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Melanin is a central polymer in living organisms, yet our understanding of its molecular structure remains unresolved. Here, we apply a biosynthetic approach to explore the composite structures accessible in one type of melanin, eumelanin. Using a combination of solid-state NMR, dynamic nuclear polarization, and electron microscopy, we reveal how a variety of monomers are enzymatically polymerized into their corresponding eumelanin pigments. We demonstrate how this approach can be used to unite structure with an understanding of enzymatic activity, substrate scope, and the regulation of nanostructural features. Overall, this data reveals how intermediate metabolites of the Raper-Mason metabolic pathway contribute to polymerization, allowing us to revisit the original proposal of how eumelanin is biosynthesized.

Melanin is a central polymer in living organisms, yet our understanding of its molecular structure remains unresolved. Here, we apply a biosynthetic approach to explore the composite structures accessible in one type of melanin, eumelanin. Using a combination of solid-state NMR, dynamic nuclear polarization, and electron microscopy, we reveal how a variety of monomers are enzymatically polymerized into their corresponding eumelanin pigments. We demonstrate how this approach can be used to unite structure with an understanding of enzymatic activity, substrate scope, and the regulation of nanostructural features. Overall, this data reveals how intermediate metabolites of the Raper-Mason metabolic pathway contribute to polymerization, allowing us to revisit the original proposal of how eumelanin is biosynthesized.

Xuan Feng,1,2 Feng Xue,3 Guihua He,4 Suiping Huang,4 Qing Ni1,3 1Institute of Translational Medicine, Medical College, Yangzhou University, Yangzhou, 225001, Jiangsu, People’s Republic of China; 2Jiangsu Key Laboratory of Integrated Traditional Chinese and Western Medicine for Prevention and Treatment of Senile Diseases, Yangzhou, 225001, Jiangsu, People’s Republic of China; 3Department of Surgery, Affiliated Hospital of Yangzhou University, Yangzhou, 225000, Jiangsu, People’s Republic of China; 4Department of Gastroenterology, The Second Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, 510120, People’s Republic of ChinaCorrespondence: Suiping Huang; Qing Ni Email gzdoctorhsp@126.com; nqingnn@163.comPurpose: Banxia xiexin decoction (BXXX) is a classical Chinese herbal compound for the treatment of gastrointestinal diseases. Its ingredients are also considered helpful for cancer rehabilitation. Here, we will explore the regulatory mechanism of BXXX acting on PD-L1 in gastric cancer (GC).Methods: GC samples and the general baseline data of the patients were collated. Immunohistochemical (IHC) detected the expression of programmed cell death-ligand 1(PD-L1), hypoxia-inducible factor-1 (HIF-1), epidermal growth factor receptor (EGFR), interferon-γ receptor (IFNGR) and Toll-like receptor 4 (TLR4). ELISA detected the expressions of EGF, IFNG and IL-6 in serum samples. Network tools were used to analyze the potential molecules of BXXX. In the cell experiment, CCK-8 detected the cell proliferation. Tunel detected the apoptosis. Western blot detected the expression of related proteins. In animal experiments, the tumor volume of GC-bearing mice was observed. Expression of EGF, IFNG and IL-6 in the serum of tumor-bearing GC mice were detected by ELISA. Western blot detected the expression of related proteins.Results: The expressions of PD-L1, HIF-1, EGFR, IFNGR and TLR4 in the tissues of GC

