Выделение некоторых органохлорсиланов методом препаративной газовой хроматографии

The preparative gas chromatography method has been used for isolation and analysis of the organochlorsilanes isomers. The reaction of the organochlorsilanes with vapour of the water in the air has been studied. The method for isolation of the organochlorsilanes is proposed. It is based on using chromatographic column with efficiency up to 10000 theoretical plates. A high degree of purity (up to 99%) of the isolated compounds is achieved by an increase of separation selectivity, which is turned results from a temperature decrease. The effect of the parameters of chromatographic experiment (the column length, impregnation degree, the rate of gas-carrier) on the isolation of the compounds boiling up to 400o C was investigated.Метод газовой хроматографии, основанный на использовании хроматографических колонок с эффективностью до 10000 теоретических тарелок, предложен для выделения и анализа некоторых изомеров органохлорсиланов, которые активно реагируют с влагой воздуха. Высокая чистота (до 99%) выделенных соединений достигается за счет увеличения селективности путем понижения температуры. Исследованы условия выделения некоторых изомеров органо- хлорсиланов c температурами кипения до 400о С методом препаративной газовой хроматографии. Показаны пути преодоления методических трудностей, возникающих при выделении высококипящих изомеров. Приведены данные по выделению изомеров хлорсиланов, содержащих различные радикалы (метил-, винил-, фенил-, адамантил-

Использование отечественных кремнийорганических жидкостей в качестве неподвижных фаз в газожидкостной хроматографии

The thermal stability of organosilicon stationary phases for gas-liquid chromatography has been tested under conditions approximating the real operation of chromatographic column.Проведены испытания термостойкости отечественных кремнийорганических неподвижных фаз в условиях, приближенных к обычным условиям работы хроматографических колонн. Показано, что значения верхнего температурного предела большинства кремнийорганических неподвижных фаз были завышены. Определены значения верхнего температурного предела этих неподвижных фаз, соответствующие современным требования

Выделение некоторых высококипящих элементоорганических соединений методом препаративной газовой хроматографии

Preparative gas chromatography is proposed to isolate some high-boiling organometallic compounds. Isolation of high-boiling substances should be conducted at a column temperature significantly below the boiling point, because most isolated compounds are thermally unstable at such temperatures. Stationary phases for preparative gas chromatography have a temperature limit of 350°C. The reduction of the column temperature is based on simultaneous changing the parameters of the chromatographic experiment (column length, impregnation degree, flow rate of the carrier gas). The influence of reducing the column temperature on the shape of the chromatographic peak is shown. The peak has an asymmetric shape, and its width increases. Therefore, the possibility of high-boiling substances preparative isolation depends on temperature decrease as the column separation efficiency is maintained.Метод препаративной газовой хроматографии предложен для выделения некоторых высококипящих элементоорганических соединений. Выделение высококипящих веществ необходимо проводить при температуре, значительно ниже температуры кипения, так как большинство выделяемых соединений термически неустойчивы при таких температурах. Неподвижные фазы для препаративной газовой хроматографии имеют температурный предел 350ºС. Рассмотрены особенности выделения высококипящих веществ при снижении температуры колонки относительно температуры кипения вещества. Понижение температуры колонки достигнуто путем одновременного изменения параметров хроматографического опыта (длины колонки, степени пропитки, скорости газа-носителя). Однако при увеличении отношения температуры кипения к температуре колонки наблюдается изменение формы пика, возрастание его ширины. Поэтому возможность препаративного выделения высококипящих веществ зависит от снижения температуры колонки при сохранении эффективности разделения

Выделение некоторых кремнийорганических гетероциклических соединений методом препаративной газовой хроматографии

The preparative gas chromatography method has been used for isolation of heterocyclic organosilicon compounds boiling up to 400o C. The ways are shown for solution of problems which arise in the course of isolation of such high boiling substances.Проведено выделение ряда кремнийорганических гетероциклических соединений c температурами кипения до 400 о С методом препаративной газовой хроматографии. Показаны пути преодоления методических трудностей, возникающих при выделении подобных веществ

