Spatial Heterogeneity of b Values in Northeastern Tibetan Plateau and Its Interpretation.

The northeastern margin of the Tibetan Plateau (NE Tibetan Plateau) exhibits active geological structures and has experienced multiple strong earthquakes, with M ≥ 7, throughout history. Particularly noteworthy is the 1920 M81/2 earthquake in the Haiyuan region that occurred a century ago and is documented as one of the deadliest earthquakes. Consequently, analyzing seismic risks in the northeastern margin of the Tibetan Plateau holds significant importance. The b value, a crucial parameter for seismic activity, plays a pivotal role in seismic hazard analyses. This study calculates the spatial b values in this region based on earthquake catalogs since 1970. The study area encompasses several major active faults, and due to variations in b values across different fault types, traditional grid-search methods may introduce significant errors in calculating the spatial b value within complex fault systems. To address this, we employed the hierarchical space-time point-process (HIST-PPM) method proposed by Ogata. This method avoids partitioning earthquake samples, optimizes parameters using Akaike's Bayesian Information Criterion (ABIC) with entropy maximization, and theoretically allows for a higher spatial resolution and more accurate b value calculations. The results indicate a high spatial heterogeneity in b values within the study area. The northwestern and southeastern regions exhibit higher b values. Along the Haiyuan fault zone, the central rupture zone of the Haiyuan earthquake has relatively higher b values than other regions of this fault zone, which is possibly related to the sufficient release of stress during the main rupture of the Haiyuan earthquake. The b values vary from high in the west to low in the east along the Zhongwei fault. On the West Qinling fault zone, the epicenter of the recent Minxian-Zhangxian earthquake is associated with a low b value. In general, regions with low b values correspond well to areas with moderate-strong seismic events in the past 50 years. The spatial differences in b values may reflect variances in seismic hazards among fault zones and regions within the same fault zone.

Transport and interaction of cadmium and active sludge extracellular polymeric substances in saturated sand influenced by ionic strength and composition.

Artificial groundwater recharge with reclaimed water (secondary effluent from wastewater treatment plants) has become an important approach to solving water scarcity worldwide. Microorganisms in activated sludge can secrete many extracellular polymeric substances (EPS). However, information on the impact of EPS on the movement of heavy metals in porous media and their environmental effects on underground networks is limited. To assess this risk, we extracted EPS from the aerobic section of a wastewater treatment plant using hot sodium hydroxide and conducted experiments using one-dimensional sand columns to investigate how ion composition and strength affect the movement and interaction of cadmium (Cd) and EPS in porous media. The results showed that EPS facilitated Cd migration in porous media. Sodium (Na) and calcium (Ca) ions promoted the migration of Cd in porous media and EPS-Cd complexation. The effect of Ca was more significant than that of Na. As the Na adsorption ratio increased, the migration ability of Cd in porous media and the complexation ability of EPS with Cd decreased. Therefore, when estimating the migration of EPS and Cd in subsurface environments, careful consideration should be given to prevent the risk of groundwater pollution.

Research progress on the potential novel analgesic BU08028.

Pain is a common symptom accompanying several clinical conditions and causes serious distress to patients. Addressing pain management is an important aspect of disease treatment, including cancer therapy. Opioid analgesics used to manage pain in human and veterinary medicine have been associated with substance dependence and other adverse effects, thereby limiting their application. Thus, the development of opioid analgesics with good safety profiles with minimal adverse effects and no addictive effects, is presently the focus of pain research. As a new potential analgesic, (2S)-2-[(5R,6R,7R,14S)-N-cyclopropylmethyl-4,5-epoxy-6,14-ethano-3-hydroxy-6-methoxymorphinan-7-yl]-3,3-dimethylpentan-2-ol (BU08028) has fewer adverse effects than other analgesics and is expected to be a safer alternative. In this review, we discuss the development of the opioid analog BU08028 and summarize its analgesic effects and biological characteristics, including efficiency, safety, and tolerance. Furthermore, we elaborate on studies showing the bifunctional effect of BU08028, which targets both mu opioid peptide and nociceptin-orphanin FQ peptide receptors, as well as the unique advantages of using BU08028 over single-target opioid agonists. Previous studies have suggested that BU08028 can not only weaken the reward and abuse effects of opioids and other drugs, but also enhance the anti-nociceptive effect of the mu opioid peptide receptors, making it a potent analgesic. Besides, we describe studies suggesting that BU08028 inhibits the effects of alcohol, making it a candidate drug for the management of alcohol addiction. Our review suggests that BU08028 is a potential novel medicine for managing pain and addiction.

