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The conjugated bis-guanidinate-supported zinc hydride [{LZnH}

In this work, the molecular aluminium dihydride complex bearing an N, N'-chelated conjugated bis-guanidinate (CBG) ligand is used as a catalyst for reducing a wide range of aryl and alkyl esters with good tolerance of alkene (C=C), alkyne (C≡C), halides (Cl, Br, I and F), nitrile (C≡N), and nitro (NO

Herein, a remarkable conjugated bis-guanidinate (CBG) supported zinc hydride, [{LZnH}2 ; L={(ArHN)(ArN)-C=N-C=(NAr)(NHAr); Ar=2,6-Et2 -C6 H3 }] (I) catalyzed partial reduction of heteroallenes via hydroboration is reported. A large number of aryl and alkyl isocyanates, including electron-donating and withdrawing groups, undergo reduction to obtain selectively N-boryl formamide, bis(boryl) hemiaminal and N-boryl methyl amine products. The compound I effectively catalyzes the chemoselective reduction of various isocyanates, in which the construction of the amide bond occurs. Isocyanates undergo a deoxygenation hydroboration reaction, in which the C=O bond cleaves, leading to N-boryl methyl amines. Several functionalities such as nitro, cyano, halide, and alkene groups are well-tolerated. Furthermore, a series of kinetic, control experiments and structurally characterized intermediates suggest that the zinc hydride species are responsible for all reduction steps and breaking the C=O bond.

The reaction of LH [L = {(ArNH)(ArN)-C=N-C=(NAr)(NHAr)}; Ar =2,6-Et2-C6H3] with a commercially available alane amine adduct (H3Al·NMe2Et) in toluene resulted in the formation of a conjugated bis-guanidinate (CBG)-supported aluminum dihydride complex, i.e., LAlH2 (1), in good yield. The new complex has been thoroughly characterized by multinuclear magnetic resonance, IR, mass, and elemental analyses, including single-crystal structural studies. Further, we have demonstrated the aluminum-catalyzed hydroboration of a variety of nitriles and alkynes. Moreover, aluminum-catalyzed hydroboration is expanded to more challenging substrates such as alkene, pyridine, imine, carbodiimide, and isocyanides. More importantly, we have shown that the aluminum dihydride catalyzed both intra- and intermolecular chemoselective hydroboration of nitriles and alkynes over other reducible functionalities for the first time.

Currently employed diagnostic ultrasonography provides clinically relevant information about cerebral hemodynamic changes in patients with cerebrovascular ischemia. The information thus obtained is often helpful to the physician for establishing or confirming the diagnosis and prognosis as well as in taking appropriate therapeutic decisions. It is associated with a high temporal resolution and can be performed bedside for rapid diagnosis as well as prolonged monitoring. Transcranial Doppler (TCD) ultrasonography is a non-invasive diagnostic modality that provides physiological information regarding various intracranial hemodynamic alterations in patients with cerebrovascular ischemia. Extended applications of TCD are useful in understanding various pathophysiological mechanisms responsible for the clinical manifestations of cerebrovascular ischemia. Thus, TCD is aptly called as the 'stethoscope' of a stroke neurologist. Cerebrovascular ultrasonography is considered as an essential component of a comprehensive stroke center. We have reviewed various recent patents pertaining to the applications of cerebrovascular ultrasonography employed in the selection of stroke patients for various therapeutic interventions.

Intravenous tissue plasminogen activator (IV-TPA), administered within 4.5 h of symptom onset, is the only therapeutic agent approved for achieving arterial recanalization in acute ischemic stroke. Current major guidelines recommend the use of a standard dose (0.9 mg/kg bodyweight; maximum 90 mg) of IV-TPA. However, comparable efficacy of IV-TPA was demonstrated in the observational studies from Japan when a lower dose (0.6 mg/kg bodyweight; maximum 60 mg) was used and later approved by the regulatory authorities. Although limited in numbers, considerable variations in the dose of IV-TPA are noted in recent publications from Asia, with variable results and optimal dose of TPA in Asia remains controversial. The authors present a systemic review of the existing literature and compare the efficacy and safety of standard-versus the low-dose IV-TPA therapy in acute ischemic stroke.

