O moiety

The transmembrane potential derived from a concentration gradient is calculable by means of the Nemst equation. If K+ were the only permeable ion then the membrane potential would be given by Eq. 1. With an ion activity (concentration) gradient for K+ of 10 1 from one side to the other of the membrane at 20 °C, the membrane potential that develops on addition of Valinomycin approaches a limiting value of 58 mV87). This is what is calculated from Eq. 1 and indicates that cation over anion selectivity is essentially total. As the conformation of Valinomycin in nonpolar solvents in the absence of cation is similar to that of the cation complex 105), it is quite understandable that anions have no location for interaction. One could with the Valinomycin structure construct a conformation in which a polar core were formed with six peptide N—H moieties directed inward in place of the C—O moieties but... 

In the latter case the M—N—O moiety is highly bent (130-140°), the N—O bond length shortened and its polarization increased by about three times in comparison to free NO molecule. Such changes indicate that the NO acquires electrophilic properties upon the coordination, and is characterized by vNO > 1850 cm-1 [53], Examples are given by the p fCoNO 8, 171 NiNO 9, and 171 CuNO 10 complexes. 

The dinitrosyl complex exhibits the repulso conformation with both Ni—N—O moieties bent outwardly, with the angle /J = 125(1)° and the ON—Ni—NO angle 6 = 97°... 

The synthesis of C60-based dyads in which the Ccm core is covalently attached to a strong electron acceptor moiety, has been carried out by 1,3-dipolar cycloaddition of in situ generated nitrile oxides with C(,o- As expected, the obtained adducts show reduction waves of the fullerene core that are anodically shifted in comparison with the parent Cr>o. This indicates that they are remarkably stronger acceptors than Ceo-The electron acceptor organic addend also undergoes an anodic shift due to the electronic interaction with the C(,o moiety (545). 

Initial degradation of silicone surfactants is thought to occur predominantly as hydrolyis of the silicone Si—O moiety, and this is known to be enhanced at acidic or alkaline pH values [3,11,12]. At neutral pH the surfactants are generally considered stable, but residual acidity or basicity of glassware is also known to catalyse their hydrolytic degradation [7]. Silicone polyether surfactants possessing the Si—O—C... 

The second fixation reaction that has been the subject of theoretical study is the nickel(0)-catalyzed coupling reaction of C02 with acetylene (equation 1), which was theoretically investigated with the ab initio SD-CI method [25]. The theoretical calculations clearly showed that if the nickel(O) moiety was eliminated from the reaction system, the activation barrier increased very much, and that the C-C bond formation between C02 and acetylene was accelerated by the charge-transfer from the nickel(O) d orbital to the orbital resulting from the combination between n orbitals of acetylene and CO2. Actually, the HOMO contour map of Ni(PH3)(C02)(C2H2) clearly displays this orbital mixing in the transition state. 

A very interesting approach is the combination of charge-transfer donor-acceptor sites in one molecule as it was demonstrated for compounds consisting of oligophenylenevinylene and C o moieties [281, 282]. By microphase separation, a bicontinous network is formed for the charge transport. The efficiencies are, however, quite low (0.01-0.03%). 

Replacement of an X = O moiety by a strong electron acceptor, such as X = NTf, is known to enhance significantly the acid ity of a Brpnsted acid (Fig. 15) [83]. 

A number of l,3-dioxan-2-ylium ions have been studied with respect to the preferred conformation. From a detailed H and C NMR study (790MR616) and the X-ray crystal structural analysis (94CJC2084), it was concluded that the 1,3-dioxan-2-ylium ions adopt the envelope conformation with the C —O —C —O—moiety in one plane (due to mesomerism) and C —C —forming the flap (Scheme 16). Ring interconversion 19a 19b and a 1 1 conformational equilibrium was assumed. 

The trans isomer turned out to be favored over the cis isomer by 41.8 kJmol at B3LYP/aug-cc-pvTZ level of theory. In both isomers the C—N—O moiety is strongly polarized. The charges are 4-0.24 e for both nitrogens and —0.50 and 0.51 e for both... 

More recently, an interesting reaction was discovered which provides the means for the synthesis of a wide variety of methylcarbamate derivatives containing the N-sulfinyl [N-S(O)] moiety (34). In attempting to prepare isopropoxy-N-methyliminoyl chloride by the reaction between Isopropyl methylcarbamate and thionyl chloride, an unexpected product, isopropyl ll-chloro-sulfinyl-N-methylcarbamate was obtained according to the equation below. The same product also was obtained when the... 

Finally, we point to the possibility of P = 0 bond formation from 1-alkoxy-X -phosphorin derivatives 124 or 125 by cleavage of alkyl cations. Also the reverse process, /. e. alkylation of the P = O moiety to form P—O—R groups is possible. The synthesis of X -phosphorins having functional groups at the C-atoms of the phosphorin ring was first made possible by the preparation of new stable X -phosphorin carbenium ions 140. Here again, the fundamental difference between phosphorin and pyridine systems comes to light Whereas carbanionic structures 139 b are stabilized in the pyridine series, in the X -phosphorin series carbenium ions as 140 b are stabilized. 

It is generally accepted that C02 is somewhat unreactive towards transition metal complexes and that the metal C02 linkage is favoured by a nucleophilic metal centre such as a tertiary phosphine metal(O) moiety. 

Thus, ketenes (2) can react as dienophiles with (E)-l,3-diazabuta-l,3-dienes (E)-(25) to yield either [4 + 2] cycloaducts (26) or (27) depending on the participation of the C = C or C = O moieties of the ketenes (Scheme 7). Claisen rearrangement of 3,6-dihydro-2-methylene-2//-l,3,5-oxadiazines (27) yields the p-lactams (28). Alternatively, reaction between ketenes (2) and (Z)-l,3-diaza-buta-1,3-dienes (Z)-(25) leads to the usual zwitterionic intermediates (29), whose conrotatory electrocyclation leads to p-lactams (28). No computational data including solvent effects have been reported for these reactions. 

P contact shifts in ligands coordinating through P-O moieties in oxovana-dium(IV), cobalt(II) and nickel(II) complexes are downfield and of the order of 103 ppm [69-71]. Smaller downfield shifts are observed for nickel-coordinated P-S moieties [72]. Direct P-M coordination gives rise to even larger hyperfine coupling than in P-O moieties. In low spin cobalt(H) complexes A/h values of the order of 102 MHz are found [73]. 

Intermolecular addition and addition-cyclization reactions of aminium cation radicals with electron-rich alkenes such as ethyl vinyl ether (EVE) allow an entry into products containing the N—C—C—O moiety of 13-amino ethers 70 or the equivalent of /3-amino aldehydes 71. The mild conditions under which aminium cation radicals are generated from PTOC carbamates makes the reactions described in Scheme 22 possible. In the absence of hydrogen atom donors, the /3-amino ethoxy(2-pyridylthio) acetal 71 was the major product. The mixed acetal can easily be converted... 

At infinite separation between the FenO and Fe O moieties, 3xP. and 3xF+do not interact with 3vF3- Hund s rule requires that 3vF gives the dissociation products of lowest energy. Eq.(18) indicates that each of them involves an S = 1 state. A variation on the derivation of this result is provided in Ref. [47(a)], where three 5=1 and Ms = 0 wavefunctions are used to describe the electronic structure of the FeII02FeII(5 =1) complex. 

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