Well, I only contributed with the theoretical section by doing electronic structure calculations, so it isn’t really a paper we can ascribe to this particular lab, however it is really nice to see my name in JACS along such a prominent researcher as Prof. Chad Mirkin from Northwestern University, in a work closely related to my area of research interest as macrocyclic recognition agents.
In this manuscript, a calixarene is allosterically opened and closed reversibly by coordinating different kinds of ligands to a platinum center linked to the macrocycle. (This approach has been referred to as the weak link approach.) I recently visited Northwestern and had a great time with José Mendez-Arroyo, the first author, who showed me around and opened the possibility for further work between our research groups.
Closed, semi-open and fully open conformations; selectivity is modulated through cavity size. (Ligands: Green = Chloride; Blue = Cyanide)
Here at UNAM we calculated the interaction energies for the two guests that were successfully inserted into the cavity: N-methyl-pyridinium (Eint = 57.4 kcal/mol) and Pyridine-N-oxide (Eint = +200.0 kcal/mol). Below you can see the electrostatic potential mapped onto the electron density isosurface for one of the adducts. Relative orientation of the hosts within the cavity follows the expected (anti-) alignment of mutual dipole moments. At this level of theory, we could easily be inclined to assert that the most stable interaction is indeed the one from the semi-open compound and that this in turn is due to the fact that host and guest are packed closer together but there is also an orbital issue: Pyridine Oxide is a better electron acceptor than N-Me-pyridinium and when we take a closer look to the (Natural Bonding) orbitals interacting it becomes evident that a closer location does not necessarily yields a stronger interaction when the electron accepting power of the ligand is weaker (which is, in my opinion, both logic and at the same time a bit counterintuitive, yet fascinating, nonetheless).
All calculations were performed at the B97D/LANL2DZ level of theory with the use of Gaussian09 and NBO3.1 as provided within the former. Computing time at UNAM’s supercomputer known as ‘Miztli‘ is fully acknowledged.
The full citation follows:
A Multi-State, Allosterically-Regulated Molecular Receptor With Switchable Selectivity
Jose Mendez-Arroyo †, Joaquín Barroso-Flores §,Alejo M. Lifschitz †, Amy A. Sarjeant †, Charlotte L. Stern †, and Chad A. Mirkin *†
Thanks to José Mendez-Arroyo for contacting me and giving me the opportunity to collaborate with his research; I’m sure this is the first of many joint projects that will mutually benefit our groups.
Just as last year, the “Dolphin Summer Internship Program” (Programa Delfín) has started and this time it coincided with #RealTimeChem week. Four students from various cities (and accents) around Mexico have come to our lab in Toluca in order to spend about 7 weeks of research in the field of molecular modeling and within our research of molecular recognition in biochemistry. Karen, Cynthia, Jesús and Marco have started their training today as they arrived to CCIQS so we went over the (very) basics of quantum chemistry, the (very) basics of Linux and the basics of Gaussian09. (I should really think about developing some web tutorials or something because this impromptu training is very exhausting!)
Their academic backgrounds are mostly centered around pharmaceutics and biochemistry although their ages range from the second to the fourth year of college education. Computational chemistry is pretty unknown to all of them; I’ll do my best to change that, while at the same time I make them aware of its power as a research tool and as a research field in itself.
Here is to a very productive summer! I hope we manage to get enough data for a paper and, more importantly, that they all get a good experience out of their time here, make new friends and learn something new that enriches their skills in this increasingly competitive world.
A couple of weeks ago I was invited to give a talk to a small university in southern Mexico called ‘Universidad de la Cañada‘ in the state of Oaxaca, one of the most underprivileged states in our nation. This institution is a rather small one but the work they are doing over there with as little resources as they have is truly remarkable . UNCA offers degrees in pharmacy, pharmacology, food sciences, clinical chemistry and other topics that aim to supply the needed human resources for the various industries that are settled in the region. There is a true feeling of togetherness at UNCA since they have little pieces of equipment yet they are all fully shared among researchers regardless of who received the finance to acquire them. Last year, two of their students came for a two months stay, after which, Alberto and Eduardo got their names on a publication of our research group. It was nice to see them again and even nicer to learn they are about to finish their studies and that they will come back again to our lab in late July.
