Internalization and processing of the EGF receptor in the induction of DNA synthesis in cultured fibroblasts: the endocytic activation hypothesis.

The addition of EGF to cultured murine 3T3 cells produces a decrease in EGF binding activity with concomitant internalization and degradation of the initially bound EGF. When the EGF receptor on cultured 3T3 cells is affinity labeled with high specific activity 125I-EGF, and the fate of the affinity labeled EGF-receptor complex determined, the loss in binding activity was accounted for by receptor internalization and subsequent proteolytic processing of the EGF receptor molecules in the lysosomes. Studies of the effects of EGF concentration on EGF binding by cells, EGF-induced receptor internalization and EGF-induced stimulation of 3H-thymidine uptake into cellular DNA show that there is a direct correlation between EGF-induced receptor internalization and EGF-induced stimulation of DNA synthesis, but not between EGF binding and EGF-induced stimulation of DNA synthesis. This correlation is lost at high EGF concentrations, where stimulation of DNA synthesis is suboptimal. Optimal stimulation of DNA synthesis requires a minimum of 6 h of incubation of EGF with cells, and the suboptimal stimulation of DNA synthesis at high EGF concentration is intensified when the period of incubation of EGF with cells is less than 6 h. These data are consistent with a model of hormone signal transmission by Endocytic Activation, wherein the activation of EGF-induced processes requires constant EGF-induced internalization of receptor for a requisite 6-8 h period as an obligatory step in production of "second messenger" in the action of this hormone.     

Studies on the kinetics and mechanism of dissociation of copper(II) and nickel(II) complexes of the macrocyclic ligand 1, 5, 9, 13-tetraaza-2, 4, 4, 10, 12, 12-hexamethyl-cyclohexadecane-1, 9-diene in perchloric acid media

Summary Acid catalysed dissociation of the copper(II) and nickel(II) complexes (ML²⁺ of the quadridentate macrocyclic ligand 1, 5, 9, 13-tetraaza-2, 4, 4, 10, 12, 12-hexamethyl-cyclohexadecane-1, 9-diene (L) has been studied spectrophotometrically. Both complexes dissociate quite slowly with the observed pseudo-first order rate constants (k_obs) showing acid dependence; for the nickel(II) complex (k_obs)=k_O+k_H[H⁺], the k_o path is however absent with the copper(II) complex. At 60°C (I=0.1M) the k_H values areca 10^–4 M^–1 s^–1 for both complexes; k _H ^Cu /k _H ^Ni =ca. 3.9, comparable to some other square-planar complexes of these metal ions. The rate difference is primarily due to H values [copper(II) complex, 29.4±0.5 kJ mol^–1; nickel(II) complex, 35.6±1.5 kJ mol^–1] with highly negative S values [for copper(II), –215.5 ±6.1 JK^–1 mol^–1 and for nickel(II), –208.1 ±5.6 JK^–1 mol^–1] which are much higher than the entropy of solvation of Ni²⁺ (ca. –160 JK^–1 mol^–1) and Cu²⁺ (ca. –99 JK^–1 mol^–1) ions; significant solvation of the released metal ions and the ligand is indicated.     

Surface modified ormosil nanoparticles

Organically modified silanes (ORMOSIL) such as vinyl triethoxysilane readily aggregate in the aqueous cores of reverse micelles where the triethoxysilane moieties are hydrolyzed to form a hydrated silica network and the vinyl groups protruded out from the surface of the nanoparticles toward the hydrophobic side of the micellar interface. These particles are spherical and the size distribution of the particles is relatively narrow, with an average diameter of 87 nm. Surface vinyl silica nanoparticles so formed have been oxidized to surface carboxylic silica nanoparticles, followed by chemical conjugation with polyethyleneglycol amine (PEG amine) through the ethyl-3-(3-dimethylaminopropyl) (EDCI) carbodiimide reaction. The characteristic surface groups have been identified by Fourier transform infrared spectroscopy, while the size and the morphology of the particles have been studied by dynamic light scattering and transmission electron microscopy. It has been found that about 80-85% of the carboxylic groups are PEGylated during the EDCI reaction.     

Kinetics and mechanisms of the reactions of thiosulphato-amine complexes of cobalt(III). Part I. Isomerization and base hydrolysis ofcis andtrans isomers of dithiosulphatobis(ethylenediamine) cobalt(III) ion in aqueous solution

Summary Investigations were carried out on the isomerization and base hydrolysis ofcis andtrans forms of dithiosulphatobis-(ethylenediamine)cobalt(III) ions. Thecis form isomerizes to thetrans form in neutral aqueous medium, rates being 1.15, 2.30 and 4.0×10^–5s^–1, respectively at 42, 50 and 58 °C. Thetrans complex isomerizes to thecis form in basic solution only, the rate varying with pH in a sigmoid pattern. In presence of OH^–, an acid-base equilibrium of the complex ion sets in, but only the basic form takes part in the isomerization reaction. Hydrolysis of thecis isomer proceeds through a base-dependent path only, but that of thetrans isomer proceeds both through base-dependent and base-independent paths. The mechanisms are associative in nature. Thetrans form reacts faster thancis in all cases.     

Investigation of electronic structure and associated nuclear quadrupole interaction of adsorbed fluorine atoms on silicon surface

The electronic energy levels and wave functions of fluorine and chlorine atoms adsorbed at the <111> surface of silicon are obtained by the Hartree-Fock procedure applied to clusters simulating the surface structure. Minimising the total energy with respect to the positions of the halogen atoms, the Si-Cl distance in the adsorbed system was found to be in good agreement with that from a recent SEXAFS measurement, there being no corresponding data presently available for fluorine on silicon surface. The calculated¹⁹ f ^* nuclear quadrupole coupling constants using the electronic wave functions for SiH₃F and the larger cluster Si₄H₉F, simulating the surface, differed substantially in contrast to the situation for the Si-F distance, indicating that the quadrupole coupling is a more sensitive indicator of the adequacy of the cluster chosen to represent the surface system. Experimental results for the coupling constants are awaited for comparison with theory.     

