Machine Learning-Assisted Computational Screening of Adhesive Molecules Derived from Dihydroxyphenyl Alanine.

Marine mussels adhere to virtually any surface via 3,4-dihydroxyphenyl-L-alanines (L-DOPA), an amino acid largely contained in their foot proteins. The biofriendly, water-repellent, and strong adhesion of L-DOPA are unparalleled by any synthetic adhesive. Inspired by this, we computationally designed diverse derivatives of DOPA and studied their potential as adhesives or coating materials. We used first-principles calculations to investigate the adsorption of the DOPA derivatives on graphite. The presence of an electron-withdrawing group, such as nitrogen dioxide, strengthens the adsorption by increasing the π-π interaction between DOPA and graphite. To quantify the distribution of electron charge and to gain insights into the charge distribution at interfaces, we performed Bader charge analysis and examined charge density difference plots. We developed a quantitative structure-property relationship (QSPR) model using an artificial neural network (ANN) to predict the adsorption energy. Using the three-dimensional and quantum mechanical electrostatic potential of a molecule as a descriptor, the present quantum NN model shows promising performance as a predictive QSPR model.

Depolymerized Chitosan-g-[Poly(MMA-co-HEMA-cl-EGDMA)] Based Nanogels for Controlled Local Release of Bupivacaine.

This study is designed to formulate and characterize chitosan-based nanogels that provide the controlled delivery of anesthetic drugs, such as bupivacaine (BPV), for effective postoperative pain management over prolonged periods of time. Drug carriers of chitosan/poly (MMA-co-HEMA-cl-EGDMA) (CsPMH) nanogels were prepared by varying the composition of comonomers such as MMA, HEMA, and redox initiator CAN. The nanogels were then characterized using FTIR, TGA, SEM, and TEM. The CsPMH nanogels showed greater encapsulation efficiencies from 43.20-91.77%. Computational studies were also conducted to evaluate the interaction between the drug and CsPMH nanoparticles. Finally, BPV-loaded nanoparticles were used to examine their in vitro release behavior. At pH 7.4, all the drug carriers displayed the "n" value around 0.7, thus the BPV release follows anomalous diffusion. Drug carrier 7 demonstrated a steady and sustained release of BPV for approximately 24 h and released about 91% of BPV, following the K-P mechanism of drug release. On the other hand, drug carrier 6 exhibited controlled release for approximately 12 h and released only 62% of BPV.

A density functional theory study on the underwater adhesion of catechol onto a graphite surface.

Mussel foot proteins (MFPs) strongly adhere to both hydrophilic and hydrophobic surfaces under wet conditions. This water-resistant adhesion of MFP is ascribed to catechol (1,2-dihydroxybenzene) which is highly contained in the MFP. Currently, little is known about the molecular details of the underwater adhesion of catechol onto a nonpolar hydrophobic surface. By using the density functional theory, we investigate the adhesion of catechol onto a wet graphite surface. We unveil the molecular geometry and energy in the course of the wet adhesion of catechol. Catechol adheres through π-π stacking with the underlying graphite. The surrounding water molecules further strengthen the adhesion by forming hydrogen bonds with catechol. In addition, a significant charge transfer has been observed from wet graphite to the catechol. Consequently, catechol adheres onto the present hydrophobic surface as strongly as onto a hydrophilic silica surface.

Gas-phase basicity and proton affinity measurements of Alzheimer's disease drugs by the extended kinetic method and a theoretical investigation.

This study has been carried out to obtain the thermochemical parameters of drugs used for Alzheimer's disease. The measurement of gas-phase basicity (GB) and proton affinity (PA) values of four important and commercially available drugs for Alzheimer's disease namely, rivastigmine, galantamine, memantine, and tacrine, is attempted for the first time. This study also includes the measurement of GB and PA values for the proposed drug curcumin, a natural product. We calculated the GB and PA values for all these drugs by applying electrospray ionization tandem mass spectrometry (ESI-MS/MS) with the extended kinetic method. Since, all these drugs possessing amino groups (basic nature), the PA values for all these drugs are high i.e., the PA values range from 923.6 to 979.7 kJ/mol and the GB values range from 886.2 to 943.3 kJ/mol. The GB and PA values obtained from the mass spectrometric experiments are well supported with the theoretical calculations. A high-level theoretical B3LYP/6-311 + G(d,p) method is used for the PA and GB calculation and the deviations are in the acceptable range.

Adenine-Based Zn(II)/Cd(II) Metal-Organic Frameworks as Efficient Heterogeneous Catalysts for Facile CO2 Fixation into Cyclic Carbonates: A DFT-Supported Study of the Reaction Mechanism.

