NobleBlocks

Jilin Medical University

UniversityJilin City, China

Research output, citation impact, and the most-cited recent papers from Jilin Medical University (China). Aggregated across the NobleBlocks index of 300M+ scholarly works.

Total works
28.4K
Citations
1.2M
h-index
263
i10-index
24.6K
Also known as
Jilin Medical University吉林医药学院

Top-cited papers from Jilin Medical University

Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)
Daniel J. Klionsky, Kotb Abdelmohsen, Akihisa Abe, Md. Joynal Abedin +4 more
2016· Autophagy6.0Kdoi:10.1080/15548627.2015.1100356

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. For example, a key point that needs to be emphasized is thatthere is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure flux through the autophagy pathway (i.e., the completeprocess including the amount and rate of cargo sequestered and degraded). In particular, a block in macroautophagy that results in autophagosome accumulation must be differentiated from stimuli that increase autophagic activity, defined as increasedautophagy induction coupled with increased delivery to, and degradation within, lysosomes (inmost higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in manycases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. It is worth emphasizing here that lysosomal digestion is a stage of autophagy and evaluating its competence is a crucial part of the evaluation of autophagic flux, or complete autophagy. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as forreviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multipleassays to monitor autophagy. Along these lines, because of the potential for pleiotropic effects due to blocking autophagy through genetic manipulation, it is imperative to target by gene knockout or RNA interference more than one autophagyrelated protein. In addition, some individual Atg proteins, or groups of proteins, are involved in other cellular pathways implying that not all Atg proteins can be used as a specific marker for an autophagic process. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular assays, we hope to encourage technical innovation in the field.

Noble metal-free hydrogen evolution catalysts for water splitting
Xiaoxin Zou, Yu Zhang
2015· Chemical Society Reviews5.9Kdoi:10.1039/c4cs00448e

Sustainable hydrogen production is an essential prerequisite of a future hydrogen economy. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion based on photochemical and photoelectrochemical water splitting are promising pathways for sustainable hydrogen production. All these techniques require, among many things, highly active noble metal-free hydrogen evolution catalysts to make the water splitting process more energy-efficient and economical. In this review, we highlight the recent research efforts toward the synthesis of noble metal-free electrocatalysts, especially at the nanoscale, and their catalytic properties for the hydrogen evolution reaction (HER). We review several important kinds of heterogeneous non-precious metal electrocatalysts, including metal sulfides, metal selenides, metal carbides, metal nitrides, metal phosphides, and heteroatom-doped nanocarbons. In the discussion, emphasis is given to the synthetic methods of these HER electrocatalysts, the strategies of performance improvement, and the structure/composition-catalytic activity relationship. We also summarize some important examples showing that non-Pt HER electrocatalysts could serve as efficient cocatalysts for promoting direct solar-to-hydrogen conversion in both photochemical and photoelectrochemical water splitting systems, when combined with suitable semiconductor photocatalysts.

The photoluminescence mechanism in carbon dots (graphene quantum dots, carbon nanodots, and polymer dots): current state and future perspective
Shoujun Zhu, Yubin Song, Xiaohuan Zhao, Jieren Shao +2 more
2015· Nano Research2.8Kdoi:10.1007/s12274-014-0644-3

At present, the actual mechanism of the photoluminescence (PL) of fluorescent carbon dots (CDs) is still an open debate among researchers. Because of the variety of CDs, it is highly important to summarize the PL mechanism for these kinds of carbon materials; doing so can guide the development of effective synthesis routes and novel applications. This review will focus on the PL mechanism of CDs. Three types of fluorescent CDs were involved: graphene quantum dots (GQDs), carbon nanodots (CNDs), and polymer dots (PDs). Four reasonable PL mechanisms have been confirmed: the quantum confinement effect or conjugated π-domains, which are determined by the carbon core; the surface state, which is determined by hybridization of the carbon backbone and the connected chemical groups; the molecule state, which is determined solely by the fluorescent molecules connected on the surface or interior of the CDs; and the crosslink-enhanced emission (CEE) effect. To give a thorough summary, the category and synthesis routes, as well as the chemical/physical properties for the CDs, are briefly introduced in advance.

