Benefits of Silica Core-Shell Structures on the Temperature Sensing Properties of Er,Yb:GdVO4 Up-Conversion Nanoparticles.

We studied the temperature-dependent luminescence of GdVO4 nanoparticles co-doped with Er(3+) (1 mol %) and Yb(3+) (20 mol %) and determined their thermal sensing properties through the fluorescence intensity ratio (FIR) technique. We also analyzed how a silica coating, in a core-shell structure, affects the temperature sensing properties of this material. Spectra were recorded in the range of biological temperatures (298-343 K). The absolute sensitivity for temperature determination calculated for the core-shell nanoparticles is double the one calculated for bare nanoparticles, achieving a thermal resolution of 0.4 K. Moreover, silica-coated nanoparticles show good dispersibility in different solvents, such as water, DMSO, and methanol. Also, they show good luminescence stability without interactions with solvent molecules. Furthermore, we also observed that the silica coating shell prevents progressive heating of the nanoparticles during prolonged excitation periods with the 980 nm laser, preventing effects on their thermometric applications.

White light upconversion in Yb-sensitized (Tm, Ho)-doped KLu(WO4)2 nanocrystals: the effect of Eu incorporation.

Monoclinic Yb-sensitized (Tm, Ho)-doped KLu(WO4)2 nanocrystals of ~100 nm size have been synthesized by the modified Pechini sol-gel method. Their diode laser near-infrared (~980 nm) excited upconversion emission properties have been characterized at power densities in the range 30-355 W cm(-2). Bright white light composed of blue ~475 nm, green ~540 nm, and red ~650 nm emissions, corresponding to Tm(3+ 1)G4 → (3)H6, Ho(3+ 5)S2, (5)F4 → (5)I8, and Ho(3+ 5)F5 → (5)I8 electronic transitions, respectively, was generated by adjusting the Yb, Tm, and Ho contents in KLu(WO4)2 nanocrystalline samples. Chromaticity coordinates of the emitted white light can be tuned by modifying the excitation power density. The effect of Tm and Ho on the luminescence dynamics has been described by analyzing the upconverted emission intensity dependence on the excitation power, as well as from Stokes and decay time measurements. The effect on upconversion properties of further codoping with Eu in these (Tm, Ho, Yb)-doped KLu(WO4)2 nanocrystals has also been studied.

Spectroscopic characterization and laser performance of resonantly diode-pumped Er(3+)-doped disordered NaY(WO4)2.

We report what is believed to be the first resonantly pumped laser operation based on Er(3+)-doped disordered double tungstate single crystal. Efficient laser operation of an Er(3+):NaY(WO(4))(2) laser at ∼1609.6 nm was demonstrated with the naturally wideband, ∼20 nm, InGaAsP/InP laser diode pumping at ∼1501 nm. Laser wavelength tunability of ∼34 nm was also demonstrated based on disorder-broadened emission features of Er(3+):NaY(WO(4))(2) single crystal.

Femtosecond (191 fs) NaY(WO4)2 Tm,Ho-codoped laser at 2060 nm.

We report, for the first time to our knowledge, femtosecond-pulse operation of a Tm,Ho:NaY(WO(4))(2) laser at around 2060 nm. Transform-limited 191 fs pulses are produced with an average output power of 82 mW at a 144 MHz pulse repetition frequency. Maximum output power of up to 155 mW is generated with a corresponding pulse duration of 258 fs. An ion-implanted InGaAsSb quantum-well-based semiconductor saturable absorber mirror is used for passive mode-locking maintenance.

Optical spectroscopic study of Eu3+ crystal field sites in Na3La9O3(BO3)8 crystal.

Time-resolved line-narrowed fluorescence spectroscopy of Eu(3+) ions in a new oxyborate Na(3)La(9)O(3)(BO(3))(8) crystal shows the existence of four independent symmetry crystal field sites for the rare-earth ion. A crystal field analysis and simulation of the experimental results have been performed in order to parametrize the crystal field at the Eu(3+) sites. A plausible argument about the crystallographic nature of these sites is given.

Laser operation of Yb3+ in disordered Li0.75Gd0.75Ba0.5(MoO4)2 crystal with small quantum defect.