We synthesized two new adenine-based Zn(II)/Cd(II) metal-organic frameworks (MOFs), namely, [Zn2(H2O)(stdb)2(5H-Ade)(9H-Ade)2]n (PNU-21) and [Cd2(Hstdb)(stdb)(8H-Ade)(Ade)]n (PNU-22), containing auxiliary dicarboxylate ligand (stdb = 4,4'-stilbenedicarboxylate). Both MOFs were characterized by multiple analytical techniques such as single-crystal X-ray diffraction (SXRD), powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscopy, as well as temperature program desorption and Brunauer-Emmett-Teller measurements. Both MOFs were structurally robust and possessed unsaturated Lewis acidic metal centers [Zn(II) and Cd(II)] and free basic N atoms of adenine molecules. They were used as heterogeneous catalysts for the fixation of CO2 into five-membered cyclic carbonates. Significant conversion of epichlorohydrin (ECH) was attained at a low CO2 pressure (0.4 MPa) and moderate catalyst (0.6 mol %)/cocatalyst (0.3 mol %) amounts, with over 99% selectivity toward the ECH carbonate. They showed comparable or even higher catalytic activity than other previously reported MOFs. Because of high thermal stability and robust architecture of PNU-21/PNU-22, both catalysts could be reused with simple separation up to five successive cycles without any considerable loss of their catalytic activity. Densely populated acidic and basic sites in both Zn(II)/Cd(II) MOFs facilitated the conversion of ECH to ECH carbonate in high yields. The reaction mechanism of the cycloaddition reaction between ECH and CO2 is described by possible intermediates, transition states, and pathways, from the density functional theory calculation in correlation with the SXRD structure of PNU-21.

The impact of heteroatom substitution on cross-conjugation and its effect on the photovoltaic performance of DSSCs - a computational investigation of linear vs. cross-conjugated anchoring units.

The unusual bonding pattern and proximal heteroatom substitution in π-cross conjugation produced distinct changes in the energy levels and photophysical behaviour of the dyes. To seek an understanding of the origin of these fluctuations, we have carried out a detailed computational investigation on a series of D-π1-π2 (A1)-A2 structured dyes comprised of common donor-spacer (auxiliary acceptor) units but varied the anchoring parts. In this study, we introduced a novel dimethylamino substituted fluorene-based triarylamine donor unit and evaluated its donating strength. Based on the comparison of DFT computed energy levels with experimental results, we have proposed an orbital splitting pattern to explain the energy level and photophysical properties of the linear vs. cross-conjugated dyes with respect to the linking position of the anchoring unit and benzo[1,2,5]thiadiazole (BTD) substitution. The smallest HOMO-LUMO gap of B3 mainly originated from the weak overlap of the directionality mismatch of the orbital interaction imposed by cross-conjugation. The inefficient overlap in B3 can possibly influence the energy levels but failed to enhance the charge transfer transitions upon photoexcitation. On the other hand, ß-heteroatom substitution in bridged dyes partially enhanced π-delocalization over the cross conjugation and produced a significant ICT absorption with an optoelectronic response in the NIR region. BTD acceptor substitution increased the HOMO-LUMO gap of the bridged dyes. NBO analysis was performed to corroborate our predictions. DOS-PDOS analysis of the dyes@TiO2 was employed to investigate the electron injection rate of linear vs. bridged dyes. The anchoring pattern and large torsional deviation of the carboxylate anchoring group upon TiO2 adsorption drastically decreased the photovoltaic performance of the bridged dyes. The results obtained from this study provided a detailed understanding of how to surmount the cross-conjugation with the aid of ß-heteroatom substitution. These design guidelines would be helpful in developing novel NIR dyes with better hole mobility for various optoelectronic applications. Furthermore, π-delocalization over the cross-conjugation concept opens a new pathway in the field of functional molecular devices to increase the charge conductance over several orders of magnitude with a significant reduction of destructive quantum interference at the molecular junction.

Molecular Engineering and Structure-Related Properties of Squaraine Dyes Based on the Core and Wings Concept.

Three new squaraine-based functional π-conjugated molecules were synthesized considering the core and wings concept. The molecules, SQ-DICN, SQ-DIEt-RH, and SQ-DICN-RH, were end-capped with three different wings, such as malononitrile, 2-(3-hexyl-4-oxothiazolidin-2-ylidene)malononitrile, and 3-ethyl-2-thioxothiazolidin-4-one. Among the three dyes, SQ-DICN-RH showed the highest molar extinction coefficient. The photoluminescence of all the dyes showed an opposite trend to that of the absorption maximum. The electrochemical results showed that the lowest unoccupied molecular orbital level of all the dyes ranged from -3.72 to -3.82 eV, whereas the highest occupied molecular orbital ranged from -4.89 to -4.94 eV. Solvatochromism was carried out to observe the effects of the solvent containing the dyes. The electronic structure of the dyes was examined using ab initio simulations. The dyes were characterized theoretically, and the red-shifted absorption of SQ-DICN-RH was explained and correlated with its biradicaloid character and singlet-triplet energy gap.

