Formulation and characterization of in situ generated copper nanoparticles reinforced cellulose composite films for potential antimicrobial applications

Cellulose was dissolved in aq.(LiOH C urea) solution pre-cooled to –12.5 C and the wet films were prepared using ethyl alcohol coagulation bath. The gel cellulose films were dipped in 10 wt.% Cassia alata leaf extract solution and allowed the extract to diffuse into them. The leaf extract infused wet cellulose films were dipped in different concentrated aq. copper sulphate solutions and allowed for in situ generation of copper nanoparticles (CuNPs) inside the matrix. The morphological, structural, antibacterial, thermal, and tensile properties of dried cellulose/CuNP composite films were carried out. The presence of CuNPs was established by EDX spectra and X-ray diffraction. The composite films displayed higher thermal stability than the matrix due to the presence of CuNPs. Cellulose/CuNP composite films possessed better tensile strength than the matrix. The composite films showed good antibacterial activity against E.coli bacteria. We conclude that good antibacterial activity and better tensile properties of the cellulose/CuNP composite films make them suitable for antibacterial wrapping and medical purposes

Electronic nonadiabatic interactions and ultrafast internal conversion in phenylacetylene radical cation

Quantum chemistry and dynamics of the ground X^~ 2B₁ and low-lying excited A^~ 2A₂, B^~ 2B₂, and C^~ 2B₁ electronic states of phenylacetylene radical cation are examined here in striving to understand its photostability, long-lived excited electronic states, and resolved (<10 meV) vibrational energy level spectrum. The electronic potential energy surfaces and their nonadiabatic coupling are computed ab initio. A model Hamiltonian is constructed in a diabatic electronic basis for the nuclear dynamical simulations from first principles. Analysis of electronic structure data reveals the relevance of 24 vibrational degrees of freedom in the quantum dynamics of the X˜-Ã-B˜-C˜ coupled electronic states of the radical cation. The complex vibrational energy level spectrum of this coupled electronic manifold is calculated and assigned. Theoretical results are in excellent accord with the experimental photoelectron spectroscopy data. The agreements and discrepancies of the theoretical results are also recorded and discussed with the mass-analyzed threshold ionization and photoinduced Rydbergionization and photodissociation spectroscopy results of the X˜ and C˜ electronic states, respectively. The lifetimes of the excited electronic states of phenylacetylene radical cation are estimated from the decay of electronic population and are discussed in relation to the available experimental data

Ultrafast ESIPT dynamics of 4-methyl-2,6-diformylphenol

We investigate the gas-phase photodynamics associated with the S1 (nπ*), S2 (ππ*) and S3 (nπ*) states of 4-methyl-2,6-diformylphenol using trajectory-based surface hopping dynamics simulations. A rapid internal conversion would populate S1 and S3 upon initiating the trajectories on “bright” S2. This nonadiabatic population behavior would lead to intramolecular proton-transfer tautomerization via three states, where the predominant tautomerization happens via S2. An average timescale of ∼ 44 fs is estimated for the tautomerization. The triplet formation can occur via energetically feasible S1-T3 (at the Franck-Condon geometry of normal tautomer) and S1-T2 (at the S1 equilibrium minimum of proton-transferred tautomer) pathways. Intersystem crossing and the forbidden nature of S1 (nπ*) makes the molecule exhibit weak fluorescence

Photostability of electronically excited polyacenes: a case study of vibronic coupling in the naphthalene radical cation

Novel issues of electronic nonadiabatic coupling in the excited state dynamics of prototypical naphthalene radical cation of polycyclic aromatic hydrocarbon of the polyacene family are theoretically investigated. A benchmark ab initio quantum dynamical study is performed and its complex vibronic spectra and nonradiative decay are examined. The findings are in very good accord with the experiment, unambiguously establishing the crucial role of intricate electron-nuclear coupling in the photoinduced dynamical processes of this system

Theoretical study of the electronically excited radical cations of naphthalene and anthracene as archetypal models for astrophysical observations. Part II. Dynamics consequences

Nuclear dynamics is investigated theoretically from first principles by employing the ab initio vibronic models of the prototypical naphthalene and anthracene radical cations developed in Part I. This Part is primarily aimed at corroborating a large amount of available experimental data with a specific final goal to establish an unambiguous link with the current observations in astrophysics and astronomy. The detailed analyses presented here perhaps establish that these two prototypical polycyclic aromatic hydrocarbon radical cations are indeed potential carriers of the observed diffuse interstellar bands

First principles quantum dynamical investigation provides evidence for the role of polycyclic aromatic hydrocarbon radical cations in interstellar physics

Inspired by the recent astronomical discovery of new diffused interstellar bands (DIBs) assigned to the electronic transitions in the naphthalene radical cation based on complementary laboratory measurements, we attempt here an ab initio quantum dynamical study to validate this assignment. In addition, the existence and mechanistic details of nonradiative deactivation of electronically excited polycyclic aromatic hydrocarbon (PAH) radical cations in the interstellar medium and their identity as carriers of DIBs are established here focusing on the prototypical naphthalene and anthracene radical cations of the PAH family

