A 13C NMR investigation of some tetrakisisocyanocopper(I) tetrafluoroborate complexes: Chemical shift of,and coupling to,the isocyano carbon

The ¹³C n.m.r. spectra twelve isocyanides, RNC, and their Cu(I) complexes, Cu(RNC)₄BF₄, were recorded in the solvents CDCl₃ and DMSO. The resonances of the isocyano carbon, C⁰, could be observed for both free and coordinated isocyanides. In the spectra of the complexes this C⁰ resonance was present as a broad line. For some complexes the ¹⁴N? ¹³C⁰ coupling could only be detected after heating the sample or by adding small amounts (<7 mo1%) of Cu(CH₃CN)₄BF₄. For the remaining complexes neither J(¹⁴N? ¹³C⁰) nor J(¹⁴N? ¹³C¹), could be detected. No carbon-copper coupling could be detected. The line shape of C⁰ is discussed in terms of exchange of an isocyanide ligand and in terms of quadrupolar nitrogen and copper relaxation. In most complexes exchange seems to be dominant, whereas in other complexes quadrupolar nitrogen relaxation is also of importance. On coordination of the isocyanide, the C⁰ resonance shifts upfield (15 to 20 ppm) and J(¹⁴N? ¹³C⁰) shows a threefold increase. The upfield shift is associated with a larger excitation energy while the increase of J(¹⁴N? ¹³C⁰) is ascribed to a larger effective nuclear charge on C⁰. The chemical shifts of the α-carbon, the β-carbon and the solvent effect on all n.m.r. parameters in both free and coordinated isocyanides are also discussed.     

Contents of the Supplement S3 to Vol. 50 (2000)

Volume Contents

Contents of the Supplement S3 to Vol. 50 (2000)     

A Clifford analysis approach to superspace

A new framework for studying superspace is given, based on methods from Clifford analysis. This leads to the introduction of both orthogonal and symplectic Clifford algebra generators, allowing for an easy and canonical introduction of a super-Dirac operator, a super-Laplace operator and the like. This framework is then used to define a super-Hodge coderivative, which, together with the exterior derivative, factorizes the Laplace operator. Finally both the cohomology of the exterior derivative and the homology of the Hodge operator on the level of polynomial-valued super-differential forms are studied. This leads to some interesting graphical representations and provides a better insight in the definition of the Berezin-integral.     

Relationship between neural and hemodynamic signals during spontaneous activity studied with temporal kernel CCA

Functional magnetic resonance imaging (fMRI) based on the so-called blood oxygen level-dependent (BOLD) contrast is a powerful tool for studying brain function not only locally but also on the large scale. Most studies assume a simple relationship between neural and BOLD activity, in spite of the fact that it is important to elucidate how the “when” and “what” components of neural activity are correlated to the “where” of fMRI data. Here we conducted simultaneous recordings of neural and BOLD signal fluctuations in primary visual (V1) cortex of anesthetized monkeys. We explored the neurovascular relationship during periods of spontaneous activity by using temporal kernel canonical correlation analysis (tkCCA). tkCCA is a multivariate method that can take into account any features in the signals that univariate analysis cannot. The method detects filters in voxel space (for fMRI data) and in frequency–time space (for neural data) that maximize the neurovascular correlation without any assumption of a hemodynamic response function (HRF). Our results showed a positive neurovascular coupling with a lag of 4–5 s and a larger contribution from local field potentials (LFPs) in the γ range than from low-frequency LFPs or spiking activity. The method also detected a higher correlation around the recording site in the concurrent spatial map, even though the pattern covered most of the occipital part of V1. These results are consistent with those of previous studies and represent the first multivariate analysis of intracranial electrophysiology and high-resolution fMRI.     

On the algebra of symmetries of Laplace and Dirac operators

We consider a generalization of the classical Laplace operator, which includes the Laplace–Dunkl operator defined in terms of the differential-difference operators associated with finite reflection groups called Dunkl operators. For this Laplace-like operator, we determine a set of symmetries commuting with it, in the form of generalized angular momentum operators, and we present the algebraic relations for the symmetry algebra. In this context, the generalized Dirac operator is then defined as a square root of our Laplace-like operator. We explicitly determine a family of graded operators which commute or anticommute with our Dirac-like operator depending on their degree. The algebra generated by these symmetry operators is shown to be a generalization of the standard angular momentum algebra and the recently defined higher-rank Bannai–Ito algebra.     