Every year at UNCA there is a Pharmacology Day on which the students show the results to their research projects during a poster session and listen to lectures by guest speakers from various universities around Mexico. Most of their projects were aimed to the isolation of natural products from local resources and their usage in several kinds of consumer products. UNCA is in a very small town, village I might say, surrounded by mountains and vegetation; the view was spectacular as you may see from the pictures below. Thank you very much to my good friend Dr. Carmen Hernández-Galindo for inviting me to participate and share our work with their students, I hope we may go back again and keep a fruitful exchange between our groups.
During this talk, I took the opportunity to talk about the aforementioned paper in the context of molecular recognition and their in silico design but I think I should have talked more about the computational strategies that are most employed in the pharmaceutical industry. Never mind. I hope I get the opportunity to right this wrong. Still it was nice to give Alberto and Eduardo the opportunity to brag a little about being published authors.
Kudos to Rola Aburto, Dr. Margarita Bernabé, Dr. Rocío Rosas, and all the academic staff at UNCA for their invaluable dedication to teaching science against all odds, I can testify, through the hard work of their students, hat their effort is paying off.
So the World Cup is once again on top of us. I’m not a Football (Soccer) enthusiast but I’ve got to admit that the expectation of such a large and widely covered event is pretty contagious. This year, however, I’m very excited about the inaugural kick-off ceremony because a paraplegic teen will be the one to set the ball in motion, thanks to the use of an exoskeleton developed by the illustrious Brazilian researcher, Dr. Miguel Nicolelis, this patient will not only walk again but also perform a feat of equilibrium: kicking a football. More impressive than the exoskeleton itself is the brain-computer-machine interface since the patient will control the entire process by himself. Miguel Nicolelis is widely known and highly regarded in the scientific community; I’m not sure if he is that famous outside academia, but if he isn’t, he should be. The natural question about Dr. Nicolelis is what is he? Is he a robotics engineer? a neurologist? a programmer? a physician? The answer could be no other than ‘all of the above‘.
And even more impressive than all that, if that’s even possible, is the fact that this huge achievement of technology is presented at one of the most viewed sporting events on the planet. Brazilian organizers could have selected many things to kick-off this event: From Adriana Lima to Pelé; from a Samba line to aboriginal Amazonian people, but instead they chose to go with a scientific and technological breakthrough achieved by one of their own. I wonder if this is a way to tell the world they are interested in investing in science and technology as a way to pave the way of their economical and social development. Brazil is currently regarded as a fast growing nation economically although the social disparity seems to be still quite large. The message I’m getting, at least in principle, is that Brazil is a modern nation with high regard for scientific development on which they will rely their future.
Kudos to the Brazilian organizers who thought of placing this large scientific breakthrough in a sporting event, proving that this world should become boundless and the way to do it is through science.
On Friday May 30th, my good friend Dr. Josefina Aldeco, my wife and I, visited a children’s home in Querétaro (central Mexico) and brought them a few cool chemistry experiments for a short show. This event was promoted by a non-profit organization called “Anímate a estudiar” (Dare to study), namely by Mrs. Paulina Milanés who is always looking for ways to encourage kids from poor backgrounds to pursue their goals through study; among other things, they provide backpacks with school supplies to orphan kids like the girls we visited.
As a way to inspire them, we handed each girl a balloon drawn in the shape of a brain and asked them to inflate them daily by reading; by doing their homework; by asking questions all the time; by working hard in pursuit of a brighter future for which their brains are the most powerful muscles.
