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In this work we employ the state of the art pseudopotential method, within a generalized gradient approximation to the density functional theory, to investigate the interaction process (i.e. adsorption and dissociation) of cyclic hydrocarbons (cyclopentene, cyclohexene, and 1,4-cyclohexadiene) with the silicon ( 0 0 1 ) surface. Our first-principles calculations suggest that all considered cyclic hydrocarbons are adsorbed on the Si( 0 0 1 ) surface via a [2+2] cycloaddition reaction with adsorption energies of 35, 23, and 31 kcal/mol for cyclopentene, cyclohexene, and 1,4-cyclohexadiene, respectively. Possible reaction pathways for the dissociation of the methyl radicals and the breaking of the Si–Si dimers of the surface are considered. In addition, we present theoretical STM images of possible adsorbed systems, with a view to contribute to further experimental investigations.

The general term "enaminone" is applied to any compound bearing the conjugated system N-C=C-C=O. Enaminones are typical capto-dative ethylenes, showing particular properties due to pi-electron delocalization. Their reactivity can be predicted by structural patterns of substitution, conformation and configuration, making them versatile synthetic building blocks. In this review, a variety of methods for the synthesis of enaminones is described. The methods were divided into condensation of amines to beta-dicarbonyl compounds, addition of amines to a,b-unsaturated carbonyl compounds, condensation between carbonyl compounds and N-unsaturated functions and other methods, covering the period from 1993 to 2001.

Based on a first-principles pseudopotential calculation, within the local density approximation, we have studied a series of different structural models for the In-rich InAs(0 0 1) surface, including a very recent model proposed by Kumpf et al. based in X-ray diffraction experiments. Our data suggests that the ζ(4 × 2) model corresponds to the most probable structure, from the energetic point of view. The stability of the ζ(4 × 2) structure is mainly attributed to electrostatic and structural characteristics of the surface. The atomic and electronic structure of this system is analysed in detail. Experimental scanning tunnelling microscopy images are reinterpreted in the lights of our theoretical simulated images for the proposed structure, with a view to explain contradicting experimental and theoretical results.

Using a first-principles pseudopotential method we have investigated the adsorption of oxygen atoms over the CdTe(110) surface. Our calculations suggest that the oxidation process of the CdTe(110) surface could be understood as follows: (i) an oxygen atom is adsorbed over Cd and Te sites in a bridge configuration; (ii) a second oxygen atom is adsorbed over this system forming an oxygen complex composed of Cd–O2 and Te–O bonds; and (iii) a third oxygen atom is adsorbed over this system forming a new complex with Te–O2–O and Cd–O–O bonds. The final adsorbed complex is characterised by the breaking of the Cd–Te bond and the formation of Te–O, Cd–O and O–O bonds, explaining why apparent contradicting experimental observations are reported by different groups. Our calculated electronic structure for the adsorbed complex suggest that the so expected passivation effect does not occur. In addition we present calculated vibrational modes for the adsorbed system in order to contribute to further experimental investigation.

6-Methoxy-1-tetralone was transformed in six steps into an indan derivative related to the sesquiterpenes mutisianthol and jungianol. Key steps involve a thalium(III)-promoted ring-contraction (to assemble the indan unit)and a Wittig olefination (to attach the side chain).

Using a first-principles pseudopotential technique, we have investigated the adsorption of C 2 H 2 on the Ge(0 0 1) surface. We have found that, at low temperatures, the di-σ bond configuration is the most stable structure from the energetic point of view. According to our calculations, it is not possible to conclude if C 2 H 2 adsorbs preferentially on alternate or adjacent dimer sites. The di-σ adsorbed system is characterized by symmetric and slightly elongated Ge–Ge dimers, and by a symmetric C–C bond with length close to the double carbon bond length of the ethylene molecule. Our total energy calculations suggest that other meta-stable configurations, like the 1,2-hydrogen transfer model, are also possible. This behaviour was also observed for the silicon based system. In addition, we present theoretical scanning tunneling microscopy images and calculated vibrational modes for the adsorbed system with a view to contribute to further experimental investigations.

