Thermal Stress Conditions Research Articles

LC-MS-MS Characterization of Forced Degradation Products of Fidarestat, a Novel Aldose Reductase Inhibitor: Development and Validation of a Stability-Indicating RP-HPLC Method.

An accurate, precise, robust and selective stability-indicating liquid chromatographic (LC) method has been developed for the monitoring of fidarestat in the presence of its forced degradants. The drug was subjected to hydrolysis (acid, alkali and neutral degradation), oxidation, photolysis and thermal stress conditions. The drug degraded significantly under hydrolytic (basic, acidic and neutral) and oxidative stress conditions, whereas it was found to be stable in photolytic and thermal conditions. The chromatographic separation was achieved on a Grace C18, (250 mm × 4.6 mm × 5 μm) column using gradient mobile phase system consisting of 10 mM of ammonium acetate buffer at pH 4 and acetonitrile at a flow rate of 1 mL/min with UV detection at 283 nm. The developed method was extended to liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC-QTOF-MS-MS) for characterization of all the degradation products. A total of five new degradation products were identified and characterized by LC-QTOF-MS-MS. The developed LC method was validated as per ICH guideline Q2 (R1). The proposed method was found to be successively applied for the quality control of fidarestat in bulk drug analysis.

Thermal stability and hydration behavior of ritonavir sulfate: A vibrational spectroscopic approach

Ritonavir sulfate is a protease inhibitor widely used in the treatment of acquired immunodeficiency syndrome. In order to elucidate the inherent stability and sensitivity characteristics of ritonavir sulfate, it was investigated under forced thermal and hydration stress conditions as recommended by the International Conference on Harmonization guidelines. In addition, competency of vibrational (infrared and Raman) spectroscopy was assessed to identify structural changes of the drug symbolizing its stress degradation. High performance liquid chromatography was used as a confirmatory technique for both thermal and hydration stress study, while thermogravimetric analysis/differential thermal analysis and atomic force microscopy substantiated the implementation of vibrational spectroscopy in this framework. The results exhibited high thermal stability of the drug as significant variations were observed in the diffuse reflectance infrared Fourier transform spectra only after the drug exposure to thermal radiations at 100°C. Hydration behavior of ritonavir sulfate was evaluated using Raman spectroscopy and the value of critical relative humidity was found to be >67%. An important aspect of this study was to utilize vibrational spectroscopic technique to address stability issues of pharmacological molecules, not only for their processing in pharmaceutical industry, but also for predicting their shelf lives and suitable storage conditions.

Identification and characterization of related substances in pomalidomide by hyphenated LC–MS techniques

The current study dealt with the separation, identification and characterization of related substances in pomalidomide by hyphenated techniques. Complete separation was obtained with an Inertsil ODS-SP column (250mm×4.6mm, 5μm) by linear gradient elution using a mobile phase consisting of 0.1% formic acid solution and acetonitrile. They were characterized by hyphenated chromatographic techniques with the accurate mass determination using high resolution LC–TOF–MS methods as well as the product MS spectra determination and elucidation. The degradation behaviors of pomalidomide under ICH prescribed stress conditions were also conducted. Pomalidomide was found to be labile to degrade under acid, alkaline, oxidative and thermal stress conditions, while it was relatively stable to photolytic stress. 13 related substances were detected and identified to be 10 degradation products and three process related substances. The hyphenated LC–MS method with high resolution accurate mass determination facilitated the qualitative analysis of the unknown compounds than that of the conventional HPLC–UV. The related compounds identified are valuable for pomalidomide manufacturing process optimization and quality control.

