Polyurethane films formation from microcrystalline cellulose as a polyol and cellulose nanocrystals as additive: Reactions favored by the low viscosity of the source of isocyanate groups used.

To simultaneously form films while synthesizing solvent-free and catalyst-free bio-based polyurethanes, hexamethylene diisocyanate trimer was selected as an isocyanate group source to produce a low-viscosity reaction medium for dispersing high contents of microcrystalline cellulose (MCC, polyol) and cellulose nanocrystals (CNC). Castor oil was used as an additional polyol source. Up to 80 % of the MCC was dispersed, producing a film exhibiting the highest Tg (72 °C), tensile strength (18 MPa), and Young's modulus (522.4 MPa). 12.5 % (30 % MCC) and 7.5 % (50 % MCC) of CNC dispersed in the reaction medium formed films stiffer than their counterparts. All the films exhibited transparency and high crystallinity. The contact angle/zeta potential (ζ) indicated hydrophobic film surfaces. At pH 7.4, ζ suggested that the films interacted with physiological fluids favorably. The films were non-cytotoxic, and the composites exhibited cell growth compared with the control. The reported results, as far as it is known, are unprecedented.

Microencapsulation of reactive isocyanates for application in self-healing materials: a review.

Microencapsulation of curing agents is a major strategy for the development of self-healing polymers. Isocyanates are among the most promising compounds for the development of one-part, catalyst free, self-healing materials, but their microencapsulation is challenging due to their high reactivity. To keep the healing agent intact in the liquid state and containing free-NCO groups, the monitoring of several synthesis parameters is essential. This review aims to summarise the outcomes in the microencapsulation of isocyanates, emphasising the efforts reported in the literature to modulate the microcapsule properties. In this regard, the main synthesis procedures are presented, followed by the most relevant characterisation methods used to assess microcapsule properties. The correlation between these properties and synthesis parameters is also discussed, and finally the main potential and challenges for industrial applications are highlighted.

Antibacterial phase change microcapsules obtained with lignin as the Pickering stabilizer and the reducing agent for silver.

This paper provides a novel and facile method to synthesize antibacterial phase change microcapsules (microPCMs) decorated with silver particles, where lignin was acting as both the Pickering stabilizer and the reducing agent for silver. First lignin Pickering emulsions at various oil-to-water ratios and lignin loading were prepared. Then, n-eicosane encapsulated in polyurea (PU) shells was prepared via interfacial polymerization of isophorone diisocyanate (IPDI) and ethylene diamine/diethylene triamine (EDA/DETA) in a Pickering emulsion stabilized by lignin particles. The results showed that the lignin particles were embedded in the microPCMs shell. These lignin particles were utilized to reduce silver ions, resulting in silver particles decorated microPCMs (Ag/lignin microPCMs). The resulting Ag/lignin microPCMs exhibited a well-defined core-shell spherical morphology with high phase-transition enthalpy (177.6 J/g), high encapsulation efficiency (69.0%) and good thermal durability. As well, the Ag/lignin microPCMs presented good antibacterial activity, showing great potential in industrial applications such as biomedical, textile and construction areas.

Efficacy of Hydromer-Coated and Antibiotic- Impregnated Shunt Systems in Reducing Early Shunt Infections in the Pediatric Population.

OBJECTIVE: Shunt infection is the most common complication following a Cerebrospinal fluid (CSF) diversion procedure with devastating consequences. This study analyzes the efficacy of different shunt systems in reducing early shunt infections in the pediatric population. METHODS: Retrospective case study analysis of 177 pediatric patients with hydrocephalus de novo shunted using hydromer-coated (HC) shunt systems, antibiotic-impregnated (AI) shunt systems and standard non impregnated shunt systems was performed and compared for the incidence of shunt infection in the early postoperative period. RESULTS: Group A consisted of standard shunt systems with 63 patients, Group B were HC shunt systems with 67 patients and group C consisted of 47 patients with antibiotic-impregnated shunt systems. Mean age in Group A was 1.36 +/- 3.36 years Mean age in Group B was 2.32 +/- 4.69 years. Mean age in Group C: 0.64 +/- 1.70 years. In terms of shunt infections, HC group had 4 shunt infections (6.25%), as compared to the control group, where 7 patients (10.45%) had infections. The AI group had 1 infection (2.13%). When comparing HC systems versus Standard Non-Impregnated There were 3 shunt malfunction in Group A (4.8%), 2 shunt malfunction in group B (3.3%) and 0 shunt malfunction in Group C (0%). CONCLUSION: Hydromer-coated shunt systems and antibiotic-impregnated shunt system represent a superior alternative to standard shunt systems for the reduction of shunt infection in the early post operative period.

