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991.
Fujitani H Tanida Y Ito M Jayachandran G Snow CD Shirts MR Sorin EJ Pande VS 《The Journal of chemical physics》2005,123(8):084108
Direct calculations of the absolute free energies of binding for eight ligands to FKBP protein were performed using the Fujitsu BioServer massively parallel computer. Using the latest version of the general assisted model building with energy refinement (AMBER) force field for ligand model parameters and the Bennett acceptance ratio for computing free-energy differences, we obtained an excellent linear fit between the calculated and experimental binding free energies. The rms error from a linear fit is 0.4 kcal/mol for eight ligand complexes. In comparison with a previous study of the binding energies of these same eight ligand complexes, these results suggest that the use of improved model parameters can lead to more predictive binding estimates, and that these estimates can be obtained with significantly less computer time than previously thought. These findings make such direct methods more attractive for use in rational drug design. 相似文献
992.
Dr. Hiroshi Ito Prof. Hiroshi Tsukube Prof. Satoshi Shinoda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(10):3330-3339
A series of quadruple‐stranded Na+ and Ca2+ complexes with octadentate cyclen ligands was synthesized to produce complexes that contained four different side‐arm combinations (one triazole? coumarin group and three pyridine groups ( 1 ), four pyridine groups ( 2 ), one triazole? coumarin group and three quinoline groups ( 3 ), and four quinoline groups ( 4 )). X‐ray crystallographic analysis revealed that no significant changes occurred in the stereostructure of these complexes upon replacing one pyridine group with a triazole? coumarin moiety, or by replacing Na+ ions with Ca2+ ions, although the coordination number of the complexes in the solid state decreased when pyridine groups were replaced by quinoline groups. In solution, all of the side arms were arranged in a propeller‐like pattern to yield an enantiomer pair of Δ and Λ forms in each metal complex. The addition of a tert‐butoxycarbonyl (Boc)‐protected amino acid anion, that is, a coordinative chiral carboxylate anion, to the cyclen? Ca2+ complex induced circular dichroism (CD) signals in the aromatic region by forming a 1:1 mixture of diastereomeric ternary complexes with opposite complex chirality, whilst the corresponding Na+ complexes rarely showed any response. In complexes 1 ‐Ca2+ and 3 ‐Ca2+, this chirality‐transfer process was efficiently followed by considering the induction of the CD signals at two different wavelengths, that is, the coumarin‐chromophore region and the aza‐aromatic region. The sign and intensity of the CD signal were significantly dependent on both the nature of the aza‐aromatic moiety and the enantiomeric purity of the external anion. These Ca2+ complexes worked as effective probes for the determination of the enantiomeric excess of the chiral anion. The cyclen? Ca2+ complexes also interacted with the non‐coordinative Δ‐TRISPHAT anion through an ion‐pairing mechanism to achieve chirality transfer from the anion to the metal complex; both complexes 1 ‐Ca2+ and 3 ‐Ca2+ clearly showed induced CD signals in the coumarin‐chromophore region, owing to ion‐paring interactions with the Δ‐TRISPHAT anion. Thus, the proper combination of an octadentate cyclen ligand and a metal center demonstrated effective chirality transfer. 相似文献
993.
Bacterial quorum-sensing regulatory systems can be summarized in a simple model wherein an autoinducer molecule accumulates
in cultures and stimulates regulatory changes in gene expression upon reaching a critical threshold concentration. Although
quorum sensing was originally thought to be an isolated phenomenon governing the regulation of a handful of processes in only
a few bacteria, it is now considered to be a widespread mechanism for coordinating bacterial gene expression. Over decades
of research, investigations of autoinducer-mediated regulation have revealed that these systems are far more complicated than
originally appreciated, and such discoveries have accelerated recently with the application of molecular and genomic tools.
The focus of this review is to highlight recent advances describing complexities that go beyond the simple model of quorum
sensing. These complexities include the regulation of autoinducer production and degradation, the presence of multiple quorum-sensing
systems in individual bacteria that regulate diverse genes, often in coordination with other regulatory elements, and the
influence of interorganismal interactions on quorum sensing. 相似文献
994.
Hirota Masahiro Higaki Shogo Ito Shigeki Ishida Yoshiyuki Terao Keiji 《Journal of Radioanalytical and Nuclear Chemistry》2021,328(2):659-667
Journal of Radioanalytical and Nuclear Chemistry - Effect of 2-hydroxypropyl α-cyclodextrin (α-HPCD) on the iodine adsorption onto activated carbon (AC) was investigated. The iodine... 相似文献
995.
Liquid‐Crystalline Biomacromolecular Templates for the Formation of Oriented Thin‐Film Hybrids Composed of Ordered Chitin and Alkaline‐Earth Carbonate
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Dr. Tatsuya Nishimura Ken Toyoda Takahiro Ito Dr. Yuya Oaki Yukiko Namatame Prof. Takashi Kato 《化学:亚洲杂志》2015,10(11):2356-2360
Macroscopically ordered inorganic thin films have been formed on unidirectionally oriented, liquid‐crystalline chitin matrices. In the presence of poly(acrylic acid) (PAA), unidirectionally oriented chitin films act as templates for the formation of oriented thin‐film crystals of alkaline‐earth carbonates such as SrCO3 and BaCO3. The morphology and orientation of crystals are dependent on the metal ion concentration. For SrCO3 crystallization, unidirectional thin films and hexagonal‐shaped thin films have been deposited from 200 and 25 mm concentration strontium solutions, respectively. 相似文献
996.