Forced degradation studies, and effect of surfactants and titanium dioxide on the photostability of paliperidone by HPLC

Forced degradation study of paliperidone under hydrolytic, oxidative, thermal and photolytic stress conditions was conducted using HPLC. The drug was found to be labile under hydrolytic, oxidative and photolytic stress conditions; whereas, it was stable under dry heat stress conditions. Effect of anionic, cationic and non-ionic surfactants applied to the concentration exceeding critical micellar concentration on the photostability of paliperidone was also studied by exposing the samples to sunlight for 72h. Major degradation of the drug was found in presence of cationic and non-ionic surfactants. Effect of titanium dioxide on the photo-degradation of paliperidone in solution state was also studied and it was found that 53% of the drug was degraded after 72h of exposure to sunlight. A common degradation peak was observed in oxidative and TiO2 photocatalysed samples. This peak may be due to the generation of N-oxide of paliperidone. The same degradation peak was also observed in all other photostability samples. Chromatographic separation of drug and its degradation products was achieved on an Alltima C8 (250mm×4.6mm, 5μm) analytical column, using a mobile phase consisting of acetonitrile-ammonium acetate buffer with 0.2% triethylamine (pH 3.5; 20mM) (60:40, v/v) at a flow rate of 1mL/min. Quantification was performed with UV detection at 280nm. The method was validated as per ICH guidelines.

Development and validation of UHPLC-DAD method for the determination of cholesteryl-hexahydrophthaloyl-5-fluorouracil in lipid nanoemulsion

An ultra HPLC-diode array detector (UHPLC-DAD) method was developed and validated for rapid determination of cholesteryl-hexahydrophthaloyl-5-fluorouracil (CH5F) conjugate in standard drug, lipid nanoemulsion and dissolution samples. The chromatographic identification of this conjugate was achieved on Hypersil GOLD 50 × 2.1 mm reversed phase C18 column having a 1.9 μm packing as a stationary phase using methanol-water (80: 20, v/v) as a mobile phase, at a flow rate of 0.4 mL/min with DAD detection at 276 nm. The proposed UHPLC-DAD method is linear in the concentration range of 1–50 μg/mL with correlation coefficient of 0.998. The proposed method is precise, accurate, robust, sensitive and specific for analysis of the conjugate. High assay value (98.7%) of CH5F conjugate in lipid nanoemulsion was obtained by the proposed method. Forced degradation studies indicated that conjugate was sufficiently stable under oxidative stress conditions degraded under acid, base and thermal stress conditions. The proposed UHPLC-DAD method successfully and resolved drug conjugate peak in the presence of its degradation products which established stability and indicating property of the method. Results of the present study indicated that the proposed UHPLC-DAD method can be successfully used for routine determination of CH5F conjugate in standard drug and pharmaceutical formulations.

A study on separating of a silicon wafer with moving laser beam by using thermal stress cleaving technique

This study describes the characteristics of separating a silicon wafer with a moving Nd:YAG laser beam by using a thermal stress cleaving technique. The applied laser energy produces a thermal stress that causes the wafer to split along the irradiation path. The wafer separation is similar to crack extension. In this study, the micro-groove was prepared at the leading edge of the silicon wafer to facilitate the fracture. In order to study the thermal effect in the separating process, the temperature at the laser spot was measured by using a two-color pyrometer with an optical fiber, and the mechanism of crack propagation was observed by using an acoustic emission (AE) sensor. The influence of the micro-groove length and depth was also examined. Thermal stress distribution was calculated using the finite-element method (FEM) by considering the temperature from the experimental result. The result indicates that the wafer separation occurred in two stages, fracture initiation and intermittent crack propagation. A higher temperature resulted in faster fracture initiation and higher repetition of the crack propagation signal. The wave mark on the cleaved surface was consistent with the AE signal. The influences of laser power, temperature and the groove parameters to the fracture initiation, crack propagation and cleaved surface features are explained based on the experimental results, while the thermal stress condition is clarified with FEM analysis.

Selective separation and characterization of the stress degradation products of ondansetron hydrochloride by liquid chromatography with quadrupole time-of-flight mass spectrometry.

