Chemical Science Blog

A new class of MRI (magnetic resonance imaging) contrast agents developed by scientists in the UK is promising to deliver clearer images in less time. ‘In any NMR experiment you are chasing sensitivity. We have enhanced the intrinsic ability to observe an MRI probe signal by a factor of 20,’ explains David Parker of Durham University who led the study. 

MRI is used in clinical settings to image the inside of the body. It uses strong magnetic fields and radio waves to probe the behaviour of nuclei that possess nuclear spin. Chemical shifts from proton NMR normally fall between 0–12ppm but water and fat resonate at 4.7 and 1.3ppm, respectively, and can overlap with MRI probe signals. Parker’s new probes shunt the spectral window of MRI scans well away from these interfering signals, a concept he describes as ‘moving the goalposts’. The probes consist of lanthanide complexes with a t-butyl group and the distance between the lanthanide and t-butyl group was fixed to optimise the rate of decay of the t-butyl signal as well as move its chemical shift. Data acquisition was possible just a few minutes after administering the probe and the signal from the lanthanide induced relaxation of the nine protons in the t-butyl groups has been shifted by up to 80ppm. 

Proton NMR spectra showing the shifted t-butyl resonances in some of the new dysprosium and thulium complexes

  Read the full article in Chemistry World»

Read the original journal article in Chemical Science:
Moving the goal posts: enhancing the sensitivity of PARASHIFT proton magnetic resonance imaging and spectroscopy
Peter Harvey, Andrew M. Blamire, J. Ian Wilson, Katie-Louise N. A. Finney, Alexander M. Funk, P. Kanthi Senanayake and David Parker  
Chem. Sci., 2013,4, 4251-4258, DOI: 10.1039/C3SC51526E

Scientists from Japan have harvested light energy using an exceptionally large number of light absorbers to relay photons via antennas into one final energy acceptor. This two-step sequence closely mimics natural photosynthesis, resulting in greater and more efficient energy transfer.

Previously, researchers had only used one-step light harvesting systems, greatly limiting the number of absorbers able to feed light into a single reaction centre. Now, by imitating photosynthetic systems, Osamu Ishitani at the Tokyo Institute of Technology, Shinji Inagaki at the Toyota Central R&D labs and their co-workers have efficiently harvested light using the highest number of artificial leaves to date.

Read the full article in Chemistry World»

Read the original journal article in Chemical Science:
Efficient Light Harvesting via Sequential Two-Step Energy Accumulation Using a Ru–Re5 Multinuclear Complex Incorporated into Periodic Mesoporous Organosilica
Yohei Yamamoto, Hiroyuki Takeda, Tatsuto Yui, Kotaro Ueda, Kazuhide Koike, Shinji Inagaki and Osamu Ishitani 
Chem. Sci., 2013, Accepted Manuscript, DOI: 10.1039/C3SC51959G

Ligation of anti-cancer drugs to self-assembling ultrashort peptides by click chemistry for localized therapy
Michael R Reithofer, Kiat-Hwa Chan, Anupama Lakshmanan, Dang Hoang Lam, Archana Mishra, Began Gopalan, Mangesh Joshi, Shu Wang and Charlotte A. E. Hauser
Chem. Sci., 2013, Accepted Manuscript
DOI: 10.1039/C3SC51930A, Edge Article

Free to access until 1st December 2013

Inaccessibility of the μ-hydride species in [FeFe] hydrogenases
Arndt R. Finkelmann, Martin T. Stiebritz and Markus Reiher
Chem. Sci., 2014, Advance Article
DOI: 10.1039/C3SC51700D, Edge Article

Free to access until 1st December 2013

Development of cell-impermeable coelenterazine derivatives
Eric Lindberg, Shin Mizukami, Keiji Ibata, Takashi Fukano, Atsushi Miyawaki and Kazuya Kikuchi
Chem. Sci., 2013,4, 4395-4400
DOI: 10.1039/C3SC51985F, Edge Article

Free to access until 1st December 2013

Mechanism of electrophilic fluorination with Pd(IV): fluoride capture and subsequent oxidative fluoride transfer
Jochen R. Brandt, Eunsung Lee, Gregory B. Boursalian and Tobias Ritter
Chem. Sci., 2014, Advance Article
DOI: 10.1039/C3SC52367E, Edge Article

Free to access until 1st December 2013

Click here for more free HOT Chemical Science articles for October!

Carbon nanotube (CNT) fragments are exciting materials for the fields of supramolecular chemistry and nanotechnology. This is due to their tunable optical and physical properties, as well as their potential for host-guest chemical interactions. The authors from Boston and Drexel Universities and co-workers, report here for the first time, the synthesis of the radical cation of [8]-cycloparaphenylene, prepared by reaction of [8]-cycloparaphenylene with the oxidant triethyloxonium hexachloroantimonate (Et3O+SbCl6-
). A vivid colour change, from yellow to orange to deep purple, accompanied the oxidation. The product remained stable when dry for several days, and was readily reduced back to [8]-cycloparaphenylene on reaction with zinc dust.

Surprisingly, electron paramagnetic resonance (EPR) experiments on solutions of the radical cation, did not give detailed information, other than a characteristic signal for one unpaired electron.  The material also proved difficult to crystallise in a pure form. Therefore, the focus shifted to photophysical, electrochemical and theoretical properties. As seen in the figure above, on the right, the radical cation of [8]-cycloparaphenylene has two major absorptions at at 535 and 1115nm, which follow closely the values determined by density functional calculations (DFT), and are characteristically different to the parent neutral material.

Theoretical calculations also suggest a change to a highly delocalised structure in the radical cation and its dimer with the neutral compound, compared to benzene like character in [8]-cycloparaphenylene. This should prove useful for potential applications in electronic and photovoltaic devices. Detailed results from computational studies on the electronic structures of the radical cation of [8]-cycloparaphenylene ([8]-CPP) and its resonance dimer, as well as the 6, 10 and 12 ring-containing ‘hoops’ are given. This article sheds valuable new light on the properties of  intra- and inter-molecularly delocalised systems based on cycloparaphenylenes.

Read this HOT Chemical Science Edge Article today!

Photophysical and theoretical investigations of the [8]cycloparaphenylene radical cation and its charge-resonance dimer
Matthew R. Golder, Bryan M. Wong and Ramesh Jasti
Chem. Sci., 2013, Advance Article
DOI: 10.1039/C3SC51861B

Kevin Murnaghan is a guest web-writer for Chemical Science. He is currently a Research Chemist in the Adhesive Technologies Business Sector of Henkel AG & Co. KGaA, based in Düsseldorf, Germany. His research interests focus primarily on enabling chemistries and technologies for next generation adhesives and surface treatments. Any views expressed here are his personal ones and not those of Henkel AG & Co. KGaA.