Carbonyl-carbonyl n→π* interactions where a lone pair (n) of the oxygen atom of a carbonyl group is delocalized over the π* orbital of a nearby carbonyl group have attracted a lot of attention in recent years due to their ability to affect the 3D structure of small molecules, polyesters, peptides, and proteins. In this paper, we report the discovery of a “reciprocal” carbonyl-carbonyl interaction with substantial back and forth n→π* and π→π* electron delocalization between neighboring carbonyl groups. We have carried out experimental studies, analyses of crystallographic databases and theoretical calculations to show the presence of this interaction in both small molecules and proteins. In proteins, these interactions are primarily found in polyproline II (PPII) helices. As PPII are the most abundant secondary structures in unfolded proteins, we propose that these local interactions may have implications in protein folding.

We study the stability of drum-shaped transition metal (TM)-doped boron clusters, M@B n with n = 14 and 16, and M = 3d, 4d, and 5d TM atom using ab initio calculations. Our results show that drum-shaped M@B 14 clusters are favored for M = Cr, Mn, Fe, Co, and Ni, while in other cases, open conical or bowl shaped structures become more favorable. The isoelectronic Ni@B 14 and Co@B 14 − clusters have large highest occupied molecular orbital−lowest unoccupied molecular orbital gaps and these are magic clusters. Their stability has been correlated with the occurrence of magic behavior with 24 valence electrons in a disk jellium model, while for Fe@B 14 case the drum structure is deformed and the stability occurs at 22 delocalized valence electrons. The bonding nature in these clusters has been studied by analyzing the electron density at bond and ring critical points, the Laplacian distribution of the electron density, the electron localization function, the source function, and electron localization-delocalization indices, all of which suggest two-and threecenter σ bonding within and between the two B 7 rings, respectively, and hybridization between the TM d orbitals and the π bonded molecular orbitals of the drum. The infrared and Raman spectra of these magic clusters show all real frequencies, suggesting the dynamical stability of the drum-shaped structures. There is a low frequency mode associated with the M atom. Results of the electronic spectra of the anion clusters are also presented that may help to identify these species in future experiments. Further, we discuss the stability of 24 delocalized valence electron systems Mn@B 16 anion, Fe@B 16 , Co@B 16 cation, and other related clusters. Assembly of Co@B 14 clusters has been shown to stabilize a carbon nanotube-like nanotube of boron with Co atomic nanowire inside while a nanotube of boron with triangular network has been obtained with the assembly of Fe@ B 16 drum-shaped clusters. Both the nanotubes are metallic.

Tackling air pollution has become of utmost importance since the last few decades. Different statistical as well as deep learning methods have been proposed till now, but seldom those have been used to forecast future long-term pollution trends. Forecasting long-term pollution trends into the future is highly important for government bodies around the globe as they help in the framing of efficient environmental policies. This paper presents a comparative study of various statistical and deep learning methods to forecast long-term pollution trends for the two most important categories of particulate matter (PM) which are PM2.5 and PM10. The study is based on Kolkata, a major city on the eastern side of India. The historical pollution data collected from government set-up monitoring stations in Kolkata are used to analyse the underlying patterns with the help of various time-series analysis techniques, which is then used to produce a forecast for the next two years using different statistical and deep learning methods. The findings reflect that statistical methods such as auto-regressive (AR), seasonal auto-regressive integrated moving average (SARIMA) and Holt–Winters outperform deep learning methods such as stacked, bi-directional, auto-encoder and convolution long short-term memory networks based on the limited data available.

