Cooperative Catalysis

Cooperative catalysis occurs when the synergic catalytic effect of at least two different entities acts together, increasing the rate of a chemical reaction beyond what is possible when either of the two entities is used independently. The idea of “Cooperative Catalysis” has inspired synthetic chemists to create artificial dual activation catalysts. Such a Cooperative Catalytic pathway is often used in enzymatic catalysis. Enzymes are continue to be a source of inspiration for (designing and) developing new catalytic reactions that are high in efficiency & selectivity and minimal waste.

Urease is a dinuclear metalloenzyme which catalyzes the hydrolysis of urea into carbon-di-oxide and ammonia. The dimeric nickel center of this enzyme is (the active site) responsible for cooperative catalysis. Urea co-ordinates with one Ni-center, thus activate the electrophile (act as Lewis Acid), whereas water coordinates with the second Ni. It is thus acidified and can be deprotonated by histidine to generate hydroxide as a nucleophile (generate nucleophile), which is, now in close to the electrophile, and, can attack in an intramolecular fashion.

A similar cooperative catalytic activity with Bronsted and Lewis acidities can be generated by simultaneous incorporation of multiple elements in the silica framework is quite interesting and holds promises of unprecedented catalytic performances.

We recently prepared a similar natural mimic, a bimetallic nano-porous catalytic system, which would be able to perform cooperative catalysis for the selective synthesis of ortho-prenylated phenols and 2,2-dimethyl chroman, starting from phenol and allylic alcohol. Prenylated phenols are widely distributed in nature and are known to be an important structural unit of pharmaceutical compounds. Similarly, 2,2-dimethylchroman derivatives also exhibit broad range of interesting physiological properties, we are able to synthesis the important structural motif by using the new cooperative catalytic systems.

The amount of aluminum present in the framework dictates the acidity of the catalyst, and by fine-tuning the aluminum content, we can develop the catalyst with the desired catalytic property. Catalyst developed in such a manner was found to be highly active and selective. The products obtained were good and satisfactory. Additionally, the synergistic effect of the bimetals (Cu and Al) in the nanoporous catalysts controls the selectivity of the final products.

Nobel Advice

Are you a Nobel aspirant, young researcher, or want to be part of good science? Here is an advice from Prof. Avram Hershko ( Winner of 2004 Nobel Prize -for the discovery of ubiquitin-mediated protein degradation)

Here is a lesson from his life in science that he presented at the Lindau Nobel Meeting 2013."

• It is very important to have good mentors- you cant learn how to do good science just from reading the literature.
• Find an important subject that is not yet interesting to others the big guys will get there before you! Do not go with the mainstream. 
• Accidental observations may be the most important ones. Grab your Luck. 
• Use whatever experimental approach is needed for your objective. It may not necessarily be the most fashionable (“state-of-the-art”) technology. Of course, biochemistry will always be needed. 
• Science should be a curious driven adventure. You should have a lot of excitement and fun. 
• Never leave bench work, and shall continue to get a lot of excitement and fun.

Inspired by Nobel

It is a great honor, not to mention my good fortune as well, to be nominated and sponsored by Department of Science and Technology, India, as one of the 23 young researchers who will be attending the 63rd Lindau Nobel Laureate Meeting as part of the Indian delegation.

With much anticipation, I await to listen to the eminent speakers at the Lindau stellar, who need no elaborate introduction. The work of most of the scholars have formed a basis for my own work as well as for thousands of other scientists and students around the world. We ceaselessly draw inspiration from their work. I have long admired these scholars, but to listen to them in person would be an awe-inspiring experience, which I am sure would vouch for it.

“It is the quest for knowledge that drives the scientific community.” Armed with this belief, I look forward to meet and interact with personalities of scientific excellence at close quarters. The informal setting at the Lindau Meeting, I hope, will allow us to discuss our work in a relaxed manner. I believe this meeting will be a great platform to learn directly from the masters and to meet peers from across the globe.

Read More at the Lindau blogs website

Click Chemistry for Pyrrole Synthesis

The Pyrrole heterocycle is an important chemical motif, found widely in pharmaceuticals, natural products, agrochemicals, and advanced materials. The introduction of new methods or further the work on technical improvements in order to overcome the limitations (such as low efficiency and selectivity) found in pyrrole synthesis is still a pressing experimental challenge. 

The concept of “Click Chemistry” is gaining rapidly due to its high efficiency, selectivity, and yield under mild reaction conditions with a wide variety of readily available starting materials. The copper-catalyzed azide-alkyne cycloaddition (CuAAC) has emerged as the premier example of click chemistry and plays a significant role in organic synthesis. 

