Collagen: mobile water content of frozen fibers

From the change in the nuclear magnetic resonance splitting of heavy water in oriented wet collagen fibers at low temperatures, it is estimated that about 0.6 gram of heavy water per gram of collagen does not freeze. This estimate has been confirmed by a measurement of the heat evolved on melting "frozen" wet collagen. The water that does not freeze retains liquid-like mobility even at temperatures as low as -50 degrees C.     

Structure of water in microemulsions: electrical, birefringence, and nuclear magnetic resonance studies

Microemulsions, which are optically transparent oil-water dispersions, were produced by mixing hexadecane, hexanol, potassium oleate, and water. As the amount of water is increased, the microemulsion exhibits a clear to turbid to clear transition. In contrast to the clear regions, the turbid region possesses birefringence. The development of birefringence is also accompanied by a sharp decrease in the electrical resistance. The high-resolution (220 megacycle) nuclear magnetic resonance data suggest that water exists in two distinct molecular environments in the birefringent region; the first environment is characterized by relatively less mobile water molecules than oil molecules, whereas in the second environment oil molecules are less mobile than water molecules. The electrical, birefringence, and nuclear magnetic resonance data are in agreement with the proposed mechanism of change in the structure of water from water spheres to water cylinders to water lamellae. The chemical shift of water protons suggests that the molecular environment of water in spheres is different from that of water in cylinders or that of water in lamellae.     

低场NMR研究pH对肌原纤维蛋白热诱导凝胶的影响

 【目的】探讨pH对猪肉肌原纤维蛋白热诱导凝胶保水性及水的移动性影响。【方法】从猪肉中提取肌原纤维蛋白,用低场NMR（nuclear magnetic resonance）研究pH对肌原纤维蛋白热诱导凝胶中水的T2弛豫性质的影响。同时用离心法测量pH对肌原纤维蛋白凝胶保水性（water holding capacity,WHC）影响。【结果】NMR结果拟合后得到水有4个组分,合并为对应水的3种状态即不可移动水、可移动水和自由水。随着pH升高,pH偏离肌原纤维蛋白的等电点（pI）,代表可移动水的T2弛豫时间显著增加,其所占峰的面积和凝胶的WHC也随之增加。主成分分析结果发现,处于等电点附近的样品在样品评分图上与其它pH样品显著不同。【结论】凝胶保水性的增加主要是可移动水的增加,凝胶WHC增加的原因可能是肌原纤维凝胶后孔径增加,从而可以容纳更多的水。     

Magnetic resonance studies of lunar samples

Electron spin resonance searches at 9.5 gigahertz on several fines samples and portions of several rocks have yielded signals whose lineshapes and temperature dependences show that the samples are principally ferromagnetic in nature. Proton magnetic resonance searches at 60 megahertz of these samples have not revealed any signals ascribable to water or any other types of hydrogen in concentrations greater than 0.0001 percent by weight contained in narrow lines (5 oersteds wide or less) and 0.01 percent by weight in wide lines (as wide as 100 oersteds).     

利用核磁共振自由感应衰减曲线测定木材含水率

为定量测定木材含水率,以水分子中的质子为探针,利用核磁共振技术探究木材内部水分的变化情况。通过对胡桃木、红橡木和水曲柳解吸过程中,水分变化的核磁共振自由感应衰减曲线（FID）进行分析,发现木材的含水率与核磁共振的FID信号量高度线性相关,相关系数均超过0.99;因此,可以通过建立含水率与核磁共振FID信号的标准曲线实现木材含水率的核磁共振定量测量。同时,可以根据绝干木材的核磁共振FID信号量比较不同材种基本密度的大小。      

Cadmium-Resistant Pseudomonas putida Synthesizes Novel Cadmium Proteins

Three cysteine-rich proteins of molecular weight 4000 to 7000, containing 4 to 7 gram atoms of cadmium, zinc, and copper per mole were isolated from Pseudomonas putida growing in 3 mM cadmium. The three proteins were induced during different phases of growth, and the smallest (molecular weight 3600; 3 gram atoms of cadmium) was released into the medium when the cells lysed. The results of amino acid analyses and of ultraviolet, circular dichroism, electron paramagnetic resonance, and cadmium-113 nuclear magnetic resonance spectroscopy suggest a novel cadmium(II)-zinc(II)-copper(I) cluster structure for the major protein.     

