Does single-visit root canal treatment of permanent teeth provide more benefit than a multiple-visit approach?

DATA SOURCES: Cochrane Oral Health's Trials Register, Cochrane Central Register of Controlled Trials in the Cochrane Library, MEDLINE Ovid, Embase Ovid. STUDY SELECTION: Randomised controlled trials and quasi-randomised controlled trials were included. POPULATION: Participants aged ≥ 10 with a permanent tooth possessing a completely formed apex and without resorption; Intervention: Root canal treatment (RoCT) carried out in a single visit; Comparison: RoCT carried out over multiple visits; Outcome: Primary outcome was treatment success (retention of tooth or radiographic evidence of healing), with secondary outcomes investigating post-operative symptoms (pain, swelling, sinus tract formation). DATA EXTRACTION AND SYNTHESIS: Standard Cochrane methods to assess internal validity were used. The Robins 1 tool (for quasi randomised controlled trials) or risk of bias (RoB) 1 tool (for randomised controlled trials) were used to assess RoB whereby a judgement was assigned as 'low', 'high' or 'unclear'. GRADE (GRADEpro GDT software) was used to assess certainty of evidence for each outcome. The certainty of evidence was defined as high, moderate, low or very low, having no downgrade, downgrade of one level, downgrade of two levels and downgrade of three or more levels, respectively. Of the various subgroups investigated to determine their relevance, only pretreatment conditions (vital teeth versus necrotic teeth) and endodontic technique (manual versus mechanical instrumentation) were available for subgroup analysis. The Cochrane's test for heterogeneity and I2 test were used to assess the variation in treatment effects. A random-effects model was used to combine risk ratio (RR) for dichotomous data and mean difference (MD) for continuous data. Sensitivity analysis was performed for each outcome, excluding studies at overall high or unclear RoB. RESULTS: Forty-seven studies were included in the meta-analysis and internal validity assessment, with 5693 teeth analysed. Ten studies were found to have a low RoB, 17 with a high RoB and 20 with an unclear RoB. No evidence was identified suggesting a difference between treatment carried out in a single visit compared to a multiple visits approach for the primary outcome measure, but there was very low certainty about the findings (RR 0.46, 95% confidence interval (CI) 0.09 to 2.50; I 2 = 0%; 2 studies, 402 teeth). No evidence was identified suggesting a difference between treatment carried out in a single visit compared to multiple visits with regards to radiological failure (RR 0.93, 95% CI: 0.81 to 1.07; I 2 = 0%; 13 studies, 1505 teeth; moderate-certainty evidence), participants reporting pain up to 72 h post obturation (RR 0.97, 95% CI: 0.81 to 1.16; I 2 = 70%; 12 studies, 1329 teeth; low-certainty evidence), pain for 72 h post obturation (MD 0.26, 95% CI: -4.76 to 5.29; I 2 = 98%; 12 studies, 1258 teeth; low-certainty evidence) or pain at 1 week post obturation (RR 1.05, 95% CI: 0.67 to 1.67; I2 = 61%; 9 studies, 1139 teeth; very low-certainty evidence). Similarly, no evidence was identified to prove that there was a difference between treatment carried out in a single visit compared to multiple visits with regards to swelling or flare-up (RR 0.56 95% CI: 0.16-1.92; I 2 = 0%; 6 studies; 605 teeth; very low-certainty evidence), analgesic use (RR 1.25 95% CI: 0.75-2.09; I 2 = 36%; 6 studies, 540 teeth; very low-certainty evidence) and sinus tract or fistula presence (RR 1.00, 95% CI: 0.24-4.28; I 2 = 0%; 5 studies, 650 teeth; very low-certainty evidence). Interestingly, however, there was evidence to show that more participants reported pain after 1 week following RoCT completed in a single visit, compared to those in multiple visit groups (RR 1.55, 95% CI: 1.14-2.09; I 2 = 18%; 5 studies, 638 teeth; moderate-certainty evidence). Subgroup analysis showed there was an increase in post-treatment pain after 1 week for RoCT carried out in a single visit on vital teeth (RR 2.16, 95% CI: 1.39-3.36; I 2 = 0%; 2 studies, 316 teeth), and with the use of mechanical instrumentation (RR 1.80, 95% CI: 1.10-2.92; I 2 = 56%; 2 studies, 278 teeth). CONCLUSIONS: The current evidence shows that RoCT carried out in a single visit is no more effective than RoCT carried out over multiple visits; after 12 months, there is no difference in pain or complications with either approach. However, single visit RoCT has been shown to have increased post-operative pain after 1 week compared to RoCT completed over multiple visits.

