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Plants and animals that thrive in arid regions utilize the diurnal changes in environmental temperature and humidity to optimize their water budget by combining water-harvesting mechanisms and morphophysiological traits. The Athel tamarisk (Tamarix aphylla) is a halophytic desert shrub that survives in arid, hypersaline conditions by excreting concentrated solutions of ions as droplets on its surface that crystallize into salt crystals and fall off the branches. Here, we describe the crystallization on the surface of the plant and explore the effects of external conditions such as diurnal changes in humidity and temperature. The salt mixtures contain at least ten common minerals, with NaCl and CaSO4·2H2O being the major products, SiO2 and CaCO3 main sand contaminants, and Li2SO4, CaSO4, KCl, K2Ca(SO4)2·H2O, CaMg(CO3)2 and AlNaSi3O8 present in smaller amounts. In natural conditions, the hanging or sitting droplets remain firmly attached to the surface, with an average adhesion force of 275 ± 3.5 µN measured for pure water. Rather than using morphological features of the surface, the droplets adhere by chemical interactions, predominantly by hydrogen bonding. Increasing ion concentration slightly increases the contact angle on the hydrophobic cuticle, thereby lowering surface wettability. Small amounts of lithium sulfate and possibly other hygroscopic salts result in strong hygroscopicity and propensity for deliquescence of the salt mixture overnight. Within a broader context, this natural mechanism for humidity harvesting that uses environmentally benign salts as moisture adsorbents could provide a bioinspired approach that complements the currently available water collection or cloud-seeding technologies.
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Emission from crystalline organic solids is often quenched by nonemissive energy-transfer deexcitation processes. While dispersion of fluorophores in polymers or other hosts has been used to enhance the emission intensity, this strategy results in randomization of guest orientation and optical losses at grain boundaries. Here, we report the doping of inherently nonemissive single crystals of anilinium bromide with three fluorescent organic molecules. The doping process equips the crystal with emission characteristics that tune from blue to deep orange. The emission intensity can be reversibly modulated by ferroelastic twinning, which causes the material to function as a multiemissive force sensor. This approach opens up new pathways in the manipulation of emissive properties in organic crystals and may have substantial implications for optoelectronic devices and sensors.
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The chemical reactions underlying the emission of light in fireflies and other bioluminescent beetles are some of the most thoroughly studied processes by scientists worldwide. Despite these remarkable efforts, fierce academic arguments continue around even some of the most fundamental aspects of the reaction mechanism behind the beetle bioluminescence. In an attempt to reach a consensus, we made an exhaustive search of the available literature and compiled the key discoveries on the fluorescence and chemiluminescence spectrochemistry of the emitting molecule, the firefly oxyluciferin, and its chemical analogues reported over the past 50+ years. The factors that affect the light emission, including intermolecular interactions, solvent polarity, and electronic effects, were analyzed in the context of both the reaction mechanism and the different colors of light emitted by different luciferases. The collective data points toward a combined emission of multiple coexistent forms of oxyluciferin as the most probable explanation for the variation in color of the emitted light. We also highlight realistic research directions to eventually address some of the remaining questions related to firefly bioluminescence. It is our hope that this extensive compilation of data and detailed analysis will not only consolidate the existing body of knowledge on this important phenomenon but will also aid in reaching a wider consensus on some of the mechanistic details of firefly bioluminescence.
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Besouros , Vaga-Lumes , Animais , Besouros/química , Vaga-Lumes/química , Luciferases/química , Luminescência , Medições LuminescentesRESUMO
Cataracts are the leading cause of blindness worldwide, however, there is currently no drug-based treatment. Plants that exhibit antioxidant properties have shown promising anticataract effects, likely because they supplement the activity of glutathione, the major antioxidant in lens cells. An extract of Cleome rupicola, a desert plant found in the United Arab Emirates, has traditionally been used to treat cataracts. Phytochemical screening of the aqueous extract established the presence of flavonoids, tannins, steroid derivatives, and reducing sugars. Fractioning of extracts from the fruits using high-performance liquid chromatography (HPLC) yielded the isolation of the anthelmintic compound cleomin, and its structure was confirmed using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy.
