Structural and chemical characterization of monofluoro-substituted oligo(phenylene-ethynylene) thiolate self-assembled monolayers on gold

Monolayers of oligo(phenylene-ethynylene) (OPE) molecules have exhibited promise in molecular electronic test structures. This paper discusses films formed from a novel molecule within this class, 2-fluoro-4-phenylethynyl-1-[(4-acetylthio)phenylethynyl]benzene (F-OPE). The conditions of self-assembled monolayer (SAM) formation were systematically altered to fabricate reproducible high-quality molecular monolayers from the acetate-protected F-OPE molecule. Detailed characterization of the F-OPE monolayers was performed by using an array of surface probes, including reflection absorbance infrared spectroscopy (RAIRS), contact angle (CA) measurements, spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and atomic force microscopy (AFM). XPS and RAIRS established that the SAM formed without removal of the F substituent and without oxidation of the thiol. The monolayer thickness, determined from SE and AFM based nanolithography, was consistent with the formation of a densely packed monolayer. The valence electronic structure of the SAM was consistent with an aromatic structure shifted by the electron-withdrawing fluorine substituent and intermolecular coupling within an oriented array of molecules.     

Rapid fixation of methylene chloride by a macrocyclic amine

A simple macrocyclic amine is alkylated by methylene chloride to give a quaternary ammonium chloride salt. When methylene chloride is the solvent, the reaction exhibits pseudo-first-order kinetics, and the reaction half-life at 25.0 degrees C is 2.0 min. The reaction half-life for a structurally related, acyclic amine is approximately 50 000 times longer. Detailed calculations favor a mechanism where the methylene chloride associates with the macrocycle to form an activated prereaction complex. The macrocyclic nitrogen subsequently attacks the methylene chloride with a classic SN2 trajectory, and although the carbon-chlorine bond breaks, the chloride leaving group does not separate from the newly formed cationic macrocycle, such that the product is a tightly associated ion-pair. X-ray crystal structures of the starting amine and the product salt, as well as kinetic data, support this mechanism.     

The use of surface tension to predict the formation of 2D arrays of latex spheres formed via the Langmuir-Blodgett-like technique

Highly ordered hexagonal arrays of latex spheres on highly ordered pyrolytic graphite (HOPG) have been prepared from a Langmuir-Blodgett-like (LB-like) technique using both polymers and surfactants as spreading agents. The role of spreading agent concentration in forming a well-ordered, stable monolayer at the air-liquid interface was studied by means of atomic force microscopy, scanning electron microscopy, optical microscopy, and surface tension measurements for three different systems: a nonionic surfactant, octylphenoxy poly(ethyleneoxy)ethanol (Igepal CO 630); an anionic surfactant, sodium dodecyl sulfate; and a low-molecular-weight, water-soluble polymer, polyacrylamide. For both the anionic surfactant and the water soluble polymer, a correlation was found between a unique feature in surface tension measurements of the latex-spreading agent mixture and the concentrations at which hexagonal arrays of latex spheres form on the surface of HOPG. For the nonionic surfactant, no ordered structures were found on HOPG for any surfactant concentration, consistent with no appearance of the unique feature in surface tension measurements. These results show that a tensiometer can be used to determine the conditions under which well-ordered latex films have the possibility of forming on a substrate using the LB-like technique; however, other factors, such as pulling speed and surface chemistry, play a role as well.     

Total synthesis of pyridovericin: studies toward the biomimetic synthesis of pyridomacrolidin

[reaction: see text] The total synthesis of the novel metabolite pyridovericin 1 is reported. The synthesis of this key intermediate in our proposed biomimetic synthesis of pyridomacrolidin 2 has been accomplished in good yield from readily available 2,4-dihydroxypyridine.     

Cyclopentene carbocyclic nucleosides related to the antitumor nucleoside clitocine and their conversion to 8-Aza-neplanocin analogues. Synthesis and antiviral activity

Synthesis of the cyclopentene carbocyclic analogue of the naturally occurring nucleoside clitocine ( 1 ) is reported. Starting with racemic cyclopentenylamine ( 10 ), the heterocyclic moieties of the clitocine analogue 4 and related 1,6-dihydro-6-oxo, 5 , and 2-amino-1,6-dihydro-6-oxo, 6 , analogues were constructed. These compounds were respectively converted to 8-aza-neplanocin A (7) , 8-aza-neplanocin D ( 8 , the inosine analogue), and the corresponding 8-aza-guanosine analogue 9 after reduction of the nitro group followed by nitrous acid cyclization. Extensive antiviral evaluation revealed that only 8-aza-neplanocin A ( 7 ) had enough antiviral activity to warrant further studies. This compound showed weak antiviral activity against HSV-1, HSV-20 and the thymidine kinase deficient (TK-) HSV-1. However, it displayed good antiviral activity against human cytomegalovirus (HCMV) at a concentration of 0.40–2.50 μg/ml, well below the cytotoxicity threshold. This activity profile is consistent with a mechanism of action involving the inhibition of the enzyme adenosylhomo-cysteine hydrolase.     