A fritura é uma operação que confere aos alimentos características de odor, sabor, cor e textura de grande aceitabilidade sensorial. O óleo ou gordura pode, entretanto, se tornar um ingrediente capaz de introduzir alterações químicas provocadas pelo aquecimento prolongado. Neste trabalho, estudou-se o comportamento do óleo de soja refinado em fritura de imersão intermitente, em restaurante universitário, sob temperatura controlada entre 170ºC e 180ºC, por um período de 30 horas. Foram utilizados 101 litros de óleo de soja para processar 373kg de vegetais, como batata, couve-flor, abobrinha e mandioca. Analisou-se o óleo mediante determinações físicas de absortividade no u.v. (A232nm e A270nm) e cor (Lovibond), e químicas (índice de acidez (IA) e compostos polares (CP)). Análise sensorial de aceitabilidade foi realizada nos produtos. Os parâmetros-limite que determinaram o descarte do óleo foram: 25% de compostos polares, 1% de ácidos graxos livres e média de 7,0 para o teste de aceitabilidade. Os resultados ao final do período foram: IA, 0,282; CP, 18,8%; cor Lovibond 14Y/2R; A232nm de 9,213; A270nm de 2,409 e 7,96 para o teste de aceitabilidade. Com base nos resultados obtidos, concluiu-se que, apesar do aquecimento do óleo ter levado a alterações hidrolíticas e oxidativas, os parâmetros não atingiram o nível de descarte, indicando que o óleo de soja submetido a essas condições de fritura pode ser usado por 30 horas.Deep fat frying is an important operation that imparts characteristics of flavor, color and texture in the fried products, however oil or fat becomes an ingredient that induces chemical alterations during prolonged heating periods. The performance of refined soybean oil was studied under intermittent deep fat frying conditions at a university cafeteria, at temperatures between 170ºC (338ºF) and 180ºC (356ºF), for a period of 30 hours. During this period, 101 liters of soy oil were used to process 373kg of vegetables (potato, cauliflower, squash and cassava). The oil quality was assessed by means of physical (uv absorptivity A232nm and A270nm, Lovibond color) and chemical (free fatty acids (FFA) and polar compounds (PC)) determinations. Sensorial analysis in the deep fat fried foods was performed through the acceptability test. The limits for alteration of the oils were established at 27% PC, 1% FFA and an average of 7.0 for acceptability. The results obtained at the end of the period were 0.282% FFA, 18.8% PC, 14Y/2R for Lovibond color, 9.213 for A232nm and 2.409 for A270nm and an average of 7.96 for the acceptability test. It can be concluded that the hydrolytic and oxidative alterations induced by the soybean oil under the heating conditions studied did not warrant discarding the oil after 30 hours.

Using a first-principles pseudopotential method we have compared the interaction processes involved in the adsorption of ethylene on the silicon and germanium surfaces. We have found that, at low temperatures, the di-σ bond configuration is the most stable structure from the energetic point of view. According to our calculations C2H4 adsorbs preferentially on the alternate dimer sites, corresponding to a coverage of 0.5 ML. The di-σ adsorbed system is characterized by symmetric and slightly elongated Si–Si (Ge–Ge) dimers, and by a symmetric C–C bond close to the single carbon bond length of the ethane molecule. The electronic band structure derived from our calculations suggest that the adsorption of the C2H4 molecule leaves a surface state in the fundamental band gap that is mainly localized around the adsorbate. Finally, our ab initio vibrational spectra further support the di-σ model for the ethylene adsorption on IV(0 0 1)-(2×2).

In this work we describe the cyclofunctionalization of eleven differently substituted alkenyl-beta-dicarbonyl compounds, employing three electrophilic reagents, namely, iodine, p-methoxyphenyltellurium trichloride, and phenylselenenyl bromide. The reactions occur through the enolic form of the substrates, to afford the corresponding iodo-, telluro-, or selenocyclic enol ethers. Substrates bearing trisubstituted double bonds failed in reacting with the selenium and tellurium reagents. In general, beta-diketones reacted faster than beta-keto esters with the three studied electrophiles.

The reaction of a series of six-membered ring 3-alkenols with thallium trinitrate (TTN) in three different experimental conditions was studied. Either cyclization products or ring contraction products were obtained, depending on the structure of the substrate as well as the nature of the solvent. The reaction of a seven-membered ring 3-alkenol with TTN led to the ring contraction product exclusively.

This review summarizes the papers dealing with the synthesis of mintlactone and isomintlactone, two natural monoterpenic lactones found in mint oils. 1 Introduction 2 Syntheses 2.1 Transformation of Monoterpenes 2.1.1 From (+)-Menthofuran 2.1.2 From (+)-Citronellal 2.1.3 From (-)-Isopulegol 2.1.4 From Geraniol and Nerol 2.2 From 4-Methyl Cyclohexanone 2.3 From Cyclohexenone Derivatives 2.4 From 3-Methyl Cyclohexanone 3 Conclusion.

