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1.
Rodríguez L Lima JC Pina F Cacciapaglia R Di Stefano S Ruggi A 《The journal of physical chemistry. A》2011,115(2):123-127
The photophysical properties of two atropisomeric naphthalenophanes (1 and 2) have been studied. Their structure only differs in the relative arrangement, syn (1) or anti (2), of the two aromatic units. The compounds emission is mainly excimeric and is strongly quenched in the presence of oxygen. Comparison of emission intensities obtained from steady state and from decay times provides clear evidence of the formation of ground state charge transfer complexes between oxygen and the naphthalenophanes 1 and 2. The calculated values for the association constants are on the order of 10(3) M(-1) (ethanol, room temperature) for both naphthalenophanes. 相似文献
2.
We have investigated the formation of gas-phase adducts of trimethylaluminum and trimethylgallium with ammonia using room-temperature Fourier transform infrared experiments and density functional theory calculations. Our results indicate for the first time that, at higher partial pressures, a product distinct from the well-known (CH3)3M:NH3 adduct grows in for both M = Al and M = Ga. Comparison of the experimental and calculated IR spectra, along with calculations of the energetics, indicates that this second product is the result of hydrogen bonding of a second NH3 molecule to the (CH3)3M:NH3 adduct and can be written as (CH3)3M:NH3...NH3. The binding energy of this hydrogen-bonded adduct is calculated to be 26.8 kcal/mol for M = Al and 18.4 kcal/mol for M = Ga and is lower in energy (more stable) relative to the 1:1 (CH3)3M:NH3 adduct by 7.2 kcal/mol for M = Al and 6.6 kcal/mol for M = Ga. In contrast, an alternative complex involving the formation of two separate M-N donor-acceptor bonds, which is written as H3N:(CH3)3M:NH3, is calculated to be lower in energy relative to (CH3)3M:NH3 by only 0.1 kcal/mol for M = Al and 0.2 kcal/mol for M = Ga and is not observed experimentally. These results show that hydrogen bonding plays an important role in the interaction of ammonia with metal organic precursors involving Al, Ga, and In, under typical metal organic chemical vapor deposition AlGaInN growth conditions. 相似文献
3.
[reaction: see text] Experimental evidence is reported for the reversible formation of the singlet diazenyl diradical ((1)DZ), photolytically generated from the structurally elaborate DBH-type azoalkane. Reversiblity of the (1)DZ formation manifests itself through the decrease of the photodenitrogenation quantum yield over a ca. 40-fold viscosity variation (from 0.5 to 19.3 cP). This viscosity behavior is interpreted in terms of frictional effects on the competitive reaction modes of the diazenyl diradical. 相似文献
4.
1-(Ferrocenyl)ethanol has been immobilized within polypyrrole films during their electrochemical deposition, or following their deposition, via its adduct with boron trifluoride. Dissociation of H+ from this adduct, formed in a solution of boron trifluoride diethyl ether (BFEE) in acetonitrile, produces an anion that can act as a counterion for oxidized polypyrrole. Its subsequent hydrolysis produces a polypyrrole film containing neutral 1-(ferrocenyl)ethanol which was found to be strongly retained. In addition to producing a novel type of polypyrrole–ferrocene composite, this work provides clear evidence to support the efficacy of this methodology for the incorporation of neutral species within conducting polymer films. 相似文献
5.
Simon Beuck Tobias Schwabe Stefan Grimme Nils Schlörer Matthias Kamber Wilhelm Schänzer Mario Thevis 《Journal of the American Society for Mass Spectrometry》2009,20(11):2034-2048
The study of the collision-induced dissociation behavior of various substituted isoquinoline-3-carboxamides, which are amongst
a group of drug candidates for the treatment of anemic disorders (e.g., FG-2216), allowed for the formulation of the general
mechanisms underlying the unusual fragmentation behavior of this class of compounds. Characterization was achieved with high-resolution/high
accuracy LTQ-Orbitrap tandem mass spectrometry of the protonated precursor ions. Presented data were substantiated by the
synthesis and analysis of proposed gas-phase intermediate structures and stable isotope labeled analogues, as well as by density
functional theory calculations. Exemplary, CID of protonated N-[(1-chloro-4-hydroxy-7-isopropoxy-isoquinolin-3-yl)carbonyl]glycine
gives rise to the isoquinoline-3-carboxy-methyleneamide product ion which nominally eliminates a fragment of 11 u. This was
attributed to the loss of methyleneamine (−29 u) and a concomitant spontaneous and reversible water addition (+18 u) to the
resulting acylium ion to yield the protonated isoquinoline-3-carboxylic acid. The same water addition pattern is observed
after loss of propylene (−42 u). A further nominal loss of 10 u is explained by the elimination of carbon monoxide (−28 u)
followed by another water adduct formation (+18 u) to yield the protonated 1-chloro-3,4,7-trihydroxy-isoquinoline. The source
of the multiple gas-phase water addition remained unclear. This atypical fragmentation pattern proved to be highly characteristic
for all studied and differentially substituted isoquinoline-3-carboxamides, and offers powerful analytical tools for the establishment
of a LC/MS(/MS) based screening procedure for model HIF-stabilizers and their potential metabolites in clinical, forensic
and sports drug testing. 相似文献
6.