Design of Silica-Oligourethane-Collagen Membranes for Inflammatory Response Modulation: Characterization and Polarization of a Macrophage Cell Line.

The polarization of macrophages M0 to M1 or M2 using molecules embedded in matrices and hydrogels is an active field of study. The design of biomaterials capable of promoting polarization has become a paramount need nowadays, since in the healing process macrophages M1 and M2 modulate the inflammatory response. In this work, several immunocytochemistry and ELISA tests strongly suggest the achievement of polarization using collagen-based membranes crosslinked with tri-functionalized oligourethanes and coated with silica. Measuring the amount of TGF-ß1 secreted to culture media by macrophages growth on these materials, and quantifying the macrophage morphology, it is proved that it is possible to stimulate the anti-inflammatory pathway toward M2, having measurements with p ≤ 0.05 of statistical significance between the control and the collagen-based membranes. Furthermore, some physicochemical characteristics of the hybrid materials are tested envisaging future applications: collagenase degradation resistance, water uptake, collagen fiber diameter, and deformation resistance are increased for all the crosslinked biomaterials. It is considered that the biological and physicochemical properties make the material suitable for the modulation of the inflammatory response in the chronic wounds and promising for in vivo studies.

A new method for the preparation of biomedical hydrogels comprised of extracellular matrix and oligourethanes.

This paper reports a new method to modify hydrogels derived from the acellular extracellular matrix (ECM) and consequently to improve their properties. The method is comprised of the combination of liquid precursors derived from hydrolyzed acellular small intestinal submucosa (hECM) and water-soluble oligourethanes that bear protected isocyanate groups, synthesized from poly(ethylene glycol) (PEG) and hexamethylene diisocyanate (HDI). The results demonstrate that the reactivity of oligourethanes, along with their water solubility, properly induce simultaneously the polymerization of type I collagen and its crosslinking. The polymerization rate and the gel network parameters such as fiber diameter, porosity, crosslinking degree, mechanics, swelling, in vitro degradation and cell proliferation, keep a direct relationship with the oligourethane concentration. Consequently, the hybrid hydrogels formulated with 15 wt.% of oligourethane exhibit enhanced storage modulus and degradation resistance, while maintaining the cell viability and impeding the fibroblast-induced contraction in comparison with the hECM hydrogels without oligourethanes. Therefore, this method is adequate to prepare novel hydrogels where the adjustment of the crosslinking degree controls the materials structure and their properties. This new method offers advantages for regulating the features of ECM-derived templates, thereby extending their possibilities for tissue engineering (TE) applications.

Characterization of methacrylate-based composites containing thio-urethane oligomers.

OBJECTIVE: To evaluate the ability of thio-urethane oligomers to improve the properties of restorative composite resins. METHODS: Oligomers were synthesized by combining 1,6-hexanediol-diissocyante (aliphatic) with pentaerythritol tetra-3-mercaptopropionate (PETMP) or 1,3-bis(1-isocyanato-1-methylethyl)benzene (aromatic) with trimethylol-tris-3-mercaptopropionate (TMP), at 1:2 isocyanate:thiol, leaving pendant thiols. Oligomers were added at 0-20 wt% to BisGMA-TEGDMA (70-30 wt%). Silanated inorganic fillers were added (70 wt%). Materials were photoactivated at 800 mW/cm(2) filtered to 320-500 nm. Near-IR was used to follow degree of methacrylate conversion (DC). Mechanical properties were evaluated in three-point bending with 2 mm × 2 mm × 25 mm bars for flexural strength/modulus and toughness (FS/E, and T) according to ISO 4049, and 2 mm × 5 mm × 25 mm notched specimens for fracture toughness (KIC). Polymerization stress (PS) was measured on the Bioman. Results were analyzed with ANOVA/Tukey's test (α=5%). RESULTS: Significant increase in DC was observed in thio-urethane-containing materials especially for the group with 20 wt% of aliphatic version. Materials composed by oligomers also promoted higher FS, E, and KIC in comparison to controls irrespective of thio-urethane type. A significant increase in toughness was detected by ANOVA, but not distinguished in the groups. The PS was significantly reduced by the presence of thio-urethane for almost all groups. CONCLUSIONS: The use of thio-urethane oligomer to compose methacrylate-based restorative composite promote increase in DC, FS, E and KIC while significant reduces PS. SIGNIFICANCE: A simple additive was shown to reduce stress while increasing convrersion and mechanical properties, mainly fracture toughness. This has he potential of increasing the service life of dental composites, without changing current operatory procedures.

