Estimation of homogeneous rate constants of reaction of electrochemically generated ortho‐benzoquinones with 1,3‐indandione

Electrochemical oxidation of some catechol derivatives has been studied in the presence of 1,3‐indandione as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate the participation of electrochemically produced o‐benzoquinones in the Michael reaction with 1,3‐indandione to form the corresponding new catechol derivatives. On the basis of the EC mechanism, the observed homogeneous rate constants (k_obs) of reaction of produced o‐benzoquinones with 3‐indandione were estimated by comparing the experimental cyclic voltammograms with the digitally simulated results. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 605–613, 2007     

DFT study and NBO analysis of the mutual interconversion of cumulene compounds

The B3LYP/6‐31G* method was used to investigate the configurational properties of allene (1,2‐propadiene) ( 1 ), 1,2,3‐butatriene ( 2 ), 1,2,3,4‐pentateriene ( 3 ), 1,2,3,4,5‐hexapentaene ( 4 ), 1,2,3,4,5,6‐heptahexaene ( 5 ), 1,2,3,4,5,6,7‐octaheptaene ( 6 ), 1,2,3,4,5,6,7,8‐nonaoctaene ( 7 ), and 1,2,3,4,5,6,7,8,9‐decanonaene ( 9 ). The calculations at the B3LYP/6‐31G* level of theory showed that the mutual interconversion energy barrier in compounds 1 – 8 are: 209.73, 131.77, 120.34, 85.00, 80.91, 62.19, 55.56, and 46.83 kJ mol^?1, respectively. The results showed that the difference between the average C?C double bond lengths ( ) values in cumulene compounds 1 and 2 , is larger than those between 7 and 8 , which suggest that with large n (number of carbon atoms in cumulene chain), the values approach a limiting value. Accordingly, based on the plotted data, the extrapolation to n = ∞, gives nearly the same limiting (i. e., ). Also, NBO results revealed that the sum of π‐bond occupancies, , decrease from 1 to 8 , and inversely, the sum of π‐antibonding orbital occupancies, , increase from compound 1 to compound 8 . The decrease of values for compounds 1 – 8 , is found to follow the same trend as the barrier heights of mutual interconversion in compounds 1 – 8 , while the decrease of the barrier height of mutual interconversion in compounds 1 – 8 is found to follow the opposite trend as the increase in the number of carbon atom. Accordingly, besides the previously reported allylic resonant stabilization effect in the transition state structures, the results reveal that the values, , Δ(E_HOMO ? E_LUMO), and the C atom number could be considered as significant criteria for the mutual interconversion in cumulene compounds 1 – 8 . This work reports also useful predictive linear relationships between mutual interconversion energy barriers ( ) in cumulene compounds and the following four parameters: , , Δ(E_HOMO ? E_LUMO), and C_Number. Copyright © 2007 John Wiley & Sons, Ltd.     

DFT studies of functionalized zigzag and armchair boron nitride nanotubes as nanovectors for drug delivery of collagen amino acids

The interaction of collagen amino acids with (5, 5) armchair and (9, 0) zigzag single-walled boron nitride nanotubes (BNNTs) are studied using density functional theory. Our results show that the BNNTs can act as a suitable drug delivery vehicle of collagen amino acids within biological systems. DFT-LDA/DNP calculations revealed that the binding and solvation energies were negative for (5, 5)/(9, 0) BNNTs–collagen amino acid complexes implying the thermodynamic favorability and spontaneous interactions of collagen amino acids with BNNTs sidewall. These results were extremely relevant in order to identify the potential applications of functionalized BNNTs as drug delivery systems.     

Thermal analysis study on the simultaneous grain refinement and modification of 380.3 aluminum alloy

In this research, effect of integrated Al–10Sr–1Ti–2B master alloy has been studied on the microstructure and solidification characteristics of 380.3 aluminum alloy. Thermal Analysis has been used as a technique to study the cooling curves and first derivative curves during solidification of the alloy. Effect of integrated grain refiner and modifier on solidification parameters such as α-Al dendrite growth temperature (T _G,α), α-Al dendrite recalescence undercooling (?T _R,α), aluminum–silicon eutectic growth temperature (T _G,E), and eutectic recalescence undercooling (?T _R,E) has been determined. By increasing master alloy content, T _G,α and ?T _R,E have been increased, but, ?T _R,E has been decreased, and T _G,E increases first and then decreases. Aluminum–silicon eutectic depression temperature ( $ \Updelta T_{\text{G,E}}^{{{\text{Al}} - {\text{Si}}}} $ ) can be used as a parameter to control the modification of eutectic silicon. The results of this research indicate that the optimum level of Al–10Sr–1Ti–2B master alloy for the simultaneous grain refinement and modification of 380.3 alloy is about 0.5 mass%.     