Does an interim dressing with calcium hydroxide reduce endotoxins between endodontic appointments?

Data sources PubMed, Cochrane Library, LILACS/Biblioteca Brasileira de Odontologica, Web of Science, Embase, Scopus, grey literature.Study selection Randomised and non-randomised clinical studies, experimental studies. Population: human studies with permanent dentition; Intervention: evaluation of lipopolysaccharide (LPS) after dressing with calcium hydroxide (CH); Comparison: evaluation of LPS before dressing with CH; Outcome: antimicrobial efficacy against LPS.Data extraction and synthesis A modified Cochrane Risk of Bias (RoB) tool was used to evaluate internal validity of randomised controlled trials, Robins-1 tool for non-randomised controlled trials, and the 'Before and After' tool for experimental studies. Meta-analyses were conducted by subgrouping according to CH use, chemo-mechanical preparation (CMP), antimicrobial substance (AS), and irrigant. Further analyses explored incidence of LPS reduction. All subgroups were assessed for heterogeneity through I2 test and the random-effect model was applied. Sensitivity analysis was performed to evaluate the influence of studies with RoB in effect significance.Results Nine studies were included for qualitative assessment, of which seven were included for meta-analysis. Three studies were assessed as low RoB, one was medium risk, with two having a high RoB. Three studies presented with 'some concerns'. After dressing with CH, no AS resulted in 61.7% of teeth with reduction in LPS (95% CI: 37.7%-82.9%, I2 = 96.7%), compared to AS where 98.9% of teeth showed an LPS reduction (95% CI: 97.4%-99.8%, I2 = 38.6%). Where mean reductions in LPS were compared, CH with or without AS, reduced mean LPSs before (standardised mean difference [SMD] = 21.087 [CI: 21.453 to 20.721], P = 0.001, I2 = 58.7%) and after CMP (SMD = 20.919 [CI: 21.156 to 20.682], P = 0.001, I2 = 24.7%) using a CH dressing. Considering the irrigant solutions, the overall results showed a reduction before (SMD = 21.053 [CI: 21.311 to 20.795], P = 0.001, I2 = 58.7%) and after CMP (SMD = 20.938 [CI: 21.147 to 20.729], P = 0.001, I2 = 24.6%) using a CH dressing. There was a reduction in mean LPS over time, up to 30 days. All analyses presented a very low certainty of evidence.Conclusions An interim dressing with CH reduces LPS levels below those achieved with CMP and AS, but does not eliminate LPS completely. No evidence is presented on improved clinical outcomes following multiple-visit treatment with CH dressing.

Periodontal health in the shortened dental arch.

Design Multi-centre randomised controlled clinical trial with two prosthetic intervention arms conducted in 14 dental schools and universities in Germany from October 2000.Case selection Adults aged ≥35 years with bilateral missing molars, both canines and at least one premolar present on each side in one jaw were eligible for inclusion. Participants were randomly allocated to restoration of posterior teeth using a removable partial denture (RPD), or a fixed prosthesis (that is, a bridge) adhering to the concepts of the shortened dental arch (SDA) principles (no replacement posterior to the second molar). Randomisation was completed centrally using randomly permuted blocks stratified by age. Data were collected at baseline (following pre-prosthetic treatment) and patients were followed up at six months, annually for five years, eight years and ten years.Data analysis In total, 215 participants were randomised and allocated to either RPD group (n = 109) or SDA group (n = 106). Intention to treat (ITT) and modified per-protocol analysis were performed on both the RPD group (n = 79) and SDA group (n = 71). Per-protocol analysis was also undertaken on both the RPD group (n = 25) and SDA group (n = 22). The level of significance was set to a two-sided p value of 0.05. The confidence interval was set at 95%.Results When considering the differences in ten-year vertical clinical attachment loss measurements, ITT analysis showed the differences between the RPD and SDA groups were statistically significant (p ≤0.05) in both the study jaw (0.79 mm) and in all teeth (0.69 mm) in favour of the SDA group. Furthermore, the SDA group also performed more favourably in both bleeding on probing and plaque index parameters, with statistically significant changes demonstrated using positive regression coefficients.Conclusions There is evidence of reduced impact on the periodontium from an SDA approach compared to an RPD approach, although the difference is unlikely to be clinically significant.

