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991.
Carçabal P Jockusch RA Hünig I Snoek LC Kroemer RT Davis BG Gamblin DP Compagnon I Oomens J Simons JP 《Journal of the American Chemical Society》2005,127(32):11414-11425
The conformation of phenyl-substituted monosaccharides (mannose, galactose, and glucose) and their singly hydrated complexes has been investigated in the gas phase by means of a combination of mass selected, conformer specific ultraviolet and infrared double resonance hole burning spectroscopy experiments, and ab initio quantum chemistry calculations. In each case, the water molecule inserts into the carbohydrate at a position where it can replace a weak intramolecular interaction by two stronger intermolecular hydrogen bonds. The insertion can produce significant changes in the conformational preferences of the carbohydrates, and there is a clear preference for structures where cooperative effects enhance the stability of the monosaccharide conformers to which the water molecule chooses to bind. The conclusions drawn from the study of monosaccharide-water complexes are extended to the disaccharide lactose and discussed in the light of the underlying mechanisms that may be involved in the binding of carbohydrate assemblies to proteins and the involvement, or not, of key structural water molecules. 相似文献
992.
Ni2(PO2NH)4 · 8 H2O is isotypic with M2(PO2NH)4 · 8 H2O (M = Mg, Mn, Co, Zn) and crystallizes in the space group P21/c, Z = 2, with a = 641.25(1), b = 1041.42(1), c = 1278.18(2) pm and β = 104.243(1)°. The structure is composed of Ni2+ and (PO2NH)44? ions as well as crystal water molecules. The P4N4 rings of the (PO2NH)44? ions exhibit a slightly distorted chair–2 conformation, which has been described by torsion angles, displacement asymmetry parameters and puckering parameters. The tetrametaphosphimate anions are connected forming layers. These layers are linked solely by hydrogen bonds, forming a three‐dimensional network. 相似文献
993.
Anthony Fratiello Vicki Kubo-Anderson Rebecca Lee Marquis Patrick Richard Perrigan Tanya Porras Shantanu Sharma Stephanie Stoll 《Journal of solution chemistry》2002,31(9):681-702
An 1H, 13C, and 15N NMR study has been completed for the complexes of La(III), Tm(III), and Yb(III) with nitrate and isothiocyanate in aqueous solvent mixtures. Signals for four complexes are observed for both the Tm3+–NO3
– and Yb3+–NO3
– solutions, with the species identified as the mono-, di-, tetra-, and either the penta - or hexanitrato. These results are consistent with those determined for the nitrate complexes of the Ce(III)–Eu(III) metal ions. The chemical shifts for the Tm(III) and Yb(III) nitrate complexes indicate a pseudocontact binding mechanism prevails. The complexes of diamagnetic La(III) with NO3
– produce three signals in the 15NO3
– spectra, with assignments paralleling those observed with the paramagnetic lanthanides. Three complexes are formed in the La3+–NCS– solutions, with signals assigned to the mono-, di-, and triisothiocyanato species. 相似文献
994.
Dr. Pushpak Mizar Rebecca Niebuhr Matthew Hutchings Prof. Dr. Umar Farooq Prof. Dr. Thomas Wirth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(5):1614-1617
An efficient thioamination of alkenes mediated by iodine(III) reagents is described. The use of different sulfur nucleophiles allows the flexible synthesis of 1,2‐aminothiols from alkenes. By employing chiral iodine(III) reagents, a stereoselective version of the thioamination protocol has also been developed. 相似文献
995.
996.
997.
A synthetic strategy to prepare peptide-polymer conjugates with precise sites of attachment is described. Amino acids modified with atom transfer radical polymerization (ATRP) initiators for the polymerization of styrenes and methacrylates were prepared. Fmoc-4-(1-chloroethyl)-phenylalanine (5) was synthesized in four steps from Fmoc-tyrosine. HATU-mediated amidation with glycine-OMe resulted in dipeptide (6). The initiator was effective for Cu(I)/bipyridine mediated bulk polymerization of styrene. Kinetic studies indicated a controlled polymerization, with high conversion (97%), and a polydispersity index (PDI) of 1.25. Fmoc-O-(2-bromoisobutyryl)-serine tert-butyl ester (10) was synthesized from Fmoc-Ser(OTrt)-OH in three steps. This initiator was employed in the ATRP of 2-hydroxyethyl methacrylate (HEMA), and kinetic studies indicated a controlled polymerization. Different monomer to initiator ratios resulted in poly(HEMA) of different molecular weights and narrow PDIs (1.14-1.25). Conversions were between 70 and 99%. HEMA modified with N-acetyl-D-glucosamine (GlcNAc) was also polymerized to 84% conversion and the resulting PDI was 1.19. The t-butyl ester protecting group of 10 was removed, and the resulting amino acid (11) was incorporated into VM(11)VVQTK by standard solid-phase peptide synthesis. Polymerization resulted in the glycopolymer-peptide conjugate in 93% conversion and a PDI of 1.14. 相似文献
998.
