Silylation of 5′-O-DMT-2′-Deoxyncleosides Using Dibenzo [18] Crown-6 and PTC

3′O-silylated derivatives of 5′-O-DMT-2′deoxynucleoside (2) were synthesized in high yield by reaction of 5′-O-DMT-2′-deoxynucleosides (1) with tert-butyl dimethylsilylchloride using sodium hydride, benzyltriethylammonlum chloride [TEBA] and a catalytic amount of dibenzo-[18]-crown-6 [DB-18-C-6] or 15-crown-5 [15-C-51 under mild reaction conditions.     

Radiation dose reconstruction from L-band in vivo EPR spectroscopy of intact teeth: Comparison of methods

In vivo EPR tooth dosimetry is a more challenging problem than in vitro EPR dosimetry because of several potential additional sources of variation associated with measurements that are made in the mouth of a living subject. For in vivo measurement a lower RF frequency is used and, unlike in the in vitro studies, the tooth cannot be processed to optimize the amount and configuration of the enamel that is measured. Additional factors involved with in vivo measurements include the reproducibility of positioning the resonator on the surface of the tooth in the mouth, irregular tooth geometry, and the possible influence of environmental noise. Consequently, in addition to using the theoretical and empirical models developed for analyzing data from measurements of teeth in vitro, other unconventional and more robust methods of dose reconstruction may be needed. The experimental parameter of interest is the peak-to-peak amplitude of the spectrum, which is correlated to the radiation dose through a calibration curve to derive the reconstructed dose. In this study we describe and compare the results from seven types of computations to measure the peak-to-peak amplitude for estimation of the radiation induced signal. The data utilized were from three sets of in vivo measurements of irradiated teeth. Six different teeth with different doses were placed in the mouth of a volunteer in situ and measurements of each tooth were carried out on three different days. The standard error of dose prediction (SEP) is used as a figure of merit for quantifying precision of the reconstruction. We found that many of the methods gave fairly similar results, with the best error of prediction resulting from a computation based on a Lorentzian line model whose center field corresponds to the known parameter of the radiation-induced EPR spectra of teeth, with corrections from a standard sample that was measured as part of the data acquisition scheme. When the results from the three days of measurement were pooled, the SEP decreased dramatically, which suggests that one of the principal sources of variation in the data is the ability to precisely standardize the measurements conditions within the mouth. There are very plausible ways to accomplish improvements in the existing procedures.     

Co-Catalyzed Metal-Ligand Cooperative Approach for N-alkylation of Amines and Synthesis of Quinolines via Dehydrogenative Alcohol Functionalization

Herein we report a cobalt-catalyzed sustainable approach for C−N cross-coupling reaction between amines and alcohols. Using a well-defined Co-catalyst 1 a bearing 2-(phenyldiazenyl)-1,10-phenanthroline ligand, various N-alkylated amines were synthesized in good yields. 1 a efficiently alkylates diamines producing N, N′-dialkylated amines in good yields and showed excellent chemoselectivity when oleyl alcohol and β-citronellol, containing internal carbon-carbon double bond were used as alkylating agents. 1 a is equally compatible with synthesizing N-heterocycles via dehydrogenative coupling of amines and alcohols. 1H-Indole was synthesized via an intramolecular dehydrogenative N-alkylation reaction, and various substituted quinolines were synthesized by coupling of 2-aminobenzyl alcohol and secondary alcohols. A few control reactions and spectroscopic experiments were conducted to illuminate the plausible reaction mechanism, indicating that the 1 a -catalyzed N-alkylation proceeds through the borrowing hydrogen pathway. The coordinated arylazo ligand participates actively throughout the reaction; the hydrogen eliminated during dehydrogenation of alcohols was set aside in the ligand backbone and subsequently gets transferred in the reductive amination step to imine intermediates yielding N-alkylated amines. On the other hand, 1 a -catalyzed quinoline synthesis proceeds through dehydrogenation followed by successive C−C and C−N coupling steps forming H₂O₂ as a by-product under air.     

Analysis of PPMMA films from oxygen plasma using X-ray photoelectron spectroscopy

Plasma polymerized methyl methacrylate (PPMMA) films have been synthesised on silicon substrates in RF glow discharge using oxygen plasma. The electron beam delineation sensitivity of the PPMMA films has been studied systematically by varying oxygen and monomer flow rates. X-ray photoelectron spectroscopy (XPS) analysis clearly illustrates how C/O ratio in the films determines the properties of PPMMA films as electron beam resist. © 1994 John Wiley & Sons, Inc.     

A chemoenzymatic asymmetric synthesis of the hydroxy acid segment of schulzeines B and C

A chemoenzymatic asymmetric synthesis of the title compound was developed by a building-block approach. The key steps of the synthesis were (i) an enantioselective lipase-catalyzed acylation of a secondary alcohol, (ii) an efficient diastereoselective addition of an alkyl-lithium reagent to a glyceraldehyde derivative, (iii) conversion of an epoxide to a one-carbon homologated allylic alcohol via a sulphorane addition, and (iv) a cross metathesis between two chiral allylic alcohols and subsequent functionalization to obtain the ethyl ester of the hydroxy acid unit of the schulzeines.     

Experimental Procedures for Sensitive and Reproducible In Situ EPR Tooth Dosimetry

In vivo electron paramagnetic resonance (EPR) tooth dosimetry provides a means for non-invasive retrospective assessment of personal radiation exposure. While there is a clear need for such capabilities following radiation accidents, the most pressing need for the development of this technology is the heightened likelihood of terrorist events or nuclear conflicts. This technique will enable such measurements to be made at the site of an incident, while the subject is present, to assist emergency personnel as they perform triage for the affected population. At Dartmouth Medical School this development is currently being tested with normal volunteers with irradiated teeth placed in their mouths and with patients who have undergone radiation therapy. Here we describe progress in practical procedures to provide accurate and reproducible in vivo dose estimates.     

Study of C centres in NaCl by positron angular correlation

The nature of C centres in NaCl has been experimentally studied by the positron annihilation technique. The results are in support of a previously proposed model for the C centres [1]. The approximate size of C centres has been estimated to be of the order 6.3 ± 0.7 Å.     

Release of Warfarin from Human Serum Albumin by Water-soluble CdSe Nanotetrapods

Water soluble CdSe nanotetrapods are prepared by ligand exchange from organic-soluble ones. In order to achieve this, oleic acid, which is the capping agent for as prepared water-insoluble nanotetrapods, is exchanged with mercaptopropanoic acid (MPA). Shape and size of nanotetrapods are conserved upon ligand exchange. Ground state bleach recovery dynamics remain the same as well. However, they are completely non-emissive. These water-soluble nanotetrapods disrupt the secondary structure of Human Serum Albumin (HSA) and consequently, release warfarin bound to the protein.