The effect of high-speed dental handpiece coolant delivery and design on aerosol and droplet production.

OBJECTIVES: High-speed dental instruments produce aerosol and droplets. The objective of this study was to evaluate aerosol and droplet production from a novel electric micromotor handpiece (without compressed air coolant) in real world clinical settings. METHODS: 10-minute upper incisor crown preparations were performed in triplicate in an open-plan clinic with mechanical ventilation providing 3.45 air changes per hour. A 1:5 ratio electric micromotor handpiece which allows water coolant without compressed air (Ti-Max Z95L, NSK) was used at three speeds: 60,000 (60 K), 120,000 (120 K), and 200,000 (200 K) revolutions per minute. Coolant solutions contained fluorescein sodium as a tracer (2.65 mmol L - 1). High-speed air-turbine positive control, and negative control conditions were conducted. Aerosol production was evaluated at 3 locations (0.5 m, 1.5 m, and 1.7 m) using: (1) an optical particle counter (OPC; 3016-IAQ, Lighthouse) to detect all aerosol; and (2) a liquid cyclone air sampler (BioSampler, SKC Ltd.) to detect aerosolised fluorescein, which was quantified by spectrofluorometric analysis. Settled droplets were detected by spectrofluorometric analysis of filter papers placed onto a rig across the open-plan clinic. RESULTS: Local (within treatment bay) settled droplet contamination was elevated above negative control for all conditions, with no difference between conditions. Settled droplet contamination was not detected above negative controls outside the treatment bay for any condition. Aerosol detection at 1.5 m and 1.7 m, was only increased for the air-turbine positive control condition. At 0.5 m, aerosol levels were highly elevated for the air-turbine, minimally elevated for 200 K and 120 K, and not elevated for 60 K. CONCLUSIONS: Electric micromotor handpieces which use water-jet coolant alone without compressed air produce localised (within treatment bay) droplet contamination, but are unlikely to produce aerosol contamination beyond the immediate treatment area (1.5 m), allowing them to be used safely in most open-plan clinic settings.

Endodontic procedures produce bacterial droplet contamination - but what about viruses?

Research question The study aims to investigate spread, distance and spatial distribution of aerosolised microorganisms generated through various endodontic procedures.Study design A case-control study carried out at the University of Maryland, US in 2020. The study investigated the aerosolised microorganisms produced during three endodontic treatments: emergency pulpotomy, emergency pulpectomy and non-surgical root canal therapy (NSRCT), with 15 participants in each group (n = 45). Patients diagnosed with symptomatic apical periodontitis were included. The use of settle plates for passive air sampling was employed, in a 4 x 4 m room with closed doors. The number of colony-forming units (CFUs) and composition of bacterial species were analysed. Variables within the study included: distance of plate to patient's mouth (0.5 m or 2 m), positioning of plate (directly in front of or diagonal to the participant's mouth), type of endodontic treatment performed and the duration of treatment. A baseline sample was collected (room at rest) as a control. All dental treatment was carried out under rubber dam, after patients had undergone a pre-operative 0.12% chlorhexidine digluconate mouth rinse for 60 seconds. An extraoral suction system (ADS EOS Dental System Inc; Ontario, CA, USA) was also placed directly in front of the patient's mouth throughout treatment.Results A significantly greater number of CFUs were recorded after endodontic treatments (all treatments), compared to negative control. CFUs were lower in the emergency pulpotomy group compared to the other two groups. There was a significantly lower number of CFUs found at plates situated 0.5 m, compared to 2 m, away from the patient. There was a positive correlation between the procedure duration and CFU count. The main bacterial species detected were Staphylococcus aureus (48.8%), Staphlococcus epidermidis (42.2%) and oral streptococci (33.1%). Pseudomonas aeruginosa and fungi were not detected.Conclusion Emergency pulpectomy and NSRCT created greater microbial contamination than an emergency pulpotomy. Greater numbers of microorganisms were found after longer treatment times and closer to the patient's mouth.

