Time-resolved refractive index change during the bacteriorhodopsin photocycle

Kinetic refractive index spectroscopy has been applied to the study of the bacteriorhodopsin photocycle. A fully hydrated purple membrane film was examined in the temperature range from 10° to 40°C using 532 nm excitation (doubled Nd YAG laser) and 633 nm (He–Ne laser) testing beam. Multiexponential fitting of the data revealed five processes. Four of them are well known from kinetic optical absorption studies. The fifth process has only recently been observed in optical absorption experiments where it has a relatively small amplitude. In our refractive index experiments it has an amplitude of up to 30% of the full signal amplitude. It is characterized by an Arrhenius temperature dependence with an activation enthalpy of 40±5 kJ/mol and a decay time of about 0.8 ms at 20°C.     

Optimizing of Gold Nanoparticles on Porous Silicon Morphologies for a Sensitive Carbon Monoxide Gas Sensor Device

A set of carbon monoxide (CO) gas sensors based on porous silicon (PSi)/gold nanoparticle (AuNP) hetro structures were fabricated. Different forms of PSi surface morphologies were studied as a substrate for growth of AuNPs. Simple dipping process of PSi in hydrogen tetrachloroaurate (III) solution (HAuCl₄) at fixed concentrations of 10⁻² M/3.5 HF was used to synthesize AuNPs. The n-type PSi was equipped through photo-electrochemical etching process at current density value of 10 mA/cm² under illumination condition of 530-nm wavelength and laser illumination intensity of 20 to 80 mW/cm². Three different forms of PSi morphology, meso, macro, and double layers with pore shapes and sizes, were prepared. The structural and surface morphology properties of PSi-based substrate before and after deposition of AuNPs were investigated through studying of scanning electron microscopy (SEM), photoluminescence (PL), and X-ray diffraction (XRD). The electrical property (J-V) was carried out in primary vacuum and CO at low pressure. The results show that PSi surface morphologies strongly influenced the AuNP sizes and hence the sensor performance. It was found that decrease the AuNP sizes could be occasioned in high and fast current response.

     

The efficiency of two-photon photolysis of a "caged" fluorophore, o-1-(2-nitrophenyl)ethylpyranine, in relation to photodamage of synaptic terminals

Localized photolysis of caged neurotransmitters with the two-photon effect for investigations at synaptic preparations was evaluated by determining the toxicity to synaptic transmission of pulsed near-IR laser light focused into the terminals of the snake neuromuscular junction, and measuring the extent of photolysis of a conventional caging group with similar irradiation in microcuvette experiments. Photodamage was seen in synaptic terminals as a large, irreversible increase of spontaneous synaptic activity with laser flashes of 5 ms at 1 Hz at average powers > 5 mW and was due to multiphoton absorption. Localized photolysis due to two-photon absorption was investigated for a representative caged fluorophore, the 1-(2-nitrophenyl)ethyl ether of pyranine (NPE-HPTS). Irradiation of NPE-HPTS at 5 mW with the same optical arrangement produced very low rates of photolysis. NPE-HPTS photolysis mechanisms were investigated at high laser powers by measuring (1) the kinetics of two-photon fluorescence generated by two-photon photolysis in the focal volume and (2) the rates of HPTS accumulation inside closed 2-10 microm radius vesicles, measured with one-photon excitation during two-photon photolysis by repetitive 10 micros laser exposures. The two-photon crosssection of NPE-HPTS photolysis calculated from the rates is 0.02-0.04 GM (10(-50) cm4 x s/photon) and limits the efficiency of photolysis at 5 mW. With free diffusional exchange, 50% steady-state cage depletion in the focal volume was estimated to occur only at high laser powers of ca. 72 mW, masked in experiments by multiphoton bleaching. Based on these results, the two-photon photolysis cross-section needed for 50% steady-state photolysis of a caged neurotransmitter at 5 mW is calculated as 31 GM, much higher than in existing caged compounds.     

