Hailu Zhang

Theoretical Predictions of 31P NMR Chemical Shift Threshold of Trimethylphosphine Oxide Absorbed on Solid Acid Catalysts

The 31P NMR chemical shifts of adsorbed trimethylphosphine oxide (TMPO) and the configurations of the corresponding TMPOH+ complexes on Brønsted acid sites with varying acid strengths in modeled zeolites have been predicted theoretically by means of density functional theory (DFT) quantum chemical calculations. The configuration of each TMPOH+ complex was optimized at the PW91/DNP level based on an 8T cluster model, whereas the 31P chemical shifts were calculated with the gauge including atomic orbital (GIAO) approach at both the HF/TZVP and MP2/TZVP levels. A linear correlation between the 31P chemical shift of adsorbed TMPO and the proton affinity of the solid acids was observed, and a threshold for superacidity (86 ppm) was determined. This threshold for superacidity was also confirmed by comparative investigations on other superacid systems, such as carborane acid and heteropolyoxometalate H3PW12O40. In conjunction with the strong correlation between the MP2 and the HF 31P isotropic shifts, the 8T cluster model was extended to more sophisticated models (up to 72T) that are not readily tractable at the GIAO-MP2 level, and a 31P chemical shift of 86 ppm was determined for TMPO adsorbed on zeolite H-ZSM-5, which is in good agreement with the NMR experimental data.

31P Chemical Shift of Adsorbed Trialkylphosphine Oxides for Acidity Characterization of Solid Acids Catalysts

A comprehensive study has been made to predict the adsorption structures and (31)P NMR chemical shifts of various trialkylphosphine oxides (R3PO) probe molecules, viz., trimethylphosphine oxide (TMPO), triethylphosphine oxide (TEPO), tributylphosphine oxide (TBPO), and trioctylphosphine oxide (TOPO), by density functional theory (DFT) calculations based on 8T zeolite cluster models with varied Si-H bond lengths. A linear correlation between the (31)P chemical shifts and proton affinity (PA) was observed for each of the homologous R3PO probe molecules examined. It is found that the differences in (31)P chemical shifts of the R3POH(+) adsorption complexes, when referring to the corresponding chemical shifts in their crystalline phase, may be used not only in identifying Brønsted acid sites with varied acid strengths but also in correlating the (31)P NMR data obtained from various R3PO probes. Such a chemical shift difference therefore can serve as a quantitative measure during acidity characterization of solid acid catalysts when utilizing (31)P NMR of various adsorbed R3PO, as proposed in our earlier report (Zhao; et al. J. Phys. Chem. B 2002, 106, 4462) and also illustrated herein by using a mesoporous H-MCM-41 aluminosilicate (Si/Al = 25) test adsorbent. It is indicative that, with the exception of (TMPO), variations in the alkyl chain length of the R3PO (R = C(n)H(2n+1); n > or = 2) probe molecules have only negligible effect on the (31)P chemical shifts (within experimental error of ca. 1-2 ppm) either in their crystalline bulk or in their corresponding R3POH(+) adsorption complexes. Consequently, an average offset of 8 +/- 2 ppm was observed for (31)P chemical shifts of adsorbed R3PO with n > or = 2 relative to TMPO (n = 1). Moreover, by taking the value of 86 ppm predicted for TMPO adsorbed on 8T cluster models as a threshold for superacidity (Zheng; et al. J. Phys. Chem. B 2008, 112, 4496), a similar threshold (31)P chemical shift of ca. 92-94 ppm was deduced for TEPO, TBPO, and TOPO.

Rational Design and Synthesis of γFe2O3@Au Magnetic Gold Nanoflowers for Efficient Cancer Theranostics

An γFe2 O3 @Au core/shell-type magnetic gold nanoflower-based theranostic nano-platform is developed. It is integrated with ultrasensitive surface-enhanced Raman scattering imaging, high-resolution photo-acoustics imaging, real-time magnetic resonance imaging, and photothermal therapy capabilities.

