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531.
The O–H bond dissociation enthalpy (BDE) of 3,5-dimethylphenol has been determined, by using the EPR radical equilibration technique, as 362.5 ± 1.5 kJ/mol. This value is 7 kJ/mol smaller than that of phenol, this indicating that alkyl substitution of the meta hydrogens of phenol induces a weakening of the O–H bond, in contrast with what was reported in a recent calorimetric study. 相似文献
532.
Vicinelli V Ceroni P Maestri M Balzani V Gorka M Vögtle F 《Journal of the American Chemical Society》2002,124(22):6461-6468
We have investigated the complexation of the luminescent Nd(3+), Eu(3+), Gd(3+), Tb(3+), Er(3+), and Yb(3+) ions by a polylysin dendrimer containing 21 amide groups in the interior and, in the periphery, 24 chromophoric dansyl units which show an intense fluorescence band in the visible region. Most of the experiments were performed in 5:1 acetonitrile/dichloromethane solution at 298 K. On addition of the lanthanide ions to dendrimer solutions, the fluorescence of the dansyl units is quenched; in Nd(3+), Er(3+), and Yb(3+), a sensitized near-infrared emission of the lanthanide ion is observed. At low metal ion concentrations, each dendrimer hosts only one metal ion and when the hosted metal ion is Nd(3+) or Eu(3+), the fluorescence of all the 24 dansyl units of the dendrimer is quenched with unitary efficiency. Quantitative measurements were performed in a variety of experimental conditions, including protonation of the dansyl units and measurements in rigid matrix at 77 K where a sensitized Eu(3+) emission could also be observed. The results obtained have been interpreted on the basis of the energy levels and redox potentials of dendrimer and metal ions. 相似文献
533.
Saudan C Balzani V Gorka M Lee SK Maestri M Vicinelli V Vögtle F 《Journal of the American Chemical Society》2003,125(15):4424-4425
We have investigated the formation of metal complexes between Zn2+ and two derivatives, 1 and 2, of the well-known 1,4,8,11-tetraazacyclotetradecane (cyclam) ligand. Compound 1 is 1,4,8,11-tetrakis(naphthylmethyl) cyclam, and compound 2 is a dendrimer consisting of a cyclam core with appended 12 dimethoxybenzene and 16 naphthyl units. Compound 1 exhibits an emission band with a maximum around 480 nm, assigned to the formation of exciplexes between amine and excited naphthyl units. Dendrimer 2 exhibits three types of weak emission bands, assigned to naphthyl localized excited states (lambdamax = 337 nm), naphthyl excimers (lambdamax ca. 390 nm), and naphthyl-amine exciplexes (lambdamax = 480 nm). In CH3CN-CH2Cl2 1:1 v/v, titration of ligand 1 with Zn2+ causes the disappearance of the exciplex emission and the appearance of a strong naphthyl localized fluorescence; the titration plot is linear and reaches a plateau for a 1:1 stoichiometry, showing that a highly stable [Zn(1)]2+ complex is formed. In the case of 2, titration with Zn2+ causes the disappearance of the exciplex band, with a concomitant increase in the excimer and naphthyl localized emissions; the titration plot is again linear, but in this case it reaches a plateau for a 2:1 stoichiometric ratio, showing the unexpected formation of a [Zn(2)2]2+ complex. Such an unexpected stoichiometry for the complex of the dendritic ligand has been fully confirmed by 1H NMR titrations. The results obtained show that the dendrimer branches not only do not hinder, but in fact favor coordination of cyclam to Zn2+. 相似文献
534.
Lau BP Scott PM Lewis DA Kanhere SR Cléroux C Roscoe VA 《Journal of chromatography. A》2003,998(1-2):119-131
Alternariol (AOH) and alternariol monomethyl ether (AME) are among the main mycotoxins formed in apples and other fruits infected by Alternaria alternata. For determination of AOH and AME by LC, apple juice and other fruit beverages were cleaned up on C18 and aminopropyl solid-phase extraction columns. Positive and negative ion mass spectra of AOH and AME under electrospray (ESI) and atmospheric pressure chemical ionization (APCI) conditions were obtained. Collision-induced dissociation of the [M+H]+ and [M-H]- ions for both compounds were also studied. The phenolic anions of both compounds are more stable with less fragmentation. In quantitative analysis, negative ion detection also offers lower background and better sensitivity. Sensitive LC-MS and LC-MS-MS confirmatory procedures based on APCI with negative ion detection were applied to confirm the natural occurrence of AOH in nine samples of apple juice and in single samples of some other clear fruit beverages--grape juice, cranberry nectar, raspberry juice, red wine, and prune nectar (which also contained 1.4 ng AME/ml)--at levels of up to 6 ng AOH/ml. Electrospray LC-MS-MS with negative ion detection and in multiple reaction monitoring mode offers higher sensitivity and specificity. Absolute detection was better than 4 pg per injection for both compounds. 相似文献
535.
