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1.
The synthesis and crystal structure (100 K) of the title compound, [Fe(C10H11BrN3OS)2]NO3·H2O, is reported. The asymmetric unit consists of an octahedral [FeIII(HL)2]+ cation, where HL? is H-5-Br-thsa-Et or 5-bromosalicylaldehyde 4-ethylthiosemicarbazonate(1?) {systematic name: 4-bromo-2-[(4-ethylthiosemicarbazidoidene)methyl]phenolate}, a nitrate anion and a noncoordinated water molecule. Each HL? ligand binds via the thione S, the imine N and the phenolate O atom, resulting in an FeIIIS2N2O2 chromophore. The ligands are orientated in two perpendicular planes, with the O and S atoms in cis and the N atoms in trans positions. This [Fe(HL)2](anion)·H2O compound contains the first known cationic FeIII entity containing two salicylaldehyde thiosemicarbazone derivatives. The FeIII ion is in the high-spin state at 100 K. In addition, a comparative IR spectroscopic study of the free ligand and the ferric complex is presented, demonstrating that such an analysis provides a quick identification of the degree of deprotonation and the coordination mode of the ligand in this class of metal compounds. The variable-temperature magnetic susceptibility measurements (5–320 K) are consistent with the presence of a high-spin FeIII ion with a zero-field splitting D = 0.439 (1) cm?1.  相似文献   
2.
The 3D shape of glycosyl oxocarbenium ions determines their stability and reactivity and the stereochemical course of SN1 reactions taking place on these reactive intermediates is dictated by the conformation of these species. The nature and configuration of functional groups on the carbohydrate ring affect the stability of glycosyl oxocarbenium ions and control the overall shape of the cations. We herein map the stereoelectronic substituent effects of the C2-azide, C2-fluoride and C4-carboxylic acid ester on the stability and reactivity of the complete suite of diastereoisomeric furanoses by using a combined computational and experimental approach. Surprisingly, all furanosyl donors studied react in a highly stereoselective manner to provide the 1,2-cis products, except for the reactions in the xylose series. The 1,2-cis selectivity for the ribo-, arabino- and lyxo-configured furanosides can be traced back to the lowest-energy 3E or E3 conformers of the intermediate oxocarbenium ions. The lack of selectivity for the xylosyl donors is related to the occurrence of oxocarbenium ions adopting other conformations.  相似文献   
3.

We consider load balancing in service systems with affinity relations between jobs and servers. Specifically, an arriving job can be assigned to a fast, primary server from a particular selection associated with this job or to a secondary server to be processed at a slower rate. Such job–server affinity relations can model network topologies based on geographical proximity, or data locality in cloud scenarios. We introduce load balancing schemes that assign jobs to primary servers if available, and otherwise to secondary servers. A novel coupling construction is developed to obtain stability conditions and performance bounds. We also conduct a fluid limit analysis for symmetric model instances, which reveals a delicate interplay between the model parameters and load balancing performance.

  相似文献   
4.
Six new hexanuclear niobium cluster compounds of the general formula [Nb6Cl14L4] · x(solvent molecule) [L = neutral O or N donor ligand, x = 0–2.5; pyrimidine ( 1 ), 1‐methyl imidazole ( 2 ), isobutyronitrile ( 3 ), isopropyl alcohol ( 4 ), triphenylphosphine oxide ( 5 ), dimethyl sulfoxide ( 6 )] were prepared. The syntheses were carried out by dehydration of the precursor [Nb6Cl14(H2O)4] · 4H2O with different water scavangers, like acetic anhydride, trimethyl acetic anhydride and diethylcarbonate in the presence of the corresponding neutral ligand. The structures are determined by single‐crystal X‐ray diffraction. The specific bonding situations of the ligands to the [Nb6Cl12]2+ cluster cores are compared and discussed. The phenomenon of the observed M6 distortion is explained and interpreted based on the matrix effect and the terminal ligand effect. In addition, other interactions between the cluster units, such as hydrogen bonding and π–π stacking are discussed.  相似文献   
5.
