Raman spectroscopic insights into the glass transition of poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA) is a very versatile polymer which is used as a glass substitute or as an economical alternative to polycarbonate for many types of important applications, due to its particular physical properties. In this study we deal with the Raman spectroscopic characterization of the glass transition of PMMA, the value of the glass transition temperature being generally a decisive parameter for determining the application of polymers. The information obtained by two-dimensional correlation spectroscopy (2DCOS) analysis and perturbation-correlation moving-windows spectroscopy (PCMW2D) analysis of the temperature dependent depolarized Raman spectra enabled us to recognize that the glass transition of PMMA is ruled by intermolecular interactions which influence the vibrational modes of the molecular groups associated with ν(C[double bond, length as m-dash]O), δa(C-H) of α-CH3 and/or O-CH3, ν(C-O-C), ν(C-COO), and ν(C-C-O). This information was employed for the temperature dependent study of the Raman shift and of the full width at half maximum of the Raman peaks obtained through anisotropic and isotropic Raman spectra, of the depolarization ratio, of the Raman spectroscopic noncoincidence effect, and of the Raman peak intensities represented by Arrhenius-type plots, all results supporting the outcomes of this work. The comparison with results obtained by differential scanning calorimetry and with published results in molecular dynamics studies was also part of this work. As the main result, one can highlight the peak associated with the ν(C-O-C) stretching mode at around 812 cm-1 as the one which presents the better outcome for explaining the glass transition from the molecular point of view.

Using Raman spectroscopy and an exponential equation approach to detect adulteration of olive oil with rapeseed and corn oil

This study presents a method to determine adulteration of olive oil (obtained from Olea europea, i.e. olives) with rapeseed oil (obtained from Brassica napus) or with corn oil (also named maize oil, obtained from Zea mays, i.e. maize) using Raman spectroscopy and a mathematical method based on exponential equation fit. The samples were prepared by mixing olive oil with volume fractions (0-100%) of rapeseed or corn oil. The oils were differentiated spectroscopically using intensity ratio for specific Raman peaks; Raman spectroscopy is able to detect changes within a liquid molecular environment without the need for sample treatment. It was possible to determine rapeseed or corn oil volume fractions added into the olive oil using the method proposed. Thus, the potential of Raman spectroscopy as a technique for determining adulteration of olive oil was corroborated clearly, opening the potential to investigate adulteration of other liquid foods, without any need for sample preparation.

Investigation of the Brill transition in nylon 6,6 by Raman, THz-Raman, and two-dimensional correlation spectroscopy

The Brill transition is a phase transition process in polyamides related with structural changes between the hydrogen bonds of the lateral functional groups (CO) and (NH). In this study, we have used the potential of Raman spectroscopy for exploring this phase transition in polyamide 6,6 (nylon 6,6), due to the sensitivity of this spectroscopic technique to small intermolecular changes affecting vibrational properties of relevant functional groups. During a step by step heating and cooling process of the sample we collected Raman spectra allowing us from two-dimensional Raman correlation spectroscopy to identify which spectral regions suffered the largest influence during the Brill transition, and from Terahertz Stokes and anti-Stokes Raman spectroscopy to obtain complementary information, e.g. on the temperature of the sample. This allowed us to grasp signatures of the Brill transition from peak parameters of vibrational modes associated with (CC) skeletal stretches and (CNH) bending, and to verify the Brill transition temperature at around 160°C, as well as the reversibility of this phase transition.

Towards a better understanding of Ipomoea asarifolia toxicity: evidence of the involvement of a leaf lectin

Natural intoxication of livestock by ingestion of Ipomoea asarifolia leaves has been reported to occur widely in Brazil. Previous studies carried out by our research group provided strong evidence that a lectin could be involved with the toxic properties of I. asarifolia. To reinforce this hypothesis, a lectin-enriched fraction (LEF) was isolated from I. asarifolia leaves and its toxic effects were assessed. Leaves of I. asarifolia were excised from plants growing widely in the field, mechanically wounded and maintained in a chamber at 25 ± 3 °C for 72h in the dark, under near 100% relative humidity. The leaf proteins were extracted, ammonium sulfate precipitated, chromatographed on DEAE-cellulose and Phenyl-Sepharose to produce LEF that under SDS-PAGE showed a molecular mass of 44.0 kDa and after N-terminal amino acid analysis a primary sequence composed of AGYTPVLDIGAEVLAAGEPY. The in vivo toxicity of LEF assessed by intraorbital injection in mice showed induced severe uncoordinated movements without death. LEF reduced the muscular contraction in a dose depend way and at 29.8 μg/mL (CE(50)) it produces 50% inhibition of contraction, suggesting that LEF blunts autonomic neurotransmission. Isolated rat kidneys were perfused with LEF and no effects on the perfusion pressure or renal vascular resistance were observed, but urinary flow and glomerular filtration rate increased. Moreover, the percentage of tubular transport of Na(+), K(+) and Cl(-) decreased. Histological examination of the kidneys perfused with LEF exhibited little alterations. These toxic effects observed above were concomitant with the increase of LEF hemagglutination activity, which strongly suggest that one of the toxic principles of I. asarifolia is a lectin present in its leaves.