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Produtos Biológicos , Catarata , Cleome , Antioxidantes/farmacologia , Antioxidantes/análise , Extratos Vegetais/farmacologia , Extratos Vegetais/química , Cleome/química , Frutas/química , Flavonoides/análise , Cromatografia Líquida de Alta PressãoRESUMO
The melting of any pure crystalline material at constant pressure is one of its most fundamental properties, and it has been used to identify organic compounds or to verify their chemical or phase purity since the early times of chemistry. Here, we report that a mechanical deformation of plastic organic single crystals such as bending results in a small yet significant decrease in their melting point of about 0.3-0.4 K. The bent section of the crystal was found to be mechanically softer relative to the straight sections, and the softening temperature preceding the melting was also lower on the convex (outer) side of the bent crystal. Melting of the bent crystal starts at the kink and often appears as splitting of the respective endothermic peak in its thermal (DSC) fingerprint, while unilateral compression of the crystal results in multiple peaks. These thermomechanical effects become more pronounced with heavier mechanical damage due to an increased concentration of defects and ultimately result in a large temperature spread of the associated phase change in addition to melting-point depression in deformed or damaged crystals relative to their pristine counterparts. Within a broader context, the results show that mechanical treatment during sample preparation has a profound effect on the melting of a pure substance, and this could be critically important where the exact melting point is used as a means for polymorph identification.
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The anticipated shift in the focal point of interest of solid-state chemists, crystal engineers, and crystallographers from structure to properties to function parallels the need to apply our accumulated understanding of the intricacies of crystal structure to explaining the related properties, with the ultimate goal of harnessing that knowledge in applications that require soft, lightweight, or biocompatible organic solids. In these developments, the adaptive molecular crystals warrant particular attention as an alternative choice of materials for light, flexible, and environmentally benign devices, primarily memories, capacitors, sensors, and actuators. Some of the outstanding requirements for the application of these dynamic materials as high-efficiency energy-storage devices are strongly induced polarization, a high switching field, and narrow hysteresis in the case of reversible dynamic processes. However, having been studied almost exclusively by chemists, molecular crystals still lack the appropriate investigations that reliably evaluate their reproducibility, scalability, and actuating performance, and some important drawbacks have diverted the interest of engineers from these materials in applications. United under the umbrella term crystal adaptronics, the recent research efforts aim to realistically assess the appositeness of dynamic crystals for applications that require fast, reversible, and continuous operation over prolonged periods of time. With the aim of highlighting the most recent developments, this Perspective discusses their assets and pitfalls. It also provides some hints on the likely future developments that capitalize on the untapped, sequestered potential of this distinct materials class for applications.
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Mechanochemical analogues have recently been established for several enzymatic reactions, but they require periodic interruption of the reaction for sampling, dissolution, and (bio)chemical analysis to monitor their progress. By applying a mechanochemical procedure to induce bioluminescence analogous to that used by the marine ostracod Cypridina (Vargula) hilgendorfii, here we demonstrate that the light emitted by a bioluminescent reaction can be used to directly monitor the progress of a mechanoenzymatic reaction without sampling. Mechanical treatment of Cypridina luciferase with luciferin generates bright blue light which can be readily detected and analyzed spectroscopically. This mechanically assisted bioluminescence proceeds through a mechanism identical to that of bioluminescence in solution, but has higher activation energy due to being diffusion-controlled in the viscous matrix. The results suggest that luciferases could be used as light-emissive reporters of mechanoenzymatic reactions.