Temporomandibular disorders and dietary changes: A cross-sectional survey.

BACKGROUND: Advice about a 'soft diet' may be useful in the short-term alleviation of temporomandibular disorders (TMD) but may contradict the long-term aims of multi-dimensional approaches if a poor nutritional state is caused or exacerbated. The changes patients with TMD make to their diet, because of their condition or its management, have not previously been explored. OBJECTIVES: To explore the relationship and trends between TMD, TMD interventions and diet using self-report measures. METHODS: Registrants of the Temporomandibular Joint Association (TMJA) were invited to participate. After completing a screening questionnaire to check for eligibility, participants completed a questionnaire exploring demographics, TMD interventions and dietary habits, as well as jaw functional limitation scale (JFLS) score, graded chronic pain scale score, self-assessed limitation of opening and patient health questionnaire 4 (PHQ-4). This was followed by a validated 3-day electronic diet diary. Descriptive and inferential statistics were used to explore the data for trends and differences in the dietary intake of those participating according to various strata including demographic variables; experience of surgery; other interventions for TMD; duration of TMD; and limitation of mouth opening. RESULTS: Eighty-five registrants of the TMJA completed the questionnaire, of which 42 (49%) completed the 3-day diet diary. Most participants (66/85 [77.6%]) reported modifying their diet due to their TMD. The most common modification was to cut food into smaller pieces (61/85 [71.8%]) followed by boiling until soft (36/85 [42.4%]) and mashing (34/85 [40%]). Higher JFLS scores were associated with participants reduced enjoyment of food (t(83) = 2.78, p = .007), limitations in the foods they can eat (t(83) = 2.99, p = .004), necessity for modified food preparation (t(83) = 3.38, p = .001) and self-reported weight change (F(2, 82) = 9.31, p = .0002). CONCLUSION: This study suggests a significant proportion of patients with TMD make alterations to their diet which may impact the nutritional value of their diet. However, self-reported symptoms and interventions for TMD made little difference to nutritional intake as measured by a 3-day diary. Patients reporting self-assessed limited opening had more pain as measured by validated tools, suggesting patients' self-reporting of opening is a useful proxy for clinical measurement in monitoring TMD.

Evaluating splatter and settled aerosol during orthodontic debonding: implications for the COVID-19 pandemic.

Introduction Dental procedures produce splatter and aerosol which have potential to spread pathogens such as SARS-CoV-2. Mixed evidence exists on the aerosol-generating potential of orthodontic procedures. The aim of this study was to evaluate splatter and/or settled aerosol contamination during orthodontic debonding.Material and methods Fluorescein dye was introduced into the oral cavity of a mannequin. Orthodontic debonding was undertaken with surrounding samples collected. Composite bonding cement was removed using a speed-increasing handpiece with dental suction. A positive control condition included a water-cooled, high-speed air-turbine crown preparation. Samples were analysed using digital image analysis and spectrofluorometric analysis.Results Contamination across the eight-metre experimental rig was 3% of the positive control on spectrofluorometric analysis and 0% on image analysis. Contamination of the operator, assistant and mannequin was 8%, 25% and 28% of the positive control, respectively.Discussion Splatter and settled aerosol from orthodontic debonding is distributed mainly within the immediate locality of the mannequin. Widespread contamination was not observed.Conclusions Orthodontic debonding is unlikely to produce widespread contamination via splatter and settled aerosol, but localised contamination is likely. This highlights the importance of personal protective equipment for the operator, assistant and patient. Further work is required to examine suspended aerosol.

Evaluating aerosol and splatter following dental procedures: Addressing new challenges for oral health care and rehabilitation.