A thermally re-mendable cross-linked polymeric material

We have developed a transparent organic polymeric material that can repeatedly mend or "re-mend" itself under mild conditions. The material is a tough solid at room temperature and below with mechanical properties equaling those of commercial epoxy resins. At temperatures above 120 degrees C, approximately 30% (as determined by solid-state nuclear magnetic resonance spectroscopy) of "intermonomer" linkages disconnect but then reconnect upon cooling, This process is fully reversible and can be used to restore a fractured part of the polymer multiple times, and it does not require additional ingredients such as a catalyst, additional monomer, or special surface treatment of the fractured interface.     

大球盖菇多糖的分子质量分布及其单糖的组成

 【目的】从大球盖菇(Stropharia rugoso-annulata)中提取多糖,并对其分子质量及组成糖进行研究。【方法】采用水提法提取大球盖菇多糖,利用高效液相色谱法研究大球盖菇多糖分子质量分布及提取过程中多糖分子质量的变化,并采用红外光谱、核磁共振法对其组成糖进行研究。【结果】大球盖菇多糖水溶性多糖类物质的分子质量分布于22 kD附近;大球盖菇多糖同时存在α和β糖苷键,以吡喃糖为主,由5种单糖构成,其中有D-果糖、D-葡萄糖和D-木糖。【结论】以稀盐溶液为流动相的检测手段更能真实地反映大球盖菇多糖的分子质量分布情况,大球盖菇多糖是由5种单糖组成的杂多糖。     

Unitary control in quantum ensembles: maximizing signal intensity in coherent spectroscopy

Experiments in coherent magnetic resonance, microwave, and optical spectroscopy control quantum-mechanical ensembles by guiding them from initial states toward target states by unitary transformation. Often, the coherences detected as signals are represented by a non-Hermitian operator. Hence, spectroscopic experiments, such as those used in nuclear magnetic resonance, correspond to unitary transformations between operators that in general are not Hermitian. A gradient-based systematic procedure for optimizing these transformations is described that finds the largest projection of a transformed initial operator onto the target operator and, thus, the maximum spectroscopic signal. This method can also be used in applied mathematics and control theory.     

Nuclear magnetic resonance imaging of the vitreous body

Imaging with proton nuclear magnetic resonance is a valuable new tool for studying the vitreous body of the eye. It is particularly suited for the detection of vitreal liquefaction and intraocular hemorrhage because of the dependence of the signal on the physical environment of water. Conversely, the vitreous body provides a new model for studying changes in proton relaxation times of protein solutions in biological systems.     

Conformational switches modulate protein interactions in peptide antibiotic synthetases

Protein dynamics plays an important role in protein function. Many functionally important motions occur on the microsecond and low millisecond time scale and can be characterized by nuclear magnetic resonance relaxation experiments. We describe the different states of a peptidyl carrier protein (PCP) that play a crucial role in its function as a peptide shuttle in the nonribosomal peptide synthetases of the tyrocidine A system. Both apo-PCP (without the bound 4'-phosphopantetheine cofactor) and holo-PCP exist in two different stable conformations. We show that one of the apo conformations and one of the holo conformations are identical, whereas the two remaining conformations are only detectable by nuclear magnetic resonance spectroscopy in either the apo or holo form. We further demonstrate that this conformational diversity is an essential prerequisite for the directed movement of the 4'-PP cofactor and its interaction with externally acting proteins such as thioesterases and 4'-PP transferase.     

Blood velocity measurements in intact subjects

Venous blood velocities in intact human forearms can be measured by the use of nuclear magnetic resonance techniques. In essence, two separated coils are placed over the vein, and the arm is held in a magnetic field. Radio-frequency energy in one coil "flips" over the protons in the blood stream, and the second coil detects the arrival of the "flipped" protons. Human blood in vivo and in vitro has a nominal nuclear magnetic resonance relaxation time of 0.4 second.     

Noncovalent binding of a spin-labeled inhibitor to ribonuclease

The stable free radical 2,2,6, 6-tetramethyl-4-hydroxypiperidin-1-oxyl monophosphate has been synthesized; it binds to ribonuclease. The selective changes in the nuclear magnetic resonance spectrum of the enzyme produced by the free radical make it possible to define qualitatively the region of the enzyme to which it binds. The radical appears to occupy a site similar to that to which inorganic phosphate binds which is close to or within the active site of the enzyme.     

Protein hydration in aqueous solution

High-resolution proton nuclear magnetic resonance studies of protein hydration in aqueous solution show that there are two qualitatively different types of hydration sites. A well-defined, small number of water molecules in the interior of the protein are in identical locations in the crystal structure and in solution, and their residence times are in the range from about 10(-2) to 10(-8) second. Hydration of the protein surface in solution is by water molecules with residence times in the subnanosecond range, even when they are located in hydration sites that contain well-ordered water in the x-ray structures of protein single crystals.     

