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To gain insight into microscopic hydrogen bond networks, we measured ultraviolet photodissociation (UVPD) spectra of the phenol-methanol 1:3 cluster cation, [PhOH(MeOH)3]+ trapped in a variable temperature ion trap. At low temperatures, an isomer with a ring-type hydrogen bond structure dominates, whereas at higher temperatures the chain-type isomers become dominant due to the flexibility of their hydrogen bond structures. We also found a clear temperature dependence of the spectral features, such as band position and width. In addition to the above measurement, we observed the infrared (IR) induced isomerization of [PhOH(MeOH)3]+ to study the dynamical aspects of hydrogen bond networks. We succeeded in observing IR-induced isomerization from the ring to chain forms of [PhOH(MeOH)3]+ at low temperature. The isomerization was clearly identified as a change in the UVPD spectra. The time evolution of the UVPD spectra after IR excitation indicated that the IR-induced isomerization occurs within a nanosecond. The chain-type isomers produced by the IR-induced isomerization are then converted back to the ring-type form by collisions with cold He buffer gas in the trap. This backward isomerization proceeds with a time constant of 100 µs under our experimental conditions. In this study, we evaluated the temperatures of the chain isomers during the backward isomerization on the basis of the spectral features.
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BACKGROUND: Large language models have propelled recent advances in artificial intelligence technology, facilitating the extraction of medical information from unstructured data such as medical records. Although named entity recognition (NER) is used to extract data from physicians' records, it has yet to be widely applied to pharmaceutical care records. OBJECTIVE: In this study, we aimed to investigate the feasibility of automatic extraction of the information regarding patients' diseases and symptoms from pharmaceutical care records. The verification was performed using Medical Named Entity Recognition-Japanese (MedNER-J), a Japanese disease-extraction system designed for physicians' records. METHODS: MedNER-J was applied to subjective, objective, assessment, and plan data from the care records of 49 patients who received cefazolin sodium injection at Keio University Hospital between April 2018 and March 2019. The performance of MedNER-J was evaluated in terms of precision, recall, and F1-score. RESULTS: The F1-scores of NER for subjective, objective, assessment, and plan data were 0.46, 0.70, 0.76, and 0.35, respectively. In NER and positive-negative classification, the F1-scores were 0.28, 0.39, 0.64, and 0.077, respectively. The F1-scores of NER for objective (0.70) and assessment data (0.76) were higher than those for subjective and plan data, which supported the superiority of NER performance for objective and assessment data. This might be because objective and assessment data contained many technical terms, similar to the training data for MedNER-J. Meanwhile, the F1-score of NER and positive-negative classification was high for assessment data alone (F1-score=0.64), which was attributed to the similarity of its description format and contents to those of the training data. CONCLUSIONS: MedNER-J successfully read pharmaceutical care records and showed the best performance for assessment data. However, challenges remain in analyzing records other than assessment data. Therefore, it will be necessary to reinforce the training data for subjective data in order to apply the system to pharmaceutical care records.
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This study aimed to determine whether adolescents' leisure screen time differed during the coronavirus disease 2019 (COVID-19) pandemic compared to before the pandemic, and to identify factors that affect leisure screen time among Japanese high school students. The Health Behavior in School Children questionnaire was used to investigate differences in eating habits and physical and mental health. The results showed that the leisure screen time of Japanese high school students was 2.6 h (SD = 1.4) before the pandemic, and 3.2 h (SD = 1.5) during the pandemic. The factors that increased leisure screen time were found to differ between boys and girls. No significant deterioration in physical and mental health was observed. The impact of the pandemic on eating habits differed in boys and girls. Boys reported "not feeling great about life" as a factor that increased leisure screen time during the pandemic, suggesting that negative emotions influenced the increase in leisure screen time. The pandemic had a significant impact on girls' leisure screen time. Longer screen time should be carefully monitored because it can lead to sleep disturbances, worsening of mental health, and obesity. Compared with before the pandemic, the health status of boys and girls changed little. Eating habits tended to improve for both boys and girls.