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Luciferases/metabolismo , Medições Luminescentes , Animais , Crustáceos , Luciferina de Vaga-Lumes/química , Luciferina de Vaga-Lumes/metabolismo , Luciferases/química , Estrutura MolecularRESUMO
The photochemical conversion of 1,8a-dihydroazulene-1,1-dicarbonitrile (DHA) to vinylheptafulvene (VHF) is a positive T-type photoswitch that is well understood in solution, but has not been explored in the solid state. Upon excitation with UV light, DHA is converted into VHF in the solid state, with a distinct color change from yellow to deep-red, and retention of crystallinity. The structure of the ring-opened product was assigned to syn-VHF using variable-temperature infrared spectroscopy, and determined by X-ray photodiffraction in a crystal enriched with the product by two-photon excitation. A radical pathway becomes an observable photoreaction channel at low temperatures, and includes a strongly colored, short-lived diradical intermediate.
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The mention of the word "crystal" invokes images of minerals, gems, and rocks, all of which are inevitably solid, hard, and durable entities with well-defined smooth faces and straight edges. With the discovery in the first half of the 20th century that many molecular crystals are soft and can be deformed in a similar way as rubber or plastic, this perception is changing, and both the concept and formal definition of what a crystal is may require reinterpretation. The seemingly naïve question posed in the title of this Minireview does not have a simple answer. Here, we discuss how the effects of the elastic and plastic deformation of molecular crystals on the diffraction signature give primary evidence of their degree of crystallinity. In most cases, the definition of a crystal holds for both elastically and plastically deformed crystals and, unless there is significant or complete physical separation of the crystal during the deformation, they can safely be considered (deformed) single crystals with a high concentration of defects.
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Ischemic heart disease often leads to myocardial infarction and remains the most common cause for death in humans. Although the exact impetus for the infarction remains elusive, a mechanism has been proposed that relates the disease to the observed high cholesterol levels in the body. The mechanism claims that cholesterol crystallizes inside the arterial plaque into needle-shaped crystals. The crystals puncture the fibrous cap of the plaque, whereby the necrotic contents of the plaque are spilled, subsequently clotting the blood vessels. This hypothesis has not been given sufficient attention partly due to the purported softness of the organic crystals and the common platy habit of the known crystal forms of cholesterol. In this work it is shown that, from hydrophobic solutions that attempt to emulate the plaque contents, a new solid form of cholesterol crystallizes as prisms with mucronate tips, and they are sufficiently strong to puncture a lamb pericardium, which mimics the plaque cap. The properties of the crystals were assessed by mechanical, structural, and crystallographic analyses. The results support the hypothesis that the cholesterol crystals can be considered, at least within the framework of the proposed mechanism, a possible cause of myocardial infarction.
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Colesterol/química , Pericárdio , Animais , Fenômenos Biomecânicos , Óleo de Milho/química , Cristalização , Humanos , Modelos Moleculares , Octanóis/química , Azeite de Oliva/química , Placa Aterosclerótica , Óleo de Brassica napus/química , Ovinos , SoluçõesRESUMO
One of the most inevitable limitations of any material that is exposed to mechanical impact is that they are inexorably prone to mechanical damage, such as cracking, denting, gouging, or wearing. To confront this challenge, the field of polymers has developed materials that are capable of autonomous self-healing and recover their macroscopic integrity similar to biological organisms. However, the study of this phenomenon has mostly remained within the soft materials community and has not been explored by solid-state organic chemists. The first evidence of self-healing in a molecular crystal is now presented using crystals of dipyrazolethiuram disulfide. The crystals were mildly compressed and the degree of healing was found to be 6.7 %. These findings show that the self-healing properties can be extended beyond mesophasic materials and applied towards the realm of ordered solid-state compounds.
