Cooperative halogen bonding and polarized π-stacking in the formation of coloured charge-transfer co-crystals

Red co-crystals are formed between the matched complementary electron rich halogen bond acceptors, isomeric 4-(N,N-dimethylamino)phenylethynylpyridines and the electron poor halogen bond donor, 1-(3,5-dinitrophenylethynyl)-2,3,5,6-tetrafluoro-4-iodobenzene. The red 1 : 1 cocrystals exhibit strong halogen bonding and strong π-stacking. The N⋯I distances range from 2.80 to 2.85 Å and the C-I⋯N angles are between 169.9 and 175.8°. In all four structures the donor and acceptor molecules are alternately π-stacked with the centroid to centroid distances between the dinitrophenyl moiety and the dimethylaminophenyl moiety ranging from 3.61 to 3.73 Å. The calculated π-π stacking binding energy is -22.24 kcal mol-1 for the complex between 4-[4-(N,N-dimethylamino)phenylethynyl]pyridine and 1-(3,5-dinitrophenylethynyl)-2,3,5,6-tetrafluoro-4-iodobenzene while the calculated halogen bond binding energy between the same couple is -7.97 kcal mol-1

Effects of Halogen and Hydrogen Bonding on the Electronics of a Conjugated Rotor

The electronic properties of a pyrazine-containing arylene ethynylene unit are influenced by hydrogen bond and halogen bond donors that are held in proximity of the pyrazine rotor. These interactions are evident with iodine- and bromine-centered halogen bonds and O-H- and C-H-based hydrogen bonds. Bathochromic shifts of UV-vis and fluorescence signals are the best indicators of this intramolecular attraction. The effects can be attenuated in solvents that are less favorable for intramolecular halogen or hydrogen bonding, such as 2-propanol, and amplified in solvents that are supportive, such as toluene. Intramolecular attractions promote planarity in the pyrazine ethynylene system, likely increasing the effective conjugation of the unsaturated backbone. Additionally, computations at the B3LYP and M062X levels of theory using 6-311++G(2d,p) and aug-cc-pVTZ basis sets suggest that the Lewis acidity of the halogen and hydrogen atoms influences electronic behavior even in the absence of conformational constraints

Effects of Halogen and Hydrogen Bonding on the Electronics of a Conjugated Rotor

The electronic properties of a pyrazine-containing arylene ethynylene unit are influenced by hydrogen bond and halogen bond donors that are held in proximity of the pyrazine rotor. These interactions are evident with iodine- and bromine-centered halogen bonds and O–H- and C–H-based hydrogen bonds. Bathochromic shifts of UV–vis and fluorescence signals are the best indicators of this intramolecular attraction. The effects can be attenuated in solvents that are less favorable for intramolecular halogen or hydrogen bonding, such as 2-propanol, and amplified in solvents that are supportive, such as toluene. Intramolecular attractions promote planarity in the pyrazine ethynylene system, likely increasing the effective conjugation of the unsaturated backbone. Additionally, computations at the B3LYP and M062X levels of theory using 6-311++G­(2d,p) and aug-cc-pVTZ basis sets suggest that the Lewis acidity of the halogen and hydrogen atoms influences electronic behavior even in the absence of conformational constraints

N-Terminal Labeling of Filamentous Phage To Create Cancer Marker Imaging Agents

We report a convenient new technique for the labeling of filamentous phage capsid proteins. Previous reports have shown that phage coat protein residues can be modified, but the lack of chemically distinct amino acids in the coat protein sequences makes it difficult to attach high levels of synthetic molecules without altering the binding capabilities of the phage. To modify the phage with polymer chains, imaging groups, and other molecules, we have developed chemistry to convert the N-terminal amines of the ~4,200 coat proteins into ketone groups. These sites can then serve as chemospecific handles for the attachment of alkoxyamine groups through oxime formation. Specifically, we demonstrate the attachment of fluorophores and up to 3,000 molecules of 2 kD poly(ethylene glycol) (PEG2k) to each of the phage capsids without significantly affecting the binding of phage-displayed antibody fragments to EGFR and HER2 (two important epidermal growth factor receptors). We also demonstrate the utility of the modified phage for the characterization of breast cancer cells using multicolor fluorescence microscopy. Due to the widespread use of filamentous phage as display platforms for peptide and protein evolution, we envision that the ability to attach large numbers of synthetic functional groups to their coat proteins will be of significant value to the biological and materials communities

Overview of the DESI Legacy Imaging Surveys

The DESI Legacy Imaging Surveys (http://legacysurvey.org/) are a combination of three public projects (the Dark Energy Camera Legacy Survey, the Beijing–Arizona Sky Survey, and the Mayall z-band Legacy Survey) that will jointly image ≈14,000 deg2 of the extragalactic sky visible from the northern hemisphere in three optical bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. The combined survey footprint is split into two contiguous areas by the Galactic plane. The optical imaging is conducted using a unique strategy of dynamically adjusting the exposure times and pointing selection during observing that results in a survey of nearly uniform depth. In addition to calibrated images, the project is delivering a catalog, constructed by using a probabilistic inference-based approach to estimate source shapes and brightnesses. The catalog includes photometry from the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12, and 22 μm) observed by the Wide-field Infrared Survey Explorer satellite during its full operational lifetime. The project plans two public data releases each year. All the software used to generate the catalogs is also released with the data. This paper provides an overview of the Legacy Surveys project

Inflation and Dark Energy from Spectroscopy at z>2z > 2

The expansion of the Universe is understood to have accelerated during two epochs: in its very first moments during a period of Inflation and much more recently, at $z < 1$, when Dark Energy is hypothesized to drive cosmic acceleration. The undiscovered mechanisms behind these two epochs represent some of the most important open problems in fundamental physics. The large cosmological volume at $2 < z < 5$, together with the ability to efficiently target high-$z$ galaxies with known techniques, enables large gains in the study of Inflation and Dark Energy. A future spectroscopic survey can test the Gaussianity of the initial conditions up to a factor of ~50 better than our current bounds, crossing the crucial theoretical threshold of $\sigma(f_{NL}^{\rm local})$ of order unity that separates single field and multi-field models. Simultaneously, it can measure the fraction of Dark Energy at the percent level up to $z = 5$, thus serving as an unprecedented test of the standard model and opening up a tremendous discovery space

Inflation and Dark Energy from Spectroscopy at z>2z > 2

The expansion of the Universe is understood to have accelerated during two epochs: in its very first moments during a period of Inflation and much more recently, at $z < 1$, when Dark Energy is hypothesized to drive cosmic acceleration. The undiscovered mechanisms behind these two epochs represent some of the most important open problems in fundamental physics. The large cosmological volume at $2 < z < 5$, together with the ability to efficiently target high-$z$ galaxies with known techniques, enables large gains in the study of Inflation and Dark Energy. A future spectroscopic survey can test the Gaussianity of the initial conditions up to a factor of ~50 better than our current bounds, crossing the crucial theoretical threshold of $\sigma(f_{NL}^{\rm local})$ of order unity that separates single field and multi-field models. Simultaneously, it can measure the fraction of Dark Energy at the percent level up to $z = 5$, thus serving as an unprecedented test of the standard model and opening up a tremendous discovery space