Spiropyran/Merocyanine Amphiphile in Various Solvents: A Joint Experimental–Theoretical Approach to Photophysical Properties and Self-Assembly

This joint experimental-theoretical work focuses on molecular and photophysical properties of the spiropyran-containing amphiphilic molecule in organic and aqueous solutions. Being dissolved in tested organic solvents, the system demonstrates positive photochromism, i.e., upon UV stimulus the colorless spiropyran form is transformed into colorful merocyanine isomer. However, the aqueous solution of the amphiphile possesses a negative photochromism: the orange-red merocyanine form becomes thermodynamically more stable in water, and both UV and vis stimuli lead to the partial or complete photobleaching of the solution. The explanation of this phenomenon is given on the basis of density functional theory calculations and classical modeling including thermodynamic integration. The simulations reveal that stabilization of merocyanine in water proceeds with the energy of ca. 70 kJ mol−1, and that the Helmholtz free energy of hydration of merocyanine form is 100 kJ mol−1 lower as compared to the behavior of SP isomer in water. The explanation of such a difference lies in the molecular properties of the merocyanine: after ring-opening reaction this molecule transforms into a zwitterionic form, as evidenced by the electrostatic potential plotted around the opened form. The presence of three charged groups on the periphery of a flat conjugated backbone stimulates the self-assembly of merocyanine molecules in water, ending up with the formation of elongated associates with stack-like building blocks, as shown in molecular dynamics simulations of the aqueous solution with the concentration above critical micelle concentration. Our quantitative evaluation of the hydrophilicity switching in spiropyran/merocyanine containing surfactants may prompt the search for new systems, including colloidal and polymeric ones, aiming at remote tuning of their morphology, which could give new promising shapes and patterns for the needs of modern nanotechnology

A behavioral approach to singular systems

The notion of behaviors introduced by Willems gives a good description of dynamical systems without reference to any particular representation of the system in terms of equations. In this note, we introduce a notion of behaviors that allows us to describe singular systems in a very natural way. The new definition of behaviors given here is closely related to that of a sheaf over the projective line, and we make this connection precise

A behavioral approach to singular systems

The notion of behaviors introduced by Willems gives a good description of dynamical systems without reference to any particular representation of the system in terms of equations. In this note, we introduce a notion of behaviors that allows us to describe singular systems in a very natural way. The new definition of behaviors given here is closely related to that of a sheaf over the projective line, and we make this connection precise

Comparative Analysis of the Laws of Georgia and the Republic of Kazakhstan on the State Language

The article uses a comparative-legal method to conduct an analysis of the Law on Languages of the Republic of Kazakhstan and the Organic Law on the State Language of Georgia. The structure of these laws, their preambles, the constitutional status of the state languages, types of languages, the scope of use of the state languages, issues of their protection and development, responsibility for breaking the law and the issues of compulsory knowledge of the state language are compared in this article. By a comparative analysis of the aforementioned aspects not only the importance of languages, as of social mechanisms associated with the means of communication and the identity of people but also the threats that they encounter over time are indicated. The difficulties faced by state languages of both countries, how legislation solves challenges and how Georgia and Kazakhstan can share each other’s experiences in this field were studied

Quivers, Geometric Invariant Theory, and Moduli of Linear Dynamical Systems

We use geometric invariant theory and the language of quivers to study compactifications of moduli spaces of linear dynamical systems. A general approach to this problem is presented and applied to two well known cases: We show how both Lomadze's and Helmke's compactification arises naturally as a geometric invariant theory quotient. Both moduli spaces are proven to be smooth projective manifolds. Furthermore, a description of Lomadze's compactification as a Quot scheme is given, whereas Helmke's compactification is shown to be an algebraic Grassmann bundle over a Quot scheme. This gives an algebro-geometric description of both compactifications. As an application, we determine the cohomology ring of Helmke's compactification and prove that the two compactifications are not isomorphic when the number of outputs is positive.Comment: 24 pages, based on my Diplomarbeit completed in February 2005, to appear in Linear Algebra and its Applications (LAA

Tuning the Volume Phase Transition Temperature of Microgels by Light

Temperature-responsive microgels find widespread applications as soft materials for designing actuators in microfluidic systems, as carriers for drug delivery or catalysts, as functional coatings, and as adaptable sensors. The key property is their volume phase transition temperature, which allows for thermally induced reversible swelling/deswelling. It is determined by the gel's chemical structure as well as network topology and cannot be varied easily within one system. Here a paradigm change of this notion by facilitating a light-triggered reversible switching of the microgel volume in the range between 32 and 82 °C is suggested. Photo-sensitivity is introduced by photosensitive azobenzene containing surfactant, which forms a complex with microgels consisting of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-AAc) chains when assuming a hydrophobic trans-state, and prefers to leave the gel matrix in its cis-state. Using a similar strategy, it is demonstrated that at a fixed temperature, for example, 37 °C, one can reversibly change the microgel radius by a factor of 3 (7–21 µm) by irradiating either with UV (collapsed state) or green light (swollen state). It is envisaged that the possibility to deploy a swift external means of adapting the swelling behavior of microgels may impact and redefine the latter's application across all fields. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH Gmb