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21.
22.
Senthil Kumar Karuppannan Alejandro Martín-Rodríguez Eliseo Ruiz Phimphaka Harding David J. Harding Xiaojiang Yu Anton Tadich Bruce Cowie Dongchen Qi Christian A. Nijhuis 《Chemical science》2021,12(7):2381
Herein, we report the first room temperature switchable Fe(iii) molecular spin crossover (SCO) tunnel junction. The junction is constructed from [FeIII(qsal-I)2]NTf2 (qsal-I = 4-iodo-2-[(8-quinolylimino)methyl]phenolate) molecules self-assembled on graphene surfaces with conductance switching of one order of magnitude associated with the high and low spin states of the SCO complex. Normalized conductance analysis of the current–voltage characteristics as a function of temperature reveals that charge transport across the SCO molecule is dominated by coherent tunnelling. Temperature-dependent X-ray absorption spectroscopy and density functional theory confirm the SCO complex retains its SCO functionality on the surface implying that van der Waals molecule—electrode interfaces provide a good trade-off between junction stability while retaining SCO switching capability. These results provide new insights and may aid in the design of other types of molecular devices based on SCO compounds.Herein, we report the first room temperature switchable Fe(iii) molecular spin crossover (SCO) tunnel junction. 相似文献
23.
Dr. Aaron R. Finney Dr. Sébastien Lectez Dr. Colin L. Freeman Prof. John H. Harding Dr. Stephen Stackhouse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(37):8725-8740
A better understanding of the solution chemistry of the lanthanide (Ln) salts in water would have wide ranging implications in materials processing, waste management, element tracing, medicine and many more fields. This is particularly true for minerals processing, given governmental concerns about lanthanide security of supply and the drive to identify environmentally sustainable processing routes. Despite much effort, even in simple systems, the mechanisms and thermodynamics of LnIII association with small anions remain unclear. In the present study, molecular dynamics (MD), using a newly developed force field, provide new insights into LnCl3(aq) solutions. The force field accurately reproduces the structure and dynamics of Nd3+, Gd3+ and Er3+ in water when compared to calculations using density functional theory (DFT). Adaptive-bias MD simulations show that the mechanisms for ion pairing change from dissociative to associative exchange depending upon cation size. Thermodynamics of association reveal that whereas ion pairing is favourable, the equilibrium distribution of species at low concentration is dominated by weakly bound solvent-shared and solvent-separated ion pairs, rather than contact ion pairs, reconciling a number of contrasting observations of LnIII–Cl association in the literature. In addition, we show that the thermodynamic stabilities of a range of inner sphere and outer sphere coordination complexes are comparable and that the kinetics of anion binding to cations may control solution speciation distributions beyond ion pairs. The techniques adopted in this work provide a framework with which to investigate more complex solution chemistries of cations in water. 相似文献
24.
I. H. Harding 《Colloid and polymer science》1985,263(1):58-66
Amphoteric polystyrene latex colloids were prepared by the emulsifier-free emulsion polymerization of styrene. Two co-monomers, methacrylic acid (MA) (anionic) and dimethyl aminoethyl methacrylate (DMAM) (cationic) were used to promote the amphoteric nature of the resultant surfaces. Parameters such as particle size and the isoelectric point (IEP) were measured as a function of polymerization recipe. Particle size decreased with increasing initiator concentration according to the equation: log [d
w]=–0.67 log [I] + 0.316 whered
w is the weight average particle diameter andI is the concentration of initiator (potassium persulphate).The particle size also decreased with increasing temperature, increasing pH and addition of surfactant. Particle size was unaffected by the methacrylic acid content. The isoelectric point pH was decreased on decreasing initiator concentration and on increasing methacrylic acid content.The polymerization pathway was deduced to involve the cationic DMAM during the initiation phase and to involve the anionic MA as well as styrene, during the growth stage. A full polymerization pathway involving the formation of oligomeric DMAM micelles was postulated. 相似文献
25.
