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2.
Crystals of the first sodalite‐type zeolite containing an all‐iron framework, a ferrolite, Ba8(Fe12O24)Nay(OH)6?x H2O, were synthesized using the hydroflux method in nearly quantitative yield. Ba8(Fe12O24)Nay(OH)6?x H2O crystallizes in the cubic space group with a=10.0476(1) Å. Slightly distorted FeO4 tetrahedra are linked to form Fe4O4 and Fe6O6 rings, which in turn yield channels and internal cavities that are characteristic of the sodalite structure. Barium, sodium, and hydroxide ions and water molecules are found in the channels and provide charge balance. Magnetic measurements indicate that the ferrolite exhibits magnetic order up to at least 700 K, with the field‐cooled and zero‐field‐cooled curves diverging. Analysis of the 57Fe Mössbauer spectra revealed two spectral components that have equal spectral areas, indicating the presence of two subsets of iron centers in the structure. Dehydrated versions of the ferrolite were also prepared by heating the sample.  相似文献   
3.
Primary alkyl amines (RNH2) have been empirically used to engineer various colloidal semiconductor nanocrystals (NCs). Here, we present a general mechanism in which the amine acts as a hydrogen/proton donor in the precursor conversion to nanocrystals at low temperature, which was assisted by the presence of a secondary phosphine. Our findings introduce the strategy of using a secondary phosphine together with a primary amine as new routes to prepare high‐quality NCs at low reaction temperatures but with high particle yields and reproducibility and thus, potentially, low production costs.  相似文献   
4.
Over the last century, a large number of physical and mathematical developments paired with rapidly advancing technology have allowed the field of quantum chemistry to advance dramatically. However, the lack of computationally efficient methods for the exact simulation of quantum systems on classical computers presents a limitation of current computational approaches. We report, in detail, how a set of pre-computed molecular integrals can be used to explicitly create a quantum circuit, i.e. a sequence of elementary quantum operations, that, when run on a quantum computer, obtains the energy of a molecular system with fixed nuclear geometry using the quantum phase estimation algorithm. We extend several known results related to this idea and discuss the adiabatic state preparation procedure for preparing the input states used in the algorithm. With current and near future quantum devices in mind, we provide a complete example using the hydrogen molecule of how a chemical Hamiltonian can be simulated using a quantum computer.  相似文献   
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Key advances within the past 10 years have transformed copper‐mediated radical polymerization from a technique which was not very tolerant of protic media into a range of closely related processes capable of controlling the polymerization of a wide range of monomers in pure water at ppm catalyst loadings. This approach has afforded water‐soluble macromolecules of desired molecular weight, architecture, and chemical functionality, with applications ranging from drug delivery to oil processing. In this Review we highlight and critically evaluate the synthetic methods that have been developed to control radical polymerization in water by using copper complexes as well as identify future areas of interest and challenges still to be overcome.  相似文献   
7.
Although long postulated, the existence of glycopyranosyl oxacarbenium ions as intermediates or transition states (TS) in chemical glycosylation reactions has not been convincingly demonstrated experimentally. It is anticipated that elucidation of such reactive species will greatly assist synthetic chemists to control the α/β stereoselectivity by rational means. Previous density functional theory (DFT) calculations from our group found that the torsion potential about C-2-O-2 in protected glycopyranosyl donors changed from a conventional 3-fold rotor to a 2-fold rotor with a strong syn (CH-2-C-2-O-2-CPg) preference once the donor was ionized to its oxacarbenium ion. This suggested to us that if CPg of the protecting group was a chiral carbon, then diastereoselectivity might be observed in glycosylation reactions that proceed through oxacarbenium ions. The hypothesis to test is as follows: if a nonparticipating O-2 racemic chiral protecting group exhibits diastereoselectivity in glycosylation reactions, then the reaction probably proceeds through an oxacarbenium ion intermediate or TS. We present data for O-2 ether-protected d-glucopyranosyl donors where the racemic protecting group 1-methyl 1'-methylcyclopropylmethyl (MCPM) provides the chirality. MCPM proves to be more activating than the O-2-benzyl ether, and in cases where the donor is otherwise deactivated, several examples of moderate diastereoselectivity are found. These results can be interpreted to indicate that a continuum of reactivity exists where some glycosyl donors form oxacarbenium ions in glycosylation reactions but more reactive donors do not. The strongly activating properties of the cyclopropylmethyl ether functionality and the ability to induce diastereoselectivity with chiral derivatives strongly suggest widespread applications.  相似文献   
8.
A polymerase chain reaction (PCR) derived method for preparing long DNA, consisting of multiple repeat units of one to ten base pairs, is described. Two seeding oligodeoxynucleotides, so‐called oligoseeds, which encode the repeat unit and produce a duplex with 5′‐overhangs, are extended using a thermostable archaeal DNA polymerase. Multiple rounds of heat–cool extension cycles, akin to PCR, rapidly elongate the oligoseed. Twenty cycles produced long DNA with uniformly repeating sequences to over 20 kilobases (kb) in length. The polynucleotides prepared include [A]n/[T]n, [AG]n/[TC]n, [A2G]n/[T2C]n, [A3G]n/[T3C]n, [A4G]n/[T4C]n, [A9G]n/[T9C]n, [GATC]n/[CTAG]n, and [ACTGATCAGC]n/[TGACTAGTCG]n, indicating that the method is extremely flexible with regard to the repeat length and base sequence of the initial oligoseeds. DNA of this length (20 kb≈7 μm) with strictly defined base reiterations should find use in nanomaterial applications.  相似文献   
9.
Legionaminic acid, Leg5,7Ac2, a nonulosonic acid like 5‐acetamido neuraminic acid (Neu5Ac, sialic acid), is found in cell surface glycoconjugates of bacteria including the pathogens Campylobacter jejuni, Acinetobacter baumanii and Legionella pneumophila. The presence of Leg5,7Ac2 has been correlated with virulence in humans by mechanisms that likely involve subversion of the host's immune system or interactions with host cell surfaces due to its similarity to Neu5Ac. Investigation into its role in bacterial physiology and pathogenicity is limited as there are no effective sources of it. Herein, we construct a de novo Leg5,7Ac2 biosynthetic pathway by combining multiple metabolic modules from three different microbial sources (Saccharomyces cerevisiae, C. jejuni, and L. pneumophila). Over‐expression of this de novo pathway in Escherichia coli that has been engineered to lack two native catabolic pathways, enables significant quantities of Leg5,7Ac2 (≈120 mg L?1 of culture broth) to be produced. Pure Leg5,7Ac2 could be isolated and converted into CMP‐activated sugar for biochemical applications and a phenyl thioglycoside for chemical synthesis applications. This first total biosynthesis provides an essential source of Leg5,7Ac2 enabling study of its role in prokaryotic and eukaryotic glycobiology.  相似文献   
10.
The NMR interactions of crystalline phases in the system Na2O-ZrO2-SiO2 have been studied by a combination of static and magic angle spinning NMR methods for the first time. A full multinuclear (17O, 23Na, 29Si and 91Zr) approach has been employed that allows the phases to be clearly identified. NMR interactions such as 29Si isotropic chemical shift correlate with the known structural units present. For 23Na the different sites can often be distinguished on the basis of differing quadrupolar interactions.  相似文献   
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