Strength of π-Stacking, from Neutral to Cation: Precision Measurement of Binding Energies in an Isolated π-Stacked Dimer

π-Stacking interactions are ubiquitious across chemistry and biochemistry, impacting areas from organic materials and photovoltaics to biochemistry and DNA. However, experimental data is lacking regarding the strength of π-stacking forces—an issue not settled even for the simplest model system, the isolated benzene dimer. Here, we use two-color appearance potential measurements to determine the binding energies of the isolated, π-stacked dimer of fluorene (C13H10) in ground, excited, and ionic states. Our measurements provide the first precise values for π-stacking interaction energies in these states, which are key benchmarks for theory. Indeed, theoretical predictions using ab initio and carefully benchmarked DFT methods are in excellent agreement with experiment

Parallel evolutionary pathways to antibiotic resistance selected by biocide exposure

OBJECTIVES: Biocides are widely used to prevent infection. We aimed to determine whether exposure of Salmonella to various biocides could act as a driver of antibiotic resistance. METHODS: Salmonella enterica serovar Typhimurium was exposed to four biocides with differing modes of action. Antibiotic-resistant mutants were selected during exposure to all biocides and characterized phenotypically and genotypically to identify mechanisms of resistance. RESULTS: All biocides tested selected MDR mutants with decreased antibiotic susceptibility; these occurred randomly throughout the experiments. Mutations that resulted in de-repression of the multidrug efflux pump AcrAB-TolC were seen in MDR mutants. A novel mutation in rpoA was also selected and contributed to the MDR phenotype. Other mutants were highly resistant to both quinolone antibiotics and the biocide triclosan. CONCLUSIONS: This study shows that exposure of bacteria to biocides can select for antibiotic-resistant mutants and this is mediated by clinically relevant mechanisms of resistance prevalent in human pathogens

Формирование мгновенных дифференциальных и тормозных токов дифференциальной защиты сборных шин

The methods of forming differential and restraining currents for busbar differential protection are reviewed; their advantages and disadvantages are considered. It is noted that differential protection according to instantaneous values has a shorter proper response time than for current ones, since it does not use digital filters. The response characteristic and principles of setting selection are studied. The effect of sampling on the operation of differential protection according to instantaneous values is analyzed. It was found that without the use of special measures, depending on the sampling step and the frequency of the signal, the response current would fluctuate within the mathematical error caused by sampling. A solution to this problem has been proposed. The method consists in applying piecewise quadratic interpolation and determining the values of inflection points of instantaneous differential and restraining current signals. The efficiency of the proposed method has been evaluated. It was found that its use reduces the error in determining the response current. For a sinusoidal signal, the maximum possible error was 0.02 %. The trajectories of operating point s of differential protection in case of external fault with saturation of current transformers have been analyzed. In this mode, protection for instantaneous values is more susceptible to false positives than for active ones. The method of exponential smoothing of the restraining current was considered and investigated. An exponential smoothing algorithm has been proposed and analyzed. It is concluded that exponential smoothing increases the stability of the differential protection according to instantaneous values to external faults. Exponential smoothing does not exclude the possibility of false positive of differential protection in case of external fault.Рассмотрены способы формирования тормозных и дифференциальных токов для дифференциальной защиты шин, их преимущества и недостатки. Отмечено, что дифференциальная защита по мгновенным значениям имеет меньшее собственное время срабатывания, чем по действующим, поскольку не использует цифровые фильтры. Исследованы характеристика срабатывания и принципы выбора уставок. Проанализировано влияние дискретизации на работу дифференциальной защиты по мгновенным значениям. Выявлено, что без применения специальных мер в зависимости от шага дискретизации и частоты сигнала ток срабатывания будет колебаться в пределах математической погрешности, вызываемой дискретизацией. Предложено решение данной проблемы. Способ заключается в применении кусочно-квадратической интерполяции и в определении значений точек перегиба сигналов мгновенного дифференциального и тормозного токов. Произведена оценка эффективности предложенного способа. Установлено, что его использование уменьшает погрешность определения тока срабатывания. Для синусоидального сигнала максимально возможная погрешность составила 0,02 %. Проанализированы траектории движения рабочих точек дифференциальной защиты при внешнем коротком замыкании с насыщением трансформаторов тока. В данном режиме защита по мгновенным значениям более подвержена ложным срабатываниям, чем по действующим. Рассмотрен и исследован метод экспоненциального сглаживания тормозного тока. Предложен и проанализирован алгоритм экспоненциального сглаживания. Сделан вывод, что экспоненциальное сглаживание повышает устойчивость дифференциальной защиты по мгновенным значениям к внешним коротким замыканиям. Экспоненциальное сглаживание не исключает возможность ложного срабатывания дифференциальной защиты при внешних коротких замыканиях

