Ground state energy of a bound piezoelectric polaron

The ground state energy of a piezoelectric polaron bound in a Coulomb potential is calculated analytically in the weak coupling limit.     

Energy levels of hydrogenic impurity states in GaAs-Ga1−xAlxAs quantum well structures

Binding energies of the ground state and of four excited states of a hydrogenic impurity in quantum well structures consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga_1?xAl_xAs are calculated using a variational approach. The ground-state binding energy is calculated as a function of the barrier potential for a given size of the GaAs quantum well and is found to be linearly dependent on the inverse of the square root of the barrier potential except for very small potentials. The variation of the binding energies of all five states as a function of the size of the GaAs quantum well are also calculated and their behavior is discussed.     

Halide and complex halogeno anions as salts of oxinato bis(η5-indenyl)titanium(IV)/zirconium(IV) chelates

Bis(η⁵-indenyl)titanium(IV) dichloride and bis(η⁵-indenyl)zirconium(IV) dichloride, when treated with 8-hydroxyquinoline (oxine) in aqueous medium form ionic derivatives of the type [(η⁵-C₉H₇)₂ML]⁺Cl^? (M = Ti(IV), Zr(IV), L is the conjugate base of oxine). A number of halide and complex halogeno anions present in aqueous solution were isolated as salts of these ionic complexes giving derivatives of the type, [(η⁵-C₉H₇)₂ML]⁺X^? (X = Br^?, I^?, ZnCl₃(H₂O)^?, CdCl₄^2?, HgCl₃^?). Conductivity measurements in nitrobenzene indicate that these complexes are electrolytes. Both the IR and ¹H NMR spectral studies demonstrate that the ligand L is chelating. Consequently there is tetrahedral coordination about the titanium(IV) or zirconium(IV) ion.     

Synthesis of Pd and Rh metal nanoparticles in the interlayer space of organically modified montmorillonite

This study reports the synthesis of palladium and rhodium metal nanoparticles supported on montmorillonite (MMT) and partially organically modified MMT (POMM) using tetraamine palladium and hexaamine rhodium complex as precursor for palladium and rhodium respectively. The synthesized nanoparticles were characterized by powder X-ray diffraction PXRD and TEM. The PXRD study shows characteristic crystallographic planes for Pd and Rh metal and confirm the formation of metal nanoparticles in MMT and POMM. The TEM images reveal the effect of organic modification of MMT on decreasing particle size of Pd and Rh metal. The Pd and Rh metal nanoparticles are agglomerated in pristine MMT while nanoparticles are well dispersed in POMM. ICP-AES analysis was carried out to estimate quantitative amount of Pd and Rh metal in MMT and POMM.     

Synthesis of modular building blocks using glycosyl phosphate donors for the construction of asymmetric N-glycans

Glycosyl phosphates are known as versatile donors for the synthesis of complex oligosaccharides both chemically and enzymatically. Herein, we report the stereoselective construction of modular building blocks for the synthesis of N-glycan using glycosyl phosphates as donors. We have synthesized four trisaccharide building blocks with orthogonal protecting groups, namely, Manβ2GlcNAc(OAc)₃β6GlcNAc (9), Manβ2GlcNAc-β6GlcNAc(OAc)₃ (15), Manβ2GlcNAc(OAc)₃β4GlcNAc (18) and Manβ2GlcNAcβ4GlcNAc(OAc) (22) for further selective elongation using glycosyltransferases. The glycosylation reaction using glycosyl phosphate was found to be high yielding with shorter reaction time. Initially, The phthalimide protected glucosamine donor was exploited to ensure the formation of β-glycosidic linkage and later converted to the N-acetyl group before the enzymatic synthesis. The selective deprotection of O-benzyl group was performed prior to enzymatic synthesis to avoid its negative interference.     