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Yam (Dioscorea spp.) is of great importance to food security, especially in West Africa. However, the loss of soil fertility due to dwindling fallow lands with indigenous nutrient supply poses a challenge for yam cultivation. This study aimed to determine shoot and tuber biomass and nutrient use efficiency of white Guinea yam (Dioscorea rotundata) grown under low- and high-NPK conditions. Six white Guinea yam genotypes were used in field experiments conducted at Ibadan, Nigeria. Experiments were conducted with low soil NPK conditions with zero fertilizer input and high soil NPK conditions with mineral fertilizer input. Differences in response to soil NPK conditions, nutrient uptake, and nutrient use efficiency (apparent nutrient recovery efficiency) were observed among the tested genotypes. The genotypes TDr1499 and TDr1649, with high soil fertility susceptibility index (SFSI>1) and an increase in shoot and tuber biomass with fertilizer input, were recognized as susceptible to soil NPK conditions. There was a marked difference in apparent nutrient recovery efficiency; however, there was no varietal difference in physiological efficiency. Differences in apparent nutrient recovery efficiency among genotypes affected the fertilizer response (or susceptibility to soil NPK conditions) and the nutrient uptake. In contrast, the genotype TDr2029, with SFSI<1 and low reduction in shoot and tuber production between non-F and +F conditions, was recognized as a less susceptible genotype to soil NPK status. It was revealed that NPK fertilization did not reduce tuber dry matter content, regardless of genotype differences in susceptibility to soil NPK conditions. Hence, this could be helpful to farmers because it implies that yield can be increased without reducing tuber quality through a balanced application of soil nutrients. Our results highlight genotypic variation in sensitivity to the soil NPK availability, nutrient uptake, and nutrient use efficiency white Guinea yam. Differences in susceptibility to soil NPK conditions could be due to the genotypic variations in nutrient recovery efficiency white Guinea yam. Our findings could contribute to breeding programs for the development of improved white Guinea yam varieties that enhance productivity in low soil fertility conditions with low and high-input farming systems.
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Therapeutic drug monitoring, which is used to determine appropriate drug doses, is critical in pharmacological therapy. In this study, we developed thermoresponsive chromatography columns with various cationic properties for effective therapeutic drug monitoring. Thermoresponsive cationic copolymer poly(N-isopropylacrylamide-co-n-butyl methacrylate-co-N,N-dimethylaminopropyl acrylamide) (P(NIPAAm-co-BMA-co-DMAPAAm))-modified silica beads, which were used as the chromatographic stationary phase, were prepared by modifying the radical initiator of the silica beads, followed by radical polymerization. Characterization of the prepared silica beads demonstrated that thermoresponsive polymers with various cationic properties successfully modified the beads. The elution behavior of several steroids in the prepared bead-packed columns at various temperatures indicated that the optimal column operating temperature was 30 °C. Appropriate measurement conditions for 13 drugs were investigated by varying the cationic properties of the columns and the pH of the mobile phase. Drug concentrations in serum samples were determined using the developed columns and mobile phases with a suitable pH. Voriconazole concentrations in human serum samples were determined using the developed columns with all-aqueous mobile phases. We anticipate that the developed chromatography columns can be used for therapeutic drug monitoring because drug concentrations can be measured using all-aqueous mobile phases that are suitable in clinical settings.
