Helvetica Chimica Acta

Journal: Helvetica Chimica Acta

Abbreviation

Helv. Chim. Acta

Publisher

Wiley‐VHCA

ISSN

0018-019X
1522-2675

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Publications1 - 10 of 340

Grafting of Group-10 Organometallic Complexes on Silicas: Differences and Similarities, Surprises and Rationale
Gioffrè, Domenico; Rochlitz, Lukas; Payard, Pierre-Adrien; et al. (2022)
Helvetica Chimica Acta
Surface organometallic chemistry (SOMC) represents a unique synthetic platform for the preparation of model heterogeneous catalysts resembling those broadly applied in industry. SOMC techniques usually rely on the grafting of tailored molecular precursors onto the surface OH groups of oxide supports. The development of such precursors and the understanding of their reactivity with the supports are therefore crucial for the development of well-defined surface species. While a large number of organometallic precursors of early transition metals are known, only few examples of group-10 metal complexes are reported, in spite of the great interest for heterogeneous catalysts based on the Pt-group elements. Herein, we report the reactivity of a family of group-10 (Ni, Pd and Pt) alkyl complexes, towards partially dehydroxylated SiO2 yielding well-defined supported species. We studied the effect of the metal, ligand, and support on the grafting mechanism of such precursors through a combined experimental and computational approach. Ultimately, we showed that at least two grafting pathways are possible for these compounds, namely the protonolysis of the M-alkyl bond by surface OH groups and the opening of strained siloxane bridges: the proportion of the two depending on the nature of the metal and its ancillary ligand.
Novel Cs-Symmetric 1,4-Diphosphine Ligands in the Copolymerization of Propene and Carbon Monoxide: High Regio- and Stereocontrol in the Catalytic Performance
Leone, Antonella; Consiglio, Giambattista (2005)
Helvetica Chimica Acta
New Cs-symmetric aryl 1,4-diphosphine ligands were synthesized and tested in the copolymerization of carbon monoxide and propene. The electronic properties of the two different P-atoms did not affect the high enantioselectivity of the catalyst precursors, thus resulting in high ‘regio’- and ‘stereoregular’ copolymers.
On the Use of a Supramolecular Coarse-Grained Model for the Solvent in Simulations of the Folding Equilibrium of an Octa-beta-peptide in MeOH and H2O
Huang, Wei; Hansen, Niels; van Gunsteren, Wilfred F. (2014)
Helvetica Chimica Acta
Oligosaccharide Analogues of Polysaccharides. Part 26
Kadiyala, M.V.S.N.; Xie, Tong; Bernet, Bruno; et al. (2006)
Helvetica Chimica Acta
The anthraquinone derivatives T‐x‐x (x = 2, 4, and 8), possessing two cellobiosyl, cellotetraosyl, and cellooctaosyl chains, respectively, C‐glycosidically bonded at C(1) and C(8) were synthesised as potential mimics of cellulose I. The anthraquinone template enforces a parallel orientation of the cellodextrin chains at a distance corresponding to the one between the crystallographically independent chains of cellulose I, and the ethynyl and buta‐1,3‐diynyl linker units ensure an appropriate phase shift between them. The H‐bonding of the T‐x‐x mimics was analysed and compared to the one of the mono‐chained analogues T‐x and of the known cellulose II mimics N‐x‐x and N‐x where one or two cellodextrin chains are O‐glycosidically bonded to naphthalene‐1,8‐diethanol, or to naphthalene‐1‐ethanol. The OH signals of T‐x and T‐x‐x in solution in (D₆)DMSO were assigned on the basis of DQFCOSY, HSQC, and TOCSY (only of T‐4, T‐4‐4, and T‐8‐8) spectra and on a comparison with the spectra of N‐x and N‐x‐x. Hydrogen bonding was analysed on the basis of the chemical shift of OH groups and its temperature dependence, coupling constants, SIMPLE ¹H‐NMR experiments, and ROESY spectra. T‐4‐4 and T‐8‐8 in (D₆)DMSO appear to adopt a V‐shape arrangement of the cellosyl chains, avoiding inter‐chain H‐bond interactions. The well‐resolved solid‐state CP/MAS ¹³C‐NMR spectra of the mono‐chained T‐x (x = 1, 2, 4, and 8) show that only T‐8 is a close mimic of cellulose II. While the solid‐state CP/MAS ¹³C‐NMR spectrum of the C₁‐symmetric diglucoside T‐1‐1 is well‐resolved, the spectra of T‐2‐2 and T‐4‐4 show broad signals, and that of T‐8‐8 is rather well resolved. The spectrum of T‐8‐8 resembles that of cellulose Iβ. A comparison of the X‐ray powder‐diffraction spectra of T‐8‐8 and T‐8 with those of celluloses confirms that T‐8‐8 is a H‐bond mimic of cellulose I and T‐8 one of cellulose II.Surprisingly, there is little difference between the CP/MAS ¹³C‐NMR spectra of the acetyl protected mono‐chained C‐glycosylated anthraquinone derivatives A‐x and the double‐chained A‐x‐x (x = 2, 4, and 8). The spectra of A‐4 and A‐4‐4 resemble strongly the one of cellulose triacetate I (CTA I). The (less