Spectres de rotation de la molécule de chlorobenzéne : I. Variétés isotopiques monosubstituées et structure rs

The microwave spectra of chlorobenzene “(1)-³⁵Cl”, all eight mono-[“(1)-³⁷Cl”, “(1)-³⁵Cl, (2)D”, “(1)-³⁵Cl, (3)D”, “(1)-³⁵Cl, (4)D”, “(1)-³⁵Cl, (1)-¹³C”, “(1)-³⁵Cl, (2)-¹³C”, “(1)-³⁵Cl, (3)-¹³C”, “(1)-³⁵Cl, (4)-¹³C”], one di[“(1)-³⁵Cl, (2,6)D₂,”] and one trisubstituted species [“(1)-³⁷Cl, (2,6)D₂”] have been investigated. From the moments of inertia of the vibrational ground state the r_s structure was derived. The reliability of the two small a coordinates could be enhanced through use of the multiply substituted species. The errors of the moments of inertia were propagated to the structural parameters. It could be shown that the benzene ring is deformed. However the quantitative deformation could not be established due to the rather large errors of some structural parameters.     

Fulvalene ions—I: Calculations on calicene ions

Calculations on planar and 90°-twisted calicene and the mono- and di-ions derived from it are reported. Both all-valence-electron and π-electron calculations were performed, utilizing an “all aromatic” geometry throughout. Calculated ionization energies indicate that there should be no appreciable gain in resonance stabilization upon radical formation, however the radicals should be amenable to preparation. Good general agreement was obtained between the π-electron charge and spin distributions predicted by the INDO and PPP methods. In addition, these are generally in good agreement with simple predictions based on Hu¨ckel's (4n + 2) rule.     

Concerning the theory of chirality functions : Part I. Construction and discussion of chirality functions by means of [2.2] metacyclophanes

By means of [2.2]metacyclophane (skeleton symmetry C_2h) the construction of qualitatively-complete chirality functions via the first and second “Naherungsansatze” is demonstrated. In this context, a detailed comment concerning the algebraic theory of chirality functions is given. As the first term of the chirality function (“abridged Ansatz”), both methods furnish a simple superposition rule (“quadrant rule”). The second component as deduced via the method of polynomials is of third degree in ligand specific parameters. A particular property of the second approximation method is derived. The consequences with respect to observables of the chirality phenomenon, in the case of the approximations being valid, are discussed.     

Neue C-spektroskopische untersuchungen zur struktur von allylmetall-verbindungen

High-resolution ¹³C NMR spectra of terminally monodeuterated allyl(earth)-alkalimetal compounds confirm earlier structure assignments: allylmagnesium bromide exists in a σ-covalent structure, which rapidly and reversibly goes over into its “metallomeric” mirror-image; allyllithium forms a distorted π-complex; allylpotassium and allylcaesium have the shape of perfectly symmetrical or slightly asymmetrical π-complexes. No NMR spectroscopic evidence is found in tetrahydrofuran solution for the presence of aggregates and mixed aggregates resulting from dimerization or oligomerization of monomeric allylmetal species.     

Spectral study of the structure of compartmental complexes of europium and copper

Compartmental complexes [EuH₂(fsa)₂en]Cl·3H₂O and [CuH₂(fsa)₂en]·0.5H₂O have been synthesized and characterized. The compartmental ligand (H₄(fsa)₂en) is N,N′-bis(3-carboxysalicy- lidene)ethylenediamine. Spectral study indicates that Eu(III) and Cu(II) are coordinated by the ---O₂O₂ coordinating atoms (outside) and the ---N₂O₂ coordinating atoms (inside), respectively. Since there is a considerable difference in the ligand field strength between the “outside” and “inside” coordination spheres, their different fluorescence properties have been investigated by photoacoustic spectroscopy and fluorescence spectroscopy.     

