Pseudo-Riemannian manifolds with recurrent spinor fields

The existence of a recurrent spinor field on a pseudo-Riemannian spin manifold $(M,g)$ is closely related to the existence of a parallel 1-dimensional complex subbundle of the spinor bundle of $(M,g)$. We characterize the following simply connected pseudo-Riemannian manifolds admitting such subbundles in terms of their holonomy algebras: Riemannian manifolds; Lorentzian manifolds; pseudo-Riemannian manifolds with irreducible holonomy algebras; pseudo-Riemannian manifolds of neutral signature admitting two complementary parallel isotropic distributions.Comment: 13 pages, the final versio

Smart Photochromic Materials Triggered with Visible Light

Molecular photoswitches reversibly convert the energy of light into a variety of structural changes at the molecular level. They can be integrated into smart materials with broad range of applicability. While most photochromic systems require UV light for activation, application of photoswitches operational entirely within the visible or NIR range of light brings considerable benefits, such as biocompatibility, better light penetration through the material, propelling with sunlight, or a possibility to design dual systems that are mutually activated with UV or visible light frequencies for two distinct functions. In this Review, we discuss the most relevant classes of molecular photoswitches, and demonstrate a selection of photochromic polymers, gels, porous materials, surfaces, energy-storing materials and other systems triggered with visible light

Molecular Syringe for Cargo Photorelease: Red‐Light‐Triggered Supramolecular Hydrogel

Photochromic supramolecular hydrogels are versatile materials that show macroscopic effects upon irradiation, like liquefaction or shape changes. Here, we demonstrate a simple photochromic cyclic dipeptide (2,5-diketopiperazine-based) supergelator, composed of (S)-lysine and an azobenzene analogue of phenylalanine, that forms supramolecular hydrogels even at 0.1 wt% loading. The gels can physically encapsulate cargo molecules and release them to the environment in a controllable manner upon irradiation with red light, thus working as a “molecular syringe”. As the material is biocompatible and operational in the “therapeutic window” of light (>650 nm) that deeply penetrates soft human tissues, it is applicable to smart drug-delivery systems

How to find the holonomy algebra of a Lorentzian manifold

Manifolds with exceptional holonomy play an important role in string theory, supergravity and M-theory. It is explained how one can find the holonomy algebra of an arbitrary Riemannian or Lorentzian manifold. Using the de~Rham and Wu decompositions, this problem is reduced to the case of locally indecomposable manifolds. In the case of locally indecomposable Riemannian manifolds, it is known that the holonomy algebra can be found from the analysis of special geometric structures on the manifold. If the holonomy algebra $\mathfrak{g}\subset\mathfrak{so}(1,n-1)$ of a locally indecomposable Lorentzian manifold $(M,g)$ of dimension $n$ is different from $\mathfrak{so}(1,n-1)$, then it is contained in the similitude algebra $\mathfrak{sim}(n-2)$. There are 4 types of such holonomy algebras. Criterion how to find the type of $\mathfrak{g}$ are given, and special geometric structures corresponding to each type are described. To each $\mathfrak{g}$ there is a canonically associated subalgebra $\mathfrak{h}\subset\mathfrak{so}(n-2)$. An algorithm how to find $\mathfrak{h}$ is provided.Comment: 15 pages; the final versio

Reversible photodissipation of composite photochromic azobenzene-alginate supramolecular hydrogels

Supramolecular smart materials can quickly elicit macroscopic changes upon external stimulation. Here we report that an azobenzene-containing cyclic dipeptide can form composite supramolecular hydrogels with alginate based on the charge complementarity, at lower loading than the critical gelation concentrations of either component. The gels can reversibly dissipate to fluids with UV light. They can also encapsulate and photorelease fluorescent cargo. Upon treatment of the gels with aqueous calcium salts, the alginate component is permanently cross-linked and the photochromic component is solubilized

On the local structure of Lorentzian Einstein manifolds with parallel distribution of null lines

We study transformations of coordinates on a Lorentzian Einstein manifold with a parallel distribution of null lines and show that the general Walker coordinates can be simplified. In these coordinates, the full Lorentzian Einstein equation is reduced to equations on a family of Einstein Riemannian metrics.Comment: Dedicated to Dmitri Vladimirovich Alekseevsky on his 70th birthda

Fluorinated Azobenzenes Switchable with Red Light

Molecular photoswitches triggered with red or NIR light are optimal for photomodulation of complex biological systems, including efficient penetration of the human body for therapeutic purposes (“therapeutic window”). Yet, they are rarely reported, and even more rarely functional under aqueous conditions. In this work, fluorinated azobenzenes are shown to exhibit efficient E→Z photoisomerization with red light (PSS660nm >75 % Z) upon conjugation with unsaturated substituents. Initially demonstrated for aldehyde groups, this effect was also observed in a more complex structure by incorporating the chromophore into a cyclic dipeptide with propensity for self-assembly. Under physiological conditions, the latter molecule formed a supramolecular material that reversibly changed its viscosity upon irradiation with red light. Our observation can lead to design of new photopharmacology agents or phototriggered materials for in vivo use

Protocolos laboratoriais de análise molecular para investigação de doenças genéticas

The application of molecular analysis in the investigation of genetic diseases has been used as routine evaluation in laboratories worldwide in the last decade. More recently, the identification of specific mutations responsible for hereditary disorders made molecular diagnosis quicker and more efficient, making this analysis an excellent tool for the diagnosis of many diseases. Several techniques can be used and, among them, the Polymerase Chain Reaction (PCR) was a mark in the “molecular era”. In the last few years, the procedures have been automated gradually, which will allow the realization of a greater number of tests in a limited amount of time. The use of knowledge in Molecular Biology Techniques has been applied in many fields of Medicine. The advances made in the last decade demonstrate a huge potential of these technologies, which can be used not only for diagnosis, but also for treatment and prevention of hereditary disorders. The perspectives for the new century are very promising and indicate the possibility of great advances in the treatment of genetic diseases. The present article describes the main techniques used in the molecular analysis for the investigation of genetic diseases.A aplicação da análise molecular na investigação de doenças genéticas começou a ser utilizada como avaliação rotineira em laboratórios no decorrer da última década. Mais recentemente, a identificação de mutações específicas responsáveis por doenças hereditárias tornou o diagnóstico molecular mais rápido e eficaz, fazendo desta análise uma ótima ferramenta para diagnóstico de muitas destas doenças. Diversas técnicas laboratoriais são utilizadas para a análise molecular de doenças genéticas. Dentre estas destaca-se a reação em cadeia da polimerase (Polymerase Chain Reaction - PCR), que foi um marco na “era molecular”. Nos últimos anos, os procedimentos vem sendo automatizados gradativamente, o que irá propiciar a realização de maior número de testes num curto espaço de tempo. O uso dos conhecimentos da Biologia Molecular vem sendo aplicado nas mais variadas áreas da Medicina. No campo da genética molecular, os avanços das últimas décadas demostram um enorme potencial desta tecnologia, que pode ser utilizada não somente no diagnóstico mas também no tratamento e prevenção de doenças hereditárias. As perspectivas para o novo século são bastante promissoras e indicam a possibilidade de grandes avanços no tratamento de doenças. O presente artigo descreve as principais técnicas de análise molecular utilizadas para a investigação de doenças genéticas