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PubMed1991

Substrate analog inhibitors of HIV-1 protease containing phenylnorstatine as a transition state element.

Substrates of HIV-1 protease are classified into three groups (A, B and C) based on the amino acid residues present at P1' and P2' sites. Replacement of the scissile amide bond by phenylnorstatine in representative substrate analog sequences from class A, B and C, yielded inhibitors of HIV-1 protease. Of the twelve inhibitors synthesized in this series, class C substrate analog inhibitors are more potent inhibitors (Ki's 3.3-24 microM) than either class A or class B inhibitors. In this series of inhibitors, the (2S,3S) isomer of phenylnorstatine is preferred over the other isomers as a "transition state element" for design of inhibitors of HIV-1 protease.

Amino Acid Sequence↗
PubMed1982

Reorganization of cytoskeletal and contractile elements during transition of human monocytes into adherent macrophages.

Indirect immunofluorescence microscopy was used to study the reorganization of contractile and cytoskeletal elements of human monocytes during their in vitro transition into macrophage-like cells. In freshly isolated monocytes, actin, myosin, alpha-actinin, and vinculin all had a diffuse distribution, whereas microtubules and vimentin-type intermediate filaments showed a distinct fibrillar organization. In culture, the cells differentiated within 1 week to two distinct cell types: bipolar fibroblastoid cells and flattened epithelioid cells. A conspicuous redistribution of actin, alpha-actinin, and vinculin from a diffuse cytoplasmic location into distinct punctate foci at the substratum-facing side of the cells was seen already at the early attachment phase of the spreading monocytes. In spread cells the punctate foci occupied the whole ventral surface of the cells, and in flattened, fully spread cells these proteins formed distinct punctate plaques at the under surface of the cells excluding however, the ruffle edge-like membrane regions. At the plaques, a close co-distribution of actin and vinculin was seen in double indirect immunofluorescence microscopy. Myosin showed a distinctly different reorganization during the transition process changing from a diffuse cytoplasmic location to a striated, surface-associated distribution. Interference reflection microscopy revealed large areas of close adhesion but no focal adhesion sites in spreading monocytes. Cytochalasin B treatment lead to a rapid distortion of the actin organization and resulted in clump-like cytoplasmic aggregates and nuclear paracrystals of actin concomitantly with the rounding up of the cells. Vimentin filaments were seen as a perinuclear aggregate until the acquisition of the fully spread morphology. At this stage both vimentin filaments and microtubules displayed a fibrillar appearance throughout the cytoplasmic domain. Treatment of the spread monocytes with antimitotic drugs caused a retraction of the cell from beyond the attachment plaques but had no effect on the punctate actin organization. The results show that in the monocyte-macrophage transition there is an extensive cytoskeletal reorganization that can be correlated with the different phases of the cell-to-substratum attachment process.

Actinin↗
PubMed2006

Bivariate- distribution for transition matrix elements in Breit-Wigner to Gaussian domains of interacting particle systems.

Interacting many-particle systems with a mean-field one-body part plus a chaos generating random two-body interaction having strength lambda exhibit Poisson to Gaussian orthogonal ensemble and Breit-Wigner (BW) to Gaussian transitions in level fluctuations and strength functions with transition points marked by lambda = lambda c and lambda = lambda F, respectively; lambda F >> lambda c. For these systems a theory for the matrix elements of one-body transition operators is available, as valid in the Gaussian domain, with lambda > lambda F, in terms of orbital occupation numbers, level densities, and an integral involving a bivariate Gaussian in the initial and final energies. Here we show that, using a bivariate-t distribution, the theory extends below from the Gaussian regime to the BW regime up to lambda = lambda c. This is well tested in numerical calculations for 6 spinless fermions in 12 single-particle states.

Journal Article↗
PubMed2002

Liquid-liquid phase transition in elemental carbon: a first-principles investigation.

It has been recently suggested that elemental carbon may be a promising candidate to exhibit a liquid-liquid phase transition (LLPT). We report the results of first-principles molecular dynamics simulations showing no evidence of LLPT in carbon, in the same temperature and pressure range where such a transition was found using empirical calculations. Our simulations indicate a continuous evolution from a primarily sp-bonded liquid to an sp(2)-like and an sp(3)-like fluid, as a function of pressure, above the graphite melting line. The discrepancy between quantum and classical simulations is attributed to the inability of empirical potentials to describe complex electronic effects in condensed carbon phases.