(B+E⊗b)⊗e Jahn–Teller and pseudo-Jahn–Teller effects in the spiropentane radical cation

In this paper we examine the Jahn–Teller (JT) and pseudo-Jahn–Teller (PJT) effects in the spiropentane radical cation (SP<SUP>+</SUP>) by an ab initio quantum dynamical method. Spiropentane (SP) possesses D<SUB>2d</SUB> symmetry at its equilibrium configuration. The two low-lying electronic states of SP<SUP>+</SUP> belong to X&#732;<SUP>2</SUP>B<SUB>2</SUB> and &#195;<SUP>2</SUP>E symmetry, respectively. SP<SUP>+</SUP> in the degenerate &#195;state is susceptible to JT distortions along the vibrational modes of b symmetry. The &#195; state of SP<SUP>+</SUP> is vertically ∼0.51 eV spaced from its X&#732; state. Symmetry rule allows a coupling of the X&#732; and &#195; states via the degenerate e vibrational modes. This is termed as the (B + E ⊗ b) ⊗ e JT and PJT effects revealing the symmetry of the electronic states and the coupling vibrational modes. The theoretical findings establish significant impact of the JT and PJT coupling in the observed complex structure of the X&#732;–&#195;bands of SP<SUP>+</SUP>

Vibronic interactions in the photodetachment spectroscopy of phenide anion

Photodetachmentspectroscopy of phenide anion C₆H₅^- is theoretically studied with the aid of electronic structure calculations and quantum dynamical simulations of nuclear motion. The theoretical results are compared with the available experimental data. The vibronic structure of the first, second, and third photoelectron bands associated with the ground X^~2A₁ and low-lying excited A^˜2B₁ and B^˜2A₂ electronic states of the phenyl radical C6H5 is examined at length. While the X˜ state of the radical is energetically well separated and its interaction is found to be rather weak with the rest, the A^~ and B^~ electronic states are found to be only ∼0.57eV apart in energy at the vertical configuration. Low-energy conical intersections between the latter two states are discovered and their impact on the nuclear dynamics underlying the second and third photoelectron bands is delineated. The nuclear dynamics in the X˜ state solely proceeds through the adiabatic path and the theoretically calculated vibrational level structure of this state compares well with the experimental result. Two Condon active totally symmetric (a1) vibrational modes of ring deformation type form the most dominant progression in the first photoelectron band. The existing ambiguity in the assignment of these two vibrational modes is resolved here. The A˜-B˜ conical intersections drive the nuclear dynamics via nonadiabatic paths, and as a result the second and third photoelectron bands overlap and particularly the third band due to the B˜ state of C₆H₅ becomes highly diffused and structureless. Experimental photodetachmentspectroscopy results are not available for these bands. However, the second band has been detected in electronic absorption spectroscopy measurements. The present theoretical results are compared with these absorption spectroscopy data to establish the nonadiabatic interactions between the A˜ and B˜ electronic states of C₆H₅

Bio-mediated Synthesis of Nanomaterials for Packaging Applications

Change in lifestyle of humans in this present generation with huge dependence on packaging materials has encouraged several studies on development of new variety of packaging materials. Emphasis on replacement of existing non-biodegradable packaging materials with biodegradable materials paved the way for the use of biopolymers. Lack of properties, such as thermal stability and mechanical strength in biopolymers led to the development of bio-polymer nano-composites by adding metal/metal oxide nanoparticles as fillers into the biopolymers. Metal/metal oxide nano-particles improve mechanical/tensile strength, thermal stability as well as antimicrobial properties of the binding and receiving polymer matrix. Bio-mediated synthesis of metal/metal oxide nanoparticles result to development of novel packaging materials at a low cost and without releasing hazardous wastes into the environments. Novel packaging materials with metal/metal oxide nanoparticles as additives are capable of increasing the shelf life of food stuffs, in certain cases they act as indicators of quality food inside the package. Summarily, this present chapter focuses on bio-mediated synthesis of various metal/metal oxide nano-particles and their applications in food packaging.Peer reviewe

Indirect Intersystem Crossing (S₁ → T₃/T₂ → T₁) Promoted by the Jahn–Teller Effect in Cycloparaphenylenes

Vibronic-coupling effects play a key role for excited-state charge- and energy-transfer processes in organic molecular systems. Here, we demonstrate how the Jahn–Teller effect in triplet excited states of highly symmetric cycloparaphenylenes triggers an indirect intersystem crossing deactivation pathway. Strong Jahn–Teller distortion in the doubly degenerate second excited triplet state (T₂) brings the molecular system energetically close to the lowest triplet state (T₁), thereby opening the possibility for an extremely rapid internal conversion. Quantum dynamics simulations reveal an initial T₂ → T₁ population decay within 50 fs. Experimental observation of size-dependent intersystem crossing rates of cycloparaphenylenes is explained based on the proposed S₁ → T₃/T₂ → T₁ mechanism