Remote participation during glycosylation reactions of galactose building blocks: Direct evidence from cryogenic vibrational spectroscopy

The stereoselective formation of 1,2‐cis‐glycosidic bonds is challenging. However, 1,2‐cis‐selectivity can be induced by remote participation of C4 or C6 ester groups. Reactions involving remote participation are believed to proceed via a key ionic intermediate, the glycosyl cation. Although mechanistic pathways were postulated many years ago, the structure of the reaction intermediates remained elusive owing to their short‐lived nature. Herein, we unravel the structure of glycosyl cations involved in remote participation reactions via cryogenic vibrational spectroscopy and first principles theory. Acetyl groups at C4 ensure α‐selective galactosylations by forming a covalent bond to the anomeric carbon in dioxolenium‐type ions. Unexpectedly, also benzyl ether protecting groups can engage in remote participation and promote the stereoselective formation of 1,2‐cis‐glycosidic bonds

Accumulation pattern of total nonstructural carbohydrate in strawberry runner plants and its influence on plant growth and fruit production

The pattern of total nonstructural carbohydrate (TNC) accumulation in strawberry (Fragaria ananassa Duch.) nursery runner plants, cv. eCamarosaf, was determined for three growing seasons. Plant growth and fruit production patterns were also evaluated. The experiments were carried out on plants propagated in high latitude (41‹50' N) and high elevation (1292 m) nurseries in Siskiyou County, California. Plants were sampled beginning in late summer through early autumn and analyzed for dry mass (DM) and TNC. Plants from different digging dates were established in growth chambers (GC) at UC Davis or fruit evaluation plots in Irvine, California. In the nursery, TNC concentration in storage tissues increased steadily from the second week of September to the third week of October, and crown and root TNC concentration was positively correlated with the accumulation of chilling units (hours .7.2‹C). The root TNC concentration consistently increased from 6 to 10% DM from mid-September to the first week of October. Transplant growth and fruiting pattern were affected by digging date. Overall, the roots were more sensitive to chilling in terms of TNC accumulation, than the crowns. Therefore, roots would be the appropriate organ for assessing TNC status and potential digging dates of strawberry nursery runner plants early in the fall.Key words: Transplant, carbohydrate, chilling, growth analysis

Magneto-electrical subbands of freely suspended quantum point contacts

We present a versatile design of freely suspended quantum point contacts with particular large one-dimensional subband quantization energies of up to 10meV. The nanoscale bridges embedding a two-dimensional electron system are fabricated from AlGaAs/GaAs heterostructures by electron-beam lithography and etching techniques. Narrow constrictions define quantum point contacts that are capacitively controlled via local in-plane side gates. Employing transport spectroscopy, we investigate the transition from electrostatic subbands to Landau-quantization in a perpendicular magnetic field. The large subband quantization energies allow us to utilize a wide magnetic field range and thereby observe a large exchange splitted spin-gap of the two lowest Landau-levels

Studying the Key Intermediate of RNA Autohydrolysis by Cryogenic Gas-Phase Infrared Spectroscopy

Over the course of the COVID-19 pandemic, mRNA-basedvaccineshave gained tremendous importance. The development and analysis of modified RNA moleculesbenefit from advanced mass spectrometry and require sufficient understanding of fragmentation processes.Analogous tothe degradation of RNA in solution by autohydrolysis,backbone cleavage of RNA strands wasequally observedin the gas phase; however, the fragmentation mechanism remained elusive.In this work,autohydrolysis-like intermediates weregenerated from isolated RNA dinucleotidesin the gas phaseand investigatedusing cryogenic infrared spectroscopy in helium nanodroplets.Data from both experiment and density functional theory provide evidence forthe formation of a five-membered cyclic phosphateintermediateand rule outlinear orsix-membered structures. Furthermore, the experiments show that another prominent condensed-phase reactionof RNA nucleotides can be induced in the gas phase: the tautomerization of cytosine.Both observed reactions aretherefore highlyuniversal and intrinsic properties of the investigated molecules

Implications of albedo changes following afforestation on the benefits of forests as carbon sinks

Increased carbon storage with afforestation leads to a decrease in atmospheric carbon dioxide concentration and thus decreases radiative forcing and cools the Earth. However, afforestation also changes the reflective properties of the surface vegetation from more reflective pasture to relatively less reflective forest cover. This increase in radiation absorption by the forest constitutes an increase in radiative forcing, with a warming effect. The net effect of decreased albedo and carbon storage on radiative forcing depends on the relative magnitude of these two opposing processes. <br></br> We used data from an intensively studied site in New Zealand's Central North Island that has long-term, ground-based measurements of albedo over the full short-wave spectrum from a developing <i>Pinus radiata</i> forest. Data from this site were supplemented with satellite-derived albedo estimates from New Zealand pastures. The albedo of a well-established forest was measured as 13 % and pasture albedo as 20 %. We used these data to calculate the direct radiative forcing effect of changing albedo as the forest grew. <br></br> We calculated the radiative forcing resulting from the removal of carbon from the atmosphere as a decrease in radiative forcing of −104 GJ tC<sup>−1</sup> yr<sup>−1</sup>. We also showed that the observed change in albedo constituted a direct radiative forcing of 2759 GJ ha<sup>−1</sup> yr<sup>−1</sup>. Thus, following afforestation, 26.5 tC ha<sup>−1</sup> needs to be stored in a growing forest to balance the increase in radiative forcing resulting from the observed albedo change. Measurements of tree biomass and albedo were used to estimate the net change in radiative forcing as the newly planted forest grew. Albedo and carbon-storage effects were of similar magnitude for the first four to five years after tree planting, but as the stand grew older, the carbon storage effect increasingly dominated. Averaged over the whole length of the rotation, the changes in albedo negated the benefits from increased carbon storage by 17–24 %

