用叶轮粘度计测定发酵液的流动特性

为了克服常规粘度计在测定扭矩时碰到的困难,利用叶轮粘度计测定了九种丝状菌发酵液的流变特性。这些发酵液均为拟塑性,大多数发酵液的流动特性指数小于0.3。庆大霉素发酵液的最大稠度系数达22.4Ns~n/m~2,但用少量水稀释后就大大下降。温度对丝状菌发酵液的流动特性影响不大,但取样后的放置时间则有明显影响。     

小牛血清去蛋白提取物活性物质理化性质的实验研究

目的研究小牛血清去蛋白提取物（deproteinated extract of calf blood,DECB）中生物活性物质的物理化学性质。方法分别将小牛血清去蛋白提取物进行加热、加酸、加碱、烘烤、有机溶剂萃取、接种微生物发酵等方法处理,然后分别用微量呼吸检压法检测呼吸活性。结果采用加热、加碱、加酸,接种微生物发酵的方法进行处理,DECB刺激呼吸活性的能力没有明显改变,而采用烘烤的方法处理,DECB的活性完全消失;用有机溶剂萃取DECB,可明显降低DECB刺激呼吸活性的能力,而有机相中含有了刺激呼吸活性物质。结论小牛血清去蛋白提取物（DECB）中刺激呼吸的活性物质耐高温、耐酸、耐碱,并且不易被普通微生物降解,但不耐烘烤,较易被有机溶剂萃取,由理化性质推测DECB中的活性物质可能是一种活性脂类。     

Three-Point Bending Properties of Hybrid Multi-Materials Using Adhesive Bonding Dependent on Strength Difference between Steel and Aluminum

The mechanical behaviors of two multi-materials, DP590 (steel sheet)–A356 (cast aluminum alloy) and SS330 (steel sheet)–A5052 (aluminum sheet), were studied. A structural adhesive was used for the joining of steel and aluminum at adhesion strengths of 10, 22, and 30 MPa. To demonstrate that the three-point bending properties depend on the difference in strength between steel and aluminum and adhesion strength, optical microscopy (OM), scanning electron microscopy (SEM), and finite-element analysis (FEA) were performed. According to the results of the bending tests on both multi-materials under the same stacking conditions, the flexural stress increased with the improvement in the adhesion strength until interface separation or aluminum fracture. At the same adhesion strength, the DP590 (lower)–A356 (upper) and SS330 (upper)–A5052 (lower) configurations exhibited a tendency to decrease in the sudden stress drop due to aluminum fracture and interface separation. The bending results were analyzed through the FEA and the stress distribution as a function of the stacking and adhesion strength was confirmed.     

针灸作用原理的基本规律、特征和优势

系统回顾了中国针灸作用原理五十年研究工作.认为针灸作用的基本特征是调节作用,包括整体性调节和双向性调节两方面.针灸作用的基本规律是通过调控神经-内分泌-免疫网络途径实现其效应,具有多环节和多靶向特点.针灸作用原理研究的优势在于,为现代生命科学提供研究思路,丰富生命科学内涵,并成为最有望取得原始创新突破的我国传统学科领域.     

4种室温固化基托材料的力学性能比较

目的:比较4种室温固化基托材料的力学性能,为临床应用提供理论依据。方法:根据ISO1567标准,使用不锈钢模具制备试样,在试验机上测定材料的弯曲强度、弹性模量、冲击强度、布氏硬度。结果:4种室温固化PMMA材料(Tokuyama、日进、贺利氏、上齿)的弯曲强度顺序为:日进≥上齿≈贺利氏>TOKUYAMA。弹性模量和冲击强度的顺序为:日进≈上齿≈贺利氏>TOKUYAMA。布氏硬度的顺序为:日进≈上齿>贺利氏≈TOKUYAMA。结论:4种室温固化基托材料相比较TOKUYAMA弯曲强度最低,日进的弯曲强度近似最高。日进、上齿与贺利氏三者的弹性模量和冲击强度相似,TOKUYAMA弹性模量和冲击强度最低。日进与上齿的硬度高于贺利氏与TOKUYAMA。     