A new strategy has been developed to enhance the optical bandwidths of rare earth dopants by partial substitution of the divalent cation (D) in the original DWO(4) or DMoO(4) crystal structures. For demonstration, the monoclinic (space group C2/c) Yb-doped Li(0.75)Gd(0.75)Ba(0.5)(MoO(4))(2) crystal was grown in a Li(2)Mo(2)O(7) flux, and 300 K Yb(3+) laser operation is reported. The laser emission is characterized by rather short wavelengths related to the specific features of the absorption and emission spectra, which leads to very small quantum defect, i.e., as low as 0.7% for E//b-axis. Using a Ti:sapphire laser at 976.6 nm, up to 295 mW of cw power are obtained without special cooling while the tunability range extends over 33 nm around 1020 nm.

Tunable laser operation of ytterbium in disordered single crystals of Yb:NaGd(WO4)2.

Lasing of Yb3+ in a disordered single crystal host, NaGd(WO4)2, is reported. Pump efficiencies as high as 20% and slope efficiencies as high as 30% are achieved for both sigma- and pi-polarizations with Ti:sapphire laser pumping. The emission of Yb:NaGd(WO4)2 is centered near 1030 nm. Tunability between 1016 and 1049 nm is obtained with a Lyot filter.

Vibrational and 57Fe-Mössbauer spectra of FeTbGe2O7.

The infrared, Raman and 57Fe-Mössbauer spectra of FeTbGe2O7 were recorded and analyzed on the basis of its crystallographic data. For comparative purposes, similar measurements were also performed with FeYGe2O7 and with other isostructural compounds containing different lanthanide cations.

Inhibitors of farnesylation of Ras from a microbial natural products screening program.

Mutant ras oncogenes are associated with various human tumors such as pancreas, colon, lung, thyroid, bladder and several types of leukemia. Prenylation of Ras proteins plays a major role in cell proliferation of both normal and cancerous cells. Normal and oncogenic Ras proteins are posttranslationally modified by a farnesyl group that promotes membrane binding. Inhibitors of farnesyl protein transferase (FPTase), the enzyme that catalyzes the prenylation of Ras proteins, inhibit growth of tumor cells. In an effort to identify structurally diverse and unique inhibitors of FPTase, a program devoted to screening of natural products was initiated. This effort led to the identification of 10 different families of compounds, all of which selectively inhibit FPTase with a variety of mechanisms that are reviewed in this manuscript. These compounds originated from the fermentations of a number of microorganisms, either actinomycetes or fungi, isolated from different substrates collected in tropical and temperate areas. A chemotaxonomic discussion on the distribution of each compound among single or different types of microorganisms, either phylogenetically related or unrelated species, is included.

A Germanium Zeotype Containing Intratunnel Transition Metal Complexes.

A new zeolite-type structure is adopted by (NH(4))(+)[M(NH(3))(2)](+)(Ge(9)O(19))(2-) (M=Cu, Ag; shown in the picture). These compounds are the first microporous germanates containing a transition metal complex inside their tunnels. The large separation between the metal centers and the unhindered access of reactants to these active sites through uniformly sized channels make these materials a good point of departure for designing new catalysts.

Oreganic acid, a potent inhibitor of ras farnesyl-protein transferase.

A sulfated tricarboxylic acid fungal metabolite is an inhibitor of human farnesyl-protein transferase (FPTase). The compound, designated as oreganic acid, has a molecular weight of 494, an empirical formula of C22H38O10S and inhibits FPTase with an IC50 value of 14 nM. Oreganic acid is a selective inhibitor of FPTase because it does not inhibit human geranylgeranyl-protein transferase type I (GGPTase-I). It is not a time-dependent inhibitor, reversibly inhibits FPTase, is competitive with respect to farnesyl diphosphate and non-competitive with respect to the Ras acceptor peptide. The structure of oreganic acid resembles that of farnesyl diphosphate and most likely inhibits FPTase by mimicking farnesyl diphosphate at the active site of the enzyme.

Actinoplanic acids A and B as novel inhibitors of farnesyl-protein transferase.

Actinoplanic acids A and B are macrocyclic polycarboxylic acids that are potent reversible inhibitors of farnesyl-protein transferase. Actinoplanic acids A and B were isolated from Actinoplanes sp. MA 7066 while actinoplanic acid B was isolated from both MA 7066 and Streptomyces sp. MA 7099. Actinoplanic acids A and B are competitive with respect to farnesyl diphosphate and are selective inhibitors of farnesyl-protein transferase because they do not inhibit geranylgeranyl-protein transferase type 1 or squalene synthase. MA 7066 is believed to be a novel species of actinomycetes while MA 7099 is believed to be a novel strain of Streptomyces violaceusniger on the basis of morphological, biochemical and chemotaxonomic characteristics as well as its production of actinoplanic acids.

