant two-photon ionization spectroscopy. The S-0 and S-1 equilibrium structures and normal-mode frequencies are calculated by density functional (B3LYP) and correlated ab initio methods (MP2 and approximate second-order coupled-cluster, CC2). The S-1 <- S-0 vibronic assignments are based on configuration interaction singles (CIS) and CC2 calculations. A doubly H-bonded bridged structure of C-S symmetry is predicted, in agreement with that of Held and Pratt [J. Am. Chem. Soc. 1993, 115, 9718]. While the B3LYP and MP2 calculated rotational constants are in very good agreement with experiment, the calculated H2NH center dot center dot center dot O=C H-bond distance is approximate to 0.7 angstrom shorter than that derived by Held and Pratt. On the other hand, this underlines their observation that ammonia can act as a strong H-bond donor when built into an H-bonded bridge. The CC2 calculations predict the H2NH center dot center dot center dot O distance to increase by 0.2 angstrom upon S-1 <- S-0 electronic excitation, while the (2PY)NH center dot center dot center dot NH3 H-bond remains nearly unchanged. Thus, the expansion of the doubly H-bonded bridge in the excited state is asymmetric and almost wholly due to the weakening of the interaction of ammonia with the keto acceptor group.

N-H center dot center dot center dot pi hydrogen-bonding and large-amplitude tipping vibrations in jet-cooled pyrrole-benzene

The N-H center dot center dot center dot pi hydrogen bond is an important intermolecular interaction in many biological systems. We have investigated the infrared (IR) and ultraviolet (UV) spectra of the supersonic-jet cooled complex of pyrrole with benzene and benzene-d(6) (Pyr center dot Bz, Pyr center dot Bz-d(6)). DFT-D density functional, SCS-MP2 and SCS-CC2 calculations predict a T-shaped and (almost) C(s) symmetric structure with an N-H center dot center dot center dot pi hydrogen bond to the benzene ring. The pyrrole is tipped by omega(S(0)) = +/- 13 degrees relative to the surface normal of Bz. The N center dot center dot center dot ring distance is 3.13 angstrom. In the S(1) excited state, SCS-CC2 calculations predict an increased tipping angle omega(S(1)) = +/- 21 degrees. The IR depletion spectra support the T-shaped geometry: The NH stretch is redshifted by -59 cm(-1), relative to the "free" NH stretch of pyrrole at 3531 cm(-1), indicating a moderately strong N-H center dot center dot center dot pi interaction. The interaction is weaker than in the (Pyr)(2) dimer, where the NH donor shift is -87 cm(-1) [Dauster et al., Phys. Chem. Chem. Phys., 2008, 10, 2827]. The IR C-H stretch frequencies and intensities of the Bz subunit are very similar to those of the acceptor in the (Bz)(2) dimer, confirming that Bz acts as the acceptor. While the S(1) <- S(0) electronic origin of Bz is forbidden and is not observable in the gas-phase, the UV spectrum of Pyr center dot Bz in the same region exhibits a weak 0(0)(0) band that is red-shifted by 58 cm(-1) relative to that of Bz (38 086 cm(-1)). The origin appears due to symmetry-breaking of the p-electron system of Bz by the asymmetric pyrrole NH center dot center dot center dot pi hydrogen bond. This contrasts with (Bz)(2), which does not exhibit a 0(0)(0) band. The Bz moiety in Pyr center dot Bz exhibits a 6a(0)(1) band at 0(0)(0) + 518 cm(-1) that is about 20x more intense than the origin band. The symmetry breaking by the NH center dot center dot center dot pi hydrogen bond splits the degeneracy of the v(6)(e(2g)) vibration, giving rise to 6a' and 6b' sub-bands that are spaced by similar to 6 cm(-1). Both the 0(0)(0) and 6(0)(1) bands of Pyr center dot Bz carry a progression in the low-frequency (10 cm(-1)) excited-state tipping vibration omega', in agreement with the change of the omega tipping angle predicted by SCS-MP2 and SCS-CC2 calculations.