Prof. Aiwen Lei and coworkers, Wuhan University, Hubei, have developed a silver catalyst “click reaction” for the synthesis of pyrrole, by cycloaddition. This system benefits from readily-available starting materials, low catalyst loading (0.1 eq), short reaction times (2 h), and excellent chemo-selectivity. Moreover it works for both internal and alkyl-substituted terminal alkynes in the presence of many functional groups. The extremely mild conditions used make this reaction synthetically attractive. 

This mechanism involves the formation of silver–acetylide complex and silver–isocyanide complex. Subsequently, the cyclo-addition between complexes would afford the key intermediate complex to be followed by protonation and tautomerization of the intermediate complex to form the desired product. 

The catalytic synthesis protocol tolerates many functional groups, including methylthio, methylsulfonyl, and ethynyl groups. Moreover, alkyl-substituted terminal alkynes were also found to be suitable reaction partners. Interestingly, both Cu(II) and Cu(I) turned out to be ineffective.

Useful chemicals and fuel from carbon dioxide

Carbon dioxide is an abundant, non-toxic, inexpensive, and renewable source of carbon. This makes CO2 the most coveted compound by Green Chemistry enthusiasts. Industries are always on the lookout for ways to enable the effective use of to act as synthetic building blocks for producing fuels like Methane, Di-methyl-ether, and Methanol fine-chemicals. Furthermore, CO2 conversion could also help reduce atmospheric CO2 levels, popularly known as “Green House Gas”, and thus, protect the climate.

Nature has been highly successful in using CO2 as synthetic building blocks in photosynthesis. For decades, scientists have been trying to understand this phenomenon at a molecular level. Such studies have proved useful in developing biomimetic catalysts for CO2 conversion. Chlorophyll (Porphyrin molecules) in green plants convert incident sunlight and atmospheric CO2 into sugars (energy). So, this makes them a promising target for testing activation catalysts for CO2 adsorption. Effective CO2 adsorption using man-made catalysts is indeed our end-goal. Much research is being conducted in this area to further the economic viability of the processes that utilize CO2. Several companies are pursuing the idea/concept of thermochemical and electrochemical conversion of CO2 into chemical feedstock or polymers. Research and development are currently focused on increasing the catalyst life and bringing down the temperature of conversion.

Future research must emphasize the rational design of highly active catalysts to satisfy the economic development of CO2 conversion. However, the development of such efficient catalysts requires a complete understanding of CO2 and CO2-catalyst interactions.

In order to develop such a catalyst, the following points should be considered,

1. CO2 has a strong affinity towards nucleophiles and electron-donating reagents due to its carbonyl-carbon's electron deficiency; if the designed catalysts has nitrogen or base-functionality (basic), it will have an increased affinity towards CO2 (e.g., Porphyrin, Grignard reagents).
2. With low-valent metals and alkene, CO2 undergoes “oxidative cycloaddition.”
3. New CO2 soluble catalysts may increase efficiency.
4. Homogeneous catalysis in compressed CO2 may increase selectivity.
5. The catalyst in supercritical CO2 may also increase stability. It is essential to use CO2, based on the unique physical properties as that of the supercritical fluid, either as a solvent, or as an anti-solvent, or reactant, or a combination of all.
6. Photoelectrochemistry, the study of using solar energy to split CO2, is an emerging method for clean production of chemicals. It is also essential to develop catalysts (Semiconducting materials) for the electrochemical conversion of CO2.
7. The use of high-energy starting materials may ease the catalyst role.
8. The catalyst will be more efficient if it has both CO2 adsorption and activation functionality. E.g., designer MOF that contains Lewis-base sitewill donate electron to CO2, in contrast to the Lewis-acids sites in traditional MOFs for adsorbing CO2.
9. A computational tool such as Density Function Theory (DFT) may help improve the catalytic activity or find a new catalyst.
10. Chemical reactions can also benefit from using CO2 as a mild oxidant or as a selective source of O2 atoms because dissociation of CO2 on a catalyst-surface could produce active O2 species.

The trend towards converting CO2 to valuable chemicals and fuels will probably intensify in the near future. This could, in turn, lead to effective management to tackle climate change and the energy crisis.

As Whitesides emphasizes, managing CO2 and conversion into valuable chemicals and energy will be the reinvention of chemistry, and it is also a chemistry/ molecular solution to the critical problem facing society. He says

 “Some of the most interesting problems in science, and many of the most important facing society, need chemistry for their solution. Examples include: understanding life as a network of chemical reactions; interpreting the molecular basis of disease; global stewardship; the production, storage, and conservation of energy and water; and the management of carbon dioxide."

Issues pertaining to CO2 are truly global and a major opportunity to develop sustainable energy options and environmental preservation. So, the use of CO2 to synthesize useful chemicals & fuels will mark a new field in chemistry. It is important to establish university-industry-collaboration to search for new-reactions & new-catalysts in this field.