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Frédéric A. Perras

@fredaperras.bsky.social
167 followers 39 following 95 posts

NMR Spectroscopist. Staff Scientist at Ames National laboratory and Adjunct Associate Professor at Iowa State University. Opinions are my own.

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Frédéric A. Perras @fredaperras.bsky.social · 01/10/2026
Wait, so are you saying that this antique machine is a fraud? www.youtube.com/watch?v=APxE...
youtube.com
The Carbonaro Effect - Antique Chest With Modern Flair
YouTube video by truTV
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Amrit Venkatesh @amrit-venkatesh.bsky.social · 22/09/2026
Please repost. NMR/EPR/DNP colleagues: we are searching for a postdoc to join our group to develop dynamic nuclear polarization NMR. Please see the ad below, and I would be grateful if you could share it with interested candidates. #NMRchat #EPRchat #chemsky
uva.wd1.myworkdayjobs.com
Research Associate in Chemistry
The Venkatesh research group in the Department of Chemistry at the University of Virginia (UVA) invites applications for a Postdoctoral Research Associate to develop dynamic nuclear polarization (DNP)-enhanced NMR methodologies. The successful candidate will develop and implement new DNP-enhanced NMR methods and apply them to materials characterization; publish research findings in peer-reviewed journals and present results at scientific conferences; mentor graduate and undergraduate researchers; and contribute to collaborative research efforts within and beyond UVA. The postdoctoral researcher will help define and pursue new research directions in DNP, with opportunities to develop independent ideas, initiate collaborations, and contribute to the growth of an emerging DNP research program. Research Environment The group has access to a comprehensive suite of magnetic resonance instrumentation and characterization facilities, including: A 400 MHz MAS-DNP spectrometer equipped with 1.3 HX and 3.2 mm HXY DNP probes A 600 MHz solid-state NMR spectrometer equipped with 1.3 HX, 2.5 mm HFXY, and 5.0 mm MAS and static HX probes X-band benchtop EPR spectrometer In addition, the group has access to solution-state NMR, pulsed electron paramagnetic resonance, X-ray and microscopy facilities and high-performance computing resources at UVA. The group fosters a collaborative and supportive research environment, with opportunities to lead interdisciplinary collaborations, mentor trainees, and collaborate with internationally recognized research groups and industries. Qualifications Required: PhD in Chemistry, Chemical Engineering, Materials Science, or a related field by the start date with a strong background in NMR spectroscopy, and demonstrated ability to conduct independent scientific research. Preferred: Experience with DNP-enhanced NMR, hyperpolarization methods, advanced solid-state NMR or EPR spectroscopy. Record of peer-reviewed publications and scientific presentations. Ability to work independently and effectively in a collaborative research environment. Interest in mentoring graduate and undergraduate researchers. Application Procedure: Apply online at https://jobs.virginia.edu/us and search for position number R0087636. Submit (1) a 1-2 page cover letter describing your experience relevant to this position, and your past and future research interests, (2) curriculum vitae with a complete list of publications, and (3) contact information for three individuals who can provide professional reference letters. Application deadline: Review of applications will begin on October 3, 2026, but the position will remain open until filled. The University will perform background checks on all new hires prior to employment. The anticipated salary is $60,000 - $65,000, commensurate with experience. This is a one-year appointment; however, the appointment may be renewed for an additional year contingent upon available funding and satisfactory performance. For questions regarding this position, please contact Amrit Venkatesh, Assistant Professor, at amrit.venkatesh@virginia.edu. For questions about the application process, please contact Rich Haverstrom, Academic Recruiter, at rkh6j@virginia.edu For more information on the benefits available to postdoctoral associates at UVA, visit postdoc.virginia.edu and hr.virginia.edu/benefits. More information about Charlottesville as a place to live can be found on the UVA HR website. The University of Virginia is an equal opportunity employer. All interested persons are encouraged to apply, including veterans and individuals with disabilities. Learn more about UVA’s commitment to non-discrimination and equal opportunity employment. PLEASE READ: The job postings for this page have been moved to a new location. Please visit the UVA Careers Websites to navigate to the appropriate site, or click UVA Careers in the upper right corner of this page to view open positions. If have already applied and need to log in to your existing Workday account, please click Sign In in the upper right corner of this page. Please do not sign in until you have visited and applied through a UVA Careers website.
