Water Exchange and Rotational Dynamics of the Dimeric Gadolinium(III) Complex [BO{Gd(DO3A)(H(2)O)}(2)]: A Variable-Temperature and -Pressure (17)O NMR Study(1)

Rapid water exchange and slow rotation are essential for high relaxivity MRI contrast agents. A variable-temperature and -pressure (17)O NMR study at 14.1, 9.4, and 1.4 T has been performed on the dimeric BO(DO3A)(2), 2,11-dihydroxy-4,9-dioxa-1,12-bis[1,4,7,10-tetraaza-4,7,10-tris(carboxymethyl)cyclododecyl]dodecane, complex of Gd(III). This complex is of relevance to MRI as an attempt to gain higher (1)H relaxivity by slowing down the rotation of the molecule compared to monomeric Gd(III) complexes used as contrast agents. From the (17)O NMR longitudinal and transverse relaxation rates and chemical shifts we determined the parameters characterizing water exchange kinetics and the rotational motion of the complex, both of which influence (1)H relaxivity. The rate constant and the activation enthalpy for the water exchange, k(ex) and DeltaH(), are (1.0 +/- 0.1) x 10(6) s(-)(1)and (30.0 +/- 0.2) kJ mol(-)(1), respectively, and the activation volume, DeltaV(), of the process is (+0.5 +/- 0.2) cm(3) mol(-)(1), indicating an interchange mechanism. The rotational correlation time becomes about three times longer compared to monomeric Gd(III) polyamino-polyacetate complexes studied so far: tau(R) = (250 +/- 5) ps, which results in an enhanced proton relaxivity by raising the correlation time for the paramagnetic interaction.     

Synthesis and Diversification of Macrocyclic Alkynediyl Sulfide Peptides

The synthesis of rare macrocyclic alkynediyl sulfides by a Cu-catalyzed C_sp−S cross-coupling is presented. The catalytic protocol (Cu(MeCN)₄PF₆/dtbbpy) promotes macrocyclization of peptides, dipeptides and tripeptides at ambient temperature (14 examples, 23→73 % yields) via thiols and bromoalkynes, and is chemoselective with regards to terminal alkynes. Importantly, the underexplored alkynediyl sulfide functionality incorporates a rigidifying structural element and opens new opportunities for diversification of macrocyclic frameworks through S oxidation, halide addition and azide–alkyne cycloaddition chemistries to integrate sulfones, halides or valuable fluorophores (7 examples, 37→92 % yields).     

Coffee adulterant quantification by derivative thermogravimetry and chemometrics analysis

Journal of Thermal Analysis and Calorimetry - Coffee quality is determined by analyzing its chemical, physical, sensory and hygienic-sanitary characteristics. It is a product consumed worldwide...     

Behaviour of tyres in fire

Journal of Thermal Analysis and Calorimetry - The increasing numbers of used tyres constitute a serious threat to the natural environment. The progress made in recent years in the management of...     

Biochemical Examination of the General Defense System of Plants by OPLC

JPC – Journal of Planar Chromatography – Modern TLC - Plant resistance breeding has, so far, been based on specific resistance genes which regulate hypersensitive reaction, resulting in...     

The atomic and electron structure of ZrO2

The atomic structure of amorphous and crystalline zirconium dioxide (ZrO₂) films is studied using X-ray diffraction and extended X-ray absorption fine structure techniques. The electron structure of ZrO₂ is experimentally determined using X-ray and UV photoelectron spectroscopy, and the electron energy band structure is theoretically calculated using electron density functional method. According to these data, the valence band of ZrO₂ consists of three subbands separated by an ionic gap. The upper subband is formed by the O2p states and Zr4d states; the medium subband is formed by the O2s states; and the narrow lower subband is formed predominantly by the Zr4p states. The bandgap width in amorphous ZrO₂, as determined using the electron energy loss spectroscopy data, amounts to 4.7 eV. The electron band structure calculations performed for a cubic ZrO₂ phase point to the existence of both light (0.3m ₀) and heavy (3.5m ₀) holes, where m ₀ is the free electron mass. The effective masses of band electrons in ZrO₂ fall within (0.6–2.0)m ₀.     

Method of kinematic projecting of pulsar-emission profiles

A method for constructing profiles of incoherent pulsar emission based on the instantaneous angular phase distribution function of radiant power emitted by a relativistic source that moves in the magnetosphere of a neutron star is suggested. In general, this phase function depends on the kinematic parameters of the radiation source (its velocity and acceleration) and on the direction of radiation emission with respect to the rotating neutron star (the observation direction). The method is illustrated by the example of calculated profiles of fan pulsar radiation with the use of the phase function of synchrotron radiation. It is stated that his method can easily be generalized for other types of relativistic radiation. Tomsk State University; Tomsk State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 26–31, January, 2000.     

Holographic DFB laser with fan-shaped grating for a spectrofluorimeter

A method for recording fan-shaped transmitting phase holographic gratings that ensure tuning of the wavelength of emission for a DFB (distributed-feedback) dye laser is presented. Traditional optical elements are used in the scheme of grating recording. A change in the degree of grating fanning is reached here without replacement of gratings. The possibility of obtaining frequency-tuned emission by means of the fan-shaped gratings created is demonstrated experimentally. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 48–51, January–February, 2000.     

Structure of polyethylene films containing copper nanoparticles

We have used IR spectroscopy to study the effect of Cu nanoparticles on the degree of crystallinity in nanostructured high-pressure polyethylene (PE) films. We have shown that for ∼1 mass % Cu in the polyethylene films, we observe the maximum degree of crystallinity. This is connected with commensurability between the nanoparticle sizes and the periodicity of the three-dimensional structure of the straightened polyethylene chains in its transitional phase. Dielectric measurements on the nanostructured polyethylene films are support for the features observed in the IR spectra for the systems under study. From the data obtained, we hypothesize that we can control degree of crystallinity of the polymer by varying the sizes of the nanoparticles and the type of polymer. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 408–410, May–June, 2006.