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

Elements4D – Exploring Chemistry with Augmented Reality


joaquinbarroso:

A bit outside the scope of this blog (maybe), but just too cool to overlook. Augmented reality in chemistry education.

Originally posted on :

This is a guest post from Samantha Morra of EdTechTeacher.org, an advertiser on FreeTech4Teachers.com. 

Augmented Reality (AR) blurs the line between the physical and digital world. Using cues or triggers, apps and websites can “augment” the physical experience with digital content such as audio, video and simulations. There are many benefits to using AR in education such as giving students opportunities to interact with items in ways that spark inquiry, experimentation, and creativity. There are a quite a few apps and sites working on AR and its application in education.

Elements4D, an AR app from Daqri, allows students explore chemical elements in a fun way while learning about real-life chemistry. To get started, download Elements4D and print the cubes.

There are 6 physical paper cubes printed with different symbols from the periodic table. It takes a while to cut out and put together the cubes, but it…

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Nice Energy Level Diagrams with rxnlvl


joaquinbarroso:

Once again our friend at Eutactic has provided us with a way to create nice energy level diagrams and was kind enough to let me reblog his post. If you haven’t checked his blog please do so and encourage him to write more often.
This post is best served with: http://joaquinbarroso.com/2012/06/13/1027/

Originally posted on eutactic:

I have written a bit of code lately which automates the process of constructing chemical reaction energy level diagrams rather well. It’s called rxnlvl. It’s written in Python, outputs to SVG (Scalable Vector Graphics) and is GPL3. I’m not a ninja programmer by any stretch of the imagination, however the program is basically functional, and in my estimation yields quite attractive results.

ImageYou can check it out at https://github.com/eutactic/rxnlvl

Enjoy, and if you find it useful I encourage you to show me what you’ve done with it.

 

Regards,

    -r

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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.

Goodbye 2013, welcome 2014!


Another year is almost done and as I write my annual report I realize this year has had several milestones for me as a researcher, most of which got recorded in this blog.

I published three papers in peer reviewed journals, one of which actually made the cover of J. Inclusion Phenomena, the other two were published in J. Phys. Chem. C and Eur. J. Inorg. Chem.; two more papers are currently under the reviewing process, one of which is further down the line in a journal whose title I dare not speak for fear of jinxing it! A small article on computational chemistry basics, entitled “Chemistry without Flasks” for a magazine edited by the National Council for Research and Technology (CONACyT) was also published early this year; during the summer we had the visit of quite a few internship students who got gather some data despite my absence; my more regular students, Maru and Howard presented one poster each at the National Congress of Chemistry organized by the Mexican Chemical Society, and Howard also presented another poster at the Mexican Reunion of Theoretical Physical Chemistry; Maru wrote and defended her thesis in May, which makes her the first student ever to graduate from my research group; I participated once again as a juror of the Mexican Science and Engineering Fair;  and last but not least I got a promotion at the National System of Researchers (SNI).

New immediate challenges lie ahead and I shall face them rationally and passionately.

These are small accomplishments for larger research groups, I know, but I’m truly happy to see how our combined efforts, along with the support of the National Autonomous University of Mexico and the Institute of Chemistry, are slowly paying off! One can only hope the growth curve is not linear but exponential.

Thanks to every reader who has interacted with me through this blog; thanks for your comments, ratings, sharing and ‘likes’. May you all have a happy holiday season, winter break or New Year party, whatever it is you get to do these days!

Joaquín

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
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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

Negotiations gone wrong and other recent scandals


About a month ago my wife and I got invited by our good friend Dr. Ruperto Fernandez (his PhD is in transport logistics and engineering) to his final presentation for a course in managerial skills he’d taken for over six months, and while I wasn’t all that thrilled about waking up at 8 AM on a Saturday, I went to cheer my good friend and show him my sleepy support. His presentation dealt with negotiations and the required skills to master them, and while he agreed that there is a huge amount of talent involved in being a good negotiator, he also pointed out that some basic knowledge of the procedure can go a long way in helping us with little to no talent in achieving the best possible outcome. Basically, a negotiation involves the agreement between a person with something which another person wants; meeting both parties expectations at the fullest extent possible is the ideal endpoint for an iterative give-and-take between them. Or so it goes.