Metal–organic framework membranes: from synthesis to separation application
Shilun Qiu, Ming Xue, Guangshan Zhu
2014· Chemical Society Reviews1.6Kdoi:10.1039/c4cs00159a

Metal-organic framework (MOF) materials, which are constructed from metal ions or metal ion clusters and bridging organic linkers, exhibit regular crystalline lattices with relatively well-defined pore structures and interesting properties. As a new class of porous solid materials, MOFs are attractive for a variety of industrial applications including separation membranes - a rapidly developing research area. Many reports have discussed the synthesis and applications of MOFs and MOF thin films, but relatively few have addressed MOF membranes. This critical review provides an overview of the diverse MOF membranes that have been prepared, beginning with a brief introduction to the current techniques for the fabrication of MOF membranes. Gas and liquid separation applications with different MOF membranes are also included (175 references).

Induction of APOBEC3G Ubiquitination and Degradation by an HIV-1 Vif-Cul5-SCF Complex
Xianghui Yu, Yunkai Yu, Bindong Liu, Kun Luo +3 more
2003· Science1.2Kdoi:10.1126/science.1089591

Human immunodeficiency virus-1 (HIV-1) Vif is essential for viral evasion of host antiviral factor CEM15/APOBEC3G. We report that Vif interacts with cellular proteins Cul5, elongins B and C, and Rbx1 to form an Skp1-cullin-F-box (SCF)-like complex. The ability of Vif to suppress antiviral activity of APOBEC3G was specifically dependent on Cul5-SCF function, allowing Vif to interact with APOBEC3G and induce its ubiquitination and degradation. A Vif mutant that interacted with APOBEC3G but not with Cul5-SCF was functionally inactive. The Cul5-SCF was also required for Vif function in distantly related simian immunodeficiency virus mac. These results indicate that the conserved Cul5-SCF pathway used by Vif is a potential target for antiviral development.

The Dry‐Style Antifogging Properties of Mosquito Compound Eyes and Artificial Analogues Prepared by Soft Lithography
Xuefeng Gao, Xiang Yan, Xi Yao, Lu Xu +4 more
2007· Advanced Materials1.0Kdoi:10.1002/adma.200601946

The antifogging properties of mosquito compound eyes (see figure) result from their elaborate superhydrophobic surface structure, which consists of hexagonally non-close-packed nipples at the nanoscale and hexagonally close-packed hemispheres at the microscale. A soft-lithography approach is adopted to fabricate artificial compound eyes for exploring the effects of the hierarchical micro- and nanostructure on surface hydrophobicity.

Design and applications of three dimensional covalent organic frameworks
Xinyu Guan, Fengqian Chen, Qianrong Fang, Shilun Qiu
2020· Chemical Society Reviews885doi:10.1039/c9cs00911f

Covalent organic frameworks (COFs), as an emerging class of crystalline porous polymers connected by dynamic covalent bonds, have been well studied over the past decade. Recently, three dimensional (3D) COFs have attracted extensive interest for the synthesis and applications of novel COFs. The principal reason for this rising trend is based on their unique porous features and excellent performances compared to previously reported two dimensional (2D) frameworks with the layered AA-stacking mode. This critical review describes the current state-of-the-art development of 3D COFs in the design principles, synthetic methods, functionalization strategies, and potential applications. Some major challenges associated with future perspectives are further discussed, inspiring the development of 3D COFs.

Investigation from chemical structure to photoluminescent mechanism: a type of carbon dots from the pyrolysis of citric acid and an amine
Yubin Song, Shoujun Zhu, Shitong Zhang, Yu Fu +3 more
2015· Journal of Materials Chemistry C792doi:10.1039/c5tc00813a

We clarified the chemical structure of typical “bottom-up” CDs and proved that IPCA is the molecular state photoluminescence center.

