The i.r. spectra of matrix isolated water species—I. Assignment of bands to (H2O)2, (D2O)2 and HDO dimer species in argon matrices.

Frequencies corresponding to the perturbed monomer frequencies are assigned to the dimer species (H₂O)₂, (D₂O)₂ and dimers involving HDO in argon matrices on the basis of the variation of the i.r. spectra over a large matrix/water ratio and the changes in the spectra on annealing. Annealing is necessary to help distinguish between bands due to water dimers and to non-rotating monomers.     

How does it become possible to treat delocalized and/or open-shell systems in fragmentation-based linear-scaling electronic structure calculations? The case of the divide-and-conquer method

The authors have developed a fragmentation-based linear-scaling electronic structure calculation strategy named the divide-and-conquer (DC) method, which has been implemented into the Gamess program package. Although there are many sorts of fragmentation-based linear-scaling schemes, most of them require the charge and spin multiplicity of each fragment a priori. Therefore, their applications to delocalized and/or open-shell systems have been limited. However, the DC method is a notable exception because the distribution of electrons in the entire system is automatically determined by the universal Fermi level. In this perspective, the authors have summarized the performance of the linear-scaling self-consistent field (SCF) and post-SCF calculations of delocalized and/or open-shell systems based on the DC method. Furthermore, some future prospects of the method have been discussed.     

Long-range spin–spin interactions in the 13C-n.m.r. spectra of the nickel(II) complex of the Schiff base of (S)-N-benzylproline (2-benzoylphenyl)amide and glycine. Quantum-chemical calculations and possible donation of electron density from the π-system of the benzyl group to nickel

Long-range [ ⁿ J(¹³C, ¹³C), ⁿ J(¹⁵N, ¹⁵N) and ⁿ J(¹⁵N, ¹³C)] interactions in the ¹³C-n.m.r. spectra of CDCl₃ solutions of selectively labeled nickel(II) complexes of the Schiff base derived from (S)-N-benzylproline (2-benzoylphenyl)amide and glycine provide experimental evidence for the necessity of the donation of electron density from the -system of the benzyl ring to the nickel orbitals. No such interactions were observed in (²H)DMSO solutions, where the complex exists in a different conformation.     

Why are the hydroxy groups of partially protected N-acetylglucosamine derivatives such poor glycosyl acceptors, and what can be done about it? A comparative study of the reactivity of N-acetyl-, N-phthalimido-, and 2-azido-2-deoxy-glucosamine derivatives in glycosylation. 2-Picolinyl ethers as reactivity-enhancing replacements for benzyl ethers.

Competition experiments were used to determine that the 4-OH of a 2-deoxy-2-azidoglucose derivative is more reactive than that of the corresponding N-phthalimido glucose derivative which, in turn, is more easily glycosylated than the N-acetyl derivative. Glycosylation of the 4-OH groups of the N,N-diacetyl and N-acetyl-N-benzyl glucosamine was also found to be superior to that of the simple N-acetyl substance. The 3-O-picolinyl ether of a 4,6-O-benzylidene-protected N-acetylglucosamine was shown to have a strong intramolecular hydrogen bond to the adjacent acetamide group. This interaction does not persist in the 3-O-picolinyl-6-O-benzyl N-acetylglucosamine derivative, owing to a probable competing hydrogen bond between the 4-OH and the picolinyl ether. However, in the 3-O-picolinyl-4-O-benzyl N-acetylglucosamine regioisomer the picolinyl-acetamide hydrogen bond persists and leads to an enhancement of reactivity of the 6-OH, over and above that in the corresponding 3-O-benzyl ether, due to disruption of the typical intermolecular amide hydrogen bonding scheme. It is demonstrated that the picolinyl ether is readily removed by hydrogenolysis at atmospheric pressure and room temperature.     

Regiochemistry of S-alkyl-substituted alkynes in Pauson-Khand reactions. Is a correlation with X-ray data and charge distribution calculations of the Co(2)(CO)(6)-alkyne complexes possible?

[reaction: see text] Pauson-Khand reactions (PKR) of RSCtbd1;CR' (6-10) yielded in all cases as the main product the regioisomer with the alkyl-S group disposed alpha to the CO group (16a-22a). Correlation of these results with X-ray data and charge distribution calculations of the corresponding dicobalthexacarbonyl complexes proves that a recently postulated "trans effect" in these complexes is not suitable for predicting the regiochemical outcome of the PKR unambiguously.     