2-(3,4-Dihydro-1-naphthalen-1-yl)propan-1-ol was protected with several groups. The reaction of these alkenol derivatives with thallium trinitrate (TTN) was then investigated. Oxidation of the methyl, benzyl and 4-phenylbenzyl ether led to the ring contraction product, as a single diastereomer, in reasonable yields (63-71%). The high diastereoselectivity can be explained by coordination between thallium(III) and oxygen during the rearrangement step. When treated with TTN under similar conditions, the acetate and benzoate derivatives were recovered unchanged. However, using excess of the oxidant, these esters led to indans as a 1:1 mixture of diastereomers, in 12-24% yield, together with a naphthalene derivative, in 9-24% yield. Treatment of the silyl ether derivatives with TTN promotes the cleavage of the protecting group, yielding the starting alkenol, which underwent oxidation, furnishing the expected indan in 37-57%.

Many natural products influence neurotransmission and are used clinically. In particular, facilitatory agents can enhance neurotransmission and are potentially useful for treating neuromuscular diseases in which muscular weakness is the major symptom. In this work, we investigated the facilitatory effect of apolar to polar fractions of Casearia sylvestris Sw. (guaçatonga) on contractility in mouse phrenic nerve-diaphragm (PND) and chick biventer cervicis (BC) neuromuscular preparations exposed to indirect (via the nerve; 3 V stimuli) and direct (30 V stimuli) muscle stimulation in the absence and presence of pharmacological antagonists. Methanolic and ethyl acetate fractions, but not hexane or dichloromethane fractions, exerted a facilitatory effect on PND (indirect stimulation). The methanolic fraction was chosen for further assays to assess the involvement of: 1) presynaptic sites (axons or nerve terminals), 2) postsynaptic sites (cholinergic receptors, sarcolemma or T-tubules), and 3) the synaptic cleft (acetylcholinesterase enzyme). In preparations treated with d-tubocurarine, the methanolic fraction did not cause facilitation in response to direct stimuli; this fraction was also unable to reverse dantrolene-induced blockade (indirect stimulation). In curarized preparations, the methanolic fraction either restored neuromuscular transmission (mimicking the effect of neostigmine) or failed to cause any recovery of neurotransmission. In the presence of 3,4-diaminopyridine (3,4-DAP), the methanolic fraction decreased twitch amplitude, whereas at a high frequency of stimulation (40 Hz) there was an increase in tetanic tension. In BC preparations, the methanolic fraction did not affect contractures to exogenous acetylcholine or potassium chloride. Incubation with atropine showed there was certain modulation by prejunctional nicotinic receptors, whereas treatment with nifedipine showed that the neurofacilitation required the entry of extracellular calcium. Tetrodotoxin did not prevent the facilitatory effect of 3,4-DAP or neostigmine, but antagonized the response to the methanolic fraction. These findings indicate that neuronal sodium channels have an important role in the facilitatory response to the methanolic fraction, with extracellular calcium entry via calcium channels modulating this neurofacilitation. Possible modulation of prejunctional cholinoceptors was not excluded, particularly in view of certain antagonism by the methanolic fraction at muscarinic receptors. Since facilitation by the methanolic fraction involved enhanced acetylcholine release, use of this fraction could be potentially beneficial in neuromuscular diseases and in the reversal of residual paralysis in the post-operative period or after local anaesthesia.

Pterostilbene and piceatannol, two derivatives of resveratrol, are bioactive food compounds that mediates many cellular targets involved in cancer signaling pathways. The p53 tumor suppressor protein plays an essential role in preventing cancer development by inducing cell cycle arrest or apoptosis in response to cellular stress. This protein has been suggested to have a role in the anticancer properties of resveratrol and its structural analogues. Thus, the present study was aimed to check the cytotoxic and pro-apoptotic effects of pterostilbene and piceatannol on human breast cancer cells. MTT reduction cell viability assays showed that resveratrol derivatives (0-100 µM) promoted a cytotoxic effect on MCF-7 and MDA-MB-231 breast cancer cells in a dose- and time-dependent manner. The effects induced by pterostilbene were more pronounced than those triggered by piceatannol in both cell lines. Furthermore, cell treatment with 100 µM of pterostilbene for 24h increased phosphatidylserine exposure on cell sur...

p53 has an essential role in preventing cancer development by inducing cell cycle arrest and/or apoptosis in response to cellular stress. Mutations in the p53 gene are described in over 50% of all ...

