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991.
A microemulsion of decane droplets stabilized by a nonionic surfactant film is progressively charged by substitution of a nonionic surfactant molecule by a cationic surfactant. We check that the microemulsion droplets remain identical within the explored range of volume fraction (0.02-0.18) and of the number of charges per droplet (0-40). We probe the dynamics of these microemulsions by dynamic light scattering. Despite the similar structures of the uncharged and charged microemulsions, the dynamics are very different. In the neutral microemulsion, the fluctuations of polarization relax, as is well-known, via the collective diffusion of the droplets. In the charged microemulsions, two modes of relaxation are observed. The fast one is ascribed classically to the collective diffusion of the charged droplets coupled to the diffusion of the counterions. The slow one has, to our knowledge, not been observed previously neither in similar microemulsions nor in charged spherical colloids. We show that the slow mode is also diffusive and suggest that its possible origin is the relaxation of local charge fluctuations via the local exchange of droplets bearing different numbers of charges. The diffusion coefficient associated with this mode is then the self-diffusion coefficient of the droplets. 相似文献
992.
Dr. Matthew Tredwell Dr. Sean M. Preshlock Nicholas J. Taylor Dr. Stefan Gruber Dr. Mickael Huiban Dr. Jan Passchier Dr. Joël Mercier Dr. Christophe Génicot Prof. Véronique Gouverneur 《Angewandte Chemie (International ed. in English)》2014,53(30):7751-7755
Molecules labeled with fluorine‐18 are used as radiotracers for positron emission tomography. An important challenge is the labeling of arenes not amenable to aromatic nucleophilic substitution (SNAr) with [18F]F?. In the ideal case, the 18F fluorination of these substrates would be performed through reaction of [18F]KF with shelf‐stable readily available precursors using a broadly applicable method suitable for automation. Herein, we describe the realization of these requirements with the production of 18F arenes from pinacol‐derived aryl boronic esters (arylBPin) upon treatment with [18F]KF/K222 and [Cu(OTf)2(py)4] (OTf=trifluoromethanesulfonate, py=pyridine). This method tolerates electron‐poor and electron‐rich arenes and various functional groups, and allows access to 6‐[18F]fluoro‐L ‐DOPA, 6‐[18F]fluoro‐m‐tyrosine, and the translocator protein (TSPO) PET ligand [18F]DAA1106. 相似文献
993.
Marie-JosPhe Brienne Jacqueline Gabard Martine Leclercq Jean-Marie Lehn Michel Chev 《Helvetica chimica acta》1997,80(3):856-875
The chiral biyclic bis-lactams of structures 3 and 4 were synthesized from the key intermediate 2′b , the N,N′-bis(4-methoxybenzyl) derivative of 2 (X = MeO) (Scheme 6). The synthesis of this intermediate involved two key steps: (1) a double condensation of glyoxylic acid/anisamide (= oxoacetic acid/4-methoxybenzamide) adduct 11c with veratrole (1,2-dimethoxybenzene; 10 ) allowed the introduction of two glycine units at the 4,5-positions of the veratrole ring to give 18c (Schemes 3 and 4); (2) in order to circumvent the hydrolysis of 4-methoxybenzoyl protective groups which proved to be unfeasible, these groups were transformed into 4-methoxybenzyl groups through a sequence involving thiocarbonylation followed by reduction (Scheme 5). Thereafter, the double intramolecular cyclization of the resulting diamino diester 22c proceeded easily to afford 2′b. This intermediate may be transformed via the tetrol 2′g or the diol 2′h into the N-protected derivatives of 2 (X = OR) and of 3 (X = OCOR). Cleavage of the 4-alkuxybenzyl groups was achieved by ceric ammonium nitrate. However, when the aromatic ring bore ether functions (N-protected 2 ), this normal reaction was accompanied by the oxidative ring cleavage to give the diene-diester structure 4 (Schemes 5 and 6). 相似文献
994.
Edink E Rucktooa P Retra K Akdemir A Nahar T Zuiderveld O van Elk R Janssen E van Nierop P van Muijlwijk-Koezen J Smit AB Sixma TK Leurs R de Esch IJ 《Journal of the American Chemical Society》2011,133(14):5363-5371
Optimization of fragment hits toward high-affinity lead compounds is a crucial aspect of fragment-based drug discovery (FBDD). In the current study, we have successfully optimized a fragment by growing into a ligand-inducible subpocket of the binding site of acetylcholine-binding protein (AChBP). This protein is a soluble homologue of the ligand binding domain (LBD) of Cys-loop receptors. The fragment optimization was monitored with X-ray structures of ligand complexes and systematic thermodynamic analyses using surface plasmon resonance (SPR) biosensor analysis and isothermal titration calorimetry (ITC). Using site-directed mutagenesis and AChBP from different species, we find that specific changes in thermodynamic binding profiles, are indicative of interactions with the ligand-inducible subpocket of AChBP. This study illustrates that thermodynamic analysis provides valuable information on ligand binding modes and is complementary to affinity data when guiding rational structure- and fragment-based discovery approaches. 相似文献
995.