Magnetism and crystal structures of CuMn and CuNi ordered bimetallic chains

The syntheses, crystal structures and magnetic properties of the new bimetallic compounds {CuL_α[Ni(NCS)₄(H₂O)₂]} (1) and {CuL_α[Mn(NCS)₄(H₂O)₂]} (2), where L = N-dl-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene, are reported. Both structures consist of well-separated and magnetically equivalent layers which are composed of thiocyanate-bridged Cu(II)–Mn(II) or Cu(II)–Ni(II) binuclear units and create infinite polymeric zig-zag-like chains in the crystal lattices. The [Ni(NCS)₄(H₂O)₂] and [Mn(NCS)₄(H₂O)₂] molecular fragments have a distorted octahedral symmetry. The geometry of the Cu(II) unit is octahedral with the apical positions occupied by bridging thiocyanate ligands and the basal ones by four nitrogen atoms from the macrocyclic ring. The shortest intramolecular M–M distances are: 6.342 Å (Cu–Ni) and 6.421 Å (Cu–Mn). Magnetic susceptibility and magnetization measurements for the examined compounds have been carried out over the range 1.8–300 K. The data suggest antiferromagnetic interactions through the thiocyanate bridge. Finally, the magnitudes of the Cu(II)–M(II) interactions (M = Ni and Mn) have been compared and qualitatively rationalised.     

Vibrationally resolved photofragment translational spectroscopy of CH3I from 277 to 304 nm with increasing effect of the hot band

The photodissociation dynamics of CH(3)I from 277 to 304 nm is studied with our mini-TOF photofragment translational spectrometer. A single laser beam is used for both photodissociation of CH(3)I and REMPI detection of iodine. Many resolved peaks in each photofragment translational spectrum reveal the vibrational states of the CH(3) fragment. There are some extra peaks showing the existence of the hot-band states of CH(3)I. After careful simulation with consideration of the hot-band effect, the distribution of vibrational states of the CH(3) fragment is determined. The fraction σ of photofragments produced from the hot-band CH(3)I varies from 0.07 at 277.38 nm to 0.40 at 304.02 nm in the I* channel and from 0.05 at 277.87 nm to 0.16 at 304.67 nm in the I channel . E(int)/E(avl) of photofragments from ground-state CH(3)I remains at about 0.03 in the I* channel for all four wavelengths, but E(int)/E(avl) decreases from 0.09 at 277.87 nm to 0.06 at 304.67 nm in the I channel . From the ground-state CH(3)I, the quantum yield Φ(I*) is determined to be 0.59 at 277 nm and 0.05 at 304 nm. The curve-crossing probability P(cc) from the hot-band CH(3)I is lower than that from the ground-state CH(3)I. The potential energy at the curve-crossing point is determined to be 32,740 cm(-1).     

A pH dependent thermo-sensitive copolymer drug carrier incorporating 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (4-NH2-TEMPO) residues for electron spin resonance (ESR) labeling

The fabrication of a new amphiphilic block copolymer composed of a poly DL-lactic acid (PLA) hydrophobic backbone and pH dependent thermo-sensitive poly (N-isopropyl) methacrylamide-co-N-isopropylmaleamic acid-co-10-undecenoic acid (PNIPAAm-co-NIPMMA-co-UA) entities as hydrophilic domains as well as carrying 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) residues for electron spin resonance (ESR) labeling is reported. The lower critical solution temperature (LCST) of the copolymer was determined by optical absorbance measurements. The LCST was pH dependent and varied in a narrow practical range, 35.4 °C at pH 5.0, 37.5 °C at pH 6.5 and 39.4 °C at pH 7.4, which was below, near and above nominal physiological temperature respectively. The assembly of the copolymer into micelles in aqueous solution at temperatures below the LCST was confirmed by FT-IR, (1)H NMR and fluorescence spectroscopy. It is demonstrated that the anticancer drug, 5-fluorouracil (5-FU) can be loaded effectively within the polymeric micelles and released in response to environmental stimuli- namely, pH and temperature.     

Optical and magnetooptical characterization of FeNi/Cu multilayers

A series of [FeNi(1.7 nm)/Cu(t_Cu)]₃₀/Fe(10 nm) multilayers with the range of t_Cu from 0.36nm to 4.32nm deposited on glass substrates was studied by measuring the effective optical constants n and k, saturation magnetooptical polar Kerr rotation θ _k and ellipticity η_k and evaluating the effective complex off-diagonal elements of the dielectric tensor ε _xy ^′ and ε _xy ^″ . It was found that the four primary quantities ε _xy ^′ , ε _xy ^″ , n and k vary concurrently with respect to t_Cu, while the dependences of θ _k and η _k on t_Cu differ drastically. To explain this difference the contributions of both the real and imaginary parts of the off- diagonal dielectric tensor elements and the effect of complex optical constants have to be considered. No obvious correlation was found between the variation of ñ, ε~ _xy and the oscillations of GMR of the multilayers.