The Characterization of High‐Fat Diet and Multiple Low‐Dose Streptozotocin Induced Type 2 Diabetes Rat Model
Ming Zhang, Xiaoyan Lv, Jing Li, Zhigang Xu +1 more
2008· Journal of Diabetes Research667doi:10.1155/2008/704045

AIM: Based on the previously established method, we developed a better and stable animal model of type 2 diabetes mellitus by high-fat diet combined with multiple low-dose STZ injections. Meanwhile, this new model was used to evaluate the antidiabetic effect of berberine. METHOD: Wistar male rats fed with regular chow for 4 weeks received vehicle (control groups), rats fed with high-fat diet for 4 weeks received different amounts of STZ once or twice by intraperitoneal injection (diabetic model groups), and diabetic rats were treated with berberine (100 mg/kg, berberine treatment group). Intraperitoneal glucose tolerance test and insulin tolerance test were carried out. Moreover, fasting blood glucose, fasting insulin, total cholesterol, and triglyceride were measured to evaluate the dynamic blood sugar and lipid metabolism. RESULT: The highest successful rate (100%) was observed in rats treated with a single injection of 45 mg/kg STZ, but the plasma insulin level of this particular group was significantly decreased, and ISI has no difference compared to control group. The successful rate of 30 mg/kg STZ twice injection group was significantly high (85%) and the rats in this group presented a typical characteristic of T2DM as insulin resistance, hyperglycemia, and blood lipid disorder. All these symptoms observed in the 30 mg/kg STZ twice injection group were recovered by the treatment of berberine. CONCLUSION: Together, these results indicated that high-fat diet combined with multiple low doses of STZ (30 mg/kg at weekly intervals for 2 weeks) proved to be a better way for developing a stable animal model of type 2 diabetes, and this new model may be suitable for pharmaceutical screening.

A General Route to Prepare Low‐Ruthenium‐Content Bimetallic Electrocatalysts for pH‐Universal Hydrogen Evolution Reaction by Using Carbon Quantum Dots
Yuan Liu, Xue Li, Qinghua Zhang, Weidong Li +4 more
2019· Angewandte Chemie International Edition641doi:10.1002/anie.201913910

Abstract A challenging but pressing task to design and synthesize novel, efficient, and robust pH‐universal hydrogen evolution reaction (HER) electrocatalysts for scalable and sustainable hydrogen production through electrochemical water splitting. Herein, we report a facile method to prepare an efficient and robust Ru‐M (M=Ni, Mn, Cu) bimetal nanoparticle and carbon quantum dot hybrid (RuM/CQDs) for pH‐universal HER. The RuNi/CQDs catalysts exhibit outstanding HER performance at all pH levels. The unexpected low overpotentials of 13, 58, and 18 mV shown by RuNi/CQDs allow a current density of 10 mA cm −2 in 1 m KOH, 0.5 m H 2 SO 4 , and 1 m PBS, respectively, for Ru loading at 5.93 μgRu cm −2 . This performance is among the best catalytic activities reported for any platinum‐free electrocatalyst. Theoretical studies reveal that Ni doping results in a moderate weakening of the hydrogen bonding energy of nearby surface Ru atoms, which plays a critical role in improving the HER activity.

Synthesis of new zeolite structures
Jiyang Li, Avelino Corma, Jihong Yu
2015· Chemical Society Reviews622doi:10.1039/c5cs00023h

The search for new zeolites is of continuous interest in the field of zeolite science because of their widespread application in catalysis and adsorption-separation. To this end, considerable efforts have been devoted to the preparation of new zeolites with novel porous architectures and compositions. Taking account of the key factors governing the formation of zeolites (e.g., guest species, framework elements, construction processes, etc.), several synthetic strategies have been developed recently. These allow the discovery of many new zeolites with unprecedented structural features, such as hierarchical pores, odd-ring numbers (11-, 15-rings), extra-large pores (16-, 18-, 20-, 28-, and 30-rings), chiral pores, and extremely complex framework topologies, etc. In this review, we will present the advances in the synthesis of new zeolite structures in the last decade, which are achieved by utilization of the synthetic strategies based on pre-designed structure-directing agents, heteroatom substitution, and topotactic transformations.

