摘要:

AbstractThe complexation kinetics of the two macrocycles1and2with Co2+, Ni2+, Cu2+and Zn2+have been measured by pH‐stat techniques. The rates are first order in metal and ligand concentration and depend upon the pH. This results from the different reactivities of the various protonated species of the macrocyclic tetraamines. The resolved rate constants are given inTable 2.In comparison with other 14‐membered cyclic aliphatic tetraazasystems1and2react more slowly with metal ions. This might be a consequence of the more rigid structure induced by the pyridine r

ISSN:0018-019X    

DOI:10.1002/hlca.19780610702

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

AbstractThe 12‐16 membered tetraazamacrocycles1‐6were synthesized, their protonation constants and complexation kinetics measured at 25° and I = 0.50. The results ofTable 1Show that pK 3His strongly influenced by the ring size whereas pK 2Hand pK 1Hare relatively insensitive to it. This can be understood in terms of electrostatic interactions of the positive charges when located on adjacent amino groups.The kinetics of complex formation between the macrocyclic ligands and several transition metal ions have been studied by pH‐stat and stopped‐flow techniques and the results have been analyzed as bimolecular reactions between the metal ion and the different protonated species of the ligands. The rate constants, given inTable 2, show that the macrocycles react less rapidly than analogous open chain amines. However, for a given protonated species of the ligand the rate of complexation follows the order Cu2+>Zn2+>Co2+>Ni2+which parallels the sequence of their water exchange rates. For the diprotonated tetraamines LH 22reacting with Cu2+the slower rates seem to be mainly a consequence of electrostatic interactions, since a correlation between logk LH 2Cuand pK 3Hexists. For LH+, however, the complexation rates of a metal ion with the different macrocycles are all in one order of magnitude and do not depend in a regular way on the ring size or the basicity of the ligand. It is therefore suggested that in this case other factors such as unfavourable preequilibria must be c

ISSN:0018-019X    

DOI:10.1002/hlca.19780610703

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

AbstractMetal reduction of pyrene and of pyrene isomers under carefully controlled conditions yields the corresponding dianions. The properties of the neutral compounds and of the dianions are studied via1H‐NMR. spectroscopy. Whereas the former exhibit similar behaviour, the charge distribution within the dianionic species proves to be very different. As a consequence, some of the polycyclic dianions can be regarded essentially as (4n)π‐perimeters, an approach which is satisfactorily rationalized by simple MO‐models. Further evidence in favour of this bonding scheme comes from the ESR. spectroscopic measurement of the spin density distribution within the corresponding radical

ISSN:0018-019X    

DOI:10.1002/hlca.19780610704

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

AbstractInvestigation by gas liquid chromatography of a small but organoleptically typical subfraction ofOrientaltobacco condensate led to the identification of 47 compounds. Of these 21 have hitherto not been reported asOrientaltobacco constituents, and 14 appear to be novel to all tobacco types. The latter are (E)‐3‐methyl‐non‐2‐en‐4‐one (1), (E)‐1‐(2, 3, 6‐trimethylphenyl)‐but‐2‐en‐1‐one (3), pentadecan‐15‐olide (12), 8α, 13:9α, 13‐diepoxy‐15, 16‐dinorlabdane (17), (Z)‐octadec‐9‐en‐18‐olide (18), (E)‐2‐ethylidene‐6, 10, 14‐trimethylpentadecanal (21), the norlabdanoids9,10,11,14,15,16, tridecan‐2‐one, and 2‐phenylethyl isovalerate. The macrolides12and18represent the first musk compounds detected in tobacco. Identification were made by direct comparison (MS. and/or1H‐NM

ISSN:0018-019X    

DOI:10.1002/hlca.19780610705

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

Constituents ofOsmanthusAbsolute, 4th Communication.Megastigma‐5, 7 (E), 9‐triene‐4‐one and Megastigma‐5, 8 (E)‐diene‐4‐oneIn continuation of our communications on constituents ofOsmanthusabsolute, we now report on the occurrence of the two title compounds1and2ain this natural substrate (0.01‐0.02% each). Their structures were confirmed by synthesis starting from β‐iononeviathe common intermediate 4‐oxo‐β‐ionol (9). Some further minor components bearing corresponding structural features are tabulated in view of possible biogenetic pathways leading to1or2a, respectively.In order to clarify the olfactory behaviour, we also synthesized some analogous derivatives in the irone series, these substances be