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Monitoreo de Drogas , Polímeros , Cationes , Cromatografía , Humanos , Polímeros/química , Dióxido de Silicio/química , TemperaturaRESUMEN
Crop genetic diversity is a sine qua non for continuous progress in the development of improved varieties, hence the need for germplasm collection, conservation and characterization. Over the years, cowpea has contributed immensely to the nutrition and economic life of the people in Togo. However, the bulk of varieties grown by farmers are landraces due to the absence of any serious genetic improvement activity on cowpea in the country. In this study, the genetic diversity and population structure of 255 cowpea accessions collected from five administrative regions and the agricultural research institute of Togo were assessed using 4600 informative diversity array technology (DArT) markers. Among the regions, the polymorphic information content (PIC) ranged from 0.19 to 0.27 with a mean value of 0.25. The expected heterozygosity (He) varied from 0.22 to 0.34 with a mean value of 0.31, while the observed heterozygosity (Ho) varied from 0.03 to 0.07 with an average of 0.05. The average inbreeding coefficient (FIS) varied from 0.78 to 0.89 with a mean value of 0.83, suggesting that most of the accessions are inbred. Cluster analysis and population structure identified four groups with each comprising accessions from the six different sources. Weak to moderate differentiation was observed among the populations with a genetic differentiation index varying from 0.014 to 0.117. Variation was highest (78%) among accessions within populations and lowest between populations (7%). These results revealed a moderate level of diversity among the Togo cowpea germplasm. The findings of this study constitute a foundation for genetic improvement of cowpea in Togo.
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Variación Genética , Genética de Población , Vigna/genética , Filogenia , Polimorfismo de Nucleótido Simple , Banco de Semillas , TogoRESUMEN
Yam (Dioscorea spp.) is a major food security crop for millions of resource-poor farmers, particularly in West Africa. Soil mineral deficiency is the main challenge in yam production, especially with the dwindling of fallow lands for the indigenous nutrient supply. Cultivars tolerant to available low soil nutrients and responsive to added nutrient supply are viable components of an integrated soil fertility management strategy for sustainable and productive yam farming systems in West Africa. This study's objective was to identify white Guinea yam (D. rotundata) genotypes adapted to available low soil nutrients and responsive to externally added nutrient supply. Twenty advanced breeding lines and a local variety (Amula) were evaluated under contrasting soil fertility, low to expose the crop to available low soil nutrient supply and high to assess the crop response to added mineral fertilizer (NPK) input at Ibadan, Nigeria. The genotypes expressed differential yield response to low soil fertility (LF) stress and added fertilizer input. Soil fertility susceptibility index (SFSI) ranged from 0.64 to 1.34 for tuber yield and 0.60 to 1.30 for shoot dry weight. The genotypes R034, R041, R050, R052, R060, R100, and R125 combined lower SFSI with a low rate of reduction in tuber yield were identified as tolerant to LF stress related to the soil mineral deficiency. Likewise, the genotypes R109, R119, and R131 showed high susceptibility to soil fertility level and/or fertilizer response. Genotypes R025 and R034 had the tuber yielding potential twice of that the local variety under low soil nutrient conditions. Shoot dry weight and tuber yield showed a positive correlation both under low and high soil fertility conditions (r = 0.69 and 0.75, respectively), indicating the vigor biomass may be a morphological marker for selecting genotypes of white Guinea yam for higher tuber yield. Our results highlight genotypic variation in the tolerance to low soil nutrients and mineral fertilizer response in white Guinea yam to exploit through breeding and genetic studies to develop improved genotypes for low and high input production systems in West Africa.
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To investigate microscopic characters of Si-Hâ¯H-O type dihydrogen bonds, we observed OH and SiH stretch bands in both the S0 and S1 states of phenol-ethyldimethylsilane (PhOH-EDMS) clusters by infrared (IR)-ultraviolet (UV) and UV-IR double resonance spectroscopies. Density functional theory (DFT) calculations and energy decomposition analysis were also performed. Structures of two isomers identified were unambiguously determined through the analysis of IR spectra and DFT calculations. To discuss the strength of dihydrogen bond in various systems, we performed theoretical calculations on clusters of EDMS with several acidic molecules in addition to PhOH. It was revealed that charge-transfer interaction energies from a bonding σ orbital of SiH bond to an anti-bonding σ* orbital of OH bond well reflect strengths of dihydrogen bonds. Additionally, it was found that the red shift of SiH stretch frequencies can be used as a crude measure of the strength of dihydrogen bonds. Relationship between the red shifts of OH/SiH stretch frequencies and various electrostatic components of the interaction energy was examined. In the S1 state, large increases in red shifts were observed for both the OH and SiH stretch frequencies. Since the EDMS moiety is not associated with the electronic excitation in a cluster, the strength of dihydrogen bonds in the S1 and S0 states was able to be directly compared based on the red shifts of the SiH stretch bands. A significant increase in the red shift of SiH stretch frequency indicates a strengthening of the dihydrogen bonds during the electronic excitation of the PhOH moiety.