Changes of moisture distribution and migration in fresh ear corn during storage

Understanding of moisture changes in fresh ear corn (Zea mays L.) during storage is imperative for maintaining fresh corn quality. The changes of moisture distribution and migration in fresh ear corn during storage were investigated using low-field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). Water loss was greater than water migration in fresh ear corn within the first hour of storage; thereafter, water loss was weaker than water migration. With the extension of storage time, the signal intensity of MRI in different parts of sliced fresh corn with cob showed a downward trend, and the rate of signal intensity reduction was higher in the peripheral area than at the central part of sliced fresh corn with cob. The relative proportion of bound water increased with a concomitant drop in that of free water, when the total water content reduced in fresh ear corn under storage. In conclusion, NMR and MRI are useful and non-destructive tools for real-time monitoring of moisture distribution, migration, and loss in fresh ear corn during storage to assess its quality. These results can be used for future design of the preserving and processing conditions for fresh ear corn.     

A synthetic lectin analog for biomimetic disaccharide recognition

Carbohydrate recognition is biologically important but intrinsically challenging, for both nature and host-guest chemists. Saccharides are complex, subtly variable, and camouflaged by hydroxyl groups that hinder discrimination between substrate and water. We have developed a rational strategy for the biomimetic recognition of carbohydrates with all-equatorial stereochemistry (beta-glucose, analogs, and homologs) and have now applied it to disaccharides such as cellobiose. Our synthetic receptor showed good affinities, not unlike those of some lectins (carbohydrate-binding proteins). Binding was demonstrated by nuclear magnetic resonance, induced circular dichroism, fluorescence spectroscopy, and calorimetry, all methods giving self-consistent results. Selectivity for the target substrates was exceptional; minor changes to disaccharide structure (for instance, cellobiose to lactose) caused almost complete suppression of complex formation.     

Membrane-mediated assembly of filamentous bacteriophage Pf1 coat protein

Filamentous bacteriophage Pf1 assembles by a membrane-mediated process during which the viral DNA is secreted through the membrane while being encapsulated by the major coat protein. Neutron diffraction studies showed that in the virus most of the coat protein consists of two alpha-helical segments arranged end-to-end with an intervening mobile surface loop. Nuclear magnetic resonance studies of the coat protein in the membrane-bound form have shown that the secondary structure is essentially identical to that in the intact virus. A comparison indicates that during membrane-mediated viral assembly, while the secondary structure of the coat protein is largely conserved, its tertiary structure changes substantially.     

Resolving the motional modes that code for RNA adaptation

Using a domain elongation strategy, we decoupled internal motions in RNA from overall rotational diffusion. This allowed us to site-specifically resolve a manifold of motional modes in two regulatory RNAs from HIV-1 with the use of nuclear magnetic resonance spin relaxation methods. Base and sugar librations vary on a picosecond time scale and occur within helical domains that move collectively at diffusion-limited nanosecond time scales. Pivot points are short, functionally important, and highly mobile internal loops. These spontaneous changes in RNA conformation correlate quantitatively with those that follow adaptive recognition of diverse targets. Thus, ligands may stabilize existing RNA conformations rather than inducing new ones.     

Temperature-induced hydrophobic-hydrophilic transition observed by water adsorption

The properties of nanoconfined and interfacial water in the proximity of hydrophobic surfaces play a pivotal role in a variety of important phenomena such as protein folding. Water inside single-walled carbon nanotubes (SWNTs) can provide an ideal system for investigating such nanoconfined interfacial water on hydrophobic surfaces, provided that the nanotubes can be opened without introducing excess defects. Here, we report a hydrophobic-hydrophilic transition upon cooling from 22 degrees C to 8 degrees C via the observation of water adsorption isotherms in SWNTs measured by nuclear magnetic resonance. A considerable slowdown in molecular reorientation of such adsorbed water was also detected. The observed transition demonstrates that the structure of interfacial water could depend sensitively on temperature, which could lead to intriguing temperature dependences involving interfacial water on hydrophobic surfaces.     

高速逆流色谱分离紫苏酮的研究

紫苏酮是一种对试验动物肺部具有潜在毒性的物质. 该文采用高速逆流色谱分离法从紫苏叶中分离出了紫苏酮. 结果表明,以V(正己烷)∶V(乙醇)∶V(水)＝6∶5∶1 为溶剂系统,上相为固定相,下相为流动相,转速为 800 r/min,流动相流速为 1.2 mL/min,进样 1 g 粗提物,6 h 后分离出 280 mg 紫苏酮,经气相色谱测定,组分纯度达到 98.8%,并用核磁共振等方法进行了结构鉴定.