Ondansetron hydrochloride was subjected to forced degradation studies under various conditions of hydrolysis (acidic, basic, and neutral), oxidation, photolysis, and thermal as prescribed by International Conference on Harmonisation guideline Q1A (R2). A simple, selective, precise, and accurate high-performance liquid chromatography method was developed on a Waters Xterra C18 (150 × 4.6 mm id, 3.5 μm) column using 10 mM ammonium formate (pH 3.0)/methanol as a mobile phase in gradient elution mode at a flow rate of 0.6 mL/min. The method was extended to liquid chromatography quadrupole time-of-flight tandem mass spectrometry for identification and structural characterization of stress degradation products of ondansetron. The drug showed significant degradation in base hydrolytic and photolytic stress conditions in the liquid state, while it was found to be stable in neutral, acidic, thermal, and oxidative stress conditions. A total of five degradation products were characterized and most probable mechanisms for the formation of degradation products have been proposed on the basis of a comparison of the fragmentation of the [M + H](+) ions of the drug and its degradation products. Finally, the developed method was validated in terms of specificity, linearity, accuracy, precision, and robustness as per International Conference on Harmonisation guideline Q2 (R1).

Development and validation of a novel stability-indicating HPLC method for the quantitative determination of eleven related substances in ezetimibe drug substance and drug product

Ezetimibe is a novel lipid-lowering agent that inhibits intestinal absorption of dietary and biliary cholesterol. In the present work, a simple, sensitive and reproducible gradient reverse phase high performance liquid chromatographic (RP-HPLC) method for separation and determination of the related substances of ezetimibe was developed and validated. Eleven potential process-related impurities (starting materials, (3S,4S,3'S)-isomer, degradants and byproducts) were identified in the crude samples. Tentative structures for all the impurities were assigned primarily based on comparison of their retention time and mass spectrometric data with that of available standards and references. This method can be applied to routine analysis in quality control of both bulk drugs and commercial tablets. Separation of all these compounds was performed on a Phenomenex Luna Phenyl-Hexyl (100mm×4.6mm, 5μm) analytical column. The mobile phase-A consists of acetonitrile–water (pH adjusted to 4.0 with phosphoric acid)–methanol at 15:75:10 (v/v/v), and mobile phase-B contains acetonitrile. The eluted compounds were monitored at 210nm. Ezetimibe was subjected to hydrolytic, acid, base, oxidative, photolytic and thermal stress conditions as per ICH serves to generate degradation products that can be used as a worst case to assess the analytical method performance. The drug showed extensive degradation in thermal, acid, oxidative, base and hydrolytic stress conditions, while it was stable to photolytic degradation conditions. The main degradation product formed under thermal, acid, oxidative, base and hydrolytic stress conditions corresponding to (2R,3R,6S)-N, 6-bis(4-fluorophenyl)-2-(4-hydroxyphenyl)-oxane-3-carboxamide (Ezetimibe tetrahydropyran impurity) was characterized by LC-MS/MS analysis. The degradation products were well resolved from the main peak and its impurities, thus proved the stability-indicating power of the method. The developed method was validated as per international conference on harmonization (ICH) guidelines with respect to specificity, linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy, precision and robustness.

The use of lightweight aggregate saturated with PCM as a temperature stabilizing material for road surfaces

This paper presents the possibility of adding lightweight building aggregates to increase the stability – mechanical as well as thermal – of constructions and road objects. This stability can be achieved through saturating the porous granules of aggregate with a phase-change material (PCM) that allows the accumulation of solar heat. Intense solar radiation, especially during the summer, can cause the asphalt on road surfaces, bridges and parking lots to melt, thus protecting the structure from further overheating. The absence of asphalt layers results in thermal stress and strain conditions causes accelerated wear of road surface. Lightweight aggregate, previously used to reduce the weight of the structures, while maintaining the bearing capacity similar to that offered by conventional concrete structures, thereby gains a new functionality, as a temperature stabilizing material. The paper contains a review of several phase-change materials as well as a study justifying the choice of ceresin, a product of crude oil distillation, as a suitable material for such applications. Information about the aggregate and its possible applications, and a proposed method of saturating the aggregate with ceresin has also been collected and presented. With the help of quantitative research conducted through the use of differential scanning calorimetry, the characteristic of thermodynamic parameters of pure ceresin and expanded clay aggregate (Pollytag) saturated with ceresin was determined. Simulation tests conducted under real conditions on two asphalt surfaces (0.32 × 0.22 × 0.15 m), one of which contained the PCM while the other did not, have shown that even a small addition of ceresin (3% mass relative to the weight of the ground) causes a reduction in surface temperature of about 5 K within the tested temperature range of 318.15–338.15 K.