Many reactions took place that Friday; not only inside the flasks and beakers before our little audience but also in their faces and their engagement with us. Little by little these girls got out of their shells and became more excited, up to the point of performing their own chemical reaction themselves by polymerizing some glue with borax in hot water. This was for sure the first time they got in contact with chemistry but the true goal was to set up a spark in their minds that one day may turn into a life opportunity. We are aware that one small chemistry show can’t really have that effect, but if many more scientists reach out to these kids there is a bigger chance of creating a ripple effect that convince disenfranchised children that studying is the way to take the wheel of their own future.
Science is about development; its about spreading knowledge and the love for knowledge. Although we most times sit high on our ivory towers it is paramount to remember that there is also a social component to the scientific activity. Kids are eager to learn, but most school systems do their very best to limit their curiosity and ambition. We hope these girls find in studying a way to a better, happier and safer future. Mexico has a large economic disparity; climbing the social ladder is very hard and even more so for women which makes these girls a very vulnerable social group in the next generation.
It only takes one day. One day and some potassium iodide; some mentos on a diet-coke (sorry, Gina, for the squirt!); some cobalt chloride on paper; some balloons some glue and some borax in hot water. But above all it takes a big commitment.
I hope you readers, computational and experimental chemists alike, take some time out of your busy schedules and share your passion for science with kids, specially those with the lowest opportunities of getting in touch with real scientists. You can also contribute to this noble effort by making a small pay-pal donation to www.animateaestudiar.org or to any other similar organization in your local community.
It only takes one day.
P.S. Thanks to Josefina from Universidad Autónoma de Querétaro for providing material and reagents. Please go and check out her blogs (here and here) and encourage her to write more often! (Did I mention she published in Science a few years ago?)
A couple of weeks ago I posted a solution for a common error regarding .fchk files that will display the error below when opened with GaussView5.0. As I expected, this error has to do with the use of diffuse functions in the basis set and is related to a change of format between Gaussian versions.
CConnectionGFCHK::Parse_GFCHK() Missing or bad data: Alpha Orbital Energies Line Number 1234
Although the method described in the previous post works just fine, the following update is a better approach. Due to a change of spelling between G03 and G09 (which has been corrected for G09 but not available for GV versions prior to 5.0.9) one must change “independent” for “independant“
To make the change directly from the terminal the following command is needed:
sed -i 's/independent/independant/g' file.fchk
Alternatively you can redirect the output to a new file
sed -e 's/independent/independant/g' file.fchk > newfile.fchk
if you want to keep the old version and work with a new one.
Of course this edition can be performed manually with any text editor available (for example if you work in Windows) but solutions from the terminal always seem easier and a lot more fun to me.
Thanks to Dr. Fernando Cortés for sharing his insight into this issue.
I’ve found the following error regarding the opening of .fchk files in GaussView5.0.
CConnectionGFCHK::Parse_GFCHK() Missing or bad data: Alpha Orbital Energies Line Number 1234
The error is prevented to a first approximation (i.e. it at least will allow GV to open and visualize the file but other issues may arise) by opening the file and modifying the number of basis functions to equal the number of independent functions (which is lower)
FILE HEADER FOpt RM062X 6-311++G(d,p) Number of atoms I 75 Info1-9 I N= 9 163 163 0 0 0 110 2 18 -502 Charge I 0 Multiplicity I 1 Number of electrons I 314 Number of alpha electrons I 157 Number of beta electrons I 157 Number of basis functions I 1199 Number of independent functions I 1199 Number of point charges in /Mol/ I 0 Number of translation vectors I 0 Atomic numbers I N= 75 ... ... ... ...
Once both numbers match you can open the file normally and work with it. My guess is this will continue to happen with highly polarized basis sets but I need to run some tests.
So many things have happened since I last updated this blog but I will come to write on them when appropriate. Right now I’d like to share an invitation by Prof. Ponnadurai Ramasami from the University of Mauritius to the upcoming Virtual Conference on Computational Chemistry from the 1st to the 31st of August. Deadlines can be consulted here and the most important is the abstract submission on June 30th. This conference is part of the official celebrations of the International Year of Crystallography so talks involving experimental determination of electron densities will be well suited.
