Large Negative Shift Research Articles

Reflective vertical cavity quantum-well saturable absorber as an all-optical nonlinear phase-shifting element

A scheme of an all-optical nonlinear phase-shifting element is proposed, based on a reflective vertical cavity semiconductor (quantum-well) saturable absorber (R-VCSSA). The nonlinear round-trip phase shift in a low-intensity resonant VCSSA is obtained at an input intensity due to the saturating nonlinearity in index change and optically induced thermal effects. An enhanced large nonlinear positive or negative phase shift incurred in a reflected signal is investigated analytically with the wavelength tuning of the probe signal around the low-intensity resonant wavelength of a Fabry–Perot cavity. The device may be useful in compensating the phase of an input signal, either positive or negative, in long-haul fiber communications. A representative InGaAs/InP quantum-well-based VCSSA is considered to demonstrate the phase shift in the pump–probe configuration. With a device speed of 10 GHz, maximum phase shifts of −0.24 and +0.14  rad at pump power of 19.2 mW are observed for the operations at probe wavelengths of 1555.6 and 1557.8 nm, respectively.

Regulation of BK channels by auxiliary γ subunits.

The large-conductance, calcium- and voltage-activated potassium (BK) channel has the largest single-channel conductance among potassium channels and can be activated by both membrane depolarization and increases in intracellular calcium concentration. BK channels consist of pore-forming, voltage- and calcium-sensing α subunits, either alone or in association with regulatory subunits. BK channels are widely expressed in various tissues and cells including both excitable and non-excitable cells and display diverse biophysical and pharmacological characteristics. This diversity can be explained in part by posttranslational modifications and alternative splicing of the α subunit, which is encoded by a single gene, KCNMA1, as well as by tissue-specific β subunit modulation. Recently, a leucine-rich repeat-containing membrane protein, LRRC26, was found to interact with BK channels and cause an unprecedented large negative shift (~-140 mV) in the voltage dependence of the BK channel activation. LRRC26 allows BK channels to open even at near-physiological calcium concentration and membrane voltage in non-excitable cells. Three LRRC26-related proteins, LRRC52, LRRC55, and LRRC38, were subsequently identified as BK channel modulators. These LRRC proteins are structurally and functionally distinct from the BK channel β subunits and were designated as γ subunits. The discovery of the γ subunits adds a new dimension to BK channel regulation and improves our understanding of the physiological functions of BK channels in various tissues and cell types. Unlike BK channel β subunits, which have been intensively investigated both mechanistically and physiologically, our understanding of the γ subunits is very limited at this stage. This article reviews the structure, modulatory mechanisms, physiological relevance, and potential therapeutic implications of γ subunits as they are currently understood.

Total ionizing dose response of fluorine implanted Silicon-On-Insulator buried oxide

A comparison is made of the behavior of silicon on insulator buried oxides and wet thermal oxides before and after fluorine implantation and irradiation. Before irradiation, the electrical characteristics of the thermal oxide and buried oxide are significantly different. The fluorine implantation in the smart-cut® buried oxide results in a large negative threshold shift due to the trapping of positive charges. These charges are associated with positively charged fluorine ions on implantation and are trapped at pre-existing trap sites, particularly at the bonding interface, and at additional defects caused by the ion implantation damage. This shift is absent in the wet thermal oxide. After Co60 irradiation up to 500Krad(Si), the negative flatband and threshold voltage shift in the fluorine implanted buried oxide is larger than in the unimplanted buried oxide indicating that any potential positive effect of fluorine on the passivation of interface states is more than offset by the additional trapping sites created during implantation. These results demonstrate that in the design of a transistor utmost care must be taken to prevent any fluorine being implanted into the buried oxide.