Spectral, Electrochemical and Computational Investigations of Binding of n-(4-Hydroxyphenyl)-imidazole with p-Sulfonatocalix[4]arene.

The interaction of n-(4-hydroxyphenyl)-imidazole with p-sulfonatocalix[4]arene is studied using fluorescence technique. The quenching of fluorescence intensity explains the efficiency of binding via binding constant and quenching constant. The excited state lifetime of n-(4-hydroxyphenyl)-imidazole is decreased upon interaction with p-sulfonatocalix[4]arene. The cyclic voltametric studies emphasized the interaction of n-(4-hydroxyphenyl)-imidazole with p-sulfonatocalix[4]arene. Quantum chemical calculations are carried out to study the interactions as well as charge transfer between the host and the guest upon complexation. The simulations revealed that the n-(4-hydroxyphenyl)-imidazole interacts with p-sulfonatocalix[4]arene with horizontal orientation with in the p-sulfonatocalix[4]arene cavity.

Inkjet-Printable Hydrochromic Paper for Encrypting Information and Anticounterfeiting.

Developing rewritable papers has gathered immense interest in recent times in view of developing sustainability in print media without exhausting environmental resources. We herein present a rapid and facile procedure for the fabrication of a communication medium by treating the surface of a paper with synthetic organic molecules, after which plain water could be used as an ink to print and reprint numerous times on the treated paper before disposal. Interestingly, as the paper comes in contact with water, the molecules are driven to reorganize in a slip-stacked arrangement. This alters their ground and excited state properties by hydrogen-bond-assisted nonradiative decay, in which the associated changes are visible to the naked eye. The changes evolved are sensitive to the solubility parameter of the solvent and thermally reversible, thus linking the hydrochromic property to the paper. Against a background of concerns over a rise in counterfeiting and leaks of confidential information, prospects for encrypted communications and anticounterfeiting is herein demonstrated.

Synthesis, Spectral Properties and DFT Calculations of new Ruthenium (II) Polypyridyl Complexes; DNA Binding Affinity and in Vitro Cytotoxicity Activity.

In this paper a novel ligand debip (2-(4-N,N-diethylbenzenamine)1H-imidazo[4,5-f] [1, 10]phenanthroline) and its Ru(II) polypyridyl complexes [Ru(L)2(debip)]2+, (L = phen (1), bpy (2) and dmb (3)) have been synthesized and characterized by spectroscopic techniques. The DNA binding studies for all these complexes were examined by absorption, emission, quenching studies, viscosity measurements and cyclic voltammetry. The light switching properties of complexes 1-3 have been evaluated. Molecular docking, Density Functional Theory (DFT) and time dependent DFT calculations were performed. The Ru(II) complexes exhibited efficient photocleavage activity against pBR322 DNA upon irradiation and exhibited good antimicrobial activity. Also investigated 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay, lactate dehydrogenase (LDH) release assay and reactive oxygen species (ROS) against selected cancer cell lines (HeLa, PC3, Lancap, MCF-7 and MD-MBA 231).

Substituent effects on the croconate dyes in dye sensitized solar cell applications: a density functional theory study.

Using the density functional theory (DFT), we studied two model croconate dyes, one with an electron-donating substituent (CR1) and the other with an electron-withdrawing group (CR2). The geometric, electronic, and optical properties of these dyes were compared. Upon switching from CR1 to CR2, a considerable bathochromic shift was observed in the electronic absorption spectrum. We also investigated the adsorption behavior of the two dyes on a TiO2 (101) anatase surface by employing periodic DFT simulations. The periodic electronic-structure calculations revealed that the diketo group of CR1 bound more strongly to the TiO2 surface than that of CR2, with a binding strength comparable to that of a typical organic D-π-A dye. In this work we evaluate in particular the effect of the electron withdrawing/donating nature of the substituent on the electronic, optical, and adsorption properties of the croconate dyes. Finally, we hope that the present study will help in the design of highly efficient dyes for dye sensitized solar cells by considering substituent effects. Graphical abstract Effect of substituent on binding energy and charge transfer.

Density functional theory study on the cross-linking of mussel adhesive proteins.

