Hückel and Möbius annulenes: relationships between their Hückel-level orbitals and their Hückel-level energies

The problem of convenient access to quantitative Hückel-level descriptions of Möbius and Hückel annulenes for undergraduate lectures about aromaticity is discussed. Frost circle, Zimmerman circle, double circle and Langler semicircular mnemonics are described. The relationship between spectra (complete sets of secular equation roots) for an isoconjugate pair of Hückel and Möbius annulenes and the corresponding acyclic polyene with one less carbon is fully developed. In addition to providing an alternative path to exact spectrum roots, this relationship provides immediate access to almost half of the eigenfunctions for an isoconjugate annulene pair. The remaining eigenfunctions may be obtained very easily.

Polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and polychlorinated biphenyls (PCB): main sources, environmental behaviour and risk to man and biota

Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofuranes (PCDF) and polychlorinated biphenyls (PCB) are types of persistent and bioaccumulating organic pollutants with enhanced chronic toxicity and carcinogenic properties and can be considered as environmental indicators of anthropogenic activities since their occurrence in the environment can always be linked to anthropogenic activities. The present paper reviews the main sources and behaviour of these compounds in the environment as well as the risks they represent to man and biota.

Quantitative structure-retention relationships analysis of retention index of essential oils

Genetic algorithm and multiple linear regression (GA-MLR), partial least square (GA-PLS), kernel PLS (GA-KPLS) and Levenberg-Marquardt artificial neural network (L-M ANN) techniques were used to investigate the correlation between retention index (RI) and descriptors for 116 diverse compounds in essential oils of six Stachys species. The correlation coefficient LGO-CV (Q²) between experimental and predicted RI for test set by GA-MLR, GA-PLS, GA-KPLS and L-M ANN was 0.886, 0.912, 0.937 and 0.964, respectively. This is the first research on the QSRR of the essential oil compounds against the RI using the GA-KPLS and L-M ANN.

WOMAN IN CHEMISTRY. JANE MARCET, A RELEVANT FIGURE IN CHEMISTRY EDUCATION

A historiographical study of Jane Marcet’s role in spreading chemistry knowledge to a wider audience in the 19th century is presented here. Her efforts to spread scientific knowledge were crucial to sharing the most important theories of chemistry among different audiences, particularly women and young people. Through her book, “Conversations on Chemistry,” which was published in several editions from 1806 to 1853, she contributed significantly to chemistry education. Despite controversy over the large number of editions, this text is a strong witness to the active participation of women in science. Her scientific rigor and contribution to narrative strategies in chemistry pedagogy have given Jane Marcet consideration not only as an important woman in the scientific community of England during the first half of the 19th century but also as a central figure in the early development of chemistry diffusion and education.

Relationships and estimates of longitudinal growth stress in Eucalyptus dunnii at different ages

The objective of this study was to obtain estimates of longitudinal growth stresses in standing trees of the Eucalyptus dunnii Maiden at eight, thirteen, fifteen and nineteen years of age and to determine their relationships with wood characteristics. The longitudinal growth stresses were indirectly measured by the "CIRAD-Forêt" method and estimated from both the dynamic modulus of elasticity and the modulus of elasticity in tension parallel to the grain. The longitudinal residual strain (LRS) and the estimates of the longitudinal growth stresses tended to increase with the age of the material. The LRS correlated positively and significantly with all the growth stresses estimates. The largestes magnitudes were at 13, 15 and 19 years of age. The basic density presented high, positive and significant correlations with the dynamic modulus of elasticity, estimated in the longitudinal direction, for wood saturated and at 12% moisture content, for all the ages assessed. All the growth stresses estimates presented high, positive and significant correlations between themselves.