Prof. Dr. David J. Harding Darunee Sertphon Prof. Dr. Phimphaka Harding Prof. Dr. Keith S. Murray Dr. Boujemaa Moubaraki Prof. Dr. John D. Cashion Harry Adams 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):1082-1090
A new synthesis of (8‐quinolyl)‐5‐methoxysalicylaldimine (Hqsal‐5‐OMe) is reported and its crystal structure is presented. Two FeIII complexes, [Fe(qsal‐5‐OMe)2]Cl ? solvent (solvent=2 MeOH ? 0.5 H2O ( 1 ) and MeCN ? H2O ( 2 )) have been prepared and their structural, electronic and magnetic properties studied. [Fe(qsal‐5‐OMe)2] Cl ? 2 MeOH ? 0.5 H2O ( 1 ) exhibits rare crystallographically independent high‐spin and low‐spin FeIII centres at 150 K, whereas [Fe(qsal‐5‐OMe)2]Cl ? MeCN ? H2O ( 2 ) is low spin at 100 K. In both structures there are extensive π–π and C? H???π interactions. SQUID magnetometry of 2 reveals an unusual abrupt stepped‐spin crossover with T1/2=245 K and 275 K for steps 1 and 2, respectively, with a slight hysteresis of 5 K in the first step and a plateau of 15 K between the steps. In contrast, 1 is found to undergo an abrupt half‐spin crossover also with a hysteresis of 10 K. The two compounds are the first FeIII complexes of a substituted qsal ligand to exhibit abrupt spin crossover. These conclusions are supported by 57Fe Mössbauer spectroscopy. Both complexes exhibit reversible reduction to FeII at ?0.18 V and irreversible oxidation of the coordinated qsal‐5‐OMe ligand at +1.10 V. 相似文献
26.
[reaction: see text] Glucuronyl iodide 1 has been studied in detail as a "disarmed" glycosyl donor. In a model reaction, using N-iodosuccinimide (NIS) as a promoter and 2-phenylethanol as acceptor, best results were obtained using NIS with I(2), followed by trimethylsilyltrifluoromethanesulfonate (TMSOTf). When a series of primary and secondary alcohols was glycosylated using these conditions, yields of 60-83% of beta-glucuronides were obtained. Various "nonheavy" metal salts also effectively catalyzed the model reaction but led to significant amounts of alpha-product with less reactive secondary alcohols. 相似文献
27.
Margaret M. Harding Ulrich Koert Jean-Marie Lehn Annie Marquis-Rigault Claude Piguet Jay Siegel 《Helvetica chimica acta》1991,74(3):594-610
A general strategy for the synthesis of oligobipyridine ligands 2 – 5 containing from two to five 2,2′-bipyridine subunits, for helical metal complexes is described (sec Scheme). Both the unsubstituted parent strands ( a series) as well as their derivatives bearing fester or amide functions in the 4,4′-positions of the bipyridine moieties ( b – d series) have been obtained. 相似文献
28.
29.
Harding LP Jeffery JC Riis-Johannessen T Rice CR Zeng Z 《Dalton transactions (Cambridge, England : 2003)》2004,(16):2396-2397
The amide-substituted unsymmetrical ligand L(1) upon coordination to Co(2+) forms the dinuclear triple helicate [Co(2)(L(1))(3)](4+) which exists as both possible C(1) and C(3) symmetric geometric isomers in solution, however, upon addition of nitrate ions, the formation of an anion binding cavity is favoured and hence the sole product is the C(3) symmetric isomer in which all three amide substituents are hydrogen bonded to the nitrate anion. 相似文献
30.
Harding K 《Cryo letters》2004,25(1):3-22
Cryopreservation techniques exist for some 100-plant species. Cryopreservation for the long-term conservation of in vitro germplasm results in the exposure of tissues to physical, chemical and physiological stresses causing cryoinjury. Although, the effects of cryoinjury upon the genome are often unknown, any accumulative DNA polymorphisms may not be induced by cryopreservation per se but are the result of the whole culture-cryoprotection-regeneration process. It is desirable to assess the genetic integrity of plants surviving cryogenic storage to determine if they are true to type after cryopreservation. This can be done at the phenotypic, histological, cytological, biochemical and molecular levels. The relevance of these approaches to stability investigations is discussed with their limitations. This review provides a definition for Cryobionomics - a novel term describing the re-modelled concept of genetic stability and the re-introduction of cryopreserved plants into the environment. 相似文献