- Orthogonal or simultaneous use of disulfide and hydrazone exchange in dynamic covalent chemistry in aqueous solution
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Hydrazone and disulfide exchange have been combined in a single system, but can be addressed independently: by adjusting the pH of the solution from acidic to mildly basic it is possible to switch from exclusively hydrazone exchange to exclusively disulfide exchange, while at intermediate pH both reactions occur simultaneously. The Royal Society of Chemistry.
- Rodriguez-Docampo, Zaida,Otto, Sijbren
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- Controlling the biological effects of spermine using a synthetic receptor
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Polyamines play an important role in biology, yet their exact function in many processes is poorly understood. Artificial host molecules capable of sequestering polyamines could be useful tools for studying their cellular function. However, designing synthetic receptors with affinities sufficient to compete with biological polyamine receptors remains a huge challenge. Binding affinities of synthetic hosts are typically separated by a gap of several orders of magnitude from those of biomolecules. We now report that a dynamic combinatorial selection approach can deliver a synthetic receptor that bridges this gap. The selected receptor binds spermine with a dissociation constant of 22 nM, sufficient to remove it from its natural host DNA and reverse some of the biological effects of spermine on the nucleic acid. In low concentrations, spermine induces the formation of left-handed DNA, but upon addition of our receptor, the DNA reverts back to its right-handed form. NMR studies and computer simulations suggest that the spermine complex has the form of a pseudo-rotaxane. The spermine receptor is a promising lead for the development of therapeutics or molecular probes for elucidating spermine's role in cell biology.
- Vial, Laurent,Ludlow, R. Frederick,Leclaire, Julien,Perez-Fernandez, Ruth,Otto, Sijbren
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- Photodeoxygenation of dibenzothiophene S-oxide derivatives in aqueous media
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The use of atomic oxygen (O(3P)) as potent oxidant In water has suffered from the lack of a facile, efficient source. The photodeoxygenatlon of aromatic sulfoxides to the corresponding sulfides in organic solvents has been suggested to produce O(3P) in low quantum yields. The photolysis of 4,6-dihydroxymethyldibenzothiophene S-oxide and 2,8- dihydroxymethyldibenzothiophene S-oxide in water results in deoxygenation at significantly higher quantum yields than In organic solvents. Depending upon conditions, a variable amount of oxidation of the hydroxymethyl substituent into an aldehyde was observed to accompany deoxygenation. Analysis of the photoproducts Indicated the deoxygenation occurred by at least two different pH-sensitive mechanisms. Under basic conditions, photoinduced electron transfer yielding a hydroxysulfuranyl radical that decomposed by heterolytlc S-O cleavage was thermodynamically feasible. The thermodynamics of photoinduced electron transfer were expected to become increasingly unfavorable as the pH of the solution decreased. Thus, at neutral and acidic pH, an S-O bond scission mechanism was suspected. The observed increase In the photodeoxygenation quantum yields was consistent with charge separation accompanying S-O bond scission. Oxidative cleavage of alkenes In aerobic conditions suggested O(3P) was produced during photolysis In these conditions; however, the formation of discrete O-/HO may occur, particularly at low pH.
- Korang, James,Grither, Whitney R.,McCulla, Ryan D.
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supporting information; experimental part
p. 4466 - 4476
(2010/06/13)
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- THE AQUEOUS PERIODATE OXIDATION OF AROMATIC AND ALIPHATIC CARBOXYLIC ACID DISULFIDES
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The water-soluble carboxylic acid-functionalized aromatic disulfides, 3,3'-dithiodibenzoic acid and 5,5'-dithiodiisophthalic acid (5,5'-dithiodi(1,3-benzenedicarboxylic acid)) were prepared and their rates of periodate oxidation to the sulfonic acids were determined.The reaction is first order in each of the reactants which indicates that the slow step is the initial oxidative cleavage step.These aromatic disulfides are oxidized to the sulfonic acids 4-8 times more slowly than a typical aliphatic disulfide.In all cases, water solubility of the disulfide is of prime importance.The periodate oxidation of two aliphatic carboxylic acid analogs were also examined, however, in these cases, the reactions were multiphasic and intermediate thiosulfinates were observed by 1H NMR along with the sulfonic acids.Key words: Periodate; disulfide; thiosulfonate; sulfonic acid, carboxylic acid, ABTS.
- Evans, Brian J.,Doi, Joyce Takahashi,Musker, W. Kenneth
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- Investigations on Benzothiirene
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Thermolysis and photolysis of 1,2,3-benzothiadiazole 10c furnish the products 11c - 15c. 13C-labelling experiments demonstrate that an intermediate benzothiirene 1c is not formed.Isotopomeric reaction products are due to H-shifts.Electron withdrawing ester groups in 6-position enable the ring closure to the substituted benzothiirenes 1d, e on the photochemical but not on the thermal route.A proof is given by an extensive study of the disulfides 14d, e, 14d', e', and 14d'', e'', generated in the thermolysis, photolysis and by an independent procedure.The results are based on 13C and 1H NMR measurements.Unequivocal signal correlations were made by deuterations and heteronuclear double resonances.
- Meier, Herbert,Konnerth, Ursula,Graw, Sylvia,Echter, Toni
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p. 107 - 126
(2007/10/02)
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