Depolymerizing self-immolative polymeric lanthanide chelates for vascular imaging.

Medical imaging is widely used clinically and in research to understand disease progression and monitor responses to therapies. Vascular imaging enables the study of vascular disease and therapy, but exogenous contrast agents are generally needed to distinguish the vasculature from surrounding soft tissues. Lanthanide-based agents are commonly employed in MRI, but are also of growing interest for micro-CT, as the position of their k-edges allows them to provide enhanced contrast and also to be employed in dual-energy micro-CT, a technique that can distinguish contrast-enhanced blood vessels from tissues such as bone. Small molecule Gd3+ chelates are available, but are excreted too rapidly. At the same time, a lack of rapid clearance from the body for long-circulating agents presents toxicity concerns. To address these challenges, we describe here the use of self-immolative polymers for the development of new degradable chelates that depolymerize completely from end-to-end following the cleavage of a single end-cap from the polymer terminus. We demonstrate that tuning the end-cap allows the rate of depolymerization to be controlled, while tuning the polymer length enables the polymer to exhibit long circulation times in the blood of mice. After successfully providing one hour of blood contrast, depolymerization led to excretion of the resulting small molecule chelates into the bladder. Despite the high doses required for micro-CT, the agents were well tolerated in mice. Thus, these self-immolative polymeric chelates provide a new platform for the development of medical imaging contrast agents

Deposition of copper by plasma-enhanced atomic layer deposition using a novel N-Heterocyclic carbene precursor

Two novel N-heterocyclic carbene (NHC)-containing copper(I) amides are reported as atomic layer deposition (ALD) precursors. 1,3-Diisopropyl-imidazolin-2-ylidene copper hexamethyldisilazide (1) and 4,5-dimethyl-1,3-diisopropyl-imidazol-2-ylidene copper hexamethyldisilazide (2) were synthesized and structurally characterized. The thermal behavior of both compounds was studied by thermogravimetric analysis (TGA), and they were both found to be reasonably volatile compounds. Compound 1 had no residual mass in the TGA and showed long-term stability at temperatures as high as 130 °C, while 2 had a residual mass of 7.4%. Copper metal with good resistivity was deposited using 1 by plasma-enhanced atomic layer deposition. The precursor demonstrated self-limiting behavior indicative of ALD, and gave a growth rate of 0.2 Å/cycle. Compound 2 was unsuccessful as an ALD precursor under similar conditions. Density functional theory calculations showed that both compounds adsorb dissociatively onto a growing copper film as long as there is some atomic roughness, via cleavage of the Cu-carbene bond

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Ferrocenyl-Substituted Tris(pyrazolyl)boratesA New Ligand Type Combining Redox Activity with Resistance to Hydrogen Atom Abstraction

The low-temperature syntheses of ferrocenyl-substituted tris­(pyrazolyl)­borate ligands Tp^Fc* (hydrobis­(3-ferrocenylpyrazolyl)­mono­(5-ferrocenylpyrazolyl)­borate), Tp^Fc,Me* (hydrobis­(3-ferrocenyl-5-methylpyrazolyl)­mono­(5-ferrocenyl-3-methylpyrazolyl)­borate), and Tp^Fc,iPr (hydrotris­(3-ferrocenyl-5-isopropylpyrazolyl)­borate) are reported. The Tl salts of Tp^Fc* and Tp^Fc,Me* can be thermally isomerized to the symmetric Tp^Fc (hydrotris­(3-ferrocenylpyrazolyl)­borate) and Tp^Fc,Me (hydrotris­(3-ferrocenyl-5-methylpyrazolyl)­borate) species, respectively. Conversely, upon heating, the thermal isomerization of Tp^Fc,iPr results in the generation of a mixture of regioisomers. These ligands display a reversible three-electron oxidation. The preparations of Tp^CF3,FcTl (hydrotris­(3-trifluoromethyl-5-ferrocenylpyrazolyl)­borate) and PhTp^Fc (phenyltris­(3-ferrocenylpyrazolyl)­borate) are also reported

Phenylcyanamidoruthenium scorpionate complexes

Nine [Ru(Tp)(dppe)L] complexes, where Tp is hydrotris(pyrazol-1-yl)borate, dppe is ethylenebis(diphenylphosphine), and L is (4-nitrophenyl)cyanamide (NO2pcyd-), (2-chlorophenyl)cyanamide (2-Clpcyd -), (3-chlorophenyl)cyanamide (3-Clpcyd-), (2,4-dichlorophenyl)cyanamide (2,4-Cl2pcyd-), (2,3-dichlorophenyl)cyanamide (2,3-Cl2pcyd-), (2,5-dichlorophenyl)cyanamide (2,5-Cl2pcyd-), (2,4,5-trichlorophenyl)cyanamide (2,4,5-Cl3pcyd-), (2,3,5,6-tetrachlorophenyl)cyanamide (2,3,5,6-Cl4pcyd-), and (pentachlorophenyl)cyanamide (Cl5pcyd-), and the dinuclear complex [{Ru(Tp)(dppe)}2(μ-adpc)], where adpc 2- is azo-4,4-diphenylcyanamide, have been prepared and characterized. The crystal structures of [Ru(Tp)(dppe)(Cl5pcyd)] and [{Ru(Tp)(dppe)}2(μ-adpc)] reveal the RuII ion to occupy a pseudooctahedral coordination sphere in which the cyanamide ligand coordinates to RuII by its terminal nitrogen atom. For both complexes, the cyanamide ligands are planar, indicating significant π mixing between the cyanamide and phenyl moieties as well as the azo group in the case of adpc2-. The optical spectra of the nominally ruthenium(III) species [Ru(Tp)(dppe)L]+ were obtained through spectroelectrochemistry measurements and showed an intense near-IR absorption band. Time-dependent density functional theory calculations of these species revealed that oxidation of the ruthenium(II) species led to species where partial oxidation of the cyanamide ligand had occurred, indicative of noninnocent character for these ligands. The spin densities reveal that while the 3-Clpycd species h

