Noncanonical RNA Nucleosides as Molecular Fossils of an Early Earth—Generation by Prebiotic Methylations and Carbamoylations

The RNA‐world hypothesis assumes that life on Earth started with small RNA molecules that catalyzed their own formation. Vital to this hypothesis is the need for prebiotic routes towards RNA. Contemporary RNA, however, is not only constructed from the four canonical nucleobases (A, C, G, and U), it also contains many chemically modified (noncanonical) bases. A still open question is whether these noncanonical bases were formed in parallel to the canonical bases (chemical origin) or later, when life demanded higher functional diversity (biological origin). Here we show that isocyanates in combination with sodium nitrite establish methylating and carbamoylating reactivity compatible with early Earth conditions. These reactions lead to the formation of methylated and amino acid modified nucleosides that are still extant. Our data provide a plausible scenario for the chemical origin of certain noncanonical bases, which suggests that they are fossils of an early Earth.     

Structural studies of NaPO3-MoO3 glasses by solid-state nuclear magnetic resonance and Raman spectroscopy

Vitreous samples were prepared in the (100 - x)% NaPO(3)-x% MoO(3) (0 相似文献   

Promoting effect of ionic liquids on ligand substitution reactions

Ionic liquid solvents N-hexylpyridinium bistrifylimide ([C₆pyr][Tf₂N]] and 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) promoted the displacement of anionic ligands by pyridine derivatives in trans-(Ph₃P)₂Rh(CO)NO₃ to a much greater extent than did dichloromethane. Thus, addition of a slight excess of 2-fluoropyridine to trans-(Ph₃P)₂Rh(CO)NO₃ in [C₄mim][PF₆] gave a 29:71 product mixture of trans-(Ph₃P)₂Rh(CO)NO₃:[trans-(Ph₃P)₂Rh(CO)(2-fluoropyridine)][NO₃], while the ratio was 91:9 in dichloromethane.     

Fingerprint analysis and the application of HPTLC to the determination of identity and quality of botanicals, from an industry perspective

There are many examples of botanical identity methodology currently in use today; all have associated levels of confidence and, hence, application for their intended purpose. This paper addresses the application of some of these methods to identify and qualify commonly traded herbs. The relevance of botanical identity and quality within the dietary supplement industry has seen a dramatic increase in the last several years, and now with the current Good Manufacturing Practices (cGMPs) recently published and the requirement for 100% identity testing, there is an increased need for reliable methods of analysis and subsequent interpretation of the results or data derived from these methods, given the diversity of samples and matrixes seen on a daily basis in a commercial setting. Example applications of methods described herein illustrate how one can confidently and effectively satisfy the 100% identity rule of the cGMPs to identify crude raw materials and their powdered or liquid extracts as well as identify a majority of such ingredients in finished products with diverse matrixes. The three techniques discussed in this paper are viewed from a qualitative perspective with primary emphasis on the application of HPTLC to a variety of complex samples with varying degrees of difficulty of analysis and interpretation. The three methods discussed are (1) HPTLC, for its fingerprint/pattern recognition capabilities as well as marker compound analysis; (2) microscopy, for identification/recognition of unique cellular, anatomic features and characteristics of the target plant or adulterants; and (3) HPLC for marker compound identification, quantitation, and/or other fingerprint qualities it may contribute to the data set. To support the applications and methods described herein, this paper presents four key approaches to assist in the interpretation of the data collected in order to correctly determine the identity of botanicals and their powdered extracts: the "marker approach," the "multicomponent-based approach", the "pattern approach," and the "multipattern approach", and how these approaches can be used with a vanguard/rearguard strategy in analytical testing as well as forming a basis for the "functional fingerprint" and the concept of phytoequivalence.     

Breakup of air bubbles in water: memory and breakdown of cylindrical symmetry

Using high-speed video, we have studied air bubbles detaching from an underwater nozzle. As a bubble distorts, it forms a thin neck which develops a singular shape as it pinches off. As in other singularities, the minimum neck radius scales with the time until the breakup. However, because the air-water interfacial tension does not drive the breakup, even small initial cylindrical asymmetries are preserved throughout the collapse. This novel, nonuniversal singularity retains a memory of the nozzle shape, size, and tilt angle. In the last stages, the air appears to tear instead of pinch.     

A discussion on mean excess plots

The mean excess plot is a tool widely used in the study of risk, insurance and extreme values. One use is in validating a generalized Pareto model for the excess distribution. This paper investigates some theoretical and practical aspects of the use of the mean excess plot.     

Three-dimensional shear in granular flow

The evolution of granular shear flow is investigated as a function of height in a split-bottom Couette cell. Using particle tracking, magnetic-resonance imaging, and large-scale simulations, we find a transition in the nature of the shear as a characteristic height H* is exceeded. Below H* there is a central stationary core; above H* we observe the onset of additional axial shear associated with torsional failure. Radial and axial shear profiles are qualitatively different: the radial extent is wide and increases with height, while the axial width remains narrow and fixed.