"Lego" chemistry for the straightforward synthesis of dendrimers

A new straightforward method of synthesis of dendrimers, using two branched monomers (CA(2) and DB(2)), is described. Each generation is obtained in a single quantitative step, with only N(2) or H(2)O as byproducts; generation 4 is obtained in only four steps. The end groups are alternatively phosphines and hydrazines; their versatile reactivity is illustrated by the reaction of generation 4 with a branched CD(5) monomer, which increases the number of end groups in a single step from 48 to 250.     

Reactions of Polycyclic Ketones with Dimethoxycarbene; a Convenient Route for a ‘One‐Pot’ Preparation of Some α‐Hydroxycarboxylic Acid Esters

Polycyclic ‘cage’ ketones, such as pentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecan‐8‐one ( 10 ), pentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecane‐8,11‐dione ( 11 ), and adamantan‐2‐one ( 16 ) were treated with the nucleophilic dimethoxycarbene (DMC; 1 ), which was generated thermally from 2,5‐dihydro‐2,2‐dimethoxy‐5,5‐dimethyl‐1,3,4‐oxadiazole ( 4a ) in boiling toluene. In this ‘one‐pot’ procedure, the α‐hydroxycarboxylic acid ester 12 or a corresponding derivative 15 or 17 was obtained (Schemes 4–7). Additionally, ‘cage’ thione 21 was treated with DMC under the same conditions yielding dimethoxythiirane 22 (Scheme 8). Subsequent hydrolysis or desulfurization (followed by hydrolysis on silica gel) of 22 gave α‐mercaptocarboxylate 25 and the corresponding desulfurized ester 24 , respectively. In all cases, the addition of DMC occurred stereoselectively, and the addition from the exo‐face is postulated to explain the structures of the isolated products.     

1,3-Dipole mit zentralem S-Atom aus der Umsetzung von Aziden mit Thiocarbonyl-Verbindungen: Eine unerwartete MeS-Wanderung im Abfangprodukt eines ‘Thiocarbonyl-aminids’ mit Dithiobenzoesäure-methylester

1,3-Dipoles with a Central S-Atom from the Reaction of Azides and Thiocarbonyl Compounds: An Unexpected MeS Migration in the Trapping Product of a ‘Thiocarbonyl-aminide’ with Methyl Dithiobenzoate Reaction of PhN₃ with O-methyl thiobenzoate ( 11a ) and thioacetate ( 11c ) as well as with the dithio esters 11b,d at 80° yields the corresponding imidates and thioimidates 12 (Scheme 3). The formation of 12 is rationalized by a 1,3-dipolar cycloaddition of the azide and the C?S group followed by successive elimination of N₂ and S. In the three-component reaction of 11b , PhN₃, and the sterically crowded thioketone 1a , 1,2,4-trithiolane 13a and 1,4,2-dithiazolidine 3a are formed in addition to 12b (Scheme 4). The heterocycles 13a and 3a are trapping products of 1a and ‘thiocarbonyl-thiolate’ 5a and ‘thiocarbonyl-aminide’ 2a (Ar?Ph), respectively (Scheme 6). These 1,3-dipoles are formed as reactive intermediates. Surprisingly, in the presence of catalytic amounts of acids, the major product is the (methyldithio)cyclobutyl thioimidate of type 14 (Scheme 5), formed by an acid-catalyzed MeS migration in dithiazolidine 17 . A reaction mechanism is proposed in Scheme 7.     

12H-naphtho[1′,2′:5,6]pyrano[2,3-d]pyrimidine derivatives

Reaction of 1-oxo-2-formyl-3-dimethylamino-1H-naphtho[2,1-b]pyran with amidines, guanidine, O-methylisourea, S-methylisothiourea afforded 9-substituted 12-oxo-12H-naphtho[1′,2′:5,6]pyrano[2,3-d]pyrimidines. When the reaction with O-methylisourea was carried out in anhydrous pyridine, 10,20-dioxo-10H,20H-dinaphtho[1,2-e:1′,2′-e′][1,5]diazocino[2,3-b:6,7-b′]dipyran was formed.     

Viscoelastic properties of dendrimers in the melt from nonequlibrium molecular dynamics

The viscoelastic properties of dendrimers of generation 1-4 are studied using nonequilibrium molecular dynamics. Flow properties of dendrimer melts under shear are compared to systems composed of linear chain polymers of the same molecular weight, and the influence of molecular architecture is discussed. Rheological material properties, such as the shear viscosity and normal stress coefficients, are calculated and compared for both systems. We also calculate and compare the microscopic properties of both linear chain and dendrimer molecules, such as their molecular alignment, order parameters and rotational velocities. We find that the highly symmetric shape of dendrimers and their highly constrained geometry allows for substantial differences in their material properties compared to traditional linear polymers of equivalent molecular weight.     

