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Peptide bond formation has drawn more and more attention due to its importance in medicinal chemistry and drug discovery. Using active esters to construct peptide bonds is an indispensable strategy in this field. We herein report a fast and efficient amination reaction to synthesize peptides from catechol diesters. Catechol monoesters are good active esters in peptide synthesis due to the anchimeric assistance effect. In previously reported work, the amination reaction was inactivated if the 2-hydroxyl group in the catechol esters was functionalized. However, we found an unusual acceleration of the amination reactivity when the 2-hydroxyl group was functionalized as an ester group. The reaction can be complete in 2–3 min in some cases. This acceleration was found through experimental studies to not result from the anchimeric assistance effect. We proposed a π*−π* interaction pathway between the two proximal ester groups. Some computational studies were made to support this assumption.

Background and objectives: Acute cholecystitis causes acute abdominal pain and may necessitate emergency surgery or intensive antibiotic therapy and percutaneous drainage, depending on the patient’s condition. The symptoms of acute cholecystitis in older patients may be atypical and difficult to diagnose, causing delayed treatment. Clarifying the risk factors for delayed diagnosis among older patients could lead to early diagnosis and treatment of acute cholecystitis. This study aimed to explore the risk factors for delayed diagnosis of acute cholecystitis among rural older patients. Material and Methods: This retrospective cohort study included patients aged over 65 years diagnosed with acute cholecystitis at a rural community hospital. The primary outcome was the time from symptom onset to acute cholecystitis diagnosis. We reviewed the electronic medical records of patients with acute cholecystitis and investigated whether they were diagnosed and treated for the condition at the time of symptom onset. Results: The average ages of the control and exposure groups were 77.71 years (standard deviation [SD] = 14.62) and 80.13 years (SD = 13.95), respectively. Additionally, 41.7% and 64.1% of the participants in the control and exposure groups, respectively, were men. The logistic regression model revealed that the serum albumin level was significantly related to a time to diagnosis > 3 days (odds ratio = 0.51; 95% confidence interval, 0.28–0.94). Conclusion: Low serum albumin levels are related to delayed diagnosis of cholecystitis and male sex. The presence of abdominal pain and a high body mass index (BMI) may be related to early cholecystitis diagnosis. Clinicians should be concerned about the delay in cholecystitis diagnosis in older female patients with poor nutritional conditions, including low serum albumin levels, a low BMI, vague symptoms, and no abdominal pain.

Since thoracic MR imaging was first used in a clinical setting, it has been suggested that MR imaging has limited clinical utility for thoracic diseases, especially lung diseases, in comparison with x-ray CT and positron emission tomography (PET)/CT. However, in many countries and states and for specific indications, MR imaging has recently become practicable. In addition, recently developed pulmonary MR imaging with ultra-short TE (UTE) and zero TE (ZTE) has enhanced the utility of MR imaging for thoracic diseases in routine clinical practice. Furthermore, MR imaging has been introduced as being capable of assessing pulmonary function. It should be borne in mind, however, that these applications have so far been academically and clinically used only for healthy volunteers, but not for patients with various pulmonary diseases in Japan or other countries. In 2020, the Fleischner Society published a new report, which provides consensus expert opinions regarding appropriate clinical indications of pulmonary MR imaging for not only oncologic but also pulmonary diseases. This review article presents a brief history of MR imaging for thoracic diseases regarding its technical aspects and major clinical indications in Japan 1) in terms of what is currently available, 2) promising but requiring further validation or evaluation, and 3) developments warranting research investigations in preclinical or patient studies. State-of-the-art MR imaging can non-invasively visualize lung structural and functional abnormalities without ionizing radiation and thus provide an alternative to CT. MR imaging is considered as a tool for providing unique information. Moreover, prospective, randomized, and multi-center trials should be conducted to directly compare MR imaging with conventional methods to determine whether the former has equal or superior clinical relevance. The results of these trials together with continued improvements are expected to update or modify recommendations for the use of MRI in near future3 [ABSTRACT FROM AUTHOR]