Анализ полиметилфенилсилоксановой жидкости ПФМС-5 методом ВЭЖХ

Polymethylphenylsiloxane liquid PFMS-5 is used as a high temperature heat transfer fluid and a working fluid in the high-vacuum pumps. It is one of the most high-temperature stationary phases in gas chromatography. However, some samples have an upper temperature limit of 280 to 350°С. The composition of this fluid was studied by HPLC. For identification a set of compounds isolated by preparative gas chromatography was obtained. A previously synthesized product consisting of linear polymethylphenylsiloxanes with the number of silicon atoms from 3 to 120 was used. By using a diode array detector the UV-spectra of all the components in the obtained chromatogram were recorded. On the basis of these data it can be concluded that the liquid PFMS-5 consists of polymer homologues with the number of silicon atoms from 3 to 13. In addition to linear methylphenyloligosiloxanes methylphenylsiloxanes of other structure are present in the liquid. Linear methylphenyloligosiloxanes were identifiedПолиметилфенилсилоксановая жидкость ПФМС-5 применяется как высокотемпературный теплоноситель, рабочая жидкость в высоковакуумных насосах и является одной из самых высокотемпературных стационарных фаз в газовой хроматографии. Однако некоторые образцы имеют верхний температурный предел от 280 до 350°С. Состав этой жидкости был изучен методом ВЭЖХ. Для идентификации был получен набор веществ, выделенных препаративной газовой хроматографией. Был использован ранее синтезированный продукт, состоящий из линейных полиметилфенилсилоксанов с числом атомов кремния от 3 до 120. С помощью детектора с диодной матрицей были получены Уф-спектры всех компонентов, представленных на хроматограмме. На основании полученных данных можно заключить, что жидкость состоит из полимергомологов с числом атомов кремния от 3 до 13. Помимо линейных олигосилоксанов в жидкости присутствуют метилфенилсилоксаны другого строения. Линейные метилфенилолигосилоксаны были идентифицированы

Facilitating Memory for Novel Characters by Reducing Neural Repetition Suppression in the Left Fusiform Cortex

Gui Xue is with Beijing Normal University and University of Southern California, Leilei Mei is with Beijing Normal University and University of California Irvine, Chuansheng Chen is with University of California Irvine, Zhong-Lin Lu is with University of Southern California, Russell A. Poldrack is with UT Austin, Qi Dong is with Beijing Normal University.Background -- The left midfusiform and adjacent regions have been implicated in processing and memorizing familiar words, yet its role in memorizing novel characters has not been well understood. Methodology/Principal Findings -- Using functional MRI, the present study examined the hypothesis that the left midfusiform is also involved in memorizing novel characters and spaced learning could enhance the memory by enhancing the left midfusiform activity during learning. Nineteen native Chinese readers were scanned while memorizing the visual form of 120 Korean characters that were novel to the subjects. Each character was repeated four times during learning. Repetition suppression was manipulated by using two different repetition schedules: massed learning and spaced learning, pseudo-randomly mixed within the same scanning session. Under the massed learning condition, the four repetitions were consecutive (with a jittered inter-repetition interval to improve the design efficiency). Under the spaced learning condition, the four repetitions were interleaved with a minimal inter-repetition lag of 6 stimuli. Spaced learning significantly improved participants' performance during the recognition memory test administered one hour after the scan. Stronger left midfusiform and inferior temporal gyrus activities during learning (summed across four repetitions) were associated with better memory of the characters, based on both within- and cross-subjects analyses. Compared to massed learning, spaced learning significantly reduced neural repetition suppression and increased the overall activities in these regions, which were associated with better memory for novel characters. Conclusions/Significance -- These results demonstrated a strong link between cortical activity in the left midfusiform and memory for novel characters, and thus challenge the visual word form area (VWFA) hypothesis. Our results also shed light on the neural mechanisms of the spacing effect in memorizing novel characters.This study was supported by the Program for New Century Excellent Talents in University, the National Science Foundation (grant numbers BCS 0823624 and BCS 0823495), the National Institute of Health (grant number HD057884-01A2), and the 111 Project of China (B07008). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Psycholog

Challenges for Allergy Diagnosis in Regions with Complex Pollen Exposures

Over the past few decades, significant scientific progress has influenced clinical allergy practice. The biological standardization of extracts was followed by the massive identification and characterization of new allergens and their progressive use as diagnostic tools including allergen micro arrays that facilitate the simultaneous testing of more than 100 allergen components. Specific diagnosis is the basis of allergy practice and is always aiming to select the best therapeutic or avoidance intervention. As a consequence, redundant or irrelevant information might be adding unnecessary cost and complexity to daily clinical practice. A rational use of the different diagnostic alternatives would allow a significant improvement in the diagnosis and treatment of allergic patients, especially for those residing in complex pollen exposure areas