Preparation of Aun quantum clusters with catalytic activity in ß-cyclodextrin polyurethane nanosponges.

Here we report the use of ß-cyclodextrin polyurethane nanosponges cross-linked with 1,6-hexamethylene diisocyanate as a template for the preparation of Aun quantum clusters, by the core-etching of glutathione-capped Au nanoparticles. The study of temporal evolution of the core-etching process using different Au concentrations indicated that formation of Aun clusters embedded in the nanosponge is favored by the use of lower Au concentrations, since it began at shorter times and lead to higher cluster loading. An estimation of the number of Au atoms based on the maximum photoluminescence wavelength suggested that, depending on the Au concentration and the core etching time, clusters with 11-15 atoms were formed. After excluding the possibility of an inclusion complex formation, evaluation of the catalytic activity of nanosponge-loaded Aun clusters toward the reduction of 4-nitrophenol has shown that the reaction is catalyzed by the Aun clusters with no induction time, following the Langmuir-Hinshelwood kinetic model.

The role of nanocrystalline cellulose on the microstructure of foamed castor-oil polyurethane nanocomposites.

Nanocrystalline cellulose (CNC), obtained by sulphuric acid hydrolysis, was used to synthesize polyurethane foams (PUFs) based on a functionalized castor oil polyol and a Methylene diphenyl diisocyanate (MDI). Formulations with varying isocyanate index (FI) and NCO number were prepared. At 0.5 wt.%, SEM's of the fractured surface underlined that the CNC acted both as a nucleation agent and as a particulate surfactant with cell geometries and apparent density changing selectively. The chemical structure of the PUF (FTIR) changed after the incorporation of CNC by a relative change of the amount of urea, urethane and isocyanurate groups. A low NCO number and isocyanate index contributed to the migration of the CNC to the Hard Segment (HS), acting as reinforcement and improving substantially the compressive mechanical properties (Ec and σc improvements of 63 and 50%, respectively). For a high NCO number or isocyanate index, the CNC migrated to the Soft Segment (SS), without causing a reinforcement effect. The migration of the CNC was also detected with DSC, TGA and DMA, furtherly supporting the hypothesis that a low NCO number and index contributed both to the formation of a microstructure with a higher content of urethane groups.

Thio-urethane oligomers improve the properties of light-cured resin cements.

Thio-urethanes were synthesized by combining 1,6-hexanediol-diissocyante (aliphatic) with pentaerythritol tetra-3-mercaptopropionate (PETMP) or 1,3-bis(1-isocyanato-1-methylethyl)benzene (aromatic) with trimethylol-tris-3-mercaptopropionate (TMP), at 1:2 isocyanate:thiol, leaving pendant thiols. Oligomers were added at 10-30 phr to BisGMA-UDMA-TEGDMA (5:3:2, BUT). 25 wt% silanated inorganic fillers were added. Commercial cement (Relyx Veneer, 3M-ESPE) was also evaluated with 10-20 phr of aromatic oligomer. Near-IR was used to follow methacrylate conversion (DC) and rate of polymerization (Rpmax). Mechanical properties were evaluated in three-point bending (ISO 4049) for flexural strength/modulus (FS/FM, and toughness), and notched specimens (ASTM Standard E399-90) for fracture toughness (KIC). Polymerization stress (PS) was measured on the Bioman. Volumetric shrinkage (VS, %) was measured with the bonded disk technique. Results were analyzed with ANOVA/Tukey's test (α=5%). In general terms, for BUT cements, conversion and mechanical properties in flexure increased for selected groups with the addition of thio-urethane oligomers. The aromatic versions resulted in greater FS/FM than aliphatic. Fracture toughness increased by two-fold in the experimental groups (from 1.17 ± 0.36 MPam(1/2) to around 3.23 ± 0.22 MPam(1/2)). Rpmax decreased with the addition of thio-urethanes, though the vitrification point was not statistically different from the control. VS and PS decreased with both oligomers. For the commercial cement, 20 phr of oligomer increased DC, vitrification, reduced Rpmax and also significantly increased KIC, and reduced PS and FM. Thio-urethane oligomers were shown to favorably modify conventional dimethacrylate networks. Significant reductions in polymerization stress were achieved at the same time conversion and fracture toughness increased.

