Structure and Bonding in First‐Row Transition‐Metal Dicarbides: Are They Related to the Stability of Met‐cars?

First-row transition-metal dicarbides MC(2) (M=Sc-Zn) have been investigated by using quantum-mechanical techniques. The competition between cyclic and linear isomers in these systems has been studied and the bonding scheme for these compounds is discussed through topological analysis of electron density. All of the systems have been found to prefer a C(2v)-symmetric arrangement, although for ZnC(2) the energy difference between this and the linear isomer is rather small. In most cases the C(2v)-symmetric structure corresponds to a T-shaped structure, with the exceptions of TiC(2), CoC(2), and NiC(2) which have been shown to be true rings. A detailed analysis of the variation of the energy of the system with geometry has been carried out. An analysis of the bonding, taking into account the main interactions between the valence orbitals of both fragments, the M atom and the C(2) molecule, has allowed the main features of these compounds to be interpreted. A clear correlation between the dissociation energies of the first-row transition-metal dicarbides and the bonding energies of the corresponding met-cars was observed.     

Structure and bonding in first-row transition metal dicarbide cations MC2+

A theoretical study of the first-row transition metal dicarbide cations MC2+ (M=Sc-Zn) has been carried out. Predictions for different molecular properties that could help in their eventual experimental detection have been made. Most MC2+ compounds prefer a C2v symmetric arrangement over the linear geometry. In particular, the C2v isomer is specially favored for early transition metals. Only for CuC2+ is the linear isomer predicted to be the global minimum, although by only 1 kcal/mol. In all cases the isomerization barrier between cyclic and linear species seems to be very small (below 2 kcal/mol). The topological analysis of the electronic density shows that most C2v isomers are T-shaped structures. In general, MC2+ compounds for early transition metals have larger dissociation energies than those formed by late transition metals. In most cases the dissociation energies for MC2+ compounds are much smaller than those obtained for their neutral analogues. An analysis of the bonding in MC2+ compounds in terms of the interactions between the valence orbitals of the fragments helps to interpret their main features.     

Adsorbed para-nitrophenol on HDTMAB organoclay--a TEM and infrared spectroscopic study

para-Nitrophenol adsorbed on hexadecyltrimethylammonium bromide modified montmorillonite has been studied using a combination of X-ray diffraction TEM and infrared spectroscopy. Upon formation of the organoclay, the properties change from hydrophilic to hydrophobic. It is proposed that para-nitrophenol is adsorbed onto the water in the cation hydration sphere of the organoclay. As the cation is replaced by the surfactant molecules the para-nitrophenol replaces the surfactant molecules in the clay interlayer. Significant changes in the water vibrations occur in this process. Bands attributed to CH stretching and bending vibrations in general decrease as the concentration of the surfactant (CEC) increases up to 1.0 CEC. After this concentration the bands increase approaching a value the same as that of the surfactant. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that para-nitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.     

Near infrared spectroscopy of stearic acid adsorbed on montmorillonite

The adsorption of stearic acid on both sodium montmorillonites and calcium montmorillonites has been studied by near infrared spectroscopy complimented with infrared spectroscopy. Upon adsorption of stearic acid on Ca–Mt additional near infrared bands are observed at 8236 cm^?1 and is assigned to an interaction of stearic acid with the water of hydration. Upon adsorption of the stearic acid on Na–Mt, the NIR bands are now observed at 5671, 5778, 5848 and 5912 cm^?1 and are assigned to the overtone and combination bands of the CH fundamentals. Additional bands at 4177, 4250, 4324, 4337, 4689 and 4809 cm^?1 are attributed to CH combination bands resulting from the adsorption of the stearic acid. Stearic acid is used as a model molecule for adsorption studies. The application of near infrared spectroscopy to the study of this adsorption proved most useful.     

Gold nano-popcorn-based targeted diagnosis, nanotherapy treatment, and in situ monitoring of photothermal therapy response of prostate cancer cells using surface-enhanced Raman spectroscopy

Prostate cancer is the second leading cause of cancer-related death among the American male population, and the cost of treating prostate cancer patients is about $10 billion/year in the United States. Current treatments are mostly ineffective against advanced-stage prostate cancer and are often associated with severe side effects. Driven by these factors, we report a multifunctional, nanotechnology-driven, gold nano-popcorn-based surface-enhanced Raman scattering (SERS) assay for targeted sensing, nanotherapy treatment, and in situ monitoring of photothermal nanotherapy response during the therapy process. Our experimental data show that, in the presence of LNCaP human prostate cancer cells, multifunctional popcorn-shaped gold nanoparticles form several hot spots and provide a significant enhancement of the Raman signal intensity by several orders of magnitude (2.5 × 10(9)). As a result, it can recognize human prostate cancer cells at the 50-cells level. Our results indicate that the localized heating that occurs during near-infrared irradiation can cause irreparable cellular damage to the prostate cancer cells. Our in situ time-dependent results demonstrate for the first time that, by monitoring SERS intensity changes, one can monitor photothermal nanotherapy response during the therapy process. Possible mechanisms and operating principles of our SERS assay are discussed. Ultimately, this nanotechnology-driven assay could have enormous potential applications in rapid, on-site targeted sensing, nanotherapy treatment, and monitoring of the nanotherapy process, which are critical to providing effective treatment of cancer.     

