Transition-state spectroscopy via negative ion photodetachment

1993 ◽  
Vol 26 (2) ◽  
pp. 33-40 ◽  
Author(s):  
Daniel M. Neumark
Keyword(s):  
Transition State ◽  
Negative Ion

scholarly journals Fullerene Negative Ions: Formation and Catalysis

2020 ◽  
Author(s):  
Zineb Felfli ◽  
Kelvin Suggs ◽  
Nantambu Nicholas ◽  
Alfred Z. Msezane
Keyword(s):  
Transition State ◽  
Cross Sections ◽  
Water Oxidation ◽  
Regge Pole ◽  
Negative Ions ◽  
Negative Ion ◽  
Total Cross Sections ◽  
Hydrogen Bond Strength ◽  
Low Energy Electron ◽  
Fundamental Mechanism

We first explore negative-ion formation in fullerenes C44, C60, C70, C98, C112, C120, C132 and C136 through low-energy electron elastic scattering total cross sections calculations using our Regge-pole methodology. Water oxidation to peroxide and water synthesis from H2 and O2 are then investigated using the anionic catalysts C44ˉ to C136ˉ. The fundamental mechanism underlying negative-ion catalysis involves hydrogen bond strength-weakening in the transition state. DFT transition state calculations found C60ˉ numerically stable for both water and peroxide synthesis, C100ˉ increases the energy barrier the most and C136ˉ the most effective catalyst in both water synthesis and oxidation to H2O2.

scholarly journals Fullerene Negative Ions: Formation and Catalysis

2020 ◽  
Vol 21 (9) ◽  
pp. 3159
Author(s):  
Zineb Felfli ◽  
Kelvin Suggs ◽  
Nantambu Nicholas ◽  
Alfred Z. Msezane
Keyword(s):  
Transition State ◽  
Cross Sections ◽  
Water Oxidation ◽  
Density Functional ◽  
Regge Pole ◽  
Negative Ions ◽  
State Density ◽  
Negative Ion ◽  
Functional Theory ◽  
Total Cross Sections

We first explore negative-ion formation in fullerenes C44 to C136 through low-energy electron elastic scattering total cross sections calculations using our Regge-pole methodology. Then, the formed negative ions C44ˉ to C136ˉ are used to investigate the catalysis of water oxidation to peroxide and water synthesis from H2 and O2. The exploited fundamental mechanism underlying negative-ion catalysis involves hydrogen bond strength-weakening/breaking in the transition state. Density Functional Theory transition state calculations found C60ˉ optimal for both water and peroxide synthesis, C100ˉ increases the energy barrier the most, and C136ˉ the most effective catalyst in both water synthesis and oxidation to H2O2.

Ion cyclotron resonance and deuterium kinetic isotope studies of the gas-phase reactions of the alkoxide negative ions with anhydrides and esters

1981 ◽  
Vol 34 (3) ◽  
pp. 507 ◽  
Author(s):  
G Klass ◽  
DJ Underwood ◽  
JH Bowie
Keyword(s):  
Transition State ◽  
Carbonyl Group ◽  
Isotope Effects ◽  
Negative Ions ◽  
Alkyl Ester ◽  
Negative Ion ◽  
Nucleophilic Attack ◽  
Ion Cyclotron Resonance ◽  
Gas Phase Reactions ◽  
Rearrangement Reaction

(i) The i.c.r. spectrum of the CD3O-/acetic anhydride system shows the occurrence of the negative ion McLafferty rearrangement [reaction (1)] and the characteristic elimination shown in reaction (2) (R = COMe) CD3O-+ (MeCO)2O → (CD3O)(Me)(HO)C-O-+ CH2CO (1) CD30-+ MeCO2R → -CH2C02CD3+ ROH (2) (ii) The i.c.r. spectra of CD3O-/alkyl ester systems show major peaks due to [ester-H+]- ions, together with small peaks corresponding to [ester+CD3O-]- adducts. Carboxylate and alkoxide anions (derived from the ester) are also observed in certain spectra; peaks due to these ions increase in intensity with elaboration of alkyl substituents. Reaction (2) is characteristic of all esters studied (illustrated above for acetates) which have at least one hydrogen substituent on the carbon atom α to the carbonyl group. The reaction must occur by nucleophilic attack of the alkoxide anion at the carbonyl group of the ester. Negative ion McLafferty rearrangements do not occur in alkyl ester systems. (iii) The H transfer reactions (1) and (2) show deuterium isotope effects kH/kD of 3.0 and 1.5 respectively (when the carbon adjacent to the carbonyl group contains one deuterium substituent). Isotope effect calculations suggest that reaction (1) proceeds through a 'near symmetrical' six membered transition state, whereas (2) goes through a 'reactant-like' but distorted four-centred transition state.

Memapsin 2, a drug target for Alzheimer's disease

2003 ◽  
Vol 70 ◽  
pp. 213-220 ◽  
Author(s):  
Gerald Koelsch ◽  
Robert T. Turner ◽  
Lin Hong ◽  
Arun K. Ghosh ◽  
Jordan Tang
Keyword(s):  
Crystal Structure ◽  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Transition State ◽  
Amyloid Precursor Protein ◽  
Therapeutic Target ◽  
Drug Target ◽  
Aspartic Protease ◽  
Precursor Protein ◽  
Memapsin 2

Mempasin 2, a ϐ-secretase, is the membrane-anchored aspartic protease that initiates the cleavage of amyloid precursor protein leading to the production of ϐ-amyloid and the onset of Alzheimer's disease. Thus memapsin 2 is a major therapeutic target for the development of inhibitor drugs for the disease. Many biochemical tools, such as the specificity and crystal structure, have been established and have led to the design of potent and relatively small transition-state inhibitors. Although developing a clinically viable mempasin 2 inhibitor remains challenging, progress to date renders hope that memapsin 2 inhibitors may ultimately be useful for therapeutic reduction of ϐ-amyloid.

Collisional dynamics of Ca1D + HBr reactions: evidence for transition-state motions

1999 ◽  
Vol 97 (8) ◽  
pp. 967-976 ◽  
Author(s):  
M. Garay Salazar, J. M. Orea Rocha, A.
Keyword(s):  
Transition State ◽  
Collisional Dynamics
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