Quantitative characterization of reversible macromolecular associations via sedimentation equilibrium: an introduction 总被引:1,自引:0,他引:1
Minton AP 《Experimental & molecular medicine》2000,32(1):1-5
The measurement and analysis of sedimentation equilibrium provides one of the most powerful and widely applicable methods for the characterization of reversible associations of macromolecules in solution. Recent developments in instrumentation, experimental design, and data analysis have substantially broadened the range of systems to which this technique may be applied, simplified its application, and reduced the cost of acquiring analytical capability. 相似文献
7.
The15N NMR chemical shifts for the analogous diamagnetic adduct of 3,5-dipropyl-4-ethylpyrazole with cadmium dibromide were measured to obtain reference data for estimating the isotropic paramagnetic NMR shifts of nitrogen in paramagnetic adducts of alkylpyrazoles with transition metal salts. The13C and1H NMR spectra were obtained for the same adduct in conditions of frozen protometallotropic rearrangement of the hydrogen in the NH group and the temperature-dependent NMR spectra of isotopes of Cd were made.A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, Moscow 117813. N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 756–761, June, 1998. 相似文献
8.
A metal-templated synthetic route to cyclic (aryl)(ylidic) mesoionic carbenes (CArY-MICs) featuring an endocyclic P-ylide is presented. This approach, which requires metal templates with two cis-positioned open coordination sites, is based on the controlled cyclisation of a P,P′-diisopropyl-substituted 2,2′-diphosphinotolane (1) and leads to chelate complexes coordinated by a phosphine donor and the CArY-MIC carbon atom. The C–P bond formation involved in the former partial cyclisation of 1 proceeds under mild conditions and was shown to be applicable all over the d-block. In the presence of a third fac-positioned open coordination site, the P–C bond formation was found to be reversible, as shown for a series of molybdenum complexes. DFT modelling studies are in line with an interpretation of the target compounds as CArY-MICs.A metal-templated synthesis of cyclic (aryl)(ylidic)mesoionic carbene complexes (CArY-MICs) is presented. In the case of molybdenum carbonyls, the crucial P–C bond formation, which occurs during CArY-MIC formation, was found to be reversible. 相似文献
9.
In the present study, we have modelled the nucleophilic attack of water and a hydroxyl anion on the carbonyl carbon of a succinimide derivative leading to aspartate and aspartic acid. Calculations have been carried out at the B3LYP/6-31 +G* level in a vacuum. The IEF-PCM methodology has been used to carry out single point calculations in solution. In neutral medium, hydrolysis is facilitated by the presence of a polar continuum, whereas in basic medium the polar environment hinders the hydrolysis of succinimide. The deltaH degrees and deltaS degrees values for the cyclization reactions of aspartic acid yielding succinimide are 29.2 kJ mol(-1) and 133.5 kJ mol(-1) K(-1) respectively in accordance with the experimental results on the isomerization of the Ac-Asp-Gly-NHMe dipeptide unit. In a neutral medium, the isoaspartate: aspartate is found to be 2.2:1 in a vacuum and 3.4:1 in solution, in line with the experimental findings based on the hydrolysis of a tetrapeptide (Ac-Gly-Asn-Gly-Gly-NHMe) and a hexapeptide (Val-Tyr-Pro-Asn-Gly-Ala) where this ratio was found to be 3.1:1. 相似文献
10.
Abdul R. Asif Michael Oellerich Victor W. Amstrong Uwe Gross Utz Reichard 《Electrophoresis》2010,31(12):1947-1958
Invasive aspergillosis caused by the mould Aspergillus fumigatus is a life‐threatening lung or systemic infection in the immunocompromised host. In this study, a protective immune response against the disease was achieved in two infected rabbits, and the cellular fungal antigenic proteome that mediated such a response was investigated against the background of vaccine development efforts. Altogether, 59 different Aspergillus proteins were found becoming reactive in the course of the developing immunity, many of which are described in this context for the first time. These included proteins related to oxidative stress management, glycolysis and other metabolic pathways. As oxidative stress is suspected to be one of the major defense mechanisms, the results may indicate at least in part a continuous response of the pathogen to evade the host's immune system. In addition, proteins with suspected cell surface association or crucial function for fungal cell development were identified. As these antigens are newly recognized during the process of the developing immunoprotection, they may not only represent valuable infection markers but also importantly broaden the list of possible vaccine candidates. 相似文献
11.