A new dinuclear ferrocene with amide–thiourea binding sites for dual electrochemical sensing to Hg(II) and anions

A new dinuclear ferrocene-base receptor bearing amide and thiourea binding sites, 1, was prepared and characterized by X-ray crystal structure analysis. This receptor shows a dual electrochemical sensing to Hg(II) and anions. Upon the addition of Hg(II), its redox potential shows a positive shift for the mercury-promoted intramolecular cyclic guanylation mechanism. In addition, 1 also shows distinctive electrochemical sensing to H2PO4− over other anions with a large negative shift of its redox potential for N–H…anion hydrogen bond interaction between anion and 1.

Tuning of Metal–Metal Interactions in Mixed-Valence States of Cyclometalated Dinuclear Ruthenium and Osmium Complexes Bearing Tetrapyridylpyrazine or -benzene

New dinuclear ruthenium or osmium complexes with cyclometalated bonds in either tridentate bridging (BL) or ancillary ligands (L), [(L)M(BL)M(L)] (where M = Ru, Os; L = bis(N-methylbenzimidazolyl)pyridine, -benzene; BL= tetrapyridylpyrazine (tppz), -benzene (tpb)), were synthesized, and their mixed-valence-state characteristics were investigated. All of the complexes showed successive one-electron redox processes, each of which correspond to M(II/III) (M = Ru, Os) or ligand reduction waves. In addition, an M(III/IV) couple was observed in cyclometalated [M2(bis(benzimidazolyl)benzene)2(BL)] complexes (M = Ru, Os). Effects of the cyclometalated bonds on the redox behaviors and the accessibility to the mixed-valence M(II)–M(III) dinuclear complexes are discussed. Introduction of a cyclometalated bond induced a large negative potential shift in the redox potentials of dinuclear ruthenium and osmium complexes, depending on either bridging or ancillary sites of the cyclometalated bonds: the change falls within...

Nonlinear-Optical Properties of α-Diiminedithiolatonickel(II) Complexes Enhanced by Electron-Withdrawing Carboxyl Groups

We report the synthesis, characterization, nonlinear-optical (NLO) properties, and density functional theory (DFT) calculations for three nickel diiminedithiolate complexes [Ni(4,4'-R2carboxy-bpy)(L)] [R = methyl, L = 1,2-benzenedithiolate (bdt), 1; R = ethyl, L = 5,6-dihydro-1,4-dithine-2,3-dithiolate (dddt), 2; R = ethyl, L = 1-(N-methylindol-5-yl)ethene-1,2-dithiolate (mi-5edt), 3]. The crystal structure of 1 shows a square-planar coordination for the nickel ion and bond distances consistent with a diiminedithiolate description for the complex. For all complexes, the cyclic voltammetry measurements show two reversible reduction processes (-1.353/-1.380 V and -0798/-0.830 V, respectively) and an anodic wave (+0.372/+0.601 V). The UV-vis spectra present a band around 600-700 nm (ε = 4880-6000 dm(3) mol(-1) cm(-1)) mainly attributed to a charge-transfer highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) transition, which shows a large negative solvatochromic shift, characteristic of push-pull complexes, and is responsible for the NLO properties of these molecules. The charge-transfer character of this electronic transition is confirmed by DFT calculations, with the HOMO mainly centered on the dithiolate moiety and the LUMO on the bpy ligand, with important contribution given by the carboxyl groups (≈13%). Small contributions from the nickel(II) ion are present in both of the frontier orbitals. The carboxyl groups enhance the optical properties of this class of complexes, confirmed by comparison with the corresponding unsubstituted compounds. The second-order NLO properties have been measured by an electric-field-induced second-harmonic-generation technique using a 10(-3) M solution in N,N-dimethylformamide and working with a 1.907 μm incident wavelength, giving for μβ1.907 (μβ0) values of -1095 (-581), -2760 (-954), and -1650 (-618) × 10(-48) esu for 1-3, respectively. These values are among the highest in the class of square-planar push-pull complexes, similar to those found for dithionedithiolate compounds. Moreover, spectroelectrochemical experiments demonstrate the possibility of using these complexes as redox-switchable NLO chromophores.