Untersuchung des reaktiven Intermediats der RNA Autohydrolyse mittels kryogener Infrarotspektroskopie in der Gasphase

Im Laufe der COVID-19 Pandemie haben mRNA-basierte Impfstoffe an immenser Bedeutung gewonnen. Massenspektrometrie ist für die Entwicklung und Analyse von modifizierten RNA Molekülen unerlässlich, setzt jedoch ein grundlegendes Verständnis über Fragmentierungsprozesse voraus. Analog zu der Zersetzung von RNA in Lösung durch Autohydrolyse, kann die Spaltung des RNA Rückgrats ebenso in der Gasphase stattfinden. Bislang sind die Fragmentierungsmechanismen jedoch unzureichend untersucht. In dieser Arbeit wurden Intermediate aus isolierten RNA Dinukleotiden in der Gasphase generiert und mittels kryogener Infrarotspektroskopie in Helium-Nanotröpfchen untersucht. Die experimentellen Daten, unterstützt durch Dichtefunktionaltheorie, liefern Hinweise dafür, dass die Bildung eines fünfgliedrigen zyklischen Phosphat-Intermediats begünstigt ist, während lineare oder sechsgliedrige Strukturen ausgeschlossen werden können. Weiterhin zeigen die Experimente, dass eine zusätzliche, bekannte Reaktion von RNA Nukleotiden in Lösung auch in der Gasphase induziert werden kann: die Tautomerisierung von Cytosin. Die beiden beobachteten Reaktionen spiegeln daher universelle und intrinsische Eigenschaften der untersuchten Moleküle wider

Romidepsin in peripheral and cutaneous T-cell lymphoma: mechanistic implications from clinical and correlative data

Romidepsin is an epigenetic agent approved for the treatment of patients with cutaneous or peripheral T-cell lymphoma (CTCL and PTCL). Here we report data in all patients treated on the National Cancer Institute 1312 trial, demonstrating long-term disease control and the ability to retreat patients relapsing off-therapy. In all, 84 patients with CTCL and 47 with PTCL were enrolled. Responses occurred early, were clinically meaningful and of very long duration in some cases. Notably, patients with PTCL receiving romidepsin as third-line therapy or later had a comparable response rate (32%) of similar duration as the total population (38%). Eight patients had treatment breaks of 35months to 10years; in four of six patients, re-initiation of treatment led to clear benefit. Safety data show slightly greater haematological and constitutional toxicity in PTCL. cDNA microarray studies show unique individual gene expression profiles, minimal overlap between patients, and both induction and repression of gene expression that reversed within 24h. These data argue against cell death occurring as a result of an epigenetics-mediated gene induction programme. Together this work supports the safety and activity of romidepsin in T-cell lymphoma, but suggests a complex mechanism of action

The Influence of the Electron Density in Acyl Protecting Groups on the Selectivity of Galactose Formation

The stereoselective formation of 1,2-cis-glycosidic bonds is a major bottleneck in the synthesis of carbohydrates. We here investigate how the electron density in acyl protecting groups influences the stereoselectivity by fine-tuning the efficiency of remote participation. Electron-rich C4-pivaloylated galactose building blocks show an unprecedented α-selectivity. The trifluoroacetylated counterpart with electron-withdrawing groups, on the other hand, exhibits a lower selectivity. Cryogenic infrared spectroscopy in helium nanodroplets and density functional theory calculations revealed the existence of dioxolenium-type intermediates for this reaction, which suggests that remote participation of the pivaloyl protecting group is the origin of the high α-selectivity of the pivaloylated building blocks. According to these findings, an α-selective galactose building block for glycosynthesis is developed based on rational considerations and is subsequently employed in automated glycan assembly exhibiting complete stereoselectivity. Based on the obtained selectivities in the glycosylation reactions and the results from infrared spectroscopy and density functional theory, we suggest a mechanism by which these reactions could proceed

I=3/2 KπK \pi Scattering in the Nonrelativisitic Quark Potential Model

We study $I=3/2$ elastic $K\pi$ scattering to Born order using nonrelativistic quark wavefunctions in a constituent-exchange model. This channel is ideal for the study of nonresonant meson-meson scattering amplitudes since s-channel resonances do not contribute significantly. Standard quark model parameters yield good agreement with the measured S- and P-wave phase shifts and with PCAC calculations of the scattering length. The P-wave phase shift is especially interesting because it is nonzero solely due to $SU(3)_f$ symmetry breaking effects, and is found to be in good agreement with experiment given conventional values for the strange and nonstrange constituent quark masses.Comment: 12 pages + 2 postscript figures, Revtex, MIT-CTP-210