Cellulosic polyelectrolytes: synthetic pathways to regioselectively substituted ammonium and phosphonium derivatives

Cationic polysaccharide polyelectrolytes are important synthetic targets for drug and gene delivery, especially by encapsulation of nucleic acids and proteins through electrostatic interactions. They also have potential as paracellular permeability enhancers that may increase transport across the gastrointestinal (GI) epithelium, especially for therapeutic hydrophilic macromolecules. Semisynthetic chitosan has been more heavily investigated as a cationic polysaccharide polyelectrolyte. This study explores the synthetic conditions needed to produce ammonio and phosphonio cellulose derivatives regioselectively by halogen displacement at C-6 while maximizing the degree of substitution (DS) of cationic substituent. Regioselective substitution was successful, however there were found to be some limitations to the DS and solubility of ammonium derivatives prepared in this way (highest DS 0.43); conversely, water-soluble 6-phosphonio-6-deoxycellulose derivatives were produced with DS > 0.5, with highest DS of 0.73. The repulsion between accumulating positive charges was confirmed as a likely source of DS limitation since high DS (0.9) of 6-triethylamino cellulose was synthesized under comparable conditions. Further reaction of 6-ammonio-co-6-bromo derivatives with a thiol produced 6-ammonio-co-6-thiolated products with improved aqueous solubility. The thiol DS of 0.68 determined by elemental analysis confirmed substitution of residual bromide from low DS (0.30) ammonium products to give essentially complete substitution at C-6.     

Probing the structure of single-molecule surface-enhanced Raman scattering hot spots

We present here a detailed study of the specific nanoparticle structures that give rise to single-molecule surface-enhanced Raman scattering (SMSERS). A variety of structures are observed, but the simplest are dimers of Ag nanocrystals. We chose one of these structures for detailed study using electrodynamics calculations and found that the electromagnetic SERS enhancement factors of 10(9) are easily obtained and are consistent with single-molecule SERS activity.     

2-Methylimidazole-assisted Morphology Modulation of a Copper-based Metal-organic Framework Transducer for Enhanced Electrochemical Peroxidase-like Activity

A tailored metal-organic framework transducer material Cu−BDC(NH₂)@2-MI was synthesized with 2-methylimidazole as competitive ligand for the modulation of its morphology and catalytic activity. 2-MI effectively helped the deprotonation of 2-aminoterephthalic acid and enabled the fast generation of MOF crystals at room temperature. More importantly, this 2-MI-doped MOF exhibited well-tuned morphology and was able to assist efficient redox procedures in electrochemical H₂O₂ reduction. Therefore, a prototype H₂O₂ sensor can present decent linear ranges from 10 μM to 13.28 mM and a detection limit of 0.97 μM. This novel design could boost the utilization of proprietary MOFs materials out of laboratory.     

Prebiotic Synthesis and Isomerization in Interstellar Analog Ice: Glycinal,Acetamide, and Their Enol Tautomers

Glycinal (HCOCH₂NH₂) and acetamide (CH₃CONH₂) are simple molecular building blocks of biomolecules in prebiotic chemistry, though their origin on early Earth and formation in interstellar media remain a mystery. These molecules are formed with their tautomers in low temperature interstellar model ices upon interaction with simulated galactic cosmic rays. Glycinal and acetamide are accessed via barrierless radical-radical reactions of vinoxy (⋅CH₂CHO) and acetyl (⋅C(O)CH₃), and then undergo keto-enol tautomerization. Exploiting tunable photoionization reflectron time-of-flight mass spectroscopy and photoionization efficiency (PIE) curves, these results demonstrate fundamental reaction pathways for the formation of complex organics through non-equilibrium ice reactions in cold molecular cloud environments. These molecules demonstrate an unconventional starting point for abiotic synthesis of organics relevant to contemporary biomolecules like polypeptides and cell membranes in deep space.     

Organic thin-film transistors based on carbonyl-functionalized quaterthiophenes: high mobility N-channel semiconductors and ambipolar transport

New carbonyl-functionalized quaterthiophenes, 5, 5' '-diheptanoyl-2,2':5',2' ':5' ',2' '-quaterthiophene (DHCO-4T), 5, 5' '-diperfluorohexylcarbonyl-2,2':5',2' ':5' ',2' '-quaterthiophene (DFHCO-4T), and 2,7-[bis-(5-perfluorohexylcarbonylthien-2-yl)]-4H-cyclopenta[2,1-b:3,4-b']-dithiophen-4-one (DFHCO-4TCO) have been synthesized and characterized. Field-effect transistors fabricated with these materials exhibit high electron mobilities both in a vacuum (up to 0.6 cm2 V-1 s-1) and in air (up to 0.02 cm2 V-1 s-1) and very high Ion:Ioff currents ratios (>107). DHCO-4T is the first organic material exhibiting excellent ambipolar transport (mue/muh up to 0.1/0.01 cm2 V-1 s-1, (Ion:Ioff)e/(Ion:Ioff)h up to 107/108 for the same device) over a broad range of deposition temperatures. These materials are therefore promising for organic complementary circuits.     

CdO as the archetypical transparent conducting oxide. Systematics of dopant ionic radius and electronic structure effects on charge transport and band structure

A series of yttrium-doped CdO (CYO) thin films have been grown on both amorphous glass and single-crystal MgO(100) substrates at 410 degrees C by metal-organic chemical vapor deposition (MOCVD), and their phase structure, microstructure, electrical, and optical properties have been investigated. XRD data reveal that all as-deposited CYO thin films are phase-pure and polycrystalline, with features assignable to a cubic CdO-type crystal structure. Epitaxial films grown on single-crystal MgO(100) exhibit biaxial, highly textured microstructures. These as-deposited CYO thin films exhibit excellent optical transparency, with an average transmittance of >80% in the visible range. Y doping widens the optical band gap from 2.86 to 3.27 eV via a Burstein-Moss shift. Room temperature thin film conductivities of 8,540 and 17,800 S/cm on glass and MgO(100), respectively, are obtained at an optimum Y doping level of 1.2-1.3%. Finally, electronic band structure calculations are carried out to systematically compare the structural, electronic, and optical properties of the In-, Sc-, and Y-doped CdO systems. Both experimental and theoretical results reveal that dopant ionic radius and electronic structure have a significant influence on the CdO-based TCO crystal and band structure: (1) lattice parameters contract as a function of dopant ionic radii in the order Y (1.09 A) < In (0.94 A) < Sc (0.89 A); (2) the carrier mobilities and doping efficiencies decrease in the order In > Y > Sc; (3) the dopant d state has substantial influence on the position and width of the s-based conduction band, which ultimately determines the intrinsic charge transport characteristics.     

Three-dimensional source reconstruction with a scanned pinhole camera

We present a simple reconstruction algorithm for three-dimensional (3D) incoherent source distributions imaged by a laterally scanned pinhole camera. We consider digital sampling of multiple pinhole images for 3D reconstruction and implement an experimental demonstration with lateral resolution of 2x10(-3) rad and longitudinal resolution of approximately 0.14z(2) m , where z is the object-to-pinhole distance in meters.