1,2-fused pyrimidines. V. Synthesis of 1-alkyl or phenyl-2H-dipyrido-[1,2-a:2′,3′-d]pyrimidine-2,5(1H)-diones

The reaction of 2-[(N-acyl, N-alkyl or phenyl)amino]-4H-pyrido[1,2-a]pyrimidin-4-ones 8a-g with the N,N-dimethylformamide/phosphorus oxychloride Vilsmeier reagent 1 (95°, 90 minutes) afforded 1-alkyl or phenyl-2H-dipyrido[1,2-a:2′,3′-d]pyrimidine-2,5(1H)^?diones, 3-alkyl substituted or not, 10a-g . The starting compounds 8 were prepared by treating 2-amino-4H-pyrido[1,2-a]pyrimidin-4-ones N-alkyl substituted 7a,b or N-phenyl substituted 4 with excess anhydrides (130°, 7 hours) when the 2-(alkylamino) derivatives 7 were used in the reaction, compounds 8 were obtained along with very small amounts of 3-acyl-2-(alkylamino)-4H-pyrido[1,2-a]pyrimidin-4-ones 9 .     

Polonium 210Po activities in human blood of patients with ischaemic heart disease from Gdańsk in Poland

The determination of polonium ²¹⁰Po in human blood samples is presented and discussed in this paper. The human blood samples were collected from patients of Medical University of Gdańsk with ischaemic heart disease (morbus ischaemicus cordis, MIC). The polonium concentrations in analyzed human blood samples are very differentiated. ²¹⁰Po is of particular interest in public health and although is present in the environment in extremely low amounts, it is easily bioaccumulated to the human body. The study shows that the amount of ²¹⁰Po that is incorporated into the human body depends on the food habits and some difference in its levels could be observed between smokers and non-smokers.     

Material profile influences in bulk‐heterojunctions

The morphology in mixed bulk‐heterojunction films are compared using three different quantitative measurement techniques. We compare the vertical composition changes using high‐angle annular dark‐field scanning transmission electron microscopy with electron tomography and neutron and x‐ray reflectometry. The three measurement techniques yield qualitatively comparable vertical concentration measurements. The presence of a metal cathode during thermal annealing is observed to alter the fullerene concentration throughout the thickness of the film for all measurements. However, the absolute vertical concentration of fullerene is quantitatively different for the three measurements. The origin of the quantitative measurement differences is discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1291–1300     

Simultaneous Anodic Stripping Voltammetric Determination of Pb and Cd,Using a Vibrating Gold Microwire Electrode,Assisted by Chemometric Techniques

Simultaneous anodic stripping voltammetric determination of Pb and Cd is restricted on gold electrodes as a result of the overlapping of these two peaks. This work describes the quantitative determination of a binary mixture system of Pb and Cd, at low concentration levels (up to 15.0 and 10.0 µg L^?1 for Pb and Cd, respectively) by differential pulse anodic stripping voltammetry (DPASV; deposition time of 30 s), using a green electrode (vibrating gold microwire electrode) without purging in a chloride medium (0.5 M NaCl) under moderate acidic conditions (HCl 1.0 mM), assisted by chemometric tools. The application of multivariate curve resolution alternating least squares (MCR‐ALS) for the resolution and quantification of both metals is shown. The optimized MCR‐ALS models showed good prediction ability with concentration prediction errors of 12.4 and 11.4 % for Pb and Cd, respectively. The quantitative results obtained by MCR‐ALS were compared to those obtained with partial least squares (PLS) and classical least squares (CLS) regression methods. For both metals, PLS and MCR‐ALS results are comparable and superior to CLS. For Cd, as a result of the peak shift problem, the application of CLS was unsuitable. MCR‐ALS provides additional advantage compared to PLS since it estimates the pure response of the analytes signal. Finally, the built up multivariate calibration models, based either in MCR‐ALS or PLS regression, allowed to quantify concentrations of Pb and Cd in surface river water samples, with satisfactory results.     

Bis(diisopropylammonium) thiosulfate and bis(tert‐butylammonium) thiosulfate

Two new dialkylammonium thiosulfates, namely bis(diisopropylammonium) thiosulfate, 2C₆H₁₆N⁺·S₂O₃²⁻, (I), and bis(tert‐butylammonium) thiosulfate, 2C₄H₁₂N⁺·S₂O₃²⁻, (II), have been characterized. The secondary ammonium salt (I) crystallizes with Z = 4, while the primary ammonium salt (II), with more hydrogen‐bond donors, crystallizes with Z = 8 and a noncrystallographic centre of inversion. In both salts, the organic cations and thiosulfate anions are linked within extensive N—H...O and N—H...S hydrogen‐bond networks, forming extended two‐dimensional layers. Layers are parallel to (10) in (I) and to (002) in (II), and have a polar interior and a nonpolar hydrocarbon exterior. The layered structure and hydrogen‐bond motifs observed in (I) and (II) are similar to those in related ammonium sulfates.