Journal Article↗
PubMed1986

Temperature and energy dependence of secretory protein transport in the exocrine pancreas.

Pancreatic lobules pulse-labeled with [3H]leucine have been incubated at temperatures between 0 and 37 degrees C in the presence or absence of ongoing oxidative phosphorylation. Subcellular fractionation methods and electron microscopic autoradiography have been used to monitor the progress of intracellular transport of newly synthesized secretory proteins. Over the period studied, exit from the rough endoplasmic reticulum (RER) occurs only at greater than 10 degrees C while traversal of the Golgi complex and entry into condensing vacuoles requires greater than 22 degrees C. Both steps of transport require ongoing ATP production. Incubation at 10 or 20 degrees C does not diminish ATP levels, relative to 37 degrees C controls. Remarkable and unprecedented alterations of the ultrastructure of transitional elements of the RER accompany the arrest of exit from the RER: at 10 degrees C transitional elements are much more numerous and longer than in controls; in the absence of ATP production they are essentially absent. These observations are interpreted in terms of a cyclic model of RER-to-Golgi vesicular traffic. Inhibition of ATP production also causes an increase in the rigid cisternae and coated elements in the distal Golgi area.

Adenosine Triphosphate↗
PubMed1996

Transition Element-Like Chemistry for Potassium Under Pressure

At high pressure the alkali metals potassium, rubidium, and cesium transform to metals that have a d1 electron configuration, becoming transition metal-like. As a result, compounds were shown to form between potassium and the transition metal nickel. These results demonstrate that the chemical behavior of the alkali metals under pressure is very different from that under ambient conditions, where alkali metals and transition metals do not react because of large differences in size and electronic structure. They also have significant implications for the hypothesis that potassium is incorporated into Earth's core.

Journal Article↗
PubMed2006

Exhaled metallic elements and serum pneumoproteins in asymptomatic smokers and patients with COPD or asthma.

STUDY OBJECTIVES: The aim of this study was to characterize the elemental composition of exhaled breath condensate (EBC) in order to identify new biomarkers of exposure and susceptibility in COPD patients. Serum pneumoproteins were used as lung-specific biomarkers of effect. DESIGN: EBC was obtained from 50 healthy subjects, 30 healthy smokers, 30 asthmatics, and 50 patients with stable COPD, and was collected by cooling exhaled air. Trace elements and toxic metals in the samples were measured by means of inductively coupled plasma-mass spectrometry and electrothermal atomic absorption spectroscopy. The serum pneumoproteins were immunoassayed. RESULTS: The EBC of COPD subjects had higher levels of such toxic elements as lead, cadmium, and aluminum, and lower levels of iron and copper, than that of the nonsmoking control subjects. There were no between-group differences in surfactant protein (SP)-A and SP-B levels. Clara-cell protein and SP-D levels were negatively and positively influenced, respectively, by tobacco smoke. CONCLUSIONS: Our results show that toxic metals and transition elements are detectable in the EBC of studied subjects. We propose new biomarkers of exposure as a means of assessing the target tissue dose of carcinogenic and pneumotoxic substances from tobacco smoke or polluted workplaces, and the use of the transition elements involved in redox systems of oxidative stress as disease biomarkers associated with effect or susceptibility. Together with biomarkers of effect, such as serum pneumoproteins, the elemental composition of EBC may be clinically useful in distinguishing similar diseases.

Adult↗
PubMed1986

Insertion elements and transitions in cloned mouse mammary tumour virus DNA: further delineation of the poison sequences.

The provirus of mouse mammary tumour virus (MMTV) is reputed to contain sequences within the viral gag gene that prevent or inhibit its propagation as a recombinant DNA clone in Escherichia coli. Here we report the successful isolation of several lambda and plasmid clones comprising the 5' virus-host DNA junction fragments from integrated MMTV proviruses in BR6 mice. Although the lambda clones appeared intact, almost all of the plasmids were found to contain the bacterial insertion sequences IS1 or IS2 within a small region of the gag gene. One nondisrupted clone was recovered which had undergone multiple G to A transitions, some of which created stop codons in gag. These results have provided more precise information as to the location of the poison sequences and are discussed in relation to possible explanations for the phenomenon.

Amino Acid Sequence↗
PubMed2001

Characterisation of zeolitic materials with a HEU-type structure modified by transition metal elements: definition of acid sites in nickel-loaded crystals in the light of experimental and quantum-chemical results.

