Role of Magnetic Exchange Interactions in the Magnetization Relaxation of {3d–4f} Single‐Molecule Magnets: A Theoretical Perspective

Combined density functional and ab initio calculations are performed on two isomorphous tetranuclear {Ni₃^IIILn^III} star‐type complexes [Ln=Gd ( 1 ), Dy ( 2 )] to shed light on the mechanism of magnetic exchange in 1 and the origin of the slow magnetization relaxation in complex 2 . DFT calculations correctly reproduce the sign and magnitude of the J values compared to the experiments for complex 1 . Acute ?Ni?O?Gd bond angles present in 1 instigate a significant interaction between the 4f_xyz orbital of the Gd^III ion and 3d orbital of the Ni^II ions, leading to rare and strong antiferromagnetic Ni???Gd interactions. Calculations reveal the presence of a strong next‐nearest‐neighbour Ni???Ni antiferromagnetic interaction in complex 1 leading to spin frustration behavior. CASSCF+RASSI‐SO calculations performed on complex 2 suggest that the octahedral environment around the Dy^III ion is neither strong enough to stabilize the m_J |±15/2〉 as the ground state nor able to achieve a large ground‐state–first‐excited‐state gap. The ground‐state Kramers doublet for the Dy^III ion is found to be the m_J |±13/2〉 state with a significant transverse anisotropy, leading to very strong quantum tunneling of magnetization (QTM). Using the POLY_ANISO program, we have extracted the J_NiDy interaction as ?1.45 cm^?1. The strong Ni???Dy and next‐nearest‐neighbour Ni???Ni interactions are found to quench the QTM to a certain extent, resulting in zero‐field SMM behavior for complex 2 . The absence of any ac signals at zero field for the structurally similar [Dy(AlMe₄)₃] highlights the importance of both the Ni???Dy and the Ni???Ni interactions in the magnetization relaxation of complex 2 . To the best of our knowledge, this is the first time that the roles of both the Ni???Dy and Ni???Ni interactions in magnetization relaxation of a {3d–4f} molecular magnet have been established.     

Statistical optimization of conditions for protease production fromBacillus sp. and its scale-up in a bioreactor

A statistical approach, response surface methodology (RSM), was used to study the production of extracellular protease fromBacillus sp., which has properties of immense industrial importance. The most influential parameters for protease production obtained through the method of testing the parameters one at a time were starch, soybean meal, CaCl₂, agitation rate, and inoculum density. This method resulted in the production of 2543 U/mL of protease in 48 h fromBacillus sp. Based on these results, face-centered central composite design falling under RSM was employed to further enhance protease activity. The interactive effect of the most influential parameters resulted in a 1.50-fold increase in protease production, yielding 3746 U/mL in 48 h. Analysis of variance showed the adequacy of the model and verification experiments confirmed its validity. On subsequent scale-up in a 30-L bioreactor using conditions optimized through RSM, 3978 U/mL of protease was produced in 18 h. This clearly indicated that the model remained valid even on a large scale. RSM is a quick process for optimization of a large number of variables and provides profound insight into the interactive effect of various parameters involved in protease production.     

Probing CP-violating Higgs contributions in γγ → f$$ \bar f $$

We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct polarization asymmetries which can isolate the contribution of a Higgs boson ϕ in γγ → f , f = τ/t, from that of the QED continuum. This can help in getting information on the γγϕ coupling in case ϕ is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case ϕ has indeterminate CP. Furthermore, we take the MSSM with CP violation as an example to demonstrate the potential of these asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well as its CP properties over a wide range of MSSM parameters.      

Green synthesis of nanocomposites consisting of silver and protease alpha chymotrypsin

The synergy of ultrasonication and the exposure to light radiation was found to be necessary in the formation of nanocomposites of silver and a protease alpha chymotrypsin. The reaction was carried out in aqueous medium and the process took just less than 35 min. Ultrasonication alone formed very negligible number of nanoparticles of <100 nm size whereas light alone produced enough number but the size of the particles was >100 nm.The effects of pH (in the range of 3–5, 9–10), ultrasonication time periods (0–30 min), ultrasonication intensity (33–83 W cm^?2), energy of light radiation (short UV, long UV and Fluorescent light) and time period of exposure (5–60 min) to different light radiations were studied.The formation of nanocomposites under these effects was followed by surface plasmon resonance (SPR) spectra, dynamic light scattering (DLS), transmission electron microscopy (TEM). Ag–chymotrypsin nanocomposites of sizes ranging from 13 to 72 nm were formed using the synergy of ultrasonication and exposure to short UV radiation. Results show that ultrasonication promoted nuclei formation, growth and reduction of polydispersity by Ostwald ripening.     

