Multigram Scale Total Synthesis of Piperarborenines C-E

We report the development of a multigram scale total synthesis of heterodimeric β-truxinic imides piperarborenines C-E using a catechol-mediated diastereoselective intramolecular [2+2] photocycloaddition. Key innovations lie in the use of (1) catechol as a highly selective auxiliary for the robust and scalable synthesis of homo- and heterodimeric β-truxinates, (2) UV LEDs for direct excitation in the [2+2] cycloaddition step, and (3) a bis pentafluorophenyl ester and LDA for the challenging installation of the syn dihydropyridinone imides. This approach is exceptionally scalable – requiring minimal chromatography, no photocatalysts, and no cryogenic conditions - and will enable thorough evaluation of the biological properties and anticancer profiles of piperaborenines C-E and derivatives thereof.

Charging and ultralong phosphorescence of lanthanide facilitated organic complex

Emission from the triplet state of an organo-lanthanide complex is observed only when the energy transfer to the lanthanide ion is absent. The triplet state lifetime under cryogenic conditions for organo-lanthanide compounds usually ranges up to tens of milliseconds. The compound LaL1(TTA)3 reported herein exhibits 77 K phosphorescence observable by the naked eye for up to 30 s. Optical spectroscopy, density functional theory (DFT) and time-dependent DFT techniques have been applied to investigate the photophysical processes of this compound. In particular, on-off continuous irradiation cycles reveal a charging behaviour of the emission which is associated with triplet-triplet absorption because it shows a shorter rise lifetime than the corresponding decay lifetime and it varies with illumination intensity. The discovery of the behaviour of this compound provides insight into important photophysical processes of the triplet state of organo-lanthanide systems and may open new fields of application such as data encryption, anti-counterfeiting and temperature switching.

A Comparison of Structure Determination of Small Organic Molecules by 3D Electron Diffraction at Cryogenic and Room Temperature

3D electron diffraction (3D ED), also known as micro-crystal electron diffraction (MicroED), is a rapid, accurate, and robust method for structure determination of submicron-sized crystals. 3D ED has mainly been applied in material science until 2013, when MicroED was developed for studying macromolecular crystals. MicroED was considered as a cryo-electron microscopy method, as MicroED data collection is usually carried out in cryogenic conditions. As a result, some researchers may consider that 3D ED/MicroED data collection on crystals of small organic molecules can only be performed in cryogenic conditions. In this work, we determined the structure for sucrose and azobenzene tetracarboxylic acid (H4ABTC). The structure of H4ABTC is the first crystal structure ever reported for this molecule. We compared data quality and structure accuracy among datasets collected under cryogenic conditions and room temperature. With the improvement in data quality by data merging, it is possible to reveal hydrogen atom positions in small organic molecule structures under both temperature conditions. The experimental results showed that, if the sample is stable in the vacuum environment of a transmission electron microscope (TEM), the data quality of datasets collected under room temperature is at least as good as data collected under cryogenic conditions according to various indicators (resolution, I/σ(I), CC1/2 (%), R1, Rint, ADRA).

Seed Cryopreservation and Germination of Rhus glabra and the Critically Endangered Species Rhus michauxii

Rhus michauxii is a perennial rhizomatous shrub native to the southeastern United States that is found mainly in sunny, dry, open rocky or sandy woodlands. Moreover, it is found on ridges or river bluffs in the inner coastal plane and lower piedmont of Virginia, Georgia, and the Carolinas. Habitat conversion to agriculture, suppression of fires, and low reproduction have caused R. michauxii to become rare and it is now federally listed as threatened. Methods are needed to multiply and conserve R. michauxii. Protocols were developed for seed cryopreservation, in vitro germination, and micropropagation for R. glabra and R. michauxii. Seed scarification in concentrated sulfuric acid for 6 h and germination on ½ MS medium resulted in germination up to 96% for control and cryopreserved seeds of R. glabra and 70 and 40% for control and cryopreserved seeds of R. michauxii. Shortly after germination in vitro, young seedlings were established in a greenhouse potting mix providing new plants from the endemic Georgia R. michauxii populations. Several of the findings meet goals within the R. michauxii recovery plan by providing methods for sexual and asexual multiplication and long-term seed storage under cryogenic conditions. The protocols developed will assist in the safeguarding and conservation of dwindling natural R. michauxii populations.

Biomolecular Perturbations in In-Cell Dynamic Nuclear Polarization Experiments

In-cell DNP is a growing application of NMR to the study of biomolecular structure and function within intact cells. An important unresolved question for in-cell DNP spectroscopy is the integrity of cellular samples under the cryogenic conditions of DNP. Despite the rich literature around cryopreservation of cells in the fields of stem cell/embryonic cell therapeutics, cell line preservation and in cryo-EM applications, the effect of cryopreservation procedures on DNP parameters is unclear. In this report we investigate cell survival and apoptosis in the presence of cryopreserving agents and DNP radicals. We also assess the effects of these reagents on cellular enhancements. We show that the DNP radical AMUPol has no effect on membrane permeability and does not induce apoptosis. Furthermore, the standard aqueous glass forming reagent, comprised of 60/30/10 d8-glycerol/D2O/H2O (DNP juice), rapidly dehydrates cells and induces apoptosis prior to freezing, reducing structural integrity of the sample prior to DNP analysis. Preservation with d6-DMSO at 10% v/v provided similar DNP enhancements per √unit time compared to glycerol preservation with superior maintenance of cell size and membrane integrity prior to freezing. DMSO preservation also greatly enhanced post-thaw survival of cells slow-frozen at 1°C/min. We therefore demonstrate that in-cell DNP-NMR studies should be done with d6-DMSO as cryoprotectant and raise important considerations for the progression of in-cell DNP-NMR towards the goal of high quality structural studies.