well‐resolved) spectra of the cellooctaosides A‐8 and A‐8‐8, however, resemble the one of CTA II. The similarity between the solid‐state CP/MAS ¹³C‐NMR spectra of A‐4 and A‐4‐4 to the one of CTA I, and of A‐8 and A‐8‐8 to the one of CTA II is opposite to the observations in the acetylated cellodextrin series.The mono‐chained A‐x cellulose triacetate mimics 21 (A‐2), 32 (A‐4), and 55 (A‐8) were synthesised by Sonogashira coupling of the cellooligosyl‐ethynes 15, 28, and 50, followed by selective deacetylation. Complete deacetylation provided the corresponding T‐x mimics. The double‐chained A‐x‐x mimics 24 (A‐2‐2), 35 (A‐4‐4), and 58 (A‐8‐8) were prepared from A‐x by triflation and Sonogashira coupling with the cellosyl‐buta‐1,3‐diynes 19, 31, and 53. Their deacetylation provided the corresponding T‐x‐x mimics 25, 36, and 59. The cellooligosyl‐ethynes and cellooligosyl‐buta‐1,3‐diynes required for the Sonogashira coupling were prepared by stepwise glycosylation of the partially O‐benzylated β‐cellobiosyl‐ethyne and β‐cellobiosyl‐buta‐1,3‐diyne 13 and 17, respectively, with the cellobiosyl donor 2 and the cellohexaosyl donor 47.
Paneth, IUPAC, and the naming of elements
Koppenol, Willem H. (2005)
Helvetica Chimica Acta
Tautomerism in 5,8-Diaza-7,9-dicarbaguanine (‘Alloguanine’)
Wagner, Trixie; Han, Bo; Koch, Guido; et al. (2005)
Helvetica Chimica Acta
An X‐ray structure analysis of the title compound reveals that this purinoid exists in the crystal as two tautomers which interact with each other in the mode of a reverse‐Watson–Crick base pair.
Hydrogen as a Bio-orthogonal Trigger for Spatiotemporally Controlled Caged Prodrug Activation
Herzog, Antoine F.; Schneider, Elia M.; Stark, Wendelin J. (2018)
Helvetica Chimica Acta
The use of a p‐nitrobenzyloxycarbonyl (pNZ) protecting group on the FDA‐approved lung cancer drug gemcitabine affords a caged drug with very low in vitro toxicity in a human model cell line (A549). To activate this type of caged potent drug, simultaneous presence of two items is needed: platinum nanoparticles and hydrogen‐containing gas mixtures. This combination may later allow a more precise and controlled local delivery of highly potent cytostatic compounds, and may eventually permit reduction of the severe side effects of such chemotherapy treatments. Hydrogen, though an unusual medical agent, is well tolerated, and here used mixtures are derived from diving (deep diving gas). Pt nanoparticles at here used concentrations may eventually be locally deposited into the lungs through minimal invasive inhalation. We demonstrate the use of hydrogen as an on/off uncaging switch and show repeated use of the Pt nanoparticles for a series of uncaging events.
What Changes in Topochemistry when Going from Small Molecule Dimerizations to Polymerizations in Single Crystals?
Salzillo, Tommaso; Brillante, Aldo; Weber, Thomas; et al. (2023)
Helvetica Chimica Acta
This publication promotes the increased necessity for strain management in topochemical reactions with an enlarged structural extension of the molecular products formed, i. e., when going from small molecule dimerizations, through linear polymerizations to the formation of 2D polymers. Further, it promotes to combine the trap model for photon absorption with concrete molecular scale consequences of this absorption on topochemical transformations and briefly discusses the expected consequences topological dimensionality of the forming (macro)molecular products has on trap location. The time appears ripe for going in this direction because local information concerning structural changes within single crystals is now accessible by the 3D-delta PDF method. This method greatly facilitates the analysis of diffuse X-ray scattering providing access to concrete values of pair distribution functions and, thus, factual information on which and how distances change near a reaction site. Although only based on a first case where distance changes could be quantified in a lateral polymerization, the thoughts put forward may ignite more research towards a full understanding of all the action that occurs when a photochemically triggered topochemical reaction takes place. The 3D-delta PDF method is so attractive for this purpose because it provides otherwise inaccessible local information in pair correlation functions rather than average structure information, which is used through the ubiquitous Bragg scattering.
Syntheses and CD-spectroscopic investigations of longer-chain beta-peptides
Arvidsson, Per I.; Frackenpohl, Jens; Seebach, Dieter (2003)
Helvetica Chimica Acta
Ab initio emulsion polymerization by RAFT (reversible addition-fragmentation chain transfer) through the addition of cyclodextrins
Apostolovic, Bojana; Quattrini, Francesca; Butte, Alessandro; et al. (2006)
Helvetica Chimica Acta

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