On equilibrium structures of the water molecule

Equilibrium structures are fundamental entities in molecular sciences. They can be inferred from experimental data by complicated inverse procedures which often rely on several assumptions, including the Born-Oppenheimer approximation. Theory provides a direct route to equilibrium geometries. A recent high-quality ab initio semiglobal adiabatic potential-energy surface (PES) of the electronic ground state of water, reported by Polyansky et al. [ ibid. 299, 539 (2003)] and called CVRQD here, is analyzed in this respect. The equilibrium geometries resulting from this direct route are deemed to be of higher accuracy than those that can be determined by analyzing experimental data. Detailed investigation of the effect of the breakdown of the Born-Oppenheimer approximation suggests that the concept of an isotope-independent equilibrium structure holds to about 3 x 10(-5) A and 0.02 degrees for water. The mass-independent [Born-Oppenheimer (BO)] equilibrium bond length and bond angle on the ground electronic state PES of water is r(e) (BO)=0.957 82 A and theta e (BO)=104.48(5) degrees , respectively. The related mass-dependent (adiabatic) equilibrium bond length and bond angle of H2 (16)O is r(e) (ad)=0.957 85 A and theta e (ad)=104.50(0) degrees , respectively, while those of D2 (16)O are r(e) (ad)=0.957 83 A and theta e (ad)=104.49(0) degrees . Pure ab initio prediction of J=1 and 2 rotational levels on the vibrational ground state by the CVRQD PESs is accurate to better than 0.002 cm(-1) for all isotopologs of water considered. Elaborate adjustment of the CVRQD PESs to reproduce all observed rovibrational transitions to better than 0.05 cm(-1) (or the lower ones to better than 0.0035 cm(-1)) does not result in noticeable changes in the adiabatic equilibrium structure parameters. The expectation values of the ground vibrational state rotational constants of the water isotopologs, computed in the Eckart frame using the CVRQD PESs and atomic masses, deviate from the experimentally measured ones only marginally, especially for A0 and B0. The small residual deviations in the effective rotational constants are due to centrifugal distortion, electronic, and non-Born-Oppenheimer effects. The spectroscopic (nonadiabatic) equilibrium structural parameters of H2 16O, obtained from experimentally determined A'0 and B'0 rotational constants corrected empirically to obtain equilibrium rotational constants, are r(e) (sp)=0.957 77 A and theta e (sp)=104.48 degrees .     

Unprecedented cyclizations of calix[4]arenes with glycols under the Mitsunobu protocol, part 2.(1) O,O-and O,S-bridged calixarenes

[reaction: see text] Cycloalkylations of p-tert-butylcalix[4]arene (CA) and p-tert-butylthiacalix[4]arene (TCA) with various aliphatic glycols were performed under the Mitsunobu protocol using the DEAD/TPP system. CA gave 1,3-dialkylated diols, while C(2)-C(10) glycols gave 1,2- and 1,3-bridged calixarenes. The reaction of TCA with C(2) diols afforded sulfonium phenoxide betaines via O,S-cyclization, which is the first example for the alkylation of the sulfide bridge.     

The Preorganization Effect of the Calix[4]arene Platform on the Extraction Properties of Acetylhydrazide Groups with Transition Metal Ions

The binding properties of the cone conformer of O,O,O,O-tetrakis[hydrazinocarbonylmethyl]-4-tert-butylcalix[4]arene, the cone and the 1,3-alternate conformers of the corresponding thia analogue have been evaluated by means of liquid–liquid extraction for a large variety of metal ions. The extraction constants and the stoichiometries of the complexes formed have been determined. Comparison of the extraction properties of calix[4]arenes with their acyclic monomeric analogue clearly demonstrated, that the preorganization of acetylhydrazide groups on the calix[4]arene platform is the cause for a significant improvement of its binding properties. The presence of additional “soft” nitrogen binding sites in acetylhydrazide derivatives of calix[4]arenes compared to their amide derivatives leads to a shift from their classical selectivity for alkali and alkaline earth cations to transition metals. The cone conformer of tetrathiacalix[4]arene shows higher selectivity in a series of d-metal ions compared with its “classical” analogue. The 1,3-alternate conformer exhibits an excellent extraction selectivity for Cu²⁺ and Hg²⁺.     