Ligands with reactive carbon sites in the periphery of a metal center have emerged as a powerful approach for metal–ligand bond activation. These reactive carbon sites are commonly generated by deprotonation strategies. Carbon–silicon bond cleavage is a potential alternative to access such constructs. Herein, the monodesilylation of bis-silyl-substituted P,N scaffold PNSi2 in the coordination sphere of [RhI(Cl)(CO)( PNSi2 )] ( 1 ) with sodium azide is disclosed. This affords a unique dinucleating anionic κ2-C,N1-P ligand with a carbanionic methine carbon atom directly bound to rhodium as part of a four-membered Rh-N-C-C rhodacycle. This dimer undergoes meta-pyridine C−H activation facilitated by weak bases, which leads to a desymmetrization of the system and provides a σ,π-bridging 3-pyridyl fragment bound to RhI. The facile Si−C cleavage strategy may pave the way to studying the reactivity and functionalization of a variety of κ2-C,N-coordinated pyridine scaffolds for selective transformations.  相似文献   
6.
Herein, we present an approach that integrates molecular logic functions using surface-confined metallo-organic assemblies. These assemblies are electrochromic and mimic the behaviour of logic elements. The logic elements are addressed individually by electrochemical methods, and their outputs are simultaneously read-out optically by UV/Vis absorption spectroscopy. The versatility of our setup is demonstrated by the integration of two multi-component assemblies; each acting as ternary logic elements. We used also a laminated cell configuration to demonstrate color-to-color and color-to-transparent transitions. This concept offers a route for the future development of devices with multiple logic states.  相似文献   
7.
A comprehensive understanding of the structure, self-assembly mechanism, and dynamics of one-dimensional supramolecular polymers in water is essential for their application as biomaterials. Although a plethora of techniques are available to study the first two properties, there is a paucity in possibilities to study dynamic exchange of monomers between supramolecular polymers in solution. We recently introduced hydrogen/deuterium exchange mass spectrometry (HDX-MS) to characterize the dynamic nature of synthetic supramolecular polymers with only a minimal perturbation of the chemical structure. To further expand the application of this powerful technique some essential experimental aspects have been reaffirmed and the technique has been applied to a diverse library of assemblies. HDX-MS is widely applicable if there are exchangeable hydrogen atoms protected from direct contact with the solvent and if the monomer concentration is sufficiently high to ensure the presence of supramolecular polymers during dilution. In addition, we demonstrate that the kinetic behavior as probed by HDX-MS is influenced by the internal order within the supramolecular polymers and by the self-assembly mechanism.  相似文献   
8.
Designs, Codes and Cryptography - The paper introduces a method for constructing 2-resolvable t-designs for $$t=3,4$$ . The main idea is based on the assumption that there exists a partition of a...  相似文献   
9.
Molecular Diversity - In a pilot study, eleven pyrrolopyridine and pyrrolopyrimidine derivatives (specifically, 7-azaindole and 7-deazapurine derivatives) were synthesised by Suzuki cross-coupling...  相似文献   
10.
Stimuli-responsive soft materials enable controlled release of loaded drug molecules and biomolecules. Controlled release of potent chemotherapeutic or immunotherapeutic agents is crucial to reduce unwanted side effects. In an effort to develop controlled release strategies that can be triggered by using Cerenkov luminescence, we have developed polymer hydrogels that can release bovine serum albumin and immunoglobulin G by using light (254 nm–375 nm) as a trigger. We describe the synthesis and photochemical characterization of two light sensitive phenacyl bis-azide crosslinkers that are used to prepare transparent self-supporting hydrogel patches. One crosslinker was designed to optimize the overlap with the Cerenkov luminescence emission window, bearing an π-extended phenacyl core, resulting in a high quantum yield (14 %) of photocleavage when irradiated with 375 nm light. We used the extended phenacyl crosslinker for the preparation of protein-loaded dextran hydrogel patches, which showed efficient and selective dosed release of bovine serum albumin or immunoglobulin G after irradiation with 375 nm light. Cerenkov-triggered release is as yet inconclusive due to unexpected side-reactivity. Based on the high quantum yield, efficient release and large overlap with the Cerenkov window, we envision application of these photosensitive soft materials in radiation targeted drug release.  相似文献   
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