Highly prevalent TERT promoter mutations in aggressive thyroid cancers
Xiaoli Liu, Justin A. Bishop, Yuan Shan, Sara I. Pai +4 more
2013· Endocrine Related Cancer608doi:10.1530/erc-13-0210

Mutations 1 295 228 C>T and 1 295 250 C>T (termed C228T and C250T respectively), corresponding to -124 C>T and -146 C>T from the translation start site in the promoter of the telomerase reverse transcriptase (TERT) gene, have recently been reported in human cancers, but not in thyroid cancers yet. We explored these mutations in thyroid cancers by genomic sequencing of a large number of primary tumor samples. We found the C228T mutation in 0 of 85 (0.0%) benign thyroid tumors, 30 of 257 (11.7%) papillary thyroid cancers (PTC), 9 of 79 (11.4%) follicular thyroid cancers (FTC), 3 of 8 (37.5%) poorly differentiated thyroid cancers (PDTC), 23 of 54 (42.6%) anaplastic thyroid cancers (ATC), and 8 of 12 (66.7%) thyroid cancer cell lines. The C250T mutation was uncommon, but mutually exclusive with the C228T mutation, and the two mutations were collectively found in 11 of 79 (13.9%) FTC, 25 of 54 (46.3%) ATC, and 11 of 12 (91.7%) thyroid cancer cell lines. Among PTC variants, the C228T mutation was found in 4 of 13 (30.8%) tall-cell PTC (TCPTC), 23 of 187 (12.3%) conventional PTC, and 2 of 56 (3.6%) follicular variant PTC samples. No TERT mutation was found in 16 medullary thyroid cancer samples. The C228T mutation was associated with the BRAF V600E mutation in PTC, being present in 19 of 104 (18.3%) BRAF mutation-positive PTC vs 11 of 153 (7.2%) the BRAF mutation-negative PTC samples (P=0.0094). Conversely, BRAF mutation was found in 19 of 30 (63.3%) C228T mutation-positive PTC vs 85 of 227 (37.4%) C228T mutation-negative PTC samples (P=0.0094). We thus for the first time, to our knowledge, demonstrate TERT promoter mutations in thyroid cancers, that are particularly prevalent in the aggressive thyroid cancers TCPTC, PDTC, ATC and BRAF mutation-positive PTC, revealing a novel genetic background for thyroid cancers.

Alpha-helical cationic antimicrobial peptides: relationships of structure and function
Huang Yi, Jinfeng Huang, Yuxin Chen
2010· Protein & Cell577doi:10.1007/s13238-010-0004-3

Antimicrobial peptides (AMPs), with their extraordinary properties, such as broad-spectrum activity, rapid action and difficult development of resistance, have become promising molecules as new antibiotics. Despite their various mechanisms of action, the interaction of AMPs with the bacterial cell membrane is the key step for their mode of action. Moreover, it is generally accepted that the membrane is the primary target of most AMPs, and the interaction between AMPs and eukaryotic cell membranes (causing toxicity to host cells) limits their clinical application. Therefore, researchers are engaged in reforming or de novo designing AMPs as a 'single-edged sword' that contains high antimicrobial activity yet low cytotoxicity against eukaryotic cells. To improve the antimicrobial activity of AMPs, the relationship between the structure and function of AMPs has been rigorously pursued. In this review, we focus on the current knowledge of α-helical cationic antimicrobial peptides, one of the most common types of AMPs in nature.