A new, rapid, stability-indicating UPLC method for separation and determination of impurities in amlodipine besylate, valsartan and hydrochlorothiazide in their combined tablet dosage form

A new rapid stability-indicating UPLC method for separation and determination of impurities in amlodipine besylate, valsartan and hydrochlorothiazide in their combined tablet dosage form was developed. The separation of Ph. Eur. related substances of amlodipine besylate (A, B, D, E, F, G), hydrochlorothiazide (A, B, C), valsartan (B, C), two other valsartan impurities (S)-2-(N-{[2′-cyanobiphenyl-4-yl]methyl}pentanamido)-3-methylbutanoic acid and (S)-3-methyl-2-{[2′-(1H-tetrazol-5-yl)biphenyl-4-yl]methylamino}butanoic acid and several unknown impurities was achieved by reversed phase liquid chromatography with UV detection. The detection wavelengths were set as follows: 225nm for valsartan, its impurities and for the impurity D of amlodipine, 271nm for hydrochlorothiazide and its impurities and 360nm for amlodipine and its impurities except for impurity D. Zorbax Eclipse C8 RRHD (100mm×3.0mm, 1.8μm) was used as a separation column and the analytes were eluted within 11min by a programmed gradient mixture of 0.01M phosphate buffer pH 2.5 and acetonitrile. The method was successfully validated in accordance to the International Conference of Harmonization (ICH) guidelines for amlodipine besylate and its impurity D, valsartan and its impurity C and hydrochlorothiazide and its impurities A, B and C. The triple-combined tablets were exposed to thermal, higher humidity, acid, alkaline, oxidative and photolytic stress conditions. Stressed samples were analyzed by the proposed method. All the significant degradation products and impurities were satisfactory separated from each other and from the principal peaks of drug substances. The peak purity test complied for peaks of amlodipine, valsartan and hydrochlorothiazide in all the stressed samples and indicated no co-elution of degradation products. The method was found to be precise, linear, accurate, sensitive, specific, robust and stability-indicating and could be used as a routine purity test method for amlodipine besylate, valsartan, hydrochlorothiazide and their pharmaceutical combinations.

Characterization of degradation products of ivabradine by LC-HR-MS/MS: a typical case of exhibition of different degradation behaviour in HCl and H2SO4 acid hydrolysis.

A validated stability-indicating HPLC method was established, and comprehensive stress testing of ivabradine, a cardiotonic drug, was carried out as per ICH guidelines. Ivabradine was subjected to acidic, basic and neutral hydrolysis, oxidation, photolysis and thermal stress conditions, and the resulting degradation products were investigated by LC-PDA and LC-HR-MS/MS. The drug was found to degrade in acid and base hydrolysis. An efficient and selective stability assay method was developed on Phenomenex Luna C18 (250 × 4.6 mm, 5.0 µm) column using ammonium formate (10 mM, pH 3.0) and acetonitrile as mobile phase at 30 °C in gradient elution mode. The flow rate was 0.7 ml/min and detection wavelength was 286 nm. A total of five degradation products (I-1 to I-5) were identified and characterized by LC-HR-MS/MS in combination with accurate mass measurements. The drug exhibited different degradation behaviour in HCl and H2SO4 hydrolysis conditions. It is a unique example where two of the five degradation products in HCl hydrolysis were absent in H2SO4 acid hydrolysis. The present study provides guidance to revise the stress test for the determination of inherent stability of drugs containing lactam moiety under hydrolytic conditions. Most probable mechanisms for the formation of degradation products have been proposed on the basis of a comparison of the fragmentation pattern of the drug and its degradation products. In silico toxicity revealed that the degradation products (I-2 to I-5) were found to be severe irritants in case of ocular irritancy. The analytical assay method was validated with respect to specificity, linearity, range, precision, accuracy and robustness.