Production of polycrystalline silicon from monosilane in the electron-beam plasma

The results of experimental studies concerned with deposition of solar-grade silicon from monosilane in the electron-beam plasma are reported. With the laboratory equipment, the silicon deposition rate attains up to 40 g h⁻¹ at the expenditure of energy for the process 78 kW h kg⁻¹ and the efficiency of conversion of monosilane into silicon at about 50%. Analysis of the chemical composition of the resulting material shows that the material fits the requirements imposed on solar-grade silicon. The method suggested in the study holds promise in industrial-scale applications.     

Microwave radiation (2450 MHz) alters the endotoxin-induced hypothermic response of rats

The parenteral administration of bacterial endotoxin to rats causes a hypothermia that is maximal after approximately 90 minutes. When endotoxin-injected rats were held in a controlled environment at 22°C and 50% relative humidity and exposed for 90 minutes to microwaves (2450 MHz, CW) at 1 mW/cm², significant increases were observed in body temperature compared with endotoxintreated, sham-irradiated rats. The magnitude of the response was related to power density (10 mW/cm² > 5 mW/cm² > 1 mW/cm²). Saline-injected rats exposed for 90 minutes at 5 mW/cm² (specific absorption rate approximately 1.0 mW/g) showed no significant increase in body temperature compared with saline-injected, sham-irradiated rats. The hypothermia induced by endotoxin in rats was also found to be affected by ambient temperature alone. Increases in ambient temperature above 22°C in the absence of microwaves caused a concomitant increase in body temperature. This study reveals that subtle microwave heating is detectable in endotoxin-treated rats that have an impaired thermoregulatory capability. These results indicate that the interpretation of microwave-induced biological effects observed in animals at comparable rates and levels of energy absorption should include a consideration of the thermogenic potential of microwaves.     

Pyrolysis of grape bagasse: effect of pyrolysis conditions on the product yields and characterization of the liquid product

In this study, pyrolysis of grape bagasse was investigated with the aim to study the product distribution and their chemical compositions and to identify optimum process conditions for maximizing the bio-oil yield. Particular investigated process variables were temperature (350-600 °C), heating rate (10-50 °C/min) and nitrogen gas flow rate (50-200 cm³/min). The maximum oil yield of 27.60% was obtained at the final pyrolysis temperature of 550 °C, sweeping gas flow rate of 100 cm³/min and heating rate of 50 °C/min in a fixed-bed reactor. The elemental analysis and heating value of the bio-oils were determined, and then the chemical composition of the bio-oil was investigated using chromatographic and spectroscopic techniques such as column chromatography, ¹H NMR and FTIR. The fuel properties of the bio-oil such as flash point, viscosity and density were also determined. The bio-oils obtained from grape bagasse were presented as an environmentally friendly feedstock candidate for bio-fuels.     

Osmotic water permeability of small intestinal brush-border membranes

Summary A stopped-flow nephelometric technique was used to examine osmotic water flow across small intestinal brush-border membranes. Brush-border membrane vesicles (BBMV) were prepared from rat small intestine by calcium precipitation. Scattered 500 nm light intensity at 90° to incident was a linear function of the number of vesicles in suspension, and of the reciprocal of the suspending medium osmolality. When BBMV were mixed with hyperosmotic mannitol solutions there was a rapid increase in the intensity of scattered light that could be fit to a single exponential function. The rate constant for vesicle shrinking varied with temperature and the size of the imposed osmotic gradient. At 25°C and an initial osmotic gradient of 50 mOsm, the rate constant was 1.43±0.044 sec^–1. An Arrhenius plot of the temperature dependence of vesicle shrinking showed a break at about 25°C with an activation energy of 9.75±1.04 kcal/mole from 11 to 25°C and 17.2±0.55 kcal/mole from 25 to 37°C. The pore-forming antibiotic gramicidin increased the rate of osmotically driven water efflux and decreased the activation energy of the process to 4.51±0.25 kcal/mole. Gramicidin also increased the sodium permeability of these membranes as measured by the rate of vesicle reswelling in hyperosmotic NaSCN medium. Gramicidin had no effect on mannitol permeability. Assuming spherical vesicles of 0.1 m radius, an osmotic permeability coefficient of 1.2×10^–3 cm/sec can be estimated for the native brush-border membranes at 25°C. These fesults are consistent with the solubility-diffusion model for water flow across small intestinal BBMV but are inconsistent with the existence there of large aqueous pores.     