ОПРЕДЕЛЕНИЕ ПОВРЕЖДЕНИЯ ТОКОВЫХ ЦЕПЕЙ ДИФФЕРЕНЦИАЛЬНОЙ ТОКОВОЙ ЗАЩИТЫ

False operation of the differential current protection leads to tripping of the most important electrical power objects. Fault of current transformer’s secondary circuits is one of the most often cause of false operation of the differential current protection. Early determination of this malfunction increases the reliability of the differential current protection and reduces the number of false trips. In the present article the methods of secondary open circuit determining for the differential protection are described. Some of the methods react instantly to the malfunction of secondary current circuits, and the other part identifies fault after a certain time delay. Each of considered methods has its advantages and disadvantages. A new method for determination secondary open current circuits based on the analysis of increments of the RMS values of differential and braking currents has been proposed. In this case, increments are calculated for half the period of the industrial frequency, which provides quick fault determining. The use of the sum and the difference between the increments of the brake and differential currents makes it possible to determine the open circuits in the most sensitive way. The method can be adapted to work with any type of differential protection, including transformer protection. The evaluation of the increment of the RMS current value is performed taking into account the transient process in the Fourier filter. With the aid of a computational experiment, the error limit of such an estimate is determined. The block diagram of algorithm of determination of open circuits on the basis of the analysis of increments of the acting values of brake and differential currents is presented; the principle of its functioning is described. The parameters of operation are determined. The limits of sensitivity of the method are determined, too. The time characteristics of the algorithm have been determined by the method of computational experiment with the of the MatLab Simulink simulation environment.Ложная работа дифференциальной токовой защиты приводит к отключению наиболее ответственных электроэнергетических объектов. Повреждение вторичных цепей трансформаторов тока является одной из наиболее частых причин ложной работы защиты. Своевременное определение данной неисправности повышает надежность работы дифференциальной токовой защиты и уменьшает количество ложных отключений. В статье рассмотрены способы определения обрыва вторичных токовых цепей для дифференциальной защиты. Часть способов мгновенно реагирует на неисправность вторичных токовых цепей, а другая часть идентифицирует повреждение по истечении определенной выдержки времени. Каждый из рассмотренных способов обладает своими преимуществами и недостатками. Предложен новый метод определения обрыва вторичных токовых цепей на основе анализа приращений действующих значений дифференциального и тормозного токов. При этом приращения вычисляются за половину периода промышленной частоты, что обеспечивает быстрое определение неисправности. Использование суммы и разности приращений тормозного и дифференциального токов позволяет с наибольшей чувствительностью определить обрыв токовых цепей. Метод может быть адаптирован для работы с любым типом дифференциальной защиты, в том числе с защитой трансформатора. Оценка приращения действующего значения тока выполняется с учетом переходного процесса в фильтре Фурье. С помощью вычислительного эксперимента установлен предел погрешности такой оценки. Представлена блок-схема алгоритма определения обрыва токовых цепей на основании анализа приращений действующих значений тормозного и дифференциального токов, описан принцип его функционирования. Произведено определение параметров срабатывания. Установлены пределы чувствительности способа. Методом вычислительного эксперимента с использованием среды моделирования MatLab Simulink определены временные характеристики алгоритма

