Density Functional Theory and Low-Temperature Matrix Investigations of CO-Loss Photochemistry from [(C<Subscript>5</Subscript>R<Subscript>5</Subscript>)Ru(CO)<Subscript>2</Subscript>]<Subscript>2</Subscript> (R = H,Me) Complexes

The photochemical CO-loss products of the diruthenium complexes [CpRu(CO) ₂]₂ (5; Cp = ⁵-C₅H₅), [Cp*Ru(CO)₂]₂ (5*; Cp* = ⁵-C₅(CH₃)₅) and CpCp*[Ru(CO)₂]₂ (5) have been studied experimentally in low-temperature (96 K) matrices in 3-methylpentane by using IR spectroscopy. It is proposed that all three complexes undergo single-CO-loss chemistry but that the products have different structures. The single-CO-loss product from 5 is proposed to have one bridging and two terminal carbonyl ligands, whereas 5* and 5 generate triply bridged CO-loss products similar to that observed from [CpFe(CO)₂]₂ and [Cp*Fe(CO)₂]₂. Double-CO-loss from 5* and 5* 9 is also apparently observed. Relativistic DFT calculations have been carried out on various isomers of the starting materials and on potential CO-loss products from 5. The calculations suggest that the triply bridged product Cp₂Ru₂(-CO)₃ (6) might have a singlet ground state in contrast to the corresponding diiron complex Cp₂Fe₂(-CO)₃ (3), which has a triplet ground state.     

Protein crystal nucleation: is the pair interaction potential the primary determinant of kinetics?

Fundamental understanding of protein crystal nucleation facilitates crystallization of biological macromolecules for structure determination and control of crystal size distribution. In the studies presented here, nucleation kinetics of hen egg-white lysozyme crystals were measured at solution conditions that exhibited equal solubility by adjusting pH, temperature, or sodium chloride concentration. It was observed that solution conditions that lead to equal solubility resulted in equal nucleation rates and hence kinetic parameters. Since the solubility of globular proteins correlates with the osmotic second virial coefficient, B(22), an integral measure of the protein pair interaction potential, this observation indicates that the protein pair interaction plays a key role in determining nucleation kinetic parameters.     

DNA interchain cross-links formed by acrolein and crotonaldehyde

Acrolein and higher alpha,beta-unsaturated aldehydes are bifunctional genotoxins. The deoxyguanosine adduct of acrolein, 3-(2-deoxy-beta-d-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2-a]purin-10(3H)-one (8-hydroxy-1,N(2)-propanodeoxyguanosine, 2a), is a major DNA adduct formed by acrolein. The potential for oligodeoxynucleotide duplexes containing 2a to form interchain cross-links was evaluated by HPLC, CZE, MALDI-TOF, and melting phenomena. Interchain cross-links represent one of the most serious types of damage in DNA since they are absolute blocks to replication. In oligodeoxynucleotides containing the sequence 5'-dC-2a, cross-linking occurred in a slow, reversible manner to the extent of approximately 50%. Enzymatic digestion to form 3-(2-deoxy-beta-d-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-(N(2)-2'-deoxyguanosinyl)pyrimido[1,2-a]purin-10(3H)one (5a) and reduction with NaCNBH(3) followed by enzymatic digestion to give 1,3-bis(2'-deoxyguanosin-N(2)-yl)propane (6a) established that cross-linking had occurred with the exocyclic amino group of deoxyguanosine. It is concluded that the cross-link is a mixture of imine and carbinolamine structures. With oligodeoxynucleotide duplexes containing the sequence 5'-2a-dC, cross-links were not detected by the techniques enumerated above. In addition, (15)N-(1)H HSQC and HSQC-filtered NOESY spectra carried out with a duplex having (15)N-labeling of the target amino group established unambiguously that a carbinolamine cross-link was not formed. The potential for interchain cross-link formation by the analogous crotonaldehyde adduct (2b) was evaluated in a 5'-dC-2b sequence. Cross-link formation was strongly dependent on the configuration of the methyl group at C6 of 2b. The 6R diastereomer of 2b formed a cross-link to the extent of 38%, whereas the 6S diastereomer cross-linked only 5%.     

The Measurement of Time: Children's Construction of Transitivity,Unit Iteration,and Conservation of Speed

One hundred twenty children in kindergarten and grades 2, 4, and 6 were individually interviewed with five Piagetian tasks to determine the grade level at which most have constructed transitive reasoning, unit iteration, and the conservation of speed. The responses were categorized as “successful,”“unsuccessful,” or “transitional.” By combining the “successful” and “transitional” categories, it was found that the children reasoned transitively by second grade (70.0%) and demonstrated unit iteration and conservation of speed by sixth grade (70.0% and 83.3%, respectively). It was concluded that the construction of the logic necessary to make sense of the measurement of time is generally not complete before sixth grade.     