An efficient four step protocol for the construction of functionalized indans was developed. 1-Tetralones were transformed into unsaturated esters by Reformatsky reaction with bromo-esters (ethyl 2-bromopropionate, ethyl bromoacetate or ethyl 2-bromobutyrate), followed by dehydration of the β-hydroxy-ester formed. Reduction of the ester moiety led to homoallylic alcohols bearing an endocyclic double bond. The oxidative rearrangement of these 3-alkenols was performed by thallium trinitrate (TTN) in a 2:1 mixture of AcOH/H 2 O, leading to the ring contraction products in moderate to very good yield. Fourteen examples of this sequence were studied. The oxidation of 3-alkenols prepared from 2-tetralones with TTN was also investigated. With these substrates the ring contraction reaction was not observed.

The reaction of a series of 1-tetralones with thallium trinitrate supported on Montmorillonite K-10 clay led to products of ring contraction (methyl indan-1-carboxylates) and/or alpha-oxidation (2-methoxy-1-tetralones), in variable yields. A reação de uma série de 1-tetralonas com trinitrato de tálio adsorvido em Montmorilonita K-10 forneceu produtos de contração de anel (1-indanocarboxilatos de metila) e/ou alfa-oxidação (2-metóxi-1-tetralonas), em rendimentos bastante variáveis.

Using a first-principles pseudopotential method we have studied the adsorption and dissociation of the common n-type dopant molecule PH3 on the Si(0 0 1)-(2×1) surface. We have found that phosphine adsorbs molecularly on one side of the Si–Si dimer and, at temperatures around 110 K, fully dissociates into PH2+H, with each component attached to one side of the dimer. After dissociation, the surface is characterized by an elongated dimer, symmetric for the dissociated case and asymmetric for the molecular case. The H–P–H angles and H–P bond lengths for the dissociative case have exactly the same values as obtained for the PH3 molecule. However, for the molecular case, while the H–P bond lengths are the same as observed for the PH3 molecule, the H–P–H angles are ∼8% bigger. Our dissociative adsorption model is further supported by our calculated vibrational modes, which are in good agreement with available experimental works.

Using a first-principles pseudopotential method we have studied the adsorption and dissociation of NH3, PH3, and AsH3 on the Si(001)–(2×1) surface. Apart from the existence of a barrier for the adsorption of the precursor state for arsine, we observe that the global behavior for the chemisorption of the XH3 molecules considered in this work is as follows: the gas phase XH3 adsorbs molecularly to the electrophilic surface Si atom and then dissociates into XH2 and H, bonded to the electrophilic and nucleophilic surface silicon dimer atoms, respectively. The energy barrier, corresponding to a thermal activation, is much smaller than the usual growth temperature, indicating that all three molecules will be observed in their dissociated states at room temperature. All adsorbed systems are characterized by elongated Si–Si dimers that are (almost) symmetric in the dissociative case but asymmetric in the molecular case. According to our first-principles calculations, all XH3 and XH2 systems retain the pyramidal g...

This work describes a comparative study between PhSeBr, ArTeCl3 and I2 toward the electrophilic cyclization of some unsaturated β-keto esters and β-diketones. The oxidation/elimination reaction of the obtained selenides was also studied.

Oxidation of 1,2-dihydronaphthalenes with thallium trinitrate was studied. 1,2-dihydronaphthalene, 1-methyl-1,2-dihydronaphthalene, 6- and 8-methoxy-1,2-dihydronaphthalenes gave rise to the respective ring contraction products in good yields, whereas the rearrangement was not observed using 4-methyl-1,2-dihydronaphthalene and 1-n-butyl-4-methyl-1,2-dihydronaphthalene as substrates.

Using existing and new results obtained from first-principles pseudopotential calculations, we have studied the atomic relaxation and its dependence on the chemical bonding, on III–N(110) surfaces. It is found that the characteristics of III–N(110) surfaces differ from other III–V(110) and II–VI(110) surfaces in two important aspects: a significantly reduced surface bond rotation, and a much lower binding energy of the highest occupied surface state. Furthermore the results obtained for AlN and InN corroborate our previously proposed model of a linear relationship between the vertical buckling of the top layer and the relaxed surface bond length not only for III–N, but also for III–V and II–VI semiconductors in general.