Chaetomella acutiseta produces chaetomellic acids A and B which are reversible inhibitors of farnesyl-protein transferase.

Chaetomellic acids A and B, isolated from Chaetomella acutiseta, are specific inhibitors of farnesyl-protein transferase that do not inhibit geranylgeranyl transferase type 1 or squalene synthase. Chaetomellic acids A and B are reversible inhibitors, resemble farnesyl diphosphate and probably inhibit FPTase by substituting for farnesyl diphosphate. Chaetomellic acid production appears to be widespread within the genus Chaetomella.

Thioacetamide alters the regulation of cytidylyltransferase activity.

Using the weak hepatocarcinogen thioacetamide, we found a 73% decrease in microsomal CTP: Phosphocholine cytidylyltransferase (CT) activity after two months of treatment. We investigated the effect of different effectors on this enzyme activity. Results show that incubation of liver homogenates of treated animals in the presence of either oleate or spermine restored control values of microsomal activity. Incubation of thioacetamide homogenates in the presence of cAMP showed no changes in CT activity, while incubation of control and thioacetamide homogenates in the presence of Ca2+ induced an activation in microsomal activity, although of less intensity in thioacetamide homogenates than in control preparations. Results suggest that thioacetamide alters the regulation of cytidylyltransferase activity.

Alterations in hepatic peroxidation mechanisms in thioacetamide-induced tumors in rats. Effect of a rhodium(III) complex.

A model of liver hyperplastic noduligenesis was induced in rats in vivo by long-term administration of thioacetamide (TAM; 100 mg/kg day i.p.). Three doses of 50 mg/kg of an antitumoral rhodium(III) complex were administered at 14, 9 and 5 days before the end of TAM treatment. Blood and liver were obtained from either TAM, Rh(III) complex or TAM plus Rh(III) complex-treated rats in order to determine the interaction of both (tumoral and antitumoral) substances with the biochemical pathways related to glutathione redox cycle, enzyme activities involved in the oxidative stress coupled to the NADPH/NADP pair and enzymes related to the mono-oxygenase P450 system. The results showed that TAM induced an imbalance between the activities of glutathione-coupled enzymes. Glutathione reductase activity increased along with the intoxication, while glutathione peroxidase activity decreased. Alterations in the activity of soluble glutathione peroxidase were parallel to those of catalase. These results, together with decreased activities of enzymes related to cytochrome P450 mono-oxygenase system, NADPH cytochrome P450 reductase and NADH cytochrome b5 reductase, suggest that liver cells are not protected against the peroxidative stress produced by chronic administration of TAM. The Rh(III) complex did not produce significant changes in the parameters assayed when administered alone. When this complex was administered to TAM-treated rats, significant restoration of the following activities was observed: those of NADPH-generating enzymes (glucose-6-phosphate dehydrogenase and malic enzyme), that of glutathione reductase (NADPH-consuming enzyme), NADPH-cytochrome P450 reductase and total catalase. These results, together with others in previous studies, suggest that the altered liver function induced by chronic administration of TAM can be partially restored by this rhodium complex. The mechanisms by which this complex counteracts the TAM-induced changes have not yet been established.

Translocation of phosphatidate phosphohydrolase from the cytosol to microsomal membranes in thioacetamide-induced liver tumours in rats.

The translocation of phosphatidate phosphohydrolase induced by oleate was higher (two-fold) in liver homogenates obtained from long-term thioacetamide-treated rats than from control rats. These differences between thioacetamide-treated and control livers were noticeably higher (four-fold) in the presence of physiological concentrations of salt (0.15 M KCl). In homogenates from control rats, there was a lack of response when physiological concentrations of the salt were present. The enhanced response to translocate phosphatidate phosphohydrolase activity in liver homogenates from thioacetamide-treated rats was due to an increased binding ability of microsomal membranes.

Lipogenesis and cholesterogenesis de novo in liver and adipose tissue. Alterations of lipid metabolism by the effect of short- and long-term thioacetamide administration to rats.