天鹅型记忆接骨器对大白兔骨折愈合骨矿含量及力学性能的影响

目的　探讨天鹅记忆接骨器 (SMC)对实验性骨折愈合的骨矿含量和力学性能的影响 ,揭示其促进骨折愈合的机制。方法　 40只新西兰大白兔双侧肱骨干截骨后 ,随机选取一侧用天鹅型形状记忆接骨器固定 (SMC组 ) ,对侧用 4孔加压接骨板 (DCP)固定 (DCP组 ) ,分别在术后 2、4、8、12、16周时杀死取材 ,行骨折部骨矿密度测量和抗拉伸力学性能测试 ,观察固定段骨矿含量和力学性能变化。结果　术后 4周开始 ,SMC组骨矿含量开始高于DCP组 (P <0 0 1) ,至术后 16周时 ,两组含量接近。在同一时间段内 ,SMC组的抗拉伸刚度明显优于DCP组 (P <0 0 5或P <0 0 1)。DCP组术后 12周以后 ,其力学性能即不再增加。结论　SMC与DCP相比 ,具有材料特性和几何构型上的优势 ,有助于骨折愈合过程中骨矿物质的沉积 ,防止固定段骨骨质疏松发生 ,使骨的力学性能尽早恢复     

镉染毒对大鼠骨生物力学性能的影响

目的: 探讨镉对大鼠股骨和腰椎生物力学性能的影响。方法: 24只8周龄雄性SD大鼠随机分成4组，分别背部皮下注射生理盐水0.5ml（对照组）和0.1mg/kg bw(低剂量组)，0.5mg/kg bw（中剂量组），1.5mg/kg bw（高剂量组）CdCl2，每周称体重，并根据体重调整注射量。染毒后第12周，收集全血、腰椎及股骨，分别用于血镉测定、骨镉测定、骨密度测定及生物力学测定。结果: 染毒组大鼠体内血镉及骨镉水平明显高于对照组，差异有统计学意义（P < 0.05）；中、高剂量染毒组大鼠骨密度较对照组显著下降（P < 0.05）；染毒组大鼠股骨和腰椎生物力学性能较对照组有不同程度的的降低，其中高剂量染毒组大鼠股骨生物力学性能的下降和对照组相比有显著差异（P < 0.01）；中剂量和高剂量染毒组大鼠腰椎生物力学性能和对照组相比差异有统计学意义（P < 0.01）。结论: 镉能影响大鼠股骨和腰椎的生物力学性能，并且腰椎生物力学性能的改变要早于股骨。     

A new concept of the contraction–extension property of the left ventricular myocardium

ObjectivesUsing newly developed ultrasonic technology, we attempted to disclose the characteristics of the left ventricular (LV) contraction–extension (C–E) property, which has an important relationship to LV function.MethodsStrain rate (SR) distribution within the posterior wall and interventricular septum was microscopically measured with a high accuracy of 821 μm in spatial resolution by using the phase difference tracking method. The subjects were 10 healthy men (aged 30–50 years).ResultsThe time course of the SR distribution disclosed the characteristic C–E property, i.e. the contraction started from the apex and propagated toward the base on one hand, and from the epicardial side toward the endocardial side on the other hand. Therefore, the contraction of one area and the extension of another area simultaneously appeared through nearly the whole cardiac cycle, with the contracting part positively extending the latter part and vice versa. The time course of these propagations gave rise to the peristalsis and the bellows action of the LV wall, and both contributed to effective LV function.The LV contraction started coinciding in time with the P wave of the electrocardiogram, and the cardiac cycle was composed of 4 phases, including 2 types of transitional phase, as well as the ejection phase and slow filling phase. The sum of the measurement time duration of either the contraction or the extension process occupied nearly equal duration in normal conditions.ConclusionThe newly developed ultrasonic technology revealed that the SR distribution was important in evaluating the C–E property of the LV myocardium. The harmonious succession of the 4 cardiac phases newly identified seemed to be helpful in understanding the mechanism to keep long-lasting pump function of the LV.     

Identifying the origin of local flexibility in a carbohydrate polymer

Correlating the structures and properties of a polymer to its monomer sequence is key to understanding how its higher hierarchy structures are formed and how its macroscopic material properties emerge. Carbohydrate polymers, such as cellulose and chitin, are the most abundant materials found in nature whose structures and properties have been characterized only at the submicrometer level. Here, by imaging single-cellulose chains at the nanoscale, we determine the structure and local flexibility of cellulose as a function of its sequence (primary structure) and conformation (secondary structure). Changing the primary structure by chemical substitutions and geometrical variations in the secondary structure allow the chain flexibility to be engineered at the single-linkage level. Tuning local flexibility opens opportunities for the bottom-up design of carbohydrate materials.

