A Perspective is presented on the history and current understanding of molecular gels and the factors that must be considered to characterize them. The abilities of the most important structural, ...dynamic, and rheological tools available currently to provide the information necessary to follow the formation of a molecular gel from its initial sol phase and then to define it at different distance and time scales are discussed. Approaches to determining a priori when a molecule will gelate a selected liquid, as well as possible methodologies for overcoming current limitations in understanding molecular gels, are presented. Finally, some of the many potential and realized applications for these materials are enumerated.
This Account presents recent advances in understanding how and why dilute solutions/sols of low-molecular-mass organic gelators (LMOGs) undergo microscopic phase separation to form self-assembled ...fibrillar networks in molecular organogels. Concepts are illustrated structurally at the subnanometer (molecular) to several millimeter (bulk) length scales and dynamically over time scales that follow the assembly of supersaturated solutions/sols into gel phases. Examples include both structurally complicated (ALS molecules with aromatic, linking, and steroidal groups) and simple (n-alkanes or n-alkanes along whose chains a hetero-group has been inserted) LMOGs in a wide range of organic liquids.
Molecular Gels Weiss, Richard G; Terech, Pierre
2005, 2005-12-12
eBook
"Molecular Gels: Materials with Self-Assembled Fibrillar Networks" is a comprehensive treatise on gelators, especially low molecular-mass gelators and the properties of their gels. The structures and ...modes of formation of the self-assembled fibrillar networks (SAFINs) that immobilize the liquid components of the gels are discussed experimentally and theoretically. The spectroscopic, rheological, and structural features of the different classes of low molecular-mass gelators are also presented. Many examples of the application of the principal analytical techniques for investigation of molecular gels (including SANS, SAXS, WAXS, UV-vis absorption, fluorescence and CD spectroscopies, scanning electron, transmission electron and optical microscopies, and molecular modeling) are presented didactically and in-depth, as are several of the theories of the stages of aggregation of individual low molecular-mass gelator molecules leading to SAFINs. Several actual and potential applications of molecular gels in disparate fields (from silicate replication of nanostructures to art conservation) are described. Special emphasis is placed on perspectives for future developments.
This book is an invaluable resource for researchers and practitioners either already researching self-assembly and soft matter or new to the area. Those who will find the book useful include chemists, engineers, spectroscopists, physicists, biologists, theoreticians, and materials scientists.
Properties and applications of synthetic thiol- and disulfide-based materials, principally polymers, are reviewed. Emphasis is placed on soft and self-assembling materials in which interconversion of ...the thiol and disulfide groups initiates stimulus-responses and/or self-healing for biomedical and non-biomedical applications.
Although a rich record of Pleistocene human-associated archaeological assemblages exists, the scarcity of hominin fossils often impedes the understanding of which hominins occupied a site. Using ...targeted enrichment of mitochondrial DNA, we show that cave sediments represent a rich source of ancient mammalian DNA that often includes traces of hominin DNA, even at sites and in layers where no hominin remains have been discovered. By automation-assisted screening of numerous sediment samples, we detected Neandertal DNA in eight archaeological layers from four caves in Eurasia. In Denisova Cave, we retrieved Denisovan DNA in a Middle Pleistocene layer near the bottom of the stratigraphy. Our work opens the possibility of detecting the presence of hominin groups at sites and in areas where no skeletal remains are found.
Complicated vascular anomalies have limited therapeutic options and cause significant morbidity and mortality. This Phase II trial enrolled patients with complicated vascular anomalies to determine ...the efficacy and safety of treatment with sirolimus for 12 courses; each course was defined as 28 days.
Treatment consisted of a continuous dosing schedule of oral sirolimus starting at 0.8 mg/m(2) per dose twice daily, with pharmacokinetic-guided target serum trough levels of 10 to 15 ng/mL. The primary outcomes were responsiveness to sirolimus by the end of course 6 (evaluated according to functional impairment score, quality of life, and radiologic assessment) and the incidence of toxicities and/or infection-related deaths.
Sixty-one patients were enrolled; 57 patients were evaluable for efficacy at the end of course 6, and 53 were evaluable at the end of course 12. No patient had a complete response at the end of course 6 or 12 as anticipated. At the end of course 6, a total of 47 patients had a partial response, 3 patients had stable disease, and 7 patients had progressive disease. Two patients were taken off of study medicine secondary to persistent adverse effects. Grade 3 and higher toxicities attributable to sirolimus included blood/bone marrow toxicity in 27% of patients, gastrointestinal toxicity in 3%, and metabolic/laboratory toxicity in 3%. No toxicity-related deaths occurred.
Sirolimus was efficacious and well tolerated in these study patients with complicated vascular anomalies. Clinical activity was reported in the majority of the disorders.
