| 1091. |
- Sun, Jian-Ke, et al.
(författare)
-
Enhancing crystal growth using polyelectrolyte solutions and shear flow
- 2020
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 579:7797, s. 73-79
-
Tidskriftsartikel (refereegranskat)abstract
- The ability to grow properly sized and good quality crystals is one of the cornerstones of single-crystal diffraction, is advantageous in many industrial-scale chemical processes(1-3), and is important for obtaining institutional approvals of new drugs for which high-quality crystallographic data are required(4-7). Typically, single crystals suitable for such processes and analyses are grown for hours to days during which any mechanical disturbances-believed to be detrimental to the process-are carefully avoided. In particular, stirring and shear flows are known to cause secondary nucleation, which decreases the final size of the crystals (though shear can also increase their quantity(8-14)). Here we demonstrate that in the presence of polymers (preferably, polyionic liquids), crystals of various types grow in common solvents, at constant temperature, much bigger and much faster when stirred, rather than kept still. This conclusion is based on the study of approximately 20 diverse organic molecules, inorganic salts, metal-organic complexes, and even some proteins. On typical timescales of a few to tens of minutes, these molecules grow into regularly faceted crystals that are always larger (with longest linear dimension about 16 times larger) than those obtained in control experiments of the same duration but without stirring or without polymers. We attribute this enhancement to two synergistic effects. First, under shear, the polymers and their aggregates disentangle, compete for solvent molecules and thus effectively 'salt out' (that is, induce precipitation by decreasing solubility of) the crystallizing species. Second, the local shear rate is dependent on particle size, ultimately promoting the growth of larger crystals (but not via surface-energy effects as in classical Ostwald ripening). This closed-system, constant-temperature crystallization driven by shear could be a valuable addition to the repertoire of crystal growth techniques, enabling accelerated growth of crystals required by the materials and pharmaceutical industries.
|
|
| 1092. |
- Sun, Junliang, et al.
(författare)
-
The ITQ-37 mesoporous chiral zeolite
- 2009
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 458, s. 1154-1157
-
Tidskriftsartikel (refereegranskat)abstract
- The synthesis of crystalline molecular sieves with pore dimensions that fill the gap between microporous and mesoporous materials is a matter of fundamental and industrial interest. The preparation of zeolitic materials with extralarge pores and chiral frameworks would permit many new applications. Two important steps in this direction include the synthesis of ITQ-33, a stable zeolite with 18 × 10 × 10 ring windows, and the synthesis of SU-32, which has an intrinsically chiral zeolite structure and where each crystal exhibits only one handedness. Here we present a germanosilicate zeolite (ITQ-37) with extralarge 30-ring windows. Its structure was determined by combining selected area electron diffraction (SAED) and powder X-ray diffraction (PXRD) in a charge-flipping algorithm. The framework follows the SrSi2 (srs) minimal net and forms two unique cavities, each of which is connected to three other cavities to form a gyroidal channel system. These cavities comprise the enantiomorphous srs net of the framework. ITQ-37 is the first chiral zeolite with one single gyroidal channel. It has the lowest framework density (10.3 T atoms per 1,000 Å3) of all existing 4-coordinated crystalline oxide frameworks, and the pore volume of the corresponding silica polymorph would be 0.38 cm3 g-1. Keywords: srs-net, powder X-ray, charge flipping, electron microscopy
|
|
| 1093. |
- Sund, Johan, et al.
(författare)
-
Principles of stop-codon reading on the ribosome
- 2010
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 465:7300, s. 947-U12
-
Tidskriftsartikel (refereegranskat)abstract
- In termination of protein synthesis, the bacterial release factors RF1 and RF2 bind to the ribosome through specific recognition of messenger RNA stop codons and trigger hydrolysis of the bond between the nascent polypeptide and the transfer RNA at the peptidyl-tRNA site, thereby releasing the newly synthesized protein. The release factors are highly specific for a U in the first stop-codon position 1 and recognize different combinations of purines in the second and third positions, with RF1 reading UAA and UAG and RF2 reading UAA and UGA. With recently determined crystal structures of termination complexes(2-4), it has become possible to decipher the energetics of stop-codon reading by computational analysis and to clarify the origin of the high release-factor binding accuracy. Here we report molecular dynamics free-energy calculations on different cognate and non-cognate termination complexes. The simulations quantitatively explain the basic principles of decoding in all three codon positions and reveal the key elements responsible for specificity of the release factors. The overall reading mechanism involves hitherto unidentified interactions and recognition switches that cannot be described in terms of a tripeptide anticodon model. Further simulations of complexes with tRNA(Trp), the tRNA recognizing the triplet codon for Trp, explain the observation of a 'leaky' stop codon 5 and highlight the fundamentally different third position reading by RF2, which leads to a high stop-codon specificity with strong discrimination against the Trp codon. The simulations clearly illustrate the versatility of codon reading by protein, which goes far beyond tRNA mimicry.