Using the first-principles pseudopotential–generalized gradient approximation (GGA) approach, we have performed an accurate determination of the atomic and electronic structure of the dissociative adsorption for nitrogen trifluoride on Si(001)-(2×1). The chemisorbed system is energetically favourable and occurs in a very similar way to that found for the ammonia molecule: the NF 3 molecule dissociates with the formation of SiNF 2 and SiF bonds. We find that the system is characterized by elongated (around 6%) and symmetric silicon dimers (the tilt angle is just 1.5°), and by the fact that the SiNF 2 group retains the pyramidal geometry of the nitrogen trifluoride molecule. We also observe that the SiN bond is inclined at almost 8.6° with respect to the surface normal. The NSi bond length is 1.85 A and the NF bond length is 1.47 A. Finally, our electronic structure calculations suggest that the adsorption of NF 3 molecules almost completely passivates the silicon surface.

The adsorption process, atomic geometry, electronic structure and energetics of a Si(001) surface covered by Te atoms have been studied using first-principles total-energy calculations. Our findings indicate that the Te atoms adsorb in the ‘bridge’ site on the surface Si dimer bond, in agreement with recent experimental results. We have also verified that the Si dimers (underneath adsorbed Te atoms) do not dissociate. The subsequent atomic exchange between the adsorbed Te atom and the surface Si atom, giving rise to an interdiffusion process of Te atoms towards Si substrate, is not an exothermic process. We have considered a number of possible coverages of Te atoms on Si(001) surface and our results indicate that for a coverage of one monolayer (1 ML), the Si(001)/Te-(1×1) surface represents the energetically more stable configuration. For a coverage of 2/3 ML, we have verified the formation of TeSiTe mixed trimers, in a (3×1) reconstructed surface. At 1/3 ML coverage, we have obtained the formation of Si dimers with a single Te atom at the surface, in a (3×1) reconstruction. Finally, for a coverage of 1/2 ML, we have obtained the formation of SiTe mixed dimers, in a (2×1) reconstructed surface, but the calculated formation energy indicates that this atomic configuration is not energetically favourable.

We investigate the structural properties, formation energies, and electronic structure of oxygen impurities in GaAs using first-principles total-energy calculations. Five charge states of oxygen occupying an arsenic site (OAs) and various interstitial sites (O i) were considered. For the OAs defect in negative charge states we find off-center configurations withC2v symmetry as reported experimentally. Our results for the formation energies reveal a negative-U behavior for the OAs defect, in which the paramagnetic 22 charge states is never stable. For the Oi defect, we find three equilibrium configurations for the O atom, which are present in all the charge states investigated. The stable configuration for the neutral defect shows the O atom between an As-Ga pair forming the As-O-Ga structure. However, for the negative charge states, the stable configuration shows the O atom exactly at the tetrahedral interstitial site, bonding with four gallium first neighbors. Further, we find that the 12 charge state is never stable, suggesting that the interstitial defect also exhibits a negative- U behavior. Based on our results, we suggest that the A, B8, and B bands of the local-vibrational-mode absorption spectrum of oxygen in GaAs are due to the off-center OAs defect. Also we show that this spectrum cannot be associated with an interstitial-oxygen configuration as previously proposed.

The first thallium trinitrate (TTN) mediated ring contraction of cyclic homoallylic alcohols, using a 1:1 mixture of AcOH and H2O as solvent, is described. The reaction of two of these alcohols with excess of TTN in pentane gave α-spirocyclopentyl-γ-butirolactones in reasonable yields.

In this report we present the analysis of two overlapping mouse cosmid clones that contain the entire Kcnk6, Map3k11 and Pcnxl3 genes, as well as part of the Sipa1 gene. The sequence and genomic organisation of the Kcnk6 and Map3k11 genes are described in detail. Sipa1 and Map3k11, which have independently been mapped with low resolution to the centromeric region of mouse chromosome 19, are shown here to lie close to each other and to the Kcnk6 gene, which has not previously been mapped. This gene cluster maps to the vicinity of the Dancer (Dc) mutation, which involves inner ear abnormalities and circling phenotypes. Since potassium channels have been implicated in deafness disorders, we have analysed the Kcnk6 gene, which encodes a two-P domain potassium channel, in the Dc mutant. No Dc-causing mutation in the Kcnk6 coding region could be identified. However, we detected a polymorphism in the Kcnk6 gene that leads to a C-terminal extension of the encoded protein by eight amino acids.