Yohei Takahashi Masatoshi Endo Kazuaki Ito 《Journal of inclusion phenomena and macrocyclic chemistry》2014,79(1-2):237-245
The synthesis, characterization and binding studies with anions for biaryl-based anion receptors bearing thiourea groups have been described. The results revealed that receptors (1 and 2) showed good selectivity and binding affinity for F?, and among them binaphthyl-based receptor (1a) showed the best binding affinity for F? in comparison to other tested anions (Cl?, Br?, I?, $ {\text{NO}}_{3}^{ - } ,\;{\text{HSO}}_{4}^{ - } , $ AcO? and $ {\text{H}}_{2} {\text{PO}}_{4}^{ - } $ ). This is probably due to the fact that the moderate rigidity of binaphthyl skeleton in 1a is able to provide the better geometry of two thiourea groups for incorporating F? into the binding pocket. The higher basicity of F? also participated in this selectivity. 相似文献
997.
Regioselective Dichlorination of a Non‐Activated Aliphatic Carbon Atom and Phenolic Bismethylation by a Multifunctional Fungal Flavoenzyme
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Pranatchareeya Chankhamjon Dr. Yuta Tsunematsu Dr. Mie Ishida‐Ito Yuzuka Sasa Florian Meyer Dr. Daniela Boettger‐Schmidt Barbara Urbansky Klaus‐Dieter Menzel Dr. Kirstin Scherlach Prof. Dr. Kenji Watanabe Prof. Dr. Christian Hertweck 《Angewandte Chemie (International ed. in English)》2016,55(39):11955-11959
The regioselective functionalization of non‐activated carbon atoms such as aliphatic halogenation is a major synthetic challenge. A novel multifunctional enzyme catalyzing the geminal dichlorination of a methyl group was discovered in Aspergillus oryzae (Koji mold), an important fungus that is widely used for Asian food fermentation. A biosynthetic pathway encoded on two different chromosomes yields mono‐ and dichlorinated polyketides (diaporthin derivatives), including the cytotoxic dichlorodiaporthin as the main product. Bioinformatic analyses and functional genetics revealed an unprecedented hybrid enzyme (AoiQ) with two functional domains, one for halogenation and one for O‐methylation. AoiQ was successfully reconstituted in vivo and in vitro, unequivocally showing that this FADH2‐dependent enzyme is uniquely capable of the stepwise gem‐dichlorination of a non‐activated carbon atom on a freestanding substrate. Genome mining indicated that related hybrid enzymes are encoded in cryptic gene clusters in numerous ecologically relevant fungi. 相似文献
998.
Photosensitizing Electron Transfer Processes of Fullerenes,Carbon Nanotubes,and Carbon Nanohorns
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Osamu Ito 《Chemical record (New York, N.Y.)》2017,17(3):326-362
In this account, studies on the photosensitizing electron transfer of nanocarbons, such as fullerenes, single‐walled carbon nanotubes (SWCNTs), and carbon nanohorns (CNH), performed in our laboratory for about 15 years in the early 21st century have been briefly reviewed. These novel nanocarbons act as excellent electron acceptors, when they are linked to light‐absorbing electron donors, such as porphyrins or phthalocyanines. For such molecule–nanocarbon hybrids, the direct confirmation of fast, transient, electron‐transfer phenomena must be performed with time‐resolved spectroscopic methods, such as transient absorption spectral measurements, in addition to fluorescence time‐profile measurements in the wide‐wavelength regions. Careful use of these methods affords useful information to understand photoinduced electron‐transfer mechanisms. In addition, kinetic data obtained by these methods can assist in the construction of light‐active devices, such as photovoltaic cells and solar H2‐generation systems. 相似文献
999.
RNA-mediated gene regulation and expression are critically dependent on both nucleic acid architecture and recognition. We present a novel mechanism for the regulation of gene expression through direct RNA-RNA interactions between small RNA and mRNA in human cells. Using mRNA reporters containing G-rich sequences in the 5'-untranslated region (5'-UTR), in the coding region, or both, we showed that G-rich small RNAs bind to the reporter mRNAs and form an intermolecular RNA G-quadruplex that can inhibit gene translation in living cells. Using a combination of circular dichroism (CD) and RNase footprinting in vitro, we found that the intermolecular G-quadruplexes show a parallel G-quadruplex structure. We next investigated whether the intermolecular G-quadruplex is present in living cells. Employing the fluorophore-labeled probes, we found that two G-rich RNA molecules form an intermolecular G-quadruplex structure in living cells. These results extend the concept of small RNA-mediated expression and suggest an important role for such RNA structures in the inhibition of mRNA translation. 相似文献
1000.
Using the general connection between the upper limit on the neutrino mass and the upper limits on certain types of non-standard-model interactions that can generate loop corrections to the neutrino mass, we derive constraints on some non-standard-model d --> ue- nu interactions. When cast into limits on n --> pe- nu coupling constants, our results yield constraints on scalar and tensor weak interactions improved by more than an order of magnitude over the current experimental limits. When combined with the existing limits, our results yield absolute value(C(S)/C(V)) approximately < 5 x 10(-3), absolute value(C'(S)/C(V)) approximately < 5 x 10(-3), absolute value(C(T)/C(A)) approximately < 1.2 x 10(-2), and absolute value(C'(T)/C(A)) approximately < 1.2 x 10(-2). 相似文献