Thermal dependence of reproductive allocation in a tropical lizard

In ectotherms, environmental temperature is the most prominent abiotic factor that modulates life-history traits. We explored the influence of environmental temperature on reproduction in the Madagascar ground gecko (Paroedura picta) by measuring reproductive traits of females at constant temperatures (24, 27, 30 °C). Females of this species lay clutches of one or two eggs within short intervals. For each female, we measured egg mass for the first five clutches. For one clutch, we also measured the energetic content of eggs via bomb calorimetry. Temperature positively influenced the rate of egg production, but females at 30 °C laid smaller eggs than did females at either 24 or 27 °C. Dry mass of eggs scaled allometrically with wet mass, but this relationship was similar among thermal treatments. Females at all temperatures produced eggs with similar energy densities. Females at 24 °C allocated less energy per time unit (≈8 mW) to reproduction than did females from higher temperatures (≈12 mW). However, females at either 24 or 27 °C allocated significantly more energy per egg than did females at 30 °C. Our results demonstrate that a complex thermal sensitivity of reproductive rate can emerge from distinct thermal sensitivities of egg size, egg composition and clutch frequency.     

Tissue Responses to Postoperative Laser Therapy in Diabetic Rats Submitted to Excisional Wounds

In a previous study about low-level laser therapy biomodulation on a full-thickness burn model we showed that single and fractionated dose regimens increased wound healing and leukocyte influx similarly when compared with untreated control. In order to verify if this finding would be similar in an impaired wound model, we investigated the effect of single and multiple irradiations on wound closure rate, type of inflammatory infiltrate, myofibroblasts, collagen deposition, and optical retardation of collagen in diabetic rats. Female Wistar rats in the same estrous cycle had diabetes induced with streptozotocin and an 8-mm excisional wound performed with a punch. The experimental groups were: control group – untreated ulcer; single-dose group – ulcer submitted to single dose of diode laser therapy (λ = 660 ± 2 nm; P = 30 mW; energy density: 4 J/cm²) and fractionated-dose group – ulcer submitted to 1 J/cm² laser therapy on Days 1, 3, 8, and 10. The ulcers were photographed on the experimental days and after euthanasia tissue samples were routinely processed for histological and immunohistochemistry analyses. Independently of the energy density, laser therapy accelerated wound closure by approximately 40% in the first three days in comparison to the control group. Laser therapy increased acute inflammatory infiltrate until Day 3. Both laser groups exhibited more myofibroblasts and better collagen organization than the control group. The findings demonstrate that low-level laser therapy in the immediate postoperative period can enhance the tissue repair process in a diabetes model. Similar effects were achieved with laser therapy applied a single time with an energy density of 4 J/cm² and applied four times with an energy density of 1 J/cm². The application of laser therapy in the inflammatory phase was the most important factor to the enhancement of the tissue repair process.     

Effect of cations on the temperature sensitivity of Ca2+ transport in rat-liver mitochondria and safranine uptake by liposomes