Thio-urethanes improve properties of dual-cured composite cements.

This study aims at modifying dual-cure composite cements by adding thio-urethane oligomers to improve mechanical properties, especially fracture toughness, and reduce polymerization stress. Thiol-functionalized oligomers were synthesized by combining 1,3-bis(1-isocyanato-1-methylethyl)benzene with trimethylol-tris-3-mercaptopropionate, at 1:2 isocyanate:thiol. Oligomer was added at 0, 10 or 20 wt% to BisGMA-UDMA-TEGDMA (5:3:2, with 25 wt% silanated inorganic fillers) or to one commercial composite cement (Relyx Ultimate, 3M Espe). Near-IR was used to measure methacrylate conversion after photoactivation (700 mW/cm(2) × 60s) and after 72 h. Flexural strength and modulus, toughness, and fracture toughness were evaluated in three-point bending. Polymerization stress was measured with the Bioman. The microtensile bond strength of an indirect composite and a glass ceramic to dentin was also evaluated. Results were analyzed with analysis of variance and Tukey's test (α = 0.05). For BisGMA-UDMA-TEGDMA cements, conversion values were not affected by the addition of thio-urethanes. Flexural strength/modulus increased significantly for both oligomer concentrations, with a 3-fold increase in toughness at 20 wt%. Fracture toughness increased over 2-fold for the thio-urethane modified groups. Contraction stress was reduced by 40% to 50% with the addition of thio-urethanes. The addition of thio-urethane to the commercial cement led to similar flexural strength, toughness, and conversion at 72h compared to the control. Flexural modulus decreased for the 20 wt% group, due to the dilution of the overall filler volume, which also led to decreased stress. However, fracture toughness increased by up to 50%. The microtensile bond strength increased for the experimental composite cement with 20 wt% thio-urethane bonding for both an indirect composite and a glass ceramic. Novel dual-cured composite cements containing thio-urethanes showed increased toughness, fracture toughness and bond strength to dentin while demonstrating reduced contraction stress. All of these benefits are derived without compromising the methacrylate conversion of the resin component. The modification does not require changing the operatory technique.

Synthesis of pharmacologically active 1-amino-isoquinolines prepared via silver triflate-catalyzed cyclization of o-alkynylbenzaldoximes with isocyanates.

The synthesis of a series of 1-amino-isoquinolines prepared via electrophilic cyclization [3+2] cycloaddition/rearrangement reactions of o-alkynylbenzaldoxime 1 with isocyanates 2 in the presence of catalytic amount of AgOTf was demonstrated. The cyclized products were obtained in good yields under an air atmosphere. 1-Amino-isoquinoline derivatives 3a, 3b, 3j and 3t were screened in vitro for the antioxidant potential and efficacy to inhibit cerebral monoamine oxidase (MAO) activity. The antidepressant-like action of some 1-amino-isoquinolines was performed in the mouse forced swimming test (FST). The pharmacological screening of 1-amino-isoquinoline derivatives indicated that 3a, 3b, 3j and 3t were antioxidants and inhibited cerebral MAO-A and B activities at low concentrations. Although at different doses 3a, 3b, 3j and 3t were effective antidepressant-like drugs in the mouse FST. None of 1-amino-isoquinolines tested caused acute cerebral, hepatic or renal toxicity in mice.

A theoretical systematic study of a series of isocyanopolyynes.