SOIL ORGANIC CARBON, CARBON STOCK AND THEIR RELATIONSHIPS TO PHYSICAL ATTRIBUTES UNDER FOREST SOILS IN CENTRAL AMAZONIA

ABSTRACT The soil carbon under Amazonian forests has an important roles in global changing, making information on the soil content and depths of these stocks are considerable interest in efforts to quantify soil carbon emissions to the atmosphere.This study quantified the content and soil organic carbon stock under primary forest up to 2 m depth, at different topographic positions, at Cuieiras Biological Reserve, Manaus/ ZF2, km 34, in the Central Amazon, evaluating the soil attributes that may influence the permanence of soil carbon. Soil samples were collected along a transect of 850 m on topographic gradient Oxisol (plateau), Ultisol (slope) and Spodosol (valley). The stocks of soil carbon were obtained by multiplying the carbon content, soil bulk density and trickiness of soil layers. The watershed was delimited by using STRM and IKONOS images and the carbon contend obtained in the transects was extrapolated as a way to evaluate the potential for carbon stocks in an area of 2678.68 ha. The total SOC was greater in Oxisol followed by Spodosol and Ultisol. It was found direct correlations between the SOC and soil physical attributes. Among the clay soils (Oxisol and Ultisol), the largest stocks of carbon were observed in Oxisol at both the transect (90 to 175.5 Mg C ha-1) as the level of watershed (100.2 to 195.2 Mg C ha-1). The carbon stocks under sandy soil (Spodosol) was greater to clay soils along the transect (160-241 Mg C ha-1) and near them in the Watershed (96.90 to 146.01 Mg C ha-1).

Implante tumoral em sítio de trocarte após colecistectomia laparoscópica

The authors present two cases of unsuspected carcinoma of the gallbladder after laparoscopic cholecystectomy in which trocar site metastasis developed during their follow-up. In the first case, a 68 year-old woman with cholecystolithiasis underwent an uneventful laparoscopic cholecystectomy. Histologic examination revealed adenocarcinoma invading the mucosa and muscular layers of the gallbladder. The patient refused additional treatment. Seven months later, metastasis developed in the umbilical port site, which was excised. In the second case, laparoscopic cholecystectomy was performed for a symptomatic gallstone in a 78 year-old man. The gallbladder inspection showed thickenning of the infundibulum wall. Histological examination revealed adenocarcinoma invading serosa. No additional treatment was performed because of the patient's advanced age. A metastasis was identified in the 5 mm port site nine months after the operation. Two hepatic metastasis were also demonstrated by ultrasonography.

Long term dietary deficiency in steers: vital functions and T3 and IGF-1 relationships

To evaluate the influence of diets with different degrees of energy deficiency on the hormonal profile and vital functions, 12 steers were randomly distributed into 3 groups of 4 animals. For 140 days, each group received (G1) a diet to promote a weight gain of 900gr/day (17.7 Mcal/d DE and 13% CP), (G2) 80% of the maintenance requirements (5.8 Mcal/d DE and 7% CP), or (G3) 60% of the maintenance requirements (4.7 Mcal/d DE and 5% CP). In G2 and G3, the energy deficit caused a marked decrease in the heart rate and respiratory rate and a reduction in the blood levels of Insulin like growth factor-1 (IGF-1) and triiodothyronine (T3). The decrease in heart rate, respiratory movement and, to a lesser extent, reduction of the rectal temperature, reflected the low status of energy and was negatively impacted by the low levels of T3. There was a strong correlation between the hormones T3 and IGF-1 (r=0.833). There were also strong correlations between T3 and HR (r=0.701), T3 and RR (r=0.632), IGF-1 and HR (r=0.731), and IGF-1 and RR (r=0.679). There were intermediate correlations between T3 and TºC (r=0.484), T3 and insulin (r=0.506), IGF-1 and insulin (r=0.517), and IGF-1 and TºC (r=0.548). This study showed the influence of a long period of providing an energy-deficient diet on animal performance, correlating hormonal status and vital functions in growing cattle. The results indicated that the evaluated parameters represent an important tool for the early detection of dietary deficiency.

Climate, soil and tree flora relationships in forests in the state of São Paulo, southeastern Brasil

ABSTRACT - (Climate, soil and tree flora relationships in forests in the state of São Paulo, southteastern Brasil). With the aim of verifying possible influences of abiotic features on the spatial distribution of forest tree species and families, thirteen surveys in the state of São Paulo were selected, representing different conditions (localization at the extreme coordenates and altitudes, succesional stages, surveying methods). By applying Jaccard's Index to the binary matrices of 806 synonymized specific binomina and 79 families (Cronquist's system) phenograms were constructed using the method of the unweighted pair grouping by mathematical average (UPGMA). The species formed two floristic blocks: hygrophyllous (yearly rainfall greater than 2000 mm without dry season) and mesophyllous (yearly rainfall about 1400 mm with variable dry season). The latter was divided in two other groups: the high-altitudinal (median altitudes higher than 750 m, frost average frequency greater than 3 days/year) and low-altitudinal. Both mesophyllous floristic blocks were subdivided according to soil conditions (texture, eutrophism, acid or allic dystrophism, iron content). At the family level the relations were weak, but also showed the soil nutritional status as a possible constraint to the spatial partition of families.