Diffusion-weighted MRI: influence of intravoxel fat signal and breast density on breast tumor conspicuity and apparent diffusion coefficient measurements

Promising recent investigations have shown that breast malignancies exhibit restricted diffusion on diffusion-weighted imaging (DWI) and may be distinguished from normal tissue and benign lesions in the breast based on differences in apparent diffusion coefficient (ADC) values. In this study, we assessed the influence of intravoxel fat signal on breast diffusion measures by comparing ADC values obtained using a diffusion-weighted single shot fast spin-echo sequence with and without fat suppression. The influence of breast density on ADC measures was also evaluated. ADC values were calculated for both tumor and normal fibroglandular tissue in a group of 21 women with diagnosed breast cancer. There were systematic underestimations of ADC for both tumor and normal breast tissue due to intravoxel contribution from fat signal on non–fat-suppressed DWI. This ADC underestimation was more pronounced for normal tissue values (mean difference=40%) than for tumors (mean difference=27%, P<.001) and was worse in women with low breast tissue density vs. those with extremely dense breasts (P<.05 for both tumor and normal tissue). Tumor conspicuity measured by contrast-to-noise ratio was significantly higher on ADC maps created with fat suppression and was not significantly associated with breast density. In summary, robust fat suppression is important for accurate breast ADC measures and optimal lesion conspicuity on DWI.     

Electrical characteristics of Mg-doped GaN activated with Ni catalysts

Electrical characteristics of Mg-doped p-GaN activated with Ni catalytic layers have been investigated by means of temperature-dependent Hall effect measurements. It has been revealed that the Ni layer on GaN enhances activation of the acceptor in the whole annealing temperature range. This enhancement is remarkable especially at temperatures below 500 °C and can be attributed to the catalytic effect for the hydrogen desorption. We have found that the donor concentrations in the samples activated with the Ni catalysts are also higher than those activated without Ni. This is probably due to the catalytic effect of Ni for the nitrogen desorption. In addition, it has been found that the ionization energies of the Mg acceptors in GaN activated with the Ni layer are decreased from 170 to 118 meV as the acceptor concentration increases.     

A Multi‐Addressable Switch Based on the Dimethyldihydropyrene Photochrome with Remarkable Proton‐Triggered Photo‐opening Efficiency

A series of photochromic derivatives based on the trans‐10b,10c‐dimethyl‐10b,10c‐dihydropyrene (DHP, “closed form”) skeleton has been synthesized and their photoisomerization leading to the corresponding cyclophanediene (CPD, “open form”) isomers has been investigated by UV/Vis and ¹H NMR spectroscopies. Substitution of the DHP core with electron‐withdrawing pyridinium groups was found to have major effects on the photoisomerization efficiency, the most remarkable examples being to enhance the quantum yield of the opening reaction and to allow fast and quantitative conversions at much lower radiant energies. This effect was rationalized by theoretical calculations. We also show that the reverse reaction, that is, going from the open form to the closed form, can be electrochemically triggered by oxidation of the CPD unit and that the photo‐opening properties of pyridine‐substituted DHPs can be efficiently tuned by protonation, the system behaving as a multi‐addressable molecular switch. These multi‐addressable photochromes show promise for the development of responsive materials.     

The Cancer Genetics Network: recruitment results and pilot studies

OBJECTIVE: The National Cancer Institute established the Cancer Genetics Network (CGN) to support collaborative investigations into the genetic basis of cancer susceptibility, explore mechanisms to integrate this new knowledge into medical practice, and identify ways of addressing the associated psychosocial, ethical, legal, and public health issues. SUBJECTS AND METHODS: The CGN has developed the complex infrastructure required to support the projects, including the establishment of guidelines and policies, uniform methods, standard questionnaires to be used by all of the centers, and a standard format for submission of data to the Informatics Center. Cancer patients and their family members have been invited to enroll and be included in a pool of potential study participants. The Information Technology Group is responsible for support of the design, implementation, and maintenance of the multicenter Network-wide research protocols. RESULTS: As of January 2004, the CGN contained data on 23,995 probands (participants) and 425,798 family members. As a resource for cancer genetic studies, the CGN has a large number of probands and first-degree relatives with and without cancer and with multiple ethnicities. Different study designs can be used including case-control, case-case, and family studies. CONCLUSIONS: The unique resources of the CGN are available for studies on cancer genetic susceptibility, translational research, and behavioral research. The CGN is now at a point where approved collaborators may have access to enrolled patients and their families for special studies, as well as to the clinical, environmental and family cancer history data banked in the Informatics Center.     

On the nature of the low-lying states of TiO

A series of CAS SCF calculations are used to describe the lowest states of TiO. TiO is described as having polarized double bonds involving the Ti 3d orbitals. The nature of the excited states is discussed.