Estimation of the limit of detection using information theory measures

Definitions of the limit of detection (LOD) based on the probability of false positive and/or false negative errors have been proposed over the past years. Although such definitions are straightforward and valid for any kind of analytical system, proposed methodologies to estimate the LOD are usually simplified to signals with Gaussian noise. Additionally, there is a general misconception that two systems with the same LOD provide the same amount of information on the source regardless of the prior probability of presenting a blank/analyte sample. Based upon an analogy between an analytical system and a binary communication channel, in this paper we show that the amount of information that can be extracted from an analytical system depends on the probability of presenting the two different possible states. We propose a new definition of LOD utilizing information theory tools that deals with noise of any kind and allows the introduction of prior knowledge easily. Unlike most traditional LOD estimation approaches, the proposed definition is based on the amount of information that the chemical instrumentation system provides on the chemical information source. Our findings indicate that the benchmark of analytical systems based on the ability to provide information about the presence/absence of the analyte (our proposed approach) is a more general and proper framework, while converging to the usual values when dealing with Gaussian noise.     

Analysis of electron delocalization in aromatic systems: individual molecular orbital contributions to para-delocalization indexes (PDI)

Our research group has recently defined two new aromaticity indexes based on the analysis of electron delocalization in aromatic species using the quantum theory of atoms-in-molecules. One of these indexes is the para-delocalization index (PDI) that measures the electronic delocalization between para-related carbon atoms in six-membered rings. In this paper, we show that this index can be partitioned into individual molecular orbital contributions. We have applied this PDI decomposition to several polycyclic aromatic hydrocarbons showing that this partitioning provides new insight into the origin of aromaticity.     

Autocatalytic demetalation of a Zn(salphen) complex provoked by unprotected N-heterocycles

The interaction of Zn(salphen) complex with biologically important structures such as (benz)imidazoles and purine has been studied and revealed in the case of unprotected purine and (benz)imidazole derivatives a demetalated product, whereas for structurally related 1-methyl-(benz)imidazole the formation of 1 : 1 coordination complexes was evidenced by NMR, MS and X-ray crystallography.     

Preparation and structure of three solvatomorphs of the polymer [Co(dbm)2(4ptz)]n: spin canting depending on the supramolecular organization

The syntheses and X-ray structures of three isomeric 1D coordination polymers are reported. The complex [Co(dbm)2(MeOH)2] (1) was used as a precursor in these reactions. The preparation and structure of 1 is also presented; this mononuclear complex is in the cis configuration because this allows the formation of a network of intermolecular hydrogen bonds in the solid state. Reaction of 1 with 2,4,6-tris-(4-pyridyl)-1,3,5-triazine (4ptz) yields the polymers [Co(dbm)2(4ptz)]n.nTHF (2a), [Co(dbm)2(4ptz)]n.0.75nTHF.0.5nEt2O (2b), and [Co(dbm)2(4ptz)]n.3nDMF (2c) in the form of zigzag chains, instead of the expected honeycomb architectures. This is because of the establishment of extended pi-pi stacking throughout these solids, which could not have occurred otherwise. Compounds 2a, 2b, and 2c are solvatomorphs, and formation of either one of them depends on the exact conditions of crystallization, which lead to significant differences in the supramolecular organization of the chains. Bulk magnetic measurements on 2a reveal weak antiferromagnetic exchange within the chains and small ordering throughout the solid that results in the manifestation of the phenomenon of spin canting, whereas for 2c the different supramolecular organization causes the antiferromagnetic exchange not to result in spin canting.     

Synthesis and Characterization of [(1,4‐diamine)dichloro]platinum(II) Compounds Preliminary Studies on their Biological Activity

Two 1,4‐diamine ligands were synthesized having 1,2‐bis(aminomethyl)‐cyclohexane and 1,2‐bis(aminomethyl)‐benzene structures. The two ligands have different electron density in the six‐membered ring: a cyclohexane versus a phenyl ring. The organic synthesis of the ligands was carried out by synthetic pathways of seven and four steps, respectively, starting from 1,2,3,6‐tetrahydrophthalic anhydride and diethyl phthalate. The coordination of platinum to these ligands afforded platinum(II) complexes which are analogue to the clinical drug cisplatin but form a seven‐membered chelate ring. The interaction of the platinum compounds with DNA was studied in order to know the relationship between the electron density of ligands and their capability to chelate DNA, by using three techniques: Circular Dichroism, Agarose Gel Electrophoresis and Atomic Force Microscopy. The degree of interaction of both compounds with DNA was slightly different, but both complexes showed a cisplatin‐like behaviour and are promising candidates to follow an extensive study of their cytotoxic activity.     

Sensing Abilities of Crown Ether Functionalized Polythiophenes

Tuning sensing abilities! The affinity of three different [15]crown‐5 ether functionalized polythiophenes for alkali ions has been explored (see figure). Ab initio and DFT quantum mechanical calculations show that the binding energy between neutral conducting polymers and metallic ions, which interact attractively, decreases as the size of the ion increases. Oxidation of these polythiophene derivatives significantly reduces their affinity towards alkali ions, becoming low or even nonexistent.