The activation energy of mitochondrial Ca²⁺ transport has been studied in various conditions by Arrhenius plots in the temperature range 6–20°C. In the presence of Mg²⁺ the activation energy is decreased to 18 kJ/mole from that of 40 kJ/mole found in a sucrose medium. In the presence of the polyamine spermine the activation energy is practically 0 kJ/mole. A lanthanide Eu³⁺, which is a potent inhibitor of Ca²⁺ transport, has no significant effect on the activation energy. In a KCl medium the activation energy is increased to 70 kJ/mole. When both K⁺ and Mg⁺ are present the activation energy is nonlinear between 11 and 18°C. In the presence of K⁺ and spermine it is about 0 kJ/mole between 6 and 13°C and at higher temperatures 68 kJ/mole. Neither Mg²⁺ nor spermine affect the slope of the Arrhenius plot for state 4 respiration. Spermine decreases slightly the activation energy of Ca²⁺-stimulated respiration. Spermine also decreases the activation energy of valinomycin- or gramicidin-induced safranine uptake by liposomes from 68 to almost 0 kJ/mole between 17 and 30°C. The results indicate that Ca²⁺ binding to the polar head groups of the phospholipids at the membrane surface is the rate-limiting step of mitochondrial Ca²⁺ transport, because agents that inhibit Ca²⁺ binding to these sites (Mg²⁺, spermine, K⁺) have the most marked effect, whereas Eu³⁺, which, because of the small concentration used, ought to interact mainly with the mitochondrial Ca²⁺ transport system, has no significant effect on the temperature sensitivity of mitochondrial Ca²⁺ transport.     

Pyrolysis characteristics and kinetics of Arundo donax using thermogravimetric analysis

The increase of the price of fossil means, as well as their programmed disappearing, contributed to increase among appliances based on biomass and energy crops. The thermal behavior of Arundo donax by thermogravimetric analysis was studied under inert atmosphere at heating rates ranging from 5 to 20 °C min⁻¹ from room temperature to 750 °C. Gaseous emissions as CO₂, CO and volatile organic compounds (VOC) were measured and global kinetic parameters were determined during pyrolysis with the study of the influence of the heating rate. The thermal process describes two main phases. The first phase named active zone, characterizes the degradation of hemicellulose and cellulose polymers. It started at low temperature (200 °C) comparatively to wood samples and was finished at 350 °C. The pyrolysis of the lignin polymer occurred during the second phase from 350 to 750 °C, named passive zone. Carbon oxides are emitted during the active zone whereas VOC are mainly formed during the passive zone. Mass losses, mass loss rates and emission factors were strongly affected by the variation of the heating rate in the active zone. It was found that the global pyrolysis of A. donax can be satisfactorily described using global independent reactions model for hemicellulose and cellulose in the active zone. The activation energy for hemicellulose was not affected by a variation of the heating rate with a value close to 110 kJ mol⁻¹ and presented a reaction order close to 0.5. An increase of the heating rate decreased the activation energy of the cellulose. However, a first reaction order was observed for cellulose decomposition. The experimental results and kinetic parameters may provide useful data for the design of pyrolytic processing system using A. donax as feedstock.     

n-carbamoyl-d-p-hydroxyphenylglycine production using immobilized d-hydantoinase from recombinant E. coli

An immobilized d-hydantoinase was characterized and employed to produce n-carbamoyl-d-p-hydroxyphenylglycine (CpHPG) in a repeated batch process. The V_max and K_m of the immobilized d-hydantoinase at 50°C were 6.28 mm min⁻¹ g⁻¹ biocatalyst and 71.6 mm, respectively. The product CpHPG did not inhibit the activity of d-hydantoinase. Optimal reaction temperature was 60°C. A decrease in activity of immobilized d-hydantoinase due to thermal inactivation could be described as first-order decay; the deactivation energy was 23.97Kcal mol⁻¹. Under process conditions (50°C, 10% w/v substrate, and pH 8.5), the half-life of the immobilized d-hydantoinase was eight batches. The attrition of immobilized d-hydantoinase particles with a large amount of insoluble substrate particles during stirring resulted in fine biocatalyst particles. In addition to the thermal inactivation, the loss of fine biocatalyst particles during the recovery step contributed to the low operational stability.     

