Infra-red spectrum of water dimer in carbon tetrachloride solution

Geometries of six low-lying excited states of ozone are calculated by a limited SCF-CI procedure and are analysed in detail on the basis of the bonding properties of the molecular orbitals involved in the corresponding excitations. The triplet and singlet A ₂ states are sharply bent with a valence angle of 99°. Differences between triplet and singlet states of same spatial symmetry are also accounted for with special emphasis on the B ₂ states.     

Holz, Cellulose

Ohne Zusammenfassung     

Femtosecond ligand/core dynamics of microwave-assisted synthesized silicon quantum dots in aqueous solution

A microwave-assisted reaction has been developed to produce hydrogen-terminated silicon quantum dots (QDs). The Si QDs were passivated for water solubility via two different methods: hydrosilylation produced 3-aminopropenyl-terminated Si QDs, and a modified St?ber process produced silica-encapsulated Si QDs. Both methods produce water-soluble QDs with maximum emission at 414 nm, and after purification, the QDs exhibit intrinsic fluorescence quantum yield efficiencies of 15 and 23%, respectively. Even though the QDs have different surfaces, they exhibit nearly identical absorption and fluorescence spectra. Femtosecond transient absorption spectroscopy was used for temporal resolution of the photoexcited carrier dynamics between the QDs and ligand. The transient dynamics of the 3-aminopropenyl-terminated Si QDs is interpreted as a formation and decay of a charge-transfer (CT) excited state between the delocalized π electrons of the carbon linker and the Si core excitons. This CT state is stable for ~4 ns before reverting back to a more stable, long-living species. The silica-encapsulated Si QDs show a simpler spectrum without CT dynamics.     

Arsenic-Induced Biochemical Changes in Labeo rohita Kidney: An FTIR Study

ABSTRACT

Arsenic is a toxic heavy metal that occurs naturally in water, soil, and air. It is widespread in the environment as a consequence of both anthropogenic and natural processes. In the current study, an attempt has been made to analyze the arsenic-induced molecular changes in macromolecular components like proteins and lipids in the kidney tissues of edible fish Labeo rohita using Fourier transform infrared (FTIR) spectroscopy. The FTIR spectrum of kidney tissue is quite complex and contains several bands arising from the contribution of different functional groups. The detailed spectral analyses were performed in three distinct wave number regions, namely 3600–3050 cm^?1, 3050–2800 cm^?1, and 1800–800 cm^?1. The current study shows that the kidney tissues are more vulnerable to arsenic intoxication. FTIR spectra reveal significant differences in both absorbance intensities and areas between control and arsenic-intoxicated kidney tissues; this result indicates that arsenic intoxication induces significant alteration on the major biochemical constituents such as lipids and proteins and leads to compositional and structural changes in kidney tissues at the molecular level. The current study confirms that FTIR spectroscopy can be successfully applied to toxicologic and biological studies.     

Solid-phase synthesis of m-phenylene ethynylene heterosequence oligomers

Both homo- and heterosequence m-phenylene ethynylene oligomers are synthesized using a conceptually simple iterative solid-phase strategy. Oligomers are attached to Merrifield's resin through a known triazene-type linkage. The phenylene ethynylene molecular backbone is constructed through a series of palladium-mediated cross-coupling reactions. The strategy employs two types of monomers that bear orthogonal reactivity, one being a monoprotected bisethynyl arene and the other being a 3-bromo-5-iodo arene. The catalyst conditions are tailored to the requirements of each monomer type. The monoprotected bisethynyl arene is coupled to the growing chain in 2 h at room temperature using a Pd(I) dimer precatalyst ((t)Bu3P(Pd(mu-Cl)(mu-2-methyl allyl)Pd)P(t)Bu3) in conjunction with ZnBr2 and diisopropylamine. In alternate steps, the resin is deprotected in situ with TBAF and coupled to the 3-bromo-5-iodo arene using the iodo selective Pd(tri-2-furylphosphine)4 catalyst in conjunction with CuI and piperidine; this reaction is also completed in 2 h at room temperature. These cross-coupling events are alternated until an oligomer of the desired length is achieved. The oligomer is then cleaved from the resin using CH(2)I(2)/I(2) at 110 degrees C and purified using preparatory GPC. Using this method, a series of homo- and heterosequence oligomers up to 12 units in length in excellent yield and purity were synthesized on the 100 mg scale. Longer oligomers were attempted; however, deletion sequences were found in oligomers longer than 12 units.     

The role of electron exchange in cidep

An alternative vector model of chemically induced electron polarization is introduced and a scheme for exhibiting the role of exchange is described.     

Radiopharmaceuticals

The special requirements, production and utilization of radiopharmaceuticals are reviewed. The growth of nuclear medicine as a medical specialty in the past few years has coincided with the development of newer radiopharmaceuticals, particularly in kit form, to take advantage of the favorable physical and dosimetric aspects of short-lived radionuclides such as ^99mTc. Studies can now be performed to evaluate morphology and function of many more organs and body regions than was possible only a few years ago. These studies are performed in a non-invasive manner using the tracer principle.     

Interaction of glutathione S-transferase with hypericin: A photophysical study

The photophysics of hypericin have been studied in its complex with two different isoforms, A1-1 and P1-1, of the protein glutathione S-transferase (GST). One molecule of hypericin binds to each of the two GST subunits. Comparisons are made with our previous results for the hypericin/human serum albumin complex (Photochem. Photobiol. 1999, 69, 633-645). Hypericin binds with high affinity to the GSTs: 0.65 microM for the A1-1 isoform and 0.51 microM for the P1-1 isoform (Biochemistry 2004, 43, 12761-12769). The photophysics and activity of hypericin are strongly modulated by the binding protein. Intramolecular hydrogen-atom transfer is suppressed in both cases. Most importantly, while there is significant singlet oxygen generation from hypericin bound to GST A1-1, binding to GST P1-1 suppresses singlet oxygen generation to almost negligible levels. The data are rationalized in terms of a simple model in which the hypericin photophysics depends entirely upon the decay of the triplet state by two competing processes, quenching by oxygen to yield singlet oxygen and ionization, the latter of these two are proposed to be modulated by A1-1 and P1-1.