Synthesis of two new crown ethers containing selenium and the complexation of one of them with silver and lead

Two new macrocyclic crown ethers containing one or two selenium donor atoms have been prepared. Diselena-18-crown-6 (2) was found to transport silver ions through a methylene chloride bulk membrane at about the same rate as the analogous dithia- (3) and diaza-18-crown-6 (4) compounds and transported lead ions about the same as dithia-18-crown-6 but better than diaza-18-crown-6.     

Density-functional theory calculations of optical rotatory dispersion in the nonresonant and resonant frequency regions

The complex linear response function, which can be employed for calculations of second-order molecular properties in regions of strong absorption, is here extended to encompass the mixed electric-dipole-magnetic-dipole polarizability. The mixed electric-dipole-magnetic-dipole polarizability determines the optical rotation and, when absorption is taken into account, the full anomalous optical rotatory dispersion (ORD) spectra of chiral molecules can be calculated using first-principle quantum-chemical methods. Gauge-origin independence of the results is ensured through the use of London atomic orbitals. To illustrate the importance of taking the absorption process properly into account, we here apply this methodology to the study of the anomalous ORD of hydrogen peroxide, 3R-methylcyclohexanone, 4R-1,1-dimethyl-[3]-(1,2)-ferrocenophan-2-on, and the D(2) isomer of the C(84) fullerene.     

Ion interaction approach to calculations of volumetric properties of aqueous multiple-solute electrolyte solutions

The ion interaction approach developed by Pitzer was used for the prediction of volumetric properties of mixed electrolyte solutions at 25°C based on parameters calculated from experimental data for single-solute electrolyte solutions. Such an approach was shown to be especially effective for application to the calculation of volumetric properties of natural hypersaline brines and of industrial electrolyte solutions of large complexity. The use of the latest recommended sets of volumetric ion interaction parameters for single electrolyte solutions and symmetrical mixing parameters for Na–K–Cl ion combinations considerably improved the precision of the density calculations of highly concentrated mixed electrolyte solutions and of various natural waters.     

Investigation of cationic organic dyes used as molecular probes by liquid secondary ion mass spectrometry

The positive-ion mass spectra of twelve organic dyes used as molecular probes were measured using liquid secondary ion mass spectrometry (LSIMS). Nine of the twelve dyes were singly charged cations and the other three were doubly charged cations. The mass spectra of each of the dyes in m-nitrobenzyl alcohol contain abundant signals for the intact cation, C⁺ (singly charged cation dyes), or for singly-charged forms of the doubly charged cation formed by proton loss, [C²⁺? H⁺]⁺, or halogen counter ion attachment, [C²⁺ + X^?]⁺. Fragmentation is usually minimal under the conditions used. However, the cations of five of the singly charged compounds appear to undergo charge-remote fragmentation. Collision-induced dissociation experiments on a hybrid mass spectrometer of EBqQ geometry at collision energies up to 300 eV failed to access this fragmentation pathway. In contrast to the LSIMS of many other doubly charged organic compounds, two of the dicationic dyes produced a doubly charged ion of reasonable abundance (2–20%) in the mass spectrum. When glycerol was used as a matrix solvent, the addition of the matrix modifier trifluoroacetic acid increased the abundance of C²⁺.     

Hydrogen-bonding contributions to the lattice energy of salts for second harmonic generation

The lattice energies of a series of organic dihydrogenphosphate salts capable of second harmonic generation (SHG) have been calculated. These calculations, coupled with empirical data, indicate that a minimum of 20–25% of the lattice energy arises from hydrogen-bond interactions. Hydrogen bonding is shown to be a strong enough force to have a profound effect on the overall packing and crystal geometry of such ionic materials, and is thus an important factor to consider for crystal engineering.     

