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At least 739 records · Page 41Linked to original sources
PubMed1998

An interleukin-1 receptor fragment blocks ambient temperature-induced increases in brain temperature but not sleep in rabbits.

The effects of intracerebroventricular injection (i.c.v.) of an interleukin-1 (IL-1) inhibitor, a soluble IL-1 receptor fragment (IL-1RF), on sleep and brain temperature (Tbr) responses of rabbits induced by mild increases in ambient temperature (Tamb) were determined. Each rabbit was recorded under three conditions: (1) 21 degrees C Tamb plus pyrogen-free saline (PFS); (2) 27 degrees C Tamb plus PFS; (3) 27 degrees C Tamb plus the IL-1RF. The higher Tamb significantly increased Tbr during the warming period; this effect was attenuated by pretreatment with the IL-1RF. The higher Tamb alone (6 h exposure) significantly increased non-rapid eye movement sleep (NREMS) across the 23-h recording period. However, during the 6-h warming period NREMS values, obtained after IL-1 RF treatment, were not significantly different from those obtained from PFS-treated animals at 27 degrees C Tamb. The ability of the IL-1 RF to block Tamb-induced changes in Tbr and the failure of the IL-1RF to block Tamb-induced NREMS responses is different from previous results which indicated that a tumor necrosis factor receptor fragment (TNF-RF) inhibits warm Tamb-induced sleep but not Tbr responses. Thus, brain IL-1 and TNF sleep and thermo mechanisms are, in part, different.

Animals↗
PubMed2000

A set of temperature sensitive-replication/-segregation and temperature resistant plasmid vectors with different copy numbers and in an isogenic background (chloramphenicol, kanamycin, lacZ, repA, par, polA).

A set of plasmid vectors conferring chloramphenicol resistance (Cm(R)), 3064bp in size, or kanamycin resistance (Km(R)), 2972bp in size, were developed, having multiple cloning sites in lacZ' genes for alpha-complementation. pTH18cs1, pTH19cs1, pTH18ks1 and pTH19ks1 are temperature-sensitive (ts) in DNA replication (ts-Rep); pTH18cs5, pTH19cs5, pTH18ks5 and pTH19ks5 are ts in plasmid segregation (ts-Seg); and pTH18cr, pTH19cr, pTH18kr and pTH19kr are temperature resistant (tr) in both. They are based on the pSC101 replicon consisting merely of the replication origin and repA gene, compatible with ColE1/pMB1/p15-derived plasmids, and thus do not require polA function of host cells. The copy numbers of the ts-Rep, tr and ts-Seg plasmids were 14, 5 and 1 per chromosome at 30 degrees C, respectively. These plasmids are fairly stable when inherited at 30 degrees C, but not above 37 degrees C or 41.5 degrees C, depending on the repA mutations and host strains. They are isogenic apart from the ts mutations in the repA gene, and thus provide with useful tools for having appropriate controls in various experiments including bacterial gene-targeting, transposon mutagenesis, toxic gene expression, differential substitution on host functions, gene dosage analysis and so on.

Bacterial Proteins↗
PubMed2002

Temperature-rate profiles by polarimetric variable-temperature kinetic experiments to study racemization reactions.

The racemization of (-)-adrenaline was followed by polarimetric variable-temperature kinetic experiments obtaining activation parameters and k(obs)(T) profile in one tenth of the time usually spent for traditional kinetic runs. A polarimeter connected to a computer for the acquisition and processing of the analytical data was used. The kinetic profiles were processed by both an integral method and a differential method. The results are in good agreement with each other and with those obtained by constant-temperature kinetics.

Drug Stability↗
PubMed2005

Low-temperature activation and deactivation of high-Curie-temperature ferromagnetism in a new diluted magnetic semiconductor: Ni2+-Doped SnO2.

We report the synthesis of colloidal Ni(2+)-doped SnO(2) (Ni(2+):SnO(2)) nanocrystals and their characterization by electronic absorption, magnetic circular dichroism, X-ray absorption, magnetic susceptibility, scanning electron microscopy, and X-ray diffraction measurements. The Ni(2+) dopants are found to occupy pseudooctahedral Sn(4+) cation sites of rutile SnO(2) without local charge compensation. The paramagnetic nanocrystals exhibit robust high-Curie-temperature (T(C)) ferromagnetism (M(s)(300 K) = 0.8 mu(B)/Ni(2+), T(C) >> 300 K) when spin-coated into films, attributed to the formation of interfacial fusion defects. Facile reversibility of the paramagnetic-ferromagnetic phase transition is also observed. This magnetic phase transition is studied as a function of temperature, time, and atmospheric composition, from which the barrier to ferromagnetic activation (E(a)) is estimated to be 1200 cm(-1). This energy is associated with ligand mobility on the surfaces of the Ni(2+):SnO(2) nanocrystals. The phase transition is reversed under air but not under N(2), from which the microscopic identity of the activating defect is proposed to be interfacial oxygen vacancies.