Natural polymers adopt a multitude of three-dimensional structures that enable a wide range of functions (1). Polynucleotides store and transfer genetic information; polypeptides function as catalysts and structural materials; and polysaccharides play important roles in cellular structure (2–6), recognition (5), and energy storage (7). The properties of these polymers depend on their structures at various hierarchies: sequence (primary structure), local conformation (secondary structure), and global conformation (tertiary structure).Automated solid-phase techniques provide access to these polymers with full sequence control (8–12). The correlation between the sequence, the higher hierarchy structures, and the resulting properties is relatively well established for polynucleotides (13, 14) and polypeptides (15, 16), while comparatively little is known for polysaccharides (17). Unlike polypeptides and polynucleotides, polysaccharides are based on monosaccharide building blocks that can form multiple linkages with different configurations (e.g., α- or β-linkages) leading to extremely diverse linear or branched polymers. This complexity is exacerbated by the flexibility of polysaccharides that renders structural characterization by ensemble-averaged techniques challenging (17). Imaging single-polysaccharide molecules using atomic force microscopy has revealed the morphology and properties of polysaccharides at mesoscopic, submicrometer scale (18–22). However, imaging at such length scales precludes the observation of individual monosaccharide subunits required to correlate the polysaccharide sequence to its molecular structure and flexibility, the key determinants of its macroscopic functions and properties (23).Imaging polysaccharides at subnanometer resolution by combining scanning tunnelling microscopy (STM) and electrospray ion-beam deposition (ES-IBD) (24, 25) allows for the observation of their monosaccharide subunits to reveal their connectivity (26–28) and conformation space (29). Here, we use this technique to correlate the local flexibility of an oligosaccharide chain to its sequence and conformation, the lowest two structural hierarchies. By examining the local freedom of the chain as a function of its primary and secondary structures, we address how low-hierarchy structural motifs affect local oligosaccharide flexibility—an insight critical to the bottom-up design of carbohydrate materials (30).We elucidate the origin of local flexibility in cellulose, the most abundant polymer in nature, composed of glucose (Glc) units linked by β-1,4–linkages (31–33). Unveiling what affects the flexibility of cellulose chains is important because it gives rise to amorphous domains in cellulose materials (34–37) that change the mechanical performance and the enzyme digestibility of cellulose (38). Cellohexaose, a Glc hexasaccharide (Fig. 1A), was used as a model for a single-cellulose chain as it has been shown to resemble the cellulose polymer behavior (12). Modified analogs prepared by Automated Glycan Assembly (AGA) (11, 12) were designed to manipulate particular intramolecular interactions responsible for cellulose flexibility. Cellohexaose, ionized as a singly deprotonated ion in the gas phase ([M-H]⁻¹) was deposited on a Cu(100) surface held at 120 K by ES-IBD (24) (Materials and Methods). The ions were landed with 5-eV energy, well suited to access diverse conformation states of the molecule without inducing any chemical change in the molecule (29). The resulting cellohexaose observed in various conformation states allowed its mechanical flexibility (defined by the variance in the geometrical bending between two residues) to be quantified for every intermonomer linkage. The observed dependence of local flexibility on the oligosaccharide sequence and conformation thus exemplifies how primary and secondary structures tune the local mechanical flexibility of a carbohydrate polymer.Open in a separate windowFig. 1.STM images of cellohexaose (AAAAAA) and its analogs (AXAAXA). Structures and STM images of cellohexaose (A) and its substituted analogs (B–E). Cellohexaose contains six Glcs (labeled as A; colored black) linked via β-1,4–glycosidic bonds. The cellohexaose analogs contain two substituted Glcs, as the second and the fifth residues from the nonreducing end, that have a single methoxy (–OCH₃) at C(3) (labeled as B; colored red), two methoxy groups at C(3) and C(6) (labeled as C; colored green), a single carboxymethoxy (–OCH₂COOH) at C(3) (labeled as D; colored blue), and a single fluorine (–F) at C(3) (labeled as F; colored purple).The effect of the primary structure on the chain flexibility was explored using sequence-defined cellohexaose analogs (Fig. 1). Cellohexaose, AAAAAA (Fig. 1A), was compared with its substituted analogs, ABAABA, ACAACA, ADAADA, and AFAAFA (written from the nonreducing end) (Fig. 1 B–E), where A is Glc, B is Glc methylated at OH(3), C is Glc methylated at OH(3) and OH(6), D is Glc carboxymethylated at OH(3), and F is Glc deoxyfluorinated at C(3). These substitutions are designed to alter the intramolecular hydrogen bonding between the first and the second as well as between the fourth and fifth Glc units (Fig. 1). These functional groups also affect the local steric environment (i.e., the bulky