The seed coat as a modulator of seed-environment relationships in Fabaceae

The seed coat is one of the main determinants of seed germination, vigor and longevity potentials. It is also intimately associated with temporal and spatial dispersion of seed germination in a large number of plant species. The understanding of its properties and characteristics may explain, anticipate or even allow the modification of seed performance under certain environmental conditions. There is a growing volume of evidence associating seed coat characteristics to specific seed problems. For example, susceptibility to mechanical damage is related to lignin content of the seed coat, while seed longevity and tolerance to field weathering depends on seed coat integrity. Seed performance in many legumes has been associated with certain seed coat structures, such as the hilum, strophiole and micropyle. In soybean, permeability is also related with porosity, color, and cerosity, that affect seed vigor, storage potential, resistance to shrinking and fungi infection, and to susceptibility to imbibition damage. The understanding of these associations is necessary before genetic alterations through breeding for desirable characteristics and is fundamental for the development and improvement of seed pre-sowing treatments, production, handling and quality evaluation procedures, which may ultimately result in reduction of seed quality losses and increase the efficiency of agricultural production systems.

Floristic relationships among inland swamp forests of Southeastern and Central-Western Brazil

We evaluated the floristic relationships among 20 swamp forests of Southeastern and Central-Western Brazil using multivariate analyses. Detrended correspondence analysis (DCA) and TWINSPAN (Two way indicator species analysis) indicated two distinct floristic groups among forests, according to the Phytogeographic Province (Paranaense or Cerrado) and their climate conditions, phytophysiognomies, and species composition. Within the same province, edaphic conditions and geographical distance, among other factors, may be responsible for similarities or dissimilarities among the forests floras. Our results indicated that, despite the low a diversity, γ diversity is high among the forests, as a result of the low floristic similarities among the remnants and the high number of unique species (55% of all species). Although floristically distinct, we concluded that the inland swamp forests of Southeastern Brazil and the gallery swamp forests of Central Brazil are part of the same forest formation. These forests have in common, in addition to the swampy environment, low plant species diversity and species that have high local densities, such as Calophyllum brasiliense Cambess., Cecropia pachystachya Trécul, Dendropanax cuneatus Decne. & Planch., Guarea macrophylla Vahl, Magnolia ovata (A. St.-Hil.) Spreng., Protium spruceanum (Benth.) Engl. and Tapirira guianensis Aubl.

Relationships between crown architecture and available irradiance in two cerrado species with different leaf phenologies

Structural differences between cerrado species with different leaf phenologies are linked to crown architecture, leaf production, and biomass allocation to shoots and leaves. The present study characterized crown structures and the patterns of biomass allocation to leaves and shoots in two woody cerrado species with contrasting leaf phenologies and quantified the irradiance reaching their leaves to determine the best period during the day for photosynthetic activity. The shoots and leaves of five individuals of both Annona coriacea (deciduous) and Hymenaea stigonocarpa (evergreen) were collected along a 50 m transect in a cerrado fragment within the urban perimeter of Catalão - GO, to determine their patterns of biomass allocation in their crowns. The evergreen H. stigonocarpa had significantly higher mean values of shoot inclination (SI), petiole length (PL), leaf area (LA), leaf display index (LDI), and individual leaf area per shoot (ILA), while the deciduous species A. coriacea had significantly higher leaf numbers (LN). The more complex crown of H. stigonocarpa had shoots in more erect positions (orthotropic), with intense self-shading within shoots; A. coriacea, on the other hand, had slanting (plagiotropic) shoots in the crown, allowing similar irradiance levels to all leaf surfaces. The production of plagiotropic shoots by the deciduous species (A. coriacea) is a strategy that enables its use of incident sunlight early in the morning and preventing excessive water loss or excessive irradiance. Hymenaea stigonocarpa (an evergreen), by contrast, had orthotropic shoots and uses intense self-shading as a strategy to avoid excessive irradiance, especially at midday. Differences in crown architectures between evergreen and deciduous species of cerrado sensu stricto can therefore be viewed as adaptations to the environmental light regime.