The role of indomethacin and tezosentan on renal effects induced by Bothrops moojeni Lys49 myotoxin I

Renal changes determined by Lys49 myotoxin I (BmTx I), isolated from Bothrops moojeni are well known. The scope of the present study was to investigate the possible mechanisms involved in the production of these effects by using indomethacin (10 microg/mL), a non-selective inhibitor of cyclooxygenase, and tezosentan (10 microg/mL), an endothelin antagonist. By means of the method of mesenteric vascular bed, it has been observed that B. moojeni myotoxin (5 microg/mL) affects neither basal perfusion pressure nor phenylephrine-preconstricted vessels. This fact suggests that the increase in renal perfusion pressure and in renal vascular resistance did not occur by a direct effect on renal vasculature. Isolated kidneys from Wistar rats, weighing 240-280 g, were perfused with Krebs-Henseleit solution. The infusion of BmTx-I increased perfusion pressure, renal vascular resistance, urinary flow and glomerular filtration rate. Sodium, potassium and chloride tubular transport was reduced after addition of BmTx-I. Indomethacin blocked the effects induced by BmTx-I on perfusion pressure and renal vascular resistance, however, it did not revert the effect on urinary flow and sodium, potassium and chloride tubular transport. The alterations of glomerular filtration rate were inhibited only at 90 min of perfusion. The partial blockade exerted by indomethacin treatment showed that prostaglandins could have been important mediators of BmTx-I renal effects, but the participation of other substances cannot be excluded. The blockage of all renal alterations observed after tezosentan treatment support the hypothesis that endothelin is the major substance involved in the renal pathophysiologic alterations promoted by the Lys49 PLA(2) myotoxin I, isolated from B. moojeni. In conclusion, the rather intense renal effects promoted by B. moojeni myotoxin-I were probably caused by the release of renal endothelin, interfering with the renal parameters studied.

Effects of Thalassophryne nattereri fish venom in isolated perfused rat kidney

Thalassophryne nattereri, popularly known as Niquim, is a venomous fish responsible for many accidents in fishermen in the Northeast of Brazil. The effects of T. nattereri venom on renal physiology has not been tested. Isolated kidneys from Wistar rats of 240-280 g weight were perfused with Krebs-Henseleit solution containing 6g% of previously dialyzed bovine serum albumin. The effects of Niquim venom were studied on the perfusion pressure (PP), renal vascular resistance (RVR), urinary flow (UF), glomerular filtration rate (GFR), percent of sodium tubular transport (%TNa(+)), percent of potassium tubular transport (%TK(+)) and percent of chloride tubular transport (%TCl(-)). The venom of T. nattereri (0.3, 1.0, and 3.0 microg/ml) was always added to the system 30 minutes after the beginning of each experiment (n=6). All experiments were preceded by 30 minutes internal control period and an external control group, where kidneys were perfused with only Krebs-Henseleit solution. All three doses tested promoted increases in PP and RVR. The first two doses also increased GFR and UF. The higher dose promoted decreases in GFR, UF, %TNa(+), %TK(+), %TCl(-). In the treated groups we observed hyalin casts inside all tubules and proteinaceous material in the urinary space. We conclude that the effects resulted from niquim venom agents that promoted a direct effect in kidney cells causing the release of vasoactive factors.

The role of phospholipase A(2) and cyclooxygenase in renal toxicity induced by microcystin-LR

We have shown previously that exposure to microcystin-LR (MCLR) causes renal toxic effects in isolated perfused rat kidney. That study was extended further to approach the perspective of pharmacological blockade of renal toxic effects by MCLR through the use of experimental therapeutic agents. An isolated kidney perfusion system was utilized and samples of urine and perfusate were collected at 10min intervals to determine the levels of inulin, sodium, potassium and osmolality. Dexamethasone (20microg ml(-1)) and indomethacin (10microg ml(-1)) were administered in the beginning of the perfusion and MCLR was employed in a dose of 1microg ml(-1) after an internal control of 30min to evaluate the perfusion pressure (PP), renal vascular resistance (RVR), glomerular filtration rate (GFR) and urinary flow (UF). Dexamethasone and indomethacin antagonized the toxic effects of MCLR on PP, RVR, GFR and UF. Histologic analysis of dexamethasone and indomethacin treated groups did not show any vascular or interstitial alterations. MCLR potentially impairs the renal function, probably causing vascular and glomerular lesions and, promoting renal alterations through direct or indirect actions. These data seem to indicate that the renal alterations promoted by MCLR involves also phospholipase A(2) and arachidonic acid-derived mediators.

