Transition Temperature

转变温度
  • 文章类型: Journal Article
    我们在此讨论与使用熔点来表征多组分反应(MCR)产物和中间体相关的问题。虽然令人惊讶,发现其中这些MCR最终加合物(或其中间体)仅通过将熔点与其他报道中的熔点进行比较来表征的制品并不罕见。在专门文章中进行的简短调查突出了这种做法存在的严重和明显的问题,因为例如,发现了多达25个非常不同的熔点归因于相同的MCR加合物的情况。的确,它似乎合乎逻辑的假设,固有的非确认性质的熔点可能是极大的误导作为一个方案的结构确认,但仍有许多出版物(也在Q1和Q2四分位数中)坚持使用它。该程序与有机合成的最佳实践相矛盾,和文章充满了局限性和误导性结论已经发表在MCRS领域。这种做法固有的缺点确实很严重,并且误导了MCR的发展。因此,我们建议采取一些预防措施,以避免未来的混乱。
    We discuss herein the problems associated with using melting points to characterize multicomponent reactions\' (MCRs) products and intermediates. Although surprising, it is not rare to find articles in which these MCRs final adducts (or their intermediates) are characterized solely by comparing melting points with those available from other reports. A brief survey among specialized articles highlights serious and obvious problems with this practice since, for instance, cases are found in which as many as 25 quite contrasting melting points have been attributed to the very same MCR adduct. Indeed, it seems logical to assume that the inherent non-confirmatory nature of melting points could be vastly misleading as a protocol for structural confirmation, but still many publications (also in the Q1 and Q2 quartiles) insist on using it. This procedure contradicts best practices in organic synthesis, and articles fraught with limitations and misleading conclusions have been published in the MCRs field. The drawbacks inherent to this practice are indeed serious and have misguided MCRs advances. We therefore suggest some precautions aimed at avoiding future confusions.
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  • 文章类型: Journal Article
    Rapid, reliable and accurate molecular typing methods are essential for outbreaks detection and infectious diseases control, for monitoring the evolution and dynamics of microbial populations, and for effective epidemiological surveillance. The introduction of a novel method based on the analysis of melting temperature of amplified products, known as High Resolution Melting (HRM) since 2002, has found applications in epidemiological studies, either for identification of bacterial species or molecular typing, as well as an extensive and increasing use in many research fields. HRM method is based on the use of saturating third generation dyes, advanced real-time PCR platforms, and bioinformatics tools.
    To describe, by a comphrehensive review of the literature, the use, application and usefulness of HRM for the genotyping of bacterial pathogens in the context of epidemiological surveillance and public health.
    A literature search was carried out during July-August 2016, by consulting the biomedical databases PubMed/Medline, Scopus, EMBASE, and ISI Web of Science without limits. The search strategy was performed according to the following keywords: high resolution melting analysis and bacteria and genotyping or molecular typing. All the articles evaluating the application of HRM for bacterial pathogen genotyping were selected and reviewed, taking into account the objective of each study, the rationale explaining the use of this technology, and the main results obtained in comparison with gold standards and/or alternative methods, when available.
    HRM method was extensively used for molecular typing of both Gram-positive and Gram-negative bacterial pathogens, representing a versatile genetic tool: a) to evaluate genetic diversity and subtype at species/subspecies level, based also on allele discrimination/identification and mutation screening; b) to recognize phylogenetic groupings (lineage, sublineage, subgroups); c) to identify antimicrobial resistance; d) to detect and screen for mutations related to drug-resistance; e) to discriminate gene isoforms. HRM method showed, in almost all instances, excellent typeability and discriminatory power, with high concordance of typing results obtained with gold standards or comparable methods. Conversely, for the evaluation of genetic determinants associated to antibiotic-resistance or for screening of associated mutations in key gene fragments, the sensitivity and specificity was not optimal, because the targeted amplicons did not encompass all the crucial mutations.
    Despite the recent introduction of sequencing-based methods, the HRM method deserves consideration in research fields of infectious diseases, being characterized by low cost, rapidity, flexibility and versatility. However, there are some limitations to HRM assays development, which should be carefully considered. The most common application of HRM for bacterial typing is related to Single Nucleotide Polymorphism (SNP)-based genotyping with the analysis of gene fragments within the multilocus sequence typing (MLST) loci, following an approach termed mini-MLST or Minim typing. Although the resolving power is not totally correspondent to MLST, the Simpson\'s Index of Diversity provided by HRM method typically >0.95. Furthermore, the cost of this approach is less than MLST, enabling low cost surveillance and rapid response for outbreak control. Hence, the potential of HRM technology can strongly facilitate routine research and diagnostics in the epidemiological studies, as well as advance and streamline the genetic characterization of bacterial pathogens.