Graphene Oxide Based Theranostic Platform for T1-Weighted Magnetic Resonance Imaging and Drug Delivery

Magnetic resonance imaging (MRI) is a powerful and widely used clinical technique in cancer diagnosis. MRI contrast agents (CAs) are often used to improve the quality of MRI-based diagnosis. In this work, we developed a positive T1 MRI CA based on graphene oxide (GO)-gadolinium (Gd) complexes. In our strategy, diethylenetriaminepentaacetic acid (DTPA) is chemically conjugated to GO, followed by Gd(III) complexation, to form a T1 MRI CA (GO-DTPA-Gd). We have demonstrated that the GO-DTPA-Gd system significantly improves MRI T1 relaxivity and leads to a better cellular MRI contrast effect than Magnevist, a commercially used CA. Next, an anticancer drug, doxorubicin (DOX), was loaded on the surface of GO sheets via physisorption. Thus-prepared GO-DTPA-Gd/DOX shows significant cytotoxicity to the cancer cells (HepG2). This work provides a novel strategy to build a GO-based theranostic nanoplatform with T1-weighted MRI, fluorescence imaging, and drug delivery functionalities.

Physicochemical characterization of felodipine-kollidon VA64 amorphous solid dispersions prepared by hot-melt extrusion

To improve the dissolution and hence the oral bioavailability, amorphous felodipine (FEL) solid dispersions (SDs) with Kollidon® VA 64 (PVP/VA) were prepared. Hot-melt extrusion was employed with an extruding temperature below the melting point (Tm ) of FEL. X-ray powder diffraction (XRPD) and (13) C CP/MAS nuclear magnetic resonance (NMR) measurements show that the extrudates are amorphous. The intermolecular interaction between FEL and PVP/VA in SDs was investigated by Fourier transform infrared spectroscopy, (15) N CP/MAS NMR, and (1) H high-resolution MAS NMR. Furthermore, a single glass transition temperature (Tg ) was detected by differential scanning calorimetry in addition to a single (1) H T1 or T1rho relaxation time detected by (13) C NMR signals. These results confirm that the extrudates contain FEL dispersed into the polymer matrix at a molecular level with no detectable phase separation. This molecular-scale mixing results in a significantly faster dissolution rate compared with the pure crystalline FEL. Additionally, the molecular-scale mixing prevents the amorphous drug from recrystallizing even after being stored at 40°C/75% Relative Humidity for 2 months.

2 : 1 5-Fluorocytosine–acesulfame CAB cocrystal and 1 : 1 5-fluorocytosine–acesulfame salt hydrate with enhanced stability against hydration

5-Fluorocytosine (FC), a widely used antifungal drug, has poor physical stability under different relative humidity (RH) conditions, which may trigger serious challenges during its drug product development. In this contribution, a conjugate acid–base (CAB) cocrystal and a salt hydrate of FC were obtained with an artificial sweetener, acesulfame (AH), in molar ratios of 2 : 1 (FCAH21) and 1 : 1 (FCAH11), respectively. The resulting products were characterized by a variety of analytical methods, including single-crystal and powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and dynamic vapor sorption (DVS). 13C and 15N solid-state NMR spectra provide solid evidence for the CAB cocrystal/salt formation. At room temperature, moisture sorption data show that the new forms are nonhygroscopic/slightly hygroscopic and resistant to FC hydrate formation under high RH conditions (>80%). FCAH21 has a higher FC content and presents more favorable thermal stability than FCAH11, which make it more attractive for further pharmaceutical application.

Rotavirus capsid surface protein VP4-coated Fe3O4 nanoparticles as a theranostic platform for cellular imaging and drug delivery

The development of a theranostic nanoplatform based on rotavirus structural protein VP4-coated Fe(3)O(4) nanoparticles (NPs) for dual modality magnetic resonance/fluorescence cellular imaging and drug delivery is reported. VP4 protein was obtained from Escherichia coli approach, and then chemically conjugated to Fe(3)O(4) NPs premodified with meso-2,3-dimercaptosuccinnic acid (DMSA) in the presence of 1-ethyl-3-(3-dimethyaminopropyl) carbodiimide (EDC). Next, the VP4-coated Fe(3)O(4) NPs were loaded with doxorubicin (DOX), a typical anticancer drug, via formation of amide bond through the EDC approach. Prussian blue staining analysis reveals that the VP4-coated Fe(3)O(4) NPs can be internalized efficiently by MA104 and HepG2 cells, thereby significantly improving cellular MRI sensitivity, compared with dextran- and BSA-coated Fe(3)O(4) NPs. In addition, DOX loaded on the VP4-coated Fe(3)O(4) NPs exhibits significant cytotoxicity to the cancer cells (HepG2). The current work provides a general approach toward the rational design and synthesis of a versatile theranostic nanoplatform based on functional protein-coated magnetic NPs with good biocompatibility, biodegradability, and capability of simultaneously performing multimodality imaging and therapy for optimal clinical outcomes.