Colloids↗
PubMed2006

Study of aromatic nucleophilic substitution with amines on nitrothiophenes in room-temperature ionic liquids: are the different effects on the behavior of para-like and ortho-like isomers on going from conventional solvents to room-temperature ionic liquids related to solvation effects?

The kinetics of the nucleophilic aromatic substitution of some 2-L-5-nitrothiophenes (para-like isomers) with three different amines (pyrrolidine, piperidine, and morpholine) were studied in three room-temperature ionic liquids ([bmim][BF4], [bmim][PF6], and [bm(2)im][BF4], where bmim = 1-butyl-3-methylimidazolium and bm(2)im = 1-butyl-2,3-dimethylimidazolium). To calculate thermodynamic parameters, a useful instrument to gain information concerning reagent-solvent interactions, the reaction was carried out over the temperature range 293-313 K. The reaction occurs faster in ionic liquids than in conventional solvents (methanol, benzene), a dependence of rate constants on amine concentration similar to that observed in methanol, suggesting a parallel behavior. The above reaction also was studied with 2-bromo-3-nitrothiophene, an ortho-like derivative able to give peculiar intramolecular interactions in the transition state, which are strongly affected by the reaction medium.

Amines↗
PubMed2006

Low-temperature heat capacity of room-temperature ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

Heat capacities of liquid, stable crystal, and liquid-quenched glass of a room-temperature ionic liquid (RTIL), 1-hexyl-3-methylimidazolium bis(trifluromethylsulfonyl)imide were measured between 5 and 310 K by adiabatic calorimetry. Heat capacity of the liquid at 298.15 K was determined for an IUPAC project as (631.6 +/- 0.5) J K(-1) mol(-1). Fusion was observed at T(fus) = 272.10 K for the stable crystalline phase, with enthalpy and entropy of fusion of 28.34 kJ mol(-1) and 104.2 J K(-1) mol(-1), respectively. The purity of the sample was estimated as 99.83 mol % by the fractional melting method. The liquid could be supercooled easily and the glass transition was observed around T(g) approximately 183 K, which was in agreement with the empirical relation, T(g) approximately ((2)/(3)) T(fus). The heat capacity of the liquid-quenched glass was larger than that of the crystal as a whole. In the lowest temperature region, however, the difference between the two showed a maximum around 6 K and a minimum around 15 K, at which the heat capacity of the glass was a little smaller than that of crystal.

Imidazoles↗
PubMed1999

The effect of excipients on the molecular mobility of lyophilized formulations, as measured by glass transition temperature and NMR relaxation-based critical mobility temperature.

PURPOSE: The dependence of the molecular mobility of lyophilized formulations on pharmaceutical polymer excipients was studied. Molecular mobility as determined by NMR relaxation-based critical temperature of molecular mobility (Tmc) and glass transition temperature (Tg) is discussed in relation to the plasticizing effect of water in formulations. METHODS: The Tmc and Tg of lyophilized gamma-globulin formulations containing 6 different polymer excipients such as dextran, polyvinylpyrrolidone (PVP) and methylcellulose (MC) was determined by NMR and DSC. The molecular mobility of water in the formulations was determined by proton NMR and dielectric relaxation spectrometry (DRS). RESULTS: Tmc varied with polymer excipients. Tmc increased as the ratio of bound water to mobile water increased and as the molecular mobility of mobile water decreased. The formulation containing MC exhibited a lower Tmc than the formulation containing dextran because of the smaller ratio of bound water and the higher molecular mobility of mobile water. The Tmc of the formulation containing PVP was higher than that expected from the higher T2 values of water because of the lower molecular mobility of mobile water regardless of the higher ratio of mobile water. The Tmc of these lyophilized formulations was higher than their T(g) by 23 degrees C to 34 degrees C, indicating that the formulations became a NMR-detected microscopically liquidized state below their T(g). CONCLUSIONS: The quantity and the molecular mobility of mobile water in lyophilized formulations can be considered to affect the T(mc) of lyophilized formulations, which in turn governs their stability.

