Enantioselective Visible-Light-Mediated Formation of 3-Cyclopropylquinolones by Triplet-Sensitized Deracemization

3-Allyl-substituted quinolones undergo a triplet-sensitized di-π-methane rearrangement reaction to the corresponding 3-cyclopropylquinolones upon irradiation with visible light (λ=420 nm). A chiral hydrogen-bonding sensitizer (10 mol %) was shown to promote the reaction enantioselectively (88-96 % yield, 32-55 % ee). Surprisingly, it was found that the enantiodifferentiation does not occur at the state of initial product formation but that it is the result of a deracemization event. The individual parameters that control the distribution of enantiomers in the photostationary state have been identified.

Triplet-sensitised di-π-methane rearrangement of N-substituted 2-azabarrelenones

When irradiated at λ = 366 nm or at λ = 420 nm in the presence of an appropriate sensitiser the title compounds underwent a di-π-methane rearrangement which led to the formation of tricyclic azasemibullvalenones (2a,2a1,2b,4a-tetrahydroazacyclopropa[cd]pentalenones) in yields of 63-87%.

Strain intermittency due to avalanches in ferroelastic and porous materials

The avalanche statistics in porous materials and ferroelastic domain wall systems has been studied for slowly increasing compressive uniaxial stress with stress rates between 0.2 and 17 kPa s^-1. Velocity peaks [Formula: see text] are calculated from the measured strain drops and used to determine the corresponding Energy distributions [Formula: see text]. Power law distributions [Formula: see text] have been obtained over 4-6 decades. For most of the porous materials and domain wall systems an exponent [Formula: see text] was obtained in good agreement with mean-field theory of the interface pinning transition. For charcoal, shale and calcareous schist we found significant deviations of the exponents from mean-field values in agreement with recent acoustic emission experiments.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4 , whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

Enantioselective Intermolecular [2 + 2] Photocycloaddition Reactions of 2(1H)-Quinolones Induced by Visible Light Irradiation

In the presence of a chiral thioxanthone catalyst (10 mol %) the title compounds underwent a clean intermolecular [2 + 2] photocycloaddition with electron-deficient olefins at λ = 419 nm. The reactions not only proceeded with excellent regio- and diastereoselectivity but also delivered the respective cyclobutane products with significant enantiomeric excess (up to 95% ee). Key to the success of the reactions is a two-point hydrogen bonding between quinolone and catalyst enabling efficient energy transfer and high enantioface differentiation. Preliminary work indicated that solar irradiation can be used for this process and that the substrate scope can be further expanded to isoquinolones.

Fourier Monte Carlo renormalization-group approach to crystalline membranes

The computation of the critical exponent η characterizing the universal elastic behavior of crystalline membranes in the flat phase continues to represent challenges to theorists as well as computer simulators that manifest themselves in a considerable spread of numerical results for η published in the literature. We present additional insight into this problem that results from combining Wilson's momentum shell renormalization-group method with the power of modern computer simulations based on the Fourier Monte Carlo algorithm. After discussing the ideas and difficulties underlying this combined scheme, we present a calculation of the renormalization-group flow of the effective two-dimensional Young modulus for momentum shells of different thickness. Extrapolation to infinite shell thickness allows us to produce results in reasonable agreement with those obtained by functional renormalization group or by Fourier Monte Carlo simulations in combination with finite-size scaling. Moreover, our method allows us to obtain a decent estimate for the value of the Wegner exponent ω that determines the leading correction to scaling, which in turn allows us to refine our numerical estimate for η previously obtained from precise finite-size scaling data.

Frictional dynamics of stiff monolayers: from nucleation dynamics to thermal sliding

