Continuous electrowetting via electrochemical diodes

We describe a novel method for droplet transport combining electrowetting on dielectric (EWOD) and the diode-like behavior of valve metals to achieve unique actuation performance. While traditional EWOD droplet transport requires switching of voltage between multiple electrodes, our method, which we term continuous rectified electrowetting, utilizes a simple single electrode and a DC voltage to move a 50 μl droplet 28 mm with velocities up to 32 mm s(-1).     

Monofunctionalized pillar[5]arene as a host for alkanediamines

Alkanediamines serve as neutral guests for the recently discovered host pillar[5]arene. The proposed [2]pseudorotaxane nature of the superstructure of the 1:1 host-guest complexes is supported by the template-directed synthesis of a related [2]rotaxane. A synthetic route to monofunctional pillar[5]arenes has also been developed, allowing for the creation of a fluorescent sensor for alkylamine binding. The precursors to this host could act as starting points for a large library of monofunctional pillar[5]arene macrocycles.     

A novel fourier transform ion cyclotron resonance mass spectrometer with improved ion trapping and detection capabilities

A novel Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer has been developed for improved biomolecule analysis. A flared metal capillary and an electrodynamic ion funnel were installed in the source region of the instrument for improved ion transmission. The transfer quadrupole is divided into 19 segments, with the capacity for independent control of DC voltage biases for each segment. Restrained ion population transfer (RIPT) is used to transfer ions from the ion accumulation region to the ICR cell. The RIPT ion guide reduces mass discrimination that occurs as a result of time-of-flight effects associated with gated trapping. Increasing the number of applied DC bias voltages from 8 to 18 increases the number of ions that are effectively trapped in the ICR cell. The RIPT ion guide with a novel voltage profile applied during ion transfer provides a 3- to 4-fold increase in the number of ions that are trapped in the ICR cell compared with gated trapping for the same ion accumulation time period. A novel ICR cell was incorporated in the instrument to reduce radial electric field variation for ions with different z-axis oscillation amplitudes. With the ICR cell, called trapping ring electrode cell (TREC), we can tailor the shape of the trapping electric fields to reduce dephasing of coherent cyclotron motion of an excited ion packet. With TREC, nearly an order of magnitude increase in sensitivity is observed. The performance of the instrument with the combination of RIPT, TREC, flared inlet, and ion funnel is presented.     

Molecular Modeling,Synthesis, and Biological Evaluation of Macrocyclic Calpain Inhibitors

The design and elaboration of a series of macrocyclic templates that exhibit a propensity to adopt a β‐strand‐like peptide‐backbone conformation led to potent and selective inhibitors of calpain 2. Macrocycle 1 retarded calcium‐induced opacification in an ovine‐lens culture assay and is a lead compound for the development of a drug for cataract treatment. Cbz=carbobenzyloxy.

     

Angle-dependent electronic effects in 4,4'-bipyridine-bridged Ru3 triangle and Ru4 square complexes

Use of 1,4,7,10-tetraazacyclododecane (cyclen) as a capping ligand and 4,4'-bipyridine (4,4'-bpy) as a bridging ligand enables assembly of redox-active Ru3 triangle and Ru4 square complexes. The former is produced by reacting [(cyclen)Ru(DMSO)Cl]Cl with 4,4'-bpy in a 3:1 ethanol:water mixture to precipitate [(cyclen)3Ru3(4,4'-bpy)3]Cl6.18H2O.THF (4), whereas the latter is generated as [(cyclen)4Ru4(4,4'-bpy)4](CF3SO3)8.2CF3SO3H.5MeOH (7) by reacting (cyclen)Ru(CF3SO3)3 with 4,4'-bpy in methanol. The crystal structure of 4.11H2O reveals an equilateral triangle in which the 4,4'-bpy bridges are bowed outward, such that the pyridine rings are all forced to be perpendicular to the Ru3 triangle. Consequently, adjacent pyridine rings are essentially coplanar, and the cyclic voltammogram of [(cyclen)3Ru3(4,4'-bpy)3]6+ in acetonitrile displays three distinct one-electron oxidation events. Cyclic voltammetry measurements reveal redox processes centered at E(1/2) = 0.207, 0.342, and 0.434 V versus Cp2Fe(0/+) that are assigned to 6+/7+, 7+/8+, and 8+/9+ couples of the [(cyclen)3Ru3(4,4'-bpy)3]n+ triangle, respectively. In contrast, the structure of [(cyclen)4Ru4(4,4'-bpy)4]8+ features a regular square geometry wherein the rings of the bridging 4,4'-bpy ligands are free to rotate, leading to just one four-electron oxidation couple centered at 0.430 V. Density functional theory calculations performed on [(cyclen)3Ru3(4,4'-bpy)(3)]6+ reveal metal-based orbitals with contributions from the pi system of the bridging 4,4'-bpy ligands, providing a likely pathway for electron transfer.     

Evaluation of Baylis–Hillman Routes to 3-(Aminomethyl)coumarin Derivatives

The relative merits of two different Baylis–Hillman approaches toward the preparation of coumarin derivatives, containing peptide-like side chains, have been explored. In one approach, use of methyl acrylate as the activated alkene requires a protecting group strategy, an approach that is not necessary when using tert-butyl acrylate.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Synthesis of [(HIPTNCH2CH2)3N]Cr Compounds (HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3) and an evaluation of chromium for the reduction of dinitrogen to ammonia

Red-black [HIPTN3N]Cr (1) ([HIPTN3N]3- = [(HIPTNCH2CH2)3N]3- where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3 = HexaIsoPropylTerphenyl) can be prepared from CrCl3, while green-black [HIPTN3N]Cr(THF) (2) can be prepared from CrCl3(THF)3. Reduction of {1|2} (which means either 1 or 2) with potassium graphite in ether at room temperature yields [HIPTN3N]CrK (3) as a yellow-orange powder. There is no evidence that dinitrogen is incorporated into 1, 2, or 3. Compounds that can be prepared readily from {1|2} include red [HIPTN3N]CrCO (4), blood-red [HIPTN3N]CrNO (6), and purple [HIPTN3N]CrCl (7, upon oxidation of {1|2} with AgCl). The dichroic (purple/green) Cr(VI) nitride, [HIPTN3N]CrN (8) was prepared from Bu4NN3 and 7. X-ray studies have been carried out on 4, 6, and 7, and on two co-crystallized compounds, 7 and [HIPTN3N]CrN3 (65:35) and [HIPTN3N]CrN3 and 8 (50:50). Exposure of a degassed solution of {1|2} to an atmosphere of ammonia does not yield "Cr(NH3)" as a stable and well-behaved species analogous to Mo(NH3). An attempt to reduce dinitrogen under conditions described for the catalytic reduction of dinitrogen by [HIPTN3N]Mo compounds with 8 yielded a substoichiometric amount (0.8 equiv) of ammonia, which suggests that some ammonia is formed from the nitride but none is formed from dinitrogen.     

Coordination of diatomic ligands to heme: simply CO

The synthesis and molecular structures of three iron(II) porphyrinates with only CO as the axial ligand(s) are reported. Two five-coordinate [Fe(OEP)(CO)] derivatives have Fe-C = 1.7077(13) and 1.7140(10) A, much shorter than those of six-coordinate [Fe(OEP)(Im)(CO)], although nu(C-O) is 1944-1948 cm(-1). The six-coordinate species [Fe(OEP)(CO)2] has also been studied. The competition for pi-back-bonding of two CO ligands leads to Fe-C distance of 1.8558(10) A and nu(C-O) being increased to 2021 cm(-1). The M?ssbauer spectrum has a quadrupole splitting constant of 0 mm/s at 4.2 K, indicating high electronic symmetry.     

Light- and pH-regulated Water-soluble Pseudorotaxanes Comprising a Cucurbit[7]uril and a Flavylium-based Axle

A linear double pyridinium-terminated thread comprising a central chalcone moiety is shown to provide two independent binding sites with similar affinity for cucurbit[7]uril (CB7) macrocycles in water as judged from NMR, UV-Visible and fluorescence spectroscopies. Association results in [2] and [3]pseudorotaxanes, which are both pH and photosensitive. Switching from the neutral chalcone to the cationic flavylium form upon irradiation at 365 nm under acidic conditions provided an enhanced CB7 association (K_1:1 increases from 1.2×10⁵ M⁻¹ to 1.5×10⁸ M⁻¹), limiting spontaneous on-thread cucurbituril shuttling. This co-conformational change in the [2]pseudorotaxane is reversible in the dark with k_obs=4.1×10⁻⁴ s⁻¹. Threading the flavylium moiety into CB7 leads to a dramatic increase in the fluorescence quantum yield, from 0.29 in the free axle to 0.97 in the [2]pseudorotaxane and 1.0 in the [3]pseudorotaxane.