Rose MJ Fry NL Marlow R Hinck L Mascharak PK 《Journal of the American Chemical Society》2008,130(27):8834-8846
Three nitrosyl-dye conjugates, namely, [(Me 2bpb)Ru(NO)(Resf)] ( 1-Resf), [(Me 2bQb)Ru(NO)(Resf)] ( 2-Resf), and [((OMe) 2bQb)Ru(NO)(Resf)] ( 3-Resf) have been synthesized via direct replacement of the chloride ligand of the parent {Ru-NO} (6) nitrosyls of the type [(R 2byb)Ru(NO)(L)] with the anionic tricyclic dye resorufin (Resf). The structures of 1-Resf- 3-Resf have been determined by X-ray crystallography. The dye is coordinated to the ruthenium centers of these conjugates via the phenolato-O atom and is trans to NO. Systematic red shift of the d pi(Ru) --> pi*(NO) transition of the parent nitrosyls [(R 2byb)Ru(NO)(L)] due to changes in R and y in the equatorial tetradentate ligand R 2byb (2-) results in its eventual merge with the intense absorption band of the dye around 500 nm in 3-Resf. Unlike the UV-sensitive parent [(R 2byb)Ru(NO)(L)] nitrosyls, these dye-sensitized nitrosyls rapidly release NO when exposed to visible light (lambda >/= 465 nm). Comparison of the photochemical parameters reveals that direct coordination of the light-harvesting chromophore to the ruthenium center in the present nitrosyls results in a significantly greater extent of sensitization to visible light compared to nitrosyls with appended chromophore (linked via alkyl chains). 1-Resf has been employed as a "trackable" NO donor to promote NO-induced apoptosis in MDA-MB-231 human breast cancer cells under the control of light. The results of this work demonstrate that (a) the d pi(Ru) --> pi*(NO) transition (photoband) of {Ru-NO} (6) nitrosyls can be tuned into visible range via careful alteration of the ligand frame(s) and (b) such nitrosyls can be significantly sensitized to visible light by directly ligating a light-harvesting chromophore to the ruthenium center. The potential of these photosensitive nitrosyl-dye conjugates as (i) biological tools to study the effects of NO in cellular environments and (ii) "trackable" NO donors in photodynamic therapy of malignancies (such as skin cancer) has been discussed. 相似文献
999.
Dr. Ayan Dasgupta Yara van Ingen Michael G. Guerzoni Dr. Kaveh Farshadfar Prof. Jeremy M. Rawson Dr. Emma Richards Prof. Alireza Ariafard Prof. Rebecca L. Melen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(45):e202201422
An efficient and mild reaction protocol for the decarbonylation of isocyanates has been developed using catalytic amounts of Lewis acidic boranes. The electronic nature (electron withdrawing, electron neutral, and electron donating) and the position of the substituents (ortho/meta/para) bound to isocyanate controls the chain length and composition of the products formed in the reaction. Detailed DFT studies were undertaken to account for the formation of the mono/di-carboxamidation products and benzoxazolone compounds. 相似文献
1000.
Gies AP Ellison ST Vergne MJ Orndorff RL Hercules DM 《Analytical and bioanalytical chemistry》2008,392(4):627-642
MALDI-TOF/TOF CID experiments are reported for hydroxylated poly(α-methylstyrene) precursor ions (PAMS: m/z 1,445.9 (n = 10), 2,036.3 (n = 15), 2,626.7 (n = 20), 3,217.1 (n = 25), and 3,807.5 (n = 30), where the number of repeat units n corresponds to the oligomer mass numbers). The influences of structure, molecular weight, and kinetic energy on degradation
mechanisms were examined to test the generality of our multi-chain fragmentation model developed for polystyrene. Our results
indicate that poly(α-methylstyrene) free radicals are formed initially through multiple chain breaks and subsequently undergo
a variety of depolymerization reactions to yield predominantly monomer and dimer species; the intensity of each species depends
on the effective kinetic energy selected for the CID process. Each depolymerization mechanism is presented in detail with
experimental and computational data to justify/rationalize the process and its kinetic energy dependence. These processes
show the complex interrelationships between the various pathways along with preferred production of tertiary radicals, which
suppresses the appearance of primary radicals. Additionally, Py-GC/MS experimental data are presented to allow a comparison
of the multimolecular free radical reactions in pyrolysis with the unimolecular fragmentation reactions of MS/MS.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献