Calorimetry, Differential Scanning↗
PubMed1999

Determination of the glass transition temperatures of some new methyl methacrylate copolymers using modulated temperature differential scanning calorimetry (MTDSC).

PURPOSE: The purpose of this study was to determine the glass transition temperatures of new graft copolymers using Modulated Temperature Differential Scanning Calorimetry (MTDSC), and to assess the differences between starch and cellulosic derivatives of methyl methacrylate and between two different drying methods used in their preparation. METHODS: Graft copolymers of methyl methacrylate were synthesized and dried by oven or freeze-drying. Surface area measurements and different thermal analysis techniques (Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA) and MTDSC) were used to characterize these copolymers. Results. DSC was not sensitive enough to identify the T(g)s of the copolymers, however they were clearly identifiable by MTDSC. T(g) values obtained may depend on the method of preparation that also altered their physical characteristics e.g. specific surface area. Cellulose derivatives showed lower T(g)s than starch derivatives. The results also depended on the drying method used, thus, freeze dried products had slightly lower T(g)s than oven dried products. CONCLUSIONS: MTDSC represents a useful thermal technique that allows the identification of glass transitions in these new copolymers with higher sensitivity and resolution than conventional DSC, separating the transition from overlapping phenomena such as decomposition or dehydration. The Tg of this new class of copolymers appeared to be dependent on polymer composition and drying method used.

Calorimetry, Differential Scanning↗
PubMed1996

Reversal of the temperature-shift-induced growth restriction of a temperature-sensitive simian virus 40 T-antigen-transformed human fibroblast cell line by treatment with retinoic acid.

We previously established a human fibroblast cell line, HFL 6-2, that contains a temperature sensitive simian virus 40 (SV40) T antigen, permitting cell growth at 35 degrees C but restricting growth at 39 degrees C. p21 (Waf1/Cip1) was significantly induced by temperature shifts in HFL 6-2 cells. Here we show that all-trans-retinoic acid (RA) treatment prevented the growth restriction of HFL 6-2 cells at 39 degrees C. In the presence of RA, HFL 6-2 cells proliferated into sizeable colonies even at 39 degrees C. [3H]Thymidine incorporation and flow cytometry analysis revealed that cells exposed to RA maintained DNA synthesis at 39 degrees C. Prevention of growth restriction by RA was correlated with a lack of induction of p21 at the transcription level. These observations suggest that RA may prevent the senescence process by repressing p21 gene expression, and perturb the growth regulation of somatic cells.

Antigens, Polyomavirus Transforming↗
PubMed1974

The effects of increased temperature on electroretinograms of temperature-sensitive paralysis mutants of Drosophila melanogaster.

Mutations within the shibire locus of Drosophila melanogaster are non-complementing alleles which result in reversible paralysis at 29 degrees but retention of normal locomotor behavior at 22 degrees . Electroretinograms of six of the mutants have been recorded at various temperatures. Two changes occurred in the electroretinograms of flies carrying most of the alleles at high temperature: they lost the "on"- and "off"- transients of the normal electroretinogram, and the fast decay of the receptor potential was attenuated. For flies with four of the alleles, a base-line oscillation was also observed. Analysis of electroretinograms of mosaic shibire flies indicates that the loss of the transients can be attributed to both a pre-synaptic and a post-synaptic effect.

Alleles↗
PubMed1978

Temperature-sensitive Escherichia coli mutant producing a temperature-sensitive sigma subunit of DNA-dependent RNA polymerase.

A gene affecting the sigma subunit of DNA-dependent RNA polymerase is tightly linked to dnaG at 66 min on the Escherichia coli chromosome. In order to create an easily selectable marker in this region, we inserted transposon-10, which carries a gene determining resistance to tetracycline (tet) near 66 min, and the order tolC-dnaG-sigma-tet was determined. We used frequency of contransduction with tet as a criterion to screen a collection of spontaneous temperature-sensitive Escherichia coli mutants that might affect the sigma subunit. One such mutant was found to map at the sigma locus. The sigma subunit isolated from this mutant is unstable at 46 degrees C in vitro and has an altered electrophoretic mobility. The temperature sensitivity of RNA synthesis in this mutant indicates that most transcription in E. coli is sigma dependent.

Chromosome Mapping↗
PubMed2000

A common temperature-sensitive allelic form of human tyrosinase is retained in the endoplasmic reticulum at the nonpermissive temperature.

