Exciplex fluorescence emission from simple organic intramolecular constructs in non-polar and highly polar media as model systems for DNA-assembled exciplex detectors

Organic intramolecular exciplexes, N-(4-dimethylaminobenzyl)-N-(1-pyrenemethyl)amine (1) and N'-4-dimethylaminonaphthyl-N-(1-pyrenemethyl)amine (2), were used as model systems to reveal major factors affecting their exciplex fluorescence, and thus lay the basis for developing emissive target-assembled exciplexes for DNA-mounted systems in solution. These models with an aromatic pyrenyl hydrocarbon moiety as an electron acceptor appropriately connected to an aromatic dimethylamino electron donor component (N,N-dimethylaminophenyl or N,N-dimethylaminonaphthyl) showed strong intramolecular exciplex emission in both non-polar and highly polar solvents. The effect of dielectric constant on the maximum wavelength for exciplex emission was studied, and emission was observed for 1 and 2 over the full range of solvent from non-polar hydrocarbons up to N-methylformamide with a dielectric constant of 182. Quantum yields were determined for these intramolecular exciplexes in a range of solvents relative to that for Hoechst 33,258. Conformational analysis of 1 was performed both computationally and via qualitative 2D NMR using (1)H-NOESY experiments. The results obtained indicated the contribution of pre-folded conformation(s) to the ground state of 1 conducive to exciplex emission. This research provides the initial background for design of self-assembled, DNA-mounted exciplexes and underpins further development of exciplex-based hybridisation bioassays.     

Organic rectifying junctions from an electron-accepting molecular wire and an electron-donating phthalocyanine

Self-assembled monolayers (SAMs) of arylene-ethynylene oligomers that incorporate electron-accepting 9-fluorenone and 9-[(4-pyridyl)methylene]fluorene units in the backbone exhibit symmetrical current-voltage (I-V) characteristics, but rectifying junctions with current ratios of 20-80 at +/-1 V have been obtained by protonating these wire-like molecules and ionically coupling with anionic donors.     

160 GHz harmonic mode-locked AlGaInAs 1.55 μm strained quantum-well compound-cavity laser

We characterized the reflectivity and the modal discrimination of intracavity reflectors (ICRs) with different numbers of slots and presented harmonic mode-locking operation of a monolithic semiconductor laser comprising a compound cavity formed by a single deeply etched slot ICR fabricated from 1.55 μm AlGaInAs strained quantum well material. Gaussian pulses were generated at a 161.8 GHz repetition rate with a pulse duration of 1.67 ps and a time-bandwidth product of 0.81.     

A Metallaphotoredox Strategy for the Cross‐Electrophile Coupling of α‐Chloro Carbonyls with Aryl Halides

Here, we demonstrate that a metallaphotoredox‐catalyzed cross‐electrophile coupling mechanism provides a unified method for the α‐arylation of diverse activated alkyl chlorides, including α‐chloroketones, α‐chloroesters, α‐chloroamides, α‐chlorocarboxylic acids, and benzylic chlorides. This strategy, which is effective for a wide variety of aryl bromide coupling partners, is predicated upon a halogen atom abstraction/nickel radical‐capture mechanism that is generically successful across an extensive range of carbonyl substrates. The construction and use of arylacetic acid products have further enabled two‐step protocols for the delivery of valuable building blocks for medicinal chemistry, such as aryldifluoromethyl and diarylmethane motifs.     

Hydrostibination

A rigid naphthalenediamine framework has been used to prepare antimony hydrides that feature LUMO shapes and energies similar to those found in secondary boranes. By exploiting this feature, we introduce the first examples of uncatalyzed hydrostibination reactions of robust C≡C, C=C, C=O, and N=N bonds as new elementary hydrometalation reactions analogous to hydroboration. These results endorse the notion of a diagonal relationship between the lightest p‐block element and the heaviest Group 15 elements and may lead to the conception of novel reaction chemistry.     