ISSN:0018-019X    

DOI:10.1002/hlca.19780610706

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

AbstractThe unstrained 3‐chloroalcohols1a,2aand3ado not undergo solvolytic fragmentation in neutral and weakly acidic 80% ethanol, only substitution and elimination products being formed by the limitingSN1‐E1mechanisms. This also applies to the corresponding ethers1band3b. Addition of sodium hydroxide causes the observed rate constants for the 3‐chloroalcohols to rise steeply by factors of at least 103to 105. These level off at higher base concentrations due to an opposing ionic strength effect. Whereas3afragments quantitatively in the presence of base,1aand2afragment in competition with elimination to the Δ3‐olefins9aand10, respectively.2aalso yields 2% of the oxetane6b.These results support a concerted base‐induced fragmentation mechanism which competes with intramolecular base‐induced elimination (Ei) in the case of the acyclic chloroalcohols1aand2a. The formation of small amounts of the oxetane6bfrom2ais attributed to intramolecular nucleophilic substitution at the tertiary

ISSN:0018-019X    

DOI:10.1002/hlca.19780610707

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

AbstractSubstituted 2, 4, 5‐trithiahexanes1, a class of substances recently found in roasted meat, have been synthesizedviatwo different route

ISSN:0018-019X    

DOI:10.1002/hlca.19780610708

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

AbstractThe purpose of this investigation is to provide synthetic proof for the structure of dogfish (Squalus acanthias) α‐MSH and to investigate the consequences of the presence of methionine in position 13 and the lack of theN‐terminal acetyl group in this hormone. Because of the facile oxidation of methionine (13) during handling or storage, a number of specifically oxidized hormones (Met4and Met13) as well as tripeptides belonging to theC‐terminal second message sequence were investigated. All the products were prepared by classical methods in homogeneous solution; intermediate and end products were extensively purified and characterized (Tables 3 and 4). The assays for melanotropic activity were performedin vitrowith the modified reflectometric assay using the skin ofRana pipiens. It is concluded that the structures assigned to dogfish α‐MSH I and II are correct and that the isolated samples contain slight quantities of [13‐methionine (S‐oxide)]dogfish α‐MSH and [4, 13‐bis‐methionine (S‐oxide)]dogfish α‐MSH. The peptides with methionine in position 13 are as active in this assay as those containing valine. This also holds for the NH2/OH interchange distinguishing dogfish α‐MSH I from dogfish α‐MSH II. However, the lack of theN‐terminal acetyl group strongly reduces the biological activity. Its introduction into dogfish α‐MSH I results in a product that is equipotent with mammalian α‐MSH. These an

ISSN:0018-019X    

DOI:10.1002/hlca.19780610709

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

Clark‐like Hydrogen DetectorA quantitative hydrogen detector, similar to theClarkoxygen electrode, has been proposed byGreen et al.[1] in 1967. Such a detector gives a signal which is directly proportional to the hydrogen partial pressure without consuming any hydrogen itself. We have taken up the proposal ofGreen et al., and have realized a very sensitive and under many circumstances also a selective detector, which is easy to handle and which can be used in gaseous phase as well as in aqueous solution. Sensitivity of 0.1 Torr or even better can be achieved. The main differences to theClarkelectrode are that a platinized platinum electrode has to be used instead of a blank platinum electrode and that a more positive potential has to be applied. We give a detailed description of the construction and the handling of theClark‐like hydrogen detec

ISSN:0018-019X    

DOI:10.1002/hlca.19780610710

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

Chloroacylation and bromoacylation of carbonyl compounds IV. Investigations of the reaction mechanismThe kinetics of theLewisacid catalyzed reaction between acyl chlorides and carbonyl compounds (especially aldehydes) is investigated by1H‐NMR.‐spectroscopy. With acetyl chloride as starting material a second order reaction is observed; the rate of the reaction increases in polar solvents as well as with increasing electron‐donating capacity of the aldehyde. ‐ With benzoyl chloride as starting material the reaction is first order with respect to benzoyl chloride, but zero order with respect to the aldehyde. The reaction rate is strongly influenced by the substituents of the benzoyl chloride. ‐ Two polar reaction mechanisms which are in accord with these results are outlined and

ISSN:0018-019X    

DOI:10.1002/hlca.19780610711

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY