Identification of the matrix shift: a fingerprint for neutral neon complex?

Ar-NiCO and Ne-NiCO have been predicted as novel neutral noble gas charge-transfer complexes, with binding energies of 7.70 and 2.16 kcal/mol, respectively, by the highly correlated coupled-cluster singles and doubles including a perturbational estimate of triple excitations calculations. The calculated shifts in the Ni-C-O bending frequency are 48 and 36 cm(-1) for Ar-NiCO and Ne-NiCO, while the corresponding experimental matrix shifts are 46 and 36 cm(-1), respectively. The anharmonicity effects for these frequencies are verified to be very small. The interaction between a noble gas atom and NiCO is discussed through natural population analyses and the electron density difference map. We further examined the noble gas matrix effects on the geometrical structure and vibrational frequencies of NiCO by performing density functional theory calculations for the Ng31-NiCO (Ng = Ar, Ne, He) system. The present results will inspire the further experimental investigation on the complexes of noble gas and transition metal compounds generated in the matrix isolation experiments.     

The relationship between the eigenvalues and eigenvectors of a similarity matrix and its associated Carbó index matrix

The eigenvalues and eigenvectors of a quantum similarity matrix are also generalized eigenvalues and eigenvectors of the associated matrix of Carbó indices. This establishes bounds on the spectrum of the Carbó index matrix; for example, a quantum similarity matrix is positive semidefinite if and only if the associated Carbó index matrix is also positive semidefinite. The generalized eigenvalue problem for the Carbó index matrix has a diagonal metric matrix on the right-hand-side. Every generalized eigenvalue problem can be written in this diagonal form (i.e., this form is not special to this application). This diagonally structure generalized eigenvalue problem is especially convenient because it can be converted to a conventional eigenvalue problem by a particularly simple partial Löwdin transformation.     

Correlation between the properties of a compound and the polynomial coefficients of a molecular Graph’s adjacency matrix

An additive scheme with 11 constants is derived from the coefficients of characteristic polynomials (CCPs) of adjacency matrix A of irregular molecular graphs (IMG) for molecules that contain a bivalent heteroatom -SH or -OH at the beginning of the chain. The structural significance of the CCPs to adjacency matrix A′ is established. Our formula is used to calculate the enthalpies of formation Δ_f H _{liq 298K} ^○ of liquid alkanethiols (mercaptanes) C _n H_{2n + 1}SH and Δ_f H _{liq 298K} ^○ of liquid saturated monoalcohols C _n H_{2n + 1}OH that remain unstudied experimentally.     

Chemical reactivity of the imidazole: a semblance of pyridine and pyrrole?

It has been suggested that pyridine and pyrrole could be patterns for imidazole reactivity studies due to the amine (-NH-) and aza (-N═) nitrogen atoms. The analyses of the local and global electronic indexes prove and quantify that imidazole has an intermediate analogy between pyrrole and pyridine.     

“Salt in a porous matrix” adsorbents: Design of the phase composition and sorption properties

This review formulates the concept of target-oriented synthesis of two-component “salt in a porous matrix” (SPM) adsorbents designed for processes such as gas dewatering, moisture control, heat conversion in adsorption heat pumps, and equilibrium shifting in catalytic reactions. In terms of this approach, the requirements imposed on an ideal adsorbent, which is optimal for a particular application, are initially formulated; then, a material with nearly optimal properties is synthesized. Methods for the target-oriented synthesis of SPM adsorbents with the required properties are considered. The effects of the nature of the salt and the matrix, the salt content, the pore size of the matrix, and the synthesis conditions on the phase composition and adsorption properties of the SPM adsorbents are studied.     

Marelene Rayner-Canham and Geoff Rayner-Canham,Chemistry was their life: Pioneering British women chemists, 1880–1949

Structural Chemistry -     

Brightening,Blinking, Bluing and Bleaching in the Life of a Quantum Dot: Friend or Foe?

Semiconductor nanocrystals or quantum dots (QDs) are highly photoluminescent materials with unique optical attributes that are being exploited in an ever‐increasing array of applications. However, the complex surface chemistry of these finite‐sized fluorophores gives rise to a number of photophysical phenomena that can complicate their use in imaging applications. Fluorescence intermittency (FI), photoluminescence enhancement (PLE) and spectral bluing are properties of QD emission that would appear, at first sight, detrimental to quantitative measurement. Fortunately, developments in rational QD synthesis and surface modification are promising to minimize the effects of these fluorescence instabilities, while applications that exploit them are now coming to the fore. We review recent experimental and theoretical studies of FI, PLE and bluing, highlighting the benefits, as well as complications, they bring to key applications.     

