Category Archives: Computational Chemistry

New paper in Computational and Theoretical Chemistry


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-[1]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.

Fig 1. Calixarenes under study and their complexes with GTP

Fig 1. Calixarenes under study and their complexes with GTP

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.

NBO Del interaction energies B97D/6-31G(d,p)

NBO Del interaction energies B97D/6-31G(d,p)

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!

fig8

Donor and acceptor H-bond sites increases the probability of keeping the drug in place for a higher retention rate

Donor and acceptor H-bond sites increases the probability of keeping the drug in place for a higher retention rate

Internal Symposium at CCIQS – 2014 edition


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.

20140220-221553.jpg

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.

20140220-221627.jpg

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.

20140220-221638.jpg

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!

Cheers!

20140220-221653.jpg

New paper in Journal of Chemical Theory and Computation


Happy new year to all my readers!

Having a new paper published is always a matter of happiness for this computational chemist but this time I’m excedingly excited about anouncing the publishing of a paper in the Journal of Chemical Theory and Computation, which is my highest ranked publication so far! It also establishes the consolidation of our research group at CCIQS as a solid and competitive group within the field of theoretical and computational chemistry. The title of our paper is “In Silico design of monomolecular drug carriers for the tyrosine kinase inhibitor drug Imatinib based on calix- and thiacalix[n]arene host molecules. A DFT and Molecular Dynamics study“.

In this article we aimed towards finding a suitable (thia-) calix[n]arene based drug delivery agent for the drug Imatinib (Gleevec by Novartis), which is a broadly used powerful Tyrosine Kinase III inhibitor used in the treatment of Chronic Myeloid Leukaemia and, to a lesser extent, Gastrointestinal Stromal Tumors; although Imatinib (IMB) exhibits a bioavailability close to 90% most of it is excreted, becomes bound to serum proteins or gets accumulated in other tissues such as the heart causing several undesired side effects which ultimately limit its use. By using a molecular capsule we can increase the molecular weight of the drug thus increasing its retention, and at the same time we can prevent Imatinib to bind, in its active form, to undesired proteins.

We suggested 36 different calix and thia-calix[n]arenes (CX) as possible candidates; IMB-CX complexes were manually docked and then optimized at the B97D/6-31G(d,p) level of theory; Stephan Grimme’s B97D functional was selected for its inclusion of dispersion terms, so important in describing π-π interactions. Intermolecular interaction energies were calculated under the Natural Bond Order approximation; a stable complex was needed but a too stable complex would never deliver its drug payload! This brings us to the next part of the study. A monomolecular drug delivery agent must be able to form a stable complex with the drug but it must also be able to release it. Molecular Dynamics simulations (+100 ns) and umbrella sampling methods were used to analyse the release of the drug into the aqueous media.

Optimized geometries for all complexes under study (B97D/6-31G*)

Optimized geometries for the 20 most stable complexes under study (B97D/6-31G*)

Potential Mean Force profiles for the four most stable complexes for position N1 and  N2 from the QM simulations are shown below (Red, complexes in the N1 position, blue, N2 position). These plots, derived from the MD simulations  give us an idea of the final destination of the drug respect of the calixarene carrier. In the next image, the three preferred structures (rotaxane-like; inside; released) for the final outcome of the delivery process are shown. The stability of the complexes was also assessed by calculating the values of ΔG binding through the use of the Poisson equations.

PMF for the most stable compounds

PMF for the most stable compounds

General MD simulation final structures

General MD simulation final structures

Thanks to my co-authors Maria Eugenia Sandoval-Salinas and Dr. Rodrigo Galindo-Murillo for their enormous contributions to this work; without their hard work and commitment to the project this paper wouldn’t have been possible.

Transition State Search (QST2 & QST3) and IRC with Gaussian09


Theoretical evaluation of a reaction mechanism is all about finding the right transition states (TS) but there are no guarantees within the available methods to actually find the one we need. Chemical intuition in the proposal of a mechanism is paramount. Let’s remember that a TS is a critical point on a Potential Energy Surface (PES) that is a minimum in every dimension but one. For a PES with more than two degrees of freedom, a hyper-surface, envisioning the location of a TS is a bit tricky, in the case of a three dimensional PES (two degrees of freedom) the saddle point constitutes the location of the TS as depicted in figure 1 by a section of a revolution hyperboloid.

400px-Saddle_point

Fig1. Saddle point on a surface (min in one direction; max in the other)

Fig 1a Pringles chips -Yuck-. They exhibit a maximum on the direction parallel to the screen and a minimum on the direction perpendicular to the screen at the same point.