Effect of H-Bonding on the Electrochemistry of a p-Phenylenediamine-Based Urea. Competition Between Another Urea and a Cyclic Diamide Guest

In previous work done by our group, we reported the observation of strong oxidation-based redox dependent hydrogen bonding between an electroactive urea 1-phenyl-3-(p-N,N-dimethylaminophenyl)urea U(H)H and a cyclic diamide 1,4-dimethylpiperizine-2,3-dione (PZD) in methylene chloride.1Large negative shifts in the apparent, reversible one electron oxidation of U(H)H are observed upon addition of PZD, consistent with strong H-bonding of PZD to the radical cation of U(H)H.However, with further study of U(H)H and similar molecules, it is clear that the electrochemistry and the mechanism is not as straightforward as once believed. Instead of undergoing a simple one electron oxidation, a variety of data now suggests that U(H)H actually undergoes a two electron oxidation to the quinoidal form with transfer of a proton to another U(H)H, which deactivates the second U(H)H. Thus the overall process corresponds to one electron per urea. Because acetonitrile is more polar than methylene chloride, it can better solvate the quinoidal urea and the protonated, unoxidized urea to prevent them from hydrogen bonding to each other. In contrast, stronger H-bonding between the quinoidal urea and the protonated, unoxidized urea is expected in the less polar solvent, methylene chloride and we believe this is what facilitates the observed reversible electrochemistry.In the current study we are re-investigating the addition of PZD to U(H)H in light of our better understanding of the electrochemistry of U(H)H by itself. According to our new NMR titration data, PZD is H-bonded to U(H)H even without oxidation, which is consistent with our previous study. The binding constants, K, measured in different electrolyte solutions between PZD and U(H)H show that there is an electrolyte effect. In the NMR titration experiment without electrolyte, due to the solvent effect, PZD is more strongly H-bonded to U(H)H in the less polar solvent CH2Cl2 than in CH3CN (K in CH2Cl2 = 60.4 M− 1and K in CH3CN = 17.8 M− 1). With a large anion electrolyte, NBu4B(C6F5)4 in CH2Cl2 , the binding constant is greater (K = 95.9 M− 1) than with a small anion electrolyte, NBu4PF6 in CH2Cl2 (K = 48.6 M− 1). This is consistent with the larger potential shift observed with the addition of PZD in NBu4B(C6F5)4 in CH2Cl2 solution relative to NBu4PF6 in CH2Cl2. This suggests that the smaller PF6−ion may be competing with PZD for the binding site.Re-examination of the cyclic voltammetry of U(H)H suggests the same overall reaction, 2e− oxidation of half the urea with proton transfer to the other half, is occurring with or without PZD present. However, the peak potentials are affected by the presence of PZD indicating the overall reaction is facilitated by PZD.1. Jessica E. Woods, Yu Ge, and Diane K. Smith, Journal of the American Chemical Society 2008 130 (31), 10070-10071.