The inherently nonlinear dynamics of two surfaces as they are driven past each other, a phenomenon known as dry friction, has yet to be fully understood on an atomistic level. New experiments on colloidal monolayers forced over laser-generated substrates now offer the opportunity to investigate friction with single-particle resolution. Here, we use analytical theory and computer simulations to study the effect of thermal fluctuations on the stick-slip mechanism characteristic for the frictional response of a stiff colloidal monolayer on a commensurate substrate. By performing a harmonic expansion of the energy and employing elementary statistical mechanics, we map the motion of the monolayer onto a simple differential equation. Analytical expressions derived from our approach predict a transition from nucleation dynamics, where the monolayer moves in a sequence of activated hops over energy barriers, to "thermal sliding", in which the effective substrate barrier opposing the motion of the monolayer disappears due to thermal fluctuations, leading to continuous, uninterrupted sliding motion. Furthermore, we find that the average velocity of the monolayer for large driving forces obeys a simple scaling behavior that is consistent with the existence of a static friction. For small forces, however, nucleation provides a mode of motion that leads to a small but non-vanishing mobility of the monolayer. Data obtained from simulations confirm this picture and agree quantitatively with our analytical formulae. The theory developed here holds under general conditions for sufficiently strong inter-particle repulsions and it yields specific predictions that can be tested in experiments.

Microcanonical determination of the interface tension of flat and curved interfaces from Monte Carlo simulations

The investigation of phase coexistence in systems with multi-component order parameters in finite systems is discussed and, as a generic example, Monte Carlo simulations of the two-dimensional q-state Potts model (q = 30) on L × L square lattices (40 ≤ L ≤ 100) are presented. It is shown that the microcanonical ensemble is well suited both to find the precise location of the first-order phase transition and to obtain an accurate estimate for the interfacial free energy between coexisting ordered and disordered phases. For this purpose, a microcanonical version of the heat bath algorithm is implemented. The finite size behaviour of the loop in the curve describing the inverse temperature versus energy density is discussed, emphasizing that the extrema do not have the meaning of van der Waals-like 'spinodal points' separating metastable from unstable states, but rather describe the onset of heterophase states: droplet/bubble evaporation/condensation transitions. Thus all parts of these loops, including the parts that correspond to a negative specific heat, describe phase coexistence in full thermal equilibrium. However, the estimates for the curvature-dependent interface tension of the droplets and bubbles suffer from unexpected and unexplained large finite size effects which need further study.

Positive Tolman length in a lattice gas with three-body interactions

We present a new method to determine the curvature dependence of the interface tension between coexisting phases in a finite volume from free energies obtained by Monte Carlo simulations. For the example of a lattice gas on a 3D fcc lattice with nearest neighbor three-body interactions, we demonstrate how to calculate the equimolar radius R(e) as well as the radius R(s) of the surface of tension and thus the Tolman length δ(R(s))=R(e)-R(s). Within the physically relevant range of radii, δ(R(s)) shows a pronounced R(s) dependence, such that the simple Tolman parametrization for the interface tension is refutable. For the present model, extrapolation of δ(R(s)) to R(s)→∞ by various methods clearly indicates a positive limiting value.

Crossover from classical to 3d-Ising critical behaviour near the antiferrodistortive phase transition of lawsonite

Results of X-ray scattering intensities and peak profiles of lawsonite single crystals are presented in a wide temperature range including the antiferrodistortive phase transition Cmcm – (T c ∼ 270 K) → Pmcn. In the integrated intensities of the superlattice reflections above T c pronounced pretransitional tails similar to those detected recently in birefringence [P. Sondergeld et al., Phys. Rev. B62, 6143 (2000)] and in excess entropy data [S. A. Hayward et al., Eur. J. Min. 14, 1145 (2002)] are observed. These tails correspond to diffuse Lorentzian shaped scattering peaks. The temperature variation of the diffuse scattering intensity and profile can be well described within a Landau-Ginzburg model. In combination with entropy data we obtain a complete set of free energy parameters. Using these coefficients we are able to fit the spontaneous part and the precursor tails of the integrated intensities, the excess birefringence and entropy in a broad temperature range outside a temperature interval of about ±3 K around T c. In the vicinity of T c the experimental data are in excellent agreement with the predictions of a crossover model, the effective critical exponent α eff(τ) varying from the classical (α eff = 0.5) to the 3d Ising limit (α eff = 0.11). Lawsonite therefore represents an ideal system to study the crossover from classical to critical behavior.

