Molecule protonated

Some of the target molecules gain so much excess internal energy in a short space of time that they lose an electron and become ions. These are the molecular cation-radicals found in mass spectrometry by the direct absorption of radiation. However, these initial ions may react with accompanying neutral molecules, as in chemical ionization, to produce protonated molecules. 

Protonated molecule. An ion formed by interaction of a molecule with a proton abstracted from an ion, as often occurs in chemical ionization according to the reaction ... 

The symbolism (M + H)+ can also be used to represent the protonated molecule. The widely used term protonated molecular ion to describe the MH+ ion is not recommended because it suggests an association product of a proton with a molecular ion. 

The destmction of the total TT-system causes the color to vanish the protonated molecule absorbs light in the uv region. Protonation has been proved by H/D exchange to be reversible (62,63). 

Nitration of cinnolin-4(lFf)-one yields a mixture of the 3-nitro (0.9%), 5-nitro (0.38%), 6-nitro (58.4%), 7-nitro (0.36%) and 8-nitro (39.9%) derivatives. The 3-nitro isomer is postulated to result from nitration of the free base, while the other mononitro isomers are formed from the protonated molecule. 

According to a kinetic study which included (56), (56a) and some oxaziridines derived from aliphatic aldehydes, hydrolysis follows exactly first order kinetics in 4M HCIO4. Proton catalysis was observed, and there is a linear correlation with Hammett s Ho function. Since only protonated molecules are hydrolyzed, basicities of oxaziridines ranging from pii A = +0.13 to -1.81 were found from the acidity rate profile. Hydrolysis rates were 1.49X 10 min for (56) and 43.4x 10 min for (56a) (7UCS(B)778). O-Protonation is assumed to occur, followed by polar C—O bond cleavage. The question of the place of protonation is independent of the predominant IV-protonation observed spectroscopically under equilibrium conditions all protonated species are thermodynamically equivalent. 

Dimerization is markedly subject to steric hindrance, thus, whereas 3-n-propylindole dimerizes readily, neither 3-isopropyl- nor Z-tert-butyl-indole dimerizes. This failure is most probably the result of steric hindrance of approach of the electrophilic reagent to position 2 by the bulky 3-substituent in the unprotonated molecule. On the other hand, models show that approach of a nucleophilic reagent to position 2 of a 3-protonated molecule is quite open, it should, there-... 

Transport by the VMATs involves the exchange of two lumenal protons for one cytoplasmic, apparently protonated molecule of transmitter, predicting accumulation of transmitter inside vesicles 104-105 the... 

It may be noted that the additions of protonic molecules HA (alcohols, amines, thiols, etc. see Section III,C) to isocyanides may be related to these reactions, in the formalistic sense anyway, since they involve additions of A (in conjunction with H+) to the isocyanide. In a few instances the additions of HA can be accomplished by adding first A" and then H to the reactant species. However, no studies on HA additions have yet elucidated a mechanism for these reactions, so to draw a conclusion on the similarities of these reactions on mechanistic grounds is not appropriate. Because of this, and also for convenience, these subjects will be treated separately. 

The stability of cyanidin 3-glncosyl-arabinoside was investigated in different solvents, water, and dimethyl snlfoxide (DMSO, an aprotic solvent) under the same conditions. The valnes nnexpectedly showed that the anthocyanin was more stable in water solntion. DMSO was chosen as a solvent so that it would make the addition of DMSO to C-2 difficnlt and thus the anthocyanin would be more stable in DMSO than in a water solntion. However, since the experiment took place in acidic solntion (pK > pKj,), the preferential addition at C-2 or C-4 of the flavylium ion probably took place by a protonated molecule of DMSO. ... 

Because carotenes lack heteroatoms such as oxygen to which protons or sodium cations might attach, no ions are usually detected for these hydrocarbon compounds during ESI in positive mode, although protonated molecules and sodium adducts were observed for xanthophyUs under normal conditions with MeOH, MTBE, and H2O as a mobile phase from HPLC. Addition of a heptafluorobutanol oxidant at 0.1 or 0.5% produced abundant molecular ions of p-carotene with high reproducibility. Substitution of MeOH for acetonitrile produced similar limits of detection. ... 

Desorption/ionisation techniques such as LSIMS are quite practical, as they give abundant molecular ion signals and fragmentation for structural information. In the conditions of Jackson et al. [96], all the molecular ion and/or protonated molecule ion species were observed in the LSIMS spectrum when only 1 pmol of each additive was placed on the probe tip. However, as mentioned above, in LSIMS/MS experiments the choice of the matrix (e.g. NBA, m-nitrobenzylalcohol) is very important. Matrix effects can lead to suppression of the generation of molecular ions for some additives. LSIMS is not ideal for the quantitative detection of polymer additives, as matrix effects are very important [96]. 

DI methods tend to produce even-electron ions such as protonated molecules [M + H]+, or cationised molecules such as [M + Na]+ these stable ions undergo only a minimum amount of fragmentation. Desorption/ionisation mass-spectral methods (in particular FD, EH and LD) may be used for determining molecular... 

The formation of the ether occurs by an Sn2 mechanism with one molecule of the alcohol acting as the nucleophile and with another protonated molecule of the alcohol acting as the substrate. 

Protonated Molecule An ion formed by interaction of a molecule with a proton, and represented by the symbol [M+H]+. The term protonated molecular ion is deprecated this would correspond to a species carrying two charges. The terms pseudo-molecular ion and quasi-molecular ion are deprecated a specific term such as protonated molecule, or a chemical description such as [M+Na]+, [M-HJ, etc., should be used [1],... 

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