Synthesis of novel chiral NiII complexes of dehydroalanine Schiff bases and their reactivity in asymmetric nucleophilic addition reactions. Novel synthesis of (S)-2-carboxypiperazine

New chiral Ni^II complexes of Schiff bases of dehydroalanine with modified chiral auxiliaries (S)-2-N-[N′-(3,4-dichlorobenzyl)prolyl]aminobenzophenone (3,4-DCBPB), (S)-2-N-[N′-(3,4-dimethylbenzyl)prolyl]aminobenzophenone (3,4-DMBPB), (S)-2-N-[N′-(2-chlorobenzyl)prolyl]aminobenzophenone (2-CBPB), and (S)-2-N-[N′-(2-fluorobenzyl)prolyl]-aminobenzophenone (2-FBPB) have been synthesized. Asymmetric Michael addition reactions of primary and secondary amines and thiols to the dehydroalanine moieties of the complexes were studied. (S)-2-FBPB was found to be the best chiral auxiliary in terms of both selectivity of the reactions (de ～92–96%) and reactivity of the complexes. A novel synthetic route toward (S)-2-carboxypiperazine was developed based on the auxiliary.     

Current status of gross alpha/beta activity analysis in water samples: a short overview of methods

Gross alpha/beta measurement is one of the simplest radioanalytical procedures which are applied widely as a screening technique in the field of radioecology, environmental monitoring and industrial applications as well. Due to the uncertainties of gross alpha/beta measurements this method is often the subject of discussions and debates. The aim of this work is to collect information about recently used standard and routine methods concerning gross alpha/beta activity determination in drinking waters in order to get an overview about the current situation and evaluate their possibilities. Sample preparation methods—e.g. evaporation, co-precipitation—and detection systems—e.g. gas flow proportional counting, liquid scintillation counting and scintillation counting—are compared on the ground of literature data. In the course of our work, the following parameters were analyzed and discussed: background, counting efficiency, interferences, sample capacity, minimal detectable activity, typical counting time, time demand of sample preparation.     

Synthesis,Properties, and Reactions of 5-Substituted Derivatives of 2,3-Diphenylquinoxaline [1]

Summary. Catalytic hydrogenation of 5-nitro-2,3-diphenylquinoxaline led to the corresponding amine which, in turn, afforded products of nucleophilic substitution on reaction with alkoxymethylene derivatives. Thermal cyclization of selected alkoxymethylene derivatives yielded substituted pyridoquinoxalines. The conditions for successful hydrolysis of ester, decarboxylation of the acid, following chlorination of pyridone and reductive removal of the chlorine atom from it to produce parental heterocycle 2,3-diphenyl-pyrido[2,3-f]quinoxaline were found. All of the tested products of the nucleophilic substitution showed no antibacterial activity.Dedicated to Prof. Dr. M. Uher on the occasion of his 65^th birthday     

Electrocatalytic activity of DNA on electrodes as an indication of hybridisation

Electron transfer between metal electrodes and ferro/ferricyanide is completely suppressed at low ionic concentration. We describe here a new phenomenon related to this reaction: an immobilisation of thiolated single-stranded DNA on gold electrodes retains this activity at low ionic strength up to the level corresponding to the high ionic strength. In contrast, a hybridisation of the complementary DNA with the thiolated single-stranded DNA followed by a binding onto the electrodes, attenuated the electrocatalytic effect. These effects can be used for discrimination between single-stranded DNA and double-stranded DNA and for semi-quantitative measurement of complementary DNA in a sample.     

Na2Ge3P3 and Na5Ge7P5 Comprising Heteroatomic Polyanions Mimicking the Structure of Fibrous Red Phosphorus

Recently lithium phosphidogermanates were discovered as fast lithium ion conductors for potential usage as solid electrolytes in all solid-state batteries. In this context we also studied sodium phosphidogermanates since sodium ion conductors are of equal interest. Na₂Ge₃P₃ and Na₅Ge₇P₅ both crystallize in the monoclinic space group C2/m with unit cell parameters of a = 17.639(4) Å, b = 3.6176(7) Å, c = 11.354(2) Å, β = 92.74(3)° and a = 16.168(5) Å, b = 3.6776(7) Å, c = 12.924(4) Å, β = 91.30(3)°, respectively. Both show linearly condensed 9-atom cages of four Ge / five P and five Ge / four P atoms, respectively. These cages contain Ge–Ge bonds and form one-dimensional tubes by sharing three atoms. The parallel tubes are paired through further Ge–Ge bonds. Both structures are closely related to the one of the fibrous type of crystalline red phosphorus. A comparison with other compounds such as NaGe₃P₃ and GeP reveals recurring structural motifs with a broad variety of connection patterns. According to the general formula Na_4+xGe_6+xP_6–x with x = 0 and 1, the two novel structures hint for the possibility of a variable Na content which might allow Na ion mobility.