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Frédéric A. Perras @fredaperras.bsky.social · 21/09/2026
A fun short paper where we compare different saturation pulses used in RESPDOR distance measurements using cross-peaks in an EXSY J multiplet. doi.org/10.1016/j.jm...
doi.org
Redirecting
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Frédéric A. Perras @fredaperras.bsky.social · 14/09/2026
To me, the result we found in this work was truly shocking. @carlfleischer.bsky.social was able to improve the performance of dipolar recoupling used in S-REDOR/S-RESPDOR by a factor of 5 over the status quo SR4 sequence!!! This means a near doubling of the distance scale! doi.org/10.1039/D6CP...
doi.org
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Frédéric A. Perras @fredaperras.bsky.social · 17/08/2026
Félicitations!
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Frédéric A. Perras @fredaperras.bsky.social · 30/07/2026
I don't disagree. In most instances relaxation delay is a suitable term, but it cannot be used as a blanket term for 'd1' as there are edge cases where calling it such is inappropriate. Recycle delay is simply a more general term applicable to all pulse sequences with such a delay.
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Frédéric A. Perras @fredaperras.bsky.social · 30/07/2026
Brilliant counterpoint. In that case, calling it a delay of any kind would not be accurate though and I would argue against recovery delay, relaxation delay, and recycle delay. Probably calling it recovery period would be better.
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Frédéric A. Perras @fredaperras.bsky.social · 29/07/2026
A sequence like SOFAST-HMQC is another example of a scenario where recovery delay is inappropriate whereas recycle delay is not.
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Frédéric A. Perras @fredaperras.bsky.social · 29/07/2026
I do not disagree but we can be more pedantic. In a saturation recovery experiment there is d1 (the recycle delay inserted to avoid high duty cycles) and a separate recovery delay that is not d1. In this sequence the recycle delay is not used for magnetization recovery, purely for cycling.
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Frédéric A. Perras @fredaperras.bsky.social · 29/07/2026
I would say that this is an error in the textboo, given that the time between successive repetitions is objectively not a delay.
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Frédéric A. Perras @fredaperras.bsky.social · 28/07/2026
The recycle delay is a delay needed to complete the cycle but it is not the duration of the entire cycle. This would be more accurately described as a cycle duration. The mere fact that we use the word "delay" implies that it is not the entire cycle.
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Frédéric A. Perras @fredaperras.bsky.social · 28/07/2026
Recovery delay has its own issues since most NMR experiments are not performed on a fully relaxed sample. I would view the time required for a signal to recover (recovery delay) to be 5*T1. But, most experiments will use zg30 to use a shorter recycle delay or use the optimal value of 1.3*T1
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Frédéric A. Perras @fredaperras.bsky.social · 21/07/2026
Check out this new paper by @carlfleischer.bsky.social in @jacs.acspublications.org where he used dipolar dephasing methods to determine the surface reconstructions of perovskite nanocrystals. doi.org/10.1021/jacs... In collaboration with Ken Poeppelmeier and Wenyu Huang's groups
doi.org
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Frédéric A. Perras @fredaperras.bsky.social · 19/05/2026
We discovered that placing metal complexes in zeolites leads to forces being exerted on their ligands which in turn promotes ligand dissociation and the formation of under coordinated sites. (cool 2H VT SSNMR) doi.org/10.1039/D6CC...
doi.org
Labilized Ligands Under Ultra-Confinement: A Solid-State 2H NMR Investigation of Ln(BH4)2(THF)2/HY30
Variable-temperature 2H NMR reveals that the THF ligands are highly labile in Ln(BH4)2(THF)2/HY30, undergoing exchange between Ln sites under confinement via low-coordinate intermediates. Potency in c...
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Frédéric A. Perras @fredaperras.bsky.social · 13/05/2026
Don't leave us hanging! What is it?
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Frédéric A. Perras @fredaperras.bsky.social · 29/04/2026
TBF, if you are growing onions, an onion hoe would be ideal.
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Magnetic Resonance News @nmr900.bsky.social · 28/04/2026
New equipment expands DNP-NMR research capabilities at Ames Lab www.ameslab.gov/news/new-equ... #NMRchat 🧲
New equipment expands DNP-NMR research capabilities at Ames Lab
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Damien Culver @damien-culver.bsky.social · 17/04/2026
I’m excited to share our latest research now published in @jacs.acspublications.org! A huge thank you to the entire @amesnatlab.bsky.social team, for their hard work, and a special shoutout to my co-corresponding author, Long Qi, for his invaluable partnership. pubs.acs.org/doi/10.1021/...