The defect-free gamma-V(2)O(5)(001) surface and ordered structures of oxygen vacancies have been studied for a wide range of defect concentrations, Theta ((1)/(6) monolayer (ML) < or = Theta < or = 1 ML), combining density functional theory and statistical thermodynamics. The gamma polymorph of V(2)O(5) is characterized by two structurally different vanadium sites, V(A) and V(B). The V(A) sites having a weaker bond to an adjacent crystal layer are easier to reduce. Up to (1)/(2) ML, the V(A) defect structures with defects aligned along the [010] direction are increasingly more stable as in alpha-V(2)O(5)(001). At higher defect concentrations, the different coordination of the V(B) vanadium atoms at the gamma-V(2)O(5) surface causes an increase in the vacancy formation energy of approximately 0.8 eV/atom at Theta = 1.0 compared to Theta = (1)/(2). For alpha-V(2)O(5), this increase amounts to 0.2 eV/atom only. Under conditions (low oxygen partial pressures and high temperatures) at which the alpha-V(2)O(5)(001) surface would be fully reduced, the gamma-V(2)O(5)(001) surface is only partially reduced. The presence of surface vanadyl oxygen groups at V(B) sites may change the surface reactivity compared to that of alpha-V(2)O(5)(001). 相似文献
536.
Bo Deng Gary H. Meisters Gaetano Zampieri 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1995,46(6):872-882
We consider Keller's functions, namely polynomial functionsf:C
n C
n with detf(x)=1 at allx C
n. Keller conjectured that they are all bijective and have polynomial inverses. The problem is still open.Without loss of generality assumef(0)=0 andf'(0)=I. We study the existence of certain mappingsh
, > 1, defined by power series in a ball with center at the origin, such thath(0)=I andh
(f(x))=h
(x). So eachh
conjugates f to its linear part I in a ball where it is injective.We conjecture that for Keller's functionsf of the homogeneous formf(x)=x +g(x),g(sx)=s
dg(x),g(x)n=0,xC
n,sC the conjugationh
for f is anentire function. 相似文献
537.
Let X be a complex analytic manifold,
a C
2 submanifold,
an openset with C
2 boundary
.Denote by
(resp.
) the microlocalization along M (resp.
) of the sheaf
of holomorphic functions.In the literature (cf. [A-G], [K-S 1,2])one encounters two classical results concerning the vanishing of the cohomology groups
.The most general gives the vanishing outside a range of indices j whose length is equal to
(with
being the number of respectively positive, negative and null eigenvalues for themicrolocal Levi form
).The sharpest result gives the concentration in a single degree, provided that the difference
is locally constant for
near p (with
for z the base point of p).The first result was restated for the complex
in [D'A-Z 2], in the case codim
We extend it here to any codimension and moreover we also restate for
the second vanishing theorem.We also point out that the principle of our proof, related to a criterion for constancy of sheaves due to [K-S 1], is a quite new one. 相似文献
538.
Reviews are listed in order of appearance in the sources indicated. In multidisciplinary review journals, only those reviews which fall within the scope of this Journal are included. Sources are listed alphabetically in three categories: regularly issued review journals and series volumes, contributed volumes, and other monographs. Titles are numbered serially, and these numbers are used for reference in the index. Major English-language sources of critical reviews are covered. Encyclopedic treatises, annual surveys such as Specialist Periodical Reports, and compilations of symposia proceedings are omitted. This installment of Recent Reviews covers principally the middle part of the 1996 literature. Previous installment: J. Org. Chem.1996, 61(14), 4860-8. These Recent Review articles are now also available in a database form on the ACS Organic Division WWW site http://www.organic.emory.edu/acsorg/index.html. 相似文献
539.
This paper concerns the asymptotic behavior of solutions and their gradients to linear and nonlinear elliptic equations with singular coefficients of fuchsian type. 相似文献
540.
Martin Baron Heather Abbott Dr. Oleksandr Bondarchuk Dr. Dario Stacchiola Dr. Alexander Uhl Dr. Shamil Shaikhutdinov Dr. Hans‐Joachim Freund Prof. Dr. Cristina Popa Dr. Maria Veronica Ganduglia‐Pirovano Dr. Joachim Sauer Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(43):8006-8009