Study of Monomeric Copper Complexes Supported by N-Heterocyclic and Acyclic Diamino Carbenes

The thermal properties of a series of monomeric copper(I) hexamethyldisilazide complexes supported by N-heterocyclic and acyclic diamino carbenes were evaluated to study the impact of N-alkyl substituents and backbone character on volatility and thermal stability of copper amides. The series of complexes were either liquids or solids with melting points in the broad range of 45-184 °C. Vaporization rates were measured by stepped-isothermal TGA experiments and found to be between 110-170 °C. Enthalpies of vaporization were determined to be 63-90 kJ/mol. Temperatures for 1 Torr vapor pressure were estimated to be 143-172 °C, showing a general dependence on molecular weight. The imidazolylidene complexes were thermally unstable with convincing evidence indicating the unsaturated backbone as a point of weakness. The imidazolinylidene complexes showed excellent thermal stability with comparable results for the formamidinylidenes complexes. The steric parameter of the carbene, %VBur, was calculated for all complexes characterized by single crystal X-ray diffraction

Preventing thermolysis: Precursor design for volatile copper compounds

A copper(i) iminopyrrolidinate was synthesized and evaluated by thermal gravimetric analysis (TGA), solution based 1H NMR studies and surface chemistry to determine its thermal stability and decomposition mechanism. Copper(i) tert-butyl-imino-2,2-dimethylpyrrolidinate (1) demonstrated superior thermal stability and showed negligible decomposition in TGA experiments up to 300 °C as well as no decomposition in solutions at 165 °C over 3 weeks

Copper iminopyrrolidinates: A study of thermal and surface chemistry

Several copper(I) iminopyrrolidinates have been evaluated by thermogravimetric analysis (TGA) and solution based 1H NMR studies to determine their thermal stability and decomposition mechanisms. Iminopyrrolidinates were used as a ligand for copper(I) to block previously identified decomposition routes of carbodiimide deinsertion and β-hydrogen abstraction. The compounds copper(I) isopropyl-iminopyrrolidinate (1) and copper(I) tert-butyl-iminopyrrolidinate (2) were synthesized for this study, and compared to the previously reported copper(I) tert-butyl-imino-2,2- dimethylpyrrolidinate (3) and the copper(I) guanidinate [Me2NC( iPrN)2Cu]2 (4). Compounds 1 and 2 were found to be volatile yet susceptible to decomposition during TGA. At 165 C in C 6D6, they had half-lives of 181.7 h and 23.7 h, respectively. The main thermolysis product of 1 and 2 was their respective protonated iminopyrrolidine ligand. β-Hydrogen abstraction was proposed for the mechanism of thermal decomposition. Since compound 3 showed no thermolysis at 165 C, it was further studied by chemisorption on high surface area silica. It was found to eliminate an isobutene upon chemisoption at 275 C. Annealing the sample at 350 C showed further evidence of the decomposition of the surface species, likely eliminating ethene, and producing a surface bound methylene diamine

Nickel-Catalyzed Cross Couplings of Benzylic Ammonium Salts and Boronic Acids: Stereospecific Formation of Diarylethanes via C–N Bond Activation

We have developed a nickel-catalyzed cross coupling of benzylic ammonium triflates with aryl boronic acids to afford diarylmethanes and diarylethanes. This reaction proceeds under mild reaction conditions and with exceptional functional group tolerance. Further, it transforms branched benzylic ammonium salts to diarylethanes with excellent chirality transfer, offering a new strategy for the synthesis of highly enantioenriched diarylethanes from readily available chiral benzylic amines

Study of Monomeric Copper Complexes Supported by <i>N</i>‑Heterocyclic and Acyclic Diamino Carbenes

The thermal properties of a series of monomeric copper­(I) hexamethyldisilazide complexes supported by <i>N</i>-heterocyclic and acyclic diamino carbenes were evaluated to study the impact of <i>N</i>-alkyl substituents and backbone character on volatility and thermal stability of copper amides. The series of complexes were either liquids or solids with melting points in the broad range of 45–184 °C. Vaporization rates were measured by stepped-isothermal TGA experiments and found to be between 110–170 °C. Enthalpies of vaporization were determined to be 63–90 kJ/mol. Temperatures for 1 Torr vapor pressure were estimated to be 143–172 °C, showing a general dependence on molecular weight. The imidazolylidene complexes were thermally unstable with convincing evidence indicating the unsaturated backbone as a point of weakness. The imidazolinylidene complexes showed excellent thermal stability with comparable results for the formamidinylidenes complexes. The steric parameter of the carbene, %<i>V</i>_Bur, was calculated for all complexes characterized by single crystal X-ray diffraction