Proton migration in protonated glycylglycylglycine (GGG) has been investigated by using density functional theory at the B3LYP/6-31++G(d,p) level of theory. On the protonated GGG energy hypersurface 19 critical points have been characterized, 11 as minima and 8 as first-order saddle points. Transition state structures for interconversion between eight of these minima are reported, starting from a structure in which there is protonation at the amino nitrogen of the N-terminal glycyl residue following the migration of the proton until there is fragmentation into protonated 2-aminomethyl-5-oxazolone (the b(2) ion) and glycine. Individual free energy barriers are small, ranging from 4.3 to 18.1 kcal mol(-)(1). The most favorable site of protonation on GGG is the carbonyl oxygen of the N-terminal residue. This isomer is stabilized by a hydrogen bond of the type O-H.N with the N-terminal nitrogen atom, resulting in a compact five-membered ring. Another oxygen-protonated isomer with hydrogen bonding of the type O-H.O, resulting in a seven-membered ring, is only 0.1 kcal mol(-)(1) higher in free energy. Protonation on the N-terminal nitrogen atom produces an isomer that is about 1 kcal mol(-)(1) higher in free energy than isomers resulting from protonation on the carbonyl oxygen of the N-terminal residue. The calculated energy barrier to generate the b(2) ion from protonated GGG is 32.5 kcal mol(-)(1) via TS(6-->7). The calculated basicity and proton affinity of GGG from our results are 216.3 and 223.8 kcal mol(-)(1), respectively. These values are 3-4 kcal mol(-)(1) lower than those from previous calculations and are in excellent agreement with recently revised experimental values.

The complexes of silver ion, Ag+, with the twenty naturally occurring amino acids have been calculated using hybrid density functional theory at the B3LYP/DZVP level. For all of these silver complexes, several possible structures were examined, but as there are remarkable similarities between all the structures at the global minima, only summarized data are reported. All of the complexes, except that with proline, are solvated ions. Amino acids containing only hydrocarbon side chains are bidentate, coordinating through the amino and carbonyl groups and the remaining amino acids (with the exception of proline) are tricoordinate with the same two interactions as in the simpler amino acids and an additional interaction through the side chain. The proline complex contains zwitterionic proline with the Ag+ ion attached to the carboxylate anion. Enthalpies (at 298 K) for dissociation of Ag+ from the complexes range from 49.3 kcal mol-1 for glycine to 80.4 kcal mol-1 for arginine. Free energies for these reactions are in the range of 40.7 kcal mol-1 for glycine to 70.3 kcal mol-1 for arginine. Comparison of the calculated free energies (relative to that of glycine) with those measured by the kinetic method shows good agreement, with the largest discrepancy being 3.9 kcal mol-1 for aspartic acid. There are some systematic trends with theory giving lower values than experiment for amino acids containing aromatic groups in the side chains (phenylalanine, tryptophan, and tyrosine) and higher values for the four amino acids with carbonyl groups in their side chains (aspartic acid, asparagine, glutamic acid, and glutamine).

Tandem mass spectrometry performed on a pool of 18 oligopeptides shows that the product ion spectra of argentinated peptides, the [bn + OH + Ag]+ ions and the [yn - H + Ag]+ ions bearing identical sequences are virtually identical. These observations suggest strongly that these ions have identical structures in the gas phase. The structures of argentinated glycine, glycylglycine, and glycylglycylglycine were calculated using density functional theory (DFT) at the B3LYP/DZVP level of theory; they were independently confirmed using HF/LANL2DZ. For argentinated glycylglycylglycine, the most stable structure is one in which Ag+ is tetracoordinate and attached to the amino nitrogen and the three carbonyl oxygen atoms. Mechanisms are proposed for the fragmentation of this structure to the [b2 + OH + Ag]+ and the [Y2 - H + Ag]+ ions that are consistent with all experimental observations and known calculated structures and energetics. The structures of the [b2 - H + Ag]+ and the [a2 - H + Ag]+ ions of glycylglycylglycine were also calculated using DFT. These results confirm earlier suggestions that the [b2 - H + Ag]+ ion is an argentinated oxazolone and the [a2 - H + Ag]+ an argentinated immonium ion.

Density functional calculations at B3LYP/DZVP were used to obtain structural information, relative free energies of di †erent isomers and binding energies for the following reaction in the gas phase : Mẁ here M \ Ag or Cu and n \ 0È2. For the complexes with Cu`, ] (glycyl)n glycine ] MÈ(glycyl) n glycine`, optimizations were also performed at B3LYP/6È31&&G(d,p) and single-point calculations at MP2(fc)/6È311&&G(2df,2p)//B3LYP/DZVP. The calculated binding energies for the Cu`complexes are all higher than those of the structurally similar Ag`ions. These calculated binding energy di †erences become larger as the size of the ligand increases. For all the Cu`complexes examined, the coordination number of the copper ion does not exceed two, whereas for the silver complexes tri-and tetracoordinate Ag`structures are calculated to be at low energy minima. SigniÐcant structural and relative free energy di †erences occur between the lowest energy " zwitterionic Ï forms of the complexes. MÈ(glycyl) n glycineÌ

