Solid-state NMR is an important and powerful tool for studying the structure and molecular dynamics of solid polymer. There are many solid-state NMR methods that can be used to illustrate the details of molecular dynamics occuring in a wide frquency range from Hz to MHz. These methods have been commonly used to study of the multiscale molecular dynamics in polymer solids. In this article, the NMR principles for studying the molecular dynamics of different time scale were briefly reviewed, as well as the structure and multiscale molecular dynamics features in polymer solids. Several examples were presented to show how solid-state NMR methods can be used to investigate the multiscale molecular dynamics in polymer solids.

The fragment based drug screening and design emerged in the past decade, and has gained important applications. Many fragmentderived drugs have entered clinical trials. Probing the weak interactions between the target protein and small molecule fragments Modern NMR techniques play a vital role in fragment based lead discovery. In this article, the basic procedures of NMR fragment screening and the relevant key concepts (i.e., target validation, fragment library design, quality control and prevailing NMR fragment screening techniques) were first introduced. The theoretical framework of the NMR techniques commonly used in fragment based lead discovery stage, including chemical shift perturbation, intermolecular NOE, residual dipolar coupling and paramagnetic spin label etc., were also reviewed. Examples were given to show how these techniques can be used to resolve the structure of target/ligand complexs. Strategies of fragment growth, linking and merging were also discussed.

Protein-protein interactions (PPIs) play  key roles in multiple cellular processes. Both X-ray crystallography and NMR techniques are commonly used to illustrate the structural basis of PPIs. Although most of the available structures of protein complexes are determined by X-ray crystallography, NMR proves to be the technique of choice under special circumstances such as crystallization-resistance, weak binding, and complicated dynamic behavior presented by protein complexes. Chemical shift perturbation analysis, inter-molecular NOE detection, paramagnetic relaxation enhancement and residual dipolar coupling detection are the four major NMR techniques used for studing PPI. The principles and strengths of these NMR techniques and their applications in studying the ubiquitin-proteasome pathway are reviewed in this article.  

Wettability is an important parameter reflecting the water/oil distribution in reservoirs. Studying the surface wettability of the rocks in the reservoir is important for oil recovery. Compared to one-dimensional relaxation spectroscopy, two-dimensional diffusion-relaxation correlation spectroscopy showed greatly improved capability in distinguishing oil and water. In this article, we showed that two-dimensional diffusion-relaxation correlation spectroscopy can be used to measure the surface wettability of glass beads and artificial cores under oilwater coexistence. It was shown that oil/water separation in artificial cores could only be achieved by two-dimentional spectroscopy, but not by traditional 1D NMR relaxation spectroscopy. In conclusion, two-dimensional diffusion-relaxation correlation spectroscopy is an important tool to measure rock surface wettability.

Using a CPMG pulse sequence, NMR logging tool transmits high-power radiofrequency (RF) pulses, receives weak echo signals following timing schedule of the CPMG pulse sequence, and dissipates energy stored in the antenna after transmitting the RF pulse. In this article, the control logic of the NMR logging tool is introduced. Field programmable gate array (FPGA) was used to control the timing of the CPMG pulse. The principles and timing requirement of transmitter, Q-switch and de-coupler were given. Simulation results were provided. The control logic introduced was used in a prototype NMR logging tool successfully.

Water production rate is a key parameter for classifying flooding level in water-flooded zone. How to calculate water production rate from water saturation index is a main problem in evaluating water-flooded zone. In this work, rocks with different water production rate were first produced with the water-injection preperation commonly used for evaluating oil/water relative permeability, and then analyzed by steadystate magnetic resonance measurements for mud logging (MR-ML) spectroscopy. Based on the response characterisics of the rocks, an empirical formula to calculate water production rate from the water saturation index was proposed, which takes advantage of the oil production test data and oil/water relative permeability curve from sealed core analysis. The feasibility of using the water production rate derived to evaluate flooding level was investigated. The results from practical applications showed that MR-ML spectroscopy can be used for rapid identification of water flooded layer, classifying water flooding level, with high accuracy.

The interactions between drug and plasma proteins play a major role in drug absorption, metabolism and its efficacy. Previous reports demonstrated that diffusion and relaxation-weighted NMR combined with principal components analysis (PCA) could be used to characterize individual variations of plasma-drug interactions. In this research, using plasma with/without drug ibuprofen (IBP) as model, the NMR parameters including diffusion time, gradient strength for diffusion-weighted NMR and echo time for relaxation-weighted NMR were optimized. The results showed that gradient strength of 1.52×10^-3 T/cm~1.90×10^-3 T/cm under diffusion time of 0.1 s~0.14 s for diffusion-weighted NMR and echo time of 70 ms~110 ms for relaxation-weighted NMR are optimal for characterizing individual variations of plasma-drug interactions.

