Search results for "substitution"

Studies on the mechanism of PMN activation. I. By dextran sulfates.

1982

Evidence is presented that enhanced reduction of the dye nitroblue-tetrazolium (NBT) by polymorphonuclear leukocytes (PMN) which are stimulated by dextran sulfates (DS) is not exclusively due to the phagocytosis of particles formed by NBT and DS. Not only the size of phagocytizable particles but the degree of substitution determines the acceleration of NBT-reduction. A likely cause of this acceleration is the triggering of the alternative pathway of the complement activation.

Studies of the synthesis of heterocyclic compounds. Part VII. The preparation of some new 3- and 5-amino-pyrazoles by endocyclicN-substitution of 3(5…

1982

By reaction of some 4-carbethoxy(or cyano)-3(5)-R-5(3)-aminopyrazoles 1 with 2-nitrobenzoyl chloride or 2-nitrobenzenesulfonyl chloride, a number of novel 3- and 5-amino-1-(2-nitrobenzoyl or 2-nitrobenzene-sulfonyl)pyrazoles 6 and 7 were obtained. Every compound appearing during the endocyclic N-substitution process can be identified and determined by glc. The use of nmr offers a rapid, unambigous method for determining the proposed structures.

Book Review: Electrophilic Aromatic Substitution. By R. Taylor

1991

Donor-acceptor substituted polyenes : orientation in mono- and multilayers

1992

Large molecules containing different chemical units whose interactions within the molecule result in new macroscopically observable effects, have become increasingly important.The organization of molecules of this type in ordered structures leads to functional molecular materials.Their use in molecular electronics requires that the units exhibit specific electronic properties. Recently, we reported on the intramolecular energy transfer through terminally substituted conjugated polyenes. An intramolecular electron transfer within donor-acceptor substituted polyenes can be achieved by introducing suitable terminal groups.

Organometallic nucleophiles. Mechanism of halide displacement at saturated carbon by 2-pyridyl and 4-Pyridyl complexes [M(dmtc)(C5H4N-Cn)(L)] (M  Pd…

1992

Abstract A mechanistic study is reported of nucleophilic halide substitution by pyridyl complexes [M(dmtc)C 5 H 4 N- C 2 )(L)] (M  Pd or Pt; L  PMe 3 , PEt 3 or PPh 3 ) and [Pd(dmtc)C 5 H 4 N- C 4 )(L)] (L  PMe 3 or PPh 3 ) on organic halides XCH 2 R (X  Cl or Br; R  CHCH 2 , COMe, Ph, or CN) in various solvents, yielding the pyridylium derivatives [M(dmtc)1-CH 2 R)C 5 H 4 N- C 2 (L)] + and [Pd(dmtc)(1-CH 2 R)(C 5 H 4 N- C 4 (L)] + , respectively. The kinetics obey a second-order rate law: rate  k 2 [XCH 2 R][Complex]. A similar rate law is observed for the analogous reactions involving 4-dimethyl-aminopyridine (4-dmapy) as the nucleophile. The effects of solvent and leaving group, a…

High Yield SNAr on 8-Halogenophenyl-BODIPY with Cyclic and Acyclic Polyamines

2014

Selective nucleophilic aromatic substitutions with several polyamines were performed in very good yields on halogeno-phenyl BODIPY derivatives containing an activating nitro group.

Oligo(phenylenvinylene) mit terminaler Donor-Acceptor-Substitution

2002

Determination of relative chlorophyll binding affinities in the major light-harvesting chlorophyll a/b complex.

2002

The major light-harvesting complex (LHCIIb) of photosystem II can be reconstituted in vitro from its recombinant apoprotein in the presence of a mixture of carotenoids and chlorophylls a and b. By varying the chlorophyll a/b ratio in the reconstitution mixture, the relative amounts of chlorophyll a and chlorophyll b bound to LHCIIb can be changed. We have analyzed the chlorophyll stoichiometry in recombinant wild type and mutant LHCIIb reconstituted at different chlorophyll a/b ratios in order to assess relative affinities of the chlorophyll-binding sites. This approach reveals five sites that exclusively bind chlorophyll b. Another site exhibits a slight preference of chlorophyll b over ch…

Exchange of Pigment-Binding Amino Acids in Light-Harvesting Chlorophyll a/b Protein

1999

Four amino acids in the major light-harvesting chlorophyll (Chl) a/b complex (LHCII) that are thought to coordinate Chl molecules have been exchanged with amino acids that presumably cannot bind Chl. Amino acids H68, Q131, Q197, and H212 are positioned in helixes B, C, A, and D, respectively, and, according to the LHCII crystal structure [Kühlbrandt, W., et al. (1994) Nature 367, 614-621], coordinate the Chl molecules named a(5), b(6), a(3), and b(3). Moreover, a double mutant was analyzed carrying exchanges at positions E65 and H68, presumably affecting Chls a(4) and a(5). All mutant proteins could be reconstituted in vitro with pigments, although the thermal stability of the resulting mut…

The Folding State of the Lumenal Loop Determines the Thermal Stability of Light-Harvesting Chlorophyll a/b Protein

2004

The major light-harvesting protein of photosystem II (LHCIIb) is the most abundant chlorophyll-binding protein in the thylakoid membrane. It contains three membrane-spanning alpha helices; the first and third one closely interact with each other to form a super helix, and all three helices bind most of the pigment cofactors. The protein loop domains connecting the alpha helices also play an important role in stabilizing the LHCIIb structure. Single amino acid exchanges in either loop were found to be sufficient to significantly destabilize the complex assembled in vitro [Heinemann, B., and Paulsen, H. (1999) Biochemistry 38, 14088-14093. Mick, V., Eggert, K., Heinemann, B., Geister, S., and…