The magnetizability of excited-state hydrogen: temperature-independent paramagnetism in the B1Σ+u state

Components, of the magnetizability tensor for the B¹Σ⁺_u and a ³Σ⁺_g states ot the hydrogen molecule have been calculated for fixed bond lengths near equilibrium. Explicitly correlated “generalised James-Coolidge” type wavefunctions were used. It is found thilt in the B 1Σ⁺_u state the molecular magnetizability is a positive quantity.     

Location of saddle points and minimum energy paths by a constrained simplex optimization procedure

Two methods are proposed, one for the location of saddle points and one for the calculation of steepest-descent paths on multidimensional surfaces. Both methods are based on a constrained simplex optimization technique that avoids the evaluation of gradients or second derivative matrices. Three chemical reactions of increasing structural complexity are studied within the PRDDO SCF approximation. Predicted properties of reaction hypersurfaces are in good overall agreement with those determined by gradient minimization and gradient following algorithms in connection with various ab initio SCF methods. Computational efforts required by the new procedures are discussed.     

Quantum chemical study of several monocyclic complex β‐lactam C‐3, C‐4, and N‐derivatives,and β‐ring model molecules

A quantum chemical study of several complex monocyclic 4‐benzoyl‐4‐phenyl‐β‐lactam derivatives was carried out using cyclobutane, azetidine, 2‐azetidinone, 1‐methyl‐2‐azetidinone, and 3‐methyl‐2‐azetidinone as model compounds. The optimum geometry was obtained for the different conformations. The planarity of the ring was discussed in terms of the influence of the substituents on the amide resonance. To better analyze the amide resonance and the activity of the β‐lactam ring, a vibrational study was also carried out. To examine the influence of solvent polarity on the carbonyl bands, the Fourier transform–infrared (FT‐IR) spectra of the β‐lactam monocyclic derivatives were recorded in CCl₄, C₆H₆, and CHCl₃ solutions. The normal vibrations of the β‐lactam ring in the model compounds were characterized and used in the analysis of the β‐ring of more complex derivatives. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Isomerisierung bei der Komplexbildung von 3-Acetyl-tetramsäure: Struktur und magnetische Eigenschaften des CuII- und NiII-Komplexes von 2,7-Bis(1′, 5′, 5′-trimethylpyrrolidin-2′, 4′-dion-3′ -yl)-3, 6-diazaocta-2, 6-dien

Isomerization at the Complexation of 3-Acetyltetramic Acid: Structure and Magnetic Properties of the Cu^II- and Ni^II-Complex of 2,7-Bis (1′, 5′, 5′ -trimethylpyrrolidin-2′,4′ -dion-3′ -yl)-3,6-diazaocta-2,6-dien 2,7-Bis(1′, 5′, 5′ -trimethylpyrrolidin-2′, 4′ -dion-3′ -yl)-3,6-diazaoctadien formes Cu^II and Ni^II complexes with different constitutions (because of the Z/E isomerization). Results of X-ray analysis of N,N′ -ethylenbis(1′, 5′, 5′ -trimethylpyrrolidin-2′, 4′ -dion-3′ -acetiminato)nickel(II) 1 respectively -copper(II) 2 shows, that the complexing agent in 1 occurs in the E-form, whereas the ligand of the Cu^II complex forms the Z-form. Magnetic susceptibility and shift effects of the ¹³C-NMR signals point to a weak paramagnetism of the Ni^II complex. ESR-spectra are obtained from 2 only. Furthermore, the Cu^II complex reduces the relaxation times T₁ and T₂ of ¹H and ¹⁷O nuclei spins from water. From the temperature dependence of the shortening of the relaxation times an activation energy is calculated which describes the reorientation of the copper complex in the “water matrix”.     

Synthesis and reactivity of thieno[2,3-<Emphasis Type="Italic">b</Emphasis>]pyridine-2,3-diamines

It has been established that the interaction of N¹-(2-hydroxyphenylmethylthieno[2,3-b]pyrid-3-yl)arylamides with hydrazine hydrate leads to thieno[2,3-b]pyridine-2,3-diamines. It was shown that the reaction of the latter with acetylacetone and acetoacetic ester occurs regioselectively at the amino group in position 3 of the thiophene ring. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1400–1408, September, 2007.     

Oxidative cyclocondensation of cyclic thio-and selenoureas. 5. 2-Thioxothieno-and 2-thioxopyrido[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidin-4-ones

A study was carried out on the oxidative cyclocondensation of 2-thioxothieno-and 2-thioxopyrido[2,3-d]pyrimidin-4-ones. The thiophene ring with excess π-electron density facilitates the reaction, while the pyridine ring with diminished π-electron density hinders it. 2-Thioxothieno-[2,3-d]pyridimin-4-ones were converted into previously unreported 7H,13H-[1,2,4]thiadiazolo-[3,2-b:5,4-b′]bis(thieno[2,3-d]pyridimine-7,13-diones). __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1424–1427, September, 2007.     