|
|
| 1094. |
- Sundin, Josefin
(författare)
-
Reply to: Methods matter in repeating ocean acidification studies
- 2020
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 586, s. E25-E27
-
Tidskriftsartikel (refereegranskat)abstract
- Pioneering papers by Munday and colleagues have reported profound effects of end-of-century ocean acidification—simulated by experimentally elevated CO2 levels in seawater—on the behaviour of coral reef fishes, such as extreme attraction of prey species to the chemical cues of their predators. Later studies by the same group reported that a range of other behaviours of coral reef fishes, including swimming activity, behavioural lateralization, homing and different predator avoidance behaviours, were also impaired by ocean acidification and that predator-escape behaviours in a coral reef mollusc were also impaired through the same physiological mechanism reported for fishes (that is, through effects on ‘GABAA-like receptors’), which led to the idea that “elevated-CO2 could cause behavioural impairment in a broad suite of marine animals”. In 2014, we initiated experiments to further explore the physiological mechanism(s) that impaired coral reef fish behaviour in elevated levels of CO2; however, we immediately ran into a problem: despite several attempts, and many improvements to the standard methodology used in this field, we were unable to observe an effect of ocean acidification on fish behaviour. Our initial goal changed from what was meant to be a series of original experiments into a three-year effort to transparently examine behavioural effects of ocean acidification in coral reef fishes; the findings of our study are the basis for the accompanying Comment by Munday et al.
|
|
| 1095. |
- Suzuki, Ken, et al.
(författare)
-
Genetic drivers of heterogeneity in type 2 diabetes pathophysiology
- 2024
-
Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 627:8003, s. 347-357
-
Tidskriftsartikel (refereegranskat)abstract
- Type 2 diabetes (T2D) is a heterogeneous disease that develops through diverse pathophysiological processes1,2 and molecular mechanisms that are often specific to cell type3,4. Here, to characterize the genetic contribution to these processes across ancestry groups, we aggregate genome-wide association study data from 2,535,601 individuals (39.7% not of European ancestry), including 428,452 cases of T2D. We identify 1,289 independent association signals at genome-wide significance (P < 5 × 10−8) that map to 611 loci, of which 145 loci are, to our knowledge, previously unreported. We define eight non-overlapping clusters of T2D signals that are characterized by distinct profiles of cardiometabolic trait associations. These clusters are differentially enriched for cell-type-specific regions of open chromatin, including pancreatic islets, adipocytes, endothelial cells and enteroendocrine cells. We build cluster-specific partitioned polygenic scores5 in a further 279,552 individuals of diverse ancestry, including 30,288 cases of T2D, and test their association with T2D-related vascular outcomes. Cluster-specific partitioned polygenic scores are associated with coronary artery disease, peripheral artery disease and end-stage diabetic nephropathy across ancestry groups, highlighting the importance of obesity-related processes in the development of vascular outcomes. Our findings show the value of integrating multi-ancestry genome-wide association study data with single-cell epigenomics to disentangle the aetiological heterogeneity that drives the development and progression of T2D. This might offer a route to optimize global access to genetically informed diabetes care.
|
|
| 1096. |
- Svedberg, The
(författare)
-
Determination of the molecular weight of insulin
- 1931
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 127, s. 438-439
-
Tidskriftsartikel (refereegranskat)abstract
- AT the suggestion of Dr. H. Jensen, of the Johns Hopkins University, Baltimore, an ultracentrifugal investigation of insulin has been carried out in my laboratory by Mr. B. Sjögren. A quantity of 0.25 gm. crystalline insulin was kindly put at my disposal by Dr. Jensen, and this small sample proved sufficient for a fairly complete study of the molecular weight and pH-stability region of insulin.
|
|
| 1097. |
|
|
| 1098. |
|
|
| 1099. |
- Säterberg, Torbjörn, et al.
(författare)
-
High frequency of functional extinctions in ecological networks
- 2013
-
Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 499:7459, s. 468-
-
Tidskriftsartikel (refereegranskat)abstract
- Intensified exploitation of natural populations and habitats has led to increased mortality rates and decreased abundances of many species(1,2). There is a growing concern that this might cause critical abundance thresholds of species to be crossed(1,3-5), with extinction cascades and state shifts in ecosystems as a consequence(4,6,7). When increased mortality rate and decreased abundance of a given species lead to extinction of other species, this species can be characterized as functionally extinct even though it still exists. Although such functional extinctions have been observed in some ecosystems(3,4,8), their frequency is largely unknown. Here we use a new modelling approach to explore the frequency and pattern of functional extinctions in ecological networks. Specifically, we analytically derive critical abundance thresholds of species by increasing their mortality rates until an extinction occurs in the network. Applying this approach on natural and theoretical food webs, we show that the species most likely to go extinct first is not the one whose mortality rate is increased but instead another species. Indeed, up to 80% of all first extinctions are of another species, suggesting that a species ecological functionality is often lost before its own existence is threatened. Furthermore, we find that large-bodied species at the top of the food chains can only be exposed to small increases in mortality rate and small decreases in abundance before going functionally extinct compared to small-bodied species lower in the food chains. These results illustrate the potential importance of functional extinctions in ecological networks and lend strong support to arguments advocating a more community-oriented approach in conservation biology, with target levels for populations based on ecological functionality rather than on mere persistence(8-11).
|
|
| 1100. |
|
|
