Magnetic susceptibility of alkali-tetracyanoquinodimethane salts and extended Hubbard models with bond order and charge density wave phases

The molar spin susceptibilities χ(T) of Na-tetracyanoquinodimethane (TCNQ), K-TCNQ, and Rb-TCNQ(II) are fit quantitatively to 450 K in terms of half-filled bands of three one-dimensional Hubbard models with extended interactions using exact results for finite systems. All three models have bond order wave (BOW) and charge density wave (CDW) phases with boundary V = V(c)(U) for nearest-neighbor interaction V and on-site repulsion U. At high T, all three salts have regular stacks of TCNQ(-) anion radicals. The χ(T) fits place Na and K in the CDW phase and Rb(II) in the BOW phase with V ≈ V(c). The Na and K salts have dimerized stacks at T < T(d) while Rb(II) has regular stacks at 100 K. The χ(T) analysis extends to dimerized stacks and to dimerization fluctuations in Rb(II). The three models yield consistent values of U, V, and transfer integrals t for closely related TCNQ(-) stacks. Model parameters based on χ(T) are smaller than those from optical data that in turn are considerably reduced by electronic polarization from quantum chemical calculation of U, V, and t of adjacent TCNQ(-) ions. The χ(T) analysis shows that fully relaxed states have reduced model parameters compared to optical or vibration spectra of dimerized or regular TCNQ(-) stacks.     

Straightforward synthesis of 1-alkyl-2-(trifluoromethyl)aziridines starting from 1,1,1-trifluoroacetone

An efficient and straightforward approach towards the synthesis of 1-alkyl-2-(trifluoromethyl)aziridines starting from 1,1,1-trifluoroacetone via imination, α-chlorination, hydride reduction and ring closure was developed. In addition, novel primary β-iodo amines were obtained by regioselective ring opening of these 2-(trifluoromethyl)aziridines using alkyl iodides, and their synthetic potential was demonstrated by converting them into novel α-CF(3)-β-phenylethylamines upon treatment with lithium diphenylcuprate.     

Computational studies of bacterial resistance to β-lactam antibiotics: mechanism of covalent inhibition of the penicillin-binding protein 2a (PBP2a)

β-Lactam resistance of methicillin-resistant Staphylococcus aureus (MRSA), a pathogenic bacterium that causes staph infections, represents a serious threat to public health. This arises primarily due to the inability of β-lactam antibiotics to inhibit the transpeptidase activity of penicillin-binding protein 2a (PBP2a). Effective inhibition of PBP2a to prevent the bacterial cell wall biosynthesis is of great importance for the treatment of a variety of clinically challenging infectious diseases caused by MRSA. To gain fundamental insights into the mode of covalent inhibition of the enzyme, we have carried out computational studies of the acylation reactions between small β-lactam molecules (methicilin and nitrocefin) and PBP2a using the B3LYP/6-31G* and ONIOM(B3LYP/6-31G*:AMBER) hybrid quantum mechanical/molecular mechanical methods. Our calculations show that the acylation involves two transition states and that methicilin and nitrocefin undergo acylation in slightly different manners. The acylation of nitrocefin is more facile, which is attributed to the larger release of ring strain and the larger resonance stabilization gained upon ring opening. We suggest that, in addition to the nonbonded interactions between the ligand and the protein, these quantum chemical factors, which are associated with efficiency of the acylation step, should be taken into account and carefully controlled in designing novel β-lactam inhibitors of PBP2a.     

Synchrotron radiation phase-contrast X-ray CT imaging of acupuncture points

Three-dimensional (3D) topographic structures of acupuncture points were investigated by using synchrotron radiation in-line X-ray phase contrast computerized tomography. Two acupuncture points, named Zhongji (RN3) and Zusanli (ST36), were studied. We found an accumulation of microvessels at each acupuncture point region. Images of the tissues surrounding the acupuncture points do not show such kinds of structure. This is the first time that 3D images have revealed the specific structures of acupuncture points.     