Recently a scandal that involved the biology freelance blogger DNLee, who blogs for Scientific American with the column The Urban Scientist. DNLee was asked by Biology-Online.org to write for them. Then the negotiation started; she had something the editors wanted: her texts. She agreed to do it and waived her fee (second part of the negotiation process: “I got what you want and here is what I ask in return for it“), instead of having an offer made (third part of the negotiation process: “ok, that is what you want but this is what I can give you“) the blogger got a nasty message, which I believe maybe was intended to elicit a response to better accommodate the editor’s demands but that was nothing more than a plain nasty insult: The editor asked if she was the urban scientist or the urban whore (end of negotiation; nobody got anything. Furthermore, feelings were hurt, reputations questioned and the door for future negotiations between both parties was shut completely). If the editor was unable to pay any fee at all then the editor should have tried to convince the blogger of participating for free; I would have offered her a bigger space than a regular blogger, or maybe even invited her to participate as an editor. I’m not sure they have some sort of business model but something could have been arranged. Had this negotiation not met at any point in the middle then a polite thank you could have left the door open for a future time. DNLee has a reputation that allows her to waive her fee, had it been me, I’d probably had done it for free but because I need more exposure than her who is already famous. Internet support came promptly and hard as can be seen here and here, not that it wasn’t called for, of course!

But the issue, sadly, didn’t end there, DNLee wrote about this in her blog at SciAm, but the post was later on deleted by the editors. Dr. Mariette DiChristina tweeted that the post wasn’t related to science so it didn’t fit in the site. Pressure in blogs and other social networks prompted SciAm to place the article back on the site. Click here to go to the post.

Calling someone a whore is simply unacceptable.

During his presentation, my friend Dr. Ruperto Fernandez, talked about a negotiation he had with a potential employer. According to his account of the process, it ended quite swiftly when he was offered a much lower salary than the one he currently earns. He said the offer had some good points that could have made him accept even 5 to 10% less income respect to his current salary, but much less than that would not help him cover the bills and that was a total deal-breaker. But the talk didn’t end there, some other joint projects were laid for them to work on together and the door is still open for the future when they may be able to match my friend’s expectations as biology-online should have done with DNLee.

It has been a rough couple of weeks for the Scientific American community; first this and now the leaving of a great science writer, Bora Zivcovic whose misconduct has forced his exit out of the popular magazine. So now the aftermath for both issues remains to be seen. Sexism, though could be found to be a common denominator in both cases: one was a victim of it, the other one is guilty of inflicting it through various instances of sexual harassment. Should this mean that biology-online, Bora Zivcovic and the affiliated-to-the-two-previous parties, the Scientific American Magazine, are to be deemed as unworthy? I hardly think so. None of us is close to sanctity and we all make mistakes, some of them willingly and other unwillingly but we are accountable for each and every one of them but we should also be able to separate both sides of each story and keep the best of each side while keeping a close eye (and even a loud mouth) about the wrong in each side.

I wish nothing but the best to every person involved in any of these recent events. Why is it so hard for people to just ‘play nice‘? I’ve heard many times this world would be a better place if we cared more for each other, but sometimes it seems that its actually the opposite; that this world would be be better if we didn’t care so much: if we didn’t care about the color of our skin; our gender; our nationality or ethnicity; our sexual orientation; our social status. This brings me back yet again to that presentation by Dr. Fernandez, where he was asked to describe the way he was perceived by others at his workplace and he said he didn’t quite enjoy social interactions so he is perceived as serious and aloof but was always willing to join a new project, so when reached out for one of these he’s all smiles and work. Shouldn’t we all back off a little bit from each other from time to time?

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!)

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