Activated Ribonucleotides Undergo a Sugar Pucker Switch upon Binding to a Single-Stranded RNA Template

Template-directed polymerization of chemically activated ribonucleotide monomers, such as nucleotide 5′-phosphorimidazolides, has been studied as a model for nonenzymatic RNA replication during the origin of life. Kinetic studies of the polymerization of various nucleotide monomers on oligonucleotide templates have suggested that the A-form (C3′-<i>endo</i> sugar pucker) conformation is optimal for both monomers and templates for efficient copying. However, RNA monomers are predominantly in the C2′-<i>endo</i> conformation when free in solution, except for cytidine, which is approximately equally distributed between the C2′-<i>endo</i> and C3′-<i>endo</i> conformations. We hypothesized that ribonucleotides undergo a switch in sugar pucker upon binding to an A-type template and that this conformational switch allows or enhances subsequent polymerization. We used transferred nuclear Overhauser effect spectroscopy (TrNOESY), which can be used for specific detection of the bound conformation of small-molecule ligands with relatively weak affinity to receptors, to study the interactions between nucleotide 5′-phosphorimidazolides and single-stranded oligonucleotide templates. We found that the sugar pucker of activated ribonucleotides switches from C2′-<i>endo</i> in the free state to C3′-<i>endo</i> upon binding to an RNA template. This switch occurs only on RNA and not on DNA templates. Furthermore, activated 2′-deoxyribonucleotides maintain a C2′-<i>endo</i> sugar pucker in both the free and template-bound states. Our results provide a structural explanation for the observations that activated ribonucleotides are superior to activated deoxyribonucleotides and that RNA templates are superior to DNA templates in template-directed nonenzymatic primer-extension reactions

Nickel Catalyzed Cross-Coupling of Aryl C–O Based Electrophiles with Aryl Neopentylglycolboronates

The efficiency of mesylates, sulfamates, esters, carbonates, carbamates, and methyl ethers as C–O-based electrophiles attached to the 1- or 2-position of naphthalene and to activated and nonactivated phenyl substrates was compared for the first time in Ni-catalyzed cross-coupling with phenyl neopentylglycolboronates containing electron-rich and electron-deficient substituents in their <i>para</i>-position. These experiments were performed in the presence of four different Ni­(II)- and Ni(0)-based catalysts. Ni­(II)-based catalysts mediate the cross-coupling of most 2-naphthyl C–O electrophiles with both arylboronic acids and with neopentylglycolboronates when K₃PO₄ is used as base. The same catalysts are not efficient when CsF is used as base. However, Ni(0)-based catalysts exhibit selective efficiency, and when reactive, their efficiency is higher than that of Ni­(II)-based catalysts in the presence of both K₃PO₄ and CsF. These results provide both reaction conditions for the cross-coupling, and for the elaboration of orthogonal cross-coupling methodologies of various C–O based electrophiles with aryl neopentylglycolboronates. With the exception of mesylates and sulfamates the efficiency of all other 2-naphthyl C–O electrophiles was lower in cross-coupling with aryl neopentylglycolboronates than with arylboronic acid

Data_Sheet_1_Dehydration and rehydration affect brain regional density and homogeneity among young male adults, determined via magnetic resonance imaging: A pilot self-control trial.docx

The effects of dehydration and rehydration on brain regional density and homogeneity are unknown and have been infrequently studied. In this pilot self-control study, twelve participants aged 18-25 years were recruited and the brain was scanned using magnetic resonance imaging for three tests under different hydration statuses. In three tests, urine osmolality was determined to assess hydration status. Test 1 was conducted after 12 h of overnight fasting. Test 2 was conducted in a dehydration state induced by 36 h of water deprivation. Test 3 was conducted in a rehydration state, which was induced by 1.5 L of purified water supplementation. Compared with test 1, participants under the dehydration state in test 2 had higher cerebrospinal fluid density (p < 0.001). Compared with test 2, participants under the rehydration state in test 3 showed an extensive increase in gray matter density in widespread brain regions, mainly involving the left middle temporal gyrus, cuneus, right thalamus, left rolandic opercula, Brodmann area 39, right precentral, left postcentral gyrus, and cingulate gyrus (p < 0.001); a higher white matter density in the temporal lobe, sub-lobar, and sub-gyral areas; and a lower cerebrospinal fluid density (p < 0.001). The multimodal, multiscale neuroimaging marker of the human brain connection—the regional homogeneity (ReHo) index—was used for evaluating the connectivity of nodes in the brain. Compared with test 1, participants in test 2 had a lower ReHo value in the right amygdala, left occiput median, right lingual, opercula part of right inferior frontal gyrus, and right precuneus (p < 0.01). Compared with test 2, participants in test 3 had a higher ReHo value in the right amygdala, right lingual, opercula part of the right inferior frontal gyrus, and right precuneus (p < 0.01). Dehydration state increased cerebrospinal fluid density, decreased brain regional homogeneity. Rehydration state increased brain gray matter and white matter density widespreadly, and increased brain regional homogeneity.</p

Modeling the effects of capillary pressure with the presence of full tensor permeability and discrete fracture models using the mimetic finite difference method

