Dealuminated Hβ zeolite for selective conversion of fructose to furfural and formic acid

The fructose-to-furfural transformation is facing major challenges in the selectivity and high efficiency. Herein, we have developed a simple and effective approach for the selective conversion of fructose to furfural using Hβ zeolite modified by organic acids for dealuminization to regulate its textural and acidic properties. It was found that citric acid-dealuminized Hβ zeolite possessed high specific surface areas, wide channels and high Brønsted acid amount, which facilitated the selective conversion of fructose to furfural with a maximum yield of 76.2% at433 K for 1 h in the γ-butyrolactone(GBL)-H_(2)O system, as well as the concomitant formation of 83.0% formic acid. The^(13)C-isotope labelling experiments and the mechanism revealed that the selective cleavage of C1–C2 or C5–C6 bond on fructose was firstly occurred to form pentose or C5 intermediate by weak Brønsted acid, which was then dehydrated to furfural by strong Brønsted acid. Also this dealuminized Hβ catalyst showed the great recycling performance and was active for the conversion of glucose and mannose.

用于精准蛋白降解和癌症治疗的刺激响应型PROTAC进展

刺激响应型蛋白质降解靶向嵌合体(PROTAC)前药可在特定刺激条件下激活PROTAC分子,实现特定区域和细胞的靶蛋白降解,从而克服不可控蛋白降解导致的毒副作用,是改善PROTAC疗效和成药性的有效策略.本文系统总结了目前用于特异性降解病灶组织目标蛋白从而精准治疗肿瘤的各种刺激响应型PROTAC前药策略.首先,本文介绍了PROTAC的发展历程和作用原理,以及目前进入临床试验阶段的PROTAC分子;然后,介绍了细胞内原位生成PROTAC的前药策略,以及各种刺激手段激活的PROTAC前药,包括外源性的光、X-射线以及内源性的肿瘤微环境的乏氧、活性氧和酶等;接着,概括了配体修饰型的主动靶向PROTAC前药,包括抗体、叶酸、适配体等修饰策略.本文重点强调了基于纳米递药系统的PROTAC前药策略,其可实现特异性肿瘤组织药物递送和精准蛋白降解.最后,本文对PROTAC的未来发展进行了探讨和展望.

URBAN TRANSIT ASSIGNMENT MODEL BASED ON AUGMENTED NETWORK WITH IN-VEHICLE CONGESTION AND TRANSFER CONGESTION

This paper presents an augmented network model to represent urban transit system.Through such network model,the urban transit assignment problem can be easily modeled like a generalized traffic network.Simultaneously,the feasible route in such augmented transit network is then defined in accordance with the passengers＇ behaviors.The passengers＇ travel costs including walking time,waiting time,in-vehicle time and transfer time are formulated while the congestions at stations and the congestions in transit vehicles are all taken into account.On the base of these,an equilibrium model for urban transit assignment problem is presented and an improved shortest path method based algorithm is also proposed to solve it.Finally,a numerical example is provided to illustrate our approach.

MODELING THE CONGESTION COST AND VEHICLE EMISSION WITHIN MULTIMODAL TRAFFIC NETWORK UNDER THE CONDITION OF EQUILIBRIUM

Traditional system optimization models for traffic network focus on the treatment of congestion, which usually have an objective of minimizing the total travel time. However, the negative externality of congestion, such as environment pollution, is neglected in most cases. Such models fall short in taking Greenhouse Gas （GHG） emissions and its impact on climate change into consideration. In this paper, a social-cost based system optimization （SO） model is proposed for the multimodal traffic network considering both traffic congestion and corresponding vehicle emission. Firstly, a variation inequality model is developed to formulate the equilibrium problem for such network based on the analysis of travelers＇ combined choices. Secondly, the computational models of traffic congestion and vehicle emission of whole multimodal network are proposed based on the equilibrium link-flows and the corresponding travel times. A bi-level programming model, in which the social-cost based SO model is treated as the upper-level problem and the combined equilibrium model is processed as the lower-level problem, is then presented with its solution algorithm. Finally, the proposed models are illustrated through a simple numerical example. The study results confirm and support the idea of giving the priority to the development of urban public transport, which is an effective way to achieve a sustainable urban transportation.

The nucleation and growth of borophene on the Ag(111)surface

B sheets have been intently studied, and various candidates with vacancies have been reported in theoretical investigations, including their possible growth on metal surfaces. However, a recent experiment reported that the borophene formed on a Ag (111) surface consisted of a buckled triangular lattice without vacancies. Our calculations propose a novel nucleation mechanism of B clusters and emphasize the B–Ag interaction in the growth process of borophene, demonstrating the structural evolution of triangular fragments with various profiles and vacancy distributions. Compared with the triangular lattice without vacancies, we have confirmed that the sheet energetically favored during the nucleation and growth is that containing 1/6 vacancies in a stripe pattern, whose scanning tunneling microscopy image is in better agreement with the experimental observation. [Figure not available: see fulltext.] © 2015, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.