Calcium-ion efflux from brain tissue: Power-density versus internal field-intensity dependencies at 50-MHz RF radiation

In previous experiments changes were found in calcium-ion efflux from chickbrain tissue that had been exposed in vitro to 147-MHz radiation across a specific range of power densities when the field was amplitude modulated at 16 Hz. In the present study, 50-MHz radiation, similarly modulated as a sinusoid, was found to produce changes in calcium-ion efflux from chick brains exposed in vitro in a Crawford cell. Exposure conditions were optimized to broaden any power-density window and to enhance the opportunity to detect changes in the calcium-ion efflux. The results of a power-density series demonstrated two effective ranges: One spanning a range from 1.44 to 1.67 mW/cm², and the other including 3.64 mW/cm², which were bracketed by no-effect results at 0.72, 2.17, and 4.32 mW/cm². Peaks of positive findings are associated with near-identical rates of energy absorption: 1.4 μW/g at 147 MHz, and 1.3 μW/g at 50 MHz, which indicates that the enhanced-efflux phenomenon is more dependent on the intensity of fields in the brain than on the power density of incident radiation. In addition, the phenomenon appears to occur at multiples of some, as yet unknown, rate of radiofrequency (RF) energy absorption. Because of the extremely small increments of temperature associated with positive findings (< 4 × 10^?4°C), and the existence of more than one productive absorption rate, a solely thermal explanation appears extremely unlikely.     

Thermal conversion of alkaline lignin and its structured derivatives to porous carbonized materials

Alkaline lignin was thermally converted to microporous carbon in ca. 50% yield by heating up from room temperature to 900 °C without activation process under flowing of an argon gas. The carbonized material prepared by heating up conditions of 1 °C min⁻¹ showed 530 m²/g of the Brunauer-Emmett-Teller (BET) specific surface area, which increased to 740 m²/g after washing with water. Furthermore, alkaline lignin derivatives were structured as micron scale particles by micelle formation and polymer gelation techniques. Carbonization of the structured lignins could afford high porous materials having BET surface areas above 1000 m²/g without surface activation processes.     

Microbiological degradation of the herbicide dicamba

Summary Pseudomonas paucimobilis was isolated from a consortium which was capable of degrading dicamba (3,6-dichloro-2-methoxybenzoic acid) as the sole source of carbon. The degradation of dicamba byP. paucimobilis and the consortium was examined over a range of substrate concentration, temperature, and pH. In the concentration range of 100–2000 mg dicamba L^–1 (0.5–9.0 mM), the degradation was accompanied by a stoichiometric release of 2 mol of Cl^– per mol of dicamba degraded. The cultures had an optimum pH 6.5–7.0 for dicamba degradation. Growth studies at 10°C, 20°C, and 30°C yielded activation energy values in the range of 19–36 kcal mol^–1 and an average Q₁₀ value of 4.0. Compared with the pure cultureP. paucimobilis, the consortium was more active at the lower temperature.     

Runaway electron beams in the gas discharge for UV nitrogen laser excitation

The review of the methods for obtaining the runaway electron beams in the gas discharge is performed. The new method is offered, using which the beam is first formed in a narrow gap (∼1 mm) between the cathode and the grid and then it is accelerated by the field of the plasma column of the anomalous self-sustained discharge in the main gap (10–20 mm long). The electron beams with an energy of about 10 keV and current density of 10³ A/cm² at a molecular nitrogen pressure of up to 100 Torr have been obtained experimentally. The results of research of the UV nitrogen laser with an excitation via runaway electron beam and radiation of energy of ∼1 mJ are given. The UV nitrogen laser generation with the energy of ∼1 mJ has been obtained by the runaway electron beams.     

Enzymatic enantioselective transcyanation of silicon-containing aliphatic ketone with (S)-hydroxynitrile lyase from Manihot esculenta