Jacqueline Loris-Teghem 《Queueing Systems》1988,3(1):41-52
This paper deals with a queueing system with finite capacity in which the server passes from the active state to the inactive state each time a service terminates withv customers left in the system. During the active (inactive) phases, the arrival process is Poisson with parameter (0). Denoting byu
n
the duration of thenth inactive phase and byx
n
the number of customers present at the end of thenth inactive phase, we assume that the bivariate random vectors {(v
n
,x
n
),n 1} are i.i.d. withx
n
v+l a.s. The stationary queue length distributions immediately after a departure and at an arbitrary instant are related to the corresponding distributions in the classical model. 相似文献
996.
Kawulka K Sprules T McKay RT Mercier P Diaper CM Zuber P Vederas JC 《Journal of the American Chemical Society》2003,125(16):4726-4727
The complete primary and three-dimensional solution structures of subtilosin A (1), a bacteriocin from Bacillus subtilis, were determined by multidimensional NMR studies on peptide produced using isotopically labeled [(13)C,(15)N]medium derived from Anabaena sp. grown on sodium [(13)C]bicarbonate and [(15)N]nitrate. Additional samples of 1 were also generated by separate incorporations of [U-(13)C,(15)N]phenylalanine and [U-(13)C,(15)N]threonine using otherwise unlabeled media. The results demonstrate that in addition to having a cyclized peptide backbone (N and C termini), three cross-links are formed between the sulfurs of Cys13, Cys7, and Cys4 and the alpha-positions of Phe22, Thr28, and Phe31, respectively. Such posttranslational linkage of a thiol to the alpha-carbon of an amino acid residue is very unusual in natural peptides or proteins. Subtilosin A (1) belongs to a new class of bacteriocins. 相似文献
997.
This paper describes a purely electronic mechanism by which ≈ 20 eV excitations in condensed phases relax to lower energy states. The mechanism utilizes an “energy fission” process whereby an ionic or excitonic state splits into two lower energy states, at least one being localized. The mechanism explains not only the known rapidity of such processes but also suggests an explanation for the proportionation of the chemistry between ionic and electronically excited states. 相似文献
998.
Ruth Naigre Thomas Chenal Isabelle Ciprs Philippe KalckJean-Claude Daran Jacqueline Vaissermann 《Journal of organometallic chemistry》1994,480(1-2):91-102
A palladium precursor and SnCl2 as cocatalyst were used under 4 MPa of carbon monoxide for the catalytic alkoxycarbonylation of several monoterpenes into C11 esters. The active catalyst involves a palladium-hydride species whose formation was investigated. In the case of the model substrate 3-phenylpropene, the source of the hydrido ligand was determined to be the alkene itself. Allylic hydrogen abstraction seems to be a general way to produce the active hydridopalladium species since monoterpenes having labile allylic hydrogens were converted under exceptional mild conditions. An X-ray crystal structure analysis was carried out on [(Ph3PCH2CH =MPh)4(PdCl6)(SnCl6)]. kw]Palladium; X-ray structure; Terpenes; Carbonylation; Hydroesterification 相似文献
999.
Marvaud V Decroix C Scuiller A Guyard-Duhayon C Vaissermann J Gonnet F Verdaguer M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(8):1677-1691
Following a bottom-up approach to nanomaterials, we present a rational synthetic route from hexacyanometalates [M(CN)(6)](3-) (M=Cr(III), Co(III)) cores to well-defined heptanuclear complexes. By changing the nature of the metallic cations and using a localised orbital model it is possible to control and to tune the ground state spin value. Thus, with M=Cr(III), d(3), S=3/2, three heptanuclear species were built and characterised by mass spectrometry in solution, by single-crystal X-ray diffraction and by powder magnetic susceptibility measurements, [Cr(III)(CNbondM'L(n))(6)](9+) (M'=Cu(II), Ni(II), Mn(II), L(n)=polydentate ligand), showing spin ground states S(G)=9/2 [Cu(II)], with ferromagnetic interactions J(Cr,Cu)=+45 cm(-1), S(G)=15/2 [Ni(II)] and J(Cr,Ni)=+17.3 cm(-1), S(G)=27/2 [Mn(II)], with an antiferromagnetic interaction J(Cr,Mn)=-9 cm(-1), (interaction Hamiltonian H=-J(Cr,M) [S(Cr)Sigma(i)S(M)(i)], i=1-6). With M=Co(III), d(6), S=0, the heptanuclear analogues [Co(III)(CN-M'L(n))(6)](9+) (M'=Cu(II), Ni(II), Mn(II)) were similarly synthesised and studied. They present a singlet ground state and allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'. 相似文献
1000.
Collin J Daran JC Schulz E Trifonov A 《Chemical communications (Cambridge, England)》2003,(24):3048-3049
The complexes (Li(THF)4)(Ln[(R)-C20H12N2(C10H22)]2) (Ln = Sm, Yb) have been synthesized, fully characterized and found to be efficient and enantioselective catalysts for intramolecular hydroamination of 1-(aminomethyl)-1-allylcyclohexane. 相似文献