Nickel-loaded HEU-type zeolite crystals have been obtained by well-known synthetic procedures and characterised by X-ray fluorescence (XRF), scanning-electron microscopy/ energy-dispersive spectroscopy (SEM-EDS), FT-IR, diffuse reflectance UV/ Vis spectroscopy (DR(UV/Vis)S) and X-ray photoelectron spectroscopy (XPS) measurements as non-homoionic and non-stoichiometric substances containing exchangeable hydrated Ni2+ ions in the micropores and nickel hydroxide phases supported on the surface. Thermogravimetric analysis/differential gravimetry (TGA/DTG) and differential thermal analysis (DTA) demonstrated that full dehydration below approximately 400 degrees C follows a clearly endothermic process, whereas at higher temperatures the zeolite is amorphised and finally partially recrystallised to Ni(Al,Si) oxides, detected by powder X-ray powder diffraction (XRD). The solid acidity of NiHEU, initially determined by temperature-programmed desorption (TPD) of ammonia to be 8.93 mgg(-1) NH3, is attributed to the weak acid sites (fundamentally Lewis sites) resolved at approximately 183 degrees C, and to the strong acid sites (essentially Brønsted sites) resolved at approximately 461 degrees C in the TPD pattern. A more sophisticated study based on in situ/ex situ FT-IR with in situ/ex situ 27Al MAS NMR and pyridine (Py) as a probe molecule, revealed that the Lewis acid sites can be attributed primarily to Ni2+ ions, whereas the Brønsted ones can probably be associated with the surface-supported nickel hydroxide phases. The spectroscopic measurements in conjunction with powder XRD and 29Si MAS NMR data strongly suggest that distorted Al tetrahedra are formed during the dehydration process and Py chemisorption/complexation (NiHEU-Py), whereas the crystal structure is remarkably well preserved in the rehydrated material (NiHEU-Py/R). The structural, electronic, energetic and spectroscopic properties of all possible nickel(II) aqua and dihydroxy complexes absorbed in the zeolite micropores or supported on the zeolite surface were studied theoretically by density functional theory (DFT). The computed proton affinity, found to be in the range 182.0-210.0 kcalmol(-1), increases with increasing coordination number of the aqua and dihydroxy nickel(II) complexes.

Journal Article↗
PubMed2006

Chemical bonding in phosphane and amine complexes of main group elements and transition metals.

The geometries and bond dissociation energies of the main group complexes X3B-NX3, X3B-PX3, X3Al-NX3, and X3Al-PX3 (X = H, Me, Cl) and the transition metal complexes (CO)5M-NX3 and (CO)5M-PX3 (M = Cr, Mo, W) have been calculated using gradient-corrected density functional theory at the BP86/TZ2P level. The nature of the donor-acceptor bonds was investigated with an energy decomposition analysis. It is found that the bond dissociation energy is not a good measure for the intrinsic strength of Lewis acidity and basicity because the preparation energies of the fragments may significantly change the trend of the bond strength. The interaction energies between the frozen fragments of the borane complexes are in most cases larger than the interaction energies of the alane complexes. The bond dissociation energy of the alane complexes is sometimes higher than that of the borane analogues because the energy for distorting the planar equilibrium geometry of BX3 to the pyramidal from in the complexes is higher than for AlX3. Inspection of the three energy terms, DeltaE(Pauli), DeltaE(orb), and DeltaE(elstat), shows that all three of them must be considered to understand the trends of the Lewis acid and base strength. The orbital term of the donor-acceptor bonds with the Lewis bases NCl3 and PCl3 have a higher pi character than the bonds of EH3 and EMe3, but NCl3 and PCl3 are weaker Lewis bases because the lone-pair orbital at the donor atoms N and P has a high percent s character. The calculated DeltaE(int) values suggest that the trends of the intrinsic Lewis bases' strengths in the main-group complexes with BX3 and AlX3 are NMe3 > NH3 > NCl3 and PMe3 > PH3 > PCl3. The transition metal complexes exhibit a somewhat different order with NH3 > NMe3 > NCl3 and PMe3 > PH3 > PCl3. The slightly weaker bonding of NMe3 than that of NH3 comes from stronger Pauli repulsion. The bond length does not always correlate with the bond dissociation energy, nor does it always correlate with the intrinsic interaction energy.

Journal Article↗