Protonation effects

Voityuk AA, MichelBeyerle ME, Rosch N (1997) Protonation effects on the chromophore of green fluorescent protein. Quantum chemical study of the absorption spectrum. Chem Phys... 

Baker, B.M. and K.P. Murphy. 1996. Evaluation of linked protonation effects in protein binding reactions using isothermal titration calorimetry. Biophys J 71 2049-2055. 

Coordination by oxygen atoms is preferable for the alkali metal and alkaline earth ions. Nitrogen atoms produce undesirable protonation effects. 

In the case of fluorescence spectra, it is the emission of the radiation from the excited state that is measured, rather than its absorption. This also provides valuable information. As an example, tetraethylorthosilicate (TEOS)-based gels were doped with two optically active organic indicators, thionin and nile blue A. Before trapping in a solgel host, thionin and nile blue A were both evaluated for solvent and protonation effects on their spectral properties. Only extreme pH values provided by HCl, NaOH, and NH4OH produced new absorption and/or fluorescence bands. The absorption and fluorescence spectra revealed a decrease in a pH 11 solution of NH4OH compared to neutral conditions (Krihak et al., 1997). 

Protonation effects for N7 at pH 3 have disappeared, except for H8(l), because this base has no platinum at N7 (and can still be protonated)... 

Intruder states are certainly not unique to the Z=50 region of nuclei [HEY83]. In fact, much larger neutron-proton effects are expected for nuclei near Z=82 since the neutrons are in the 82-126 shell. The evolution of an intruding configuration in a series of Pb nuclei were reported recently [VAN85]. The effects of the neutron-proton quadrupole interaction have... 

Protonation Effects in Protein Binding Reactions Using Isothermal Titration Calorimetry. 

How strong is the tendency to fill an empty external cluster orbital The linked cluster pair shown in Figure 2.22 is instructive. Oxidation of [B10H10]2- results in the loss of two electrons and a proton (effectively H- is lost). The shape remains the same so the 11 sep associated with cluster bonding are unaffected. Hence, an external outward-pointing empty orbital is generated. Dimerization to form [B2oHi8]2-arises by formation of two three-center-two-electron bonds between the clusters. 

Under these conditions, the carbonyl group is protonated, effectively increasing the electron deficiency of the carbon atom. 

Many rDA reactions are carried out at temperatures of 150 C or more in solution phase and often at temperatures of 400-600 C using the flash vapor pyrolysis (FVP) method individual conditions are referenced throughout the text. However, an accelerating effect by anionic, cationic and radical substimtion on either the dienophile or at the termini of the diene fragments has been predicted by Carpenter.Experimentally, this prediction has been substantiated only for anionic substitution. In 1967, Hart reported what is likely the first example of an oxyanion-accelerated rDA reaction. Both oxyanionic " and car-banionic substituents accelerate the cycloreversion reaction such that they proceed rapidly at room temperature (for example, equation 3). In addition, acid-catalyzed rDA reactions have been reported in which protonation effectively makes the dienophile fragment of the adduct more electron deficient. Grieco has utilized a room temperature retro aza DA reactitm useful for the N-methylation of dipeptides and amino acid derivatives (equatitm 4). ... 

Consistent with its 22 n-electron formulation, the free-base form of isosmar-agdyrin (6.11b) appears to be aromatic, as judged from a preliminary H NMR spectral analysis. On the other hand, the protonated form (6.11a) appears to be non-aromatic, as evidenced by the lack of any diamagnetic ring-current effects in its H NMR spectrum. Based upon integration of the NMR signals, the lack of aromaticity for 6.11a appears to be the result of protonation at one of the meso-positions of the macrocycle. This protonation effect thus resembles that observed for the 18 7c-electron corroles discussed in Chapter 2. 

The reaction between the thiocarbene complex 413 and (Cp3)2C=NC(0)R (R = Ph, P-FQH4) leads to scission of the carbene ligand and transfer of the nucleophilic SMe fragment to the electrophilic center of the acylamine. Protonation, effected either by the rest of the carbene or the solvent, results in a thioether derivative (414) (249). 

Heteronuclear coherence transfer periods of HSQC or HMQC experiments are often incorporated into semi-constant-time proton chemical shift evolution to reduce the effective relaxation and thus improve sensitivity. This method was further extended by Bazzo et to utilise N chemical shift evolution period of HMQC-NOESY experiment for further reduction of the proton effective relaxation rate. This is achieved by changing the position of refocusing pulse in the middle of the heteronuclear MQ evolution period when evolution is encoded. As the result the MQ evolution period that is... 

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