The ‘funny’ side of sepsis

The ‘funny’ current (If) of pacemaker cells is the main membrane mechanism generating the diastolic depolarization, the phase of the action potential responsible for cardiac spontaneous activity. If is also responsible for heart rate (HR) modulation by the autonomic nervous system (DiFrancesco, 2010). In the heart, both during development and in adulthood, the kinetic properties and expression levels of If match the need of the cells to perform pacemaker activity. While at immature stages of embryonic development all cardiomyocytes are autorhythmic and express a robust If current activated within the physiological range of voltages, shortly after birth the pacemaker activity and If expression become restricted to cells of the conduction system only, while in the working myocardium the current is downregulated and its activation is shifted to more negative, non-physiological voltages (DiFrancesco, 2010). The characteristics of native If are the results of a complex interplay of different factors. The kinetic properties and expression levels of the f-channels, encoded by the HCN genes (HCN1–4), are finely regulated by auxiliary proteins (caveolin-3, MiRP-1, KCR-1, SAP97, TRP8) and lipids (phosphatidylinositol 4,5-bisphosphate) and also by post-translational modifications (phosphorylation and glycosylation). Any alteration of these regulatory pathways may modify the contribution of If to the action potential and become arrhythmogenic (Baruscotti et al. 2010). It is known that lipopolysaccharides (LPS) released from Gram-negative bacteria during severe sepsis reduce both native If and HCN2-or HCN4-mediated currents and shift their activation to more negative potentials. However, the basic mechanism involved was still unexplored. In this issue of The Journal of Physiology, Klockner et al. have elucidated molecular aspects of the process underlying such modulation (Klockner et al. 2014). Using the cell-attached configuration of the patch-clamp technique, Klockner et al. have shown that the LPS effect is not mediated by any of the intracellular modulatory pathways affecting HCN channels, but is instead due to a direct interaction with the channel. Klockner et al. have also shown that alterations of HCN current require the integrity of the LPS molecule, since neither the pro-inflammatory lipid A alone nor the O-chain polysaccharidic region alone are effective (Klockner et al. 2014). The effect of LPS on HCN currents has some unusual features and may represent a novel channel modulatory mechanism. While the decrease of current amplitude may simply reflect a direct blocking action on the channel pore, the large (∼20 mV) negative shift of the activation curve implies an interaction with the voltage sensor or at least a distortion of the electrical field sensed by the voltage sensor. Another unusual feature of LPS action is that the HCN channel voltage dependence is modified by an extracellular agent. The extracellular action of LPS is confirmed by experiments showing that HCN channel glycosylation partly prevents LPS action, while de-glycosylation of HCN channels significantly amplifies it (Klockner et al. 2014). Further specific experiments will be required to more fully clarify the details of LPS action on the channel structure. HR and heart rate variability (HRV), the beat-to-beat change of the duration of the R–R interval, are important indicators of cardiovascular conditions, and it is well established that low HR and high HRV are associated with a lower risk of life-threatening cardiac events (Papaioannou et al. 2013). Two components affect HR and HRV: the balance between the sympathetic and parasympathetic outputs, and intrinsic cellular factors (Papaioannou et al. 2013). Because of its involvement in the generation of the heartbeat and HR modulation, the contribution of the funny current may be especially relevant to HRV. It is known for example that supplementation with fish oil (rich in ω-3 polyunsaturated fatty acids (ω-3 PUFAs)) decreases HR, an effect attributable to a reduced If current, and increases HRV (Billman, 2013). Also, the ivabradine-induced pharmacological blockade of If induces a HR reduction and a HRV increase (DiFrancesco & Camm, 2004; Papaioannou et al. 2013). During sepsis, If is specifically decreased by LPS but HRV is decreased too, rather than increased. This atypical behaviour can be explained since as well as inhibiting If, LPS also have a stimulating effect on sympathetic output. In the presence of LPS, the If current is essentially fully inhibited, since although the LPS-induced decrease of If conductance is quantitatively similar to that produced by ω-3 PUFAs or by ivabradine (about 30%), the concurrent hyperpolarizing shift in the voltage dependence effectively zeroes its contribution. An increased sympathetic drive and a concurrent abolishment of the If-mediated rate control narrow the range of physiological rate modulation and are likely to make the system more susceptible to failure under stressful conditions. In summary, the work of Klockner et al. indicates that LPS release during sepsis can modify the If properties by shifting them out of their physiological range, which may impair normal rate control and decrease the cardiac safety factor, making the system more prone to life-threatening perturbations.