Interaction of vitamins A,B1, C,B3 and D with zigzag and armchair boron nitride nanotubes: A DFT study

In this work, based on the density functional theory, the interaction of vitamins A, B1, C, B3 and D with (5, 5) armchair and (9, 0) zigzag single-walled boron nitride nanotubes (BNNTs) are studied. It is found that binding of vitamins A, B1, C, B3 and D with (9, 0) and (5, 5) BNNTs is thermodynamically favorable. Calculated solvation energies show that the solubility of functionalized (9, 0) BNNTs is higher than that of functionalized (5, 5) BNNT, and both dissolutions in water are spontaneous. The results showed that BNNTs can act as a suitable drug delivery vehicle for vitamins A, B1, C, B3 and D within biological systems. This study may provide a new insight into the development of the functionalized boron nitride nanotubes as drug delivery systems for virtual applications.     

Preparation and evaluation of a new neurotensin analog labeled with 99mTc for targeted imaging of neurotensin receptor positive tumors

Neurotensin receptors are overexpressed in several human tumors and can be targets for tumors diagnosis and therapy. In this study, a new neurotensin analogue was labeled with ^99mTc via HYNIC and tricine/EDDA as coligands and investigated further. [HYNIC⁰, Gly⁷, Lys⁹, d-Tyr¹¹]-Neurotensin (7–13) was synthesized using a standard Fmoc strategy. Labeling with ^99mTc was performed at 100 °C for 10 min and radiochemical analysis involved ITLC and HPLC methods. The stability of radiopeptide was checked in the presence of humane serum at 37 °C up to 24 h. The receptor bound internalization and externalization rates were studied in neurotensin receptor expressing HT-29 cells. Biodistribution of radiopeptide was studied in nude mice bearing HT-29 tumor. Labeling yield of 98.6 ± 0.54 % (n = 3) was obtained corresponding to a specific activity of 81 MBq/nmol. Peptide conjugate showed good stability in the presence of human serum. The radioligand showed specific internalization into HT-29 cells (12.43 ± 0.52 % at 4 h). In biodistribution studies, a receptor-specific uptake was observed in neurotensin receptor positive organs so that after 1 h the uptakes in mouse intestine and tumor were 0.87 ± 0.16 and 0.63 ± 0.12 % ID/g respectively.     

Efficient thioacetalisation of carbonyl compounds

The thioacetalisation of a variety of heterocyclic, aromatic, and aliphatic carbonyl compounds (1 mmol) with ethane-1,2-dithiol (1 mmol) using silica sulphuric acid (SSA) is presented as an efficient heterogeneous catalyst under mild and solvent-free conditions at 60°C. The thioacetals were formed within a short reaction time (1–34 min) and isolated with 90–98 % yield following an extractive procedure and chromatography on silica gel. The competitive protection reaction between aldehyde and ketone with ethane-1,2-dithiol afforded the protected derivatives of benzaldehyde and acetophenone with 92 % and 8 % yields, respectively, indicating some selectivity.     

Trichloroisocyanuric Acid (TCCA) and N-Chlorosuccinimide (NCS) as Efficient Reagents for the Direct Oxidative Conversion of Thiols and Disulfides to Sulfonyl Chlorides

Abstract

Trichloroisocyanuric acid (TCCA) and N-chlorosuccinimide (NCS) were found to be mild and efficient reagents for the direct oxidative conversion of sulfur compounds to the corresponding arenesulfonyl chlorides in good-to-excellent yields through the oxidative chlorination. The overall process is simple and practical, and it provides convenient access to a variety of aryl or heteroarylsulfonyl chlorides. The mild reaction conditions and the broad substrate scope render this method attractive and complementary to existing syntheses of aryl or heteroarylsulfonyl chlorides.     

Kinetics and Mechanistic Study of Acetaminophen‐Captopril Interaction by Electrochemical Methods

In this work kinetics parameters and electrochemical mechanism for electrooxidation of acetaminophen in the absence and presence of captopril in a condition close to acetaminophen natural oxidation pathway was investigated. The electrooxidation of acetaminophen in the presence of captopril was investigated by voltammetry and coulometry methods. The results of this work show that acetaminophen is oxidized to its respective p‐quinoneimine. The quinoneimine attacked by captopril, forms thioether. The proposed electrochemical mechanism is ECEC. The estimated value for homogeneous rate constant k_obs is 3.1×10⁴±155 M^?1s^?1 and k_f/k_b is 1.6×10⁸±8.0×10⁵.