Highly Efficient IR to NIR Upconversion in Gd2O2S: Er3+ for Photovoltaic Applications

Upconversion (UC) is a promising option to enhance the efficiency of solar cells by conversion of sub-bandgap infrared photons to higher energy photons that can be utilized by the solar cell. The UC quantum yield is a key parameter for a successful application. Here the UC luminescence properties of Er3+-doped Gd2O2S are investigated by means of luminescence spectroscopy, quantum yield measurements, and excited state dynamics experiments. Excitation into the maximum of the 4I15/2 → 4I13/2 Er3+ absorption band around 1500 nm induces very efficient UC emission from different Er3+ excited states with energies above the silicon bandgap, in particular, the emission originating from the 4I11/2 state around 1000 nm. Concentration dependent studies reveal that the highest UC quantum yield is realized for a 10% Er3+-doping concentration. The UC luminescence is compared to the well-known Er3+-doped β-NaYF4 UC material for which the highest UC quantum yield has been reported for 25% Er3+. The UC internal quantum yields were measured in this work for Gd2O2S: 10%Er3+ and β-NaYF4: 25%Er3+ to be 12 ± 1% and 8.9 ± 0.7%, respectively, under monochromatic excitation around 1500 nm at a power of 700 W/m2. The UC quantum yield reported here for Gd2O2S: 10%Er3+ is the highest value achieved so far under monochromatic excitation into the 4I13/2 Er3+ level. Power dependence and lifetime measurements were performed to understand the mechanisms responsible for the efficient UC luminescence. We show that the main process yielding 4I11/2 UC emission is energy transfer UC.

A Pt(II) complex with both a phenanthroline and a tetrathiafulvalene-extended dithiolate ligand: Synthesis, crystal structure, electrochemical and spectroscopic properties

The reaction of 4,5-bis(2'-cyanoethylsulfanyl)-4',5'-dipropylthiotetrathiafulvalene with Pt(phen)Cl-2 (phen = 1,10-phenanthroline) with CsOH as base in CH3OH-THE affords the target complex I in 44% yield. This complex crystallizes in the monoclinic space group P2(1)/c, M = 790.01, a = 12.1732(12), b = 15.851(2), c = 14.5371(16) angstrom, beta = 107.693(12)degrees, V = 2672.4(5) angstrom(3) and Z = 4. It undergoes two reversible single-electron oxidation and two irreversible reduction processes. An intense electronic absorption band at 15200 cm(-1) (658 nm) in CH2Cl2 is assigned to the intramolecular mixed metal/ligand-to-ligand charge transfer (LLCT) from a tetrathiafulvalene-extended dithiolate-based HOMO to a phenanthroline-based LUMO. This band shifts hypsochromically with increasing solvent polarity. Systematic changes in the optical spectra upon oxidation allow precise tuning of the oxidation states of 1 and reversible control over its optical properties. Irradiation of 1 at 15625 cm(-1) (640 nm) in glassy solution below 150K results in emission from the (LLCT)-L-3 excited state. GRAPHICS (C) 2013 Elsevier Ltd. All rights reserved.

Tetrathiafulvalene - Benzothiadiazoles as Redox-Tunable Donor - Acceptor Systems: Synthesis and Photophysical Study

Electrochemical and photophysical analysis of new donoracceptor systems 2 and 3, in which a benzothiadiazole (BTD) unit is covalently linked to a tetrathiafulvalene (TTF) core, have verified that the lowest excited state can be ascribed to an intramolecular-charge-transfer (ICT) (TTF)*(benzothiadiazole) transition. Owing to better overlap of the HOMO and LUMO in the fused scaffold of compound 3, the intensity of the 1ICT band is substantially higher compared to that in compound 2. The corresponding CT fluorescence is also observed in both cases. The radical cation TTF+. is easily observed through chemical and electrochemical oxidation by performing steady-state absorption experiments. Interestingly, compound 2 is photo-oxidized under aerobic conditions.

Optical and scintillation properties of CsBa2I5:Eu2+

The scintillation and luminescence properties of pure CsBa2I5 and CsBa2I5 doped with 0.5% Eu and 5% Eu were studied between 78 K and 600 K. Single crystals were grown by the vertical Bridgman method from the melt. CsBa2I5:5% Eu showed a light yield of 80,000 photons/MeV, an energy resolution of 2.3% for the 662 key full absorption peak, and an excellent proportional response. Two broad emission bands centered at 400 nm and 600 nm were observed in the radioluminescence spectrum of pure CsBa2I5. The Eu2+ 5d-4f emission band was observed at 430 nm. The radiative lifetime of the Eu2+ excited state was determined as 350 ns. With increasing temperature and Eu concentration the Eu2+ emission shifts to longer wavelengths and its decay time lengthens as a result of self-absorption of the Eu2+ emission. Multiple thermoluminescence glow peaks and a sharp decrease of the light yield at temperatures below 200 K were observed and related to the presence of the charge carrier traps in CsBa2I5:Eu.