Enhanced direct sunlight photocatalytic oxidation of methanol using nanocrystalline TiO2 calcined at different temperature

The pharmacokinetics (PK) of carrier-mediated agents (CMA) is dependent upon the carrier system. As a result, CMA PK differs greatly from the PK of small molecule (SM) drugs. Advantages of CMAs over SMs include prolonged circulation time in plasma, increased delivery to tumors, increased antitumor response, and decreased toxicity. In theory, CMAs provide greater tumor drug delivery than SMs due to their prolonged plasma circulation time. We sought to create a novel PK metric to evaluate the efficiency of tumor and tissue delivery of CMAs and SMs. We conducted a study evaluating the plasma, tumor, liver, and spleen PK of CMAs and SMs in mice bearing subcutaneous flank tumors using standard PK parameters and a novel PK metric entitled relative distribution over time (RDI-OT), which measures efficiency of delivery. RDI-OT is defined as the ratio of tissue drug concentration to plasma drug concentration at each time point. The standard concentration versus time area under the curve values (AUC) of CMAs were higher in all tissues and plasma compared with SMs. However, 8 of 17 SMs had greater tumor RDI-OT AUC_0–last values than their CMA comparators and all SMs had greater tumor RDI-OT AUC_0–6 h values than their CMA comparators. Our results indicate that in mice bearing flank tumor xenografts, SMs distribute into tumor more efficiently than CMAs. Further research in additional tumor models that may more closely resemble tumors seen in patients is needed to determine if our results are consistent in different model systems.     

Enantioselective O-acetylcyanation/cyanoformylation of aldehydes using catalysts with built-in crown ether-like motif in chiral macrocyclic V(V) salen complexes

Chiral macrocyclic V(V) salen complexes 1a-f derived from macrocyclic ligands obtained by the reaction of 1R,2R-(−) diaminocyclohexane/(1R,2R)-(+)-1,2-diphenylethylenediamine with bis-aldehydes 2 and 3 were synthesized and used as efficient catalysts in asymmetric cyanation reactions. The V(V) catalysts demonstrated excellent performance (product yields and ees up to 99%) with potassium cyanide (KCN) and sodium cyanide (NaCN). The catalytic system also performed very well with a safer source of cyanide-ethyl cyanoformate to give cyanohydrin carbonates in excellent yield and ee (up to 97%). The V(V) macrocyclic salen complex 1b retained its performance at multi-gram level and was conveniently recycled for a number of times.     

DNP enhanced frequency-selective TEDOR experiments in bacteriorhodopsin

We describe a new approach to multiple ¹³C–¹⁵N distance measurements in uniformly labeled solids, frequency-selective (FS) TEDOR. The method shares features with FS-REDOR and ZF- and BASE-TEDOR, which also provide quantitative ¹⁵N–¹³C spectral assignments and distance measurements in U-[¹³C,¹⁵N] samples. To demonstrate the validity of the FS-TEDOR sequence, we measured distances in [U-¹³C,¹⁵N]-asparagine which are in good agreement with other methods. In addition, we integrate high frequency dynamic nuclear polarization (DNP) into the experimental protocol and use FS-TEDOR to record a resolved correlation spectrum of the Arg-¹³C_γ–¹⁵N_ε region in [U-¹³C,¹⁵N]-bacteriorhodopsin. We resolve six of the seven cross-peaks expected based on the primary sequence of this membrane protein.     

Synthesis of composite gold/tin-oxide nanoparticles by nano-soldering

Composite Au–SnO₂ nanoparticles (NPs) are synthesized by nano-soldering of pure Au and SnO₂ NPs. The multi-step process involves synthesis of pure Au and SnO₂ NPs separately by nanosecond pulse laser ablation of pure gold and pure tin targets in deionized water and post-ablation laser heating of mixed solution of Au colloidal and SnO₂ colloidal to form nanocomposite. Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used to study the effect of laser irradiation time on morphology of the composite Au–SnO₂ NPs. The spherical particles of 4 nm mean size were obtained for 5 min of post-laser heating. Increased mean size and elongated particles were observed on further laser heating. UV–vis spectra of Au–SnO₂ nanocomposites show red shift in the plasmon resonance absorption peak and line shape broadening with respect to pure Au NPs. The negative binding energy shift of Au 4f_7/2 peak observed in X-ray Photoelectron Spectra (XPS) indicates charge transfer in the nano-soldered Au–SnO₂ between gold and tin oxide and formation of soldered nanocomposite.