BACKGROUND: Dental procedures often produce aerosol and splatter which have the potential to transmit pathogens such as SARS-CoV-2. The existing literature is limited. OBJECTIVE(S): To develop a robust, reliable and valid methodology to evaluate distribution and persistence of dental aerosol and splatter, including the evaluation of clinical procedures. METHODS: Fluorescein was introduced into the irrigation reservoirs of a high-speed air-turbine, ultrasonic scaler and 3-in-1 spray, and procedures were performed on a mannequin in triplicate. Filter papers were placed in the immediate environment. The impact of dental suction and assistant presence were also evaluated. Samples were analysed using photographic image analysis and spectrofluorometric analysis. Descriptive statistics were calculated and Pearson's correlation for comparison of analytic methods. RESULTS: All procedures were aerosol and splatter generating. Contamination was highest closest to the source, remaining high to 1-1.5 m. Contamination was detectable at the maximum distance measured (4 m) for high-speed air-turbine with maximum relative fluorescence units (RFU) being: 46,091 at 0.5 m, 3,541 at 1.0 m and 1,695 at 4 m. There was uneven spatial distribution with highest levels of contamination opposite the operator. Very low levels of contamination (≤0.1% of original) were detected at 30 and 60 minutes post-procedure. Suction reduced contamination by 67-75% at 0.5-1.5 m. Mannequin and operator were heavily contaminated. The two analytic methods showed good correlation (r = 0.930, n = 244, P < .001). CONCLUSION: Dental procedures have potential to deposit aerosol and splatter at some distance from the source, being effectively cleared by 30 minutes in our setting.

Evaluating contaminated dental aerosol and splatter in an open plan clinic environment: Implications for the COVID-19 pandemic.

OBJECTIVES: Identify splatter/aerosol distribution from dental procedures in an open plan clinic and explore aerosol settling time after dental procedures. METHODS: In two experimental designs using simulated dental procedures on a mannequin, fluorescein dye was introduced: (1) into the irrigation system of an air-turbine handpiece; (2) into the mannequin's mouth. Filter papers were placed in an open plan clinic to collect fluorescein. An 8-metre diameter rig was used to investigate aerosol settling time. Analysis was by fluorescence photography and spectrofluorometry. RESULTS: Contamination distribution varied across the clinic depending on conditions. Unmitigated procedures have the potential to deposit contamination at large distances. Medium volume dental suction (159 L/min air) reduced contamination in the procedural bay by 53%, and in other areas by 81-83%. Low volume suction (40 L/min air) was similar. Cross-ventilation reduced contamination in adjacent and distant areas by 80-89%. In the most realistic model (fluorescein in mouth, medium volume suction), samples in distant bays (≥5 m head-to-head chair distance) gave very low or zero readings (< 0.0016% of the fluorescein used during the procedure). Almost all (99.99%) of the splatter detected was retained within the procedural bay/walkway. After 10 min, very little additional aerosol settled. CONCLUSIONS: Cross-infection risk from dental procedures in an open plan clinic appears small when bays are ≥ 5 m apart. Dilution effects from instrument water spray were observed, and dental suction is of benefit. Most settled aerosol is detected within 10 min indicating environmental cleaning may be appropriate after this. CLINICAL SIGNIFICANCE: Aerosols produced by dental procedures have the potential to contaminate distant sites and the majority of settled aerosol is detectable after 10 min. Dental suction and ventilation have a substantial beneficial effect. Contamination is likely to be minimal in open plan clinics at distances of 5 m or more.

Brief post-surgical electrical stimulation accelerates axon regeneration and muscle reinnervation without affecting the functional measures in carpal tunnel syndrome patients.

Electrical stimulation (ES) of injured peripheral nerves accelerates axonal regeneration in laboratory animals. However, clinical applicability of this intervention has never been investigated in human subjects. The aim of this pilot study was to determine the effect of ES on axonal regeneration after surgery in patients with median nerve compression in the carpal tunnel causing marked motor axonal loss. A randomized control trial was conducted to provide proof of principle for ES-induced acceleration of axon regeneration in human patients. Carpel tunnel release surgery (CTRS) was performed and in the stimulation group of patients, stainless steel electrode wires placed alongside the median nerve proximal to the surgical decompression site for immediate 1 h 20 Hz bipolar ES. Subjects were followed for a year at regular intervals. Axonal regeneration was quantified using motor unit number estimation (MUNE) and sensory and motor nerve conduction studies. Purdue Pegboard Test, Semmes Weinstein Monofilaments, and Levine's Self-Assessment Questionnaire were used to assess functional recovery. The stimulation group had significant axonal regeneration 6-8 months after the CTRS when the MUNE increased to 290+/-140 (mean+/-SD) motor units (MU) from 150+/-62 MU at baseline (p<0.05). In comparison, MUNE did not significantly improve in the control group (p>0.2). Terminal motor latency significantly accelerated in the stimulation group but not the control group (p>0.1). Sensory nerve conduction values significantly improved in the stimulation group earlier than the controls. Other outcome measures showed a significant improvement in both patient groups. We conclude that brief low frequency ES accelerates axonal regeneration and target reinnervation in humans.

