alpha-Nitration of Ketones via Enol Silyl Ethers. Radical Cations as Reactive Intermediates in Thermal and Photochemical Processes

Highly colored (red) solutions of various enol silyl ethers and tetranitromethane (TNM) are readily bleached to afford good yields of alpha-nitro ketones in the dark at room temperature or below. Spectral analysis show the red colors to be associated with the intermolecular 1:1 electron donor-acceptor (EDA) complexes between the enol silyl ether and TNM. The formation of similar vividly colored EDA complexes with other electron acceptors (such as chloranil, tetracyanobenzene, tetracyanoquinodimethane, etc.) readily establish enol silyl ethers to be excellent electron donors. The deliberate irradiation of the diagnostic (red) charge-transfer absorption bands of the EDA complexes of enol silyl ethers and TNM at -40 degrees C affords directly the same alpha-nitro ketones, under conditions in which the thermal reaction is too slow to compete. A common pathway is discussed in which the electron transfer from the enol silyl ether (ESE) to TNM results in the radical ion triad [ESE(*)(+), NO(2)(*), C(NO(2))(3)(-)]. A subsequent fast homolytic coupling of the cation radical of the enol silyl ether with NO(2)(*)() leads to the alpha-nitro ketones. The use of time-resolved spectroscopy and the disparate behavior of the isomeric enol silyl ethers of alpha- and beta-tetralones as well as of 2-methylcyclohexanone strongly support cation radicals (ESE(*)(+)) as the critical intermediate in thermal and photoinduced electron-transfer as described in Schemes 1 and 2, respectively.     

A New Ultrasensitive Chromogenic Chelating Reagent for use in the Chromatographic Separation and Detection of Metal Ions

JPC – Journal of Planar Chromatography – Modern TLC - The heavy metal ions Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Bi3+, and Ag+ can be visualized as violet, black, green, yellow-green,...     

Lipschitz-Nikolski\imath constants and asymptotic simultaneous approximation on theM n -operatorsconstants and asymptotic simultaneous approximation on theM n -operators

This note is a study of approximation of classes of functions and asymptotic simultaneous approximation of functions by theM _n -operators of Meyer-König and Zeller which are defined by $$(M_n f)(x) = (1 - x)^{n + 1} \sum\limits_{k = 0}^\infty {f\left( {\frac{k}{{n + k}}} \right)} \left( \begin{array}{l} n + k \\ k \\ \end{array} \right)x^k , n = 1,2,....$$ Among other results it is proved that for 0<α≤1 $$\mathop {\lim }\limits_{n \to \infty } n^{\alpha /2} \mathop {\sup }\limits_{f \in Lip_1 \alpha } \left| {(M_n f)(x) - f(x)} \right| = \frac{{\Gamma \left( {\frac{{\alpha + 1}}{2}} \right)}}{{\pi ^{1/2} }}\left\{ {2x(1 - x)^2 } \right\}^{\alpha /2} $$ and if for a functionf, the derivativeD ^m+2 f exist at a pointx∈(0, 1), then $$\mathop {\lim }\limits_{n \to \infty } 2n[D^m (M_n f) - D^m f] = \Omega f,$$ where Ω is the linear differential operator given by $$\Omega = x(1 - x)^2 D^{m + 2} + m(3x - 1)(x - 1)D^{m + 1} + m(m - 1)(3x - 2)D^m + m(m - 1)(m - 2)D^{m - 1} .$$      

Quinalizarin anchored on Amberlite XAD-2. A new matrix for solid-phase extraction of metal ions for flame atomic absorption spectrometric determination