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We describe the synthesis, characterization, photochemical isomerization, and rotational dynamics of a crystalline molecular gyroscope containing an azobenzene bridge (trans-2) that spans from one end of the stator to other, with the intention of exploring its function as a molecular brake. While single crystal X-ray diffraction analysis of a photochemically inactive dichloromethane solvate was used to confirm the molecular and packing structures of trans-2, a nanocrystalline pseudopolymorph was shown to be photoactive, and it was analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy, and variable temperature solid state (2)H NMR before and after photoisomerization. It was shown that the nanocrystalline suspension irradiated with λ = 340 nm reaches a photostationary state with 34% of cis-isomer, as compared to that observed in solution where the corresponding value is 74%. Line shape analysis of solid state (2)H NMR spectra of a phenylene-d4 isotopologue, obtained as a function of temperature, indicated that rotation in crystals of the trans-2 isomer, with a mean activation energy of 4.6 ± 0.6 kcal/mol and a pre-exponential factor exp(29.4 ± 1.7), is ten times faster than that of samples containing the cis-2 isomer, which has a higher mean activation energy of 5.1 ± 0.6 kcal/mol and a lower pre-exponential factor of exp(27.9 ± 1.3).
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Chemical and morphological traits of natural substrates that can propel and transport fluids over their surfaces have long provided inspiration for the engineering of artificial materials that can harvest and collect water from aerial humidity. Here we report that the gradual widening of parallel microchannels on a surface of a slowly subliming hexachlorobenzene crystal can promote the autonomous and bidirectional transduction of condensed aerial water. Driven by topology changes on the surface of the crystal and water exchange with the gas phase, droplets of condensed water migrate over the crystal. These droplets are also able to transport silver particles and other particulate matter, such as dust. The velocity of the particles was shown to be dependent on both the sublimation rate of the crystal and the relative humidity of its environment. This example of a sublimation-powered water flow demonstrates that topological surface changes accompanying crystal phase transitions can be harnessed to transport liquid and solid matter over surfaces.
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The outstanding performance and facile processability turn hybrid organic-inorganic perovskites into one of the most sought-after classes of semiconducting materials for optoelectronics. Yet, their translation into real-world applications necessitates that challenges with their chemical stability and poor mechanical robustness are first addressed. Here, centimeter-size single crystals of methylammoniumlead(II) iodide (MAPbI3 ) are reported to be capable of autonomous self-healing under minimal compression at ambient temperature. When crystals are halved and the fragments are brought in contact, they can readily self-repair as a result of a liquid-like behavior of their lattice at the contact surface, which leads to a remarkable healing with an efficiency of up to 82%. The successful reconstitution of the broken single crystals is reflected in recuperation of their optoelectronic properties. Testing of the healed crystals as photodetectors shows an impressive 74% recovery of the generated photocurrent relative to pristine crystals. This self-healing capability of MAPbI3 single crystals is an efficient strategy to overcome the poor mechanical properties and low wear resistance of these materials, and paves the way for durable and stable optoelectronic devices based on single crystals of hybrid perovskites.
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We describe the synthesis and characterization of six bridged molecular gyroscopes with m-alkoxy-substituted trityl stators and dialkynylphenylene rotators. All of the bridged molecular gyroscopes were synthesized convergently to form the phenolic stator-rotator framework, while the alkyl and benzophenone bridges were installed in one step by relatively efficient one-pot reactions to form macrocyclic diether or diester linkages. The isolated yield per bond-forming reaction varied from ca. 42% to 80%, with one exception where macrocyclization failed to produce the desired product. The molecular structure and crystal packing of each of the bridged molecular gyroscopes were determined via single crystal X-ray diffraction. Like most molecular gyroscopes with open topologies previously studied, the singly bridged structures pack by interdigitating one trityl stator in one molecule next to the rotator of an adjacent molecule in the lattice. In contrast, the triply bridged molecular gyroscopes were found to pack in lamellar sheets that prevent the rotator-stator interdigitation of adjacent molecules. However, solvent molecules and conformationally flexible bridges tend to fill in the packing volume by collapsing next to the rotator or by extending one of their bridges into the cavity of a neighboring molecule.