Electronically varied manganese tris-arylacetamide tripodal complexes

Abstract

This report details the synthesis and characterization of six new Mn(II) complexes coordinated to systematically varied 2,2',2''-nitrilotris(N-arylacetamidate) ligands (L^R; R?=?NO₂, Cl, Br, H, Me, and OMe). The complexes are synthesized as the di-tetramethylammonium salts [Me₄N]₂[MnL^R(OAc)]. The nitro variant Mn^NO2 afforded crystals suitable for X-ray diffraction and its molecular structure is reported. We previously reported the crystal structures of Fe^NO2 and Zn^NO2 and additionally report herein the synthesis and characterization of Co^NO2. Using these four molecules, we conduct a brief comparison of the bond metrics to demonstrate that the primary difference governing structural changes is likely due to ionic crystal radii changes rather than electronic properties. The electrochemical properties of the Mn^R complexes were additionally explored with cyclic voltammetry, which revealed that the series is modulated by the various electronic substituents on the aryl groups of the ligands. The electrochemical studies also revealed, consistent with our previous report, that the acetate ligand on the Mn^R complexes is labile. Finally, a Hammett plot was constructed using the potentials obtained from cyclic voltammetry, which is compared with a few other similar transition metal complexes.     

Metallaphotoredox Difluoromethylation of Aryl Bromides

Herein, we report a convenient and broadly applicable strategy for the difluoromethylation of aryl bromides by metallaphotoredox catalysis. Bromodifluoromethane, a simple and commercially available alkyl halide, is harnessed as an effective source of difluoromethyl radical by silyl‐radical‐mediated halogen abstraction. The merger of this fluoroalkyl electrophile activation pathway with a dual nickel/photoredox catalytic platform enables the difluoromethylation of a diverse array of aryl and heteroaryl bromides under mild conditions. The utility of this procedure is showcased in the late‐stage functionalization of several drug analogues.     

Selective Hydrogen Atom Abstraction through Induced Bond Polarization: Direct α‐Arylation of Alcohols through Photoredox,HAT, and Nickel Catalysis

The combination of nickel metallaphotoredox catalysis, hydrogen atom transfer catalysis, and a Lewis acid activation mode, has led to the development of an arylation method for the selective functionalization of alcohol α‐hydroxy C?H bonds. This approach employs zinc‐mediated alcohol deprotonation to activate α‐hydroxy C?H bonds while simultaneously suppressing C?O bond formation by inhibiting the formation of nickel alkoxide species. The use of Zn‐based Lewis acids also deactivates other hydridic bonds such as α‐amino and α‐oxy C?H bonds. This approach facilitates rapid access to benzylic alcohols, an important motif in drug discovery. A 3‐step synthesis of the drug Prozac exemplifies the utility of this new method.     

Phorbasides A-E, cytotoxic chlorocyclopropane macrolide glycosides from the marine sponge Phorbas sp. CD determination of C-methyl sugar configurations

Five new cytotoxic macrolide glycosides phorbasides A-E (3-7), each possessing a macrolide ring appended to a rare ene-yne-trans-2-chlorocyclopropane, were isolated from the same Western Australian sponge (Phorbas sp.) that provided phorboxazoles A and B. The structures of 3-7 were solved by analysis of spectroscopic data including NMR, MS, and CD. A synthesis of methyl 2-O-methyl-alpha-L-evalose from L-rhamnose was completed and used for configurational assignment of the sugar residue in 3. Acid-catalyzed methanolysis of 3 followed by two-step derivatization of the liberated O-methyl glycoside gave a vicinal 4-O-naphthoyl/tertiary 3-N-(2-aminonaphthyl)carbamate derivative that exhibited exciton coupled CD identical with that of the derivative prepared from synthetic 1,2- O-dimethyl-alpha-L-evalose.     

Fluctuation theorems and 1/f noise from a simple matrix

Here we present a model for a small system combined with an explicit entropy bath that iscomparably small. The dynamics of the model is defined by a simple matrix, M. Each row ofM corresponds to a macrostate of the system, e.g. net alignment, while the elements in therow represent microstates. The constant number of elements in each row ensures constantentropy, which allows reversible fluctuations, similar to information theory where aconstant number of bits allows reversible computations. Many elements in M come from themicrostates of the system, but many others come from the bath. Bypassing the bath statesyields fluctuations that exhibit standard white noise; whereas with bath states the powerspectral density varies as S(f) ∝ 1 /f overa wide range of frequencies, f. Thus, the explicit entropy bath is the mechanismof 1/f noisein this model. Both forms of the model match Crooks’ fluctuation theorem exactly,indicating that the theorem applies not only to infinite reservoirs, but also tofinite-sized baths. The model is used to analyze measurements of 1/f-like noise from asub-micron tunnel junction.