Lactating performance, water and feed consumption of rabbit does reared under a Mediterranean summer circadian cycle of temperature v. comfort temperature conditions

The general aim of this research was to study the effect of high ambient temperature on the performance of does during lactation, specifically the following factors: average daily feed (ADFI) and water (ADWI) intakes, daily milk yield (DMY); milk composition: dry matter (DM), CP and gross energy (GE); doe BW (DW); individual kit weaning weight (IWW) and litter survival rate during lactation (SR). The study was undertaken comparing the performance of two groups of contemporary does reared under the same management, feeding regime and environmental conditions, except the environmental temperature and humidity. A total of 80 females were randomly allocated, at 60 days of age, into two identical and continuous rooms. In one room, the temperature was maintained permanently within the thermo-neutral zone (between 18°C to 22°C); thus, environmental conditions in this room were considered as comfort conditions. In the second room, the environmental temperature pattern simulated the daily temperature cycles that were characteristic of the summer in Mediterranean countries (24°C at 0800 h, increasing up to 29°C until 1100 h; maintenance at 29°C to 31°C for 4 h and decreasing to about 24°C to 26°C around 1700 h until 0800 h of the following day), which were considered as thermal stress conditions. Females followed a semi-intensive reproductive rhythm, first artificial insemination at 4.5 months of age, with subsequent 42-day reproductive cycles. Traits were recorded from a total of 138 lactations. Does were controlled up to the 5th lactation. Data were analyzed using linear and linear mixed models. High ambient temperature led to a lower ADFI (−9.4%), DW (−6.2%) and IWW (−8%), but it did not affect ADWI. No significant difference was found either for DMY, milk composition (DM, CP and GE) and SR during the lactation period. Heat stress was moderate, and does were able to adapt to it behaviorally by decreasing feed intake (to reduce heat production), but also live weight, allowing them to preserve milk yield and composition for assuring litter survival. On the other hand, water consumption could not be the main animal mechanism to overcome heat stress.

Identification and Characterization of Hydrolytic Degradation Products of Cefditoren Pivoxil using LC and LC-MS/TOF.

The present research work was carried out to determine stability of cefditoren pivoxil, an orally absorbed prodrug that is rapidly hydrolysed by intestinal esterases to the active cephalosporin cefditoren. Cefditoren was subjected to stress conditions recommended by the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use guideline Q1A (R2). Cefditoren pivoxil was susceptible for degradation under acidic, alkaline and neutral hydrolytic conditions while it was stable under photolytic and thermal stress conditions. Separation of cefditoren and degradation products were carried out by using HPLC. The unknown degradation products were characterized by liquid chromatography-mass spectrometry/time of flight studies. Structures were proposed for each fragment based on best possible molecular formula and complete degradation pathways were reported for cefditoren and its degradants.

Stress testing in the evaluation of vigour in maize seed

When sowing maize, such adverse factors as flooding and temperatures below those recommended can hinder establishment of the stand. There is therefore a need to find alternatives for the determination of seed vigour under adverse conditions, with a view to helping the system of production. This work aimed to estimate the physiological quality of maize seed under conditions of hydric and thermal stress, studying the methodology of testing by submersion in water and germination at low temperatures. To carry out the experiments, ten lots of two single hybrids (30F35R and 30P70H) were used, giving five lots of each. Evaluation of the initial quality of the lots was determined by water content, the cold test and the tests of germination and seedling emergence; the methodologies studied to evaluate vigour were: a) submersing the seeds in water, combining different periods (24, 36 , 48 and 72 hours) and temperatures (20, 25 and 30 °C); and b) germination at low temperature, testing at 15 °C for eight days and at 16, 17 and 18 °C for seven days. The test for submersion in water is promising for the evaluation of the vigour of maize seeds under conditions of stress through immersion of the seeds in water for 48 hours at 25 °C.