Flavonoid glycosides from Chromolaena odorata leaves and their in vitro cytotoxic activity

Two new flavonoid glycosides, (1, 2), and eleven known compounds, (3-13), were isolated from from a 70% EtOH extract of the leaves of Chromolaena odorata (Asteraceae). Their structures were elucidated by 1D and 2D NMR spectroscopic interpretation as well as by chemical studies. The newly isolated compounds were tested in vitro for their cytotoxic activities against the LLC and HL-60 cancer cell lines. Compound 1 showed cytotoxicity against LLC and HL-60 cancer cell lines with IC(50) values of 28.2 and 11.6 μM, respectively. Compound 2 exhibited significant cytotoxic activity in the inhibition of HL-60 cancer cell lines with IC(50) value of 10.8 μM.     

Photo retro-Diels-Alder reactions

Photo-retro-Diels-Alder (PrDA) reactions of a variety of Diels-Alder (DA) adducts were studied. Experimental results showed that the photoreactivity (quantum yield) depends on the electron-donating ability of the diene component and the electron-withdrawing ability of the dienophile component. The mechanism was studied by trapping the reaction intermediate, O(2) quenching, time-resolved absorption, and fluorescence spectroscopy. All the results support a mechanism that involves a charge-separated intermediate generated from a singlet excited state. The PrDA reaction may find applications in photoresponsive materials, photolithography, drug delivery, and mechanistic research.     

Multifunctional amphiphilic carbonaceous microcapsules catalyze water/oil biphasic reactions

Multifunctional amphiphilic hollow carbonaceous spheres assembled into Pickering emulsions exhibit reversible pH-dependent phase-transfer behavior and can efficiently catalyze water/oil biphasic reactions, facilitating the recycling of the catalysts and separation of the products.     

Two one-dimension copper(II) coordination polymers based on imine-based bidentate Schiff-base ligand: synthesis, crystal structure and luminescent properties

Two new one-dimension copper(II) coordination polymers [CuL(2)(NCS)(2)](n) (1) and [CuL(2)(NO(3))(2)](n) (2) (L=(C(5)H(4)N)C(CH(3))=N-N=(CH(3))C(C(5)H(4)N)) have been synthesized and characterized by IR, elemental analysis, TG technique and X-ray crystallography. Each Cu(II) atom has a distorted octahedral N(6) (1) or N(4)O(2) (2) environment with four pyridyl N atoms from four ligands and two N atoms from two NCS(-) anions for polymer 1 or two O atoms from two NO(3)(-) anions for polymer 2, respectively. A pair of bis-monodentate bridging ligands links two Cu(II) centers to form one dimension chain structure containing bimetallic 22-membered macrometallacyclic rings. 1D chain is held together with its neighboring ones via C-H?S hydrogen bonds for 1 and C-H?O hydrogen bonds, C-H?π interactions for 2 to form a 3D supramolecular structure, respectively. The luminescent properties of the polymers 1 and 2 were investigated in the solid state at room temperature.     

Synthesis, crystal structure and luminescence properties of one inorganic-organic hybrid compound [FTMA]2[Co(NCS)4] (FTMA = ferrocenylmethyltrimethylammonium cation)

A new inorganic-organic hybrid compound [FTMA](2)[Co(NCS)(4)] (FTMA = ferrocenylmethyltrimethylammonium cation) has been synthesized and characterized by IR, UV, elemental analysis and X-ray crystallography. Co(II) atom has a distorted tetrahedral environment with four N atoms of four NCS(-) anions. In the solid state there are C-H?π interactions between adjacent ferrocenyl cations, which generate one-dimensional (1-D) supramolecular chain, and C-H?S hydrogen bonds between [FTMA](+) cations and cobalt thiocyanate anions. The title compound shows strong purple fluorescence emission in the solid state at room temperature.     

Experimental investigation on the heat transfer characteristics of novel rectangle radial microchannel heat exchangers in two-phase flow cooling system for data centers

Journal of Thermal Analysis and Calorimetry - Biobased odd–odd poly(propylene dicarboxylate)s, based on 1,3-propanediol and three odd diacids [i.e., glutaric acid (C5), pimelic acid (C7) or...