Energy and charge transfer dynamics in DNA based light harvesting antennae

DNA can serve as a versatile scaffold for chromophore assemblies. For example, light-harvesting antennae have been realized by incorporating phenanthrene and pyrene building blocks into DNA strands. It was shown that by exciting at 320 nm (absorption of phenanthrene), an emission at 450 nm is observed which corresponds to a phenanthrene-pyrene exciplex. The more phenanthrenes are added into the DNA duplex, the higher is the fluorescence intensity with no significant change in quantum yield. This shows that phenanthrene acts as a donor and efficiently transfers the excitation energy to the pyrene. Up to now, the mechanism of this energy transfer and exciplex formation is not known. Therefore, we first aim at studying the photo-cycle of such DNA assemblies through transient absorption spectroscopy. Based on the results, we will explore ways to manipulate the energy transfer by application of intense THz fields. Ground as well as excited state Stark effect dynamics will be investigated.

Experimental and Calculated Spectra of π-Stacked Mild Charge-Transfer Complexes: Jet-Cooled Perylene·(Tetrachloroethene) n , n = 1,2

The S0 ↔ S1 spectra of the mild charge-transfer (CT) complexes perylene·tetrachloroethene (P·4ClE) and perylene·(tetrachloroethene)2 (P·(4ClE)2) are investigated by two-color resonant two-photon ionization (2C-R2PI) and dispersed fluorescence spectroscopy in supersonic jets. The S0 → S1 vibrationless transitions of P·4ClE and P·(4ClE)2 are shifted by δν = −451 and −858 cm–1 relative to perylene, translating to excited-state dissociation energy increases of 5.4 and 10.3 kJ/mol, respectively. The red shift is ∼30% larger than that of perylene·trans-1,2-dichloroethene; therefore, the increase in chlorination increases the excited-state stabilization and CT character of the interaction, but the electronic excitation remains largely confined to the perylene moiety. The 2C-R2PI and fluorescence spectra of P·4ClE exhibit strong progressions in the perylene intramolecular twist (1au) vibration (42 cm–1 in S0 and 55 cm–1 in S1), signaling that perylene deforms along its twist coordinate upon electronic excitation. The intermolecular stretching (Tz) and internal rotation (Rc) vibrations are weak; therefore, the P·4ClE intermolecular potential energy surface (IPES) changes little during the S0 ↔ S1 transition. The minimum-energy structures and inter- and intramolecular vibrational frequencies of P·4ClE and P·(4ClE)2 are calculated with the dispersion-corrected density functional theory (DFT) methods B97-D3, ωB97X-D, M06, and M06-2X and the spin-consistent-scaled (SCS) variant of the approximate second-order coupled-cluster method, SCS-CC2. All methods predict the global minima to be π-stacked centered coplanar structures with the long axis of tetrachloroethene rotated by τ ≈ 60° relative to the perylene long axis. The calculated binding energies are in the range of −D0 = 28–35 kJ/mol. A second minimum is predicted with τ ≈ 25°, with ∼1 kJ/mol smaller binding energy. Although both monomers are achiral, both the P·4ClE and P·(4ClE)2 complexes are chiral. The best agreement for adiabatic excitation energies and vibrational frequencies is observed for the ωB97X-D and M06-2X DFT methods.

Empowering Interactions. Political Cultures and the Emergence of the State. in Europe 1300-1900

The emergence of the state in Europe is a topic that has engaged historians since the establishment of the discipline of history. Yet the primary focus of has nearly always been to take a top-down approach, whereby the formation and consolidation of public institutions is viewed as the outcome of activities by princes and other social elites. Yet, as the essays in this collection show, such an approach does not provide a complete picture. By investigating the importance of local and individual initiatives that contributed to state building from the late middle ages through to the nineteenth century, this volume shows how popular pressure could influence those in power to develop new institutional structures. By not privileging the role of warfare and of elite coercion for state building, it is possible to question the traditional top-down model and explore the degree to which central agencies might have been more important for state representation than for state practice. The studies included in this collection treat many parts of Europe and deal with different phases in the period between the late middle ages and the nineteenth century. Beginning with a critical review of state historiography, the introduction then sets out the concept of 'empowering interactions' which is then explored in the subsequent case studies and a number of historiographical, methodological and theoretical essays. Taken as a whole this collection provides a fascinating platform to reconsider the relationships between top-down and bottom-up processes in the history of the European state.

