First iron and cobalt(ii) hexabromoclathrochelates: structural, magnetic, redox, and electrocatalytic behavior

Hexafluorodiacetonealcohol, HFDA, HOC(CF3)2CH2COCH3, is sufficiently acidic to coordinate to metal ions in an ionized form as a chelating, uninegative ligand. Complexes of Ni2 + and Cu2+ may be isolated, most conveniently by using a tridentate nitrogen-containing macrocycle as co-ligand so that five-coordinate unipositive compounds are produced. In the presence of metal ions, HFDA readily undergoes template condensation reactions with diamino-ethane or -propane to give conplexes of ionized β-imino alcohols, e.g. -OC(CF3)2- CH2C(CH3) : N(CH2)2N : C(CH3)CH2C(CF3)20- ; these conplexes are neutral and square planar but become five-coordinate by solvation in, e.g., pyridine. The use of triamines H2N- (CH2),NH(CH2).NH2 (where n = 2 or 3) in template syntheses with HFDA gives complexes in which the metal ion is five-coordinate; these do not undergo solvation.

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Metal ion promoted synthesis of pentaazamacrocyclic complexes of a few first row transition metal series derived from 2,6-diaminopyridine

Journal of the Serbian Chemical Society ◽

10.2298/jsc0511273k ◽

2005 ◽

Vol 70 (11) ◽

pp. 1273-1281

Author(s):

Ali Khan ◽

Shabana Tabassum ◽

Nishat Begum ◽

Poonam Chingsubam

Keyword(s):

Magnetic Susceptibility ◽

Transition Metal ◽

1H Nmr ◽

Elemental Analysis ◽

Metal Ion ◽

Condensation Reaction ◽

Spectroscopic Techniques ◽

Conductivity Measurements ◽

Template Condensation ◽

Square Planar

Anew series of dichloro/dinitrato (2,6,9,13,18-pentaazacbicyclo [12.3.1]octadeca -1(18),14,16-triene) metal(II) [MLX2](M = Mn(II), Co(II), Ni(II) and Zn(II); X = Cl or NO3) and (2,6,9,13,18-pentaazacyclo[12.3.1]octadeca-1(18),14,16-triene) copper(II) dichloride/dinitrate [CuL]X2 (X = Cl or NO3) have been synthesized by the template condensation reaction of 2,6-diaminopyridine with 1,2-diaminoethane and 1,3-dibromopropane. The complexes were studied by elemental analysis, magnetic susceptibility and conductivity measurements. Various spectroscopic techniques, viz. IR, 1H-NMR, EPR, UV/Vis, were used to establish their structures. Except for the complexes of copper(II), which are square planar, all other complexes have octahedral structures.

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Unusual Ligand Isomerization Dictated by Coordination Requirements of the Metal Ion: A Double-Bond Shift in Cu(II)-Assisted Template Condensation between Diacetylpyridine and a Tripodal Tetramine

Inorganic Chemistry ◽

10.1021/ic990027n ◽

1999 ◽

Vol 38 (12) ◽

pp. 2974-2980 ◽

Cited By ~ 33

Author(s):

Elena V. Rybak-Akimova ◽

Alexander Y. Nazarenko ◽

Svetlana S. Silchenko

Keyword(s):

Double Bond ◽

Metal Ion ◽

Template Condensation ◽

Coordination Requirements ◽

Double Bond Shift

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Aspects of high-resolution imaging with a scanning ion microprobe

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010014511x ◽

1986 ◽

Vol 44 ◽

pp. 750-751

Author(s):

R. Levi-Setti ◽

J. M. Chabala ◽

Y. L. Wang

Keyword(s):

Metal Ion ◽

Secondary Ion Mass Spectrometry ◽

Chromatic Aberration ◽

Ion Source ◽

Ion Microprobe ◽

Emission Pattern ◽

Intrinsic Resolution ◽

Resolution Imaging ◽

20 Nm ◽

Secondary Ion

We have shown the feasibility of 20 nm lateral resolution in both topographic and elemental imaging using probes of this size from a liquid metal ion source (LMIS) scanning ion microprobe (SIM). This performance, which approaches the intrinsic resolution limits of secondary ion mass spectrometry (SIMS), was attained by limiting the size of the beam defining aperture (5μm) to subtend a semiangle at the source of 0.16 mr. The ensuing probe current, in our chromatic-aberration limited optical system, was 1.6 pA with Ga+ or In+ sources. Although unique applications of such low current probes have been demonstrated,) the stringent alignment requirements which they imposed made their routine use impractical. For instance, the occasional tendency of the LMIS to shift its emission pattern caused severe misalignment problems.

