Fullerenes without symmetry: crystallographic characterization of C1(30)-C90 and C1(32)-C90

Fullerenes are generally considered as highly symmetric, yet fullerene isomers with only C(1) symmetry, such as C(1)(30)-C(90) and C(1)(32)-C(90) whose structures are reported here, become increasingly numerous as fullerene size increases.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Free surface on a simple fluid between rotating eccentric cylinders. Part II: Experiments

This paper summarizes the results from an experimental investigation of the effects of eccentricity and rotational speed on the free surface shape on a viscoelastic liquid between eccentric cylinders. In the experimental geometry, the inner cylinder rotates and the outer cylinder is stationary. The experiments show that there is a circumferential pressure gradient (the lubrication effect) which has a dominant influence on the free surface shape at all eccentricities and rotational speeds. For a liquid with small normal stress effects, the normal-stress induced component of the deformation tends to be overwhelmed by the lubrication effect, whereas a liguid with large normal stress effects exhibits characteristics normal-stress induced deformations at small eccentricities and rotational speeds. There is good agreement between experiment and second order predictions for the large normal stress liquid under these conditions. The ranges of eccentricities and rotational speeds for which second order theory describes the low normal stress liquid appear to be much more limited and are difficult to reproduce experimentally.     

Boronic acid-based bipyridinium salts as tunable receptors for monosaccharides and alpha-hydroxycarboxylates

Several novel diboronic acid-substituted bipyridinium salts were prepared and, using a fluorescent reporter dye, were tested for their ability to selectively bind various monosaccharides and alpha-hydroxycarboxylates in an aqueous medium. The fluorescence sensing mechanism relies on the formation of a ground-state charge-transfer complex between the dye and bipyridinium. An X-ray crystal structure of this complex is described herein. Glucose selectivity over fructose and galactose was achieved by designing the bipyridinium-based receptors to be capable of attaining a 1:1 receptor/substrate stoichiometry via cooperative diboronic acid binding.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Single samarium atoms in large fullerene cages. Characterization of two isomers of Sm@C92 and four isomers of Sm@C94 with the X-ray crystallographic identification of Sm@C1(42)-C92, Sm@C(s)(24)-C92, and Sm@C3v(134)-C94

Two isomers of Sm@C(92) and four isomers of Sm@C(94) were isolated from carbon soot obtained by electric arc vaporization of carbon rods doped with Sm(2)O(3). Analysis of the structures by single-crystal X-ray diffraction on cocrystals formed with Ni(II)(octaethylporphyrin) reveals the identities of two of the Sm@C(92) isomers: Sm@C(92)(I), which is the more abundant isomer, is Sm@C(1)(42)-C(92), and Sm@C(92)(II) is Sm@C(s)(24)-C(92). The structure of the most abundant form of the four isomers of Sm@C(94), Sm@C(94)(I), is Sm@C(3v)(134)-C(94), which utilizes the same cage isomer as the previously known Ca@C(3v)(134)-C(94) and Tm@C(3v)(134)-C(94). All of the structurally characterized isomers obey the isolated pentagon rule. While the four Sm@C(90) and five isomers of Sm@C(84) belong to common isomerization maps that allow these isomers to be interconverted through Stone-Wales transformations, Sm@C(1)(42)-C(92) and Sm@C(s)(24)-C(92) are not related to each other by any set of Stone-Wales transformations. UV-vis-NIR spectroscopy and computational studies indicate that Sm@C(1)(42)-C(92) is more stable than Sm@C(s)(24)-C(92) but possesses a smaller HOMO-LUMO gap. While the electronic structures of these endohedrals can be formally described as Sm(2+)@C(2n)(2-), the net charge transferred to the cage is less than two due to some back-donation of electrons from π orbitals of the cage to the metal ion.     

First palladium(II) and platinum(II) complexes from employment of 2,6-diacetylpyridine dioxime: synthesis, structural and spectroscopic characterization, and biological evaluation

Employment of the monoanion of 2,6-diacetylpyridine dioxime (dapdoH(2)) as a tridentate chelate in palladium(II) and platinum(II) chemistry is reported. The syntheses, crystal structures, spectroscopic and physicochemical characterization, and biological evaluation are described of [PdCl(dapdoH)] (1) and [PtCl(dapdoH)] (2). Reaction of PdCl(2) with 2 equivs of dapdoH(2) in MeOH under reflux gave 1, whereas the same reaction with PtCl(2) in place of PdCl(2) gave 2 in comparable yields (70-80%). The divalent metal center in both compounds is coordinated by a terminal chloro group and a N,N',N"-tridentate chelating (η(3)) dapdoH(-) ligand. Thus, each metal ion is four coordinate with a distorted square planar geometry. Characterization of both complexes with (1)H and (13)C NMR and UV-vis and electrospray ionization mass spectroscopies confirmed their integrity in DMSO solutions. Interaction of the complexes with human and bovine serum albumin has been studied with fluorescence spectroscopy, revealing their affinity for these proteins with relatively high values of binding constants. UV study of the interaction of the complexes with calf-thymus DNA (CT DNA) has shown that they can bind to CT DNA, and the corresponding DNA binding constants have been evaluated. Cyclic voltammograms of the complexes in the presence of CT DNA solution have shown that the interaction of the complexes with CT DNA is mainly through intercalation, which has been also shown by DNA solution viscosity measurements. Competitive studies with ethidium bromide (EB) have revealed the ability of the complexes to displace the DNA-bound EB, suggesting competition with EB. The combined work demonstrates the ability of pyridyl-dioxime chelates not only to lead to polynuclear 3d-metal complexes with impressive structural motifs and interesting magnetic properties but also to yield new, mononuclear 4d- and 5d-metal complexes with biological implications.