Mechanism, Regio-, and Diastereoselectivity of Rh(III)-Catalyzed Cyclization Reactions of N-Arylnitrones with Alkynes: A Density Functional Theory Study.

Nitrones have been used for rhodium-catalyzed cyclization C-H bond activation and O atom transfer of arylnitrones with alkynes by Chang et al. ( J. Am. Chem. Soc. 2015 , 137 , 4908 - 4911 ). Density functional theory method has been used to study the mechanism, regio-, and diastereoselectivity of type reactions. The results elucidated that the reaction pathway for Rh(III)-catalyzed cyclization of N-arylnitrones with alkyne contains a C-H bond activation, an alkyne insertion into Rh-C bond, a reductive elimination to form a Rh(I) complex, an oxidative addition leading to N-O cleavage, an imine insertion into the Rh-C bond, and the final protonolysis to regenerate the products and the active catalyst. The regioselectivity of this reaction with asymmetric alkyne is controlled by the electronic effect in alkyne insertion type instead of steric effects. The distortion-interaction analysis is also used to explain the regioselectivity. The diastereoselectivity is controlled by the imine insertion step. In this step, the sterically less hindered transition state is favored, leading to stereoselective product formation.

N,N-Dimethyl-N,N-diphenyl-pyrimidine-4,5,6-triamine.

In the title compound, C(18)H(19)N(5), the pyrimidine ring makes dihedral angles of 56.49 (9) and 70.88 (9)° with the phenyl rings. The dihedral angle between the two phenyl rings is 72.45 (9)°. No significant inter-molecular inter-actions are observed in the crystal structure.

N,N-Dimethyl-5-nitro-N,N-diphenyl-pyrimidine-4,6-diamine.

In the title compound, C(18)H(17)N(5)O(2), the pyrimidine ring makes dihedral angles of 66.09 (12), 71.39 (13) and 56.7 (3)° with two phenyl rings and the nitro group, respectively. The dihedral angle between the two phenyl rings is 44.05 (14)°.

6-Chloro-N-methyl-N-phenyl-pyrimidine-4,5-diamine.

In the title compound, C(11)H(11)ClN(4), the dihedral angle between the aromatic rings is 66.47 (8)°. In the crystal, mol-ecules are linked by N-H⋯N hydrogen bonds, generating C(5) chains propagating in [010]. Slipped aromatic π-π stacking between centrosymmetrically related pairs of pyrim-idine rings also occurs [centroid-centroid separation = 3.7634 (12)Å and slippage = 1.715 Å].

6-Chloro-N-methyl-5-nitro-N-phenyl-pyrimidin-4-amine.

In the title compound, C(11)H(9)ClN(4)O(2), the dihedral angle between the aromatic rings is 79.67 (8)°. π-π stacking between centrosymmetrically related pairs of pyrimidine rings occurs along [100] [centroid-centroid separations = 3.4572 (8) and 3.5433 (7) Å].

Density functional theory study on the mechanism of Rh-catalyzed decarboxylative conjugate addition: diffusion- and ligand-controlled selectivity toward hydrolysis or ß-hydride elimination.

The mechanism of Rh-catalyzed decarboxylative conjugate addition has been investigated with Density Functional Theory (DFT). Calculations indicate that the selectivity toward hydrolysis or ß-hydride elimination of the investigated reaction is a compromise between diffusion control and kinetic control. Ligand control can be adjusted by modifying the intermolecular interaction between the Rh(I) enolate intermediate and water.

(11-Methyl-pyrido[2,3-b][1,4]benzo-diazepin-6-yl)(phen-yl)methanone.

In the title compound, C(20)H(15)N(3)O, the diazepine ring adopts a boat conformation. The dihedral angle between pyridine and benzene rings is 55.2 (1)°. The benzoyl phenyl ring forms dihedral angles of 49.4 (1) and 75.9 (1)°, respectively, with the pyridine and benzene rings. In the crystal, mol-ecules are linked into centrosymmetric dimers by pairs of C-H⋯N hydrogen bonds.

N-heterocyclic carbene-catalyzed cross-coupling of aldehydes with arylsulfonyl indoles.