Aptamer-Modified Temperature-Sensitive Liposomal Contrast Agent for Magnetic Resonance Imaging

A novel aptamer modified thermosensitive liposome was designed as an efficient magnetic resonance imaging probe. In this paper, Gd-DTPA was encapsulated into an optimized thermosensitive liposome (TSL) formulation, followed by conjugation with AS1411 for specific targeting against tumor cells that overexpress nucleolin receptors. The resulting liposomes were extensively characterized in vitro as a contrast agent. As-prepared TSLs-AS1411 had a diameter about 136.1 nm. No obvious cytotoxicity was observed from MTT assay, which illustrated that the liposomes exhibited excellent biocompatibility. Compared to the control incubation at 37 °C, the liposomes modified with AS1411 exhibited much higher T1 relaxivity in MCF-7 cells incubated at 42 °C. These data indicate that the Gd-encapsulated TSLs-AS1411 may be a promising tool in early cancer diagnosis.

The interplay of T1- and T2-relaxation on T1-weighted MRI of hMSCs induced by Gd-DOTA-peptides.

Three Gd-DOTA-peptide complexes with different peptide sequence are synthesized and used as T1 contrast agent to label human mesenchymal stem cells (hMSCs) for magnetic resonance imaging study. The peptides include a universal cell penetrating peptide TAT, a linear MSC-specific peptide EM7, and a cyclic MSC-specific peptide CC9. A significant difference in labeling efficacy is observed between the Gd-DOTA-peptides as well as a control Dotarem. All Gd-DOTA-peptides as well as Dotarem induce significant increase in T1 relaxation rate which is in favor of T1-weighted MR imaging. Gd-DOTA-CC9 yields the maximum labeling efficacy but poor T1 contrast enhancement. Gd-DOTA-EM7 yields the minimum labeling efficacy but better T1 contrast enhancement. Gd-DOTA-TAT yields a similar labeling efficacy as Gd-DOTA-CC9 and similar T1 contrast enhancement as Gd-DOTA-EM7. The underlying mechanism that governs T1 contrast enhancement effect is discussed. Our results suggest that T1 contrast enhancement induced by Gd-DOTA-peptides depends not only on the introduced cellular Gd content, but more importantly on the effect that Gd-DOTA-peptides exert on the T1-relaxation and T2-relaxation processes/rates. Both T1 and particularly T2 relaxation rate have to be taken into account to interpret T1 contrast enhancement. In addition, the interpretation has to be based on cellular instead of aqueous longitudinal and transverse relaxivities of Gd-DOTA-peptides.

Progress in development and application of solid-state NMR for solid acid catalysis

Solid acid catalysts have been widely used in petrochemical industry and their catalytic activities are normally dictated by their acidities. Unlike conventional acidity characterization techniques such as titration, infrared, or temperature-programmed desorption, detailed acid features of solid acids, such as type, distribution, concentration, and strength of acid sites may be attained by advanced methods involving pertinent probe molecules and state-of-the-art solid-state nuclear magnetic resonance (SSNMR) techniques, i.e. double resonance and two-dimensional correlation spectroscopies. In addition, in situ solid-state NMR method is capable of probing the guest/host properties of the reactant at the active centers of the catalysts as well as the intermediate species formed during conversion. It provides direct experimental evidence for exploring the mechanism of catalytic reaction. In this report, the fundamental theory and the recent developments in solid-state NMR are reviewed with specific focus on relevant applications in structure and acidity characterization of solid acid catalysts and catalytic mechanisms