/var/lib/ureadahead/debugfs And Disk Space “Recovery” In Ubuntu 10.04

And happy new year.

I had thought this was something involving Gaussian09 memory usage until I restarted a machine and found the same problem occurring in Ubuntu. Below is a quick fix (and reminder for the future).

Checking disk space with df -all :

user@machine:~$ df -all
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1            147550696   5863896 134191632   5% /
proc                         0         0         0   -  /proc
none                         0         0         0   -  /sys
none                         0         0         0   -  /sys/fs/fuse/connections
none                         0         0         0   -  /sys/kernel/debug
none                         0         0         0   -  /sys/kernel/security
none                   3053752       260   3053492   1% /dev
none                         0         0         0   -  /dev/pts
none                   3058264         0   3058264   0% /dev/shm
none                   3058264        84   3058180   1% /var/run
none                   3058264         0   3058264   0% /var/lock
none                   3058264         0   3058264   0% /lib/init/rw
none                         0         0         0   -  /var/lib/ureadahead/debugfs
nfsd                         0         0         0   -  /proc/fs/nfsd
binfmt_misc                  0         0         0   -  /proc/sys/fs/binfmt_misc

… we find /var/lib/ureadahead/debugfs both existing but taking up no space to speak of. Several seconds later (after a reboot), we find the following…

user@machine:~$ df -all
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1            147550696   5864268 134191260   5% /
proc                         0         0         0   -  /proc
none                         0         0         0   -  /sys
none                         0         0         0   -  /sys/fs/fuse/connections
none                         0         0         0   -  /sys/kernel/debug
none                         0         0         0   -  /sys/kernel/security
none                   3053752       260   3053492   1% /dev
none                         0         0         0   -  /dev/pts
none                   3058264         0   3058264   0% /dev/shm
none                   3058264        84   3058180   1% /var/run
none                   3058264         0   3058264   0% /var/lock
none                   3058264         0   3058264   0% /lib/init/rw
none                 147550696   5864268 134191260   5% /var/lib/ureadahead/debugfs
nfsd                         0         0         0   -  /proc/fs/nfsd
binfmt_misc                  0         0         0   -  /proc/sys/fs/binfmt_misc

Properly updated machines (as per below) both do not contain this /var/lib/ureadahead/debugfs directory and do not subsequently “blow up” and eat disk space (to date. This may not be the real problem, but disk space usage will increase to +60% and, to my mind, the machine will noticeably slow down).

Fix Steps:

sudo aptitude update
sudo aptitude upgrade

Update your 10.04. Some web pages report that the problem with /var/lib/ureadahead/debugfs is attributable to a bug in mountall (now fixed. See bugs.launchpad.net/ubuntu/+source/mountall/+bug/736512).

sudo mv /etc/init/ureadahead.conf /etc/init/ureadahead.conf.disable

If you do NOT perform this move, the machine restart will produce the same /var/lib/ureadahead/debugfs error above. Kudos to ubuntuguide.net/howto-fix-ureadahead-problem-after-upgrading-to-ubuntu-10-04 for pointing this out.

sudo shutdown -r now

System restart, problem (for me, at least) solved.

The Vibrational Spectrum Of Parabanic Acid By Inelastic Neutron Scattering Spectroscopy And Simulation By Solid-State DFT

Available as an ASAP in The Journal of Physical Chemistry A. As a general rule in computational chemistry, the smaller the molecule, the harder it is to get right. As a brief summary, parabanic acid has several interesting properties of significance to computational chemists as both a model for other systems containing similar sub-structures and as a complicated little molecule in its own right.

1. The solid-state spectrum requires solid-state modeling. This should be of no surprise (see the figure below for the difference in solid-state (top) and isolated-molecule (bottom)). This task was undertaken with both DMol3 and Crystal06, with DMol3 calculations responsible for the majority of the analysis of this system (as has always been the case in the neutron studies reported on this site).

