Nonionic poly(ethylene
oxide) alkyl ether (C
i
E
j
) surfactants self-assemble
into aggregates of various sizes and
shapes above their critical micelle concentration (CMC). Knowledge
on solution attributes such as CMC as well as aggregate characteristics
is crucial to choose the appropriate surfactant for a given application,
e.g., as a micellar solvent system. In this work, we used static and
dynamic light scattering to measure the CMC, aggregation number (
N
agg
), and hydrodynamic radius (
R
h
) of four different C
i
E
j
surfactants
(C
8
E
5
, C
8
E
6
, C
10
E
6
, and C
10
E
8
). We examined the
influence of temperature, concentration, and molecular structure on
the self-assembly in the vicinity of the CMC. A minimum in the CMC
vs temperature curve was identified for all surfactants investigated.
Further, extending the hydrophilic and hydrophobic chain lengths leads
to an increase and decrease of the CMC, respectively. The size of
the aggregates strongly depends on temperature.
N
agg
and
R
h
increase with increasing
temperature for all surfactants investigated. Additionally,
N
agg
and
R
h
both
increase with increasing surfactant concentration. The data obtained
in this work further improve the understanding of the influence of
temperature and molecular structure on the self-assembly of C
i
E
j
surfactants and will further foster their use
in micellar solvent systems.
Biphasic hydrocarbon functionalizations catalyzed by recombinant microorganisms have been shown to be one of the most promising approaches for replacing common chemical synthesis routes on an industrial scale. However, the formation of stable emulsions complicates downstream processing, especially phase separation. This fact has turned out to be a major hurdle for industrial implementation. To overcome this limitation, we used supercritical carbon dioxide (scCO(2)) for both phase separation and product purification. The stable emulsion, originating from a stereospecific epoxidation of styrene to (S)-styrene oxide, a reaction catalyzed by recombinant Escherichia coli, could be destabilized efficiently and irreversibly, enabling complete phase separation within minutes. By further use of scCO(2) as extraction agent, the product (S)-styrene oxide could be obtained with a purity of 81% (w/w) in one single extraction step. By combining phase separation and product purification using scCO(2), the number of necessary workup steps can be reduced to one. This efficient and easy to use technique is generally applicable for the workup of biphasic biocatalytic hydrocarbon functionalizations and enables a cost effective downstream processing even on a large scale.
The majority of all newly identified
active pharmaceutical ingredients
(APIs) have a low solubility in water (partly smaller than marble).
In order to enhance their solubility and bioavailability, the formulation
of these APIs, as part of therapeutic deep eutectic systems (THEDES),
has been recently shown to be a promising approach. By choosing the
right excipient, the melting point of the API/excipient mixture can
be lowered below body temperature or even room temperature, resulting
in a liquid formulation. To date, because of a lack of mechanistic
understanding of how THEDES are formed, the identification of suitable
excipients for a given API is almost exclusively based on heuristic
decisions and trial-and-error-based approaches. This is both very
time-consuming and expensive. The purpose of this work is to reduce
the experimental effort to identify suitable excipients for a given
API solely based on the melting properties (melting temperature and
melting enthalpy) of the API and excipient and accounting for intermolecular
interactions via a predictive thermodynamic model [in this case, UNIFAC(Do)].
Lidocaine, ibuprofen, and phenylacetic acid were considered as model
APIs, whereas thymol, vanillin, lauric acid, para-toluic acid, benzoic acid, and cinnamic acid were considered as
model excipients. The formation of THEDES from these components was
predicted and confirmed using differential scanning calorimetry. The
results indicate that the experimental effort for the identification
of suitable API/excipient combinations can be drastically reduced
by thermodynamic modeling, leading to more efficient and tailor-made
formulations in the future.
Emulsion stability plays a crucial role for mass transfer and downstream processing in organic-aqueous bioprocesses based on whole microbial cells. In this study, emulsion stability dynamics and the factors determining them during two-liquid phase biotransformation were investigated for stereoselective styrene epoxidation catalyzed by recombinant Escherichia coli. Upon organic phase addition, emulsion stability rapidly increased correlating with a loss of solubilized protein from the aqueous cultivation broth and the emergence of a hydrophobic cell fraction associated with the organic-aqueous interface. A novel phase inversion-based method was developed to isolate and analyze cellular material from the interface. In cell-free experiments, a similar loss of aqueous protein did not correlate with high emulsion stability, indicating that the observed particle-based emulsions arise from a convergence of factors related to cell density, protein adsorption, and bioreactor conditions. During styrene epoxidation, emulsion destabilization occurred correlating with product-induced cell toxification. For biphasic whole-cell biotransformations, this study indicates that control of aqueous protein concentrations and selective toxification of cells enables emulsion destabilization and emphasizes that biological factors and related dynamics must be considered in the design and modeling of respective upstream and especially downstream processes.
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