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2018., Cataloged from PDF version of thesis., Includes bibliographical references., Bacteriorhodopsin (bR) is comprised of 7 trans-membrane helices that enclose a retinylidene chromophore formed by a Schiff base (SB) between the retinal and Lys216. Due to bR's relative availability, it serves as a model for other members of the rhodopsin family, ion channels and GPCRs. Since its discovery in the 1970's, bR has been intensely studied by various methods including: X-ray crystallography, EM, FT-IR, molecular simulations, and NMR, etc. Despite numerous advances, details of its pump mechanism remain elusive due to experimental limitations in sensitivity and/or resolution. Here, dynamic nuclear polarization (DNP) is employed to boost the ¹H NMR signal. With an enhancement of 75, multidimensional spectra of low gyromagnetic nuclei were made possible. The cryogenic experimental temperature also traps the various bR photocycle intermediates, allowing them to be studied in situ. We are able to answer the one lingering question regarding bR's primary proton transfer pathway and conduct distance measurements near the active site. The pathway of bR's primary proton transfer has been the subject of scrutiny for many years. DNP MAS NMR bond length measurements of the SB proton reveal an elongated N-H bond in L, the transfer of ¹H in deprotonated MO, and a tight N-H bond in N intermediate. The ¹H chemical shift of ~3.6 ppm in M₀ indicates an alcohol hydrogen donor partner. This strongly supports the SB H+ being relayed from the SB to Asp85 via Thr89 as the pathway for bR's primary proton transfer. Distance measurements obtained here are the first set of long-range DNP MAS NMR measurements conducted on a uniformly labeled bR system. We find that the SB-D85 distance shrinks in the first half of the photocycle and is released after the primary proton transfer. The decrease in distance between the two indicates helix C and helix G are moving toward each other, which could be the reason why functional L is difficult to achieve. The subsequent release of helix G provide, by Qing Zhe Ni., Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2018., Cataloged from PDF version of thesis., Includes bibliographical references., Bacteriorhodopsin (bR) is comprised of 7 trans-membrane helices that enclose a retinylidene chromophore formed by a Schiff base (SB) between the retinal and Lys216. Due to bR's relative availability, it serves as a model for other members of the rhodopsin family, ion channels and GPCRs. Since its discovery in the 1970's, bR has been intensely studied by various methods including: X-ray crystallography, EM, FT-IR, molecular simulations, and NMR, etc. Despite numerous advances, details of its pump mechanism remain elusive due to experimental limitations in sensitivity and/or resolution. Here, dynamic nuclear polarization (DNP) is employed to boost the ¹H NMR signal. With an enhancement of 75, multidimensional spectra of low gyromagnetic nuclei were made possible. The cryogenic experimental temperature also traps the various bR photocycle intermediates, allowing them to be studied in situ. We are able to answer the one lingering question regarding bR's primary proton transfer pathway and conduct distance measurements near the active site. The pathway of bR's primary proton transfer has been the subject of scrutiny for many years. DNP MAS NMR bond length measurements of the SB proton reveal an elongated N-H bond in L, the transfer of ¹H in deprotonated MO, and a tight N-H bond in N intermediate. The ¹H chemical shift of ~3.6 ppm in M₀ indicates an alcohol hydrogen donor partner. This strongly supports the SB H+ being relayed from the SB to Asp85 via Thr89 as the pathway for bR's primary proton transfer. Distance measurements obtained here are the first set of long-range DNP MAS NMR measurements conducted on a uniformly labeled bR system. We find that the SB-D85 distance shrinks in the first half of the photocycle and is released after the primary proton transfer. The decrease in distance between the two indicates helix C and helix G are moving toward each other, which could be the reason why functional L is difficult to achieve. The subsequent release of helix G provide, by Qing Zhe Ni., Ph. D.