Dediazoniation of 2,4,6-trimethylbenzenediazonium tetrafluoroborate, 1-ArN2BF4 (for the z-Ar compounds described in this paper, z refers to the length of the carbon chain of the substituent at C4 of the benzene ring), in aqueous solutions containing sodium methyl sulfate, NaMeSO4, or sodium methanesulfonate, NaMeSO3, yields 2,4,6-trimethylphenol, 1-ArOH, 2,4,6-trimethylphenyl methyl sulfate, 1-ArOSO3Me and 2,4,6-trimethylphenyl methanesulfonate, 1-ArO3SMe, respectively. The relative yields of 1-ArO3SMe or 1-ArOSO3Me and 1-ArOH depend on the NaMeSO4 or NaMeSO3 concentrations. 4-n-Hexadecyl-2,6-dimethylbenzenediazonium tetrafluoroborate, 16-ArN2BF4, was used to determine the local head group concentration in sodium dodecyl sulfate and sodium dodecanesulfonate micelles by chemical trapping comparing the relative product yields with those obtained in water using the short chain analogs. Ab initio calculations of the spontaneous dediazoniation of phenyldiazonium ion in the gas phase, as well as in aqueous solution with, or without, added MeSO3−, yield potential energy surfaces for the reaction. For this model the calculated and experimental values of the spontaneous dediazoniation rate constants in aqueous solution, as well as the product composition, were similar to those obtained with 1-ArN2+. These results suggest that in aqueous solution nucleophiles can only compete with water if a diazonium ion·nucleophile complex is formed prior to N2 loss. Calculations show that the addition of nucleophiles to the arenediazonium ion occurs without a saddle point in the potential energy surface, suggesting that the free phenyl cation is not an obligatory intermediate in aqueous solutions. p

We investigate the stability and electronic structure of 1×2 and 2×2 GaAs(001):Te and InAs(001):Te surfaces with different degrees of tellurium coverage (qTe = , , , 1), by means of rst-principles pseudopotential calculations within density-functional theory. The adsorption stability decreases as the tellurium coverage increases. The adsorption on InAs(001) is more stable than on GaAs(001). As-Ga (or As-In) bonds for the uppermost As atoms are s2p2 -like (nearly planar), while the Te bonds at the surfaces are sp3-like. The hetero-dimers in qTe = modify the character of GaAs(001):Te and InAs(001):Te surfaces resulting in a semiconductor structure.

The iodocyclization of a series of alkenyl-substituted β-enamino esters and ketones, followed by base-promoted dehydroiodination, led to the formation of the corresponding pyrrole or tetrahydroindole derivatives. In the absence of base, the iodo-β-enamino esters 5 and 7 underwent spontaneous aromatization after dehydroiodination, furnishing the 4, 5, 6, 7-N-substituted-tetrahydroindoles 19 and 20 . All the elimination reactions proceeded smoothly, in yields ranging from 71% to 99%. Starting from the β-allyl-dimedone 21 , it was possible to prepare the oxotetrahydroindole 24 , in moderate overall yield.

The reaction of six β,γ-unsaturated carboxylic acids with thallium triacetate (TTA) was studied. The nature of the products is highly sensitive to the substitution pattern of the substrates. Aliphatic acids gave mainly lactones, while those bearing an aromatic ring furnished only decarboxylation products.

Using the first-principles pseudopotential approach, we have performed calculations of the total energy, atomic structure, and chemical bonding for the bulk and surfaces of GaAs and cubic GaN to assess the role of the generalized gradient approximation (GGA) for the exchange-correlation energy. Our calculations show that the combined effect of nonlinear core correction and GGA is responsible for significant changes in the structural parameters and electronic band structure of the (001) surface, regardless of the ionicity of the compound studied, but not for bulk or the nonpolar (110) surface.