Momentum-shell renormalization-group flow from simulation

Our recently developed Fourier Monte Carlo algorithm permits a nonperturbative calculation of momentum-shell renormalization-group flows by simulation which despite its apparent simplicity is illustrative both numerically as well as conceptually interesting. We study the example of a varphi(4) model with long-range lattice interaction. For this model we show that the topology of the renormalization flow is globally accessible in a particularly convenient way. The nontrivial fixed point of Wilson-Fisher type is observed its accompanying critical exponents are numerically determined from fitting its surrounding flow pattern to a linearized renormalization-group transformation. The results are compared to those obtained from perturbation theory, -expansion and earlier Monte Carlo simulations. Application of our method is also expected to be rewarding in other models with long-range interactions.

Supra-additive effects of tramadol and acetaminophen in a human pain model ☆

The combination of analgesic drugs with different pharmacological properties may show better efficacy with less side effects. Aim of this study was to examine the analgesic and antihyperalgesic properties of the weak opioid tramadol and the non-opioid acetaminophen, alone as well as in combination, in an experimental pain model in humans. After approval of the local Ethics Committee, 17 healthy volunteers were enrolled in this double-blind and placebo-controlled study in a cross-over design. Transcutaneous electrical stimulation at high current densities (29.6+/-16.2 mA) induced spontaneous acute pain (NRS=6 of 10) and distinct areas of hyperalgesia for painful mechanical stimuli (pinprick-hyperalgesia). Pain intensities as well as the extent of the areas of hyperalgesia were assessed before, during and 150 min after a 15 min lasting intravenous infusion of acetaminophen (650 mg), tramadol (75 mg), a combination of both (325 mg acetaminophen and 37.5mg tramadol), or saline 0.9%. Tramadol led to a maximum pain reduction of 11.7+/-4.2% with negligible antihyperalgesic properties. In contrast, acetaminophen led to a similar pain reduction (9.8+/-4.4%), but a sustained antihyperalgesic effect (34.5+/-14.0% reduction of hyperalgesic area). The combination of both analgesics at half doses led to a supra-additive pain reduction of 15.2+/-5.7% and an enhanced antihyperalgesic effect (41.1+/-14.3% reduction of hyperalgesic areas) as compared to single administration of acetaminophen. Our study provides first results on interactions of tramadol and acetaminophen on experimental pain and hyperalgesia in humans. Pharmacodynamic modeling combined with the isobolographic technique showed supra-additive effects of the combination of acetaminophen and tramadol concerning both, analgesia and antihyperalgesia. The results might act as a rationale for combining both analgesics.

Evidence for Fisher renormalization in the compressible phi4 model

We present novel Fourier Monte Carlo simulations of a compressible phi4-model on a simple-cubic lattice with linear-quadratic coupling of order parameter and strain, focusing on the detection of fluctuation-induced first-order transitions and deviations from standard critical behavior. The former is indeed observed in the constant stress ensemble and for auxetic systems at constant strain, while for regular isotropic systems at constant strain, we find strong evidence for Fisher-renormalized critical behavior and are led to predict the existence of a tricritical point.

Modulation of Remifentanil-Induced Postinfusion Hyperalgesia by Propofol

BACKGROUND

Experimental and clinical studies suggest that brief opioid exposure can enhance pain sensitivity. During anesthesia, however, opioids are commonly administered in combination with either IV or inhaled hypnotic drugs. In this investigation we sought to determine the analgesic and antihyperalgesic properties of propofol in subhypnotic concentrations on remifentanil-induced postinfusion hypersensitivity in an experimental human pain model.

METHODS

Fifteen healthy volunteers were included in this randomized, double-blind, and placebo-controlled study in a cross-over design. Transcutaneous electrical stimulation at high current densities (41.7 +/- 14.3 mA) induced spontaneous acute pain (numerical rating scale = 6 of 10) and stable areas of hyperalgesia. Pain intensities and areas of hyperalgesia were assessed before, during and after a 30 min target-controlled infusion of propofol (1.5 microg/mL) and remifentanil (0.05 microg x kg(-1) x min(-1)), either alone or in combination (propofol 1.5 microg/mL with remifentanil 0.025 or 0.05 microg x kg(-1) x min(-1)).

RESULTS

During infusion, propofol significantly reduced the electrically evoked pain to 72% +/- 21% of control. Subhypnotic concentrations of propofol did not lead to any hyperalgesic effects. Coadministration of remifentanil led to synergistic analgesic effects (to 62% +/- 26% and 58% +/- 25% of control, for 0.025 or 0.05 microg x kg(-1) x min(-1), respectively), but upon withdrawal, pain and hyperalgesia increased above control level.

