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New in asymmetric photochemistry

22 November 2014 - Origins

CLP Rijeesh  Rijeesh et al. report a novel photoinduced enantioselective reaction DOI It has been done before: in 1971 Kagan directed circularly polarized light (CLP) at a complex hydrocarbon forming a chiral helicene. The CLP handedness matched that of the helicene handedness.

In the novel reaction the substrate is azobenzene EE. By CLP irradiation EE isomerizes to EZ and ZE which are each other mirror images. On further irradiation the final product ZZ is again achiral. It turns out EZ and ZE form in unequal amounts. The calculated enantiomeric excess is 0.4%.

According to the researchers EZ and ZE form in equal amounts, EZ and ZE cannot interconvert but depending on the handedness of the CLP used , one enantiomer isomerizes faster to either the final product ZZ or back to EE.

More researches appear to have rediscovered CLP as evidenced by a recent chiral coordination polymer (DOI) and a recent chiral nanowire (DOI). Background on asymmetric photochemistry here

Krug on nanosafety

15 November 2014 - The hard truth

Nanosafety Research? Are We on the Right Track? Harald F. Krug claims 16 pages of the Angewandte Chemie to talk about nanotoxicology (DOI). With 10,000 papers published on the topic and not a single human casualty on record the question on nanosafety should be: YES! nanotech is safe! Move on! The main conclusions however in this review are: yes, engineered nanomaterials are safe because the human body knows how to deal with them but no, most studies carried out thus far are flawed. So if it up to Harald Krug it is not mission accomplished! but rather lets find funding for an additional 10,000 reports and do it right this time.

So how did these studies break the rules? Here are some of the findings. Materials studied were poorly defined and for example used "as purchased". Prior to testing materials were diluted in unsuitable solvents to unrealistic concentrations. According to Krug it is too easy to bury cells with a layer of nanoparticles denying it nutrients. During experimentation nanomaterials can also dissolve in the medium making the study nano non-relevant. There are some weird test-animal practises: in testing the skin barrier, skin is unrealistically stretched. In testing the lung barrier nanomaterial is injected (instilled) rather than inhaled. Other offences found in studies: lack of control samples, lack of standard operation procedures, lack of toxicological expertise.

In summary according to Krug "nanotoxicology has clearly failed to equip itself with the same fundamental rules as are applied to toxicology" and "researchers who do not know or apply these rules should no longer be given financial support for toxicologically oriented research programs."

Chemists are in general not critical of their discipline let alone about their colleagues. This lecture from an opinionated professional not sparing anyone is a refreshing read.

A computational nanoreactor

13 November 2014 - Movie time

TeraChem is chemical software build on the same graphics processing units that can also be found in mobile phones and especially adapted for parallel computing. It was recently put to use as an ab initio nanoreactor by a group of Standford University researchers. (DOI). They looked for 560 picoseconds at 156 acetylene molecules polymerizing in one million steps. To speed things up shock waves were sent at regular intervals, increasing pressure and reaction rates and creating temperatures of up to 10000 K. At the end of the simulation compounds were formed like 5-methylcyclopenta-1,3-diene and benzene but also larger linear and branched chains. Surprisingly highly strained cyclopropene and highly antiaromatic cyclobutadiene also made the list. The article is fuzzy about the computational expenses made. My guess is that for the 500 picosecond movie, the researchers spent the equivalent of 40,000 regular CPU's running for one hour.