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Freshwater mussels (Bivalvia: Unionidae) is a diverse family with around 700 species being widespread in the Northern Hemisphere and Africa. These animals fulfill key ecological functions and provide important services to humans. Unfortunately, populations have declined dramatically over the last century, rendering Unionidae one of the world's most imperiled taxonomic groups. In Far East Asia (comprising Japan, Korea, and Eastern Russia), conservation actions have been hindered by a lack of basic information on the number, identity, distribution and phylogenetic relationships of species. Available knowledge is restricted to studies on national and sub-national levels. The present study aims to resolve the diversity, biogeography and evolutionary relationships of the Far East Asian Unionidae in a globally comprehensive phylogenetic and systematic context. We reassessed the systematics of all Unionidae species in the region, including newly collected specimens from across Japan, South Korea, and Russia, based on molecular (including molecular species delineation and a COIâ¯+â¯28S phylogeny) and comparative morphological analyses. Biogeographical patterns were then assessed based on available species distribution data from the authors and previous reference works. We revealed that Unionidae species richness in Far East Asia is 30% higher than previously assumed, counting 43 species (41 nativeâ¯+â¯2 alien) within two Unionidae subfamilies, the Unioninae (32â¯+â¯1) and Gonideinae (9â¯+â¯1). Four of these species are new to science, i.e. Beringiana gosannensissp. nov., Beringiana fukuharaisp. nov., Buldowskia kamiyaisp. nov., and Koreosolenaia sitgyensisgen. & sp. nov. We also propose a replacement name for Nodularia sinulata, i.e. Nodularia breviconchanom. nov. and describe a new tribe (Middendorffinaiini tribe nov.) within the Unioninae subfamily. Biogeographical patterns indicate that this fauna is related to that from China south to Vietnam until the Mekong River basin. The Japanese islands of Honshu, Shikoku, Kyushu, Hokkaido, and the Korean Peninsula were identified as areas of particularly high conservation value, owing to high rates of endemism, diversity and habitat loss. The genetically unique species within the genera Amuranodonta, Obovalis, Koreosolenaiagen. nov., and Middendorffinaia are of high conservation concern.
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Unionidae/clasificación , Animales , Evolución Biológica , Agua Dulce , Japón , Corea (Geográfico) , Filogenia , Filogeografía , Federación de Rusia , Unionidae/genéticaRESUMEN
Infrared (IR) spectra in a region of the OH stretch band of phenol (PhOH)-ethyldimethylsilane (EDMS), phenol (PhOH)-triethylsilane (TES), and phenol (PhOH)-t-butyldimethylsilane (BDMS) dihydrogen-bonded clusters in the S1 state were observed. All of the species exhibited unconventional band patterns in which many combination bands appeared with comparable intensities to those of allowed bands. Such a behavior is sometimes called a Franck-Condon-like pattern. In the case of the PhOH-BDMS, one intermolecular vibrational mode is involved in this behavior. The observed IR spectra were well reproduced based on the concept of the Franck-Condon-like behavior. As an alternative treatment, we analyzed the band patterns on the concept of intensity borrowing due to the vibrational anharmonic interaction. The analysis was based on an effective Hamiltonian involving an anharmonic interaction between the OH stretch and intermolecular vibrational modes. Two treatments provided the same results. Thus, it was confirmed that the Franck-Condon-like behavior originates from vibrational anharmonic interactions. In the cases of the PhOH-EDMS and PhOH-TES, we carried out a two-dimensional Franck-Condon and an effective Hamiltonian analysis to interpret the Franck-Condon-like patterns. We examined vibrational wave functions obtained by the latter analysis. Shapes of the wave functions suggest that a recombination of the intermolecular vibrational modes occurs during the excitation of OH stretch mode in these clusters, which is a similar behavior to the Duschinsky effect in the electronic transition.