12.
Xu F Armstrong JD Zhou GX Simmons B Hughes D Ge Z Grabowski EJ 《Journal of the American Chemical Society》2004,126(40):13002-13009
A practical, one-pot process for the preparation of beta-keto amides via a three-component reaction, including Meldrum's acid, an amine, and a carboxylic acid, has been developed. Key to development of an efficient, high-yielding process was an in-depth understanding of the mechanism of the multistep process. Kinetic studies were carried out via online IR monitoring and subsequent principal component analysis which provided a means of profiling the concentration of both the anionic and free acid forms of the Meldrum's adduct 6 in real time. These studies, both in the presence and absence of nucleophiles, strongly suggest that formation of beta-keto amides from acyl Meldrum's acids occurs via alpha-oxoketene species 2 and rule out other possible reaction pathways proposed in the literature, such as via protonated alpha-oxoketene intermediates 3 or nucleophilic addition-elimination pathways. 相似文献
13.
Described is an efficient synthesis of the complex bioactive natural product, elisapterosin B, a potent in vitro inhibitor of Mycobacterium tuberculosis H37Rb. The synthesis elisapterosin B, prepared in its enantiomeric form, proceeds by a highly stereocontrolled sequence commencing with a simple glutamic acid derived compound. Pivotal steps in the sequence include (a) a pinacol-type ketal rearrangement to transfer chirality, (b) an IMDA reaction of an E,Z-diene to construct the elisabethin skeleton, and (c) a biosynthesis-inspired oxidative cyclization of the elisabethin precursor to elisapterosin B. 相似文献
14.
15.
Experimental evidence for the formation of HXeCCH: the first hydrocarbon with an inserted rare-gas atom 总被引:1,自引:0,他引:1
Feldman VI Sukhov FF Orlov AY Tyulpina IV 《Journal of the American Chemical Society》2003,125(16):4698-4699
Combined FTIR and EPR studies of acetylene irradiated with fast electrons in a solid xenon matrix provide experimental evidence for the formation of HXeCCH, a novel-type organic molecule with an inserted rare-gas atom. The new species resulting from the reaction of H atoms with CCH radicals in xenon was characterized by an intense IR absorption at 1486.0 cm(-1) corresponding to Xe-H stretching. 相似文献
16.
Reaction of tetraphenylcyclopentadienone with cyclic olefins: an NMR probe of adduct stereochemistry
The Diels Alder adducts of tetraphenylcyclopentadienone with cyclohexene and norbornene are reported. The effect of cyclic olefin adduct stereochemistry on the multiplicity pattern in the aromatic region of the proton spectrum is discussed as a probe to adduct stereochemistry with this diene system. 相似文献
17.
The kinetics and mechanisms of the reaction of cysteine with cysteine thiosulfinate ester in aqueous solution have been studied by stopped-flow spectrophotometry between pH 6 and 14. Two reaction pathways were observed for pH > 12: (1) an essentially pH-independent nucleophilic attack of cysteinate on cysteine thiosulfinate ester, and (2) a pH-dependent fast equilibrium protonation of cysteine sulfenate that is followed by rate-limiting comproportionation of cysteine sulfenic acid with cysteinate to give cystine. For 6 < pH < 12, the rate-determining reaction between cysteinate and cysteine thiosulfinate ester becomes pH-dependent due to the protonation of their amine groups. Hydrolysis of cysteine thiosulfinate ester does not play a role in the aforementioned mechanisms because the rate-determining nucleophilic attack by hydroxide is relatively slow. 相似文献
18.
19.
Albert A. Tuinman Kelsey D. Cook 《Journal of the American Society for Mass Spectrometry》1992,3(4):318-325
Fast atom bombardment promotes condensation between trimethyl tetradecyl ammonium cations and the glycerol matrix. Bond formation at both the head and tail of the surfactant is demonstrated by low energy collision-induced dissociation (ClD) of deuterium-labeled precursors, with a preponderance of the reaction apparently occurring at the tail. Two distinct ClD pathways are identified for each kind of adduct (head- and tail-attack). Evidence is presented for the detection of distonic radical cations of the surfactant, complexed (solvated) with glycerol. 相似文献
20.
Jean-Jacques Vasseur Bernard Rayner Jean-Louis Imbach 《Journal of heterocyclic chemistry》1988,25(2):389-392
We have elucidated the exact mechanism of apurinic oligodeoxynucleotide d(Tp[AP]pT) cleavage by phenylhydrazine and shown that the final isolated product is in fact a 3-substituted derivative of 1-phenyl-pyrazole. 相似文献