In DNP MAS NMR experiments at ∼80–110 K, the structurally important −¹³CH₃ and −¹⁵NH₃⁺ signals in MAS spectra of biological samples disappear due to the interference of the molecular motions with the ¹H decoupling. Here we investigate the effect of these dynamic processes on the NMR line shapes and signal intensities in several typical systems: (1) microcrystalline APG, (2) membrane protein bR, (3) amyloid fibrils PI3-SH3, (4) monomeric alanine-CD₃, and (5) the protonated and deuterated dipeptide N-Ac-VL over 78–300 K. In APG, the three-site hopping of the Ala-Cβ peak disappears completely at 112 K, concomitant with the attenuation of CP signals from other ¹³C’s and ¹⁵N’s. Similarly, the ¹⁵N signal from Ala-NH₃⁺ disappears at ∼173 K, concurrent with the attenuation in CP experiments of other 15N’s as well as 13C’s. In bR and PI3-SH3, the methyl groups are attenuated at ∼95 K, while all other 13C’s remain unaffected. However, both systems exhibit substantial losses of intensity at ∼243 K. Finally, with spectra of Ala and N-Ac-VL, we show that it is possible to extract site specific dynamic data from the temperature dependence of the intensity losses. Furthermore, 2H labeling can assist with recovering the spectral intensity. Thus, our study provides insight into the dynamic behavior of biological systems over a wide range of temperatures, and serves as a guide to optimizing the sensitivity and resolution of structural data in low temperature DNP MAS NMR spectra., National Institute of Biomedical Imaging and Bioengineering (U.S.) (Grant EB-001960), National Institute of Biomedical Imaging and Bioengineering (U.S.) (Grant EB-002804), National Institute of Biomedical Imaging and Bioengineering (U.S.) (Grant EB-002026), National Institute of Biomedical Imaging and Bioengineering (U.S.) (Grant EB-001035)

A principal advantage of magic angle spinning (MAS) NMR spectroscopy lies in its ability to determine molecular structure in a noninvasive and quantitative manner. Accordingly, MAS should be widely applicable to studies of the structure of active pharmaceutical ingredients (API) and formulations. However, the low sensitivity encountered in spectroscopy of natural abundance APIs present at low concentration has limited the success of MAS experiments. Dynamic nuclear polarization (DNP) enhances NMR sensitivity and can be used to circumvent this problem provided that suitable paramagnetic polarizing agent can be incorporated into the system without altering the integrity of solid dosages. Here, we demonstrate that DNP polarizing agents can be added in situ during the preparation of amorphous solid dispersions (ASDs) via spray drying and hot-melt extrusion so that ASDs can be examined during drug development. Specifically, the dependence of DNP enhancement on sample composition, radical concentration, relaxation properties of the API and excipients, types of polarizing agents and proton density, has been thoroughly investigated. Optimal enhancement values are obtained from ASDs containing 1% w/w radical concentration. Both polarizing agents TOTAPOL and AMUPol provided reasonable enhancements. Partial deuteration of the excipient produced 3× higher enhancement values. With these parameters, an ASD containing posaconazole and vinyl acetate yields a 32-fold enhancement which presumably results in a reduction of NMR measurement time by ∼1000. This boost in signal intensity enables the full assignment of the natural abundance pharmaceutical formulation through multidimensional correlation experiments.

Dynamic nuclear polarization (DNP) is a technique used to enhance signal intensities in NMR experiments by transferring the high polarization of electrons to their surrounding nuclei. The past decade has witnessed a renaissance in the development of DNP, especially at high magnetic fields, and its application in several areas including biophysics, chemistry, structural biology and materials science. Recent technical and theoretical advances have expanded our understanding of established experiments: for example, the cross effect DNP in samples spinning at the magic angle. Furthermore, new experiments suggest that our understanding of the Overhauser effect and its applicability to insulating solids needs to be re-examined. In this article, we summarize important results of the past few years and provide quantum mechanical explanations underlying these results. We also discuss future directions of DNP and current limitations, including the problem of resolution in protein spectra recorded at 80–100 K., National Institute for Biomedical Imaging and Bioengineering (U.S.) (EB-002804), National Institute for Biomedical Imaging and Bioengineering (U.S.) (EB-001960), National Institute for Biomedical Imaging and Bioengineering (U.S.) (EB-003151), National Institute for Biomedical Imaging and Bioengineering (U.S.) (EB-002026)

National Institutes of Health (U.S.) (EB-002804), National Institutes of Health (U.S.) (EB-002026)