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To discuss the temperature effect on microscopic hydration structures in clusters, relative populations of the isomers having different hydration structures at well-defined temperatures are quite important. In the present study, we measured ultraviolet photodissociation spectra of the temperature-controlled hydrated phenol cation [PhOH(H2O)5]+ trapped in the 22-pole ion trap. Two isomers having a distinct hydration motif with each other are identified in the spectra, and a clear change in the relative populations is observed in the temperature range from 30 to 150 K. This behavior is quantitatively interpreted by statistical mechanical estimation based on density functional theory calculations. A ring with tail-type hydration motif is dominant in cold conditions, whereas a chain-like motif is dominant in hot conditions. The present study provides very quantitative information about the temperature effect on the microscopic hydration structures.
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Spectroscopic and theoretical investigations have been carried out for neutral phenol-triethylsilane clusters to reveal an intrinsic nature of the Si-H···H-O type dihydrogen bond. On the basis of the laser-induced fluorescence and infrared spectra, four isomers are identified. Three of them have a structure in which the dihydrogen bond and the dispersion interaction are competing in the stabilization of the cluster. However, the other isomer is found to have a distinct structure in which the dihydrogen bond is much stronger than the other isomers. In addition to the neutral clusters, cationic phenol(+)-diethylmethylsilane and phenol(+)-triethylsilane clusters are investigated by infrared photodissociation spectroscopy. It is found that the dihydrogen bond is the dominant intermolecular interaction in these clusters. On the basis of the red shifts of the OH stretching bands, it is revealed that the strength of the Si-H···H-O dihydrogen bond is stronger than that of the π-type hydrogen bond. The proton affinities of triethylsilane and diethylmethylsilane estimated by the theoretical calculation are larger than those of benzene and ethylene. These results are consistent with our experimental observations.
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We recently demonstrated the circadian clock modulated water dynamics in the roots of a small model plant, Arabidopsis thaliana, by the Nuclear Magnetic Resonance (NMR) microimaging technique. Our developed technique was able to visualize the water distribution that depended on differences in the (1)H signal among region in the shoot, such as the shoot apex, the hypocotyl and the root shoot junction. Water content in the shoot increased during periods of light in comparison with dark periods, and continued through the early stage of seedling growth until the dark period. When the water content changed, elongation and/or movement occurred in the hypocotyl, and these events were synchronized. The water dynamics of the shoot also displayed an opposite phase with the root water dynamics.
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Arabidopsis/fisiología , Relojes Circadianos , Hipocótilo/fisiología , Luz , Fotoperiodo , Raíces de Plantas/fisiología , Brotes de la Planta/fisiología , Agua/metabolismo , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Ritmo Circadiano , Hipocótilo/crecimiento & desarrollo , Hipocótilo/metabolismo , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Brotes de la Planta/metabolismoRESUMEN
Ionization potentials (IPs) of [(CH(3))(2)NH](m)(NH(3))(n)-H hypervalent radical clusters produced by an ArF excimer laser photolysis of dimethylamine (DMA)-ammonia mixed clusters are determined by the photoionization threshold measurements. The IPs of the DMA(1)(NH(3))(n)-H hypervalent radicals decrease rapidly with the number of ammonia up to n=4, and then its decrease rate becomes much slower for n ≥ 5. This trend is very similar to that found for NH(4)(NH(3))(n) clusters. The calculated results on the stable structures and IP as well as the observed IP for DMA(1)(NH(3))(n)-H indicate that the hydrogen atom-localized site is the NH(3) moiety for n=1, while the doubly coordinated DMA-H is favorable for n=2-4, and then 4-fold-coordinated NH(4) is again more stable for n ≥ 5. These changes are consistent with the results on the femtosecond pump-probe experiments of DMA(n)-H clusters. Switching of the hydrogen atom-localized site is ascribed to the instability of DMA-H against a hydrogen-atom dissociation.