Effects of microcystin-LR in isolated perfused rat kidney

Microcystin is a hepatotoxic peptide which inhibits protein phosphatase types 1 and 2A. The objective of the present study was to evaluate the physiopathologic effects of microcystin-LR in isolated perfused rat kidney. Adult Wistar rats (N = 5) of both sexes (240-280 g) were utilized. Microcystin-LR (1 microg/ml) was perfused over a period of 120 min, during which samples of urine and perfusate were collected at 10-min intervals to determine the levels of inulin, sodium, potassium and osmolality. We observed a significant increase in urinary flow with a peak effect at 90 min (control (C) = 0.20 +/- 0.01 and treated (T) = 0.32 +/- 0.01 ml g-1 min-1, P<0.05). At 90 min there was a significant increase in perfusate pressure (C = 129.7 +/- 4.81 and T = 175.0 +/- 1.15 mmHg) and glomerular filtration rate (C = 0.66 +/- 0.07 and T = 1.10 +/- 0. 04 ml g-1 min-1) and there was a significant reduction in fractional sodium tubular transport at 120 min (C = 78.6 +/- 0.98 and T = 73.9 +/- 0.95%). Histopathologic analysis of the perfused kidneys showed protein material in the urinary space, suggestive of renal toxicity. These data demonstrate renal vascular, glomerular and urinary effects of microcystin-LR, indicating that microcystin acts directly on the kidney by probable inhibition of protein phosphatases.

Effects of Crotalus durissus cascavella venom in the isolated rat kidney

Crotalus durissus cascavella (C.d.c) is a snake usually found in scrubland of Brazilian Northeast and its bite constitutes an important public health problem. Isolated kidneys from wistar rats, weighing 240 to 280 g, were perfused with Krebs Henseleit solution containing 6 g% of previously dialysed bovine serum albumin. The effects of C.d.c venom were studied on the perfusion pressure (PP), urinary flow (UF), glomerular filtration rate (GFR), percent of sodium tubular transport (%TNa+) and percent of proximal tubule sodium transport (%pTNa+). All experiments were preceded by a 30 min internal control period and an external control group. The infusion of C.d.c (10 microg ml(-1)) increased the PP, UF at 60 and 90min of perfusion, and decreased the GFR, %TNa+ and %pTNa+ at 120 min of perfusion. The proximal renal tubule was the major site for this toxic effect. In the group treated with the venom we found hyalin cylinders inside all tubules and proteinaceous material, alternating from moderate to intense presence in urinary space. Dexamethasone (Dexa 20 microg ml(-1)) protected against the increase in PP, UF, and against the decrease in GFR, it produced the reversion of the effect also in %TNa+ and %pTNa+. Indomethacin (Indo 10 microg ml(-1)) antagonized the effect observed in PP and UF, but was not able to reverse the changes in GFR, %TNa+ and %pTNa+. Nifedipine (Nif 10 microg ml(-1)) promoted a reversion of almost all functional changes, except the %pTNa+ was not reversed. We conclude that these alterations may be caused by a direct action of the venom on the kidneys and indirectly by the release of mediators from endothelial cells. Dexa protected against renal lesions caused by the venom, perhaps by inhibiting phospholipase A2 a toxic component of the venom. The reversion partially induced by indo may be due to cyclooxygenase inhibition that will inhibit the formation of prostaglandins. Nif blocked the renal alterations that may involve cell calcium influx that resulted from the venom aggression.

Involvement of the central nervous system in dengue fever: three serologically confirmed cases from Fortaleza Ceará, Brazil

Three cases of dengue fever involving the central nervous system (CNS) are reported. All occurred in 1994 during a dengue (DEN) epidemic caused by serotypes DEN-1 and DEN-2. The first case examined was a 17-year-old girl who complained of fever, nuchal rigidity and genital bleeding. Three blood samples were positive by anti-dengue IgM ELISA and showed hemagglutination-inhibition (HI) test titers > or = 1,280. The second case concerned a 86-year-old women with fever, muscle and joint pains, altered consciousness, syncope, nuchal rigidity and meningismus. Her blood sample showed an HI titer of 1:320 for flaviviruses, and an IgM ELISA positive for dengue. The third case was a 67-year-old women with fever, abnormal behaviour, seizures, tremor of extremities, thrombocytopenia, increased hematocrit and leukopenia. The patient suffered a typical case of dengue hemorrhagic fever with ensuing shock and a fatal outcome. A single blood sample showed HI antibodies of > or = 1,280 and an IgM ELISA positive for dengue. No virus could be isolated from any patient by inoculation of blood into C6/36 cells and suckling mice. No other agent of disease was encountered in the patient.

Protective effect of ternatin, a flavonoid isolated from Egletes viscosa less., in experimental liver injury

The effect of ternatin, a tetramethoxyflavone from Egletes viscosa Less., on liver injury induced by carbon tetrachloride (CCl4) was investigated in rats. Twenty-four hours following CCl4 insult (2.5 ml/kg s.c.), changes in the serum enzymes, alanine aminotransferase, aspartate aminotransferase and gamma-glutamyltransferase, as well as liver cell histology were used as indices of hepatic dysfunction. The results show that ternatin (30 mg/kg i.p. daily for 5 consecutive days) causes marked inhibition of CCl4-induced serum enzymes and morbid histologic changes. The observation suggests that ternatin possesses antihepatotoxic activity.