4H-SiC MISFETs With 4H-AlN Gate Insulator Isopolytypically Grown on 4H-SiC $(11\bar{2}0)$

4H silicon carbide (4H-SiC) metal-insulator- semiconductor field-effect transistors (MISFETs) with 4H aluminum nitride (4H-AlN) gate insulators have been demonstrated. The 4H-AlN layers are isopolytypically grown on 4H-SiC (1120) by molecular-beam epitaxy. Gate controlled transistor operation was realized using the AlN/SiC MISFETs. The MISFETs exhibit a low gate leakage current (<;10-10 A) and normally ON characteristics with a threshold voltage of approximately -10 V and a field-effect mobility of 0.5 cm2V-1s-1. Capacitance-voltage measurements of AlN/SiC MIS capacitors reveal a large negative flat band shift of -10.9 V, which is consistent with the normally ON characteristics.

Screening of Novel Modulators for BKCa Channel by the Cell-Based Assay Platform Employing A Hyperactive Mutant Channel

Development of a cell-based functional assay for large-conductance calcium-activated potassium (BKCa) channels has been challenging due to its unique requirement of membrane depolarization and intracellular Ca2+ increase for channel activation. We recently developed a novel cell-based assay system utilizing a hyperactive mutant BKCa channel. The mutant channel was generated by introducing two point-mutations into the cytosolic flexible interface between the two RCK domains of the wild-type BKCa channel. The mutant channel exhibited a large negative shift in its conductance-voltage relationship, which indicates activation by modest depolarization at resting concentrations of intracellular Ca2+. When tested in a commercially available K+ channel assay, cell-lines stably expressing the hyperactive BKCa channel generated a strong fluorescence signal under conditions that are typical for voltage-gated K+ channels. By screening over 2,000 compounds in the libraries of chemical and natural products, we were able to obtain several new BKCa channel modulators either potentiating or inhibiting the channel activity. We are currently investigating the mechanism of action for these compounds using electrophysiological means. Thus, our new cell-based assay platform can be used efficiently to screen novel modulators of BKCa channels in a high-throughput manner.∗ This work was supported by grants for the National Leading Research Laboratories [2011-0028665] and the Science Research Center of Excellence Program [2007-0056157] of National Research Foundation of Korea.

5,6-EET potently inhibits T-type calcium channels: implication in the regulation of the vascular tone

T-type calcium channels (T-channels) are important actors in neuronal pacemaking, in heart rhythm, and in the control of the vascular tone. T-channels are regulated by several endogenous lipids including the primary eicosanoid arachidonic acid (AA), which display an important role in vasodilation via its metabolism leading to prostanoids, leukotrienes, and epoxyeicosatrienoic acids (EETs). However, the effects of these latter molecules on T-currents have not been investigated. Here, we describe the effects of the major cyclooxygenase, lipoxygenase, and cytochrome P450 epoxygenase products on the three human recombinant T-channels (Cav3.1, Cav3.2, and Cav3.3), as compared to those of AA. We identified the P450 epoxygenase product, 5,6-EET, as a potent physiological inhibitor of Cav3 currents. The effects of 5,6-EET were observed at sub-micromolar concentrations (IC50 = 0.54μM), occurred in the minute range, and were reversible. The 5,6-EET inhibited the Cav3 currents at physiological resting membrane potentials mostly by inducing a large negative shift in their steady-state inactivation properties. Using knockout mice for Cav3.1 and Cav3.2, we demonstrated that the vasodilation of preconstricted mesenteric arteries induced by 5,6-EET was specifically impaired in Cav3.2 knockout mice. Overall, our results indicate that inhibition of Cav3 currents by 5,6-EET is an important mechanism controlling the vascular tone.

Amplitude control of the Goos–Hänchen shift via a Kerr nonlinearity

The influence of the Kerr nonlinearity on the group index of a dispersive intracavity medium is revisited using a Raman gain based scheme to obtain amplitude control of the Goos–Hänchen (GH) shift in the reflected light. The intracavity medium exhibits a Raman gain process which is accompanied by anomalous dispersion, i.e., superluminal pulse propagation (Dogariu et al 2000 Nature 406 277). In the presence of a Kerr field, the gain–dispersion properties of the intracavity medium are modified, which leads to enhancement in the positive and negative group indices of the medium. The behavior of the GH shift in the reflected light due to the enhancement in the group indices in the presence of the Kerr field is investigated, and relatively large positive and negative GH shifts can be obtained.