A Validated Stability–Indicating HPLC Method estimation of Clonazepam In the bulk drug and Pharmaceutical Dosage Form

A rapid, accurate, linear, and sensitive RP-HPLC method has been developed and validated for estimation of Clonazepam in the bulk and Pharmaceutical Dosage Form. The chromatographic separation was performed on C18 Column (250 mm × 4.6 mm, 5 μm particle size) using a mobile phase Acetonitrile: Methanol (60:40 v/v) at flow rate of 1.0 ml/min and 30°C column temperature with the detection wavelength at 254 nm. The Clonazepam (RT 6.11 min).The linearity was performed in the concentration range of 5 to 25 μg/ml for Clonazepam R2 0.9993, Clonazepam. The percentage purity of Clonazepam was found to be 99-101%. Precision (Inertday) of the system was found to be 0.48% Clonazepam and all the method was found to be specific and found to be within the limits of the acceptance criteria. The limit of detection was 0.092 μg/ml and limit of quantification was 0.97 μg/ml. Clonazepam was found to be specific. The Proposed method has been validated for which were within the acceptance limit according to ICH guidelines. Forced degradation conditions of hydrolysis (neutral, acidic and alkaline), oxidation, photolysis and thermal stress, as suggested in the ICH guideline Q1A (R2). The drug showed instability in alkaline and oxide, while it remained stable in acid conditions.

Validated RP-HPLC-PDA method for simultaneous determination of Zidovudine, Lamivudine, and Nevirapine in pharmaceutical formulation

Aim and Objectives: A simple, rapid, and sensitive high performance liquid chromatographic method with ultraviolet detection has been developed and validated according to the International Conference on Harmonization (ICH) guidelines for the quantitation and qualification of zidovudine (ZID), lamivudine (LAM), and nevirapine (NEV) in pharmaceutical dosage forms. Materials and Methods: The proposed method was based on the separation of the drugs in reversed phase mode using Water's C18 250 cm × 4.6 mm, 5 μ particle size column maintained at an ambient temperature. The optimum mobile phase consisted of Water: Methanol (70:30 v/v), pH adjusted to four with orthophosphoric acid (OPA). The flow rate of mobile phase was set 1.0 mL min -1 and photodiode array detection was performed at 275 nm with a total run time of 8 min which is very short for accurate analysis of simultaneous estimation of three analytes. The method was validated according to ICH guidelines. Results: The method was linear over the concentration range of 25-75 μg mL -1 with limit of quantifications (LOQ) of 13, 0.49, and 0.40 ng mL -1 for ZID, LAM and NEV respectively and limit of detection (LOD) of 4, 0.14, and 0.12 ng mL -1 for ZID, LAM and NEV respectively. Accuracy (% recovery studies) and precision values of both inter and intraday obtained from six different replicates for all the analytes ranged from 99.00% to 100.00% and % relative standard deviation of precision (assay) was between 0.64 and 1.28, respectively. All the three analytes and their combination drug product were exposed to thermal, photolytic, hydrolytic, reductive, oxidative and peroxide stress conditions and the stressed samples were analyzed by the proposed method. There were no interfering peaks from excipients, impurities or degradation products due to variable stress conditions and the proposed method is specific for the simultaneous estimation of ZID, LAM and NEV in the presence of their degradation products. Conclusion: The proposed method can be successfully applied in the quality control and stability samples of pharmaceutical dosage forms.

Lifespan Extension of Fermented Zizyphus jujuba Fruits in Caenorhabditis elegans

Objectives : Zizyphus jujuba fruits(ZJF), a traditional Korean medicine has various biological activities such as anti-inflammatory, anti-oxidative and neuro-protective effects. However, it is still unclear whether ZJF has any biological effect on anti-aging. In this study, we examined the effect of ZJF on lifespan and thermal stress in C. elegans. Methods and Results : ZJF water extracts were fermented for 7 days(F7-ZJF) and 14 days(F14-ZJF) by Laetiporus sulphureus to increase secondary metabolites such as aglycone of flavonoids and terpenoids. In the lifespan assay, ZJF water extracts and fermented ZJF were treated on the agar medium plate with age synchronized egg stage of C. elegans. Treatment of F7-ZJF- with OP-50 E. coli and F14-ZJF- with OP-50 E. coli significantly increased life span of C. elegans(N2) at thermal stress condition of . Moreover mRNA levels of lifespan associated HSP 16.1, HSP 70, and HSF-1 were increased at thermal stress condition of . However, in the equilibration temperature of after stress condition of for 2 hr, F-14-ZJF- treatment decreased the levels of heat shock protein in hsp16.2/GFP C. elegans. Conclusions : Our study indicates that prolong role of fermented-ZJF in C. elegans is mediated by control HSPs production.