Archaeal protein SSO6904 is a newly-discovered protein with weak calcium-binding activity. Protein SSO6904 is an all-helices protein. Protein purification by gel filtration discovered both monomer and dimer forms of SSO6904. ¹H NMR spectra indicated that the monomer and dimer have similar structural core. Analysis of 2D ¹H-¹⁵N HSQC spectra revealed that the major structural difference between the monomer and dimer was at the two loops connecting helices 2 and 3, and helices 5 and 6, respectively. These two loops form a key structural region for constructing the dimer, while other regions of monomer and dimer have the same structures. Structural analysis proposed a domain-swapped model of the SSO6904 dimer. The domain-swapped dimer may regulate the stability and function of SSO6904.

Butyrate metabolites are present in animals, plants and some microorganisms with various important biological functions. Many molecular features of the metabolites remain to be fully understood, including the characteristics of their structures in the solid states, molecular dynamics and the relationships between these two aspects. In this paper, the ¹³C chemical shifts of a series of amino- and hydroxylbutyrate metabolites were analyzed with ¹³C CP MAS NMR spectroscopy. Some structure-property relationships were observed. These metabolites had significant differences for their ¹³C chemical shifts in solution and the solid state. In the solid state, the presence of amino and hydroxyl groups had obvious contributions to such differences due to their participation in hydrogen-bonding whereas participation of methyl groups in hydrophobic interactions also had observable effects. These findings provide essential basic information for further understanding the structures, molecular dynamics and perhaps polymorphisms for these metabolites.

A field programmable gate array (FPGA)-based multi-channel receiver module was developed for magnetic resonance imaging (MRI), with its performance evaluated by MRI experiments. Based on a single FPGA, this apparatus operates direct sampling, digital down conversion and data flow control for multi-channel MR signals. The system-level digital signal processing (DSP) development tools offered by Xilinx company——System Generator was used for FPGA function modeling, simulation and automatic code generation of HDL. The sampling rate of this module is 80 MSPS and the receiver bandwidth can be varied between 1 kHz and 1 MHz, thus the module is suitable for an MRI system with a magnetic field lower than 1 T. Inside the FPGA, digital quadrature demodulation, decimation filtering and data stream processing of one to four channels of sampled signals are performed, and the module is expandable to 8 channels. This module has features of small size, highly integrated and reconfigurable and low cost, providing a high-performance digital solution for multi-channel reception system of an MRI spectrometer.

The segmental motions of two nanocomposites, in which polyhedral oligomeric silsequi-oxane (POSS) is respectively copolymerized with n-butyl methacrylate (BMA) and methyl methacrylate (MMA), were investigated by solid-state NMR techniques in combination with transmission electron microscopy (TEM). The results indicated that the POSS molecules are thoroughly dispersed in the two polymer matrix. The POSS/PMMA and POSS/PBMA nanocomposites showed a homogenous structure with almost one component, and the segmental motions more constrained in the POSS/PMMA nanocomposite than the POSS/PBMA nanocomposite. The 2D HETCOR results indicated the distance between the polymer and POSS unit is shorter in the POSS/PBMA nanocomposite than in the POSS/PMMA nanocomposite.  

Based on the comprehensive summarization and analysis of reported data of ^19F NMR chemical shift, a empirical formula using parameters from 20 substitutents as variables to calculate ¹⁹F NMR chemical shifts of fluoroaromatics (δ_cal=-113.5+Δo+Δm+Δp+C) was derived with linear least-squares regression. A F-test was used to evaluate the formula obtained. The confidence limit was found to be 99.5%, average deviation 0.628 and standard deviation 4.720. The calculating errors for about 93.2% of the compounds were found to be less than 7.0 (with relative errors of 0.7%).

Poly[2-(diethylamino)ethylmethacry-late](PDMAEMA) with narrow molecular-weight distribution was synthesized by the atom transfer radical polymerization (ATRP) method. The thermo-sensitive, pH-sensitive and ionic sensitive behaviors of PDMAEMA chains in D₂O solution were investigated by measuring ¹H NMR spectra and relaxation times. It was found that the mobility, temperature-induced lower critical solution temperature (LCST) transition and ionic-strength-induced phase separation of PDMAEMA chains depend on pH of the solution. The mobility of PDMAEMA chains decreased with increasing pH value at room temperature. Ionic-strength-induced phase separation was observed at lower pH values, but not LCST transition. On the contrary, the LCST transition occurred at higher pH values, but not the ionic-strength-induced phase separation.

A static three-dimensional structure alone does not fully interpret the physiological functions of a protein in many cases. Dynamics studies can disclose internal motions of a protein on different time scales, providing a better link between dynamic structures and biological functions. In this review, the theoretical and experimental methods for protein dynamics studied by NMR spin relaxation are summarized. The reduced spectral density mapping and the Modelfree formulism are employed to describe fast motions on the ps~ns time scale. Slow motions on the μs~ms time scale, associated with conformational and chemical exchanges, are often analyzed by CPMG and R_1ρ  relaxation dispersion curves. NMR-based dynamics studies promote protein structures from the three-dimensional date to the fourdimensional era.