The π → π* transitions of more than 100 organic dyes from the major classes of chromophores (quinones, diazo, ...) have been investigated using a Time-Dependent Density Functional Theory (TD-DFT) procedure relying on large atomic basis sets and the systematic modeling of solvent effects. These calculations have been performed with pure (PBE) as well as conventional (PBE0) and long-range (LR) corrected hybrid functionals (LC-PBE, LC-ωPBE, and CAM-B3LYP). The computed wavelengths are systematically guided by the percentage of exact exchange included at intermediate interelectronic distance, i.e., the λmax value always follows the PBE > PBE0 > CAM-B3LYP > LC-PBE > LC-ωPBE > HF sequence. The functional giving the best estimates of the experimental transition energies may vary, but PBE0 and CAM-B3LYP tend to outperform all other approaches. The latter functional is shown to be especially adequate to treat molecules with delocalized excited states. The mean absolute error provided by PBE0 is 22 nm (0.14 eV) wit...

TD-DFT Performance for the Visible Absorption Spectra of Organic Dyes: Conventional versus Long-Range Hybrids

Aryl sulfonyl chlorides (e.g. Ts-Cl) are beloved of organic chemists as the most commonly used S(VI) electrophiles, and the parent sulfuryl chloride, O2 S(VI) Cl2 , has also been relied on to create sulfates and sulfamides. However, the desired halide substitution event is often defeated by destruction of the sulfur electrophile because the S(VI) Cl bond is exceedingly sensitive to reductive collapse yielding S(IV) species and Cl(-) . Fortunately, the use of sulfur(VI) fluorides (e.g., R-SO2 -F and SO2 F2 ) leaves only the substitution pathway open. As with most of click chemistry, many essential features of sulfur(VI) fluoride reactivity were discovered long ago in Germany.6a Surprisingly, this extraordinary work faded from view rather abruptly in the mid-20th century. Here we seek to revive it, along with John Hyatt's unnoticed 1979 full paper exposition on CH2 CH-SO2 -F, the most perfect Michael acceptor ever found.98 To this history we add several new observations, including that the otherwise very stable gas SO2 F2 has excellent reactivity under the right circumstances. We also show that proton or silicon centers can activate the exchange of SF bonds for SO bonds to make functional products, and that the sulfate connector is surprisingly stable toward hydrolysis. Applications of this controllable ligation chemistry to small molecules, polymers, and biomolecules are discussed.

Sulfur(VI) Fluoride Exchange (SuFEx): Another Good Reaction for Click Chemistry

This review describes the various manifestations of the pyrimidine system (alkylated, glycosylated, benzo-annelated.). These comprise pyrimidine nucleosides as well as alkaloids and antibiotics – some of them have been discovered and isolated from natural sources already long time ago, others have been reported very recently. A short overview on pyrimidine syntheses (prebiotic synthesis, biosynthesis, and metabolism) is given. The biological activities of most of the pyrimidine analogs are briefly described, and, in some cases, syntheses are formulated.

Pyrimidine as constituent of natural biologically active compounds.

Seed galactomannans are vegetable, heterogeneous polysaccharides widely distributed in nature. Generally, they possess (1-->4)-linked D-mannopyranose (Man) main chains to which are attached (1-->6)-linked D-galactopyranosyl (Gal) units. The Man/Gal ratios differ from gum to gum, resulting in a change in structure, which, in turn, determines the various industrial applications of seed galactomannans. These materials are important in paper, textile, petroleum-drilling, pharmaceutics, food, cosmaceutics, and explosives industries. In this review, the biodiversified applicability of galactomannan gums is discussed, particularly with respect to structural aspects, properties, human consumption, and technical applications. Especially important is that the solution properties (rheological behaviour, viscosity, emulsifying tendency, etc.) of natural and chemically modified galactomannans can be tuned by interaction with other (carbohydrate-based) monomers or polymers.

Wilhelm Traube

Papers

Ueber eine neue Synthese des Guanins und Xanthins

Der synthetische Aufbau der Harnsäure, des Xanthins, Theobromins, Theophyllins und Caffeïns aus der Cyanessigsäure

Ueber das Verhalten der Alkylenoxyde zu Malonester und Acetessigester

Zur Kenntnis des Sulfamids

Ueber eine neue Additionsreaction der Alkylenoxyde