Electron correlation effects on the shape of the Kohn–Sham molecular orbital

Even systems in which strong electron correlation effects are present, such as the large near-degeneracy correlation in a dissociating electron pair bond exemplified by stretched H₂, are represented in the Kohn–Sham (KS) model of non-interacting electrons by a determinantal wavefunction built from the KS molecular orbitals. As a contribution to the discussion on the status and meaning of the KS orbitals we investigate, for the prototype system of H₂ at large bond distance, and also for a one-dimensional molecular model, how the electron correlation effects show up in the shape of the KS σ _g orbital. KS orbitals φ^HL and φ^FCI obtained from the correlated Heitler-London and full configuration interaction wavefunctions are compared to the orbital φ^LCAO, the traditional linear combination of atomic orbitals (LCAO) form of the (approximate) Hartree-Fock orbital. Electron correlation manifests itself in an essentially non-LCAO structure of the KS orbitals φ^HL and φ^FCI around the bond midpoint, which shows up particularly clearly in the Laplacian of the KS orbital. There are corresponding features in the kinetic energy density t _s of the KS system (a well around the bond midpoint) and in the one-electron KS potential v _s (a peak). The KS features are lacking in the Hartree-Fock orbital, in a minimal LCAO approximation as well as in the exact one. Received: 11 December 1996 / Accepted: 10 January 1997     

Poly(N-vinyl-2-pyrrolidone) and 1-Octyl-2-pyrrolidinone Modified Ionic Microemulsions

The influence of the nonionic polymer poly(N-vinyl-2-pyrrolidone) (PVP) in comparison to the surfactant 1-octyl-2-pyrrolidinone (OP) on the phase behavior of the system SDS/pentanol/xylene/water was studied. In both modified systems a strong increase in the water solubilization capacity was found, accompanied by a change in the spontaneous curvature toward zero. In the polymer-modified system an isotropic phase channel is formed with increasing polymer content that connects the L1 and the L2 phase. The lamellar liquid crystalline phase is destabilized in both cases. In the L1 phase the adsorption of PVP at the surface of the microemulsion droplets and the formation of a cluster-like structure is proven by several methods like ¹³C NMR T₁ relaxation time measurments, zeta potential measurements, and rheology. In the L2 phase a modification of the interface of the inverse droplets is detected by a shift in the percolation boundary (conductivity) and ¹³C NMR T₁ relaxation measurements. The formation of a cluster-like structure can be assumed on the basis of our rheological measurements.     

Optimization of the process parameters of synthesis of vinblastine imprinted polymer

Molecularly imprinted polymers (MIPs) are tailor-made polymers with high selectivity for the template molecule. This selectivity arises from the synthetic procedure followed to prepare the MIP. In this work, the influence of process parameters on the preparation of vinblastine (VLB) imprinted polymers was presented. In the procedure of polymerization, VLB (0.1 mmol) was used as the template molecule and a commonly used initiator, azobisisobutyronitrile (AIBN), was employed to initiate the reaction at 60 °C. The influence of the following parameters was investigated: the moles of functional monomer (MAA, 0.3-1.0 mmol), the moles of cross-linker (EDMA, 1.5-5.0 mmol) and the porogenic solvent (toluene or acetonitrile). A mathematical method of uniform design was applied to optimize these selected parameters in order to increase the selectivity of MIP for template molecule. The experimental data were analyzed to obtain the regression model and the optimal conditions were achieved by optimization with uniform design software. The MIP was synthesized under the optimal conditions that 1.0 mmol of MAA and 5.0 mmol of EDMA copolymerized in toluene in the presence of 0.1 mmol of VLB. After removal of the template molecule, the obtained MIP was then employed as the sorbents of solid-phase extraction (SPE) to separate VLB from Catharanthus roseus extract. The results showed that the polymer exhibited high affinity to the template molecule and could separate and enrich VLB from C. roseus extract effectively. The recovery of VLB on the optimal MIP was 89.00%, which agreed closely with the predicted recovery. Therefore it is possible to further improve the nature of the polymer by optimizing the polymerization parameters with the method of uniform design.     

Simple Method for Simultaneous Determination of Selenium and Arsenic in Human Hair by Means of Atomic Fluorescence Spectrometry with Hydride Generation Technique

This study describes a simple, rapid and reliable method for simultaneous determination of selenium and arsenic in human hair by means of atomic fluorescence spectrometry combined with a hydride generation technique (HG-AFS). The procedure developed encompasses microwave digestion of a sample in the nitric acid environment only. The interferences caused by nitrous oxides are eliminated by removing a gas from above the digested solution with a stream of argon. The sample is then chemically treated in a flow-through hydride generation system and exposed to measurements in a double-channel atomic fluorescence spectrometer. The method permits determining both analytes in the linear range of 0.5–100µgL^–1 with a detection limit equal to 0.2µgL^–1, as well as with very good repeatability not exceeding 1% for Se and 2% for As. No mutual interferences from either of the analytes in the concentrations ranges matching the hair composition were found. The method was verified in terms of accuracy with the use of a reference material and then applied to the analysis of the natural samples of human hair.