Thermodynamics of ternary salts in dioxane—water mixtures from conductance measurements

Studies of electrolytic conductance in dioxane—water mixtures of varying dioxane content were initiated in 1978 [1]. In the present communication, an attempt has been made to evaluate the thermodynamic function ΔG⁰_t for the transfer of Mg(ClO₄)⁺, Mg(NO₃)⁺, BaCl⁺, BaBr⁺, Ba(ClO₄⁺, Ba(NO₃)⁺, SrCl⁺, Sr(NO₃)⁺, CaCl⁺ and Ca(NO₃)⁺ from water to dioxane—water media, which would give some information regarding ionic solvation.     

A comparative study on textural characterization: cation-exchange and sorption properties of crystalline alpha-zirconium(IV), tin(IV), and titanium(IV) phosphates

Tetravalent metal phosphates (M=Zr, Ti, and Sn) were prepared and characterized by XRD, surface properties, and TG-DTA. The cation exchange and sorption behavior of these metal phosphates toward transition metal ions such as Cu(2+), Co(2+), and Ni(2+) have been studied comparatively as a function of temperature and concentration. The adsorption process was found to increases with increase in temperature and concentration. The selectivity order for alpha-titanium and alpha-tin phosphates is Cu(2+)>Co(2+)>Ni(2+), whereas for alpha-zirconium phosphate it is Cu(2+)>Ni(2+)>Co(2+). The ion exchange capacity of alpha-titanium phosphate is greater than those of other phosphates, which is explained on the basis of the surface behavior, disorderness of the system, degree of hydrolysis of incoming guest adsorbate metal ions, and structural steric hindrance of the exchangers during adsorption and sorption. The distribution coefficient, Gibbs free energy, enthalpy, and entropy values indicate that the ion-exchange processes are spontaneous.     

Spectroscopic constants and molecular properties of CN−, SiH−, PO−, SO−, SF−, and SiS−: Density functional study

Spectroscopic constants and molecular properties of selected diatomic anions namely CN^?, SiH^?, PO^?, SO^?, SF^?, and SiS^? in their ground states have been studied in detail using the hybrid HF/DF B3LYP method. The consistency of the calculated values has been verified with four different basis sets, with improved quality. The spectroscopic constants and molecular properties calculated with the aug‐cc‐pVTZ basis set agree very well with the experimental and theoretical values wherever available. Most of the spectroscopic constants and molecular properties of the selected diatomic anions, particularly the spectroscopic constants and molecular properties of SO^? and SiS^? are reported for the first time. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

UVB irradiation of normal human skin favors the development of type-2 T-cells in vivo and in primary dermal cell cultures

To determine the effect of UVB exposure on the balance of type-1 or type-2 T-cells in skin, we examined the expression of key markers interferon (IFN)-gamma and interleukin (IL)-4 in cryostat sections. IFN-gamma mRNA was clearly detectable in nonirradiated control skin, and IFN-gamma protein was found in 2% of the dermal CD3pos T-cells, whereas IL-4 mRNA was hardly detectable, and no IL-4 protein was found. In contrast, IL-4 mRNA expression increased upon irradiation, and IL-4 was found in 2% of the T-cells at day 2 after UVB-exposure. Concomitantly, IFN-gamma mRNA expression decreased, and IFN-gamma protein became absent. We also analyzed T-cells present in primary dermal cell cultures, which were used as an in vitro equivalent of the in vivo situation. As compared with T-cells from control skin, T-cells in dermal cell cultures from UVB-exposed skin displayed an increased IL-4 and decreased IFN-gamma expression. No such skewing occurred when the T-cells from irradiated skin were cloned in the absence of a dermal microenvironment. Except for an occasional positive T-cell, type-1-associated cell-surface markers (CCR5, CXCR3) or type-2 markers (CCR3, CD30, CRTH2) were undetectable in situ. But these markers were expressed on cultured dermal T-cells from UVB-exposed and control skin at a comparable level, but did not correlate with the IFN-gamma and IL-4 production. Altogether, UVB-induced changes of the dermal microenvironment favor the development of type-2 T-cells.     

Ion exchange separation of different oxidation states of sulphur formed by35Cl(n,p)35S reaction in alkali halides

Cesium and potassium were determined in muscle-tissues of squid, dover sole, albacore, and bocaccio by NAA. Potassium was measured instrumentally, while cesium was radio-chemically separated. For the separation of cesium, hydrated antimony pentoxide (HAP) was used to retain²⁴Na, and ammonium molybdophosphate (AMP) was used to absorb quantitatively the radiocesium,^134mCs. The cesium and potassium contents were based on measuring the short-lived radionuclide of cesium, 2.90 h-^134mCs, and 12.4 h-⁴²K. The mean concentrations of cesium found, based on 3–4 replicate measurements for each fish, were: 4.18±0.32 ng/g squid, 11.51±0.30 ng/g dover sole, 43.64±1.03 ng/g albacore, and 56.85±3.61 ng/g bocaccio. The mean concentrations of potassium found were: 1.28±0.10 mg/g squid, 2.78±0.29 mg/g dover sole, 3.69±0.06 mg/g albacore, and 4.18±0.10 mg/g bocaccio.