Self-assembly of ordered water tetramers in an encapsulated [Br(H2O)12]- complex

An unanticipated anion-water cluster is assembled by one bromide and three highly-ordered "water tetramers" within the cavity of a receptor, providing a perfect C(3) symmetric propeller-shaped bromide-water cluster of [Br(H(2)O)(12)](-).     

Spectroscopic, structural, and theoretical studies of halide complexes with a urea-based tripodal receptor

A urea-based tripodal receptor L substituted with p-cyanophenyl groups has been studied for halide anions using (1)H NMR spectroscopy, density functional theory (DFT) calculations, and X-ray crystallography. The (1)H NMR titration studies suggest that the receptor forms a 1:1 complex with an anion, showing a binding trend in the order of fluoride > chloride > bromide > iodide. The interaction of a fluoride anion with the receptor was further confirmed by 2D NOESY and (19)F NMR spectroscopy in DMSO-d(6). DFT calculations indicate that the internal halide anion is held by six NH···X interactions with L, showing the highest binding energy for the fluoride complex. Structural characterization of the chloride, bromide, and silicon hexafluoride complexes of [LH(+)] reveals that the anion is externally located via hydrogen bonding interactions. For the bromide or chloride complex, two anions are bridged with two receptors to form a centrosymmetric dimer, while for the silicon hexafluoride complex, the anion is located within a cage formed by six ligands and two water molecules.     

Microwave enhanced Akabori reaction for peptide analysis

The Akabori reaction, devised in 1952 for the identification of C-terminus amino acids, involves the heating of a linear peptide in the presence of anhydrous hydrazine in a sealed tube for several hours. We report here a modified Akabori reaction that rapidly identifies the C-terminus amino acid in a polypeptide including its amino acid sequence information at both the C-terminus and the N-terminus. This modified methodology demonstrates the fundamentals of microwave chemistry applied to bioanalytical problems. In this modified process, hydrazinolysis has been accelerated by the application of microwave irradiation. In our reaction, the linear peptide and hydrazine solution, contained in a loosely covered conical flask, was exposed to a few minutes of irradiation using an unmodified domestic microwave oven. While the classical Akabori reaction required several hours, the microwave assisted reaction takes just minutes. If dimethyl sulfoxide is added to dilute the reaction mixture, the process is retarded enough to allow aliquots of the reaction mixture to be drawn every few minutes over a period of about an hour in order to study the progress of hydrazinolysis. Reaction products were monitored by mass spectrometry-primarily FAB-MS. In addition to providing sequence information, the microwave enhanced Akabori reaction quickly detects the presence of arginine (Arg) by converting each Arg to ornithine (Orn). Furthermore, certain amino acids, containing beta-SH, CO2H, and CONH2 groups in their side chain, are susceptible to modification by hydrazine, thereby, providing rapid confirmation of the presence of these amino acid residues. In these preliminary studies, the following oligopeptides were analyzed to demonstrate the effectiveness of our approach; the dipeptide (Trp-Phe), the tripeptide (Tyr-Gly-Gly), the tetrapeptide (Pro-Phe-Gly-Lys), the heptapeptide (Ala-Pro-Arg-Leu-Arg-Phe-Tyr), and a N-terminal blocked tripeptide (N-acetyl-Met-Leu-Phe).     

Anion Cluster: Assembly of Dihydrogen Phosphates for the Formation of a Cyclic Anion Octamer

Structural characterization of a dihydrogen phosphate complex of triprotonated tris[2-(2-thienylmethylamino)ethyl] amine shows that eight dihydrogen phosphate anions are assembled around the host by strong interactions of H-bond donors and acceptors to form a new type of cyclic anion octamer as (H(2)PO(4) (-))(8), an analogy of cyclic water octamer. The presence of an anion cluster has also been identified by electrospray ionization mass spectrometry and (31)P NMR experiments.     

Study of effective parameters on wear behavior of rubbers based on statistical methods

This study investigates the wear, surface roughness, and temperature buildup (TBU) of styrene butadiene rubber (SBR), natural rubber (NR), and nitrile butadiene rubber (NBR) while sliding over abrasives of different sizes with the variation of normal load. Rubber properties such as tensile strength (s) and elongation at break (e) were considered as input parameters. Individual, as well as interacting effects of different parameters, were analyzed in‐depth by using statistical methods. Overall wear of rubber depends not only on the tribological system but also on mechanical properties that contribute different wear mechanisms in addition to abrasion. The abrasive particle size and 1/(se) are the first and second most significant contributing factors, respectively, to all output parameters except the wear rate where the second contributing factor is the applied load and abrasive size is the highest contributor. Larger abrasive particles deepen ploughing marks, which is enhanced by the higher load, and lead to higher surface roughness. The effect of load on TBU is negligible because of the soft nature of the rubber material.     