The diamagnetic VO(2+)-iminobenzosemiquinonate anion radical (L(R)(IS)(•-), R = H, Me) complexes, (L(-))(VO(2+))(L(R)(IS)(•-)): (L(1)(-))(VO(2+))(L(H)(IS)(•-))•3/2MeOH (1•3/2MeOH), (L(2)(-))(VO(2+))(L(H)(IS)(•-)) (2), and (L(2)(-))(VO(2+))(L(Me)(IS)(•-))•1/2 L(Me)(AP) (3•1/2 L(Me)(AP)), incorporating tridentate monoanionic NNO-donor ligands {L = L(1)(-) or L(2)(-), L(1)H = (2-[(phenylpyridin-2-yl-methylene)amino]phenol; L(2)H = 1-(2-pyridylazo)-2-naphthol; L(H)(IS)(•-) = o-iminobenzosemiquinonate anion radical; L(Me)(IS)(•-) = o-imino-p-methylbenzosemiquinonate anion radical; and L(Me)(AP) = o-amino-p-methylphenol} have been isolated and characterized by elemental analyses, IR, mass, NMR, and UV-vis spectra, including the single-crystal X-ray structure determinations of 1•3/2MeOH and 3•1/2 L(Me)(AP). Complexes 1•3/2MeOH, 2, and 3•1/2 L(Me)(AP) absorb strongly in the visible region because of intraligand (IL) and ligand-to-metal charge transfers (LMCT). 1•3/2MeOH is luminescent (λ(ext), 333 nm; λ(em), 522, 553 nm) in frozen dichloromethane-toluene glass at 77 K due to π(diimine→)π(diimine)* transition. The V-O(phenolato) (cis to the V═O) lengths, 1.940(2) and 1.984(2) Å, respectively, in 1•3/2MeOH and 3•1/2 L(Me)(AP) are consistent with the VO(2+) description. The V-O(iminosemiquinonate) (trans to the V═O) lengths, 2.1324(19) in 1•3/2MeOH and 2.083(2) Å in 3•1/2 L(Me)(AP), are expectedly ∼0.20 Å longer due to the trans influence of the V═O bond. Because of the stronger affinity of the paramagnetic VO(2+) ion to the L(H)(IS)(•-) or L(Me)(IS)(•-), the V-N(iminosemiquinonate) lengths, 1.908(2) and 1.921(2) Å, respectively, in 1•3/2MeOH and 3•1/2 L(Me)(AP), are unexpectedly shorter. Density functional theory (DFT) calculations using B3LYP, B3PW91, and PBE1PBE functionals on 1 and 2 have established that the closed shell singlet (CSS) solutions (VO(3+)-amidophenolato (L(R)(AP)(2-)) coordination) of these complexes are unstable with respect to triplet perturbations. But BS (1,1) M(s) = 0 (VO(2+)-iminobenzosemiquinonate anion radical (L(R)(IS)(•-)) coordination) solutions of these species are stable and reproduce the experimental bond parameters well. Spin density distributions of one electron oxidized cations are consistent with the [(L(-))(VO(2+))(L(R)(IQ))](+) descriptions [VO(2+)-o-iminobenzoquinone (L(R)(IQ)) coordination], and one electron reduced anions are consistent with the [(L(•2-))(VO(3+))(L(R)(AP)(2-))](-) descriptions [VO(3+)-amidophenolato (L(R)(AP)(2-)) coordination], incorporating the diimine anion radical (L(1)(•2-)) or azo anion radical (L(2)(3-)). Although, cations and anions are not isolable, but electro-and spectro-electrochemical experiments have shown that 3(+) and 3(-) ions are more stable than 1(+), 2(+) and 1(-), 2(-) ions. In all cases, the reductions occur with simultaneous two electron transfer, may be due to formation of coupled diimine/azo anion radical-VO(2+) species as in [(L(•2-))(VO(2+))(L(R)(AP)(2-))](2-).

Boron atomic clusters show several interesting and unusual size-dependent features due to the small covalent radius, electron deficiency, and higher coordination number of boron as compared to carbon. These include aromaticity and a diverse array of structures such as quasi-planar, ring or tubular shaped, and fullerene-like. In the present work, we have analyzed features of the computed electron density distributions of small boron clusters having up to 11 boron atoms, and investigated the effect of doping with C, P, Al, Si, and Zn atoms on their structural and physical properties, in order to understand the bonding characteristics and discern trends in bonding and stability. We find that in general there are covalent bonds as well as delocalized charge distribution in these clusters. We associate the strong stability of some of these planar/ quasiplanar disc-type clusters with the electronic shell closing with effectively twelve delocalized valence electrons using a disc-shaped jellium model. -B , 9 B 10 , B 7 P, and B 8 Si, in particular, are found to be exceptional with very large gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, and these are suggested to be magic clusters.