CONCLUSIONS

The results suggest clinically relevant interactions of propofol and remifentanil in humans, since propofol led to a delay and a weakening of remifentanil-induced postinfusion anti-analgesia in humans. Nevertheless, pronociceptive effects were not completely antagonized by propofol, which may account for the increased demand for analgesics after remifentanil-based anesthesia in clinical practice.

Effects of oral pregabalin and aprepitant on pain and central sensitization in the electrical hyperalgesia model in human volunteers †

BACKGROUND

Central sensitization is an important mechanism of neuropathic pain; its human models could be useful for early detection of efficacy of novel treatments. The electrical hyperalgesia model invokes central sensitization by repetitive stimulation of the skin. To assess its predictive value, we have investigated pregabalin, a standard neuropathic pain treatment, and aprepitant, an NK(1) antagonist, as an example of a drug class active in animal models but not in neuropathic pain patients. Furthermore, we explored if combinations of either of these drugs with the COX-2 inhibitor parecoxib could improve its efficacy.

METHODS

This was a double-blind, two-period, placebo-controlled study using incomplete block design. Thirty-two healthy volunteers received either oral pregabalin (titrated to 300 mg) or aprepitant (titrated to 320 mg), or matching placebo over 6 days before testing. Sensitization was assessed over 3 h; at 2 h, subjects received either parecoxib (40 mg) or saline i.v.

RESULTS

Pregabalin significantly reduced the areas of punctate mechanical hyperalgesia and dynamic touch allodynia vs placebo (both P < 0.0001); no significant reduction in the area of hyperalgesia or allodynia vs placebo was observed with aprepitant. In the pregabalin + parecoxib treated group, the area of allodynia was significantly reduced (P < 0.0001) and the area of hyperalgesia insignificantly attenuated (P = 0.09) vs placebo + parecoxib; no efficacy improvement was observed with aprepitant + parecoxib.

CONCLUSIONS

The model can serve to predict analgesic efficacy in early human development and investigate the mechanism of action. The model could also be used to explore efficacy of analgesic combinations to provide a rationale for patient studies.

Modulation of Remifentanil-induced Analgesia and Postinfusion Hyperalgesia by Parecoxib in Humans

Background

Numerous experimental and clinical studies suggest that brief opioid exposure can enhance pain sensitivity. It is suggested that spinal cyclooxygenase activity may contribute to the development and expression of opioid tolerance. The aim of the investigation was to determine analgesic and antihyperalgesic properties of the cyclooxygenase-2 inhibitor parecoxib on remifentanil-induced hypersensitivity in humans.

Methods

Fifteen healthy male volunteers were enrolled in this randomized, double-blind, placebo-controlled study in a crossover design. Transcutaneous electrical stimulation at high current densities was used to induce spontaneous acute pain (numeric rating scale 6 of 10) and stable areas of pinprick hyperalgesia. Pain intensities and areas of hyperalgesia were assessed before, during, and after a 30-min intravenous infusion of remifentanil (0.1 microg x kg x min) or placebo (saline). Parecoxib (40 mg) was administered intravenously either with onset of electrical stimulation (preventive) or in parallel to the remifentanil infusion.

Results

Remifentanil reduced pain and mechanical hyperalgesia during the infusion, but upon withdrawal, pain and hyperalgesia increased significantly above control level. Preventive administration of parecoxib led to an amplification of remifentanil-induced antinociceptive effects during the infusion (71.3 +/- 7 vs. 46.4 +/- 17% of control) and significantly diminished the hyperalgesic response after withdrawal. In contrast, parallel administration of parecoxib did not show any modulatory effects on remifentanil-induced hyperalgesia.

Conclusion

The results confirm clinically relevant interaction of mu opioids and prostaglandins in humans. Adequate timing seems to be of particular importance for the antihyperalgesic effect of cyclooxygenase-2 inhibitors.