PKM2, function and expression and regulation
Ze Zhang, Xinyue Deng, Yuanda Liu, Yahui Liu +2 more
2019· Cell & Bioscience503doi:10.1186/s13578-019-0317-8

Pyruvate kinase (PK), as one of the key enzymes for glycolysis, can encode four different subtypes from two groups of genes, although the M2 subtype PKM2 is expressed mainly during embryonic development in normal humans, and is closely related to tissue repair and regeneration, with the deepening of research, the role of PKM2 in tumor tissue has received increasing attention. PKM2 can be aggregated into tetrameric and dimeric forms, PKM2 in the dimer state can enter the nuclear to regulate gene expression, the transformation between them can play an important role in tumor cell energy supply, epithelial-mesenchymal transition (EMT), invasion and metastasis and cell proliferation. We will use the switching effect of PKM2 in glucose metabolism as the entry point to expand and enrich the Warburg effect. In addition, PKM2 can also regulate each other with various proteins by phosphorylation, acetylation and other modifications, mediate the different intracellular localization of PKM2 and then exert specific biological functions. In this paper, we will illustrate each of these points.

Recent progress in the mechanochromism of phosphorescent organic molecules and metal complexes
Pengchong Xue, Jipeng Ding, Panpan Wang, Ran Lu
2016· Journal of Materials Chemistry C478doi:10.1039/c6tc01503d

Phosphorescent mechanochromic materials may change their luminescence color and intensity with large spectral shifts under a mechanical force stimulus.

Recent advances in zeolite chemistry and catalysis
Bert M. Weckhuysen, Jihong Yu
2015· Chemical Society Reviews469doi:10.1039/c5cs90100f

Guest editors Bert M. Weckhuysen and Jihong Yu introduce the Recent Advances in Zeolite Chemistry and Catalysis issue of <italic>Chemical Society Reviews</italic>

&lt;p&gt;The Role of Erastin in Ferroptosis and Its Prospects in Cancer Therapy&lt;/p&gt;
Yue‐Chen Zhao, Yanqing Li, Ruifeng Zhang, Feng Wang +2 more
2020· OncoTargets and Therapy453doi:10.2147/ott.s254995

Abstract: Erastin was initially discovered as a small molecule compound that selectively kills tumor cells expressing ST and RAS V12 and was later widely investigated as an inducer of ferroptosis. Ferroptosis is a recently discovered form of cell death caused by peroxidation induced by the accumulation of intracellular lipid reactive oxygen species (L-ROS) in an iron-dependent manner. Erastin can mediate ferroptosis through a variety of molecules including the cystine-glutamate transport receptor (system X C − ), the voltage-dependent anion channel (VDAC), and p53. Erastin is able to enhance the sensitivity of chemotherapy and radiotherapy, suggesting a promising future in cancer therapy. We hope that this review will help to better understand the role of erastin in ferroptosis and lay the foundation for further research and the development of erastin-based cancer therapies in the future. Keywords: erastin, ferroptosis, system X C − , p53, VDAC, cancer

Impact of common genetic determinants of Hemoglobin A1c on type 2 diabetes risk and diagnosis in ancestrally diverse populations: A transethnic genome-wide meta-analysis
Eleanor Wheeler, Aaron Leong, Ching‐Ti Liu, Marie‐France Hivert +4 more
2017· PLoS Medicine445doi:10.1371/journal.pmed.1002383