We demonstrate application of precise adiabatic vacuum calorimetry to observation of phase transition in the tripeptide l-alanyl-l-prolyl-glycine monohydrate (APG) from 6 to 320 K and report the standard thermodynamic properties of the tripeptide in the entire range. Thus, the heat capacity of APG was measured by adiabatic vacuum calorimetry in the above temperature range. The tripeptide exhibits a reversible first-order solid-to-solid phase transition characterized by strong thermal hysteresis. We report the standard thermodynamic characteristics of this transition and show that differential scanning calorimetry can reliably characterize the observed phase transition with <5 mg of the sample. Additionally, the standard entropy of formation from the elemental substances and the standard entropy of hypothetical reaction of synthesis from the amino acids at 298.15 K were calculated for the studied tripeptide., National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-003151), National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-001960), National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-002026)

The electroactive nanocomposite films were fabricated using polyurethane (PU) with modified carbon nanotubes (CNTs) as the filler. The CNTs were modified using microwave-induced polymerization route and they were found to be highly dispersed in polar solvents such as dimethylformamide. The modified CNTs were characterized using transmission electron microscopy, field emission scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. To evaluate these films we mainly focused on electrical properties such as actuation behavior, resistivity, impedance analysis, and space charge measurements. We found that the PU/CNT films bent toward the cathode when an electric field was applied and they reverted to its original position when the electric field was removed. Upon the incorporation of CNTs as the filler for the polymer, the electrical properties of the films improved significantly. Asymmetric charge accumulation was observed from space charge measurements in some of the films and this explains the bending deformation and the actuation behavior.

The electroactive nanocomposite films were fabricated using polyurethane (PU) with modified carbon nanotubes (CNTs) as the filler. The CNTs were modified using microwave-induced polymerization route and they were found to be highly dispersed in polar solvents such as dimethylformamide. The modified CNTs were characterized using transmission electron microscopy, field emission scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. To evaluate these films we mainly focused on electrical properties such as actuation behavior, resistivity, impedance analysis, and space charge measurements. We found that the PU/CNT films bent toward the cathode when an electric field was applied and they reverted to its original position when the electric field was removed. Upon the incorporation of CNTs as the filler for the polymer, the electrical properties of the films improved significantly. Asymmetric charge accumulation was observed from space charge measurements in some of the films and this explains the bending deformation and the actuation behavior.

The electroactive nanocomposite films were fabricated using polyurethane (PU) with modified carbon nanotubes (CNTs) as the filler. The CNTs were modified using microwave-induced polymerization route and they were found to be highly dispersed in polar solvents such as dimethylformamide. The modified CNTs were characterized using transmission electron microscopy, field emission scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. To evaluate these films we mainly focused on electrical properties such as actuation behavior, resistivity, impedance analysis, and space charge measurements. We found that the PU/CNT films bent toward the cathode when an electric field was applied and they reverted to its original position when the electric field was removed. Upon the incorporation of CNTs as the filler for the polymer, the electrical properties of the films improved significantly. Asymmetric charge accumulation was observed from space charge measurements in some of the films and this explains the bending deformation and the actuation behavior.

The electroactive nanocomposite films were fabricated using polyurethane (PU) with modified carbon nanotubes (CNTs) as the filler. The CNTs were modified using microwave-induced polymerization route and they were found to be highly dispersed in polar solvents such as dimethylformamide. The modified CNTs were characterized using transmission electron microscopy, field emission scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. To evaluate these films we mainly focused on electrical properties such as actuation behavior, resistivity, impedance analysis, and space charge measurements. We found that the PU/CNT films bent toward the cathode when an electric field was applied and they reverted to its original position when the electric field was removed. Upon the incorporation of CNTs as the filler for the polymer, the electrical properties of the films improved significantly. Asymmetric charge accumulation was observed from space charge measurements in some of the films and this explains the bending deformation and the actuation behavior.