Enzyme activities related to fatty acid synthesis were determined in liver extracts of rats treated with thioacetamide (TAM) for 8 weeks. Lipogenesis and cholesterogenesis in vivo were evaluated both in liver and in epididymal adipose tissue. The enzymatic activities of ATP-citrate lyase, acetyl CoA carboxylase, fatty acid synthetase, glycerol kinase and NAD-kinase decrease progressively when TAM was chronically administered. However, in the same experimental conditions malic enzyme and other NADP-enzymes were noticeably increased. This increase can be related to an excess of NADPH production necessary for detoxification rather than for lipogenesis. The rate of in vivo incorporation of 3H2O into non-saponifiable fraction in liver showed an increase in the acute phase (1-3 days) of TAM-treatment. In the chronic phase of TAM intoxication this rate returned to values close to normality. The rate of in vivo incorporation of 3H2O to fatty acid fraction increased in the liver during the acute phase of TAM-treatment and showed a sharp decrease during the subacute and chronic phases of the intoxication. At the end of the 60-day period of TAM-treatment, the radioactivity incorporated into fatty acids was significantly lowered. These data showed that the alterations in hepatic lipogenesis observed during TAM administration are related to changes in the activities of lipogenic enzymes and probably are a consequence of alterations in plasma insulin concentration. Disturbances in lipid metabolism should play an important role in the pathogenesis of liver damage and its physiological significance could involve metabolic changes in proliferative and neoplastic liver diseases.

Age-related changes in the translocation of phosphatidate phosphohydrolase from the cytosol to microsomal membranes in rat liver.

The effects of oleate, spermine and chlorpromazine were assayed in the presence or absence of 0.15 M KCl on the translocation of phosphatidate phosphohydrolase activity from cytosol to endoplasmic reticulum membranes in liver homogenates obtained from rats aged 1, 30, 60, 180 and 360 days. Marked age-associated decreases in phosphatidate phosphohydrolase distribution onto the membranes were demonstrated under nearly all conditions. In liver homogenates taken from 1-day-old rats and incubated with 0.15 M KCl, most of the enzyme was active (associated with the membranes). Physiological salt concentration (0.15 M KCl) produced a 2-fold increase of oleate-induced translocation of phosphatidate phosphohydrolase activity in liver homogenates from 1-day-old rats; it had no effect on those from 60-day-old rats, and produced a notable decline in liver homogenates obtained from 180- and 360-day-old rats. The promoting effect of spermine on oleate-induced translocation of this enzyme activity was higher in younger rats when incubated in the absence of 0.15 M KCl. Chlorpromazine did not show its usual antagonizing effect on oleate-induced translocation of phosphatidate phosphohydrolase when added to homogenates taken from 1-day-old rats. The antagonizing effect was slightly apparent in liver homogenates from 30-day-old rats and was more pronounced in those from 60-day-old rats in which the values diminished to one-half and to one-third either in the presence or absence of 0.15 M KCl.

Effect of a rhodium complex on alterations of hepatic function in thioacetamide-induced hyperplastic noduligenesis in rats.

An in vivo model of liver hyperplastic noduligenesis was induced in rats by long-term administration of thioacetamide (TAM) (50 mg/kg/day i.p.). Three doses of 50 mg/kg of an antitumoral Rh(III) complex were administered at 14, 9 and 5 days before the end of TAM treatment. Plasma and urine were obtained from either TAM or Rh(III) complex or TAM plus Rh(III) complex treated rats to determine the interactions of both substances with the biochemical parameters related to liver function. The rise in alkaline phosphatase (ALP), leucine aminopeptidase (LAP), gamma-glutamyl transferase (GGT) and the unchanged activities in the aspartate and alanine aminotransferases (AST, ALT) in plasma of TAM-treated rats indicated that the disease induced by this substance can be considered as a chronic obstructive biliary disease with indices of cell proliferation and tumors. The increased concentration of bilirubin both in the plasma and urine of TAM-treated rats suggested liver cholestasis and hepatobiliary obstruction. The very low values of creatinine clearance indicated that there was some degree of kidney failure due to the effect of TAM. The increased concentration of ammonia both in plasma and urine were probably a consequence of the decreased flux in the urea cycle in the liver. The Rh(III) complex alone did not produce significant changes in the plasma enzyme activities. The only significant changes were found in the concentrations of uric acid and ammonia in the urine. When the Rh(III) complex was administered to TAM-treated rats, significant restoration of the following parameters were observed: plasma enzymatic activities, blood bilirubin and ammonia, uric acid and creatinine in the urine and the creatinine clearance. These results suggest that the altered liver function induced by TAM can be restored by Rh(III) complex. The mechanisms by which this complex acts to counteract the TAM-induced changes are not yet established.