Superior pedicle breast reduction techniques increase the risk of postoperative drainage.

BACKGROUND: The most frequent complication after bilateral reduction mammoplasty (BRM) is the formation of seromas and hematomas. If a group of patients who are at increased risk of seroma and hematoma are identified, the use of drains in this group would be beneficial. We hypothesized that superior pedicle reductions would have increased postoperative drainage. METHODS: A prospective observational study was conducted to identify independent risk factors for increased drainage after BRM. Blinded research nurses were employed to record the amount of drainage during the postoperative period. Univariate and multivariate regression analyses were used to identify risk factors for increased postoperative drainage. RESULTS: The study included a total of 111 patients. Univariate analysis identified the amount of preoperative infiltration (P < 0.001), the amount of liposuction (P < 0.001), the amount of surgically resected tissue (P = 0.001), the type of reduction (P < 0.001), the patient's chest circumference (P = 0.035), and the patient's body mass index (BMI) (P = 0.015) as significant predictors of postoperative drainage. Multivariate regression analysis identified the amount of tissue resected and the type of reduction as the only 2 independent predictors of postoperative drainage. The use of superior pedicle technique predicted 43% of the variability in postoperative wound drainage. CONCLUSIONS: The use of the superior pedicle technique for BRM is associated with a significant increase in postoperative drainage. Surgeons using this technique should consider the routine use of drains to avoid possible complications of seroma, infection, and poor wound healing.

Completely autologous platelet gel in breast reduction surgery: a blinded, randomized, controlled trial.

BACKGROUND: The objective of this study was to assess the effectiveness of topical application of completely autologous platelet gel during breast surgery to reduce postoperative wound drainage. An increasing number of surgical centers are using tissue sealants to reduce postoperative drainage and improve surgical outcomes. However, there is a paucity of randomized, double-blind, controlled trials assessing the efficacy of these agents. METHODS: The authors conducted a within-patient, randomized, patient- and assessor-blinded, controlled trial assessing the use of completely autologous platelet gel in 111 patients undergoing bilateral reduction mammaplasty. Patients were randomized to receive the gel applied to the left or right breast after hemostasis was achieved; the other breast received no treatment. The primary outcome was the difference in wound drainage over 24 hours. Secondary outcomes included subjective and objective assessments of pain and wound healing. RESULTS: No statistically significant differences in the drainage, level of pain, size of open areas, clinical appearance, degree of scar pliability, or scar erythema were noted. CONCLUSION: The authors' results do not support the use of completely autologous platelet gel to improve outcomes after reduction mammaplasty.

Normative values and the effects of age, gender, and handedness on the Moberg Pick-Up Test.

The Moberg Pick-Up Test is a standardized test for assessing hand dexterity. Although reduction of sensation in the hand occurs with aging, the effect of age on a subject's performance of the Moberg Pick-Up Test has not been examined. The primary goal of this study was to examine the impact of aging and, secondarily, the impact of gender and handedness, on performance of the Moberg Pick-Up Test in 116 healthy subjects. The average time to complete each of the four subsets of the test was analyzed using the Kruskal-Wallis, Mann-Whitney U, and Wilcoxon signed-rank tests. The results show that hand dexterity of the subjects was significantly affected by age, with young subjects being the fastest and elderly subjects the slowest. Women accomplished the test faster than men, and task performance with the dominant hand was faster than with the non-dominant hand. Use of normative values established based on age and gender is a valuable objective tool to gauge hand function in patients with different neurologic disorders.

Near edge X-ray absorption fine structure spectroscopy of bacterial hydroxamate siderophores in aqueous solutions.