Calix[n]bispyrrolylbenzenes: synthesis, characterization, and preliminary anion binding studies

A series of novel calixpyrrole-like macrocycles, calix[n]bis(pyrrol-2-yl)benzene (calix[n]BPBs, n=2-4) 9 a-11 a, have been synthesized by means of the TFA-catalyzed condensation reaction of bis(pyrrol-2-yl)benzene 8 a with acetone. Calix[2]BPB 9 a represents an expanded version of calix[4]pyrrole in which two of the four meso bridges are replaced by benzene rings. By contrast, systems 10 a and 11 a, which bear great considerable to calixbipyrroles 2 and 3, represent higher homologues of the basic calix[n]BPB motif. Solution-phase anion binding studies, carried out by means of (1)H NMR spectroscopic titrations in [D2]dichloromethane and isothermal titration calorimetry (ITC) in 1,2-dichloroethane, reveal that 9 a binds typical small anions with substantially higher affinities than 1, even though the same number of hydrogen bonding donor groups are found in both compounds. The basic building block for 9 a, benzene dipyrrole 8 a, also displays a higher affinity for anions than the building block for 1, dimethyldipyrromethane 16. Structural studies, carried out by single-crystal X-ray diffraction analyses, are consistent with the solution-phase results and reveal that 9 a is able to stabilize complexes with chloride and nitrate in the solid state. Structures of the PF6- and NO3- complexes of 10 a were also solved as were those of the acetone adduct of 9 a and the ethyl acetate adduct of 11 a.     

Structural, topographical, and shear characteristics of milk protein and monoglyceride monolayers spread at the air-water interface

In this contribution we are concerned with the study of structure, topography, and surface rheological characteristics under shear conditions of monoglyceride (monopalmitin and monoolein) and milk protein (beta-casein, kappa-casein, caseinate, and WPI) spread monolayers at the air-water interface. Combined surface chemistry (surface film balance and surface shear rheometry) and microscopy (Brewster angle microscopy: BAM) techniques have been applied in this study to pure emulsifiers (proteins and monoglycerides) spread at the air-water interface. To study the shear characteristics of spread films, a homemade canal viscometer was used. The experiments have demonstrated the sensitivity of the surface shear viscosity (eta(s)) of protein and monoglyceride films at the air-water interface, as a function of surface pressure (or surface density). The surface shear viscosity was higher for proteins than for monoglycerides. In addition, eta(s) was higher for the globular WPI than for disordered beta-casein and caseinate due to the strong forces acting on spread globular proteins. This technique makes it possible to distinguish between beta-casein and caseinate spread films, with the higher eta(s) values for the later due to the presence of kappa-casein. The eta(s) value varies greatly with the surface pressure (or surface density). In general, the greater the surface pressure, the greater the values of eta(s). Finally, the eta(s) value is also sensitive to the monolayer structure, as was observed for monoglycerides with a rich structural polymorphism (i.e., monopalmitin).     

Understanding the Effects of Binders in Gas Sorption and Acidity of Aluminium Fumarate Extrudates

Understanding the impact of shaping processes on solid adsorbents is critical for the implementation of MOFs in industrial separation processes or as catalytic materials. Production of MOF-containing shaped particles is typically associated with loss of porosity and modification of acid sites, two phenomena that affect their performance. Herein, we report a detailed study on how extrusion affects the crystallinity, porosity, and acidity of the aluminium fumarate MOF with clays or SiO₂ gel binders. Thorough characterization showed that the clay binders confer the extrudates a good mechanical robustness at the expense of porosity, while silica gel shows an opposite trend. The CO₂ selectivity towards CH₄, of interest for natural gas separation processes, is maintained upon the extrusion process. Moreover, probe FTIR spectroscopy revealed no major changes in the types of acid sites. This study highlights that these abundant and inexpensive clay materials may be used for scaling MOFs as active adsorbents.     

Long-range JCH heteronuclear coupling constants in cyclopentane derivatives. Part II

Here we report the detailed measurement of long-range heteronuclear spin-spin coupling constants, especially 2, 3JCH spin-spin couplings for eight different cyclopentane derivatives. These 2, 3JCH constants were shown to be a useful tool in the determination of the relative stereochemistry in these rings. The coupling constant measurements reported here are based on two different experiments: a 2D heteronuclear correlation experiment named G-BIRDR, X-CPMG-HSQMBC and the 2D-coupled gHSQC {1H-13C} experiment