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The accessory HIV-1 Nef protein is essential for viral replication, high virus load, and progression to AIDS. These functions are mediated by the alteration of signaling and trafficking pathways and require the membrane association of Nef by its N-terminal myristoylation. However, a large portion of Nef is also found in the cytosol, in line with the observation that myristoylation is only a weak lipidation anchor for membrane attachment. We performed biochemical studies to analyze the implications of myristoylation on the conformation of Nef in aqueous solution. To establish an in vivo myristoylation assay, we first optimized the codon usage of Nef for Escherichia coli expression, which resulted in a 15-fold higher protein yield. Myristoylation was achieved by coexpression with the N-myristoyltransferase and confirmed by mass spectrometry. The myristoylated protein was soluble, and proton NMR spectra confirmed proper folding. Size exclusion chromatography revealed that myristoylated Nef appeared of smaller size than the unmodified form but not as small as an N-terminally truncated from of Nef that omits the anchor domain. Western blot stainings and limited proteolysis of both forms showed different recognition profiles and degradation pattern. Analytical ultracentrifugation revealed that myristoylated Nef prevails in a monomeric state while the unmodified form exists in an oligomeric equilibrium of monomer, dimer, and trimer associations. Finally, fluorescence correlation spectroscopy using multiphoton excitation revealed a shorter diffusion time for the lipidated protein compared to the unmodified form. Taken together, our data indicated myristoylation-dependent conformational changes in Nef, suggesting a rather compact and monomeric form for the lipidated protein in solution.

Recent studies using a thin film balance of free-standing thin aqueous films (foam films) containing polyelectrolytes resulted in jump-like discontinuities in the film thickness with increasing outer pressure. These jumps in film thickness correspond to an oscillation of the disjoining pressure. The oscillation period of the disjoining pressure scales as c -0.5 with the polyelectrolyte concentration c. A mesoscopic ordering of the chains in the film similar to that found in aqueous semidilute polyelectrolyte solutions is assumed. In experiments presented in this work, the electrostatic effect is investigated by adding low molecular salt and varying the degree of charge of the polyelectrolyte chains. The studies reveal that the amplitudes of the disjoining pressure oscillations are reduced with increasing ionic strength and decreasing degree of charge. The results show that the jumps in film thickness and therefore the structuring are due to the electrostatic repulsions between the polyelectrolyte chains.

The fluorescence of dye molecules embedded in a photonic crystal is known to be inhibited by the presence of a pseudo-gap acting in their emission range. Here we present the first account of the influence that an incomplete photonic band gap or pseudo-gap has on the fluorescence emission and fluorescence resonant energy transfer. By inserting synthetic, donor (D)-acceptor (A)-labeled oligonucleotide structures in self-organized colloidal photonic crystals, we were able to measure simultaneously the emission spectra and lifetimes of both donor and acceptor. Our results clearly show an inhibition of the donor emission together with an enhancement of the acceptor emission spectra, indicating improved energy transfer from donor to acceptor. These results are mainly attributed to a decrease of the number of available photonic modes for radiative decay of the donor in a photonic crystal in comparison to that of the effective homogeneous medium. The fluorescence decay parameters are also dominated by the pseudo-gap acting on the energy-transfer efficiency.

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When atoms come together and bond, these new states are called molecules and their properties determine many aspects of our daily life. Strangely enough, it is conceivable for light and molecules to bond, creating new hybrid light–matter states with far‐reaching consequences for these strongly coupled materials. Even stranger, there is no “real” light needed to obtain the effects; it simply appears from the vacuum, creating “something from nothing.” Surprisingly, the setup required to create these materials has become moderately straightforward. In its simplest form, one only needs to put a strongly absorbing material at the appropriate place between two mirrors, and quantum magic can appear. Only recently has it been discovered that strong coupling can affect a host of significant effects at a material and molecular level, which were thought to be independent of the “light” environment: phase transitions, conductivity, chemical reactions, etc. This review addresses the fundamentals of this opportunity: the quantum mechanical foundations, the relevant plasmonic and photonic structures, and a description of the various applications, connecting material chemistry with quantum information, entanglement, nonlinear optics, and chemical reactivity. Ultimately, revealing the interplay between light and matter in this new regime opens attractive avenues for various new technologies.

Disjoining pressure isotherms of free-standing liquid films (foam films) consisting of different polyelectrolyte/ surfactant combinations are measured in a thin film pressure balance (TFPB). In dependence of the charge of polyelectrolyte and surfactant, a transition from an electrostatically stabilized common black film (CBF) to a sterically stabilized Newton black film (NBF) can be induced in some cases while for other polyelectrolyte/ surfactant combinations the film is a CBF up to several thousands of pascals. The thinner NBF is less stable, and the film breaks after a few minutes. An exchange of the polymers by monomers leads to the same kind of film as that for the respective polymer, while the addition of, for example, simple salt leads always to a transition from CBF to NBF. The typical stratification of polyelectrolyte/surfactant films is not observed in monomer/surfactant films.

In this letter, we present a new procedure to determine completely the complex modular values of arbitrary observables of pre-and post-selected ensembles, which works experimentally for all measurement strengths and all post-selected states. This procedure allows us to discuss the physics of modular and weak values in interferometric experiments involving a qubit meter. We determine both the modulus and the argument of the modular value for any measurement strength in a single step, by controlling simultaneously the visibility and the phase in a quantum eraser interference experiment. Modular and weak values are closely related. Using entangled qubits for the probed and meter systems, we show that the phase of the modular and weak values has a topological origin. This phase is completely defined by the intrinsic physical properties of the probed system and its time evolution. The physical significance of this phase can thus be used to evaluate the quantumness of weak values.In 1988, Aharonov, Albert, and Vaidman (AAV) introduced the weak value of a quantum observable from an extension of the von Neumann measurement scheme [1]. They pointed out that the result of a measurement involving a weak coupling between a meter and the observable of a system with a pre-selected initial state |ψ i , and a post-selected final state |ψ f depends directly on the weak value:an unbounded complex number. In particular, they showed that the shift of the average detected position due to post-selection is proportional to the real part of the weak value. Since for weak measurements in the absence of post-selection, this shift is proportional to the average of the observable ψ i |Â|ψ i / ψ i |ψ i , a direct but bold physical interpretation of the weak value assumes it represents somehow the average of in the pre-and post-selected ensemble. They also related the imaginary part of the weak value to the shift of the average impulsion. Beside the AAV approach, weak values may also appear using a meter strongly coupled to the observablê A [2][3][4][5][6][7]. In these instances, the effective weak interaction is achieved by selecting particular initial states of the meter system, so that the probability of actually measurinĝ A is low and the probed system is left unperturbed most of the time. Therefore, both methods transform the standard von Neumann procedure to a weak measurement with a high incertitude. Weak values and weak measurements proved useful in many fields of physics and chemistry [8][9][10][11][12][13][14][15][16][17][18][19][20]. Nevertheless, the proper physical interpretation of weak values remains highly debated. For example, weak values were used to develop a time-symmetrized approach to standard quantum theory, the two-state vector formalism [21], where they appear as purely quantum objects.Oppositely, a purely classical view of the occurrence of unbounded, real weak values -and possibly of complex ones -was proposed recently [22] (which is criticizable though [23-25]).In this letter, we uncover a physical interpretati...