Direct Imaging of Radiation-Sensitive Organic Polymer-Based Nanocrystals at Sub-Ångström Resolution.

Seeing the atomic configuration of single organic nanoparticles at a sub-Å spatial resolution by transmission electron microscopy has been so far prevented by the high sensitivity of soft matter to radiation damage. This difficulty is related to the need to irradiate the particle with a total dose of a few electrons/Å2, not compatible with the electron beam density necessary to search the low-contrast nanoparticle, to control its drift, finely adjust the electron-optical conditions and particle orientation, and finally acquire an effective atomic-resolution image. On the other hand, the capability to study individual pristine nanoparticles, such as proteins, active pharmaceutical ingredients, and polymers, with peculiar sensitivity to the variation in the local structure, defects, and strain, would provide advancements in many fields, including materials science, medicine, biology, and pharmacology. Here, we report the direct sub-ångström-resolution imaging at room temperature of pristine unstained crystalline polymer-based nanoparticles. This result is obtained by combining low-dose in-line electron holography and phase-contrast imaging on state-of-the-art equipment, providing an effective tool for the quantitative sub-ångström imaging of soft matter.

Use of pyridazinediones for tuneable and reversible covalent cysteine modification applied to peptides, proteins and hydrogels.

Reversible cysteine modification has been found to be a useful tool for a plethora of applications such as selective enzymatic inhibition, activity-based protein profiling and/or cargo release from a protein or a material. However, only a limited number of reagents display reliable dynamic/reversible thiol modification and, in most cases, many of these reagents suffer from issues of stability, a lack of modularity and/or poor rate tunability. In this work, we demonstrate the potential of pyridazinediones as novel reversible and tuneable covalent cysteine modifiers. We show that the electrophilicity of pyridazinediones correlates to the rates of the Michael addition and retro-Michael deconjugation reactions, demonstrating that pyridazinediones provide an enticing platform for readily tuneable and reversible thiol addition/release. We explore the regioselectivity of the novel reaction and unveil the reason for the fundamental increased reactivity of aryl bearing pyridazinediones by using DFT calculations and corroborating findings with SCXRD. We also applied this fundamental discovery to making more rapid disulfide rebridging agents in related work. We finally provide the groundwork for potential applications in various areas with exemplification using readily functionalised "clickable" pyridazinediones on clinically relevant cysteine and disulfide conjugated proteins, as well as on a hydrogel material.

"Click" labeling strategy for M(CO)(3) (M = Re, (99m)Tc) prostate cancer targeted flutamide agents.

Two distinct "click" chemistry labeling approaches were investigated with dipyridylamine alkyne derivatives and M(CO)(3)(+) (M = Re, (99m)Tc). The triazole ring was found uncoordinated and was incorporated into the preparation of a crossover androgen receptor targeting inhibitor for prostate cancer.

Investigation of the coordination interactions of S-(pyridin-2-ylmethyl)-L-cysteine ligands with M(CO)(3)(+) (M = Re, (99m)Tc).

Development of new ligands for fac-M(OH(2))(3)(CO)(3)(+) (M = Re, (99m)Tc) led the investigation with S-(pyridin-2-ylmethyl)-l-cysteine, 1. The ligand 1 has potential to coordinate with the metal through three different tridentate modes: tripodal through cysteine (O,N,S) and two linear involving the S-pyridyl and cysteine (O,S,N(Py), N,S,N(Py)). From the reaction with 1, two species were observed in the (1)H NMR, where the primary product was the linear fac-Re(N,S,N(Py)-1)(CO)(3)(+), 2a, complex. To identify the coordination mode of the minor product, functionalized analogues of 1 were prepared from S-(pyridin-2-ylmethyl)-Boc-l-cysteine-methyl ester, 3, with orthogonal protecting groups on the C terminus (methyl ester) in S-(pyridin-2-ylmethyl)-l-cysteine methyl ester, 4, or N terminus (Boc) in S-(pyridin-2-ylmethyl)-Boc-l-cysteine, 6, that specifically directed the coordination mode of fac-M(H(2)O)(3)(CO)(3)(+) to either N,S,N(Py) or O,S,N(Py), respectively. Two diastereomers [fac-Re(CO)(3)(N,S,N(Py)-4)](+), 5a and 5b, were observed and independently characterized by X-ray structure analysis and NMR in high yield with 4. Surprisingly, the O,S,N(Py) Re complex with ligand 6 was not observed and simplified versions, 3-(pyridin-2-ylmethylthio) propanoic acid, 7, and 2-(pyridin-2-ylmethylthio)acetic acid, 8, were investigated. Ligand 7 did not yield the desired linear tridentate O,S,N(Py) product. However, the shorter ligand 8 formed fac-Re(CO)(3)(O,S,N(Py)-8), 9, in high yield. (99m)Tc labeling studies were conducted and yielded similar results to the rhenium complex and effective (>99%) at 10(-5) M ligand concentration.