2. The agreement in the hydrogen-bonded N-H…O vibrations is, starting from the crystal structure, in poor agreement with experiment. You’ll note the region between 750 and 900 cm-1 is a little too high (and for clarification, the simulated spectrum is in red below). According to the kitchen sink that Matt threw at the structure, the problem is not the same anharmonicity one would acknowledge by Dr. Walnut’s “catalytic handwaving” approach to spectrum assignment (Dr. Walnut does not engage in this behavior, rather endeavors to find it in others where it should not be).

3. The local geometry of the hydrogen-bonding network in this molecular solid leads to notable changes in parabanic acid structure that, in turn, leads to the different behavior of the N-H…O vibrational motions. There is one potentially inflammatory comment in the Conclusions section that results from this identification. The parabanic acid molecule is, at its sub-structure, a set of three constrained peptide linkages that under go subtle but vibrationally-observable changes to their geometry because of crystal packing and intermolecular hydrogen bond formation. This means that the isolated molecule and solid-state forms are different and that peptide groups are influenced by neighboring interactions.

So, why should one care? Suppose one is parameterizing a biomolecular force field (CHARMM, AMBER, GROMOS, etc.) using bond lengths, bond angles, etc., for the amino acid geometry and vibrational data for some aspect of the force constant analysis. The structural data for these force fields often originates with solid-state studies (diffraction results). This means, to those very concerned with structural accuracy, that a geometry we know to be influenced by solid-state interactions is being used as the basis for molecular dynamics calculations that will NOT be used in their solid-state forms. Coupled with the different spectral properties due to intermolecular interactions, the description being used as the basis for the biomolecular force field likely being used in solution (solvent box approaches) is based on data in a phase where the structure and dynamics are altered from their less conformationally-restricted counterpart (in this case, solid-state).

A subtle point, but that’s where applied theoreticians do some of their best work.

Matthew R. Hudson, Damian G. Allis, and Bruce S. Hudson

Department of Chemistry, 1-014 Center for Science and Technology, Syracuse University, Syracuse, New York 13244-4100

Abstract: The incoherent inelastic neutron scattering spectrum of parabanic acid was measured and simulated using solid-state density functional theory (DFT). This molecule was previously the subject of low-temperature X-ray and neutron diffraction studies. While the simulated spectra from several density functionals account for relative intensities and factor group splitting regardless of functional choice, the hydrogen-bending vibrational energies for the out-of-plane modes are poorly described by all methods. The disagreement between calculated and observed out-of-plane hydrogen bending mode energies is examined along with geometry optimization differences of bond lengths, bond angles, and hydrogen-bonding interactions for different functionals. Neutron diffraction suggests nearly symmetric hydrogen atom positions in the crystalline solid for both heavy-atom and N-H bond distances but different hydrogen-bonding angles. The spectroscopic results suggest a significant factor group splitting for the out-of-plane bending motions associated with the hydrogen atoms (N-H) for both the symmetric and asymmetric bending modes, as is also supported by DFT simulations. The differences between the quality of the crystallographic and spectroscopic simulations by isolated-molecule DFT, cluster-based DFT (that account for only the hydrogen-bonding interactions around a single molecule), and solid-state DFT are considered in detail, with parabanic acid serving as an excellent case study due to its small size and the availability of high-quality structure data. These calculations show that hydrogen bonding results in a change in the bond distances and bond angles of parabanic acid from the free molecule values.

pubs.acs.org/doi/abs/10.1021/jp9114095
pubs.acs.org/journal/jpcafh
en.wikipedia.org/wiki/Computational_chemistry
accelrys.com/products/materials-studio/quantum-and-catalysis-software.html
www.crystal.unito.it
en.wikipedia.org/wiki/Anharmonicity
chemistry.syr.edu/faculty/walnut.html
en.wikipedia.org/wiki/Hydrogen_bond
en.wikipedia.org/wiki/Peptide
en.wikipedia.org/wiki/Force_field_%28chemistry%29
www.charmm.org
ambermd.org
gromacs.org
en.wikipedia.org/wiki/Molecular_dynamics

Exploring the Implications of Vitamin B12 Conjugation to Insulin on Insulin Receptor Binding and Cellular Uptake