In this paper, we describe the design and experimental results from the rebuild of a 250 GHz gyrotron used for Dynamic Nuclear Polarization enhanced Nuclear Magnetic Resonance spectroscopy on a 380 MHz spectrometer. Tuning bandwidth of approximately 2 GHz is easily achieved at a fixed magnetic field of 9.24 T and a beam current of 95 mA producing an average output power of >10 W over the entire tuning band. This tube incorporates a double disk output sapphire window in order to maximize the transmission at 250.58 GHz. DNP Signal enhancement of >125 is achieved on a [superscript 13]C-Urea sample using this gyrotron., National Institutes of Health (U.S.) (Grant EB002804), National Institutes of Health (U.S.) (Grant EB003151), National Institutes of Health (U.S.) (Grant EB002026), National Institutes of Health (U.S.) (Grant EB001960), National Institutes of Health (U.S.) (Grant EB001035), National Institutes of Health (U.S.) (Grant EB001965), National Institutes of Health (U.S.) (Grant EB004866)

Fully hydrolyzed ultra-high-molecular-weight polyvinyl alcohol (PVA) electrospun fibers with uniform diameters of about 200 nm were fabricated by reducing the viscosity of PVA in aqueous solution. A novel viscosity-modifier (hydrazine monochloride, HMC) gradually reduces the viscosity of PVA aqueous solution over a period of several days. This phenomenon is counter to the usual effect of ionic salt addition. After being stored for several days, the viscosity decreased by up to 60 % compared to that of an equivalent pure PVA solution. Using HMC to control the viscosity of the PVA solution made it possible to fabricate ultrafine electrospun fibers. In addition, the hot water resistance of the fibers was obviously improved by annealing.

A novel flower-shaped Bi(2)O(3) superstructure has been successfully synthesized by calcination of the precursor, which was prepared via a citric acid assisted hydrothermal process. The precursor and Bi(2)O(3) were characterized with respect to morphology, crystal structure and elemental chemical state by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was shown that both the precursor and Bi(2)O(3) flower-shaped superstructure were constructed of numerous nanosheets while the nanosheets consisted of a great deal of nanoparticles. Furthermore, key factors for the formation of the superstructures have been proposed; a mechanism for the growth of the superstructure has been presented based on the FESEM investigation of different growth stages.

We synthesized zinc ferrite nanochains assembled from nanoparticles using a carbon nanotubes (CNTs) template method The resulting nanochains were systematically characterized with respect to crystal structure morphology elemental composition magnetic properties and specific surface area by X-ray diffraction (XRD) transmission electron microscopy (TEM) field emission scanning electron microscopy (FESEM) X-ray photoelectron spectroscopy (XPS) superconducting quantum interference device (SQUID) magnetometry and the N(2) adsorption method The morphology results showed that the zinc ferrite particles with diameters of 10-20 rim were structurally linked to form nanochains The magnetic property investigation indicated that the zinc ferrite nanochains exhibited ferromagnetic behavior and possessed a saturation magnetization of 45 4 emu g(-1) at 300K We addressed the growth mechanism by analyzing the experimental conditions and characterization results This method may be applicable to synthesizing other metal oxide nanochains as well

A novel one-step process using potassium persulfate (KPS) as oxidant is proposed in this paper to prepare water-soluble single-walled carbon nanotubes (SWNTs). The process without the need for organic solvents and acids is a low-cost, eco-friendly, facile method. Morphology observation by atomic force microscopy (AFM) indicates that the KPS-treated SWNTs were effectively debundled without obvious shortening in their length. The functional groups and thermal stability of the treated SWNTs were analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). XPS results show that several functional groups such as potassium carboxylate (-COOK), carbonyl (-C=O) and hydroxyl (-C-OH) groups were formed on the surfaces of the SWNTs, while the TGA results reveal that the quantity of the functional groups can reach to approximately 20%.