pubs.acs.org
Group 4 Metallocenes Supported on Sulfated Zirconium Oxide Catalyze Benzene C–H Borylation
C–H bond functionalization of arenes with boranes continues to be a challenge in catalysis, with late transition and rare earth metals shown to be catalytically active. In this study, group 4 metallocenes grafted onto acidic sulfated zirconia (SZO) are demonstrated to catalyze arene borylation with pinacolborane (HBpin). Catalysis studies at partial HBpin conversions (59–68%) using Cp2M(Me)/SZO (M = Ti, Zr, or Hf; Cp = cyclopentadienyl) catalysts reveal that Zr exhibits greater selectivity and activity than Ti and Hf. At 0.16 mol % of Zr, Cp2ZrMe/SZO achieves 332 turnovers at high HBpin conversion (86%), making this catalyst comparably active to previously reported Ir and Rh C–H borylation catalysts. At 160 °C, a maximum chemoselectivity of 82% for PhBpin was observed at 24% HBpin conversion. The superior activity of ionic Cp2ZrMe/SZO compared to neutral Cp2ZrMe/SiO2 demonstrates the borylation mechanism relies on the highly electrophilic, coordinatively unsaturated cationic sites stabilized by the weakly coordinating sulfated support. Furthermore, both catalysts significantly outperform their molecular analogues, Cp2ZrMe2 and [Cp2ZrMe][B(C6F5)4], suggesting that the support enhances catalytic performance by stabilizing the active species.
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Frédéric A. Perras @fredaperras.bsky.social · 17/04/2026
To clarify in the pulse programming manual it states the following which suggests power is scaled. I suggest the manual be updated to clarify the language:
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Frédéric A. Perras @fredaperras.bsky.social · 17/04/2026
Thank you. The manual is somewhat ambiguous on the matter and seems to suggest power. So I panicked for a moment that all shapes generated by the shapetool were wrong. Glad that they are not.
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Frédéric A. Perras @fredaperras.bsky.social · 16/04/2026
Thank you Clemens. Just to clarify, it is the value in Watts that is scaled, not the rf amplitude? So if you have a value of 25% in the file, the radiofrequency amplitude will only be reduced to 50%?
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Frédéric A. Perras @fredaperras.bsky.social · 16/04/2026
Does anyone know is the amplitude values in Bruker shaped pulse files are scaling the power (Watts) being applied, or the radiofrequency amplitudes? Documentation is vague but hints that it is the power, however, Bruker-generated shapes, like DFS, clearly modulate the radiofrequency amplitude.
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Frédéric A. Perras @fredaperras.bsky.social · 06/03/2026
I kid you not, I just gave copilot a screenshot of a Hamiltonian matrix and it immediately identified what it was and where I had made a mistake in my code. First time this thing has done something useful for me.
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Frédéric A. Perras @fredaperras.bsky.social · 23/02/2026
I don't think they are particularly common here either. We have a very nice local bike shop here and I went with the intention of buying a fatbike for the winter and the owner talked me out of it and told me to just get winter tires instead. Great guy.
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Frédéric A. Perras @fredaperras.bsky.social · 20/02/2026
I have winter tires on my bike. They have metal studs and a softer rubber compound to maintain traction on snow and ice. I never feel like I am slipping.
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Frédéric A. Perras @fredaperras.bsky.social · 20/02/2026
First tracks
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Damien Culver @damien-culver.bsky.social · 16/02/2026
Our first publication of 2026 is available now! In this study, we introduce a new family of hybrid materials designed to support Pt(0) complexes for regioselective hydrosilylation catalysis. Link: pubs.acs.org/doi/10.1021/...
pubs.acs.org
Regioselective Hydrosilylation Catalysis with Supported Well-Defined Pt(0) Complexes: Effects of Surface Anions and Phosphenium Ligands
Achieving stable, selective single-atom catalysts is challenging because localsurface-site structures are difficult to control. Surface organometallic chemistry and organic–inorganic hybrid materials ...
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Damien Culver @damien-culver.bsky.social · 15/02/2026
We are hiring a postdoc to join our team at @amesnatlab.bsky.social! If interested apply here: isu.wd1.myworkdayjobs.com/en-US/IowaSt...
isu.wd1.myworkdayjobs.com
Postdoctoral Research Associate - Ames National Laboratory
Position Title: Postdoctoral Research Associate - Ames National Laboratory Appointment Type: Post Doc/Trainee Job Description: Summary of Duties and Responsibilities: As a U. S. Department of Energy (...
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Frédéric A. Perras @fredaperras.bsky.social · 02/02/2026
Counterintuitively, here your peak shifts upfield as the magnetic field decreases. We should really avoid using these terms as they are evidently confusing and obviously antiquated.
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Frédéric A. Perras @fredaperras.bsky.social · 30/01/2026
I sent you an email.