     

Understanding conjugation and hyperconjugation from electronic delocalization measures

The concepts of conjugation and hyperconjugation play an important role to provide an explanation for several fundamental phenomena observed in organic chemistry. Because these effects cannot be directly measured experimentally, their assessment became a primary concern for chemists from the very beginning. In general, the stabilization produced by both phenomena has been studied by means of isodesmic reactions and energy based analysis such as the energy decomposition analysis. In recent years, electronic delocalization measures have been successfully applied to elucidate the nature of chemical bonding and the aromatic character of all kind of molecules. Because conjugation and hyperconjugation stabilizations are strongly linked to the concept of electron delocalization, this paper will give an account of both effects from the point of view of electronic delocalization measures calculated within the framework of the quantum theory of atoms in molecules. In particular, we focus our attention in the controversial case of the stabilization by conjugation in 1,3-butadiyne and 1,3-butadiene. Unexpectedly, theoretical calculations based on the scheme proposed by Kistiakowsky to quantify the extent of stabilization due to conjugation predicted that the conjugation of 1,3-butadiyne was zero. Subsequent energetic analyses contradicted this observation. These studies pointed out the presence of hyperconjugation stabilization in the hydrogenated product of 1,3-butadiyne and 1,3-butadiene that were used as reference systems in the Kistiakowsky's scheme. Consequently, the extra stabilization of 1-butyne due to hyperconjugation hides the stabilization by conjugation of 1,3-butadiyne. Our results based on electron delocalization measures confirm both the presence of conjugation in 1,3-butadiene and 1,3-butadiyne and hyperconjugation stabilization in their respective hydrogenated products, 1-butene and 1-butyne.     

Systematic evaluation of the conformational properties of aliphatic omega-hydroxy acids

A systematic conformational study of omega-hydroxy acids, HO-(CH(2))(n)()-COOH with n ranging from 2 to 5, has been performed using quantum mechanical calculations at the MP2 level. To distinguish between intrinsic and environmentally induced conformational preferences, calculations have been carried out in both gas phase and chloroform solution, a polarizable continuum solvation model being used to represent the latter. Results indicate a consistent conformational behavior, as reflects the feature that the lowest energy minimum for n = 2, 3, 4, and 5 corresponds to the g+g-t, g+g+g-t, g-g+g+g-t, and g+g-g+g+g-t conformations, respectively. Furthermore, the stability of the extended and semi-extended conformations increases systematically with the size of the central aliphatic segment. The relationship between the size of the aliphatic segment and the stability of folded conformations is analyzed and discussed.     

Synthesis, structure, and reactivity of new tetranuclear Ru-Hbpp-based water-oxidation catalysts

The preparation of three new octadentate tetranucleating ligands made out of two Ru-Hbpp-based units [where Hbpp is 3,5(bispyridyl)pyrazole], linked by a xylyl group attached at the pyrazolate moiety, of general formula (Hbpp)(2)-u-xyl (u = p, m, or o) is reported, together with its dinucleating counterpart substituted at the same position with a benzyl group, Hbpp-bz. All of these ligands have been characterized with the usual analytical and spectroscopic techniques. The corresponding tetranuclear ruthenium complexes of general formula {[Ru(2)(trpy)(2)(L)](2)(μ-(bpp)(2)-u-xyl)}(n+) [L = Cl or OAc, n = 4; L = (H(2)O)(2), n = 6] and their dinuclear homologues {[Ru(2)(trpy)(2)(L)](μ-bpp-bz)}(n+) [L = Cl or OAc, n = 2; L = (H(2)O)(2), n = 3] have also been prepared and thoroughly characterized both in solution and in the solid state. In solution, all of the complexes have been characterized spectroscopically by UV-vis and NMR and their redox properties investigated by means of cyclic voltammetry techniques. In the solid state, monocrystal X-ray diffraction analysis has been carried out for two dinuclear complexes {[Ru(2)(trpy)(2)(L)](μ-bpp-bz)}(2+) (L = Cl and OAc) and for the tetranuclear complex {[Ru(2)(trpy)(2)(μ-OAc)](2)(μ-(bpp)(2)-m-xyl)}(4+). The capacity of the tetranuclear aqua complexes {[Ru(2)(trpy)(2)(H(2)O)(2)](2)(μ-(bpp)(2)-u-xyl)}(6+) and the dinuclear homologue {[Ru(2)(trpy)(2)(H(2)O)(2)](μ-bpp-bz)}(3+) to act as water-oxidation catalysts has been evaluated using cerium(IV) as the chemical oxidant in pH = 1.0 triflic acid solutions. It is found that these complexes, besides generating significant amounts of dioxygen, also generate carbon dioxide. The relative ratio of [O(2)]/[CO(2)] is dependent not only on para, meta, or ortho substitution of the xylylic group but also on the concentration of the starting materials. With regard to the tetranuclear complexes, the one that contains the more sterically constrained ortho-substituted ligand generates the highest [O(2)]/[CO(2)] ratio.