The binding energies at 0 K of sodium and silver ions to ammonia, methylamine, ethylamine, acetonitrile, and benzonitrile were determined using threshold collision-induced dissociation (CID) and molecular orbital calculations at the ab initio and density functional theory levels. There is good agreement between experimental and calculated binding energies. For the five ligands, threshold CID/CCSD(t)(fu)/6-311++G(2df,p)//MP2(fu)/6-311++G(d,p) Na+ binding energies are the following:  ammonia, 25.6 ± 2.8/24.8; methylamine, 27.0 ± 1.4/25.9; ethylamine, 27.7 ± 2.3/27.1; acetonitrile, 30.0 ± 2.3/30.3; and benzonitrile, 32.7 ± 1.4/35.0 (B3LYP/6-311++G(d,p)//B3LYP/6-311++G(d,p)) kcal/mol. Threshold CID and B3LYP/DZVP Ag+ binding energies are the following:  ammonia, 40.6 ± 3.0/38.9; methylamine, 41.5 ± 2.3/41.1; ethylamine, 42.9 ± 1.4/43.2; acetonitrile, 40.8 ± 2.0/39.3; and benzonitrile, 41.5 ± 2.8/43.1 kcal/mol. Wherever comparisons with literature data are possible, the Na+ binding energies determined in this study are in good agreement with established data. For Ag+ binding energies, agreement with the few published theoretical values is not as good. A comparison of Na+ and Ag+ binding energies for the five N-containing ligands in this study and those for water, methanol, and ethanol published earlier (El Aribi, H.; Shoeib, T.; Ling, Y.; Rodriquez, C. F.; Hopkinson, A. C.; Siu, K. W. M. J. Phys. Chem. A 2002, 106, 2908−2914) shows that for every ligand the Ag+ binding energy is higher than the Na+ binding energy. As a group, the amines exhibit the largest differences between Ag+ and Na+ binding energies, followed by the nitriles; the alcohols exhibit the smallest differences. These results are in line with previous observations that Ag+ prefers binding with nitrogen to binding with oxygen.

The binding enthalpies at 0 K of the silver ion to water, methanol, ethanol, diethyl ether, and acetone were calculated using density functional theory (DFT) using the hybrid B3LYP level of theory with the DZVP basis set; they were also measured using the threshold collision-induced dissociation (CID) method. There is good agreement between the two sets of data. For the five ligands, the DFT/threshold CID values are:  water, 28.1/31.6 ± 2.5; methanol, 30.1/33.0 ± 3.7; ethanol, 32.0/33.9 ± 3.5; diethyl ether, 33.3/33.2 ± 1.5; and acetone, 36.2/38.0 ± 1.4 kcal/mol. The average of the absolute differences between the DFT and threshold CID results is 2.0 kcal/mol, a value smaller than the average experimental uncertainty of 2.5 kcal/mol. For identical ligands, the silver ion binding energies are lower than the lithium ion binding energies, but higher than the sodium ion binding energies.

Density functional calculations at B3LYP/DZVP are used to obtain the binding enthalpies and free energies for the reaction Ag + + XCN f AgNCX + , where X ) H, CH 3 , NH 2 , OH, F, CF 3 , CN, NO 2 , N(CH 3 ) 2 , C 6 H 5 , p-C 6 H 4 N(CH 3 ) 2 , p-C 6 H 4 NO 2 , and p-C 6 H 4 NH 2 . The calculated binding enthalpies at 298 K range from 52.2 kcal mol -1 for X ) p-C 6 H 4 N(CH 3 ) 2 to 21.3 kcal mol -1 for X ) NO 2 . Calculations at this level of theory are also used to optimize the structures of Ag(NCCH 3 ) n + and Ag(NCH) n + ions, where n ) 1-6. The binding enthalpies for the addition of the first and second molecules of CH 3 CN are 40.1 and 35.3 kcal mol -1 , whereas for HCN, they are calculated to be 31.2 and 28.3 kcal mol -1 , respectively. The binding enthalpies of the third and fourth ligands are much smaller at 15.9 and 10.8 kcal mol -1 for CH 3 CN and 13.5 and 9.7 kcal mol -1 for HCN. The 5-and 6-coordinate structures have positive free energies of formation with both ligands. Electrospraying a solution of AgNO 3 and acetonitrile in water shows the dominant ions to be Ag + , AgNCCH 3 + , and Ag(NCCH 3 ) 2 + , with the Ag(NCCH 3 ) 3 + ion being observed only in very small amounts and only under relatively mild conditions. Energy-resolved collision-induced dissociation (CID) experiments confirm the Ag-(NCCH 3 ) 3 + ion to be a loosely bound species, while the Ag(NCCH 3 ) 2 + and AgNCCH 3 + ions have substantially higher and comparable binding energies. Using the threshold method, we determined the binding energies at 0 K of NCCH 3 to Ag + and of NCCH 3 to AgNCCH 3 + to be 38.7 and 34.6 kcal mol -1 , respectively; the corresponding energies at 298 K are 39.4 and 34.7 kcal mol -1 . 710

Fragrant and antimicrobial properties were conferred to cotton fabrics following microencapsulation using green materials. Limonene and vanillin microcapsules were produced by complex coacervation using chitosan/gum Arabic as shell materials and tannic acid as hardening agent. The effect of two emulsifiers; Span 85 and polyglycerol polyricinoleate (PGPR), on the encapsulation efficiency (EE%), microcapsule's size and morphology, and cumulative release profiles was studied. The mean diameter of the produced microcapsules ranged between 10.4 and 39.0 μm, whereas EE% was found to be between 90.4% and 100%. The use of Span 85 resulted in mononuclear morphology while PGPR gave rise to polynuclear structures, regardless of the core material (vanillin or limonene). The obtained microcapsules demonstrated a sustained release pattern; namely the total cumulative release of the active agents after 7 days at 37 ± 1°C was 75%, 52% and 19.4% for the polynuclear limonene microcapsules, the mononuclear limonene microcapsules and the polynuclear vanillin microcapsules, respectively. Grafting of the produced microcapsules onto cotton fabrics through an esterification reaction using citric acid as a nontoxic cross-linker followed by thermofixation and curing, was confirmed by SEM and FTIR spectroscopy. Standard antibacterial assays conducted on both microcapsules alone and impregnated onto the fabrics indicated a sustained antibacterial activity.