3-(1-Arylsulfonylalkyl)indoles as electrophiles in the N-heterocyclic carbene-catalyzed umpolung reaction of aldehydes were realized for the first time. This intermolecular Stetter-type reaction features the commercially available catalyst and mild reaction conditions, providing alpha-(3-indolyl) ketone derivatives in high yields for a wide range of substrates.

Origins of enantioselectivity in the chiral Brønsted acid catalyzed hydrophosphonylation of imines.

The results of an experimental and ONIOM-based computational investigation of the mechanism and the origins of enantioselectivity in the asymmetric synthesis of alpha-amino phosphonates by an enantioselective hydrophosphonylation of imines catalyzed by chiral Brønsted acids are reported. It was found that the enantioselectivity observed in the enantioselective hydrophosphonylation of the imine with a benzothiazole moiety was poor. A detailed computational study with a two-layer ONIOM (B3LYP/6-31G(d)/AM1) method on the mechanism of the investigated reaction was carried out to explore the origins of the enantioselectivity. Calculations indicate that the investigated reaction is a two-step process involving proton-transfer and nucleophilic addition, which is the stereo-controlling step. The investigated reaction prefers a di-coordination pathway to a mono-coordination pathway. The different enantioselectivities exhibited by three kinds of catalyst and two kinds of nucleophile were rationalized. Calculations indicate that si-facial attack is higher in energy than re-facial attack by only 0.1 kcal/mol, which accounts well for the low ee value observed in the enantioselective hydrophosphonylation of the imine with a benzothiazole moiety. The energy barrier for phosphonate-phosphite tautomerism catalyzed by chiral Brønsted acid in toluene is only 1.8 kcal/mol, which could explain why the investigated reaction can take place at room temperature.

DFT study of the mechanisms of in water Au(I)-catalyzed tandem [3,3]-rearrangement/Nazarov reaction/[1,2]-hydrogen shift of enynyl acetates: a proton-transport catalysis strategy in the water-catalyzed [1,2]-hydrogen shift.

A computational study with the Becke3LYP density functional was carried out to elucidate the mechanisms of Au(I)-catalyzed reactions of enynyl acetates involving tandem [3,3]-rearrangement, Nazarov reaction, and [1,2]-hydrogen shift. Calculations indicate that the [3,3]-rearrangement is a two-step process with activation free energies below 10 kcal/mol for both steps. The following Nazarov-type 4pi electrocyclic ring-closure reaction of a Au-containing dienyl cation is also easy with an activation free energy of 3.2 kcal/mol in CH2Cl2. The final step in the catalytic cycle is a [1,2]-hydride shift, and this step is the rate-limiting step (with a computed activation free energy of 20.2 kcal/mol) when dry CH2Cl2 is used as the solvent. When this tandem reaction was conducted in wet CH2Cl2, the [1,2]-hydride shift step in dry solution turned to a very efficient water-catalyzed [1,2]-hydrogen shift mechanism with an activation free energy of 16.4 kcal/mol. Because of this, the tandem reaction of enynyl acetates was found to be faster in wet CH2Cl2 as compared to the reaction in dry CH2Cl2. Calculations show that a water-catalyzed [1,2]-hydrogen shift adopts a proton-transport catalysis strategy, in which the acetoxy group in the substrate is critical because it acts as either a proton acceptor when one water molecule is involved in catalysis or a proton-relay stabilizer when a water cluster is involved in catalysis. Water is found to act as a proton shuttle in the proton-transport catalysis strategy. Theoretical discovery of the role of the acetoxy group in the water-catalyzed [1,2]-hydrogen shift process suggests that a transition metal-catalyzed reaction involving a similar hydrogen shift step can be accelerated in water or on water with only a marginal effect, unless a proton-accepting group such as an acetoxy group, which can form a hydrogen bond network with water, is present around this reaction's active site.

An efficient and regiospecific strategy to N7-substituted purines and its application to a library of trisubstituted purines.

A regiospecific strategy for the preparation of N(7)-substituted purines in an efficient manner was devised. This approach to 6,7,8-trisubstituted purines relies on the cyclization reactions of suitably substituted pyrimidines (1) with either a carboxylic acid or an aldehyde. The method development for the five-step synthetic strategy outlined here was completed using 5-amino-4,6-dichloropyrimidine (4) as the starting material. The utility of this methodology was demonstrated through the preparation of a 40-membered library of 6,7,8-trisubstituted purines (3) in good yields and high purity.