Fig 1a Pringles chips -Yuck-. They exhibit a maximum on the direction parallel to the screen and a minimum on the direction perpendicular to the screen at the same point.

The following procedure considers gas phase calculations. Nevertheless, the use of the SCRF keyword activates the implicit solvent calculation of choice in order to evaluate to some degree the solvent influence on the reaction energetics at different temperatures with the use of the temperature keyword.

The first step consists of a high level optimization of all minimums involved, such as reagents, products and intermediates, with a subsequent frequency analysis that includes no imaginary eigenvalues.

In order to find the structures of the transition states we use in Gaussian the Synchronous Transit-guided Quasi-Newton method [1] through the keywords QST2 or QST3. In the former case, coordinates for the reagents and products are needed as input; for the latter keyword, coordinates for the TS structure guess is needed also.

QST2)

%chk=file.chk
%nprocshared=n
%mem=nGB

#p opt=(qst2,redundant) m062x/6-31++G(d,p) freq=noraman Temperature=373.15 SCRF=(Solvent=Water)

Title card for reagents

Q M
Cartesian Coordinates for reagents
blank line
Title card for products

Q M
Cartesian Coordinates for products
blank line

QST3)

%chk=file.chk
%nprocshared=n
%mem=nGB

#p opt=(qst3,redundant) m062x/6-31++G(d,p) freq=noraman Temperature=373.15 SCRF=(Solvent=Water)

Title Card for reagents

Q M
Cartesian Coordinates for reagents
blank line
Title card for products

Q M
Cartesian Coordinates for products
blank line–
Title card for TS
Q M
Cartesian Coordinates for TS
blank line

NOTE: It is fundamental that the numbering order is kept constant throughout the molecular specifications of all two, or three, input structures. Hence, I recommend to build a set of molecules, save their structure, and then modified the coordinates on the same file to produce the following structure, that way the number for every atom will remain the same for every step.

As I wrote above, there are no guarantees of finding the right TS so many attempts are probably needed. Once we have the optimized structures for all the species involved in our mechanistic proposal we can plot their energies very simply with MS Excel the way we’ve previously described in this blog (reblogged from eutactic.wordpress.com)

Once we’ve succeeded in finding the structure of our TS we may run an Internal Reaction Coordinate (IRC) calculation. This calculation will connect the TS structure to those of the products and the reagents. Initial constant forces are required and these are commonly retrieved from the TS calculation checkpoint file through the RCFC keyword.

%chk=QST3_2p.chk
%nprocshared=8

#p m062x/6-31++G(d,p) IRC=(Maxpoints=50,RCFC,phase=(2,1))Temperature=373.15 SCRF=(Solvent=Water) geom=allcheck

Title Card

Q M
blank line

Finally, the IRC path can be visualized with GaussView from the Results menu. A successful IRC will link both structures along a single reaction coordinate proving that both reagents and products are linked by the obtained TS.

Hat tip to Howard Diaz who has become quite skillful in calculating these mechanisms as proven by his recent poster at the XII RMFQT a couple of weeks back. And as usual thanks to everyone who reads, comments, likes, recommends, rates and shares my silly little posts.

XIIth Mexican Reunion on Theoretical Physical Chemistry


As every year this month we had the yearly Mexican Reunion on Theoretical Physical Chemistry organized by prominent researchers in the field, such as Dr. Emilio Orgaz (UNAM), Dr. Alberto Vela (CINVESTAV) and many other. Over 150 different works were presented during this edition which took place in Juriquilla, Querétaro at one of the many campuses of the National Autonomous University of Mexico scattered all around the country. Below you can see some pictures from the talks and the first poster session.

20131119-154119.jpg20131119-154102.jpg20131119-154222.jpg

This time we contributed with a small poster on a mechanism proposed by Howard Diaz (an undergrad student from UAEM) on the equilibrium transformation of dihydrocinolines into 1-amino-indoles by an intramolecular rearrangement. May this post also serve as the starting point of a -mini-tutorial on how to evaluate a mechanism theoretically using QST3 and IRC in implicitly solvated environments (PCM)

20131119-154028.jpg

Howard Diaz posing next to his poster

The equilibrium under study and the proposed mechanism  by which it occurs, originally proposed by Frontana-Uribe et al. looks a bit like this:

equilibrium

Dihydrocinolines in equilibrium with 1-aminoindole

mechanism

Mechanistic proposal by Frontana-Uribe et al.

