Structural Studies on Na6Si8O19 — A Monophyllosilicate with a New Type of Layered Silicate Anion.

ChemInform ◽  
2006 ◽  
Vol 37 (6) ◽  
Author(s):  
H. Krueger ◽  
V. Kahlenberg ◽  
R. Kaindl
Keyword(s):  
Layered Silicate ◽  
Structural Studies ◽  
Silicate Anion ◽  
New Type

Structural studies of organoboron compounds. LVI. 1-Benzyl-7-methyl-3,5-diphenyl-2,4,6-trioxa-1-azonia-3-bora-5-boratabicyclo[3.3.0]octane and 1,4,6,9-tetramethyl-2,7-diphenyl-3,8,11,12-tetraoxa-1,6-diazonia-2,7-diboratatricyclo[5.3.1.12,6]dodecane

1992 ◽  
Vol 70 (11) ◽  
pp. 2809-2817 ◽  
Author(s):  
Wolfgang Kliegel ◽  
Gottfried Lubkowitz ◽  
Steven J. Rettig ◽  
James Trotter
Keyword(s):  
Solid State ◽  
Gas Phase ◽  
Phenylboronic Acid ◽  
Direct Methods ◽  
Structural Studies ◽  
Triclinic Space Group ◽  
Full Matrix ◽  
X Ray ◽  
Molar Ratios ◽  
New Type

The preparation of the N-(2-hydroxypropyl)-N-alkylhydroxylamines, 6a (R = CH3) and 6b (R = CH2Ph), and their reactions with phenylboronic acid are described. Regardless of the molar ratios of reactants employed, the reaction with 6b leads to the 1:2 condensate 1-benzyl-7-methyl-3,5-diphenyl-2,4,6-trioxa-1-azonia-3-bora-5-boratabicyclo[3.3.0]octane, 7, while that with 6a gives rise to the 1:1 condensate 1,4,6,9-tetramethyl-2,7-diphenyl-3,8,11,12-tetraoxa-1,6-diazonia-2,7-diboratatricyclo[5.3.1. 12,6]dodecane, 11 (the cyclic BONBON dimer of 4,6-dimethyl-2-phenyl-1,3-dioxa-4-aza-2-boracyclohexane, 9). Compounds 7 and 11 both crystallize in the triclinic space group [Formula: see text]: for 7; a = 13.126(1), b = 15.337(1), c = 10.9469(5) Å, α = 91.727(5), β = 104.647(5), γ = 72.922(7)°, Z = 4; and for 11; a = 9.0807(4), b = 9.1653(3), c = 6.4876(2) Å, α = 97.708(3), β = 108.830(3), γ = 89.188(4)°, Z = 1. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.038 and 0.032 for 5879 and 1827 reflections with I ≥ 3σ(F2), respectively. Compound 7 has the expected bicyclic pyroboronate structure, but represents the first reported N-substituted example of this type of compound. Bond lengths involving boron in 7 are (C) O—B(sp3) = 1.428(2) and 1.420(2), (B)O—B(sp3) = 1.472(2) and 1.468(2), N—B(sp3) = 1.737(2) and 1.762(2), C(phenyl)—B(sp3) = 1.588(2) and 1.584(2), (N)O—B(sp2) = 1.402(2) and 1.404(2), (B)O—B(sp2) = 1.331(2) and 1.329(2), C(phenyl)—B(sp2) = 1.555(3) and 1.553(2) Å. The X-ray analysis establishes a centrosymmetric, twofold N → B coordinated, dimeric structure in the solid state for 11 in which each B—O—N segment of a central six-membered BONBON ring is bridged by an O—C—C moiety. Compound 11 represents the first fully characterized example of a new type of "BONBON" compound. Bond distances involving the boron atom are (N)O—B = 1.465(1), (C)O—B = 1.428(1), N—B = 1.695(2), and C(phenyl)—B = 1.607(2) Å. Spectroscopic evidence indicates that in solution and in the gas phase this material exists predominantly as the monomer 9.

scholarly journals Novel polyadenylylation-dependent neutralization mechanism of the HEPN/MNT toxin/antitoxin system

2020 ◽  
Vol 48 (19) ◽  
pp. 11054-11067 ◽  
Author(s):  
Jianyun Yao ◽  
Xiangkai Zhen ◽  
Kaihao Tang ◽  
Tianlang Liu ◽  
Xiaolong Xu ◽  
...  
Keyword(s):  
Physiological Function ◽  
Shewanella Oneidensis ◽  
Tyrosine Residue ◽  
Structural Studies ◽  
Gene Module ◽  
Enzymatic Assays ◽  
New Type ◽  
Domain Protein

Abstract The two-gene module HEPN/MNT is predicted to be the most abundant toxin/antitoxin (TA) system in prokaryotes. However, its physiological function and neutralization mechanism remains obscure. Here, we discovered that the MntA antitoxin (MNT-domain protein) acts as an adenylyltransferase and chemically modifies the HepT toxin (HEPN-domain protein) to block its toxicity as an RNase. Biochemical and structural studies revealed that MntA mediates the transfer of three AMPs to a tyrosine residue next to the RNase domain of HepT in Shewanella oneidensis. Furthermore, in vitro enzymatic assays showed that the three AMPs are transferred to HepT by MntA consecutively with ATP serving as the substrate, and this polyadenylylation is crucial for reducing HepT toxicity. Additionally, the GSX10DXD motif, which is conserved among MntA proteins, is the key active motif for polyadenylylating and neutralizing HepT. Thus, HepT/MntA represents a new type of TA system, and the polyadenylylation-dependent TA neutralization mechanism is prevalent in bacteria and archaea.