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Scanning ion microscopy images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010012583x ◽

1987 ◽

Vol 45 ◽

pp. 180-181

Author(s):

R. Levi-Setti ◽

J.M. Chabala ◽

Y.L. Wang

Keyword(s):

Metal Ion ◽

Secondary Emission ◽

Scanning Method ◽

Ion Channeling ◽

Secondary Ions ◽

High Resolution Images ◽

Ion Microscopy ◽

Z Contrast ◽

Focused Beams ◽

Microscopy Images

Finely focused beams extracted from liquid metal ion sources (LMIS) provide a wealth of secondary signals which can be exploited to create high resolution images by the scanning method. The images of scanning ion microscopy (SIM) encompass a variety of contrast mechanisms which we classify into two broad categories: a) Emission contrast and b) Analytical contrast.Emission contrast refers to those mechanisms inherent to the emission of secondaries by solids under ion bombardment. The contrast-carrying signals consist of ion-induced secondary electrons (ISE) and secondary ions (ISI). Both signals exhibit i) topographic emission contrast due to the existence of differential geometric emission and collection effects, ii) crystallographic emission contrast, due to primary ion channeling phenomena and differential oxidation of crystalline surfaces, iii) chemical emission or Z-contrast, related to the dependence of the secondary emission yields on the Z and surface chemical state of the target.

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Freeze-etch TEM of aqueous polymer gel network morphology

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100145327 ◽

1986 ◽

Vol 44 ◽

pp. 796-797

Author(s):

J. A. N. Zasadzinski ◽

R. K. Prud'homme

Keyword(s):

Metal Ion ◽

Polymer Network ◽

Polymer Gels ◽

Polymer Gel ◽

Deformation History ◽

Crosslinked Polymer ◽

Aqueous Polymer ◽

History Of ◽

Gel Network ◽

Network Morphology

The rheological and mechanical properties of crosslinked polymer gels arise from the structure of the gel network. In turn, the structure of the gel network results from: thermodynamically determined interactions between the polymer chain segments, the interactions of the crosslinking metal ion with the polymer, and the deformation history of the network. Interpretations of mechanical and rheological measurements on polymer gels invariably begin with a conceptual model of,the microstructure of the gel network derived from polymer kinetic theory. In the present work, we use freeze-etch replication TEM to image the polymer network morphology of titanium crosslinked hydroxypropyl guars in an attempt to directly relate macroscopic phenomena with network structure.

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Structures of c-di-GMP/cGAMP degrading phosphodiesterase VcEAL: identification of a novel conformational switch and its implication

Biochemical Journal ◽

10.1042/bcj20190399 ◽

2019 ◽

Vol 476 (21) ◽

pp. 3333-3353 ◽

Cited By ~ 3

Author(s):

Malti Yadav ◽

Kamalendu Pal ◽

Udayaditya Sen

Keyword(s):

Active Site ◽

Metal Binding ◽

Metal Ion ◽

Triosephosphate Isomerase ◽

Catalytic Mechanism ◽

Degradation Mechanism ◽

Structural Basis ◽

Conserved Residues ◽

Phosphodiester Bond ◽

Cyclic Dinucleotides

Cyclic dinucleotides (CDNs) have emerged as the central molecules that aid bacteria to adapt and thrive in changing environmental conditions. Therefore, tight regulation of intracellular CDN concentration by counteracting the action of dinucleotide cyclases and phosphodiesterases (PDEs) is critical. Here, we demonstrate that a putative stand-alone EAL domain PDE from Vibrio cholerae (VcEAL) is capable to degrade both the second messenger c-di-GMP and hybrid 3′3′-cyclic GMP–AMP (cGAMP). To unveil their degradation mechanism, we have determined high-resolution crystal structures of VcEAL with Ca2+, c-di-GMP-Ca2+, 5′-pGpG-Ca2+ and cGAMP-Ca2+, the latter provides the first structural basis of cGAMP hydrolysis. Structural studies reveal a typical triosephosphate isomerase barrel-fold with substrate c-di-GMP/cGAMP bound in an extended conformation. Highly conserved residues specifically bind the guanine base of c-di-GMP/cGAMP in the G2 site while the semi-conserved nature of residues at the G1 site could act as a specificity determinant. Two metal ions, co-ordinated with six stubbornly conserved residues and two non-bridging scissile phosphate oxygens of c-di-GMP/cGAMP, activate a water molecule for an in-line attack on the phosphodiester bond, supporting two-metal ion-based catalytic mechanism. PDE activity and biofilm assays of several prudently designed mutants collectively demonstrate that VcEAL active site is charge and size optimized. Intriguingly, in VcEAL-5′-pGpG-Ca2+ structure, β5–α5 loop adopts a novel conformation that along with conserved E131 creates a new metal-binding site. This novel conformation along with several subtle changes in the active site designate VcEAL-5′-pGpG-Ca2+ structure quite different from other 5′-pGpG bound structures reported earlier.

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