The energy profile, in which all transition states were calculated with the QST3 method, is presented below, calculated at various levels of theory. Also, the Internal Reaction Coordinate (IRC) connecting both states was calculated and is shown further below in the full poster.

Energy Profile

Energy Profile

From this results we believe that a new mechanistic proposal is needed since the energy barrier for the first step is quite high (~60 kcal/mol) and hence a bit unlikely to occur through that transition state. Nevertheless this is a first approach to elucidating a mechanism and the more knowledge about it the higher the control will be on this chemical transformation.

A full version of the poster is shown below for your convenience (Spanish). See you all at the next RMFQT in Morelia 2014!

Full Poster

Full Poster

The Nobel Prize in Chemistry 2013


I’m quite late to jump on this wagon but nonetheless I’m thrilled about this year’s Nobel Prize in Chemistry being awarded to three awesome computational chemists: Martin Karplus (Harvard), Michael Levitt (Stanford) and Arieh Warshel (USC) for the development of computational models at the service of chemistry; most prominently, the merging of computations both at the classical . and quantum levels, the former allows for a computationally feasible calculation while the latter provides the needed accuracy for the description of a chemical process.

Nobel Laureates in Chemistry 2013 (source: NBC.com)

Nobel Laureates in Chemistry 2013 (source: NBC.com)

As a computational chemist myself I must say that, at some level, it feels as some sort of vindication of the field, which makes me wonder if it indeed needs it, I don’t think so but maybe some might. Last week, Nobel week, I attended a symposium on the Advances in Quantum Chemical Topology where big names such as Paul Ayers, Paul Popelier and Chérif Matta among many others participated along with my friends and colleagues from CCIQS, Fernando Cortés (whom actually organized the whole thing! Kudos, Fer!) and Vojtech Jancik who contributed to the experimental (X-ray diffraction methods) part of the symposium. Surprisingly nobody at the conferences mentioned the Nobel Prize! Not even during the round table discussion titled “The Future of Quantum Chemical Topology“. At some point during this discussion the issue of usefulness came out. I  pointed out chemists have this inherent need of feeling useful, including computational chemists, as opposed to physicists of any denomination. Computational or theoretical chemists try to be like physicists yet still have chemistry behavior baggage. Even more baffling is the fact that at such an abstract conference usefulness is discussed, yet those theoretical chemists who do not develop new methods, nor dwell into equations or propose new Hamiltonians, but rather make use of well established methodologies for tackling and solving particular problems in chemistry become somewhat ostracized by the theoretical chemistry community*.

Much controversy among the comp.chem. community was aroused by this much deserved award (try reading the comment section on this post by the great Derek Lowe at In The Pipeline). Here in Mexico we have a saying: “Ni son todos los que están ni están todos los que son” which is hard to translate given the two different meanings of the verb To Be, but it can be roughly translated as “Not all the ones who should be are present, nor the ones that are present are all that should be“, or something like that. Of course there are many other computational chemists that are left behind from this prestigious prize, but the contributions of Karplus, Levitt and Warshel to chemistry through the use of computational chemistry can be denied. In fact this does vindicate the field of comp.chem. by acknowledging the importance of modelling in molecular design and reactivity understanding.

Congratulations from a Mexican fan to Professors Karplus, Levitt and Warshel for the most deserved Nobel Prize in Chemistry 2013!

PS a much better post on this topic can be found at the curious wavefunction.

Thanks for reading, liking, rating and commenting

*Of course this is just my opinion and views (which is redundant to state since this is my very own blog!)

Summer internships are Over


For the last five weeks we had guests in our lab coming from different places of the country: Tepic (west), León (Center) and Mexico City (Right in the middle!). During those five weeks they worked in the field of computational chemistry helping our research efforts with a couple of drug carrying molecules. They learned about computational chemistry and drug design; about wavefunctions and density functionals; about population analysis and vibrational frequency analysis. Dead hours were a bit complicated to handle because the convergence of each calculation takes some time and, as opposed to a wet-chemistry lab, I couldn’t just ask them to purify starting materials or distillate solvents. A question to other theoretical/computational chemists: What could I have asked young undergrad students (with backgrounds ranging from engineering to pharmacy) to do during those dead hours? What did I do wrong? Anyway, they manage to spend a good time since they all got along quite well.

Now they are back to their hometowns getting ready for the congress, hosted by the same organization that awarded them the stipend to come and spend their summer with us (The Dolphin Program / Programa Delfín) as well as to going back to school in a few more weeks. I asked* them to write a guest post for the blog telling their experience, which is presented below. Thanks to you all for choosing our lab to get your internship this summer!