Synthesis and comparative spectroscopic analysis of two chenodeoxycholic acid (CDCA) derivatives with closely related 7α-ester moieties

3α-Hydroxyl-7α-(4-pentenoyloxy)-5β-cholanoic acid (5) has been synthesized in four step reactions starting from CDCA. The serendipitous synthesis of methyl 3α-(ethoxycarbonyloxy)-7α-(allyloxycarbonyloxy)-5β-cholanoate (7) has led us to compare the spectroscopic difference of the 7α-(allyloxycarbonyloxy) group versus the 7α-(4-pentenoyloxy) group. The molecular structures of these compounds were confirmed by X-ray crystallography. Methyl 3α-(ethoxycarbonyloxy)-7α-(allyloxycarbonyloxy)-5β-cholanoate was obtained by a method, which may prove useful in the synthesis of ¹⁴C-labeled derivatives for metabolic studies.     

Modification of the surfaces of Wyoming montmorillonite by the cationic surfactants alkyl trimethyl, dialkyl dimethyl, and trialkyl methyl ammonium bromides

Surfaces of a Wyoming SWy-2 sodium montmorillonite were modified using microwave radiation through intercalation with the cationic surfactants octadecyl-trimethyl ammonium bromide, dimethyldioctadecylammonium bromide, and methyl-tri-octadecyl ammonium bromide by an ion exchange mechanism. Changes in the surfaces and structure were characterized using X-ray diffraction (XRD), thermal analysis (TG) and infrared (IR) spectroscopy. Different configurations of surfactants within montmorillonite interlayer are proposed based on d(001) basal spacings. A range of surfactant molecular environments within the surface-modified montmorillonite are proposed based upon their thermal decomposition. IR spectroscopy using a smart endurance single bounce diamond attenuated total reflection (ATR) cell has been used to study the changes in the spectra of CH asymmetric and symmetric stretching modes of the surfactants to provide more information of the surfactant molecular configurations.     

Application of organoclays for the adsorption of recalcitrant organic molecules from aqueous media

Water purification is imperative for the welfare of a healthy population. Water is widely contaminated by recalcitrant organic chemicals such a pesticides, herbicides and hormones. One inexpensive method for purifying water from these types of molecules is through adsorption. One suite of materials for this adsorption is based upon organoclays. This paper reviews the adsorption of organics on organoclays.     

Photophysical and theoretical insights on non-covalently linked fullerene-zinc phthalocyanine complexes

The photo-physical aspects of non-covalently linked assemblies of a series of fullerenes, namely, C60, C70, tert-butyl-(1,2-methanofullerene)-61-carboxylate (1) and [6,6]-phenyl C70 butyric acid methyl ester (2) with a designed zinc phthalocyanine (ZnPc), viz., zinc-1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (3) in toluene medium are studied employing absorption spectrophotometric, steady state and time resolved fluorescence spectroscopic measurements. Of central interest in these investigations is the preferential binding of various fullerenes with ZnPc in toluene. The ground state interaction between fullerenes and 3 is first evidenced from UV-Vis measurements. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 3 in presence of both underivatized and derivatized fullerenes. K values for the complexes of C60, C70, 1 and 2 with 3 are determined to be 6500, 22,230, 47,800 and 54,770 dm3 mol(-1), respectively. The magnitude of K suggests that 3 preferentially binds C70 and derivatized C70 in comparison to C60 and 1. Time resolved emission measurements establish that C(70)-3 and 2-3 complexes are stabilized much more in comparison to C(60)-3 and 1-3 systems in terms of charge separation process. Semi empirical calculations employing third parametric method substantiate the strong binding of C70 and its derivative with 3 in terms of heat of formation values of the respective complexes, and at the same time, determine the orientation of bound guest (here fullerenes) with the molecular plane of 3.     

Structural analyses and magnetic properties of 3D coordination polymeric networks of nickel(II) maleate and manganese(II) adipate with the flexible 1,2-bis(4-pyridyl)ethane ligand

Two novel inorganic-organic hybrid 3D extended networks of Ni(II) and Mn(II) having molecular formulas [(maleate)(2)Ni(3)(bpe)(4)(H(2)O)(4)](NO(3))(2).H(2)O (1) and [(adipate)Mn(bpe)] (2) (bpe = 1, 2-bis(4-pyridyl)ethane), respectively, have been synthesized and characterized by single-crystal X-ray diffraction studies and low-temperature (300-2 K) magnetic measurements. Compound 1 crystallizes in the monoclinic system, space group C2/c (No. 15), with chemical formula C(56)H(62)N(10)Ni(3)O(19), a = 30.955(4) A, b = 12.705(3) A, c = 17.058(5) A, beta = 117.26(2) degrees, and Z = 4. Compound 2 crystallizes in the triclinic system, space group Ponemacr; (No. 2), with chemical formula C(18)H(20)MnN(2)O(4), a = 8.492(2) A, b = 9.444(2) A, c = 11.533(3) A, alpha = 97.19(1) degrees, beta = 94.64(1) degrees, gamma = 105.02(1) degrees, and Z = 2. The structure determination reveals for both a 3D network. Compound 1 contains two crystallographically independent Ni(II) ions in different octahedral environments. Ni(1) lies on an inversion center, and its coordination environment comprises two chelating maleate anions and two bpe nitrogen donors, while the Ni(2) ion is surrounded by meridionally disposed three bpe N atoms, two water molecules, and one oxygen donor from the dicarboxylate anion. Of the three crystallographic independent bpe ligand, one presents an anti and the others a gauche conformation. The corresponding N-to-N distances are 9.344, 6.543, and 6.187 A. Variable-temperature magnetic susceptibility measurement of the complex reveals the existence of a dominant ferromagnetic interaction within the molecule. Compound 2 is composed of Mn(2) dimer units linked by adipate anions to form corrugated 2D sheets which, on interconnection through bpe (anti conformation, N-to-N distance of 9.391 A), produces an interpenetrated 3D alpha-polonium-related type net. Complex 2 reveals to be antiferromagnetic fitting data using a dimeric Mn(II) model that considers negligible magnetic transmission through the carbon skeleton of adipate and the bpe pathway.