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Frédéric A. Perras @fredaperras.bsky.social · 29/01/2026
In undergrad the University of Ottawa offered a scientific communication class for chemistry students. It covered how to read, organize, and write a scientific paper, what not to do, and how to communicate in general. It was fantastic. Dave had provided some NMR examples of particularly bad writing.
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Make Money - Do Magnets @sararah.bsky.social · 05/12/2025
Iowa State Dept of Molecular Biology is hiring for biomolecular solution NMR facility staff #NMRchat #Chemjobs #Chemsky (I am NOT the hiring manager for this position, but I will refer any questions you have to the appropriate person.) isu.wd1.myworkdayjobs.com/IowaStateJob...
isu.wd1.myworkdayjobs.com
Biomolecular NMR Facility Manager
Position Title: Biomolecular NMR Facility Manager Job Group: Professional & Scientific Required Minimum Qualifications: Bachelor’s degree and 5 years of related experience Preferred Qualifications...
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Frédéric A. Perras @fredaperras.bsky.social · 14/11/2025
Josef Zwanziger, @aaronrossini.bsky.social, and I published a rebuttal of a recent Nature Commun. paper claiming that enantiomers produce large differences in J coupling constants. doi.org/10.1038/s414...
doi.org
DFT calculations and theory do not support enantiospecificity in NMR J-coupling constants - Nature Communications
Nature Communications - DFT calculations and theory do not support enantiospecificity in NMR J-coupling constants
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Frédéric A. Perras @fredaperras.bsky.social · 13/11/2025
Apparently, there is a company using DNP (yes, specifically DNP-NMR) for.... propulsion in warp drives? www.falconspace.org
falconspace.org
Falcon Space - Advanced Propulsion Research & Development
Falcon Space is working to make the dream of advanced propulsion a reality through innovative experiments and UAP Reverse-Engineering.
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Frédéric A. Perras @fredaperras.bsky.social · 31/10/2025
Those fits to the CP build-up curves are incredible. Very nice.
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Frédéric A. Perras @fredaperras.bsky.social · 08/10/2025
Crazy event. Here is another article that is not pay-walled: www.voxweb.nl/en/lab-direc...
voxweb.nl
Lab director on building occupation: ‘Protesters are in mortal danger’ - Vox magazine
The occupation of the Goudsmitpaviljoen could be life-threatening, warns lab director Arno Kentgens. He urges the campaigners to allow technicians access at all times. ‘The protesters could suffocate ...
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Frédéric A. Perras @fredaperras.bsky.social · 25/09/2025
We prepared a 17O-enriched boron monoxide material which allowed us to gain a greater clarity on the long-range structure of the material. Data seems to point at BO being a 1D polymer. Same structure as initially proposed in 1955. doi.org/10.1039/D5CC...
doi.org
Boron Monoxide is a One-Dimensional Polymer
It was recently reported that boron monoxide (BO) is formed through the cross-linking of B4O2 structural building units. Multiple theoretical phases agree with this description. Using pycnometry, mult...
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Frédéric A. Perras @fredaperras.bsky.social · 23/09/2025
Sorry to hear that. I hope you get better soon.
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Frédéric A. Perras @fredaperras.bsky.social · 22/09/2025
I will die on this hill; lacquer is the superior finish. Spray on, always perfect, ready to recoat basically after you are done spraying the last one.
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The Amsterdam Modeling Suite (SCM) @ams-software.bsky.social · 19/09/2025
DFT calculations with the ADF program can now 𝗽𝗿𝗲𝗱𝗶𝗰𝘁 𝘁𝗵𝗲 𝗢𝘃𝗲𝗿𝗵𝗮𝘂𝘀𝗲𝗿 𝗲𝗳𝗳𝗲𝗰𝘁 𝗶𝗻 𝗗𝗡𝗣 𝗿𝗮𝗱𝗶𝗰𝗮𝗹𝘀. Computed hyperfine couplings and rotation barriers match experiments, showing computational chemistry can guide radical design before synthesis. zurl.co/7iJHH #matsky #compchemsky
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Frédéric A. Perras @fredaperras.bsky.social · 12/09/2025
Can you use DNP-enhanced 1H-17O D-RINEPT build-up curves to measure more or less "free" geometrical information in grafted metal complexes? doi.org/10.1021/acs.... (Yes!)