P-glycoprotein-mediated resistance to chemotherapy in cancer cells: using recombinant cytosolic domains to establish structure-function relationships

Resistance to chemotherapy in cancer cells is mainly mediated by overexpression of P-glycoprotein (Pgp), a plasma membrane ATP-binding cassette (ABC) transporter which extrudes cytotoxic drugs at the expense of ATP hydrolysis. Pgp consists of two homologous halves each containing a transmembrane domain and a cytosolic nucleotide-binding domain (NBD) which contains two consensus Walker motifs, A and B, involved in ATP binding and hydrolysis. The protein also contains an S signature characteristic of ABC transporters. The molecular mechanism of Pgp-mediated drug transport is not known. Since the transporter has an extraordinarily broad substrate specificity, its cellular function has been described as a "hydrophobic vacuum cleaner". The limited knowledge about the mechanism of Pgp, partly due to the lack of a high-resolution structure, is well reflected in the failure to efficiently inhibit its activity in cancer cells and thus to reverse multidrug resistance (MDR). In contrast to the difficulties encountered when studying the full-length Pgp, the recombinant NBDs can be obtained in large amounts as soluble proteins. The biochemical and biophysical characterization of recombinant NBDs is shown here to provide a suitable alternative route to establish structure-function relationships. NBDs were shown to bind ATP and analogues as well as potent modulators of MDR, such as hydrophobic steroids, at a region close to the ATP site. Interestingly, flavonoids also bind to NBDs with high affinity. Their binding site partly overlaps both the ATP-binding site and the steroid-interacting region. Therefore flavonoids constitute a new promising class of bifunctional modulators of Pgp.

The use of protein structure/activity relationships in the rational design of stable particulate delivery systems

The recombinant heat shock protein (18 kDa-hsp) from Mycobacterium leprae was studied as a T-epitope model for vaccine development. We present a structural analysis of the stability of recombinant 18 kDa-hsp during different processing steps. Circular dichroism and ELISA were used to monitor protein structure after thermal stress, lyophilization and chemical modification. We observed that the 18 kDa-hsp is extremely resistant to a wide range of temperatures (60% of activity is retained at 80ºC for 20 min). N-Acylation increased its ordered structure by 4% and decreased its ß-T1 structure by 2%. ELISA demonstrated that the native conformation of the 18 kDa-hsp was preserved after hydrophobic modification by acylation. The recombinant 18 kDa-hsp resists to a wide range of temperatures and chemical modifications without loss of its main characteristic, which is to be a source of T epitopes. This resistance is probably directly related to its lack of organization at the level of tertiary and secondary structures.

Effect of the establishment of dominance relationships on cortisol and other metabolic parameters in Nile tilapia (Oreochromis niloticus)

The objective of the present study was to investigate the influence of the establishment of dominance relationships and social stress on plasma cortisol and metabolite levels in Nile tilapia (Oreochromis niloticus). During the 30-day experiment, the fish weighing 236 ± 29 g were kept in individual aquaria, except for two pairings lasting 6 h each. Blood samples were taken from the animals before and after pairing. Display, approach, attack, rebuff, chase flight, and coloration were carried out on days 16 and 30. Activities and behaviors characteristic of the establishment of dominance relationships were described. It was possible to classify all experimental fish (N = 30) as dominant or subordinate. No differences were detected between dominant (N = 15) and subordinate (N = 15) fish during isolation or after pairing in cortisol (isolated: 5.76 ± 0.98 vs 5.42 ± 0.63; paired: 10.94 ± 1.62 vs 11.21 ± 2.45 µg/dl), glucose (isolated: 60.02 ± 4.9 vs 67.85 ± 16.16; paired: 110.44 ± 15.72 vs 136.26 ± 22.46 mg/dl), triglyceride (isolated: 167.87 ± 5.06 vs 185.68 ± 7.24; paired: 210.85 ± 13.40 vs 221.82 ± 12.70 mg/dl) or total protein levels (isolated: 7.01 ± 0.42 vs 6.69 ± 0.59; paired: 9.21 ± 0.62 vs 9.51 ± 0.66 g/dl). However, when isolated (N = 30) and paired (N = 30) tilapia were compared, there were significant differences in cortisol and metabolite levels. The similar response presented by dominant and subordinate tilapia indicates that establishment of dominance relationships was a stressor for both groups.