Oculocutaneous albinism type 1TS is caused by mutations that render the melanocyte-specific enzyme tyrosinase temperature-sensitive (ts); the enzyme is inactive in cells grown at 37 degrees C but displays full activity in cells grown at 31 degrees C. To distinguish whether the ts phenotype of the common R402Q variant of human tyrosinase is due to altered enzymatic activity or to misfolding and a defect in intracellular trafficking, we analyzed its localization and processing in transiently transfected HeLa cells. R402Q tyrosinase accumulates in the endoplasmic reticulum (ER) at 37 degrees C but exits the ER and accumulates in endosomal structures in cells grown at 31 degrees C. The inability of the R402Q variant to exit the ER is confirmed by the failure to acquire endoglycosidase H resistance at 37 degrees C and cannot be accounted for solely by enhanced proteasome-mediated degradation. ER retention at 37 degrees C is mediated by the lumenal domain of R402Q tyrosinase, is not dependent on tethering to the membrane, and is irreversible. Finally, a wild-type allelic form of tyrosinase is partially ts in transiently transfected HeLa cells. The data show that human tyrosinase expressed in non-melanogenic cells folds and exits the ER inefficiently and that R402Q tyrosinase exaggerates this defect, resulting in a failure to exit the ER at physiologic temperatures.

Alleles↗
PubMed1986

Temperature and the formation of radiation-induced chromosome aberrations. II. The temperature dependence of lesion repair and lesion interaction.

Dicentric chromosome aberration yields have been measured after single-exposure and split-dose irradiations of human lymphocytes with 150 kV X-rays. Various temperature programmes between 4 and 37 degrees C were applied before, during and after irradiations and in the radiation-free interval. It was found that chromatin lesion repair was completely suppressed at 21 degrees C and below, whereas lesion formation is reduced only below 17 degrees C. The interaction between repairable lesions which leads to exchange-type aberrations is also suppressed by low temperatures. Hypothermic suppression of chromatin lesion repair and interaction is fully reversible at least up to 12 h of maintenance of the 'stored' state of these lesions.

Chromosome Aberrations↗
PubMed1953

The effect of temperature on the growth of virus-induced frog carcinoma. II. The temperature coefficient of growth in vitro.

The temperature coefficient of van't Hoff, Q(10), for growth of frog carcinoma in vitro over a range of 20-35 degrees C, averages 2.5. This value is closely similar to those obtained for various forms of normal growth. The values of the temperature coefficient slightly but progressively decrease with advancing age of the cancer colonies. A similar relation obtains in many but not in all forms of normal growth. Thus, the law of van't Hoff is found to hold equally for growth of the malignant tissue now under discussion and for normal tissue.

In Vitro Techniques↗
PubMed1979

Nonelectrophoretic genetic variability in mosquitoes: polymorphism for temperature-resistant and temperature-sensitive phosphoglucomutase alleles in Culex pipiens.

Homogenates of single individuals of two natural populations and five laboratory populations of Culex pipiens were examined by combining electrophoresis and heat denaturation studies on phosphoglucomutase (PGM). All populations showed a high degree of polymorphism for isoelectrophoretic temperature-resistant (tr) and temperature-sensitive (ts) alleles. Formal genetic data on the heat stability differences of the PGM are given. If both electrophoretic and isoelectrophoretic alleles are taken into account, the mean increase in the degree of heterozygosity is quite remarkable, i.e., about 65%.--The data are considered in relation to the biological significance that this new type of variability of structural genes could have in natural populations.

Alleles↗
PubMed1977

Temperature-sensitive mutants of influenza virus. XIII. Evaluation of influenza A/Hong Kong/68 and A/Udorn/72 ts and wild-type viruses in tracheal organ culture at permissive and restrictive temperatures.

For development of an in vitro assay of attenuation for virus vaccine candidates, tracheal ring organ cultures from young ferrets were infected with influenza A/Hong Kong/68 and A/Udorn/72 temperature-sensitive (ts) recombinant and wild-type viruses and observed for 21 days at permissive (33 C) and restrictive (37 C) temperatures for effects on ciliated epithelium and viral replication. Results were compared with the known effects of these viruses in humans. Viruses that damaged ferret cilia and grew to high titers at 37 C were insufficiently attenuated for humans, and viruses that failed to damage cilia and grew to low titers at 33 C were excessively attenuated for humans. This system did not completely differentiate the relative virulence of A/Hong Kong/68 ts recombinants for humans but was successful for the A/Udorn/72 ts recombinants. This organ culture system has adjunctive usefulness for detection of most insufficiently attenuated influenza A vaccine candidates and for identification of excessively attenuated candidates that might contain non-ts lesions.

Animals↗