The orbital: a pivotal concept in the relationship between chemistry and physics? A comment to the work by Fortin and coauthors

The present work is a comment of a recent paper by Fortin and coauthors (Fortin et al. in Found Chem 19:43–59, 2017) in which the authors propose the introduction of Bohmian mechanics (BM) in the philosophy of chemistry and the use of standard quantum mechanics (SQM) as a mere instrument of prediction. This way would allow overcoming the obstacles found in linking molecular chemistry and quantum mechanics. Starting from some remarks on the orbital concept, we highlight and discuss some general issues that need to be taken into account when two scientific theories coexist within the same investigation field, i.e. SQM and BM.     

The role of the sol–gel route on the interaction between rhodamine B and a silica matrix

A series of silica xerogels having rhodamine B (RhB) as a template and Ti centers were synthesized by distinct sol–gel routes, namely, acid-catalyzed, base-catalyzed, acid-catalyzed with base-catalyzed (two steps) hydrolytic routes and a FeCl₃-catalyzed non-hydrolytic route. The interaction of RhB with the prepared silica matrix was investigated by Fourier transform infrared spectroscopy, attenuated total reflectance, diffuse reflectance spectroscopy in the ultraviolet–visible region, Raman spectroscopy, mass spectrometry, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and confocal microscopy. Raman spectroscopy suggested the presence of Ti–O and Si–O–Ti moieties within the silica matrix. Infrared band shifts provided insight into potential interaction sites. Taking into account the results from ART, XPS, PL and confocal microscopy, encapsulation of RhB preferentially occurs inside the silica network for acid 1, basic and two-steps routes, and the presence of Ti occurs on the surface of the silica occurs for acid 2, basic and two-steps routes. Also, we have shown that although the structural characteristics of the encapsulated and extracted systems are affected by the route, the molecular structure is conserved during and after the encapsulation process.     

Formation and structure of Co₂O₄: a combined IR matrix isolation and theoretical study

The formation and structure of dicobalt tetroxide (Co?O?) has been investigated using matrix isolation in solid neon and argon coupled to infrared spectroscopy and quantum chemical methods. It is found that Co?O? can be formed by dimerization of cobalt dioxide without activation energy by diffusion of ground state CoO? molecules at 9 K in the dark. The IR data on eight fundamentals, isotopic effects and quantum chemical calculations are both consistent with a centro-symmetrical structure with two pairs of equivalent oxygen atoms, engaged in a stronger terminal Co-O bond and in a weaker bridging Co-O-Co position. Evidence for other, metastable states is also presented, but the data are not conclusive. The electronic structure and formation pathway has been investigated using the Tao-Perdew-Staroverov-Scuseria/triple-zeta valence polarived basis set (TPSS/TZVP) and broken symmetry unrestricted density functional theory (BS-UDFT) approach and the ground electronic state is predicted to be an open shell 1Ag singlet with the quintet, triplet, septet, and nonet states above by 3.3, 4.9, 9.3, and 27.7 kcal/mol, respectively, but certainly has a complex multireference character that hinders the use of more precise multireference approaches. Different formation pathways have been considered, and the 2(O═Co═O) → Co?O? dimerization reaction is found to be the only barrierless channel and to be strongly exothermic. Comparisons with another transition metal (TM) oxide system (V?O?) suggests that the difference in predicted ground state geometries in TM?O? systems might be due in HOMO-LUMO shapes of the isolated dioxide subunits and optimal overlap configurations.     

‘Apples’ and ‘oranges’: comparing the structural aspects of biomineral- and ice-interaction proteins

The title of this review describes structural comparisons of protein classes whose task is to identify and interact with biological solids (minerals and ice). To date, the following trends have been noted: (1) biomineral-interaction proteins typically adopt unfolded, open conformations, and, where mineral binding motifs have been identified, these sequences exhibit structural trends towards extended, random coil, or other unstable secondary structures; (2) ice-interaction proteins typically adopt folded structures, featuring stable secondary structure preferences (α-helix, β-sheet, β-helix, etc.) and stable, planar ice binding motifs that exploit hydrophobicity and van der Waals’ interactions for ice binding.