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  • 文章类型: Journal Article
    Knowing plant volatile chemodiversity and its distribution is essential in order to study biological processes, to estimate the plants\' value in use, and to establish sustainable exploitation practices. Yet, attempts to collect and assess data on scent diversity and properties in well-defined geographical areas are rare. Here, we developed a geo-referenced database of the plant volatilome in Greece by consolidating the results included in 116 research articles published in the last 25 years. The data set compiled includes 999 volatile organic compounds distributed into 178 plant taxa, 59 genera, and 19 families. Distillation is the acquisition method almost exclusively used, whereas headspace techniques that would allow the study of subtle ecological processes are generally lacking. Sesquiterpenes show the greatest richness of compounds, followed by monoterpenes and aliphatics. We assess the volatility of the compounds using the normal boiling point (nBP) as its reverse indicator, and we present the volatility spectra of the blends of the genera studied. Mean nBPs vary among genera, with maximal differences as wide as 118.4°. Finally, we feature basic chemodiversity maps for three aromatic plants, and discuss their importance and prospects as a special case of natural resources maps.
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  • 文章类型: Journal Article
    The high-resolution melting curve analysis (HRMA) might be a good alternative method for rapid detection of BRAF mutations. However, the accuracy of HRMA in detection of BRAF mutations has not been systematically evaluated. We performed a systematic review and meta-analysis involving 1324 samples from 14 separate studies. The overall sensitivity of HRMA was 0.99 (95% confidence interval (CI) = 0.75-0.82), and the overall specificity was very high at 0.99 (95% CI = 0.94-0.98). The values for the pooled positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio were 68.01 (95% CI = 25.33-182.64), 0.06 (95% CI = 0.03-0.11), and 1263.76 (95% CI = 393.91-4064.39), respectively. The summary receiver operating characteristic curve for the same data shows an area of 1.00 and a Q* value of 0.97. The high sensitivity and specificity, simplicity, low cost, less labor or time and rapid turnaround make HRMA a good alternative method for rapid detection of BRAF mutations in the clinical practice.
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  • 文章类型: Journal Article
    Canola Council of Canada, Winnipeg, Manitoba, Canada The rising costs of nonrenewable feedstocks and environmental concerns with their industrial usage have encouraged the study and development of renewable products, including thermoplastic starch (TPS). Starch is an abundant, plant-based biodegradable material with interesting physicochemical characteristics that can be exploited, and this has received attention for development of TPS products. Starch exhibits usable thermoplastic properties when plasticizers, elevated temperatures, and shear are present. The choice of plasticizer has an effect on TPS, even when these have similar plasticization principles. Most TPS have glass transition temperature, Tg, in the range of approximately -75 to 10°C. Glassy transition of TPS is detected by differential scanning calorimeter (DSC) and thermodynamic analyzer (DMA), although DMA has been found to be more sensitive and effective. TPS has low tensile properties, typically below 6 MPa in tensile strength (TS). The addition of synthetic polymers, nanoclay, and fiber can improve TS and water-resistance ability. The moisture sorption behavior of TPS is described in GAB and BET models, from which monolayer moisture content and specific area are derived. Current studies on surface tension, gas permeability, crystallinity, and so on of the TPS are also reviewed.
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  • 文章类型: Journal Article
    The use of recycled and waste thermoplastics has been recently considered for producing wood plastic composites (WPCs). They have great potential for WPCs manufacturing according to results of some limited researches. This paper presents a detailed review about some essential properties of waste and recycled plastics, important for WPCs production, and of research published on the effect of recycled plastics on the physical and mechanical properties of WPCs.
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  • 文章类型: Journal Article
    Bioabsorbable fixation plates often require adaptation to the bone. This is typically accomplished by heating the plates to above the glass transition temperature and placing the softened plates against the bone or a prebent template until cool. Upon cooling, the plates regain stiffness and can be attached to bone to obtain anatomic fixation. This procedure is both efficient and effective and has been used throughout the craniofacial skeleton. There are many types of equipment available to heat the plates, each with advantages and disadvantages. Although a conceptually simple process, there are several nuances that have been reported in the literature, including transient effects on plate mechanical properties, memory effects, differences between wet and dry heating, and others. Upon the backdrop of the overwhelming clinical success of heat adaptation, this review critically evaluates the method and provides a comprehensive examination and explanation of the basic science and technology involved. This should help give surgeons a better understanding of the process that can help improve their use and further advance the technology.
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    文章类型: Journal Article
    There are a number of substances described in the published literature which inhibit ice nucleation. Certain bacterial strains, mostly found among the nonfluorescent pseudomonade species, release material into the growth medium which reduces the nucleation temperature of water droplets to below that of distilled water. Extracts from the seeds of food crops including apricot, peach and plum can reduce the nucleation temperature of water droplets and dispersions of silver iodide. Antifreeze glycoproteins can reduce the nucleation temperature of saline solutions. Antifreeze proteins can inhibit the activity of some biological ice nucleators but not others. Certain novel polymers have been shown to inhibit the nucleation activity of dispersions of silver iodide and ice-nucleating bacteria.
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