Strengthening Erdös–Pósa property for minor‐closed graph classes

Let ?? and ?? be graph classes. We say that ?? has the Erd?s–Pósa property for ?? if for any graph G ∈??, the minimum vertex covering of all ??‐subgraphs of G is bounded by a function f of the maximum packing of ??‐subgraphs in G (by ??‐subgraph of G we mean any subgraph of G that belongs to ??). Robertson and Seymour [J Combin Theory Ser B 41 (1986), 92–114] proved that if ?? is the class of all graphs that can be contracted to a fixed planar graph H, then ?? has the Erd?s–Pósa property for the class of all graphs with an exponential bounding function. In this note, we prove that this function becomes linear when ?? is any non‐trivial minor‐closed graph class. © 2010 Wiley Periodicals, Inc. J Graph Theory 66:235‐240, 2011     

Nasal in situ gel containing hydroxy propyl ��-cyclodextrin inclusion complex of artemether: development and in vitro evaluation

The objective of the present investigation was to explore the formulation and evaluation of in situ gel for the nasal delivery of artemether (ARM), a poorly water-soluble antimalarial agent using temperature induced gelation technique using Pluronic with mucoadhesive polymer Hydroxy Propyl Methyl Cellulose (HPMC) K4M in different ratios. Initially, due to low water solubility, an inclusion complex of the antimalarial artemether (ARM) in hydroxypropyl-??-cyclodextrin (HP??CD) was prepared and characterized. The in situ gels so prepared were characterized for its gelation properties, viscosity, gel strength, mucoadhesion, drug content, drug release rate and for its histopathological studies. Pluronic and HPMC based in situ gel (PLH2) showed the effective gelation, viscosity, gel strength and drug release properties along with good mucoadhesive strength, it is further subjected for stability studies carried out at 30 ± 2 °C and 60 ± 5% RH for 90 days in order to know the influence of temperature and relative humidity on drug content and on drug release profile. Histological examination of formulations did not show any remarkable damage to nasal mucosa. The formulation also retained the good stability at accelerated conditions over the period of 90 days. Owing to these properties it can be used as an effective delivery system for the nasal route. These in situ gelling systems would be definitely useful for cerebral malaria.     

Perspectives on ab initio molecular simulation of excited-state properties of organic dye molecules in dye-sensitised solar cells

In this mini-review, we summarise and critique the emerging field of quantum-based molecular simulation of dye-sensitised solar cells (DSSCs), with particular focus on the deployment of organic-based dyes therein. We assess the underlying methodologies, including developments, pitfalls and challenges, whilst gauging predictive performance vis-à-vis experimental performance. The predictive capabilities of simulation methods with respect to elucidation of underlying methods is considered in the light of progress towards the ultimate goal of predictive in silico design of DSSCs, to complement hand-in-hand experimental approaches in the development of state-of-the-art DSSC devices.     

Spin‐1 Bose Hubbard Model with Nearest Neighbour Extended Interaction

A spinor () Bose gas is studied in presence of a density‐density interaction through a mean field approach and a perturbation theory for either sign of the spin dependent interaction, namely the antiferromagnetic (AF) and the ferromagnetic cases. In the AF case, the charge density wave (CDW) phase appears to be sandwiched between the Mott insulating (MI) and the supersolid phases for small values of the extended interaction strength. But the CDW phase completely occupies the MI lobe when the extended interaction strength is larger than a certain critical value related to the width of the MI lobes and hence opens up the possibilities of spin singlet and nematic CDW insulating phases. In the ferromagnetic case, the phase diagram shows similar features as that of the AF case and are in complete agreement with a spin‐0 Bose gas. The perturbation expansion calculations nicely corroborate the mean field phase results in both these cases. Further, we extend our calculations in presence of a harmonic confinement and obtained the momentum distribution profile that is related to the absorption spectra in order to distinguish between different phases.