Several isocyanopolyynes, HCnNC (n=0, 2,…,16), are analyzed in this theoretical work. We performed calculations at MP2/cc-pVTZ (n=0-16), CCSD/cc-pVDZ (n=0-12) and CCSD/cc-pVTZ (n=0-6) levels. The dipole moments from the best treatment, CCSD/cc-pVTZ, are in much closer agreement with those obtained in CCSD/cc-pVDZ calculations (deviations up to 0.05 Debye) than with the results from MP2/cc-pVTZ (discrepancies that can reach 0.55 Debye). Moreover, the CCSD/cc-pVTZ level yields values in excellent accordance with experimental dipole moments for HNC and HC2NC. Hence, this allows concluding that the correct treatment of electron correlation is more important than increments in basis sets for this electric property in isocyanopolyynes and CCSD/cc-pVDZ values are indicated as the best estimates available for large isocyanopolyynes. The findings from infrared intensities of fundamental vibrational bands are also similar (mean deviations of 3.1 km mol(-1) for CCSD/cc-pVDZ and 12.6 km mol(-1) for MP2/cc-pVTZ with respect to CCSD/cc-pVTZ results). Thus, we decided to use the charge - charge flux - dipole flux (CCFDF) model from multipoles given by the Quantum Theory of Atoms in Molecules (QTAIM), which were obtained at the CCSD/cc-pVDZ level, to investigate the variations in infrared intensities of some selected modes along these systems. The intensity of the band associated with CH stretching shows an increase with the size of these molecules (from 96 to 146 km mol(-1) between n=4 and 12) that is readily explained by variations in the charge flux contribution to this mode, in a similar way as found before for cyanopolyynes. Furthermore, the degenerate CH bending vibrations present almost constant intensities in these isocyanopolyynes (around 37-38 km mol(-1) from n=4 up to n=12) and this pattern is supported by CCFDF/QTAIM contributions. The band mostly assigned to stretching of the NC triple bond, which can also be described as asymmetric stretching mode of all pairs of adjacent triple bonds, shows an increase of intensity up to n=6 and is associated to values around 96-102 km mol(-1) in the remaining larger members. Another important mode detected is a symmetric stretching of NC and CC triple bonds belonging to the isonitrile end (between 66 and 101 km mol(-1) when n=6-12) for which the charge contribution is nearly constant and dynamic contributions change in a more complicated way. The most intense fundamental band in each isocyanopolyyne from n=4 to 12 is assigned to vibrations of triple bonds in both ends of these systems (from 129 to 164 km mol(-1)) and an alternating behavior according with even or odd numbers of CC triple bonds is observed for these values and also for respective CCFDF/QTAIM contributions. Finally, this work also brings values derived from regressions that are indicated as the best estimates of rotational constants and dipole moments to be used for detection of large isocyanopolyynes in the interstellar medium.

Solvent-free synthesis, DNA-topoisomerase II activity and molecular docking study of new asymmetrically N,N'-substituted ureas.

A new series of asymmetrically N,N'-substituted ureas 20–25 was prepared using solvent free conditions, which is an eco-friendly methodology, starting with Schiff bases derived from cinnamaldehyde and p-substituted anilines, which are subsequently submitted to reduction reactions that afford the corresponding asymmetric secondary amines. All of the intermediates were prepared using solvent free reactions, which were compared to traditional methodologies. All of the reactions required a remarkably short amount of time and provided good yields when solvent free conditions were employed compared to other methodologies. The DNA-topoisomerase II-α (topo II-α) activity was evaluated in relaxation assays, which showed that all of the compounds inhibited the enzyme activity at 10 μM, except for urea 24. Furthermore, a molecular docking study indicated that the compounds 20–25 binding to the topo II-α are able to interact with the same binding site as the anticancer drug etoposide, suggesting that the ureas could inhibit the enzyme by the same mechanism of action observed for etoposide, which prevents re-ligation of the DNA strands.

Synthesis and characterization of poly-O-methyl-[n]-polyurethane from a d-glucamine-based monomer.

Aminoalditol 1-amino-1-deoxy-D-sorbitol (1) was readily converted into 2,3,4,5-tetra-O-methyl derivative 5, a key precursor of a sugar-based [n]-polyurethane. For the polymerization, the free amino or primary hydroxyl groups of 5 were selectively activated and employed as starting monomers in two alternative procedures. Thus, the amino function of 5 was converted into the isocyanate derivative by treatment with di-tert-butyltricarbonate, and polymerized in situ in the presence of Zr(IV) acetylacetonate. The resulting poly(1-amino-1-deoxy-2,3,4,5-tetra-O-methyl-D-sorbitol)urethane (8) had a moderate molecular weight and showed the presence of urea units. The alternative synthesis of 8 involved the activation of the free hydroxyl group of 5 as the corresponding phenylcarbonate. The polymerization of this α-amino-ω-phenylcarbonate alditol monomer does not require a metal catalyst. The resulting material exhibited an improved molecular weight and higher purity than that obtained via the isocyanate. [n]-polyurethane 8 was highly soluble in water as well as in common organic solvents (chloroform, acetone, ethyl acetate, etc) and was obtained as an amorphous material which was characterized thermally and spectroscopically.