Differences in the gut microbiota between Gurkhas and soldiers of British origin

Previous work indicated that the incidence of travellers’ diarrhoea (TD) is higher in soldiers of British origin, when compared to soldiers of Nepalese descent (Gurkhas). We hypothesise that the composition of the gut microbiota may be a contributing factor in the risk of developing TD in soldiers of British origin. This study aimed to characterise the gut microbial composition of Gurkha and non-Gurkha soldiers of the British Army. Recruitment of 38 soldiers (n = 22 Gurkhas, n = 16 non-Gurkhas) and subsequent stool collection, enabled shotgun metagenomic sequencing-based analysis of the gut microbiota. The microbiota of Gurkhas had significantly (P < 0.05) lower diversity, for both Shannon and Simpson diversity indices, using species level markers than the gut microbiota of non-Gurkha soldiers. Non-metric Multidimensional Scaling (NMDS) of the Bray-Curtis distance matrix revealed a significant difference in the composition of the gut microbiota between Gurkhas and non-Gurkha soldiers, at both the species level (P = 0.0178) and the genus level (P = 0.0483). We found three genera and eight species that were significantly enriched in the non-Gurkha group and one genus (Haemophilus) and one species (Haemophilus parainfluenzae) which were enriched in the Gurkha group. The difference in the microbiota composition between Gurkha soldiers and soldiers of British origin may contribute to higher colonization resistance against diarrhoeal pathogens in the former group. Our findings may enable further studies into interventions that modulate the gut microbiota of soldiers to prevent TD during deployment

Differences in the gut microbiota between Gurkhas and soldiers of British origin

Previous work indicated that the incidence of travellers’ diarrhoea (TD) is higher in soldiers of British origin, when compared to soldiers of Nepalese descent (Gurkhas). We hypothesise that the composition of the gut microbiota may be a contributing factor in the risk of developing TD in soldiers of British origin. This study aimed to characterise the gut microbial composition of Gurkha and non-Gurkha soldiers of the British Army. Recruitment of 38 soldiers (n = 22 Gurkhas, n = 16 non-Gurkhas) and subsequent stool collection, enabled shotgun metagenomic sequencing-based analysis of the gut microbiota. The microbiota of Gurkhas had significantly (P < 0.05) lower diversity, for both Shannon and Simpson diversity indices, using species level markers than the gut microbiota of non-Gurkha soldiers. Non-metric Multidimensional Scaling (NMDS) of the Bray-Curtis distance matrix revealed a significant difference in the composition of the gut microbiota between Gurkhas and non-Gurkha soldiers, at both the species level (P = 0.0178) and the genus level (P = 0.0483). We found three genera and eight species that were significantly enriched in the non-Gurkha group and one genus (Haemophilus) and one species (Haemophilus parainfluenzae) which were enriched in the Gurkha group. The difference in the microbiota composition between Gurkha soldiers and soldiers of British origin may contribute to higher colonization resistance against diarrhoeal pathogens in the former group. Our findings may enable further studies into interventions that modulate the gut microbiota of soldiers to prevent TD during deployment

Tetrahydropyrazolo[1,5-a]Pyrimidine-3-Carboxamide and N-Benzyl-6′,7′-Dihydrospiro[Piperidine-4,4′-Thieno[3,2-c]Pyran] analogues with bactericidal efficacy against Mycobacterium tuberculosis targeting MmpL3

Mycobacterium tuberculosis is a major human pathogen and the causative agent for the pulmonary disease, tuberculosis (TB). Current treatment programs to combat TB are under threat due to the emergence of multi-drug and extensively-drug resistant TB. As part of our efforts towards the discovery of new anti-tubercular leads, a number of potent tetrahydropyrazolo[1,5-a]pyrimidine-3-ca​rboxamide(THPP) and N-benzyl-6′,7′-dihydrospiro[piperidine-4,​4′-thieno[3,2-c]pyran](Spiro) analogues were recently identified against Mycobacterium tuberculosis and Mycobacterium bovis BCG through a high-throughput whole-cell screening campaign. Herein, we describe the attractive in vitro and in vivo anti-tubercular profiles of both lead series. The generation of M. tuberculosis spontaneous mutants and subsequent whole genome sequencing of several resistant mutants identified single mutations in the essential mmpL3 gene. This ‘genetic phenotype’ was further confirmed by a ‘chemical phenotype’, whereby M. bovis BCG treated with both the THPP and Spiro series resulted in the accumulation of trehalose monomycolate. In vivo efficacy evaluation of two optimized THPP and Spiro leads showed how the compounds were able to reduce >2 logs bacterial cfu counts in the lungs of infected mice