Contribution to interpretation of metal uptake dependence upon the growth phase of microorganisms. The case of uranium (VI) uptake by common yeasts,cultivated at different temperatures,with or without aeration

The dependence of U(VI) uptake on the temperature of cell culture, the air flow during the cultivation process and the age of cells were studied. Saccharomyces cerevisiae, Kluyveromyces marxianus and Debaromyces hansenii were chosen as typical yeasts, which are widely used, in food industries. Our results revealed that the highest metal uptake was obtained from exponential phase cells, which had been cultivated at the optimum temperature of growth, while the air flow during the cultivation process, exhibited no significant effect on the metal uptake. A qualitative interpretation of bibliographic data, concerning the metal uptake on the age of cells is proposed, assuming that qualitative changes in the cell wall structure take place, as the cells pass from exponential to stationary phase, in addition to quantitative modifications, which have been reported in the literature. According to our interpretation, the relative abundances among quantitative and qualitative alterations of cell wall, determine which cells (exponential or stationary) exhibit the higher metal capacity. One type of the suggested qualitative modifications of surface constituent of cell wall, may have been caused by a shortening of a carboxylic acid carbon chain. This type of modification implies, as prerequisite, the decrease of pK _a values of cell wall carboxyl groups, with the age of cells. An evidence, supporting our approach, may be the fact that the decrease of pK _a values mentioned above, has been observed by other authors.     

The Liquid Junction Potential in Potentiometric Titrations. XII. The Calculation of Potentials for Emf Cells with Liquid Junctions, of the Type, AY | AY + A2MoO4+HY, Involving the Formation of Iso-Polymolybdates in the Range ?log?10[H+]��7, at [A+]=C mol?L?1, Constant, and 25?��C

Equations are derived, in a general form, and valid in the range 0.5??C??3 mol?L^?1, for the calculation of the total potential anomalies (??E _H) for emf cells where the formation of iso-polymolybdates takes place, according to the equilibria: $$p \mathrm{H}^{+} (h) + q \mathrm{MoO}_{4}^{2 -} (b)\rightleftharpoons [(\mathrm{H}^{+})_{p}(\mathrm{MoO}_{4}^{2-})_{q} ] ^{p - 2q} (cpx _{pq})$$ by measuring [H⁺]=h, in NaClO₄ ionic medium (A⁺, Y^?) at [Na⁺]=3 mol?L^?1. The total cell emf (E _H), can be defined as: $$E_{\mathrm{H}} = E_{\mathrm{0H}} + g \log_{10} h + g\log_{10} f_{\mathrm{HTS}2} +E_{\mathrm{D}} + E_{\mathrm{D}f}$$ where: E _0H is an experimental constant, E _D+E _Df =E _J, the classical liquid junction potential, and glog?₁₀ f _JTS2+E _D+E _Df =??E _H. Here, $\mathrm{MoO}_{4}^{2 -}$ is the central ??metal ion??, E _D is the ideal diffusion potential (Hendersson equation), E _Df is the contribution of the activity coefficients to E _D. f _HTS2 denotes the activity coefficient of the H⁺ ions in the terminal solution TS2. The investigations of this system made by Sasaki and Sillén are critically analyzed. Some emf cells are supposed for the determination of the interaction coefficients involved. All calculations are valid at 25?°C. The revised equilibrium constants are presented in Table 14.     

Can halogen bond energy be reliably estimated from electron density properties at bond critical point? The case of the (A)nZ—Y•••X− (X,Y = F,Cl, Br) interactions

Relationships between the Y•••X bond critical point (BCP) properties or the Y•••X distance and the halogen bond interaction energy were analyzed in detail by theoretical methods for the series of structures [(A)_nZ—Y•••X]⁻ (X,Y = F, Cl, Br; totally 441 structures). No relationship was found for the whole set of structures or for the series [(A)_nZ—F•••X]⁻, [(A)_nZ—Cl•••X]⁻, and [(A)_nZ—Br•••X]⁻. The interaction energies may be roughly estimated from the BCP properties for the series [(A)_nZ—Y•••F]⁻, [(A)_nZ—Y•••Cl]⁻, and [(A)_nZ—Y•••Br]⁻ as well as for [(A)_nZ—Y•••X]⁻ (when (A)_nZ is variable, X and Y are constant) with the mean absolute deviation values 2.04-4.38 kcal/mol. The corresponding recommended relationships are provided and they are significantly different from the popular dependencies deduced previously for other types of noncovalent interactions. Tremendous effect of the computational method and basis set on the relationships under analysis was discovered. Computational results clearly indicate that, for practical purposes, the E_int(BCP property) dependencies should be established not simply for each global type of interactions (hydrogen bond, halogen bond, chalcogen bond, etc.) but for each combination of the first and second order atoms taking into account also the computational method and basis set.     

Synthesis of a new camphor derived P,S(O) ligand. The importance of C-H?O bonding in the ligand exchange reactions with Co2(μ-alkyne)(CO)6 complexes

Herein we describe the synthesis and structure of a new chiral bidentate P,S(O) ligand containing a stereogenic sulfur atom. We also report on its coordination properties to acetylene dicobalt hexacarbonyl complexes, providing X-ray structures of the ligand alone and of a ligand-cobalt complex. Solid state structure of complex 4 shows the formation of a weak C-H?O bond between a polarised methine group in the ligand and a sulfone group on the alkyne that helps to stabilize the bridged coordination mode.     

