Anions cross sensitivity

Two types of potentiometric electrodes are usually described, the ISE, which was developed to selectively recognize ions and used to analyze ions (anions or cations) in a solution and the cross-sensitivity electrodes (CSE), used in sensor arrays for solution analysis, which due to their low selectivity gives, as output, a matrix fingerprint. E-tongue systems (multisensor systems with several low-selective sensors) are an example of this application. 

An automated electronic tongue consisting of an array of potentiometric sensors and an artificial neural network (ANN) was developed to resolve mixtures of anionic surfactants. The sensor array was formed by five different flow-through sensors for anionic surfactants, based on polyvinyl chloride membranes having cross-sensitivity features. 

Anthraquinones are nearly perfect sensitizers for the one-electron oxidation of DNA. They absorb light in the near-UV spectral region (350 nm) where DNA is essentially transparent. This permits excitation of the quinone without the simultaneous absorption of light by DNA, which would confuse chemical and mechanistic analyses. Absorption of a photon by an anthraquinone molecule initially generates a singlet excited state however, intersystem crossing is rapid and a triplet state of the anthraquinone is normally formed within a few picoseconds of excitation, see Fig. 1 [11]. Application of the Weller equation indicates that both the singlet and the triplet excited states of anthraquinones are capable of the exothermic one-electron oxidation of any of the four DNA bases to form the anthraquinone radical anion (AQ ) and a base radical cation (B+ ). 

In this analysis, the activation barrier for both C1-C6 and C1-C5 cyclizations of enediyne radical-anions can be described as the avoided crossing between the out-of-plane and in-plane MOs (configurations). One-electron reduction populates the out-of-plane LUMO of the enediyne moiety. At the TS (the crossing), the electron is transferred between the orthogonal re-systems to the new (in-plane) LUMO. This effect leads to the accelerated cyclization of radical-anions of benzannelated enediynes, a large sensitivity of this reaction to re-conjugative effects of remote substituents and the fact that this selectivity is inverse compared to that of the Bergman cyclization. Similar electronic effects should apply to the other reductive cyclization reactions that were mentioned in the introduction. 

Quantum yields for isomerization of t-1 to c-1 via intersystem crossing are similar to those obtained in triplet sensitization, indicating that t is formed with near unit efficiency. Similar results were reported for the interaction of t with inorganic anion electron donors (127b). Rate constants for intersystem crossing of the t-1-ethyldiisopropylamine and triethylamine exciplexes obtained from the measured exciplex lifetimes are 5 x 107 s"1 (116), similar to the values for the exciplexes of pyrene (128) and naphthalene (121) with triethylamine. Larger intersystem crossing rate constants are observed for the exciplexes of t-1 with the bicyclic amines l-azabicyclo[2.2.2]-... 

Soppimath KS, Kulkarni AR, and Aminabhavi TM. Chemically modified polyacrylamide-g-guar gum-hased cross-linked anionic microgels as pH-sensitive dmg delivery systems Preparation and characterization. Journal of Controlled Release 2001 75 331-345. 

The main limitations of using organoboronic acids in cross-coupling chemistry are threefold. These compounds are quite reactive towards many nucleophiles and oxidants, which prohibits installation of the boronic acid functional group early in a synthetic sequence. Moreover, purification of boronic acids is often problematic. Finally, since the C—B bond is relatively nonpolar, transmetalation of an organoboron reagent to Pd(ll) will not occur without coordination of an anionic base or a fluoride ion to the boron atom to afford a four-coordinate ate -complex (e.g. 20 shown below). This requirement poses some limitations with respect to transformations of base- or fluoride-sensitive substrates, although these... 

Immobilized semiquinones often are detected in membrane systems. In most instances analysis of their ESR spectra has been limited to measurement of a g value and a linewidth. More detailed analysis [154,155] could provide additional structural information to help identify the radical, its ionization state, and its local environment. The g value usually measured is that for the cross-over in the first derivative spectrum. While certainly useful in providing an approximate indication of the radical structure, it is generally frequency-dependent because of the anisotropy in the radical spectrum. It cannot give the more precise information on structure and environment that is available from the isotropic g value. The latter can readily be obtained from spectra of immobilized species by the method of Hyde and Pilbrow [156]. Related information is available from linewidth considerations [154] in general, spectra for neutral semiquinones are approximately twice as broad as those for semiquinone anions and are sensitive to deuteration of solvent. Information of this kind can be of great help in assigning a spectrum of an unknown to a given radical species. The point has been... 

In 1971 a new variation on the transmission method was introduced by Sanche and Schulz (13). The technique incorporated the trochoidal monochromator of Stamatovlc and Schulz (14) and a modulation scheme to obtain the derivative of the electron current transmitted through a gas cell. This combination provides a relatively simple and very sensitive means of locating resonances as they appear in the total scattering cross section. In particular the energy resolution (20-50 meV), which is substantially better than that found in most trapped electron and SFg scavenger studies, is sufficient to observe the vibrational structure possessed by anions long lived enough to... 

The above guidelines for the acrylic rheology modifiers are most useful in simple systems that are mainly water. However, in more complex matrices such as many finished formulations the situation can be very different. Both the carbomer and the cross-polymer type of rheology modifier are very sensitive to the presence of electrolytes, and this has a dramatic effect on the efficiency of the polymer, as well as on clarity. It is frequently found that in systems containing electrolytes, be they inorganic salts or anionic surfactants, the efficiency of a crosslinked ASE... 

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