The water-resistant adhesion of mussel adhesive proteins (MAPs) to a wet surface requires a cross-linking step, where the catecholic ligands of MAPs coordinate to various transition-metal ions. Fe(III), among the range of metal ions, induces particularly strong cross-linking. The molecular details underlying this cross-linking mediated by transition-metal ions are largely unknown. Of particular interest is the metal-ligand binding energy, which is the molecular origin of the mechanical properties of cross-linked MAPs. Using density functional theory, this study examined the structures and binding energies of various trivalent metal ions (Ti-Ga) forming coordination complexes with a polymeric ligand similar to a MAP. These binding energies were 1 order of magnitude larger than the physisorption energy of a catechol molecule on a metallic surface. On the other hand, the coordination strength of Fe(III) with the ligand was not particularly strong compared to the other metal ions studied. Therefore, the strong cross-linking in the presence of Fe(III) is ascribed to its additional ability as an oxidant to induce covalent cross-linking of the catecholic groups of MAPs.

Blue and blue-green light-emitting cationic iridium complexes: synthesis, characterization, and optoelectronic properties.

Two new cationic iridium complexes, [Ir(ppy)2(phpzpy)]PF6 (complex 1) and [Ir(dfppy)2(phpzpy)]PF6 (complex 2), bearing a 2-(3-phenyl-1H-pyrazol-1-yl)pyridine (phpzpy) ancillary ligand and either 2-phenylpyridine (Hppy) or 2-(2,4-difluorophenyl)pyridine (Hdfppy) cyclometalating ligands, were synthesized and fully characterized. The photophysical and electrochemical properties of these complexes were investigated by means of UV-visible spectroscopy, emission spectroscopy, and cyclic voltammetry. Density functional theory (DFT) and time dependent DFT (TD-DFT) calculations were performed to simulate and study the photophysical and electrochemical properties of both complexes. Light-emitting electrochemical cells (LECs) were fabricated by incorporating complexes 1 and 2, which respectively exhibit blue-green (488 and 516 nm) and blue (463 and 491 nm) emission colors, achieved through the meticulous design of the ancillary ligand. The luminance and current efficiency measurements recorded for the LEC based on complex 1 were 1246 cd m(-2) and 0.46 cd A(-1), respectively, and were higher than those measured for complex 2 because of the superior balanced carrier injection and recombination properties of the former.

Thiocyanate-free cyclometalated ruthenium(II) sensitizers for DSSC: a combined experimental and theoretical investigation.

In an effort to bring out efficient thiocyanate-free dyes for dye sensitized solar cells (DSSC) we have designed, synthesized and characterized four novel cyclometalated ruthenium(II) dyes (M1 to M4) with superior photochemical properties. All dyes contain terpyridyl ligands (TPY) with carboxylic acids as anchoring groups and cyclometalated ligand (TPY-C) with substituents for fine tuning the electronic properties. We obtain a broad absorption band which extends up to 725 nm due to metal to ligand charge transfer (MLCT) when donating groups are used, which slightly blue-shifts when a withdrawing group is used. In addition to the CT, small HOMO-LUMO gaps are obtained from electrochemical measurements which indicate characteristics of an ideal sensitizer. All four dyes were used as sensitizers for DSSC and photoelectrochemical measurements were carried out. Reasonably good efficiency (7.1%) has been achieved for . We have carried out periodic-DFT studies of these dyes adsorbed on the (TiO2)38 cluster. They revealed that, in bidentate bridging mode the dyes preferably bind with the help of two carboxylic groups onto the TiO2. To the best of our knowledge we are the first to do DFT studies of thiocyanate free cyclometalated ruthenium(ii) dyes tethered to TiO2.

Enantiomeric differentiation of ß-amino alcohols under electrospray ionization mass spectrometric conditions.

The enantiomeric differentiation of a series of chiral ß-amino alcohols (A) is attempted, for the first time, by applying the kinetic method using L-proline, L-tryptophan, 4-iodo-L-phenylalanine or 3, 5-diiodo-L-tyrosine as the chiral references (Ref) and Cu(2+) or Ni(2+) ion (M) as the central metal ion. The trimeric diastereomeric adduct ions, [M+(Ref)2+A-H](+), formed under electrospray ionization conditions, are subjected for collision-induced dissociation (CID) experiments. The products ions, formed by the loss of either a reference or an analyte, detected in the CID spectra are evaluated for the enantiomeric differentiation. All the references showed enantiomeric differentiation and the R(chiral) values are better for the aromatic alcohols than for aliphatic alcohols. Notably, the R(chiral) values of the aliphatic amino alcohols enhanced when Ni(2+) is used as the central metal ion. The experimental results are well supported by computational studies carried out on the diastereomeric dimeric complexes. The computational data of amino alcohols is correlated with that of amino acids to understand the structural interaction of amino alcohols with reference molecule and central metal ion and their role on the stabilization of the dimeric complexes. Application of flow injection MS/MS method is also demonstrated for the enantiomeric differentiation of the amino alcohols.