Nonlocal optical effects on the Goos–Hänchen shift at an interface of a composite material of metallic nanoparticles

We present a theoretical study on the nonlocal optical effects on the Goos-Hänchen (GH) shift of reflected light from a composite material of metallic nanoparticles (MNPs). Using different nonlocal effective medium models, it is observed that such effects can be significant for small MNP of sizes down to a few nanometers. For small metallic volume fractions, the composite behaves like dielectric and the nonlocal effects lead to significant different Brewster angles, at which large negative GH shifts take place. For larger volume fractions or shorter wavelengths, the composite behaves more like metals and the nonlocal effects also lead to different Brewster angles but at values close to grazing incidence. These results will have significant implications in the application of different effective medium models for the characterization of these nanometallic composites when the MNPs are down to a few nanometers in size.

Development of cell-based assay system that utilizes a hyperactive channel mutant for high-throughput screening of BKCa channel modulators

Development of a cell-based functional assay for large-conductance calcium-activated potassium (BKCa) channels is challenging because of the unique requirement of both voltage and high concentrations of Ca2+ for activation of these channels. Here, we describe a new cell-based assay system that utilizes a hyperactive mutant BKCa channel. The hyperactive mutant was generated by introducing two point-mutations into the cytosolic flexible interface between the two RCK domains of the wild-type BKCa channel. The mutant channel exhibited a large negative shift in its conductance–voltage relationship, which indicates activation by modest depolarization at resting concentrations of intracellular Ca2+. Unlike the wild-type BKCa channel, the hyperactive mutant did not require a concomitant increase of intracellular Ca2+ for activation. Despite the observed shift in its voltage activation profile, activity of the mutant channel was further potentiated by a known BKCa channel activator. When tested in a commercially available cell-based K+ channel assay, cell-lines stably expressing the hyperactive BKCa channel generated a strong fluorescence signal under conditions that are typical for voltage-gated K+ channels. In summary, cell-lines expressing the hyperactive mutant BKCa channel represent a new cell-based assay system for investigation of BKCa channels that can be used to screen for novel modulators of these channels.

Development of an innovative microcantilever-based biosensor for 17β-estradiol detection in bovine muscles: preliminary results

17&beta;-estradiol is the most powerful substance with estrogenic effect, commonly used as illegal growth promoter in livestock production. To avoid health risks for consumers, sensitive, reliable and low-cost methods for quantification of extremely low concentrations of such carcinogenic residues in food are needed. Antibody-immobilised microcantilever resonators were proposed as innovative biosensors able to quantify an adsorbed target mass thanks to a shift in resonance frequency. Furthermore, the quantification of masses on the order of few picograms has recently shown to be successfully achievable with very high precision. In this study, we analysed the performance of our microcantilever sensors using extracted samples of bovine muscle from experimental animals, containing variable concentrations of 17&beta;-estradiol (HPLC-MS/MS tested). Preliminary data showed that treated animals are correctly revealed, exhibiting large negative frequency shifts. More experiments, though, are needed to obtain a correct quantification of 17&beta;-estradiol concentration.

Stable isotope paleoecology of White River ungulates during the Eocene–Oligocene climate transition in northwestern Nebraska