X-ray absorption spectroscopy (XAS) is widely used to explore the coordination environments and structures of metal complexes in aqueous solutions and disordered phases. Although soft-XAS studies on gaseous phases, solid phases and their interfaces have shown that XAS is a versatile tool in studying the functional group composition of organic molecules, the application of XAS to studying aqueous solutions is seriously limited because of experimental difficulties. In this report, using a modified synchrotron endstation geometry, we show how soft-XAS was used to study the changes in electronic states of reactive functional groups in a bacterial macromolecule, desferrioxamine B (desB, a hydroxamate siderophore) and its structural analogue (acetohydroxamic acid (aHa)). We collected C, N, and O near edge X-ray absorption fine structure (NEXAFS) spectra of these molecules in aqueous solutions and complemented their spectral interpretation with calculated X-ray spectra of "hydrated" aHa. The experimental spectra of desB are similar to those for aHa at the C, N, and O K-edges. In addition, the electronic transitions of amide and hydroxamate functional groups in the macromolecule can be distinguished from the N spectra. Small energy differences in the pi*(C=O)NO and the transitions at the C- and N-edges of aHa and desB indicate that the substituent attached to N in desB ((CH2)n) determines the electron density in the (C=O)NO core. As the solution pH increased, the pi*(C=O)NO transition of the hydroxamate group of these two molecules exhibit energy shifts at the C-, N-, and O-edges, which are consistent with increased electron delocalization in the (C=O)NO core of aHa (and desB), predicted from the calculations. The spectra of the aHa(H2O)3- anion also provide evidence for partial N-deprotonation at pH values usually attributed to an O-acid. These results indicate that soft-XAS is well suited for studying the electronic states of different functional groups in aqueous organic macromolecules.

The local structure of protonated water from x-ray absorption and density functional theory.

We present a combined x-ray absorption spectroscopy/computational study of water in hydrochloric acid (HCl) solutions of varying concentration to address the structure and bonding of excess protons and their effect on the hydrogen bonding network in liquid water. Intensity variations and energy shifts indicate changes in the hydrogen bonding structure in water as well as the local structure of the protonated complex as a function of the concentration of protons. In particular, in highly acidic solutions we find a dominance of the Eigen form, H(3)O(+), while the proton is less localized to a specific water under less acidic conditions.

Hard and soft X-ray absorption spectroscopic investigation of aqueous Fe(III)-hydroxamate siderophore complexes.

Microorganisms release organic macromolecules, such as siderophores, to obtain Fe(III) from natural systems. While the relative stabilities of Fe(III)-siderophore complexes are well-studied, the structural environments of Fe(III) and ligands in the complex are not well-understood. Using the X-ray absorption spectroscopy (XAS) at the Fe- and N-K absorption edges, we characterized the nature of Fe(III) interactions with a hydroxamate siderophore, desferrioxamine B (desB), and its small structural analogue, acetohydroxamic acid (aHa), as a function of pH (1.4-11.4). These experimental studies are complemented with DFT calculations. The Fe-XAS studies suggest that Fe(aHa)3 is the dominant species in aqueous solutions in the pH range of 2.8-10.1, consistent with thermochemical information. However, the N-XAS and resonance Raman studies show that the chemical state of the ligand in the Fe(aHa)3 complex changes significantly with pH, and these variations are correlated with further deprotonation of the Fe(aHa)3 complex. The N-XAS studies also indicate that the overlap of Fe 3d orbitals with the molecular orbitals of the hydroxamate group is significant. The Fe- and N-XAS studies of Fe(III)-desB complexes indicated that Fe(desB)+ is the dominant species between pH values of 1.4 and 11.4, consistent with predicted stability constants. This information is useful in understanding the role of iron in bacterial transport, siderosis treatment, and actinide sequestration at contaminated sites. This is the first N-XAS study of aqueous metal ligand complexes, which demonstrates the applications of soft-XAS in studying the electronic structure of metal complexes of organic macromolecules in aqueous solutions.

X-ray absorption spectroscopy study of the hydrogen bond network in the bulk water of aqueous solutions.

We utilized X-ray absorption spectroscopy (XAS) and X-ray Raman scattering (XRS) in order to study the ion solvation effect on the bulk hydrogen bonding structure of water. The fine structures in the X-ray absorption spectra are sensitive to the local environment of the probed water molecule related to the hydrogen bond length and angles. By varying the concentration of ions, we can distinguish between contributions from water in the bulk and in the first solvation sphere. We show that the hydrogen bond network in bulk water, in terms of forming and breaking hydrogen bonds as detected by XAS/XRS, remains unchanged, and only the water molecules in the close vicinity to the ions are affected.