Solvent properties play a central role in mediating the aggregation and self-assembly of molecular gelators and their growth into fibers. Numerous attempts have been made to correlate the solubility ...parameters of solvents and gelation abilities of molecular gelators, but a comprehensive comparison of the most important parameters has yet to appear. Here, the degree to which partition coefficients (log P), Henry’s law constants (HLC), dipole moments, static relative permittivities (εr), solvatochromic E T(30) parameters, Kamlet–Taft parameters (β, α, and π), Catalan’s solvatochromic parameters (SPP, SB, and SA), Hildebrand solubility parameters (δ i ), and Hansen solubility parameters (δp, δd, δh) and the associated Hansen distance (R ij ) of 62 solvents (covering a wide range of properties) can be correlated with the self-assembly and gelation of 1,3:2,4-dibenzylidene sorbitol (DBS) gelation, a classic molecular gelator, is assessed systematically. The approach presented describes the basis for each of the parameters and how it can be applied. As such, it is an instructional blueprint for how to assess the appropriate type of solvent parameter for use with other molecular gelators as well as with molecules forming other types of self-assembled materials. The results also reveal several important insights into the factors favoring the gelation of solvents by DBS. The ability of a solvent to accept or donate a hydrogen bond is much more important than solvent polarity in determining whether mixtures with DBS become solutions, clear gels, or opaque gels. Thermodynamically derived parameters could not be correlated to the physical properties of the molecular gels unless they were dissected into their individual HSPs. The DBS solvent phases tend to cluster in regions of Hansen space and are highly influenced by the hydrogen-bonding HSP, δh. It is also found that the fate of this molecular gelator, unlike that of polymers, is influenced not only by the magnitude of the distance between the HSPs for DBS and the HSPs of the solvent, R ij , but also by the directionality of R ij : if the solvent has a larger hydrogen-bonding HSP (indicating stronger H-bonding) than that of the DBS, then clear gels are formed; opaque gels form when the solvent has a lower δh than does DBS.
The self-assembly behavior of a series of glucono-appended 1-pyrenesulfonyl derivatives containing α,ω-diaminoalkane spacers (Pn , where n , the number of methylene units separating the amino groups, ...is 2, 3, 4, 6, 7, and 8) in v:v tetrahydrofuran (THF):water mixtures is examined at room temperature. The Pn at 2 w/v % concentrations do not dissolve in either THF or water at room temperature. However, the Pn can be dissolved in some THF:water mixtures, and they form gels spontaneously in other compositions without dissolving completely. The self-assembly of the Pn in the liquid mixtures has been investigated using a variety of techniques. The particle sizes of the Pn in their solutions/sols, critical gelation concentrations, microstructures, thermal and mechanical stabilities of the gels, and molecular packing modes of Pn molecules in their gel networks are found to be very dependent on the composition of the liquid mixtures. Correlations between the self-assembly behavior of the Pn and the polarity of the liquid mixtures, as probed by E T(30) and Hansen solubility parameters, yield both qualitative and quantitative insights into why self-assembly of the Pn can or cannot be achieved in different liquid compositions. As revealed by UV–vis and fluorescence spectroscopy studies, π–π stacking of the pyrenyl groups occurs as part of the aggregation process. Correlations between the rheological properties of the gels and the Hansen solubility parameters of the Pn and the solvent mixtures indicate that hydrogen-bonding interactions are a major contributor to the mechanical stability. Overall, the results of this study offer a new strategy to investigate the balance between dissolution and aggregation of molecular gelators. To the best of our knowledge, this is the first example of the spontaneous formation of molecular gels without heating by placing gelators in mixtures of liquids in which they are insoluble in the neat components.
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The structural and dynamic properties of molecular gels, made from 9 structurally-related mono-, di, and tri-hydroxymethylated alkanamide gelators, have been examined at different ...distance scales. The subtle changes in the gelator structures, in terms of the number of hydroxymethyl groups and the length of the alkanamide chain, have been correlated with the type of the self-assembled fibrillar networks and the viscoelasticity of the gels as well as the characteristics of the liquid as indicated by Hansen solubility parameters.
Some of the gels exhibit high degrees of thixotropy and very rapid recovery after the cessation of destructive strain. Gelation efficiencies—based upon the range of liquids gelated, the critical gelator concentrations, and the gel-sol transition temperatures—depend upon both the length of the fatty acid chain and the number of hydroxymethyl groups: the best gelator of the series contains the longest alkyl chain examined (hexadecyl) and two hydroxymethyl groups (i.e., better than the gelators with one or three groups). FT-IR and powder X-ray diffraction data indicate that hydrogen-bonding and molecular packing modes in the gels and the neat gelator powders are very similar. Polarizing optical microscopy images of the gels show that the morphology of the gel networks can be tuned by changing the cooling processes used to transform the sols into gels. In total, the observations and conclusions derived provide useful insights into the relationship between gelator structure and gel properties. These data will be useful to those interested in the a priori design of new gelators or other molecules undergoing a variety of self-assembly processes that lead to robust thermal- and mechano-reversible materials.
Molecular Gas in Three z ∼ 7 Quasar Host Galaxies Venemans, Bram P.; Walter, Fabian; Decarli, Roberto ...
Astrophysical journal/The Astrophysical journal,
08/2017, Letnik:
845, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present ALMA band 3 observations of the CO(6-5), CO(7-6), and C i 369 m emission lines in three of the highest-redshift quasar host galaxies at . These measurements constitute the highest-redshift ...CO detections to date. The target quasars have previously been detected in C ii 158 m emission and the underlying FIR dust continuum. We detect (spatially unresolved, at a resolution of >2″, or 14 kpc) CO emission in all three quasar hosts. In two sources, we detect the continuum emission around 400 m (rest-frame), and in one source we detect C i at low significance. We derive molecular gas reservoirs of (1-3) × 1010 in the quasar hosts, i.e., approximately only 10 times the mass of their central supermassive black holes. The extrapolated C ii-to-CO(1-0) luminosity ratio is 2500-4200, consistent with measurements in galaxies at lower redshift. The detection of the C i line in one quasar host galaxy and the limit on the C i emission in the other two hosts enables a first characterization of the physical properties of the interstellar medium in z ∼ 7 quasar hosts. In the sources, the derived global CO/C ii/C i line ratios are consistent with expectations from photodissociation regions, but not X-ray-dominated regions. This suggest that quantities derived from the molecular gas and dust emission are related to ongoing star-formation activity in the quasar hosts, providing further evidence that the quasar hosts studied here harbor intense starbursts in addition to their active nucleus.
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