Capillary dominated flow or imbibition—whether spontaneous or forced—is an important physical phenomena in understanding the behavior of naturally fractured water-driven reservoirs (NFR’s). When the water flows through the fractures, it imbibes into the matrix and pushes the oil out of the pores due to the difference in the capillary pressure. In this paper, we focus on modeling and quantifying the oil recovered from NFR’s through the imbibition processes using a novel fully implicit mimetic finite difference (MFD) approach coupled with discrete fracture/discrete matrix (DFDM) technique. The investigation is carried out in the light of different wetting states of the porous media (i.e., varying capillary pressure curves) and a full tensor representation of the permeability. The produced results proved the MFD to be robust in preserving the physics of the problem, and accurately mapping the flow path in the investigated domains. The wetting state of the rock affects greatly the oil recovery factors along with the orientation of the fractures and the principal direction of the permeability tensor. We can conclude that our novel MFD method can handle the fluid flow problems in discrete-fractured reservoirs. Future works will be focused on the extension of MFD method to more complex multi-physics simulations.Other Information Published in: Transport in Porous Media License: https://creativecommons.org/licenses/by/4.0See article on publisher's website: http://dx.doi.org/10.1007/s11242-021-01585-3</p

Multilayered Core–Shell Structure in an Impact Polypropylene Copolymer Investigated by Atomic Force Microscopy–Infrared

The balanced mechanical properties of impact polypropylene copolymer (IPC) are largely attributed to the core–shell structure of its dispersed rubber particles, yet experimental observation of the outer shell interface between the rubber phase and the polypropylene (PP) matrix is challenging. In this article, atomic force microscopy-infrared (AFM-IR) was employed to study a commercial IPC to determine its phase structure. Quantitative analysis of the nanodomain composition in situ by AFM-IR in combination with the chain structure of the copolymers obtained ex situ by fractionation and NMR revealed a core surrounded by a rubber layer, comprising the ethylene–propylene segmented copolymer (EsP) and ethylene–propylene random copolymer (EPR), respectively, which suggests the existence of an outer shell for the particle composed of the ethylene–propylene block copolymer (EbP). The EbP fraction in the IPC was then replaced by an ethylene-deuterated propylene diblock copolymer (EbDP), which was then melt-blended with all other fractions to reconstruct the IPC. Both AFM-IR spectroscopic analysis and imaging of the nanodomains in the reconstructed IPC showed that the EbDP molecules are located at the interface between the rubber phase and the PP matrix, forming an outer shell for the particle. The results provide direct and unambiguous experimental evidence for the multilayered particle structure in the IPC. Mechanical test results further demonstrated that the outer shell for the rubber particle was beneficial to the tensile and impact properties of the alloy

Geometric calibration of a stationary digital breast tomosynthesis system based on distributed carbon nanotube X-ray source arrays - Fig 5

<p>Comparisons of input values and extracted values of the coordinates of the CNT sources (Zs) (a) and the coordinates of the sources’ projections (<i>v</i>) (b).</p

Schematic representation of the imaging geometry, with two linear arrays of CNT sources arranged opposite the detectors to form the rectangular sDBT system.

<p>Schematic representation of the imaging geometry, with two linear arrays of CNT sources arranged opposite the detectors to form the rectangular sDBT system.</p

Sulfur-Doped MXene-Based Nanocomposites for Efficient Electromagnetic Wave Absorbers via Polarization and Magnetization

Ti3C2Tx (MXene) materials with multilayered structures have been widely investigated as promising absorption materials. However, the electromagnetic wave absorption performance of a single Ti3C2Tx MXene has always been limited by interface mismatches due to high reflectivity. In this work, sulfur-doped MXene-based nanocomposites were constructed by a mild doping and calcination method and performance was regulated by manipulating chemical composition, loading ratio, electromagnetic parameters, or impedance matching. Here, sulfur-doped MXene and titanium dioxide produced via high-temperature calcination (S-MXene (TiO2)) provided abundant defects and functional groups, resulting in dipole polarization relaxation. The introduction of Ag improved the electrical conductivity, and the CoNi alloy could enhance the magnetic loss and improve impedance matching. The electromagnetic wave absorption ability was enhanced thanks to the combined effects of suitable conductivity, dipole polarization, interface polarization, and magnetic loss. The S-MXene (TiO2)/Ag/CoNi nanocomposites exhibited a high reflection loss of −63.1 dB at a thickness of 2.1 mm and a wide effective absorption bandwidth of 5.2 GHz at a thickness of 2.0 mm. Moreover, by adjusting the mass ratio of nanocomposites’ components, the minimum reflection loss value was up to −80.9 dB at only 1.5 mm. This mechanism of increasing material loss through doping is of great significance for improving the electromagnetic wave absorption of MXene-based nanocomposites

Comparisons of the set geometric parameters and the extracted simulation parameters.

<p>Comparisons of the set geometric parameters and the extracted simulation parameters.</p

Comparisons of the input geometric parameters and the extracted simulation parameters.

<p>Comparisons of the input geometric parameters and the extracted simulation parameters.</p