Activation of Naloxone-Sensitive and -Insensitive Inhibitory Systems in a Human Pain Model

We investigated naloxone effects in a model of electrically induced pain and hyperalgesia. In a double-blind, placebo-controlled, cross-over study, 15 volunteers underwent four 150-minute sessions of high-current-density electrical stimulation of their forearms. After 60 minutes, naloxone or placebo was given intravenously (increasing plasma concentrations of 0.1, 1, and 10 ng/mL; 30 minutes each) in 3 of the 4 sessions. Pain ratings and areas of mechanical hyperalgesia were assessed at regular intervals during all sessions. The low doses of naloxone did not cause any significant change of pain rating of areas of hyperalgesia. In terms of intrasession effects, pain ratings and areas of hyperalgesia significantly decreased during the sessions to 62% (pain rating), 70% (area of punctuate hyperalgesia), and 82% (area of allodynia) of the initial values. Naloxone (10 ng/ml) reversed these decreases. In terms of between-session effects, the time course of pain ratings remained constant from session to session. In contrast, the areas of punctate hyperalgesia successively decreased to 60% of initial value at the fourth repetition. The session effect was not reversed by naloxone. High-current-density electrical stimulation provokes central sensitization, but in addition inhibitory systems are activated that are only partly naloxone-sensitive.

PERSPECTIVE

Endogenous inhibitory systems are of major importance for clinical pain conditions, but are not reflected in traditional human pain models. Here we show activation of a naloxone-sensitive short-term and a naloxone-insensitive long-term inhibitory system in a new model of electrically induced pain and hyperalgesia.

Wang-Landau sampling with self-adaptive range

We report a self-adapting version of the Wang-Landau algorithm that is ideally suited for application to systems with a complicated structure of the density of states. Applications include determination of two-dimensional densities of states and high-precision numerical integration of sharply peaked functions on multidimensional integration domains.

How to couple Landau theory to an equation of state

We show how to construct a Landau-type free energy based on a primary order parameter coupled to finite strain with an elastic energy derived from an arbitrary equation of state V = V(P). The resulting class of models provides an excellent and efficient framework for the systematic study of phase transformations for a wide range of materials up to ultrahigh pressures.

Lesion volume and clinical outcome in stereotactic pallidotomy and thalamotomy

Postoperative lesion volume and clinical outcome were assessed in 19 Parkinson's disease (PD) patients who received posteroventral pallidotomy, and in 14 essential tremor (ET) patients who received ventrolateral thalamotomy. Before and after surgery, PD patients were evaluated using the Unified PD Rating Scale (UPDRS), and ET patients were evaluated using the Fahn-Tolosa-Marin (FTM) tremor rating scale. Inner and total lesion volumes were determined with postoperative MR imaging and three-dimensional data segmentation. Lesion volumes were compared to percent improvement in UPDRS and FTM scores, using Spearman's rank-order correlation test. No rank-order correlations were found between lesion volume and clinical improvement in either the PD or the ET patients. In performing stereotactic surgery for movement disorders, any lesion volume within a prescribed range may be equally effective in relieving symptoms associated with PD or ET.

Comparative magnetic resonance image-based evaluation of thalamotomy and pallidotomy lesion volumes

Acute thalamotomy and pallidotomy lesion volumes based on magnetic resonance (MR) images were measured in 22 patients (11 thalamotomy and 11 pallidotomy patients). Thalamotomy inner lesion volumes (0.06 +/- 0.04 ml; thermocoagulative zone) were smaller than pallidotomy inner lesion volumes (0.14 +/- 0.08 ml) as determined using T(1)-weighted 3D-MPRAGE (1.5-mm slice spacing). Similar results were found using T(1)-weighted (6-mm slice spacing) image sets (0.09 +/- 0.05 ml, thalamotomy; 0.13 +/- 0.05 ml, pallidotomy). No differences were found when comparing thalamic or pallidal inner lesion volumes when the comparison was based on T(2) weighted images. Thalamotomy total lesion volumes (thermocoagulative and surrounding edematous zones) were less than pallidotomy total lesion volumes independent of the MR protocol. The difference in thalamotomy and pallidotomy lesion volumes is most likely based on the distance between each discrete lesion placed along the lesioning tracts. In 7 of 11 thalamotomies, this distance was 1 mm with the remaining having 2 mm between each discrete lesion. All pallidotomy discrete lesions were 2 mm apart. More overlap between discrete lesioning sites for thalamotomies is likely to produce reduced lesion volumes.