Total synthesis of (+)-mupirocin H from D-glucose

Enantioselective total synthesis of mupirocin H is accomplished starting from D-glucose featuring strategic application of D-glucose derived chirality, diastereoselective Still-Barrish hydroboration, and further elaboration of carbon chain to furnish a phenyltetrazolyl sulfone intermediate, which on coupling with (2S,3S)-2-methyl-3-(triisopropylsilyloxy)butanal under Julia-Kocienski olefination conditions gave an advanced E-olefinic intermediate selectively. The E-olefin was transformed to the 4-hydroxynitrile, a prefinal substrate, which on acid-catalyzed oxidative lactonization furnished the target molecule mupirocin H in 19 steps from known compound 6 (longest linear sequence) with an overall yield of 4.96%.     

119Sn Mössbauer characterization of self assembled organotin(IV) complexes with Schiff bases containing amino acetate skeletons

Several organotin(IV) compounds, viz., diorganotin(IV) compounds of the types Ph₂SnLH (monomer), ⁿBu₂SnLH·OH₂ (monomer), [Me₂SnLH·OH₂]₂ (centrosymmetric dimer), [ⁿBu₂SnLH]₃ (cyclic trinuclear), [Ph₂SnLH] _n (polymer), {[ⁿBu₂Sn(LH)]₂O}₂ (centrosymmetric tetranuclear), dinuclear di-/tri-mixed organotin(IV) compounds Ph₂SnLH·Ph₃SnCl (monomer) and triorganotin(IV) compounds of the types [Bz₃SnLH]₂ (centrosymmetric dimer) and [Me₃SnL¹H] _n (Polymer) (LH = Schiff base carboxylate) have been studied in the solid state at liquid nitrogen temperature using ¹¹⁹Sn Mössbauer spectroscopy. The tin coordination geometry of the compounds determined from crystallography was correlated with the ¹¹⁹Sn Mössbauer results.     

Simultaneous Hydrogen Generation and Exciplex Stimulated Emission in Photobasic Carbon Dots

Photocatalytic water splitting is a promising approach to generating sustainable hydrogen. However, the transport of photoelectrons to the catalyst sites, usually within ps-to-ns timescales, is much faster than proton delivery (∼μs), which limits the activity. Therefore, the acceleration of abstraction of protons from water molecules towards the catalytic sites to keep up with the electron transfer rate can significantly promote hydrogen production. The photobasic effect that is the increase in proton affinity upon excitation offers means to achieve this objective. Herein, we design photobasic carbon dots and identify that internal pyridinic N sites are intrinsically photobasic. This is supported by steady-state and ultrafast spectroscopic measurements that demonstrate proton abstraction within a few picoseconds of excitation. Furthermore, we show that in water, they form a unique four-level lasing scheme with optical gain and stimulated emission. The latter competes with photocatalysis, revealing a rather unique mechanism for efficiency loss, such that the stimulated emission can act as a toggle for photocatalytic activity. This provides additional means of controlling the photocatalytic process and helps the rational design of photocatalytic materials.     

Thermoreversible polyaniline gels

Polyaniline (PANI) forms thermoreversible gels in different sulphonic acids e.g. dinonyl napthalene sulphonic acid (DNNSA), dinonylnapthalene disulphonic acid (DNNDSA), ± camphor ‐ 10 ‐ sulphonic acid (CSA) and dodecyl sulphonic acid (DSA) when processed from the formic acid medium. The surfactant concentration has been varied from weight fraction of PANI (W_PANI)=0.05−0.60. In most cases at W_PANI=0.05−0.40 compositions fibrillar network structures are observed from SEM study. They also exhibit reversible first order phase transition during both heating and cooling in DSC. The melting temperature and the gelation temperature increases with increase in surfactant concentration of the gel. From the WAXS pattern it is concluded that crystallization of the surfactant tails anchored from the nitrogen atom of PANI through its SO₃ H head group is responsible for gelation. The conductivity of all the gels with increase in PANI concentration showed a maximum with composition. The maximum conductivity is ∼0.01 S/cm, for W_PANI=0.22. The conductivity variation has been explained by considering it as a function of both interchain and intrachain contributions.