Extreme genetic fragility of the HIV-1 capsid

Genetic robustness, or fragility, is defined as the ability, or lack thereof, of a biological entity to maintain function in the face of mutations. Viruses that replicate via RNA intermediates exhibit high mutation rates, and robustness should be particularly advantageous to them. The capsid (CA) domain of the HIV-1 Gag protein is under strong pressure to conserve functional roles in viral assembly, maturation, uncoating, and nuclear import. However, CA is also under strong immunological pressure to diversify. Therefore, it would be particularly advantageous for CA to evolve genetic robustness. To measure the genetic robustness of HIV-1 CA, we generated a library of single amino acid substitution mutants, encompassing almost half the residues in CA. Strikingly, we found HIV-1 CA to be the most genetically fragile protein that has been analyzed using such an approach, with 70% of mutations yielding replication-defective viruses. Although CA participates in several steps in HIV-1 replication, analysis of conditionally (temperature sensitive) and constitutively non-viable mutants revealed that the biological basis for its genetic fragility was primarily the need to coordinate the accurate and efficient assembly of mature virions. All mutations that exist in naturally occurring HIV-1 subtype B populations at a frequency >3%, and were also present in the mutant library, had fitness levels that were >40% of WT. However, a substantial fraction of mutations with high fitness did not occur in natural populations, suggesting another form of selection pressure limiting variation in vivo. Additionally, known protective CTL epitopes occurred preferentially in domains of the HIV-1 CA that were even more genetically fragile than HIV-1 CA as a whole. The extreme genetic fragility of HIV-1 CA may be one reason why cell-mediated immune responses to Gag correlate with better prognosis in HIV-1 infection, and suggests that CA is a good target for therapy and vaccination strategies

BRCA1 mutations in women with familial or early-onset breast cancer and BRCA2 mutations in familial cancer in Estonia

<p>Abstract</p> <p>Background</p> <p>The aim of this study was to identify BRCA1 and BRCA2 mutations in the Estonian population. We analyzed genetic data and questionnaire from 64 early-onset (< 45 y) breast cancer patients, 47 familial cases (patients with breast or ovarian cancer and a case of these cancers in the family), and 33 predictive cases (patients without breast or ovarian cancer, with a family history of such diseases) from Estonia for mutations in the BRCA1 gene. A sub-set of familial cases and predictive cases were also analyzed for mutations in the BRCA2 gene.</p> <p>Methods</p> <p>For mutation detection, we used the Polymerase Chain Reaction-Single Stranded Conformation Polymorphism Heteroduplex Analysis (PCR-SSCP-HD), followed by direct DNA sequencing.</p> <p>Results</p> <p>We identified three clinically important mutations in the BRCA1 gene, including seven occurrences of the c.5382insC mutation, three of c.4154delA, and one instance of c.3881_3882delGA. We also detected six polymorphisms: c.2430T>C, c.3232A>G, c.4158A>G, c.4427T>C, c.4956A>G, and c.5002T>C. Four sequence alterations were detected in introns: c.560+64delT, c.560+ [36-38delCTT, 52-63del12], c.666-58delT, and c.5396+60insGTATTCCACTCC. In the BRCA2 gene, two clinically important mutations were found: c.9610C>T and c.6631delTTAAATG. Additionally, two alterations (c.7049G>T and c.7069+80delTTAG) with unknown clinical significance were detected.</p> <p>Conclusions</p> <p>In our dataset, the overall frequency of clinically important BRCA1 mutations in early-onset patients, familial cases, and predictive testing was 7.6% (144 cases, 11 mutation carriers). Pathogenic mutations were identified in 4 of the 64 early-onset breast cancer cases (6.3%). In familial cases, clinically important mutations in the BRCA1 gene were found in 6 of the 47 individuals analyzed (12.8%). In predictive cases, 1 clinically important mutation was detected in 33 individuals studied (3%). The occurrence of clinically important mutations in BRCA2 in familial cases of breast cancer was 2 of the 16 individuals analyzed (12.5%).</p