carboxymethyl group) (Fig. 1D) and the local electronic properties (i.e., the electronegative fluorine group) (Fig. 1E). When compared with the unsubstituted parent cellohexaose, these modified cellohexaoses exhibit different aggregation behavior and are more water soluble (12).All cellohexaose derivatives adsorbed on the surface were imaged with STM at 11 K (Fig. 1). The oligosaccharides were deposited as singly deprotonated species and were computed to adsorb on the surface via a single covalent RO–Cu bond, except for ADAADA which was deposited as doubly deprotonated species and was computed to adsorb on the surface via two covalent RCOO–Cu bonds (R = sugar chain). All cellohexaoses appear as chains containing six protrusions corresponding to the six constituent Glcs. The unmodified cellohexaose chains (Fig. 1A) mainly adopt a straight geometry, while the substituted cellohexaoses (Fig. 1 B–E) adopt both straight- and bent-chain geometries. Chemical substitution thus increases the geometrical freedom of the cellulose chain, consistent with the reported macroscopic properties (12).Large-chain bending between neighboring Glc units is observed exclusively for the substituted cellohexaose (Fig. 1). The large, localized bending reveals the substitution site and allows for the nonreducing and the reducing ends of the chain to be identified. These chains are understood to bend along the surface plane via the glycosidic linkage without significant tilting of the pyranose ring that remains parallel to the surface (illustrated in SI Appendix, Fig. S1), as indicated by the ∼2.0-Å height of every Glc (29).The bending angle measured for AA and AX linkages (Fig. 2; Materials and Methods has analysis details) shows that, while both AA and AX prefer the straight, unbent geometry, AX displays a greater variation of bending angles than AA. AX angular distribution is consistently ∼10° wider than that for AA, indicating that AX has a greater conformational freedom than AA. This increased bending flexibility results from the absence of the intramolecular hydrogen bonding between OH(3) and O(5) of the neighboring residue. Methylation of OH(6), in addition to methylation of OH(3), results in similar flexibility (Fig. 2 B and C), suggesting the greater importance of OH(3) in determining the bending flexibility. Steric effects were found to be negligible since AD displayed similar flexibility to other less bulky AX linkages.Open in a separate windowFig. 2.Bending flexibility of AA linkage and substituted AX linkages. Chain bending (Fig. 1) is quantified as an angle formed between two neighboring Glcs (Materials and Methods). The results are given in A for AA, in B for AB, in C for AC, in D for AD, and in E for AF, showing that AX (where X = B, C, D, F) has a higher conformational freedom than AA. The angle distributions (bin size: 10°) are fitted with a Gaussian (solid line) shown with its half-width half-maximum. The computed potential energy curves are shown with the half-width at 0.4 eV and fitted with a parabola to estimate its stiffness (k; in millielectronvolts per degree²).Density functional theory (DFT) calculations support the observations, showing that substitution of OH(3) decreases the linkage stiffness by up to ∼40% (Fig. 2). Replacing OH(3) with other functional groups weakens the interglucose interactions by replacing the OH(3)··O(5) hydrogen bond with weak Van der Waals interactions. The similar flexibility between AB and AC linkages is attributed to the similar strength of the interglucose OH(2)··OH(6) hydrogen bond in AB (Fig. 2B) and the OH(2)··OMe(6) hydrogen bond in AC (Fig. 2C). The negligible steric effect in AD is attributed to the positional and rotational freedom of the bulky moiety that prevents any “steric clashes” and diminishes the contribution of steric repulsion in the potential energy curve. Comparing the potential landscape in the gas phase and on the surface shows that the stiffness of the adsorbed cellohexaoses is primarily dictated by their intramolecular interactions instead of molecule–surface interactions (SI Appendix, Fig. S2). Primary structure alteration by chemical substitution modifies the interglucose hydrogen bonds and enables chain flexibility to be locally engineered at the single-linkage level.We subsequently investigate how molecular conformation (secondary structure) affects the local bending flexibility. We define the local secondary structure as the geometry formed between two Glcs, here exemplified by the local twisting of the chain (Fig. 3). The global secondary structure is defined as the overall geometry formed by all Glcs in the chain, here exemplified by the linear and cyclic topologies of the chain (Fig. 4).Open in a separate windowFig. 3.Bending flexibility of untwisted and twisted AA linkages. (A) STM image of a cellohexaose containing two types of AA linkages: untwisted (HH and VV) and twisted (HV and VH; from the nonreducing end). The measured bending angles and the computed potential curve are given in B for HH, in C for HV, and in D for VV, showing that the twisted linkage (HV) is more flexible than the untwisted ones (HH and VV). In the molecular structures, interunit hydrogen bonds are given as dotted blue lines, and the pyranose rings are colored red for the horizontal ring (H) and green for vertical (V). The angle distributions (bin size: 10°) are fitted with a Gaussian distribution (solid line) labeled with its peak and half-width half-maximum. The computed potential curves are labeled with its half-width at 0.4 eV and fitted with a parabola to estimate its stiffness (k; in millielectronvolts per degree²).Open in a separate windowFig. 