Using a non-spin flip model to rationalize the irregular patterns observed in the activation of the C–H and Si–H bonds of small molecules by CpMCO (M = Co, Rh) complexes

2017 ◽  
Vol 19 (36) ◽  
pp. 25115-25121 ◽  
Author(s):  
Guadalupe Castro ◽  
Fernando Colmenares
Keyword(s):  
Small Molecules ◽  
Reaction Scheme ◽  
Radical Species ◽  
Spin Flip

Irregularities observed in activation reactions of the C–H and Si–H bonds by CpCoCO and CpRhCO are explained in terms of a two-step reaction scheme involving radical species.

scholarly journals Applying a Nonspin-Flip Reaction Scheme to Explain for the Doublet Sulfide Oxides SMO2 Observed for the Reactions of SO2 with V(4F), Nb(6D), and Ta(4F)

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Carlos Velásquez ◽  
Ana E. Torres ◽  
Jorge M. Seminario ◽  
Fernando Colmenares
Keyword(s):  
Matrix Isolation ◽  
Electronic States ◽  
Reaction Scheme ◽  
Stable Structure ◽  
Radical Species ◽  
Oxide Product ◽  
Energy Profiles

Energy profiles linking the reactants M + SO2 (M = V(4F), Nb(6D;4F), and Ta(4F)) with the products observed for these reactions under matrix-isolation conditions, mainly the oxide complex OV(η2-SO) and the sulfide oxides SVO2, SNbO2, and STaO2, have been obtained from DFT and CASSCF-MRMP2 calculations. For each of these interactions, the radical fragments MO + SO can be reached from the lowest-lying quadruplet electronic states of the reactants. As the quadruplet and doublet radical asymptotes that vary only in the spin of the unpaired parallel electrons of the nonmetallic fragment are degenerated, a second reaction leading to the rebounding of the radical fragments can take place through both multiplicity channels. Reaction along the doublet pathway leads in each case to the most stable structure for the oxide SMO2. For the vanadium interaction, recombination of the radical species through the quadruplet channel explains for the oxide product OV(η2-SO).

Gap junctions in the prothoracic glands of the tobacco hornworm, Manduca sexta

1992 ◽  
Vol 50 (1) ◽  
pp. 706-707
Author(s):  
Ji-da Dai ◽  
M. Joseph Costello ◽  
Lawrence I. Gilbert
Keyword(s):  
Gap Junctions ◽  
Small Molecules ◽  
Manduca Sexta ◽  
Freeze Fracture ◽  
Cell Communication ◽  
Cellular Level ◽  
Thin Sections ◽  
Prothoracic Glands ◽  
Polyhydroxylated Steroids ◽  
Stimulation Of

Insect molting and metamorphosis are elicited by a class of polyhydroxylated steroids, ecdysteroids, that originate in the prothoracic glands (PGs). Prothoracicotropic hormone stimulation of steroidogenesis by the PGs at the cellular level involves both calcium and cAMP. Cell-to-cell communication mediated by gap junctions may play a key role in regulating signal transduction by controlling the transmission of small molecules and ions between adjacent cells. This is the first report of gap junctions in the PGs, the evidence obtained by means of SEM, thin sections and freeze-fracture replicas.

Time-Resolved Cryo-Electron Microscopy of Oscillating Microtubules

1990 ◽  
Vol 48 (1) ◽  
pp. 502-503
Author(s):  
Eva-Maria Mandelkow ◽  
Ron Milligan
Keyword(s):  
Electron Microscopy ◽  
Dynamic Instability ◽  
Entire Solution ◽  
Reaction Scheme ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
A Chain ◽  
Ray Scattering

Microtubules form part of the cytoskeleton of eukaryotic cells. They are hollow libers of about 25 nm diameter made up of 13 protofilaments, each of which consists of a chain of heterodimers of α-and β-tubulin. Microtubules can be assembled in vitro at 37°C in the presence of GTP which is hydrolyzed during the reaction, and they are disassembled at 4°C. In contrast to most other polymers microtubules show the behavior of “dynamic instability”, i.e. they can switch between phases of growth and phases of shrinkage, even at an overall steady state [1]. In certain conditions an entire solution can be synchronized, leading to autonomous oscillations in the degree of assembly which can be observed by X-ray scattering (Fig. 1), light scattering, or electron microscopy [2-5]. In addition such solutions are capable of generating spontaneous spatial patterns [6].In an earlier study we have analyzed the structure of microtubules and their cold-induced disassembly by cryo-EM [7]. One result was that disassembly takes place by loss of protofilament fragments (tubulin oligomers) which fray apart at the microtubule ends. We also looked at microtubule oscillations by time-resolved X-ray scattering and proposed a reaction scheme [4] which involves a cyclic interconversion of tubulin, microtubules, and oligomers (Fig. 2). The present study was undertaken to answer two questions: (a) What is the nature of the oscillations as seen by time-resolved cryo-EM? (b) Do microtubules disassemble by fraying protofilament fragments during oscillations at 37°C?

Fusion and Fission Processes in Exocytosis: Possible Roles for Synexin and Osmotic Lysis in the Two Events

1980 ◽  
Vol 38 ◽  
pp. 594-597
Author(s):  
H.B. Pollard ◽  
C.E. Creutz ◽  
C.J. Pazoles ◽  
J.H. Scott
Keyword(s):  
Small Molecules ◽  
Chromaffin Cells ◽  
Adrenal Glands ◽  
General Concept ◽  
Extracellular Calcium ◽  
Large Protein ◽  
Granule Membrane ◽  
Osmotic Lysis ◽  
Per Se ◽  
Chemical Evidence

Exocytosis is a general concept describing secretion of enzymes, hormones and transmitters that are otherwise sequestered in intracellular granules. Chemical evidence for this concept was first gathered from studies on chromaffin cells in perfused adrenal glands, in which it was found that granule contents, including both large protein and small molecules such as adrenaline and ATP, were released together while the granule membrane was retained in the cell. A number of exhaustive reviews of this early work have been published and are summarized in Reference 1. The critical experiments demonstrating the importance of extracellular calcium for exocytosis per se were also first performed in this system (2,3), further indicating the substantial service given by chromaffin cells to those interested in secretory phenomena over the years.

Innovative Radiotracer: Peptide und Small Molecules

2009 ◽  
Vol 181 (S 01) ◽  
Author(s):  
HJ Wester ◽  
I Dijkgraaf ◽  
M Schottelius ◽  
G Henriksen ◽  
M Schwaiger
Keyword(s):  
Small Molecules
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