We use the carbon and oxygen stable isotope content of mammalian tooth enamel to evaluate ancient biomes, habitat partitioning, and water use among 12 ungulate taxa from the White River Group in Nebraska. The White River Group spans an interval of climate change from the upper Eocene to the lower Oligocene when global climate cooled in a heterogeneous fashion. We test whether changes in biome structure or mammalian ecology occurred during this interval. We find that mean δ13C values for both Eocene and Oligocene faunas are consistent with dry, open biomes (e.g., woodland-savanna or woody scrubland). A significant increase in mean faunal δ13C values (+0.4‰) occurs in the lower Oligocene, primarily from the loss of individuals feeding in wetter–denser parts of the ecosystem. In the upper Eocene, Megacerops sp. (brontothere) and Perchoerus probus (peccary) have low mean δ13C values consistent with feeding in wetter, denser habitats (presumably riparian), whereas significantly higher mean values in the cursorial horse, Mesohippus spp., and the clawed oreodont, Agriochoerus antiquus, are consistent with feeding in more open, drier habitats. The extinctions of Megacerops sp. and Trigonias sp., a rhinocerotid with relatively low δ13C values, along with a decrease in the abundance of P. probus and other taxa, suggests reduction in the extent of wet habitats in the Oligocene. The rare tapir Colodon sp. is the only taxon sampled with a mean δ13C value low enough to indicate consistent feeding in a wet habitat in the Oligocene. However, range-through taxa occupy the same relative positions in isotopic space in both the Eocene and Oligocene faunas suggesting stability in drier habitats. A significant increase also occurs in mean faunal δ18O values (+1.0‰) in the Oligocene, primarily from the loss or reduction in abundance of water dependent species. Variance in δ18O values increases significantly in the Oligocene, which is consistent with greater water stress in plants from drier conditions. Oxygen values increase in A. antiquus (+0.9‰), the most aridity-sensitive species in both faunas, as expected for drier conditions, but values in another aridity-sensitive taxon (Mesohippus spp.) are virtually unchanged. Together, δ13C and δ18O enamel values generally suggest a shift to drier conditions in the early Oligocene although δ13C values yielded more consistent results. The lack of a large negative shift in δ18O values, expected with a decrease in mean annual temperature, suggests that any temperature changes in the early Oligocene were relatively small in the continental interior of North America.

Goos-Hänchen shift of self-collimated beam in Kretschmann configuration based on photonic crystal

We perform the finite-difference time-domain (FDTD) simulations and analyze a dual-beam-reflection phenomenon for a Gaussian beam illuminating a Kretschmann configuration composed of a lossless dielectric waveguide between a photonic-crystal-made prism and air. One reflection beam has a small positive shift and the other has a large negative shift in the dual-beam-reflection phenomenon. The FDTD shows that the specific phenomenon takes place just when the corresponding leaky surface mode supported in the Kretschmann configuration is excited. Field profile of the surface mode demonstrates a strong localized stationary field in the dielectric waveguide. We find that the maximum negative lateral shift is -23.23a, corresponding to 4.99 times of the incident wavelength, which is 1.1615 times of the beam waist.

Stable carbon isotopes of invertebrate remains: do they reveal past methane release from lakes?

Lakes are a source of methane, an important greenhouse gas in the atmosphere. In order to understand increasing methane emissions in the present, it is important to study the variations of methane release during past periods of climate change. However, records of methane release from lakes over time scales longer than a few years are extremely rare. In this thesis a method is explored to reconstruct past methane availability in lakes based on the stable carbon isotope composition (delta 13C) of aquatic invertebrate remains. Methane-derived 13C-depleted carbon can be an alternative carbon source to plant-derived material for invertebrates in the sediment and water column of lakes, that can lead to markedly depleted delta 13C values in invertebrate tissues. Using culturing experiments, it was demonstrated that methane-derived carbon is incorporated into chironomid head capsules. Also, it was shown that chemical pre-treatments that are commonly used for sediment processing do not have a noticeable effect on delta 13C values of chironomid remains and that a minimum of 20 microgram chitinous material is required for reproducible delta 13C measurements. In study lakes in Sweden and Siberia, delta 13C values of chitinous remains of several invertebrate taxa in surface sediments were negatively correlated with diffusive methane fluxes. Strong and significant correlations are observed between diffusive methane fluxes and delta 13C of Chironomini and Daphnia remains. Similar correlations were also observed within two Swedish lakes, in which surface sediment cores were obtained along depth transects. Delta 13C values of Chironomini and Daphnia were lower in sections of the lake basin in which the sediments had higher methane release rates. This suggests that delta 13C in remains of several invertebrates, especially Chironomini and Daphnia can be indicative of methane availability in lakes. In contrast, Orthocladiinae and Ephemeroptera, always had relatively high delta 13C values, indicating a plant-derived carbon source. In a sediment record from a Siberian thermokarst lake, delta 13C values of the remains of Chironomini and Daphnia showed relatively large negative delta 13C shifts in warm periods (AD 850-1150 and since AD 1970) compared with delta 13C values of Orthocladiinae remains and bulk sediment. Based on the observed correlations between methane fluxes and delta 13C values of Chironomini and Daphnia in surface sediment samples, this suggests that more methane-derived carbon was available in warm periods compared with colder periods. The research in this thesis demonstrates the potential to use taxon-specific stable carbon isotopes analysis of invertebrate remains for qualitative reconstructions of methane availability in lakes. This new method can lead to a better understanding of lake methane emissions in relation to climate change