The Structure of Gaseous Carbon Tetraiodide from Electron Diffraction and All Carbon Iodides,CIn (n = 1–4), and Their Dimers,C2I2n (n = 1–3) from High-Level Computation. Any Other Carbon-Iodide Species in the Vapor?

The geometry of a series of carbon iodides have been determined, CI₄ by gas-phase electron diffraction and CI _n (n = 1–4) and C₂I_2n (n = 1–3) by high-level quantum chemical calulations. The bond length of the tetrahedral CI₄ molecule from electron diffraction is (r _g):2.157(10) Å. The indication of about 20% I₂ in the vapor suggests partial decomposition and it has been thoroughly investigated what other carbon iodide species might be present beside CI₄. There is no appreciable amount of either of the dimeric species in the vapor phase, in spite of the suggestion from thermodynamics. On the other hand, the electron diffraction data are compatible with the presence of about 18% of either of the monomeric free radicals, CI₃ or CI₂, beside CI₄ and I₂. Possible reasons for these observations are discussed. Our correlated level computations, in agreement with other high level computations, found the singlet ¹A₁ state to be the ground state for CI₂. This is in contrast with a recent photoelectron spectroscopic study according to which the triplet state is the ground state though with a large margin of error (1 ± 3 kcal/mol energy difference). The computed singlet-triplet separation strongly depends on the level of the computation, but it is at least 9 kcal/mol. Geometrical parameters, singlet-triplet separations, and dipole moments have been calculated for the CX₂ series (X = F, Cl, Br, I, H) and their variations are discussed. The thermodynamic stability of different carbon iodide species has also been investigated.     

Metal-stabilized carbanions IX. The influence of metal basicity on the η6 ⇄ η5 Haptotropic equilibrium of (fluorenyl)-Cr-(CO)2L anions (L = CO,P(OPh),3, PPh3, P(n-Bu)3)

The (fluorene)Cr(CO)₂L complexes (L = CO, P(OPh)₃, PPh₃, P(n-Bu)₃) have been synthesized and metallated with KH in THF to form the corresponding η⁶-anions, which in turn equilibrate at room temperature with the η⁵-hapto isomers. All theses species have been fully characterized by ¹³C and ³¹P NMR spectroscopy. The rate of metallation, the reduction potential, the IR carbonyl stretching frequencies, and the η⁶ ⇄ η⁵ haptotropic equilibrium are strongly influcned by the nature of L.     

Domino reactions in the synthesis of benzothieno[2,3-c]pyridines. New one-pot method of preparing 2-([1]benzothieno-[2,3-c]pyridin-1-yl)benzoic acids and 8,13b-dihydro[1]benzothieno[2',3':3,4]pyrido-[2,1-a]isoindol-5(7?H)-ones

A series of previously unknown 2-([1]benzothieno[2,3-c]pyridin-1-yl)benzoic acids and 8,13b-dihydro-[1]benzothieno[2',3':3,4]pyrido[2,1-a]isoindol-5(7 H)-ones has been synthesized using domino reactions, taking place at the cyclization of 2-[3-oxo-4-(phenylsulfanyl)butyl]-1,3-isoindolinediones in polyphosphoric acid.     

The reactions of (η5-C5H5)NiO(s)3(μ-H)3(CO)9 with group V donor ligands. Spectroscopic characterization of the disubstituted derivatives,and crystal structure of (η5-C5H5)NiO(s)3(μ-H)3(CO)7(PMe2Ph)2

The complex (η⁵-C₅H₅NiO(s)₃(μ-H)₃(CO)₉ (1 reacts with phosphines in the presence of Me₃NO to give monosubsituted derivatives, the main products, along with smaller amounts of disubstituted derivatives. The IR and NMR spectroscopic characterizations of two representative disubstituted derivatives are described.The crystal structure of (η⁵-C₅H₅)NiO(s)(μ-H)₃(CO)₇(PMe₂Ph)₂ has been determined by X-ray diffraction. The crystals are monoclinic, space group P2₁/a with Z = 4 in a unit cell of dimensions a 18.198(8), b 20.865(8), c 8.656(5) Å, β 99.67(2)°. The structure was solved by direct and Fourier methods and refined by full-matrix least-squares to R = 0.061 for 3139 observed reflections. The structure can be regarded as derived from that of 1 (which has a tetrahedral NiO(s) core with three hydride hydrogen atoms bridging the OsOs edges, a cyclopentadienyl group coordinated to the Ni atom,and nine terminal carbonyls bound to the Os atoms, three for each Os atom) by replacing two axial carbonyls by two PMe₂Ph ligands.