BACKGROUND: Glycated hemoglobin (HbA1c) is used to diagnose type 2 diabetes (T2D) and assess glycemic control in patients with diabetes. Previous genome-wide association studies (GWAS) have identified 18 HbA1c-associated genetic variants. These variants proved to be classifiable by their likely biological action as erythrocytic (also associated with erythrocyte traits) or glycemic (associated with other glucose-related traits). In this study, we tested the hypotheses that, in a very large scale GWAS, we would identify more genetic variants associated with HbA1c and that HbA1c variants implicated in erythrocytic biology would affect the diagnostic accuracy of HbA1c. We therefore expanded the number of HbA1c-associated loci and tested the effect of genetic risk-scores comprised of erythrocytic or glycemic variants on incident diabetes prediction and on prevalent diabetes screening performance. Throughout this multiancestry study, we kept a focus on interancestry differences in HbA1c genetics performance that might influence race-ancestry differences in health outcomes. METHODS & FINDINGS: Using genome-wide association meta-analyses in up to 159,940 individuals from 82 cohorts of European, African, East Asian, and South Asian ancestry, we identified 60 common genetic variants associated with HbA1c. We classified variants as implicated in glycemic, erythrocytic, or unclassified biology and tested whether additive genetic scores of erythrocytic variants (GS-E) or glycemic variants (GS-G) were associated with higher T2D incidence in multiethnic longitudinal cohorts (N = 33,241). Nineteen glycemic and 22 erythrocytic variants were associated with HbA1c at genome-wide significance. GS-G was associated with higher T2D risk (incidence OR = 1.05, 95% CI 1.04-1.06, per HbA1c-raising allele, p = 3 × 10-29); whereas GS-E was not (OR = 1.00, 95% CI 0.99-1.01, p = 0.60). In Europeans and Asians, erythrocytic variants in aggregate had only modest effects on the diagnostic accuracy of HbA1c. Yet, in African Americans, the X-linked G6PD G202A variant (T-allele frequency 11%) was associated with an absolute decrease in HbA1c of 0.81%-units (95% CI 0.66-0.96) per allele in hemizygous men, and 0.68%-units (95% CI 0.38-0.97) in homozygous women. The G6PD variant may cause approximately 2% (N = 0.65 million, 95% CI 0.55-0.74) of African American adults with T2D to remain undiagnosed when screened with HbA1c. Limitations include the smaller sample sizes for non-European ancestries and the inability to classify approximately one-third of the variants. Further studies in large multiethnic cohorts with HbA1c, glycemic, and erythrocytic traits are required to better determine the biological action of the unclassified variants. CONCLUSIONS: As G6PD deficiency can be clinically silent until illness strikes, we recommend investigation of the possible benefits of screening for the G6PD genotype along with using HbA1c to diagnose T2D in populations of African ancestry or groups where G6PD deficiency is common. Screening with direct glucose measurements, or genetically-informed HbA1c diagnostic thresholds in people with G6PD deficiency, may be required to avoid missed or delayed diagnoses.

Single-atom alloy catalysts: structural analysis, electronic properties and catalytic activities
Tianjun Zhang, Andrew G. Walsh, Jihong Yu, Peng Zhang
2020· Chemical Society Reviews444doi:10.1039/d0cs00844c

Monometallic catalysts, in particular those containing noble metals, are frequently used in heterogeneous catalysis, but they are expensive, rare and the ability to tailor their structures and properties remains limited. Traditionally, alloy catalysts have been used instead that feature enhanced electronic and chemical properties at a reduced cost. Furthermore, the introduction of single metal atoms anchored onto supports provided another effective strategy to increase both the atomic efficiency and the chance of tailoring the properties. Most recently, single-atom alloy catalysts have been developed in which one metal is atomically dispersed throughout the catalyst via alloy bonding; such catalysts combine the traditional advantages of alloy catalysts with the new feature of tailoring properties achievable with single atom catalysts. This review will first outline the atomic scale structural analysis on single-atom alloys using microscopy and spectroscopy tools, such as high-angle annular dark field imaging-scanning transmission electron microscopy and extended X-ray absorption fine structure spectroscopy. Next, progress in research to understand the electronic properties of single-atom alloys using X-ray spectroscopy techniques and quantum calculations will be presented. The catalytic activities of single-atom alloys in a few representative reactions will be further discussed to demonstrate their structure-property relationships. Finally, future perspectives for single-atom alloy catalysts from the structural, electronic and reactivity aspects will be proposed.

A 2D azine-linked covalent organic framework for gas storage applications
Zhongping Li, Xiao Feng, Yongcun Zou, Yuwei Zhang +3 more
2014· Chemical Communications439doi:10.1039/c4cc05665e

A new azine-linked covalent organic framework, ACOF-1, was synthesized by condensation of hydrazine hydrate and 1,3,5-triformylbenzene under solvothermal conditions. ACOF-1 has a high surface area and a small pore size, and it can store up to 177 mg g(-1) of CO2, 9.9 mg g(-1) of H2, and 11.5 mg g(-1) of CH4, at 273 K and 1 bar, with high selectivity towards CO2 over N2 and CH4.