Polyurethanes as supports for human retinal pigment epithelium cell growth.

PURPOSE: The transplant of retinal pigment epithelium (RPE) cells on supports may well be an effective therapeutic approach to improve the visual results of patients with age-related macular degeneration. In this study, two biodegradable polyurethanes were investigated as supports for human RPE cells (ARPE-19). METHODS: Polyurethane aqueous dispersions based on poly(caprolactone) and/or poly(ethylene glycol) as soft segments, and isophorone diisocyanate and hydrazine as hard segments were prepared. Polyurethane films were produced by casting the dispersions and allowing them to dry at room temperature for one week. The ARPE-19 cells were seeded onto the polyurethane films and they were investigated as supports for in vitro adhesion, proliferation, and uniform distribution of differentiated ARPE-19 cells. Additionally, the in vivo ocular biocompatibility of the polyurethane films was evaluated. RESULTS: The RPE adhered to and proliferated onto the polyurethane supports, thus establishing cell-PUD surface interactions. Upon confluence, the cells formed an organized monolayer, exhibited a polygonal appearance, and displayed actin filaments which ran along the upper cytoplasm. At 15 days of seeding, the occluding expression was confirmed between adjacent cells, representing the barrier functionality of epithelial cells on polymeric surfaces and the establishment of cell-cell interactions. Results from the in vivo study indicated that polyurethanes exhibited a high degree of short-term intraocular biocompatibility. CONCLUSIONS: Biodegradable polyurethane films display the proper mechanical properties for an easy transscleral-driven subretinal implantation and can be considered as biocompatible supports for a functional ARPE-19 monolayer.

Bioresorbable poly(ester-ether urethane)s from L-lysine diisocyanate and triblock copolymers with different hydrophilic character.

Bioresorbable linear poly(ester-ether urethane)s with different hydrophilic character were synthesized from block copolymers of poly(epsilon-caprolactone)-poly(ethylene oxide)-poly(epsilon-caprolactone) (PCL-PEO-PCL) as macrodiols, and L-lysine diisocyanate (LDI). A series of PCL-PEO-PCL triblock copolymers with different PEO and PCL chain length was obtained by reacting PEO with epsilon-caprolactone. Polyurethanes were synthesized by reacting the triblock copolymers with LDI in solution using stannous 2-ethylhexanoate as catalyst. The prepared triblock copolymers and polyurethanes were fully characterized by proton nuclear magnetic resonance spectroscopy, size exclusion chromatography, differential scanning calorimetry, and wide-angle X-ray diffraction. Water uptake, hydrolytic stability, and tensile properties of polyurethanes with different composition were evaluated and discussed in terms of the chain length and molecular weight of the polymers and its block components. Water uptake seems to depend on the ethylene oxide unit content of the polyurethane regardless of the triblock structure. Mechanical properties of the synthesized polymers were strongly affected by the molecular weight achieved during polymerization. The use of triblock macrodiols with different hydrophilicity allowed the preparation of a series of polyurethanes having a broad range of properties.

Double transacetalization of diacylium ions.

A novel gas-phase reaction of diacylium ions of the O=C=X(+)=C=O type (X = N, CH) is reported: double transacetalization with cyclic acetals or ketals. The reaction is exothermic and highly efficient, and forms members of a new class of highly charged-delocalized ions: cyclic ionic diketals. Pentaquadrupole double- and triple-stage mass spectrometric (MS(2) and MS(3)) experiments reveal the high double transacetalization reactivity of O=C=N(+)=C=O and O=C=CH(+)=C=O, whereas the synthesis of differently substituted cyclic ionic diketals is performed in MS(3) experiments via sequential mono- and double transacetalization of O=C=N(+)=C=O and O=C=CH(+)=C=O with different acetals. With cyclic acetals, the acylium-thioacylium ion O=C=N(+)=C=S reacts promptly and selectively by mono-transacetalization at its acylium site, but the free thiacylium site of its cyclic ionic ketal is nearly unreactive by double transacetalization. Therefore, only the acylium site of O=C=N(+)=C=S can be efficiently protected by transacetalization. Low-energy MS(3) collision-induced dissociation of the cyclic ionic diketals of O=C=N(+)=C=O and O=C=CH(+)=C=O sequentially frees each of the protected acylium site to form the mono-derivatized ion, and then the fully deprotected diacylium ion.