Zur nomenklatur der phane—II

The new term “Phanes” has been clearly defined and a nomenclature system tentatively developed. This system is comprehensible and of general application and at the same time relatively simple. The notations “nucleus”, “bridge”, “number of bridge members” and “number of ring members” are defined. In order to get a definite characterisation of the phanes which contain a carbocyclic nucleus, a carbocyclic and heterocyclic bridge the following terms: “carbophanes”, “carba-phanes” and “hetera-phanes” have been newly introduced. The prefix “hetera-” has been proposed as a general expression and as a representative term for the syllables “aza-”, “oxa-”, “thia-” and so on. The so called “a-nomenclature” is clearly called “hetera-nomenclature”. The new expressions “heteralogous” and “substitulogous” are explained. As the various examples will show, the “Phane-Nomenclature” can also be applied to the naming of complicated metallocenophanes.     

A localized molecular orbital study on the bonding of> Mo3S4]2Mo> and> Mo3S4]CuI> versus (C6H6)2Cr and C6H6Cr(CO)3

The energy-localized CNDO/2 molecular orbitais have been calculated for the clusters containing molybdenum, > {Mo₃S₄₂Mo}⁸⁺ and> Mo₃S₄]CuI> ⁴⁺, versus the prototype arene-metal sandwich (C₆H₆)₂Cr and half-sandwich complexes C₆H₆Cr(CO)₃. The bonding characteristics of these compounds are described from a localization bonding viewpoint. There are two typical M-arene and M-[Mo₃S₄] bondings. One is formed by electron donation from the three-center two-electron π-bonds in the arene or [Mo₃S₄]⁴⁺ ligands into the vacant hybrid orbitais of the “stranger” metal atom. In the other M-arene or M-[Mo₃S₄] bond there is very little donation by the lone electron pair occupying the d AOs of the “stranger” metal atom to the arene or [Mo₃S₄]⁴⁺ ligands. The analogy of the ligand [Mo₃S₄]⁴⁺ in the clusters studied with the ligand benzene is also briefly discussed.     

Synthetic possibilities of the 2,4-pentanedione-1,2-diaminoethane system: An overall view

Single condensation of acetylacetone (AcacH) with 1,2-diaminoethane (En) yields the terdentate “half-unit” 7-amino-4-methyl-5-aza-3-hepten-2-one (abbreviated as AEH). In the presence of a metal ion, this ligand leads to the macrocycle 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclo tetradeca-4,6,11,13-tetraene, which can be considered as resulting from the condensation of two molecules of (AcacH) with two molecules of (En). This “half-unit” can also be used to obtain acyclic ligands and complexes made with one (AcacH) molecule and two (En) molecules (1:2) or conversely two (AcacH) molecules and one (En) molecule (2:1). Using reagents other than (AcacH) and (En), this “half-unit” may yield homo and heterodinuclear complexes, macrocyclic compounds and non-symmetrical tetradentate Schiff bases.     

Calculation of equilibrium constants from multiwavelength spectroscopic data-IV Model-free least-squares refinement by use of evolving factor analysis

The newly developed algorithm of evolving factor analysis has been supplemented by iterative refinement. It allows the completely model-free calculation of concentration profiles and spectra from spectrophotometric and other spectroscopic data. Not even implicit use is made of the law of mass action. The results are practically identical with those based on a specific chemical model and classical least-squares refinement. Iterative evolving factor analysis is based on applying factor analysis successively to the set of the first 1,2 M spectra of a spectrometric titration. The analysis is repeated from the opposite end and the eigenvalues thus calculated are combined into “concentration profiles” of completely abstract “species”. These “concentration profiles” are iteratively refined by normalization, calculation of the absorption spectra from the normalized concentrations and recalculation of the concentration profiles from the absorption spectra. Evolving factor analysis is not restricted to spectrometric titrations, and can also be applied to peak resolution in chromatography using a multiwavelength (diode array) photometric or mass-spectrometric detection system, or to any other ordered set of multichannel data.     

The behaviour of some selenoglycollic acid derivatives in aqueous solutions and spectrophotometric determination of constants of the system Pd(II)/ethylene-bis- selenoglycollic acid

Interactions between ethylselenoglycollic, selenoglycollic and ethylene-bis- selenoglycollic acids and some “soft”, “borderline” and “hard” metallic ions have been studied. The interactions of [PdCl₄]_aq²⁻ with the three ligands were verified conductometrically and spectrophotometrically. The stability constants β₁ and β₂ for the system [PdCl₄]^2-- ethylene-bis-selenoglycollic acid have been determined at 25°C at ionic strength 3.0 M (NaCl). The stoichiometric ionization constant of the mentioned acid was also studied.     