The cis-trans isomerization of azo chromophores covalently bound to semicrystalline polymer films was investigated. Various azo chromophores were introduced onto the functionalized semicrystalline polymer films by a chemical transformation reaction and their isomerization behavior was investigated by UV-visible spectroscopy and a contact-angle goniometer. The thermal Z → E isomerization rate of the azo moiety covalently bound to low-density polyethylene (LDPE) and polypropylene (PP) films was determined. The rate of thermal isomerization was also compared between amorphous and semicrystalline polymer films bearing azo chromophores. The effect of the intramolecular steric factor and the nature of chromophores was studied on the thermal isomerization rate of the polymer films.

Succinic anhydride groups have been introduced on the surface of and in bulk poly(ethylene) film by a mild photochemical process. These groups on the poly(ethylene) film undergo facile transformation to various functional groups such as acids, esters, or amides by reaction with water, amine compounds, or PEG, etc. The surface functionality has been quantitatively estimated by using gravimetry, ATR-FTIR, XPS, and UV-visible spectroscopy. Surface hydrophilicity was characterized by contact angle goniometry. The poly(ethylene) bound to the azobenzene group, exhibiting interesting responses to external stimuli such as photoinduced and thermally induced E:Z isomerization.

Hindered-amine light stabilizers (HALS) were surface anchored to polyolefin films by reacting the HALS, namely, 1,2,2,6,6-pentamethyl-4-piperidinol and 1,2,2,6,6-pentamethyl-4-aminopiperidine, with succinic anhydride functionalized polyolefin surfaces. The photostability of polyolefin films with surface-anchored HALS were compared with films stabilized with commercial HALS (Tinuvin 770) by melt blending. It is shown that the photostabilizing efficiency of surface-anchored HALS is superior that of melt-blended polyolefins.

The control synthesis of copolymer based on aniline and ortho -anisidine monomers was performed using 1 H -NMR spectroscopy. The Langmuir films formation of copolymers was optimised at pH 1 at various concentrations of solutions and compression speeds. The Langmuir–Schaefer (LS) films of such copolymers were fabricated, and analysed by using UV–VIS, atomic force microscopy, electrical conductivity and cyclic voltammetric techniques, respectively. The UV–VIS absorption at 328 nm, and cyclic voltammetric (CV) peak potential current at 668 mV were used to verify the linearity in deposition process. The electrochemical surveying parameters were investigated by chronoamperometric technique. The atomic force microscopic measurements on such copolymer LS films allowed us to distinguish the copolymeric structure different than that obtained from polyaniline or poly( ortho -anisidine) Langmuir–Blodgett (LB) films. The photoelectrochemical properties of copolymer LS films were investigated at length.

The Langmuir monolayer behaviour of poly[(2-methoxy-5-(2′-ethyl-hexyloxy)phenylene vinylene] (MEH-PPV) conducting polymer in a subphase containing various anions was investigated at the air–water interface. The Langmuir–Schaefer (LS) films were prepared in deionized water that showed the minimum area per molecule, and were found to be essential for the formation of Langmuir monolayer at the air–water interface of MEH-PPV conjugated polymer. The LS films of MEH-PPV were investigated by using UV–VIS absorption, electrochemical and atomic force microscopic techniques. A uniform deposition of monolayers was shown by optical technique, whereas a higher number of monolayers resulted in the tiny island morphology in MEH-PPV LS films. The influence of concentration of anions on the redox properties of the LS films was studied by cyclic voltammetric measurements. The nature of anions in electrochemical investigation revealed the significant changes in the redox properties of the MEH-PPV LS films. The photoelectrochemical current transient of MEH-PPV LS films was compared with those obtained by the solution cast technique. This work also focused on the influence of the nature of the electrolytes, the applied potential, the type of the film and the presence of dissolved oxygen on the photoelectrochemical properties of MEH-PPV conducting polymer.

A self-assembly layer-by-layer (LBL) technique was used for the sequential adsorption of polycation, poly(diallyldimethylammonium chloride) (PDDA) and polyanion, sulfonated polyaniline (SPANI) on glass, indium-tin-oxide (ITO) coated glass plates, polystyrene sulfonate (PSS)/glass and PSS/ITO surfaces, respectively. The building up of such multilayers was characterized by the increment of the adsorbed amount through UV-visible spectroscopy and cyclic voltammetry. The atomic force microscopic study showed the granular surface topology of such self-assembled films of sulfonated polyaniline. PDDA/SPANI LBL films were electrically active and detailed electrochemical parameters were investigated.