Observation of an Excited B±c Meson State with the ATLAS Detector

A search for excited states of the B ± c meson is performed using 4.9  fb −1 of 7 TeV and 19.2  fb −1 of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decay B ± c →J/ψπ ± . The state appears in the m(B ± c π + π − )−m(B ± c )−2m(π ± ) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842±4±5  MeV , where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S -wave state of the B ± c meson, B ± c (2S) .

Measurement of charged-particle event shape variables in inclusive √(s)=7 TeV proton-proton interactions with the ATLAS detector

The measurement of charged-particle event shape variables is presented in inclusive inelastic pp collisions at a center-of-mass energy of 7 TeV using the ATLAS detector at the LHC. The observables studied are the transverse thrust, thrust minor, and transverse sphericity, each defined using the final-state charged particles' momentum components perpendicular to the beam direction. Events with at least six charged particles are selected by a minimum-bias trigger. In addition to the differential distributions, the evolution of each event shape variable as a function of the leading charged-particle transverse momentum, charged-particle multiplicity, and summed transverse momentum is presented. Predictions from several Monte Carlo models show significant deviations from data.

Direct adipotropic actions of atorvastatin: differentiation state-dependent induction of apoptosis, modulation of endocrine function, and inhibition of glucose uptake

Statins exert anti-inflammatory, anti-atherogenic actions. The mechanisms responsible for these effects remain only partially elucidated. Diabetes and obesity are characterized by low-grade inflammation. Metabolic and endocrine adipocyte dysfunction is known to play a crucial role in the development of these disorders and the related cardiovascular complications. Thus, direct modulation of adipocyte function may represent a mechanism of pleiotropic statin actions. We investigated effects of atorvastatin on apoptosis, differentiation, endocrine, and metabolic functions in murine white and brown adipocyte lines. Direct exposure of differentiating preadipocytes to atorvastatin strongly reduced lipid accumulation and diminished protein expression of the differentiation marker CCAAT/enhancer binding protein-beta (CEBP-beta). In fully differentiated adipocytes, however, lipid accumulation remained unchanged after chronic atorvastatin treatment. Furthermore, cell viability was reduced in response to atorvastatin treatment in proliferating and differentiating preadipocytes, but not in differentiated cells. Moreover, atorvastatin induced apoptosis and inhibited protein kinase B (AKT) phosphorylation in proliferating and differentiating preadipocytes, but not in differentiated adipocytes. On the endocrine level, direct atorvastatin treatment of differentiated white adipocytes enhanced expression of the pro-inflammatory adipokine interleukin-6 (IL-6), and downregulated expression of the insulin-mimetic and anti-inflammatory adipokines visfatin and adiponectin. Finally, these direct adipotropic endocrine effects of atorvastatin were paralleled by the acute inhibition of insulin-induced glucose uptake in differentiated white adipocytes, while protein expression of the thermogenic uncoupling protein-1 (UCP-1) in brown adipocytes remained unchanged. Taken together, our data for the first time demonstrate direct differentiation state-dependent effects of atorvastatin including apoptosis, modulation of pro-inflammatory and glucostatic adipokine expression, and insulin resistance in adipose cells. These differential interactions may explain variable clinical observations.

Hypnotic and opioid anesthetic drug interactions on the CNS, focus on response surface modeling

This chapter will present the conceptual and applied approaches to capture the interaction of anesthetic hypnotic drugs with opioid drugs, as used in the clinical anesthetic state. The graphic and mathematical approaches used to capture hypnotic/opiate anesthetic drug interactions will be presented. This chapter is not a review article about interaction modeling, but focuses on specific drug interactions within a quite narrow field, anesthesia.

Crystal structure of the yeast eIF4A-eIF4G complex: an RNA-helicase controlled by protein-protein interactions

Translation initiation factors eIF4A and eIF4G form, together with the cap-binding factor eIF4E, the eIF4F complex, which is crucial for recruiting the small ribosomal subunit to the mRNA 5' end and for subsequent scanning and searching for the start codon. eIF4A is an ATP-dependent RNA helicase whose activity is stimulated by binding to eIF4G. We report here the structure of the complex formed by yeast eIF4G's middle domain and full-length eIF4A at 2.6-A resolution. eIF4A shows an extended conformation where eIF4G holds its crucial DEAD-box sequence motifs in a productive conformation, thus explaining the stimulation of eIF4A's activity. A hitherto undescribed interaction involves the amino acid Trp-579 of eIF4G. Mutation to alanine results in decreased binding to eIF4A and a temperature-sensitive phenotype of yeast cells that carry a Trp579Ala mutation as its sole source for eIF4G. Conformational changes between eIF4A's closed and open state provide a model for its RNA-helicase activity.