A tighter steering criterion using the Robertson–Schrödinger uncertainty relation

We consider quantum steering by non-Gausssian entangled states. The Reid steering criterion based on the Heisenberg uncertainty relation fails to detect steerability for many categories of such states. Here, we derive a tighter steering criterion using the Robertson–Schrödinger uncertainty relation. We show that our steering condition is able to detect steerability of several classes of non-Gaussian states such as entangled eigenstates of the two-dimensional harmonic oscillator, the photon subtracted squeezed vacuum state and the NOON state.     

Nanoparticle decoration with surfactants: Molecular interactions,assembly, and applications

Nanostructures of diverse chemical nature are used as biomarkers, therapeutics, catalysts, and structural reinforcements. The decoration with surfactants has a long history and is essential to introduce specific functions. The definition of surfactants in this review is very broad, following its lexical meaning “surface active agents”, and therefore includes traditional alkyl modifiers, biological ligands, polymers, and other surface active molecules. The review systematically covers covalent and non-covalent interactions of such surfactants with various types of nanomaterials, including metals, oxides, layered materials, and polymers as well as their applications. The major themes are (i) molecular recognition and noncovalent assembly mechanisms of surfactants on the nanoparticle and nanocrystal surfaces, (ii) covalent grafting techniques and multi-step surface modification, (iii) dispersion properties and surface reactions, (iv) the use of surfactants to influence crystal growth, as well as (v) the incorporation of biorecognition and other material-targeting functionality. For the diverse materials classes, similarities and differences in surfactant assembly, function, as well as materials performance in specific applications are described in a comparative way. Major factors that lead to differentiation are the surface energy, surface chemistry and pH sensitivity, as well as the degree of surface regularity and defects in the nanoparticle cores and in the surfactant shell. The review covers a broad range of surface modifications and applications in biological recognition and therapeutics, sensors, nanomaterials for catalysis, energy conversion and storage, the dispersion properties of nanoparticles in structural composites and cement, as well as purification systems and classical detergents. Design principles for surfactants to optimize the performance of specific nanostructures are discussed. The review concludes with challenges and opportunities.     

A chelating resin containing bis(2-benzimidazolylmethyl)amine: synthesis and metal-ion uptake properties suitable for analytical application

A new stable chelating resin was synthesized by incorporating the bis(2-benzimidazolyl methyl)amine into Merrifield polymer through CN covalent bond and characterized by elemental analysis, IR and thermal study. The sorption capacity of the newly formed resin for Ag(I), Cu(II), Fe(III), Hg(II) and Pb(II) as a function of pH have been studied. The resin exhibits no affinity for alkali or alkaline earth metals. In column operation it has been observed that Ag(I) in trace quantities can be separated from different complex matrices and Hg(II) can be removed from the river water spiked with Hg(II) at usual pH of natural waters.     

A C Symmetric Nitrate Complex with a Thiophene-Based Tripodal Receptor

A thiophene-based tripodal receptor has been synthesized and its complexes with nitrate and iodide have determined by single-crystal X-ray analysis. In the nitrate complex, one nitrate is encapsulated in a selective orientation forming a C(3) symmetric complex, which is bonded to three protonated secondary amines with six NH···O bonds. The anion is coordinated in a plane perpendicular to the principal rotation axis passing through the tertiary nitrogen of the receptor and the nitrogen of the encapsulated nitrate. High-level DFT calculations support the crystallographic results demonstrating that an adduct with trigonal binding of three oxygen atoms is more stable than that of one oxygen atom of the encapsulate nitrate. On the other hand, in the structure of the iodide complex, all three iodides lie outside the cavity. (1)H NMR titration studies indicate that the receptor forms a 1:1 complex with nitrate with a binding constant of K = 315 M(-1) in chloroform, showing a moderate selectivity over halides and perchlorate.     

The Mott T−14 law from the rate equation formalism

The Mott $\text{T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>4</mtext>}}$ law for the dc hopping conductivity for amorphous semiconductors is derived from the rate equation formalism by using the methodology of Butcher and Hayden. This formula is then fitted to the experimental data for a-Si, a-Ge, partially compensated heavily doped n-type Ge and polymer PPIB at 640 atmospheric pressures. It is found that the “simplified Butcher formula” approximately fits the experimental data for a-Si and a-Ge. The values of the density of states at the Fermi level calculated from the expression for the prefactor of this formula are much more reasonable values than those obtained from the original Mott formula. The origin of this significant improvement is found to lie not in improved approximations but in the choice of the values of the characteristics frequency R₀.