Omnidirectional photoluminescence (ODPL) measurement using an integrating sphere was carried out to absolutely quantify the quantum efficiency of radiation (η) in high quality GaN single crystals. The total numbers of photons belonging to photoluminescence (PL photons) and photons belonging to an excitation source (excitation photons) were simultaneously counted in the measurement, and η was defined as a ratio of the number of PL photons to the number of absorbed excitation photons. The ODPL spectra near the band edge commonly showed a two-peak structure, which originates from the sharp absorption edge of GaN. A methodology for quantifying internal quantum efficiency (ηint) from such experimentally obtained η is derived. A record high ηint of typically 15% is obtained for a freestanding GaN crystal grown by hydride vapor phase epitaxy on a GaN seed crystal synthesized by the ammonothermal method using an acidic mineralizer, when the excitation photon energy and power density were 3.81 eV and 60 W/cm2, respectively. [ABSTRACT FROM AUTHOR]

The conformational properties of N-acyl azoles (imidazole, pyrazole, and triazole) were examined. The N-2',4',6'-trichlorobenzoyl azoles were stable in methanol at room temperature, and no hydrolyzed products were observed over 7 days in the presence of 5% trifluoroacetic acid or 5% triethylamine in CDCl3. The high stability may be explained by the double-bond amide character caused by the steric hindrance due to the ortho-substituents in the benzoyl group. While specific E-amide preferences were observed in N-acyl pyrazoles/triazoles, the amides of the imidazoles gave a mixture of E and Z. One of the conceivable ideas to rationalize this conformational preference may be repulsive interaction between two sets of lone-pair electrons on the pyrazole 2-nitrogen (nN) and the carbonyl oxygen atoms (nO) in the Z-conformation of N-acyl pyrazoles/triazoles. However, analysis of orbital interactions suggested that in the case of the E-conformation of N-acyl pyrazoles, such electron repulsion is small because of distance. The interbond energy calculations suggested that the Z-conformer is involved in strong vicinal σ-σ repulsion along the amide linkage between the σN1N2 and σC1C2 orbitals in the anti-periplanar arrangement and between the σN1C5 and σC1C2 orbitals in the syn-periplanar arrangement, which lead to the overwhelming E-preference in N-acyl pyrazoles/triazoles. In the case of N-acyl imidazoles, similar vicinal σ-σ repulsions were counterbalanced, leading to a weak preference for the E-conformer over the Z-conformer. The chemically stable and E-preferring N-acyl azoles may be utilized as scaffolds in future drug design. [ABSTRACT FROM AUTHOR]

For rating unambiguous performance of a light-emitting semiconductor material, determination of the absolute quantum efficiency (AQE) of radiation, which is basically a product of internal quantum efficiency (IQE) and light-extraction efficiency, is the most delightful way. Here, we propose the use of omnidirectional photoluminescence (ODPL) spectroscopy for quantifying AQE of the near-band-edge (NBE) emission, in order to evaluate bulk GaN crystals and wafers. When the measurement was carried out in the air, the AQE showed a continuous decrease most likely due to the formation of extrinsic nonradiative recombination channels at the surface by photo-pumping. However, such an influence was suppressed by measuring ODPL in an inert ambient such as nitrogen or in vacuum. Consequently, AQE was revealed to depend on the photo-pumping density. The increase in AQE of the NBE emission caused by the increase in the excess carrier concentration was significant, indicating gradual saturation of nonradiative recombination centers in the bulk of GaN. The highest AQE value (8.22%) ever reported for the NBE emission of GaN at room temperature, which corresponds to IQE of 70.9%, was eventually obtained from the GaN wafer grown by hydride vapor phase epitaxy on a GaN seed crystal manufactured by the acidic ammonothermal method, when the cw photo-pumping density was 66 W/cm2. [ABSTRACT FROM AUTHOR]

The effect of the thermal annealing on an acidic ammonothermal gallium nitride (GaN) crystal grown toward the c- and m-directions was investigated. The specific annihilation of hydrogenated Ga vacancies was confirmed for the GaN crystal grown toward the m-direction but not for that grown toward the c-direction. A transparent and yellow luminescence-free ammonothermal GaN substrate was realized. The annihilation of the hydrogenated Ga vacancies was explained by the difference in the diffusion of F incorporated as a mineralizer between the c- and m-directions. [ABSTRACT FROM AUTHOR]