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We have developed a plant growth system to analyze water dynamics in the roots of a small model plant, Arabidopsis thaliana, by nuclear magnetic resonance (NMR) microscopic imaging. Using the two-dimensional slice technique, we obtained a series of images with high signal-to-noise ratio indicating the water distribution in the root. To demonstrate light regulation of water transport in the root and involvement of aquaporin gene expression, we visualized the distribution of water in Arabidopsis roots under various light conditions and compared the data with the expression profiles of two aquaporin genes. (1)H-NMR imaging revealed that water content in Arabidopsis roots is lower in the light than in the dark. This diurnal variation in water content was clearly observed in the basal zone of the root. In addition, an autonomous rhythm of water dynamics was observed under continuous light (LL) and darkness (DD). However, the circadian oscillation in water dynamics was obscured in the early-flowering 3 (elf3) mutant under LL. The expression of both the aquaporin genes, AtPIP1;2 and AtPIP2;1, oscillated with the circadian rhythm under LL conditions in wild-type seedlings, but not in the elf3 mutant. These results demonstrate the advantages of our technique for monitoring water dynamics in roots of living Arabidopsis seedlings, and suggest that the circadian clock modulates water dynamics and aquaporin expression.
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Acuaporinas/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiología , Relojes Circadianos , Agua/metabolismo , Acuaporinas/genética , Arabidopsis/genética , Arabidopsis/metabolismo , Arabidopsis/efectos de la radiación , Proteínas de Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas , Luz , Espectroscopía de Resonancia Magnética , Raíces de Plantas/metabolismo , Raíces de Plantas/fisiología , ARN de Planta/genéticaRESUMEN
To investigate the ground-state double proton transfer (GSDPT) reaction, we carried out a laser spectroscopic study on the tautomeric dimer of 7-azaindole in a supersonic jet. We have recorded an infrared (IR) spectrum of the tautomeric dimer in the S(0) state. The NH band exhibits a broad and less-structured pattern. The band pattern is discussed on the basis of the hierarchical vibrational interaction mechanism. As a result, much higher density of state (DOS) at the NH stretch level is expected than that of the normal dimer. Such a high DOS should be related to the anharmonicity of the potential energy surface near the barrier of the GSDPT reaction. To get more information, an N-D deuteration effect is examined. In the present experiment, five deuterated dimers are identified by visible-visible or IR-visible population labeling spectroscopy. The IR band pattern of the NH-ND dimer is very different from that of the NH-NH dimer. Among several N-D deuteration effects, a change in a condition between the inter- or intramolecular vibrational energy flows due to the single N-D deuteration is considered to be important.
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Simulación por Computador , Indoles/química , Modelos Químicos , Protones , Teoría Cuántica , Dimerización , Fluorescencia , Espectrofotometría InfrarrojaRESUMEN
Photodissociation spectroscopy of solvated clusters of protonated tryptophan (TrpH(+)) and dipeptides containing tryptophan (Val-TrpH(+), Ala-TrpH(+), and Gly-TrpH(+)) has been carried out at low temperature to investigate the protonation and solvation effects on the electronic spectrum. For the protonated dipeptides, the S(1)-S(0) transition exhibits a substantial red shift due to the stronger interaction between the NH(3)(+) group and the indole pi ring. The S(1)-S(0) spectra of TrpH(+)(CH(3)OH)(n) clusters exhibit a drastic change with the number of methanol molecules. This behavior is interpreted in terms of the decrease in the interaction between the pi pi* and the repulsive pi sigma* states. Ala-TrpH(+) and Gly-TrpH(+) exhibit an extensive spectral change with addition of two methanol molecules. This change is ascribed to a conformational change, which is induced by the insertion of solvent molecule in between the NH(3)(+) group and the indole pi ring.