Cupric decamolybdodivanadophosphate. A coordination polymer heterogeneous catalyst for rapid, high conversion, high selectivity sulfoxidation using the ambient environment

A new type of coordination network polymer involving the redox-active polyanion, PV(2)Mo(10)O(40)(5)(-), and bridging -Cu(II)(OH(2))(4)- units, [[(Cu(II)(OH(2))(4))(3)(OH)]PV(2)Mo(10)O(40)](n)() (1), has been characterized by X-ray crystallography and several other methods. It is the first efficient heterogeneous (insoluble) catalyst for selective and rapid sulfoxidation using only the ambient environment (air at room temperature). Catalytic activity is enhanced by soluble nitrate in nontoxic perfluoropolyether (PFPE) media.     

Field method for determination of traces of thiols in natural waters

Derivatization with 2,2′-dithiobis(5-nitropyridine) (DTNP) was used to stabilize thiols in field samples and to determine these compounds by liquid chromatography (LC) with ultraviolet detection. Alternatively, the thiols can be regenerated from DTNP derivatives using tributylphosphine (TBP) and derivatized with o-phthalaldehyde (OPA). The DTNP derivatives were stable at pH 5 and 6 for more than 2 weeks in the reaction mixture, but the stability was considerably lower at pH values > 8. Derivatization at pH 6 was routinely done and the reaction was complete within 5 min. The derivatives can be extracted quantitatively on commercial C₁₈ cartridges, which allows several-fold sample enrichment. The cartridge-adsorbed derivatives are stable at 0–5 °C for long periods and, therefore, can be stored for LC separation at a later date. DTNP derivatives of ten low-molecular-weight thiols were separated on a C₁₈ microbore column using gradient elution and a flow-rate of 200 μl min^?1. The relative standard deviation based on repeated analyses of standards is about 5% in the range 0.5–2 nM. Without C₁₈ cartridge enrichment, the detection limits of the studied thiols are in the range 50–100 nM. These limits are further reduced by about 100-fold by using the OPA method after regeneration of thiols from the DTNP derivatives using TBP. Applications of the method to coastal sediment pore water and anoxic Black Sea water are illustrated.     

ROSEOFLAVIN AS A BLUE LIGHT RECEPTOR ANALOG: SPECTROSCOPIC CHARACTERIZATION

Abstract— The blue light absorption band of roseoflavin is polarized along the axis roughly connecting N₃-C₈ positions. A weak, second π→π* transition with a polarization angle of ca. 25° is hidden under the short wavelength side of the blue absorption band. The excited state of roseoflavin is somewhat more basic than the ground state, by a 1.5 p K _a unit. The fluorescence quantum yield and lifetime of roseoflavin are substantially lower than those of other flavins, thus making it kinetically less efficient as a blue light photoreceptor.     

Formation of nanostructured polymer filaments in nanochannels

We describe the use of hard etching methods to create nanodimensional channels and their use as templates for the formation of polymer filament arrays with precise dimensional and orientational control in a single integrated step. The procedure is general as illustrated by the radical, coordination, and photochemical polymerizations that were performed in these nanochannels. The nanochannel templates (20 nm high, 20-200 nm wide, and 100 mum long) were fabricated by the combined use of electron-beam lithography and a sacrificial metal line etching technique. Radical polymerization of acrylates, metal-catalyzed polymerization of norbornene, and photochemical polymerization of 1,4-diiodothiophene were carried out in these nanochannels. The polymers grown follow the dimensions and orientation of the channels, and the polymer filaments can be released without breaking. The approach opens up the possibility of just-in-place manufacturing and processing of patterns and devices from nanostructured polymers using well-established polymer chemistry.     

The different steric environments of the 5-exo- and 5-endo- substituent for a pair of isomeric tricarbonyl(methoxycyclohexa-1,-diene)irons

A shift reagent has been employed to demonstrate the sterically-hindered environment of the methoxy group in tricarbonyl(5-endo-methoxycyclohexa-1,-diene)iron relative to that of the methoxy group in the 5-exo analogue.