Moderate Thermal Stress Causes Active and Immediate Expulsion of Photosynthetically Damaged Zooxanthellae (Symbiodinium) from Corals.

The foundation of coral reef biology is the symbiosis between corals and zooxanthellae (dinoflagellate genus Symbiodinium). Recently, coral bleaching, which often results in mass mortality of corals and the collapse of coral reef ecosystems, has become an important issue around the world as coral reefs decrease in number year after year. To understand the mechanisms underlying coral bleaching, we maintained two species of scleractinian corals (Acroporidae) in aquaria under non-thermal stress (27°C) and moderate thermal stress conditions (30°C), and we compared the numbers and conditions of the expelled Symbiodinium from these corals. Under non-thermal stress conditions corals actively expel a degraded form of Symbiodinium, which are thought to be digested by their host coral. This response was also observed at 30°C. However, while the expulsion rates of Symbiodinium cells remained constant, the proportion of degraded cells significantly increased at 30°C. This result indicates that corals more actively digest and expel damaged Symbiodinium under thermal stress conditions, likely as a mechanism for coping with environmental change. However, the increase in digested Symbiodinium expulsion under thermal stress may not fully keep up with accumulation of the damaged cells. There are more photosynthetically damaged Symbiodinium upon prolonged exposure to thermal stress, and corals release them without digestion to prevent their accumulation. This response may be an adaptive strategy to moderate stress to ensure survival, but the accumulation of damaged Symbiodinium, which causes subsequent coral deterioration, may occur when the response cannot cope with the magnitude or duration of environmental stress, and this might be a possible mechanism underlying coral bleaching during prolonged moderate thermal stress.

Current Density-Dependent Thermal Stability of ZnSe Nanowire in M-S-M Nanostructure

To enhance the thermal stability of metal-semiconductor nanowire(NW)-metal (M-S-M) nanostructure under high electrical and thermal stress conditions, current-induced failure of ZnSe NWs in the M-S-M nanostructure is studied by in situ transmission electron microscopy. When the single NW is replaced by a bundle of NWs, the large current density flowing through the single NW protruding out of the bundle of NWs is responsible for the electrical breakdown of NWs. In this case, the failure mechanism of the NW changes from the bias polarity-dependent mode to the current density-dependent mode. Consequently, a decrease of current density at the reversely biased metal-semiconductor (M-S) nanocontacts can significantly improve the thermal stability of ZnSe NWs in the M-S-M nanostructure and can enhance the performance of the semiconductor NW-based nanoelectronics.

Effects of thermal and mechanical stress on the physical stability of human growth hormone and epidermal growth factor.

Thermal and mechanical stress conditions were applied to two model proteins, human growth hormone (hGH) and epidermal growth factor (EGF), to evaluate protein stability during the manufacturing process, focusing on protein secondary structure and aggregation. The samples were analyzed with differential scanning calorimetry (DSC), circular dichroism (CD), and size-exclusion chromatography (SEC). The monomer and aggregation contents were obtained by SEC and the proteins' secondary structure on exposure to thermal stress was evaluated by CD. DSC showed that the transition temperature (T m) of hGH and EGF was 74.43 and 79.11 °C, respectively. The accelerated thermal stress temperature was set at 70 °C. The monomer content of hGH decreased from 97.8 to 82.3 % in response to thermal stress. However, the monomer content of EGF decreased significantly from 33.73 to 5.61 %. The hGH and EGF showed an increase in α-helix content and a decrease in β-sheet (antiparallel and parallel β-sheet). Moreover, the contents changed significantly during the first 1 h and then changed slightly for the remaining time. On the other hand, shaking stress showed that hGH was highly affected compared to EGF. The hGH monomer steadily decreased and only the half the monomer content remained at 3 h. It is suspected that the shaking stress induced hGH adsorption to the gas-liquid interface, which may facilitate protein denaturation. The results indicate that protective excipients might be necessary for inevitable stress conditions during the developmental process. The stability of each protein differed with respect to specific stress conditions. Therefore, an array of complementary analytical methods might be required to evaluate the protein stability.