Redox Activity in a Vanadium(V)–o‐Dioxolene Complex Is Modulated by Protonation State As Indicated by 51V Solid‐State NMR Spectroscopy and Density Functional Theory

AbstractMost known vanadium(V) complexes with redox‐active o‐dioxolene ligands are non‐innocent. Since the vanadium(V) complex [VO(gsal)(HCat)] is innocent, its properties were investigated by 51V solid‐state NMR spectroscopy and density functional theory (DFT). The innocent ligand behavior manifested itself by the upfield isotropic chemical shift and large negative chemical shift anisotropy observed in the solid state. The electronic structure and NMR spectroscopic parameters of this complex were addressed by DFT calculations and found to be consistent with the NMR spectroscopic observations indicating that the complex is redox‐inactive. The observed increase in the HOMO–LUMO gap for the innocent complex is concomitant with the 51V NMR chemical shift of –460 ppm and consistent with the high redox stability of this molecule. The stabilization was traced to the overall charge of [VO(gsal)(HCat)] facilitated by the coordination of the minus‐one‐charged o‐dioxolene ligand and rendering the overall complex neutral. These studies suggest that protonation may prove to be an effective way in which vanadium(V) complexes with redox‐active ligands can be stabilized.

Chiral Interconversions of Pd and/or Au Bis-Metalated [32]Octaphyrins(1,0,1,0,1,0,1,0) Involving Hückel and Möbius Macrocyclic Topologies: A Theoretical Prediction

Several Pd and/or Au bis-metalated [32]octaphyrins(1,0,1,0,1,0,1,0) were theoretically designed with rich conformations of Hückel or Möbius topology. The conformations and hence properties of macrocycles were tuned by twisting the active pyrrolic ring either clockwise (through multistep reactions with several Hückel and Möbius macrocyclic intermediates) or anticlockwise (via a direct Hückel-Hückel chiral interconversion). The encapsulated metal atoms, M(1), M(2) = Pd, Au, give different impacts on these two reaction processes. Facile occurrences of chiral interconversions between two enantiomers of bis-metalated octaphyrins were predicted with the largest activation barrier less than 40 kcal/mol. Some Au-coordinated octaphyrins (M(1) = Au) were demonstrated to be thermodynamically stable with large negative nucleus-independent chemical shift (NICS) values, which are comparable to those of the synthetic Pd-coordinated complexes. The free-base [32]octaphyrins(1,0,1,0,1,0,1,0) display the characteristic absorption spectra with distinct sharp Soret-like bands. After metalation, the Soret-like bands are red-shifted in different degrees along with the appearance of rather weak Q-like band. The heterometal-coordinated complexes (i.e., M(1) ≠ M(2)) show stronger and more splitting absorptions than the homometal-coordinated ones with M(1) = M(2). The hyperpolarizabilities sharply augment with the metalation in Hückel systems due to the destruction of the centrosymmetry and the increase in polarizability by coordinated metal atoms.