An evident issue in performing GaN growth along the c-direction is the generation of V-shaped pits on its surface. Here, we investigated the transition of the angle of facets forming a V-shaped pit via three-photon excitation photoluminescence (3PPL). The intermittent doping of Ge was introduced to GaN growth to observe the growth front. The size of the V-shaped pit composed of {} facets decreased along the growth direction, whereas that composed of {} facets, increased. Furthermore, planar growths of c-GaN and semipolar GaN having various surface orientations revealed that the V-shaped pit composed of {} was likely to annihilate rather than that of {} under the growth condition of N2 carrier gas, which coincides with the result of 3PPL. [ABSTRACT FROM AUTHOR]

Fundamental electronic and optical properties of a low-resistivity m-plane GaN single crystal, which was grown by hydride vapor phase epitaxy on a bulk GaN seed crystal synthesized by the ammonothermal method in supercritical ammonia using an acidic mineralizer, were investigated. The threading dislocation and basal-plane staking-fault densities of the crystal were around 104 cm−2 and less than 100 cm−1, respectively. Oxygen doping achieved a high electron concentration of 4 × 1018 cm−3 at room temperature. Accordingly, a photoluminescence (PL) band originating from the recombination of hot carriers was observed at low temperatures, even under weak excitation conditions. The simultaneous realization of low-level incorporation of Ga vacancies (VGa) less than 1016 cm−3 was confirmed by using the positron annihilation technique. Consistent with our long-standing claim that VGa complexes are the major nonradiative recombination centers in GaN, the fast-component PL lifetime of the near-band-edge emission at room temperature longer than 2 ns was achieved. [ABSTRACT FROM AUTHOR]

Dispersion relationships of the refractive index and extinction coefficient of m-plane Al1−xInxN epitaxial films (x = 0.00, 0.23, and 0.30) grown on a freestanding m-plane GaN substrate were determined by spectroscopic ellipsometry measurement. The experimentally obtained ellipsometric parameters tan Ψ and cos Δ, which represent the differences in the p- and s-polarized amplitudes and phases of the incident light, respectively, were well fitted using the standard analytical functions. As the measurement was carried out at photon energies between 1.55 and 5.40 eV, the dispersion curves of the extinction coefficient k exhibited local maxima at approximately the Al1−xInxN bandgap energies of x = 0.23 and 0.30, and the sample with x = 0.00 showed an ordinal absorption spectrum with a bandtail formed owing to high-concentration residual impurities. A large and x-dependent energy difference between the absorption and emission spectra (Stokes’ shift) was observed for the Al1−xInxN films, suggesting the presence of carrier localization phenomena. [ABSTRACT FROM AUTHOR]

In this paper, we discusse the origin of basal-plane stacking faults (BSFs) generated in the homoepitaxial hydride vapor phase epitaxy (HVPE) growth of m-plane gallium nitride (GaN). We investigated the effects of seed quality, especially dislocation density, on BSF generation during homoepitaxy. The results clearly identify basal-plane dislocation in the seed as a cause of BSF generation. We realized high-quality m-plane GaN substrates with a 2-in. diameter using HVPE on low-dislocation-density m-plane seeds. [ABSTRACT FROM AUTHOR]

An m-plane freestanding GaN substrate satisfying both low resistivity (ρ = 8.5 × 10−3 Ω·cm) and a low point-defect concentration, being applicable to vertically conducting power-switching devices, was grown by hydride vapor phase epitaxy on a nearly bowing-free bulk GaN seed wafer synthesized by the ammonothermal method in supercritical ammonia using an acidic mineralizer. Its threading dislocation and basal-plane staking-fault densities were approximately 104 cm−2 and lower than 100 cm−1, respectively. A record-long fast-component photoluminescence lifetime of 2.07 ns at room temperature was obtained for the near-band-edge emission, reflecting a significantly low concentration of nonradiative recombination centers composed of Ga vacancies. [ABSTRACT FROM AUTHOR]

Local excitation and emission dynamics of an isolated “Type-I1” basal-plane stacking-fault (BSF) in very low dislocation density GaN were studied using spatio-time-resolved cathodoluminescence. The low temperature lifetime of the BSF emission was quantified to be 640 ps. The carrier diffusion length was estimated by observing the temporal delay of the BSF peak relative to the free-exciton signal as a function of distance from the BSF. The results indicate that the near-band-edge emission leads to subsequent optical excitation of the BSF that increases the apparent diffusion length. Limiting the observation volume can improve the spatial resolution. [ABSTRACT FROM AUTHOR]