Javier Camacho (Mexico City)

Javier_Delfin_2013Hi, I’m Javier from ESIQIE-IPN
The dolphin program has given me the opportunity to experience how is to be in a high-level scientific research. Login to CCIQS next to the imminent Dr. Joaquin Barroso Flores, left me a pleasant experience. The great contribution that gives this line of research has allowed me to meet new horizons, beyond the area of engineering, to which I belong.
The theoretical chemistry and computational chemistry together, are a great weapon to develop virtual optimizations that allow us to find drug transport agents, without making the vast amount of laboratory tests that are required. Explaining that this is one of the many applications that can be used.
To undertake this experience has left me very satisfied, be guiding a person who likes his work and want to show what he knows, it makes me very happy. After these long weeks of work and perseverance, with certainty affirm the interesting and productive it is to be part of the investigation in Mexico.
I thank the Dolphin Program, gives CCIQS the UAEM-UNAM and Dr. Joaquin for opening the doors to this great opportunity to start my story as a researcher.

 

Paulina Pintado (Tepic, Nayarit)

la fotoHi my name’s Paulina and I came as part of Dolphin Research Program that gives the opportunity of participates in a real work of investigation with a professional at the topic. In this occasion I came to work with Ph.D. Joaquin Barroso in a small project of his line of research; namely theoretical drug carriers design. In this six weeks besides to learn more aspects about my career, in this case Theoretical Chemistry applied to pharmaceutical industry; I tested the experience of travel to another town just by myself, live with people from different parts of the country with distinct customs and visit few places of the town.
This summer will always be memorable ‘cause this internship is an important event for my professional experience and also for my personal development and I hope many others students have the courage to try get into the world of scientific research.
So just remains for me to thank to Ph.D. Joaquin Barroso for giving me the chance to do this internship in his lab I hope you continue having success in your work, I feel pretty glad to met him and my others research’s mates.

 

 

Daniel Carteño (Mexico City)

Ey my name’s  Daniel and this summer of  2013  i had been the opportunity to do a research  internship in Toluca under P.H.D. Joaquin Barroso, and during this period of time I´ve learnt a bit about His research work, not only this is  an important experience for my educational history, but it also is for my personal life. Learnt about theoretical chemistry open my vision of this discipline, because when I thought about chemistry I´ve never imagine a computational laboratory, this the most important part, nowadays the researches have been removed due to  they are so expensive and finally the conclusion  is not expected, when you use a super computer like me and my work team used, it doesn’t matter if you have a mistake  or do something wrong, only you have to write again the keywords and the only thing you spend is time. Even in Mexico theoretical chemistry is not famous in my opinion is a useful work tool. This research internship was highly satisfactory and hope do it again i´m glad

*Their contributions were completely voluntary and no editing of their original texts has been made.

First graduated student!


Today is truly a landmark in our lab because on this day, María Eugenia “Maru” Sandoval-Salinas has defended her thesis and has thus obtained her B. Sc. in Chemistry. She is the first student under my supervision to achieve this goal, and I hope it won’t be long until we get some more, although now the bar has been set quite high. For the time being, Maru is pursuing a career in the pharmaceutical industry but has every intention of coming back to the lab for her Masters degree; she has a reserved spot here with us at CCIQS.

Hard work pays off - We wait for you to come back for your Masters Degree!

Hard work pays off – We wait for you to come back for your Masters Degree!

Maru’s thesis deals mainly, but not exclusively, with calculating the interaction energies of calix- and thia-calix[n]arenes with the tyrosine kinase inhibitor Imatinib, which is widely used in the treatment of Chronic Myeloid Leukemia (CML), in order to rationally design a drug delivery agent for this drug. Her work is (a huge) part of an article currently under revision that I only wish had been published before her defense. Still, we await for that paper to be published in the next few weeks.

Throughout her stay at our lab, Maru was a dedicated student willing to learn new skills every time. As she replied today to one of the questions: “it’s not so much how many calculations I got right, but how many I got wrong!“. I find deep meaning in this sentence, perhaps deep enough as to consider it an aphorism, because indeed the more we try the more we fail, and the more we fail the more we learn and the closer we get to success.

Congratulations, Maru! I personally thank you for all the hard work invested in your thesis, all the long hours in front of the computer and your disposition to learn and work during the last 1.5 years. I’m certain you’ll find success in any venture you undertake; and I’m certain of it because you never stop trying.

Taking the Oath after being unanimously approved

Taking the Oath after being unanimously approved

Follow

Get every new post delivered to your Inbox.

Join 1,052 other followers

%d bloggers like this: