Enhancing Water Stability of Metal-Organic Frameworks via Phosphonate Monoester Linkers

A new porous metal-organic framework (MOF), barium tetraethyl-1,3,6,8-pyrenetetraphosphonate (CALF-25), which contains a new phosphonate monoester ligand, was synthesized through a hydrothermal method. The MOF is a three-dimensional structure containing 4.6 ? × 3.9 ? rectangular one-dimensional pores lined with the ethyl ester groups from the ligand. The presence of the ethyl ester groups makes the pores hydrophobic in nature, as determined by the low heats of adsorption of CH(4), CO(2), and H(2)O (14.5, 23.9, and 45 kJ mol(-1), respectively) despite the polar and acidic barium phosphonate ester backbone. The ethyl ester groups within the pores also protect CALF-25 from decomposition by water vapor, with crystallinity and porosity being retained after exposure to harsh humid conditions (90% relative humidity at 353 K). The use of phosphonate esters as linkers for the construction of MOFs provides a method to protect hydrolytically susceptible coordination backbones through kinetic blocking.     

Microdroplet-etched highly birefringent low-loss fiber tapers

We use hydrofluoric acid microdroplets to directly etch highly birefringent biconical fiber tapers from standard single-mode fibers. The fiber tapers have micrometer-sized cross sections, which are controlled by the etching condition. The characteristic teardrop cross section leads to a high group birefringence of B(G)≈0.017 and insertion losses <0.7 dB over waist lengths of about 2.1 mm.     

Synthesis of glucaminium-based ionic liquids and their application in the removal of boron from water

A novel class of ionic liquids (ILs), exhibiting high selectivity towards boron species as well as the ability to phase separate from water, were synthesized from N-methyl-D-glucamine. The complexation of boric acid/borate with the ILs was confirmed using (11)B NMR.     

Analysis of Why Boron Avoids sp2 Hybridization and Classical Structures in the BnHn+2 Series

We performed global minimum searches for the B_nH_n+2 (n=2‐5) series and found that classical structures composed of 2c–2e B? H and B? B bonds become progressively less stable along the series. Relative energies increase from 2.9 kcal mol^?1 in B₂H₄ to 62.3 kcal mol^?1 in B₅H₇. We believe this occurs because boron atoms in the studied molecules are trying to avoid sp² hybridization and trigonal structure at the boron atoms, as in that case one 2p‐AO is empty, which is highly unfavorable. This affinity of boron to have some electron density on all 2p‐AOs and avoiding having one 2p‐AO empty is a main reason why classical structures are not the most stable configurations and why multicenter bonding is so important for the studied boron–hydride clusters as well as for pure boron clusters and boron compounds in general.     

Profiling energetics and spectroscopic signatures in prototropic tautomers of asymmetric phthalocyanine analogues

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) were used to explain discrepancies in UV-vis and MCD spectra of the metal-free tribenzo[b,g,l]thiopheno[3,4-q]porphyrazine (1), substituted tribenzo[b,g,l]porphyrazine (2), and 2,3-bis(methylcarboxyl)phthalocyanine (3). On the basis of gas-phase and polarized continuum solvation model (PCM) DFT and TDDFT calculations, it was suggested that both NH tautomers contribute to the spectroscopic signature of 1, whereas the Q-band region of 2 and 3 is dominated by a single NH tautomer. For all tested compounds, it was found that the combination of the BP86 exchange-correlation functional, 6-31G(d) basis set, and TDDFT-PCM approach provides the best accuracy in energies of the Q(x)- and Q(y)-bands of the individual NH tautomers as well as correctly describes their relative energy differences, which are important in understanding of experimental spectroscopy of the target systems.     

An alternative energy bound derivation for a generalized Hasegawa-Mima equation

We present an alternative derivation of the H¹-boundedness of solutions to a generalized Hasegawa-Mima equation, first investigated by Grauer (1998) [2]. We apply a Lyapunov function technique similar to the one used for constructing energy bounds for the Kuramoto-Sivashinsky equation. Different from Grauer (1998) [2], who uses this technique in a Fourier space approach, we employ the physical space construction of the Lyapunov function, as developed in Bronski and Gambill (2006) [11]. Our approach has the advantage that it is more transparent in what concerns the estimates and the dominant terms that are being retained. A key tool of the present work, which replaces the algebraic manipulations on the Fourier coefficients from the other approach, is a Hardy-Rellich type inequality.     

The Modulational Instability for a Generalized Korteweg–de Vries Equation

We study the spectral stability of a family of periodic standing wave solutions to the generalized Korteweg–de Vries in a neighborhood of the origin in the spectral plane using what amounts to a rigorous Whitham modulation theory calculation. In particular we are interested in understanding the role played by the null directions of the linearized operator in the stability of the traveling wave to perturbations of long wavelength. A study of the normal form of the characteristic polynomial of the monodromy map (the periodic Evans function) in a neighborhood of the origin in the spectral plane leads to two different instability indices. The first, an orientation index, counts modulo 2 the total number of periodic eigenvalues on the real axis. This index is a generalization of the one which governs the stability of the solitary wave. The second, a modulational instability index, provides a necessary and sufficient condition for the existence of a long-wavelength instability. This index is essentially the quantity calculated by Hǎrǎguş and Kapitula in the small amplitude limit. Both of these quantities can be expressed in terms of the map between the constants of integration for the ordinary differential equation defining the traveling waves and the conserved quantities of the partial differential equation. These two indices together provide a good deal of information about the spectrum of the linearized operator. We sketch the connection of this calculation to a study of the linearized operator—in particular we perform a perturbation calculation in terms of the Floquet parameter. This suggests a geometric interpretation attached to the vanishing of the orientation index previously mentioned.     

Acyclic Stereocontrol in the Additions of Nucleophilic Alkenes to α-Chiral N-Sulfonyl Imines

Diastereoselective Lewis acid-mediated additions of nucleophilic alkenes to N-sulfonyl imines are reported. The canonical polar Felkin–Anh model describing additions to carbonyls does not adequately describe analogous additions to N-sulfonyl imines. Herein, we describe the development of conditions to produce both syn and anti products with high diastereoselectivity and good yields. A stereoelectronic model consistent with experimental outcomes is also proposed.     

Synthesis and Anti‐proliferative Activity of N,N′‐bis‐substituted 1,2,4‐Triazolium Salts against Breast Cancer and Prostate Cancer Cell Lines

A series of 1,4‐N,N′‐bis‐substituted 1,2,4‐triazolium bromide salts were synthesized and tested for anti‐proliferative activity. 1,4‐Bis(naphthalen‐2‐ylmethyl)‐1,2,4‐triazolium bromide ( 2 ) showed activity against MDA‐MB‐468 breast cancer and PC‐3 prostate cancer cell lines.