Amberlite XAD-2 has been functionalized by coupling it to quinalizarin [1,2,5,8-tetrahydroxyanthraquinone] by means of an -N = N- spacer. Elemental analysis, thermogravimetric analysis, and infrared spectra were used to characterize the resulting new polymer matrix. The matrix has been used to preconcentrate Cu(II), Cd(II), Co(II), Pb(II), Zn(II), and Mn(II) before their determination by flame atomic absorption spectrometry (FAAS). UO₂(II) has been preconcentrated for fluorimetric determination. The optimum pH values for maximum adsorption of the metals are between 5.0 and 7.0. All these metal ions are desorbed (recovery 91–99%) with 4 mol L^–1 HNO₃. The adsorptive capacity of the resin was found to be in the range 0.94–5.28 mg metal g^–1 resin and loading half-life (t_1/2) between 5.3 and 15.0 min. The effects of NaF, NaCl, NaNO₃, Na₂SO₄, Na₃PO₄, Ca(II), and Mg(II) on the adsorption of these metal ions (0.2 μg mL^–1) are reported. The lower limits of detection for these metal ions are between 1 and 15.0 μg L^–1. After enrichment on this matrix flame AAS has been used to determine these metal ions (except the uranyl ion) in river water samples (RSD ≤ 6.5%); fluorimetry was used to determine uranyl ion in well water samples (RSD ≤ 6.3%). Cobalt from pharmaceutical vitamin tablets was preconcentrated by use of this chelating resin and estimated by FAAS (RSD ～ 4%).     

Process analytical technology (PAT) for biopharmaceutical products

The “Pharmaceutical Current Good Manufacturing Practices (CGMPs) for the 21st Century—A Risk Based Approach” initiative announced by the FDA in August 2002 to improve and modernize pharmaceutical manufacturing facilitated adoption of process analytical technology (PAT) by the pharmaceutical industry. The potential for improved operational control and compliance resulting from continuous real-time quality assurance was highlighted as a likely benefit that would result from PAT implementation. A considerable amount of work has been done on this topic by academic and industrial contributors in the last decade. In this paper, we will start with a brief overview of evolution of PAT concepts and a review of their application in the wider pharmaceutical industry. The rest of the paper focuses on PAT applications for biotech processes with emphasis on developments in the last five years. It is our observation that while significant advances have been accomplished with regard to our ability to analyze/monitor key process and quality attributes in the biotech industry, much more needs to be done with regard to utilizing the collected data for subsequent control of the process, to achieve optimum yield and product quality. The latter is necessary to achieve the benefits that will result from PAT implementation.     

Regioselective synthesis of multifunctional hybrid polysiloxanes achieved by Pt-nanocluster catalysis

The first example of "Pt"-nanocluster-catalyzed regioselective generation of hybrid polymers via attachment of organic functionalities to evenly distributed Si-H bonds of poly(methylhydro)siloxane is described. In addition, participation of Pt-nanoclusters as an active catalyst was evidenced by various spectroscopic techniques during the catalytic transformations.     

Silver(I) complexation of (poly)aromatic ligands. Structural criteria for depth penetration into cis-stilbenoid cavities

Silver(I) complexes with aromatic donors are thoroughly analyzed (with aid of the Cambridge Crystallographic Database) to identify the basic structural factors inherent to the bonding of an arene ligand. Most strikingly, the distance parameter d (which simply measures the normal separation of Ag from the mean aromatic plane) is singularly invariant at d = 2.41 +/- 0.05 A for all silver/arene complexes, independent of the hapticity (eta 1 or eta 2), hybridization, or multiple coordination. As such, a systematic series of stilbenoid ligands has been successfully designed to precisely modulate the penetration of silver(I) into the ligand cleft, and a multicentered poly(arene) ligand (X) designed to form a one-dimensional assembly of Ag/arene units. Simply stated, the depth penetration of silver(I) into the aromatic cavities of various cis-stilbenoid donors can be precisely predicted with a single parameter gamma that measures the separation of the two cofacial aryl groups comprising the cleft. This simple geometric consideration must be taken into account in any successful design of novel (poly)aromatic ligands for silver(I) complexation to constitute new molecular architectures.     

Synthesis of a calix[4]arene derivative for isolation of a stable cation radical salt for use as a colorimetric sensor of nitric oxide

We have designed and synthesized a modified calixarene derivative (1) that allows, for the first time, the isolation of a stable cation radical salt that binds a single molecule of nitric oxide deep within its cavity with remarkable efficiency (KNO >108 M-1), as demonstrated by isolation of a crystalline complex [1, NO]+ and its characterization by X-ray crystallography as well as by optical spectroscopy. Furthermore, the ready accessibility of the calixarene cation radical will allow the exploration of its use for developing efficient sensing devices for nitric oxide based on the accompanied color changes.