The mechanical stability of graphene nanoribbons (GNRs) is an important mechanical property to study, when GNRs are used as components in sensors or other nanodevices. In this paper, nonlocal effects are considered in a continuum model based theoretical analysis of the critical buckling stress of cantilevered double-layer GNRs (DLGNRs) that are subjected to an axial compressive load. The results show that the nonlocal effect has an inverse relationship with the buckling stress, and the nonlocal effect decreases with increasing aspect ratio of DLGNRs. Moreover, to the best of our knowledge this is the first report that, for DLGNRs in anti-phase modes, lower buckling mode can endure higher buckling stress because of van der Waals (vdW) interaction.

A theoretical vibrational analysis of the radial breathing mode (RBM) of double-walled carbon nanotubes (DWCNTs) subjected to pressure is presented based on an elastic continuum model. The results agree with reported experimental results obtained under different conditions. Frequencies of the RBM in DWCNTs subjected to increasing pressure depend strongly on circumferential wave numbers, but weakly on the aspect ratio and axial half-wave numbers. For the inner and outer tubes of DWCNTs, the frequency of the RBM increases obviously as the pressure increases under different conditions. The range of variation is smaller for the inner tube than the outer tube.

Multi-walled carbon nanotubes (MWCNTs) with improved dispersion property have been prepared by a mild and fast hydrothermal treatment. The hydrothermal process avoids using harsh oxidants and organic solvents, which is environmental friendly and greatly decreases the damage to intrinsic structure of MWCNTs. The modified MWCNTs were highly soluble in polar solvents such as water, ethanol and dimethylformamide. Morphological observation by TEM indicated that the diameter and inherent structure were well reserved in modified MWCNTs. X-ray photoelectron spectroscopy and Raman spectroscopy were used to quantify functional groups created on the MWCNT surface, and to determine rational parameters of hydrothermal process.

Graphene nanoribbons (GNRs), the finite-wide counterparts of crystalline graphene sheets, have been potential materials used in nano-devices because of their excellent electronic, thermal and mechanical properties. In this work, a theoretical analysis of nonlocal elasticity theory for the free vibrational characteristics of embedded double-layer GNRs (DLGNRs) is proposed based on continuum and Winkler spring models. We find two types of vibrational modes, in-phase mode (IPM) and anti-phase mode (APM). The results show that the vibrational properties of DLGNRs show different behaviors in IPM and APM. The natural frequencies of DLGNR embedded in an elastic matrix are significantly influenced by nonlocal effects, the aspect ratio of DLGNRs and the Winkler foundation modulus.

Hollow poly(aniline-co-pyrrole)-Fe3O4 (HPAP-Fe3O4) nanospheres with significant electromagnetic properties were successfully prepared via the oxidative polymerization of a mixture of aniline and pyrrole in the presence of a magnetic fluid, using a non-ionic surfactant as a template. The products were characterized by field emission scanning electron microscopy, transmission electron microscopy. Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis and Xray photoelectron spectroscopy. The electromagnetic (EM) and microwave absorbing properties of the nanocomposites were also investigated. The HPAP-Fe3O4 nanospheres exhibit superparamagnetic properties, and the conductivity increases with Fe3O4 content. The reflection loss evaluation based on the absorbing wall theory at 2 mm thickness shows that the reflection loss is reinforced in the frequency range of 0.5-10 GHz by the presence of Fe3O4 nanoparticles, and the frequency of minimum reflection loss shifts to a higher value with increasing Fe3O4 content. HPAP-Fe-06 exhibits the best microwave absorbing property between 0.5 and 10 GHz.

Based on 2501 clinical cases of type 2 diabetes, the pathogenesis of type 2 diabetes was studied using the latent structural model, and the symptoms–pathogenesis relationship was established. The results show that the latent structure model, which is nonlinear, may serve as a good tool for investigating the nonlinear and complex traditional Chinese medicine symptoms.

Based on 2501 clinical cases of type 2 diabetes, the pathogenesis of type 2 diabetes was studied using the latent structural model, and the symptoms–pathogenesis relationship was established. The results show that the latent structure model, which is nonlinear, may serve as a good tool for investigating the nonlinear and complex traditional Chinese medicine symptoms.