(S)-Hydroxynitrile lyase from Manihot esculenta (MeHNL) was shown for the first time to be able to catalyze the enantioselective transcyanation of acetyltrimethylsilane (ATMS) with acetone cyanohydrin to form (S)-2-trimethylsilyl-2-hydroxyl-propionitrile in an aqueous/organic biphasic system. To better understand the reaction, various influential variables were examined. The most suitable organic phase, optimal buffer pH, aqueous phase content, shaking rate, temperature, concentration of ATMS, acetone cyanohydrin and crude enzyme were diisopropyl ether (DIPE), 5.4, 13% (v/v), 190 rpm, 40°C, 10 mM, 20 mM, and 35 U/ml, respectively, under which the initial reaction rate, substrate conversion and product enantiomeric excess (e.e.) were 19.5 mM/h, 99.0% and 93.5%, respectively. A comparative study demonstrated that silicon atoms in the substrate had a great effect on the reaction, and that ATMS was a much better substrate for MeHNL than its carbon analogue 3,3-dimethyl-2-butanone (DMBO) with respect to the initial reaction rate, substrate conversion and product e.e. MeHNL has greater affinity towards ATMS than its carbon analogue as indicated by the much lower K_m. The activation energy of MeHNL-catalyzed transcyanation of ATMS was also markedly lower than that of DMBO. The silicon effect on the reaction was rationalized on the basis of the special characteristics of silicon atoms and the catalytic mechanism of MeHNL.     

Purification and characterization of β-galactosidase from a strain of Bacillus coagulans

-Galactosidase from B. coagulans strain L4 is produced constitutively, has a mol. wt. of 4.3×10⁵ and an optimal temperature of 55°C. The optimal pH at 30°C is 6.0 whereas at 55°C it is 6.5. The energy of activation of enzyme activity is 41.9 kJ/mol (10 kcal/mol). No cations are required. The K_m with ONPG as substrate is 4.2–5.6mm and with lactose is 50mm. The K_i for inhibition by galactose is 11.7–13.4mm and for dextrose is 50mm. Galactose inhibited competitively while dextrose inhibited noncompetitively. The purified and unprotected enzyme is 70% destroyed in 30 min at 55°C whereas in the presence of 2 mg/ml of BSA 42% of the activity is destroyed in 30 min at 55°C. An overall purification of 75.3-fold was achieved.     

Thermal stability and thermodynamic analysis of native and methoxypolyethylene glycol modified trypsin

Four methoxypolyethylene glycols (MPEG, molecular masses 350, 750, 2000 and 5000 Da), each activated by nitrophenyl chloroformate, were used to modify trypsin. Compared with the native trypsin, the MPEG-modified trypsin was more stable against temperature between 30°C and 70°C, longer chain of MPEG moiety corresponding to higher thermal stability. The T for the native and the modified trypsin (0.4 mg ml^–1) was increased from 47°C to 66°C. The stabilization effect caused by MPEG modification was the result of decreasing in both the autolysis rate and the thermal denaturation rate. The thermodynamic analysis of the thermal denaturation process showed that the activation free energy (G^*) of the native and the modified trypsin at 60°C was increased from 102.9 to 109.3 kJ mol^–1; the activation enthalpy (H^*) was increased from 57.4 to 86.9 kJ mol^–1; the activation entropy (S^*) was increased from –136 to –67 J molK^–1. A possible explanation for the decreased thermal denaturation rate caused by MPEG modification was also discussed.     

Effects of 2.8-GHz microwaves on restrained and ketamine-anesthetized rats

Summary To compare the effects of ketamine anesthesia and mild restraint on microwave-induced thermal and cardiovascular changes, sixteen Fischer 344 rats were irradiated in two states:1) unanesthetized, restrained, and2) ketamine-anesthetized (150 mg/kg, I.M.). Individual animals were exposed in H orientation to far-field continuous-wave 2.8-GHz microwaves. Irradiation was conducted at a power density of 60 mW/cm² (whole-body average specific absorption rate of 14.4 W/kg) to cyclicly increase colonic temperature from 38.5 to 39.5° C. Colonic and subcutaneous temperatures, aortic blood pressure, and heart rate were continuously monitored. The time required for colonic temperature to increase 1° C was significantly longer in the anesthetized state; however, the time to return to baseline was similar under both conditions. Heart rate and blood pressure significantly increased during irradiation in the unanesthetized state, but remained virtually unchanged in the anesthetized state. The subcutaneous temperature increase during exposure was significantly greater in the anesthetized state. The differences in responses of anesthetized and mildly restrained animals should be considered when conducting experiments on thermoregulatory responses to microwave irradiation.