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Mechanically compliant organic crystals are the foundation of the development of future flexible, light-weight single-crystal electronics, and this requires reversibly deformable crystalline organic materials with permanent magnetism. Here, we report and characterize the first instance of a plastically bendable single crystal of a permanent organic radical, 4-(4'-cyano-2',3',4',5'-tetrafluorophenyl)-1,2,3,5-dithiadiazolyl. The weak interactions between the radicals render single crystals of the ß phase of this material exceedingly soft, and the S-N interactions facilitate plastic bending. EPR imaging of a bent single crystal reveals the effect of deformation on the three-dimensional spin density of the crystal. The unusual mechanical compliance of this material opens prospects for exploration into flexible crystals of other stable organic radicals towards the development of flexible light-weight organic magnetoresistance devices based on weak, non-hydrogen-bonded interactions in molecular crystals.
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The perception of organic crystals being rigid static entities is quickly eroding, and molecular crystals are now matching a number of properties previously thought to be unique to soft materials. Here, we present crystals of a boronate ester that encompass many of the elastic and plastic mechanical properties of polymers such as bending, twisting, coiling and highly efficient self-healing of up to 67%, while they maintain their long-range structural order. The approach utilizes the concept of dynamic covalent chemistry and proves it can be applied towards ordered materials. This work expands our current understanding of the properties of crystalline molecular materials, and it could have implications towards the development of mechanically robust organic crystals that are capable of self-repair for durable all-organic electronics and soft robotics.
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Actin plays fundamental roles in both the cytoplasm and the cell nucleus. In the nucleus, ß-actin regulates neuronal reprogramming by consolidating a heterochromatin landscape required for transcription of neuronal gene programs, yet it remains unknown whether it has a role in other differentiation models. To explore the potential roles of ß-actin in osteogenesis, ß-actin wild-type (WT) and ß-actin knockout (KO) mouse embryonic fibroblasts (MEFs) are reprogrammed to osteoblast-like cells using small molecules in vitro. It is discovered that loss of ß-actin leads to an accelerated mineralization phenotype (hypermineralization), accompanied with enhanced formation of extracellular hydroxyapatite microcrystals, which originate in the mitochondria in the form of microgranules. This phenotype is a consequence of rapid upregulation of mitochondrial genes including those involved in oxidative phosphorylation (OXPHOS) in reprogrammed KO cells. It is further found that osteogenic gene programs are differentially regulated between WT and KO cells, with clusters of genes exhibiting different temporal expression patterns. A novel function for ß-actin in osteogenic reprogramming through a mitochondria-based mechanism that controls cell-mediated mineralization is proposed.
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A fluorescent hollow crystal of 9,10-dicyanoanthracene was filled with a perylene diimide derivative with complementary emissive features. The obtained crystal-in-crystal hybrid was used as a multiresponsive optical waveguide, which showed passive and active modes of light transduction and a bandwidth that extends from the visible to the infrared region.
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Chemiluminescence, a process of transduction of energy stored within chemical bonds of ground-state reactants into light via high-energy excited intermediates, is known in solution, but has remained undetected in macroscopic crystalline solids. By detecting thermally induced chemiluminescence from centimeter-size crystals of an organic peroxide here we demonstrate direct transduction of heat into light by thermochemiluminescence of bulk crystals. Heating of crystals of lophine hydroperoxide to ~115 °C results in detectable emission of blue-green light with maximum at 530 nm with low chemiluminescent quantum yield [(2.1 ± 0.1) × 10â7 E molâ1]. Spectral comparison of the thermochemiluminescence in the solid state and in solution revealed that the solid-state thermochemiluminescence of lophine peroxide is due to emission from deprotonated lophine. With selected 1,2-dioxetane, endoperoxide and aroyl peroxide we also establish that the thermochemiluminescence is common for crystalline peroxides, with the color of the emitted light varying from blue to green to red.