4.Bending flexibility of AA linkage in linear (LIN) and cyclic (CYC) chains. STM image, measured bending angle distribution, and computed potential of AA linkage are given in A for a linear cellohexaose conformer and in B for a cyclic cellohexaose conformer, showing that chain flexibility is reduced in conformations with cyclic topology. The same data are given in C for α-cyclodextrin that is locked in a conformation with cyclic topology. The measured angles (bin size: 10°) are each fitted with a Gaussian distribution (solid line) labeled with its peak and half-width half-maximum. The computed potentials are each labeled with its half-width at 0.4 eV and fitted with a parabola to estimate its stiffness (k; in millielectronvolts per degree²).The effect of local secondary structure on chain flexibility is exemplified by the bending flexibility of twisted and untwisted linkages in a cellohexaose chain (Fig. 3A). The untwisted and twisted linkages are present due to the Glc units observed in two geometries, H or V (Fig. 3), distinguished by their heights (h). H (h ∼ 2.0 Å) is a Glc with its pyranose ring parallel to the surface, while V (h ∼ 2.5 Å) has its ring perpendicular to the surface (29). These lead to HH and VV as untwisted linkages and HV and VH (written from nonreducing end) as twisted linkages.The twisted linkage is more flexible than the untwisted one, as shown by the unimodal bending angles for the untwisted linkage (HH and VV in Fig. 3 B and D, respectively) and the multimodal distribution for the twisted linkage (HV in Fig. 3C). DFT calculations attribute the increased bending flexibility to the reduction of accessible interunit hydrogen bonds from two to one. Linkage twisting increases the distance between the hydrogen-bonded pair, which weakens the interaction between Glc units and increases the flexibility at the twisting point. The increase in local chain flexibility conferred by chain twisting shows how local secondary structures affect chain flexibility.The effect of the global secondary structure on the local chain flexibility was examined by comparing the local bending flexibility of cellohexaose chains possessing different topologies. Cellohexaose can adopt either linear (Figs. 3A and ​and4A)4A) or cyclic topology (Fig. 4B), the latter characterized by the presence of a circular, head-to-tail hydrogen bond network (29). The cyclic conformation of cellohexaose is enabled by the head-to-tail chain folding from the 60° chain bending of the VV linkage. The VV segment in the cyclic chain is stiffer than in the linear chain since the bending angle distribution for the cyclic chain is 6° narrower than that for the linear chain. The observation is corroborated by DFT calculations that show that the VV linkage in the cyclic chain is about three times stiffer than that in the linear chain.To characterize the degree of chain stiffening due to the linear-to-cyclic chain folding, we compare the flexibility of the cyclic cellohexaose and α-cyclodextrin (an α-1,4–linked hexaglucose covalently locked in cyclic conformation). The α-cyclodextrin provides the referential local flexibility for a cyclic oligosaccharide chain. Strikingly, the local flexibility in α-cyclodextrin was found to be identical to that in the cyclic cellohexaose, as evidenced by the similar width of the bending angle distribution and the computed potentials (Fig. 4 B and C). The similar stiffness indicates that the folding-induced stiffening in cellohexaose is a general topological effect unaffected by the type of the interactions that give the cyclic conformation (noncovalent hydrogen bond in cellohexaose vs. covalent bond in α-cyclodextrin). The folding-induced stiffening is the result of the creation of a circular spring network that restricts the motion of Glc units and reduces their conformational freedom. The folding-induced stiffening reported here provides a mechanism by which carbohydrate structures can be made rigid. The dependence of the local chain flexibility on the chain topology shows how global secondary structures modify local flexibility.Using cellulose as an example, we have quantified the local flexibility of a carbohydrate polymer and identified structural factors that determine its flexibility. Modification of the carbohydrate primary structure by chemical substitution alters the mechanical flexibility at the single-linkage level. Changing secondary structure by chain twisting and folding provides additional means to modify the flexibility of each linkage. Control of these structural variables enables tuning of polysaccharide flexibility at every linkage as a basis for designing and engineering carbohydrate materials (30). Our general approach to identify structural factors affecting the flexibility of a specific molecular degrees of freedom in a supramolecular system should aid the design of materials and molecular machines (39) and the understanding of biomolecular dynamics.