doi.org
Determining the Conformation of Supported Complexes Using an 17O TEDOR-like NMR Experiment
Dynamic nuclear polarization surface-enhanced nuclear magnetic resonance (NMR) spectroscopy has enabled the determination of the three-dimensional configuration of surface sites, in particular supported metal complexes of relevance to single-site heterogeneous catalysis. These approaches have chiefly leveraged the application of NMR double-resonance experiments that either reveal the complex conformation via point-to-point intramolecular distances between spin-labeled atoms or the complex-surface orientation via distances between the spins and the surface plane. Either method typically requires expensive isotope labeling and each reports on different structural features. The application of an experiment that simultaneously reveals both types of distances with chemical resolution would be ideal. In this article, we describe an 17O{1H} pseudo-3D correlation experiment that achieves this goal. Specifically, Si–O–Si and Si–O–M oxygens are well-resolved by 17O NMR; therefore, distances can be simultaneously measured radially, between Si–17O–M and the 1H’s of the ligands, and vertically to the Si–17O–Si linkages of the silica support. We demonstrate the experiment using supported yttrium and zirconium complexes. Good agreement is obtained when comparing the experimental results to theoretical predictions from density functional theory calculations, highlighting the reliability of this relatively simple experiment.
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Frédéric A. Perras @fredaperras.bsky.social · 05/09/2025
For the second point, Ln(III) cations are largely chemically identical. Their f orbitals behave as core orbitals and do not participate in bonding. So while the total spin and orbital angular momentum will change, the bonding and spin density functions should be close to the same.
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Frédéric A. Perras @fredaperras.bsky.social · 05/09/2025
I am about as far from being an expert as there is, but regarding point 1, the Fermi contact interaction required spin density exactly on the nucleus. So it basically measures the amount of of the spin density function that is made up of that atom's s orbitals.
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Frédéric A. Perras @fredaperras.bsky.social · 02/09/2025
When performing spin dynamics simulations under MAS, it is necessary to do 3-angle averaging. Conventionally this is done with 2-angle averaging and a gamma-carousel average. We show that this convention should be avoided in favor of proper integrated 3-angle averaging. doi.org/10.1016/j.jm...
doi.org
Redirecting
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Frédéric A. Perras @fredaperras.bsky.social · 28/08/2025
Love it!
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Frédéric A. Perras @fredaperras.bsky.social · 20/08/2025
I am saddened and shocked to hear of the passing of Jean-Nicholas Dumez. I admired his work, and used it as inspiration for much of the work I am most proud of. The NMR community has lost one of its best young scientists.
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Frédéric A. Perras @fredaperras.bsky.social · 20/08/2025
Twitter used to be nice, and then most of the posts I was seeing were promoted posts and ads. When I quit "X" and created a bluesky account it was such a breath of fresh air and quite reminiscent of what Twitter was like when I decided to join to find and promote papers.
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Frédéric A. Perras @fredaperras.bsky.social · 08/08/2025
I have not tried it but these stores I read make me wonder why Bruker goes out of their way to avoid using Redhat. Redhat costs about the same as windows. On an instrument that typically costs over $1M... Agilent would just give you a Redhat workstation.
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Frédéric A. Perras @fredaperras.bsky.social · 31/07/2025
New nuclear quadrupole moments just dropped for 7Li and 27Al. The 7Li one is actually significantly different from the previous estimation. The 27Al one seems to instead simply include more significant figures. doi.org/10.1021/acs....
doi.org
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Frédéric A. Perras @fredaperras.bsky.social · 22/07/2025
Work led by Megan Fieser led to the first synthesis of PE-PVC block copolymers. Crazy that it took so long to make block copolymers of two of the top 3 plastics. It is an interesting read if you simply want to find out why it was such a challenge (and how it was done). doi.org/10.1021/jacs...
doi.org
Synthesis and Properties of Poly(vinyl chloride)-b-polyethylene Multiblock Copolymers through the Hydrodechlorination of PVC with Silylium Ions
Block copolymers of polyethylene (PE) and polyvinyl chloride (PVC) have remained elusive materials despite PE and PVC being the first and third most produced polymers globally, respectfully. The closest material is chlorinated polyethylene (CPE), which is commonly used as a compatibilizer and is synthesized by functionalizing PE. However, there does not exist a synthetic pathway either from monomers or via the functionalization of PE to yield a polymer that has a controlled chlorine amount and primary structure along the polymer chain. Herein, we report a series of novel block copolymers of PVC and PE, synthesized through selective hydrodechlorination of PVC. Contrary to CPE, the full range of chlorination can be obtained, and the block number can be altered. Interfacial adhesion studies reveal samples with competitive compatibilization of PVC/polyolefin elastomer (POE) blends. This method shows that postpolymerization modification can be a strategic top-down synthesis to achieve high-performance polymers that cannot be synthesized via conventional polymerization pathways.
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