The lack of well established dosimetry protocols for HDR sources is a point of great concern regarding the uniformity of procedures within a particular country and worldwide. The main objective of this paper is to report the results from ten institutions of an intercomparison of calibration procedures for HDR sources currently in use in Brazil. The treatment irradiator of one institution was calibrated by a reference system and used by all participants with their own measuring electrometers and ionization chambers under the same experimental conditions. Two methods were used: the calibration jig and the well-type ionization chamber. Each participant was allowed to use their own method and formalism. The results of this exercise were very positive since this was the first time in Brazil that a group of users gathered to share their experience and openly discuss the physical concepts behind the calibration procedures. The results were all within %, except one case where -4.6% was observed and later identified as a problem with the value for x-rays. Though the magnitude of the deviations found was generally acceptable considering the diversity of formalisms currently in use, a proposal is now being prepared to be adopted as a national protocol. The identification of the institutions was left out for the sake of confidentiality.

Nonactic Acid is the monomeric unity of the Nactines, an important class of poliether antibiotics. This review focuses on the approaches to the syntheses of the above mentioned unity, which have been accomplished in the period from 1971 to date.

p53 is a master regulatory protein that participates in cellular processes such as apoptosis, DNA repair, and cell cycle control. p53 functions as a homotetrameric tumor suppressor, and is lost in more than 50% of human cancers. Recent studies have suggested that the formation of mutant p53 aggregates is associated with loss-of-function (LoF), dominant-negative (DN), and gain-of-function (GoF) effects. We propose that these phenomena can be explained by a prion-like behavior of mutant p53. We discuss the shared properties of cancer and neurodegenerative diseases and how the prion-like properties of p53 aggregates offer potential targets for drug development.

The tumor suppressor protein p53 loses its function in more than 50% of human malignant tumors. Recent studies have suggested that mutant p53 can form aggregates that are related to loss-of-function effects, negative dominance and gain-of-function effects and cancers with a worsened prognosis. In recent years, several degenerative diseases have been shown to have prion-like properties similar to mammalian prion proteins (PrPs). However, whereas prion diseases are rare, the incidence of these neurodegenerative pathologies is high. Malignant tumors involving mutated forms of the tumor suppressor p53 protein seem to have similar substrata. The aggregation of the entire p53 protein and three functional domains of p53 into amyloid oligomers and fibrils has been demonstrated. Amyloid aggregates of mutant p53 have been detected in breast cancer and malignant skin tumors. Most p53 mutations related to cancer development are found in the DNA-binding domain (p53C), which has been experimentally shown to form amyloid oligomers and fibrils. Several computation programs have corroborated the predicted propensity of p53C to form aggregates, and some of these programs suggest that p53C is more likely to form aggregates than the globular domain of PrP. Overall, studies imply that mutant p53 exerts a dominant-negative regulatory effect on wild-type (WT) p53 and exerts gain-of-function effects when co-aggregating with other proteins such as p63, p73 and acetyltransferase p300. We review here the prion-like behavior of oncogenic p53 mutants that provides an explanation for their dominant-negative and gain-of-function properties and for the high metastatic potential of cancers bearing p53 mutations. The inhibition of the aggregation of p53 into oligomeric and fibrillar amyloids appears to be a promising target for therapeutic intervention in malignant tumor diseases.

The reaction of 3- and 4-alkylcyclohexanones with thallium trinitrate (TTN) leads to the alkylcyclopentanecarboxylic acids in good yields and with high degree of stereoselectivity. The ring contraction of 2-methylcyclohexanone gives poor yields and 2,6-dimethylcyclohexanone does not undergo contraction. The observed diastereoselectivities of the reactions agree with the mechanism proposed by McKillop et al.

p53 is a key protein that participates in cell-cycle control, and its malfunction can lead to cancer. This tumour suppressor protein has three main domains; the N-terminal transactivation domain, the CTD (C-terminal domain) and the core domain (p53C) that constitutes the sequence-specific DBD (DNA-binding region). Most p53 mutations related to cancer development are found in the DBD. Aggregation of p53 into amyloid oligomers and fibrils has been shown. Moreover, amyloid aggregates of both the mutant and WT (wild-type) forms of p53 were detected in tumour tissues. We propose that if p53 aggregation occurred, it would be a crucial aspect of cancer development, as p53 would lose its WT functions in an aggregated state. Mutant p53 can also exert a dominant-negative regulatory effect on WT p53. Herein, we discuss the dominant-negative effect in light of p53 aggregation and the fact that amyloid-like mutant p53 can convert WT p53 into more aggregated species, leading into gain of function in addition to the loss of tumour suppressor function. In summary, the results obtained in the last decade indicate that cancer may have characteristics in common with amyloidogenic and prion diseases.