Free Astronomy Magazine – January-February 2019 Issue Available For Reading And Download

Above: This illustration shows what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credit: SETI Institute.

Slightly late to the posting game – the January-February issue of Free Astronomy Magazine is available for your reading and downloading pleasure. Highlights from the original content (h/t Michele Ferrara) include an excellent introduction to panspermia and the wonderful ways in which small, dense solar systems (like TRAPPIST-1, one of the only solar systems with its own website – www.trappist.one) might serve as test beds for better understanding if such an explanation is applicable to ourselves and our Earth – either from a local source (Mars?) or from the greater beyond.

Please download, read, and pass along. Also, check out the many back issues at www.astropublishing.com

astropublishing.com/1FAM2019/ | Direct PDF

Click the Table of Contents image below for a full-size view.

Evaluating The Friction Of Rotary Joints In Molecular Machines

Howard Lovy’s name came across my calendar (happy birthday!) and Josh Hall published a fresh post to “Where is my Flying Car?” – seems like a perfect time to post an everything-new-is-still-new-for-the-first-time-type update.

Published way back in 2017 in Molecular Systems Design & Engineering; reportedly one of the most-read Q3 2017 articles to boot. Also my first foray into arxiv territory for those limited in their journal access (arxiv.org/abs/1701.08202).

Tad Hogg*a Matthew S. Moses*b and Damian G. Allis*c

a. Institute for Molecular Manufacturing, Palo Alto, USA
b. Independent Consultant, Lafayette, USA
c. Department of Chemistry, Syracuse University, Syracuse, USA

Abstract: A computationally-efficient method for evaluating friction in molecular rotary bearings is presented. This method estimates drag from fluctuations in molecular dynamics simulations via the fluctuation–dissipation theorem. This is effective even for simulation times short compared to a bearing’s energy damping time and for rotation speeds comparable to or below typical thermal values. We apply this method to two molecular rotary bearings of similar size at 300 K: previously studied nested (9,9)/(14,14) double-walled carbon nanotubes and a hypothetical rotary joint consisting of single acetylenic bonds in a rigid diamondoid housing. The acetylenic joint has a rotational frictional drag coefficient of 2 × 10^-35 kg m2 s^-1. The friction for the nested nanotubes is 120 times larger, comparable to values reported by previous studies. This fluctuation-based method could evaluate dissipation in a variety of molecular systems with similarly rigid and symmetric bearings.

Mol. Syst. Des. Eng., 2017, 2, 235-252 (10.1039/C7ME00021A, direct link)

Solution Structure And Constrained Molecular Dynamics Study Of Vitamin B12 Conjugates Of The Anorectic Peptide PYY(3-36)

#50, published in ChemMedChem (11 (2016), 9, 1015-1020), DOI:cmdc.201600073.

The key to molecular dynamics simulations is recycling – specifically, going into a first project with enough organization to know how to use everything in the next study. While that first successful connectivity table, parameter assignment, and RESP charge generation for something as Frankenstein-esque as vitamin B12 is the north face of Everest, that next simulation is simply a matter of having atom codes in your PDB file standardized.

And, speaking of PDBs, article #50 has the added bonus of having its own entry in the Protein Databank as 2NA5 – quite a treat (to me, anyway).

And furthermore, this is the first of my publications to benefit from the Research Computing infrastructure on the Syracuse University campus – the throughput of calculations for future work is completely unprecedented in my history of resource access anywhere (the drop in storage prices is very real to some of us).

2016oct5_fig_4_b12_pyy_front_v2

Authors: Henry K.E., Kerwood D.J., Allis D.G., Workinger J.L., Bonaccorso R.L., Holz G.G., Roth C.L., Zubieta J., and Doyle R.P.

Abstract: Vitamin B12-peptide conjugates have considerable therapeutic potential through improved pharmacokinetic and/or pharmacodynamic properties imparted on the peptide upon covalent attachment to vitamin B12 (B12). There remains a lack of structural studies investigating the effects of B12 conjugation on peptide secondary structure. Determining the solution structure of a B12-peptide conjugate or conjugates and measuring functions of the conjugate(s) at the target peptide receptor may offer considerable insight concerning the future design of fully optimized conjugates. This methodology is especially useful in tandem with constrained molecular dynamics (MD) studies, such that predictions may be made about conjugates not yet synthesized. Focusing on two B12 conjugates of the anorectic peptide PYY(3-36), one of which was previously demonstrated to have improved food intake reduction compared with PYY(3-36), we performed NMR structural analyses and used the information to conduct MD simulations. The study provides rare structural insight into vitamin B12 conjugates and validates the fact that B12 can be conjugated to a peptide without markedly affecting peptide secondary structure.