Conformational effects in excited-state intramolecular proton transfer in <Emphasis Type="Italic">N</Emphasis>-substituted 2-(2-aminophenyl)-4H-3,1-benzoxazin-4-ones

The conformational effects in the ground and excited states were studied for N-substituted 2-(2-aminophenyl)-4H-3,1-benzoxazin-4-ones. The structural relaxation of the excited ESIPT product was revealed, which results in the formation of a nonplanar conformer undergoing efficient nonradiative deactivation. The aggregation of fluorophore molecules was observed in saturated hydrocarbons at low temperatures for N-substituted 2-(2-aminophenyl)-4H-3,1-benzoxazin-4-ones with the amido carbonyl group. Excited-state intramolecular proton transfer was not observed in this associate, and the fluorophore molecules were shown to occur in the nonplanar conformation, in which there is no intramolecular hydrogen bonding.     

Ion-selective electrodes for determination of organic ammonium ions: Ways for selectivity control

The influence of the ISE membrane composition on the selectivity for primary, secondary, tertiary, and quaternary alkylammonium cations, as well as for cations of physiologically active amines, has been investigated. Factors studied include the effect of plasticizer (2-nitrophenyl octyl ether, o-NPOE; dibutyl phthalate, DBP; dinonyl adipate, DNA; tris(2-ethylhexyl) phosphate, TEHP) and ion exchanger (potassium tetrakis(4-chlorophenyl)borate, K(TpClPB); potassium tris(nonyloxy)benzenesulfonate, K(TNOBS)), as well as that of the lipophilic cationic additive (tetradecylammonium nitrate, (TDA)NO(3)) and neutral carrier (dibenzo-18-crown-6) presence in membrane. It has been established that plasticizer nature affects K(i,j)(pot) values both when the target and/or foreign ions have non-ionic polar groups capable of specific interaction with plasticizer, and when the only difference consists in the substitution degree of their ionic groups. K(i,j)(pot) values for quaternary alkylammonium cations over primary-tertiary ones change in the following order: TEHP>DBP approximately DNA>o-NPOE. The highest K(i,j)(pot) value change is achieved for the primary-quaternary alkylammonium cation pair, amounting to 3 and 4.7 orders for membranes containing K(TNOBS) and K(TpClPB) as ion exchangers, respectively. In its turn, the ion exchanger influence on the selectivity depends on plasticizer nature, it being maximal for o-NPOE (about 2 orders) and practically non-existent for TEHP. On the whole, as compared to K(TpClPB)-based ISEs, those based on K(TNOBS) show higher selectivity for primary-tertiary alkylammonium cations over quaternary ones. Incorporation of (TDA)NO(3) into membrane causes further improvement of selectivity for primary-tertiary alkylammonium cations in the case of K(TNOBS) only. The maximal total effect of the ion exchanger and lipophilic ionic additive is observed for ISEs with DNA-plasticized membranes and is over 3 orders. The influence of crown ether on the selectivity also depends significantly upon ion exchanger and plasticizer nature. For ISEs with o-NPOE-plasticized membranes the K(i,j)(pot) value changes can be as great as 3 (ion exchanger K(TNOBS)) and even 4.5 (ion exchanger K(TpClPB)) orders. On the contrary, for ISEs with TEHP-plasticized membranes the crown ether effect on the selectivity is unessential. The results obtained are explained by peculiarities of organic ammonium cations solvating by plasticizer and association of cations with ion exchangers.     

Synthesis and spectral-luminescence properties of 2-(2′-tosylaminophenyl)benzimidazole and its substituted derivatives

Tosylamino-substituted 2-arylbenzimidazoles have blue or green fluorescence in the crystalline state and in toluene at room temperature. The effect of the substituents on the position of the absorption and fluorescence bands and on the strength of the intramolecular hydrogen bond was investigated. An anomalously large Stokesian shift within the limits 8800–11450 cm^¡1 is characteristic for compounds that contain an o-tosylamino group.     

Dynamic behavior of Ni-H<Subscript>2</Subscript>SO<Subscript>4</Subscript> system at high anodic potentials and different electrolysis conditions

The stability and dynamic properties of the Ni-H₂SO₄ system is studied at high anodic potentials and different electrolysis modes. The systems dynamic behavior is shown to depend on the electrode reaction mechanism and the electrolysis mode that ensures consistent progress of all stages of the overall process.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 111–115.Original Russian Text Copyright © 2005 by Kovtun, Bolotin.     

Complexation in the copper(ii)—L-histidine—D-ornithine system as studied by ESR spectroscopy

Equilibria in the copper (ii)—L-histidine—D-ornithine system were investigated by ESR spectroscopy in an aqueous solution in the pH range 2—11. Analysis of the spectrum lineshape at different pH and ligand to metal ratios showed that the mixed-ligand complexes Cu(OrnH)(HisH₂)⁴⁺, Cu(OrnH₂)(HisH)³⁺, and Cu(Orn)(His) occur in the system along with the binary complexes. The stability constants, g-factors, HFC constants, and relaxation parameters of the complexes were determined, and the structures of the complexes were suggested.     

Transient fields for Ag and Pd ions IN Fe and Co;g-Factor measurements of the lowest 3/2− and 5/2− states in107,109 Ag

Transient field precessions of the 2 ₊ ¹ state of¹⁰⁸Pd were measured simultaneously with those of the 3/2 _– ¹ and 5/2 _– ¹ states of¹⁰⁷Ag and¹⁰⁹Ag as their ions traversed thin Co and Fe foils. Precessions of the 2 ₊ ¹ states of^{104,106,108,110}Pd were also measured using a natural Pd target evaporated onto 0.9 m thick Co. The results of these studies are in accord with prior predictions that the AgFe transient field might be diminished relative to that for PdFe at ion velocities appropriate for molecular orbital vacancy sharing. Transient field strengths for PdCo and PdFe were found to be consistent with scaling according to bulk magnetization of the ferromagnetic host. Gyromagnetic ratios were inferred for the first 3/2^– and 5/2^– states of^107,109Ag relative to theg factor of the 2 ₊ ¹ state of¹⁰⁸Pd. Values obtained usingg(2 ₊ ¹ ;¹⁰⁸Pd)=0.36± 0.03 are:g(3/2;¹⁰⁷Ag) =0.63±0.09,g(5/2;¹⁰⁷Ag)=0.37±0.06,g(3/2;¹⁰⁹Ag)=0.77 ±0.10,g(5/2;¹⁰⁹Ag)=0.36±0.05.     

Quantum-chemical analysis of the mechanism of action of sterically hindered amines in photostabilization of polyolefins

A quantum-chemical study was made of the reaction of sterically hindered amines with the degradation products of polyolefins. The reactivity indices of these compounds and the formation energies of their reaction products were calculated by the semiempirical CNDO/2 and MINDO/3 methods. The mechanism of the photostabilizing action of sterically hindered amines was substantiated theoretically. The criteria by means of which it is possible to determine their relative reactivities were established, and the role of the substituent was determined. The results are compared with experimental data on the photostabilizing effectiveness of these compounds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 594–597, September–October, 1989.     

Liquid crystal complexes of copper with Schiff bases

Conclusions A synthesis is reported for paramagnetic copper complexes of Schiff bases possessing liquid crystal properties.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2379–2381, October, 1984.