I participated in the latest edition and I must say it was a very enriching opportunity to learn from so many other researchers from across the world without leaving my desk. I already know what my talk will be about, now that we are so close to finish and submit a paper on the absence of reactivity for an anti-aromatic set of molecules. (I think I’ll call it “The reactivity of molecules that never existed [but that maybe should have.].) All talks are sent either as pdf, powerpoint presentations, youtube videos, etc. and Q&A are done over e-mail.
So this is a calling to other computational chemists out there who want to participate in this virtual conference. Kudos to Prof. Ponnadurai Ramasami and lets hope we can crystallize his visit to Mexico during 2014 the International Year of Crystallography (pun intended) and here’s to me going sometime to Mauritius!
I always get very happy to have a new paper out there! I find it exciting but most of all liberating since it makes you feel like your work is going somewhere but most of all that it is making its way ‘out there'; there is a strong feeling of validation, I guess.
Two very different families of calix[n]arenes (Fig 1) were tested as drug carriers for a very small molecule with a huge potential as a chemotherapeutic agent against Leukemia, namely, 3-phenyl-1H-benzofuro[3,2-c]pyrazole a.k.a. GTP which has proven to be an effective in vitro Tyrosine Kinase III inhibitor. Having such a low molecular weight it is expected to have a very high excretion rate therefore the use of a carrier could increase its retention time and hence its activity. This time we considered n = 4, 5, 6 and 8 for the size of the cavities and R = -SO3H and -OEt as functional groups on the upper rim as to evaluate only a polar coordinating group and a non-polar non-coordinating one since GTP offers two H-bond acceptor sites and one H-bond donor one along the π electron density that could form π – π stacking interactions between the aromatic groups on GTP and the walls of the calixarene.
Once again calculations were carried out at the B97D/6-31G(d,p) level of theory along with molecular dynamics simulations for over 100 ns of production runs. NBO Deletion interaction energies were computed in order to discern which hosts formed the most stable complexes.
You may find a link to the ScienceDirect website for downloading the paper from this link. Last, but certainly not least, I’d like to thank all coauthors for their contributions and patience in getting this study published: Dr. Rodrigo Galindo-Murillo; Alberto Olmedo-Romero; Eduardo Cruz-Flores; Dr. Petronela M. Petrar and Prof. Dr. Kunsági-Máté Sándor. Thanks a lot for everything!
Once again as every year we celebrate our internal symposium here at CCIQS, and like every year, my students presented some of their progress with their research projects. This time, three students, from three different levels, present posters regarding some of the data they’ve obtained.
María Eugenia ‘Maru’ Sandoval presented a poster regarding the molecular dynamics simulations performed for the drug Imatinb and a family of calix- and thia-calix[n]arenes as published here and reported in this blog here. ‘Maru’ is now a first year grad student at the National University, UNAM, after spending a year working for a pharmaceutical company. Her research in the realm of photosynthesis has only begun recently, that is why we had to rely on some other data.
Luis Enrique Aguilar is researching cation-π interactions within the aromatic cavities of calix[n]arenes in order to find suitable leads among these, our favorite macrocyles, for designing extraction agents of heavy (toxic) metals. Luis Enrique is an undergrad student here at the State University who should finish this year and has shown some interest (threatened us) in writing his dissertation thesis in our research group.
Monserrat Enriquez is a PhD student at CINVESTAV under the joint supervision of Dr. Eddie López-Honorato and myself (Dr. Eddie is her principal advisor), her research project involves both theoretical calculations and synthesis of the leads for extraction agents for several Arsenic species. For the time being, Monserrat is here with us, far from her home on the north side of the country, for this semester in which we have to finish with the theoretical section of her work. Besides her research concerning calixarenes she is also running calculations on the interactions between graphene oxide and the aforementioned As species. We are very excited about working with such a complex yet simple material that has such an exciting electronic structure.
This symposium is always interesting and important in bringing our research projects closer to all the comunity of this center. And since symposium comes from the Greek meaning ‘drinking together‘, then lets raise our glasses and toast for the data to come!