Search results for "Organic Chemicals"
showing 10 items of 728 documents
A facile cleavage of allyl ethers on solid phase
2000
Abstract A simple and efficient protocol for the cleavage of allyl ethers on solid phase using a palladium(0)-catalyzed allyl transfer reaction is reported.
Coordination-Induced Spin-State Switching with Nickel Chlorin and Nickel Isobacteriochlorin
2015
We present the first coordination-induced spin-state switching with nickel chlorin and nickel isobacteriochlorin. The spin-state switching was monitored by UV-vis spectroscopy and NMR titration experiments. The association constants (K1 and K2) and thermodynamic parameters (ΔH and ΔS) of the coordination of pyridine were determined. The first X-ray analyses of a paramagnetic nickel chlorin and a nickel isobacteriochlorin provide further information about the structure of the octahedral complexes. Nickel chlorin and even more pronounced nickel isobacteriochlorin exhibit stronger coordination of axial ligands compared to the corresponding nickel porphyrin and thus provide the basis for more e…
Study by static SIMS, XPS and UPS of the adsorption of cyanogen on (100) Ni surfaces
2000
Abstract The interaction of cyanogen with (100) Ni surfaces at room temperature was studied using secondary ion mass spectrometry in a static mode, and photoemission spectroscopies (XPS and UPS). It has been shown that cyanogen is adsorbed on this nickel surface in a dissociative mode: atomic carbon and nitrogen are present on the surface as well as CN fragments. These adsorbed species have been characterized by XPS and UPS. Increasing the temperature in the 400 K range increases the rate of the dissociation reaction of CN into atomic carbon and nitrogen. Moreover carbon is found to dissolved into the bulk for temperatures as low as 475 K. No evidence has been found of a polymerized form of…
Trace Analysis of Plutonium and Technetium by Resonance Ionization Mass Spectrometry Using an Atomic Beam and a Laser Ion Source
1990
A method for low level detection of plutonium and technetium is described with a detection limit of less than 107 atoms. Plutonium is a very toxic element due to its radioactive decay as well as its chemical behaviour. It was released to the environment in large amounts during the fifties and sixties of his century, principally by nuclear-weapon tests and some accidents. As a result about 0.4 − 4 mBq per gram 239Pu(T1/2 = 24390 y), corresponding to 4 × 108 − 4 × 109 atoms, can be found in the Northern Hemisphere in soil samples.
closo-borane conjugated regulatory peptides retain high biological affinity: synthesis of closo-borane conjugated Tyr(3)-octreotate derivatives for B…
2008
Despite the improvements in cancer therapy during the past years, high-grade gliomas and many other types of cancer are still extremely resistant to current forms of therapy. Boron neutron capture therapy (BNCT) provides a promising way to destroy cancer cells without damaging healthy tissue. However, BNCT in practice is still limited due to the lack of boron-containing compounds that selectively deliver boron to cancer cells. Since many neuroendocrine tumors show an overexpression of the somatostatin receptor, it was our aim to synthesize compounds that contain a large number of boron atoms and still show high affinity toward this transmembrane receptor. The synthetic peptide Tyr (3)-octre…
Prediction of properties of chiral compounds by molecular topology
1998
Abstract A common assumption in chemistry is that chiral behavior is associated with 3-D geometry. However, chiral information is related to symmetry, which allows the topological handling of chiral atoms by weighted graphs and the calculation of new descriptors that give a weight to the corresponding entry in the main diagonal of the topological matrix. In this study, it is demonstrated that, operating in this way, chiral topological indices are obtained that can differentiate the pharmacological activity between pairs of enantiomers. The 50% inhibitory concentration (IC50) values of the D2 dopamine receptor and the σ receptor for a group of 3-hydroxy phenyl piperidines are specifically pr…
Nano-sized I12L6 Molecular Capsules Based on the [N⋅⋅⋅I+⋅⋅⋅N] Halogen Bond
2017
Summary Self-assembly of pre-organized subunits with a concave overall shape is an effective strategy for the synthesis of supramolecular capsules. We report the synthesis of a cavitand-based hexameric capsule held together solely by 12 robust [N⋅⋅⋅I + ⋅⋅⋅N] halogen bonds and its characterization in solution and in the gas phase via 1 H NMR spectroscopy, diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY), and electrospray ionization mass spectrometry. The [N⋅⋅⋅I + ⋅⋅⋅N] halogen-bonded hexameric capsule was efficiently synthesized from the isolobal metallosupramolecular Ag + capsule by application of the [N⋅⋅⋅Ag + ⋅⋅⋅N] → [N⋅⋅⋅I + ⋅⋅⋅N] cation-exchange reaction.
Receptor-mediated uptake of boron-rich neuropeptide y analogues for boron neutron capture therapy.
2014
Peptidic ligands selectively targeting distinct G protein-coupled receptors that are highly expressed in tumor tissue represent a promising approach in drug delivery. Receptor-preferring analogues of neuropeptide Y (NPY) bind and activate the human Y1 receptor subtype (hY1 receptor), which is found in 90% of breast cancer tissue and in all breast-cancer-derived metastases. Herein, novel highly boron-loaded Y1 -receptor-preferring peptide analogues are described as smart shuttle systems for carbaboranes as (10) B-containing moieties. Various positions in the peptide were screened for their susceptibility to carbaborane modification, and the most promising positions were chosen to create a mu…
Ni(II) and Pd(II) complexes of camphor-derived diazadiene ligands: steric bulk tuning and ethylene polymerization
1998
Abstract Nickel(II) and palladium(II) centers were coordinated to a series of chiral 1,4-diazadiene ligands. The ligand backbones are camphor derivatives and the imine nitrogens are attached to independently varied 2- and 2,6-substituted aryl groups. Upon activation with methyl-aluminoxane, the dibromo nickel complexes polymerize ethylene and 1-hexene. The polymerization properties are dependent on the steric features of the aryl substituents on the imine nitrogens.
Electronic and Steric Effects: How Do They Work in Ionic Liquids? The Case of Benzoic Acid Dissociation
2010
The need to have a measure of the strength of some substituted benzoic acids in ionic liquid solution led us to use the protonation equilibrium of sodium p-nitrophenolate as a probe reaction, which was studied by means of spectrophotometric titration at 298 K. In order to evaluate the importance of electronic effect of the substituents present on the aromatic ring, both electron-withdrawing and -donor substituents were taken into account. Furthermore, to have a measure of the importance of the steric effect of the substituents both para- and ortho-substituted benzoic acids were analyzed. The probe reaction was studied in two ionic liquids differing for the ability of the cation to give hydr…