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Dipéptidos/química , Electrones , Protones , Solventes/química , Triptófano/química , Modelos Moleculares , Conformación Proteica , Espectrofotometría Ultravioleta , TemperaturaRESUMEN
In the present study, we have observed absorption, fluorescence excitation, and CP radical action spectra of the HCP molecule in the vicinity of the dissociation threshold to H((2)S) + CP(X (2)Sigma(+)). In addition, we have measured the rotational distribution of the CP radical produced from certain single rovibronic levels of the parent HCP molecule. It is found that the CP radical action spectrum starts to appear at the point where the fluorescence intensity decreases suddenly. On the basis of the precise energetic consideration between the parent and the product rovibronic energies, the dissociation energy of HCP to H((2)S) + CP(X (2)Sigma(+)) is determined to be 41 662.3 +/- 0.5 cm(-1). The energy distribution in the predissociation is found to be basically statistical; however, the prominent preferences in the rotational distributions or nonstatistical distributions are observed only when the vibronic energy of the parent level is smaller than the dissociation threshold energy. This preference is qualitatively interpreted by the inefficient energy transfer from the rotational to the vibrational degrees of freedom in the exit region of the X state potential energy surface. As a result, the dissociation proceeds along the linear H-C-P configuration, and this geometrical restriction makes nonstatistical rotational distribution of the CP radical.
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The formation and relaxation dynamics of NH4(CH3OH)m(NH3)n clusters produced by photolysis of ammonia-methanol mixed clusters has been observed by a time-resolved pump-probe method with femtosecond pulse lasers. From the detailed analysis of the time evolutions of the protonated cluster ions, NH4(+)(CH3OH)m(NH3)n, the kinetic model has been constructed, which consists of sequential three-step reaction: ultrafast hydrogen-atom transfer producing the radical pair (NH4-NH2)*, the relaxation process of radical-pair clusters, and dissociation of the solvated NH4 clusters. The initial hydrogen transfer hardly occurs between ammonia and methanol, implying the unfavorable formation of radical pair, (CH3OH2-NH2)*. The remarkable dependence of the time constants in each step on the number and composition of solvents has been explained by the following factors: hydrogen delocalization within the clusters, the internal conversion of the excited-state radical pair, and the stabilization of NH4 by solvation. The dependence of the time profiles on the probe wavelength is attributed to the different ionization efficiency of the NH4(CH3OH)m(NH3)n clusters.
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A photodissociation spectrometer, containing a spray ionization source and a temperature-variable multipole ion trap, has been constructed to examine the structure and reactivity of gas phase biological molecular ions at various temperatures. Ultraviolet (UV) and infrared (IR) photodissociation spectra of protonated alanyltryptophan (Ala-TrpH+) and tryptophanylglycine (Trp-GlyH+) have been measured. In UV spectra, the S1-S0 band origin of Ala-TrpH+ exhibits a significant red shift with respect to those of protonated tryptophan (TrpH+) and Trp-GlyH+. This red shift is ascribed to the stabilization of the excited state due to the strong interaction between the NH3+ group and indole ring. We also discuss the temperature effect on the structure and reactivity for these peptides. In addition to the UV photodissociation spectra of the dipeptides, IR spectra of the complex of Ala-TrpH+ with methanol are measured. IR photodissociation spectra of solvated ions show that Ala-TrpH+-methanol has the closed structure, which is consistent with the large spectral shift in UV spectrum of bare dipeptide.