Ribosome Structural Organization

1974 ◽  
Vol 32 ◽  
pp. 332-333
Author(s):  
James A. Lake
Keyword(s):  
Ribosomal Proteins ◽  
Structural Organization ◽  
Three Dimensional ◽  
Small Subunit ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Specific Antibodies ◽  
X Ray ◽  
E Coli ◽  
Complete Sequences

The understanding of ribosome structure has advanced considerably in the last several years. Biochemists have characterized the constituent proteins and rRNA's of ribosomes. Complete sequences have been determined for some ribosomal proteins and specific antibodies have been prepared against all E. coli small subunit proteins. In addition, a number of naturally occuring systems of three dimensional ribosome crystals which are suitable for structural studies have been observed in eukaryotes. Although the crystals are, in general, too small for X-ray diffraction, their size is ideal for electron microscopy.

Structural Studies on Mitotic Spindle Fibres

1978 ◽  
Vol 36 (3) ◽  
pp. 615-626
Author(s):  
J.R. Mcintosh
Keyword(s):  
Chemical Composition ◽  
Mitotic Spindle ◽  
Structural Studies ◽  
Mitotic Apparatus ◽  
Chemical Studies ◽  
Medical Interest ◽  
Spindle Fibres

The mitotic apparatus is a structure of obvious biological and medical interest, but it has proved to be a difficult cellular machine to understand. The chemical composition of the spindle is only slightly elucidated, largely because of the difficulties in preparing useful isolates of the structure. Chemical studies of the mitotic spindle have been reviewed elsewhere (Mcintosh, 1977), and will not be discussed further here. One would think that structural studies on the mitotic apparatus (MA) in situ would be straightforward, but even with this approach there is some disagreement in the results obtained with various methods and by different investigators. In this paper I will review briefly the approaches which have been used in structural studies of the MA, pointing out the strengths and problems of each approach. I will summarize the principal findings of the different methods, and identify what seem to be fruitful avenues for further work.

The Microstructure of Shock-Synthesized Diamond

1967 ◽  
Vol 25 ◽  
pp. 324-325
Author(s):  
Lucien F. Trueb
Keyword(s):  
Single Crystals ◽  
Preferred Orientation ◽  
High Magnification ◽  
Texture Pattern ◽  
Shock Process ◽  
New Type ◽  
Diffraction Diagram

A new type of synthetic industrial diamond formed by an explosive shock process has been recently developed by the Du Pont Company. This material consists of a mixture of two basically different forms, as shown in Figure 1: relatively flat and compact aggregates of acicular crystallites, and single crystals in the form of irregular polyhedra with straight edges.Figure 2 is a high magnification micrograph typical for the fibrous aggregates; it shows that they are composed of bundles of crystallites 0.05-0.3 μ long and 0.02 μ. wide. The selected area diffraction diagram (insert in Figure 2) consists of a weak polycrystalline ring pattern and a strong texture pattern with arc reflections. The latter results from crystals having preferred orientation, which shows that in a given particle most fibrils have a similar orientation.

Image registration with a computer driven S.T.E.M.

1978 ◽  
Vol 36 (1) ◽  
pp. 98-99
Author(s):  
A.M.H. Schepman ◽  
J.A.P. van der Voort ◽  
J.E. Mellema
Keyword(s):  
Spot Size ◽  
Scanning Transmission Electron Microscope ◽  
Small Computer ◽  
Structural Studies ◽  
Area Of Interest ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Specimen Area ◽  
On Line ◽  
Minimum Distances

A Scanning Transmission Electron Microscope (STEM) was coupled to a small computer. The system (see Fig. 1) has been built using a Philips EM400, equipped with a scanning attachment and a DEC PDP11/34 computer with 34K memory. The gun (Fig. 2) consists of a continuously renewed tip of radius 0.2 to 0.4 μm of a tungsten wire heated just below its melting point by a focussed laser beam (1). On-line operation procedures were developped aiming at the reduction of the amount of radiation of the specimen area of interest, while selecting the various imaging parameters and upon registration of the information content. Whereas the theoretical limiting spot size is 0.75 nm (2), routine resolution checks showed minimum distances in the order 1.2 to 1.5 nm between corresponding intensity maxima in successive scans. This value is sufficient for structural studies of regular biological material to test the performance of STEM over high resolution CTEM.

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