Sythesis and crystal structure of a new nickel(II)-terpyridine complex: [Ni(terpy)(NO2)(ONO)(H2O)]

The compounds Ni(terpy)Cl₂ · 3H₂O and NaNO₂ react readily in aqueous solution to give the complex [Ni(terpy)(NO₂)(ONO)(H₂O)], which has been structurally characterized by an X-ray diffraction study. The hexacoordinate nickel atom bonds to three nitrogen atoms of the terpyridine ligand, to a “nitro” group, to a “nitrite” group and to a water molecule. Distortion from an octahedron to a trigonal prism, for the complex, has been evaluated. An infrared study of the complex has been carried out and shows bands of nitro and nitrite coordination. Magnetic study reveals a Curie-Weiss behavior, giving an effective magnetic moment at room temperature 3.12 B.M.     

“Hole-burning spectra”. A new method for obtaining fine structure in absorption spectra of organic molecules

A new method is proposed for obtaining fine structure in broad-band absorption spectra of organic molecules in solid solutions at low temperature. This method is based on the laser burning of a series of narrow gaps in inhomogeneously broadened absorption spectra. A special spectral set-up has been developed for the measurement of the differential spectrum (a “hole-burning spectrum”) of “burnt” and “unburnt” samples. As an example the hole-burning spectrum of Zn-tetraphenylporphine in ethanol has been considered.     

Chemistry of the podocarpaceae—V The identification of miropinic acid and isomiropinic acid from Podocarpus ferrugineus D. Don

By reinvestigation of “isomiropinic” and “miropinic” acids from the bled resin of Podocarpus ferrugineus, the compounds have been identified as sugiol and isopimaric acid respectively. The identity of the resin acid from Dacrydium biforme has been confirmed as isopimaric acid.     

Impact of the structure of phospholipid dispersions on the stability of fluorocarbon/phospholipid emulsions for biomedical uses

The preparation of injectable fluorocarbon emulsions includes the dispersion of the phospholipids in the aqueous phase, then the admixing of the fluorocarbon to produce a crude premix; emulsification is then achieved using a high pressure mechanical procedure, followed by final heat-sterilization. In this work we report that, depending on the procedure used and energy applied, the dispersions of phospholipids consist of poorly organized unclosed “pre-liposomes”, multilamellar vesicles (MLV), or small unilamellar vesicles (SUV). This has a significant impact on the stability of the final fluorocarbon emulsions (90% (w/v) concentration), those prepared from “pre-liposomes” being more stable than those prepared from MLV or SUV. The first emulsion is shown to contain less fluorocarbon-free phospholipid vesicles than the other two. These free vesicles have previously been reported to have a detrimental effect on the stability of concentrated fluorocarbon emulsions.     

A molecular mechanics force field for the cobalt corrinoids

A force field for the cobalt (III) corrinoids (derivatives of vitamin B₁₂) for use with a modified version of the molecular mechanics program 2(87) has been developed empirically around 19 cobalt corrinoid crystal structures. Bond lengths, bond angles and torsional angles are reproduced with r.m.s. differences of 0.01 Å, 2.4 °, and 4.2 °, respectively, within the standard deviation of the mean of these parameters found in the solid state. The axial ligand occupying the lower coordination site in the cobalamins, 5,6-dimethylbenzimidazole, is shown to have very limited rotational freedom and is constrained by the downward-pointing b and d propionamide side chains of the corrin ring. Strain-energy profiles for rotation of the side chains of the corrin ring show the existence of several local energy minima and this explains the observed variability in the orientations of these side chains in the solid state. The known change in conformation which occurs in the C ring when the e side chain is epimerized from the lower to the upper face of the corrin ring in cyano-13-epicobalamin is correctly predicted, provided the starting conformation of the C ring is unbiased. A study of cyano-8-epicobalamin indicates that an analogous conformational change does not occur in the B ring and the epimerized d side chain assumes an equatorial orientation relative to the corrin ring. Parameters for the Co---C bond in alkylcobalamins were developed and the structure of methyl- and adenosylcobalamin are accurately reproduced. An examination of the strain energy consequences of rotation of the adenosyl ligand about the Co---C bond identifies a number of low-energy conformations at least two of which, in which adenosyl lies over the “southern” and “eastern” portions of the corrin ring, respectively, have been previously deduced from NMR observations. Coordinated neopentyl in neopentylcobalamin is much more hindered to rotation about the Co---C bond and the lowest conformation finds two γ(C) atoms straddling the upwardly projecting C46 methyl group of the corrin.     