In press, in the journal ChemMedChem (and, because I think it’s hip, I note that the current “obligatory” image for the wikipedia article for ChemMedChem features the image I made for the review article on the topic addressed in this new study). As with many theory papers (there’s some experiment in there, too), this very brief article summarizes several months of cyanocobalamin (B12) parameterization and molecular dynamics (MD) simulations. The purpose of the theory was to address all of the major structural snapshots in the uptake process associated with the insulin-B12 bioconjugate being developed as part of the much heralded oral insulin project in Robert Doyle’s group here at Syracuse. These structures include:

1. The structure and dynamic properties of the insulin-B12 bioconjugate
2. The binding of B12 to Transcobalamin II (TCII) (for B12 parameterization)
3. The binding of the insulin-B12 bioconjugate to TCII (and the steric demands therein)
4. The interaction of the insulin-B12 bioconjugate, bound to TCII, with the insulin Receptor (IR)

The quantum chemical (for the B12 geometry and missing force constants) and molecular dynamics (GROMACS with the GROMOS96 (53a6)) simulation work is going to serve as the basis for several posts here (eventually) about parameterization, topology generation, and force field development.

As an example of some of the insights modeling provides, the figure above shows the insulin-B12 bioconjugate (the insulin is divided into A and B chains, the A chain in blue and the important division of the insulin B chain in the front half of the rainbow). Insulin is a rather large-scale example of many of the same molecular issues that arise in the analysis of solid-state molecular crystals by either terahertz or inelastic neutron scattering spectroscopy. The packing of molecules in their crystal lattices can lead to significant changes in molecular geometry, be these changes in the stabilization of higher-energy molecular conformations or even deformations in the covalent framework. In the case of insulin, it is found that the crystal geometry (also the geometry of stored insulin in the body) is quite different from the solution-phase form. It’s even worse! The B chain end (B20-B30) in the solid-state geometry covers (protects?) the business-end of the insulin binding region to the Insulin Receptor. One can imagine the difficulty in proposing the original binding model for insulin to its receptor from the original crystal data given that the actual binding region is blocked off in the solid-state form! The “Extended” form in the figure is representative of “multiple other” conformations of the B20-B30 region (which mimics the characterized T-state of insulin), those geometries for which the insulin binding region (blue and green) is completely exposed. This extended geometry is also the one that separates the bulk of the insulin structure from the covalently-linked B12 (at Lys29) and, it is argued from the MD simulations in the paper, enables the B12 to still tightly bind to TCII despite the presence of all this steric bulk.

Amanda K. Petrus1, Damian G. Allis1, Robert P. Smith2, Timothy J. Fairchild3 and Robert P. Doyle1

1. Department of Chemistry, Syracuse University, Syracuse, NY 13244, USA
2. Department of Construction Management and Wood Products Engineering, SUNY, College of Environmental Science and Forestry, Syracuse, NY 13210, USA
3. Department of Exercise Science, Syracuse University, Syracuse, NY 13244, USA

Extract: We recently reported a vitamin B12 (B12) based insulin conjugate that produced significantly decreased blood glucose levels in diabetic STZ-rat models. The results of this study posed a fundamental question, namely what implications does B12 conjugation have on insulin’s interaction with its receptor? To explore this question we used a combination of molecular dynamics (MD) simulations and immuno-electron microscopy (IEM).

www3.interscience.wiley.com/journal/110485305/home
en.wikipedia.org
en.wikipedia.org/wiki/Chemmedchem
www3.interscience.wiley.com/journal/116323633/abstract
en.wikipedia.org/wiki/Cyanocobalamin
en.wikipedia.org/wiki/Molecular_dynamics
en.wikipedia.org/wiki/Insulin
chemistry.syr.edu/faculty/doyle.html
chemistry.syr.edu/faculty/doyle_group/index.html
www.syr.edu
en.wikipedia.org/wiki/Quantum_chemistry
www.gromacs.org
en.wikipedia.org/wiki/Terahertz
en.wikipedia.org/wiki/Inelastic_neutron_scattering
chemistry.syr.edu
www.syr.edu
www.esf.edu