Electro-osmotic studies of endothelial cell surface

The surface properties of human umbilical vein endothelial cells (HUVEC), which form the inner walls of blood vessels, have been studied by electro-osmosis measurements. The data are analyzed on the basis of an electrophoresis theory of “soft” particles (that is, particles covered by polyelectrolyte layers). This theory utilizes two parameters, i.e. the density of fixed charges in the cell surface layer and a “softness” parameter (1/λ) which corresponds to the reciprocal of the coefficient of the frictional forces exerted by the surface layer on the liquid flow in the surface layer. It is found that the “softness” parameter for HUVEC is very large, i.e. the surface of HUVEC is very soft compared with those of other biological cells such as erythrocytes or human promyelocytic leukemia cell lines (HL-60RG cells) which we have studied before. The obtained value of 1/λ is comparable to that observed for a poly (NIPAAm) hydrogel layer in a swollen state. The charge density in the surface layer of HUVEC, however, is found to be similar to those for other biological cells.     

Strong effects of the bridge configuration on photoinduced charge separation in rigidly linked donor-acceptor systems

Photoinduced electron-transfer rates are reported for two pairs of rigid bichromophoric molecules 1(6)/2(6) and 1(8)/2(8). In the first pair electron donor and acceptor are separated by six, in the second pair by eight, carbon—carbon σ bonds. While these σ bonds provide an all-trans coupling path in 1(6) and 1(8), that path contains s-cis elements in 2(6) and 2(8), which - as shown by X-ray structure data and by spectroscopic evidence - leads to a slight decrease in the effective, spatial donor-acceptor separation. Nevertheless, photoinduced electron transfer in each of the “stretched” compounds is about one order of magnitude faster than in the corresponding “bent” compound. This remarkable effect is interpreted as resulting from the unique ability of an all-trans array of σ bonds to mediate electronic through-bond interaction (TBI). Interestingly the solvent dependence of the rate of photoinduced electron transfer is significantly larger in the “bent” systems, thus indicating that superexchange via solvent molecules becomes competitive with TBI if an all-trans array is not available.     

The potential energy surfaces and the radiationless dynamics of excited states of benzene and pyrazine

The potential energy surfaces of the lowest excited states of benzene and pyrazine are investigated as a function of some of the symmetry-adapted internal coordinates by means of the INDO/S method. A large stabilization of the T₂ (ππ*) state of pyrazine (≈ 0.5 eV) along the S_8b vibrational coordinate is found. The calculated potential energy in some excited states (T₁ in benzene, T₂ and S₂ in pyrazine) is a very flat function of the S_16b vibrational coordinate, leading to a crossing with the potential energy of the ground state at relatively small excess of vibrational energy (≈ 1 eV). Thus the ν_16b vibrational mode is postulated to play an important role in the radiationless relaxation to the ground states of these systems. No such crossing has been found near the “channel three” threshold of benzene.     

FT-Raman spectra of cis–bis(thiourea)selenium(II) chloride and bromide

The FT-Raman spectra of Se(tu)₂Cl₂ and Se(tu)₂Br₂ complexes are reported for the first time. The important modifications observed in the Raman active modes of thiourea molecules demonstrate a very strong interaction between the Se(II) ion and the sulfur atom of the ligand. As a result of this coordination, and through a “resonance-assisted” mechanism, an intense hydrogen-bonded network is present in the crystal structure of the complexes with notable vibrational effects.